The first stereoselective total synthesis of the Z-isomer of cytospolide E

A convergent and highly stereoselective total synthesis of the Z-isomer of cytospolide E has been achieved via Evan’s aldol reaction, Sharpless kinetic resolution and RCM cyclisation.     

Extraction and Characterization of Cellulose Nanowhiskers from Balsa Wood

Summary: In this study cellulose nanowhiskers were obtained from balsa wood. For this purpose, fibers of balsa wood were exposed to hydrolysis reactions for lignin and hemicellulose digestion and acquisition of nano-scale cellulose. Transmission electron microscopy (TEM) results demonstrated that the obtained cellulose nanocrystals had average length and thickness of 176 (±68 nm) and 7.5 (±2.9 nm), respectively. Infrared spectroscopy (FTIR) and wide angle x-ray diffraction (WAXD) showed that the process for extracting the nanowhiskers digested nearly all the lignin and hemicellulose from the balsa fiber and still preserved the aspect ratio and crystallinity satisfactory enough for future application as nanofillers in polymer nanocomposites. The thermogravimetric analysis (TGA) showed that the onset temperature of thermal degradation of the cellulose nanocrystals (226 °C) was higher than the onset temperature of the balsa fiber (215 °C), allowing its use in molding processes with polymers melts.     

Mechanical loads on a generalized thermoelastic medium with diffusion

The disturbance caused by the application of continuous mechanical source on the free surface of a homogeneous, isotropic elastic half space in the context of the theory of generalized thermoelastic diffusion with one relaxation time parameter is investigated in the Laplace-Fourier transform domain for a two dimensional problem using eigenvalue approach. The integral transforms are inverted by using a numerical technique. The expressions for displacement components, stresses, temperature field, concentration and chemical potential so obtained in the physical domain are computed numerically and illustrated graphically at different times, for copper like material. As a special case the effect of diffusion on various expressions has also been obtained analytically and depicted graphically.     

Micellar liquid chromatographic green enantioseparation of racemic amino alcohols and determination of elution order

A micellar liquid chromatographic method was developed for the green enantioseparation of racemic amino alcohols using an aqueous solution of the mixed surfactants as an alternative for organic solvents. In this study, the derivatives of the amino alcohols were synthesized using highly reactive chiral esters of (S)-levofloxacin (Lfx) under microwave conditions, and an aqueous solution of the surfactants (Brij-35 and SDS) was used for the enantioseparation of the synthesized diastereomeric derivatives (DDs) of amino alcohols using reversed-phase HPLC. The activated ester of Lfx was synthesized by reacting with N-hydroxybenzotriazole and characterized using UV, IR, ¹H NMR, high-resolution mass spectrometry, and elemental analysis. The DDs of racemic amino alcohols were separated on a C₁₈ column using micellar LC. Chromatographic conditions were optimized by varying the concentration of the surfactants in aqueous solution and by varying the concentration and pH of the buffer. The green assessment score was calculated for the developed method (score: 82, an excellent green method). In addition, the density functional theory calculations were performed to develop the lowest energy-optimized structures of DDs. The method was validated according to the International Conference of Harmonization guidelines, and the retention factor (k), selectivity factor (α), resolution factor (R_S), limit of detection (0.198 ng mL⁻¹ or 0.291 pM mL⁻¹), and limit of quantification (0.594 ng mL⁻¹ or 0.873 pM mL⁻¹) were calculated.     

The effect of the finite size of ions and Debye layer overspill on the screened Coulomb interactions between charged flat plates

Screened repulsion between uniformly charged plates with an intervening electrolyte is analyzed for strongly overlapped electrical double layers (EDL), accounting for the steric effect of ions and their expulsion from EDL edges into the surrounding solution. As a generalization of a study by Philipse et al. which does not account for these effects, an analytical expression is derived for the repulsion pressure in the limit of infinitely long plates with a zero-field assumption, which agrees closely with the corresponding numerical solution at low inter-plate separations. Our results show an augmented repulsive pressure for finite-sized ions at strong EDL overlaps. For plates with a finite lateral size, we demonstrate a further extended domain of low inter-plate gaps where the repulsion pressure increases with ion size due to a strong interplay between the steric interaction of ions and the EDL overspill phenomenon, considered earlier in a study by Ghosal & Sherwood limited to the linear Debye-Hückel regime (which cannot account for the steric effect of ions). This investigation on a simple model should enhance our understanding of the interaction between charged particles in electrophoresis, nanoscale self-assembly, active particles, and various other electrokinetic systems.     

Core‐Shell Type Semiconducting Heterostructures for Visible Light Photocatalysis

This personal account highlights a part of the work done over the years in our group towards directed synthesis of morphologically controlled nanostructures. We begin with our efforts on the synthesis of families of nanostructured metal oxides and metal oxalates of well‐defined morphology using low temperature microemulsion and hydrothermal techniques. The parameters that govern the morphology in these syntheses e. g. choice of solvent and temperature are described. We then discuss nanostructures with core‐shell architecture and specifically their utilization to harvest visible light for photocatalysis and photoelectrochemical applications. The techniques described to utilize visible light include sensitizing wide bandgap semiconductors using 1) appropriate narrow bandgap materials and 2) metals that have surface plasmon resonance active bands. The reports are classified according to morphology with spherical, cubes and rods discussed in separate sections. A discussion of recent reports by other groups on core‐shell structures of similar composition as well as future directions and perspectives are presented at the end.       

Cancer-Cell-Specific Drug Delivery by a Tumor-Homing CPP-Gossypol Conjugate Employing a Tracelessly Cleavable Linker

Tumor-targeted drug delivery is highly important for improving chemotherapy, as it reduces the dose of cytotoxic agents and minimizes the death of healthy tissues. Towards this goal, a conjugate was synthesized of gossypol and a MCF-7 cancer cell specific CPP (cell penetrating peptide), thus providing a selective drug delivery system. Utilizing the aldehyde moiety of gossypol, the tumor homing CPP RLYMRYYSPTTRRYG was attached through a semi-labile imine linker, which was cleaved in a traceless fashion under aqueous conditions and had a half-life of approximately 10 hours. The conjugate killed MCF-7 cells to a significantly greater extent than HeLa cells or healthy fibroblasts.     

Superconductivity in the 100–120 K region in oxides of the Tl-Ca-Ba-Cu-O system

Oxides with different cation ratios 2122, 2212, 2213 and 2223 in the Ti-Ca-Ba-Cu-O system exhibit onset of superconductivity in the 110–125 K range with zero-resistance in the 95–105 K range. Electron microscopic studies show dislocations, layered morphology and other interesting features. These oxides absorb electromagnetic radiation (9.11 GHz) in the superconducting phase.     

Interaction due to mechanical sources in micropolar elastic medium with voids

The present paper is concerned with the dynamic problem of a homogeneous isotropic half-space with voids subjected to a set of normal point sources. The integral transforms have been inverted by using a numerical technique to obtain the normal force stress, normal displacement, tangential couple stress and volume fraction field in the physical domain for the two different sources. The expressions of these quantities have been given and illustrated graphically to depict the effect of micropolarity and voids.     

Investigation of ionic conduction in the mixed AgI-PbI2 system

Study of ionic conductivity in AgI-PbI₂ system has a function of composition and temperature shows that PbI₂ has a definite role in the process of superionic phase transition. It has been found that at 80 mole % of AgI, superionic phase transition temperature passes through a minimum value of as low as 105°C. The maximum conductivity (at room temperature) is also obtained in this region. The results are discussed qualitatively in terms of a lattice loosening model.