氧化槐果碱结构的测定及其振动圆二色谱研究

The Conformation of Sophocarpidin by Vibrational Circular Dichroism and DFT Calculations

采用傅里叶红外光谱仪(FTIR)和振动圆二色谱仪(VCD)测量氧化槐果碱固体的红外光谱和振动圆二色谱。采用密度泛函方法(DFT)分别在B3LYP/cc-PVTZ和B3LYP/6-311+G(d,p)水平下,对气相中氧化槐果碱分子结构进行了优化,然后在相同水平下计算了氧化槐果碱的红外光谱(IR)以及振动圆二色谱(VCD)。将实验谱图与理论计算谱图进行对照,以确定氧化槐果碱的实际构象以及构象分布。由对比结果可知:采用B3LYP/6-311+G(d,p)水平下,以吉布斯自由能进行玻尔兹曼加权平均后的理论IR和VCD谱图与实际光谱图最为接近,说明在常温下氧化槐果碱具有A/B-trans C/D-trans和A/B-trans C/D-cis两种优势构象,且玻尔兹曼分布显示两种构象均以一定比例共存,且通过对氧化槐果碱的两种优势构象分析,发现A/B环的立体结构为:椅式-椅式,C/D环的立体结构为:椅式-沙发式。

Sophocarpidin was measured in thin film using a Fourier Transform infrared spectrometer(FTIR)with a vibrational circular dichroism(VCD)module,meanwhile,the theoretical IR and VCD spectroscopy were calculated at the B3LYP/cc-PVTZ and B3LYP/6-311+G(d,p)levels of theory in density functional theory(DFT)withinthe gas phase.The VCD spectroscopy can exactly obtain the conformational distribution of Sophocarpidin at room temperature and distinctly capture the information of each conformation for the sensitivity to stereoscopic structure of conformation within VCD spectra.It is essential to the drug analysis of sophocarpidin in the future.The conformational contribution at room temperature and structures were determined through the comparison of experimental and simulated spectra.The Boltzmann-weighted IR and VCD spectra based on free energy at the B3LYP/6-311+G(d,p)level of theory show good agreement with the observed experimentalspectra.Two main conformations,i.e.A/B-trans C/D-trans and A/B-trans C/D-cis are identified.The ration of two conformations is 60%to 40%.The structure of A/B-ring and C/D-ring are chair-chair and chair-sofa respectively inboth two dominant conformation of sophocarpidin.