The enthalpy of sorption of glycine from aqueous solutions by carboxyl cationites in the copper and mixed forms

The influence of glycine solution acidity on glycine interactions with carboxyl cationites in the copper and mixed sodium-copper forms was studied by the calorimetric, sorption, and IR spectroscopy methods. The enthalpies of sorption of glycine on KB-2 and KB-4 at various pH were determined.     

Determination of the enthalpy of solute-solvent interaction from the enthalpy of solution: aqueous solutions of erythritol and L-threitol

In this work the enthalpy of the solute-solvent interaction of erythritol and L-threitol in aqueous solution was determined from the values obtained for the enthalpy of solvation. The values for this property were calculated from those determined for the enthalpies of solution and sublimation. To determine the values of the enthalpy of solute-solvent interaction, the solvation process is considered as taking place in three steps: opening a cavity in the solvent to hold the solute molecule, changing the solute conformation when it passes from the gas phase into solution, and interaction between the solute and the solvent molecules. The cavity enthalpy was calculated by the scaled particle theory and the conformational enthalpy change was estimated from the value of this function in the gas phase and in solution. Both terms were determined by DFT calculations. The solvent effect on the solute conformation in solution was estimated using the CPCM solvation model. The importance of the cavity and conformational terms in the interpretation of the enthalpy of solvation is noted. While the cavity term has been used by some authors, the conformational term is considered for the first time. The structural features in aqueous solution of erythritol and L-threitol are discussed.     

The enthalpy of formation of the praseodymium ion (3+) in an infinitely dilute aqueous solution

The enthalpy of reaction between praseodymium metal and 1.07 n HCl and the enthalpy of solution of praseodymium trichloride in 1.07 n HCl and water were measured in a swinging isoperibol calorimeter at 298.15 K. The results were used to calculate the enthalpy of formation of the praseodymium ion in the state of an infinitely dilute aqueous solution, Δ_f H°_298.15 Pr³⁺(sln, ∞H₂O) = ?687.8 ± 1.7 kJ/mol.     

树枝状大分子与双十二烷基二甲基溴化铵在溶液中的分子间相互作用

通过负染色与冷冻蚀刻透射电子显微镜(TEM)、流变学性能测试等方法,研究了以1.0代聚酰胺-胺(PAMAM)为核心、以(PO)m(EO)n(其中PO与EO分别是环氧丙烷、环氧乙烷的缩写,m和n分别代表嵌段中PO和EO的个数)为辐射臂的树枝状大分子与双十二烷基二甲基溴化铵(DDAB)的分子间相互作用,并将此混合体系的聚集行为、流变学特性与DDAB的囊泡体系进行了比较.研究表明,由于DDAB分子可能插入到树枝状大分子聚集体的疏水微区中,使得混合体系中DDAB类似于凝胶的结构几乎被破坏,随其浓度的增加,混合体系中仅形成了DDAB单层囊泡及其与树枝状大分子构成的复合物,导致剪切后的黏度大幅下降,同时体系几乎不再具有黏弹性特征.     

The temperature dependence of the exchange enthalpy of calcium and sodium ions on polymethacrylic and polyacrylic cationites

The influence of temperature on the exchange of calcium and sodium ions from solutions of 2.3–2.8 g-equiv/l concentrations on KB-2e4 gel polyacrylic cationite, KB-4P2 and KB-4 gel polymethacrylic cationites, and Purolite C104 polyacrylic cationite was studied over the temperature range 273–400 K. It was shown that, simultaneously with a substantial increase in selectivity with respect to calcium ions, the differential enthalpy of the ion exchange reaction increased linearly on all polyacrylic and polymethacrylic cationites as the temperature grew.     

Thermodynamic characteristics of the interaction between nicotinic acid and phenylalanine in an aqueous buffer solution at 298 K

The interaction between L-phenylalanine and nicotinic acid is studied by solution calorimetry in an aqueous buffer solution (pH 7.35) at different ratios of the reagents. Experimental data on the enthalpy of dissolution of amino acid in the buffer solution of nicotinic acid at 298.15 K are calculated. The values of thermodynamic parameters for the complexation of L-phenylalanine with nicotinic acid are calculated. It is shown that the formation of a 1: 2 molecular complex is stabilized by the entropy factor due to the dominant role of the dehydration effect of initial reagents.     

Molecular simulation studies on the interaction between different polymers in aqueous solution

A molecular dynamics simulation was performed to investigate the aggregates of mixing and the interaction between different polymers in aqueous solution. These polymers include partially hydrolyzed polyacryamide (HPAM), hydroxyethylcellulose (HEC) and polyvinylpyrrolidone (PVP). The structures of mixed aggregates were analyzed from the dihedral angle distribution of: (1) pure HPAM; (2) HPAM in aqueous solution; (3) HPAM with small segments of PVP or HEC in aqueous solution. At the same time, the simulated IR spectra and the calculated interaction parameters were used to distinguish the different interactions between HPAM and PVP or HEC. In order to confirm the validity of the simulated predictions, experimental IR spectra of polymer systems were made, and the specific viscosity of the HPAM and PVP or HEC system was measured using capillary viscometry. It can be seen from the viscosity measurements that the viscosity of the HPAM/PVP system in aqueous solution decreases linearly with an increase in concentration of PVP, whereas a maximum viscosity value appears with the increase in concentration of HEC in the HPAM/HEC system. The conclusion was drawn that the interaction between HPAM and HEC is stronger than the one between HPAM and PVP, and that molecular simulation can be considered as an adjunct to experiments and can provide otherwise inaccessible (or, not easily accessible) microscopic information that experimentalists can use.     

