NH2CH2COOH Research Articles

Efficient Generation of Permutationally Invariant Potential Energy Surfaces for Large Molecules

An efficient method is described for generating a fragmented, permutationally invariant polynomial basis to fit electronic energies and, if available, gradients for large molecules. The method presented rests on the fragmentation of a large molecule into any number of fragments while maintaining the permutational invariance and uniqueness of the polynomials. The new approach improves on a previous one reported by Qu and Bowman by avoiding repetition of polynomials in the fitting basis set and speeding up gradient evaluations while keeping the accuracy of the PES. The method is demonstrated for CH3–NH–CO–CH3 (N-methylacetamide) and NH2–CH2–COOH (glycine).

Glycine combusted ZnFe2O4 gas sensor: Evaluation of structural, morphological and gas response properties

A simple and robust synthesis approach to zinc based spinel ferrite (ZnFe2O4) using the glycine combustion method is reported. The route utilizes divalent zinc nitrate (Zn(NO3)2·6H2O) and trivalent iron nitrate (Fe(NO3)3·9H2O) precursors in aqueous solution (distilled H2O). Glycine (NH2–CH2–COOH) acts as a fuel for the combustion process and subsequent ferrite (ZnFe2O4) formation. As produced material powder was sintered at 700°C in the pellet form and examined for LPG, acetone, ethanol and ammonia sensing properties in the temperature range of 200–450°C. XRD and TEM analyses revealed the formation of single phase nanocrystalline material with crystallite size in the range of 25–30nm. SEM analysis confirmed the coarse structural morphology due to auto-ignition during the combustion reaction. The produced ferrite showed maximum response to both acetone (57%) and LPG (54%) at operating temperatures of 250°C and 375°C, respectively. Further, the sensor showed decent stability and reproducibility towards LPG and acetone, over the period of 30 days, which was then decreased by 2% up to 45 days. The present study confirms that the as produced ZnFe2O4 is a promising candidate for fabricating high performance sensors towards LPG and acetone sensing, in practice.

Facile and Mild Strategy Toward Biopolymer-Coated Boron Nitride Nanotubes via a Glycine-Assisted Interfacial Process

We report a simple way to obtain polymer-coated multiwalled boron nitride nanotubes (BNNTs) conducted under mild conditions compatible with fragile biopolymers. The approach converts aggregated pristine BNNTs into colloidally stable dispersions in water without requiring treatment at high temperature or in strongly oxidative conditions. The method relies on our experimental observation that glycine (NH2–CH2–COOH, Gly) interacts with BNNTs, in accordance with theoretical calculations. The role of glycine in this process is 2-fold: the Gly amine group binds to the B-sites of BNNTs, while the Gly carboxylic acid function provides ionic anchoring sites for interactions with polyelectrolytes. The formation of Gly-BNNTs proved to be essential, since they readily disperse in water as disentangled objects and spontaneously adsorb polycations, such as chitosan (CH), polyanions, such as hyaluronan (HA), and polyzwitterionic polymers, such as chitosan-phosphorylcholine (CH-PC). Treatment of aqueous dispersions of coarsely coated BNNTs with an immiscible solvent (hexane) resulted in the complete coverage of the BNNT surfaces via oil/water interfacial assembly. This work provides a rapid, mild, and scalable route to water-dispersible biofunctional BNNTs that may serve as drug delivery vehicles or scaffolds in tissue engineering.

In situ measurements of the radiation stability of amino acids at 15–140 K

We present new kinetics data on the radiolytic destruction of amino acids measured in situ with infrared spectroscopy. Samples were irradiated at 15, 100, and 140K with 0.8-MeV protons, and amino-acid decay was followed at each temperature with and without H2O present. Observed radiation products included CO2 and amines, consistent with amino-acid decarboxylation. The half-lives of glycine, alanine, and phenylalanine were estimated for various extraterrestrial environments. Infrared spectral changes demonstrated the conversion from the non-zwitterion structure NH2CH2(R)COOH at 15K to the zwitterion structure +NH3CH2(R)COO− at 140K for each amino acid studied.

