Glycine Complexes Research Articles

Reactions of the cis-diamminediaquaplatinum(II) cation with 2-aminomalonic acid and its homologs, aspartic and glutamic acids. Rearrangements of metastable complexes with carboxylate-bound ligands to N,O-chelates and formation of di- and trinuclear complexes

Reactions of cis-Pt(NH 3) 2(H 2O) 2 2+ (1) with 2-aminomalonic acid (amalH 2), aspartic acid (aspH 2), and glutamic acid (gluH 2) have been studied by multinuclear ( 1H, 13C, 195Pt, 15N) NMR spectroscopy. With aspH 2 or gluH 2, 1 gives initially a complex in which the ligand is bound through only one carboxylate group, cis-Pt(NH 3) 2(LH 2-O)(H 2O) 2+. At pH <2, the α-carboxyl group is bound predominantly, but at pH 4-5, both carboxylate groups are involved to a similar extent. Over 2-3 days at pH 1.5, a complex with five-membered N,αO-chelate ring is formed, Pt(NH 3) 2(LH-N,αO) +. Reaction of aminomalonate with 1 gives initially a complex Pt(NH 3) 2(amalH-O,O′) +, with a six-membered chelate ring. Over 2-3 days at pH 1.5, this complex converts to Pt(NH 3) 2(amalH-N,O) +, with a five-membered ring. In solutions sufficiently acidic to protonate the uncoordinated carboxyl group, decarboxylation then occurs over several days to give the glycinate complex Pt(NH 3) 2(gly-N,O) +. The carboxylate group that is not part of the five-membered chelate ring in each of the three complexes Pt(NH 3) 2(L-N,O) is able to coordinate to platinum from excess 1. With aspartic and glutamic acids, one or two Pt(NH 3) 2(L) moieties can coordinate to one diammineplatinum(II) cation, to give [{Pt(NH 3) 2(L)}{Pt(NH 3) 2(H 2O)}] 2+ or [{Pt(NH 3) 2(L)} 2{Pt(NH 3) 2}] 2+, respectively. One Pt(NH 3) 2(amal) molecule can react with 1 to give [{Pt(NH 3) 2(amal)}{Pt(NH 3) 2(H 2O)}] 2+, which is in equilibrium with [{Pt(NH 3) 2} 2(amal)] 2+, in which the carboxylate group involved in a five-membered N,O-chelate ring with one Pt atom also bridges to the second Pt atom to complete a six-membered O,O′-chelate ring.

Kinetics and mechanism of aquation of cobalt(II)-glycine complexes in aqueous solutions: a pulse radiolytic study

The kinetics of aquation of tris(glycinato)cobaltate(II), (Co(gly){sub 3}){sup {minus}}, formed by the reaction of the corresponding Co(III) complex with hydrated electrons, has been investigated by conductometric pulse radiolysis in aqueous solutions. The rate of the reactions leading to the loss of each of the three glycinate ions in (Co(gly){sub 3}){sup {minus}} were well separated from each other and were studied as a function of pH. The observed rate constants are given by k{sup 0} + k{sup H}(H{sup +}). For the glycinate ion dissociation from the Co(II) complexes with one, two, and three glycinate ions, k{sup 0} were 4.9 {times} 10, 3.5 {times} 10{sup 2}, and 4.2 {times} 10{sup 3} s{sup {minus}1}, respectively and k{sup H} were 2.1 {times} 10{sup 4}, 8.1 {times} 10{sup 5}, and 2.7 {times} 10{sup 7} M{sup {minus}1} s{sup {minus}1}, respectively. The kinetics and mechanism of the aquation reaction of (Co(gly){sub 3}){sup {minus}} are discussed and compared to those for the aquation of (Co(en){sub 3}){sup 2+} and (Co(acac){sub 3}){sup {minus}}. 26 refs., 4 figs., 1 tab.

