The structure and dynamic properties of mixed adsorption and penetration layers of α-dipalmitoylphosphatidylcholine/β-lactoglobulin at water/fluid interfaces

The interfacial tensions of mixed α-dipalmitoylphosphatidylcholine (DPPC)/β-lactoglobulin layers at the chloroform/water interface have been measured by the pendent drop and drop volume techniques. In certain intervals, the adsorption kinetics of these mixed layers was strongly influenced by the concentrations of both protein and DPPC. However, at low protein concentration, C_{β-lactoglobulin}=0.1 mg l⁻¹, the adsorption rate of mixed interfacial layers was mainly controlled by the variation of the DPPC concentration. As C_{β-lactoglobulin} was increased to 0.8 mg l⁻¹, the interfacial activity was abruptly increased, and within the concentration range of C_DPPC=10⁻⁴–10⁻⁵ mol l⁻¹, the DPPC has very little effect on the whole adsorption process. In this case, the adsorption rate of mixed layers was mainly dominated by the protein adsorption. This phenomenon also happened as the protein concentration was further increased to 3.6 mg l⁻¹. When C_DPPC>3 · 10^–5 mol l⁻¹, the adsorption behaviour was very similar to that of the pure DPPC although the protein concentration was changed. The equilibrium interfacial tensions of the mixed layers are dramatically effected by the lipid as compared to the pure protein adsorption at the same concentration. It reveals the estimation of which composition of lipid and protein decreases the interfacial tension. The combination of Brewster angle microscopy (BAM) with a conventional LB trough was applied to investigate the morphology of the mixed DPPC/β-lactoglobulin layers at the air/water interface. The mixed insoluble monolayers were produced by spreading the lipid at the water surface and the protein adsorbed from the aqueous buffer subphase. The BAM images allow to visualise the protein penetration and distribution into the DPPC monolayer on compression of the complex film. It is shown that a homogeneous distribution of β-lactoglobulin in lipid layers preferentially happens in the liquid fluid state of the monolayer while the protein can be squeezed out at higher surface pressures.     

Preparation and electrical properties of new oxide ion conductors Ce6−xDyxMoO15−δ (0.0 ≤ x ≤ 1.8)

Ce_6−xDy_xMoO_15−δ (0.0 ≤ x ≤ 1.8) were synthesized by modified sol–gel method. Structural and electrical properties were investigated by means of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The XRD patterns showed that the materials were single phase with a cubic fluorite structure. Impedance spectroscopy measurement in the temperature range between 350 °C and 800 °C indicated a sharp increase in conductivity for the system containing small amount of Dy₂O₃. The Ce_5.6Dy_0.4MoO_15−δ detected to be the best conducting phase with the highest conductivity (σ_t = 8.93 × 10⁻³ S cm⁻¹) is higher than that of Ce_5.6Sm_0.4MoO_15−δ (σ_t = 2.93 × 10⁻³ S cm⁻¹) at 800 °C, and the corresponding activation energy of Ce_5.6Dy_0.4MoO_15−δ (0.994 eV) is lower than that of Ce_5.6Sm_0.4MoO_15−δ (1.002 eV).     

Shock membrane electropotential drops and limited diffusive distance of β-amyloids in cerebral neurons are detrimental enhancement to Alzheimer's diseases

Molecular physicobiochemical calculations indicated that the metallic ion binding to beta-amyloids (Aβ) may induce production of hydrogen peroxide, which triggers the Ca ion redistribution from the extracellular to the intracellular compartmentation, resulting in a transient membrane electropotential drop by at least 208.06 mV. Moreover, using the Mark and Houwink empirical equation, we predicted that the diffusible distances of all Aβ identities would be confined in a very tiny region within a radius less than 3.96 × 10⁻⁴ cm in brain at 192 h after produced. Because of the inherent tendency of aggregation behaved by the Aβs, the maximum diffusion coefficient and inherent viscosity were 8.24 × 10⁻¹⁵ cm² s⁻¹ and 72.15 cps for the 12 mers (40.8 kDa), the largest soluble form of ABs.Conclusively, we have quantitatively predicted that the shock membrane potential drop (Δφ > 208.06 mV) and limited diffusible distance (<3.96 × 10⁻⁴ cm) in the brain would contribute the major detrimental effects to the neurons in the Alzheimer's diseases.     

