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  • General Chemistry  (643)
  • Life Sciences (General)  (415)
  • Cell & Developmental Biology  (273)
  • 1995-1999  (1,331)
  • 1945-1949
  • 1998  (1,331)
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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 177 (1998), S. 377-386 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Apoptosis in cells of different lineages is restrained by survival signals which depend upon cell-to-cell communication. The aim of this study was to determine whether colonic cells deprived of crypt ambient are doomed to die prior to their normal chronological demise. Apoptosis was studied in rat whole colonic tissue, in isolated intact crypts, and in colonic cell populations collected from the crypt axis at different stages of proliferation and differentiation. In a number of experiments, cell harvest was performed in the presence of either a tetrapeptide (YVAD-CMK) inhibitor of interleukin-1β-converting enzyme (ICE), or tyrphostin A25, a protein tyrosine kinase inhibitor, or sodium-orthovanadate, a phosphatase inhibitor. DNA fragmentation was assessed by electrophoretic and nonisotopic-labeling procedures. The ultrastructure of colonic tissue specimens and isolated cells was examined by transmission electron microscopy. Apoptosis in whole colonic tissue and in isolated crypts was confined predominantly to cells resident in the upper crypt regions. In contrast, extensive apoptotic death was observed in isolated colonic cells, irrespective of their developmental stage and positional hierarchy within the crypt continuum at harvest time. An apoptotic gradient, however, was evident. Exposure to YVAD-CMK resulted in a marked decrease in the number of apoptotic cells. Treatment with tyrphostin A25 caused a sharp rise in the apoptotic index; conversely, vanadate significantly impeded apoptosis. Cumulatively, these results indicate that disordered intercellular communication provokes unscheduled ICE-mediated apoptosis of colonocytes, and that local signals along the crypt continuum control both the reprieve from death and the timely demise of distinct colonic cell populations. Attenuation of tyrosine phosphorylation may be a contributory event in the acquisition of the apoptotic phenotype. J. Cell. Physiol. 177:377-386, 1998. © 1998 Wiley-Liss, Inc.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 177 (1998), S. 518-524 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: No abstract.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 177 (1998), S. 525-534 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: No abstract.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 177 (1998), S. 575-584 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The role of hsp27 as an inhibitor of actin polymerization was considered in the context of the actin cytoskeleton and its relationship with focal adhesion formation. The aim of this study was to evaluate the potential effects of hsp27 on focal adhesion formation as a relevant biological consequence of actin stress fiber formation. When hsp27 was overexpressed in stably transfected cells, cell attachment was delayed and recovery of disrupted stress fibers and focal adhesions was limited. In ROS 17/2.8 cells, heat shock caused the reversible disruption of stress fibers and focal adhesions. The loss of stress fibers and focal adhesions was associated with reduced phosphotyrosine on the focal adhesion kinase (FAK). Microinjection of recombinant 6-His hsp27 and phosphorylated 6-His hsp27 was used to demonstrate that nonphosphorylated hsp27 prevented the recovery of stress fibers and focal adhesions. These results provide in vivo evidence that hsp27 acts as an inhibitor of actin polymerization that can alter cellular interactions with extracellular environments by perturbation of stress fibers, and subsequently focal adhesions. J Cell Physiol 177:575-584, 1998. © 1998 Wiley-Liss, Inc.
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  • 5
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Hepatocytes entrapped in collagen gel and cultured in serum-free conditions survived longer than cells cultured on plastic (5 days vs. 3 weeks), showed fewer signs of early cell senescence (no increase in c-fos oncoprotein expression), and maintained the expression of differentiated hepatic metabolic functions over a longer period of time. Cells cultured in collagen gels retained their ability to respond to hormones. The insulin-stimulated glycogen synthesis rate remained fairly constant during 18 days in culture (between 5.4 ± 0.37 and 9 ± 2.7 nmol glucose/h/μg DNA). Collagen-cultured hepatocytes recovered glycogen stores to levels similar to those found in liver, or in hepatocytes isolated from fed rats. Urea synthesis from ammonia remained stable for more than 2 weeks (average value, 23 ± 4 nmol urea/h/μg DNA). The rate of albumin synthesis in collagen-entrapped cells was maintained above the day-1 level during 18 days in culture. Cells showed high levels of glutathione (GSH) (1,278 ± 152 pmol/μg DNA). Biotransformation activities CYP4501A1, CYP4502A2, CYP4502B1, and CYP4503A1 remained fairly stable in collagen-cultured hepatocytes. CYP4502E1 and CYP4502C11 decreased but were still measurable after 18 days. After 4 days in culture, GST activity returned to levels observed in isolated hepatocytes. In contrast with plastic cultures, cells responded to CYP450 inducers (methylcholanthrene for CYP4501A1, CYP4501A2, and gluthatione-transferase, and ethanol for CYP4502E1) for more than 2 weeks. CYP4501A1, CYP4501A2, and glutathione-transferase A2 (GST A2) induction was preceded by an increase in specific mRNA, while the effects on CYP4502E1 seemed to be at a posttranslational level. Analysis of the expression of relevant hepatic genes by reverse Northern and semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) revealed that culturing hepatocytes in collagen gels results in a sustained higher expression of key liver transcription factor genes DBP, C/EBP-α and -β, and HNF-1 and -4, as well as specific liver enzyme genes (phosphoenol pyryvate carboxykinase, and carbamoylphosphate-synthetase I). J Cell Physiol 177:553-562, 1998. © 1998 Wiley-Liss, Inc.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 177 (1998), S. 535-552 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The viral Crk oncogene (v-Crk) is known to induce sarcomas in chicken and its cellular homologs c-Crk I, c-Crk II, and Crk-like (CRKL) have been implicated in many signal transduction events. These include cell differentiation, cell migration, and the induced nonresponsiveness of T-cells to stimulation of the T-cell receptor (TCR), a state known as anergy. CRKL is also the most prominent substrate of the Bcr-Abl oncoprotein which causes human chronic myelogenous leukemias (CML). The modular composition of the Crk family adapters which largely consist of Src homology (SH2 and SH3) domains has prompted an intensive search for physiological and pathological upstream and downstream signalling partners which selectively bind to these adapters. Upstream proteins include various receptors and large multisite docking proteins, while several protein kinases and guanine nucleotide release proteins (GNRPs) have been suggested to function downstream of c-Crk and CRKL. Most Crk/CRKL SH2- and SH3-binding proteins contain several docking sites with considerable sequence similarity. Thus the binding requirements of Crk/CRKL SH2 and SH3 domains are now well defined, providing a basis for the design of small inhibitory molecules to block the function of these adapter proteins. The enzymatic cascades activated through Crk family adapters are only partially known, but stress kinases (SAPKs/JNKs) and the GTPase Rap1, as well as the B-Raf isoform of the Raf protein kinases, are affected in some systems. Several yet unidentified, highly selective Crk interacting proteins detectable in specific cell types remain to be studied. More detailed analyses of the enzymatic activities triggered through Crk-type adapters will also be crucial to fully define the signalling pathways controlled by this protein family. J Cell Physiol 177:535-552, 1998. © 1998 Wiley-Liss, Inc.
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  • 7
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have previously described a specific, saturable receptor for rat collagenase-3 in the rat osteosarcoma cell line, UMR 106-01. Binding of rat collagenase-3 to this receptor is coupled to the internalization and eventual degradation of the enzyme and correlates with observed extracellular levels of the enzyme. In this study we have shown that decreased binding, internalization, and degradation of 125I-rat collagenase-3 were observed in cells after 24 h of parathyroid hormone treatment; these activities returned to control values after 48 h and were increased substantially (twice control levels) after 96 h of treatment with the hormone. Subcellular fractionation studies to identify the route of uptake and degradation of collagenase-3 localized intracellular accumulation of 125I-rat collagenase-3 initially in Golgi-associated lysosomes and later in secondary lysosomes. Maximal lysosomal accumulation of the radiolabel and stimulation of general lysosomal activity occurred after 72 h of parathyroid hormone treatment. Preventing fusion of endosomes with lysosomes (by temperature shift, colchicine, or monensin) resulted in no internalized 125I-collagenase-3 in either lysosomal fraction. Treatment of UMR cells with the above agents or ammonium chloride decreased excretion of 125I-labeled degradation products of collagenase-3. These experiments demonstrated that degradation of collagenase-3 required receptor-mediated endocytosis and sequential processing by endosomes and lysosomes. Thus, parathyroid hormone regulates the expression and synthesis of collagenase-3 as well as the abundance and functioning of the collagenase-3 receptor and the intracellular degradation of its ligand. The coordinate changes in the secretion of collagenase-3 and expression of the receptor determine the net abundance of the enzyme in the extracellular space. J Cell Physiol 177:563-574, 1998. © 1998 Wiley-Liss, Inc.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 177 (1998), S. 585-592 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The effect of metabolic inhibitors on nontransferrin bound iron transport by K562 cells was investigated. Incubation with 1 μM rotenone, 10 μM antimycin, or 0.5 mM 2,4-dinitrophenol effectively reduced ATP levels by ∼50%. Both the rate and extent of Fe+3 uptake were impaired in ATP-depleted cells, which display a reduced Vmax for uptake. K562 cell ferrireductase activity was also lowered by metabolic inhibitors, suggesting that the apparent energy requirements for transport reside in the reduction of Fe+3 to Fe+2. However, ATP depletion was found to inhibit the rate and extent of Fe+2 uptake as well. Thus, the transbilayer passage of Fe+2 and/or Fe+3 appears to be an energy-requiring process. These features possibly reflect properties of the transport mechanism associated with a recently identified K562 cell transport protein, called SFT for “Stimulator of Fe Transport,” since exogenous expression of its activity is also affected by ATP depletion. J Cell Physiol 177:585-592, 1998. © 1998 Wiley-Liss, Inc.
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  • 9
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    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 177 (1998), S. 593-605 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Clusterin (ApoJ) is an extracellular glycoprotein expressed during processes of tissue differentiation and regression that involve programmed cell death (apoptosis). Increased clusterin expression has also been found in tumors, however, the mechanism underlying this induction is not known. Apoptotic processes in tumors could be responsible for clusterin gene activation. Alternatively, oncogenic mutations could modulate signal transduction, thereby inducing the gene. We examined the response of the rat clusterin gene to two oncogenes, Ha-ras and c-myc, in transfected Rat1 fibroblasts. While c-myc overexpression did not modify clusterin gene activity, the Ha-ras oncogene produced a seven to tenfold repression of clusterin mRNA; this down-regulation was also observed in the presence of c-myc. Since no induction of the clusterin gene was observed by the two oncogenes, we tested the alternative mechanism involving apoptosis. Growth factor withdrawal induced apoptosis, as shown by DNA degradation and micronuclei formation in the floating cells. Concomittantly we observed a three to tenfold increase in the amount of clusterin mRNA in the adhering cells of Rat1 and the c-myc transformed cell lines, and a weaker induction in the Ha-ras transformed cell line. On the basis of our results, we suggest that clusterin gene induction in the vital cells is produced by signaling molecules that are generated by the apoptotic cells. We conclude that apoptotic processes, not oncogenic mutations, are responsible for increased clusterin expression in tumors. J Cell Physiol 177:593-605, 1998. © 1998 Wiley-Liss, Inc.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 177 (1998), S. 618-627 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We previously reported that the enterocytic differentiation of human colonic Caco-2 cells correlated with down-regulation of fibronectin (FN) and laminin (LN), two extracellular matrix components interacting with cell surface integrin receptors. We now investigated whether Caco-2 cell differentiation was associated with alterations in integrin signaling with special interest in the expression and activity of focal adhesion kinase (FAK) and mitogen-activated protein (MAP) kinase. The differentiation of Caco-2 cells was associated with: (1) down-regulation of β1 integrin expression at the mRNA and protein levels; (2) increased FAK expression together with decreased FAK autophosphorylation; (3) decreased FAK's ability to associate with PI3-kinase and pp60c-src; and (4) increased MAP kinase expression along with decreased MAP activity. In addition, we show that FAK and MAP kinase belong to distinct integrin signaling pathways and that both pathways remain functional during Caco-2 cell differentiation since the coating of differentiating cells on FN and LN but not on polylysine increased the tyrosine phosphorylation of FAK and of its endogenous substrate paxillin, and stimulated MAP kinase activity. In conclusion, our results provide evidence that FAK and MAP kinase, two signaling molecules activated independently by β1 integrins in Caco-2 cells, undergo alterations of both expression and activity during the enterocytic differentiation of this cell line. J Cell Physiol 177:618-627, 1998. © 1998 Wiley-Liss, Inc.
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  • 11
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Salivary glands contain two major epithelial cell types: acinar cells which produce the primary salivary secretion, including amylase, and ductal cells which reabsorb electrolytes but also secrete kallikrein. Here we investigated salivary acinar cell differentiation in vitro using the activity of the salivary amylase and tissue kallikrein promoters as markers of acinar cell and ductal cell differentiation, respectively. Each of the promoter sequences was cloned into a replication-deficient adenoviral vector containing the luciferase reporter gene. Previous studies showed that a human submandibular gland cell line (HSG) differentiated into acinar cells when cultured on a reconstituted basement membrane matrix (Matrigel). The luciferase activity of the amylase promoter vector (AdAMY-luc) was low in HSG cells cultured on plastic, where they grow as an epithelial monolayer. The promoter activity increased approximately tenfold when HSG cells were cultured on Matrigel and developed an acinar phenotype. Under the same conditions, the luciferase activity of the kallikrein promoter (AdKALL-luc) was not induced. Because HSG cells demonstrate acinar cell morphology, but not amylase gene expression, when cultured on laminin-1, certain soluble components of Matrigel were tested for their ability to induce the amylase promoter during in vitro differentiation of acinar cells. We find that epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-α), which are present in the basement membrane, and hepatocyte growth factor (HGF) increase activity of the amylase promoter. Other basement membrane-derived growth factors such as TGF-β, basic fibroblast growth factor (bFGF), and platelet-derived growth factor (PGDF), as well as tumor necrosis factor (TNF-α), keratinocyte growth factor (KGH), nerve growth factor (NGF) and interferon gamma (IFN-γ) were inactive. This system will be further exploited to study the mechanisms by which extracellular matrix molecules and growth factors regulate salivary acinar cell differentiation. J Cell Physiol 177:628-635, 1998. Published 1998 Wiley-Liss, Inc.
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  • 12
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The role of HSP27 in cell growth and resistance to stress was investigated using murine fibrosarcoma L929 cells (normally devoid of constitutively expressed small HSPs) and human osteoblast-like SaOS-2 cells stably transfected with a human hsp27 expression vector. Our data showed that our L929 cells were more resistant to oxidative stress than generally observed for this line. Production of HSP27 in these cells led to a marked decrease in growth rate associated with a series of phenotypical changes, including cell spreading, cellular and nuclear hypertrophy, development of an irregular outline, and a tremendous accumulation of actin stress fibers. By contrast, none of these changes was observable in SaOS-2/hsp27 transfectants overexpressing the protein product. Together, these observations are consistent with a cause-to-effect cascade relationship between increased (or induced) HSP27 expression, changes in cytoskeletal organization, and decreased growth. On the other hand, whereas the transfection of the hsp27 gene increased the cell resistance to heat in both cell lines, only in SaOS-2 cells was this associated with protection to the cytotoxic action of tumor necrosis factor-alpha (TNF-α) and etoposide. Unexpectedly, L929/hsp27 transfectants exhibited an increased sensitivity to both agents and also to H2O2. These data thus imply that different mechanisms are involved in the cell resistance to heat shock and to the cytotoxic action of TNF-α, etoposide, and H2O2. They also plead against the simple view that overexpression of a phosphorylatable HSP27 would necessarily be beneficial in terms of increased cell resistance to any type of stress. Our data further indicate that the role of HSP27 in cellular resistance to stress and in cell proliferation involves different targets and that the ultimate result of its interference with these processes depends on the intracellular context in which the protein is expressed. J Cell Physiol 177:606-617, 1998. © 1998 Wiley-Liss, Inc.
