Current Physical Chemistry - Volume 10, Issue 1, 2020

Interfaces, or surfaces in particular (fluid-solid interfaces), are the boundary limits of two immiscible phases characterized by the surface free energy. Getting insight into their fundamental property is of great importance for both scientific and industrial activities. Such an approach enables us to control the formation and stabilization of colloidal systems, which consist of producing homogenous dispersions from at least two initially immiscible phases. In this mini-review, the kinetic and thermodynamic aspects of fluid surfaces are overviewed. Successively, the main phenomena occurring at the interfaces and the appropriate methodology of investigations, the role of amphiphilic molecules in modifying surface properties and generating various functionalities as a function of their chemical structure, size, and shape, and the current approaches for characterizing interactions as well as synergism or antagonism within mixed systems are treated. Relevant relationships of dynamic fundamental properties to macroscopic consequences at the solid and fluid interfaces of single and mixed amphiphile systems are illustrated.

Background: An electrochemical method based on cyclic voltametry techniques was used to measure the antioxidant activity of two ferrocene-nucleobases. Objective: The present study aims to measure the antioxidant activity of two ferrocene derivatives bearing nucleobases; the technique is based on the reaction of the in-situ electrochemical generated superoxide anion radical with ferrocene-nucleobases. Method: The decrease in the anodic peak current density of the O2 / O2 .− redox couple following the addition of ferrocene-nucleobases was used to measure the antioxidant activity and binding parameters of 1-ferrocenylmethylthymine and 1-ferrocenylmethylcytosine with superoxide anion radical. Conclusion: Both 1-Ferrocenylmethylthymine and 1-Ferrocenylmethylcytosine showed higher antioxidant activity (0.34 ± 0.03 and 0.045 ± 0.02 mg/mL respectively) than that of standard antioxidant α-tocopherol (3.04 ± 0.03 mg/mL). The value of the binding free energy ranging from -16.1 kJ.mol-1 for 1-ferrocenylmethylthymine to -21.8 kJ.mol-1 for 1- ferrocenylmethylcytosine suggests an electrostatic interaction of superoxide anion radical with both compounds which has been found to be the dominant interaction mode. The kinetics of the interaction reaction of the compounds was quantified having second-order rate constant values equal to 4.0 and 16.5 M-1 s-1 respectively.

The radiocarbon (14C) concentrations in air and vegetation samples around a nuclear research reactor were studied. Objective: 14C concentrations in the air and vegetation samples around the nuclear research reactor were measured to assess its 14C burden on the environment. Methods: Air samples were collected by converting CO2 into Na2CO3 by using a specified system. Leaf samples were carbonized to convert organic carbon into inorganic carbonates. The samples were converted into carbamate through carbosorb systems with 74% efficiency. The fractionation of 14C for each sample was corrected and normalized to a 13C composition of -25‰ Pee Dee Belemnite. Results: 14C concentrations in the air and vegetation samples around the nuclear research reactor were found to range from 158 to 406 Bq/Kg and 162 to 339 Bq/kgC, respectively. The highest concentrations of 14C were found in the samples close to the reactor and along the prevailing wind direction. The specific activities of the samples decreased with an increase in the distance from the reactor and in the opposite to prevailing wind direction. In addition to the distance from the reactor and wind direction, the local Suess effect was an additional factor affecting the 14C activities in the air and vegetation samples. Conclusion: One can conclude that other than the 14C emissions from the nuclear reactor, local Suess effects and climatic factors (wind directions) dilute and disperse 14C concentrations in the atmosphere and consequently decrease its availability for uptake and accumulation by plants at 4-5 km aerial distance from the point of release in prevailing wind direction.

