Browsing by Author "Susanta K. Sen Gupta"

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A quantitative solvent effect analysis on proton transfer equilibrium between m-fluorobenzoic acid and the carbinol base of crystal violet in apolar aprotic solvents
(1999) Susanta K. Sen Gupta; V. Radha Rani
A study of detailed pattern of solvent effects on proton transfer equilibrium between m-fluorobenzoic acid and the carbinol base of crystal violet in eight select apolar aprotic solvents shows that the solvent effect is contributed by electrostatic and dispersion interactions in an almost equal ratio (48: 52).
Acid–base equilibria and kinetics between triarylmethane dye carbinols and organic acids in apolar aprotic solvents: Relative basicities of dye carbinols in toluene
(1993) Susanta K. Sen Gupta; Udai Arvind
Equilibria and kinetics of acid–base reactions in toluene between a carboxylic acid (m‐toluic, salicylic acid) and a set of carbinol bases (derived from basic triarylmethane dyes) were studied spectrophotometrically. The results for the equilibrium and kinetic parameters were critically analysed. The rate constant of the forward step of the acid–carbinol base equilbrium was found to provide a suitable scale of basicities in toluene. The basicities of the dye carbinols chosen decrease in the order Ethyl Violet‐ >Crystal Violet‐ >Methyl Violet‐ ≈ Victoria Pure Blue BO‐ ≫ Brilliant Green‐ >Malachite Green–carbinol. This is fairly consistent with the order observed in water. A fairly good correlation between base strengths of the carbinols and σ R+ parameters of their para‐alkylamino substituents was obtained. Copyright © 1993 John Wiley & Sons, Ltd.
Cathodic contact glow discharge electrolysis: Its origin and non-faradaic chemical effects
(Institute of Physics, 2017) Susanta K. Sen Gupta; Rajshree Singh
Normal electrolysis (NE), at sufficiently high voltages, breaks down and undergoes a transition to a phenomenon called contact glow discharge electrolysis (CGDE) in which a sheath of glow discharge plasma encapsulates one of the electrodes, the anode or the cathode. The chemical effects of CGDE are highly non-faradaic e.g. a mixture of H2 and H2O2 plus O2 each in excess of the Faraday law value is liberated at the glow discharge plasma electrode from an aqueous electrolyte solution. Studies of cathodic CGDE, particularly its origin and chemical effects, in comparison to those of anodic CGDE have received significantly less attention and have not been studied in detail. The present paper is an attempt towards elucidation of the mechanisms of the growth of cathodic CGDE during NE and its non-faradaic chemical effects. The findings of the study have led to the inference that emission of secondary electrons from the metal cathode with sufficient kinetic energies, vaporization of the electrolyte solvent in the vicinity of the cathode surface induced by Joule heating and the onset of hydrodynamic instabilities in local vaporization contribute to the generation of the plasma at the cathode during NE. The findings have further shown that non-faradaic yields of CGDE at the cathode originate from energy transfer processes in two reaction zones: a plasma phase reaction zone around the cathode which accounts for ∼75% of the yields, and a liquid phase reaction zone near the plasma-catholyte solution interface accounting for the remaining ∼25% of the yields. © 2016 IOP Publishing Ltd.
Chemometric analysis of disubstituent effects on the13C chemical shifts of the carboxyl carbons (δco) of benzoic acids. A comparative study of the substituent effects on the strength of benzoic acids in apolar aprotic media
(John Wiley and Sons Ltd, 2007) Susanta K. Sen Gupta; Ruchi Shrivastava
The results of measurements of substituent induced chemical shifts of carboxyl carbons (δco) of dichloroand difluorobenzoic acids, including the monosubstituted ones with substituents at meta- and/or orthopositions, in chloroform-d and strengths of these acids (log K) in chlorobenzene show an anomalous reverse trend between δco and log K, while the electron density at carboxyl carbons should influence similarly both δco and log K. A detailed chemometric analysis of comparison of disubstituent effects between δco and log K on the basis of Fujita-Nishioka's multiparameter approach and assumption of additivity of substituent effects shows a dominance of the localized π polarization mechanism relative to simple electrostatic effects upon ico- Further, steric factors play a significant role in determining δco whereas with respect to log K they were insignificant. The overall anomaly has been rationalized keeping in mind that, while log K is a gross measure of energy differences between the ionized and unionized forms of the acids, δco is a very sensitive probe for determining changes in electron density at the carboxyl carbon of the unionized acid. Copyright © 2007 John Wiley & Sons, Ltd.