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  • 13
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Using an expression cloning approach, we identified and cloned a novel intracellular protein produced by osteoclasts that indirectly induces osteoclast formation and bone resorption, termed OSF. Conditioned media from 293 cells transiently transfected with the 0.9 kb OSF cDNA clone stimulated osteoclast-like cell formation in both human and murine marrow cultures in the presence or absence 10-9 M 1,25-dihydroxyvitamin D3. In addition, conditioned media from 293 cells transfected with the OSF cDNA clone enhanced the stimulatory effects of 1,25-(OH)2D3 on bone resorption in the fetal rat long bone assay. In situ hybridization studies using antisense oligomers showed expression of OSF mRNA in highly purified osteoclast-like cells from human giant cell tumors of the bone. Northern blot analysis demonstrated ubiquitous expression of a 1.3 kb mRNA that encodes OSF in multiple human tissues. Sequence analysis showed the OSF cDNA encoded a 28 kD peptide that contains a c-Src homology 3 domain (SH3) and ankyrin repeats, suggesting that it was not a secreted protein, but that it was potentially involved in cell signaling. Consistent with these data, immunoblot analysis using rabbit antisera against recombinant OSF demonstrated OSF expression in cell lysates but not in the culture media. Furthermore, recombinant OSF had a high affinity for c-Src, an important regulator of osteoclast activity. Taken together, these data suggest that OSF is a novel intracellular protein that indirectly enhances osteoclast formation and osteoclastic bone resorption through the cellular signal transduction cascade, possibly through its interactions with c-Src or other Src-related proteins. J Cell Physiol 177:636-645, 1998. © 1998 Wiley-Liss, Inc.
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  • 14
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The addition of dexamethasone (dex) to human fibroblast cultures has been found to elicit enhanced proliferation. This enhancement is manifested by an increase in the initial growth rate, saturation density, and proliferative life span of WI-38 fibroblast cultures grown in the presence of dex. We examined the acute effects of dex on a number of growth-related genes in WI-38 cells. Our results show a decrease in the level of the cyclin-dependent kinase inhibitor p21Waf1/Cip1/Sdi1 in response to dex. In addition, the level of the insulin-like growth factor type 1 receptor (IGF-1R) is increased in dex-treated cells. These changes are correlated with changes in the activity of the p21Waf1/Cip1/Sdi1 and IGF-1R promoters. The results presented in this report suggest that dex may delay growth arrest in response to contact inhibition, as well as during cellular senescence. Thus, dex may act at multiple levels to enhance cellular proliferation in WI-38 cells: first, to decrease the level of an inhibitor of cell-cycle progression, and second, to increase the sensitivity of WI-38 cells to the proliferative effects of IGF-1. These acute effects may cooperate with other, as yet uncharacterized effects, to result in the enhanced proliferation seen in the presence of dex. J. Cell. Physiol. 177:396-401, 1998. © 1998 Wiley-Liss, Inc.
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  • 15
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    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 177 (1998), S. 402-410 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Potassium (K+) conductances are known to be involved in cell proliferation of a number of nonexcitable cell types. The nature of the mechanism by which K+ channel inhibition reduces cell proliferation has remained elusive despite intensive search. We investigated whether such a phenomenon could be demonstrated in excitable cells, using the GH3 pituitary cell line as a cell model. Our aims were: (1) to study the effect of K+ channel inhibition on the proliferation of GH3 cells; and (2) to investigate the putative intracellular signals involved in this inhibition. Tetraethylammonium chloride (TEA), a blocker of the calcium (Ca2+)-dependent K+ conductances of GH3, was found to reversibly inhibit cell proliferation, as measured by 3H-thymidine incorporation. Cell cycle block specifically occurred at the G1/S phase of the cell cycle. This inhibition of proliferation was observed for 1-4 mM TEA, which suppressed most of the Ca2+-activated K+ current and part of the inward rectifying K+ current, as shown by electrophysiological experiments. Increasing extracellular K+ concentrations with KCl also inhibited cell proliferation in a dose-dependent manner. Both TEA and KCl depolarized the cells and increased intracellular Ca2+ levels ([Ca2+]i), showing that, in this type of excitable cell, inhibition of cell proliferation can be associated with elevated Ca2+ levels. Ca2+ and membrane resting potential (MRP) were considered as possible messengers of this inhibition. Our results suggest that cell cycle arrest of GH3 cells by K+ channel block probably involves an additional pathway, distinct from those of Ca2+ and MRP. J. Cell. Physiol. 177:402-410, 1998. © 1998 Wiley-Liss, Inc.
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  • 16
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    Journal of Cellular Physiology 177 (1998), S. 387-395 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Previously, we reported that unaggressive, growth factor-dependent FET human colon carcinoma cells downregulated their transforming growth factor alpha (TGFα) expression in a quiescent state (G0/G1) induced by growth factor and nutrient deprivation (Mulder, 1991, Cancer Res., 51:2256-2262). In contrast, highly aggressive, growth factor-independent HCT116 human colon carcinoma cells aberrantly upregulated this autocrine activity in the quiescent state (Mulder, 1991, Cancer Res., 51:2256-2262; Howell et al., 1998, Mol. Cell. Biol., 18:303-313). In this report, the role of autocrine TGFα and the mechanism of its regulation of expression during reentry into the cell cycle from a noncycling growth state were determined in FET cells. Optimal induction of DNA synthesis from a quiescent state in FET cells is dependent upon autocrine TGFα as well as exogenous transferrin and insulin. Reentry into the cell cycle resulting from treatment with exogenous transferrin and insulin resulted in ∼3-fold induction of TGFα expression within 1 hr. TGFα induction was controlled at the transcription level, and the cis-controlling element was localized to the region between bp -370--201 relative to the translation start codon within the TGFα promoter. Thus neutralization of autocrine TGFα protein revealed that the induced TGFα autocrine activity was necessary for DNA synthesis and acted only in the early G1 phase of the cell cycle. Blockade of autocrine TGFα expression early in the cell cycle resulted in the reduction of DNA synthesis, whereas treatment with neutralization antibody at later times had no effect. This suggested that autocrine TGFα functions to initiate cell growth from noncycling states. This was further confirmed by the dependence of FET cells upon autocrine TGFα for colony formation in experiments where the plating density was sufficiently low to generate a lag phase in tissue culture. In contrast, TGFα autocrine activity was not required for exponential phase cells, as evidenced by the failure of TGFα neutralizing antibody to inhibit proliferation in this growth state. Taken together, these results suggest that autocrine TGFα acts primarily in the process of growth initiation by moving cells from a noncycling state back into the cell cycle, rather than supporting cell growth already initiated. J. Cell. Physiol. 177:387-395, 1998. © 1998 Wiley-Liss, Inc.
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  • 17
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Basic fibroblast growth factor (bFGF, FGF-2) is progressively lost from mammary epithelial cells as they become malignant. To investigate the effects of restoring the expression of bFGF in breast cancer cells, we constructed MCF-7 cells that permanently overexpress 18-kD cytoplasm-localizing bFGF (MCF-7/ΔAFGF(18) cells) and cells that express both the 18-kD along with the 22- and 24-kD nucleus-localizing bFGF peptides (MCF-7/NCFFGF(18,22,24) cells), using retroviral transduction. These stable cell constructs grew more slowly and had a larger fraction of their populations in the G0/G1 phase of the cell cycle than control cells. All forms of bFGF were eluted from MCF-7/NCFFGF(18,22,24) cell monolayers with 2 M NaCl, in contrast to fibroblasts that were demonstrated to secrete only the 18-kD bFGF isoform. High-affinity binding of 18-kD 125I-bFGF to these cells was significantly decreased, probably because of competitive binding by the autocrine-secreted bFGF. Recombinant 18-kD bFGF that was previously demonstrated in our laboratory to inhibit proliferation, activate MAP kinase, and induce the cyclin-dependent kinase inhibitor p21WAF1/CIP1 in MCF-7 cells, further inhibited MCF-7/ΔAFGF(18) cells but had no effect on MCF-7/NCFFGF(18,22,24) cells. The total cellular content of the high-affinity FGF receptors 1-3 was unchanged, but FGF receptor 4 was decreased in MCF-7/NCFFGF(18,22,24) cells. Both cell types overexpressing bFGF isoforms had elevated levels of the cyclin-dependent kinase inhibitor p27Kip1 but not that of p21WAF1/CIP1. In MCF-7/ΔAFGF(18) cells, FGFR1 and MAP kinase were constitutively phosphorylated. Exogenous recombinant 18-kD bFGF did not accentuate these effects but did induce an increase in the levels of p21WAF1/CIP1 corresponding to the further inhibition induced by exogenous bFGF in these cells. In MCF-7/NCFFGF(18,22,24) cells, FGFR1 and MAP kinase were not phosphorylated at baseline nor upon stimulation with recombinant bFGF, and exogenous bFGF only had a minimal effect on low steady-state p21WAF1/CIP1 levels. However, stimulation of these cells with phorbol ester or insulin did result in MAP kinase phosphorylation. While growth-inhibited in the G1 phase of the cell cycle, MCF-7/NCFFGF(18,22,24) cells retained active isoforms of cdk2 and the hyperphosphorylated form of Rb. These data suggest that high molecular weight forms of bFGF overexpressed in MCF-7 cells do not activate the receptor-mediated MAP kinase pathway, and do not induce p21WAF1/CIP1 in an autocrine manner, but inhibit proliferation through other, possibly direct nuclear signalling mechanisms. J. Cell. Physiol. 177:411-425, 1998. © 1998 Wiley-Liss, Inc.
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  • 18
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Bone marrow stromal cells (BMSCs) are a heterogeneous population of cells derived from colony-forming units-fibroblastic (CFU-Fs). These cells reside in the bone marrow cavity and are capable of differentiating into several cell phenotypes including osteoblasts, chondroblasts, hematopoiesis-supporting stromal cells, and adipocytes. However, the factors that regulate the proliferation and differentiation of the BMSC population are for the most part unknown. Since many members of the receptor tyrosine kinase (RTK) family have been shown to participate in growth control of various mesenchymal cell populations, in this study we examined the expression and function of RTKs in the BMSC population. Degenerate oligonucleotides corresponding to two conserved catalytic domains of the RTK family and RT-PCR were used initially to determine which RTKs are expressed in the human BMSC (hBMSC) system. After subcloning the amplification product generated from mRNA of a multicolony-derived hBMSC strain, PDGF receptor (β), EGF receptor, FGF receptor 1, and Axl were identified by DNA sequencing of 26 bacterial colonies. Furthermore, PDGF and EGF were found to enhance BMSC growth in a dose-dependent manner and to induce tyrosine phosphorylation of intracellular molecules, including the PDGF and EGF receptors themselves, demonstrating the functionality of these receptors. On the other hand, bFGF was found to have little effect on proliferation or tyrosine phosphorylation. Since single colony-derived hBMSC strains are known to vary from one colony to another in colony habit (growth rate and colony structure) and the ability to form bone in vivo, the expression levels of these RTKs were determined in 18 hBMSC clonal strains by semiquantitative RT-PCR and were found to vary from one clonal strain to another. While not absolutely predictive of the osteogenic capacity of individual clonal strains, on average, relatively high levels of PDGF-receptor were found in bone-forming strains, while on average, nonbone-forming strains had relatively high levels of EGF-receptor. Taken together, these results indicate that RTKs play a role in the control of hBMSC proliferation, and that the differential pattern of RTK expression may be useful in correlating the biochemical properties of individual clonal strains with their ability to produce bone in vivo. J. Cell. Physiol. 177:426-438, 1998. © 1998 Wiley-Liss, Inc.
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  • 19
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Vascular endothelial growth factor-C (VEGF-C) is a recently characterized member of the VEGF family of angiogenic polypeptides. We demonstrate here that VEGF-C is angiogenic in vitro when added to bovine aortic or lymphatic endothelial (BAE and BLE) cells but has little or no effect on bovine microvascular endothelial (BME) cells. As reported previously for VEGF, VEGF-C and basic fibroblast growth factor (bFGF) induced a synergistic in vitro angiogenic response in all three cells lines. Unexpectedly, VEGF and VEGF-C also synergized in the in vitro angiogenic response when assessed on BAE cells. Characterization of VEGF receptor (VEGFR) expression revealed that BME, BAE, and BLE cell lines express VEGFR-1 and -2, whereas of the three cell lines assessed, only BAE cells express VEGFR-3. We also demonstrate that VEGF-C increases plasminogen activator (PA) activity in the three bovine endothelial cell lines and that this is accompanied by a concomitant increase in PA inhibitor-1. Addition of α2-antiplasmin to BME cells co-treated with bFGF and VEGF-C partially inhibited collagen gel invasion. These results demonstrate, first, that by acting in concert with bFGF or VEGF, VEGF-C has a potent synergistic effect on the induction of angiogenesis in vitro and, second, that like VEGF and bFGF, VEGF-C is capable of altering endothelial cell extracellular proteolytic activity. These observations also highlight the notion of context, i.e., that the activity of an angiogenesis-regulating cytokine depends on the presence and concentration of other cytokines in the pericellular environment of the responding endothelial cell. J. Cell. Physiol. 177:439-452, 1998. © 1998 Wiley-Liss, Inc.
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  • 20
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Cell cycle control of histone H4 gene transcription is mediated by the multipartite promoter domain H4-Site II, which supports transcriptional activation at the G1/S phase transition and modulates basal H4 gene transcription. Proliferation-specific transcription is determined by the integrated activities of three distinct promoter factors interacting with H4-Site II: the interferon regulatory factor IRF-2 (synonymous with HiNF-M), HiNF-D (a complex between the homeodomain protein CDP-cut and the cell cycle mediators CDC2, cyclin A and pRB), as well as HiNF-P/H4TF-2. However, the contribution of HiNF-D to the enhancement and/or suppression of H4 gene transcription at specific cell cycle stages remains to be established. We used a panel of synchronized HeLa S3 cell lines containing stably integrated H4 promoter/CAT reporter gene constructs with mutations in H4-Site II. The temporal regulation of CAT mRNA accumulation under the control of the H4 promoter was analyzed by RNase protection analysis. Our main finding is that mutation of the HiNF-D/CDP-cut binding site alters the timing of histone gene activation during the cell cycle. Furthermore, our data indicate that HiNF-P/H4TF-2 may functionally compensate for HiNF-M/IRF-2 at Site II to regulate histone H4 gene transcription in HeLa S3 cervical carcinoma cells during early S phase. We postulate that HiNF-D (CDP-cut/cyclin A/CDC2/pRB containing complex) promotes HiNF-M/IRF-2 (and/or HiNF-P/H4TF-2) dependent histone H4 gene activation at the G1/S phase transition and attenuates H4 gene transcription at later cell cycle stages. The mechanistic division in the gene regulatory functions of the three H4-Site II binding proteins may ensure that histone H4 gene expression is stringently coupled with the onset of S phase in response to growth factor/cytokine-induced cell cycle progression. J. Cell. Physiol. 177:453-464, 1998. © 1998 Wiley-Liss, Inc.
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  • 21
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    Journal of Cellular Physiology 177 (1998), S. 465-473 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Human dermal fibroblasts suspended in a collagen matrix exhibit a 4-day delay in cell division, while the same cells in monolayer divided by day 1. The initial rates of 3H-thymidine incorporation by cells in monolayer or suspended in collagen were not significantly different. When suspended in collagen, there was a threefold increase in the proportion of cells in a tetraploidal (4N) DNA state compared to the same cells in monolayer. Flow cytometry analysis and 3H-thymidine incorporation studies identified the delay of cell division as a consequence of a block in the G2/M of the cell cycle and not an inhibition of DNA synthesis. The inclusion of 150 μ/ml of hyaluronic acid (HA) in the manufacture of fibroblast populated collagen lattices (FPCL) caused a stimulation of cell division, as determined by cell counting; increased the expression of tubulin, as determined by Western blot analysis; and reduced the proportion of cells in a 4N state, as determined by flow cytometry. HA added to the same cells growing in monolayer produced a minimal increase in the rate of cell division or DNA synthesis. HA supplementation of FPCLs stimulated cell division as well as tubulin concentrations, but it did not enhance lattice contraction. The introduction of tubulin isolated from pig brain or purchased tubulin into fibroblasts by electroporation prior to their transfer into collagen lattices promoted cell division in the first 24 hours and enhanced FPCL contraction. It is proposed that tubulin protein, the building blocks of microtubules, is limited in human fibroblasts residing within a collagen matrix. When human fibroblasts are suspended in collagen, one effect of added HA may be to stimulate the synthesis of tubulin which assists cells through the cell cycle. J. Cell. Physiol. 177:465-473, 1998. © 1998 Wiley-Liss, Inc.
