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71.
72.
Meddah B Kamel S Giroud C Brazier M 《Journal of photochemistry and photobiology. B, Biology》2000,54(2-3):168-174
Little is known about the photodegradation of pyridinoline (Pyd) and deoxypyridinoline (Dpd), which are two mature cross-links stabilizing collagen within extracellular matrix. In this study, highly purified free Pyd and Dpd cross-links have been degraded by irradiation with ultraviolet light and we have shown that photolysis varies with the pH value. Assessment of photolysis in basic (pH 9) and neutral (pH 7) solutions by high-performance liquid chromatography as well as by UV absorbance measurement indicates that both cross-links are degraded after a 24 h UV exposure, while in acidic solution (pH 3) only Dpd is photolysed, suggesting that acid pH provides major protection against Pyd photolysis. Photodegradation products have been studied by amino-acid and mass spectral analysis. Both methods confirm the lack of Pyd degradation in acid pH. Furthermore, amino-acid analysis allows us to identify hydroxylysine and lysine as a result of Pyd and Dpd photolysis, respectively, indicating that the mechanism of photodegradation involves the cleavage of the pyridinium ring on each side of the quaternary nitrogen. Finally, we have also studied the photolysis of different molecular species of type I collagen peptides, obtained by digestion with collagenase of demineralized turkey bone. Our results indicate that even when they are part of the structure of collagen peptide, Pyd and Dpd can be photolysed. However, we have shown that the larger the peptide is, the smaller are the effects of UV irradiation. 相似文献
73.
Ferro-Luzzi M Bouwhuis M Passchier E Zhou Z Alarcon R Anghinolfi M van Bommel R Botto T van den Brand JF Buchholz M Bulten HJ Choi S Comfort J Dolfini S Ent R Gaulard C Higinbotham D de Jager CW van Klaveren EP Konstantinov E Lang J de Lange DJ Miller MA Nikolenko D Nooren GJ Papadakis N Passchier I Poolman HR Popov SG Rachek I Ripani M Six E Steijger JJ Taiuti M Unal O Vodanis N de Vries H 《Physical review letters》1996,77(13):2630-2633
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Jayakumar HK Buckingham JL Brazier JA Berry NG Cosstick R Fisher J 《Magnetic resonance in chemistry : MRC》2007,45(4):340-345
NMR spectroscopy has been used to investigate the conformational effects of single and two consecutive 3'-S-phosphorothiolate modifications within a deoxythymidine trinucleotide. The presence of a single 3'-phosphorothioate modification shifts the conformation of the sugar ring it is attached to, from a mainly south to north pucker; this effect is also transmitted to the 3'-neighbour deoxyribose. This transmission is thought to be caused by favourable stacking of the heterocyclic bases. Similar observations have been made previously by this group. When two adjacent modifications are present, the conformations of the attached deoxyribose rings are again shifted almost completely to the north, however, there is no transmission to the 3' deoxyribose ring. Base proton chemical shift analysis and molecular modelling have been used to aid elucidation of the origin of this feature. The observation for the dimodified sequence is consistent with our previously reported results for a related system in which spaced modifications are more thermodynamically stable than consecutive ones. 相似文献
77.
Lixu Yang John B. Brazier Thomas A. Hubbard David M. Rogers Scott L. Cockroft 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(3):924-928
Experimental support for the dominance of van der Waals dispersion forces in aromatic stacking interactions occurring in organic solution is surprisingly limited. The size‐dependence of aromatic stacking in an organic solvent was examined. The interaction energy was found to vary by about 7.5 kJ mol−1 on going from a phenyl–phenyl to an anthracene–pyrene stack. Strikingly, the experimental data were highly correlated with dispersion energies determined using symmetry‐adapted perturbation theory (SAPT), while the induction, exchange, electrostatic, and solvation energy components correlated poorly. Both the experimental data and the SAPT‐dispersion energies gave high‐quality correlations with the change in solvent accessible area upon complexation. Thus, the size‐dependence of aromatic stacking interactions is consistent with the dominance of van der Waals dispersion forces even in the presence of a competing polarizable solvent. 相似文献
78.
利用高里德堡态氢原子飞行时间探测技术, 在224~248 nm激发波长研究了间-吡啶基紫外光化学中的氢原子解离通道的动力学过程.氢原子光解碎片产率谱显示在234 nm附近有较宽的吸收.产物的平动能释放较小;在224~248 nm激发波长区间平均< fT>是0.12~0.19.产物的平动能分布显示产物是H+HC≡C-CH=CH-C≡N,H 3,4-吡啶和H 2,3-吡啶,以H HC≡C-CH=CH-C≡N为主要的氢原子生成通道.氢原子碎片具有各向同性的角度分布.研究结果表明,在紫外电子态激发以后,间-吡啶基经过内转换到电子基态,再经由单分子解离到H HC≡C-CH=CH-C≡N,H 3,4-吡啶和H 2,3-吡啶产物.间-吡啶基的紫外光解机理和以前报道过的邻-吡啶基的紫外光解机理相似. 相似文献
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M. C. Dubuc H. Sébastien J. L. Brazier 《Isotopes in environmental and health studies》2013,49(2):177-188
Abstract A sufficiently stable rate of 13CO2 exhalation is necessary when the diagnostic 13CO2 breath tests are performed in healthy subjects and patients. The aim of the research was to define prerequisite conditions for kinetic breath tests in order to ensure a stable 13CO2 background. A 3-part protocol was developed. Part I: a study of the one-day variation of 13CO2 abundance in expired CO2 confirmed that shifts of the basal 13C abundance in breath are inherent in nature. Part II: a study of the variations of 13C enrichment after the ingestion of different meals and beverages showed that ingestion of food items containing C4 plant sugars, such as maize, induces a significant increase in isotopic abundance. Part III: a new test breakfast containing rice grain cereal, milk and orange juice was tested. This test meal induces no significant change on the basal 13CO2 abundance in healthy subjects. This new finding allows to avoid the fasting period normally required prior to a breath test which is sometimes difficult for children and pregnant women. 相似文献