Densities,Ultrasonic Velocities,Excess Properties and IR Spectra of Binary Liquid Mixtures of Organic Esters (Ethyl Lactate,Some Organic Carbonates)

Organic esters of carbonic acid {dimethyl carbonate (DMC)/diethyl carbonate (DEC)/propylene carbonate (PC)}, in combination with a lactate ester {ethyl lactate (EL)}, with green chemistry characteristics were chosen for the present study of molecular interactions in binary liquid mixtures. Densities (ρ) and ultrasonic velocities (U) of the pure solvents and liquid mixtures were measured experimentally over the entire composition range at temperatures (303.15, 308.15, 313.15 and 318.15) K and atmospheric pressure. The experimental data was used to calculate thermodynamic and acoustic parameters \( V_{\text{m}}^{\text{E}} \), \( \kappa_{S}^{\text{E}} \), \( L_{\text{f}}^{\text{E}} \), \( \bar{V}_{\text{m,1}}^{{}} \), \( \bar{V}_{\text{m,2}}^{{}} \), \( \bar{V}_{\text{m,1}}^{\text{E}} \), \( \bar{V}_{\text{m,2}}^{\text{E}} \), \( \bar{V}_{ 1}^{\text{E,0}} \) and \( \bar{V}_{ 2}^{\text{E,0}} \) and the excess functions were fitted with the Redlich–Kister polynomial equation to obtain the binary solution coefficients and the standard deviations. It was observed that the values of \( V_{\text{m}}^{\text{E}} \), \( \kappa_{S}^{\text{E}} \) and \( L_{\text{f}}^{\text{E}} \) are positive for the mixtures of (EL + DMC/DEC) and negative for those of (EL + PC) over the entire range of composition and temperature. The positive values of \( V_{\text{m}}^{\text{E}} \), \( \kappa_{S}^{\text{E}} \) and \( L_{\text{f}}^{\text{E}} \) indicate the action of dispersion forces between the component molecules of (EL + DMC/DEC) mixtures whereas negative values for the mixture (EL + PC) suggest the existence of strong specific interactions between the component molecules, probably resulting from chemical and structural contributions. The excess properties have also been analyzed by using the reduced (\( Y^{\text{E}} /x_{1} x_{2} \)) excess function approach and the results are found to be in agreement with those from the corresponding \( Y^{\text{E}} \)(= \( V_{\text{m}}^{\text{E}} \), \( \kappa_{S}^{\text{E}} \) and \( L_{\text{f}}^{\text{E}} \)) values. This is further supported by FTIR spectral analysis.     

π-Conjugated redox-active two-dimensional polymers as organic cathode materials

Redox-active two-dimensional polymers (RA-2DPs) are promising lithium battery organic cathode materials due to their regular porosities and high chemical stabilities. However, weak electrical conductivities inherent to the non-conjugated molecular motifs used thus far limit device performance and the practical relevance of these materials. We herein address this problem by developing a modular approach to construct π-conjugated RA-2DPs with a new polycyclic aromatic redox-active building block PDI-DA. Efficient imine-condensation between PDI-DA and two polyfunctional amine nodes followed by quantitative alkyl chain removal produced RA-2DPs TAPPy-PDI and TAPB-PDI as conjugated, porous, polycrystalline networks. In-plane conjugation and permanent porosity endow these materials with high electrical conductivity and high ion diffusion rates. As such, both RA-2DPs function as organic cathode materials with good rate performance and excellent cycling stability. Importantly, the improved design enables higher areal mass-loadings than were previously available, which drives a practical demonstration of TAPPy-PDI as the power source for a series of LED lights. Collectively, this investigation discloses viable synthetic methodologies and design principles for the realization of high-performance organic cathode materials.

Redox-active two-dimensional polymers (RA-2DPs) are promising lithium battery organic cathode materials due to their regular porosities and high chemical stabilities.     

