Carbon support effects on Pd/C catalysts for the liquid-phase hydrogenation of multifunctional chemicals

Climate change due to anthropogenic greenhouse gas emissions is a major concern for nations worldwide. In order to mitigate the challenges associated with this issue, it is imperative for industrial sectors to switch to renewable feedstocks and energy sources for decreasing CO2 emissions. Lignocellulosic biomass is one such alternative that demonstrates a promising future, specifically for the sustainable production of chemicals. However, the transition from a petroleum-based to a bio-based chemical industry poses new challenges for catalysis. In contrast to petrochemical reactions that are typically conducted in the gas phase at high temperature, biomass conversion reactions often require low temperature aqueous-phase conditions to mitigate the undesired side reactions and degradation of the feedstock molecules. Metal oxide supports that are commonly used in the petroleum industry (silica, alumina) lose their structural integrity in aqueous environments and, therefore, alternative supports and catalysts need to be developed. Carbon materials represent a suitable alternative to metal oxides as carbon-carbon bonds withstand hydrolytic attacks, under both highly acidic and basic aqueous environments, even in the presence of salts, which makes them a support material of choice for a broad range of biomass conversion reactions. However, these promising materials remain poorly understood and the structure-activity relationships required to design high-performance catalysts are still missing. The present work addresses this gap in knowledge. Specifically, we built this work on the hypothesis that structure-activity correlations can be established for carbon-supported metal catalysts by decreasing the support complexity and controlling the support properties at the nanoscale. We pursued this hypothesis and were able to deconvolve the contributions of the scaffold’s surface chemistry and electronic properties to the catalytic activity of the supported metal active phase. In order to conduct a systematic study of support effects, we developed a synthetic platform based on stacked-cup carbon nanotubes (SCCNTs) as scaffolds. The key advantage of these SCCNTs is their dual structure consisting of a graphitic core and an amorphous carbon shell, which offers a handle on the graphitic character and surface chemistry through simple thermochemical treatments. Pd metal nanoparticles deposited on the SCCNTs were carefully characterized using advanced methods—aberration corrected transmission electron microscopy and synchrotron-based X-ray photoelectron spectroscopy—and the performance of the synthesized catalyst series was evaluated for the hydrogenation of cinnamaldehyde, an α,β-unsaturated aldehyde probe molecule. Strong correlations between the activity and selectivity of Pd/SCCNTs for the liquid phase hydrogenation reaction and the structure of the support were observed. Advanced characterization revealed that the observed trends could be assigned to electronic metal-support interaction (EMSI), resulting in a charge transfer and the formation of an electron-depleted Pdδ+ phase at the metal-carbon interface. Once the presence of EMSI for carbon-supported catalysts was established, we attempted to quantitatively determine the contribution of the Pdδ+ phase to the overall performance of the Pd/C catalyst. Thermal annealing of the samples enabled incremental changes in the Pd particle size and Pd-C contacts. The analysis of the corresponding catalytic results revealed major differences in the selectivity and intrinsic rate of Pd0 and Pdδ+ metal atoms, and demonstrated that controlling the structure of the carbon surface offers a powerful handle for tuning the activity of Pd/C catalysts. As the MSI effects observed in this work were electronic in nature, the catalysts were further investigated by ultraviolet photoelectron spectroscopy in an attempt to explain the origin of the charge transfer and associate it with the scaffold’s electronic properties. Linear correlations between the work function and band gap of SCCNTs and carbon nitride materials and the selectivity towards C=C bond hydrogenation were established. These results are expected to facilitate the development of strategies for rationally designing carbon supports for target biomass conversion reactions. In summary, we developed strategies to control the properties of carbon supports at the nanoscale, we demonstrated the existence of electronic metal-support interactions for carbon-supported precious metal catalysts, and we established structure-activity correlations that may guide the rational design of next-generation hydrogenation catalysts

Functionalization of gold and glass surfaces with magnetic nanoparticles using biomolecular interactions

Advances in nanotechnology have enabled the production and characterization of magnetic particles with nanometer-sized features that can be functionalized with biological recognition elements for clinical and biosensing applications. In the present study the synthesis and interactions between self assembled monolayers (SAMs) and functionalized nanoparticles have been characterized. Size and shape of magnetic nanoparticles synthesized wet chemically starting from ferrous and ferric salts were verified by transmission electron microscopy (TEM). These nanoparticles were then conjugated with FITC-labeled streptavidin through carbodiimide (EDC) chemistry. SAMs of thiol-capped biotins were synthesized on gold surfaces for capture of the conjugated nanoparticles. Characterization of nanoparticle functionalization and binding was performed using fluorescent microscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS). FT-IR spectra confirm the binding of biotin on gold via sulphur linkages. Fluorescent microscopy and XPS show streptavidin bound to the biotinylated gold surfaces. Elemental characterization from EDS indicates the binding of streptavidin-conjugated nanoparticles to biotinylated gold surfaces. Together, these techniques have application in studying the modification and behavior of functionalized nanoparticles for biological and other applications

