Glycinium Ion Research Articles

Enthalpies of Glycine Protonation in Water–Acetone and Water–Ethanol Solvents

Heat effects of the reaction of glycine protonation at 298 K in water–ethanol (µ = 0.1 (NaClO4)) and water–acetone (µ = 0.3 (NaClO4)) solvents of various compositions are determined via calorimetry. The enthalpies of the resolvation of glycinium ions in aqueous solutions of ethanol and acetone are calculated using the literature data. It is established that a minor change in the heat effect of the reaction of glycine protonation in water–ethanol and water–acetone solvents is associated with the mutual compensation of the enthalpies of proton, glycinium-ion, and glycine resolvation in these media. It is shown that the contribution from the enthalpy component to the change in the Gibbs energy of this reaction is insignificant.

Heat Effect of the Protonation of Glycine and the Enthalpies of Resolvation of Participating Chemical Species in Water–Dimethylsulfoxide Solvent Mixtures

Enthalpies of the protonation of glycine in water‒dimethylsulfoxide (DMSO) mixed solvents are determined calorimetrically in the range of DMSO mole fractions of 0.0 to 0.9, at T = 298.15 K and an ionic strength μ = 0.3 (NaClO4). It is established that the protonation of glycine becomes more exothermic with an increasing mole fraction of DMSO, and the enthalpies of resolvation of glycine and glycinium ions in water‒DMSO solvent mixtures are calculated. It is shown that the small changes in the enthalpy of protonation observed at low mole fractions of DMSO are caused by the contributions from the solvation of proton and protonated glycine cancelling each other out. The enthalpy term of the Gibbs energy of the reaction leading to the formation of glycinium ion is estimated along with the enthalpy of resolvation of the reacting species in the water‒DMSO mixed solvent.

Crystal Structure and Phase Transition of Diglycine Perchlorate

Diglycine perchlorate (DGPCl), a new 2:1 adduct formed between glycine and perchloric acid has been obtained and studied using differential scanning calorimetry and single crystal X-ray diffraction. DGPCl undergoes a reversible first-order phase transition at 261.5 K. The crystal structures at 150 and 293 K have been determined to be triclinic, space group P‐1, Z = 2, suggesting the first-order phase transition to be an isostructural phase transition. The DGPCl crystal consists of five glycinium-monoprotonated glycinium dimers and five perchlorate anions in an asymmetric unit. The glycine moieties in the glycinium-monoprotonated glycinium dimers are non-planar. Two types of hydrogen bonds are present in the crystal, strong O–H···O hydrogen bonds and a weak N–H···O hydrogen bonds. The short, strong O–H···O hydrogen bond connects the glycinium ion and mono protonated glycinium ion. In four of the dimers, the O–H and H···O bond lengths are different, indicating the hydrogen atom to be located more close to the monoprotonated glycinium ion. However, in one of the glycinium-monoprotonated glycinium dimer the O··H and H··O bond lengths are nearly equal, suggesting the hydrogen atom (O···H···O) to be attached to the oxygen atoms of both glycine moieties. On thermal transition some of these hydrogen bonds are weakened and in all dimers the hydrogen atom seems to be located more close to the mono protonated glycinium ion.

Investigation of hydrogen-bond network in bis(glycinium) oxalate using single-crystal neutron diffraction and spectroscopic studies

Single-crystal neutron diffraction investigation of bis(glycinium) oxalate was undertaken in order to study its hydrogen-bonding network, particularly the very short hydrogen bond between the glycinum and oxalate ions, indicated by the X-ray diffraction study. The non-existence of any phase transition in these crystals was attributed to the fact that the short hydrogen bond in bis(glycinium) oxalate is asymmetric in nature, with no hydrogen disorder. The potential energy landscape for the above-mentioned H atom was found to have a single minimum closer to the glycinium ion. IR and Raman investigations of the title complex supported the above result.

Electrical Properties and DC Conductivity of Phosphoric Acid Doped TGS Single Crystals

Properties of phosphoric acid (H3PO4) doped triglycine sulfate (TGSP) grown from aqueous solutions containing 0.1 to 0.5 moles of H3PO4 have been investigated. Composition analysis indicates a very low incorporation of phosphoric acid in the crystal lattice. Large sized crystals of dimension (70 mm × 40 mm × 25 mm) suitable for IR detector are obtained with 0.2 moles of H3PO4 in solution. The presence of both zwitter and glycinium ions in TGSP is explained through FT-IR analysis. The dielectric dispersion of TGSP crystals in the frequency range from 100 Hz to 100 KHz, and in the temperature range 27 to 65°C has been analyzed. The increased dielectric dispersion in TGSP crystals is found to be related to the increase in dc conductivity, and the increased domain boundary relaxation time. Doped crystals show a broad transition and suppressed value of peak dielectric constant.

