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Papers by Vaishali Samant
Journal of Chemical Sciences, 2020
Abstract The denaturation of human serum albumin (HSA) upon interaction with the surfactant sodiu... more Abstract The denaturation of human serum albumin (HSA) upon interaction with the surfactant sodium dodecyl sulphate (SDS) was examined by measuring the diffusion time of fluorophore (RITC) tagged HSA under near single-molecule conditions using fluorescence correlation spectroscopy. The diffusion time shows four distinct regions as a function of SDS concentration, which corresponds to (I) opening of the tertiary structure, (II) non-specific SDS aggregation, (III) opening of the secondary structure, and (IV) aggregation of SDS around the secondary structure. Diffusion time increases from 383 µs for the free protein to 1002 µs for the SDS bound protein, which leads to an effective increase in the hydrodynamic radius by a factor of about 2.6. Graphic abstract Synopsys Fluorescence correlation spectroscopy reveals a four-step interaction regime between SDS and HSA. The initial opening of the tertiary structure, followed by non-specific aggregation and opening up the secondary structure and finally leading to formation of protein bound micelles with an effective increase of hydrodynamic radius by a factor of 2.6.
Journal of Photochemistry and Photobiology A: Chemistry, 2013
Dynamics of photoinduced electron transfer (PET) reactions between the singlet (S 1) and the trip... more Dynamics of photoinduced electron transfer (PET) reactions between the singlet (S 1) and the triplet (T 1) excited states of 9-fluorenone or simply fluorenone and a few aromatic and aliphatic amines have been investigated under both diffusive and non-diffusive conditions. Formation of the fluorenone anion radical confirms the electron transfer (ET) from the amines to the excited states of fluorenone. Rate constants for both the forward ET process, k CS , and the charge recombination (CR) process, k CR , have been determined in acetonitrile and benzene solutions. Sub-picosecond time-resolved transient absorption study reveals that quenching of the S 1 state in acetonitrile is biexponential. Lifetime of one of these two components is independent of quencher concentration and its values determined for aniline (7.1 ps), dimethylaniline (8.5 ps) and diethylaniline (6.8 ps) are very similar. It represents the non-diffusive component of the PET reaction. But the lifetime of the other component decreases with increasing quencher concentration and the rate of this diffusive component of the PET reaction nearly agrees with the value determined using steady state fluorescence quenching method. To determine the intrinsic values of the rates of the PET reactions involving the S 1 state of fluorenone, the PET dynamics have been studied in these three neat donor solvents. The forward ET process is biexponential and the lifetimes of these two components are very similar in these solvents and vary in the range 0.3-0.5 ps and 6-8 ps. Nonexponential dynamics of the PET reactions conducted in neat donor-solvents have been discussed using a simple solvent reorientational model.
