Sapan Jain - Academia.edu (original) (raw)
Papers by Sapan Jain
Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2019
The present short communication highlights the synthesis of poly(o-phenylenediamine) (POPD)/β-cyc... more The present short communication highlights the synthesis of poly(o-phenylenediamine) (POPD)/β-cyclodextrin inclusion complex via ultrasound-assisted in-situ polymerization of o-phenylenediamine in the former. The inclusion complexes were characterized for their spectral and morphological properties. IR and UV visible studies confirmed the increase in the extent of interaction between the two moieties upon increasing the loading of POPD while XRD revealed a crystalline morphology. TEM revealed formation of spherical nanoparticles of controlled morphology. The inclusion complexes hold potential to be utilized for designing drug delivery vehicles.
Journal of Molecular Liquids, 2019
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2018
The study focuses on the formation of inclusion complexes of indole chalcone (IC) derivatives wit... more The study focuses on the formation of inclusion complexes of indole chalcone (IC) derivatives with β-cyclodextrin (β-CD), which involves absorption and steady state fluorescence spectroscopies. The formation of inclusion complexes is validated by increase in their absorbance and fluorescence intensity as well as the blue shift with increase in the concentration of β-CD in the aqueous solution. The stoichiometries and binding constants (K in) of these complexes have been investigated by monitoring their absorbance and fluorescence spectral profiles. The data are analyzed by Benesi-Hildebrand plots as well as Job's method, which indicate 1:1 stoichiometry of IC:β-CD complexes. Fluorescence measurements are also used to investigate the effect of temperature on the stability of inclusion complexes. Stability of IC:β-CD complexes is significantly affected with variation in substituents on the phenyl ring and temperature. It is observed that the stability of the inclusion complex decreases with increase in temperature; K in(293 K) > K in(298 K) > K in(308 K) > K in(318 K). All the experimental results and the geometrical data obtained using PM3 semiempirical method illustrate the partial inclusion of IC derivatives from the phenyl ring side in β-CD cavity. The binding process of IC derivatives with β-CD is found to be exothermic in nature and seems to be controlled by electrostatic and hydrophobic forces. The binding free energies calculated using semiemprical PM3 method for IC:β-CD complexes are found to be in the order: I < OH-I < Me-I < OMe-I < NH 2-I, which largely supports the findings based on the experimental binding constants.
Journal of Molecular Structure: THEOCHEM, 2004
Abstract This Parametric Method 3 (PM3) study represents one of the first attempts to investigate... more Abstract This Parametric Method 3 (PM3) study represents one of the first attempts to investigate the relative stabilities of the tautomers of dicoumarol and its derivatives. The calculations have been carried out both in the gas-phase and in a continuum model of water, on isolated tautomers of 10 systems obtained by single proton transfer and their heats of formation (Δ H f ), relative heats of formation ( δ Δ H f ) and dipole moments have been estimated. In most cases, the PM3 estimates of δ Δ H f indicate the predominance of α,γ′-benzopyran tautomeric structure in gas-phase. Macroscopic solvent effects on the tautomers have been modeled within the framework of continuum solvation model using Conductor like Screening Model (COSMO) method. In aqueous solution, the calculations imply significant qualitative differences in the δ Δ H f of the tautomers and predict the predominance of tetra-keto structure. However, in most of the cases regardless of the surrounding media, calculations indicate α,α′-benzopyran structure as the one having the largest dipole moment. The PM3 method has been demonstrated to be useful in studying such large systems which are otherwise difficult to be handled by ab initio methods for reasons of computational cost and time.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2007
Absorption and fluorescence spectra of some biologically active indole and tryptamine derivatives... more Absorption and fluorescence spectra of some biologically active indole and tryptamine derivatives have been recorded at room temperature in solvents of different polarities. The interest in the photophysical properties of these molecules arises mainly from their utility in medicinal chemistry as neurotransmitter and hallucination/hallucinic agents. Excited-state dipole moments of these molecules have been estimated from solvent-dependent Stokes shift data using a solvatochromic method based on a microscopic solvent polarity parameter (ETN). All indoles show a substantial increase in the dipole moment upon excitation to the emitting state. These results are generally consistent with the Parametric Method 3 (PM3) calculations, and are found to be quite reliable in view of the fact that the correlation of the solvatochromic Stokes shifts with the microscopic solvent polarity parameter (ETN) is superior to that obtained using bulk solvent polarity functions.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2007
