D-荧光素的结构和振动光谱的理论研究

采用密度泛函的B3LYP和B3PW91方法在6-311++G**基组水平上全优化了D-荧光素分子的平衡构型和振动光谱。采用标度量子力学力场(SQM)方法研究了D-荧光素分子的振动光谱。为了详细分析振动模式的贡献，定义了分子的局域内坐标，用改编的分子振动计算程序组将计算的笛卡尔坐标力常数转换成了局域内坐标力常数。用GF矩阵方法进行了简正坐标分析，获得了振动频率和势能分布(PEDs)。根据PEDs对所有的振动模式进行了指认。结果表明，在红外光谱中，所有振动模式均有红外活性，其中吸收强度最强的峰的振动频率为1 780 cm-1，吸收强度为507 KM·mol-1，根据计算所得的PEDs矩阵，可以清楚的看出该振动吸收峰主要由羧基C₂₁O₂₂双键伸缩振动所贡献，其PEDs为93%。在拉曼光谱中，D-荧光素分子的所有振动模式也表现出了拉曼活性，振动频率在1 200～1 700 cm-1范围的吸收峰具有较强的拉曼活性。其中吸收强度最强的吸收峰的频率为1 573 cm-1，吸收强度为297 KM·mol-1，是五元环CN键的伸缩振动所贡献。结果可为进一步研究荧光素衍生物的结构、发光活性提供一定的理论依据。

Theoretical Investigation on the Structure and Vibration Spectrum of D-Luciferin

In the present study, the geometry of D-Luciferin was fully optimized by the density functional theory at the B3LYP/6-311++G** and B3PW91/6-311++G** level, and the Cartesian coordinate force constant was calculated at the same level. The scaled quantum mechanism force field (SQM) method was performed to analyze the vibration spectrum. The local internal symmetry coordinates were defined using the method given by Pulay. The theoretical force field matrix, which was obtained through molecular vibration calculation programs, was transformed from Cartesian coordinates into the local internal coordinates. A normal coordinate analysis was carried out using GF matrix method developed by Wilson to give the scaled vibration frequencies and the potential energy distributions (PEDs). In order to make the vibration frequencies in good agreement with the experimental values, we empirically scale the theoretical force fields. According to PEDs, all vibration modes were assigned reliably to certain vibration frequencies. The calculated results show that the D-Luciferin molecule belongs to the point group C1 and involves 66 free degrees of vibration. All vibration modes are infrared and Raman activity. In the Infrared spectrum, the vibration frequency of the strongest absorption peak is 1 780 cm-1, and the absorption intensity is 507 KM·mol-1, which is mainly contributed by the stretching vibration mode of the C₂₁O₂₂ double bond with the PEDs of 93%. In the Raman spectrum, the vibration frequency in the range of 1 200～1 700 cm-1 presented strong Raman activity, the frequency of the strongest absorption peak is 1 573 cm-1, and the absorption intensity is 297 KM·mol-1, which is mainly contributed by the stretching vibration mode of the C₂₁N₂₂ double bond in the five-membered ring. The results are helpful to further studying the structure and the luminescence activity of Luciferin derivatives in experiment and theory.