Ifenprodil and SL 82.0715 potently inhibit binding of [ 3H](+)-3-PPP to σ binding sites in rat brain

SL 82.0715 and ifenprodil are potent anti-ischemic agents, which are believed to be due to non-competitive antagonism of N- methyl- d-aspartate (NMDA). It has been proposed that SL 82.0715 and ifenprodil non-competitively antagonize the actions of NMDA by interacting as antagonists with a polyamine site associated with the NMDA/phencyclidine (PCP)/glycine complex. The present study demonstrates that the actions of SL 82.0715 and ifenprodil may also be due in part to an interaction with sigma binding sites, a property that is not shared with polyamines.

Ternary complexes of cis-(NH 3) 2Pt(II) with model nucleobases (1-methylcytosine, 9-methylguanine) and N- and O-bound amino acids (gly, ala)

The formation and properties of isomeric complexes of cis-(NH 3) 2Pt(II) containing the model nucleobase 1-methylcytosine, 1-MeC, and the amino acid glycine, glyH, are reported. Depending on the pH, different protonation states of amino acid and nucleobase are present. In acidic medium, cis-[(NH 3) 2Pt(1-MeC)(H 2O)] 2+ initially forms with glyH cis-[(NH 3) 2Pt(1-MeC)(glyH- O)] 2+ ( 2b) which slowly at pH 2–3 and faster at pH 4–5 converts into cis-[(NH 3) 2Pt(1-MeC)(gly- N)] + ( 1a). 1a is protonated to give the glyH- N species with a p K a ⋍ 2.8 and deprotonated at the NH 2 group of 1-MeC with a p K a ⋍ 12.5–13. Deprotonation of 2b was not detected up to pH 6, at which point conversion 2b → 1a was complete. 1a was prepared and isolated as the nitrate salt via two different routes, starting either from the gly chelate cis-[(NH 3) 2Pt(gly- N,O)] + or from cis-[(NH 3) 2Pt(1-MeC)(H 2O)] 2+. Only the second way led to both O- and N-bound glycine complexes. In the absence of glyH, cis-[(NH 3) 2Pt(1-MeC)(H 2O)] 2+ undergoes a condensation reaction initially to the μ-hydroxo complex cis-[(NH 3) 2Pt(1-MeC)(OH)Pt(1- MeC)(NH 3) 2] 3+ ( 6) and slowly to a bis(1-methylcytosinato) bridged diplatinum(II) complex, cis-[(NH 3) 2Pt(1-MeC −) 2Pt(NH 3) 2] 2+. Analogues of 1a with 9-methylguanine (9-MeGH) instead of 1-MeC as well as mixed 1-MeC, alanine and mixed 9-MeGH, alanine complexes have also been prepared and isolated.

Non-covalent interactions in thermodynamic stereoselectivity of mixed-ligand copper(II)-D- or L-histidine complexes with L-amino acids. A possible model of metal ion-assisted molecular recognition

Formation constants of ternary complexes of copper(II), L/D-histidine and, in turn, glycine, L-alanine, L-valine, L-leucine, L-tryptophan, or L-phenylalanine have been determined potentio-metrically at 25 °C and I= 0.1 mol dm–3(KNO3). In the case of amino acids with aromatic side chains the ternary complexes containing ligands of opposite chirality are more stable than those having ligands of the same chirality; the opposite is true for amino acids with aliphatic residues. Calorimetric measurements have been carried out to obtain the enthalpy and entropy values associated with complex formation. Copper(II)–histamine ternary systems with L-alanine or L-phenylalanine have also been investigated. Comparison of the thermodynamic parameters pertinent to formation of the histamine complexes with those of the analogous histidine complexes allows one to ascertain the number of donor atoms involved in the co-ordination to copper(II), in the histidine systems. The determination of ΔH⊖ and ΔS⊖ values renders easier understanding of the factors determining Stereoselectivity in the above systems. The Stereoselectivity may be explained in terms of non-covalent interactions between side-chain residues. The role played by the histidine carboxylate in the molecular recognition of amino acids is also discussed.

Studies on positronium–glycine complex formation using a positron annihilation lifetime spectrometer with BaF2detectors

Complex formation between positronium and glycine derivatives in solutions of 30%(v/v) ethanol–water and 20%(v/v) dioxane–water is discussed. A positron annihilation lifetime spectrometer with BaF2 detectors is described. By means of this apparatus, the complex formation reaction rate constants are obtained. The results indicate that rate constants mainly depend on the conjugation effect at the benzene ring, the induction effects of the substituents on the phenyl and the solvents. There is a linear free-energy relationship between rate constants and the basicities of N-substituted phenyl glycines in ortho-positronium–glycine complex formation.

