Studies on labile chargetransfer complexes between o-chloranil and a series of phenols

The electron donor–acceptor (EDA) interactions between o-chloranil and a series of phenols have been studied in dioxan medium. Except for resorcinol, the EDA complexes are formed instantaneously on mixing the donor and the acceptor solutions and then they decay slowly into secondary products. In case of resorcinol, formation and decay of the EDA complex are slow and simultaneous. The kinetics of all these reactions have been studied spectrophotometrically and the formation constants of EDA complexes have been determined from kinetic data. The hν_CT values change systematically as the number and position of the –OH groups change in the aromatic ring of the phenol moiety. From the trends in the hν_CT values, the Hückel parameters (h_Ö and k_C–Ö) for the –OH group, required for a PMO calculation on phenols, have been obtained in a straightforward way and the values so obtained, viz., 1.8 and 1.0 respectively, are close to the ones (1.8 and 0.8) recommended by Streitwieser on the basis of other evidences.     

Spontaneous self-assembly of cerium oxide nanoparticles to nanorods through supraaggregate formation

Self-assembly of cerium oxide nanoparticles to nanorods is reported. Such nanorods have an aspect ratio of 6 with a diameter of approximately 40 nm. The formation of cylindrical supraaggregates and their subsequent growth by preferential assembling of ceria nanocrystallites along the longitudinal direction was proposed to be the probable mechanism of spontaneous self-assembly of nanorods. The supraaggregate formation was facilitated by influencing the local curvature of the micelle surface in the presence of nitrate ions as a precursor solution. The nanorods were characterized using high-resolution transmission electron microscopy with energy dispersive spectroscopy and selected area electron diffraction for their morphology, chemistry, and crystal structure.     

Sol-Gel Synthesis and Phase Evolution Behavior of Sterically Stabilized Nanocrystalline Zirconia

Nanocrystalline as well as submicron sized, non-agglomerated, spherical ZrO₂ particles have been successfully synthesized using the sol-gel technique utilizing hydroxypropyl cellulose (HPC) as a polymeric steric stabilizer. The effect of various parameters such as the ratio of molar concentration of water and alkoxide (R), the molar concentration [HPC] and the molecular weight (MW_HPC) of HPC polymer as well as the calcination temperature on ZrO₂ nanocrystallites size and their phase evolution behavior is systematically studied. The phase evolution behavior of nanocrystalline ZrO₂ is explained and correlated with the adsorption behavior of HPC polymer on ZrO₂ nanoparticles surface, which is observed to be a function of R, [HPC], MW_HPC and the calcination temperature. Optimum synthesis parameters for obtaining 100% tetragonal phase in nanocrystalline ZrO₂ are identified for the present sol-gel method of synthesizing nanoparticles.     

GdIII-19F Distance Measurements for Proteins in Cells by Electron-Nuclear Double Resonance

Studies of protein structure and dynamics are usually carried out in dilute buffer solutions, conditions that differ significantly from the crowded environment in the cell. The double electron-electron resonance (DEER) technique can track proteins’ conformations in the cell by providing distance distributions between two attached spin labels. This technique, however, cannot access distances below 1.8 nm. Here, we show that Gd^III-¹⁹F Mims electron-nuclear double resonance (ENDOR) measurements can cover part of this short range. Low temperature solution and in-cell ENDOR measurements, complemented with room temperature solution and in-cell Gd^III-¹⁹F PRE (paramagnetic relaxation enhancement) NMR measurements, were performed on fluorinated GB1 and ubiquitin (Ub), spin-labeled with rigid Gd^III tags. The proteins were delivered into human cells via electroporation. The solution and in-cell derived Gd^III-¹⁹F distances were essentially identical and lie in the 1–1.5 nm range revealing that both, GB1 and Ub, retained their overall structure in the Gd^III and ¹⁹F regions in the cell.     

The Change in Antioxidant Properties of Dextran‐Coated Redox Active Nanoparticles Due to Synergetic Photoreduction–Oxidation

Nanoparticles have proven to be novel material with resourceful applications in the field of nanomedicine. Cerium oxide nanoparticles (CNPs) coated with dextran (Dex–CNPs) have been shown to exhibit anticancer properties which is attributed to the change in oxidation states mediated at the oxygen vacancies on the surface of CNPs. In this study, the extreme sensitivity of Dex–CNPs to visible light is demonstrated using room light with a clear indication of synergetic phenomenon of photoreduction of CNPs in the presence of dextran which undergoes simultaneous oxidation. The phenomenon was further confirmed through a systematic time‐based expedited study using a high intensity visible light source. The physiochemical changes of Dex–CNPs such as dispersion stability, pH, surface chemistry, antioxidant property, cytotoxicity and the surrounding microenvironment of Dex–CNPs were significantly altered on exposure to visible light, thereby affecting the biological response. Given the significance of nanoparticles which are widely researched nanomaterials, in different fields of nanotechnology and biomedicine, this study demonstrates the significant changes in physiochemical properties of Dex–CNPs with light. The photoreduction of Dex–CNPs affects its bifunctional applications in cancer therapy and thereby this study puts forward the necessity to preserve and sustain their properties through proper storage.     