Characterization of phosphoric acid doped TGS single crystals

Single crystals of phosphoric acid (H3PO4) doped triglycine sulfate (TGSP) are grown from aqueous solution containing 10–50mol% of H3PO4. Large sized crystals of dimension (70mm×40mm×25mm) suitable for IR detector applications are obtained with 20mol% of H3PO4. They exhibit elongated domains, and the domain density is higher than in undoped TGS crystals. FT-IR analysis indicates the presence of both zwitter and glycinium ions in the doped TGSP crystals, which is due to the low incorporation of H3PO4 into the TGS crystal lattice. The dielectric properties TGSP crystals measured in the temperature range 27–65°C and in frequency range 102–105Hz show a broad transition, and the peak dielectric constant values are reduced with increasing H3PO4 concentration. Hysteresis loops with high coercive fields are observed up to 20mol% of H3PO4. At a higher concentration, double loops are observed due to the polarization switching inhibition by H3PO4 molecules. Dopant concentration is found to have a marginal influence on the spontaneous polarization of the TGSP crystals.

Vibrational spectra and phase transition in triglycine sulpho‐phosphate

AbstractInfrared and single crystal Raman spectra for various polarization geometries of Triglycine Sulpho‐Phosphate (TGSP) have been recorded and analysed. The bonds of hydrogen atoms in H2SO4 and H3PO4 groups are shown to be weak and the possibility of proton transfer from H2SO4/H3PO4 group is indicated. Two different types of glycinium ions are shown to be present in the unit cell. Temperature dependent Raman spectra of TGSP have been recorded. The phase transition detected around 325 K in TGSP is explained in terms of the flipping motion of the glycinium ion and of attaining a higher crystal symmetry.

Enthalpy of ionization of aqueous glycinium ion ( +HGly = H + + Gly) at 298 K, dependence on ionic strength, and thermodynamics of ionization

Previous investigations have led to considerably different enthalpy values (3891-5983 J mol −1) for the first ionization of aqueous glycine ( + HGly = H + + Gly) at T= 298.15 K. To resolve this uncertainty, new measurements of the enthalpy of solution of glycine in water and in excess dilute hydrochloric acid have been made. Results of these measurements lead to values of Δ H XXX 1 = 4.1±0.1 kJ mol −1, and thence Δ S XXX 1 = −131.2±0.3 J K −1 mol −1, for the first ionization of glycine at T= 298.15 K. It has been noted that there is an unusually large dependence of Δ H 1 on the ionic strength of the solution.

Deuterium atom positions in the paraelectric phase of deuterated triglycine sulfate

The structure of Deuterated Triglycine Sulfate has been determined at 65°C. Refinements were based on initial parameters from Itoh's and Mitsui's (1973) x-ray results. The proton in the short hydrogen bond between the glycine group and glycinium ion is disordered, as evidenced by a thermal amplitude of 0.4 A along the bond from a centered position. All hydrogen bonds are lengthened in the high temperature phase. The lengthening is in the Deuterium to acceptor distance. The average is about 0.06 A which seems larger than expected for an isotope effect. A possible transition mechanism is postulated.

Structural studies of triglycine sulphate part i: Low radiation dose (structure a)

The crystal structure of ferroelectric triglycine sulphate has been determined from single-crystal X-ray diffractometer data. A single-domain crystal was used and the X-ray dose was minimized in order to reduce the effects of radiation damage. The crystals are monoclinic, with unit cell dimensions a = 9.419(1), b = 12.647(1), c = 5.727(1) a, β= 110.32°, space group P21, Z = 1. Least-squares refinement using 1270 independent reflections has reached R 0.041.The structure consists of three independent glycine molecules and a sulphate ion connected by a three-dimensional hydrogen bonding network. One of the three glycine molecules, glycine I, is a non-planar glycinium ion. The other two, glycines II and III, are both planar, but one is a glycinium ion and the other a glycine zwitterion. Anomalous scattering effects have been used to determine the absolute configuration. The major displacement in ferroelectric switching is 0.9 A for the nitrogen atom of glycine I, while for glycine II and III relatively small ...

