松萝酸（C18H16O7）的晶体结构与DFT理论研究

以秦岭太白山地衣太白茶为原料,提取、分离其中的活性成分松萝酸.用高分辨快原子轰击质谱（HR-FABMS）确定了化学式,1H-NMR表征了分子结构,单晶X-射线衍射确定了晶体结构;并用Gaussian 03程序、密度泛函（DFT）方法计算了该化合物的优化结构、电荷分布、前线轨道能量及其组成.结果表明,该物质的晶体属于正交晶系,P2（1）2（1）2（1）空间群,a=8.007 4（11）A,b=18.818（3）,c=20.200（3）A,α=β=γ=90°,V=3 043.8（7）A^3,Z=8,Dc=1.503 g/cm^3,F（000）=144 0,μ（MoKa）=0.117 mm-1,R1=0.032 6,wR2=0.077 7.计算所得键长及键角与X-射线衍射结果基本相符,氢键和晶体结构一致.说明分子优化构型正确,计算方法可靠,可为进一步研究松萝酸的生理活性提供参考.

Crystal Structure and Quantum Chemical Calculation of Usnic Acid

The active compound usnic acid was extracted from the lichen of Cladonia alpestris（L.）Rabht collected from Qinling Mountains.The yellow transparent crystals were producted by recrystalization method using acetone as solvent.The title compound was characterized by HRFABMS,1H-NMR spectra and X-ray diffraction.It crystallizes in orthorhombic system,space group P2（1） 2（1） 2（1） with a=8.0074（11）A,b=18.818（3）A,c=20.200（3）A,α=β=γ=90°,V=3 043.8（7）A^3,Z=8,Dc=1.503 g/cm3,F（000）=1440,μ（Mo Ka）=0.117mm^-1,final deviation factor R1=0.0326 and wR2=0.0777.Moreover,the optimized structure,charge distribution,the energy and composition of frontier orbitals of HOMO and LUMO was calculated by quantum chemical method using Gaussian 03.The results indicated that the bond lengths,bond angles and hydrogen bonds are basically consistent with those of X-ray diffraction,suggesting the molecular geometry optimization of the structure was proper and calculation method was reliable.