Our computational studies suggest that 3-substituted xanthines are good candidates for tetrad and quadruplex structures. 3-Methylxanthine (3MX) has been synthesized from 7-benzylxanthine, and the existence of tetrameric and octameric aggregates of 3MX with NH 4 + , Na + and K + ions in the gas phase (MS) and in DMSO-d 6 solution (NMR) has been observed. The ''internal'' H-bonds (N1HÁ Á ÁO6) are stronger than the ''external'' ones (N7HÁ Á ÁO2) in these clusters (NMR). Fig. 1 Tetrads composed of 7H-3-methylxanthine (3MX) and different cations [cat + = none, Na + , K + , NH 4 + ; purine atom and spectroscopic (underlined) numbering shown in upper left ring].

No abstract

Laser acupuncture is a safe but inefficient treatment for monosymptomatic nocturnal enuresis with reduced maximal voided volume. However, we found subtle effects on bladder reservoir function.

The15 N NMR chemical shifts of N 7 -and N 9 -substituted purine derivatives were investigated systematically at the natural abundance level of the 15 N isotope. The NMR chemical shifts were determined and assigned using GSQMBC, GHMBC, GHMQC and GHSQC experiments in solution.15 N cross-polarization magic angle spinning data were recorded for selected compounds in order to study the principal values of the 15 N chemical shifts. Geometric parameters obtained by using RHF/6-31G * * and single-crystal x-ray structural analysis were used to calculate the chemical-shielding constants (GIAO and IGLO) which were then used to assign the nitrogen resonances observed in the solid-state NMR spectra and to determine the orientation of the principal components of the shift tensors.

No abstract