Paramita Das - Academia.edu (original) (raw)
Papers by Paramita Das
Chemistry and Physics of Lipids, 2008
Interaction of a biologically active -carboline based non-ionic probe, 3-acetyl-4-oxo-6,7-dihydr... more Interaction of a biologically active -carboline based non-ionic probe, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), with the liposomal vesicles of dimyristoyl-l-␣-phosphatidylcholine (DMPC) and dimyristoyl-l-␣-phosphatidylglycerol (DMPG) has been demonstrated using steady-state and time-resolved fluorescence and fluorescence anisotropy techniques. Polarity sensitive intramolecular charge transfer of AODIQ shows a large hypsochromic shift along with an enhancement in the fluorescence quantum yield and fluorescence lifetime in the bilayer membranes compared to those in aqueous buffer solution. Polarity of the immediate vicinity of the probe in the lipid environments has been determined. The fluorometric, quenching and micropolarity determination studies reveal that the fluorophore penetrates deeper in the zwitterionic DMPC membrane compared to the anionic DMPG vesicle. Enhancement in the rotational relaxation time of AODIQ in liposomal membranes suggests that the fluorophore exists in motionally restricted environments.
Journal of Physical Chemistry B, 2007
A steady-state and time-resolved photophysical study of a cationic phenazinium dye, phenosafranin... more A steady-state and time-resolved photophysical study of a cationic phenazinium dye, phenosafranin (PSF), has been investigated in well-characterized biomimetic micellar nanocavities formed by anionic surfactants of varying chain lengths, namely, sodium decyl sulfate (S(10)S), sodium dodecyl sulfate (S(12)S), and sodium tetradecyl sulfate (S(14)S). In all these micellar environments, the charge transfer fluorescence of PSF shows a large hypsochromic shift along with an enhancement in the fluorescence quantum yield as compared to that in aqueous medium. A reduction in the nonradiative deactivation rate within the hydrophobic interior of micelles led to an increase in the fluorescence yield and lifetime. The present work shows the degree of accessibility of the fluorophore toward the ionic quencher in the presence of surfactants of different surfactant chain lengths. The fluorometric and fluorescence quenching studies suggest that the fluorophore resides at the micelle-water interfacial region. The enhancements in the fluorescence anisotropy and rotational relaxation time of the probe in all the micellar environments from the pure aqueous solution suggest that the fluorophore binds in motionally restricted regions introduced by the micelles. Polarity and viscosity of the microenvironments around the probe in the micellar systems have been determined. The work has paid proper attention to the hydrophobic effect of the surfactant chain length on photophysical observations.
Langmuir, 2007
A photophysical study of norharmane (NHM), an efficient cancer cell photosensitizer, has been und... more A photophysical study of norharmane (NHM), an efficient cancer cell photosensitizer, has been undertaken in well-characterized biomimetic micellar nanocavities formed by anionic surfactants of varying chain length, namely, sodium decyl sulfate (S10S), sodium dodecyl sulfate (S12S), and sodium tetradecyl sulfate (S14S), using steady-state and time-resolved fluorescence spectroscopy. The effect of the hydrophobic chain length on the structural dynamism of the fluorophore has been reported. Experimental results demonstrate that the equilibrium of this dynamism is sensitive to the environment. Variation in the surfactant chain length plays an important role in promoting a specific prototropic form of the probe molecule. A striking feature of the present study is that an increase in the surfactant chain length (hydrophobicity) favors the cationic species of NHM. This has been rationalized on the basis of changes in the local pH and the aggregation number of the micelles. A fluorescence quenching study of the micelle-bound probe using ionic quencher Cu2+ corroborates this.
Journal of Chemical Sciences, 2007
The interaction between a bioactive molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quino... more The interaction between a bioactive molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), with human serum albumin (HSA) has been studied using steady-state absorption and fluorescence techniques. A 1:1 complex formation has been established and the binding constant (K) and free energy change for the process have been reported. The AODIQ-HSA complex results in fluorescence resonance energy transfer (FRET) from the tryptophan moiety of HSA to the probe. The critical energy-transfer distance (R 0) for FRET and the Stern-Volmer constant (K sv) for the fluorescence quenching of the donor in the presence of the acceptor have been determined. Importantly, K SV has been shown to be equal to the binding constant itself, implying that the fluorescence quenching arises only from the FRET process. The study suggests that the donor and the acceptor are bound to the same protein at different locations but within the quenching distance.
