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首頁> 外文期刊>Chemphyschem: A European journal of chemical physics and physical chemistry >Conformational distributions of N-acetyl-L-cysteine in aqueous solutions: A combined implicit and explicit solvation treatment of VA and VCD spectra
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Conformational distributions of N-acetyl-L-cysteine in aqueous solutions: A combined implicit and explicit solvation treatment of VA and VCD spectra

機(jī)譯：N-乙?；?L-半胱氨酸在水溶液中的構(gòu)象分布：VA和VCD光譜的隱式和顯式溶劑化組合處理

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The conformational distributions of N-acetyl-L-cysteine (NALC) in aqueous solutions at several representative pH values are investigated using vibrational absorption (VA), UV/Vis, and vibrational circular dichroism (VCD) spectroscopy, together with DFT and molecular dynamics (MD) simulations. The experimental VA and UV/Vis spectra of NALC in water are obtained under strongly acid, neutral, and strongly basic conditions, as well as the VCD spectrum at pH 7 in D _2O. Extensive searches are carried out to locate the most stable conformers of the protonated, neutral, deprotonated, and doubly deprotonated NALC species at the B3LYP/6-311++G(d,p) level. The inclusion of the polarizable continuum model (PCM) modifies the geometries and the relative stabilities of the conformers noticeably. The simulated PCM VA spectra show significantly better agreement with the experimental data than the gas-phase ones, thus allowing assignment of the conformational distributions and dominant species under each experimental condition. To further properly account for the discrepancies noted between the experimental and simulated VCD spectra, PCM and the explicit solvent model are utilized. MD simulations are used to aid the modelling of the NALC-(water) _N clusters. The geometry optimization, harmonic frequency calculations, and VA and VCD intensities are computed for the NALC-(water) _(3,4) clusters at the B3LYP/6-311++G(d,p) level without and with the PCM. The inclusion of both explicit and implicit solvation models at the same time provides a decisively better agreement between theory and experiment and therefore conclusive information about the conformational distributions of NALC in water and hydrogen-bonding interactions between NALC and water molecules.
機(jī)譯：使用振動吸收（VA），UV / Vis和振動圓二色譜（VCD）以及DFT和分子動力學(xué)研究了N-乙?；?L-半胱氨酸（NALC）在幾個代表性pH值下水溶液中的構(gòu)象分布（MD）模擬。在強(qiáng)酸，中性和強(qiáng)堿性條件下，獲得了NALC在水中的實(shí)驗(yàn)VA和UV / Vis光譜，以及在D _2O中pH為7時的VCD光譜。進(jìn)行了廣泛的搜索，以找到B3LYP / 6-311 ++ G（d，p）水平上質(zhì)子化，中性，去質(zhì)子化和雙去質(zhì)子化的NALC物種的最穩(wěn)定構(gòu)象。包含可極化連續(xù)體模型（PCM）會明顯改變構(gòu)象異構(gòu)體的幾何形狀和相對穩(wěn)定性。與氣相數(shù)據(jù)相比，模擬的PCM VA光譜顯示出與實(shí)驗(yàn)數(shù)據(jù)更好的一致性，因此可以分配每種實(shí)驗(yàn)條件下的構(gòu)象分布和主要種類。為了進(jìn)一步適當(dāng)考慮實(shí)驗(yàn)和模擬VCD光譜之間的差異，使用了PCM和顯式溶劑模型。 MD模擬用于輔助NALC-（水）_N團(tuán)簇的建模。在不使用PCM和使用PCM的情況下，計算B3LYP / 6-311 ++ G（d，p）級別的NALC-（水）_（3,4）簇的幾何優(yōu)化，諧波頻率計算以及VA和VCD強(qiáng)度。同時包含顯式和隱式溶劑化模型可在理論和實(shí)驗(yàn)之間提供決定性的更好協(xié)議，因此可提供有關(guān)水中NALC的構(gòu)象分布以及NALC與水分子之間氫鍵相互作用的結(jié)論性信息。

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