Background: Today, acid rain problem is one of the serious global problems to the environment in which pH of the rain water decreases, causing harmful effect to nature, buildings, monuments, vegetation and human being as well. Therefore, the objective of the paper to find out some organic inhibitors present in the atmosphere that inhibited the acid rain. Objective: In this paper, we studied the chemistry of Cu (II)-methanoic acid-S(IV)-O2 in acetate buffered medium by earlier reported methods in literature. Gravimetric analysis was carried out to find the end product and confirmed that it was sulphate with 98 % recovery. Methods: Experiments were carried out at 303 ≤ T/K ≤ 313, 4.0 ≤ pH ≤ 5.35, 1.0x10−3 mol/dm3 ≤ S(IV) ≤ 10.0x10−3 mol/dm3, 5x10−6 mol/dm3 ≤ [Cu(II)] ≤ 2.5x10−5 mol/dm3, 6x10−6 mol/dm3≤[methanoic acid]≤7x10-4 mol/dm3. The value of apparent activation energy and inhibition parameter B was calculated in the presence of methanoic acid found as 29.07 kJ mol-1and 3.18 x 103 mol dm-3, respectively. The thermodynamic parameters were found as frequency factor (1.59 x 10-6s-1), entropy (-358.92 J K-1 mol-1), enthalpy (20.97 k J mol-1), and Gibbs free energy (172.83k J mol-1), respectively. Results: We observed that methanoic acid acts as an inhibitor in copper catalyzed autoxidation of SO2 in acidic medium. Therefore, on the basis of the observed results a free radical mechanism has been identified. The results are useful for modeling rain water acidity and therefore a great use of meteorology and atmospheric chemistry. This study is important in understanding the mechanism of the oxidation of S(IV) by O2. Conclusion: This study suggests that since organic inhibitors are found in the atmosphere, their concentrations and their influence on the oxidation of aqueous SO2 should be taken into account. The intervention of methanoic acid in the autoxidation of aqueous SO2 plays a role in deciding the fate of both methanoic acid and SO2. The influence of inhibitors may be used to calculate the lifetime of SO2, Methanoic acid has high values of kinh and, therefore, it would be degraded by sulfate radical anions in atmospheric waters.

Background: Since the interactions of small anions with protein are very important in their transportation and distribution processes in biological systems, it is helpful to study these interactions to understand the nature of the transportation and distribution processes. Therefore, it is aimed to study the interaction of albumin with surfactant molecule by different physical methods. Objective: Present work attempts to work on assessing the structure, characterization of the surfactants as TEALS (tri-ethanalamine lauryl sulphate) binding sites, with albumin involved in various process of living being are discussed. Methods: The binding of surfactant TEALS to egg protein has been studied at different pH values and temperatures by spectrophotometric and equilibrium dialysis methods. The binding data were found to be pH and temperature dependent. The binding data studied by the absorbance method, were found approximately identical with those obtained from the equilibrium dialysis method. Results: The association constants and the number of binding sites were calculated from Scatchard plots and found to be at maximum at lower pH and at lower temperature. The free energy of the combining sites was lowest at higher pH and highest at low pH. Therefore, a lower temperature and a lower pH offered more sites in the protein molecule for interaction with surfactant. The ΔG (free energies of aggregation) associated with the binding interaction of the surfactants and protein were calculated. The negative values of the ΔG confirm the feasibility of interaction between the surfactant and protein. All the observations recorded in this paper indicate that the TEALS has a good affinity of binding with egg protein and the number of binding sites is dependent on various physical and chemical factors. Conclusion: On the basis of the results of the experiments which were conducted to examine the interaction between anionic surfactant and protein by measuring the various parameters of the solutions, it is concluded that the interaction of surfactant and protein gives an idea of fundamental understanding of the structure of surfactant-protein complex and their practical applications in every field.

Background: Melting of a pure crystalline material is generally treated thermodynamically which disregards the dynamic aspects of the melting process. According to the kinetic phenomenon, any process should be characterized by activation energy and preexponential factor where these kinetic parameters are derivable from the temperature dependence of the process rate. Study on such dependence in case of melting of a pure crystalline solid gives rise to a challenge as such melting occurs at a particular temperature only. The temperature region of melting of pure crystalline solid cannot be extended beyond this temperature making it difficult to explore the temperature dependence of the melting rate and consequently the derivation of the related kinetic parameters. Objective: The present study aims to explore the mechanism of the melting process of maleic anhydride in the framework of phase transition models. Taking this process as just another first-order phase transition, occurring through the formation of nuclei of new phase and their growth, particular focus is on the nucleation and growth models. Methods: Non-isothermal thermogravimetry, as well as differential scanning calorimetry studies, has been performed. Using isoconversional kinetic analysis, temperature dependence of the activation energy of melting has been obtained. Nucleation and growth models have been utilized to obtain the theoretical temperature dependencies for the activation energy of melting and these dependencies are then compared with the experimentally estimated ones. Conclusion: The thermogravimetry study indicates that melting is followed by concomitant evaporation, whereas the differential scanning calorimetry study shows that the two processes appear in two different temperature regions, and these differences observed may be due to the applied experimental conditions. From the statistical analysis, the growth model seems more suitable than the nucleation model for the interpretation of the melting mechanism of the maleic anhydride crystals.