Glycine Anion Research Articles

Complex formation in nickel(II)-glycine-β-lactam antibiotic systems

Complex formation in solutions containing Ni2+ cations, glycine anions (Gly−), and β-lactam antibiotics, namely, ampicillin (Amp), amoxicillin (Axn), and cephalexin (Cpx), is studied by pH-metric titration at 20°C and an ionic strength of 0.1 (KNO3). Mixed-ligand complexes [NiGlyAmp], [NiGlyAxn], and [NiGlyCpx], which are in equilibrium with the [NiGly]+ complexes, are formed in the systems studied in a weakly alkaline medium. The formation constants of the complexes are determined. The distribution diagrams of the complex Ni(II) forms at different pH values of the solutions are constructed.

Characterization of potassium glycinate for carbon dioxide absorption purposes

Aqueous solutions of potassium glycinate were characterized for carbon dioxide absorption purposes. Density and viscosity of these solutions, with concentrations ranging from 0.1 to 3 M, were determined at temperatures from 293 to 313 K. Diffusivity of CO 2 in solution was estimated applying the modified Stokes–Einstein relation. Solubilities of N 2 O at the same temperatures and concentrations were measured and the ion specific parameter based on Schumpe's model was determined for the glycinate anion; the solubilities of CO 2 in these solutions were then computed. The reaction kinetics of CO 2 in the aqueous solution of potassium glycinate was determined at 293, 298 and 303 K using a stirred cell reactor. The results were interpreted using the DeCoursey equation for the calculation of the enhancement factor. The rate of absorption as a function of the temperature and solution concentration for the conditions studied was found to be given by the following expression: - r CO 2 = 2.42 × 10 16 exp - 8544 T exp ( 0.44 C S ) C S C CO 2 .

The enthalpies of interaction of polyvinylbenzyltrimethylammonium hydroxide with amino acids in aqueous solutions

The enthalpies of interaction of polyvinylbenzyltrimethylammonium (PVTA) hydroxide with glycine, glutamic acid, and tyrosine anions were determined calorimetrically. The interaction of PVTA with amino acid anions was shown to be an exothermic process. The enthalpy of interaction depended on the nature and concentration of the amino acid. The reaction became less exothermic and the time of the establishment of equilibrium increased as the concentration of amino acids grew.

Catalytic asymmetric synthesis of ethyl (1 R,2 S)-dehydrocoronamate

A synthesis of (1 R,2 S)-dehydrocoronamic acid ethyl ester was developed employing a regio- and enantioselective palladium-catalysed nucleophilic ring-opening of 3,4-epoxy-1-butene with a glycine anion equivalent as the key enantiodifferentiating step. The desired selectivity was achieved using Trost’s naphthyl ligand. The subsequent activation of the free hydroxyl group and ring-closure by intramolecular S N2 reaction gave the desired amino acid ethyl ester.

Metallkomplexe mit biologisch wichtigen Liganden. CLXV N,O‐Chelat‐Komplexe von α‐Aminosäureanionen mit cyclopalladiertem N,N‐Dimethylferrocencarbothiamid

AbstractMetal Complexes of Biologically Important Ligands. CLXV N,O‐Chelate Complexes of α‐Amino Acid Anions with Cyclopalladated N,N‐DimethylferrocenecarbothioamideA short literature review on the reactions of various chlorobridged complexes with α‐aminoacidates, α‐amino acid esters, peptide ester or derivatives of amino acids is given. The chloro bridged o‐palladated N,N‐dimethylferrocenecarbothioamide [(fct)Pd(μ‐Cl)2Pd(fct)] reacts with the anions of glycine, L‐alanine, L‐proline, L‐valine, L‐phenylalanine, L‐leucine, L‐isoleucine to give the N,O‐chelates [(fct)Pd(N,O‐α‐aminocarboxylate)] (1–7). Due to the planary chirality of the unsymmetrically disubstituted cyclopentadienyl iron moiety of fct the complexes 2–7 with optically active amino acidate ligands are formed as a mixture of two diastereoisomers, which can be detected by their NMR spectra.

Dipole-Bound Anions of β-Alanine: Canonical and Zwitterionic Conformers

The remarkable stabilities of the dipole-bound anions of the canonical and zwitterionic conformers of beta-alanine are predicted at the high level of theories, in which the former is the global minimum and the latter, the anti zwitterionic anion, is the local minimum. In contrast to the dipole-bound anions of glycine, the gauche zwitterionic anion of beta-alanine is an unstable conformer. The vertical electron detachment energies for the canonical and anti zwitterionic anions are 58 and 1145 meV, respectively. The photodetachment electron spectrum of the canonical anion is theoretically simulated on the basis of the Franck-Condon factor calculations.

