Metal Complexes Of Amino Acids Research Articles

Metal Complexes of Amino Acids. VIII. Carbon-13 Nuclear Magnetic Resonances of Cobalt(III) Complexes Containing l-Aspartic and l-glutamic Acids

Abstract The 13C NMR spectra of cobalt(III) complexes containing l-aspartic acid or l-glutamic acid as unidentate, bidentate, or bridged ligand were measured, and the relationship between the coordination types and the changes in chemical shift of carboxyl carbons in these amino acid complexes was discussed. Two structural isomers were newly separated for the trans (O)-[Co en2(l-aspH2 or l-gluH2)2]X3 complex by a column chromatographic method. The structures of the earlier eluted isomers for the trans(O)-[Co en2(l-aspH2)2]X3 and -[Go en2(l-gluH2)2]X3 complexes were assigned to trans(O0) Oγ) and trans(O0, Oδ) (O0, Oγ and Oδ indicate the coordinated oxygen atoms of C0OO, CγOO, and CδOO), respectively, and the structures of the later eluted isomers for the both complexes to trans(O0, O0), on the basis of the shift patterns of carboxyl carbons.

Metal complexes of amino acids and derivatives—XIII Some nickel(II) complexes of L-arginine zwitterions or L-argininate anions. A novel ionic → bidentate perchlorate rearrangement brought about by pressure[1–5

Nickel(II) complexes have been isolated in which the ligand coordinates as an anion (Arg −) or a zwitterion (ArgH). These complexes, Ni(Arg) X· nH 2O ( X = Cl, Br, NO 3, ClO 4) and Ni(ArgH) x X 2· nH 2O ( X = Cl, NO 3, ClO 4, OH), are six-coordinate and contain a NiN 2O 4 coordination moiety. Only in the cases of Ni(ArgH) 2(NO 3) 2·H 2O and Ni(ArgH)(OH) 2·H 2O are X − groups coordinated. However, it has also been found that the complexes containing ionic perchlorate, when put under pressure, rearrange to form complexes containing bidentate perchlorato groups. The complexes have been characterised by magnetic measurements and by infrared and visible reflectance spectral methods.

Metal complexes of amino acids and derivatives—IX: Reactions of the tripeptide, glutathione, with divalent cobalt, nickel, copper and palladium salts

Complexes of α-glutamylcysteinylglycine, glutathione, a tripeptide, with some transition metal salts have been isolated. Glutathione (GluH 3) is shown to be an extremely versatile ligand complexing as the mononegative GluH 2 species in Pd (GluH 2)Cl·3H 2O, the dinegative GluH species in Cu(GluH)·4H 2O, and the trinegative species in Li[Ni(Glu)]·2H 2O and Li[Co(Gly)]·2H 2O. In these reactions it appears that the mercapto group ionises most readily, subsequent ionisations involve carboxylic acid groups.

Metal Complexes of Amino Acids. V. μ-Aminocarboxylato Bi- and Tri-nuclear Complexes of Cobalt(III)

Abstract Some new binuclear and trinuclear complexes containing μ-aminocarboxylato ligands, [(NH3)5Co(OCORNH2)Co NO2(acac)2](ClO4)2 (R=CH2, (CH2)2, and CH(CH3) for glycinato, β- and Dl-alaninato ligands) and [en2Co{(OCORNH2)Co NO2(acac)2}2]ClO4 (R=CH2 and (CH2)2), have been prepared and characterized on the basis of their elemental analyses, visible and ultraviolet absorption, infrared, and PMR spectra. It was concluded that the NH2 end of the μ-aminocarboxylato bridge occupies a coordination position trans to the NO2ligand, and the COO ends of two μ-aminocarboxylato bridges in the trinuclear complex occupy positions trans to each other.

