Abstract
The structural and electronic properties of berberine and berberrubine have been studied extensively using density functional theory (DFT) employing B3LYP exchange correlation. The geometries of these molecules have been fully optimized at the B3LYP/6โ311G** level. The chemical shift of ^1^H and ^13^C resonances in NMR spectra of these molecules have been calculated using the gauge invariant atomic model (GIAO) method as implemented in Gaussian 98. Oneโ and twoโdimensional HSQC (^1^H๏ฃฟ^13^C), HMBC (^1^H๏ฃฟ^13^C) and ROESY (^1^H๏ฃฟ^1^H) spectra were recorded at 500 MHz for the berberine molecule in D~2~O solution. All proton and carbon resonances were unambiguously assigned, and interโproton distances obtained from ten observed NOE contacts. A restrained molecular dynamics (RMD) approach was used to get the optimized solution structure of berberine. The structure of berberine and berberrubine molecules was also obtained using the ROESY data available in literature. Comparison of the calculated NMR chemical shifts with the experimental values revealed that DFT methods produce very good results for both proton and carbon chemical shifts. The importance of the basis sets to the calculated NMR parameters is discussed. It has been found that calculated structure and chemical shifts in the gas phase predicted with B3LYP/6โ311G** are in very good agreement with the present experimental data and the measured values reported earlier. Copyright ยฉ 2007 John Wiley & Sons, Ltd.