非缓冲介质中硫脲氧化的非线性动力学

研究了在非缓冲介质中高碘酸盐氧化硫脲的复杂反应动力学。实验结果表明：高碘酸盐氧化硫脲的非线性反应不但呈现多种不同的化学计量方程式,而且体系的pH、[I-]、[I2]及Pt电极电位呈现封闭条件下的准振荡和单峰振荡以及开放条件下的双稳态和衰减振荡行为。综合考虑硫价态与碘价态变化的各自非线性过程及相互耦合,提出了包含质子快速预平衡反应、碘化合物自身反应、碘化合物-硫化合物反应以及硫－硫反应的12步反应机理,模拟出了封闭体系中pH、[I-]以及[I2]的准振荡和单峰振荡以及开放体系中的双稳态行为。     

Protecting Group Free Synthesis of Carboxyl‐substituted Dihydropyrimidines Through Biginelli Reaction

Chlorotrimethylsilane‐promoted Biginelli‐type reaction of benzaldehyde, acetoacetic acid derivatives, and various carboxyl‐containing ureas was explored. It was found that the steric load of the urea substituents influenced strongly the reaction outcome; in particular, the method was efficient only in the case of unbranched mono‐substituted ureas bearing either aliphatic or aromatic groups. The method allows performing a one‐pot, protecting group free synthesis of dihydropyrimidines possessing carboxylic functionality.     

Kinetics and mechanism of the reaction between thiourea and iodate in unbuffered medium

The significances of thiourea and its derivativesnow spill into nonlinear dynamics in chemistry. A re-markable variety of complex dynamical phenomena,including oscillation, oligooscillation, variable stoichio-metries, autoinhibition, autocatalysis, bistability andbirhythmicity, traveling wave and chemical chaos,have been known in thiourea-based reaction systemsfor some time[1—7]. Also, a series of researches on thekinetics and mechanisms of the oxidations of thiourea,thiourea derivatives and …     

Recent Advances in the Construction of Trifluoromethyl‐Containing Spirooxindoles through Cycloaddition Reactions

The spirooxindole unit is one of the most widely investigated compound skeletons existing in numerous natural and pharmaceutical molecules. Thus, a large number of synthetic methodologies have already been reported to construct such a core structure. The trifluoromethyl group is another privileged unit in organic chemistry. The introduction of a CF₃ group to an organic framework can significantly improve the properties of the molecule. In this context, an efficient approach for the construction of trifluoromethyl‐containing spirooxindoles becomes a promising research direction among communities of industry and academia. In this Minireview, recent advances in the construction of trifluoromethyl‐containing spirooxindoles have been summarized and discussed. In addition, representative synthetic methodologies and the corresponding reaction mechanisms have been described as well.     

Nickel‐substituted iron‐dependent cysteine dioxygenase: Implications for the dioxygenation activity of nickel model compounds

Reported here is a density functional theory study on the ability of Ni‐substituted iron‐dependent cysteine dioxygenase (CDO) to catalyze the oxidation of cysteine to cysteine sulfinic acid. The first steps of the commonly accepted mechanism for CDO, the O₂ activation mechanism, suggests the binding of O₂ to the metal ion (where redox isomerism takes place converting O₂ to ) followed by the attack of the distal oxygen atom on the cysteine sulfur—in line with most previous evidence. An alternative mechanism entailing the attack of the cysteine sulfur on the proximal oxygen atom of the dioxygen moiety to form a persulfenate intermediate without any redox exchange between the metal ion and the O₂ ligand, is supported by an X‐ray crystal structure showing a CDO with a bound cysteine persulfenate, and also supported by data on the oxidation of thiols catalyzed by Ni(II) compounds. Our results show that the O₂ activation mechanism with a Ni‐substituted active site follows the same pattern as native CDOs albeit with much higher energy barriers for the formation of the intermediates suggesting that the reaction might not be biologically feasible. Conversely, the immediate cleavage of the persulfenate S O bond in the alternative mechanism suggests that cysteine persulfenate might not be a true intermediate in catalytic cycle of CDOs.