Conductivity of systems comprising anion-exchange membranes MA-41 and alkaline glycine solutions

The concentration dependences of the conductivity of 0.001 M NaOH + glycine solutions and the MA-41 anion-exchange membrane are studied. At glycine concentrations c = 0–0.01 M, the solution and membrane conductivities are defined by the glycine and hydroxyl equilibrium concentrations. The charge transport in the solutions proceeds via both hydrodynamic and prototropic mechanisms. At c = 0.01–0.1 M, the contribution from glycine ions carrying the charge via the prototropic mechanism increases. The conductivity of the membrane is determined by the glycine anion deprotonation in it.

(2,2′-Diamino-4,4′-bi-1,3-thiazole-κ2N,N′)bis(glycinato-κ2N,O)zinc(II) dihydrate

In the title ZnII complex, [Zn(C2H4NO2)2(C6H6N4S2)]·2H2O, the ZnII ion is coordinated by two glycinate anions and a diamino­bithia­zole (DABT) mol­ecule in a distorted octa­hedral geometry. Two thia­zole rings of the same DABT are twisted with respect to each other with a dihedral angle of 10.56 (6)°. The glycinate chelates to the ZnII ion by the amino N and carboxylate O atoms; the chelating five-membered ring displays an envelope configuration. A twofold rotation axis passes through the Zn atom and the mid-point of the C—C bond linking the two thiazole rings.

Local Hydration Environments of Amino Acids and Dipeptides Studied by X-ray Spectroscopy of Liquid Microjets

The nitrogen K-edge spectra of aqueous proline and diglycine solutions have been measured by total electron yield near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at neutral and high pH. All observed spectral features have been assigned by comparison to the recently reported spectrum of aqueous glycine and calculated spectra of isolated amino acids and hydrated amino acid clusters. The sharp preedge resonances at 401.3 and 402.6 eV observed in the spectrum of anionic glycine indicate that the nitrogen terminus is in an "acceptor-only" configuration, wherein neither amine proton is involved in hydrogen bonding to the solvent, at high pH. The analogous 1s --> sigma(NH) preedge transitions are absent in the NEXAFS spectrum of anionic proline, implying that the acceptor-only conformation observed in anionic glycine arises from steric shielding induced by free rotation of the amine terminus about the glycine CN bond. Anionic diglycine solutions exhibit a broadened 1s --> pi(CN) resonance at 401.2 eV and a broad shoulder resonance at 403 eV, also suggesting the presence of an acceptor-only species. Although this assignment is not as unambiguous as for glycine, it implies that the nitrogen terminus of most proteins is capable of existing in an acceptor-only conformation at high pH. The NEXAFS spectrum of zwitterionic lysine solution was also measured, exhibiting features similar to those of both anionic and zwitterionic glycine, and leading us to conclude that the alpha amine group is present in an acceptor-only configuration, while the end of the butylammonium side chain is fully solvated.

Catena-Poly[[chloro(2,2′-diamino-4,4′-bi-1,3-thiazole-κ2N,N′)cadmium(II)]-μ-glycinato-κ2N,O:O′

In the polymeric title complex, [Cd(C2H4NO2)Cl(C6H6N4S2)]n, the glycinate anions bridge neighbouring CdII ions to form zigzag chains along the b axis direction. The CdII ion is coordinated by two glycinate ions (one O-monodentate and one N,O-bidentate), a Cl− ion and a bidentate diamino­bithia­zole ligand in a distorted octa­hedral geometry. Various N—H⋯O and N—H⋯Cl hydrogen bonds between adjacent complex chains help to consolidate the crystal packing.

(2,2′-Diamino-4,4′-bi-1,3-thiazole-κ2N,N′)bis(glycinato-κ2N,O)cobalt(II) dihydrate

In the crystal structure of the title compound, [Ni(C2H4NO2)2(C6H6N4S2)]·2H2O, the NiII atom is located on a twofold axis and is coordinated by a diamino­bithia­zole ligand and two glycinate anions in a distorted octa­hedral geometry. The glycinate anions chelate to the NiII atom through the amino N and carboxyl O atoms, and display an envelope conformation. Hydrogen bonding consolidates the crystal structure.