Chemical Physics Letters, 2008
Journal of Physical Chemistry A, 2005
Steady-state fluorescence and time-resolved absorption measurements in pico- and femtosecond time... more Steady-state fluorescence and time-resolved absorption measurements in pico- and femtosecond time domain have been used to investigate the dynamics of hydrogen bond in the excited singlet (S(1)) state of fluorenone in alcoholic solvents. A comparison of the features of the steady-state fluorescence spectra of fluorenone in various kinds of media demonstrates that two spectroscopically distinct forms of fluorenone in the S(1) state, namely the non-hydrogen-bonded (or free) molecule as well as the hydrogen-bonded complex, are responsible for the dual-fluorescence behavior of fluorenone in solutions of normal alcoholic solvents at room temperature (298 K). However, in 2,2,2-trifluoroethanol (TFE), a strong hydrogen bond donating solvent, emission from only the hydrogen-bonded complex is observed. Significant differences have also been observed in the temporal evolution of the absorption spectroscopic properties of the S(1) state of fluorenone in protic and aprotic solvents following photoexcitation using 400 nm laser pulses. An ultrafast component representing the solvent-induced vibrational energy relaxation (VER) process has been associated with the dynamics of the S(1) state of fluorenone in all kinds of solvents. However, in protic solvents, in addition to the VER process, further evolution of the spectroscopic and dynamical properties of the S(1) state have been observed because of repositioning of the hydrogen bonds around the carbonyl group. In normal alcohols, two different kinds of hydrogen-bonded complex of the fluorenone-alcohol system with different orientations of the hydrogen bond with respect to the carbonyl group and the molecular plane of fluorenone have been predicted. On the other hand, in TFE, formation of only one kind of hydrogen-bonded complex has been observed. These observations have been supported by theoretical calculations of the geometries of the hydrogen-bonded complexes in the ground and the excited states of fluorenone. Linear correlation between the lifetimes of the equilibration process occurring because of repositioning of the hydrogen bonds and Debye or longitudinal relaxation times of the normal alcoholic solvents establish the fact that, in weakly hydrogen bond donating solvents, the hydrogen bond dynamics can be described as merely a solvation process. Whereas, in TFE, hydrogen bond dynamics is better described by a process of conversion between two distinct excited states, namely, the non-hydrogen-bonded form and the hydrogen-bonded complex.
Radiation Physics and Chemistry, 2005
Electron pulse radiolysis of four differently substituted amino derivatives of fluorenone, namely... more Electron pulse radiolysis of four differently substituted amino derivatives of fluorenone, namely, 1-amino-, 2-amino- 3-amino-, and 4-aminofluorenone, has been carried out to study the effect of structure on the spectroscopic and kinetic characteristics of the triplet excited states as well as the transient free radical intermediates formed under reducing and oxidizing conditions. The triplet states of these compounds have been generated in benzene by pulse radiolysis and in other solvents by flash photolysis technique and their spectral and kinetic properties have been investigated. Hydrated electron (eaq-) has been found to react with these fluorenone derivatives to form the anion radical species with a diffusion-controlled rate constant. The spectral and kinetic properties of the transient ketyl and anion radicals have been studied by generating them in aqueous solutions of suitable pH. The pKa values of ketyl⇌anion radical equilibria are in the range of 6.8-7.7 for these derivatives. The oxidized species have been generated by reaction with the azide radical. Hydrogen atom adducts as well as the cation radicals of these derivatives have also been generated by pulse radiolysis and characterized.
Chemphyschem, 2009
Host-guest complexation of neutral red with macrocyclic host molecules: Contrasting pK a shifts a... more Host-guest complexation of neutral red with macrocyclic host molecules: Contrasting pK a shifts and binding affinities for cucurbit [7]uril and β-cyclodextrin.
Research on Chemical Intermediates, 2006
The anion radicals of benzophenone, amino derivatives of benzophenone, fluorenone, furil and anth... more The anion radicals of benzophenone, amino derivatives of benzophenone, fluorenone, furil and antharcene have been generated by pulse radiolysis in acetonitrile solution and their spectroscopic and kinetic properties have been characterized. The G-value for generation of anion radicals in acetonitrile has been measured to be 1.01 ± 0.1 per 100 eV. We have also investigated the electron-transfer reactions from anion radicals of one kind of solutes to the ground state of another solute. This study has demonstrated that pulse radiolysis can be a useful technique for generation and characterization of anion radicals and for studying electron-transfer reactions using acetonitrile as solvent.
Radiation Physics and Chemistry, 2005
... Compound, Benzene, ACN, Methanol, IP. λ max (nm) (ε, 10 3 dm 3 mol −1 cm −1 ) a, τ (μs) b, τ ... more ... Compound, Benzene, ACN, Methanol, IP. λ max (nm) (ε, 10 3 dm 3 mol −1 cm −1 ) a, τ (μs) b, τ (μs), τ (μs), τ (μs). ... The triplet states of four amino-substituted fluorenones in acetonitrile (ACN), methanol and isopropanol (IP) have also been generated by flash photolysis method. ...
