Glycolate Anion Research Articles

Thermodynamic Properties and Crystallographic Characterization of Semiclathrate Hydrates Formed with Tetra-n-butylammonium Glycolate.

Semiclathrate hydrates are a crystalline host–guest material, which forms with water and ionic substances such as tetra-n-butylammonium (TBA) salts. Various anions can be used as a counter anion to the TBA cation, and they can modify thermodynamic properties of the semiclathrate hydrates, which are critical for applications, for example, cold energy storage and gas separation. In this study, the semiclathrate hydrates of the TBA glycolate were newly synthesized. Measurements for melting temperatures and a heat of fusion and a crystal structure analysis were performed. In comparison with the other similar materials, such as acetates, propionates, lactates, and hydroxybutyrates, the glycolate greatly changed the melting temperature and the heat of fusion. The preliminarily determined crystal structure showed that the glycolate anion builds a relatively porous structure compared to the previously reported hydrates formed with hydroxycarboxylates. The present study showed that substitution of a hydrophobic group by a hydrophilic group is an effective method to control the thermodynamic properties as well as to improve environmental, biological, and chemical properties.

Synthesis and crystal structures of new complexes of Np(V) glycolate with 2,2′-bipyridine, [NpO2(C10H8N2)(OOC2H2OH)]·1.5H2O and [NpO2(C10H8N2)(OOC2H2OH)]·2.5H2O

Single crystals were prepared, and the structures of two complexes of Np(V) glycolate with 2,2′-bipyridine of the compositions [NpO2(C10H8N2)(OOC2H2OH)]·1.5H2O (I) and [NpO2(C10H8N2)(OOC2H2OH)]·2.5H2O (II) were studied. The structures of the compounds are based on neptunyl–glycolate chains in which the glycolate anion manifests its complexation ability in different manner. In structure I, the bidentate-bridging anion links the adjacent NpO2+ cations through the oxygen atoms of the carboxylate group. The neptunyl–glycolate chains of I exhibits the mutual coordination of the NpO2+ cations acting toward each other simultaneously as ligands and coordinating centers. In compound II, the glycolate anion is bidentately coordinated to one neptunium atom to form a planar five-membered metallocycle [NpOCCO]. The O atom external with respect to the metallocycle is in the coordination environment of the adjacent neptunyl. The nitrogen-containing molecular ligand Bipy is included into the coordination environment of Np. The coordination polyhedron of the Np atoms in both structures is a pentagonal bipyramid in which the average Np–N bond length is 2.666 Å (I) and 2.596 Å (II).

Novel method for the preparation of carbon supported nano-sized amorphous ruthenium oxides for supercapacitors

Nanostructured amorphous RuO 2 · xH 2O/C composite materials are prepared via a modified sol–gel process using glycolic acid. The glycolate anion, which dissociates from glycolic acid at pH 7, behaves as a stabilizer by adsorbing onto the RuO 2 · xH 2O surface, thus resulting in particles with a size of about 2 nm. As evidenced by zeta potential measurements, the surface charge of RuO 2 · xH 2O becomes more electronegative as the amount of glycolic acid increases. After heat treatment at 160 oC to remove the stabilizer, RuO 2 · xH 2O/C is found to exhibit an amorphous structure. The specific capacitance of RuO 2 · xH 2O/C particles (40 wt% Ru) prepared in the presence of glycolic acid (0.3 g L −1) is 462 F g −1, which is 30% higher than that of the material prepared in the absence of glycolic acid. Both the nanosized particles and the amorphous structure mainly contribute to this increase in the specific capacitance.

Catena-Poly[[aquaglycolatocopper(II)]-μ-chlorido

In the crystal structure of the title compound, [Cu(C2H3O3)Cl(H2O)]n, the CuII ion is five-coordinate in a distorted square-pyramidal geometry. Two O atoms from a chelating glycolate anion, an O atom from a coordinated water mol­ecule and a chloride anion comprise the basal plane. A chloride ion from a neighbouring unit occupies the apical position and these Cu—Cl—Cu bridges link the aqua­glycolatocopper(II) units into one-dimensional chains along the [001] direction. These chains are connected by O—H⋯O and O—H⋯Cl hydrogen bonds, forming an infinite three-dimensional polymeric network.