Diffusion of Sr and Zr in BaTiO3 single crystals

The diffusion of strontium and zirconium in single crystal BaTiO₃ was investigated in air at temperatures between 1000 °C and 1250 °C. Thin films of SrTiO₃, deposited by spin coating a precursor solution and thin films of zirconium, deposited onto the sample surfaces by sputtering, were used as diffusion sources. The diffusion profiles were measured by SIMS depth profiling on a time-of-flight secondary ion mass spectrometer (ToF-SIMS). The diffusion coefficients of strontium and zirconium were given by D_Sr = 3.6 × 10^2.0±4.4 exp[−(543 ± 117) kJ mol⁻¹/(RT)] cm² s⁻¹ and D_Zr = 1.1 × 10^1.0±2.1 exp[−(489 ± 56) kJ mol⁻¹/(RT)] cm² s⁻¹. The results are discussed in terms of different diffusion mechanisms in the perovskite structure of BaTiO₃.     

Preparation of high-permeance MFI membrane with the modified secondary growth method on the macroporous α-alumina tubular support

MFI membrane with high permeance was successfully synthesized on the macroporous (pore size of 3–4 μm) α-Al₂O₃ tubular support with a novel modified secondary growth method. Before the crystallization, the seeded support was wrapped with Teflon tape in order to focalize the growth of crystals in the region of seed layer. The as-synthesized membrane was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and single-gas permeation testing. The results indicated that the as-synthesized membrane had a thickness of 6–8 μm similar to the thickness of the seed layer and exhibited high gas permeance. At room temperature, the permeance of H₂ and the ideal separation factor of H₂/SF₆ reached 1.64 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ and 71, respectively. The permeance of single-gas increased with the increasing of temperature. The ideal separation factors of H₂/i-C₄H₁₀ and H₂/SF₆ decreased with the increasing of temperature from 298 to 473 K. At 473 K, the ideal separation factors of H₂/i-C₄H₁₀ and H₂/SF₆ were 12.16 and 11.08, which were still higher than their Knudsen ratios of 5.39 and 8.54, respectively.     

Chiral imidazole metalloenzyme models: Synthesis and enantioselective hydrolysis for α-amino acid esters

Chiral imidazole hydrolytic metalloenzyme models with characteristics of chiral centers directly link to imidazole N-atoms and varieties in both alkyl chain length and number of alkyl chains, have been synthesised and investigated for enantioselective hydrolysis of Boc-α-amino acid esters. The result indicates that both hydrolysis rates and enantioselectivities are increased with increases in the alkyl chain length and the number of the alkyl chains in the lipophilic chiral imidazole-type surfactants in many cases. The lipophilic chiral imidazole 4d ((S)-1-hexadecoxy-2-(1-imidazolyl)-propane), which has one long alkyl chain, shows higher hydrolysis rate and enantioselectivity (k_D = 132.5 × 10⁻⁵, k_D/k_L = 5.38), 5d ((S)-1,5-dihexadecoxy-2-(1-imidazolyl)-pentane), which has two long alkyl chains, shows the highest hydrolysis rate and enantioselectivity (k_D = 201.5 × 10⁻⁵, k_D/k_L = 11.72). Additionally, the effects of the metals, the additives, the solvents and the substrates on the hydrolysis rates and enantioselectivities are examined.     

Effect of the acyl group and the dodecylsulfonate chain on the inclusion of pyrene inside the cavity of β-cyclodextrin

The solubilization of pyrene in aqueous solution of β-cyclodextrin (β-CD) or its derivatives such as β-CD-hexanoyl, β-CD-benzoyl and β-CD-dodecylsulfonate was investigated by spectrophotometry. Linear and non-linear regression methods were used to estimate the association constants (K₁). A 1:1 stoichiometric ratio and different effects of the hexanoyl, benzoyl and dodecylsulfonate groups on the association constant were observed for the binary inclusion complex between pyrene and β-CD. The formation constant was shown to decrease when β-CD was modified by a dodecylsulfonate chain. The value of K₁ was 190 ± 10 L mol⁻¹ for the [pyrene/β-CD] complex and 145 L mol⁻¹ for the [pyrene/β-CD-dodecylsulfonate] complex. Partitioning of the pyrene molecules between the dodecylsulfonate chains and cyclodextrin cavities can explain the decrease in the association constant value. In the cases of β-CD-hexanoyl and β-CD-benzoyl derivatives, no association constants were detected. Results suggest that the high hydrophobicity of the hexanoyl and benzoyl groups prevents the inclusion of pyrene molecules inside the cyclodextrin cavity.     

