title: Studies on haemin in dimethyl sulphoxide/water mixtures.
abstract: The nature of the complexes and equilibria shown by solutions of protohaemin in dimethyl sulphoxide/water mixtures and in the presence of acid and base were studied by u.v.-visible spectrophotometry. In neutral solutions containing from 40 to 100% dimethyl sulphoxide, haemin is present as a monomeric complex in which the Cl-ion is not coordinated. Only a single pH-dependent equilibrium pK12 is observed over the range 40-80% dimethylsulphoxide, corresponding to formation of the mu-oxo dimer. As the dimethyl sulphoxide content is lowered below 35%, so the single equilibrium (pK12) is replaced by two equilibria (pK1 and pK2); with solutions of 5 microM-haemin, pK1 decreases (from pK12 7.55 in 65% dimethyl sulphoxide to pK1 approx. 1.5 in 0.01% dimethyl sulphoxide), whereas pK2 hardly changes (from pK12 7.55 in 65% to pK2 approx. 7.5 in 0.01%).
mesh_terms: D000136:Acid-Base Equilibrium; D006418:Heme / Q000031:analogs & derivatives; D006427:Hemin; D046911:Macromolecular Substances; D013056:Spectrophotometry, Ultraviolet; D013454:Sulfoxides; D014867:Water
chemical_list: D046911:Macromolecular Substances; D013454:Sulfoxides; D014867:Water; D006418:Heme; D006427:Hemin