Investigation of carbon-supported Pt nanocatalyst preparation by the polyol process for fuel cell applications

Parametric investigation of the polyol process for the preparation of carbon-supported Pt nanoparticles as catalysts for fuel cells was carried out. It was found that the concentration of glycolate anion, which is a function of pH, plays an important role in controlling Pt particle size and loading on carbon. It was observed that Pt loading decreased with increasing alkalinity of the solution. As evidenced by zeta potential measurement, this was mainly due to poor adsorption or repulsive forces between the metal colloids and the supports. In order to modify the conventional polyol process, the effect of the gas purging conditions on the characteristics of Pt/C was examined. By the optimization of the gas environment during the reaction, it was possible to obtain high loading of 39.5 wt% with a 2.8 nm size of Pt particle. From the single cell test, it was found that operating in ambient O 2 at 70 °C can deliver high performance of more than 0.6 V at 1.44 A cm −2 .

A comparative ab initio study of intramolecular proton transfer in model α-hydroxyalkoxides

A comparative ab initio study was performed on the intramolecular proton-transfer reaction that occurs in alpha-hydroxyethanoxy, alpha-hydroxyphenoxide, and alpha-hydroxyethenoxy anions. The intramolecular proton transfer occurs in a five-member atom arrangement, between two oxygen atoms separated by a carbon-carbon bond. The chosen systems serve as models for alpha-hydroxyalkoxide molecules where the carbon-carbon bond varies from a single bond (the glycolate anion or alpha-hydroxyethanoxide anion) to a part of an aromatic ring (the alpha-hydroxyphenoxide anion), and finally to a double bond (the alpha-hydroxyethenoxide anion). Particular attention was given to the evolution along the intrinsic reaction coordinate of such properties as energies, relevant structural parameters, Mulliken charges, dipole moments, and 1H-NMR chemical shifts to reveal the similarities and differences for the proton transfer in the model systems.

Adenosylcobinamide plus exogenous, sterically hindered, putative axial bases: a reinvestigation into the cause of record levels of Co-C heterolysis.

A reinvestigation of an earlier Ph.D. thesis (Sirovatka, J. M. Ph.D. Thesis, Colorado State University, Fort Collins, CO, 1999) is reported herein. That thesis examined the thermolysis reaction of AdoCbi(+)BF(4)(-) in ethylene glycol solution with exogenous bases, N-methylimidazole (N-Me-Im) and the sterically hindered 1,2-dimethylimidazole, (1,2-Me(2)-Im), 2-methylpyridine (2-Me-py), and 2,6-dimethylpyridine (2,6-Me(2)-py). In the present work, multiple purities of each base have been utilized as a check to see if impurities in the nitrogenous bases are causing the observed homolysis and heterolysis product distributions as others have implied (Trommel, J. S.; Warncke, K.; Marzilli, L. G. J. Am. Chem. Soc. 2001, 123, 3358). The "impurity hypothesis" is disproven by a series of results, including the following: N-Me-Im displays an invariant 52 +/- 10% heterolysis and the 1,2-Me(2)-Im system displays an invariant 83 +/- 7% heterolysis as a function of different base purification methods. Moreover, 2-Me-py and 2,6-Me(2)-py also display an invariant approximately 16 +/- 5% heterolysis as a function of different purification methods. What is responsible for the high levels of Co-C heterolysis in the AdoCbi(+) plus sterically bulky base thermolyses was uncovered via a revisitation of our four, earlier alternative hypotheses for the enhanced Co-C heterolysis (Sirovatka, J. M.; Finke, R. G. Inorg. Chem. 1999, 38, 1697). Our prior number one alternative hypothesis is shown to be correct: the added bases simply deprotonate the ethylene glycol solvent, forming ethylene glycolate anion and base-H(+)() as the key agents behind the previously ill-understood Co-C heterolyses. Also reported are Co(II)Cbi(+) titrations with five bases (1,2-Me(2)-Im, N-Me-Im, pyridine, 2-MePy, and 2,6-Me(2)-py). These experiments confirm Marzilli and co-workers' (op. cit.) results by showing that sterically hindered bases do not bind to Co(II)Cbi(+); therefore, Co(II)Cbi(+) EPR literature showing binding of bulky pyridines is erroneous as is the previously reported binding of bulky pyridine bases to Co(II)Cbi(+) by UV-vis spectroscopy (Sirovatka, J. Ph.D. Thesis, op. cit.). Also reported is our current best synthesis and purification of AdoCbi(+)BF(4)(-), work that builds off our 1987 synthesis of AdoCbi(+)BF(4)(-) (Hay, B. P.; Finke, R. G. J. Am. Chem. Soc. 1987, 109, 8012). Finally, the multiple, compounding errors which have caused problems in this project are listed, notably errors in the protein X-ray crystallography literature, the EXAFS literature, the Co(II)Cbi(+) plus bulky-bases EPR literature, the misleading B(12)-model literature, the erroneous experimental work (Sirovatka, op. cit.) and thus incorrect conclusions in one of our prior papers, as well as the erroneous implications in parts of the Marzilli and co-workers paper (op. cit.). It is hoped that a forthright reporting of these errors will help others avoid similar mistakes in the future when studying complex, bioinorganic systems.