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  • 22
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    Journal of Cellular Physiology 177 (1998), S. 474-482 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In this study we examined the regulation of cdk1 expression in normal human epidermal keratinocytes (HEKs) and neoplastic keratinocytes. Keratinocytes were growth-arrested by allowing the cells to grow to confluence or by treating them with interferon-gamma (IFNγ) or 12-O-tetradecanoyl phorbol-13-acetate (TPA). RT-PCR and Western blot analysis demonstrated that cdk1 was profoundly reduced in growth-arrested HEKs when compared with dividing HEKs. In contrast, a squamous carcinoma cell line, SCC25, did not growth-arrest in response to growth inhibitors and did not downregulate cdk1 expression. Transfection of HEKs with a reporter gene driven off a 2.5-kb fragment of the human cdk1 promoter indicated that the downregulation of cdk1 upon growth arrest was transcriptional. Deletion mapping of the cdk1 promoter indicated that a repressor region was located between -949--722 bp. This repressor region was not operative in the SCC25 cells. Examination of DNA:protein binding complexes by gel-shift analysis indicated that nuclear factors from both proliferative and growth-arrested cells bound to the DNA fragment spanning -949--722 bp. Further analysis revealed that this binding could be resolved into a constitutive and growth arrest-specific complex that bound in a similar fashion to regions spanning -892--831 bp and -831--774 bp, respectively. The putative growth arrest-specific complex was not found in contact-inhibited fibroblasts and was found at very low levels in SCC25 cells, indicating that the putative repressor binding was growth arrest-specific and possibly keratinocyte-specific. The binding complexes bound to these two fragments were localized, by competition analysis, to regions -874--853 bp and -830--800 bp. This is the first report of a transcriptional repressor being operative during keratinocyte growth arrest. J. Cell. Physiol. 177:474-482, 1998. © 1998 Wiley-Liss, Inc.
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  • 23
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    Journal of Cellular Physiology 177 (1998), S. 483-492 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Treatment with the sulfhydryl oxidant diamide denatures and aggregates cellular proteins, which prior studies have implicated as an oxidative damage that activates the heat shock transcription factor and induces thermotolerance. This study was initiated to further characterize cellular response to diamide-denatured proteins, including their involvement in diamide cytotoxicity. Cytotoxic diamide exposures at 37.0°C denatured and aggregated cellular proteins in a manner that was proportional to cell killing, but this correlation was different than that established for heated cells. Diamide exposures at 24.0°C were orders of magnitude less cytotoxic, with little additional killing occurring after diamide was removed and cells were returned to 37.0°C. Thus, protein denaturation that occurred at 37.0°C, after proteins were chemically destabilized by diamide at 24.0°C [Freeman et al., J. Cell. Physiol., 164:356-366 (1995) Senisterra et al., Biochemistry 36: 11002-11011 (1997)], had little effect on cell killing. Thermotolerance protected cells against diamide cytotoxicity but did not reduce the amount of denatured and aggregated protein observed immediately following diamide exposure. However, denatured/aggregated proteins in thermotolerant cells were disaggregated within 17 h following diamide exposure, while no disaggregation was observed in nontolerant cells. This more rapid disaggregation of proteins may be one mechanism by which thermotolerance protects cells against diamide toxicity, as it has been postulated to do against heat killing. As with heat shock, nontoxic diamide exposures induced maximal tolerance against heat killing; however, there was no detectable, increased synthesis of heat shock proteins. Thus, diamide treatment proved to be a reproducible procedure for inducing a phase of thermotolerance that does not require new heat shock protein (HSP) synthesis, without having to use transcription or translation inhibitors to suppress HSP gene expression.These results complement those from studies with other stresses to establish the importance of protein denaturation/aggregation as a cytotoxic consequence of stress and a trigger for thermotolerance induction. The data also illustrate that differences in how proteins are denatured and aggregated can affect their cytotoxicity and the manner in which thermotolerance is expressed. J. Cell. Physiol. 177:483-492, 1998. © 1998 Wiley-Liss, Inc.
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  • 24
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    Journal of Cellular Physiology 177 (1998), S. 499-499 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: No abstract.
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  • 25
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    Journal of Cellular Physiology 177 (1998), S. 501-506 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: CDK9 is a cdc2-related kinase protein. Previously named PITALRE, this protein is a serine-threonine kinase involved in many physiological processes. Unlike most of the cdc2-like kinases, its activity is not cell cycle-regulated. CDK9 acts preferentially in processes different from cell-cycle regulation, such as differentiation. Its cyclin partners, cyclins of T family, recently have been isolated. CDK9 immunoprecipitates with several unidentified polypeptides that may regulate its kinase activity. CDK9 has been shown to associate with the HIV-Tat protein, suggesting a possible involvement in AIDS. CDK9 recently was shown to be responsible for the kinase activity associated with the TAK complex and with the P-TEFb complex, suggesting activity also in the transcription process. J Cell Physiol 177:501-506, 1998. © 1998 Wiley-Liss, Inc.
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  • 26
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    Journal of Cellular Physiology 177 (1998), S. 493-498 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Ultraviolet light A (UVA) is shown to play an augmentative or synergistic role with UVB in pathophysiological conditions induced by solar radiation. Thus, UVA would contribute significantly to the development of skin malignancies. It remains unclear, however, how UVA contributes to solar radiation-induced immune suppression. Keratinocytes (KC) produce cytokines which are a significant mediator of inflammatory and immunologic reactions in skin exposed to solar radiation and are a potent mediator in the induction of immune suppression. To examine if UVA alters the expression and production of cytokines from KC, normal human keratinocytes (HuSK) were cultured and exposed to UVA at doses ranging between 2.5 and 20 kJ/m2. Constitutive expression of the p35 subunit of interleukin (IL)-12 was detected by reverse transcription-polymerase chain reaction (RT-PCR) and the p40 subunit was induced by UVA irradiation dose dependently. IL-12 protein was also detected in the supernatants from UVA-irradiated HuSK by enzyme-linked imuunosorbent assay (ELISA) and confirmed by a bioassay. On the other hand, the same doses of UVA did not induce IL-10 mRNA or IL-10 protein which has been shown to be one of the cytokines responsible for the induction of UVB-induced immunosuppression. Considering that IL-12 promotes activation of Th1 cells and prevents the activation of Th2 cells and that administration of IL-12 has been shown to block the induction of immune suppression in UV-irradiated animals, our results suggest that UVA modulates skin immune function distinctively from UVB by affecting the balance between IL-10 and IL-12 produced from KC. J. Cell. Physiol. 177:493-498, 1998. © 1998 Wiley-Liss, Inc.
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  • 27
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    Journal of Cellular Physiology 177 (1998), S. 507-517 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Neuropeptides, including mammalian bombesin-like peptides, act as potent cellular growth factors and have been implicated in a variety of normal and abnormal processes, including development, inflammation, and malignant transformation. These signaling peptides exert their characteristic effects on cellular processes by binding to specific G protein-coupled receptors (GPCR) on the surface of their target cells. Typically, the binding of a neuropeptide to its cognate GPCR triggers the activation of multiple signal transduction pathways that act in a synergistic and combinatorial fashion to relay the mitogenic signal to the nucleus and promote cell proliferation. A rapid increase in the synthesis of lipid-derived second messengers with subsequent activation of protein phosphorylation cascades is an important early response to neuropeptides. An emerging theme in signal transduction is that these agonists also induce rapid and coordinate tyrosine phosphorylation of cellular proteins including the nonreceptor tyrosine kinase p125fak and the adaptor proteins p130cas and paxillin. This tyrosine phosphorylation pathway depends on the integrity of the actin cytoskeleton and requires functional Rho. The purpose of this article is to review recent advances in unraveling the pathways that play a role in transducing mitogenic and migratory responses induced by G protein-coupled neuropeptide receptor agonists. J Cell Physiol 177:507-517, 1998. © 1998 Wiley-Liss, Inc.
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  • 28
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The pentameric B subunit of verotoxin (VT) mediates the attachment to cell surface globotriaosyl ceramide (Gb3) to facilitate receptor-mediated endocytosis of the toxin. In highly toxin-sensitive tumor cells, the holotoxin and VT1 B subunit is targeted intracellularly to elements of the endoplasmic reticulum (ER)/nuclear membrane. In less sensitive cells, the toxin is targeted to components of the Golgi apparatus. We have studied two cell systems: the induced VT hypersensitivity of human astrocytoma cell lines cultured in the presence of sodium butyrate (compared to sodium propionate and capronate) and the increased VT sensitivity of multiple drug-resistant mutants as compared to parental human ovarian carcinoma cells. In both cases, a difference in the intracellular retrograde transport of the receptor-bound internalized toxin to the ER/nuclear envelope, as opposed to the Golgi, correlated with a 〉1,000-fold increase in cell sensitivity to VT. This change in intracellular routing may be due to sorting of Gb3 fatty acid isoforms, since nuclear targeting was found in turn to correlate with the preferential synthesis of Gb3 containing shorter chain (primarily C16) fatty acid species. We propose that the isoform-dependent traffic of Gb3 from the cell surface to the ER/nuclear membrane provides a new signal transduction pathway for Gb3 binding proteins. J Cell Physiol 177:646-660, 1998. © 1998 Wiley-Liss, Inc.
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  • 29
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 15-24 
    ISSN: 1434-1948
    Keywords: Chromium ; Organometallics ; Homogeneous catalysis ; Olefin polymerization ; Polyethylene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chromium-based heterogeneous catalysts are used extensively for the polymerization of olefins. There are few homogeneous model systems that allow investigation of the reaction mechanisms and unique characteristics of chromium catalysts. Coordinatively unsaturated paramagnetic chromium alkyls containing a Cp*CrIIIR fragment (Cp* = η5-C5Me5, pentamethylcyclopentadienyl) catalyze the polymerization of ethylene and α-olefins. Correlations between molecular structure and catalytic activity are reviewed.
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  • 30
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 25-27 
    ISSN: 1434-1948
    Keywords: Bite angle ; Catalysis ; P ligands ; Palladium ; Allylic alkylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of the natural bite angle (βn) of diphosphane ligands on catalyst selectivity and activity in the palladium-catalyzed allylic alkylation was investigated. The selectivity and rate of the reaction are mainly determined by steric hindrance induced by the diphosphane ligands. The steric hindrance at the palladium center increases as the natural bite angle of the ligand becomes larger. This results in an increasing selectivity at larger bite angles, but at very large bite angles the rate of the reaction drops. The ligand with the largest calculated bite angle, Xantphos, induced 100% selectivity but the reaction rate became low.
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  • 31
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 29-35 
    ISSN: 1434-1948
    Keywords: Catalysis ; Palladium ; C-C coupling ; Metallacycles ; Trisubstituted olefins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coupling reaction of 1,1-disubstituted olefins (α-methylstyrene, n-butyl methacrylate) with various aryl bromides (Heck reaction) has been studied as a new concept to synthesize trisubstituted olefins. Surprisingly, the nature of the base dramatically influences the product distribution. Thus, a systematic investigation on the role of base in Heck reactions of 1,1-disubstituted olefins was performed. Less coordinating bases like NaOAc, NaOBz or Na2CO3 yield a statistical distribution of regioisomers with the terminal olefin 10 as the major product. However, by using amines like Bu3N or diisopropylethylamine (DIPEA) as base internal olefins can be synthesized with high selectivities. With phosphapalladacycle 3 as catalyst precursor, we were able to obtain catalyst turnover numbers up to 1000, while Pd(OAc)2/2PPh3 was one order of magnitude less active. Analysis of the reaction profile by kinetic investigations led to the postulation of a reduction and subsequent oxidative addition of the catalyst precursor 3 to form 12 as catalytically active intermediate.
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  • 32
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 43-54 
    ISSN: 1434-1948
    Keywords: Asymmetric catalysis ; Allylic alkylation ; 1,5-Dimethylbarbituric acid ; Palladium catalysts ; Chiral phosphane imine ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Allylation of 1,5-dimethylbarbituric acid (BS) with allyl acetate using in situ catalysts of palladium(II) acetylacetonate and chiral phosphane imine ligands results in the enantioselective formation of 5-allyl-1,5-dimethylbarbituric acid (ABS) as the main product with up to 34% ee and 3,5-diallyl-1,5-dimethylbarbituric acid (AABS) as a possible by-product, also with up to 34% ee. This reaction is a type of allylic alkylation, the stereoselectivity of which is difficult to control because the new stereocenter is formed in the nucleophile attacking from the side opposite to the metal atom. Classical optically active ligands do not give any enantioselectivity in this palladium-catalysed reaction. Chiral phosphane imine ligands, however, are a successful class of compound, synthesized by Schiff base condensation of 2-formylphenyl(diphenyl)phosphane with optically active primary amines. An optimisation of this ligand type showed that the substituents at the stereogenic center in the imine part should be a hydroxymethyl group and a bulky alkyl group, with the best ligand being the L-tert-leucinol derivative. A screening of other types of chiral ligand, e.g. phosphane amines and phosphane trisimines, has also been performed. NMR experiments and a molecular modelling study of the cation [(η3-allyl)Pd(2a)2]+ were carried out (tripos force field). The enantioselectivity of the phosphane imine ligands is explained by an interaction of the chiral side arm of one of the ligands, which extends to about 3 Å above the allyl plane, with the incoming nucleophile.
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  • 33
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 55-59 
    ISSN: 1434-1948
    Keywords: Arsaalkenes ; Arsenic ligands ; Carbonyl complexes ; Chromium ; Iron ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of equimolar amounts of the metalloarsaalkene [(η5-C5Me5)(CO)2FeAs=C(NMe2)2] (1) with the carbonyl complexes [Ni(CO)4], [Fe2(CO)9], and [{(Z)-cyclooctene}Cr(CO)5], respectively, affords the adducts [(η5-C5Me5)(CO)2FeAs{M(CO)n}=C(NMe2)2] with [M(CO)n] = [Ni(CO)3] (2); [Fe(CO)4] (3), and [Cr(CO)5] (4). These feature η1 coordination of the arsaalkene ligand via the arsenic atom. The molecular structures of the complexes 3 and 4 have been determined by X-ray diffraction analyses.
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  • 34
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 37-41 
    ISSN: 1434-1948
    Keywords: Tripodal P ligands ; Rhodium ; Water-soluble complexes ; Immobilization ; Biphasic hydroformylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the water-soluble tripodal phosphane ligand cis,cis-1,3,5-(PPh2)3-1,3,5-[CH2(OCH2CH2)xOCH3]C6H6 (x = 30-160) (5) has been achieved in a four-step reaction sequence. The alcohol Mo(CO)3[cis,cis-1,3,5-(PPh2)3-1,3,5-(CH2OH)3C6H6] (1) is converted to the corresponding alcoholate 2, which forms the polyethylene glycol derivative 3 in a polyaddition reaction with oxirane. After methylation of the end groups of 3, the ligand 5 is obtained by a combined photochemical/oxidative demolybdenation reaction. The water-soluble tripodal phosphane 5 and the methoxymethyl functionalized tripodal ligand 6 react with Rh(PPh3)3(CO)H to form the water-soluble and water-insoluble rhodium carbonyl hydrido complexes 5a and 6a, respectively. The catalytic activity of the rhodium complex 5a in the hydroformylation of 1-hexene was found to be comparable in a single-phase system (1-hexene/methanol) with that in the biphasic system (1-hexene/water). Only traces of alcohol were found, which demonstrates that the catalyst 5a displays higher selectivity in hydroformylation than in hydrogenation.
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  • 35
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 67-72 
    ISSN: 1434-1948
    Keywords: Gallium ; Pentacoordination ; Salen(tBu) ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work is an exploration into the synthesis and reactivity of five-coordinate gallium complexes of the ligands, Salen(tBu)H2 [N,N′-ethylenebis(3,5-di-tert-butylsalicylideneimine), (1)], Salpen(tBu)H2 [N,N′-propylenebis(3,5-di-tert-butylsalicylideneimine), (2)], Salophen(tBu)H2 [N,N′-phenylenebis(3,5-di-tert-butylsalicylideneimine), (3)], and Salomphen(tBu)H2 [N,N′-(4,5-dimethyl)phenylenebis(3,5-di-tert-butylsalicylideneimine), (4)]. Fully characterized examples include those of general formula LGaX, where L = 1, X = Cl (5), Et (6); 3, X = Cl (7), Et (10); 4, X = Cl (8), Me (9) Et (11). X-ray structural data is presented for 6, 7, 9, 10, and 11. The ability of these complexes to undergo either alkane or salt elimination reactions is described. In one reaction the unusual salt: [{Salophen(tBu)Ga(MeOH)}2]+BPh-4 (12) is obtained.