The absorption and fluorescence spectral characteristics of some biologically active indoles have... more The absorption and fluorescence spectral characteristics of some biologically active indoles have been studied as a function of acidity and basicity (H_/pH/H(o)) in cationic (cetyltrimethylammonium bromide, CTAB), anionic (sodium dodecylsulphate, SDS) and aqueous phases at a given surfactant concentration. The prototropic equilibrium reactions of these probes have been studied in aqueous and micellar phases and apparent excited state acidity constant (pK(a)(*)) values are calculated. The probes show formation of different species on changing pH. Various species present in water, CTAB and SDS have been identified and the equilibrium constants have been determined by Fluorimetric Titration method. The fluorescence spectral data suggest the formation of oxonium ion through the excited state proton transfer reaction in highly acidic media and formation of photoproducts due to the base catalyzed auto-oxidative reaction in basic aqueous solutions. Variations in the apparent pK(a)(*) value have been observed in different media. The change in the apparent pK(a) values depends upon the solubilising power of the micelles, as well as on the location of the protonating site in the molecule. The observation about increase in pK(a)(*) values in SDS and decrease in CTAB compared to pure water for various equilibria is consistent with the pseudophase ion-exchange (PIE) model.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2001
The electronic absorption and fluorescence spectra of some biologically active natural flavones h... more The electronic absorption and fluorescence spectra of some biologically active natural flavones have been recorded at room temperature (298 K) in solvents of different polarities. The effects of the solvents upon the spectral properties are discussed. Difference in fluorescence intensity of flavones has been explained on the basis of intersystem crossing and degree of non-planarity calculated theoretically using Austin Model 1 (AM1) method. Excited-state dipole moments have been determined using the solvatochromic method based on the microscopic solvent polarity parameter, E(N)(T). A reasonable agreement has been observed between experimental and AM1 calculated dipole moment changes. Our results are found to be quite reliable in view of the fact that the correlation of the solvatochromic Stokes shifts with microscopic solvent polarity parameter, E(N)(T) is superior to that obtained using bulk solvent polarity functions for all the systems studied here.
Pure and Applied Chemistry, 2007
Earlier reports from our laboratory established the acetyl transferase function of calreticulin (... more Earlier reports from our laboratory established the acetyl transferase function of calreticulin (CRT), enabling CRT to transfer acetyl groups from the acetoxy groups of polyphenolic acetates (PAs) to certain receptor proteins. We have in this paper documented the ability of CRT to catalyze the possible transfer of acetyl moiety from 7-acetamido-4-methylcoumarin (7-N-AMC) to the proteins, glutathione S-transferase (GST), and NADPH cytochrome c reductase, leading to the modification of their catalytic activities. 7-Acetoxy-4-methylthiocoumarin (7-AMTC) compared to 7-acetoxy-4-methylcoumarin (7-AMC) when used as a substrate for calreticulin transacetylase (CRTAase) yielded significantly higher catalytic activity. PM3-optimized geometries suggested that the availability of electrons on the sulfur atom of the thiocarbonyl group of the thiocoumarin may render the substrate binding more favorable to the active site of the enzyme as compared to its oxygen analog. Further CRTAase activity wa...
Placenta, 2002
We have earlier established in tissues of several mammalian animal species the existence of a nov... more We have earlier established in tissues of several mammalian animal species the existence of a novel membrane bound enzyme termed 7,8-diacetoxy-4-methylcoumarin (DAMC): protein transacetylase (TAase) that possibly transfers acetyl groups from the model acetoxy drug (DAMC) to certain enzyme protein viz. glutathione S-transferase (GST), cytochrome P-450 and NADPH cytochrome C reductase leading to the drastic modulation of their catalytic activities. We have in this report extended the studies to human tissue and characterized TAase from placenta. For this purpose placental microsomes were preincubated with DAMC along with the receptor protein (cytosolic GST) followed by the addition of the substrates of GST in order to quantify the catalytic activity of GST, the extent of inhibition of GST served as a measure of TAase. Placental TAase was also found to irreversibly activate NADPH cytochrome C reductase by DAMC. Placental enzyme activated the reductase even at very low concentration of DAMC. Iodoacetamide nearly abolished the placental TAase suggesting the presence of active thiol group in the enzyme and the TAase demonstrated hyperbolic kinetics. Kinetic constants obtained by varying the concentrations of either of the substrates DAMC or cytosolic GST characterized TAase catalysed reaction as the bimolecular reaction. Further studies are in progress to delineate the physiological importance of TAase in placenta.
European Journal of Medicinal Chemistry, 2007
The earlier work carried out in our laboratory led to the identification of a novel rat liver mic... more The earlier work carried out in our laboratory led to the identification of a novel rat liver microsomal enzyme termed as acetoxy drug: protein transacetylase (TAase), catalyzing the transfer of acetyl group from polyphenolic acetates (PA) to functional proteins. In this paper, we have reported the comparison of the specificities of acetoxy derivatives of coumarins, biscoumarins, chromones, flavones, isoflavones and xanthones with special reference to the phenyl moiety/bulky group on the pyran ring of PA. The results clearly indicated that compounds having phenyl moieties, when used as the substrates, resulted in a significant reduction of TAase catalyzed activity. The alteration in TAase catalyzed activation of NADPH cytochrome c reductase and inhibition of benzene-induced micronuclei in bone marrow cells by PA were in tune with their specificities to TAase.
