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  • Artikel  (7)
  • Theoretical, Physical and Computational Chemistry  (4)
  • hydroxyapatite  (3)
  • 1995-1999  (7)
  • 1955-1959
  • 1940-1944
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  • Artikel  (7)
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Erscheinungszeitraum
  • 1995-1999  (7)
  • 1955-1959
  • 1940-1944
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  • 1
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 115-124 
    ISSN: 0894-3230
    Schlagwort(e): cross-interaction constants ; gas-phase nucleophilic substitution reactions ; PM3 MO ; benzyl chlorides ; phenoxides ; thiophenoxides ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Gas-phase nucleophilic substitution reactions of Y-benzyl chlorides with X-phenoxide and X-thiophenoxide nucleophiles were investigated theoretically using the PM3 semi-empirical MO method. The Leffler-Grunwald rate-equilibrium and Brønsted correlations predict that the degree of bond formation in the transition state (TS) is approximately 45 and 40% on the reaction coordinate for the phenoxides and thiophenoxides, respectively. For a weaker nucleophile, a later TS is obtained with an increased bond making and breaking. The variation of the TS structure with substituents in the nucleophile is thermodynamically controlled and is well correlated by rate-equilibrium relationships. In contrast, the TS variation (a tighter TS) with substituent (for a stronger acceptor Y) in the substrate is dependent only on variations of the intrinsic barrier and so cannot be correlated by such thermodynamically based rate-equilibrium relationships. The gas phase ρX and ρY values are much greater in magnitude than those in solution. A similar gas-phase theoretical cross-interaction constant, ρXY (ca -0.60), is obtained for both phenoxides and thiophenoxides, which is in good agreement with the experimental value (-0.62) for the thiophenoxide reactions in MeOH at 20.0 °C. The oxy and sulfur anion bases lead to a similar TS structure, but a lower reactivity for the former is due to a greater endothermicity of the reaction. A relatively wide range variation of the reaction energies, ΔG°, can be ascribed to the loss of resonance stabilization of anion nucleophiles upon product formation. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 10 (1997), S. 908-916 
    ISSN: 0894-3230
    Schlagwort(e): AM1-SM2.1 ; transition-state imbalance ; benzylidenemalonotriles ; nucleophilic additions ; Brønsted coefficients ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: ---Semiempirical MO theoretical studies were carried out on the nucleophilic addition of phenoxide nucleophiles to 1,1-dicyano-2-arylethenes in the gas phase and in water using the AM1 method and the Cramer-Truhlar solvation model SM2.1. The gas-phase αn and βn values are 0·81 and 0·65, respectively, leading to the positive imbalance of I=0·16; the electric polarization and dispersion interactions of water incorporated in the SM2.1 model reduce both the αn and βn values to 0·61 and 0·36, giving I=0·25. The two Brønsted coefficients obtained theoretically in water agree satisfactorily with the experimental values (αncorr=0·55 and βn=0·35) obtained with amine bases. The small imbalance found both theoretically (I=0·25) and experimentally (I≈0·20) can be ascribed to (i) a near-zero distance factor, Δd=dp-dTS≈0 and (ii) the small extent of negative charge localization by strucutral reorganization in the transition state. © 1997 John Wiley & Sons, Ltd.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 37 (1997), S. 457-464 
    ISSN: 0021-9304
    Schlagwort(e): biocompatibility ; bone ; calcium phosphate cement ; fast-setting ; hydroxyapatite ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: Fast-setting calcium phosphate cement (FSCPC) is a promising new bioactive cement with a significantly short setting time (approximately 5-6 min) compared to conventional calcium phosphate cement (c-CPC) (30-60 min) at physiologic temperatures. As a result of its ability to set quickly, it is applicable in surgical procedures where fast setting is required. In this study, FSCPC was implanted in rat tibiae to evaluate tissue response and biocompatibility. FSCPC was converted to hydroxyapatite (HAP) in bone faster than c-CPC in the first 6 h. By 24 h, significant amounts of both FSCPC and c-CPC had been converted to HAP. The conversion of FSCPC into HAP further proceeded gradually, reaching 100% within 8 weeks. Infrared spectroscopic analysis disclosed the deposition of B-type carbonate apatite, which is a biological apatite contained in human dentin or bone, on the surface of the FSCPC. Histologically, FSCPC showed a tissue response similar to that of c-CPC. A slight inflammatory reaction was observed in the soft tissue apposed to both cements in the early period, and new bone was formed along the surface of the FSCPC at the adjacent bone. However, no resorption of either cement by osteoclasts or macrophages was observed within 8 weeks. We conclude that FSCPC is superior to c-CPC in clinical applications in oral and maxillofacial, orthopedic, plastic, and reconstructive surgery, since it shows a faster setting time and higher mechanical strength in the early period that are required in these surgical procedures, as well as osteoconductivity and excellent biocompatibility similar to that of c-CPC. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 37, 457-464, 1997.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    ISSN: 0021-9304