Quantum chemical study of the coordination of glycolic acid conformers and their conjugate bases to [Ca(OH 2) n] 2+ ( n=0–4) ions

A detailed exploration of the configurational and conformational space of glycolic acid and their conjugate bases has been carried out with the aid of first principles quantum chemical techniques at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory. The most stable configuration among the eight possible glycolic acid conformers corresponds to the E- s- cis, s- trans configuration, while the highest energy E- s- trans, s- cis conformer was found at 10.88 and 12.17 kcal mol −1 higher in energy at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory, respectively. Upon dissociation of glycolic acid the s- cis( syn), and s- trans( anti) configurations of the glycolate anion can be formed. The anti conformer was found to be less stable than the syn one by 14.20 and 16.87 kcal mol −1 at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p)) levels of theory, respectively. The computed B3LYP/6-311+G(d,p) proton affinity of the syn conformer for the protonation process affording the more stable E- s- cis, s- trans conformer, in vacuum was found to be 325.35 kcal mol −1 (Δ G 0 value). From a methodological point of view, our results confirm the reliability of the integrated computational tool formed by the B3LYP density functional model. This model has subsequently been used to investigate the interaction of Ca 2+ ions with the glycolic acid conformers and their conjugate bases in vacuum and in the presence of extra water ligands. For the complexes of glycolic acid conformers the η 2–O,O–(C OOH) coordination, that is the structure that arises from the coordination of the Ca 2+ to the carboxylic group, is the global minimum of the PES, while the η 2–O( OH),O–(CO OH) coordination is a local minimum found at only 1.0 and 1.3 kcal mol −1 higher in energy at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory, respectively. Moreover, the two isomers exhibit nearly the same binding affinities, which are predicted to be 89 and 85 kcal mol −1 at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory, respectively. The same holds also true for the complexes of the glycolate anion. The η 2–O,O–(C OO −) coordination involving the syn conformer of the glycolato ligand, is the global minimum, while the η 2–O( OH),O–(C OO −) one lies at 1.5 and 5.6 kcal mol −1 higher in energy at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory, respectively. The other conformer with an η 2–O,O–(C OO −) coordination involving the anti conformer of the glycolato ligand, is less stable by only 0.2 kcal mol −1 at both levels of theory. Noteworthy is the trend seen for the incremental binding energy due to the successive addition of water molecules to [HOCH 2C(O)O]Ca 2+ species; the computed values are 30.4, 26.8, 22.9 and 16.2 kcal mol −1 at the B3LYP/6-311+G(d,p) level of theory for the mono-, di-, tri- and tetraaqua complexes, respectively. This trend arising from the repulsion of the dipoles between the water ligands and from unfavorable many body interactions is in accordance with those anticipated from electrostatic considerations. The Ca(II)-water interaction weakens with increasing coordination of the metal. Obviously, it is the electrostatic nature of the Ca(II)-water interactions that accounts well for the computed coordination geometries of the cationic (aqua)(glycolato)calcium complexes. Calculated structures, relative stability and bonding properties of the conformers and their complexes with [Ca(OH 2) n ] 2+ ( n=0–4) ions are discussed with respect to computed electronic and spectroscopic properties, such as charge density distribution, harmonic vibrational frequencies and NMR chemical shifts.