Bulletin of the Chemical Society of Japan, 2003
The electronic absorption and fluorescence spectra of some indoles were recorded at room temperat... more The electronic absorption and fluorescence spectra of some indoles were recorded at room temperature in solvents of different polarities. In order to elucidate the solvent band shifts during relaxation of the excited states, the dipole moments of the excited singlet states were estimated from solvent-dependent Stokes shift data using a solvatochromic method based on a microscopic solvent polarity parameter (E N T). All indoles show a substantial increase in the dipole moment upon excitation to the emitting state. These results are generally consistent with the Austin model 1 (AM1) calculations, and are found to be quite reliable in view of the fact that the correlation of the solvatochromic Stokes shifts with the microscopic solvent polarity parameter (E N T) is superior to that obtained using bulk solvent polarity functions in almost all the systems studied here.
Bioorganic & Medicinal Chemistry, 1999
Dihydroxy-4-methylcoumarin (1, DHMC) and 7,8-diacetoxy-4-methylcoumarin (2, DAMC) were shown to p... more Dihydroxy-4-methylcoumarin (1, DHMC) and 7,8-diacetoxy-4-methylcoumarin (2, DAMC) were shown to possess radical scavenging property and strongly inhibit membrane lipid peroxidation. Although free polyphenolic compounds are known to be antioxidants, the antioxidant action of the acetoxy compound DAMC was intriguing. Hence, pulse radiolysis studies were undertaken to explain the antioxidant action of DAMC. Accordingly, DAMC and DHMC were separately reacted with the system generating azide radicals and the resulting transient spectra were recorded. The spectra so obtained in both the cases demonstrated peak at 410 nm, characteristic of phenoxyl radical. The rate constants for the formation of phenoxyl radical from DHMC and DAMC were 34Â10 8 M À1 s À1 and 6.2Â10 8 M À1 s À1 , respectively. We propose that the free radical mediated oxidation of DAMC initially produces a radical cation that loses an acetyl carbocation to yield the phenoxyl radical. It is possible to conclude that the mechanism of the antioxidant action of DAMC follows the pathway similar to that of DHMC involving the formation of a stable phenoxyl radical.
Nanotechnology
Semiconductor photocatalysis has gained considerable attention in recent years due to their enabl... more Semiconductor photocatalysis has gained considerable attention in recent years due to their enabling nature to convert solar energy into fuels of renewable hydrocarbon. However, many of them suffer from some drawbacks like the inability to visible light irradiation and wide band gaps. Herein, we have synthesized monophasic strontium (Sr) doped SnO2 nanoparticles by a cost-effective and environmental friendly hydrothermal method. As-synthesized nanoparticles showed rutile crystalline structure with irregular and rough cubical shape and no other elemental impurities. Sr-doped SnO2 nanoparticles show a constant decrease in bandgap with increasing dopant concentration, which is estimated for excellent photocatalytic activity. The photocatalytic water splitting of as-prepared Sr-doped SnO2 nanoparticles for H2 generation shows a large influence of the increasing dopant concentration related to the narrowing bandgap on H2 generation rate. Hence, the tunable bandgap with adjusted dopant co...
New Journal of Chemistry, 2022
Driven by the quest of renewable and clean energy sources, researchers around the globe are seeki... more Driven by the quest of renewable and clean energy sources, researchers around the globe are seeking solutions to replace non-renewable fossil fuels to meet the ever-increasing energy supply requirements and solve the relevant environment concerns.
Current Pharmaceutical Biotechnology, 2021
This review summarizes the utilization of gold nanoparticles as efficient catalysts for a variety... more This review summarizes the utilization of gold nanoparticles as efficient catalysts for a variety of chemical transformations like oxidation, hydrogenation, and coupling reactions as compared to conventional catalytic materials. This review explores the gold nanoparticles-based catalysts for the liquid phase chemo-selective organic transformations which are proving to be evergreen reactions and have importance for industrial applications. Apart from organic transformation reactions, gold nanoparticles have been found to be applicable in removing the atmospheric contaminants and improving the efficiency of the fuel cells by removing the impurities of carbon monoxide.