Contact Glow Discharge Electrolysis: A Novel Tool for Manifold Applications
(Springer New York LLC, 2017) Susanta K. Sen Gupta
Contact glow discharge electrolysis (CGDE)/plasma electrolysis (PE) which is associated with the formation of a light emitting plasma around an electrode in a high conductivity electrolyte solution at moderate voltages up to ~1 kV, has in recent years attracted considerable interest as a tool for generating a large quantity of heat and a high yield of solvent-split radicals. These potentialities of CGDE/PE have, in fact, been exploited by a large number of investigators for applications ranging over areas as varied as synthetic chemistry, waste water treatment, degradation of polymers, electrosurgical tools, surface engineering, nanoparticle fabrication, machining and micro-machining, hydrogen production with very encouraging results. The article reviews comprehensively these results. © 2017, Springer Science+Business Media New York.
Contact glow discharge electrolysis: Its origin, plasma diagnostics and non-faradaic chemical effects
(Institute of Physics Publishing, 2015) Susanta K. Sen Gupta
Contact glow discharge electrolysis (CGDE) also termed plasma electrolysis is a novel electrolysis where a stable sheath of light emitting plasma develops around an electrode immersed well inside a relatively high-conductivity liquid electrolyte during normal electrolysis (NE) at several hundred volts. The phenomenon may develop in dc-, pulsed dc-, ac- as well as RF-driven electrolyses. The chemical effects of CGDE are remarkably non-faradaic in respect to the nature of the products as well as their yields. The article traces comprehensively the progress made in studies of CGDE in aqueous and non-aqueous solutions since 1844 and reviews the developments in the understanding of its origin, light emission, plasma state and non-faradaic effects leading to the elucidation of detailed mechanism of the origin of CGDE on the basis of the onset of hydrodynamic instabilities in local vaporization of the solvent near the working electrode during NE, and that of highly non-faradaic effects of CGDE based on a model of two reaction zones located within the electrode plasma and at the plasma-liquid interface producing solvent derived radicals at high local concentrations. Keeping in view the recent surge of interest in varied applications of CGDE, the article is appended with highlights of these applications across synthetic chemistry, waste water treatment, electrosurgical devices, nanoparticle fabrications, surface engineering and micro-machining. © 2015 IOP Publishing Ltd.
Effects of alkaline ferrocyanide on non-faradaic yields of anodic contact glow discharge electrolysis: Determination of the primary yield of OH . radicals
(2012) Rajeshwar Singh; Urvashi Gangal; Susanta K. Sen Gupta
Non faradaic yields of anodic contact glow discharge electrolysis (CGDE) originate through H . and OH . radical generated during the process. Scavenging effects of Fe(CN) 4-6 on OH . radicals, in alkaline media have been investigated. A kinetic analysis of the competing reactions of O - with different species in the system leads to an yield of 9.8 mol mol electron -1 of OH . and H . radicals each in the liquid phase reaction zone of anodic CGDE in good agreement with the yield reported from a study involving H . radical scavengers. © Springer Science+Business Media, LLC 2011.
