Relaxed energetic maps of κ‐carrabiose: A DFT study

Abstract

The B3LYP density function was used with the 6-31G(d) basis set to perform relaxed energetic contour maps of the charged form of kappa-carrabiose in the gas phase and for the neutral form first in the gas phase and then by simulating the presence of water as solvent using the Onsager model. Only one starting conformation has been considered to perform all the calculations. Rigid energetic maps have been then constructed either by addition of diffuse or polarization functions to the basis set obtaining in that way 6-31+G(d)//6-31G(d), 6-31+G(d,p)//6-31G(d), and 6-311++G(d,p)//6-31G(d) energetic maps that have been carefully examined. The obtained structures corresponding to the lower energy conformers have been then fully optimized using different basis sets with the B3LYP method, a reversion in term of energy has been observed for the two first minima in the case of the charged disaccharide in the gas phase, this was attributed to the large grid of 30 degrees that could lead to the exclusion of an intermediate value corresponding to the real minimum of energy. We thus suggest that after establishing potential energy maps it is essential to proceed to full optimizations of the lower energy conformers. Calculations using the more accurate correlated method MP2 with the 6-31G(d) basis set have also been performed for conformers of the two disaccharides in the gas phase.

Nonlinear optical properties DFT calculations of polyacethylene and copolymers models substituted with aldimines chromophores as side chains

“…We to the procedure we used in previous works dealing with carbohydrate molecules. [66][67][68][69] From each map (Figure 9), conformers corresponding to lower energies were located then further optimizations using As reported on Table 4, for each couple (n,m), different distributions of the two units; Vp designated as A and M1 designated as B, were considered, this in order to determine the role of the distribution of the chromophore (B) on the NLO response and to possibly elucidate the role of the separating unit (A) at the same time. We remark that the variation of the hyperpolarizability does not depend only on the concentration in chromophore B (increasing m from 1 to 3) but also on that of the separating unit A, although the latter, when considered as isolated unit, produces a very weak or even a negligible NLO response.…”

“…Three energy maps were performed using B3LYP/6‐31G (d,p) considering the variations of ψ and ɸ dihedral angles, with three possibilities for χ : χ , χ + 120° and χ + 240°, with initial values of ( ψ , ɸ, χ ) = (−128°, 167°, 131°). The energy maps were obtained according to the procedure we used in previous works dealing with carbohydrate molecules 66–69 …”

Theoretical investigation on the improper hydrogen bond in κ-carrabiose⋯Y (Y = HF, HCl, HBr, NH3, H2O, and H2S) complexes

“…In order to get more details on the H-bonding network and to verify if the disaccharide will be affected by the aqueous medium, we have implicitly solvated the κ-carrabiose using the polarizable continuum model (PCM). It is expected, in a structural point of view, for the κ-carrabiose which is a flexible molecule as other similar disaccharides [74,[83][84][85] that its conformation may be influenced by hydration, namely the explicit one. Table 1 reports differences between solvated and isolated C-H) bonds obtained by the PBE0/6-311G** calculation [a] These results represent the differences between the solvated and isolated κ-carrabiose Among 16 bonds, 14 have suffered changes upon the solvation…”

Density Functional Theory Investigations on Vibrational Spectra, Molecular Structure, and Properties of the L-Serine, L-Cysteine, and L-Aspartic Acid Molecules

“…In addition, these methods are faster than others that may provide good results but may be more time consuming. Thus, the HF and DFT methods have been used to obtain more accurate results in a shorter time . To understand the properties of the amino acid molecules, theoretical studies of their molecular structure will be helpful.…”