Preparation and Characterisation of Li‐Al‐glycine Layered Double Hydroxides (LDHs)‐Polymer Nanocomposites

AbstractLiAl‐Layered Double Hydroxides, containing glycinate anions, have been prepared using LiAlO2. The glycine containing LDHs were then exfoliated in chloroform. Dispersions of approximately 0.03 g of the LDH in 15 ml of the solvent were possible. Nanocomposites using the exfoliated LiAl‐glycine LDH and polyethyleneglycol were prepared by adding appropriate amounts of polymer to the LDH‐chloroform dispersion. The clay‐polymer nanocomposites were then characterised using powder X‐ray diffraction. The thermal and mechanical properties of the composites are reported. The results suggest that composites containing individual (exfoliated) LDH layers were obtained with the mechanical and thermal properties of the composites noticeably superior to those of the parent polymer.

A chimera encoding the fusion of an acetylcholine-binding protein to an ion channel is stabilized in a state close to the desensitized form of ligand-gated ion channels

To understand the mechanism of allosteric coupling between the ligand-binding domain and the ion channel of the Cys-loop ligand-gated ion channels (LGICs), we fused the soluble acetylcholine-binding protein (AChBP), which lacks an ion channel, to either the cationic serotonin type-3A ion channel (5HT 3A) or the anionic glycine ion channel. Both linear chimeras expressed in HEK-293 cells display high affinity for the nicotinic agonist epibatidine ( K D = 0.2 – 0.5 nM ), but are not targeted to the cell surface. Only after substituting a ring of three loops located at the putative membrane side of the AChBP three-dimensional structure by the homologous residues of 5HT 3A, the resulting chimera AChBP(ring)/5HT 3A ( i) still displayed on intact cells an apparent high affinity for epibatidine, yet with a fourfold decrease ( K D = 2.1 nM ), ( ii) displayed a high proportion of low affinity sites (11 ± 7 μM) for the resting state stabilizing competitive antagonist α-bungarotoxin and ( iii) was successfully targeted to the cell surface, as seen by immunofluorescence labelling. The AChBP(ring)/5HT 3A chimera forms a pentameric structure, as revealed by sucrose gradient sedimentation. However, no whole-cell patch-clamp currents were detectable. Interestingly, binding assays with membrane fragments prepared from cells expressing AChBP(ring)/5HT 3A showed a decrease in the apparent affinity for the agonists nicotine and epibatidine (5-fold), concomitant with an increase in the proportion of high-affinity sites (48 ± 1 nM) for α-bungarotoxin. These results indicate that fusion of AChBP to an ion channel forms a pentameric receptor exposed to the cell surface and able to convert between discrete allosteric states, but stabilized in a high affinity state for epibatidine that likely corresponds to a desensitized form of LGICs. These artificial chimeras might offer a useful system to investigate signal transduction in LGICs. To cite this article: T. Grutter et al., C. R. Biologies 328 (2005).

First insight into catalytic activity of anionic iron porphyrins immobilized on exfoliated layered double hydroxides

Mg–Al layered double hydroxide (LDH) intercalated with glycinate anions was synthesized through co-precipitation and exfoliated in formamide and the single-layer suspension was reacted with aqueous iron porphyrin solutions (Fe(TDFSPP) and Fe(TCFSPP)). The obtained materials were characterized by X-ray powder diffraction, UV–vis, and electron paramagnetic resonance and investigated in the oxidation reaction of cyclooctene and cyclohexane using iodosylbenzene as oxidant. The iron porphyrin seems to be immobilized at the surface of the glycinate intercalated LDH. The catalytic activities obtained in heterogeneous media for iron porphyrin, Fe(TDFSPP), was superior to the results obtained under homogeneous conditions, but the opposite effect was observed on the Fe(TCFSPP), indicating that, instead of the structural similarity of both iron porphyrins (second-generation porphyrins), the immobilization of each one produced different catalysts. The best catalytic activity of the Fe(TDFSPP)/Gly-LDH, compared to Fe(TCFSPP)/Gly-LDH, can be explained by the easy access of the oxidant and the substrate to the catalytic sites in the former, probably located at the surface of the layered double hydroxide pillared with glycinate anions. A model for the immobilization and a mechanism for the oxidation reaction will be discussed.

