ABSTRACT:The structural and electronic parameters of the horminone molecule, an abietan diterpene quinone, were studied by means of all-electron calculations using Hartree-Fock and density functional theory-based methods, as implemented in the Gaussian98 program. The 6-31G orbital basis sets were used for the C, H, O, and Mg atoms. The results allow the identification of the negative site of horminone (HM) most favorable for its binding to the Mg 2ϩ ion. The HM-Mg 2ϩ complex is assumed to play a significant role in the antibacterial activity. First, it penetrates the membrane cell. Then, through its interaction with rRNA, it inhibits the protein synthesis in several types of bacteria.

The coordination of the horminone molecule with hydrated magnesium and calcium divalent ions was studied by means of the density functional theory. All-electron calculations were performed with the B3LYP/6-31G method. The first layer of the water molecules surrounding the metallic cations was included. It was found that the octahedral [horminone(O(a)-O(d))-Mg-(H(2)O)(4)](2+) complex is more stable than [Mg(H(2)O)(6)](2+). That is, horminone is able to displace two water units from the hexahydrated complex. This behavior does not occur for Ca(2+). Consistently, [horminone(O(a)-O(d))-Mg-(H(2)O)(4)](2+) has a greater metal-ligand binding energy than [horminone(O(a)-O(d))-Ca-(H(2)O)(4)](2+). The preference of horminone by Mg(2+) is enlightened by these results. Moreover, its electronic structure, as shown by huge changes in the atomic populations, is strongly perturbed by Mg(2+). Indeed, horminone, bonded to [Mg(H(2)O)(4)](2+), is able to cross the bacterial membrane cell. Once inside, [horminone(O(a)-O(d))-Mg-(H(2)O)(4)](2+) binds to rRNA phosphate groups yielding [horminone(O(a)-O(d))-Mg-(H(2)O)(PO(4)H(2))(PO(4)H(3))(2)](+). These results give insights into how horminone may inhibit the initial steps of protein synthesis. The stability of the studied systems is accounted for in terms of the calculated structural and electronic properties: Mg-O and Ca-O bond lengths, charge transfers, and binding energies.

Abstract:In this study, a theoretical characterization for three 2,2-diphenyl-1,3,2-oxazaborolidin-5-ones was performed using Density Functional Theory. The analyzed molecules have antifungal activity, making them of particular interest.