Metal ion catalyzed oxidation of o-dihydroxy aromatic compounds by oxygen. 1. Redox and acid-base properties of the system 1,2-naphthoquinone-4-sulfonate/1,2-dihydroxynaphthalene-4-sulfonate

1977 ◽  
Vol 16 (9) ◽  
pp. 2221-2225 ◽  
Author(s):  
Jacques. Buffle ◽  
Arthur E. Martell
Keyword(s):  
Aromatic Compounds ◽  
Metal Ion ◽  
Acid Base ◽  
Catalyzed Oxidation ◽  
Base Properties

Synthesis and properties of water-soluble porphyrins bearing multidentate ligands

2004 ◽  
Vol 08 (08) ◽  
pp. 1047-1054 ◽  
Author(s):  
Yoshio Uemori ◽  
Masato Sakurai ◽  
Atsuko Osada ◽  
Hiroki Munakata ◽  
Hiroyasu Imai ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Aromatic Compounds ◽  
Covalent Binding ◽  
Nitrilotriacetic Acid ◽  
Association Constants ◽  
Water Soluble ◽  
Para Position ◽  
Multidentate Ligands ◽  
Acid Base ◽  
Base Properties

Water-soluble porphyrins bearing multidentate ligands were prepared by covalent binding of nitrilotriacetic acid to 5,10,15,20-tetrakis(4-aminophenyl)porphyrin or three atropisomers of 5,10,15,20-tetrakis(2-aminophenyl)porphyrin. The acid-base properties and monomer-dimer behavior of the porphyrins were affected by the positions of the multidentate ligands with respect to the porphyrin plane. Among the porphyrins, the porphyrin bearing multidentate ligands at the para position of the phenyl groups dimerized in an aqueous solution. The association constants of the porphyrins with various aromatic compounds were studied in water at pH 7.4 containing 10 mM HEPES at 25°C. These values varied with the structure and charges of both the porphyrins and the aromatic compounds. The association constants of the porphyrin bearing multidentate ligands at the 2-position of the phenyl groups were small compared to those of the porphyrin bearing multidentate ligands at the 4-position.

scholarly journals Acid-base properties of purine residues and the effect of metal ions: Quantification of rare nucleobase tautomers

2004 ◽  
Vol 76 (10) ◽  
pp. 1869-1886 ◽  
Author(s):  
H. Sigel
Keyword(s):  
Metal Ions ◽  
Metal Ion ◽  
Divalent Metal ◽  
Acid Base ◽  
Acidity Constants ◽  
Proton Proton ◽  
Ion Proton ◽  
Divalent Metal Ion ◽  
Metal Ion Interactions ◽  
Base Properties

The macro acidity constants valid for aqueous solutions of several adenine, guanine,and hypoxanthine derivatives are summarized. It is shown how the application of the corresponding constants, e.g., for 7,9-dimethyladenine, allows a quantification of the intrinsic acidic properties of the (N1)H0/+ and (N7)H+ sites via micro acidity constants, and how to use this information for the calculation of the tautomeric ratios regarding the monoprotonated species, that is, N7-N1*H versus H*N7-N1, meaning that in one isomer H+ is at the N1 site and in the other at N7. It is further shown that different metal ions coordinated to a given site, e.g., N7, lead to a different extent of acidification, e.g., at (N1)H; the effect decreases in the series Cu2+>Ni2+>Pt2+ ~Pd2+. Moreover, the application of micro acidity constants proves that the acidifications are reciprocal and identical. This means, Pt2+ coordinated to (N1)–/0 sites in guanine, hypoxanthine, or adenine residues acidifies the (N7)H+ unit to the same extent as (N7)-coordinated Pt 2+ acidifies the (N1)H0/+ site. In other words, an apparently increased basicity of N7 upon Pt2+ coordination at (N1)–/0 sites disappears if the micro acidity constants of the appropriate isocharged tautomers of the ligand are properly taken into account. There is also evidence that proton–proton interactions are more pronounced than divalent metal ion–proton interactions, and that these in turn are possibly larger than divalent metal ion–metal ion interactions. The indicated quantifications of the acid-base properties are meaningful for nucleic acids including the formation of certain nucleobase tautomers in low concentrations, which could give rise to mutations.

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