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  • Chemistry  (6)
  • Earth Resources and Remote Sensing  (5)
  • General Chemistry  (4)
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  • 2005-2009  (3)
  • 2000-2004  (11)
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  • 1
    Electronic Resource
    Electronic Resource
    Effects of Injected Volume and Applied Voltage on Column Efficiency in Capillary Electrochromatography with Open Tubular Columns of 10 μm i. d. (2000)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 373-378 
    Details
    ISSN: 0935-6304
    Keywords: Open tubular columns ; capillary electrochromatography ; column efficiency ; injected volume ; applied voltage ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of some instrumental parameters on column efficiency in open tubular capillary electrochromatography (OTCEC) has been evaluated. First, it was investigated whether band broadening due to the sample injection process is within a tolerable range when an open tubular column (OTC) of about 10 μm i. d. is used. As a result of the small injection profile factor (K2 = 1.3), injected volumes must be sufficiently small (less than 10 pL) to avoid a significant efficiency loss (〉5%) when hydrodynamic injection by siphoning is employed. Secondly, the kinetic performance of OTCs in a CEC system was estimated from the variation of the reduced plate height (h) with the reduced linear velocity (ν) which was controlled by the voltage applied. Reasonable agreement was obtained between the theoretical h versus ν curve and the experimental values for a group of polycyclic aromatic hydrocarbons used as test compounds. Values of 0.25 for minimum h at an optimum ν of 16 are estimated, which permit separations with around 400,000 plates per meter to be obtained in less than 5 min. Finally, the possibility of estimating the diffusion coefficients of the solutes in the mobile phase from the plot of the height of a theoretical plate versus electroosmotic flow velocity is shown.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Synthesis of New Seven-Membered Ring Cyclic Dipeptides From Functionalized β-Amino Acids (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 251-255 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; coupling ; N-Substituted amide ; Cyclizations ; Cyclic dipeptides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A short synthesis of new, functionalized seven-membered ring cyclic dipeptides is described. After the coupling of N-protected β-amino acids to N-substituted α-amino tert-butyl esters, the protective groups of the terminal functions were removed and the cyclization took place diastereoselectively in the presence of the coupling agent BOP. Amide substitution was found to be effective in promoting the cyclization of linear dipeptides.
    Additional Material: 1 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis of Silaproline, a New Proline Surrogate (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 807-811 
    Details
    ISSN: 1434-193X
    Keywords: Proline analogues ; Asymmetric synthesis ; Schöllkopf's method ; Silicon ; Amino acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The asymmetric synthesis of a new proline surrogate, incorporating the dimethylsilyl group at position 4 of proline using Schöllkopf's bis-lactim ether method, is described.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Reductive Cleavage of Potential Cholinomimetics Thiadiazolidinones: A New Family of Spiro Compounds (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 675-680 
    Details
    ISSN: 1434-193X
    Keywords: Thiadiazolidinones ; Spiro compounds ; Thiazoles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The design, synthesis and evaluation of a series of 1,2,4-thiadiazolidinones with potential muscarinic receptor binding properties has been performed. During the synthesis of the target compounds, we observed an interesting reductive cleavage of the thiadiazolidinone system which leads to the formation of the novel piperidine spiro triazine heterocycle. The synthesis, structural elucidation (NMR spectroscopy and X-ray diffraction) and biological evaluation of the new compounds are described. With the structures unequivocally established, a mechanism for the formation of the spiro compound is proposed.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/099462_s.pdf or from the author.