Effect of glycine substitution on the ferroelectric phase of betaine arsenate [(CH 3) 3NCH 2COO·H 3AsO 4

The present work reports an experimental investigation on the influence of glycine (NH 2CH 2COOH) substitution in the polar properties and the critical dynamics of the molecular ferroelectric betaine arsenate, (CH 3) 3NCH 2COO·H 3AsO 4. The dielectric dispersion (20 Hz<ν<3 MHz) and the thermally induced displacement currents are investigated in detail over the extended Curie region of the system (130 K< T<100 K). The results obtained for a single crystal with nominal glycine content of 20% are analyzed, compared with those obtained for pure betaine arsenate and discussed within the scope of a phenomenological Landau model previously used to describe a system with competing ferroelectric and structural instabilities.

Ultrafine particles of ZnGa 2O 4 obtained by solution combustion and complexation methods

Two soft chemistry routes – complexation and solution combustion – are explored to obtain the zinc gallate spinel ZnGa 2O 4. Three types of complexes, namely: (NH 4) 2[ZnGa 2(C 4O 6H 4) 4(OH) 2]·4H 2O, [ZnGa 2(NH 2CH 2COOH) 4.5](NO 3) 8·4H 2O and [ZnGa 2(CO(NH 2) 2) 7](NO 3) 8·9H 2O have been synthesized and characterized by IR and UV–vis spectroscopy. Zinc gallate spinels obtained by decomposition of these compounds have been investigated by XRD spectra, analytic electronic microscopy and photoluminescence spectroscopy. Zinc gallate spinels exhibited blue emission spectra in the wavelength range of 400 nm–450 nm.

EPR and optical absorption studies of copper ions in diglycine calcium chloride tetrahydrate

EPR study of copper ions in diglycine calcium chloride tetrahydrate (DGCCT), [(NH 2CH 2COOH) 2·CaCl 2·4H 2O] single crystals at room temperature is carried out. The spin Hamiltonian parameters of copper ions are determined as: g x = 2.0238 ± 0.0002, g y = 2.1122 ± 0.0002, g z = 2.2250 ± 0.0002, A x = (83 ± 2) × 10 −4 cm −1, A y = (86 ± 2) × 10 −4 cm −1 and A z = (118 ± 2) × 10 −4 cm −1. The optical study of the single crystals at room temperature is also done and the bands are assigned to d-d and charge transfer transitions. Using above data, the nature of bonding in the complex is discussed.

Electronic structure and related properties of the ferroelectric crystal triglycine sulfate

The electronic band structure and related physical properties of the crystal triglycine sulfate (TGS), (NH 2CH 2COOH) 3·H 2SO 4, in the ferroelectric phase P2 1 have been calculated using the first principles Linear Combination of Atomic Orbitals (LCAO) code CRYSTAL’06 at the B3LYP level of theory. The interactions between the quasi-separate three glycine groups and the sulfate complex have been studied by the analysis of the density of states of the crystal. The glycine 2 group was found to be the zwitterion in the optimized structure. Ten coefficients of the elastic stiffness tensor c kl , four coefficients of the tensor of the elastoelectrical effect e ki , and the spontaneous polarization P s of TGS have been calculated for the first time and have been found to agree well with experimental data. Extrema are found in the elastoelectric coefficient e 22 as a function of the strain ε 2, and in the spontaneous polarization P s as a function of the unit cell volume.

Exchange energy density and exchange potential via a hartree–fock plus mp2 study of the electron liquid in the ground-state conformer of glycine

Very recent criticisms of existing exchange-correlation functionals by Wanko et al. applied to systems of biological interest have led us to reopen the question of the ground-state conformer of glycine: the simplest amino acid. We immediately show that the global minimum of the Hartree–Fock (HF) ground-state leads to a planar structure of the five non-hydrogenic nuclei, in the non-ionized form NH2–CH2–COOH. This is shown to lie lower in energy than the zwitterion structure NHB3 +–CH2–COO−, as required by experiment. Refinement of the nuclear geometry using second-order Møller–Plesset perturbation theory (MP2) is also carried out, and bond lengths are found to accord satisfactorily with experimentally determined values. The ground-state electron density for the MP2 geometry is then redetermined by HF theory and equidensity contours are displayed. The HF first-order density matrix γ( r , r ′) is then used to obtain similar exchange-energy density (ε x ( r )) contours for the lowest conformer of glycine. At first sight, their shape looks almost the same as for the density ρ( r ), which seems to vindicate the LDA proportional to ρ( r )3/4. However, by way of an analytically soluble model for an atomic ion, it is shown that this has to be corrected to obtain an accurate HF exchange energy Ex as the volume integral of ε x ( r ). Finally, recognizing that for larger amino acids, the use of HF plus MP2 perturbation corrections will become prohibitive, we have used the HF information for ε x ( r ) and ρ( r ) to plot the truly non-local exchange potential proposed by Slater, from the density matrix γ( r , r ′). This latter calculation should be practicable for large amino acids, but there adopting Becke's one-parameter form of ε x ( r ) correcting LDA exchange. Some future directions are suggested.

