Glycinate Ion Research Articles

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.

Mixed Ligand Complexes of Mn(II), Fe(II), Co(II), Ni(II) and Cu(II) with Cytosine and Glycine as Ligands

Abstract Mixed ligand complexes of the type [MLL' (OH)H2O].H2O where M[dbnd]Mn(II), Fe(II), Co(II), Ni(II), Cu(II); L[dbnd]Cytosine and L'[dbnd]Glycinate ion; have been prepared and characterised by elemental analysis, thermogravimetric studies, magnetic moment measurements and electronic and infrared spectra. The complexes are octahedral and coordination occurs through N(3) and O(2) of cytosine and nitrogen and oxygen of the COO− group of glycinate.

Molar Volumes and Electrostriction Behavior of Dicarboxylate, Disulfonate, Tartrate, and Bis(ethylenediamine)glycinatocobalt(III) Ions in Water

Abstract The ionic partial molar volumes at infinite dilution, V∞(ion), were determined for several dicarboxylate ions, disulfonate ions, tartrate ions, and [Co(gly)(en)2]2+ (gly=glycinate ion and en=ethylenediamine) from density measurements at 25°C. The values of V∞(ion) obtained for the divalent anions generally increased with their van der Waals volumes. Significant differences in V∞(ion) were observed between geometrical isomers with dicarboxylate and disulfonate ions and were attributed to those in both of electrostriction volume and the void space volume around the anions. The former volume was decreased and the latter was increased with increasing distance between two negatively charged groups in the anions. A relatively strong electrostriction behavior of the tartrate ions, compared to the dicarboxylate ions, suggested the presence of an extra electrostriction caused by hydroxyl groups. The electrostriction strength of [Co(gly)(en)2]2+ was significantly large compared to that of [Ni(en)3]2+, rather close to those of [Cr(en)3]3+ and [Co(en)3]3+, and was attributed to the dissymmetrically localized charge distribution in the [Co(gly)(en)2]2+ ion. The effective ionic radii and apparent van der Waals volumes were estimated by using Glueckauf’s equation from the ionic partial molar volume and were discussed in comparison with those calculated from the van der Waals increments of atoms.

Thermodynamic Quantities of Transfer of Glycinato and β-Alaninato Complexes of Silver(I) and Related Species from Water to an Aqueous Dioxane Solution

Abstract Complexation of silver(I) with glycinate (gly−) and β-alaninate (β-ala−) ions have been studied by potentiometry and calorimetry in 0.2 mole fraction (55.0 %w/w) dioxane–water mixture containing 3 mol dm−3 LiClO4 as a constant ionic medium at 25 °C. Potentiometric titration curves obtained were well-explained in terms of formation of [AgL], [AgL2]−, and [AgHL]+ (L−=gly− or β-ala−) in both systems, together with [Ag(OH)L]− in the Ag(I)–β-alanine system, and their formation constants were determined. Enthalpies of formation of the complexes in the mixed solvent, as well as in water containing the same ionic medium, were calorimetrically determined on the basis of the formation constants potentiometrically determined. Solubilities and enthalpies of solution of the neutral [AgL] (L−=gly− and β-ala−) complexes and some related compounds were determined in water and the mixture, the Gibbs energies of transfer, ΔGt°, of silver(I) ion and proton from water to the mixture being also determined by potentiometry. By combining the thermodynamic quantities thus obtained, thermodynamic quantities of transfer of single species from water to the mixture were evaluated. Compared to the enthalpy, ΔHt°, and entropy, ΔSt°, of transfer of a neutral species, the ΔHt° and ΔSt° values of any charged species were significantly large with the negative sign for cations and positive one for anions. As to neutral species, [HL] and [AgL], the relation, ΔGt°>ΔHt°≅0 and ΔSt°<0, was found, suggesting that the [AgL] complexes have a similar zwitterionic structure to that of glycine and β-alanine zwitterions.