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  • 36
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 61-66 
    ISSN: 1434-1948
    Keywords: Arsenic ; Bioinorganic chemistry ; Dihydrolipoic acid ; Lipoic acid ; S ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The arsenic(III) dithiolate [PhAs(HlipS2)] (1, HlipS2-2 = reduced rac-lipoic acid) has been obtained via three different routes: (A) from (PhAsO)n and rac-dihydrolipoic acid, (B) from (AsPh)6 and rac-lipoic acid, and (C) from PhAsO(OH)2 and rac-dihydrolipoic acid. The latter method is also suitable for the preparation of [(4-NH2C6H4)As(HlipS2)] (2) from (4-NH2C6H4)AsO(OH)2. rac-Dihydrolipoic acid and Me2AsO(OH) react to give [(Me2As)2(HlipS2)] (3). These reactions indicate pathways by which mono- and diorganoarsenic compounds of various As oxidation states (I, III, and V) may inhibit enzymes that contain lipoic acid as a cofactor. X-ray structure analysis shows that 1 is a 2,4-disubstituted 1,3,2-dithiarsinane, i. e. a six-membered heterocycle. The phenyl group at the 2-position (As) adopts the axial orientation. (2RS,4RS)-1, which is the isomer found in the crystal, is thermodynamically more stable than the diastereomeric (2SR,4RS)-1 by 4.3 ± 0.8 kJ/mol (25°C). In solution, the epimerization by inversion of configuration at the ψ-tetrahedrally coordinated As atom is faster than expected, with acid catalysis (COOH groups!) being a possible cause.
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  • 37
    ISSN: 1434-1948
    Keywords: Nucleophilic phosphanylation ; Phosphanylphthalic acid ; Phosphanylphenylacetic acid ; Benzylaminophosphanes ; Water solubility ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral- and multiply-carboxylated phosphanes and phosphanyl derivatives of benzoic and phthalic acids (1-9) are accessible in high yields by nucleophilic phosphanylation of potassium or lithium salts of commercially available fluorobenzoic and 3-fluorophthalic acids with Ph2PH, Ph2PK, PhPLi2 Ph(K)P-(CH2)3-P(K)Ph in superbasic media (DMSO/KOH) or in THF and DME. The hitherto unknown phosphanylphenylacetic acids (10-13) and phosphanylbenzylamines RR′P-C6H4-CH2- NH2 (14-19, R, R′ = H, Me, Ph) with unsubstituted amino groups were also synthesized by this method. The diphenylphosphanyl derivatives 14-16 (R, R′ = Ph) are accessible by an alternative method involving LiAlH4 reduction of the phosphanylbenzonitriles (20-22), which were obtained in high yields by nucleophilic phosphanylation of the corresponding fluoro- or chlorobenzonitriles. The novel bidentate phosphanylbenzonitrile 23 has also been obtained using this synthetic route. All compounds were completely characterized by elemental analysis, NMR spectroscopy, and mass spectrometry.
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  • 38
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 83-85 
    ISSN: 1434-1948
    Keywords: Phosphorus ylides ; Bis(ylene)phosphoranes ; Halogenophosphoranes ; X-ray structure analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The iminophosphane (Me3Si)3C-P=N-Mes* (1) reacts with iodine to form the imino(methylene)phosphorane I-P(=N-Mes*)=C(SiMe3)2 (2). Upon subsequent treatment with AgCl, the corresponding chloro derivative 3 is obtained. Chlorine/bromine exchange in 3 with bromotrimethylsilane affords the bromo analogue 4. The structures of 2, 3 and 4 were confirmed by X-ray crystal structure analysis; each of the compounds features a trigonal-planar phosphorus atom.
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  • 39
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 87-91 
    ISSN: 1434-1948
    Keywords: Imido complexes ; Titanium ; Heteroallylic ligands ; Benzamidinate ligands ; Diiminophosphinate ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of Ti(NtBu)Cl2(py)2 (1, py = pyridine) with bulky heteroallylic ligands in a 1:1 molar ratio affords the monosubstituted derivatives [PhC(NSiMe3)2]Ti(NtBu)Cl(py)2 (2), [MeOC6H4C(NSiMe3)2]Ti(NtBu)Cl(py) (3), and [Ph2P(NSiMe3)2]Ti(NtBu)Cl(py) (4). Similarly, 2:1 reactions afforded the disubstitution products [PhC(NiPr)2]2Ti(NtBu)(py) (6) and [Ph2P(NSiMe3)2]2Ti(NtBu) (7). The bis(pyridine) adduct Ph2P(NSiMe3)2Li(py)2 (5) was isolated as a by-product during the preparation of 4. The molecular structures of 7 has been established by X-ray crystallography.
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  • 40
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 93-99 
    ISSN: 1434-1948
    Keywords: 2-Methyl-1,2,3,4-tetrazole-5-thiolates ; 2-Phenyl-1,2,3,4-tetrazole-5-thiolates ; Palladium ; Platinum ; Copper ; Silver ; Gold ; Molecular structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular structures of nine transition metal tetrazolethiolates have been determined by X-ray structure determinations. The ligand is invariably coordinated through its sulfur atom to the metal center [M = PdII, CuI, AgI, AuI, AuIII, and Hg]. The M-S-C bond angles vary considerably, but this cannot be correlated with variations in the C-S bond lengths. Intermolecular association occurs for Ph3PAu(SCN4Me) via Au-S contacts, leading to dimeric strands in the solid state. The copper compound (Ph3P)3Cu4(SCN4Me)4 (5), possesses a rather asymmetric structure: one Cu atom is tricoordinated by 3 sulfur atoms, the other three are tetracoordinated by P and N as well as by S atoms.
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  • 41
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 101-106 
    ISSN: 1434-1948
    Keywords: Phosphorus heterocycles ; Halogens ; Oxidations ; Electrophilic aromatic substitutions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis(phosphonio)isophosphindolide iodide 1[I] reacts with an equimolar amount of I2 to yield the trihalide 1[I3], while treatment of 1[X] (X = Br, OTf) with excess Br2 furnishes the dibromophosphonium salt 6c[X]. The bromo-substituted bis- (phosphonio)isophosphindolide cations 5a and 5b are identified as intermediates in this reaction; 5b[Br] is also obtained in pure form by reaction of 6c[Br] with Zn or NEt3. Reaction of 1[OTf] with one equivalent of PhICl2 (7) affords the dichlorophosphonium salt 8a[OTf], which undergoes further substitution reactions in the presence of excess 7 and reacts with Me3SiI to give a mixture of 1[OTf] and I2 rather than a substitution product 9[OTf]. The results of a crystal-structure determination of 8a[OTf] are reported and the mechanistic aspects of the different oxidation/substitution reactions are discussed.
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  • 42
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1-14 
    ISSN: 1434-1948
    Keywords: One-dimensional multicomponent arrays ; Energy- and electron transfer ; Molecular motions ; Ruthenium ; Osmium ; Terpyridines ; Bis-terpyridines ; Bis-cyclometallating ligands ; Porphyrins ; Copper(I) rotaxane ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transition metals are powerful three-dimensional templates, which can gather various functionalized ligands and orient them in a precise fashion so that complex multicomponent molecular systems can be obtained without constructing covalently-assembled edifices. The compounds thus prepared exhibit precise chemical or physical functions, which are governed by the design of the system. The construction of one-dimensional molecules around ruthenium(II) or osmium(II), using rigid ligands attached to the desired electroactive species, leads to systems that are able to undergo charge separation after photonic excitation. In other related compounds, a ruthenium(II)-based chromophore is, for example, connected to an osmium(II) complex by means of rod-like bridging ligand, thereby ensuring strict control over the Ru···Os distance. By tuning the length and the electronic properties of the bridge, one can control the efficiency of the electronic energy transfer between the two chromophores. In particular, the use of a bis-cyclometallating ligand is very conducive to energy transfer and allows the observation of this process up to a Ru…Os distance of ≈20 Å. By combining the building blocks of these inorganic systems with appropriate porphyrins, long-range (centre-to-centre distance between the donor and the acceptor porphyrins ≈30 Å) and relatively long-lived photoinduced charge separation has been demonstrated. Finally, with copper(I) as the template, compounds of the rotaxane family are obtained, which consist of a coordinating ring threaded by a string-like component. If this acyclic fragment is end-functionalized by two bulky stoppering groups and if it incorporates two different coordination sites (a bi- and a terdentate chelate site), novel dynamic properties are observed. The movement of a given fragment of the molecule is triggered by changing the metal oxidation state. This one-dimensional motion of the ring along the string on which it is threaded is controlled by redox manipulation, resulting in a primitive molecular machine.
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  • 43
    ISSN: 1434-1948
    Keywords: S ligands ; Transition metals ; Fluxionality ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation and characterization of RhI, PdII, and PtII complexes with chiral C2-symmetrical dithioether ligands derived from 1,1′-binaphthalene-2,2′-dithiol (BINAS) are reported. All complexes are fluxional in solution at room temp. Interconversion between the stereoisomers can take place through conformational equilibration of the chelate ring, and/or inversion of configuration at the stereogenic sulfur. In the solid state the palladium derivative of Me2BINAS shows a twisted chair conformation of the chelate ring, with both methyl groups in equatorial positions.
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  • 44
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 107-112 
    ISSN: 1434-1948
    Keywords: Silicon ; Aminosilanes ; Aziridine ; Azetidine ; Molecular conformation ; Configuration determination ; Nitrogen ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a continuation of structural investigations of poly(amino)silanes, a series of silicon derivatives of aziridine and azetidine have been prepared. Analogies with the isoelectronic phosphorus ylide species and the high barrier to inversion at nitrogen in small N heterocycles were suggestive of steeply pyramidal and rather rigid configurations at the N atoms in the title compounds. Tetrakis(N-aziridino)silane (1) and tetrakis(N-azetidino)silane (2) have been synthesized from SiCl4 and LiN(CH2)x (x = 2, 3). Compound 1 is also formed when LiN(CH2)2 and HSiCl3 are used as starting materials, but with free aziridine a non-volatile product (1a) is obtained. In neither case could any trace of HSi[N(CH2)2]3 be detected. In contrast, RSiCl3 (R = Me, Ph) could readily be converted into the corresponding tris(N-aziridino)silanes (3, 4) by treatment with excess aziridine. Tris(N-azetidino)silane (5) was accessible from HSiCl3 and excess azetidine, but the product was found to contain an unknown impurity. In order to determine the local symmetry and the dynamics of the aziridine rings, 1H-NMR spectra were recorded at low temperature (-80°C). No splitting of the signals was observed, indicating that the inversion barriers are extremely low, even in the highly strained three-membered heterocycles. Nevertheless, single-crystal X-ray diffraction studies of the N-triphenylsilyl derivatives of aziridine (6) and azetidine (7) revealed an aziridinyl group with a steeply pyramidal configuration at nitrogen in 6 (sum of the angles at N 313.32°), and an azetidinyl group with a flat geometry in 7 (sum of the angles at N 350.96°). The Si-N bond is significantly shorter in 7 as compared to that in 6.
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  • 45
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 143-153 
    ISSN: 1434-1948
    Keywords: Azaboranes ; Six-coordinate nitrogen ; Deltahedral clusters ; Cluster opening ; Cluster closure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the majority of known azaboranes NaBbHc and their derivatives, the coordination number of the nitrogen atoms within the cluster does not exceed the classical values of 3 or 4. In the azaboranes closo-NB9H10, nido-NB10H13, and closo-NB11H12 and in their derivatives, however, the nitrogen atoms are 5- or 6-coordinate and thus represent a novel bonding situation. The synthesis, structure, and reactivity of these azaboranes are reviewed in this article.
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  • 46
    ISSN: 1434-1948
    Keywords: Arene complexes ; Catalysis ; Diazadiene complexes ; Iron ; Metal vapour ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two different routes to novel [(diene)(η6-2,6-dimethylpyridine)Fe] complexes are reported, both of which utilize metal vapour reactions. The presence of two small substituents on the 2,6-position of pyridine is essential for the η6-coordination of the heterocycle. Investigations on the reactivity and stability of the [(diene)(η6-arene)Fe] complexes are presented, including those of the benzene, phosphinine, and pyridine derivatives. These investigations give some hints to the relevant factors for determining the interaction between an iron atom and a π-coordinated neutral arene ligand, and their modification by a nitrogen or a phosphorus atom. Selective substitution of the 1,5-cyclooctadiene (COD) ligand of [(COD)(η6-arene)Fe] complexes by some 1,4-diaza-1,3-diene (DAD) derivatives is possible in the case of the benzene or phosphinine arene ligands, and [(DAD)(η6-arene)Fe] complexes are formed, but all DAD derivatives tested so far cause the complete disintegration of [(COD)(η6-2,6-dimethylpyridine)Fe]. [(DAD)(η6-arene)Fe] complexes exhibit a catalytic potential, which was evaluated by experiments on the catalytic cyclodimerization of 1,3-butadiene in the presence of [(Et2AlOEt)2] as a co-catalyst. This reaction yields up to 92% of 1,5-cyclooctadiene, and an almost quantitative butadiene conversion is possible in the presence of less than 0.1% of the catalyst. Structural investigations on [(N,N′-bis(cyclohexyl)ethylenediimine)(η6-toluene)Fe] 5a reveal some details of the Fe-DAD interaction. An effective electron back-donation from occupied iron d-orbitals into the π*-LUMO of the DAD is indicated.
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  • 47
    ISSN: 1434-1948
    Keywords: Bromine ; Imidazoline-2-selone ; Hypervalent Se compounds ; Dications ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidative addition of Br2 to the imidazoline-2-selone derivatives 1a-c has been studied by spectrophotometric and conductometric techniques. The experimental results clearly indicate that this reaction involves the dications 2a-c, containing an Se-Se bond, as intermediates in the formation of the hypervalent 10-Se-3 selenium compounds 3a-c containing the Br-Se-Br group. The crystal structure of 1,2-bis(3-methyl-4-imidazolin-2-ylium dibromoselenanide)ethane (3c), a new stable hypervalent 10-Se-3 compound, is also reported.
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  • 48
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 127-135 
    ISSN: 1434-1948
    Keywords: Tungsten ; Ditungsten complexes ; Acetylene complex ; Tritungsten complex ; W-W single bond ; W-W triple bond ; Photochemistry ; C-C bond formations ; Olefins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [W2(η5-C5H5)2(CO)4(μ-η2:2-C2H2)] (1) and ethylene (A) react when irradiated with UV light at 253 K predominantly to [W2(η5-C5H5)2(CO)3(μ-η1:4-C4H5)(μ-H)] (3A), [W2(η5-C5H5)2(CO)4(μ-η1:3-C4H6)] (4A), and thermolabile [W2(η5-C5H5)2(CO)3(η4-C4H6)] (5A). Similarly, propene (B), 1-butene (C), and (E)-2-butene (D) yield mixtures of [W2(η5-C5H5)2(CO)3(μ-H)(μ-η1:4-1,3-dien-1-yl)] (3B, 3 C, 3D), [W2(η5-C5H5)2(CO)4(μ-η1:3-C4H5R] (4B, 4C), and [W2(η5-C5H5)2(CO)2(μ-η1:2-CO)(η4-1,3-diene) (5B, 5 C, 5D). With B and C also thermolabile [W2(η5-C5H5)2(CO)3(μ-η2:2-C2H2)(η2-C2H3R)] (2B, 2C) are formed. A by-product of the reaction of 1 with D is [W(η5-C5H5)(CO)(H){η4-(E)-C5H7CH3}], which is generated in two diastereomeric forms (6, 6′). In contrast, 1 yields no complexes with (Z)-2-butene (E) which contain ligands formed from coordinated acetylene and the olefin. From the reaction mixture only trinuclear [W3(η5-C5H5)3(CO)5(μ-η1:2-C2H3)] (7) was isolated, an alicyclic complex with a W-W single and a W-W triple bond. The crystal and molecular structures of 5D and 7 were determined by X-ray structure analysis. The constitutions of the other complexes were ascertained by IR and 1H-NMR spectroscopy.