Growth and characterization studies of ferroelectric diglycine nitrate (DGN) single crystals

Single crystals of diglycine nitrate [(NH 2CH 2COOH) 2HNO 3] (DGN), a ferroelectric material with Curie temperature 206 K, were grown in silica gel at room temperature by the solubility reduction method at room temperature (39 °C). Bulk crystals of dimension 21 mm × 18 mm × 11 mm have been grown by optimizing the growth conditions. The grown crystals have been characterized by structural, optical and mechanical characterization studies. Fourier transform infrared (FTIR) spectral analysis reveals that the crystal consists of all functional vibrational groups. FT-Raman spectrum, which is complement to FTIR studies, has also been recorded. Surface analysis by SEM reveals that the crystal absorbs water from the moisture. The optical transparency range and the lower cut-off of UV transmission were identified from the recorded UV–vis spectrum of DGN. The UV cut-off wavelength of DGN is 286 nm. Thermal analysis of the crystalline sample was performed by TGA and DTA methods. The crystal is thermally stable up to 217 °C. The Vicker's microhardness value of DGN crystal is decreases with increase of load. The work hardening coefficient ( n) of diglycine nitrate was determined using the least squares fit method and found to be 1.5.

Sensitive determination of phenylephrine and chlorprothixene at poly(4-aminobenzene sulfonic acid) modified glassy carbon electrode

Phenylephrine (i.e. PHE) and chlorprothixene (i.e. CPT), two effective and important antipsychotic drugs with low redox activity, were found generating an irreversible anodic peak at about +0.89 V (vs. SCE) and +1.04 V in 0.05 M HAc–NaAc (pH 5.0) or NH 2CH 2COOH–HCl (pH 2.4) buffer solution at poly(4-aminobenzene sulfonic acid) modified glassy carbon electrode (i.e. poly(4-ABSA)/GC), respectively. Sensitive and quantitative measurement for them based on the anodic peaks was established under the optimum conditions. The anodic peak current was linear to PHE and CPT concentrations from 1 × 10 −7 to 1.5 × 10 −5 M and 2 × 10 −6 to 4.5 × 10 −5 M, the detection limits obtained were 1 × 10 −8 and 1 × 10 −7 M, separately. The modified electrode exhibited some excellent characteristics including easy regeneration, high stability, good reproducibility and selectivity. The method proposed was successfully applied to the determination of PHE and CPT in drug injections or tablets and proved to be reliable compared with ultraviolet spectrophotometry. The modified electrode was characterized by electrochemical methods.

Preparation of zinc oxide (ZnO) powders with different types of morphology by a combustion synthesis method

A combustion synthesis process has been established for preparation of ZnO powders with different types of morphologies (that is, agglomerated particles, rod-like structures, and tetrapod whiskers) in air ambience. Metallic zinc and glycine (NH 2CH 2COOH) powders were used as the fuels, whereas zinc nitrate acted as the oxidant. These reactants were mixed and pressed into a compact. The compact was wrapped up with an igniting agent (i.e., Mg + Fe 3O 4) and the synthesis reaction was triggered by the combustion of the igniting agent. Both the combustion temperature and the product properties were affected by the reactant composition. A possible reaction mechanism based on thermodynamic calculations and experimental results was proposed that explains the effects of the reactant composition on the combustion reaction.

