A study of the effect of amino acid structure on the stabilities of the complexes formed with metals of group II of the periodic classification

Abstract

In a previous structural study of stability constants of oc-amino acid metal complexes (Perkins, 1952) the work was restricted to amino acids closely related to glycine. In this paper the work is extended to a wide range of a-amino acids to discover the effect of different functional groups. Most of the amino acids are closely related to a-alanine and norvaline. Albert (1952) has published stability constants for the complexes of a number of these amino acids with a selection of metal ions. In the present work only the metals beryllium, zinc, cadmium and mercury of group II of the periodic classifieation were used. EXPERIMENTAL Materials. The following A.R. salts were used in 0-01M solution: BeSOj, 4H20; ZnSO4, 7H20; 3CdSO4, 8H,20. Hg(NO3)2 was made up in 0-025a-EHNO, and excess acid back-titrated in the presence ofthe amino acid investigated.The amino acids were obtained from British Drug Houses Ltd. and Roche Products Ltd., except for 8-aminovaleric acid, for a sample of which I am indebted to Dr T. S. G. Jones and Dr S. Wilkinson of the Welcome Research Laboratories, Beckenham, Kent. All the amino acids were dried in vacuo at 100°for at least 48 hr., with the exception of cysteine hydrochloride, asparagine and glutamine which were dried in a vacuum over silica gel for 48 hr. The purity of each amino acid was checked by paper chromatography.Titrations. The ionization constants of each amino acid were determined by the potentiometric method of Albert (1950) in 001 M aqueous solution, except for tyrosine and diiodotyrosine which were determined in 0{002m solution.Titrations in the presence of metallic ions were usually carried out in 001 M amino acid and 0-005 M metal solution. The exceptions were tyrosine and diiodotyrosine, which were used in 0-002ms solution, and cysteine and histidine, which were used in 0-0025 s solution.Calculations. The two systems to be considered in caloulating the stability of each complex are:(a) M2+ + amino acid = (complex I)+, with dissociation constant = K1.

Studies on the metabolism of methyl mercury and dimethyl mercury in mice

“…The methyl mercury ion as well as other mercury compounds is known to have an extremely high affinity to animal protein and especially to the sulphydryl groups (e.g. Hughes et al, 1950;Perkins, 1952Perkins, , 1953Perkins, , 1961Hughes. 1957;Passow et al, 1961;Benesch & Benesch, 1962).…”

Interaction of chelates with macrocyclic ligands. Porphyrins and Hg(II) chelate salts

“…The study of the complex formation of macrocycles I -IV with the Hg(II) chelate salts (table) showed that the reactions of porphyrin binding with these salts differ substantially from similar binding reactions with salts of other metals, first of all, by reaction mechanisms and higher rates. The latter is very interesting, because the stability constants of the Hg(II) salts with amino acids are higher than those of other metals [12][13][14][15], which should decrease the binding rates according to [16]. Such high complex formation rates have been obtained first in [11] for α -nitroso-β -naphtholates (Hg(Nft)) and mercury(II) hydroxyquinolates (Hg(Ox)) with porphyrins I and II .…”

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The complex formation of different porphyrins (5,10,15,10,15,2,3,7,8,12,13,17,, and tertbutylphthalocyanine ( IV )) with mercury(II) valinate (Hg(Val) 2 ) in DMSO was studied. The rates of reactions of macrocycles I , II , and IV with mercury(II) valinate were found to be higher than those with valinates of other d metals, and the complex formation rates of III with Hg(Val) 2 were comparable with these characteristics for other valinates.

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Interaction of chelates with macrocyclic ligands. Porphyrins and Hg(II) chelate salts

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The complex formation of different porphyrins (5,10,15,10,15,2,3,7,8,12,13,17,, and tertbutylphthalocyanine ( IV )) with mercury(II) valinate (Hg(Val) 2 ) in DMSO was studied. The rates of reactions of macrocycles I , II , and IV with mercury(II) valinate were found to be higher than those with valinates of other d metals, and the complex formation rates of III with Hg(Val) 2 were comparable with these characteristics for other valinates.

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