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  • 49
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 159-161 
    ISSN: 1434-1948
    Keywords: Oxo clusters ; Titanium ; Metal alkoxides ; Sol-gel processes ; Carboxylato complexes ; Solid-state structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ti9O8(OPr)4(methacrylate)16 was obtained by the reaction of Ti(OPr)4 with an excess of methacrylic acid and analyzed by X-ray diffraction. The compound consists of a ring of nine [TiO6] octahedra linked by six μ2- and only two μ3-oxide bridges.
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  • 50
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 155-157 
    ISSN: 1434-1948
    Keywords: Bite angle ; Catalysis ; P ligands ; Palladium ; Cross-coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of the natural bite angle (βn) of diphosphane ligands on catalyst selectivity and activity in the palladium-catalyzed cross-coupling of sec-butyl magnesium chloride with bromobenzene was investigated. The calculated natural bite angles range from 78° for dppe (1,2-bisdiphenylphosphanoethane) to 110° for Xantphos. The natural bite angle of diphosphane ligands has a large effect on catalyst selectivity and activity. Both rate and selectivity of the cross-coupling reaction increase with increasing bite angle and reach a maximum value with DPEphos (βn = 102.7° ). Larger bite angles of the diphosphane ligands result in a decreased selectivity and activity.
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  • 51
    ISSN: 1434-1948
    Keywords: Pyridine ligands ; Bidentate bridging ligands ; Palladium ; Platinum ; N ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the new potentially tridentate ligand 3,5-bis(dimethylaminomethyl)pyridine (3) is described. Coordination chemistry of this ligand has been investigated with PdII and PtII precursor compounds. Both a bidentate bridging bonding motif and a monodentate bonding mode is observed. The latter compounds incorporate 3 by coordination through the pyridinic N atom only. The former complexes contain ligand 3 bonded to 2 metal centres by bridging through coordination of one trialkyl N donor atom and the pyridinic N atom. The solid-state structure of a ligand bridged Pd dimer has been elucidated by single-crystal X-ray diffraction and corroborates with the solid-state IR data that suggested a trans-PdCl2 unit was present.
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  • 52
    ISSN: 1434-1948
    Keywords: Ligand field spectra ; Phosphonate complexes ; X-ray structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and characterization of transition-metal coordination compounds containing the ligand diethyl 2-quinolylmethylphosphonate (2-qmpe) is described. Complexes of CoII, MnII, NiII, CdII, and ZnII were found to be mutually isomorphous according to their X-ray powder diffraction patterns and IR spectra. The new coordination compounds were identified and characterized by elemental analysis, magnetic measurements, infrared and ligand-field spectra. The crystal structures of the complexes [M(2-qmpe)4(H2O)2](ClO4)2 (M = Ni, 1; Mn, 2) reveal six-coordinate [M(2-qmpe)4(H2O)2] cations with the qmpe ligand coordinating via the oxygen rather than via the nitrogen atom, as well as lattice perchlorate anions. The metal ion is octahedrally surrounded by the four oxygen atoms of the four organic ligands. The non-participation of the pyridine nitrogen atom is unusual. The two water molecules occupy the fifth and the sixth coordination sites in a trans configuration. The coordinated water molecules are strongly hydrogen-bonded to the pyridine nitrogen atom of the 2-qmpe, further stabilizing the solid-state structure. The geometry of the metal ion can be described as distorted octahedral. For the CuII complex, a hydroxo-bridged dinuclear structure of the type [Cu(2-qmpe)2(OH)(H2O)2]2(ClO4)2 is proposed, based on its spectroscopic and magnetic properties. Ligand-field spectra of the Co and Ni compounds were found to be in agreement with the tetragonally distorted octahedral geometry.
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  • 53
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 183-189 
    ISSN: 1434-1948
    Keywords: Tripodal ligands ; Cobalt complexes ; Bridging ligands ; Exchange coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Weak antiferromagnetic exchange interactions are observed in two CoII dimers of the general formula [{(triphos)Co}2(μ-dicarboxylato)](BF4)2 where the dicarboxylate is the dianion of fumaric acid [3 ·(BF4)2] or terephthalic acid [4 ·(BF4)2] and triphos is the tridentate phosphorus ligand 1,1,1-tris(diphenylphosphanomethyl)ethane. In these complexes the metal ions are separated by 8 and 10 Å, as determined by X-ray crystallography. Insight into the interaction pathway is gained through molecular orbital calculations performed on model compounds. The influence of bridging-ligand distortions and the stereochemistry around the two cobalt centres is discussed.
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  • 54
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 177-181 
    ISSN: 1434-1948
    Keywords: Silanes ; Rearrangements ; Polysilanes ; Hypersilylalcohols ; 1,2-Trimethylsilyl migration ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the presence of strong acids, such as HCl or H2SO4, 1-hydroxyalkyltris(trimethylsilyl)silanes (Me3Si)3Si-C(OH)R1R2 (1a-f) isomerize by 1,2-Me3Si/OH exchange to give the trimethylsilylmethylsilanols (Me3Si)2Si(OH)-C(SiMe3)R1R2 (4a-f) [R1,R2: a: Me, Me; b: H, 4-MeC6H4; c: H, 4-iPrC6H4; d: H, Mes; e: H, 2-Me2NC6H4; f: H, 2,4,6-(MeO)3C6H2]. A mechanism for the isomerization is proposed. In the case of the reaction of 1d with sulfuric acid, the silylsulfate (Me3Si)2Si(OSO3H)-C(SiMe3)HMes (5) was isolated. 5 is the intermediate in the H2SO4-catalyzed isomerization of 1d and was converted in situ with methanol, acetic anhydride, HF or HCl to give the respective methoxysilane 6, acetoxysilane 7, fluorosilane 8, or chlorosilane 9. Deprotonation of 4a, d, f with sodium hydride causes a further rearrangement, a 1,3-C,O-trimethylsilyl migration, to give the siloxanes (Me3Si)2(Me3SiO)Si-CHR1R2 (11a, d, f).
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  • 55
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 191-202 
    ISSN: 1434-1948
    Keywords: Polynuclear complexes ; Carbene complexes ; Bridging ligands ; Alkynyl complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sequential reaction of two equivalents of the dimethylamino(ethynyl)carbene complexes [(CO)5M=C(NMe2)C≡CH] [M = W (1a), Cr (1b)] with two equivalents of nBuLi and one equivalent of a transition metal dichloride, [Cl2M′(Ln)], affords trinuclear biscarbene complexes of the type [(CO)5M=C(NMe2)C≡C-M′(Ln)-C≡CC(NMe)2=M(CO)5] [M′(Ln) = Ni(PEt3)2 (2a, b), Pd(PEt3)2 (3a, b), Pt(PEt3)2 (4a, b), Fe(dmpe)2 (6a), Hg (8a), Ti(η5-C5H5)2 (9a, b)] [dmpe = 1,2-bis(dimethylphosphino)ethane]. Treatment of 1a with equimolar amounts of first nBuLi and then [Cl2M′(Ln)] results in the formation of the monosubstitution products [(CO)5W=C(NMe2)C≡CM′(Ln)] [M′(Ln) = trans-Pd(PEt3)2Cl (5a), trans-Fe(dmpe)2Cl (7a)]. Additionally, the synthesis of the heterobimetallicethynylcarbene complex [(CO)5W=C(NMe2)C≡CPd(PEt3)2C≡CH] (10a), starting from 1a and [ClPd(PEt3)2C≡CH], is described. When three equivalents of 1a are treated, first with three equivalents of nBuLi and then with one equivalent of the trihalides PCl3 or BBr3, the novel tris(ethynylcarbene) complexes [{(CO)5W=C(NMe2)C≡C}3E] [E = B (11a), P (12a)] are obtained. The reaction of four equivalents of 1a,b with four equivalents of nBuLi, followed by addition of one equivalent of a group 14 tetrachloride [M′Cl4], yields the novel tetrakis(ethynylcarbene) complexes [{(CO)5M=C(NMe2)C≡C}4M′] [M′ = Si (13a, b), Ge (14a), Sn (15a, b)]. The complexes 8a, 9a, 12a, and 15a were characterized by X-ray structural analyses. All spectroscopic and structural data suggest that the carbene fragments and the central transition metal or heteroatom in these new bis-, tris-, and tetrakis(ethynylcarbene) complexes interact only weakly.
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  • 56
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 203-210 
    ISSN: 1434-1948
    Keywords: Gallium(III) halides ; Indium(III) halides ; Phosphanes, polydentate ; Complexes ; Crystallography ; Lewis acid catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of gallium and indium trihalides with 1,2-bis(diphenylphosphanyl)benzene (DP) and bis[(2-diphenylphosphanyl)phenyl]phenylphosphane (TP) lead to a variety of molecular and ionic complexes. Treatment of InCl3 with DP results in [(DP)2InCl2]+[InCl4]- (1). With InBr3 or InI3 molecular 1:1 complexes (DP)InX3 (2: X = Br, 3: X = I) and ionic 1:2 complexes [(DP)InX2]+[InX4]- (4: X = Br, 5: X = I) are obtained. With GaBr3 and GaI3 only the ionic complexes [(DP)GaX2]+[GaX4]- (6: X = Br, 7: X = I) are generated. According to single-crystal X-ray analyses the environment of the metal center is octahedral in the cation of 1, square pyramidal in 3, and tetrahedral in the cations of 5 and 7. The reactions of TP with GaI3 or InI3 afford ionic complexes [(TP)MI2]+[MI4]- (8: M = Ga, 9: M = In). As shown by 31P-NMR studies and X-ray analyses, TP acts as a bidentate ligand in both complexes. The central phosphorus atom is not engaged in coordinative bonding. The 31P resonances of all compounds appear at higher field as compared to the free ligand. This phenomenon calls for further investigations and a detailed theoretical treatment.
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  • 57
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 221-226 
    ISSN: 1434-1948
    Keywords: Polysilanes ; Polysilyl anions ; Silylpotassium ; Silicon ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is presented for the synthesis of tertiary, secondary, and primary polysilylpotassium compounds. Reaction of potassium tert-butoxide, in either DME or THF, with a suitable precursor molecule, proceeds by cleavage of a trimethylsilyl- polysilanyl bond, and formation of trimethylsilyl tert-butyl ether and a polysilanylpotassium compound. This route allows easy and flexible access to a number of novel polysilanylpotassium compounds, avoiding the hitherto common use of poisonous mercury compounds.
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  • 58
    ISSN: 1434-1948
    Keywords: Rhenium ; Oxacyclocarbene complexes ; Vinylidene comlexes ; Alkynols ; Tripodal ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various β-, γ-, and δ-alkynols have been reacted with the 16e- fragment [(triphos)Re(CO)2]+ generated in situ by H2 elimination from [(triphos)Re(CO)2(η2-H2)]BF4 [triphos = MeC(CH2PPh2)3]. Irrespective of the length of the alkyl chain between the C≡C and OH functional groups in the ω-alkynol, 2-oxacyclocarbene complexes are obtained. These include the 2-oxacyclopentylidene derivatives [(triphos)Re(CO)2{=CCH2CH2CH2O}]BF4 and [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]BF4, the 2-oxacyclohexylidene dervivatives [(triphos)Re(CO)2{=CCH2CH2CH2CH2O}]BF4 and[(triphos)Re(CO)2{=CCH2CH2CH2CH(Me)O}]BF4, and the 2-oxacycloheptylidene complex [(triphos)Re(CO)2{=CCH2CH2- CH2CH2CH2O}]BF4. The latter compound contains a unprecedented seven-membered oxacarbene ring. The rhenium-assisted δ-alkynol to 2-oxacyloheptylidene rearrangement proceeds via the hydroxybutylvinylidene kinetic intermediate [(triphos)Re(CO)2{C=C(H)CH2CH2CH2CH2OH}]BF4, which has been characterized in both the solid state and solution. An X-ray analysis has been carried out on a single crystal of [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]BF4. The structure of this complex consists of [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]+ cations and tetrafluoroborate anions with no interspersed solvent molecules. A facial triphos ligand, two cis-disposed carbonyl groups and a 2-oxacyclopentylidene ligand coordinate the Re centre in a slightly distorted octahedral environment.
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  • 59
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 227-235 
    ISSN: 1434-1948
    Keywords: Hydrostannylation ; Phosphaalkynes ; 1,2-Dihydro-1,3-diphosphetes ; Homocubanes ; Carbonyl complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydrostannylation of phosphaalkynes 8 with tin hydrides 1 depends on the stoichiometry employed: Thus, the 1,2-dihydro-1,3-diphosphetes 10 are isolated when an excess of phosphaalkyne 8 is used. On the other hand, an increase in the tin hydride concentration favors the formation of the phosphanes 11 and 12. Synthesis of the 1,2-dihydro-1,3-diphosphetes 14 and 16 was achieved by the use of diorganotin hydrides 13 or chloro(organo)tin hydrides 4, respectively. An isolated and characterized by-product of the latter reaction was the phosphorus-carbon-tin cage 17. Furthermore, the following reactions of the 1,2-dihydro-1,3-diphosphetes 10 were performed: isomerization reactions, complexation reactions with transition-metal complexes, and substitution of the hydrogen atom by iodine.
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  • 60
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 237-244 
    ISSN: 1434-1948
    Keywords: Titanium complexes ; Amido-cyclopentadienyl ligand ; Titanium alkyl ; Intramolecular coordination ; Ethene polymerization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Titanium complexes containing a linked isopropyl- or benzylamido(tetramethylcyclopentadienyl) ligand C5Me4SiMe2NR (R = iPr, CH2Ph,) and one bidentate organyl group C6H4(CH2NMe2)-2, CH2C6H4(NMe2)-2, and {η5-C5H3(CH2NMe2)-2}Fe(η5-C5H5) were prepared by salt metathesis of the corresponding dichloro complex Ti(η5:η1-C5Me4SiMe2NR)Cl2 with the lithium organyl. Single crystal X-ray structural analysis of Ti(η5:η1-C5Me4SiMe2NCH2Ph)- {C6H4(CH2NMe2)-2}Cl and of Ti(η5:η1-C5Me4SiMe2NiPr){CH2C6H4(NMe2)-2}Cl revealed the presence of intramolecular coordination with square pyramidal geometry around titanium. In the ferrocenyl derivative Ti(η5:η1-C5Me4SiMe2NCH2Ph)[{η5-C5H3(CH2NMe2)-2}Fe(η5-C5H5)]Cl the NMe2 group is not bonded at the titanium atom. Ethene polymerization catalyzed by these complexes upon activation with methylaluminoxane was examined.
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  • 61
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 245-252 
    ISSN: 1434-1948
    Keywords: Alkylamines ; Arylamines ; Zinc ; Cadmium ; Mercury ; X-ray diffraction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Homoleptic intramolecularly stabilized organozinc, -cadmium, and -mercury compounds MR2, with R bearing an amino function, have been synthesized from the corresponding metal dichlorides MCl2 and the lithium salts LiC6H4CH2NEt2-2 (1), LiC6H3(CH2NMe2)2-2,6 (2), LiC6H3(CH2NEt2)2-2,6 (3), (LiCH2CH2CH2)2NMe (4), and LiCH2CH2CH2NC5H10 (5). The crystal structures of Hg(C6H4CH2NEt2-2)2 (1c), [M(CH2CH2CH2)2NMe]2 [M = Zn (4a), Hg (4c)], and of M(CH2CH2CH2NC5H10)2 [M = Zn (5a), Cd (5b)] have been determined by X-ray diffraction. 4a and 4c form dimers with an unusual coordination number (three) of the central metal.
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  • 62
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 253-256 
    ISSN: 1434-1948
    Keywords: Titanium ; Vinylidene complexes ; [2+2] Cycloaddition ; Metallacycles ; Azatitanacyclobutanes ; Clathrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The titanocene vinylidene intermediate [Cp*2Ti=C=CH2] (9) reacted with the carbodiimides R-N=C=N-R [R = p-CH3C6H4 (19a), C6H11 (19b)] to give the N=C-cycloaddition products [Cp*2Ti{-NR-C(=NR)-(C=CH2)-}] [(R = p-CH3C6H4 (20a), C6H11 (20b)]. The X-ray structure of 20a in form of a surprisingly stable n-hexane clathrate is presented. The azatitanacyclobutane [Cp*2Ti{-NPh-C(Ph)(H)-(C=CH2)-}] (22) was formed from the reaction between 9 and benzylidene aniline [PhN=C(Ph)H (21)]. Reactivity studies showed that azatitanacyclobutanes are unreactive upon typical ring-enlargement reactions as observed for other four-membered titanacycles.