Fine powders of SrFe 12O 19 with SrTiO 3 additive prepared via a quasi-dry combustion synthesis route

This study presents a successful preparation of fine powders of strontium ferrite, SrFe 12O 19, with different contents of SrTiO 3 additive (i.e., SrFe 12O 19 + xSrTiO 3, x = 0.00, 0.05, 0.10, 0.15 and 0.20) through a quasi-dry combustion synthesis route using Sr(NO 3) 2, Fe(NO 3)·9H 2O, glycine (NH 2CH 2COOH), and Ti powder as reactants. The synthesis route included mixing and dehydration procedures to produce a flammable, homogenous dried reactant mixture with its subsequent combustion at room temperature to form a voluminous loose product. The as-synthesized powder was calcined at various temperatures to study the effects of temperature on phase development and products’ properties. Characterizations of the products were evaluated based on the X-ray diffraction, morphology observations, and magnetic properties studied using various instrumental analyses. Nearly Pure, single magnetic domain SrFe 12O 19 powder with crystalline size ranging from 55 to 75 nm was produced when x = 0.00 at 1050 °C. It had a maximum intrinsic coercivity (iH c) of 4.92 kOe, a magnetization value ( M max) of 60.13 emu/g, and a remanence magnetization ( M r) of 34.75 emu/g. Calcination at 1200 °C was found to increase the M max to 64.52 emu/g but to decrease the iH c. Experimental results suggested a possible mechanism for the formation of SrFe 12O 19. The as-synthesized powders and the calcined ones with different x values were introduced into thermal polyurethane (TPU) matrix to prepare a composite. The relative complex permittivity ( ɛ r = ɛ′ − jɛ″) and permeability ( μ r = μ′ − jμ″) of the composite specimens were measured within a frequency range of 1–12 GHz using a network analyzer. Adding SrTiO 3 to SrFe 12O 19 was demonstrated not only to improve the ɛ r but also to modify the μ r. This similar effect was observed when adjusting the calcination temperature.

Thermal decomposition of some copper–iron polynuclear coordination compounds containing glycine as ligand, precursors of copper ferrite

The thermal behaviour of three coordination compounds, precursors of copper ferrite, namely [Fe 2Cu(NH 2CH 2COOH) 4.5](NO 3) 8·4H 2O (I), [Fe 2Cu(NH 2CH 2COO) 4(OH) 3](NO 3)·H 2O (II) and [Fe 2Cu(NH 2CH 2COO) 6(NH 2CH 2COOH) 2](NO 3) 2 (III), has been investigated. For a complete and reliable assignment of the thermal transformations, the isolable intermediates and end products were characterized by IR and X-ray diffraction. The coordination compounds which undergo a stepwise decomposition in the temperature range 60–375 °C are less stable than free glycine (206–375 °C), indicating the occurrence of some self-propagating reactions. The nitrate/glycine ratio contained by the parent coordination compound, affects the final decomposition temperature (decreases as the ratio increases) but not the decomposition mechanism, and the mean particles size of the decomposition end product Fe 2CuO 4 (an optimum value has to be found in order to avoid local combustion occurrences).

Copper ferrite obtained by two “soft chemistry” routes

Nanoparticles of copper ferrites with tetragonal structure were obtained by two soft chemical methods: a complexation method and a self-propagating combustion. We demonstrated that in both these methods the precursors of copper ferrites were polynuclear coordination compounds. Three polynuclear coordination compounds with glycine as ligands: [Fe(III) 2Cu(II)(NH 2CH 2COO) 4(OH) 3](NO 3)·H 2O, [Fe(III) 2Cu(II)(NH 2CH 2COO) 6(NH 2CH 2COOH) 2](NO 3) 2 and [Fe(III) 2Cu(II)(NH 2CH 2COOH) 4.5](NO 3) 8·4H 2O were synthesized. The complex compounds were characterized by elemental chemical analysis and physico-chemical measurements (IR, UV–vis, magnetic measurements). The copper ferrites were investigated by XRD, IR spectra and magnetic measurements. The crystallite sizes of the copper ferrites were found in the range 18–29 nm.

