PHYSICO-CHEMICAL STUDIES ON THE INTERACTIONS OF LESS COMMON METALS AND METALS OF UNSTABLE VALENCE STATE WITH IMIDES AND AMINO ACIDS

Abstract

Interactions of metal ions with amides,imides (both aliphatic and aromatic) ,amino acids and proteins are interesting both from the fundamental as well as from the applied view points. On the fundamental side,the reactions can be studied in terms of biuret reaction and their relative instability in aqueous media. Korenman (1) has listed thirteen kinds of compounds all of them aliphatic which give biuret reaction. According to him the specific grouping of atom within these compounds responsible for the biuret reaction are -NHCO.N.CONHa in biurets,NHC(.NH) NCO.NHa in dicyanodiamidines, >NC(iN) NC(:NH)NH8 in biguanides. The mechanism by which these reactions would take place can be followed by various physico-chemical methods. The amides and imides can also prove to be sensitive colorimetric reagents for estimation of metal ions and this study is particularly interesting with rare earth and elements of actinlde series. Such analytical studies can be usefully extended to other rare metals. Metal-amide complexes. Metal amino acid amide complexes have been reported 2 by Rising and Yang (2). The amino acid amides gave purple colouration with copper in the absence of alkali. Rising and coworkers (3) also reported the reaction of diacid amides with copper in the presence of alkali. Malik and coworkers (4) studied polarograpiiically the biuret reaction of malonamides. Their experimental results provided evidence of the binding of two molecules of the amide with one atom of copper on this basis. Metal 1mlde complexes. A survey of the literature reveals that very little has been done so far to study the metal imide complexes on account of their hydrolysable nature. Rising (5) for the first time prepared BaCu succlnimide complex (BaCuCieN40e) which was brownish in colour. Hexahydrate copper succlnimide (6) (Cu(NC40aM4)) 6Ha0 was prepared by the action of metallic copper with mercuric acetate and a paste of mercuric succlnimide. Some gold complexes of succlnimide have also been reported (7) • Sheshadri and Rao (8) isolated lt2 Hg complexes of succlni mide and phthalimlde with ethyl alcohol. Liviocambi (9) reported nickel complexes of succlnimide,substituted succlnimide,phthalimlde and potassium salts of palladium complexes of succlnimide and phthalimlde and methyl ethyl amine salts of nickel complexes of phthalimlde and tetramethyl succlnimide. Copper nickel and cobalt complexes derived from imides have also been reported in the literature, Recently Billman and Chernln (10) have reported the use of sulfonamide derivatives for direct titration of copper. Some sulfonamide derivatives have been used in chromatographic determination of lead and copper (11) • Non aqueous titrations of sulfonamides (potentiometric and spectrophotometric (12) titrations of imides with lithium hydroxide in ammoniacal medium (13) have also been cited in the literature. Fe(III) ,Cu(II) ,Ni(II) ,Co(II) were found to give biuret reaction with 3-nitrophthalimide,succlnimide, benzofur-2-yl carboxamide N-p-toluene sulphonyl. And non biuret reactions were observed with Ce(III) ,Co(II) ,Ni(II) , Fe(III) with 3-nitrophthalimide succinimide and saccharin (14) • Schwarzenback and Gysling (15) reported the murexide (ammonium purpureate ) complex of calcium for the first time. They further observed that this imide forms complexes with other cations such as Mg(II) ,Zn(II) ,Cd(II) and Cu(II). 4 The analytical aspect of these studies have been discussed by a number of workers who have given detailed methods for the colorimetric determination of alkaline earth metals Cu(II) and Zn(II). Metal amino acid complexes. The glycinates of copper zinc and nickel have been extensively investigated (16-18) and linear complexes of Ag(I) and Hg(II) formed through amino groups are also known to exist. Other amino acids besides glycine such as alanine leucine,valine etc. also show these types of bindings (19-22). Tanford and Sarma (23) have reported cobalt arginine and copper-glutamic acid complexes. Green and Ang (24) have tried to explain more complicated reactions like one between chromium and alanine by introducing the concept of partial chelation and partial coordination. The work of Edsall (25) on copper dihistidinate is,however, more complicated. Evidence for the simultaneous combinations through sulphahydryl and amino groups of cysteln has been provided in the case of Co(II) ,Zn(II) and Cd(II). Kolthoff and Stricks (26) have investigated Fe(II) and Fe(III) complexes of cysteln in the high pH range ( 10) • The metal complexes of the aldehyde derivatives of the <<«amino acid esters are extremely interesting representatives of this class of compounds. They are prepared by treating the copper or nickel complex of salicylaldehyde with HC1 acid salts of the <*-amlno acids esters in the presence of sodium acetate. Recently Malik and coworkers (27) investigated the interaction of Cr(III) ions with glycine,lysine,leucine and aspartic acid. The reactions of hetropolyacids with amino acids are also interesting but have received little attention. Phosphotungstic acid of general formula HaP04.12W0a24Ha0 was used in the isolation of lysine from a protein hydrolysate. This tungstate forms an insoluble precipitate not only with lysine but with the other basic amino acids as well, and was employed by Hausmann (28) to estimate the total amount of arginine histidine and lysine in protein hydrolysate. Metal proteins. There are several functional groups which proteins offer for combination with metals,depending on the pH of the medium. Gurd and Goodman (29) have carried out extensive 6 studies on the binding of Zn(II) with serum albumin in pH range 5.5 to 7.5. They have concluded that the binding of Zn(II) with albumin is almost due to sixteen imidazole groups of the histidine residues. Evidence for binding through the amino group of protein is obtained in strongly basic medium. Mehl et.al. (30,31) ,KLotz and Curme(32) had shown that each metal was bound to four peptide nitrogen atoms in the case of copper complexes. Iron complexes have been mainly studied with blood plasma and competitive binding of the ferrous ions with siderophilin and p-pseudoglobulin in plasma protein (IV) were carried out by Cohn (33). On the basis of similarity in the spectrophotometrie behaviour of the iron complexes of the protein and asparaginic acid, he concluded that the metal was bound to the protein through a linkage similar to hydroxamic acid (34). Chromium complexes of proteins present a number of difficulties due to the existence of polynuclear complexes in the aqueous solution of the metal itself. Symthe and Schmidt (35) have provided a satisfactory reaction mechanism for the interaction of basic chromic salt with collagen. The interaction of metals,especially Hg(II) with the -SH group of the protein is also worth mentioning. Silver also forms 7 similar complexes with proteins and both the metals can, therefore,be employed to estimate the -SH groups of proteins. Quantitative studies on the interaction of metals with transfusion gelatin and some other well characterised proteins were recently studied by Malik and coworkers(36-42) in order to determine the nature of binding. The main features of their investigations were as follows. 1. Copper sulphate-transfusion gelatin mixtures reveal that copper was more strongly bound to the amino than the carboxyl group. 2. From amongst zinc and Cd the latter showed affinity to combine with carboxylic groups only, 3. Cr(III) -transfusion gelatin reaction indicated the binding of the metal through the carboxyl group of the protein. Similar results were obtained with cobalt and nickel ions, 4. Vlscometric measurements of mixtures of various proteins (transfusion gelatin, casein and hamoglobin ) with metal hydrous oxides (Fe,Co,Ni,Ag,Al,Cs,Be ) reveal that the metals from the hydrous oxides make themselves available for interaction with carboxylic group of protein. STRUCTURAL ASPECTS OF METAL-AMIDE.MSIAL-IMIDE AND METALAKINO ACID COMPLEXE