Materials Today: Proceedings, 2020
We have successfully synthesized the SnO 2 nanoparticles by using simple and inexpensive solvothe... more We have successfully synthesized the SnO 2 nanoparticles by using simple and inexpensive solvothermal technique. XRD pattern of as-synthesized product showed the formation of monophasic tetragonal SnO 2 nanoparticles. The morphology of SnO 2 was observed by FESEM which show irregular and rough shaped nanoparticles. Elemental and chemical composition analysis of SnO 2 nanoparticles was carried out by EDAX analysis which confirms the presence of Sn and O in as-synthesized nanoparticles. The determination of specific surface area of as-synthesized SnO 2 nanoparticles was done by BET method and it is found to be 35.5 m 2 /g. The optical properties of SnO 2 nanoparticles were studied by using UV-Visible absorption spectroscopy which gives an optical band gap of 3.34 eV. The catalytic conversion of p-nitrophenol to p-aminophenol was performed to evaluate the efficiency of as-synthesized SnO 2 nanoparticles as reducing catalyst. The catalytic reduction reaction was accomplished in presence of NaBH 4 and water at room temperature. The observed investigations signpost that as-prepared SnO 2 nanoparticles act as an effective nanocatalyst in the process of reduction.
Materials Today: Proceedings, 2020
Silver Nanoparticles have been successfully synthesized using Milletia pegunesis leaf extract at ... more Silver Nanoparticles have been successfully synthesized using Milletia pegunesis leaf extract at room temperature. X-ray diffraction studies (XRD) attributed to the formation of highly crystalline cubic silver nanoparticles. Transmission electron microscopic (TEM) studies showed the distribution of particles of silver in the range of 60-90 nm with an average particle size of 80 nm. Dynamic light scattering (DLS) measurement shows that the particle size ranges from 50-150 nm for Ag nanoparticles. Surface area measurements give the specific surface area of 26.7 m 2 g À1. UV-Visible absorption spectrum of silver nanoparticles shows surface plasmon resonance band at 430 nm. FT-IR shows the appearance of band at 1623 cm À1 which may be attributed to amide linkage and the stretching band at 3280 cm À1 is due to alcoholic and phenolic linkages present in biomolecules of Milletia pegunesis. The degradation rate of methylene blue dye in presence of silver nanoparticles under sun light was found to increase with the increase in reaction time.
Materials Today: Proceedings, 2020
Monophasic pristine and 1 to 5 mol% Zn-doped SnO 2 nanoparticles have been hydrothermally synthes... more Monophasic pristine and 1 to 5 mol% Zn-doped SnO 2 nanoparticles have been hydrothermally synthesized for catalytic reduction of 4-nitrophenol to 4-aminophenol. X-ray diffraction analysis confirms the formation of tetragonal crystal structure and successful doping of Zn over SnO 2. The particle size and morphologies of as-synthesized nanoparticles was confirmed by transmission and scanning electron microscopic studies. Band gap variation with Zn doping was analysed with UV-visible diffused reflectance spectroscopy, which confirms the reduction of band gap upto 2.5 mol% doping of Zn. BET surface area analysis shows the decrease in surface area with increase in Zn concentration. All the synthesized samples show significant catalytic activity for reduction of 4-nitrophenol in the presence of NaBH 4 as reducing agent. Catalytic studies indicate that 2.5 mol% Zn doped nanoparticles show 3 times enhanced catalytic activity as compared to that of pure SnO 2 nanoparticles.
Journal of Nanoscience and Nanotechnology, 2020
This paper reports the attempt to develop an efficient heterostructure photocatalyst by employing... more This paper reports the attempt to develop an efficient heterostructure photocatalyst by employing SrZrO3 as ferroelectric substrate with deposited nanostructured CdS semiconductor on the surface. Primarily bare SrZrO3 and CdS nanoparticles were synthesized by using polymeric citrate precursor and co-precipitation routes, respectively. The chemical deposition technique was used to develop the CdS over the surface of the pre-synthesized SrZrO3 nanoparticles. The synthesized bare nanoparticles and their heterostructure were characterized by XRD which shows the formation of orthorhombic and face centred cubic (FCC) phases of SrZrO3 and CdS, respectively. TEM was used to estimate the morphology and particle size of as-synthesized nanoparticles, which shows the average particle size of 14, 24 and 25 nm for SrZrO3, CdS and SrZrO3/CdS, respectively. The BET surface area of SrZrO3, CdS and SrZrO3/CdS samples was found to be 299, 304 and 312 m2/g respectively. Methylene blue was used as model...
Chemical Physics Letters, 2000
ABSTRACT The equilibrium geometries, vibrational frequencies and isomerism of MOH (M=Be and Mg) h... more ABSTRACT The equilibrium geometries, vibrational frequencies and isomerism of MOH (M=Be and Mg) have been investigated at the B3PW91 level using two basis sets, 6-31G* and 6-311+G(2d,2p). The calculated geometries, vibrational frequencies and zero-point vibrational energies are in good agreement with the CASSCF level studies of Kong and Boyd. The isomerization products of BeOH and MgOH are structurally similar. The M–O bond length in HMO (M=Be and Mg) is predicted to be longer than that in the corresponding MOH. The predicted reaction energies for the reactions MOH→HMO are endothermic and in good agreement with the CASSCF level results. The predicted ESR hyperfine coupling constants for MgOH and the dissociation energies for both BeOH and MgOH compare quite well with experimental results.
Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2019
The present short communication highlights the synthesis of poly(o-phenylenediamine) (POPD)/β-cyc... more The present short communication highlights the synthesis of poly(o-phenylenediamine) (POPD)/β-cyclodextrin inclusion complex via ultrasound-assisted in-situ polymerization of o-phenylenediamine in the former. The inclusion complexes were characterized for their spectral and morphological properties. IR and UV visible studies confirmed the increase in the extent of interaction between the two moieties upon increasing the loading of POPD while XRD revealed a crystalline morphology. TEM revealed formation of spherical nanoparticles of controlled morphology. The inclusion complexes hold potential to be utilized for designing drug delivery vehicles.
Journal of Molecular Liquids, 2019
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2018
The study focuses on the formation of inclusion complexes of indole chalcone (IC) derivatives wit... more The study focuses on the formation of inclusion complexes of indole chalcone (IC) derivatives with β-cyclodextrin (β-CD), which involves absorption and steady state fluorescence spectroscopies. The formation of inclusion complexes is validated by increase in their absorbance and fluorescence intensity as well as the blue shift with increase in the concentration of β-CD in the aqueous solution. The stoichiometries and binding constants (K in) of these complexes have been investigated by monitoring their absorbance and fluorescence spectral profiles. The data are analyzed by Benesi-Hildebrand plots as well as Job's method, which indicate 1:1 stoichiometry of IC:β-CD complexes. Fluorescence measurements are also used to investigate the effect of temperature on the stability of inclusion complexes. Stability of IC:β-CD complexes is significantly affected with variation in substituents on the phenyl ring and temperature. It is observed that the stability of the inclusion complex decreases with increase in temperature; K in(293 K) > K in(298 K) > K in(308 K) > K in(318 K). All the experimental results and the geometrical data obtained using PM3 semiempirical method illustrate the partial inclusion of IC derivatives from the phenyl ring side in β-CD cavity. The binding process of IC derivatives with β-CD is found to be exothermic in nature and seems to be controlled by electrostatic and hydrophobic forces. The binding free energies calculated using semiemprical PM3 method for IC:β-CD complexes are found to be in the order: I < OH-I < Me-I < OMe-I < NH 2-I, which largely supports the findings based on the experimental binding constants.
Journal of Molecular Structure: THEOCHEM, 2004
Abstract This Parametric Method 3 (PM3) study represents one of the first attempts to investigate... more Abstract This Parametric Method 3 (PM3) study represents one of the first attempts to investigate the relative stabilities of the tautomers of dicoumarol and its derivatives. The calculations have been carried out both in the gas-phase and in a continuum model of water, on isolated tautomers of 10 systems obtained by single proton transfer and their heats of formation (Δ H f ), relative heats of formation ( δ Δ H f ) and dipole moments have been estimated. In most cases, the PM3 estimates of δ Δ H f indicate the predominance of α,γ′-benzopyran tautomeric structure in gas-phase. Macroscopic solvent effects on the tautomers have been modeled within the framework of continuum solvation model using Conductor like Screening Model (COSMO) method. In aqueous solution, the calculations imply significant qualitative differences in the δ Δ H f of the tautomers and predict the predominance of tetra-keto structure. However, in most of the cases regardless of the surrounding media, calculations indicate α,α′-benzopyran structure as the one having the largest dipole moment. The PM3 method has been demonstrated to be useful in studying such large systems which are otherwise difficult to be handled by ab initio methods for reasons of computational cost and time.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2007
Absorption and fluorescence spectra of some biologically active indole and tryptamine derivatives... more Absorption and fluorescence spectra of some biologically active indole and tryptamine derivatives have been recorded at room temperature in solvents of different polarities. The interest in the photophysical properties of these molecules arises mainly from their utility in medicinal chemistry as neurotransmitter and hallucination/hallucinic agents. Excited-state dipole moments of these molecules have been estimated from solvent-dependent Stokes shift data using a solvatochromic method based on a microscopic solvent polarity parameter (ETN). All indoles show a substantial increase in the dipole moment upon excitation to the emitting state. These results are generally consistent with the Parametric Method 3 (PM3) calculations, and are found to be quite reliable in view of the fact that the correlation of the solvatochromic Stokes shifts with the microscopic solvent polarity parameter (ETN) is superior to that obtained using bulk solvent polarity functions.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2007