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  • 63
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 257-261 
    ISSN: 1434-1948
    Keywords: Phosphorus heterocycles ; 2H-Azaphosphirene complexes ; Carbene complexes ; Tungsten ; Cyclizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-yield synthesis of para-substituted pentacarbonyl(3-phenyl-2H-azaphosphirene)tungsten complexes is reported, using a multi-step rearrangement reaction. Spectroscopic and mass-spectrometric data of these heterocyclic complexes are discussed; the 31P-NMR-chemical shifts clearly reflect the electronic influence of the para-phenyl substituents and the correlation with Hammett σp-constants is almost linear.
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  • 64
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 263-270 
    ISSN: 1434-1948
    Keywords: Zinc complexes ; Pyrazolylborate ligands ; Phosphate ligands ; Hydrolytic cleavage ; Condensation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Five different (pyrazolylborate)zinc hydroxide complexes Tp*Zn-OH (1) were used as hydrolytic reagents towards esters of various acids of phosphorus. Trimethyl phosphate and trimethyl phosphite could not be cleaved. Dimethyl and diphenyl phosphite yielded TptBu,MeZn-OPHO(OR) (2, 3). Triphenyl phosphate reacted slowly producing moderate yields of Tp*Zn-OPO(OPh)2 (4). Tris(p-nitrophenyl) phosphate was cleaved rapidly, forming Tp*Zn-OPO(OC6H4NO2)2 (5) and Tp*Zn-OC6H4NO2 (6). Alkylbis(p-nitrophenyl) phosphates showed intermediate reactivity, losing p-nitrophenolate upon hydrolysis and producing Tp*Zn-OPO(OR)(OC6H4NO2) (7, 8). When phosphorus acid diesters were employed, condensation between the Zn-OH and P-OH functions occurred. This proved to be the convenient way of preparing the organophosphate complexes Tp*Zn-OPO(Ph)2 (9), Tp*Zn-OPO(OPh)2 (4), and Tp*Zn-OPO(OC6H4NO2)2 (5). Six structure determinations showed the structural variability of the resulting complexes.
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  • 65
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 271-274 
    ISSN: 1434-1948
    Keywords: Zinc complexes ; Pyrazolylborate ligands ; Hydrolytic cleavage ; Diphosphate ; Sulfonatophosphate ; Disulfonate ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three (pyrazolylborate)zinc hydroxide complexes Tp*Zn-OH were used as hydrolytic reagents to cleave the P-O-P, P-O-S, and S-O-S linkages of organic diphosphates, sulfonatophosphates, and disulfonates. The resulting complexes of the types Tp*Zn-OPO(OR)2 and Tp*Zn-OSO2R could also be obtained by condensation reactions between Tp*Zn-OH and HO-PO(OR)2 or HO-SO2R. Two of them were characterized by structure determinations.
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  • 66
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 275-281 
    ISSN: 1434-1948
    Keywords: Molybdenum ; Peroxo complexes ; Hydrogen bonds ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ring-opening reaction of epoxycyclohexane with 2-[3(5)-pyrazolyl]pyridine results in the formation of racemic trans-2-[3-(2-pyridyl)-1-pyrazolyl]cyclohexanol (1). Kinetic resolution with lipase B from candida antarctica gives the (1S,2S) enantiomer of 1, the solid-state structure of which was determined by X-ray crystallography, as an enantiomerically pure tridentate ligand. Investigation by NMR spectroscopy of the corresponding oxodiperoxomolybdenum complex 2, where 1 acts as a bidentate chelate, proves the formation of a weak intramolecular MoVI(O2)····HO-C bridge in CHCl3 solution. This H bonding is broken by solvents such as acetone, THF or DMF, which are capable of forming hydrogen bonds to alcohols. Intermolecular hydrogen bonds between the OH groups and molybdenum peroxo moieties are also found in the solid-state structure of 2, leading to a helical arrangement of the peroxo complexes.
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  • 67
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 283-289 
    ISSN: 1434-1948
    Keywords: Gold ; Chalcogenide ; Flux reaction ; Structure determination ; Metal-metal bonding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The novel compounds K2AuPS4 (1), Tl2AuPS4 (2), K2AuAsS4 (3), and KAu5P2S8 (4) have been synthesized by direct reaction of the elements with a molten alkaline polythiophosphate(arsenate) flux at 550°C. The crystal structures of these compounds have been determined by single-crystal X-ray diffraction techniques. 1, 2, and 3 crystallize in the monoclinic space group P21/m. The structures of 1, 2, and 3 consist of infinite, one-dimensional anionic chains running along the crystallographic b axis. The chains are separated by potassium or thallium ions. Neighbouring Au atoms are bridged by MS43- tetrahedra (M = P, As) in a trans orientation. Compound 4 crystallizes in the space group P21/c. The anionic chains of 4 are built up from linear AuS2 dumbbell units and PS43- tetrahedra. The chains extend along the [110] and [110] direction and are separated by charge balancing K+ cations. Each of the compounds was investigated by differential thermal analysis, FT-IR, and solid-state UV/Vis diffuse reflectance spectroscopy.
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  • 68
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 291-293 
    ISSN: 1434-1948
    Keywords: Boron ; Iron ; Boryl complexes ; η1-Coordinated borazine ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of η1-borazine complexes were obtained by the reaction of trichloroborazine with Na[(η5-C5R5)Fe(CO)2]. The compounds [{(C5R5)(CO)2Fe}nCl3-nB3N3H3] (1a, n = 1, R = Me; 1b, n = 2, C5R5 = C5H4Me; 1c, n = 3, R = H) have one to three iron-boron σ bonds and Fe-B π-interactions can be ruled out from the spectroscopic and structural results. All new borazine complexes were isolated as orange crystalline solids and characterized by multinuclear NMR methods and IR spectroscopy. The structure of 1b in the crystalline state was also determined by a single-crystal X-ray study.
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  • 69
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 295-298 
    ISSN: 1434-1948
    Keywords: Conjugate addition ; Enones ; Steroids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transmetallation of arylmagnesium halides or aryllithium with Me2AlCl results in the formation of aryldimethylaluminum compounds. These arylaluminum compounds are useful reagents for conjugate additions to enones in the presence of Ni(acac)2 as a catalyst. 3-Aryl ketones are obtained in good yields in these catalytic reactions. Starting from the 3-oxo-Δ1,4-steroids this method gives access to 1α-arylsteroids.
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  • 70
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 299-303 
    ISSN: 1434-1948
    Keywords: Calix[4]arenes ; Calix[4]arene complexes ; Molybdenum ; Tungsten ; Metal-metal bonding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Addition of p-tert-butylcalix[4]arene LH4 to the dinuclear compounds M2(NMe2)6 (M = Mo, W) results in the formation of [NH2Me2]2[L2M2] 1 (M = Mo) and 2 (M = W). Both compounds have been characterized by spectroscopic methods and single-crystal X-ray diffraction. The metal-metal distances of 1 and 2, of 2.194(1) Å and 2.293(1) Å, respectively, are consistent with the retention of the M≡M triple bond. Both „ate” complexes contain a [M≡M]6+ dimetal core, supported by two bridging μ2-κ2O,κ2O-calix[4]arene ligands in the solid state. These compounds are the first examples of a formally fourfold deprotonated calix[4]arene acting as a μ2-κ2O,κ2O bridging ligand for two transition metal centres. The calix[4]arenes in 1 and 2 are distorted from a cone conformation in the uncomplexed ligand, to an elliptical cone section. 1H-NMR data at variable temperatures suggest fluxional behaviour of 1 and 2 in solution.
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  • 71
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 305-310 
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Carbene homologues ; Boron ; Isoelectronic analogues ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: While Arduengo-type carbenes are now well established for the Group IVa elements carbon, silicon and germanium, they are experimentally unknown for the isoelectronic anions with the Group IIIa elements boron, aluminum, gallium, and indium. In the present quantum chemical investigations, the bonding features of this class of compounds are explored. As a result, they are predicted to be stable species with sizeable singlet-triplet energy separations and electron affinities. Hence, they may be considered as valid targets for experimental investigations. An analysis of the electron density distribution in the case of boron and aluminum reveals a strongly polar B-N bond for the former, and a half Al-N bond with positive charge at the aluminum, emphasizing the donor-acceptor formulation for the latter.
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  • 72
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 311-317 
    ISSN: 1434-1948
    Keywords: Molecular recognition ; Amides ; Aluminium ; Thallium ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ligands containing aromatic nitrogen heterocycles play a leading role in the molecular self assembling processes that lead to macromolecular architectures. The inductive effect of various metal fragments on those building blocks has not yet been studied systematically. To evaluate this effect we synthesized the homologous series of Group-13 metal complexes [Me2AlPy2N] (1), [Me2GaPy2N] (2), [Me2InNPy2]2 (3), and [Me2TlNPy2]∞ (4) (Py = 2-NC5H4), and characterized them by low-temperature X-ray structure analysis and 15N-NMR spectroscopy in solution. The electronic equivalence of the central and the ring nitrogen atoms leaves the energetic hyperface of the anion quite flat, and the electron density is polarized according to the requirements of the metal. In the aluminum and the gallium complexes 1 and 2 the metal center is coordinated exclusively through the nitrogen atoms within the pyridyl rings. The complexes with these hard metals are close-contact ion pairs. In the indium complex 3 the cis-cis orientation gives rise to a dimeric structure, while the unprecedented cis-trans arrangement in the thallium compound 4 leads to a polymeric structure. The complexes 3 and 4 have to be regarded as separated ion pairs of Me2M+ cations and Py2N- anions without any covalent bonds between the anionic moiety and the dimethylmetal cations, even in the solid state. The series of complexes proves the bis(2-pyridyl)amide to be an excellent self-adapting ligand. These findings are substantiated by NMR-spectroscopic studies in solution. Not only do the steric requirements of N heteroaromatic ligands have to be considered in molecular self-assembling processes but also the inductive effect of the different metal fragments.
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  • 73
    ISSN: 1434-1948
    Keywords: Palladium ; Platinum ; Bidentate nitrogen ligands ; p-Quinone ; Alkenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Compounds of the type M(N∩N-κN)(nq)2 and M2(μ2-N∩N)(μ2-pbq)2, in which nq = 1,4-naphthoquinone, pbq = 1,4-benzoquinone, and N∩N is a monodentate or bridging ligand of the α-diimine type, were obtained from reactions of Pd(dba)2 in toluene with the 3,3′-annelated-2,2′-bipyridines: 4,5-diazafluoren-9-one (dafo) and 4,5-diazafluorene (dafe) in the presence of the appropriate p-quinone. In the corresponding reactions with 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 2,2′-bipyrimidine (bpym), N,N′-dicyclohexyl-1,4-diaza-1,3-butadiene (chex-dab), bis[N-(o,o′-diisopropyl)phenylimino]acenaphthene (o,o′-iPr2-bian) and 5,6-dihydro-1,10-phenanthroline (dh-phen) only complexes of the type M(N∩N-κ2N)(Q) were formed (Q = nq, pbq). The structures of the complexes have been established by NMR in solution and by X-ray diffraction in the solid state; crystal structures of Pd(bpy-κ2N)(η2-pbq) (1) Pd(dafo-κN)(η2-nq)2 (14) and Pd2(μ2-dafo)(μ2,η2:η2-pbq)2 (16) have been determined. Of the ligands, dafo and dafe are the only ones apt to form complexes containing a monodentate or bridging N∩N ligand. This behaviour is ascribed to the geometrical constraints of dafo and dafe; the annelation by one carbon atom at the 3,3′-positions in these ligands causes an increase in bite angle from approximately 77° to 82°.
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  • 74
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 331-337 
    ISSN: 1434-1948
    Keywords: Bis(pentamethylcyclopentadienyl)phosphanes ; Aminobis(pentamethylcyclopentadienyl)phosphanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bis(1,2,3,4,5-pentamethyl-1,3-cyclopentadien-1-yl)phosphanes 3-7 are formed in good yields by the reaction of the halogenophosphanes 2a or 2b with the appropriate nucleophile. Following another route, the dialkylaminobis(pentamethylcyclopentadienyl)phosphanes 11a-c have been synthesized by the treatment of dichloro(dialkylamino)phosphanes with two equivalents of (pentamethylcyclopentadienyl)lithium. The compounds 3-11 have been characterized by multinuclear NMR spectroscopy and 3, 5, 6, and 11a have also been characterized by single-crystal X-ray diffraction studies. The molecular structure of 11a is governed by steric congestion, which typically would lead to a parallel arrangement of the two pentamethylcyclopentadienyl ligands at the phosphorus atom. However, surprisingly, the crystal structure of the (dimethylamino)phosphane 11a, exhibits a tilted, rather than a parallel, conformation of the pentamethylcyclopentadienyl groups [tilt angle: 130.6(1)°].
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  • 75
    ISSN: 1434-1948
    Keywords: Rhodium ; Phosphanes ; Ligand redistribution ; Dichloromethane activation ; Oxidative addition ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dichloromethane reacts with dinuclear rhodium complexes [{(PR3)2Rh}2(μ-Cl)2] to give the bridging-methylene complexes [{(PR3)2RhCl}2(μ-Cl)2(μ-CH2)] (PR3 = PEt3, PPh2Me). The structure of the PEt3 complex has been established by X-ray diffraction study. The early stages of the reaction of [{(C8H14)2Rh}2(μ-Cl)2] with monophosphanes have been monitored by 31P NMR, evidencing chloride bridges cleavage and phosphane redistribution processes.
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  • 76
    ISSN: 1434-1948
    Keywords: Carbene complexes ; Carbyne complexes ; Asymmetric synthesis ; Carbohydrates ; Chiral auxiliaries ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral carbene complexes [Cp(CO)2Mn=C(OR*)Ph] (4a-e) were prepared by reaction of [Cp(CO)2Mn=C(OAc)Ph] (2) with HOR* [HOR* = 1,2:3,4-di-O-isopropylidene-D-galactopyranose (3a), 2,3,4,6-tetra-O-acetyl-D-galactopyranose (3b), 2,3,4,6-tetra-O-acetyl-D-glucopyranose (3c), (S)- (3d) and (R)-1,2-O-isopropylideneglycerol (3e)]. The replacement of a CO ligand with PTol3 in 4a-e proceeded diastereoselectively to give [Cp(CO)(PTol3)Mn=C(OR*)Ph] (5a-e). The diastereoselectivity increased in the order a, b, c, d: de = 8% (5a), 33% (5b), 70% (5c), 〉 96% (5d). For (R)-5d the isomer with the (S) configuration at manganese (SMn) was formed predominantly. For (S)-5d, only (RMn,S)-5d was detected (de 〉 96%). Photolysis of (R)-4d in the presence of phosphites or phosphanes afforded (SMn)-[Cp(CO)(PR3)Mn=C(OR*)Ph] [PR3 = P(OPh)3 (8), P(OMe)3 (9), P(OMe)2Ph (10), P(OMe)Ph2 (11), PPh3 (12), P(C6H4Cl-p)3 (13)] with a de 〉 96%. Photolysis of (S)-4d in the presence of P(OMe)3 gave (RMn,S)-9. Complex (R)-14 [related to (R)-4d] was obtained from [Cp(CO)2Mn=C(OAc)Tol-p] and 3d. Replacement of CO by PR3 in (R)-14 gave (SMn,R)-[Cp(CO)(PR3)Mn=C(OR*)Tol-p] [R = Tol-p (15), OMe (16), C6H4Cl-p (17)] with a de 〉 96%. In solution, the PTol3-substituted complex 5d is configurationally stable whereas the P(OMe)3 complex 9 epimerizes slowly at room temperature in CH2Cl2, Et2O, and THF within about one week.
