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].
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.
Guided inquiry-based learning has been shown to be a promising method for science education, though, despite its advantages, it is rarely used in chemistry teaching in Hungary. One of the...
A new reagent system consisting of a Lewis acid such as BF3·Et2O or Cu(OTf)2, the mild protic acid hexafluoroisopropanol and the reducing quenching agent triethylsilane was elaborated for O-, N- and S-detritylation of nucleoside, carbohydrate and amino acid derivatives. The method is compatible with acetyl, silyl, acetal and Fmoc groups.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.