Roca-Sanjuán Daniel
Chemistry Department, Faculty of Mathematics and Natural Science, Islamic University of Indonesia, Yogyakarta, 55581, Indonesia.
Instituto de Ciencia Molecular, Universitat de València, P.O. Box 22085, 46071 Valencia, Spain.
ACS Omega. 2024 Aug 6;9(33):35356-35363. doi: 10.1021/acsomega.4c00875. eCollection 2024 Aug 20.
Among all amino acids, the three aromatic systems including phenylalanine, tyrosine, and tryptophan are known to manifest UV light absorption at the higher wavelengths. Their fluorescent properties are important for protein detection and determination of the spatial structure. Based on quantum chemical calculations, the absorption spectra in the 0-12 eV UV range of these aromatic amino acids were interpreted, and the photochemistry of the lowest-lying excited states was studied. For that, molecular ground-state geometries were determined using both the coupled-cluster single and double (CCSD) and complete active space self-consistent field (CASSCF) methods. The vertical electronic transition energies, associated oscillator strengths, and electric dipole moments of the lowest excited states were computed at the CASPT2//CASSCF level. The decay mechanisms of the lowest-energy excited states were investigated by performing minimum energy path (MEPs) computations. The results showed that the CCSD and CASSCF computations yielded similar structures. The lowest-energy S state in phenylalanine and tyrosine, and S and S in tryptophan are mainly described by the π → π* excitation localized in the aromatic ring. Upon light absorption, the main photoresponse of the molecules is driven by the benzene, phenol, and indole chromophoric units.
在所有氨基酸中，包括苯丙氨酸、酪氨酸和色氨酸在内的三种芳香体系在较高波长下表现出紫外线吸收。它们的荧光特性对于蛋白质检测和空间结构测定很重要。基于量子化学计算，解释了这些芳香族氨基酸在0-12 eV紫外线范围内的吸收光谱，并研究了最低激发态的光化学。为此，使用耦合簇单双激发（CCSD）和完全活性空间自洽场（CASSCF）方法确定了分子基态几何结构。在CASPT2//CASSCF水平上计算了最低激发态的垂直电子跃迁能量、相关振子强度和电偶极矩。通过执行最小能量路径（MEP）计算研究了最低能量激发态的衰变机制。结果表明，CCSD和CASSCF计算产生了相似的结构。苯丙氨酸和酪氨酸中的最低能量S态以及色氨酸中的S1和S2态主要由芳香环中局域化的π→π*激发来描述。分子在光吸收时的主要光响应由苯、苯酚和吲哚发色团单元驱动。
