Geometrical and energetic DFT calculations as well as GIAO and NICS chemical shifts have been calculated for 1H-azepine and 5H-dibenz[b,f]azepine and their cations. The last compound has been studied experimentally by 1H and 13C NMR in neutral and acidic conditions establishing that the cation corresponds to an N-protonated structure. The conclusion is that the neutral molecules are antiaromati...

Isotropic magnetic shielding distributions in the regions of space surrounding oxazole, imidazole, and thiazole are used to investigate aromaticity and bonding in these five-membered heterocycles with two heteroatoms. This is achieved by constructing HF-GIAO and MP2-GIAO (Hartree-Fock and second-order Møller-Plesset perturbation theory with gauge-including atomic orbitals) isotropic shielding p...

We have evaluated the NMR shielding tensors for A:T,G:C,A:U in Watson-crick, and U-quartet. We have computed NMR shielding tensors at B31YP level by using 6-31G(d) basis set. We have compute anisotropy and asymmetry in A:T,G:C,A:U and U-quartet. The NMR shielding tensors were calculated using the GIAO method. The natural bonding orbital analysis (NBO) were performed. NBO calculation have been ...

The (1)H and (13)C nuclear magnetic resonance (NMR) spectra of the retinyl chromophore in rhodopsin are investigated by using quantum mechanics/molecular mechanics (QM/MM) hybrid methods at the density functional theory (DFT) B3LYP/6-31G*:Amber level of theory, in conjunction with the gauge independent atomic orbital (GIAO) method for the ab initio self-consistent-field (SCF) calculation of NMR...

The spatial magnetic properties (through space NMR shieldings--TSNMRS) of metal complexes (with ligands such as acetylacetone, 3-hydroxy-pyran(4)one) and "metallobenzenes" have been calculated by the GIAO perturbation method and visualized as Iso-Chemical-Shielding Surfaces (ICSS) of various sizes and directions. The TSNMRS values, thus obtained, can be successfully employed to quantify and vis...

Knowledge of chemical shift-structure relationships could greatly facilitate the NMR chemical shift assignment and structure refinement processes that occur during peptide/protein structure determination via NMR spectroscopy. To determine whether such correlations exist for polar side chain containing amino acid residues the serine dipeptide model, For-L-Ser-NH(2), was studied. Using the GIAO-R...

Etheno adducts are formed in the reactions of DNA bases with chloroacetaldehyde, with lipid peroxidation products, and also with metabolites of vinyl chloride and furan. The presence of such modifications in the genetic material may lead to errors in replication with consequences of mutations and even carcinogenesis. For an understanding of the biological significance of etheno adducts it is im...

The aerial parts of Lippia javanica were investigated for biologically active chemical compounds present in them. Chromatographic separation of the ethyl acetate extract of the aerial parts yielded a new antimalarial α-pyrone, lippialactone (2). Lippialactone is active against the chloroquine-sensitive D10 strain of Plasmodium falciparum with an IC50 value of 9.1 μg/mL, and is also mildly cytot...

Abstract: The experimental C chemical shifts of five different series of organic compounds are compared with predicted C NMR chemical shifts obtained via empirically scaled GIAO shieldings. Our results indicate that the inclusion of a scaling factor allow to obtain an excellent correlation between δcalc and δexp. Although the inclusion of asymmetry improves this correlation, such enhancement wa...