Sequential Photochemical and Microbial Degradation of Organic Molecules Bound to Humic Acid

We studied the effects of photochemical processes on the mineralization by soil microorganisms of [2-C]glycine bound to soil humic acid. Microbial mineralization of these complexes in the dark increased inversely with the molecular weight of the complex molecules. Sunlight irradiation of glycine-humic acid complexes resulted in loss of absorbance in the UV range and an increase in the amount of C-labeled low-molecular-weight photoproducts and the rate and extent of mineralization. More than half of the radioactivity in the low-molecular-weight photoproducts appears to be associated with carboxylic acids. Microbial mineralization of the organic carbon increased with solar flux and was proportional to the loss of A(330). Mineralization was proportional to the percentage of the original complex that was converted to low-molecular-weight photoproducts. Only light at wavelengths below 380 nm had an effect on the molecular weight distribution of the products formed from the glycine-humic acid complexes and on the subsequent microbial mineralization. Our results indicate that photochemical processes generate low-molecular-weight, readily biodegradable molecules from high-molecular-weight complexes of glycine with humic acid.

Crystal structure of a complex of glycine with zinc chloride

Crystal structure of a complex of glycine with zinc chloride

Crystal structure of a complex of glycine with zinc chloride

Tris-glycine zinc chloride, a complex of glycine with ZnCl 2 , crystallises in an orthorhombic unit cell of dimensions a=11.230(2)A b=15.251(3)A c=15.564(4)A in the space group Pbn2 1 with Z=8. The structure has been determined using diffractometer data (2345 MoKα reflections) to a final R value of 0.034. All the six glycine molecules in an asymmetric unit exist as zwitterions, NH 3 + CH 2 COO - and are held together by a network of N—H···O and N—H···Cl type of hydrogen bonds. Each of the two zinc atoms is coordinated to two oxygen atoms and two chlorine atoms, forming a distorted tetrahedron.

Electron spin resonance study of copper(II) complexes of X-glycine and glycyl-X type dipeptides, and related tripeptides. Variation of co-ordination modes with ligand excess and pH in fluid and frozen aqueous solutions

Co-ordination modes for the various copper(II) complexes of glycine(Gly)-containing di- and tri-peptides (HL) with non-co-ordinating side-chains have been investigated. The e.s.r. spectra of predominant species at 1 : 1, 2 : 1, and 50 : 1 ligand : metal concentration ratios in the region pH ≈ 6–13 have been recorded in fluid and frozen aqueous solutions, and evaluated by computer simulation. The energies of the d–d electronic transitions have been determined by Gaussian analysis of the visible absorption spectra. Molecular-orbital coefficients characteristic of metal–ligand bonds for the various 1 : 1 and 1 : 2 complexes have been calculated assuming effective D4h symmetry. At ligand excess in alkaline solution, the temperature strongly affects the chemical equilibria: low temperature promotes the formation of 1 : 2 complexes: [Cu(LH–1)L]– at pH ≈ 9, and [Cu(LH–1)2]2– at pH ≈ 13 in the case of X-Gly type dipeptides. In the predominant isomers of these complexes one of the dipeptide molecules is co-ordinated equatorially through its amino nitrogen, deprotonated peptide nitrogen, and carboxylate oxygen atoms. The amino group of the other dipeptide occupies an axial position, while the fourth equatorial donor atom is either the peptide oxygen (pH ≈ 9) or the deprotonated peptide nitrogen (pH ≈ 13) of the second ligand. In the latter case, axial co-ordination of the second carboxylate group is also likely. Competition can be observed between the σ and π bonds in the equatorial plane on the one hand, and between the σ bonds of different symmetries on the other hand. The influence of the co-ordination modes, the type of ligand, and the temperature on the covalent character of the metal–ligand bonds is discussed.