    Additional Material: 3 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Mechanisms of Cyclopalladation Reactions in Acetic Acid: Not So Simple One-Pot Processes (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 217-224 
    Details
    ISSN: 1434-1948
    Keywords: Reaction mechanisms ; Cyclopalladation ; Acetic acid ; Pd-C bond stability ; Polynuclear species ; Palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The processes operating during the synthetic cyclopalladation reactions of imines in acetic acid have been studied from a kinetico-mechanistic point of view. These reactions include a fast initial coordination to the palladium through the N-donor atom of the imine, followed by the proper C-H bond activation to produce the acetato bridged dimeric species. At this point, the lability of the bridging acetato groups, the hydrolysis of the C-Pd bonds, and/or the hydrolysis of C=N exo bonds contribute to the generation of dark red polynuclear compounds. The processes occurring after the C-H activation have been followed kinetically, both from palladium acetate plus imine, and the synthetically pure isolated acetato dimers as starting materials. The kinetic and activation parameters have been found identical within experimental error whatever the starting material was (k323 = 1.5 × 10-4 s-1; ΔH# = 51 kJ mol-1; ΔS# = -163 JK-1 mol-1 ΔV# = +19 cm3 mol-1 for the 4-ClC6H4-CH=N-CH2-C6H5 imine derivative 1a). Acidolysis of C-Pd bonds has been found to occur in these polynuclear species. When alternative monomeric Cbenzylic-Pd bond-containing complexes are possible follow ups of the reactions produce them as final dead-end complexes (k323 = 2.2 × 10-5 s-1; ΔH# = 61 kJ mol-1; ΔS# = JK-1 mol-1 ΔV# ≈ 0 cm3 cm-1 for the [2,4,6-(CH3)3]C6H2-CH=N-CH2-[2-(CH3]C6[H4] imine derivative 3d). The same study has been carried out with primary amines in order to check the validity of the data if C=N bond hydrolysis is taking place in the imine derivatives with exo C=N bonds. For complexes with similar type of metallacycles, the results agree reasonably well with the proposed mechanism [k323 = 1.2·10-4 s-1, ΔH# = 46 kJ·mol-1, ΔS# = -180 J·K-1mol-1, ΔV# = -16 cm3·mol-1 for the polynuclear formation of the C6H5-CH2-NH2 derivative 4e; k323 = 3.0·10-4 s-1, ΔH# = 55 kJ·mol-1, ΔS
    Additional Material: 1 Ill.
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  • 6
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    Self-assembling amphiphilic siderophores from marine bacteria (2000)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2000-02-26
    Description: Most aerobic bacteria secrete siderophores to facilitate iron acquisition. Two families of siderophores were isolated from strains belonging to two different genera of marine bacteria. The aquachelins, from Halomonas aquamarina strain DS40M3, and the marinobactins, from Marinobacter sp. strains DS40M6 and DS40M8, each contain a unique peptidic head group that coordinates iron(III) and an appendage of one of a series of fatty acid moieties. These siderophores have low critical micelle concentrations (CMCs). In the absence of iron, the marinobactins are present as micelles at concentrations exceeding their CMC; upon addition of iron(III), the micelles undergo a spontaneous phase change to form vesicles. These observations suggest that unique iron acquisition mechanisms may have evolved in marine bacteria.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Martinez, J S -- Zhang, G P -- Holt, P D -- Jung, H T -- Carrano, C J -- Haygood, M G -- Butler, A -- GM38130/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 2000 Feb 18;287(5456):1245-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106-9510, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10678827" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acids/analysis ; Chemistry, Physical ; Cryoelectron Microscopy ; Evolution, Molecular ; Fatty Acids/analysis ; Ferric Compounds/metabolism ; Gammaproteobacteria/*chemistry/isolation & purification/metabolism ; Halomonas/*chemistry/isolation & purification/metabolism ; Light ; Micelles ; Phylogeny ; Physicochemical Phenomena ; Scattering, Radiation ; Seawater/microbiology ; Siderophores/*chemistry/isolation & purification/metabolism ; Surface Properties
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 7
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    The genome of the diatom Thalassiosira pseudonana: ecology, evolution, and metabolism (2004)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2004-10-02
