Oxidation of a pair of associating thiols 1 and 2, each having a binding site [–C(=O)NHC(=O)NH–] and a recognition site (R1 or R2), is examined at various temperatures as a function of mole fraction of water (xw) in aqueous binary solvents with EtOH, CH3CN, and i-PrOH. The selectivity (r) — a measure of the degree of molecular recognition in the oxidation — is represented by the logarithmic ratio of the yield of the unsymmetrical disulfide 4 to twice that of the symmetrical one 3. It is found that three distinct patterns are present in temperature–recognition profiles, depending on composition of the aqueous binary solvents: (1) “progressive decrease” in the lower xw region; (2) “presence of a maximum” in the medium xw region; (3) “progressive increase” in the higher xw region. It is also clarified that aqueous mixed solvents in the medium xw region are indispensable for maximal recognition to occur against temperature (the presence of a maximum in the temperature–selectivity relationship). Dependence of the r on the xw at lower and higher temperatures, presence of three distinct patterns in the temperature–recognition profiles, and so on are discussed in relation to the maximal recognition.
在不同的温度下,研究了在含有 EtOH、CH3CN 和 i-PrOH 的
水性二元溶剂中,一对具有结合位点 [-C(=O)NHC(=O)NH-] 和识别位点(R1 或 R2)的缔合
硫醇 1 和 2 的氧化作用与
水的摩尔分数(xw)的函数关系。选择性(r)是衡量氧化过程中分子识别程度的指标,用非对称二
硫化物 4 的产率与对称二
硫化物 3 的两倍产率的对数比来表示。研究发现,根据
水性二元溶剂的成分,温度-识别曲线有三种不同的模式:(1) 在较低 xw 区域 "逐渐降低";(2) 在中等 xw 区域 "出现最大值";(3) 在较高 xw 区域 "逐渐升高"。此外,还说明了中等 xw 区域的
水性混合溶剂对温度的最大识别是不可或缺的(温度-选择性关系中出现最大值)。此外,还讨论了在较低和较高温度下 r 与 xw 的关系、温度-识别曲线中存在的三种不同模式等与最大识别率有关的问题。