Analysis of organophosphate-Zn metalloporphyrin interactions via UV-vis spectroscopy and molecular modeling

摘要

UV-vis absorption spectra of zinc tetraphenylporphine (ZnTPP) on interaction with six organophosphorus (OP) compounds in cyclohexane were compared using ab initio methods and the molecular and solvation ligand descriptors pi*, V-x, and sigma. OPs with polarizable hydrocarbon substituents in the homologous series tri-ethyl, -pentyl, -octyl, and -phenyl phosphates and the toxicologically relevant methyl paraoxon (1a-e) each gave a red shift in the Soret band (lambda(sor)) of ZnTPP in the range of 8-10 nm. Sensitivity as Delta A(sor-b)/Delta ug OP for the spectral band of the ligand bound ZnTPP (lambda(sor-b)) decreased with increasing extent of alkyl and aromatic substitution. Calculated and combined energies for OP and ZnTPP examined as a function of distance (angstrom) between ligand and porphyrin center suggest increased steric crowding with increasing V-x, and aromatic content of the OP. Spectrally fitted K-1:1 and Delta A(sor-b)/ug OP each vary exponentially with V-x/sigma. Lack of a red shift in lambda(sor-b) where ZnTPP was titrated with the toxic diethyl chlorophosphate (1g) is consistent with a model in which the magnitude of Delta E-sor is proportional to the donor capacity of the phosphoryl-O ligand. (C) 2014 Elsevier B.V. All rights reserved.