Journal of Physical Chemistry B, 2007
Interaction of a beta-carboline based biologically active molecule, 3-acetyl-4-oxo-6,7-dihydro-12... more Interaction of a beta-carboline based biologically active molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), with alpha-, beta-, and gamma-cyclodextrins (CDs) in aqueous solution has been studied using steady state and time-resolved fluorescence and steady-state fluorescence anisotropy techniques. Polarity dependent intramolecular charge transfer (ICT) process is responsible for the remarkable sensitivity of this biological fluorophore to the CD environments. Upon encapsulation, the CT fluorescence exhibits hypsochromic shift along with enhancements in the fluorescence yield, fluorescence anisotropy (r), and fluorescence lifetime. The reduction in the nonradiative deactivation rate of the fluorophore within the CD nanocavities leads to an increase in both fluorescence yield and lifetime. Among the three CDs, gamma-CD shows the most spectacular confinement effect. The results establish the formation of 1:1 AODIQ:CD inclusion complexes in alpha- and beta-CDs. In aqueous gamma-CD solutions, however, depending on the concentration of the gamma-CD, formation of both 1:1 and 1:2 complexes have been revealed. Hydrodynamic radii of the 1:1 and 1:2 probe-gamma-CD supramolecular complexes have also been determined.
Biomacromolecules, 2007
A photophysical study on the binding interaction of an efficient cancer cell photosensitizer, nor... more A photophysical study on the binding interaction of an efficient cancer cell photosensitizer, norharmane (NHM), with model transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA), has been performed using a combination of steady-state and time-resolved fluorescence techniques. The emission profile undergoes a remarkable change upon addition of the proteins to the buffered aqueous solution of the photosensitizer. The polarity-dependent prototropic transformation is responsible for the remarkable sensitivity of this biological fluorophore to the protein environments. A marked increase in the fluorescence anisotropy in the proteinous environments indicates that the albumin proteins introduce motional restriction on the drug molecule. Light has been thrown on the denaturing action of urea on the probe-bound protein. The probable binding site of the drug in proteins has also been assessed from the combination of denaturation study, micropolarity measurement, and fluorescence resonance energy transfer (FRET) study. The present study suggests that the stability of serum albumins is enhanced upon binding with the drug.
Journal of Photochemistry and Photobiology B-biology, 2009
Steady state and time resolved fluorometric and circular dichroism (CD) techniques have been expl... more Steady state and time resolved fluorometric and circular dichroism (CD) techniques have been exploited to explore the binding interaction of a ketocyanine dye, namely, 2-[3-(N-methyl-N-phenylamino)-2-propenylidene] indanone (MPAPI) with transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA). The emission spectrum of buffered solution of the dye is found to be perturbed remarkably upon binding with the proteins. An explicit study with respect to modification of fluorescence and fluorescence anisotropy upon binding, effect of denaturant, fluorescence lifetime and CD measurements reveal that the dye binds with both BSA and HSA; the binding being stronger with the latter. Denaturation and CD studies reveal that stability of the proteins increases upon binding with the dye. The probable binding sites of the dye in the proteinous environments have been assessed from fluorescence resonance energy transfer (FRET) study. The probe is argued to be located in the inter domain cleft region of HSA (near Trp-214). From the similarity in the fluorescence behavior of the dye in BSA and HSA it is inferred that in BSA environment the probe is located near Trp-212 rather than Trp-132.
Journal of Physical Chemistry C, 2008
Time-resolved fluorescence anisotropy decay analysis, dynamic light scattering (DLS), and transmi... more Time-resolved fluorescence anisotropy decay analysis, dynamic light scattering (DLS), and transmission electron microscopy (TEM) techniques have been exploited to substantiate and characterize the formation of a substrateanchored γ-cyclodextrin nanotubular suprastructure in aqueous medium, the diameter and the length of the entity being ∼250 nm and a few micrometers, respectively. Similar aggregation is not observed with Rand -cyclodextrins. Dimensions of the substrate and the cyclodextrin cavity have been ascribed to control the formation of the substrate-induced elongated aggregates. The report projects a simple way to design nanotubes of variable dimensions with a proper choice of the anchoring probe and the cyclodextrin.
