A study of the thermodynamics of chitosan interaction with polyvinyl alcohol and polyethylene oxide by differential scanning calorimetry

Chitosan/polyvinyl alcohol and chitosan/polyethylene oxide blend films were prepared by coagulation from solutions. The interaction energy density B and interaction parameter x ₁₂ of the components were estimated from the change in the melting point of the synthetic component in the blends.     

Full factorial experimental design applied to oxalic acid photocatalytic degradation in TiO2 aqueous suspension

Full factorial experimental design technique was used to study the main effects and the interaction effects between operational parameters in the photocatalytic degradation of oxalic acid in a batch photo-reactor using TiO₂ aqueous suspension. The important parameters which affect the removal efficiency of oxalic acid such as agitation, initial concentration, volume of the solution and TiO₂ dosage were investigated. The parameters were coded as X₁, X₂, X₃ and X₄, consecutively, and were investigated at two levels (−1 and +1). The effects of individual variables and their interaction effects for dependent variables, namely, photocatalytic degradation efficiency (%) were determined. From the statistical analysis, the most effective parameters in the photocatalytic degradation efficiency were initial concentration and volume of solution. The interaction between initial concentration, volume of solution and TiO₂ dosage was the most influencing interaction. However, the interaction between agitation, initial concentration and volume of solution was the least influencing parameter.     

Synthesis and magnetic properties of an iminonitroxide-substituted phenolate–Cu complex

A new spin-chelate, iminonitroxide-substituted phenolate–copper complex (1), was designed and prepared. The structure of the complex 1 was considerably deviated from a square-planar geometry. The dihedral angle between the two planes defined by a set of copper, oxygen and nitrogen atoms was about 41°. The complex was found to have a relatively strong ferromagnetic interaction and a weaker antiferromagnetic interaction: J/k_B=+250 K and θ=−17 K using a three-spin model. The ferromagnetic interaction was assigned to the intramolecular interaction between the copper atom and the iminonitroxide. The antiferromagnetic interaction was assigned as an intermolecular interaction. These assignments were supported by susceptibility measurements for the diluted sample in polyvinyl chloride (PVC) film. The antiferromagnetic interaction was tentatively assigned due to the observed short intermolecular contacts between the C5 and O1 atoms or between the H5 and O1 atoms.     

Polaron interaction energies in reduced tungsten trioxide

Consideration of the properties of reduced tungsten trioxide suggest that the mobile charge carriers are polarons. As it is uncertain how the presence of polarons will influence the microstructures of the crystallographic shear (CS) planes present in reduced tungsten trioxide we have calculated both the polaron-CS plane and polaron-polaron interaction energy for a variety of circumstances. Three CS plane geometries were considered, {102}, {103}, and {001} 1CS plane arrays, and the nominal compositions of the crystals ranged from WO_2.70 to WO_3.0. The polarons were assumed to have radii from 0.6 to 1.0 nm and the polaron-CS plane electrostatic interaction was assumed to be screened. The results suggest that for the most part the total interaction energy is small and is unlikely to be of major importance in controlling the microstructures found in CS planes. However, at very high polaron densities the interaction energy could be appreciable and may have some influence on the existence range of CS phases.     

Investigation on the preparation and chromatographic behavior of a new para-tert-butylcalix[4]arene-1,2-crown-4 stationary phase for high performance liquid chromatography

In the present work, a new para-tert-butylcalix[4]arene-1,2-crown-4 bonded silica stationary phase (CBS4-4) was synthesized, structurally characterized, and employed to separate polycyclic aromatic hydrocarbons (PAHs), phenols, aromatic amines, benzoic acid and its derivatives. The chromatographic behaviors of the prepared stationary phase were investigated and compared with ODS. The effects of methanol concentrations on the retention index show that CBS4-4 exhibits high selectivity for the above analytes. The separation mechanisms based on the different interactions between calixarene and the analytes were discussed. With the assistance of quantum chemistry calculation, the interaction Gibbs free energy change ΔG_solv (in the mobile phase) of p, m and o-phenylenediamine positional isomers and para-tert-butylcalix[4]arene-1,2-crown-4 were obtained. The ΔG_solv values were consistent with the retention behavior of p, m and o-phenylenediamine on the CBS4-4. According to the chromatographic data, it can be concluded that the selectivity of CBS4-4 for analytes is mainly ascribed to hydrophobic interaction, accompanied by other effects such as hydrogen bonding interaction, π-π and inclusion interaction. The CBS4-4 column has been successfully employed for the analysis of benzoic acid in Sprite drink.     