The absorption and fluorescence spectral characteristics of some biologically active indoles have... more The absorption and fluorescence spectral characteristics of some biologically active indoles have been studied as a function of acidity and basicity (H_/pH/H(o)) in cationic (cetyltrimethylammonium bromide, CTAB), anionic (sodium dodecylsulphate, SDS) and aqueous phases at a given surfactant concentration. The prototropic equilibrium reactions of these probes have been studied in aqueous and micellar phases and apparent excited state acidity constant (pK(a)(*)) values are calculated. The probes show formation of different species on changing pH. Various species present in water, CTAB and SDS have been identified and the equilibrium constants have been determined by Fluorimetric Titration method. The fluorescence spectral data suggest the formation of oxonium ion through the excited state proton transfer reaction in highly acidic media and formation of photoproducts due to the base catalyzed auto-oxidative reaction in basic aqueous solutions. Variations in the apparent pK(a)(*) value have been observed in different media. The change in the apparent pK(a) values depends upon the solubilising power of the micelles, as well as on the location of the protonating site in the molecule. The observation about increase in pK(a)(*) values in SDS and decrease in CTAB compared to pure water for various equilibria is consistent with the pseudophase ion-exchange (PIE) model.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2001
The electronic absorption and fluorescence spectra of some biologically active natural flavones h... more The electronic absorption and fluorescence spectra of some biologically active natural flavones have been recorded at room temperature (298 K) in solvents of different polarities. The effects of the solvents upon the spectral properties are discussed. Difference in fluorescence intensity of flavones has been explained on the basis of intersystem crossing and degree of non-planarity calculated theoretically using Austin Model 1 (AM1) method. Excited-state dipole moments have been determined using the solvatochromic method based on the microscopic solvent polarity parameter, E(N)(T). A reasonable agreement has been observed between experimental and AM1 calculated dipole moment changes. Our results are found to be quite reliable in view of the fact that the correlation of the solvatochromic Stokes shifts with microscopic solvent polarity parameter, E(N)(T) is superior to that obtained using bulk solvent polarity functions for all the systems studied here.
Pure and Applied Chemistry, 2007
Earlier reports from our laboratory established the acetyl transferase function of calreticulin (... more Earlier reports from our laboratory established the acetyl transferase function of calreticulin (CRT), enabling CRT to transfer acetyl groups from the acetoxy groups of polyphenolic acetates (PAs) to certain receptor proteins. We have in this paper documented the ability of CRT to catalyze the possible transfer of acetyl moiety from 7-acetamido-4-methylcoumarin (7-N-AMC) to the proteins, glutathione S-transferase (GST), and NADPH cytochrome c reductase, leading to the modification of their catalytic activities. 7-Acetoxy-4-methylthiocoumarin (7-AMTC) compared to 7-acetoxy-4-methylcoumarin (7-AMC) when used as a substrate for calreticulin transacetylase (CRTAase) yielded significantly higher catalytic activity. PM3-optimized geometries suggested that the availability of electrons on the sulfur atom of the thiocarbonyl group of the thiocoumarin may render the substrate binding more favorable to the active site of the enzyme as compared to its oxygen analog. Further CRTAase activity wa...
Placenta, 2002
We have earlier established in tissues of several mammalian animal species the existence of a nov... more We have earlier established in tissues of several mammalian animal species the existence of a novel membrane bound enzyme termed 7,8-diacetoxy-4-methylcoumarin (DAMC): protein transacetylase (TAase) that possibly transfers acetyl groups from the model acetoxy drug (DAMC) to certain enzyme protein viz. glutathione S-transferase (GST), cytochrome P-450 and NADPH cytochrome C reductase leading to the drastic modulation of their catalytic activities. We have in this report extended the studies to human tissue and characterized TAase from placenta. For this purpose placental microsomes were preincubated with DAMC along with the receptor protein (cytosolic GST) followed by the addition of the substrates of GST in order to quantify the catalytic activity of GST, the extent of inhibition of GST served as a measure of TAase. Placental TAase was also found to irreversibly activate NADPH cytochrome C reductase by DAMC. Placental enzyme activated the reductase even at very low concentration of DAMC. Iodoacetamide nearly abolished the placental TAase suggesting the presence of active thiol group in the enzyme and the TAase demonstrated hyperbolic kinetics. Kinetic constants obtained by varying the concentrations of either of the substrates DAMC or cytosolic GST characterized TAase catalysed reaction as the bimolecular reaction. Further studies are in progress to delineate the physiological importance of TAase in placenta.
European Journal of Medicinal Chemistry, 2007
The earlier work carried out in our laboratory led to the identification of a novel rat liver mic... more The earlier work carried out in our laboratory led to the identification of a novel rat liver microsomal enzyme termed as acetoxy drug: protein transacetylase (TAase), catalyzing the transfer of acetyl group from polyphenolic acetates (PA) to functional proteins. In this paper, we have reported the comparison of the specificities of acetoxy derivatives of coumarins, biscoumarins, chromones, flavones, isoflavones and xanthones with special reference to the phenyl moiety/bulky group on the pyran ring of PA. The results clearly indicated that compounds having phenyl moieties, when used as the substrates, resulted in a significant reduction of TAase catalyzed activity. The alteration in TAase catalyzed activation of NADPH cytochrome c reductase and inhibition of benzene-induced micronuclei in bone marrow cells by PA were in tune with their specificities to TAase.
