Acetalization of glycerol using mesoporous MoO3/SiO2 solid acid catalyst

Acetalization of glycerol with various aldehydes has been carried out using mesoporous MoO₃/SiO₂ as a solid acid catalyst. A series of MoO₃/SiO₂ catalysts with varying MoO₃ loadings (1–20 mol%) were prepared by sol–gel technique using ethyl silicate-40 and ammonium heptamolybdate as silica and molybdenum source respectively. The sol–gel derived samples were calcined at 500 °C and characterized using various physicochemical characterization techniques. The XRD of the calcined samples showed the formation of amorphous phase up to 10 mol% MoO₃ loading and at higher loading of crystalline α-MoO₃ on amorphous silica support. TEM analyses of the materials showed the uniform distribution of MoO₃ nanoparticles on amorphous silica support. Raman spectroscopy showed the formation of silicomolybdic acid at low Mo loading and a mixture of α-MoO₃ and polymolybdate species at high Mo loadings. Moreover the Raman spectra of intermediate loading samples also suggest the presence of β-MoO₃. Acetalization of glycerol with benzaldehyde was carried out using series of MoO₃/SiO₂ catalysts with varying MoO₃ loadings (1–20 mol%). Among the series, MoO₃/SiO₂ with 20 mol% MoO₃ loadings was found to be the most active catalyst in acetalization under mild conditions. Maximum conversion of benzaldehyde (72%) was obtained in 8 h at 100 °C with 60% selectivity for the six-membered acetal using 20% MoO₃/SiO₂. Interestingly with substituted benzaldehydes under same reaction conditions the conversion of aldehydes decreased with increase in selectivity for six-membered acetals. These results indicate the potential of this catalyst for the acetalization of glycerol for an environmentally benign process.     

Enhancing the dissolution of hydrophobic guests using solid state inclusion complexation: characterization and in vitro evaluation

The objectives of the present investigation were to prepare and characterize solid inclusion complexes of Etodolac (ETD) with β-cyclodextrin (β-CD) in order to study the effect of complexation on the dissolution rate of ETD, a hydrophobic guest molecule. Phase solubility curve was classified as a typical A_L-type for the cyclodextrins (CD’s), showing that soluble complex was formed. The inclusion complexes in the molar ratio of 1:1 and 1:2 (β-CD–ETD) were prepared by various methods such as kneading, co-evaporation and in molar ratio of 1:1 by spray dried technique respectively. The molecular behaviors of ETD in all samples were characterized by nuclear magnetic resonance (NMR) spectroscopy, fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) studies and Scanning Electron microscopy (SEM) analysis. The results of these studies indicated that complexes prepared by kneading, co-evaporation and spray drying techniques showed inclusion of the ETD molecule into the CD’s cavities. The highest improvement in in vitro dissolution profiles was observed in complexes prepared with spray dried technique. Mean in vitro dissolution time indicated significant difference between the release profiles of ETD from complexes and physical mixtures and from pure ETD.     

Stereochemical preference of Candida parapsilosis ATCC 7330 mediated deracemization: E- versus Z-aryl secondary alcohols

The stereochemical preference of the biocatalyst, Candida parapsilosis ATCC 7330, was investigated with respect to the E/Z configuration in the deracemization and the asymmetric reduction of aryl secondary alcohols and prochiral ketones, respectively. The biocatalyst preferred the E-isomers over Z-isomers as substrates as evidenced from the experimental results of >99% ee and up to 86% isolated yield for E-secondary alcohols. The synthesis of enantiomerically pure E-4-phenylbut-3-ene-1,2-diol (ee >99%, isolated yield 86%) by whole cell mediated deracemization is reported here for the first time. The geometric preference of the enzymes was confirmed by using the cell free extract of this biocatalyst. Mechanistic insights using in silico studies showed that the E-isomers when located in the active site are favourably placed with respect to the catalytic triad (Ser-Tyr-Lys) for hydride transfer from NADPH.     

Chitosan-Modified Carbon Nanotubes-Based Platform for Low-Density Lipoprotein Detection

We have fabricated an immunosensor based on carbon nanotubes and chitosan (CNT-CH) composite for detection of low density lipoprotein (LDL) molecules via electrochemical impedance technique. The CNT-CH composite deposited on indium tin oxide (ITO)-coated glass electrode has been used to covalently interact with anti-apolipoprotein B (antibody: AAB) via a co-entrapment method. The biofunctionalization of AAB on carboxylated CNT-CH surface has been confirmed by Fourier transform infrared spectroscopic and electron microscopic studies. The covalent functionalization of antibody on transducer surface reveals higher stability and reproducibility of the fabricated immunosensor. Electrochemical properties of the AAB/CNT-CH/ITO electrode have been investigated using cyclic voltammetric and impedimetric techniques. The impedimetric response of the AAB/CNT-CH/ITO immunoelectrode shows a high sensitivity of 0.953?Ω/(mg/dL)/cm² in a detection range of 0–120 mg/dL and low detection limit of 12.5 mg/dL with a regression coefficient of 0.996. The observed low value of association constant (0.34 M^–1s^–1) indicates high affinity of AAB/CNT-CH/ITO immunoelectrode towards LDL molecules. This fabricated immunosensor allows quantitative estimation of LDL concentration with distinguishable variation in the impedance signal.     

