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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Photochemical Isomerization of Colchicine and Thiocolchicine
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Photochemical Isomerization of Colchicine and Thiocolchicine

机译：秋水仙碱和硫代秋水仙碱的光化学异构化

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The photochemical reactivity of colchicine and thiocolchicine is described. Although the irradiation of colchicine gave a well-known transposition reaction to β- and γ-lumicolchicines, thiocolchicine did not react. Femtosecond transient spectroscopy of colchicine showed a strong band with maximum at 510 nm appearing at τ = 0. It disappeared within few hundred femtoseconds, leaving a broad structureless band with a maximum around 470 nm. A second band is observed around 410 nm. The analysis in time showed that the 510-nm component appeared instantaneously and decayed following a biexponential low with time constants of 300 ± 150 fs. Quantum mechanical calculations on colchicine showed that his absorption is due to a S_1 → S_(11) transition. In thiocolchicine, the instantaneous formation of a structure with maxima out of the investigated spectral region was observed. A strong absorption around 650 nm indicated the presence of a band with a maximum at longer wavelengths (>700 nm) and a peak around 380 nm, which partially coincides with the ground-state absorption and therefore strongly affected by its bleaching. The instantaneous formation of an absorption around 650 nm and its rapid (～500 fs) decay was observed. At shorter wavelengths (400 nm), the decay was fitted with a biexponential curve with the first time constant of about 80 ps. the second part of the decay had a very long tail up to 500 ps. Transient spectroscopy and configuration interaction calculations are in agreement with a mechanism involving a disrotatory cyclization of colchicine in its first excited singlet state. The lack of reactivity observed in thiocolchicine was explained by considering the presence of efficient ISC to the triplet state.
机译：描述了秋水仙碱和硫代秋水仙碱的光化学反应性。尽管秋水仙碱的辐照引起了众所周知的β-和γ-卢米基水杨酸转座反应，但是硫代秋水仙碱没有反应。秋水仙碱的飞秒瞬态光谱显示一个强谱带，在510 nm处出现最大值，出现在τ= 0处。它在几百飞秒内消失，留下了一个宽阔的无结构谱带，最大值在470 nm附近。在410 nm附近观察到第二条带。时间分析表明，510-nm分量瞬间出现并在双指数低点之后以300±150 fs的时间常数衰减。秋水仙碱的量子力学计算表明，他的吸收是由于S_1→S_（11）跃迁引起的。在硫代秋水仙碱中，观察到瞬时形成最大结构超出所研究的光谱区域。 650 nm附近的强吸收表明存在一个在较长波长（> 700 nm）处具有最大值的谱带，并在380 nm附近出现一个峰，这与基态吸收部分重合，因此受其漂白强烈影响。观察到在650 nm附近吸收的瞬时形成及其快速衰减（〜500 fs）。在较短的波长（400 nm）处，衰减与双指数曲线拟合，其第一时间常数约为80 ps。衰减的第二部分有一个很长的尾巴，最高可达500 ps。瞬态光谱法和构型相互作用计算与涉及秋水仙碱在其第一个激发单重态的旋转环化的机理一致。在硫代秋水仙碱中观察到缺乏反应性的原因是考虑到有效的ISC到三重态的存在。

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