The effect of alkali metals, carbocations, and metallocenes substitutes on two ν-carrabiose disaccharide derivatives: a density functional study

Structural properties of the two ν-carrabiose disaccharide derivatives, d -galactpyranosyl-4-sulfate-(β-1,4)- d -galactopyranosyl-2,6-disulfate, and d -galactopyranosyl-2,6-disulfate (α-1,3)- d -galactopyranosyl-4-sulfate in acidic form or neutralized by monovalent cations Na + , K + , and Li + are investigated. The effect of substitutions by carbocations, toluene, di-toluene, or metallocene on the occurrence of complexation was also examined. The calculations were carried out using the density functional theory method (DFT) in order to examine the nature of the complexation in the different cases. The preferred structures of these two disaccharide derivatives were determined in the gas phase after making iso-energetic maps. Parameters describing reactivity were calculated on all the studied molecules to better understand the behavior of this type of molecules. The intramolecular hydrogen bonds were useful to explain the stability of the considered systems. Frontiers orbitals and molecular electrostatic potential surfaces (MESP) were then analyzed to get information on the polarity and the reactivity of each molecule and were in agreement with the reactivity studies and it has been found that these substitutions strongly influence the HOMO and LUMO energies. In addition, parameters such as chemical potential, hardness, electrophilic power, softness, and empirical nucleophilic index were calculated. In order to quantify the effect of these substitutions on the complexation, the thermodynamic parameters were determined and allowed us to suggest that the addition of carbocations (hydrophobic chains) weakens the solvation Gibbs energy.