Potentiometric and Calorimetric Studies on Formation of Glycinato Complexes of Nickel(II) in Water and in an Aqueous Dioxane Solution

Abstract Protonation equilibria of glycinate (gly−) ion and complex formation equilibria between nickel(II) and glycinate ions have been studied by potentiometry and calorimetry in water and in 0.2 mole fraction (55.0%w/w) dioxane–water mixture, each containing 3 mol dm−3 LiClO4 as a constant ionic medium at 25 °C. A series of mononuclear complexes, [NiLn](2−n)+ (L−=gly− and n=1–3) were found in both solutions and their formation constants, enthalpies and entropies were determined. It elucidated that the stepwise Gibbs energies of formation of the metal complexes varied in the sequence, ΔG1°<ΔG2°<ΔG3°, and the stepwise enthalpies, ΔH1°>ΔH2°>ΔH3°, and thus, the stepwise entropies markedly decreased in the order, ΔS1°>ΔS2°>ΔS3°. The result was discussed in relation to changes in the metal–water and metal–ligand bond lengths within [NiLn(H2O)6−2n](2−n)+ (n=1–3) with n. As to the solvent effects, the formation constants of each metal complex increased with the addition of dioxane to water, the increase was caused by both enthalpies and entropies of formation of the complexes, the former mainly contributing to the formation of [NiL2] and the latter to [NiL]+ and [NiL3]−. The Gibbs energies of transfer of single species from water to the dioxane–water mixture were also evaluated. The enthalpy and entropy of transfer of any ionic species mostly compensated each other, so that the Gibbs energies of transfer of ions were rather small.

An X-Ray Diffraction Study on the Structures of Mono(glycinato)zinc(II) and Tris(glycinato)zincate(II) Complexes in Aqueous Solution

Abstract The structure of zinc(II) complexes with glycinate ion in solution was investigated by the X-ray diffraction method. The measurements were performed at 20 °C for the solutions with the Cgly⁄Czn mole ratios of 1.49 (solution A) and 5.09 (solution B), where Ci denotes the total concentration of species i. From the analysis of the radial distribution curve of solution A, in which comparable amounts of the hexaaqua- and mono(glycinato)zinc(II) complexes existed, it was found that the mono(glycinato)zinc(II) complex combined with four water molecules at the distance of (2.12±0.01) Å. The Zn–OH2 bond length within the complex was longer than that within the hexaaquazinc(II) ion (2.08 Å). The Zn–O and Zn–N distances, where O and N denote oxygen and nitrogen atoms within the glyeinate ion in the [Zn(gly)(OH2)4]+ complex, were both (2.12±0.02) Å. Thus the mono(glycinato)zinc(II) complex had a regular octahedral structure. The nonbonding Zn···C distance was found to be (2.84±0.02) Å. The X-ray diffraction data of solution B, which contained the [Zn(gly)3]− ion as a predominant species, showed that the tris(glycinato)zincate(II) complex had a regular octahedral structure with the both Zn–O and Zn–N bond distances of (2.12±0.01) Å. The nonbonding Zn···C(COO), Zn···C(CH2), and Zn···O(O=C) lengths were (2.87±0.03) Å, (2.93±0.03) Å, and (4.10±0.04) Å, respectively. The solubility of the bis(glycinato)zinc(II) complex was so low that the structural determination of the complex by the present X-ray diffraction method was not possible.

Spectroscopic studies on copper (II) complexes of human lactoferrin

The interaction of Cu(II) with human lactoferrin has been studied as a function of pH, using electronic and electron spin resonance spectroscopy. Specific Cu(II) binding, with bicarbonate as the co-anion, occurs over the pH range 6 to 9. In the presence of a fiftyfold molar excess of oxalate, a monocopper(II) lactoferrin oxalate complex forms when the Cu(II) to protein is 1:1. If this ratio is increased to 2:1, a hybrid complex forms, in which the second copper utilizes bicarbonate as the co-anion, thus demonstrating, as for serum transferrin, a difference in the amon binding sites. The quenching of the intrinsic fluorescence of apolactoferrin is significantly less in the presence of oxalate than bicarbonate. The interaction of Cu(II) with apolactoferrin in the presence of the malonate, glycolate, thioglycolate, glycinate, and ethylenediaminetetraacetate ions has been examined.

