Studying the interaction between three synthesized heterocyclic sulfonamide compounds with hemoglobin by spectroscopy and molecular modeling techniques.

The interaction between synthesized heterocyclic benzene sulfonamide compounds, N-(7-benzyl-56-biphenyl-2m-tolyl-7H-pyrrolo[23-d]pyrimidine-4-yl)-benzene sulfonamide (HBS1 ), N-(7-benzyl-56-biphenyl-2-m-tolyl-7H-pyrrolo[23-d] pyrimidine-4-yl)-4-methyl- benzene sulfonamide (HBS2 ), and N-(7-benzyl-56-biphenyl-2-m-tolyl-7H-pyrrolo[23-d]pyrimidine-4-yl)-4-chloro-benzene sulfonamide (HBS3 ) with Hb was studied by fluorescence quenching, zeta potentional, circular dichroism, and molecular modeling techniques. The fluorescence spectroscopy experiments were performed in order to study the conformational changes, possibly due to a discrete reorganization of Trp residues during binding between HBS derivatives and Hb. The variation of the KSV value suggested that hydrophobic and electrostatic interactions were the predominant intermolecular forces stabilizing the complex. The KSV1 ans KSV2 values of HBS derivatives with Hb are .6 × 1013 and 3 × 1013  M-1 for Hb-HBS1 , 1 × 1013 and 4 × 1013  M-1 for Hb-HBS2 , .9 × 1013 , and 6 × 1013  M-1 for Hb-HBS3 , respectively. The molecular distances between Hb and HBS derivatives in binary and ternary systems were estimated according to Förster's theory of dipole-dipole non-radiation energy transfer. The quantitative analysis data of circular dichroism spectra demonstrated that the binding of the three HBS derivatives to Hb induced conformational changes in Hb. Changes in the zeta potential of the Hb-HBS derivatives complexes demonstrated a hydrophobic adsorption of the anionic ligand onto the surface of Hb as well as both electrostatic and hydrophobic adsorption in the case of the complex. The modeling data thus confirmed the experimental results. This study is expected to provide important insight into the interaction of Hb with three HBS derivatives to use in various toxicological and therapeutic processes.