We investigated the near-infrared spectrum of piperine using quantum mechanical calculations. We evaluated two efficient approaches, DVPT2//PM6 and DVPT2//ONIOM [PM6:B3LYP/6-311++G(2df, 2pd)] that yielded a simulated spectrum with varying accuracy versus computing time factor. We performed vibrational assignments and unveiled complex nature of the near-infrared spectrum of piperine, resulting from a high level of band convolution. The most meaningful contribution to the near-infrared absorption of piperine results from binary combination bands. With the available detailed near-infrared assignment of piperine, we interpreted the properties of partial least square regression models constructed in our earlier study to describe the piperine content in black pepper samples. Two models were compared with spectral data sets obtained with a benchtop and a miniaturized spectrometer. The two spectrometers implement distinct technology which leads to a profound instrumental difference and discrepancy in the predictive performance when analyzing piperine content. We concluded that the sensitivity of the two instruments to certain types of piperine vibrations is different and that the benchtop spectrometer unveiled higher selectivity. Such difference in obtaining chemical information from a sample can be one of the reasons why the benchtop spectrometer performs better in analyzing the piperine content of black pepper. This evidenced direct correspondence between the features critical for applied near-infrared spectroscopic routine and the underlying vibrational properties of the analyzed constituent in a complex sample.

我们使用量子力学计算研究了胡椒碱的近红外光谱。我们评估了两种有效的方法，DVPT2//PM6 和 DVPT2//ONIOM [PM6:B3LYP/6-311++G(2df, 2pd)]，它们产生的模拟光谱具有不同的精度与计算时间因素。我们进行了振动分配并揭示了胡椒碱近红外光谱的复杂性质，这是由高水平的带卷积产生的。对胡椒碱近红外吸收的最有意义的贡献来自二元组合波段。通过胡椒碱的详细近红外分配，我们解释了在我们早期研究中构建的偏最小二乘回归模型的特性，以描述黑胡椒样品中的胡椒碱含量。将两个模型与使用台式和小型光谱仪获得的光谱数据集进行了比较。这两种光谱仪采用不同的技术，在分析胡椒碱含量时，会导致仪器的巨大差异和预测性能的差异。我们得出的结论是，两种仪器对某些类型的胡椒碱振动的灵敏度不同，并且台式光谱仪具有更高的选择性。从样品中获取化学信息的这种差异可能是台式光谱仪在分析黑胡椒中胡椒碱含量方面表现更好的原因之一。这证明了对应用近红外光谱程序至关重要的特征与复杂样品中分析成分的潜在振动特性之间的直接对应关系。