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Divyalakshmi T.V.,Mahatma Gandhi University | Sreedhanya S.,Mahatma Gandhi University | Akhil G.,Mahatma Gandhi University | Aravindakumar C.T.,Mahatma Gandhi University | And 2 more authors.
Analytical Biochemistry | Year: 2013

The use of ovalbumin (OVA)-immobilized layer-by-layer-assembled chitosan/polystyrene sulfonate membranes for the detection of hydrogen peroxide (H2O2) at subpicomolar levels is reported. The detection of mercuric chloride (HgCl2) and potassium iodide (KI) was also investigated. While the detection limits of HgCl2 and KI remained in the micromolar concentration range, H2O2 could be sensed to a remarkably lower range (subpicomolar). Analysis of fluorescence quenching data of OVA by H2O2 using Stern-Volmer plots revealed a static quenching mechanism with high Stern-Volmer quenching constant (9.10 × 1012 L mol-1) and k (5.82 × 1021 L mol-1 s-1). The possibility of the conformational transition of OVA in the immobilized state is discussed using steady-state and time-resolved spectroscopic techniques. The resulting increased accessibility of tryptophan residues together with the reversibility of the bilayer for the sensing of H2O2 is also illustrated. © 2013 Elsevier Inc. Source


Disha V.J.,Mahatma Gandhi University | Aravindakumar C.T.,Mahatma Gandhi University | Aravind U.K.,Mahatma Gandhi University | Aravind U.K.,Center for Environment Education and Technology
Langmuir | Year: 2012

This work illustrates the potential use of PEI/PSS bilayers assembled via layer by layer (lbl) method on a nylon microfiltration membrane for the recovery of phosphate from water in the presence of chloride under ultrafiltration conditions. A total of nine bilayers were used for the selective recovery of phosphate. Bilayers were constructed from polyelectrolyte solutions of varying ionic strength (0 1 M of NaCl). The selected pH for deposition of PEI (5.9) and the presence of supporting salt in the polyelectrolyte solution is expected to provide membranes with high permeability and high charge density. This particular combination of bilayers yielded high flux membranes that allowed selective removal of H 2PO 4 in the presence of Cl at low pressure (0.28 bar). The magnitude of negative solute rejection of chloride showed increasing trend with the number of bilayer for a particular salt concentration. Whereas the increase in magnitude with ionic strength is so high (-6.18 to -269.17 at 0.5 M NaCl for 9 bl) that gave the best observed Cl/H 2PO 4 selectivity (310.23, flux 13.53 m 3/m 2-day). To the best of our knowledge, this is the first time a multilayer polyelectrolyte system with such a high selectivity and rejection for H 2PO 4 is reported. The solution flux decreased with the number of bilayers and ionic strength. The rejection of phosphate was dependent on feed pH, concentration of deposited polyelectrolyte solution, and composition of membrane support. © 2012 American Chemical Society. Source


Mathew M.,Mahatma Gandhi University | Sreedhanya S.,Mahatma Gandhi University | Manoj P.,Mahatma Gandhi University | Aravindakumar C.T.,Mahatma Gandhi University | And 2 more authors.
Journal of Physical Chemistry B | Year: 2014

The interaction of bisphenol-S (BPS) with serum albumins using steady-state, synchronous, time-resolved, and circular dichroism spectroscopies has been investigated. The binding interactions have also been investigated in the case of bisphenol A (BPA). The fluorescence quenching pathways are different for both of these endocrine disrupting compounds. Steady-state and time-resolved studies reveal static quenching at lower concentrations of BPS and dynamic quenching at higher concentrations. CD results also maintained the concentration dependent variation with a complete distortion of α-helices at 10-5 M BPS. Besides this, addition of sodium dodecyl sulfate (SDS) results in the further unfolding of protein in the case of BPS, whereas time-resolved studies indicated refolding for BPA denatured human serum albumin (HSA). The entire study indicates an irreversible binding of BPS with HSA. Hence, these results reveal the possible involvement of BPS in the physiological pathway raising a health threat as already their presences in body fluids are known. © 2014 American Chemical Society. Source


Sasi S.,Mahatma Gandhi University | Rayaroth M.P.,Mahatma Gandhi University | Devadasan D.,Mahatma Gandhi University | Aravind U.K.,Mahatma Gandhi University | And 2 more authors.
Journal of Hazardous Materials | Year: 2015

The study on the possible pathway of hydroxyl radicals mediated sonolytic degradation of paraben in water is reported. Methylparaben (MPB) which is the most utilized of paraben family is selected as a model emerging pollutant. The influence of common anions and some selected emerging contaminants that may coexist in typical water matrix on the degradation pattern is analyzed alongside. Among the anions, carbonate presents a negative influence which is attributed to the competition for OH radical. Some emerging contaminants also showed negative impact on degradation as was clear from HPLC data. The intermediates, analyzed by LC-Q-TOF-MS include hydroxylated and hydrolytic products. Three major steps (aromatic hydroxylation, hydroxylation at the ester chain and hydrolysis) are proposed to involve in the reaction of OH radical with MPB which ultimately leads to mineralization. The intensity of formation and decay of mono and dihydroxy products of MPB in the presence of additives have also been evaluated. COD analysis indicates a percentage reduction of 98% at 90. min of sonolysis and further increase in the degradation time resulted complete mineralization, which became evident from the mass spectrometric data. MTT assay revealed considerable decrease in the potential cytotoxicity. © 2015 Elsevier B.V.. Source


Sunil Paul M.M.,Mahatma Gandhi University | Aravind U.K.,Mahatma Gandhi University | Aravind U.K.,Center for Environment Education and Technology | Pramod G.,Nss Hindu College | Aravindakumar C.T.,Mahatma Gandhi University
Chemosphere | Year: 2013

Oxidative degradation of fensulfothion, a model organophosphorus compound, has been investigated by pulse radiolysis and H2O2/UV photolysis. A nearly complete transformation of fensulfothion was observed within 4min of irradiation. Very little Total Organic Carbon (TOC) reduction was obtained at this time scale. When the product studies at this stage were conducted using LC-MS/MS analyses, nearly 20 transformation products were obtained. The entire products were identified as from the reaction of OH with fensulfothion or with some of its initially transformed products. Nearly 80% reduction in TOC was observed when photolysis was conducted using higher concentrations of H2O2 at longer time scale. A reaction rate constant (bimolecular) of 1.10×1010dm3mol-1s-1 was obtained for the reaction of OH with fensulfothion using pulse radiolysis technique. The transient absorption spectrum obtained from the reaction of OH has a maximum at 280nm and a weak, broad maximum around 500nm along with a small shoulder around 340nm. The intermediate spectrum is assigned to the radical cation of fensulfothion (3) and the hydroxyl radical adducts (1 and 2). This assignment is supported by the intermediate spectrum (λmax at 280nm) from the reaction of sulfate radical anion (SO4-) (k2=3.20×109dm3mol-1s-1) which is a one electron oxidant. It is thus demonstrated that the combination of both pulse radiolysis and the product estimation using LC-MS/MS is ideal in probing the complete mechanism which is very important in the mineralization reactions using Advanced Oxidation Processes. © 2012 Elsevier Ltd. Source

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