Studies of the hydrogen evolution reaction on smooth Co and electrodeposited Ni–Co ultramicroelectrodes

The hydrogen evolution reaction (HER) was studied on smooth Co and on electrodeposited Ni–Co ultramicroelectrodes (UMEs) in alkaline solutions at several temperatures by steady-state polarisation curves. The real electrochemical area was previously estimated by cyclic voltammetry to account for the large difference in roughness factor of the two surfaces. The values obtained for the Tafel slopes were very close to 2.303RT/βnF while the ‘apparent’ energies of activation were 59 and 41 kJ mol⁻¹ for Co and Ni–Co, respectively. A common Volmer–Heyrovsky mechanism with Heyrovsky as the rate-determining step (RDS) was initially proposed. This was confirmed when the experimental results were mathematically treated by a non-linear fitting procedure using the kinetic equations derived for that mechanism. The calculations revealed that Ni–Co is a more efficient catalyst for the HER then pure Co, with a rate constant value of 0.16×10⁻¹⁰ mol s⁻¹ cm⁻² at 25°C for the slow step. Although this value is more than one order of magnitude smaller than that already reported for deposited Ni, it is considerably larger than the one measured here (0.02×10⁻¹⁰ mol s⁻¹ cm⁻²) for pure Co at 25°C.     

Preparation of “pore-fill” type Pd–YSZ–γ-Al2O3 composite membrane supported on α-Al2O3 tube for hydrogen separation

Mesoporous YSZ–γ-Al₂O₃ membranes were coated on α-Al₂O₃ (Ø2 mm) tube by dipping the α-Al₂O₃ support tube into mixed sol consists of nano-size YSZ and bohemite particles followed by drying and calcination at 600 °C. Addition of bohemite in YSZ sol helped a good adhesion and uniform coating of the membrane film onto α-Al₂O₃ support. The quality of the mesoporous YSZ–γ-Al₂O₃ membranes was evaluated by the gas permeability experiments. The number of defects was minimized when the γ-Al₂O₃ content became more than 40%. Addition of γ-Al₂O₃ inhibited the crystal growth of YSZ, sintering shrinkage and distortion stress. Increase of calcination temperature and time results in the increase of pore size and N₂ permeance. A hydrogen perm-selective membrane was prepared by filling palladium into the nano-pores of YSZ–γ-Al₂O₃ layer by vacuum-assisted electroless plating. Crystal growth of palladium was observed by thermal annealing of the membrane at 600 °C for 40 h. The Pd–YSZ–γ-Al₂O₃ composite membrane revealed improved thermal stability allowing long-term operation at elevated temperature (>500 °C). This has been attributed to the improved fracture toughness of YSZ–γ-Al₂O₃ layer and matching of thermal expansion coefficient between palladium and YSZ. Although fracture of the membrane did not occur, decline of H₂ flux was observed when the membrane was exposed in 600 °C. This has been attributed to the agglomeration of palladium particles by crystal growth and dense packing into the pore networks of YSZ–γ-Al₂O₃ by elevation of temperature.     

Kinetics of the R + HBr RH + Br (CH3CHBr, CHBr2 or CDBr2) equilibrium. Thermochemistry of the CH3CHBr and CHBr2 radicals

The kinetics of the reaction of the CH₃CHBr, CHBr₂ or CDBr₂ radicals, R, with HBr have been investigated in a temperature-controlled tubular reactor coupled to a photoionization mass spectrometer. The CH₃CHBr (or CHBr₂ or CDBr₂) radical was produced homogeneously in the reactor by a pulsed 248 nm exciplex laser photolysis of CH₃CHBr₂ (or CHBr₃ or CDBr₃). The decay of R was monitored as a function of HBr concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature. The reactions were studied separately from 253 to 344 K (CH₃CHBr + HBr) and from 288 to 477 K (CHBr₂ + HBr) and in these temperature ranges the rate constants determined were fitted to an Arrhenius expression (error limits stated are 1σ + Student’s t values, units in cm³ molecule⁻¹ s⁻¹, no error limits for the third reaction): k(CH₃CHBr + HBr) = (1.7 ± 1.2) × 10⁻¹³ exp[+ (5.1 ± 1.9) kJ mol⁻¹/RT], k(CHBr₂ + HBr) = (2.5 ± 1.2) × 10⁻¹³ exp[−(4.04 ± 1.14) kJ mol⁻¹/RT] and k(CDBr₂ + HBr) = 1.6 × 10⁻¹³ exp(−2.1 kJ mol⁻¹/RT). The energy barriers of the reverse reactions were taken from the literature. The enthalpy of formation values of the CH₃CHBr and CHBr₂ radicals and an experimental entropy value at 298 K for the CH₃CHBr radical were obtained using a second-law method. The result for the entropy value for the CH₃CHBr radical is 305 ± 9 J K⁻¹ mol⁻¹. The results for the enthalpy of formation values at 298 K are (in kJ mol⁻¹): 133.4 ± 3.4 (CH₃CHBr) and 199.1 ± 2.7 (CHBr₂), and for α-C–H bond dissociation energies of analogous compounds are (in kJ mol⁻¹): 415.0 ± 2.7 (CH₃CH₂Br) and 412.6 ± 2.7 (CH₂Br₂), respectively.     

