Showing papers by "Francesco Mauri published in 2000"
TL;DR: In this article, the correlation between Si-29 chemical shifts and Si-O-Si bond angles in SiO2 is determined within density-functional theory for the full range of angles present in vitreous silica.
Abstract: The correlation between Si-29 chemical shifts and Si-O-Si bond angles in SiO2 is determined within density-functional theory for the full range of angles present in vitreous silica. This relation closely reproduces measured shifts of crystalline polymorphs. The knowledge of the correlation allows us to reliably extract from the experimental NMR spectrum the mean (151 degrees) and the standard deviation (11 degrees) of the Si-O-Si angular distribution of vitreous silica. In particular, we show that the Mozzi-Warren Si-O-Si angular distribution is not consistent with the NMR data. This analysis illustrates the potential of our approach for structural determinations of silicate glasses.
151 citations
TL;DR: In this article, the results of ab initio density functional theory calculations of the NMR chemical shift of liquid water and hexagonal ice were reported, depending on the structural model used, the calculated isotrop...
Abstract: We report the results of ab initio density functional theory calculations of the NMR chemical shift of liquid water and hexagonal ice. Depending on the structural model used, the calculated isotrop...
111 citations
TL;DR: In this paper, the amplitude of the bond length alternation between single and double carbon bonds is strongly reduced in the vicinity of the protonated Schiff base nitrogen, and the correlation between 13 C chemical shift and atomic charge along the conjugated chain of retinals is found to depend strongly on the specific compound.
Abstract: molecules which constitute the chromophores of the natural pigments rhodopsin and bacteriorhodopsin. We compare our results with recent X-ray and NMR spectroscopic data on several retinylidene iminium salts characterized by different cation-anion interactions. In agreement with crystallographic data, we find that the amplitude of the bond length alternation between single and double carbon bonds is strongly reduced in the vicinity of the protonated Schiff base nitrogen. The chemical shifts along the carbon chain are in very good agreement with the experimental values for the neutral retinylidene compounds and in fairly good agreement for the charged retinylidene compounds. We find that the 13 C chemical shift is mostly affected by the cation-anion distance and to a lesser extent by the presence of hydrogen bonding interaction between the protonated Schiff base of retinal and the counterion. The correlation between 13 C chemical shift and atomic charge along the conjugated chain of retinals is found to depend strongly on the specific compound. This result suggests some caution in using atomic charges alone to establish the position of the counterion relative to the chromophore in rhodopsin.
25 citations