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  • 77
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 355-360 
    ISSN: 1434-1948
    Keywords: Gallium ; Indium ; Low-valent compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetrakis[bis(trimethylsilyl)methyl]digallane(4) (1) with a Ga-Ga single bond and the corresponding diindane(4) 2 with an In-In single bond were treated with different protic reagents: tert-Butyl alcohol did not react with 1 at all, while phenol gave a mixture of unknown products, which could not be separated. The more acidic pentafluorophenol did not react as an acid, but C-F bonds were cleaved to form almost quantitatively the dimer (R2GaF)2 5, which was characterized by a crystal-structure determination. Water and 1 yielded the dimeric dialkylgallium hydroxide 6. The Ga-Ga bond was also cleaved by the reaction of 1 with durylthiophenol (duryl = 2,3,5,6-tetramethylphenyl), which gave two main products: R2Ga(SDuryl) 7 and RGa(SDuryl)2 8. In contrast, the chelating acid dibenzoylmethane reacted by means of a substituent exchange, with the release of two equiv. of bis(trimethylsilyl)methane for each formula unit of 1, to form 9, in which the Ga-Ga bond is retained and each chelating 1,3-diphenyl-1,3-propanedionato ligand is in a terminal position bonded to only one Ga atom, in more than 80% yield. The Ga-Ga bond is shortened [244.1(1) pm] compared to that in the starting compound tetraalkyldigallane(4) 1. The In-In bond of diindane(4) 2 is, however, cleaved in a similar reaction with dibenzoylmethane, and only the fragmentation product dialkyl(1,3-diphenyl-1,3-propanedionato)indium 10 could be isolated.
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  • 78
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 367-373 
    ISSN: 1434-1948
    Keywords: Phthalocyanines ; Indium ; Indium-carbon bond ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of highly soluble chloro(phthalocyaninato)indium(III) complexes RxPcInCl (3a: R1 = tert-butyl, R2 = H, x = 4 and 4a: R1 = R2 = n-pentyl, x = 8), and their reactions with R′MgBr [R′ = p-trifluoromethylphenyl- (b), m-trifluoromethylphenyl- (c), p-fluorophenyl- (d), perfluorophenyl- (e)] leading to the stable σ-bonded aryl(phthalocyaninato)indium(III) complexes 3b-e, 4b-e are described. All compounds were characterized by IR, UV/Vis, MS, 1H, 13C and 19F NMR as well as elemental analyses. Phenyl(phthalocyaninato)indium(III) (4f) was prepared by the reaction of (n-C5H11)8PcInCl (4a) with PhLi. The high solubility of the complexes 3a-e and 4a-f is, aside from the influence of the peripheral substituents, considered to be derived from the large dipole moments present which are due to the strongly electron withdrawing axial ligands, and from the lower tendency of axially substituted phthalocyaninato metal complexes to form aggregates.
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  • 79
    ISSN: 1434-1948
    Keywords: Phosphorus ; Phosphonic anhydrides ; Oligophosphonic acids ; Peptide synthesis ; Solid-state structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By reaction of RP(O)Cl2 with RP(O)(OSiMe3)2, phosphonic anhydrides (RPO2)3 (R = tBu, 2-methylphenyl, 2,4,6-trimethylphenyl) 1a-c are conveniently obtained. In contrast to 1b and 1c, compound 1a is remarkably stable against protolysis. Intermediates of hydrolysis of 1a, namely tris(tert-butyl)triphosphonic acid (2) and bis(tert-butyl)diphosphonic acid (3), can also be isolated in good yield. The structures of 1-3 were determined mainly by NMR spectroscopy (1 H, 13C, 31P). Assuming an energetic preference for the chair conformations in solution, and considering the steric requirements of the bulky substituents R, configurations Ia (point group Cs, two R in equatorial positions) for 1a and b, and IIa (point group C3v, all R equatorial) for 1c are suggested. - Reaction of 1a with N-benzyloxycarbonylglycine (4) in methanol affords strong evidence that in the first step of peptide synthesis with (RPO2)3, a mixed anhydride of triphosphonic acid and the N-protected amino acid is formed. - The crystal structure of 1a (monoclinic, space group P21/n) widely corresponds to the suggested configuration Ia, but reveals an envelope conformation for the six-membered ring with a P3O2 plane in the crystal. In the crystal structure of the octahydrate of the disodium salt of 2 (monoclinic, space group P21/c), it can be seen that the polar end groups of the anions [tBu3P3O7]2- together with the water molecules and the Na+ cations, form hydrogen-bonded double-layers, strictly separated from each other by the non-polar tert-butyl groups of the anions.
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  • 80
    ISSN: 1434-1948
    Keywords: α-Metallated amino acids ; Palladium ; Platinum ; Oxidative addition ; α-Bromoglycinate ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidative addition of methyl N-benzoyl-2-bromoglycinate to bis(dibenzylideneacetone)palladium, in the presence of 2,2′-bipyridyl, and to (Ph3P)2Pt(η2-C2H4) gives the α-metallated glycine esters 1a and 2a. Abstraction of bromide from 1a, 2a, using AgSbF6 or AgBF4, affords the cationic C,O-chelate complexes [(bpy)Pd-CH(CO2Me)NHC(Ph)O]+ (1b,c) and [(Ph3P)2Pt-CH(CO2Me)NHC(Ph)O]+ (2b), respectively, featuring coordination of the amide O atom. The complexes 1b and 2b have been characterized by X-ray diffraction.
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  • 81
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 381-388 
    ISSN: 1434-1948
    Keywords: Phosphanes ; Phosphorus ylides ; Nucleophilic addition ; Structure elucidation ; NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chlorophosphanyl and dichlorophosphanyl alkylidene- and benzylidenephosphoranes 6 and 8 are converted by reaction with LiAlH4 to the respective phosphanes 7 and 9. The former can be isolated, but decompose on heating or on protonation to give the ylidyl diphosphane 11 and the phosphonium ylide or phosphonium salt, respectively. The final products are the cyclooligophosphanes 15-17. Only the C-tert-butyl derivative 7c is stable in both regards. The conformation of the RPH group in 7 as compared to that of the RPCl group in 6 clearly reflects their different interaction with the ylide moiety.
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  • 82
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 397-400 
    ISSN: 1434-1948
    Keywords: Polychalcogenides ; Selenium ; Selenocarbamato complexes ; 77Se NMR ; Crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of the potassium polyselenides „K2Se6” and „K2Se8” with [CpW(CO)3Cl] and 18-crown-6 in DMF lead to a mixture of the selenido complexes {[CpW(CO)3]2Se4} 1 and [(18-crown-6)K]+[CpW(Se4)2]- 3 and the Se-bonded selenocarbamato complex [CpW(CO)3SeC(O)NMe2] 2 in yields depending on the selenium content of the used potassium polyselenides („K2Se6” or „K2Se8”). A similar reaction in THF produces {[CpW(CO)3]2Se4} as the main product. X-ray structures of 1 and 2 were determined. In 1 the Se4-chain is bonded in a μ2-η1 fashion, with corresponding W-Se bond lengths of 264.0(1) and 264.3(1) pm. The Se-Se bond lengths lie in the range 232 to 237 pm. The first example of an η1 Se-bonded selenocarbamato ligand is observed in the crystal structure of 2, with a W-Se bond length of 263.1(1) pm. The 77Se-NMR data are compared with the corresponding data of related complexes.
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  • 83
    ISSN: 1434-1948
    Keywords: Rhodium ; N ligands ; Carbonyl complexes ; Methoxycarbonyl ; Dinuclear complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of 1,4,7-trimethyl-1,4,7-triazacyclononane (Cn*) with [{(CO)2Rh(μ-Cl)}2] in methanol at 0°C, followed by the addition of NH4PF6, results in the formation of the mononuclear carbonyl complex [Cn*Rh(μ-CO)2]PF6 ([1]PF6), the dinuclear carbonyl complex [Cn*Rh(μ-CO)3RhCn*](PF6)2 {[2](PF6)2} and the dinuclear methoxycarbonyl complex [Cn*Rh(C(O)OMe)(μ-CO)2RhCn*]PF6 ([3]PF6). The reaction of [2](PF6)2 with NaOMe results in formation of [3]PF6 by the attack of the methoxide at a bridging carbonyl. Treatment of [3]PF6 with NH4PF6 regenerates [2](PF6)2, thus showing that the methoxylation of [2](PF6)2 is reversible. The structures of [1]PF6, [2](PF6)2 and [3]PF6 have been determined by single-crystal X-ray diffraction. For [3]PF6 an unprecendented facile, reversible, migration of the C(O)OMe ligand between the two rhodium centres of the Rh(μ-CO)2Rh core is observed.
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  • 84
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 389-396 
    ISSN: 1434-1948
    Keywords: Substitution mechanism ; Platinum ; Pressure dependence ; Kinetics ; Dinuclear complex ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Both reaction steps observed for the substitution of water by thiourea in the complexes [Pt(en)(OH2)2]2+ and [Pt(phen)(OH2)2]2+ (en = ethylenediamine, phen = 1,10-phenanthroline) were investigated under pseudo-first-order conditions using the stopped-flow technique. The substitution of the second water molecule in each complex was also studied under high pressure. The observed pseudo-first-order rate constants kobs (s-1) obeyed the equation k1,2obs= k1,2[tu] (tu = thiourea), where “1” and “2” refer to the first and the second substitution reactions, respectively. Kinetic parameters associated with the substitution process are: k1en (25.0°C, pH = 3.0, I = 0.1 M) = 25.6 M-1 s-1, ΔH# = 51 kJ mol-1, ΔS# = -48 J K-1 mol-1; k2en (same conditions) = 12.1 M-1 s-1, ΔH# = 30 kJ mol-1, ΔS# = -124 J K-1 mol-1, ΔV# = -7 cm3 mol-1; k1phen (25.0°C, pH = 1.0, I = 0.1 M) = 2900 M-1 s-1, ΔH# = 41 kJ mol-1, ΔS# = -41 J K-1 mol-1; k2phen (same conditions) = 1170 M-1 s-1, ΔH# = 37 kJ mol-1, ΔS#= -61 J K-1 mol-1, ΔV# = -5 cm3 mol-1. The temperature and pressure dependence of all the processes studied suggest an associative substitution mechanism. The hydroxo-bridged dinuclear complex [{Pt(phen)(μ-OH)}2]2+ is formed from [Pt(phen)(OH2)2]2+ in aqueous solution unless the solution is very dilute and highly acidic. The X-ray structure of [{Pt(phen)(μ-OH)}2](F3CSO3)2 · 2 H2O was determined. It belongs to the triclinic space group P1­ and has one formula unit in the unit cell. The unit cell dimensions are a = 7.126(5), b = 9.665(5), c = 12.774(7) Å; α = 71.85(5), β = 85.52(5), γ = 73.12(5) deg; V = 799.9(8) Å3. The structure was solved with the Patterson method and refined to R = 0.061. A square planar coordination of the platinum centers is observed, with no deviations from planarity but distortions due to the small bite angle of phen and the four-membered ring. No significant lengthening of the Pt-O bond [mean value: 2.03(1) Å] is observed in comparison with [{Pt(NH3)2(μ-OH)}2]2+.
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  • 85
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 407-414 
    ISSN: 1434-1948
    Keywords: Ruthenium ; Phosphorus ; Triphos complexes ; Fluxionality ; Arm-off dissociation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structural fluxionality is apparent in the 1H- and 31P-NMR spectra of compounds of the type [Ru(L)(MeCN)(triphos)](CF3SO3), 2-5, at 25°C, where L represents a diorganyldithiocarbamate or a heterocyclic κ2N,S coordinating thioamide. In contrast, complexes [Ru(Et2NCS2)(Y)(triphos)]n+ (6, n = 1, Y = CO; 7, n = 0, Y = CN-; 8, n = 0, Y = H-) are stereochemically rigid in solution at this temperature, indicating that MeCN dissociation must occur for the crowded octahedral coordination spheres of 2-5. Reaction of [Ru(MeCN)3(triphos)](CF3SO3)2, 1, with Na(Et2NCS2) at a 1:2 molar ratio yields [Ru(Et2NCS2-κ2S)(Et2NCS2-κS)(triphos)], 9, which slowly converts to [Ru(Et2NCS2-κ2S)2(triphosO-κ2P)], 10, on recrystallization from ethanol/acetone under air [triphosO is O=P(Ph)2CH2C(CH3)(CH2PPh2)2]. A similar κ3P→κ2P arm-off dissociation leads to the formation of [Ru(mpy-κ2N,S)2(triphosO-κ2P)] (13) and [Ru(mmim-κ2N,S)2(triphosO-κ2P)] (14) (Hmpy = 2-mercaptopyridine, Hmmim = 2-mercapto-1-methylimidazole). Crystal structures are reported for [Ru(mbt-κ2N,S)(MeCN)(triphos-κ3P)](CF3SO3) (4) (Hmbt = 2-mercaptobenzothiazole), [Ru(mpym-κ2N,S)(mpym-κS)(triphos-κ3P)] (11) (Hmpym = 2-mercaptopyrimidine) and 14, the latter of which is present as the OC-6-13 isomer.
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  • 86
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 415-418 
    ISSN: 1434-1948
    Keywords: Pentacoordinate silicon ; Zwitterionic λ5Si-silicate ; SiO2N2C framework ; Hypervalent compounds ; Main-group elements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of (Me2N)3SiCH2CH2NMe2 with 2-amino-4-nitrophenol (molar ratio 1:2) in acetonitrile yields the zwitterionic spirocyclic λ5Si-silicate [2-(dimethylammonio)ethyl]bis[4-nitrobenzene-2-aminato-1-olato(2-)]silicate (7). Compound 7 was characterized by 1H, 13C, and 29Si solution-state and 29Si solid-state NMR spectroscopy, in addition to single-crystal X-ray diffraction. The SiO2N2C framework of 7 is characterized by five „normal” covalent bonds.
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  • 87
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 425-428 
    ISSN: 1434-1948
    Keywords: Ethylene polymerization ; Group 5 metal complexes ; Hydridotris(pyrazolyl)borates ; Alkyne ligands ; Migratory insertion ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituted hydridotris(pyrazolyl)borato (Tp′) niobium complexes of the type [Tp′NbMe2(PhC≡CMe)] polymerize ethylene (under 1 atm, at room temp. and in toluene) when treated with an equimolar amount of B(C6F5)3. A clear relationship is observed between the stereoelectronic nature of the complex and catalytic activity. This is discussed on the basis of electrochemical data for the dichloro complexes [Tp′NbCl2(PhC≡CMe)], and the rates of alkyl migration in [Tp′Nb(Cl)(R)(PhC≡CMe)] (R = CH2Me, CH2SiMe3). For a given electron density at the metal, the bulky TpMe2,4-Cl yields a catalyst which is more than 6 times as active as the unsubstituted Tp based catalyst.
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  • 88
    ISSN: 1434-1948
    Keywords: Alkyne complexes ; Titanium ; Zirconium ; Coordination mode ; Metallacycles ; Cyclopentadienes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of metals, alkyne substituents, Cp substitution and additional ligands on the stability of bridged and unbridged η2-alkyne-titanocene and -zirconocene complexes has been investigated. The reduction of the complex [(η5-C5H4)-SiMe2-(η5-C5H4)]TiCl2 with magnesium in the presence of tolan (PhC2Ph) does not give the expected alkyne-titanocene complex [(η5-C5H4)-SiMe2-(η5-C5H4)]Ti(η2-PhC2Ph) but by coupling of two tolan molecules the corresponding titanacyclopentadiene [(η5-C5H4)-SiMe2-(η5-C5H4)]TiC4Ph4 (1) was obtained. In the analogous reaction with Me3SiC2SiMe3 the stable η2-alkyne complex without additional ligands [(η5-C5H4)-SiMe2-(η5-C5H4)]Ti(η2-Me3SiC2SiMe3) (2) was formed, due to the sterical influence of the alkyne substituents. The compounds without additional ligands (thi)2Ti(η2-PhC2Ph) (3) and (thi)2Ti(η2- Me3SiC2SiMe3) (5) were isolated from the unbridged titanocene complex (thi)2TiCl2 (thi = tetrahydroindenyl). Two equivalents of complex 3 reacted with one equivalent of water to yield the dimeric alkylidene-μ-oxo complex [(thi)2Ti(CPh=CHPh)]2(μ-O) (6). The reaction of the unbridged zirconocene compound (thi)2ZrCl2 gave the alkyne complex (thi)2Zr(THF)(η2-Me3- SiC2SiMe3) (7) which is stabilized by THF. At higher temperature THF was eliminated from the orange complex 7 forming the green complex (thi)2Zr(η2-Me3SiC2SiMe3). This behaviour was investigated in detail using NMR spectroscopy and compared to similar complexes such as Cp2Zr(η2-Me3SiC2SiMe3) (not stable without THF), (ebthi)2Zr(η2-Me3SiC2SiMe3) (ebthi = ethylenebistetrahydroindenyl; stable without THF) and Cp*2Zr(η2-Me3SiC2SiMe3) (Cp* = pentamethyl-Cp, stable without THF). All complexes were characterized by spectroscopic methods. X-ray structural determinations were conducted for the complexes 1, 3 and 7. Compound 3 is the first example of a structurally characterized tolan-titanocene complex without additional ligands.
