Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
J Chem Phys. 2012 Feb 14;136(6):064511. doi: 10.1063/1.3683217.
Spontaneous and near-infrared/infrared (NIR/IR)-induced interconversions between two amino-hydroxy conformers of monomeric cytosine have been investigated for the compound isolated in a low-temperature argon matrix. Combined use of a laser source (which provides narrowband NIR radiation) and a broadband NIR/IR source of excitation light allowed a detailed investigation of mutual conversions of the two conformers in question. The experiments carried out within the current work demonstrated that upon broadband NIR/IR irradiation (with the IR source of FTIR spectrometer) the population ratio of the two amino-hydroxy conformers changes towards a ratio corresponding to a photostationary state. Evolution of the conformer population ratio towards the photostationary ratio occurred independent of the initial ratio of conformers, which could be prepared by a population shift (in favor of one of the forms) induced by narrowband NIR excitation. Moreover, spontaneous tunneling conversion of the higher-energy conformer into a lower-energy form was observed for cytosine isolated in a low-temperature argon matrix kept in the dark. This process is slow and occurs on a time scale of days. The tunneling process, studied for matrix-isolated cytosine, clearly follows a dispersive type of kinetics rather than the classical monoexponential kinetics.
已研究了在低温氩基质中分离出的单体胞嘧啶的两种氨基-羟基构象之间的自发和近红外/红外（NIR/IR）的相互转换。激光源（提供窄带 NIR 辐射）和宽带 NIR/IR 激发光源的组合使用允许对所讨论的两种构象的相互转换进行详细研究。当前工作中的实验表明，在宽带 NIR/IR 辐照（使用傅里叶变换红外光谱仪的 IR 源）下，两种氨基-羟基构象的种群比例朝着与光稳定态相对应的比例变化。构象种群比例朝着光稳定比例的演化与初始构象比例无关，初始构象比例可以通过窄带 NIR 激发诱导的（有利于一种形式的）种群转移来制备。此外，在黑暗中保存在低温氩基质中的胞嘧啶中观察到高能构象自发隧道转换为低能形式。这个过程是缓慢的，发生在几天的时间尺度上。对于基质分离的胞嘧啶进行的隧道过程显然遵循弥散类型的动力学，而不是经典的单指数动力学。