Metal Complexes of Amino Acids. VI. μ-l-Aspartato and μ-l-Glutamato Complexes of Cobalt(III)

Abstract Some binuclear and trinuclear complexes containing μ-l-aminocarboxylato ligands, (+)d- and (−)d-[en2-Co(OCOCH(NH2)(CH2)nCOO)Co(OH2)en2](ClO4)4, (+)d-[en2Co(OCOCH(NH2)(CH2)nCOO)Co(NH3)5]-(ClO4)4 and (+)d- and (−)d-[en2Co{(OCOCH(NH2)(CH2)nCOO)Co en2}2](ClO4)5 (n=1 for l-aspartato and n=2 for l-glutamato), have been newly prepared. The structure and vicinal CD effect of these complexes were discussed on the basis of their absorption, 13C NMR and CD spectra data. Their geometrical structures were assigned as cis to the μ-l-aminocarboxylato-OH2 binuclear complexes (with respect to the β-COO or γ-COO end of μ-aminocarboxylato bridge and the aquo ligand), and as trans to the di-μ-l-aminocarboxylato trinuclear complexes (with respect to the β-COO or γ-COO ends of two μ-aminocarboxylato bridges).

Studies on locust neuromuscular physiology in relation to glutamic acid.

ABSTRACT Two nerve-muscle preparations were used to investigate the physiology of the locust retractor unguis muscle in relation to L-glutamic acid. These were an ‘isolated preparation’, in which the muscle and its nerve were dissected out, and a ‘perfused-femur preparation’, in which the muscle suffered no mechanical disturbance. Exposure of the nerve-muscle preparations to glutamate caused a variety of responses, some of which were shown to be abnormal and due to the experimental conditions. When locust femora were perfused with saline or haemolymph the retractor unguis muscles were much more severely affected by glutamate if the hydrostatic pressure was slightly raised. At raised pressures the perfused-femur preparations were particularly prone to give repetitive and spontaneous contractions. Analysis of haemolymph from adult male locusts showed that it contained, on average, 0·2 mmol/1 L-glutamate, 45 mol/1 total non-peptide amino acids, 5·0 mmol/1 calcium, and 11·6 mmol/1 magnesium. It was calculated that approximately 50% of the calcium and 75% of the magnesium ions are bound to amino acids, and that approximately 25 % of the glutamic acid is bound to divalent metal ions. The isolated preparations were severely affected by glutamate at the concentration at which it occurs in haemolymph, and it was concluded that in the intact locust some mechanism must protect the neuromuscular synapses from haemolymph glutamate. No evidence could be obtained of the sequestration of glutamate by haemocytes, or of binding of glutamate to haemolymph proteins. Calcium and magnesium ions reduced the sensitivity of nerve-muscle preparations to glutamate to a greater extent than could be accounted for by the formation of amino acid-metal complexes. This suggests that the protection afforded by calcium and magnesium involves an interaction of the metal ions with the neuromuscular system itself. The retractor unguis muscle was much less sensitive to glutamate when it was contained within an undissected femur than in an isolated preparation. It was concluded that the muscle is normally protected from haemolymph glutamate by a diffusion barrier which is damaged on dissection. Comparison of the fine structure of retractor unguis muscles, fixed either after dissection or while still contained within the femur, showed that dissection normally caused a partial separation of muscle fibres and damage to the connective tissue sheath, with the resultant exposure of some nerve endings. The connective tissue sheath may constitute the postulated diffusion barrier. The excitatory synapses of the locust retractor unguis muscle are believed to be isolated from haemolymph glutamate by a diffusion barrier, which is tentatively identified with the connective tissue sheath that binds the muscle fibres together. Calcium and magnesium ions reduce the sensitivity of nerve-muscle preparations to glutamate, and may have such a role in the living insect.

Metal complexes of amino acids and derivatives—VIII[1]: The reaction of D,L-penicillamine with some transition and non-transition metal salts

Complexes of D,L-penicillamine (H 2pen) with a number of metal ions have been isolated. The [Ni(pen)], Li 2[Zn(pen) 2]. 4H 2O, and [Pb(pen)] complexes contain dinegative ligands, whereas in [Pd(Hpen)Cl]. H 2O the ligand coordinates as a mononegative ion. All the complexes contain −S − and −NH 2 coordination and all, save the dimeric palladium(II) derivative and the zinc(II) complex, contain coordinated −COO −.