The glycine-rich region of Escherichia coli D-serine dehydratase. Altered interactions with pyridoxal 5′-phosphate produced by substitution of aspartic acid for glycine.

Replacement of glycine by aspartic acid at either of two sites in a conserved, glycine-rich region inactivates the pyridoxal 5'-phosphate-dependent enzyme D-serine dehydratase (DSD) from Escherichia coli. To investigate why aspartic acid at position 279 or 281 causes a loss of activity, we measured the affinity of the G----D variants for pyridoxal 5'-phosphate and a cofactor:substrate analog complex and compared the UV, CD, and fluorescence properties of wild-type D-serine dehydratase and the inactive variants. The two G----D variants DSD(G279D) and DSD (G281D) displayed marked differences from wild-type D-serine dehydratase and from each other with respect to their affinity for pyridoxal 5'-phosphate and for a pyridoxal 5'-phosphate:glycine Schiff base. Compared to the wild-type enzyme, the cofactor affinity of DSD(G279D) and DSD(G281D) was decreased 225- and 50-fold, respectively, and the ability to retain a cofactor:glycine complex was decreased 765- and 1970-fold. The spectral properties of the inactive variants suggest that they form a Schiff base linkage with pyridoxal 5'-phosphate but do not hold the cofactor in a catalytically competent orientation. Moreover, the amount of cofactor aldamine in equilibrium with cofactor Schiff base is increased in DSD(G279D) and DSD(G281D) relative to that in wild-type DSD. Collectively, our findings indicate that introduction of a carboxymethyl side chain at G-279 or G-281 directly or indirectly disrupts catalytically essential protein-cofactor and protein-substrate interactions and thereby prevents processing of the enzyme bound cofactor:substrate complex. The conserved glycine-rich region is thus either an integral part of the D-serine dehydratase active site or conformationally linked to it.

ChemInform Abstract: Thermodynamics of Vanadyl(IV)‐Carboxylate Complex Formation in Aqueous Solution.

AbstractThe stability constants and the heats of formation of vanadyl‐acetate, ‐glycolate and ‐glycine complexes are determined by potentiometric and calorimetric measurements.

ChemInform Abstract: Asymmetric Synthesis of α‐Methylamino Acids by Alkylation of Chiral Ni(II)‐Complexes of Glycine, Alanine, and Phenylalanine.

ChemInform Abstract: Asymmetric Synthesis of α‐Methylamino Acids by Alkylation of Chiral Ni(II)‐Complexes of Glycine, Alanine, and Phenylalanine.

ChemInform Abstract: General Method for the Asymmetric Synthesis of α‐Amino Acids via Alkylation of the Chiral Nickel(II) Schiff Base Complexes of Glycine and Alanine.

AbstractThe Ni(II) complexes (IV), (V) of Schiff bases derived from the compounds (I) and D,L‐Ala are synthesized.

Thermodynamics of vanadyl(IV)—carboxylate complex formation in aqueous solution

The stability constants and the heats of formation of vanadyl(IV)—acetate, —glycolate, and —glycine complexes have been determined in aqueous solution by means of potentiometric and calorimetric measurements. In the pH range where the protolitic equilibria of VO 2+ is certainly negligible the acetate forms two mononuclear complexes, the glycolate three whereas the glycine reacts in its zwitterionic form. The stabilities of the glycolate complexes are considerably higher than the acetate ones, in spite of its lower basicity, indicating that the complex formation involves the coordination of the hydroxyl group to the metal ion. The enthalpy changes are positive except for the glycolate where a small negative value is found. For all systems the entropy changes are positive and therefore favourable to the complex formation.

Interaction of glycine and a glycine-based polymer with xanthate in relation to the flotation of sulfide minerals

The interaction between the amino acid glycine, a polymer (BA/13) with a glycine functional group incorporated into its backbone structure, and three sulfide minerals (chalcocite, galena and pyrite) was investigated using settling tests, electrokinetic measurements, and dissolution studies. The resulting increase in pulp stability and changes in zeta potential are related to the adsorption of metal glycinate complexes that form in aqueous solutions of the sulfide minerals. Chalcocite exhibited the greatest interaction with glycine due to the high stability of the copper glycinate complexes as compared to those of lead and iron. In flotation with xanthate as collector, glycine increased the flotability while BA/13 completely depressed all three minerals. Again these results are attributed to the adsorption of glycine-metal complexes.