Long-range interaction and the dynamics of nonadiabatic transitions in collisions of the I2(E) molecule with inert gas atoms

A special form of perturbation theory based on intermolecular interaction was used to analyze the contributions to the interaction energy between a homonuclear diatomic molecule with dipole-coupled electronic states n and n′ and a neutral particle A. At large distances, the energy of the system in both states n and n′ is determined by the induction contribution similar to the induction interaction of particle A and a polar molecule. The presence of a constant electric moment of particle A gives an electrostatic contribution to the matrix element of the nonadiabatic coupling of the states n and n′. The equations obtained were specialized to describe the interaction of the iodine molecule excited to ion-pair states with an inert gas atom and used as corrections to the potential energy surfaces of this system constructed within the diatomics-in-molecule approximation. The dynamics of transitions between the ion-pair states of the I₂ molecule induced by collisions with the Ar and He atoms was calculated. The results demonstrate the importance of correctly including long-range interaction.     

Some peculiarities of thermodynamic behaviour of oligomeric mixtures with specific interactions between components

Using inverse gas chromatography, the temperature and concentration dependences of the interaction parameter χ₂₃ were estimated for mixtures of various oligomers capable of specific interaction. Mixtures of polyethylene glycol with polypropylene glycol and polyethylene glycol adipate were studied, including mixtures of polyethylene glycol fractions of different molecular weights. It was found that there is a maximum and a minimum in the temperature dependence of χ₂₃, and the bimodal character phase diagrams was established. Experimental data were explained by aggregation or association phenomena in mixtures. The comparison of experimental values of χ₂₃ with those calculated on the basis of the new Flory theory shows essential differences, especially for enthalpy and entropy contributions, this being explained by the specific interaction between components.     

A comparative study of interaction of ibuprofen with biocompatible polymers

In this paper we are reporting the interaction of a non-steroidal anti-inflammatory drug ibuprofen (IBF) with various biocompatible polymers. Being amphiphilic, the drug interacts with the polymers similar to the interaction of surfactants and polymers. Therefore, we have considered the polymer-amphiphile interaction approach using conductimetry. The polymers of different charges (cationic, anionic, and nonionic) have been taken for the study. It was found that the critical aggregation concentration (cac) decreases on increasing the polymer concentrations of cationic as well as nonionic polymers whereas it increases for anionic polymers. The results imply that anionic IBF interacts with cationic and nonionic polymers more strongly as compared to the anionic polymers. A possible anionic-anionic repulsion is responsible for the weak interaction of IBF with anionic polymers. On the other side, the critical micelle concentration (cmc) increases for all polymers which is a usual indication of the interaction between amphiphiles and polymers. Free energies of aggregation (ΔG_agg) and micellization (ΔG_mic) were also computed with the help of degrees of micelle ionization obtained from the specific conductivity - [IBF] isotherms.     

Photoelectron spectra of organic compounds—VI : Exocyclic methylene compounds

The photoelectron spectra of methylene and dimethylene derivatives of bridged and unbridged cyclohexane and cyclohexene were recorded and interpreted on the basis of an LCBO model. The conjugative interaction is found to be appreciably smaller for exocyclic cis-dienes than for the corresponding endocyclic cis-dienes, whereas the homoconjugative interaction between exocyclic and endocyclic double bonds and between two endocyclic double bonds is about the same.     

Investigation of the Interaction Between Novel Spiro Thiazolo[3,2-a][1,3,5]Triazines and Bovine Serum Albumin by Spectroscopic Methods

The interaction between novel spiro thiazolo[3,2-a][1,3,5]triazines (NSTT) and bovine serum albumin (BSA) was investigated using fluorescence and ultraviolet spectroscopy at different temperatures (302 and 310 K) under imitated physiological conditions. The experimental results show that the fluorescence quenching mechanism between NSTT and BSA is by a static quenching mechanism. The binding constant (K _a) and number of binding sites (n) between NSTT and BSA at different temperatures were obtained. Negative values of ?G°, ?H°, and ?S° indicate that the interaction between NSTT and BSA is driven by hydrogen bonds and van der Waals forces. Using the Förster non-radiation energy transfer theory, the binding distance between BSA and NSTT was calculated. These results provide valuable information on the interaction between NSTT and BSA as well as the influence of substituent groups on the interaction.     

The interaction of polar aromatic molecules with neutral (polar) polymers and polyanions in aqueous solution

The interaction of aniline, pyridine and its homologues, phenol and benzamide with a series of neutral polar polymers and polyanions in aqueous solution has been studied by the equilibrium dialysis method. The interaction isotherms were generally sigmoidal. Significant association between polymer and organic molecule was only observed beyond some specific free organic molecule-polymer concentration ratio; i. e., after inter-chain attractive forces and solvation have been partially weakened by preliminary absorption of a surface layer of organic molecules. Benzamide, in fact, shows practically no interaction with neutral ‘coiled’ polymers. Maximum interaction is reached at up to thirty percent utilisation of ‘polar’ sites on the polymer chain. Klotz's method was modified to correct for these weak interactions at low organic molecule concentration. Equilibrium constants and free energies for the main association were then determined. Equilibrium constants are low;K=5–50 (g. moles per l.)^?1 for interaction with neutral polymers andK=20–120 (g. moles per l.)^?1 for interaction with polyions. The free energies are (?δG)=1–3RT and 3–5RT calories per g. mole respectively. Complexing is due to dipole-dipole and/or ion-dipole type interaction and is greatest for aniline, pyridine and phenol with fully extended polyion chains. Van der Waals' interaction between the aromatic ring and the organic section of the polymer backbone augments the dipole-dipole or ion-dipole binding with pyridine homologues, especially with acridine.     