    Description: Diatoms are unicellular algae with plastids acquired by secondary endosymbiosis. They are responsible for approximately 20% of global carbon fixation. We report the 34 million-base pair draft nuclear genome of the marine diatom Thalassiosira pseudonana and its 129 thousand-base pair plastid and 44 thousand-base pair mitochondrial genomes. Sequence and optical restriction mapping revealed 24 diploid nuclear chromosomes. We identified novel genes for silicic acid transport and formation of silica-based cell walls, high-affinity iron uptake, biosynthetic enzymes for several types of polyunsaturated fatty acids, use of a range of nitrogenous compounds, and a complete urea cycle, all attributes that allow diatoms to prosper in aquatic environments.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Armbrust, E Virginia -- Berges, John A -- Bowler, Chris -- Green, Beverley R -- Martinez, Diego -- Putnam, Nicholas H -- Zhou, Shiguo -- Allen, Andrew E -- Apt, Kirk E -- Bechner, Michael -- Brzezinski, Mark A -- Chaal, Balbir K -- Chiovitti, Anthony -- Davis, Aubrey K -- Demarest, Mark S -- Detter, J Chris -- Glavina, Tijana -- Goodstein, David -- Hadi, Masood Z -- Hellsten, Uffe -- Hildebrand, Mark -- Jenkins, Bethany D -- Jurka, Jerzy -- Kapitonov, Vladimir V -- Kroger, Nils -- Lau, Winnie W Y -- Lane, Todd W -- Larimer, Frank W -- Lippmeier, J Casey -- Lucas, Susan -- Medina, Monica -- Montsant, Anton -- Obornik, Miroslav -- Parker, Micaela Schnitzler -- Palenik, Brian -- Pazour, Gregory J -- Richardson, Paul M -- Rynearson, Tatiana A -- Saito, Mak A -- Schwartz, David C -- Thamatrakoln, Kimberlee -- Valentin, Klaus -- Vardi, Assaf -- Wilkerson, Frances P -- Rokhsar, Daniel S -- New York, N.Y. -- Science. 2004 Oct 1;306(5693):79-86.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Oceanography, University of Washington, Seattle, WA 98195, USA. armbrust@ocean.washington.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15459382" target="_blank"〉PubMed〈/a〉
    Keywords: Adaptation, Physiological ; Algal Proteins/chemistry/genetics/physiology ; Animals ; *Biological Evolution ; Cell Nucleus/genetics ; Chromosomes ; DNA/genetics ; Diatoms/chemistry/cytology/*genetics/metabolism ; *Ecosystem ; Energy Metabolism ; *Genome ; Iron/metabolism ; Light ; Light-Harvesting Protein Complexes/chemistry/genetics/metabolism ; Mitochondria/genetics ; Molecular Sequence Data ; Nitrogen/metabolism ; Photosynthesis ; Plastids/genetics ; Restriction Mapping ; Sequence Alignment ; *Sequence Analysis, DNA ; Silicic Acid/metabolism ; Symbiosis ; Urea/metabolism
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 8
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    A protein sensor for siRNA asymmetry (2004)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2004-11-20
    Description: To act as guides in the RNA interference (RNAi) pathway, small interfering RNAs (siRNAs) must be unwound into their component strands, then assembled with proteins to form the RNA-induced silencing complex (RISC), which catalyzes target messenger RNA cleavage. Thermodynamic differences in the base-pairing stabilities of the 5' ends of the two approximately 21-nucleotide siRNA strands determine which siRNA strand is assembled into the RISC. We show that in Drosophila, the orientation of the Dicer-2/R2D2 protein heterodimer on the siRNA duplex determines which siRNA strand associates with the core RISC protein Argonaute 2. R2D2 binds the siRNA end with the greatest double-stranded character, thereby orienting the heterodimer on the siRNA duplex. Strong R2D2 binding requires a 5'-phosphate on the siRNA strand that is excluded from the RISC. Thus, R2D2 is both a protein sensor for siRNA thermodynamic asymmetry and a licensing factor for entry of authentic siRNAs into the RNAi pathway.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Tomari, Yukihide -- Matranga, Christian -- Haley, Benjamin -- Martinez, Natalia -- Zamore, Phillip D -- GM62862-01/GM/NIGMS NIH HHS/ -- GM65236-01/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 2004 Nov 19;306(5700):1377-80.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15550672" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Argonaute Proteins ; Dimerization ; Drosophila/embryology/metabolism ; Drosophila Proteins/*metabolism ; Light ; Luciferases/genetics ; Nucleic Acid Conformation ; RNA Helicases/*metabolism ; *RNA Interference ; RNA, Double-Stranded/chemistry/metabolism ; RNA, Small Interfering/*chemistry/*metabolism ; RNA-Binding Proteins/*metabolism ; RNA-Induced Silencing Complex/*metabolism ; Ribonuclease III ; Superoxide Dismutase/genetics ; Thermodynamics ; Uracil/*analogs & derivatives/analysis