Serine Hydroxymethyltransferase: Role of Glu75 and Evidence that Serine Is Cleaved by a Retroaldol Mechanism

Serine hydroxymethyltransferase (SHMT) catalyzes the reversible interconversion of serine and glycine with tetrahydrofolate serving as the one-carbon carrier. SHMT also catalyzes the folate-independent retroaldol cleavage of allothreonine and 3-phenylserine and the irreversible conversion of 5,10-methenyltetrahydrofolate to 5-formyltetrahydrofolate. Studies of wild-type and site mutants of SHMT have failed to clearly establish the mechanism of this enzyme. The cleavage of 3-hydroxy amino acids to glycine and an aldehyde occurs by a retroaldol mechanism. However, the folate-dependent cleavage of serine can be described by either the same retroaldol mechanism with formaldehyde as an enzyme-bound intermediate or by a nucleophilic displacement mechanism in which N5 of tetrahydrofolate displaces the C3 hydroxyl of serine, forming a covalent intermediate. Glu75 of SHMT is clearly involved in the reaction mechanism; it is within hydrogen bonding distance of the hydroxyl group of serine and the formyl group of 5-formyltetrahydrofolate in complexes of these species with SHMT. This residue was changed to Leu and Gln, and the structures, kinetics, and spectral properties of the site mutants were determined. Neither mutation significantly changed the structure of SHMT, the spectral properties of its complexes, or the kinetics of the retroaldol cleavage of allothreonine and 3-phenylserine. However, both mutations blocked the folate-dependent serine-to-glycine reaction and the conversion of methenyltetrahydrofolate to 5-formyltetrahydrofolate. These results clearly indicate that interaction of Glu75 with folate is required for folate-dependent reactions catalyzed by SHMT. Moreover, we can now propose a promising modification to the retroaldol mechanism for serine cleavage. As the first step, N5 of tetrahydrofolate makes a nucleophilic attack on C3 of serine, breaking the C2-C3 bond to form N5-hydroxymethylenetetrahydrofolate and an enzyme-bound glycine anion. The transient formation of formaldehyde as an intermediate is possible, but not required. This mechanism explains the greatly enhanced rate of serine cleavage in the presence of folate, and avoids some serious difficulties presented by the nucleophilic displacement mechanism involving breakage of the C3-OH bond.

Oxide Radical Anion Reactivity with Aliphatic Amino Compounds in Aqueous Solution: Comparison of H−Atom Abstraction from C−H and N−H Groups by •O- and •OH Radicals

One-electron oxidants react with H2N−CHRR‘ amino compounds by electron transfer (ET), and direct H abstraction from N−H and C−H, giving respectively, aminium (+•NH2CHRR‘), aminyl (•NH−CHRR‘), and α-C-centered radicals (H2N-•CRR‘). The yields of these species from •O- reactions with the anions of glycine (Gly-), alanine (Ala-), and α-methylalanine (MeAla-) and with methylamine (MeNH2) have been investigated at pH ≥ 13. The results indicate an ET process is negligible. Aminyl and α-C-centered radicals appear to be formed only by direct H abstraction reactions. In line with this, the ratios of the overall rates of H abstraction from N−H and C−H, kN(-H•)/kC(-H•), for •O- reacting with different amino compounds decrease with C−H bond dissociation enthalpy (BDE) and thus follow the pattern expected for direct abstraction reactions. In contrast to •O-, the conjugate •OH radical produces significant yields of aminium radicals by ET, which evidently contribute to aminyl radical formation by subsequent proton loss from nitrogen. Thus, the kN(-H•)/kC(-H•) ratios for •OH are higher than those for •O- and do not decrease regularly with C−H BDE. Formation of α-C-centered radicals via ET and subsequent proton loss from a C−H group of the aminium radical is much less likely. The overall rates of H abstraction from C−H sites by both •OH and •O- are found to increase with the exothermicity of the reaction. Because of its spherical symmetry the steric factors for •O- reactions are larger than those for •OH, but in most cases this appears to be compensated by more favorable potential energy surfaces stemming from the 36 kJ mol-1 greater exothermicity of •OH reactions. •O- reactions with charged species are of course also susceptible to the effects of Coulombic interactions.

Enantioselective Synthesis of L‐CCG‐I.

Introduction of natural menthol as the chiral auxiliary in a c-Br-R,â-unsaturated ester leads to enantioselective generation of three chiral centers in a single step on reaction with a glycine anion equivalent to provide L-CCG-I in 94% ee.

Synthesis of 3‐Aminoaspartic Acid Derivatives from Glycine Precursors.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Enantioselective Synthesis of L-CCG-I.

Introduction of natural menthol as the chiral auxiliary in a gamma-Br-alpha,beta-unsaturated ester leads to enantioselective generation of three chiral centers in a single step on reaction with a glycine anion equivalent to provide L-CCG-I in 94% ee.

Highly Efficient ortho‐Fluoro‐dimeric Cinchona‐Derived Phase‐Transfer Catalysts.

AbstractFor Abstract see ChemInform Abstract in Full Text.