Journal of Physical Chemistry B, 2008
Absorption, steady-state fluorescence, steady-state fluorescence anisotropy, and intrinsic and in... more Absorption, steady-state fluorescence, steady-state fluorescence anisotropy, and intrinsic and induced circular dichroism (CD) have been exploited to explore the binding of calf thymus DNA (ctDNA) with three cationic phenazinium dyes, viz., phenosafranin (PSF), safranin-T (ST), and safranin-O (SO). The absorption and fluorescence spectra of all the three dyes reflect significant modifications upon interaction with the DNA. A comparative study of the dyes with respect to modification of fluorescence and fluorescence anisotropy upon binding, effect of urea, iodide-induced fluorescence quenching, and CD measurements reveal that the dyes bind to the ctDNA principally in an intercalative fashion. The effect of ionic strength indicates that electrostatic attraction between the cationic dyes and ctDNA is also an important component of the dye-DNA interaction. Intrinsic and induced CD studies help to assess the structural effects of dyes binding to DNA and confirm the intercalative mode of binding as suggested by fluorescence and other studies. Finally it is proposed that dyes with bulkier substitutions are intercalated into the DNA to a lesser extent.
Chemical Physics Letters, 2009
Excited state proton transfer (ESPT) and fluorescence resonance energy transfer (FRET) have been ... more Excited state proton transfer (ESPT) and fluorescence resonance energy transfer (FRET) have been linearly coupled, leading to an efficient pH-sensitive energy transfer from carbazole to a potentially bioactive ketocyanine dye, 2-[3-(N-methyl-N-phenylamino)-2-propenylidene]indanone (MPAPI). The prototropic product produced exclusively from the photoexcited carbazole in the presence of alkali serves as the energy donor. The efficiency of the energy transfer process has been enhanced through the introduction of cyclodextrins of suitable dimensions. The imperative feature of the present model system involving the linear coupling of ESPT and FRET processes lies in its simplicity for designing pH sensitive molecular switches.
Journal of Physical Chemistry A, 2008
Absorption, fluorescence, and fluorescence excitation spectral studies of two planar, cationic ph... more Absorption, fluorescence, and fluorescence excitation spectral studies of two planar, cationic phenazinium dyes, namely, phenosafranin (PSF) and safranin-T (ST), have been performed in protic and aprotic polar solvents. The studies reveal the formation of both J-and H-aggregates in concentrated solutions. The planarity of the phenazinium skeleton and the presence of a positive charge are attributed to be the driving force for this aggregation behavior. The aggregates are established to be dimers only. The positive inductive effect of the methyl substituents in safranin-T augments the aggregation process. The experiments reveal that for both dyes, the polar protic solvent favors the aggregation process more than the aprotic solvent.
Journal of Physical Chemistry B, 2009
Effect of variation of length of nonionic surfactants in terms of the headgroup as well as the ta... more Effect of variation of length of nonionic surfactants in terms of the headgroup as well as the tail part on the photophysical and rotational dynamical properties of a -carboline analogue, 3-acetyl-4-oxo-6,7-dihydro-12H-indolo-[2,3-a]quinolizine (AODIQ) has been investigated. Steady-state and time-resolved fluorescence and fluorescence anisotropy have been exploited for the purpose. The experiments revealed modification of the photophysics of AODIQ by the conjugate effect of polarity and rigidity of the micellar environments with varying poly(ethylene oxide) chain length in the case of Triton X series and the alkyl chain length in the case of Tween series surfactants. Fluorometric studies suggest that the fluorophore resides at the micelle-water interface in all these systems. The enhancements in the steady-state anisotropy in all the micellar media compared to those in pure aqueous solution reflect that the fluorophore is located in motionally restricted regions introduced by the nonionic micelles. Contrary to the single exponential nature of the fluorescence anisotropy decay of AODIQ in aqueous medium, they were found to be biexponential in the micellar environments. The rotational relaxation of AODIQ in the micellar environments has been discussed in light of the two-step and wobbling in a cone model. The model helps to evaluate different rotational parameters and to ascertain the location of the fluorophore in the micellar media. The significant feature is that the motional restriction decreases with an increase in the poly(ethylene oxide) chain length while it increases with an increase in the alkyl chain length. The difference in the extent of water penetration due to variation in the thickness of the palisade layer and therefore a variation in the micellar polarity with a variation of the length of poly(ethylene oxide) and alkyl chain has been argued to be responsible. * Corresponding
Journal of The American Chemical Society, 2006
Tuning of the sensory capability of a potentially bioactive indoloquinolizine system, namely, 3-a... more Tuning of the sensory capability of a potentially bioactive indoloquinolizine system, namely, 3-acetyl-4-oxo-6,7-dihydro-12Hindolo-[2,3-a]-quinolizine (AODIQ), is described in a biomimicking micellar nanocage. It has been shown that surfactant concentration dictates the sensing behavior of the fluorophore toward physiologically essential trace metals, such as Cu 2+ . This is a simple and efficient technique that allows one to utilize the sensor to its maximum efficiency.
