Nitric oxide binding to cationic and anionic ferric porphyrins in aqueous solution: reversible formation of ferrous NO species of the cationic porphyrin

摘要

Two water-soluble ferric porphyrins, sodium 5alpha,10beta,15alpha,20beta-tetrakis(2-(sulfonatoacetamido)phenyl)porphyrinatoiron(III) (Fe(III)TanP) and 5alpha,10beta,15alpha,20beta-tetrakis(2-(N,N,N-trimethylammoniumacetamido)phenyl)porphyrinatoiron(III) chloride ((FeT)-T-III-catP), were synthesized. The pK(a) values of the coordinated H2O of Fe(III)TanP and Fe(III)TcatP were evaluated to be 8.0 and 4.1, respectively. Reactions of NO with the ferric porphyrins were examined spectrophotometrically in aqueous solution. Porphyrin Fe(III)TanP binds NO reversibly to give the corresponding ferric NO species at pH 1.3 and pH 3.0, and Fe(III)TcatP reacts similarly with NO at pH 1.3. The thermodynamic data for the NO binding were estimated from van't Hoff plots. At pH 3.0, visible and ESR spectral data indicated that Fe(III)TcatP binds NO reversibly to produce ferrous NO species depending on NO partial pressures. These results were discussed based on through-space intramolecular interactions between the coordinated H2O or NO and the ionic substituents of the porphyrins. (C) 2004 Elsevier B.V. All rights reserved.