Journal of Chemical Sciences, 2020
Abstract The denaturation of human serum albumin (HSA) upon interaction with the surfactant sodiu... more Abstract The denaturation of human serum albumin (HSA) upon interaction with the surfactant sodium dodecyl sulphate (SDS) was examined by measuring the diffusion time of fluorophore (RITC) tagged HSA under near single-molecule conditions using fluorescence correlation spectroscopy. The diffusion time shows four distinct regions as a function of SDS concentration, which corresponds to (I) opening of the tertiary structure, (II) non-specific SDS aggregation, (III) opening of the secondary structure, and (IV) aggregation of SDS around the secondary structure. Diffusion time increases from 383 µs for the free protein to 1002 µs for the SDS bound protein, which leads to an effective increase in the hydrodynamic radius by a factor of about 2.6. Graphic abstract Synopsys Fluorescence correlation spectroscopy reveals a four-step interaction regime between SDS and HSA. The initial opening of the tertiary structure, followed by non-specific aggregation and opening up the secondary structure and finally leading to formation of protein bound micelles with an effective increase of hydrodynamic radius by a factor of 2.6.
Journal of Photochemistry and Photobiology A: Chemistry, 2013
Dynamics of photoinduced electron transfer (PET) reactions between the singlet (S 1) and the trip... more Dynamics of photoinduced electron transfer (PET) reactions between the singlet (S 1) and the triplet (T 1) excited states of 9-fluorenone or simply fluorenone and a few aromatic and aliphatic amines have been investigated under both diffusive and non-diffusive conditions. Formation of the fluorenone anion radical confirms the electron transfer (ET) from the amines to the excited states of fluorenone. Rate constants for both the forward ET process, k CS , and the charge recombination (CR) process, k CR , have been determined in acetonitrile and benzene solutions. Sub-picosecond time-resolved transient absorption study reveals that quenching of the S 1 state in acetonitrile is biexponential. Lifetime of one of these two components is independent of quencher concentration and its values determined for aniline (7.1 ps), dimethylaniline (8.5 ps) and diethylaniline (6.8 ps) are very similar. It represents the non-diffusive component of the PET reaction. But the lifetime of the other component decreases with increasing quencher concentration and the rate of this diffusive component of the PET reaction nearly agrees with the value determined using steady state fluorescence quenching method. To determine the intrinsic values of the rates of the PET reactions involving the S 1 state of fluorenone, the PET dynamics have been studied in these three neat donor solvents. The forward ET process is biexponential and the lifetimes of these two components are very similar in these solvents and vary in the range 0.3-0.5 ps and 6-8 ps. Nonexponential dynamics of the PET reactions conducted in neat donor-solvents have been discussed using a simple solvent reorientational model.
Chemical Physics Letters, 2008
Journal of Physical Chemistry A, 2005
Steady-state fluorescence and time-resolved absorption measurements in pico- and femtosecond time... more Steady-state fluorescence and time-resolved absorption measurements in pico- and femtosecond time domain have been used to investigate the dynamics of hydrogen bond in the excited singlet (S(1)) state of fluorenone in alcoholic solvents. A comparison of the features of the steady-state fluorescence spectra of fluorenone in various kinds of media demonstrates that two spectroscopically distinct forms of fluorenone in the S(1) state, namely the non-hydrogen-bonded (or free) molecule as well as the hydrogen-bonded complex, are responsible for the dual-fluorescence behavior of fluorenone in solutions of normal alcoholic solvents at room temperature (298 K). However, in 2,2,2-trifluoroethanol (TFE), a strong hydrogen bond donating solvent, emission from only the hydrogen-bonded complex is observed. Significant differences have also been observed in the temporal evolution of the absorption spectroscopic properties of the S(1) state of fluorenone in protic and aprotic solvents following photoexcitation using 400 nm laser pulses. An ultrafast component representing the solvent-induced vibrational energy relaxation (VER) process has been associated with the dynamics of the S(1) state of fluorenone in all kinds of solvents. However, in protic solvents, in addition to the VER process, further evolution of the spectroscopic and dynamical properties of the S(1) state have been observed because of repositioning of the hydrogen bonds around the carbonyl group. In normal alcohols, two different kinds of hydrogen-bonded complex of the fluorenone-alcohol system with different orientations of the hydrogen bond with respect to the carbonyl group and the molecular plane of fluorenone have been predicted. On the other hand, in TFE, formation of only one kind of hydrogen-bonded complex has been observed. These observations have been supported by theoretical calculations of the geometries of the hydrogen-bonded complexes in the ground and the excited states of fluorenone. Linear correlation between the lifetimes of the equilibration process occurring because of repositioning of the hydrogen bonds and Debye or longitudinal relaxation times of the normal alcoholic solvents establish the fact that, in weakly hydrogen bond donating solvents, the hydrogen bond dynamics can be described as merely a solvation process. Whereas, in TFE, hydrogen bond dynamics is better described by a process of conversion between two distinct excited states, namely, the non-hydrogen-bonded form and the hydrogen-bonded complex.