    Schlagwort(e): antibiotics ; calcium phosphate cement ; drug delivery system ; hydroxyapatite ; anti-washout type ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: The effect of added antibiotics on the basic properties of anti-washout-type fast-setting calcium phosphate cement (aw-FSCPC) was investigated in a preliminary evaluation of aw-FSCPC containing drugs. Flomoxef sodium was employed as the antibiotic and was incorporated into the powder-phase aw-FSCPC at up to 10%. The setting time, consistency, wet diametral tensile strength (DTS) value, and porosity were measured for aw-FSCPC containing various amounts of flomoxef sodium. X-ray diffraction (XRD) analysis was also conducted for the identification of products. To evaluate the drug-release profile, set aw-FSCPC was immersed in saline and the released flomoxef sodium was determined at regular intervals. The spread area of the cement paste as an index of consistency of the cement increased progressively with the addition of flomoxef sodium, and it doubled when the aw-FSCPC contained 8% flomoxef sodium. In contrast, the wet DTS value decreased with increase in flomoxef sodium content. Bulk density measurement and scanning electron microscopic observation revealed that the set mass was more porous with the amount of flomoxef sodium contained in the aw-FSCPC. The XRD analysis revealed that formation of hydroxyapatite (HAP) from aw-FSCPC was reduced even after 24 h, when the aw-FSCPC contained flomoxef sodium at ≥6%. Therefore, the decrease of wet DTS value was thought to be partly the result of the increased porosity and inhibition of HAP formation in aw-FSCPC containing large amounts of flomoxef sodium. The flomoxef sodium release from aw-FSCPC showed the typical profile observed in a skeleton-type drug delivery system (DDS). The rate of drug release from aw-FSCPC can be controlled by changing the concentration of sodium alginate. Although flomoxef sodium addition has certain disadvantageous effects on the basic properties of aw-FSCPC, we conclude that aw-FSCPC is a good candidate for potential use as a DDS carrier that may be useful in surgical operations. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 308-316, 1998.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    ISSN: 0021-9304
    Schlagwort(e): calcium phosphate cement ; non-decay type ; putty ; sodium alginate ; hydroxyapatite ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: A hydroxyapatite [(HAP) Ca10(PO4)6(OH)2] putty that behaves like a putty or self-curing resin was made by increasing the amount of sodium alginate in non-decay type fast-setting calcium phosphate cement (nd-FSCPC). nd-FSCPC became viscous as the sodium alginate concentration was increased. The best handling properties were obtained when nd-FSCPC contained 8% sodium alginate in its liquid phase. When a 2-kg glass plate was placed on the paste, HAP putty spread to form an area three times that of FSCPC paste. Thus, HAP putty is expected to be easier to use than FSCPC in the filling of bone defects. HAP putty did not decay; in fact, it set within approximately 20 min when immersed in distilled water immediately after mixing. The wet diametral tensile strength value of HAP putty was approximately 12 MPa after 24 h, the same as that for nd-FSCPC containing 0.5% sodium alginate in its liquid phase, or FSCPC that is free from sodium alginate. The elements constituting set HAP putty were examined using powder X-ray diffraction and found to be predominantly apatitic minerals after 24 h. Since the handling properties of a putty or self-curing resinlike cement are very useful in certain surgical procedures, HAP putty made by increasing the sodium alginate concentration in nd-FSCPC is potentially a valuable new biomaterial for use in plastic and reconstructive surgery, as well as oral and maxillofacial surgery. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 36, 393-399, 1997.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 1773-1784 
    ISSN: 0192-8651
    Schlagwort(e): three-membered ring formation ; intramolecular nucleophilic substitution ; ab initio molecular orbital method ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Informatik
    Notizen: Three-membered ring (3MR) forming processes of -X(SINGLE BOND)CH2(SINGLE BOND)CH2(SINGLE BOND)F and -CH2(SINGLE BOND)C((SINGLE BOND)Y)(SINGLE BOND)CH2(SINGLE BOND)F (X(DOUBLE BOND)CH2, O, or S and Y(DOUBLE BOND)0 or S) through a gas phase neighboring group mechanism (SNi) are studied theoretically using the ab initio molecular orbital method with the 6-31+G* basis set. When electron correlation effects are considered, the activation (ΔG≠) and reaction energies (ΔG0) are lowered by ca. 10 kcal mol-1, indicating the importance of the electron correlation effect in these reactions. The contribution of entropy of activation (-TΔS≠) at 298 K to ΔG≠ is very small, and the reactions are enthalpy controlled. The ΔG≠ and ΔG0 values for these ring closure processes largely depend on the stabilities of the reactants and the heteroatom acting as a nucleophilic center. The Bell-Evans-Polanyi principle applies well to all these reaction series.   © 1997 John Wiley & Sons, Inc.   J Comput Chem 18: 1773-1784, 1997
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 56-69 
    ISSN: 0192-8651
    Schlagwort(e): Chemistry ; Theoretical, Physical and Computational Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Informatik
    Notizen: The relative stabilities of the keto and enol forms [Δ E0 (enol-keto)] and the energy barriers to enolization of the keto forms [Δ E≠ (transition state-keto)] for CH3COR (R = CH3, H, F, and CN) and CH3CHY (Y = CH2, NH, and S) are investigated theoretically by Hartree-Fock and Möoller-Plesset second-order calculations with 6-31G** basis sets. Specific and bulk solvent effects are considered by incorporating one water molecule and applying the self-consistent reaction field (SCRF) method to the reaction system, respectively. The Δ E0MP2 values are all positive, in agreement with the lower stability of the enol form in the gas phase as well as in solution. In contrast to a relatively small effect of specific as well as bulk solvation on Δ E0, there is a large lowering of Δ E≠ (by ca. 30 kcal/mol) when solvent effects are accounted for. In general, both Δ E0 and Δ E≠ are depressed in solution and hence enolization is favored thermodynamically as well as kinetically. The keto form is strongly stabilized by a π donor, whereas the enol isomer is stabilized by a π as well as a σ-acceptor substituent, R. As a result, substituent R = F is the most unfavorable whereas R = CN is the most favorable for the enolization. The water catalyzed enolization in the neutral water proceeds concertedly, but carbon deprotonation is more important than carbonyl-oxygen protonation by water in the rate determining step. © 1997 by John Wiley & Sons, Inc.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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