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  • 89
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 433-436 
    ISSN: 1434-1948
    Keywords: Silicon amidinates ; Germanium amidinates ; Bidentate coordination ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of novel bis(amidinate) silicon and germanium complexes is described. The reaction of two equiv. of [MeC(NiPr)2]Li · THF (1) with SiCl4, GeCl4 or GeCl2·dioxane affords [MeC(NiPr)2]2SiCl2 (2), [MeC(NiPr)2]2GeCl2 (3) and [MeC(NiPr)2]2Ge (4), respectively. The complexes 2 and 4 have been structurally characterized. The crystallographic results confirm a bidentate coordination of the amidinate ligands at the Si/Ge center, as indicated by spectroscopic studies.
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  • 90
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 429-431 
    ISSN: 1434-1948
    Keywords: Osmium ; Thiolate ; Molecular wire ; Molecular devices ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecule (p,p)-HSC6H4C≡CC6H4C≡CC6H5 has been attached to a triosmium cluster and characterized crystallographically. The complex Os3(CO)10(μ-H)(μ-SC6H4C≡CC6H4C≡CC6H5) (1) was obtained in 49% yield from the reaction of the thiol HSC6H4C≡CC6H4C≡CC6H5 with Os3(CO)10(NCMe)2. The sulfur atom bridges two metal atoms on the edge of a triangular cluster of three osmium atoms. The three aryl rings are nearly coplanar. The ligand is 18.27(2) Å in length from the sulfur atom to the para-carbon atom of the third aryl ring. This compound may serve as a model for the coordination of thiol-terminated molecular wires to metallic probe surfaces.
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  • 91
    ISSN: 1434-1948
    Keywords: Lead(1+) ; Indium(3+) ; Organylphosphanylamide complexes ; Phosphazene ; 207Pb-NMR spectra ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of PbCl2 with LiN(PPh2)2 (1) at -78°C affords the P-P coupled phosphazene Ph2P-N=PPh2-PPh2=N-PPh2 (2) as an oxidation product and, as a reduction equivalent, the novel lead(1+) complex [(Pb1+)2(μ-Ph2P···N···PPh2-)2](Pb-Pb) (3). The crystal structure determination of the red compound 3 shows a Pb-Pb bond length of 304.1(1) pm. The 31P- and 207Pb-NMR spectra of 3 are complicated due to the presence of a higher order spin system (AA′A′′A′′′X for the mono-207Pb isotopomer, AA′A′′A′′′XX′ for the bis-207Pb isotopomer). Simulations of the 31P and 207Pb spectra both on material with natural isotope abundance and on the 207Pb-labelled compound (3*) reveal a large Pb,Pb coupling constant of 7708 Hz, indicative of a covalent Pb-Pb bond. - Though InCl3 is diagonally related to PbCl2, no significant redox process is observed in the reaction between InCl3 and 1. The yellow crystals of [In3+(Ph2P···N···PPh2-)3] (4) that are obtained were also investigated by X-ray analysis. These show a propeller-like configuration of the three four-membered chelate rings with indium(3+) as the centre.
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  • 92
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 445-449 
    ISSN: 1434-1948
    Keywords: Cerium(IV) bisporphyrinates ; Sandwich complexes ; Diporphyrins ; π Radical-cations and dications ; Cerium(III) bisporphyrinate anions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from 5-(4-hydroxyphenyl)-10,15,20-tris(4-methylphenyl)porphyrin (2a), the new bis(porphyrinyloxy)alkanes 4a and 4d were synthesized by ether formation with the α,ω-dibromoalkanes Br(CH2)nBr (n = 8, 11; 3a, 3d). 4a was obtained by a two-step reaction with the 5-[4-(8-bromooctyloxy)phenyl]-10,15,20-tris(4-methylphenyl)porphyrin (2b) as an intermediate. The diporphyrins 4a and 4d were metalated with cerium(III) acetylacetonate to yield the new (porphyrin)cerium sandwich complexes 1a and 1d which were characterized by UV/Vis, IR, 1H-NMR, 13C-NMR spectroscopy and cyclic voltammetry. The mono- and dications and the cerium(III) bisporphyrinate anions of 1a-d were produced by electrochemical oxidation and reduction, respectively, and were examined by UV/Vis/NIR spectroscopy. The length of the lateral chains does not have a specific effect on the first and second oxidation potentials of the porphyrin rings and the reduction potentials of the cerium ions in the bisporphyrinate systems, and on the energy of the NIR bands of the monocations.
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  • 93
    ISSN: 1434-1948
    Keywords: Calixarene ; Phosphinite ; Calixphosphane ; Transition metals ; X-ray diffraction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A cone-shaped calix[4]arene-derived monophosphinite, 25,27-di(ethoxycarbonylmethoxy)-26-hydroxy-28-(diphenylphosphinooxy)calix[4]arene (L1), has been prepared in two steps from calix[4]arene. Treatment of L1 with [AuCl(tetrahydrothiophene)] in tetrahydrofuran gave the phosphinite complex [AuClL1] (1). Reaction of [PdCl2(PhCN)2] with two equivalents of L1 gave selectively trans-[PdCl2L12] (2). Complex 2 · 2 CH2Cl2 crystallizes in the triclinic space group P1¯. The molecule is centrosymmetric, leading to a divergent array of the two calixarene moieties. The palladium atom resides outside both cones. As a result of steric interactions, the meta and para carbon atoms of the PPh2-bearing aryl ring are significantly pushed to the interior of the cavity. The related platinum complex trans-[PtCl2L122] (3), was obtained similarly from [PtCl2(PhCN)2] and presents in the solid state a structure which is isomorphous to that of 2. The diphosphinite 25,27-di(ethoxycarbonylmethoxy)-26,28-bis(diphenylphosphinoxy)calix[4]arene (cone) (L2) has also been prepared and reacts with [PtCl2(PhCN)2] to yield oligomeric material.
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  • 94
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 459-463 
    ISSN: 1434-1948
    Keywords: 1,2-Diboraheterocycles ; Carbon monoxide insertion ; Isonitrile insertion ; Dimerisation ; Spiro insertion products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The insertion of CO into the B-B bond of 1,2-bis(diisopropylamino)-2,5-dihydro-1H-1,2-diborole (1b) and 1,2-bis(diisopropylamino)-3-methylidene-1,2-diborolane (1c) leads to the dimeric spiro products 1,7,9,14-tetrakis(diisopropylamino)-6,13-dioxa-1,7,9,14-tetraboradispiro[4.2.4.2]tetradeca-2,10-diene (4b) and 1,7,9,14-tetrakis(diisopropylamino)bismethylidene-6,13-dioxa-1,7,9,14-tetraboradispiro[4.2.4.2]tetradecane (4c). Insertions of CO into the B-B bonds of the cyclic organo-1,2-diborane compounds 5, 6, and 7 are not observed. The reaction of 1b with tert-butyl isocyanide and 2,6-dimethylphenyl isocyanide in THF leads to the formation of the monomeric insertion products 1,3-bis(diisopropylamino)-2-tert-butylimino-1,3-diboracyclohex-4-ene (10b) and 1,3-bis-(diisopropylamino)-2-(2′,6′-dimethylphenylimino)-1,3-diboracyclohex-4-ene (11b). The treatment of 1cwith the isonitriles yields 2-tert-butylimino-1,3-bis(diisopropylamino)-4-methylidene-1,3-diboracyclohexane (10c) and 1,3-bis(diisopropylamino)-2-(2′,6′-dimethylphenylimino)-4-methylidene-1,3-diboracyclohexane (11c). The steric requirements of the isonitrile insertion products 10b, c and 11b, c prevent their dimerisation and rearrangement. 11b rearranges to 1-(diisopropylamino)-2-(diisopropylaminohydroxyboryl)-2-(2′,6′-dimethylphenylamino)-1-boracyclopent-3-ene (12b) upon reaction with water from sodium sulfate decahydrate. The compositions of the compounds are derived from the 1H-, 11B-, 13C-NMR data as well as from mass-spectral and C, H, N analyses. In the cases of of 4b and 12b they have been proven by X-ray structure analyses.
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  • 95
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 465-468 
    ISSN: 1434-1948
    Keywords: Boron ; Iron ; Boryl complexes ; Borylene complexes ; Iron-boron bond ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Depending on the nature of the amino group bound to the boron atom, the reactions of various aminodichloroboranes R2NBCl2 with Na[(η5-C5R′5)Fe(CO)2] yield either boryl or bridging borylene complexes of iron. The compounds [(C5R′5)(CO)2Fe{BCl(NR2)}] (1a, C5R′5 = C5H5, R = Me; 1b, C5R′5 = C5H4Me, R = Me; 1c, C5R′5 = C5Me5, R = Me) and [(η-BNR2)(μ-CO){(C5R′5)Fe(CO)}2] (2a, C5R′5 = C5H5, R = SiMe3; 2b, C5R′5 = C5H4Me, R = SiMe3) were isolated as orange (1a-c) or red (2a, b) crystalline solids, and characterized by multinuclear NMR methods and IR spectroscopy. The structures of 1c and 2b in the crystalline state were determined by single-crystal X-ray studies.
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  • 96
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 469-476 
    ISSN: 1434-1948
    Keywords: Cage compounds ; Crystal structure ; Hafnium ; Trimetaphosphimates ; Zirconium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The (trimetaphosphimato)hafnates and -zirconates Na4{Hf4(μ4-O)(μ-OH)6[(PO2NH)3]4} · 18 H2O [1, Pa3, a = 22.687(3) Å, Z = 8], Na4{Hf4(μ4-O)(μ-OH)6[(PO2NH)3]4} · 21 H2O [2, R3, a = 14.350(2), c = 50.348(10) Å, Z = 6], Na4{Zr4(μ4-O)(μ-OH)6[(PO2NH)3]4} · 18 H2O [3, Pa3, a = 22.693(3) Å, Z = 8], and Na4{Zr4(μ4-O)(μ-OH)6[(PO2NH)3]4} · 21 H2O [4, R3¯, a = 14.303(2), c = 50.284(10) Å, Z = 6] were obtained by the stoichiometric reaction of HfOCl2 · 8 H2O and ZrOCl2 · 8 H2O with an aqueous solution of Na3(PO2NH)3 · 4 H2O, followed by the diffusion-controlled addition of methanol. During these reactions compounds 1 and 2, or 3 and 4, crystallized simultaneously and the hafnium and zirconium complexes 1 and 3, as well as 2 and 4, were found to be isostructural and isomorphous. The characteristic structural feature which is central to 1, 2, 3, and 4 is the complex tetranuclear anion {M4(μ4-O)(μ-OH)6[(PO2NH)3]4}4- with M = Zr or Hf. The anion consists of five corner-sharing adamantanoid cages. The central cage, {M4(μ4-O)(μ-OH)6}8+, has a tetracoordinated oxygen atom in the middle, and the other cages are formed by the trimetaphosphimate ions acting as tridentate ligands which coordinate to Hf or Zr. The water content of the compounds 1-4 could not be determined unequivocally by chemical analyses since the compounds are always obtained as mixtures of the rhombohedral (2/4) and cubic (1/3) phases. Thermal decomposition of compounds 1-4 starts above 120°C and leads to the formation of HfP2O7 and ZrP2O7/NaZr2(PO4)3, with the evolution of H2O and NH3. DSC measurements gave no evidence that the compounds 1 and 2, or 3 and 4, might be transformed into each other by heating.
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  • 97
    ISSN: 1434-1948
    Keywords: Ruthenium ; Bridging bis(bidentate)tetraphosphane ligand ; Diruthenium(II) coordination complex ; Cyclometallation versus o-P,P′ chelation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tetrakis(phosphane oxide) C6H2{CH2P(O)Ph2}4-1,2,4,5 (5), has been prepared in high yield from the Arbuzov reaction of C6H2(CH2Br)4-1,2,4,5 (4), with excess (7 equiv.) of Ph2POEt. Subsequent reduction of 5 with HSiCl3 (12 equiv.) in C6H4Cl2-1,2 afforded the new tetraphosphane C6H2(CH2PPh2)4-1,2,4,5 (6), in high yield. The reaction of 6 with [RuCl2(PPh3)4] in CH2Cl2 afforded the green dinuclear ruthenium(II) coordination complex [{RuCl2(PPh3)}2{C6H2- (CH2PPh2)4-1,2,4,5-P,P′,P′′,P′′′}]·0.5 CH2Cl2 (8), in 39% isolated yield. The solid-state molecular geometry of 8, determined by X-ray analysis, shows that the tetraphosphane is ortho-P,P′-chelated to each of the two [RuIICl2(PPh3)] units.
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  • 98
    ISSN: 1434-1948
    Keywords: Heterobimetallics ; μ-Isonitrile complexes ; μ-Aminocarbyne complexes ; Bis(diphenylphosphanyl)amine ; Iron ; Platinum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Addition of isonitriles to [(OC)3Fe(μ-CO)(μ-Ph2PNHPPh2)Pt(PPh3)] 1 produces the μ-isonitrile complexes [(OC)3Fe(μ-C=NR)(μ-Ph2PNHPPh2)Pt(PPh3)] 2, which are transformed to the μ-aminocarbyne complexes [(OC)3Fe{μ-CN(El)R}(μ-Ph2PNHPPh2)Pt(PPh3)]+;3 and 4 by electrophilic addition of [El][BF4] or [El][OSO2CF3] (El = H, Me). The dppa backbone of 4 is readily deprotonated by KOSiMe3 to yield the very stable zwitterionic aminocarbyne complex [(OC)3Fe{μ-CN(Me)2,6-xylyl}(μ-Ph2PNPPh2)Pt(PPh3)] 5.
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  • 99
    ISSN: 1434-1948
    Keywords: 2-Phenyl-4-R-5(4H)-oxazolones ; Iridium ; Palladium ; Platinum ; Iron ; Chromium ; C-o,N-Bridging 2-phenyloxazolone ; Peptide labelling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of 2-phenyl-4-R-5(4H)-oxazolones (R = Me, CH2Ph, CHMeEt) with [(η5-C5Me5)IrCl2]2 afforded the cyclometallated complexes (η5-C5Me5)(Cl)Ir(L) (1-3) [L = 2-phenyl-4-R-5(4H)-oxazolone(C-o,N)]. 2-Phenyl-5(4H)-oxazolone reacts with [(η5-C5Me5)IrCl2]2 and palladium(II) acetate to give complexes with a C-o,N-bridging oxazolone [(η5-C5Me5)(Cl)Ir]2(μ-Cl)(μ-L-H+) (4) and Pd3(μ-ac)5(μ-L-H+) (5). 2-Phenyloxazolone anions were added to the π ligands of [(η5-C6H7)Fe(CO)3]+ and [(η7-C7H7)Cr(CO)3]+ to give the adducts 6-11. Dipeptide derivatives 12-18 were obtained by reaction of 1, 2 and by reaction of the adduct 6 from [(η5-C6H7)Fe(CO)3]+; and the anion of 2-phenyloxazolone with α-amino acid esters. These reactions may be used for the labelling of peptides. Saponification of 15-18 yields the organometallic substituted peptide acids 19-22. Their dianions (deprotonation of COOH and peptide amide) were used as ligands towards (Ph3P)2PtCl2 to yield the bimetallic complexes 23-25. The structures of 4, 5, 9 and 10 were determined by X-ray diffraction.
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  • 100
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 501-504 
    ISSN: 1434-1948
    Keywords: Metallomesogens ; Azo compounds ; Palladium ; Platinum ; Cyclopentadienyl complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mesogenic 4,4′-bis[4-(n-octyloxy)benzoyloxy]azobenzene (HL) ligand reacts with [(PhCN)2PdCl2] to give the dinuclear cyclometalated complex [(μ-Cl)(L)Pd]2 (1), from which the mononuclear half-sandwich [(η5-C5H5)(L)Pd] (2) species has been obtained by reaction with Tl(C5H5). The PtII analogue of 2, [(η5-C5H5)(L)Pt] (4), has been prepared in a similar manner starting from [(μ-Cl)(L)Pt]2 (3). Both dinuclear complexes 1 and 3 display a smectic C phase (SC) stable over 80°C. Whereas 4 is the first example of an 18-electron PtII mesogen, both mononuclear 2 and 4 are mesomorphic materials that exhibit a nematic phase spanning a wide temperature range.
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