Sooboo Singh

Synthesis and Characterization of Layered Double Hydroxides and Their Potential as Nonviral Gene Delivery Vehicles

Layered double hydroxides (LDHs) exhibit characteristic anion-exchange chemistry making them ideal carriers of negatively charged molecules like deoxyribonucleic acid (DNA). In this study, hydrotalcite (Mg−Al) and hydrotalcite-like compounds (Mg−Fe, Zn−Al, and Zn−Fe), also known as LDHs, were evaluated for their potential application as a carrier of DNA. LDHs were prepared by coprecipitation at low supersaturation and characterized by Powder X-ray diffraction (XRD), infrared (IR), Raman, and inductively coupled plasma—optical emission spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD patterns showed strong and sharp diffraction peaks for the (003) and (006) planes indicating well-ordered crystalline materials. TEM images yielded irregular circular to hexagonal-shaped particles of 50–250 nm in size. Varying degrees of DNA binding was observed for all the compounds, and nuclease digestion studies revealed that the LDHs afford some degree of protection to the bound DNA. Minimal toxicity was observed in human embryonic kidney (HEK293), cervical cancer (HeLa) and hepatocellular carcinoma (HepG2) cell lines with most showing a cell viability in excess of 80 %. All LDH complexes promoted significant levels of luciferase gene expression, with the DNA:Mg−Al LDHs proving to be the most efficient in all cell lines.

Solvent-free Knoevenagel condensation over iridium and platinum hydroxyapatites

The Knoevenagel condensation between various aldehydes (benzaldehyde, p-methoxybenzaldehyde and 1-naphthaldehyde) and esters (ethylcyanoacetate, ethylacetoacetate and diethylmalonoester) was carried out under solvent-free condition in the presence of iridium or platinum hydroxyapatites as a catalyst.

Solvent-Free Knoevenagel Condensation over Cobalt Hydroxyapatite

The Knoevenagel condensation between various aldehydes (benzaldehyde, 1-naphthaldehyde, p-bromobenzaldehyde and p-methoxybenzaldehyde) and esters (ethylcyanoacetate, ethylacetoacetate and diethylmalonoester) was carried out under solvent free condition in the presence of cobalt hydroxyapatite (CoHAp), as a catalyst. Good to excellent yields (35–96%) were obtained. The catalyst is found to be superior over fluorapatite and several other heterogeneous catalysts. The catalyst can be recycled at least 3 times.

Efficient Solvent Free Knoevenagel Condensation Over Vanadium Containing Heteropolyacid Catalysts

Various V/P mole ratios of vanadium substituted Keggin-type phosphomolybdic acids were synthesized by the hydrothermal method. These materials were characterized using several physico-chemical techniques such as X-ray diffraction, FT-IR, N2-sorption, Raman spectroscopy, 31P MAS NMR, SEM and NH3-TPD. FT-IR, Raman spectroscopy and 31P NMR results confirm the formation of the primary structure of the Keggin ion and its crystalline nature is shown clearly by XRD. NH3-TPD results reveal that the acidity of the materials systematically decreases with increasing vanadium content. The Knoevenagel reaction carried out over vanadium substituted phosphomolybdic acid with various V/P mole ratios indicate that the higher V/P mole ratio exhibits better catalytic performance under solvent free conditions. The catalytic properties correlate with the structural properties and the acidity of the materials.Graphical Abstract

The Role of Copper Exchanged Phosphomolybdic Acid Catalyst for Knoevenagel Condensation

Cu exchanged heteropolyacid catalysts were synthesized by ion exchange method and characterized using various physico-chemical techniques such as X-ray diffraction (XRD), FT-IR, Raman, BET surface area, temperature programmed desorption (TPD) of ammonia, 31P NMR, pyridine adsorbed FT-IR spectroscopy, ICP-AES and STEM analysis. XRD diffractograms shows crystallites of heteropolyacid, while FT-IR and Raman spectra indicate that the Keggin ion is retained in the catalysts. 31P NMR, ammonia TPD and pyridine adsorbed FT-IR spectra results suggest that acidity decreases once Cu was incorporated in the heteropolyacid catalyst. For the Knoevenagel condensation reaction, the Cu exchanged phosphomolybdic acid (Cu–PMA) exhibits better catalytic performance than the phosphomolybdic acid (PMA) catalyst and this is related closely with the structural and acidic properties of the catalyst.Graphical Abstract

CO oxidation activity enhancement of Ce0.95Cu0.05O2−δ induced by Pd co-substitution

A bimetallic, ionic, Ce0.93Pd0.02Cu0.05O2−δ catalyst was synthesized in one step using a urea-assisted solution combustion method. The structural and electronic properties of the catalyst were studied by different techniques together with those of mono-metallic analogues. The catalytic performance of the materials was investigated using CO oxidation as the model exhaust reaction and the nature of the active sites was examined by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). X-ray diffraction (XRD), Raman spectroscopy, XPS, XANES, EXAFS and high resolution transmission electron microscopy (HR-TEM) revealed that the prepared materials are single-phase, solid-solution oxides with a fluorite structure. In situ XRD studies showed that the prepared materials are metastable up to 1100 °C. The correlation of the characterization and catalytic results indicates that catalytic performance is influenced by the presence of oxygen vacancies and the existence of synergism between Pd2+, Cu2+ and cerium ions. DRIFTS results revealed that CO interacts with the active centres already at room temperature, forming Cu+ and Pd2+ carbonyls.