Structural studies of triglycine sulphate Part II: After x-irradiation/field treatment (structure B)

The crystal structure of triglycine sulphate after X-irradiation/field treatment is reported. The crystals are monoclinic with unit cell dimensions a = 9.421 (1), b = 12.656(1), c = 5.732(1) A, β = 110.35 (1)° space group P21, Z = 2. Least-squares refinement using 1267 independent X-ray reflections has.reached R = 0.049.The structure is basically similar to that determined at low X-ray dosage but there is one crucial difference. The non-planar glycine, glycine I, is found to be a neutral molecule rather than a glycinium ion. Instead a hydrogen atom is found bonded to a sulphate oxygen, thus forming a bisulphate ion. The structure could therefore be designated diglycine glycinium bisulphate. The inhibition of ferroelectric polarity reversal in irradiation/field treated triglycine sulphate is discussed in the light of these results.

The adsorption of amino acids at the mercury-water interphase Part I. Glycine in acid, neutral and base solutions

The adsorption of glycine on mercury from acid, neutral and alkaline solutions has been studied by electrocapillary and capacity methods. In neutral solutions there is a minimum in the adsorption as would be expected for a highly polar adsorbate. However, the high dipole moment of glycine is not apparent in the form of a potential shift at constant electrode charge. Hence, it is suggested that the molecule is adsorbed with the dipole essentially parallel to the electrode surface. Glycinate and glycinium ions behave as typical anions and cations, respectively. There is some evidence that the former adsorption is more closely congruent in potential than in charge.

Structure Cristalline de Dérivés D'Acides Aminés VI. Le Composé HI.2 Glycine

AbstractDiglycine hydro‐iodide is monoclinic, space group C2 with unit cell parameters a = 18.592, b = 5.160, c = 20.372 Å. β = 110.64°; Z = 8. The crystal structure has been determined using three‐dimensional diffractometer data.The asymmetric part of the unit‐cell contains two independent iodine ions, two glycinium ions NH3 +CH2COOH and two zwitter‐ions NH3 +CH2COO−. The different ions are connected by hydrogen bonds N‐H+… I−, N‐H+… O− and O‐H… O−.

Volume changes for ionization of formic, acetic, and butyric acids and the glycinium ion in aqueous solution at 25.deg.

Volume changes for ionization of formic, acetic, and butyric acids and the glycinium ion in aqueous solution at 25.deg.

Crystal Structure and Phase Transition of (Glycine)2HNO3 I. Crystal Structure Determination of Ferro- and Paraelectric Phases

The crystal structures of ferroelectric and paraelectric (Glycine) 2 HNO 3 were determined by X-ray as well as by neutron diffraction methods at -150°C and at room temperature, respectively. One of the glycine molecules has the zwitter-ion configuration and another is mono-protonated. Thus the chemical formula should be written as NH 3 + CH 2 COO - ·NH 3 + CH 2 COOH·NO 3 - . Both glycine ions as well as the nitrate ion are nearly planar within the experimental error. A short O-H…O bond, about 2.45A, connects two glycine ions of the different configuration and a proton is attached to the oxygen of the glycinium ion. The paraelectric structure is a disordered one based upon the ferroelectric structure. Such a type of the order-disorder phase transition and the above-mentioned strong hydrogen bond may play an important role for the ferroelectric behaviour of the crystal, which is very similar to the case of (Glycine) 3 H 2 SO 4 .

The Formation Mechanism of Domain Etch Patterns in Triglycine Sulfate Crystals

Conditions necessary for obtaining domain patterns in triglycine sulfate-water system were studied. Effects of surface charge, stirring, undersaturation and composition of etchants were examined by rub technique, jet technique and observation of etched crystal surfaces. Surface charge was necessary for revealing domains. Domain patterns were revealed at low undersaturations, while at high undersaturations dislocation pits. It was found that the positive glycinium ions play a major role in domain pattern detection while the negative sulfate ions a minor one. Domain pattern formation by etching in triglycine sulfate is probably due to the difference in the rate of diffusion of the glycinium ions into the solution between at the positive and at the negative ends of the dipole. The relation between the conditions required for revealing domains and those for revealing dislocation pits is discussed on the basis of current theories of crystal dissolution.