还原态烟酰胺腺嘌呤二核苷酸拉曼光谱研究

还原态烟酰胺腺嘌呤二核苷酸(NADH)在维持细胞生长、分化、能量代谢以及细胞保护方面起着非常重要的作用，NADH的无创在体检测具有非常重要的意义。运用激光拉曼散射实验和密度泛函理论(DFT)计算研究了200～3 300 cm-1光谱范围内NADH分子的振动模式特性。DFT计算采用了B3LYP杂化方法，并选用了极化6-311+G(d,p)基组。为了准确的分析NADH分子的振动模式和频率，首先运用B3LYP/6-311+G(d,p)理论对NADH分子的基态结构进行了几何优化，并计算了基态结构NADH分子的各个键长和键角。同时考虑到DFT计算中的非谐性，运用波数线性标度方法对所有计算所得振动模式波数重新进行了标度。重新标度后，DFT计算所得的振动模式波数与激光拉曼散射实验观测到的拉曼峰波数吻合的很好：在200～3 300 cm-1整个光谱范围内，计算与实验结果具有非常好的线性相关性，而且大部分振动模式的计算与实验之间的偏差都小于5 cm-1。此外，讨论了实验观察所得拉曼光谱的分子振动模式归属，分析了NADH分子中腺嘌呤、烟酰胺、及二核苷酸的特征振动模式，并初步提出了运用拉曼光谱实现NADH快速准确无创在体检测的方法。位于732 cm-1处的拉曼峰是腺嘌呤的特征振动模式，而且可以选为检测NADH分子的最特征拉曼峰。位于1 690 cm-1处的拉曼峰是烟酰胺的特征振动模式，可以选为进一步准确检测NADH分子的另一个特征拉曼峰。位于1 086和1 339 cm-1两处拉曼峰的组合可以作为二核苷酸的特征振动模式，用于进一步更准确的检测NADH分子。所以在运用拉曼光谱法实现NADH快速准确无创在体检测时，可以首先运用位于732 cm-1处NADH分子的最特征振动模式进行快速检测，然后再运用位于1 690 cm-1及1 086和1 339 cm-1组合等特征振动模式进行准确分析。

Raman Spectroscopy Study of Reduced Nicotinamide Adenine Dinucleotide

Reduced nicotinamide adenine dinucleotide (NADH) plays a crucial role in many biochemical reactions in human metabolism. Noninvasive and in vivo monitoring of the NADH level in skin tissue is of great interest. In this paper, the Raman scattering experiment and density functional theory (DFT) calculation have been applied to investigate the vibrational properties of NADH in the spectral range of 200～3 300 cm-1. The DFT calculation was performed with hybrid exchange functional using B3LYP functions with a polarized 6-311+G(d,p) basis. To achieve accurate analytical vibrational frequency calculation, the ground-state geometry of NADH molecule was first optimized at B3LYP/6-311+G(d,p) level of theory without any symmetry restrain, and the bond lengths and bond angles of NADH molecule were calculated. Then, the calculated wavenumbers were normally scaled with a necessary wavenumber linear scaling procedure by accounting for anharmonicity in DFT calculation. The DFT calculated spectrum of NADH is in good agreement with the Raman experimental spectrum: a good linear correlation between calculated and experimental wavenumbers has been obtained in the spectral range of 200～3 300 cm-1, and the deviations are smaller than 5 cm-1. In addition, the characteristic vibrational modes of the three parts adenine, nicotinamide, and dinucleotide of NADH molecule have been assigned and discussed, which would be helpful for the noninvasive and in vivo analyses of NADH. The characteristic mode of adenine at 732 cm-1 can be chosen as the most representative model for analyzing NADH. The characteristic mode of nicotinamide at 1 690 cm-1 can be chosen as another representative mode for further analyzing NADH. The characteristic modes of dinucleotide at 1 086 and 1 339 cm-1 can be chosen as a combination for further more accurately analyzing NADH. Therefore, when applying the Raman method for noninvasive and in vivo monitoring of the NADH level in skin tissue, first, the most representative mode at 732 cm-1 can be used for quick analyses, then the mode at 1 690 cm-1 and/or the combination modes of 1 086 and 1 339 cm-1 can be used for further accurate analyses.