A Potentiometric Study on Mixed Ligand Cadmium(II) Complexes with 2-Pyridinecarboxylic Acid and 2-Aminoalkanoic Acids

Abstract Formation constants of cadmium(II) complexes with 2-pyridinecarboxylic acid (Hpic) were determined in aqueous solutions containing 3 mol dm−3 LiClO4 as a constant ionic medium at 25 °C by potentiometric titrations. On the basis of the formation constants of the complexes thus determined and those of the 2-aminoalkanoate complexes previously obtained, formation constants of mixed ligand cadmium(II) complexes CdL(pic) were determined, where L− denotes a 2-aminoalkanoate ion such as glycinate (gly−), α-alaninate (ala−), 2-aminobutanoate (but−), 2-aminopentanoate (pen−), or 2-aminohexanoate (hex−) ion. The formation constants logβ111=log {[CdL(pic)]/([Cd2+][L−][pic−])} of the 1:1:1 mixed ligand cadmium(II) complexes are: Cd(gly)(pic), 8.88; Cd(ala)(pic), 8.47; Cd(but)(pic), 8.42; Cd(pen)(pic), 8.73; and Cd(hex)(pic), 8.76. The equilibrium constant of the reaction between Cd(gly)+ and pic− was larger than that between Cd(pic)+ and gly−, and much larger than the equilibrium constants between CdL+ and L′− previously studied, where L− and L′− are 2-aminoalkanoate anions.

Studies of the chemical exchange kinetics of glycinate ions in mixed ligand complexes of copper (II) and glycylglycine

Nuclear magnetic resonance studies of the chemical exchange kinetics of glycinate ions in binary and ternary complexes of copper(II) and glycylglycine indicate the increase in the exchange rate of glycinate ions in the ternary complex. This phenomenon is assumed to be due to the glycinate ion coordination in the axial—equatorial position.

A Potentiometric Study on Mixed Ligand Cadmium(II) Complexes with 2-Amino Carboxylic Acids

Abstract Formation constants of mixed ligand cadmium(II) complexes, CdLL′, were determined in aqueous solutions containing 3 mol dm−3 LiClO4 as a constant ionic medium at 25 °C by potentiometric titration, where the ligands HL and HL′ are 2-amino carboxylic acids such as glycine, α-alanine, 2-aminobutanoic acid, 2-aminopentanoic acid, and 2-aminohexanoic acid. Ten kinds of the mixed ligand cadmium(II) complexes were examined with the combination of five 2-amino carboxylic acids. The formation constant, βprs=[CdpLrLs′(2p−r−s)+]⁄([Cd2+]p×[L−]r[L′−]s), of the mixed ligand cadmium(II) complexes containing glycine as one of the ligands lie between those of the parent complexes, while the formation constants of the other complexes are larger than those of the parent complexes. No protonated mixed ligand complex has been observed. The small values of β111 of the Cd(gly)L complexes are due to the considerably small values of the first stepwise formation constants of the CdL+ complexes. On the other hand, the stepwise formation constants of the CdL+ complexes with glycinate ion are larger than the stepwise formation constants with 2-amino carboxylate ions and the second stepwise constant of the bis(glycinato)cadmium(II) complex. Interactions between the ligands through the central cadmium(II) ion are discussed. The b-values (b=log {(K110·K101)⁄(K120·K102)}, where K1rs denotes the stepwise formation constant of the complex CdLrL′s) of the mixed ligand cadmium(II) complexes containing glycinate ion as one of the components lie between 0.93 and 0.98, and are larger than those of the other complexes (b=0.83–0.90), the fact indicating that the mixed ligand glycinato complexes have larger inter-ligand interactions within the complexes than those within complexes containing other 2-amino carboxylate ions. The inter-ligand interaction may occur through the central cadmium ion within the complex.

13C NMR Spectra of Series of Bis(2,2′-bipyridine)cobalt(III) and Bis(1,10-phenanthroline)cobalt(III) Complexes

Abstract Twenty-eight cobalt(III) complexes of these types: [Co(LL)3]3+ and [CoXX(LL)2]n+ (LL=2,2′-bipyridine or 1,10-phenanthroline, and XX=2CN−, 2NO2−, ethylenediamine, 2NH3, glycinate ion, 2H2O, C2O42−, CO32−, 2SCN−, 2N3−, 2CH3COO−, 2Cl−, or 2Br−, were prepared, and their 13C NMR spectra were recorded. Most of the resonances in the complexes were assigned mainly by the technique of selective proton decoupling. In the bpy complexes, the chemical-shift difference between corresponding carbon atoms was the greatest in the C-6 and C-6′ pair. The phen complexes also gave parallel results. The main factor responsible for the chemical-shift differences of the C-6 and C-6′ pair is explained as resulting from the difference in σ-bonding ability between the pyridyl group and the ligand, X.