Intramolecular proton transfer direct dynamics in the glycolate anion: Isotope effects

We studied the dynamics of intramolecular proton transfer in the glycolate anion, and of the analogous processes in the deuterated and tritiated derivatives, by means of variational transition state theory with various multidimensional semiclassical models of tunneling. Rate constants were obtained directly from MP2/6-31++G** ab initio results scaled so that the height of the barrier coincided with the value given by QCISD/6-31++G** calculations, 3.81 kcal/mol. In this kind of system, the effective barrier height can be significantly lower for the lighter isotope. Analysis of the kinetic isotope effects (kH/kD and kH/kT) showed them reduced by tunneling but favored by certain vibrational modes.

A comparison of two methods for direct tunneling dynamics: Hydrogen exchange in the glycolate anion as a test case

Two methods for studying tunneling dynamics are compared, namely the instanton model and the approach of Truhlar and co-workers, which are based on the direct output of electronic structure calculations and thus are parameter free. They are employed to evaluate the zero-level tunneling splitting due to intramolecular hydrogen exchange in the glycolate anion. The first method was developed in a series of recent studies and presents a combination of the instanton theory with quantum-chemically computed potentials and force fields. For the compound at hand, which has 21 internal degrees of freedom, a complete potential-energy surface is generated in terms of the normal modes of the transition-state configuration. It is made up of the potential-energy curve along the tunneling coordinate and harmonic force fields at the stationary points. The level of theory used is HF/6–31++G**. All modes that are displaced between the equilibrium configuration and the transition state are linearly coupled to the tunneling mode, the couplings being proportional to the displacements in dimensionless units. These couplings affect the instanton trajectory profoundly and, depending on the symmetry of the skeletal modes, can enhance or suppress the tunneling. In the glycolate anion all modes have such displacements and thus are included in the calculation. Based on the similarity with malonaldehyde, it is argued that tunneling prevails in the studied process, and the zero-level tunneling splitting is predicted. The latter is found within the computational scheme developed earlier, which avoids explicit evaluation of the instanton path and thus greatly simpli-fies the tunneling dynamics. These results are tested by the method of large-curvature tunneling of Truhlar and co-workers implemented in a dual-level scheme. The potential energy surface needed for the dynamics calculations is generated at the semiempirical PM3 level of theory and then corrected by interpolation with high-level HF/6–31++G** results for the stationary points. The code corresponding to this approximation is in the package MORATE 6.5. The tunneling splittings found by the two approaches are in quantitative agreement. We have found that the computational scheme based on the instanton model is much less time consuming both in the static and dynamics part. This computational efficiency, also demonstrated in a number of earlier studies, merits future application of the method to fairly large systems of practical interest, such as clusters and organic compounds with excited-state proton transfer.

Voltammetric study of the electrochemical behaviour of glycolic acid solutions in sulphuric acid on platinum single-crystal electrodes with basal orientations

The electrochemical behaviour of glycolic acid has been studied on platinum single crystals with basal orientations in sulphuric acid. The bulk oxidation of glycolic acid proceeds at high potential values, where extensive adsorption of oxygen exists on the electrode surface, making the preservation of surface structure impossible. The observed behaviour at lower potentials can be summarized by two points. Evidence exists of specific adsorption of the glycolate anion, which is more strongly adsorbed than bisulphate. Blocking of electrode surfaces is also observed for the three planes studied, although no significant surface poisoning was observed under open-circuit conditions. Experimental data indicate the absence of a CO-like adsorbed species on Pt(111) and Pt(110), and suggest the existence of structures preserving the CC bond. Conversely, CO ads, is the main poison on Pt(100).

