n-sigma charge-transfer interaction and molecular and electronic structural properties in the hydrogen-bonding systems consisting of p-quinone dianions and methyl alcohol.
n-sigma charge-transfer interaction and molecular and electronic structural properties in the hydrogen-bonding systems consisting of p-quinone dianions and methyl alcohol.
复制标题
由对醌二价阴离子和甲醇组成的氢键系统中的 n-sigma 电荷转移相互作用以及分子和电子结构特性。
作者：
B. Uno;N. Okumura;M. Goto;K. Kano
利用PQ在MeCN中的电化学和光谱电化学结合从头算方法研究了对苯醌二价阴离子氢键配合物（PQ（2）（-））的分子和电子结构性质. PQ（2）（-）和MeOH之间的氢键被测量为随着MeOH浓度的增加，表观第二半波还原电位的连续正移。详细的行为分析表明，PQ（2）（-）形成1：2氢键复合物在低浓度的甲醇和1：4复合物在高浓度下，产生的形成常数。生成常数的温度依赖性使我们能够得到1，4-苯醌二价阴离子（BQ（2）（-））与MeOH形成1：2和1：4络合物的生成能分别为76.6和118.9 kJ mol（-）（1）。这些结果表明，含醌羰基的π-二价阴离子具有很强的吸氢能力。BQ（2）（-）和氯醌二价阴离子（CL（2）（-））光谱的最长波长带归属于（1）B（3 u）<--（1）A（g）带，主要由分子内电荷转移（CT）构型贡献。氢键使得BQ（2）（-）和CL（2）（-）的能带蓝移，这取决于氢键的强度。CNDO/S-CI计算表明，蓝移归因于涉及强n-sigma型CT相互作用的氢键对基态的稳定。HF/6- 31 G（d）计算结果表明，PQ（2）（-）的结构特征是C=O键的延长和苯环的形成. PQ（2）（-）氢键复合物的几何性质是C=O键稍长，氢键距离短。结果表明，这种情况是由于强的n-sigma CT相互作用的氢键。结果表明，不同的功能和性质的生物醌赋予的n-sigma CT相互作用，通过氢键的二价阴离子与它们的蛋白质环境。
Molecular and electronic structural properties of the hydrogen-bonded complexes of p-quinone dianions (PQ(2)(-)) were investigated by electrochemistry and spectroelectrochemistry of PQ in MeCN combined with ab initio MO calculations. Hydrogen bonding between PQ(2)(-) and MeOH was measured as the continuous positive shift of the apparent second half-wave reduction potentials with increasing concentrations of MeOH. Detailed analyses of the behavior reveal that PQ(2)(-) forms the 1:2 hydrogen-bonded complexes at low concentrations of MeOH and the 1:4 complexes at high concentrations, yielding the formation constants. Temperature dependence of the formation constants allows us to yield the formation energy as 76.6 and 118.9 kJ mol(-)(1) for the 1:2 and 1:4 complex formation of the 1,4-benzoquinone dianion (BQ(2)(-)) with MeOH, respectively. These results show that the pi-dianions involving the quinone carbonyl groups exhibit very strong hydrogen-accepting ability. The longest wavelength band of the spectra of BQ(2)(-) and the chloranil dianion (CL(2)(-)) is assigned to the (1)B(3u) <-- (1)A(g) band mainly contributed from an intramolecular charge-transfer (CT) configuration. Hydrogen bonding allows the band of BQ(2)(-) and CL(2)(-) to be blue-shifted, depending on the strength of the hydrogen bonds. CNDO/S-CI calculations reveal that the blue shift is ascribed to stabilization of the ground state by the hydrogen bonding involving strong n-sigma-type CT interaction. The HF/6-31G(d) calculation results show that the structure of PQ(2)(-) is characterized by a lengthening of the C=O bonds and a benzenoid ring. The geometrical properties of the hydrogen-bonded complexes of PQ(2)(-) are a slight lengthening of the C=O bonds and a short distance of the hydrogen bonds. It is demonstrated that this situation is due to the strong n-sigma CT interaction in the hydrogen bonds. The results suggest that the differing functions and properties of biological quinones are conferred by the n-sigma CT interaction through hydrogen bonding of the dianions with their protein environment.