Metal complexes of amino acids and derivatives. VI. Donor properties of S-methylcysteine and methionine. Comparison

Metal complexes of amino acids and derivatives. VI. Donor properties of S-methylcysteine and methionine. Comparison

Metal complexes of amino acids and derivatives. V. The donor properties of L-tyrosine

A convenient method for the preparation of transition metal complexes of L-tyrosine (tyrH) is reported and this has enabled eight complexes of the tyrosinate anion (tyr) to be prepared: M(tyr) 2(H 2O n (M = Co, Ni, Cu, Zn; n = 1, 2, 3), [Cu(tyr)(NO 3)], and Li[Cu(tyr) 3]. Electronic spectra and magnetic measurements imply that the nickel(II) complex contains the N 2O 4 donor set, and the similarity of the infrared spectra of the other bistyrosinate complexes to the nickel derivative suggests a similar six-coordinate structure. Experiment suggests that upon reacting Lityr with copper(II) nitrate in water the green kinetic product [Cu(tyr)(NO 3)] forms, but on standing this changes to the thermodynamically stable product, [Cu(tyr) 2].

Hydrolysis of Dipeptides with Metal Oxides

Abstract The hydrolysis of three dipeptides, Gly-Gly, Gly-l-Leu, and Gly-l-Phe, with metal oxide catalysts was studied. In most cases, the hydrolysis occurred in the pH range 5–6 accompanied by the formation of metal complexes of amino acids and dipeptides. Copper oxide, nickel oxide, cobalt oxide (III), and alumina have more catalytic activity than copper powder, cuprous oxide, commercial nickel oxide (II), and silica gel. Alumina and silica gel gave no metal complex. It is assumed that the hydrolysis proceeds by means of the formation of an active metal complex of dipeptide or by means of activation on the surface of the catalyst. The order of reactivity of the dipeptides was: Gly-Gly>Gly-l-Leu, Gly-l-Phe.

Aminoaciduria in Experimental Lead Poisoning

SummaryA “generalized” aminoaciduria occurs in lead-intoxicated rats characterized by a 1- to 3-fold elevation in renal clearances of most amino acids. The increase in histidine clearance is exceptionally large, whereas, changes in glycine and valine clearances are slight. Tyrosine clearance is actually decreased.Plasma glycine is greatly increased; lesser increases in plasma threonine and lysine were found. Plasma levels of other amino acids were the same or less than those of control rats.The increase in renal clearances of amino acids is thought to result from impaired renal tubular reabsorption secondary to an effect of lead on the metabolism of proximal renal tubular lining cells. Hyperglycinemia may be prerenal reflecting the defect in prophyrin synthesis known to occur in lead poisoning. It is also suggested that the formation of metal-amino acid complexes may contribute to the excessive aminoaciduria.

Antimicrobial Activity of Metal Cystine Complexes

Metal cystine complexes of nickel(II), mercury(II) and cadmium(II) have been synthesized and their antimicrobial activities have been evaluated. It is found that mercury(II) cystine and cadmium(II) cystine complexes have pronounced antibacterial and antifungal activities. On the other hand nickel(II) cystine shows moderate activities. The LC50 values of nickel(II) cystine, mercury(II) cystine and cadmium(II) cystine are found to be 5.2, 8.0 and 7.2 ?g ml-1, respectively. These values were obtained from cytotoxic studies indicating that they are biologically active compounds. 
 
 Key words: Antimicrobial activity, Cytotoxic activity; Metal amino acid complexes. 
 
 Dhaka Univ. J. Pharm. Sci. Vol.5(1-2) 2006
 
 The full text is of this article is available at the Dhaka Univ. J. Pharm. Sci. website

Crystal Structures of Metal-Peptide Complexes

Publisher Summary This chapter discusses crystal structures of metal–peptide complexes. Most of the crystal-structure analyses of metal–amino acid and metal–peptide complexes have been carried out on the assumption that such complexes act as models for the metal-binding sites on proteins. Crystal-structure analyses show that the geometrical features of metal complexes of amino acids, peptides and imidazole are related in systematic ways to the chemical structure, which the complexes have in the crystalline state. Moreover, the transfer of geometrical information from crystal-structure analyses to species that exist in solution depends on the assumption that the complexes found in crystals are present also in the solutions from which the crystals grow. This chapter illustrates that, the existence of cis-trans isomers coordination isomers, optical isomers, and dimeric species in the crystalline complexes emphasizes the variety of species, which must be considered when equations are written to represent metal–peptide equilibria in solution.