Equilibria and kinetics of reactions between carboxylic acids and the carbinol base of crystal violet in apolar aprotic solvents: Relative strengths of m- and o-substituted benzoic acids in toluene
(John Wiley and Sons Ltd, 1997) Susanta K. Sen Gupta; Udai Arvind
Equilibria and kinetics of proton-transfer reactions in toluene between a set of m- and o-substituted (methyl, methoxy, chloro, nitro and hydroxy) benzoic acids and the carbinol base (colourless) of Crystal Violet were studied spectrophotometrically. The data on equilibrium and kinetic parameters were critically analysed. The rate constant for the forward step of the acid-carbinol equilibrium was found to be an appropriate criterion for determining acidities in toluene. Toluene-phase acidities were found to be significantly more susceptible than aqueous-phase acidities to the structure of the substituents, particularly for the m-substituted acids. Quantitative analysis of the substituent effect on toluene-phase acidities using the Fujita-Nishioka model for the extended Hammett equation showed that the predominant factor contributing to the 'ortho effect' for benzoic acid-dye carbinol reactions in toluene is the proximity polar effect rather than the steric effect for most of the o-substituents © 1997 by John Wiley & Sons, Ltd.
Erratum: Mechanism of the breakdown of normal electrolysis and the transition to contact glow discharge electrolysis (Journal of the Electrochemical Society (2009) 156 (F131))
(2009) Urvashi Gangal; Monika Srivastava; Susanta K. Sen Gupta
[No abstract available]
General acid catalysis in benzoic acid-Crystal Violet carbinol base reactions in toluene
(2012) Susanta K. Sen Gupta; Sangeeta Mishra; V. Radha Rani; Udai Arvind
Kinetics of benzoic acid-dye carbinol base reactions in an apolar aprotic solvent exhibit a complex dependence on the concentration of the acid, indicating the occurrence of general acid catalysis, the acid playing the dual role of the substrate and the catalyst. The complex kinetic behavior observed for 23 ortho- and meta-substituted benzoic acids has been traced to overlapping participations of the monomer acid, hyperacidic open chain homoconjugated complex (dimeric and trimeric) acids, and nonreactive cyclic dimer and trimer acids. It has been found that although the degree of proton transfer in the transition state is 50-60% when the acid acts exclusively in the monomeric form, it gets enhanced to as high as more than 90% when the role of homoconjugated complex acids is taken into consideration. © 2012 Wiley Periodicals, Inc.
Highly dispersed multiwalled carbon nanotubes coupled manganese salen nanostructure for simultaneous electrochemical sensing of vitamin B2 and B6
(Elsevier B.V., 2017) Piyush Kumar Sonkar; Vellaichamy Ganesan; Susanta K. Sen Gupta; Dharmendra Kumar Yadav; Rupali Gupta; Mamta Yadav
A nanocomposite of Mn(salen)Cl (where salen is N,N′-bis(salicylidene)ethylenediamine) and multiwalled carbon nanotubes (MWCNTs) is prepared. The advantageous properties of MWCNTs and catalytic properties of Mn(salen)Cl (represented as MnIIIsalen) are combined in this new nanocomposite (represented as MWCNTs-MnIIIsalen). Several techniques including electrochemical ones are used for the characterization of the MWCNTs-MnIIIsalen nanostructure. After complete characterization it is utilized for simultaneous determination of vitamin B2 (riboflavin) and B6 (pyridoxine) using differential pulse voltammetry (DPV). MWCNTs-MnIIIsalen coated on glassy carbon electrode (GC), represented as GC/MWCNTs-MnIIIsalen exhibits high sensitivity and low detection limit. This electrode demonstrates high reproducibility (R.S.D. = 3.7% and 3.4% for vitamin B2 and B6, respectively) and long storage stability (more than 10 days under normal room temperature condition). Methodologies for the analysis of vitamins B2 and B6 using GC/MWCNTs-MnIIIsalen in pharmaceutical formulations using simple electrochemical techniques are elucidated. © 2017
Highly selective fluorescence 'turn off' sensing of picric acid and efficient cell labelling by water-soluble luminescent anthracene-bridged poly(: N -vinyl pyrrolidone)
(Royal Society of Chemistry, 2019) Rajshree Singh; Kheyanath Mitra; Shikha Singh; Sudipta Senapati; Vijay Kumar Patel; Sambhav Vishwakarma; Archana Kumari; Jaydeep Singh; Susanta K. Sen Gupta; Nira Misra; Pralay Maiti; Biswajit Ray
