Current Physical Chemistry - Volume 11, Issue 2, 2021

Background: The synthesis of Fe2O3/ZnO nanocomposites has gained wide acceptance in recent years due to its magnetic, photoluminescence and catalytic properties, and as an active element in gas sensors. This type of composite particle has potential biological and biomedical applications such as the detection of cancer cells, bacteria and viruses, and for magnetic separation. Objective: In the present study, first we synthesized the Fe2O3/ZnO nanoparticles, and then the structural, optical and surface morphological properties were investigated by XRD, HRTEM, FESEM, XRF and FTIR analyses. Methods: Fe2O3-ZnO nanoparticles were fabricated by a solgel synthesis method by combining iron chloride hexahydrate and zinc sulfate heptahydrate. In the beginning, 2g of Polyvinylpyrrolidone (PVP) stabilizer was dissolved in 100 mL deionized water and then 5 g FeCl3 was added to the solution with stirring at room temperature. Then 5g of ZnSO4 was added to the solution and synthesis temperature was increased to 100 °C. The product was evaporated for 3 hours, cooled to room temperature and finally calcined at 600 °C for 3 hours. Results: The XRD results showed single-phase Fe2O3-ZnO nanocomposites with a hexagonal wurtzite structure of ZnO and spinel phase of rhombohedral α-Fe2O3. The crystallite size of as-prepared sample was determined at about 45 nm and annealed one was calculated around 40 nm. The SEM images showed that the Fe-Zn nanoparticles changed from spherical shape to rod shape by increasing the temperature after annealing. The TEM studies showed the core-shell nanoparticles with a mean diameter of 47 nm. The sharp peaks in the FTIR spectrum determined the stretching vibrations of Fe and Zn groups in the frequencies of 620, 565 cm^-1 and 410 cm^-1. Conclusion: The XRD data indicates a single-phase Fe2O3-ZnO structure. The SEM images show that the nanoparticles changed from sphere-like shape to rod-like shape by increasing the annealing temperature. TEM image exhibits the core-shell Fe-Zn nanoparticles with an average diameter of about 37 nm. From the FTIR data, it is shown that the presence of Fe-Zn stretching mode and the intensity of the peaks increased by increasing the annealing temperature. XRF analysis showed peaks of iron and ferrite elements, and an increase in the Zn weight percent was observed from 26.35 %Wt. to 49.26 %Wt. with increasing temperature.

Objective: Mechanistic investigation of the reaction between the complex ion [Fe^III2(μ-O)(phen)4(H2O)2]⁴⁺ (1) (phen = 1,10-phenanthroline) and its hydrolytic derivatives [Fe^III2(μ-O)(phen)4(H2O)(OH)]³⁺ (1a) and [Fe^III2(μ-O)(phen)4(OH)2]²⁺ (1b) which coexist in rapid equilibria in the range pH = 3.00 to pH = 5.00 (pKa1 = 3.71 ± 0.03, pKa2 = 5.28 ± 0.07) with N2H5⁺ ion to produce [Fe(phen)3]²⁺ has been covered in this study. Methods: Rise in absorbance of the product with time was measured and rates have been determined using initial rate methods. Dependence of rate on pH and concentration of N2H5⁺ are studied in detail. Results: In the presence of excess phenanthroline, the reaction follows simple first-order exponential profile. Interestingly, in the absence of any added phenanthroline, the reaction becomes faster and the reaction profile changes to nearly linear with curvature near the end of the reaction. Slight autocatalytic nature has been observed only for the slower reactions. The observed rate constants obtained using initial rate method show first-order dependence on the concentration of N2H5⁺. An increase in rate with increasing pH has been noticed. The plot of rate versus 1/[H⁺] shows saturation beginning near pH 4.6, suggesting that the mono-deprotonated form of the complex (i.e. 1a) is the active oxidant in this pH range. Conclusion: Presumably, the reaction becomes faster in the absence of added phenanthroline because ligand dissociation from the parent complex becomes facilitated when there is no external phenanthroline ligand present. This produces a coordinatively unsaturated Fe(III) species which is a faster oxidant.