η-Pentamethylcyclopentadienylruthenium(II) complexes containing η-coordinated α-amino acids

Reaction of [Cp* RuCl₂]₂ with -alanine ( -alaH) in methanol at room temperature in the presence of NaOMe yields the complex Na[Cp* RuCl( -ala)] (1), which contains a five-membered N,O-coordinated chelate ring. The analogous complex Na[Cp* RuCl( -phe)] (2) is obtained under similar conditions but at 0°C in 90% yield. At temperatures above 20°C both 2 and the η⁶-coordinated complex [Cp* Ru( -pheH)]Cl (4) are obtained, with the proportion of the latter increasing with temperature. Compound 4 is obtained in 88% yield by refluxing [Cp* RuCl₂]₂ and -phenylalanine ( -pheH) in CH₃OH/CH₃ONa followed by separation from 2. The analogous ruthenium(II) sandwich complexes 5–10 were obtained from -tyrosine and -tryptophane and various derivatives. [Cp* Ru( -met)] (3), prepared by the reaction of [Cp* RuCl₂]₂ with -methionine ( -metH) in CH₃OH/CH₃ONa, displays N,O,S-coordination.     

Reduction of α,β unsaturated carbonyl compounds by Ni–BH4

The reduction of α,β unsaturated carbonyl compounds by sodiumborohydride is catalysed by Ni(bpy)Cl₂ (bpy=2,2′-bipyridine). Various carbonyl compounds having the general formula R₁CH=CHCRO [where R₁, R=C₆H₅, H; p-MeO---C₆H₄---,C₆H₄; p-CH₃---C₆H₄, C₆H₅; (m-OMe---)(p-OMe---)C₆H₃, C₆H₅; C₆H₅, (CH₃)₂CH---; CH₃, H; m-Br---C₆H₄---, C₆H₅] are reduced to corresponding allylicalcohol [R₁CH=CHCRHOH] at 25°C within half an hour. During these reductions the double bond is partially reduced to give saturated alcohols as minor products having the molecular formula R₁CH₂CH₂CRHOH. The reduction of trans-3-phenyl-2-propenal with NaBH₄ and catalytic amounts of Ni(bpy)Cl₂ in solvents containing active deuterium (D₂O, CD₃OD), leads to the partial incorporation of deuterium at the α and γ positions to give C---D bonded alcohols.     

Studies on kinetics of complexation of lanthanide α-hydroxycarboxylates with 1,10-phenanthroline

Kinetics of the coordination reaction of lanthanide (La^III, Eu^III) α-hydroxycarboxylates [LnL₃(H₂O)₂] with 1,10-phenanthroline (phen) in methanol-water (v/v, 3:2) were studied at 25°C by calorimetric titration. A one-step reaction process in accordance with the rate law has been suggested. The reaction is found to be first order for both lanthanide α-hydroxycarboxylates and phen. We have evaluated rate constants of the reactions. It is found that a linear free energy relationship exists between the stability constants of the lanthanide-α-hydroxycarboxylate-phen ternary complex and the rate constants. It is also found that a linear free energy relationship exists between the rate constants of La-hydroxycarboxylate with phen and the acid strength of α-hydroxy-acid as primary ligand, but the linear free energy relationship does not exist in the Eu-α-hydroxycarboxylate-phen ternary complex. The influence of other factors upon the reaction rate constants was also discussed.     