Charge-transfer complex formation between o-chloranil and a series of polynuclear aromatic hydrocarbons

The equilibrium constants, enthalpies and entropies of formation of molecular electron donor-acceptor (EDA) complexes of o-chloranil with a series of aromatic hydrocarbons have been determined spectrophotometrically. Spectroscopic and thermodynamic aspects of these complexes have been analysed.     

Analysis of unsaturated compounds by Ag+ coordination ionspray mass spectrometry: studies of the formation of the Ag+/lipid complex

Coordination ionspray mass spectrometry (CIS-MS) is a useful tool in the detection and identification of cholesterol ester and phospholipid hydroperoxides and diacyl peroxides. Extensive studies of a series of cholesterol esters using CIS-MS revealed the following: (1) Cholesterol esters with equal number of double bonds as the internal standard showed a linear relative response in the mass spectrometer while compounds with non-equal numbers of double bonds gave a nonlinear relative response. (2) Complex adducts containing cholesterol ester, silver ion, AgF, AgBF(4), and 2-propanoxide form when silver is in molar excess of cholesterol esters, reducing the [M + Ag](+) signal. (3) In a mixture of cholesterol esters where silver is limiting, Ch22:6 and Ch20:4 bind to silver at the expense of Ch18:2 and have a higher signal in the mass spectrometer. (4) In a mixture of cholesterol esters where silver concentration is twofold greater than total cholesterol ester concentration, Ch22:6 and Ch20:4 form large complex adducts more frequently than Ch18:2 and have a lower signal in the mass spectrometer.     

Magnetic interactions in alkyl substituted cyclohexane diradical systems: a broken symmetry approach

Magnetic interactions in alkyl substituted cyclohexane diradical systems have been investigated within the framework of spin flip density functional theory. The investigations suggest a ferromagnetic interaction for both the alkyl substituted cyclohexane-1,3-diyls and cyclohexane-1,4-diyls. However, in the case of cyclohexane-1,3-diyls, the ferromagnetic interaction is much stronger than its 1,4 analogue. Interestingly, it has been observed that this interaction is reduced to almost half the value from the butyl to the decyl substituted unit relative to the lower homologues up to the propyl substituted unit in cyclohexane-1,3-diyls. On the other hand, in case of alkyl substituted cyclohexane-1,4-diyls, the ferromagnetic interaction for the higher homologues, i.e., butyl to decyl substituted units, substantially reduces to almost 5-6 times the value of its lower homologue (methyl and ethyl substituted unit). In both these cyclohexane diradical systems, beyond butyl substituted unit, a saturation effect in the magnetic coupling constant (J) value is observed. The rapid decrease followed by a saturation in the singlet-triplet gap and J as well may be explained by considering positive inductive effect of the alkyl substituent.     

Searching of potential energy curves for the benzene dimer using dispersion-corrected density functional theory

The present work aims to establish the utility of dispersion-corrected density functional theory for potential energy curves of the benzene dimer, a problem that has received significant attention for a long time. The interaction energies of parallel-stacked, T-shaped and parallel-displaced benzene dimer configurations have been evaluated using both dispersion- and normal gradient-corrected Perdew-Burke-Ernzerhof functionals along with Dunning's augmented correlation-consistent polarized valence triple-zeta (aug-cc-pVTZ) basis functions and compared with explicit correlation methods. The potential energy curves for the parallel-stacked and parallel-displaced benzene dimers are in excellent agreement with highly accurate coupled cluster (CCSD(T)) results, while for the T-shaped benzene dimer the dispersion-corrected results show a distinct deviation, being closer in that case to the MP2 level of results. The overestimation of interaction energy in the T-shaped dimer may be attributed to the presence of a permanent dipole moment in this configuration and indicates a structural dependence of the dispersion-corrected density functional method.     

Is nucleus-independent chemical shift scan a reliable aromaticity index for planar heteroatomic ring systems?

Density functional theoretical investigation has been performed to explore the reliability of the nucleus-independent chemical shift (NICS) scheme in assessing aromatic behavior of some planar six-membered heteroatomic systems. It has been observed that the NICS scan and the diamagnetic and paramagnetic contributions of the in-plane and out-of-plane components are quite reliable in assessing any aromatic or antiaromatic behavior in borazine. However, for boraphosphabenzene, the aromatic stabilization energy is too small to consider it as an aromatic system but the NICS scans and the homodesmotic reactions suggest an opposite trend. Interestingly, in the case of alumazene, a very shallow minimum is observed for the out-of-plane component, which suggests the presence of weak diamagnetic ring current. However, the diamagnetic and paramagnetic contribution curves to the out-of-plane component for alumazene clearly reveal a net paramagnetic contribution. Thus we may surmise that apart from the single NICS value, the NICS scan also is not a very authentic tool for the assessment of aromaticity of planar six-membered heteroatomic systems.