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Abstract— Fluorescence lifetimes are reported for intact human lenses in vitro. Two spectral regions were investigated: The first was excited at 296nm and detected at 332 or 370nm and corresponds to emission from tryptophan residues in the lens proteins. The second spectral region was excited at 359 nm and detected at 435 nm and corresponds to non-tryptophan 'fluorogen' fluorescence. The latter displayed a constant lifetime, 3.8 ns, independent of the anatomical part of the lens excited. This value was compared with measured lifetimes for some model fluorogens. The tryptophan fluorescence lifetime (332 nm detection) was found to vary from 1.8 to 2.8 ns depending on the anatomical part of the lens excited. 相似文献
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J. F. Tassin P. Thirion L. Monnerie 《Journal of Polymer Science.Polymer Physics》1983,21(10):2109-2121
Stress measurements have been performed at constant-strain-rate stretching of narrow distribution polystyrenes with various molecular weights elongated up to 300% at about 30°C above the glass transition temperature. The experimental stress-strain curves are compared with those calculated on the basis of a new treatment of Doi's molecular model (Part I). Satisfactory agreement is obtained, leading to a rather precise estimate of the equilibration time. The latter has a theoretical dependence on the square of molecular weight. 相似文献
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Philippe Mongondry Chantal Bonnans‐Plaisance Martine Jean Jean Franois Tassin 《Macromolecular rapid communications》2003,24(11):681-685
The hydroxyl end groups of poly(ethylene glycol) (PEG) have been transformed easily and quantitatively into amino groups via the Mitsunobu reaction. Phthalimide was alkylated with PEGs and the hydrazinolysis of the resulting phthalimido‐PEGs gave the amino compounds in high yields. Quaternization of the amino groups leads to hydrophilic polymer chains bearing a positive charge on one or two ends, depending on the chosen PEG. Such products can be used to protect sterically, negatively charged particles such as clays.
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Biaxially oriented poly(ethylene terephthalate) films were prepared under well defined stretching conditions in order to mimic the three stages of the industrial inverse drawing process. Molecular orientation has been characterized through X-ray diffraction and infrared dichroism. The main orientation mechanisms in the constant-speed drawing of an amorphous film as well as in the constant-force transverse drawing of monodrawn samples are described. It is shown that relaxation phenomena dominate the orientation of an amorphous sample. Reorientation along the second drawing direction involves rotation of crystalline blocks along the draw direction and further crystalline growth. The high-temperature heating stage leads to an almost four-fold increase in the size of the crystallites. The orientation of the amorphous phase is controlled by the mechanisms occurring during crystallization (relaxation followed by extension). 相似文献
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THE PHOTOLYSIS RATES OF SOME DI- AND TRIPEPTIDES OF TRYPTOPHAN 总被引:1,自引:0,他引:1
We have measured the relative rates of photolysis of free tryptophan (trp), the dipeptides Gly-Trp, Trp-Gly, Leu-Trp, and Trp-Leu, and the tripeptides Gly-Trp-Gly and Leu-Trp-Leu. The photolyses were performed in neutral 0.1 mM aqueous solutions at 25°C using monochromatic 290 nm Xe arc radiation. Tryptophan loss was monitored by absorption, fluorescence and phosphorescence spectroscopy. The rate of tryptophan fluorescence loss was found to be different in the di-and tripeptides than in tryptophan monomer. These rate differences depended on both the identity of the neighboring amino acid (gly or leu) and on the nature of the linkage, e.g., the rate of Gly-Trp photolysis was more than 10 times greater than the rate of Trp-Gly photolysis. Degassing was found to markedly reduce (factor of 8) the photolysis rates of Trp, Trp-Gly, and Trp-Leu, but degassing only slightly reduced (less than a factor of 2) the photolysis rates of the other di-and tri-peptides. Photochemical product structures were not determined, but absorption and fluorescence spectra were obtained and products could be inferred in some cases by comparison with data of previous workers. The products appeared to differ greatly among the various peptides studied; Trp, Trp-Gly, and Trp-Leu gave oxidation products, while Gly-Trp and Leu-Trp apparently gave ring closure products, not requiring oxygen. 相似文献
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This paper on the application of potential functions in pattern recognition introduces the software package ALLOC to analytical chemistry, emphasizing the methodology of classifying objects. ALLOC is compared with other classification techniques on the basis of two data sets and is shown to perform very well. 相似文献
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Fluorescence polarization has been used to measure the orientation during stretching of a polystyrene chain embedded in a matrix of narrow-dispersion polystyrene chains of a different molecular weight and labeled by an anthracene group covalently bound at the middle of a chain. Strong coupling between the relaxation of the labeled chain and the matrix chains is evidenced, the orientation of the labeled chain being partially governed by the molecular weight of the matrix. This behavior is interpreted qualitatively on the basis of a molecular model showing that the relaxation of a polymer chain is strongly affected by the entanglements acting on the chain, the number of which is also related to the motion of the surroundings. Good agreement is found between experimental data and the behavior predicted by the model. 相似文献
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