Evaluation of Gymnema sylvestre Antimicrobial Activity in Methanol

G. sylvestre is a medicinal plant known for its sugar destroying property, as an anti-diabetic agent. The major phytoconstituents are the triterpenoid saponins, responsible for the various activities. The antimicrobial activity of this plant has been assessed in methanol as the solvent system for the extraction of active principles. The gram positive and gram negative organisms used in the study, have shown susceptibility towards the extracts, with the root extracts at acidic pH, showing higher activity. E. coli and E. cloacae were found to be the most sensitive and Pseudomonas aeruginosa, the resistant type of microorganisms, based on the results obtained from the zones of inhibition. The broad spectrum activity of the plant can be utilised in the development of new antimicrobial drugs

A Unified Framework for Sparse Non-Negative Least Squares using Multiplicative Updates and the Non-Negative Matrix Factorization Problem

We study the sparse non-negative least squares (S-NNLS) problem. S-NNLS occurs naturally in a wide variety of applications where an unknown, non-negative quantity must be recovered from linear measurements. We present a unified framework for S-NNLS based on a rectified power exponential scale mixture prior on the sparse codes. We show that the proposed framework encompasses a large class of S-NNLS algorithms and provide a computationally efficient inference procedure based on multiplicative update rules. Such update rules are convenient for solving large sets of S-NNLS problems simultaneously, which is required in contexts like sparse non-negative matrix factorization (S-NMF). We provide theoretical justification for the proposed approach by showing that the local minima of the objective function being optimized are sparse and the S-NNLS algorithms presented are guaranteed to converge to a set of stationary points of the objective function. We then extend our framework to S-NMF, showing that our framework leads to many well known S-NMF algorithms under specific choices of prior and providing a guarantee that a popular subclass of the proposed algorithms converges to a set of stationary points of the objective function. Finally, we study the performance of the proposed approaches on synthetic and real-world data.Comment: To appear in Signal Processin

Antimicrobial Activity of the Extracts of Salacia oblonga Wall.

Salacia oblonga Wall. belonging to the family celastraceae is used in the treatment of diabetes, rheumatism, gonorrhoea, itches, asthma, wound healing, amenorrhea and ear diseases. It is a woody climber distributed in Sri Lanka and Southern regions of India. In the present study antimicrobial activity of Salacia oblonga was evaluated against pathogenic strains, gram +ve Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Bacillus subtilis, Listeria monocytogenes and gram -ve Klebsiella pneumoniae, Enterobacter aerogenes, Enterobacter cloacae, Pseudomonas aeruginosa, Escherichia coli, Salmonella typhimurium. Ethyl acetate (EtOAc) aerial and root part extracts of Salacia oblonga have shown good activity towards all the pathogenic species. The zones of inhibition in the acidic EtOAc aerial and root extracts were measured to assess the antimicrobial activity

NON-HEPATIC HYPERAMMONEMIC COMA: A CASE REPORT

ABSTRACTWhile the most common cause of hyperammonemic (HA) coma is hepatic disorder, other rare etiologies to be considered include congenital causes,drug induced states, portosystemic shunts, and urinary tract infections with urea-splitting organisms. HA usually results from one of the followingthree mechanisms: A relative excessive nitrogen load on a normal functioning liver via the portal circulation (e.g., parenteral nutrition in a patientwith urea cycle defect); ammonia bypassing liver (e.g., congenital vascular malformations, portal hypertension in cirrhotic patients); or from impairedammonia metabolism. Herein, we describe a case of HA coma secondary to an interplay of multiple psychiatric drugs mainly sodium valproate andprobably an added effect by the lithium-induced hypothyroidism/myxedema.Keywords: Drug-induced, Hyperammonemia, Lithium, Myxedema, Valproic acid

Respiration rate model for mature green capsicum (Capsicum annum L.) under closed aerobic atmospheric conditions

The respiration rate of green capsicum cv. ‘Swarna’ fruits harvested at mature green stage were determined under closed system at 10, 15 and 20 ºC temperatures. A simple Michaelis-Menten kinetic model coupled with Arrhenius-type equation, which describes temperature as a function of respiration rate, was used to model the respiration rate of capsicum. The respiration rate model parameters at defined temperature were estimated by fitting the model to the experimental set of data by non-linear regression analysis method. The respiration rate of green mature capsicum was influenced by the temper¬ature. The Arrhenius equation well described the relationship between enzyme kinematics model parameters and temperature. The values of Michaelis-Menten constant for oxygen (Kmo2) and carbon dioxide (Kmco2) were found to vary from 2.14 to 3.92 and 1.33 to 3.24, respectively at different temperature. Experimental and predicted RRO2 values for mature green capsicum was found to be ranged from 9.54 to 14.54 and 11.81 to 17.52 mg/kg-h, respectively. Whereas, the experimental and predicted RRCO2 were 20.1 to 38.51 and 22.15 to 39.83 mg/ kg-h, respectively