A novel, water-soluble, luminescent anthracene-bridged AA-type bi-arm poly(N-vinylpyrrolidone) (ATC-PNVP) was synthesized using a click reaction between alkyne-terminated PNVP and 9,10-bis(azidomethyl)anthracene. The resultant anthracene-bridged PNVP (ATC-PNVP) was characterized using 1H NMR, FTIR, UV-Vis, and fluorescence spectroscopic methods and GPC analysis. ATC-PNVP showed effective fluorescence properties in an aqueous medium. It showed highly selective "turn off" sensing behaviour towards picric acid, a common nitro-aromatic explosive, with a wide linear range of detection of 0.01-0.3 mM and LOD value of 0.006 mM in water. ATC-PNVP-based paper sensors also showed very effective detection of picric acid in the concentration range 0.001-1.0 mM. Its binding with bovine serum albumin (BSA) was studied using steady-state, synchronous and 3D fluorescence spectroscopy and this study showed effective quenching of the intrinsic fluorescence of BSA and occurrence of a FRET-type interaction. Furthermore, this luminescent ATC-PNVP was efficiently used as a fluorescence microscopy labelling agent in NIH-3T3 and HeLa cells, and showed greater uptake and hence better fluorescent labelling in the cytosols of the tested cells than free 9,10-bis(azidomethyl) anthracene. The cell viability study also showed a very good biocompatible and non-toxic nature of ATC-PNVP at lower working concentrations towards each of the types of cells tested. © 2019 The Royal Society of Chemistry.
Influence of Aprotic Solvents on the Transmission of Anomalous Substituent Effects on 13C NMR Chemical Shifts at the Carboxyl Carbon (δ co) in Meta-Substituted Benzoic Acids: A Strong Evidence for π-Polarization Mechanism
(2012) Susanta K. Sen Gupta; Ruchi Shrivastava
Anomalous (reverse) substituent-induced 13C nuclear magnetic resonance chemical shifts at the carboxyl carbon (δ co) in meta-substituted benzoic acids have been studied for 11 substituents having varying electronic effects in 4 aprotic (nonhydroxylic) solvents of varying polarity by employing different dual substituent parameter models. The regression results for apolar aprotic solvents provide a strong evidence for through space π-polarization mode of transmission of reverse meta-substituent effects on the carboxyl carbon in benzoic acids. The results for dipolar aprotic solvents indicate significant specific solvation of π-polarized forms of the acids. The study showed further that an apolar aprotic solvent has a distinct preference over a dipolar aprotic one for investigating intrinsic substituent effects on chemical shifts in aromatic molecules. © 2011 Springer-Verlag.
Kinetics and mechanism of proton transfer between disubstituted benzoic acids and carbinol base of crystal violet in chlorobenzene
(2008) Susanta K. Sen Gupta; Ruchi Shrivastava
An investigation on the detailed kinetics of proton transfer between a set of di- and monofluoro- and chloro(2,3-, 2,5-, 2,6-, 3,5-, 2-, and 3-) benzoic acids (HA) and Crystal Violet carbinol base in chlorobenzene favors a mechanism in terms of fast equilibrium between HA and D to form a H-bonded complex, D⋯HA, followed by rate-limiting proton transfer along the H-bond to form the colored ion pair DH+A- under the combined influence of monomer HA catalyst, nonreactive cyclic dimer (HA)2 inhibitor, and hyperacidic homoconjugated complex H(HA2) catalyst through a transition state with nearly 60% charge separation. © 2008 American Chemical Society.
Kinetics of proton transfer between metasubstituted benzoic acids and the carbinol base of crystal violet in toluene: Specific solvent effect-free metasubstituent effect on the reactivity of benzoic acids
(2011) Susanta K. Sen Gupta; V. Radha Rani
Apolar aprotic solvents are particularly advantageous for investigating the intrinsic metasubstituent effect free from complications of specific solvent effects. A kinetic study for toluene-phase proton transfers between meta-Me, F, Cl, Br, I, OMe, OPh, COPh, CF3, CN, NO2, H benzoic acids and Crystal Violet carbinol base has shown the forward rate constant (log k 1) the most appropriate reactivity parameter in toluene. log k 1 (toluene) as compared to other reported reactivity parameters in benzene or toluene have been found more sensitive to the metasubstituent effect. The regression results of the correlation of log k1 (toluene) of the acids according to the four dual substituent parameter models are statistically significant, and the best result has been obtained using Taft's model. The overall analysis reveals that metasubstituent's effect is exerted by a 65:35 pattern of its field and second-order resonance effects. The results further demonstrate that a metasubstituent's resonance effect is virtually a relayed universal field/inductive effect. © 2011 Wiley Periodicals, Inc.
