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首页> 外文期刊>Journal of molecular modeling >Deducing the molecular properties of zwitterionic, protonated, deprotonated, and double-deprotonated forms of L-cysteine from vibrational spectroscopy (IR, Raman, VCD) and quantum chemical calculations
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Deducing the molecular properties of zwitterionic, protonated, deprotonated, and double-deprotonated forms of L-cysteine from vibrational spectroscopy (IR, Raman, VCD) and quantum chemical calculations

机译：通过振动光谱法（IR，拉曼，VCD）和量子化学计算推导两性离子，质子化，去质子化和双去质子化形式的L-半胱氨酸的分子特性

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The behavior of L-cysteine (C_3H_7NO_2S, (2R)-2-amino-3-sulfanylpropanoic acid) in water at different pH values was analyzed both experimentally and theoretically. The behavior was studied at pH values of 5.21 (at this pH, L-cysteine is a zwitterionic species), 1.00 (protonated species), 8.84 (monodeprotonated species), and 13.00 (dideprotonated species). We carried out a vibrational study using nonchiroptical (IR–Raman) and chiroptical (VCD) techniques complemented by quantum chemical calculations. We adopted a dual strategy, as follows. (i) The hybrid density functionals B3LYP andM062X and the ab initio MP2 method were employed, with the same 6-311++G (d,p) basis set, in order to characterize the relative energies and structures of an extensive set of conformers of L-cysteine. The presence of water was included by utilizing the IEF-PCM implicit solvation model. (ii) The vibrational analysis was made using a chirality-sensitive using a chirality-sensitive technique (VCD) and chirality-insensitive techniques (IR, including MIR and FIR, and Raman), especially in aqueous solution. The results obtained theoretically and experimentally were compared in order to deduce the most stable structures at each pH. Moreover, for the first time, the monodeprotonated anion of Lcysteine was detected in aqueous solution by means of IR, Raman and vibrational circular dichroism (VCD). Finally, analysis of the low-frequency region using the IR and Raman techniques was shown to be a very important way to understanding the conformational preference of the zwitterionic species.
机译：通过实验和理论分析了L-半胱氨酸（C_3H_7NO_2S，（2R）-2-氨基-3-硫烷基丙酸）在水中的行为。在5.21（在此pH下，L-半胱氨酸是两性离子物质），1.00（质子化物质），8.84（单质子化物质）和13.00（去质子化物质）的pH值下研究了该行为。我们进行了振动研究，使用了非化学疗法（IR–Raman）和化学疗法（VCD）技术，并辅以量子化学计算。我们采取了以下双重策略。 （i）采用杂化密度泛函B3LYP和M062X以及从头算MP2方法，具有相同的6-311 ++ G（d，p）基础集，以表征大量构象异构体的相对能量和结构L-半胱氨酸。利用IEF-PCM隐式溶剂化模型包括水的存在。 （ii）使用手性敏感技术，特别是在水溶液中，使用手性敏感技术（VCD）和手性不敏感技术（IR，包括MIR和FIR，以及拉曼）进行振动分析。比较理论上和实验上获得的结果，以便推断出每个pH下最稳定的结构。此外，首次通过红外光谱，拉曼光谱和振动圆二色性（VCD）在水溶液中检测到了Lcysteine的单去质子化阴离子。最后，使用IR和拉曼技术分析低频区域被证明是了解两性离子物种构象偏好的一种非常重要的方法。

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