Free‐radical copolymerization of styrene and m‐isopropenyl‐α,α′‐dimethylbenzyl isocyanate studied by 1H NMR kinetic experiments

The free‐radical copolymerization of m‐isopropenyl‐α,α′‐dimethylbenzyl isocyanate (TMI) and styrene was studied with ¹H NMR kinetic experiments at 70 °C. Monomer conversion vs time data were used to determine the ratio k_p × k_t^?0.5 for various comonomer mixture compositions (where k_p is the propagation rate coefficient and k_t is the termination rate coefficient). The ratio k_p × k_t^?0.5 varied from 25.9 × 10^?3 L^0.5 mol^?0.5 s^?0.5 for pure styrene to 2.03 × 10^?3 L^0.5 mol^?0.5 s^?0.5 for 73 mol % TMI, indicating a significant decrease in the rate of polymerization with increasing TMI content in the reaction mixture. Traces of the individual monomer conversion versus time were used to map out the comonomer mixture composition drift up to overall monomer conversions of 35%. Within this conversion range, a slight but significant depletion of styrene in the monomer feed was observed. This depletion became more pronounced at higher levels of TMI in the initial comonomer mixture. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1064–1074, 2002     

Preparation and hydrogen permeation of SrCe0.95Y0.05O3−δ asymmetrical membranes

Asymmetrical thin membranes of SrCe_0.95Y_0.05O_3−δ (SCY) were prepared by a conventional and cost-effective dry pressing method. The substrate consisted of SCY, NiO and soluble starch (SS), and the top layer was the SCY. NiO was used as a pore former and soluble starch was used to control the shrinkage of the substrate to match that of the top layer. Crack-free asymmetrical thin membranes with thicknesses of about 50 μm and grain sizes of 5–10 μm were successfully pressed on to the substrates. Hydrogen permeation fluxes (J_H2) of these thin membranes were measured under different operating conditions. At 950 °C, J_H2 of the 50 μm SCY asymmetrical membrane towards a mixture of 80% H₂/He was as high as 7.6 × 10⁻⁸ mol/cm² s, which was about 7 times higher than that of the symmetrical membranes with a thickness of about 620 μm. The hydrogen permeation properties of SCY asymmetrical membranes were investigated and activation energies for hydrogen permeation fluxes were calculated. The slope of the relationship between the hydrogen permeation fluxes and the thickness of the membranes was −0.72, indicating that permeation in SCY asymmetric membranes was controlled by both bulk diffusion and surface reaction in the range investigated.     

Benzeneacetaldehyde-4-hydroxy-alpha-oxo-aldoxime as a new analytical reagent for the spectrophotometric determination of cobalt

Benzeneacetaldehyde-4-hydroxy-α-oxo-aldoxime is proposed as a new sensitive and selective reagent for the spectrophotometric determination of cobalt. The reagent reacts with cobalt in the pH range 8.6–9.4 to form a yellow colored 1:3 chelate which is very well extracted in chloroform. Beer's law is obeyed in the concentration range 0.05–1.3 μg ml⁻¹ cobalt. The molar absorptivity of the extracted species is 2.746×10⁴ l mol⁻¹ cm⁻¹ at 390 nm. The proposed method is highly sensitive, selective, simple, rapid, accurate and has been satisfactorily applied for the determination of cobalt in synthetic mixtures, pharmaceutical samples, biological samples and alloys.     

Strictly Regiocontrolled α-Monosubstitution of Cyclic Carbonyl Compounds with Alkynyl and Alkyl Groups via Pd-Catalyzed Coupling of Cyclic α-Iodoenones with Organozincs[]

The conditions for the Pd-catalyzed cross coupling of cyclic α-iodoenones, such as 2-iodo-2-cyclohexenone, with alkynylzincs have been optimized. The use of tris(o-furyl)phosphine (TFP) as a ligand and DMF as a solvent has led to the formation of α-alkynylenones in excellent yields. This optimized procedure has been applied to the synthesis of (±)-harveynone and (±)-tricholomenyn A in high yields. Investigation of related α-alkylation reactions using alkylzincs has revealed the following. Methylzinc and primary alkylzinc derivatives readily undergo Pd-catalyzed cross coupling with α-iodoenones. Although (s-Bu)₂Zn also undergoes Pd-catalyzed cross coupling, only the n-Bu-substituted products were obtained. α-Benzylation and α-homobenzylation can proceed satisfactorily, whereas allylzinc and propargylzinc derivatives undergo only addition to the carbonyl group. Although some promising results have been obtained in α-homoallylation and α-homopropargylation, these reactions need to be further improved.     