Bulletin of the Chemical Society of Japan, 2003
The electronic absorption and fluorescence spectra of some indoles were recorded at room temperat... more The electronic absorption and fluorescence spectra of some indoles were recorded at room temperature in solvents of different polarities. In order to elucidate the solvent band shifts during relaxation of the excited states, the dipole moments of the excited singlet states were estimated from solvent-dependent Stokes shift data using a solvatochromic method based on a microscopic solvent polarity parameter (E N T). All indoles show a substantial increase in the dipole moment upon excitation to the emitting state. These results are generally consistent with the Austin model 1 (AM1) calculations, and are found to be quite reliable in view of the fact that the correlation of the solvatochromic Stokes shifts with the microscopic solvent polarity parameter (E N T) is superior to that obtained using bulk solvent polarity functions in almost all the systems studied here.
Bioorganic & Medicinal Chemistry, 1999
Dihydroxy-4-methylcoumarin (1, DHMC) and 7,8-diacetoxy-4-methylcoumarin (2, DAMC) were shown to p... more Dihydroxy-4-methylcoumarin (1, DHMC) and 7,8-diacetoxy-4-methylcoumarin (2, DAMC) were shown to possess radical scavenging property and strongly inhibit membrane lipid peroxidation. Although free polyphenolic compounds are known to be antioxidants, the antioxidant action of the acetoxy compound DAMC was intriguing. Hence, pulse radiolysis studies were undertaken to explain the antioxidant action of DAMC. Accordingly, DAMC and DHMC were separately reacted with the system generating azide radicals and the resulting transient spectra were recorded. The spectra so obtained in both the cases demonstrated peak at 410 nm, characteristic of phenoxyl radical. The rate constants for the formation of phenoxyl radical from DHMC and DAMC were 34Â10 8 M À1 s À1 and 6.2Â10 8 M À1 s À1 , respectively. We propose that the free radical mediated oxidation of DAMC initially produces a radical cation that loses an acetyl carbocation to yield the phenoxyl radical. It is possible to conclude that the mechanism of the antioxidant action of DAMC follows the pathway similar to that of DHMC involving the formation of a stable phenoxyl radical.
Nanotechnology
Semiconductor photocatalysis has gained considerable attention in recent years due to their enabl... more Semiconductor photocatalysis has gained considerable attention in recent years due to their enabling nature to convert solar energy into fuels of renewable hydrocarbon. However, many of them suffer from some drawbacks like the inability to visible light irradiation and wide band gaps. Herein, we have synthesized monophasic strontium (Sr) doped SnO2 nanoparticles by a cost-effective and environmental friendly hydrothermal method. As-synthesized nanoparticles showed rutile crystalline structure with irregular and rough cubical shape and no other elemental impurities. Sr-doped SnO2 nanoparticles show a constant decrease in bandgap with increasing dopant concentration, which is estimated for excellent photocatalytic activity. The photocatalytic water splitting of as-prepared Sr-doped SnO2 nanoparticles for H2 generation shows a large influence of the increasing dopant concentration related to the narrowing bandgap on H2 generation rate. Hence, the tunable bandgap with adjusted dopant co...
New Journal of Chemistry, 2022
Driven by the quest of renewable and clean energy sources, researchers around the globe are seeki... more Driven by the quest of renewable and clean energy sources, researchers around the globe are seeking solutions to replace non-renewable fossil fuels to meet the ever-increasing energy supply requirements and solve the relevant environment concerns.
Current Pharmaceutical Biotechnology, 2021
This review summarizes the utilization of gold nanoparticles as efficient catalysts for a variety... more This review summarizes the utilization of gold nanoparticles as efficient catalysts for a variety of chemical transformations like oxidation, hydrogenation, and coupling reactions as compared to conventional catalytic materials. This review explores the gold nanoparticles-based catalysts for the liquid phase chemo-selective organic transformations which are proving to be evergreen reactions and have importance for industrial applications. Apart from organic transformation reactions, gold nanoparticles have been found to be applicable in removing the atmospheric contaminants and improving the efficiency of the fuel cells by removing the impurities of carbon monoxide.