Destructive quantum interference in heterocyclic alkanes: the search for ultra-short molecular insulators

Designing highly insulating sub-nanometer molecules is difficult because tunneling conductance increases exponentially with decreasing molecular length. This challenge is further enhanced by the fact that most molecules cannot achieve full conductance suppression with destructive quantum interference. Here, we present results for a series of small saturated heterocyclic alkanes where we show that conductance is suppressed due to destructive interference. Using the STM-BJ technique and density functional theory calculations, we confirm that their single-molecule junction conductance is lower than analogous alkanes of similar length. We rationalize the suppression of conductance in the junctions through analysis of the computed ballistic current density. We find there are highly symmetric ring currents, which reverse direction at the antiresonance in the Landauer transmission near the Fermi energy. This pattern has not been seen in earlier studies of larger bicyclic systems exhibiting interference effects and constitutes clear-cut evidence of destructive σ-interference. The finding of heterocyclic alkanes with destructive quantum interference charts a pathway for chemical design of short molecular insulators using organic molecules.

We present a combined experimental and theoretical study of small saturated heterocyclic alkanes and show that they perform well as insulators with an electronic transmission that is suppressed due to destructive interference.     

The Antimicrobial efficacy of Elaeis guineensis: characterization, in vitro and in vivo studies

The urgent need to treat multi-drug resistant pathogenic microorganisms in chronically infected patients has given rise to the development of new antimicrobials from natural resources. We have tested Elaeis guineensis Jacq (Arecaceae) methanol extract against a variety of bacterial, fungal and yeast strains associated with infections. Our studies have demonstrated that E. guineensis exhibits excellent antimicrobial activity in vitro and in vivo against the bacterial and fungal strains tested. A marked inhibitory effect of the E. guineensis extracts was observed against C. albicans whereby E. guineensis extract at ?, 1, or 2 times the MIC significantly inhibited C. albicans growth with a noticeable drop in optical density (OD) of the bacterial culture. This finding confirmed the anticandidal activity of the extract on C. albicans. Imaging using scanning (SEM) and transmission (TEM) electron microscopy was done to determine the major alterations in the microstructure of the extract-treated C. albicans. The main abnormalities noted via SEM and TEM studies were the alteration in morphology of the yeast cells. In vivo antimicrobial activity was studies in mice that had been inoculated with C. albicans and exhibited good anticandidal activity. The authors conclude that the extract may be used as a candidate for the development of anticandidal agent.     

Diurnal and seasonal variations in h’F and foF2 over low (Indian) and mid (Japanese) latitude stations — a comparative study

Using the simultaneous data of ionosonde from a low latitude station, Waltair, India (17.7°N,83.3°E) in the Indian sector and a mid latitude station, Kokubunji, Japan (35.7°N,139.5°E) in the Japanese sector during the high sunspot year of 2001, a comparative study of the variations in the diurnal, seasonal and day to day characteristics of the ionospheric F-region parameters, such as the virtual height of the F-layer (h’F) and the critical frequency of the F₂ layer (foF2), are studied. The effect of geomagnetic activity variations of the F-region parameters over the low and mid latitude stations is also presented.     

Variability of conductance in molecular junctions

The conductance of molecular junctions, formed by breaking gold point contacts dressed with various thiol functionalized organic molecules, is measured at 293 K and at 30 K. In the presence of molecules, individual conductance traces measured as a function of increasing gold electrode displacement show clear steps below the quantum conductance steps of the gold contact. These steps are distributed over a wide range of molecule-dependent conductance values. Histograms constructed from all conductance traces therefore do not show clear peaks either at room or low temperatures. Filtering of the data sets by an objective automated procedure only marginally improves the visibility of such features. We conclude that the geometrical junction to junction variations dominate the conductance measurements.     

Growth,optical, thermal,dielectric and mechanical studies of sodium hydrogen succinate single crystal

Sodium hydrogen succinate, an alkali metallo-organic third-order nonlinear optical crystal, had been grown successfully using aqueous solution by slow evaporation technique at room temperature. Transparent single crystals were selected and subjected to single-crystal X-ray diffraction analysis to identify lattice parameters, space group and morphology. The grown crystal was further subjected to powder X-ray diffraction to analyze the crystalline quality, UV–Vis–NIR spectral analysis to reveal optical transparency, FTIR spectroscopy for confirmation of the functional group analysis and TG–DTG/DSC analysis to determine the thermal stability. The dielectric constant and dielectric loss were studied as a function of frequency at different temperatures, and the results were discussed. The mechanical properties were calculated by Vickers microhardness test, and the third-order nonlinear optical parameters such as nonlinear refractive index, nonlinear absorption coefficient and real and imaginary parts of the third-order nonlinear optical susceptibility were determined by Z-scan technique.