Introduction: Based on the dimensional analysis, ρ -u- thermodynamic and ρ -uoptical properties correlations have been applied to sixteen ionic liquids at different temperatures. The objective of the present work is to employ these relations to ionic liquids. The experimental values of ρ and u have been reported in the literature at different temperatures. We have computed thermal expansivity (α), isothermal compressibility (βT), heat capacities ratio (γ), internal pressure (Pint), pseudo-Grüneisen parameter (), the energy of vaporization (ΔEV), enthalpy of vaporization (ΔHV), cohesive energy density (ced), solubility parameter (δ), refractive index (n), molar refraction (RM) and polarisability (αp) for these liquids. Methods: Correlations between density-sound velocity and several thermodynamic properties have been derived on the basis of dimensional analysis On the basis of dimensional analysis, a number of useful and important thermodynamic relations were deduced in terms of density (ρ) and speed of sound (u). Results: Results were found to be quite satisfactory. Keeping in view = uncertainty in the experimental values of ρ and u, as well as some approximations used, the agreement between experimental and theoretical values was found to be quite satisfactory. Discussion: Density (ρ) and ultrasonic speed (u) data of sixteen RTILs at different temperatures have been taken from the literature. Calculated values of α, βT, Pint, γ, CP-CV, and, were obtained from empirical relations. The experimental values of α were given for making a comparison. Conclusion: Based on the dimensional analysis, our recently developed correlations between ρ-u- thermodynamic and ρ-u- optical properties have been found to be quite successful when applied to sixteen ionic liquids for the first time. α, βT, γ, Pint, ΔEVap, ΔHVap, ced, δ as well as RM and αp were calculated at various temperatures.

A statistical study between ‘Mesophase Lower Transition Temperatures’ (MLTTs) and their structural properties is carried out to understand the effect of structural behaviour on mesomorphic property. Introduction: To establish a “Quantitative Structure and Property Relationship (QSPR) model” a set of randomly selected thirty-nine mesomorphic compounds is constructed. The backward stepwise regression analysis method is used to find out the good correlation between the “Mesophase Lower Transition Temperatures (MLTTs)” data set and “physical descriptors” like AMR, bpol, ASP-0, DELS, SdssC, etc. Physical descriptors are selected based on their good r2-values and p-values with respective MLTTs. The derived QSPR equation shows a good correlation between structural properties and mesomorphic properties of compounds. Methods: Validation of the derived QSPR equation is carried out on the test series of eight compounds. The MLTTs of these compounds are predicted through the statistically derived QSPR equation and then compared with experimentally measured MLTTs. The average percentage error observed between predicted MLTTs and experimentally measured MLTTs is 10.95 % for all the thirty-nine compounds of the trial set and 10.64% for 8 compounds of the test series, respectively. Results & Discussion: A low average percentage error suggests a reasonably acceptable degree of accuracy of the generated QSPR model to predict MLTTs of the compounds having a similar type of structure. In the present study, not only MLTTs are predicted, but an effort is also made to predict “Latent Transition Temperatures” (LTTs) of some nonmesomorphic compounds from the derived QSPR equation. Conclusion: This computational study gives an insight into developing new QSPR models for the different type of liquid crystals homologous series, through which various types of mesomorphic properties, like mesomorphic thermal stability, mesomorphic upper transition temperature, mesophase length, phase behaviour, etc. can study and predict.

Introduction: In this reported work, we have used 80 % aqueous dimethyl sulphoxide (DMSO) for density and viscosity measurement of pyrimidine-5-carbonitrile at 298.15 K. The obtained experimental results show that as concentration increases density and viscosity increases. From the results of density and viscosity, we have found apparent molar volume, limiting apparent molar volume, semi-empirical parameters, Falkenhagen coefficients and Jones Dole coefficients. Methods: The apparent molar volume and limiting apparent molar volume having negative values indicated electostrictive solvation of ions and weak or absence of ion solvent interactions, respectively. Results & Discussion: Falkenhagen coefficients are independent of concentration and possess positive values that shows strong solute-solute interactions. Jones-Dole coefficient with negative value shows weak solute-solvent interactions. The strong solute-solute interactions were present in A-1 as compared to A-2 compound because of the high electronegativity of oxygen atom. These parameters provides information about the type of the molecular interactions such as solute-solute, solute-solvent and solvent-solvent. Conclusion: We have reported density and viscosity study of 4-amino-2-hydroxy-6- phenylpyrimidine-5-carbonitrile and 4-amino-2-mercapto-6-phenylpyrimidine-5-carbonitrile in 80 % aqueous DMSO solution at 298.15 K. A stronger molecular association is observed in A-2 than A-1 shown by negative values of Øv.

