量子化学研究L-精氨酸磷酸盐的前线分子轨道与理论振动光谱

Quantum Chemical Studies on Frontier Molecular Orbitals and Theoretical Vibration Spectra of L-arginine Phosphate Monohydrate

L-精氨酸磷酸盐(LAP)晶体是一种性能优异的半有机非线性光学材料,因其特殊的高激光损伤阈值受到众多关注。基于LAP晶体的多种特殊性质及结构中磷酸胍基间作用的相继发现,通过研究分子内基团间作用探讨分子特异性及晶体光损伤机制是一种新的合理途径。本研究根据LAP分子的基团组成建立四个相关分子模型,在M06-2X-D3/6-311++g(d,p)水平下对不同基团组合模型进行了结构优化、频率计算及前线分子轨道分析。研究发现,LAP中L-精氨酸阳离子与磷酸根阴离子具有较强的结合能,磷酸胍基间作用会弱化L-精氨酸分子构象弯曲能力,且使磷氧四面体发生畸变。LAP中磷酸基团能够降低LAP分子轨道能级间隙,有利于分子内电子转移。磷酸基团与L-精氨酸分子上各个基团均有电子相互作用,其中对胍基与氨基上N-H键具有推电子作用,且与胍基间作用更强、更明显,而对羧基表现为吸电子作用。该研究结果为进一步理解和研究晶体中磷酸根和胍基间的作用奠定了良好的理论基础。

L-arginine phosphate monohydrate(LAP)crystal is a kind of semi-organic material with excellent nonlinear optical properties,which attracts much attention due to its special high laser damage threshold.Based on the successive discovery of its uniqueness and the interaction between guanidine and phosphate groups in LAP,it is a novel and reasonable way to explore the molecular specificity and the mechanism of crystal laser damage by studying the interaction between intramolecular groups.In this work,four related molecular models were established based on the group composition of LAP molecular.The structural optimization,theoretical vibrational spectra and the frontier molecular orbital analysis of four molecule models were investigated using M06-2X-D3/6-311++g(d,p)in Gaussian 16.The results show that there is a strong binding energy between L-arginine cation and phosphate anion in LAP,and the interaction between phosphate and guanidine in LAP could weaken the conformational flexibility of L-arginine molecular and distort the phosphorus-oxygen tetrahedron.Compared with water molecular,phosphate group can significantly reduce the molecular orbital energy gap of LAP,which is conducive to the intramolecular electron transfer.In addition,there are various electronic interactions between phosphate group with all groups of L-arginine molecular.The phosphate group have the electron-pushing effect on the N-H bond of amino group and guanidine group,and there is a stronger and more obvious interaction between phosphate and guanidine groups.Moreover,it also shows an electron-pulling effect on the carboxyl group.The study can established a good theoretical foundation for further understanding and studying the interaction between phosphate and guanidine groups.