An analysis of the through-bond interaction using the localized molecular orbitals with ab initio calculations—I : Lone-pair orbital interactions in cis- and trans-hydrazines

Ab initio SCF MO calculations using STO-3G basis set were performed on the cis- and trans- hydrazines. The cannonical MOs obtained by these calculations were then transformed into the localized MOs. With the use of the localized MOs thus obtained, the variation in the lone-pair orbital energies of the molecules were pursued in the light of the through-space and/or the through-bond interactions between the specified localized MOs. As a result of this analysis, it was found that ; (a) the effect of the inner shell orbitais, l s electrons of N atoms, is not negligibly small, (b) the effect of the through-bond interaction is not so larger than the through-space interaction, and (c) the large contribution of the through-space interaction is caused from the indirect as well as direct interactions between two lone-pairs.     

Swelling behaviors, tensile properties and thermodynamic studies of water sorption of 2-hydroxyethyl methacrylate/epoxy methacrylate copolymeric hydrogels

A series of copolymeric hydrogels based on 2-hydroxyethyl methacrylate (HEMA) and epoxy methacrylate (EMA) were synthesized by bulk polymerization. Swelling behaviors and tensile properties of hydrogels were studied. Dynamic swelling behaviors of copolymeric hydrogels indicate that the swelling process of these polymers follows Fickian behavior. The equilibrium water content (EWC) decreased and volume fraction of polymer in hydrogel (?₂) increased with EMA content increasing due to its hydrophobicity. The increase of ionic strength of swelling medium or temperature results in a decrease in EWC and an increase in values of ?₂. Young’s modulus and tensile strength of hydrogels, as well as effective crosslink density (v_e), increased as EMA content increased or ionic strength of swelling medium increased, attributing to increasing interaction between hydrophobic groups and polymer-polymer interaction with an increase in EMA content or in ionic strength. The polymer-solvent interaction parameter χ reflecting thermodynamic interaction was also studied. As EMA content, ionic strength of swelling medium or temperature increased, the values of χ increased. The values of χ and its two components χ_H and χ_S varied with increasing T. The negative values and trend of the enthalpy and entropy of dilution derived from values of χ_S and χ_H, could be explained on the basis of structuring of water through improved hydrogen bonding and hydrophobic interaction.     

Methotrexate interaction with a lipid membrane model of DPPC

Dipalmitoylphosphatidylcholine (DPPC) liposomes were employed as membrane models for the investigation of the interaction occurring between methotrexate (MTX) and bilayer lipid matrix. Liposomes were obtained by hydrating a lipid film with 50 mM Tris buffer (pH 7.4). The differential scanning calorimetry (DSC) evaluation of the thermotropic parameters associated with the phase transitions of DPPC liposomes gave useful information about the kind of drug-membrane interaction. The results showed an electrostatic interaction taking place with the negatively charged molecules of MTX and the phosphorylcholine head groups, constituting the outer part of DPPC bilayers. No interaction with the hydrophobic phospholipid bilayer domains was detected, revealing a poor capability of MTX to cross through lipid membranes to reach the interior compartment of a lipid bounded structure. These findings correlate well within vitro biological experiments on MTX cell susceptibility.     

Effect of gelatin on micellization and microstructural behavior of amphiphilic amitriptyline hydrochloride drug solution: A detailed study

Herein we have investigated the dealings between amphiphilic antidepressant drug amitriptyline hydrochloride (AMT) and gelatin interaction using different proposed techniques. AMT is used for the treatment of mental/mood problems such as depression. Gelatin interacts with this drug alike fashions to the interaction of polymers and surfactants i.e., critical aggregation concentration (cac) and polymer saturation point (psp) were together achieved significantly. AMT and gelatin interaction starts due to the highly surface active complex formation as disclosed by decreasing of surface tension of gelatin solution by adding of AMT. It was uncovered from results that cac decreases on increasing the gelatin concentrations, whereas psp increases which is a sign of the attraction between AMT and gelatin. Thermodynamic parameters were also evaluated and discussed in detail. Fluorescence measurements were used to find the values of average aggregation numbers (N_agg) and various other parameters like Stern–Volmer constant (K_sv) and micropolarity. The nuclear magnetic resonance (¹H NMR) data suggested that AMT interacts with gelatin by the means of hydrophobic interaction. The ¹H NMR experiments explain that the extent of chemical shifts (δ) and line width (lw) increases with the increase in gelatin concentration. Secondary structure of gelatin was also examined via circular dichroism (CD) technique at different concentration of AMT. CD results confirmed that with increasing drug concentration the random coil portion of gelatin enhances. Field emission scanning electron microscope (FESEM) provided clear pictures of (drug + gelatin) interaction.     

