Keto‐enol tautomerism of the 4,5‐dimethyl‐2‐(2′‐hydroxyphenyl)imidazole in water solution: Modeling equilibrium between neutral forms and accurate assignment of the absorption bands,International Journal of Quantum Chemistry

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Keto‐enol tautomerism of the 4,5‐dimethyl‐2‐(2′‐hydroxyphenyl)imidazole in water solution: Modeling equilibrium between neutral forms and accurate assignment of the absorption bands
International Journal of Quantum Chemistry ( IF 2.3 ) Pub Date : 2020-11-30 , DOI: 10.1002/qua.26577
Dmitry P. Kapusta ₁ , Fedor D. Mulashkin ₁ , Maria G. Khrenova _{1,

2}

Affiliation

Tautomerizarion between keto, cis‐ and trans‐enol forms of the 4,5‐dimethyl‐2‐(2′‐hydroxyphenyl)imidazole (DMHI) is studied using molecular dynamics simulations with the quantum mechanics/molecular mechanics (QM/MM) potentials. We applied the live solvent selection approach that presumes division of water molecules to either QM or MM subsystems on the fly depending on their distances from the chromophore. This allowed us to treat a water shell around the chromophore at the QM level and to describe properly all chromophore‐water interactions. According to the calculated Gibbs energy profiles the most stable is a keto form and a cis‐enol form is ~1 kcal/mol higher. The trans‐enol form is much higher in energy and should not be observed in experiment. Vertical S_0,min − S₁ excitation energies of all neutral tautomers were calculated at the XMCQDPT2 level: both enol forms have similar values ~4 eV and keto form is red‐shifted, with the excitation energy of 3.3 eV. Thus, we conclude that two absorption bands in experimental absorption spectrum of DMHI in water solution are due to the presence of cis‐enol and keto forms of the chromophore.

中文翻译：

4,5-二甲基-2-（2'-羟基苯基）咪唑在水溶液中的酮-烯醇互变异构现象：中性形式与吸收带的精确分配之间的平衡建模

使用分子动力学模拟和量子力学/分子力学（QM / MM）势研究了4,5-二甲基-2-（2'-羟基苯基）咪唑（DMHI）的酮，顺式和反式-烯醇形式的互变异构。我们采用了活泼的溶剂选择方法，该方法假定水分子根据其与生色团的距离而动态地分配给QM或MM子系统。这使我们能够在QM级别处理发色团周围的水壳，并恰当地描述所有发色团与水之间的相互作用。根据计算得出的吉布斯能量分布图，最稳定的是酮形式，顺式-烯醇形式高约1 kcal / mol。该反式烯醇形式的能量更高，在实验中不应观察到。在XMCQDPT2水平上计算了所有中性互变异构体的垂直S _0，min - S ₁激发能：两种烯醇形式的近似值均为〜4 eV，酮形式发生红移，激发能为3.3 eV。因此，我们得出的结论是，水溶液中DMHI的实验吸收光谱中有两个吸收带是由于存在发色团的顺式-烯醇和酮形式。

更新日期：2020-11-30

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