Band structure and UV optical spectra of TGS crystals in the range of 4–10 eV

Theoretical and experimental studies of the band energy structure and optical spectra for triglycine sulphate crystal (TGS), (NH 2CH 2COOH) 3·H 2SO 4, in the ferroelectric phase have been performed for the first time. First principal DFT calculations of the band structure, density of states and dielectric functions spectra ε′( E) and ε ″ ( E ) of TGS crystal have been done using the computer package Cambridge Serial Total Energy Package (CASTEP) code. Experimental spectral dispersions of the complex reflection ratio ρ( E) have been measured using the synchrotron radiation at BESSY synchrotron source in the spectral range of 4–10 eV and the pseudo-dielectric functions 〈 ε 〉 = 〈 ε ′ 〉 + i 〈 ε ″ 〉 were evaluated. Experimental data and theoretically calculated dielectric functions have demonstrated a good agreement. The band energy dispersion of valence and conducting bands have been analyzed and were used to identify the dielectric functions peculiarities.

Glycine adsorption on single-walled carbon nanotubes

The adsorption of the amino acid glycine (NH 2CH 2COOH) on (3,3) armchair carbon nanotubes has been investigated through calculations based on density functional theory (DFT). A comparison of the adsorption energies for four adsorption models is presented, showing glycine in its zwitterionic form is generally bound stronger to the nanotube sidewall as compared to its nonionic counterparts. Adsorption through the carboxylate group of the glycine zwitterion exhibited the strongest interaction, favourably adsorbing with an adsorption energy of 0.53 eV. Further investigations on the adsorption of glycine on graphite sheets have showed weaker interactions as compared to adsorption onto the nanotube surface, suggesting a decrease in glycine adsorption strength with increasing nanotube diameter.

IR and quantum-chemical studies of carboxylic acid and glycine adsorption on rutile TiO 2 nanoparticles

Nanocrystalline TiO 2 powders of the rutile polymorph, synthesized by a sol–gel method, were treated with water solutions containing, respectively, formic, acetic, and citric acid and glycine in order to study the adsorption properties of these organic species. The samples were characterized by FTIR, Raman, powder XRD, and TEM. It was found that HCOOH, CH 3COOH and HOC(COOH)(CH 2COOH) 2—but not NH 2CH 2COOH—adsorbed onto TiO 2. The adsorption of HCOOH, CH 3COOH and NH 2CH 2COOH onto the (110) surface of rutile was also studied by quantum-chemical periodic density functional theory (DFT) calculations. The organic molecules were from the computations found to adsorb strongly to the surfaces in a bridge-coordinating mode, where the two oxygens of the deprotonated carboxylic acid bind to two surface titanium ions. Surface relaxation is found to influence adsorption geometries and energies significantly. The results from DFT calculations and ab initio molecular-dynamics simulations of formic acid adsorption onto TiO 2 are compared and match well with the experimental IR measurements, supporting the bridge-binding geometry of carboxylic-acid adsorption on the TiO 2 nanoparticles.

Band structure and optical properties of diglycine nitrate crystal

Experimental and theoretical investigations of the electron energy characteristics and optical spectra for diglycine nitrate crystal (DGN), (NH 2CH 2COOH) 2·HNO 3, in the paraelectric phase ( T = 295 K ) are presented. Spectral dispersion of light reflection R( E) have been measured in the range of 3–22 eV and the optical functions n( E) and k( E) have been calculated using Kramers–Kronig relations. First principal calculations of the electron energy characteristic and optical spectra of DGN crystal have been performed in the frame of density functional theory using CASTEP code (CAmbridge Serial Total Energy Package). Optical transitions forming the low-energy edge of fundamental absorption are associated with the nitrate groups NO 3. Peculiarities of the band structure and DOS projected onto glycine and NO 3 groups confirm the molecular character of DGN crystal.

Millimeter wave spectrum of glycine

We present new investigations of the millimeter wave spectra of the two lowest-energy conformers of glycine (NH 2CH 2COOH). Measurements of these spectra have been carried out between 75 and 260 GHz using the millimeter-wave spectrometer in Kharkov. The new data set involves rotational transitions with J up to 44 and K a up to 15 for conformer I and transitions with J up to 43 and K a up to 14 for conformer II. This represents a more than twofold expansion both in the frequency range and J quantum-number range in comparison with previous investigations. The improved sets of spectroscopic parameters obtained for both conformers provide accurate transition frequencies for the key lines necessary for radio astronomy searches for interstellar glycine.