Showing papers by "Anju Chadha published in 2013"

A Miniaturized pH Sensor With an Embedded Counter Electrode and a Readout Circuit

Abstract: Electrolyte insulator semiconductor capacitors (EISCAPs) show a shift in the measured capacitance-voltage (C-V) characteristics with changes in the pH of the electrolyte and has the potential to be used as biosensors. The choice of an electrode to the EISCAP is important for reliable measurements. Here, we discuss a silicon-based EISCAP sensor bonded to a glass wafer with an embedded electrode. Three noble metal electrodes (Pt, Au, Ag) are studied for the ease of integration and performance and it is found that the chloridized Ag electrodes exhibit the highest pH sensitivity and the lowest electrode potential drift with time. A readout system that measures the pH of the electrolyte under test is developed and implemented in a programmable system on chip. Calibration of the EISCAP to account for sensor process variations is also incorporated. The pH measurement data on the miniaturized EISCAPs is presented.

Asymmetric Reduction of Alkyl-3-oxobutanoates by Candida parapsilosis ATCC 7330: Insights into Solvent and Substrate Optimisation of the Biocatalytic Reaction

Abstract: Asymmetric reduction of alkyl-3-oxobutanoates mediated by Candida parapsilosis ATCC 7330 resulted in optically pure alkyl-3-hydroxybutanoates in good yields (up to 72 %) and excellent enantiomeric excess (up to >99 %). A detailed and systematic optimisation study was necessary and was carried out to avoid the undesired transesterification reaction during the course of asymmetric reduction. Under optimised conditions, the (S)-alkyl hydroxyesters were produced predominantly except for the methyl ester which formed the (R)-enantiomer. To the best of our knowledge, the biocatalytic asymmetric reduction of isoamyl-3-oxobutanoate to (S)-isoamyl-3-hydroxybutanoate is reported here for the first time.

Expression, purification, crystallization and preliminary X-ray diffraction analysis of carbonyl reductase from Candida parapsilosis ATCC 7330.

Abstract: The NAD(P)H-dependent carbonyl reductase from Candida parapsilosis ATCC 7330 catalyses the asymmetric reduction of ethyl 4-phenyl-2-oxobutanoate to ethyl (R)-4-phenyl-2-hydroxybutanoate, a precursor of angiotensin-converting enzyme inhibitors such as Cilazapril and Benazepril. The carbonyl reductase was expressed in Escherichia coli and purified by GST-affinity and size-exclusion chromatography. Crystals were obtained by the hanging-drop vapour-diffusion method and diffracted to 1.86 A resolution. The asymmetric unit contained two molecules of carbonyl reductase, with a solvent content of 48%. The structure was solved by molecular replacement using cinnamyl alcohol dehydrogenase from Saccharomyces cerevisiae as a search model.

A simple and efficient method for mild and selective oxidation of propargylic alcohols using TEMPO and calcium hypochlorite

Abstract: Oxidation of propargylic alcohols to the corresponding aldehydes and ketones was achieved at room temperature using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and calcium hypochlorite (Ca(OCl)2). Propargylic diols yielded corresponding dialdehydes as the product. This system was found to be very efficient for both the electron donating and electron withdrawing groups such as methoxy and nitro substituted alcohols, respectively. This method does not require any additives and demonstrates the controlled, selective oxidation of propargylic alcohols affording up to 97% isolated yield.

A novel green route for the synthesis of N-phenylacetamides, benzimidazoles and acridinediones using Candida parapsilosis ATCC 7330

Abstract: Biocatalytic preparation of various substituted N-phenylacetamides was carried out for the first time using whole cells of Candida parapsilosis ATCC 7330 under mild reaction conditions with excellent conversions (up to 93%) and good yields (up to 81%). Arylamine N-acetyltransferase (NAT) from whole cells of Candida parapsilosis ATCC 7330 is implicated in the N-acylation which is known to transfer the acetyl group from acetyl CoA (coenzyme A) to aromatic amines. Mechanistic investigation carried out using deuterated ethanol to find the source of acetyl CoA revealed that the reaction proceeds through the formation of acetaldehyde in situ, which is a potential source for the acetyl group of cytoplasmic acetyl CoA. Furthermore, experiments on regioselectivity, carried out with 2-phenylenediamine (2-PDA) resulted in a cyclised product 2-methyl benzimidazole (conversion 99%). The biocatalyst also mediates the cyclization of 3-(phenylamino)cyclohex-2-enones in the presence of the in situ generated acetaldehyde to form acridine-1,8-diones (conversion up to 70%), which is a green process reported here for the first time.

Simplified Procedure for TEMPO‐Catalyzed Oxidation: Selective Oxidation of Alcohols, α‐Hydroxy Esters, and Amides Using TEMPO and Calcium Hypochlorite.

Abstract: The method presented does not require any transition metals, acids or bases and demonstrates controlled and selective oxidation of structurally diverse alcohols.

Compact silicon biosensor for the clinical range estimation of blood serum triglycéride

Abstract: Electrolyte Insulator Semiconductor Capacitor (El S CAP) is a transducer that can detect triglycerides (TGs) in blood serum through an enzymatic response that changes the pH of the electrolyte (blood serum). This change in pH is transformed by the EISCAP to a shift in the capacitance-voltage (C-V) characteristics of the device which in turn can be mapped to the amount of TG in blood serum. We have developed a miniaturized biochip with immobilized enzyme integrated with a thin film counter electrode for the estimation of TG in blood serum within the clinical range. The miniaturized devices are tested using blood serum sample to estimate the TG concentration and compared with clinical data.