An investigation of Cu–Re–ZnO catalysts for the hydrogenolysis of glycerol under continuous flow conditions

Cu and Re monometallic and bimetallic catalysts supported on ZnO were synthesized via wet impregnation. The catalysts were characterized using XRD, TPR, Pulse TPD, TEM, SEM, XPS and BET surface area. TPR results showed that the presence of rhenium increases the reduction temperature of the catalysts and TPD showed that the presence of copper decreases the Bronsted acidity of the catalysts. SEM showed an improved distribution of metal oxide on the support after the incorporation of rhenium. These catalysts were evaluated in the hydrogenolysis of glycerol in a continuous flow fixed bed reactor in a temperature range of 150–250 °C and a H2 pressure of 60 bar. All catalysts were active, with activity being higher over the rhenium containing catalysts. At the lowest temperature (150 °C), 1,2-propanediol had the highest selectivity which decreased with increase in temperature. Subsequently, the selectivity to lower alcohols, such as methanol, ethanol and 1-propanol, and ethylene glycol increased with temperature as 1,2-propanediol reacted further to these products due to C–C bond cleavage. This was also observed when the hydrogen content was increased at constant temperature (250 °C). All catalysts were found to be stable in terms of activity and selectivity to lower alcohols over a period of at least 24 hours at 250 °C and 60 bar H2 pressure.

Ternary (Cu, Ni and Co) Nanocatalysts for Hydrogenation of Octanal to Octanol: An Insight into the Cooperative Effect

Ternary metal oxides (Cu–Ni–Co) with different wt% loadings were supported on alumina by using an ultrasonic cavitation-impregnation method. A comparative silica catalyst was also prepared. Powder X-ray diffraction (XRD) showed the presence of the metal oxides on the surface of the supports and from in situ XRD results, the formation of metallic phases under a reducing atmosphere were observed. Temperature-programmed desorption (TPD) revealed the presence of Lewis and Brønsted acidic sites in the catalysts. The metals supported on alumina showed a better dispersion compared to that on the silica support. All the catalysts were tested for the hydrogenation of octanal in a mixture of 10% octanal in octanol in a continuous flow fixed bed reactor by varying the pressure, temperature and hydrogen molar ratios. Under the hydrogenation conditions, the trimetallic catalysts (with Cu, Ni and Co) showed best catalytic performance for octanal hydrogenation when compared to bimetallic catalysts. The conversion of octanal and the selectivity towards octanol increased in proportion to an increase in the total metallic content and metal dispersion. The alumina based catalysts showed better activity compared to the silica catalyst due to higher metal dispersion. The silica supported catalyst showed a high selectivity towards C24 acetal due to its higher acidity and the product distribution over all the catalysts is in agreement with the distribution of acidic sites.Graphical Abstract

Simultaneous removal of 2,4,6-tribromophenol from water and bromate ion minimization by ozonation

The study investigates the degradation of 2,4,6-tribromophenol (2,4,6-TBP) and the influence of solution pH, alkalinity, H2O2 and O3 dosage. Debromination efficiency of 2,4,6-TBP was the highest in basic water (pH = 10.61). The extent of TOC removal compared favourably with the amount of substrate converted, suggesting favourable mineralization of oxygenated by-products (OBPs). Ozonation in basic water favoured the formation of toxicBrO3-, while in acidic water (pH = 2.27) BrO3- yield was lowest. In acidic water the presence of CO32- showed negligible effect on conversion, TOC and  BrO3- yield compared to ozonation alone. In basic water both 2,4,6-TBP conversion and TOC removal decreased with an increase in CO32-, hence minimizing BrO3- formation. The O3/H2O2 process showed an improvement in the debromination efficiency and TOC data revealed that total mineralization of OBPs was achieved. However, only 10% H2O2 was able to effectively decrease BrO3- formation. Increasing the ozone concentration from 20 to 100 ppm enhanced the conversion of 2,4,6-TBP and TOC removal. At low ozone concentrations poor mineralization of OBPs occurred, while complete mineralization was achieved at higher ozone dose. The reaction pathways for ozone degradation of 2,4,6-TBP in acidic and basic waters is proposed.

The Role of Alkali Metal Exchanged Phosphomolybdic Acid Catalysts in the Solvent Free Oxidation of Styrene to Benzaldehyde at Room Temperature

A series of alkali metal exchanged phosphomolybdic acid catalysts were synthesized by ion exchange, characterized by various physico-chemical techniques and used in the solvent free oxidation of styrene to benzaldehyde. XRD and infrared results showed that the primary structure of the Keggin ion usually present in phosphomolybdic acid is retained after metal exchange. HR-TEM analysis show a well-constructed spherical morphology of the materials with a lower degree of crystalinity. Type IV isotherms with mesoporous structure are observed from nitrogen adsorption–desorption isotherm studies and ex situ pyridine adsorption experiments reveal that Brønsted acidic sites increased after metal exchange. The K exchanged phosphomolybdic acid catalysts were most efficient in the conversion of styrene to benzaldehyde and the order of reactivity of the alkali metal exchanged phosphomolybdic acid catalysts was K > Rb > Cs. Insight into the reaction pathway by investigating the oxidation styrene oxide was obtained. The results show that phenyl acetaldehyde together with benzaldehyde are produced, providing some evidence that styrene oxidation proceeds via C=C cleavage to selectively produce benzaldehyde. The catalyst was easily recovered and was reused for up to three cycles showing stable activity.Graphical Abstract