Study on dynamic interfacial tension of 3-dodecyloxy-2-hydroxypropyl trimethyl ammonium bromide at liquid/liquid interface

Dynamic interfacial tension between aqueous solutions of 3-dodecyloxy-2-hydroxypropyl trimethyl ammonium bromide (R₁₂HTAB) and n-hexane were measured using the spinning drop method. The effects of the R₁₂HTAB concentration (the concentration below the CMC) and temperature on the dynamic interfacial tension have been investigated; the reason of the change of dynamic interfacial tension with time has been discussed. The effective diffusion coefficient, D_a, and the adsorption barrier, _a, have been obtained from the experimental data using the extended Word–Tordai equation. The results show that the dynamic interfacial tension becomes smaller while _a becomes higher with increasing R₁₂HTAB concentration in the bulk aqueous phase. D_a decreases from 5.56 × 10⁻¹² m⁻² s⁻¹ to 0.87 × 10⁻¹² m⁻² s⁻¹ while _a increases from 5.41 kJ mol⁻¹ to 7.74 kJ mol⁻¹ with the increase of concentration in the bulk solution of R₁₂HTAB from 0.5 × 10⁻³ mol dm⁻³ to 4 × 10⁻³ mol dm⁻³. Change of temperature affects the adsorption rate through altering D_a and _a. The value of D_a increases from 5.56 × 10⁻¹² m⁻² s⁻¹ to 13.98 × 10⁻¹² m⁻² s⁻¹ while that of _a decreases from 5.41 kJ mol⁻¹ to 5.07 kJ mol⁻¹ with temperature ascending from 303 K to 323 K. The adsorption of surfactant from the bulk phase into the interface follows a mixed diffusion–activation mechanism, which has been discussed in the light of interaction between surfactant molecules, diffusion and thermo-motion of molecules.     

Sub- and post-micellar catalytic and inhibitory effects of cetlytrimethylammonium bromide in the permanganate oxidation of phenylalanine

The kinetics of phenylalanine (phe) oxidation by permanganate has been investigated in absence and presence of cetlytrimethylammonium bromide (CTAB) using conventional spectrophotometric technique. The rate shows first- and fractional-order dependence on [MnO₄⁻] and [phe] in presence of CTAB. At lower values of [CTAB] (≤10.0 × 10⁻⁴ mol dm⁻³), the catalytic ability of CTAB aggregates are strong. In contrast, at higher values of [CTAB] (≥10.0 × 10⁻⁴ mol dm⁻³), the inhibitory effect was observed in absence of H₂SO₄. We find that anions (Br⁻, Cl⁻ and NO₃⁻) in the form of sodium salts are strong inhibitors for the CTAB catalyzed oxidation. Kinetic and spectrophotometric evidences for the formation of an intermediate complex and an ion-pair complex between phe and MnO₄⁻, CTAB and MnO₄⁻, respectively, are presented. A mechanism consistent with kinetic results has been discussed. Complex formation constant (K_c) and micellar binding constant (K_s) were calculated at 30 °C and found to be K_c = 319 mol⁻¹ dm⁻³ and K_s = 1127 mol⁻¹ dm⁻³, respectively.     

Dynamical Spin Chirality and Magnetoelectric Effect of α-Glycine

Dynamical spin chirality of α-glycine crystal at 301−302 K was investigated by DC (direct current)-magnetic susceptibility measurement at temperatures ranging from 2 to 315 K under the external magnetic fields (H=±1 T) parallel to the b axis. The α-glycine crystallizes in space group P2₁/n with four molecules in a cell, which has centrosymmetric charge distribution. The bifurcated hydrogen bonds N⁺(3)−H(8)···O(1) and N⁺(3)−H(8)···O(2) are stacked along the b axis with different bond intensities and angles, which form anti-parallel double layers. Atomic force spectroscopy result at 303 K indicated that the surface molecular structures of α-glycine formed a regular flexuous framework in the b axis direction. The strong temperature dependence is related to the reorientation of NH³⁺ group and the electron spin flip-flop of (N⁺H) mode. Under the opposite external magnetic field of 1 T and −1 T, the electron spins of N⁺(3)−H(8)···O(1) and N⁺(3)−H(8)···O(2) flip-flop at 301−302 K. These results suggested a mechanism of the magnetoelectric effect based on the dynamical spin chirality of (N⁺H), which induced the electric polarization to produce the onset of pyroelectricity of α-glycine around 304 K.