Background: The binary mixtures of isopropanol/isobutanol/isoamyl alcohol with an equimolar mixture of ethanol and formamide consist of different ultrasonic properties, which have been studied at room temperature at a fixed frequency of 2 MHz. The ultrasonic-related physical parameters like velocity (U), density (ρ), adiabatic compressibility (βad), intermolecular free length (Lf), acoustic impedance (Z), etc., have been studied. The theoretical evaluation of ultrasonic velocity in liquid mixtures offers a transparent method for the study of the nature of molecular interactions in the mixtures besides verifying the applicability of different theories such as Nomoto’s, Van Dael and Vangeel’s, Impedance Dependence relation, Junjie’s relation, Rao’s specific sound velocity relation, and Jacobson’s relations, Percentage deviations of theoretical ultrasonic velocities from experimental values in the mixtures of all liquid mixture and also calculated values of ultrasonic velocity from polynomials for all the schemes with mole fraction (x) of isopropanol/isobutanol/ isoamyl alcohol. Objective: The main focus of the present work was to prepare the structural changes associated with the liquid mixtures having weakly interacting components and strongly interacting components. The study of molecular association in mixtures providing exact information of thermodynamic mixing properties, such as adiabatic compressibility, intermolecular free length, free volume, internal pressure, and molar volume, has significant importance in theoretical and applied areas of research. The ultrasonic study has been a subject of keen interest during the past many years. This branch of physical sciences has played a significant role in deciding the interactions between the molecules of compounds under study. It has a potential tool for evaluating energy exchange between various degrees of freedom and nonlinear properties in binary liquid mixtures. Methods: The binary liquid mixtures were prepared by mixing two components, by weight, using an electronic analytical balance (Reptech RA-2012), accurate up to ±0.0001 g. The average uncertainty in mole fraction of binary mixtures was estimated to be ±0.0001. To avoid loss of solvent due to evaporation, mixtures were stored in specially designed ground-glass airtight ampoules and placed in a dark place to prevent photolytic effects. Results: These empirical fittings of data are described qualitatively and quantitatively using experimental speed data even in the specific interaction predominant region where non-ideal behavior of the mixture is observed. The values of sound velocities and percentage deviation (after determining the co-efficient of the polynomial equations by applying the least squares method) are compiled in the tables, respectively. Conclusion: The ultrasonic velocities and densities for all three mixtures were measured, and the values were calculated. The observed trends of V^Em, ΔkS and L^Ef indicate the presence of weak interactions, and the strength of these interactions follows the order EMM+IPA>EMM +IBA>EMM+IAA. Besides, the ultrasonic velocities measured from different velocity theories were found to be consistent with the experimentally measured ultrasonic velocities. Among these theories, Jacobson’s velocity equation showed a good result for the experimental and theoretical ultrasonic velocity values for all the binary mixtures used.

Background: Visual pH sensors have received significant attention in the fields of environmental monitoring, analytical chemistry, food safety, and biomedicine. Therefore, a single organic moiety showing both naked-eye and fluorescence sensing of pH change is rare and in higher demand. Objective: A novel phenothiazine-based Schiff base PTz-SB was synthesized via facile organic transformations. This molecule showed promising naked-eye and on-spot pH sensing application, both using UV-visible and fluorescence techniques. Methods: The novel phenothiazine-based Schiff base was synthesized via facile organic transformation. The Schiff base was applied for both naked eye and fluorescence sensing of pH, using UV-visible and fluorescence techniques, respectively. Results: A Redshifts of 27 nm and 80 nm were observed in the λmax of absorption and emission spectra, respectively, on changing the pH from 12.2 to 1. The naked-eye pH sensing may be attributed to the change in colour from blue (higher pH) to dark green (lower pH), under daylight conditions. Furthermore, the change in fluorescence spectra is more pronounced. The fluorescence colour of the compound changes from dark blue to green and then finally to orange, on changing the pH from 12.2 to 4 to 1.5, respectively. Moreover, the electrochemical studies of the Schiff base were also procured. The bandgap obtained from the cyclic voltammetry studies was found to be 2.04 eV, which is characteristic of green emission. Conclusion: The easily synthesizable novel Schiff base can be utilized for real-life, on-spot practical application of pH sensing, which does not require sophisticated analytical instruments. Moreover, the time and cost of detection of pH using this thermally robust Schiff base are also very promising.