General method for the asymmetric synthesis of α-amino acids via alkylation of the chiral nickel(II) Schiff base complexes of glycine and alanine

Nickel(II) complexes of Schiff bases derived from (S)-o-[(N-benzylprolyl)amino] benzaldehyde and alanine (3), or (S)-O-[(N-benzylpropyl)amino]benzophenone and alanine (4), or glycine (5) have been used for the asymmetric synthesis of α-amino acids under a variety of conditions. The method of choice consists of the reaction of the corresponding complex with the appropriate alkyl halide in DMF at 25 °C using solid NaOH as a catalyst. Low diastereoselective excess (d.e.) is observed for the alkylation of complex (3) with benzyl bromide and allyl bromide. Large selectivity (80%) is observed for the alkylation of complex (4). Optically pure (R)- and (S)-α-methyl-α-amino acids [(S)-α-methylphenylalanine, (S)-α-allylalanine and (S)-O-benzyl-α-methyltyrosine] were obtained (70–90%) after the alkylated diastereoisomeric complexes had been separated on SiO2 and hydrolysed with aqueous HCl. The initial chiral reagents were recovered (80–92%). The alkylation of complex (5) gave (S)-alanine, (S)-valine, (S)-phenylalanine, (S)-tryptophan, (S)-isoleucine, (S)-2-aminohexanoic acid, and 3,4dimethoxyphenylalanine with optical yields of 70–92%. The optically pure α-amino acids were obtained after the separation of the alkylated diastereoisomeric complexes on SiO2. The stereochemical mechanism of the alkylation reaction is discussed.

Application of an advanced technique of data analysis by analytical potentiometry and comparison of results by SUPERQUAD. Studies of nickel(II) – glycine, copper(II) – glycylglycyl-L-tyrosine-N-methyl amide, and zinc(II) – 3,6-diazaoctane-1,8-diamine systems

An advanced methodology for the data analysis by analytical potentiometry (Decock and Sarkar. Can. J. Chem. 65, 0000 (1987)) has been utilized to analyze three different metal–ligand systems. The results are compared with those obtained by SUPERQUAD adapted for microcomputer. An excellent agreement has been attained with the stability constant data of Ni(II)–glycine complexes of an earlier multi-laboratory study. The technique has been utilized to investigate the effect of ligand concentration in the equilibria of Cu(II) complexes of glycylglycyl-L-tyrosine-N-methyl amide. The third system studied by this technique was Zn(II) complexes of 3,6-diazaoctane-1,8-diamine, a ligand of potential therapeutic efficacy against metal toxicity.

Determination of stability constants for alkaline-earth and alkali metal ion complexes of glycine by spectrophotometry

The complex equilibria between alkaline-earth and alkali metal ions with glycine were studied by a spectrophotometric method. The following stability constant (concentration) values valid at 25° and ionic strength 1.0 M were found: K HL = 10 9.57, K LiL = 10 −1.2, K BaL = 10 −0.40, K SrL = 10 0.14, K CaL = 10 0.55, K MgL = 10 1.17.

A proton nuclear magnetic resonance relaxation study of the glycine, alanine, and lactate complexes of gadolinium(III) in aqueous solution

The 1H nuclear magnetic resonance spin-lattice and spin–spin relaxation rate enhancements induced by the gadolinium(III) ion were measured in solutions of glycine, alanine, and sodium lactate containing different amounts of Gd(III). The proton relaxation rates in the Gd(III) complexes were calculated from these data, and were used to calculate metal–hydrogen atom distances. Comparison of these data with corresponding distances calculated from literature X-ray crystallographic data for model compounds shows that in the two amino acid complexes the Gd(III) ion is coordinated in a four-membered ring through the two oxygen atoms of the carboxylate group. By contrast, in the lactate complex coordination is via a five-membered ring involving one oxygen atom of the carboxylate group and the α-hydroxyl oxygen.