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 9
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    Hyperspectral Image Classification using a Self-Organizing Map (2001)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The use of hyperspectral data to determine the abundance of constituents in a certain portion of the Earth's surface relies on the capability of imaging spectrometers to provide a large amount of information at each pixel of a certain scene. Today, hyperspectral imaging sensors are capable of generating unprecedented volumes of radiometric data. The Airborne Visible/Infrared Imaging Spectrometer (AVIRIS), for example, routinely produces image cubes with 224 spectral bands. This undoubtedly opens a wide range of new possibilities, but the analysis of such a massive amount of information is not an easy task. In fact, most of the existing algorithms devoted to analyzing multispectral images are not applicable in the hyperspectral domain, because of the size and high dimensionality of the images. The application of neural networks to perform unsupervised classification of hyperspectral data has been tested by several authors and also by us in some previous work. We have also focused on analyzing the intrinsic capability of neural networks to parallelize the whole hyperspectral unmixing process. The results shown in this work indicate that neural network models are able to find clusters of closely related hyperspectral signatures, and thus can be used as a powerful tool to achieve the desired classification. The present work discusses the possibility of using a Self Organizing neural network to perform unsupervised classification of hyperspectral images. In sections 3 and 4, the topology of the proposed neural network and the training algorithm are respectively described. Section 5 provides the results we have obtained after applying the proposed methodology to real hyperspectral data, described in section 2. Different parameters in the learning stage have been modified in order to obtain a detailed description of their influence on the final results. Finally, in section 6 we provide the conclusions at which we have arrived.
    Keywords: Earth Resources and Remote Sensing
    Type: Proceedings of the Tenth JPL Airborne Earth Science Workshop; 267-274
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  • 10
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    Spatial/Spectral Identification of Endmembers from AVIRIS Data using Mathematical Morphology (2001)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: During the last several years, a number of airborne and satellite hyperspectral sensors have been developed or improved for remote sensing applications. Imaging spectrometry allows the detection of materials, objects and regions in a particular scene with a high degree of accuracy. Hyperspectral data typically consist of hundreds of thousands of spectra, so the analysis of this information is a key issue. Mathematical morphology theory is a widely used nonlinear technique for image analysis and pattern recognition. Although it is especially well suited to segment binary or grayscale images with irregular and complex shapes, its application in the classification/segmentation of multispectral or hyperspectral images has been quite rare. In this paper, we discuss a new completely automated methodology to find endmembers in the hyperspectral data cube using mathematical morphology. The extension of classic morphology to the hyperspectral domain allows us to integrate spectral and spatial information in the analysis process. In Section 3, some basic concepts about mathematical morphology and the technical details of our algorithm are provided. In Section 4, the accuracy of the proposed method is tested by its application to real hyperspectral data obtained from the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) imaging spectrometer. Some details about these data and reference results, obtained by well-known endmember extraction techniques, are provided in Section 2. Finally, in Section 5 we expose the main conclusions at which we have arrived.
    Keywords: Earth Resources and Remote Sensing
    Type: Proceedings of the Tenth JPL Airborne Earth Science Workshop; 309-319
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