Conformation and distribution of groups on the surface of amphiphilic polyether-co-polyester dendrimers: effect of molecular architecture

Amphiphilic polyester-co-polyether (PEPE) dendrimers synthesized from poly(ethylene glycol) (PEG) were examined to understand the influence of alterations in the architecture of dendrimers on their conformation at interfaces and distribution of various groups on their surface. Effect of changes in the number of branching points, type of terminal functional groups and generation of dendrimer was primarily evaluated. Dendrimers were deposited on mica by spin coating at 0.1 mg/mL. Tapping mode atomic force microscopy (AFM) was employed for the visualization of dendrimer topographies while, X-ray photoelectron spectroscopy (XPS), AFM phase and force imaging were used as the tools for characterization of their surfaces. Individual dendrimer molecules could be imaged by AFM, which showed that they are round or oval in topography. Dendrimers were also flattened on mica but the extent of flattening differed with the chemical structure; for instance, third generation dendrimers were more flattened than second generation dendrimers whereas, dendrimers with higher number of branches had greater height above the mica surface. Hydrophilic and hydrophobic groups present towards the aerial interface existed in distinct zones rather than being distributed randomly, except in dendrimer with higher number of branches. The percentage of various hydrophobic groups on the surface of dendrimer was enhanced by increase in the number of branches but, was lowered by the presence of hydroxyl groups as the pendant terminal groups. Furthermore, the core of dendrimers was not always located towards the centre, its position was found to be altered by the number of branching points, type of terminal functional groups and the generation of dendrimer.     

Ultrathin conjugated polymer network films of carbazole functionalized poly(p-phenylenes) via electropolymerization

Ultrathin films of a cross-linked and chemically distinct conjugated poly(p-phenylene) network via electropolymerization are described. The amphiphilic network precursor was synthesized by incorporating the alkoxy carbazole group (-O(CH2)5Cb) to a poly(p-phenylene) (C6PPPOH) backbone. In order to investigate the combined thin film electrochemical and photophysical properties of poly(p-phenylene)s and polycarbazole conjugated polymers, C6PPPC5Cb was deposited on substrates using the Langmuir Blodgett Kuhn (LBK) method. The monolayer isotherm of the polymer, C6PPPC5Cb, showed a liquid expanded region slightly different from the parent polymer C6PPPOH. Multilayers (up to 30 layers) were transferred to different substrates such as quartz, gold coated LaSFN9 and ITO substrates for analysis. For conversion to a conjugated polymer network (CPN) film, the electroactive carbazole group was electropolymerized using cyclic voltammetry (CV) resulting in polycarbazole linking units. The differences in the film properties and corresponding changes in the electrochemical behavior indicate the importance of film thickness and electron/ion transport process in cross linked network films. From the electrochemical studies, the scan rate was found to have a considerable effect on electropolymerization with higher oxidation and reduction peak values found for the rigid network polymer compared to the uncrosslinked polymers.     

HPLC–QTOF–MS/MS-based rapid screening of phenolics and triterpenic acids in leaf extracts of Ocimum species and their interspecies variation

Species of genus Ocimum are traditionally used for their medicinal and flavoring properties. These are rich sources of essential oils and found as an ingredient in many Ayurvedic preparations and food products. Phenolics and triterpenic acids are the medicinally active compounds mainly concentrated in the leaves of Ocimum species. This study aimed to develop an efficient and reliable analytical method for the rapid screening and characterization of phenolics and triterpenic acids in the leaf extracts of 6 Ocimum species using high-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (HPLC–ESI–QTOF–MS/MS). A total of 50 compounds were identified and characterized on the basis of their accurate MS and MS/MS information, out of which 23 compounds were confirmed by authentic standards. Identified compounds include 28 flavonoids, 4 propenyl phenol derivatives, 2 triterpenic acids, 11 phenolic acids, and 5 phenolic acid esters. The developed method was applied to study the interspecies variation of identified compounds. Significant variation in the distribution of identified phenolics and triterpenic acids was observed among studied Ocimum species. Hence, the established method provides an effective and reliable tool for screening and characterization of phytoconstituents in Ocimum species.