前周期ⅥA和ⅦA氢化物分子与冠丙四肽结合作用的理论研究

A theoretical study on the interaction of crown tetraalanylpeptide with small ⅥA and ⅦA nonmetal hydrides

冠肽是环肽的特殊构型,其结构中的酰胺键主链呈规则排列,形成类似于冠醚的冠型构象,具有高度的对称性,易于形成实现与离子/分子结合的孔径或通道,达到预期的识别作用以及作为超分子离子载体的运输能力。借助于密度泛函理论的B3LYP方法,以冠丙四肽为模型基础,对氧、硫、硒、氟、氯、溴等常见非金属元素的氢化物分子与其结合体系进行了几何构型优化、能量、布局数等理论研究。结果表明:冠丙四肽的构型在与这些氢化物分子结合前后几乎没有改变;结合过程中电子由这些氢化物分子不同程度地移向冠肽主体:在最佳结合位时,氢化物分子中心杂原子距冠丙四肽中心的距离依次为0.278 nm、0.380 nm、0.331 nm、0.266 nm、0.376 nm和0.334 nm对比于与相应离子的结合过程,这些氢化物分子与冠丙四肽没有特别的优势结合,据此可初步预测水等分子存在时,并不影响冠丙四肽对离子实施识别。

As a kind of annular molecule, cyclic peptides, existing widely in the nature, commonly contain two species. One is the homodetic cyclopeptide, which is composed of amino acids only by imido group. The other species is heterodetic cyclopeptide, such as depsipeptide or peptolide, the main bonds of which is imido group, too, and they ring commonly recurring to -COO-, -O-, -S-S-, -S-, etc. Crown peptide is a kind of special conformation of homodetie cyelopeptide, in the structure of which there is regular array about the main chain containing imido groups, and the monolithic conformation presents coronary analogy to crown ether. They are high symmetrical ionophores belong to Cn （n=2, 3, ...） point group. The channels or apertures can form more easily in order to recognize certain ion or molecular, and the fimction of intending dual-recognition for cations and anions can be achieved. Based hybrid-method B3LYP, the density functional theory method was applied to investigate the interaction of the small VIA and VIA hydrides with crown tetraalanylpeptide, which is the coronary structures ofhomodetic cyclotetraalapeptide and has been represented as the model basic. Several properties researched including combination energy, optimum geometry structures and so on. It showed that the coronary structure was no change between C4-Ala and C4-AIa-HnX. During the combine process, the electrons move from nonmetal hydride to C4-Ala with different extent. The distances between the central atom of nonmetal hydride and the center of C4-Ala are 0.278 nm （I-120）, 0.380 nm （H2S）, 0.331 nm （H2Se）, 0.266 nm （I-IF）, 0.376 nm （HCI）, 0.334 nm （HBr）, respectively, when the energy of C4-Ala-H,,X at minimum. Additionally, values of combination energy of these hydrides do not present remarkable predominant, compared to that of corresponding ions.