Metal complexes of amino acids. 3. The circular dichroism of cobalt(3) ammine and ethylenediamine complexes with L-amino acids.

Abstract In order to study the vicinal effect of the l-amino acid coordinated in a complex on the central metal ion, a number of cobalt(III) l-amino acid complexes of three types were prepared, i. e., [Co(NH3)5(l-amH)]X3, [Co(l-am)(NH3)4]SO4, and trans-[Co en2(l-amH)2]X3, where l-amH denotes an l-amino acid, and where X is Cl, Br, or I. The circular dichroism (CD) and the rotatory dispersion (RD) spectra of their aqueous solutions were measured in the wavelength range from 650 to 300 mμ. In the region of the first absorption band, both the [Co(NH3)5(l-amH)]3+ and the trans-[Co en2(l-amH)2]3+ ions show one or two CD bands to be expected in complexes of the C4v symmetry with a structure of the [Co N5O]-type and of the D4h symmetry with a structure of the trans-[Co N4O2]-type respectively. The positions of the CD bands observed in the trans complexes coincide well with the maxima of the split components, Ia and Ib, of the first absorption band. The CD spectra of different [Co(l-am)(NH3)4]2+ ions, in which l-am is a bidentate ligand, show a variety of behavior; they are discussed from a stereochemical point of view. An intense CD band of the [Co(l-prol)(NH3)4]2+ ion at about 510 mμ can be attributed to the vicinal effect of an asymmetric nitrogen atom of the coordinated l-prolinate ion. For the trans-[Co en2(l-amH)2]X3 complexes, the rotatory parameters and rotatory strengths were calculated by means of analyses of the experimental CD and RD curves.

Ionization potentials and metal-amino acid complex formation in the sedimentary cycle

Attention is given to certain atomic properties of metals which control the formation and stabilities of complexes with the amino acids; particular emphasis is given to the ionization potential. Ionic charge and ionic radius are also considered. It is noted that ligand-field effects may be important for the transition metals, but this property (ligand-field) is not considered in detail. The study has a bearing on the distribution of metals in the sedimentary cycle because of the presence of metal binders, the amino acids for example, in the oceans and some sediments.

A CORRELATION OF STEPWISE STABILITY CONSTANT RATIOS AND SOME BONDING PROPERTIES OF TRANSITION METAL AND ZINC COMPLEXES

Stepwise stability constant ratios for some transition metal and zinc amino acid complexes are analyzed. It is shown that the observed ratios for Cu and Ni amino acid complexes are larger than the calculated ratios by a factor R, the Bjerrum rest effect. It is suggested that the rest effect is due to metal–nitrogen covalency, there being sufficient transfer of charge from ligand to metal in the first association stage to reduce markedly the electrostatic attraction between ligand and metal in the second.For Zn complexes, the observed and calculated ratios are in excellent agreement. A small rest effect would seem to be present in the Co system, but experimental errors render any conclusions uncertain.

Metal complexes of amino acids. I. The circular dichroism of copper(II) complexes with optically active amino acids.

Abstract On the basis of the CD measurements of the complexes of the [Cu(l-am)2] type, four CD components have been observed in the region of the d→d absorption band, namely, (+), (+), (−) and (−), listing from longer to shorter wavelengths. The l-configuration of the amino acids determines the signs of these CD components. Judging from the CD curves of the copper-(II) complexes with l-threonine and with l-allothreonine, it has been suggested that the vicinal effect caused by the α-asymmetric carbon atom is stronger than that caused by the β-asymmetric one. It has also been suggested that, when l-proline or l-hydroxyproline is coordinated to copper, the nitrogen atoms of these ligands are activated by the configurational stereo specificity.

Metal—Amino Acid Complexes. II. Polarographic and Potentiometric Studies on Complex Formation between Copper(II) and Amino Acid Ion1,2

Metal—Amino Acid Complexes. II. Polarographic and Potentiometric Studies on Complex Formation between Copper(II) and Amino Acid Ion^1,2