A Potentiometric Study on Complex Formation of Silver(I) Ion with Glycine and β-Alanine in Aqueous Solution

Abstract The complex formation of silver(I) ion with glycine and β-alanine was studied at 25 °C in an aqueous solution containing 3 mol dm−3 LiClO4 as a constant ionic medium by means of potentiometric titrations. At a relatively low pH region, the AgHL+ complex (L− represents glycinate and β-alaninate ions) was formed, in which the silver ion was coordinated with the carboxyl group of the ligands. At a medium pH range, the AgL and AgL2− complexes were formed. From the formation constants of the complexes, it is suggested that the silver ion within the complexes may be coordinated with the amino group of the ligands and the interaction between the metal ion and the carboxyl group within the complexes is so weak that the interaction does not appreciably stabilize the complexes. At the highest pH region, the hydrolyzed species Ag(OH)L− was formed.

Multiple isotopic labelling: Band assignments in the i.r. spectra of 2,2′-bipyridine adducts of nickel(II) glycinate and l-α-alaninate

The i.r. spectra (4000-180 cm −1) of the complexes [Ni(glycinate) 2 (2,2′-bipyridine)]·2H 2O and [Ni( l-α-alaninate) 2(2,2′-bipyridine)]·H 2O and their isotopically-labelled analogues, are discussed. 18O-, 1- 13C-, 2- 13C-, 15N- and 2,2-d 2-labelling of the glycinate ion; 18O-, 15N- and 2,3,3,3-d 4-labelling of the l-α-alaninate ion and d 8-labelling of 2,2′-bipyridine yields assignments for the internal ligand modes and the metal—ligand stretching frequencies.

STEREOSELECTIVE DEUTERATION OF MALONATE METHYLENE HYDROGENS IN SOME BIS(MALONATO)COBALT(III) COMPOUNDS

Abstract The base-catalysed hydrogen-deuterium exchange at the malonate methylenes takes place stereoselectively for [Co(mal)2(L)]n-, where mal = malonate ion, L = ethylenediamine, N-methylethylenediamine, glycinate ion, and sarcosinate ion, but not for cis-[Co(mal)2(NH3)2]−. The proton deuterated first is probably the one which is closer to the chelate L.

Stability constants of metal complexes of phosphonoacetic acid

The antiviral drug, phosphonoacetic acid (PAA), forms stable complexes with Mg 2+, Ca 2+, Cu 2+ and Zn 2+. Stability constants of these complexes were determined in aqueous solution (0.15 M in KNO 3, 37°) by potentiometric titration. Mixed ligand complex formation of Cu 2+ and Zn 2+ with PAA and glycinate ion, and with PAA and histidinate ion, was studied. In a theoretical model for blood plasma, PAA affects the distribution of Mg 2+ and, to a lesser extent, Ca 2+.

Band assignments in the i.r. spectrum of cis,cis-bis(glycinato)cis-bis(imidazole)nickel(II) by multiple isotopic labelling

Abstract The i.r. spectra of cis -[Ni(gly) 2 (Him) 2 ] (gly = glycinate ion, Him = imidazole) and its isotopically-labelled analogues have been determined over the range 4000-150 cm −1 . 18 O -, 15 N -, 1- 13 C -, 2- 13 C -, and 2,2- d 2 -labelling of the coordinated glycinate yields assignments for the internal glycinate modes and the nickel—oxygen and nickel—nitrogen stretching and bending vibrations while deuteration of imidazole (Him- d 3 ) provides assignments for the internal modes of the coordinated imidazole rings and for the nickel—imidazole vibrations. The results, combined with those of previous multiple isotopic labelling studies on glycinate complexes, enable some general conclusions to be reached on the i.r. spectra of these compounds.

Band assignments in the i.r. spectra of pyridine and pyrazine adducts of nickel(II) glycinate by multiple isotopic labelling

The i.r. spectra of [Ni(gly) 2(py) 2] (gly = glycinate ion, py = pyridine) and [Ni(gly 2(pz)] · 1 1 2 H 2O (pz=pyrazine) and their isotopically labelled analogues have been determined over the range 3300-150 cm −1. 18O-, 1- 13C-, 2- 13C-, 15N- and 2.2-d 2-Labelling of the coordinated glycinate yields assignments for the glycinate and metal-oxygen vibrations while d 5-labelled pyridine and d 4-labelled pyrazine yield assignments for the internal vibrations of the heterocyclic rings and metal—nitrogen vibrations. The results indicate that there is considerable vibrational coupling in these complexes.