Kinetics of proton transfer between ortho substituted benzoic acids and the carbinol base of crystal violet in toluene. Ortho effect on the reactivity of benzoic acids in apolar aprotic solvents
(2011) Susanta K. Sen Gupta; Sangeeta Mishra
Apolar aprotic solvents are particularly advantageous for investigating the intrinsic ortho effect free from complications of specific solvent effects. A kinetic study for toluene-phase proton transfers between ortho F, Cl, Br, I, OMe, OEt, OPh, OAc, Me, NO2, COMe, COPh, OH, NH2, and H benzoic acids and crystal violet carbinol base has shown the forward rate constant (log k+1) is the most appropriate reactivity parameter in toluene. log k+1 (toluene) as compared to other reported reactivity parameters in benzene, toluene, or chlorobenzene has been found more sensitive to the ortho substituent effect. The regression results of the correlation of log k+1 (toluene) of the acids (except OH and NH2 substituted ones) according to seven ortho effect models are all very significant, and the best result is given by Fujita-Nishiokas model. The overall analysis reveals that a substituents ortho effect pattern is a 58:24:18 ratio of its ordinary electrical, proximity electrical, and steric effects and that the proximity electrical effect is the major component to account for the peculiarity of the substituents ortho effect. The results further favor the transmission of this effect mainly through the molecular cavity. The effect may, however, be outweighed by the steric component for bulky enough substituents, e.g., Me. The enhanced strength exhibited by salicylic acid in toluene has been quantitatively described using Pytela-Liŝas δHB i parameter. The abnormally high log k+1 observed for anthranilic acid in toluene has been ascribed to a very extensive homoconjugation in its acid-acid anion complex induced by the acids three hydrogen bond donors. © 2011 American Chemical Society.
L-menthol-based initiators for atom transfer radical polymerization of styrene
(John Wiley and Sons Inc., 2019) Sambhav Vishwakarma; Archana Kumari; Kheyanath Mitra; Shikha Singh; Rajshree Singh; Jaydeep Singh; Susanta K. Sen Gupta; Biswajit Ray
Two new atom transfer radical polymerization (ATRP) initiators, 2-isopropyl-5-methylcyclohexyl 2-bromopropanoate (1) and 2-Isopropyl-5-methylcyclohexyl 2-bromo-2-methylpropanoate (2), have been synthesized by the reaction of 2-bromopropanoyl bromide and 2-bromo-2-methylpropanoyl bromide, respectively, with L-menthol and characterized by 1H and 13C NMR and FTIR spectroscopic studies. ATRP of styrene has successfully been carried out in a control manner using these initiators along with catalyst/ligand system consisting of Cu(I)Br/N,N,N/,N/,N//-pentamethyldiethylenetriamine. Polymerizations have yielded polystyrenes (PSts) of controlled molecular weight with low polydispersity index having a menthyl end group, as confirmed by 1H NMR and gel permeation chromatography [GPC]. The controlled nature of the polymerization has also been confirmed by kinetic study of the polymerization process monitored via 1H NMR and GPC. Initiator 2 has evolved as most efficient among the two. The obtained end-functional PSt has also been used as a macroinitiator for homochain extension with styrene and heterochain extension with methyl methacrylate to produce PSt-b-PMMA, showing the living nature of the polymerization process. In comparison with the PSt sample prepared using widely used initiator ethyl-2-bromo-isobutyrate with almost the same molecular weight and polydispersity, initiator 2-made L-menthyl-capped PSt has shown higher light transmission properties of its dichloromethane solution at ~259 nm, higher thermal stability, lower glass transition temperature, a broad melting temperature, and higher surface roughness over its film. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47964. © 2019 Wiley Periodicals, Inc.