Influence of wettability and surface charge on the interaction between an aqueous electrolyte solution and a solid surface

The hydrodynamic drainage force of a Newtonian aqueous electrolyte solution squeezed between two surfaces of different wettability was measured using the AFM colloidal probe technique. The surface hydrophobicity, roughness, polarity and approach velocity, and thus the shearing rate of the liquid, were controlled. A direct relationship between the mobility of the aqueous electrolyte solution close to the surfaces and the hydrophobicity of the surfaces was not established. We predict that the mobility of the liquid depends in a more complex fashion on the polarity and charge of the surfaces and on the properties of the electrolyte.     

DFT study on the interaction between monomeric aluminium and chloride ion in aqueous solution

The interaction of monomeric aluminium and chloride ion in aqueous solution is investigated by density functional theory (DFT) calculations. The computational results show that it is difficult for Cl(-) to enter the inner-coordination shell of aluminium complexes by replacing the bound water molecules, independent of pH and the concentration of Cl(-). However, pH and the concentration of Cl(-) might influence the conformations, bond lengths and natural charge populations of monomeric aluminium complexes to a given extent. Based on the computed Gibbs energies, pK(a) values of various hydrolysis species in the presence and absence of Cl(-) are evaluated, respectively. It is concluded that pK(a) increases with the introduction of Cl(-).     

Glass transition and enthalpy relaxation of ethylene glycol and its aqueous solution

Differential scanning calorimetry (DSC) and cryomicroscopy were employed to investigate the glass transition and enthalpy relaxation behaviors of ethylene glycol (EG) and its aqueous solution (50% EG) with different crystallization percent. Isothermal crystallization method was used in devitrification region to get different crystallinity after samples quenched below glass transition temperature. The DSC thermograms upon warming showed that the pure EG has a single glass transition, while the 50% EG solution has two if the solution crystallized partially. It is believed that the lower temperature transition represents the glass transition of bulk amorphous phase of EG aqueous solution glass state, while the higher one is related to ice inclusions, whose mobility is restricted by ice crystal. Cryomicroscopic observation indicated that the EG crystal has regular shape while the ice crystal in 50% EG aqueous solution glass matrix has no regular surface. Isothermal annealing experiments at temperatures lower than T_g were also conducted on these amorphous samples in DSC, and the results showed that both the two amorphous phases presented in 50% EG experience enthalpy relaxation. The relaxation process of restricted amorphous phase is more sensitive to annealing temperature.     

The standard potential of copper amalgam electrode and the activity coefficient of copper sulphate in aqueous solution

A simple and easily reproducible method for obtaining the e.m.f. of the cell Cu(Hg)/CuSO₄(m)/Hg₂SO₄, Hg and for avoiding the formation of red deposit on the amalgam electrode is described. E.M.F. readings of the cell for CuSO₄ concentration ranging from 0.01 to 1.0 m were recorded. Methods which have been used to calculate the E° of the cell have been reviewed and a value of +0.3443 V was obtained for the standard potential of the copper amalgam electrode.     

13C n.m.r. studies of the interaction of HgII with methionine and selenamethionine in the acidic aqueous solution

Summary The interactions of L-methionine (Met) and DL-selenamethionine (SeMet) with Hg²⁺ were studied using¹³C n.m.r. spectroscopy in aqueous acid. Hg²⁺ binds to the selenoether group of SeMet and the thioether group of Met exclusively. The selenoether group binds more strongly than thioether.     

Lidocaine and soyasterole-PEG-16-ether — investigations on the interaction between an amphiphilic drug and a nonionic surfactant in aqueous solution

In order to study the interactions between the surface active local anaesthetic drug lidocaine and the nonionic surfactant soyasterole-PEG-16-ether firstly the self association of the drug in aqueous solution was investigated by different methods. Transmission electron microscopy hinted at micellization and surface tension measurements resulted in a CMC of 12.9% (salt form) and 0.08% (base form), respectively, whereas solubilization experiments, NMR spectroscopy and osmotic pressure measurements obviously disproved the existence of drug micelles. The detected CMC only meant a surface saturation and the TEM pictures probably showed artifacts. In diluted systems containing both drug and surfactant no formation of mixed micelles took place, as pointed out by the tensiometric determination of the CMC of the mixtures showing no minimum in the CMC/% drug-curve. Also, gel permeation chromatography clearly separated surfactant micelles and drug molecules. In contrast to this, evident interactions between the base form of the drug and the surfactant occurred when the drug concentration was increased: the dynamic viscosity of the systems rose distinctly, probably caused by growth of the surfactant associates to a more rodlike form. The salt form had nearly no influence on the viscosity of the preparations.     

The van der Waals interaction between protein molecules in an electrolyte solution

In this report we present a general formulation to calculate the van der Waals interaction between two protein molecules in an electrolyte solution using boundary element method of solving linearized Poisson-Boltzmann equation. Our formulation is based upon an inhomogeneous dielectric model of proteins at the residue level. Our results for bovine pancreatic trypsin inhibitor at various relative orientations indicate that the anisotropy of the interaction can be tens of kBT.