Radiation Physics and Chemistry, 2005
Electron pulse radiolysis of four differently substituted amino derivatives of fluorenone, namely... more Electron pulse radiolysis of four differently substituted amino derivatives of fluorenone, namely, 1-amino-, 2-amino- 3-amino-, and 4-aminofluorenone, has been carried out to study the effect of structure on the spectroscopic and kinetic characteristics of the triplet excited states as well as the transient free radical intermediates formed under reducing and oxidizing conditions. The triplet states of these compounds have been generated in benzene by pulse radiolysis and in other solvents by flash photolysis technique and their spectral and kinetic properties have been investigated. Hydrated electron (eaq-) has been found to react with these fluorenone derivatives to form the anion radical species with a diffusion-controlled rate constant. The spectral and kinetic properties of the transient ketyl and anion radicals have been studied by generating them in aqueous solutions of suitable pH. The pKa values of ketyl⇌anion radical equilibria are in the range of 6.8-7.7 for these derivatives. The oxidized species have been generated by reaction with the azide radical. Hydrogen atom adducts as well as the cation radicals of these derivatives have also been generated by pulse radiolysis and characterized.
Chemphyschem, 2009
Host-guest complexation of neutral red with macrocyclic host molecules: Contrasting pK a shifts a... more Host-guest complexation of neutral red with macrocyclic host molecules: Contrasting pK a shifts and binding affinities for cucurbit [7]uril and β-cyclodextrin.
Research on Chemical Intermediates, 2006
The anion radicals of benzophenone, amino derivatives of benzophenone, fluorenone, furil and anth... more The anion radicals of benzophenone, amino derivatives of benzophenone, fluorenone, furil and antharcene have been generated by pulse radiolysis in acetonitrile solution and their spectroscopic and kinetic properties have been characterized. The G-value for generation of anion radicals in acetonitrile has been measured to be 1.01 ± 0.1 per 100 eV. We have also investigated the electron-transfer reactions from anion radicals of one kind of solutes to the ground state of another solute. This study has demonstrated that pulse radiolysis can be a useful technique for generation and characterization of anion radicals and for studying electron-transfer reactions using acetonitrile as solvent.
Radiation Physics and Chemistry, 2005
... Compound, Benzene, ACN, Methanol, IP. λ max (nm) (ε, 10 3 dm 3 mol −1 cm −1 ) a, τ (μs) b, τ ... more ... Compound, Benzene, ACN, Methanol, IP. λ max (nm) (ε, 10 3 dm 3 mol −1 cm −1 ) a, τ (μs) b, τ (μs), τ (μs), τ (μs). ... The triplet states of four amino-substituted fluorenones in acetonitrile (ACN), methanol and isopropanol (IP) have also been generated by flash photolysis method. ...