水杨醛甘氨酸Schiff碱的从头算构象研究

AB INITIO STUDY ON CONFORMATION OF SALICYLIDENE-GLYCINE SCHIFF BASE

运用从头算HF方法对水杨醛甘氨酸Schiff碱的构象进行了理论研究.结果表明,C N键与苯环的共轭以及分子内弱相互作用是分子能量降低的2个重要结构因素.在各存在形态的所有最稳定构象中C N键均与苯环共轭,均至少存在1条H14的弱氢键.酸式结构最稳定构象羧基上羟基氢H22背离大共轭平面;酸根形态的稳定构象羧基与苯环共面形成平面分子,且存在2条氢键;钾盐酚式最稳定构象羧基螯合成键,而醌式最稳定构象为平面分子,羧基单齿成键,且存在H14的2条弱氢键.由于具有很大的能量优势,水杨醛甘氨酸Schiff碱在水中的主要存在形态为酸式,该结论与其水溶液的实验研究结果一致.

Ab initio study on the conformation of salicylidene-glycine Schiff base is done. Two important structural factors for lowering the molecular energy are revealed, one is the conjugation of C=N bond with phenyl ring and the other is the intramolecular weak interaction. In all of the most stable conformations of each existing form, conjugation of C=N bond with phenyl ring and at least one hydrogen bond of H14 are found. In the lowest energy conformation of the acidic structure, hydroxyl H22 on carboxyl departs from the conjugating plane. In ate form, a planar molecule with two hydrogen bonds is formed by carboxyl conjugating with phenyl ring. Carboxyl chelates to potassium ion in the most stable conformation of phenol potassium salt, but it monodentately bonds to potassium ion in that of the planar quinoid molecule that has two hydrogen bond of H14. As a great deal of energy predominance, the major species of salicylidene-glycine Schiff base in water is the acidic form, which coincides with the experimental result of the aqueous solution.