The kinetics of reductions of some chloropentakis(alkylamine)cobalt(III), aquapentakis(alkylamine)cobalt(III), and trans(O, Cl)-chloroaminoacidatodiethylenetriaminecobalt(III) ions by aquavanadium(II), or aquachromium(II)

The rate of the reduction of chloropentakis(alkylamine)cobalt(III) ions, Co(Cl)(A) 5 staggered2+ , (A 5 = (NH 3) 5, trans-(NH 2CH 3)(NH 3) 4, (NH 2CH 3) 5 and (n-NH 2C 3H 7) 5) by vanadium(II) decreases in the following order: (n-NH 2C 3H 7) 5 > (NH 2CH 3) 5 > trans-(NH 2CH 3)(NH 3) 4 > (NH 3) 5. The similar result on the effect of alkylamines on the rate of the reductions of aquapentakis(alkylamine)cobalt(III) ions, Co(H 2O)(A) 5 staggered3+ by vanadium(II) and chromium(II) was obtained. The rate constants of reductions of Co(Cl)(A) 5 staggered2+ by vanadium(II) could be correlated with the rate constants of the reaction of Co(Cl)(A) 5 staggered2+ with iron(II) by the equation of log k V = 1.3 log k Fe + 3.6, where k V and k Fe are the second-order rate constant of reductions by vanadium(II) and iron(II) respectively. The steric effect of the coordinated alkylamines on the rates of reductions of Co(Cl)(A) 5 staggered2+ and Co(H 2O)(A) 5 staggered3+ by vanadium(II) and the reduction of Co(H 2O)(A) 5 staggered2+ by chromium(II) is relatively small. The effects of concentrations of perchloric acid and N,N-dimethylformamide were examined for the reduction of trans-(O,Cl)Co(Cl)(gly)(dien) + by vanadium(II), where gly and dien represent glycinate ion and diethylenetriamine respectively. An outer-sphere mechanism was suggested for the reductions of Co(Cl)(A) 5 staggered2+ and trans(O,Cl)Co(Cl)(gly)(dien) + by vanadium(II) based on the experimental results obtained.

The Inner-Sphere Mechanism Interpreted by the Hydrogen Ion Effect on the Fe2+ Reduction Rate of Oxalato-, Malonato-, Glycolato-, and Chloro-Cobalt(III) Complexes in Aqueous Solution

Abstract The hydrogen ion effect on the rate of the Fe2+ reduction of oxalato-, glycolato-, and chloro-cobalt(III) complexes was investigated kinetically. It was found that the rates of the Fe2+ reduction of cobalt(III) complexes such as trans(N)-Co(ox)(β-ala)2−, trans(N)-Co(ox)(gly)2−, trans(N)-Co(ox)(gly)(en), Co(ox)33−, and trans-(O,Cl)-Co(Cl)(am)(dien)+ (am=glycinate, α-alaninate or β-alaninate ions) increase with an increase in the hydrogen ion concentration. This result can be explained by accounting for the protonation of the oxygen atom of the carbonyl group of the nonbridging ligand. The inner-sphere mechanism can be deduced for the Fe2+ reductions of these complexes due to the hydrogen-ion effect. Moreover, a kinetic study of the Fe2+ reduction reaction of Co(Hmalo)(NH3)52+ and Co(malo)(NH3)5+ was carried out. An inner-sphere mechanism for these reactions is proposed from an analysis of the kinetic data. Discussion of the structure of the precursor complex and of the rate determining step for the Fe2+ reduction reactions of cobalt(III) complexes are also made.

A new approach to the synthesis of ‘chiral’ glycine

The stereospecific coordination of N-benzylglycinate ion in ΔR-(N-benzylglycinato) bis(ethylene-diamine) cobalt(III) chloride has been determined by X-ray crystallographic analysis, rotatory dispersion and 1H NMR spectroscopy. The chiral glycinato-N and Co centres influence the relative rates of exchange of the diastereotopic glycine methylene protons in basic solution (pH 10·5 with Na 3PO 4inD 2O) and a synthesis supposedly of S-(N-benzyl)- 2- 2H glycinate ion ≈ 80% optical purity) has been achieved.