Ultraviolet spectroscopy of sinapoyl malate, an essential UV-B screening agent in plants, was carried out in the cold, isolated environment of a supersonic expansion to explore its intrinsic UV spectral properties in detail. Despite these conditions, sinapoyl malate displays anomalous spectral broadening extending well over 1000 cm–1 in the UV-B region, presenting the tantalizing prospect that nature's selection of UV-B sunscreen is based in part on the inherent quantum mechanical features of its excited states. Jet-cooling provides an ideal setting in which to explore this topic, where complications from intermolecular interactions are eliminated. In order to better understand the structural causes of this behavior, the UV spectroscopy of a series of sinapate esters was undertaken and compared with ab initio calculations, starting with the simplest sinapate chromophore sinapic acid, and building up the ester side chain to sinapoyl malate. This "deconstruction" approach provided insight into the active mechanism intrinsic to sinapoyl malate, which is tentatively attributed to mixing of the bright V (1ππ*) state with an adiabatically lower 1nπ* state which, according to calculations, shows unique charge-transfer characteristics brought on by the electron-rich malate side chain. All members of the series absorb strongly in the UV-B region, but significant differences emerge in the appearance of the spectrum among the series, with derivatives most closely associated with sinapoyl malate showing characteristic broadening even under jet-cooled conditions. The long vibronic progressions, conformational distribution, and large oscillator strength of the V (ππ*) transition in sinapates makes them ideal candidates for their role as UV-B screening agents in plants.
· 相关产品如汞乙酸汞氯化汞氧化汞碘化汞硫酸汞硝酸汞溴化汞硝酸亚汞氯化亚汞乙酸苯汞碘化汞钾硫氰酸汞氯化氨基汞三氯生三氯氧磷三氯乙烯水合氯醛三氯化磷三氯化钌三氯化钛三氯化铱三氯化铑三氯硫磷三氯乙烷三氯甲烷三氯卡班TCC1,3,5-三氯苯1,2,4-三氯苯1,2,3-三氯苯无水氯化铝三氯乙酸酐三氯乙酸钠碘甲烷二碘甲烷三碘甲烷 三氟碘甲烷硫酸二甲酯氯磺酸苯硫酚苯硫酚钠3-氨基苯硫酚2,6-二氯苯硫酚2,4-二氯苯硫酚2,5-二氯苯硫酚2-甲氧基苯硫酚2-氯乙醇氯甲基甲醚 等均有销售.欢迎订购