Comparison between intramolecular proton transfers involving the carboxylate and alkoxide groups

We have studied the intramolecular proton transfer in the hydroxyacetate, hydrogenoxalate and glycolate anions by means of ab initio calculations. Due to the higher proton affinity of RO − as compared to R-COO −, there is only one minimum in the hydroxyacetate potential surface. Conversely, given that hydrogenoxalate and glycolate anions are symmetric systems, a transition state appears in both cases. The greater barrier in the hydrogenoxalate with respect to the glycolate anion can be attributed to the reorganisation energy of the substrate. The proton motion in the hydrogenoxalate molecule is clearly coupled to the motion of the other atoms.

Cyclic Voltammogram of Formaldehyde and Its Related Species in Electroless Copper Solution

The cyclic voltammetric method that allows the evaluation of formaldehyde concentrations in electroless copper solution is described. In this study, evidence is provided to show that methylene glycolate anion and its copper (II) complex are electroactive species in the solution. These species give a peak centered around −0.25V vs. . It is also proposed that this technique can easily be integrated into a remote monitoring system.

PH Dependence and Kinetics of Glycolate Uptake by Intact Pea Chloroplasts

Experiments in which [1-(14)C]glycolate uptake is carried out in conjunction with measurements of stromal pH indicate that only glycolic acid and not the glycolate anion is crossing the pea (Pisum sativum var. Progress No. 9, Agway) chloroplast envelope. This mechanism of glycolate transport appears to be too slow to account for observed photorespiratory carbon fluxes in C(3) plants.

Mechanism of Glycolate Transport in Spinach Leaf Chloroplasts

The incorporation of (14)CO(2) into glycolate by intact spinach leaf (Spinacia oleracea L. var. Kyoho) chloroplasts exposed to (14)CO(2) (NaH(14)CO(3), 1 millimolar) in the light was determined as a function of O(2) concentrations in the reaction media. A hyperbolic saturation curve was obtained, apparent K(m) (O(2)) of 0.28 millimolar, indicating that glycolate is produced predominantly by ribulose-1,5-bisphosphate carboxylase/oxygenase. A concentration gradient of glycolate was invariably observed between chloroplast stroma and the outside media surrounding chloroplasts during photosynthetic (14)CO(2) fixation under an O(2) atmosphere.Glycolate transport into and out of chloroplasts was studied using the silicon oil centrifugation method. Both uptake and loss of glycolate were found to be rapid, with small temperature dependencies between 0 degrees C and 25 degrees C (Q(10) = 1.1). The reaction rate as a function of the concentration of glycolate up to 30 millimolar was linear in both directions.The effect of external pH on the reaction rate in both directions was also examined. Glycolate penetrates rapidly, even at pH 8, showing a surprisingly high permeation of the glycolate anion. This rate was about 30 micromoles per milligram Chl per hour at 0 degrees C, and the initial concentration of glycolate of 10 millimolar with a pH range of 7 to 8. The observed rate is comparable to the reported value for glycolate synthesis in chloroplasts under photorespiratory conditions. The uptake of glycolate into chloroplasts was accelerated below pH 7, while the rate of excretion was considerably lowered. It is, thus, suggested that undissociated glycolic acid penetrates the chloroplast envelopes more rapidly than does the anion.

A search for a β effect: the nucleophilicity of the methylene glycolate anion

The possible existence of a β-effect (effect of a lone pair of electrons located at a β position of a nucleophile) was investigated by reacting méthyléne glycolate anion with p-nitrophenyl acetate, 2,4-dinitro-fluorobenzene and 2,4-dinitrochlorobenzene in water. For these reactions, no enhanced nucleophile reactivity was found. An upper limit of 2.5 was found for the nucleophilicity n of méthyléne glycolate on the Swain-Scott scale and 6.2±0.2 on Ritchie's N + scale.