L-menthol-based xanthate mediator for RAFT polymerization of vinyl acetate
(Taylor and Francis Inc., 2020) Sambhav Vishwakarma; Archana Kumari; Kheyanath Mitra; Shikha Singh; Rajshree Singh; Jaydeep Singh; Susanta K. Sen Gupta; Biswajit Ray
A xanthate RAFT agent 2-isopropyl-5-methylcyclohexyl 2-(ethoxycarbonothioyl)thio) propanoate has been synthesized via the reactions of L-menthol with 2-bromo-propionyl bromide in THF in the presence of triethylamine leading to the formation of 2-isopropyl-5-methylcyclohexyl 2-bromopropanoate followed by its reaction with potassium-O-ethyl xanthate in ethanol at room temperature and characterized by 1H, 13C NMR and FTIR. RAFT polymerization of vinyl acetate (VAc) using it has resulted in the formation of well-defined polyVAc in controlled manner. This is evidenced by (i) the observation of the pseudo first order kinetics upto ∼90% conversion, (ii) linear increment of molecular weight (unimodal GPC chromatogram) of the polymer keeping its PDI low with the progress of the reaction upto ∼90% conversion, (iii) the linear increment of the molecular weight of the polymers with low PDI on increasing monomer loading, (iv) chain-end analysis of the polymer using 1H NMR confirming the presence of the RAFT agent fragment at the polymer chain-ends, and (v) successful homo- and hetero-chain extension with VAc and NVP, respectively. L-Menthyl-capped polyvinyl acetate has shown higher (i) light transmission properties of its dichloromethane solution at ∼277 nm, (ii) thermal stability, and (iii) glass transition temperature in comparison to its non-L-Menthyl-capped homolog. © 2019, © 2019 Taylor & Francis Group, LLC.
Mechanism of the breakdown of normal electrolysis and the transition to contact glow discharge electrolysis
(2009) Urvashi Gangal; Monika Srivastava; Susanta K. Sen Gupta
The question of how normal electrolysis (NE) at high voltages breaks down and transforms into contact glow discharge electrolysis (CGDE) was addressed with the anode as the preferred center for the phenomenon. Because close analogies in physical characteristics exist in the NE-to-CGDE transition and the natural convection-to-stable film boiling transition observed during pool boiling of liquids, the applicability of Helmholtz-Taylor's boiling heat transfer theory to the breakdown of NE and the transition to CGDE was examined. The approach was justified by the proportionality relationships observed between the critical flux of heat dissipated by the Joule effect near the anode and the anolyte surface tension or the radius of the anode wire. The results led to a detailed mechanism of the transition of NE to CGDE at the anode consisting of the following sequences: local solvent vaporization, setting up of stable counterflows between the vapor bubbles and the liquid anolyte at the anode, collapse of this flow pattern and formation of an unstable vapor film with an overlying heavier liquid, stabilization of the vapor film, and incipience of glow discharges across the film. © 2009 The Electrochemical Society.
On the primary yield of radical products of anodic contact glow discharge electrolysis
(2014) Yamini Srivastava; Shilpi Jaiswal; Om Prakash Singh; Susanta K. Sen Gupta
Scavenging effects of Fe2+ on OH• and H 2O2 generated by anodic contact glow discharge electrolysis in acidic media have been investigated. Analysis of a kinetic scheme involving competing reactions of OH• with different species in a Fe2+ containing system leads to a primary yield of 11 mol (mol electron)-1 each for OH• and H • each in the liquid phase reaction zone of anodic CGDE. This value agrees well with the yields reported in previous studies involving H • and other OH• scavengers and thus may be accepted as a reliable measure of the primary radical yield of anodic CGDE. A comparison with the radiolytic yield of radicals suggests that the average energy of gaseous H2O+ ions bombarding the liquid H 2O molecules and producing the radicals is substantially above 100 eV.