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1.
In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and
their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically
using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L−1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition
on the protonation constants is discussed. The log10 K2 values of esters generally decreased with increasing ethanol content. However, the log10 K1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content
in contrast those of L-lysine and L-histidine esters. 相似文献
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Gorkem Yilmaz Alev Tuzun Yusuf Yagci 《Journal of polymer science. Part A, Polymer chemistry》2010,48(22):5120-5125
A thioxanthone (TX) derivative with the additional carbazole chromophore, namely thioxanthone‐carbazole (TX‐C) was synthesized and characterized. The photophysical properties and its efficiency to polymerize methyl methacrylate both in the presence and absence of N,N‐dimethylaniline (DMA) as coinitiator was investigated and compared with that of the commercially available TX. TX‐C was found to display better photophysical properties and in both cases initiate polymerization more efficiently. Detailed real‐time Fourier transform infrared studies revealed that high polymerization rates can be obtained when TX‐C in conjunction with DMA was used. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
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O. Gundogdu P.M. Jenneson U. Tuzun G.M. Gray J.N. Hay 《Applied Physics A: Materials Science & Processing》2006,85(3):317-324
Polyviologen polymers are potential template agents for hydrolytic sol–gel processing of silica particles. The resultant polyviologen-silica hybrid nanopowders are amorphous aggregates of roughly spherical shape, which can be harvested from the sol–gel solution and processed to green body products under different environmental conditions. A bench-top X-ray microtomography system, with a spatial resolution of 5 μm is used to produce three-dimensional images of the dynamic processing of the nanopowders. Various processing routes are imaged using a custom built environmental chamber where the temperature, atmospheric pressure, and compaction force can be controlled. This allows processes such as vacuum sintering and microwave sintering to be studied. The three-dimensional images reveal the axial and radial distributions of the molten polyviologen polymer within a matrix of agglomerates of the silica nanoparticles. Such observations are crucial to the optimisation of the processes that are used to produce the green body products so as to preserve desirable nano-intensive properties. PACS 82.35.Np; 87.59.-e; 81.07.Pr; 87.59.Bh 相似文献
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Robert E. Tuzun Donald W. Noid Bobby G. Sumpter 《Journal of computational chemistry》2000,21(7):553-561
Laplacians and gradient dot products are required for the recently developed internal coordinate quantum Monte Carlo method. New formulas are presented for these quantities for torsion and improper torsion angles. The Laplacians can also be used to economize calculation of sets of second derivatives used in molecular mechanics and other methods. Formulas for torsion angle gradient dot products and Laplacians, and completely new formulas for improper torsion, are presented. In addition, calculations of cos τ and sin τ, some suitable for energy subroutines and others for force subroutines, are shown. Finally, in a related development, several sets of conditions for three atom linearity or four atom planarity involving internal coordinate derivatives are reported. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 553–561, 2000 相似文献
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Robert E. Tuzun Donald W. Noid Bobby G. Sumpter 《Macromolecular theory and simulations》1996,5(4):771-788
By using two- and three-body internal coordinates and their derivatives as intermediates, it is possible to enormously simplify formulas for three- and four-body internal coordinates and their derivatives. Using this approach, simple formulas are presented for stretch (two-body), two types of bend (three-body), and wag and two types of torsion (four-body) internal coordinates and their first and second derivatives. The formulas are eminently suitable for economizing molecular dynamics and molecular mechanics calculations and normal coordinate analysis of complicated potential energy surfaces. Efficient methods for computing derivatives of entire potential energy terms, and in particular cross terms with switching functions, are presented. 相似文献