Zhenning Yan

Viscosity behavior of some α-amino acids and their groups in water–sodium acetate mixtures

Abstract Viscosities of glycine, dl -α-alanine, dl -α-amino- n -butyric acid, dl -valine and dl -leucine have been determined in water–sodium acetate mixtures at 298.15 and 308.15 K. The viscosity B -coefficients have been calculated. The corresponding activation free energies (Δμ 2 0≠ ) for viscous flow have been evaluated with the help of the Feakins equation. The contributions of the charged end group (NH 3 + ,COO − ) and CH 2 groups of the amino acids to B -coefficient and Δμ 2 0≠ have been also determined using the linear correlation between B -coefficient or Δμ 2 0≠ and the number of carbon atoms in alkyl chains of the amino acids. The results have been interpreted in the light of the solute–solvent interactions in aqueous media.

Effect of temperature on viscosity properties of some α-amino acids in aqueous urea solutions

Abstract Viscosities for solutions of glycine, dl -α-alanine, dl -α-amino- n -butyric acid, dl -valine, dl -leucine and l -serine in 5 mol kg −1 aqueous urea have been determined at 278.15, 288.15, 298.15 and 308.15 K. The viscosity B -coefficients for the amino acids in the aqueous urea solution have been calculated at different temperatures. The effect of temperature on the B -coefficients is discussed on the basis of the Feakins equation. The contribution of solute to the activation parameters (Δ μ 2 0≠ , Δ H 2 0≠ , Δ S 2 0≠ ) for viscous flow of the solution have been calculated, together with the Gibbs energy, enthalpy and entropy of transfer for the amino acids from the ground-state solvent to the hypothetical viscous transition state solvent. The contributions of the charged end group (NH 3 + , COO − ) and CH 2 groups of the amino acids to B -coefficient and Δ μ 2 0≠ have been also estimated using the linear correlations between B -coefficient or Δ μ 2 0≠ and the number of carbon atoms in the alkyl chains of the amino acids. All the activation parameters are discussed in terms of the solutesolvent interactions in the ground and transition states.

Apparent molar volume, conductivity, and fluorescence studies of ternary systems of dipeptides + ionic liquids ([Cnmim]Br, n = 10, 14) + water at different temperatures

Densities, conductivities, and fluorescence spectra of two imidazolium ionic liquids ([Cnmim]Br, n = 10, 14)-glycyl dipeptide-water mixtures were measured as a function of temperature. The density data have been utilized to calculate the apparent molar volumes, standard partial molar volumes (V2,φ0), standard partial molar volumes of transfer from water to aqueous ionic liquids solutions (ΔtV°), the hydration number (NH), partial molar expansibility (Eφ0), and Hepler’s constant of glycyl dipeptides. Through the electrical conductivity measurements, the ccmc values at different temperatures and a series of thermodynamic parameters (ΔGmo, ΔHmo, and ΔSmo) of micellization of [Cnmim]Br (n = 10, 14) in aqueous glycyl dipeptides solutions are evaluated. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of [Cnmim]Br with glycyl dipeptide, and the aggregation behavior of [Cnmim]Br (n = 10, 14). The results shown above have been explained in terms of solute–solvent interactions and structural changes in the mixed solutions. The interaction between [Cnmim]Br (n = 10, 14) and glycyl dipeptide is affected by temperature and hydrocarbon chain length of the dipeptides.

Selective electrodes for [PF6]− and [BF4]− anions based on the associates formed by ionic liquid and cationic dyes

The feasibility of the newly synthesized ionic associates L1 and L2 formed by ionic liquid [C4mim][PF6] and cationic dyes (malachite green and methylene blue) has been tested as a novel ionophore for the preparation of anion-selective polymeric membrane electrodes. The electrode exhibits Nernstian response and enhanced potentiometric selectivity towards [PF6](-) compared to many other anions. The influence of some experimental parameters such as membrane composition, nature of plasticizer and amount of additive on the potential response of the [PF6](-) sensor are investigated. Under the optimized conditions, the response slopes of the membrane electrodes towards [PF6](-) are 59.7±0.5 and 58.1±0.5 mV/decade based on ionophore L1 and L2, respectively, in 1.0×10(-5)-1.0×10(-1) or 1.0×10(-6)-1.0×10(-1) mol/L concentration range. Interestingly, the optimized electrodes based on ionophores L1 and L2 also exhibit Nernstian response characteristics (60.3±0.5 and 56.0±0.5 mV/decade) for tetrafluoroborate anion [BF4](-) in a wide concentration range. Thus, the proposed sensor has been used for the determination of [PF6](-) and [BF4](-) in aqueous ionic liquids samples and the solubility of the [PF6](-) and [BF4](-) based ionic liquids in water. The satisfactory results are obtained.

Conductometric and fluorescence probe investigations of molecular interactions between dodecyltrimethylammonium bromide and dipeptides

The effect of five dipeptides (glycylglycine, glycyl-l-valine, glycyl-l-leucine, glycyl-l-glutamine, and l-alanyl-l-glutamine) on the micellar properties of catonic surfactant dodecyltrimethylammonium bromide (DTAB) has been investigated by electrical conductivity and fluorescence spectroscopy. From the conductivity data, the critical micellar concentration (ccmc), counterion binding constant (β), and thermodynamic parameters of micellization (ΔGmo, ΔHmo and ΔSmo) have been calculated. The effect of dipeptides on the micellar properties of DTAB depends upon their nature and concentration as well as on temperature and has been used to study the interactions present in the micellar systems. Enthalpy–entropy compensation effect has also been observed. The pyrene fluorescence spectra were used as an index for the estimation of micropolarity of micellar produced by the interaction of DTAB with dipeptides and the aggregation behavior of DTAB. Comparison on the interactions between different types of surfactants and dipeptide showed that the order of the strength for these interactions is TX-100 < DTAB < SAS < SDS.