NMR studies of daidzein and puerarin: active anti-oxidants in traditional Chinese medicine.

Radix puerariae-a popular traditional Chinese medicine-is used for the treatment of diarrhea, acute dysentery, deafness, and cardiovascular diseases. It can also be used as an effective antioxidant and has been tested as an anticancer drug. Daidzein and puerarin are its main active compounds. The present contribution was focused on experimental and theoretical studies of the 1H and 13C NMR chemical shifts and nuclear magnetic shielding parameters of daidzein and puerarin. Experimental data were gained by exploring standard one-dimensional spectra and a set of two-dimensional measurements: COSY, HSQC, and HMBC. The theoretical gauge independent atomic orbital density functional theory supporting studies, were performed to determine shielding constants and chemical shifts in vacuum and methanol-d4 solvent. The correlation between experimental and theoretical data was fairly good, especially when the DFT/PBE0 approach was used. The molecular properties of daidzein and puerine related to antiradical activity were studied in the context of a single-step hydrogen atom transfer mechanism and its correlation with 13C NMR chemical shifts. Graphical abstract Electron spin density distribution for daidzein radical.

NMR absolute shielding scale and nuclear magnetic dipole moment of (207)Pb.

An absolute shielding scale is proposed for (207)Pb nuclear magnetic resonance (NMR) spectroscopy. It is based on ab initio calculations performed on an isolated tetramethyllead Pb(CH3)4 molecule and the assignment of the experimental resonance frequency from the gas-phase NMR spectra of Pb(CH3)4, extrapolated to zero density of the buffer gas to obtain the result for an isolated molecule. The computed (207)Pb shielding constant is 10 790 ppm for the isolated molecule, leading to a shielding of 10799.7 ppm for liquid Pb(CH3)4 which is the accepted reference standard for (207)Pb NMR spectra. The new experimental and theoretical data are used to determine µ((207)Pb), the nuclear magnetic dipole moment of (207)Pb, by applying the standard relationship between NMR frequencies, shielding constants and nuclear moments of two nuclei in the same external magnetic field. Using the gas-phase (207)Pb and (reference) proton results and the theoretical value of the Pb shielding in Pb(CH3)4, we find µ((207)Pb) = 0.59064 µN. The analysis of new experimental and theoretical data obtained for the Pb(2+) ion in water solutions provides similar values of µ((207)Pb), in the range of 0.59000-0.59131 µN.