Materials Today: Proceedings, 2020
We have successfully synthesized the SnO 2 nanoparticles by using simple and inexpensive solvothe... more We have successfully synthesized the SnO 2 nanoparticles by using simple and inexpensive solvothermal technique. XRD pattern of as-synthesized product showed the formation of monophasic tetragonal SnO 2 nanoparticles. The morphology of SnO 2 was observed by FESEM which show irregular and rough shaped nanoparticles. Elemental and chemical composition analysis of SnO 2 nanoparticles was carried out by EDAX analysis which confirms the presence of Sn and O in as-synthesized nanoparticles. The determination of specific surface area of as-synthesized SnO 2 nanoparticles was done by BET method and it is found to be 35.5 m 2 /g. The optical properties of SnO 2 nanoparticles were studied by using UV-Visible absorption spectroscopy which gives an optical band gap of 3.34 eV. The catalytic conversion of p-nitrophenol to p-aminophenol was performed to evaluate the efficiency of as-synthesized SnO 2 nanoparticles as reducing catalyst. The catalytic reduction reaction was accomplished in presence of NaBH 4 and water at room temperature. The observed investigations signpost that as-prepared SnO 2 nanoparticles act as an effective nanocatalyst in the process of reduction.
Materials Today: Proceedings, 2020
Silver Nanoparticles have been successfully synthesized using Milletia pegunesis leaf extract at ... more Silver Nanoparticles have been successfully synthesized using Milletia pegunesis leaf extract at room temperature. X-ray diffraction studies (XRD) attributed to the formation of highly crystalline cubic silver nanoparticles. Transmission electron microscopic (TEM) studies showed the distribution of particles of silver in the range of 60-90 nm with an average particle size of 80 nm. Dynamic light scattering (DLS) measurement shows that the particle size ranges from 50-150 nm for Ag nanoparticles. Surface area measurements give the specific surface area of 26.7 m 2 g À1. UV-Visible absorption spectrum of silver nanoparticles shows surface plasmon resonance band at 430 nm. FT-IR shows the appearance of band at 1623 cm À1 which may be attributed to amide linkage and the stretching band at 3280 cm À1 is due to alcoholic and phenolic linkages present in biomolecules of Milletia pegunesis. The degradation rate of methylene blue dye in presence of silver nanoparticles under sun light was found to increase with the increase in reaction time.
Materials Today: Proceedings, 2020
Monophasic pristine and 1 to 5 mol% Zn-doped SnO 2 nanoparticles have been hydrothermally synthes... more Monophasic pristine and 1 to 5 mol% Zn-doped SnO 2 nanoparticles have been hydrothermally synthesized for catalytic reduction of 4-nitrophenol to 4-aminophenol. X-ray diffraction analysis confirms the formation of tetragonal crystal structure and successful doping of Zn over SnO 2. The particle size and morphologies of as-synthesized nanoparticles was confirmed by transmission and scanning electron microscopic studies. Band gap variation with Zn doping was analysed with UV-visible diffused reflectance spectroscopy, which confirms the reduction of band gap upto 2.5 mol% doping of Zn. BET surface area analysis shows the decrease in surface area with increase in Zn concentration. All the synthesized samples show significant catalytic activity for reduction of 4-nitrophenol in the presence of NaBH 4 as reducing agent. Catalytic studies indicate that 2.5 mol% Zn doped nanoparticles show 3 times enhanced catalytic activity as compared to that of pure SnO 2 nanoparticles.
Journal of Nanoscience and Nanotechnology, 2020
This paper reports the attempt to develop an efficient heterostructure photocatalyst by employing... more This paper reports the attempt to develop an efficient heterostructure photocatalyst by employing SrZrO3 as ferroelectric substrate with deposited nanostructured CdS semiconductor on the surface. Primarily bare SrZrO3 and CdS nanoparticles were synthesized by using polymeric citrate precursor and co-precipitation routes, respectively. The chemical deposition technique was used to develop the CdS over the surface of the pre-synthesized SrZrO3 nanoparticles. The synthesized bare nanoparticles and their heterostructure were characterized by XRD which shows the formation of orthorhombic and face centred cubic (FCC) phases of SrZrO3 and CdS, respectively. TEM was used to estimate the morphology and particle size of as-synthesized nanoparticles, which shows the average particle size of 14, 24 and 25 nm for SrZrO3, CdS and SrZrO3/CdS, respectively. The BET surface area of SrZrO3, CdS and SrZrO3/CdS samples was found to be 299, 304 and 312 m2/g respectively. Methylene blue was used as model...
Chemical Physics Letters, 2000
ABSTRACT The equilibrium geometries, vibrational frequencies and isomerism of MOH (M=Be and Mg) h... more ABSTRACT The equilibrium geometries, vibrational frequencies and isomerism of MOH (M=Be and Mg) have been investigated at the B3PW91 level using two basis sets, 6-31G* and 6-311+G(2d,2p). The calculated geometries, vibrational frequencies and zero-point vibrational energies are in good agreement with the CASSCF level studies of Kong and Boyd. The isomerization products of BeOH and MgOH are structurally similar. The M–O bond length in HMO (M=Be and Mg) is predicted to be longer than that in the corresponding MOH. The predicted reaction energies for the reactions MOH→HMO are endothermic and in good agreement with the CASSCF level results. The predicted ESR hyperfine coupling constants for MgOH and the dissociation energies for both BeOH and MgOH compare quite well with experimental results.