Preparation of a new 1,3-alternate-calix[4]arene-bonded HPLC stationary phase for the separation of phenols, aromatic amines and drugs

We have synthesized the 1,3-alternate 25,27-dioctyloxy-26,28-bis-[3-aminopropyloxy]-calix[4]arene and then immobilized onto γ-chloropropylsilica gel (CPS). The high-performance liquid chromatographic behavior of some aromatic hydrocarbons, phenolic compounds, aromatic amines and drug compounds was studied on this 1,3-alternate-calix[4]arene-bonded silica gel stationary phase (CIMS). The effect of organic modifier content and pH of the mobile phase on retention and selectivity of these compounds were investigated. According to chromatographic data, it can be concluded that the selectivity of CIMS for analytes ascribes to various interactions between CIMS and the analytes, such as hydrophobic interaction, hydrogen bonding interaction, π-π interaction and inclusion interaction.     

Study on inclusion interaction of hydrophilic 2-chloromandelic acid with hydroxypropyl-β-cyclodextrin

The inclusion interaction between hydroxypropyl-β-cyclodextrin (HP-β-CD) and hydrophilic 2-chloromandelic acid (CMA) was studied by ultraviolet (UV) absorption spectrophotometer. A reliable determination of the complex stoichiometry was provided by the continuous variation technique. ¹H NMR spectrum and Thermo-gravimetric/differential thermal analyzer (TG/DTA) techniques were explored to further characterize the inclusion complex, and molecular modeling was used to investigate the mechanism of inclusion interaction. The results showed that HP-β-CD reacted with R,S-CMA to form inclusion complexes, with 1:1 stoichiometry and inclusion stability constants K_R and K_S were 24 and 39 L/mol determined from UV data by the method of Benesi-Hildebrand’s. Molecular modeling confirmed experimental observation and indicated that the hydrogen bonding interaction plays an important role in the interactive inclusion between HP-β-CD and CMA. Besides, compared with the HP-β-CD, molecular modeling showed R, S-CMA interact with β-CD through different binding modes, in which Vander Waals is the main intermolecular force between β-CD and R-CMA (or S-CMA) while without obvious hydrogen bonding interaction.     

Long-range interaction in the D and D′ states of H2

The interaction energy between two hydrogen atoms in the D and D′ ¹Π_u states of the hydrogen molecule has been calculated for large internuclear distances (12 ? R ? 25 bohr). The variational method and a very flexible trial wave-function were used. The results indicate that for the states under consideration the Rayleigh-Schrödinger perturbation theory with the multipole expansion of the interaction hamiltonian gives reliable results only for R > 25 bohr i.e. in the region where the interaction energies are practically negligible.     

On the interactions of N,N′-bismesitylimidazolin-2-yl and alcohols

The interaction of N,N′-bismesitylimidazolin-2-yl (IMes) with alcohols is discussed. NMR spectroscopy and X-ray crystallography were used to examine the influence of solvent and alcohol on this interaction. The stabilizing effect of these interactions may be used for the storage of nitrogen-heterocyclic carbenes (NHCs) since removal of the volatiles liberates the NHC.     

Mechanism and microstructure of Eu(Ⅲ) interaction with γ-MnOOH by a combination of batch and high resolution EXAFS investigation

In this paper,the macroscopic interaction method and high resolution EXAFS technique with a bent crystal analyzer were combined to study Eu(Ⅲ)interaction mechanism and microstructure withγ-MnOOH as a function of pH.The results indicated that Eu(Ⅲ)interaction withγ-MnOOH was apparently dependent on pH but independent of ionic strength,suggesting the formation of inner-sphere surface complexation for Eu(Ⅲ)ontoγ-MnOOH.Results of EXAFS analysis indicated that Eu was surrounded by~9.0 O atoms in first coordination shell at REu–O≈2.40,and second shell of Mn atoms at REu–Mn≈3.60 was observed for the three adsorption samples.These findings suggested formation of a bidentate surface complex with Eu(Ⅲ)bonding by edge sharing to MnO6-octahedron on γ-MnOOH surface.Both the macroscopic interaction data and the molecular level evidence of Eu(Ⅲ)microstructure at the γ-MnOOH-water interface should be factored into better understanding the fate and mobility of Eu(Ⅲ)and related radionuclides in the natural soil and water environment.