Journal of The American Chemical Society, 2006
Tuning of the sensory capability of a potentially bioactive indoloquinolizine system, namely, 3-a... more Tuning of the sensory capability of a potentially bioactive indoloquinolizine system, namely, 3-acetyl-4-oxo-6,7-dihydro-12Hindolo-[2,3-a]-quinolizine (AODIQ), is described in a biomimicking micellar nanocage. It has been shown that surfactant concentration dictates the sensing behavior of the fluorophore toward physiologically essential trace metals, such as Cu 2+ . This is a simple and efficient technique that allows one to utilize the sensor to its maximum efficiency.
![Research paper thumbnail of Fluorescence resonance energy transfer from TX-100 to 3-acetyl-4-oxo-6,7-dihydro-12 H-indolo-[2,3- a]quinolizine in premicellar and micellar environments](https://attachments.academia-assets.com/49515552/thumbnails/1.jpg)
](Journal of Molecular Liquids, 2007
The interaction between a bioactive molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quino... more The interaction between a bioactive molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), with human serum albumin (HSA) has been studied using steady-state absorption and fluorescence techniques. A 1 : 1 complex formation has been established and the binding constant (K) and free energy change for the process have been reported. The AODIQ-HSA complex results in fluorescence resonance energy transfer (FRET) from the tryptophan moiety of HSA to the probe. The critical energy-transfer distance (R 0 ) for FRET and the Stern-Volmer constant (K sv ) for the fluorescence quenching of the donor in the presence of the acceptor have been determined. Importantly, K SV has been shown to be equal to the binding constant itself, implying that the fluorescence quenching arises only from the FRET process. The study suggests that the donor and the acceptor are bound to the same protein at different locations but within the quenching distance.
Journal of Photochemistry and Photobiology C-photochemistry Reviews, 2010
The photobehavior of norharmane (9H-pyrido[3,4-b]-indole) (NHM), one of the vastly used skeleton ... more The photobehavior of norharmane (9H-pyrido[3,4-b]-indole) (NHM), one of the vastly used skeleton of drugs in therapeutic applications, has recently been the subject of increasing interest due to the finding of their phototoxic and photocarcinogenic properties. Its absorption and fluorescence behavior from different prototropic species show remarkable sensitivity towards the polarity, viscosity and local pH, exhibited by various microheterogeneous bio and biomimetic environments like micelles, reverse micelles, proteins, etc. The significant results obtained for NHM in homogeneous and a series of microheterogeneous environments is reviewed in this account. Much attention has been given to the properties of the excited states, location and biodistribution of NHM in different biological environments. The results can help in understanding the photophysics of the probe in biological environments and in assessing the correlation between different prototropic forms and biological activity.
Langmuir, 2006
Steady-state fluorescence measurements and isothermal titration calorimetric experiments have bee... more Steady-state fluorescence measurements and isothermal titration calorimetric experiments have been performed to study the interaction between a telechelic polymer, pyrene-end-capped poly(ethylene oxide) (PYPY), and sodium alkyl sulfate surfactants having decyl, dodecyl, and tetradecyl hydrocarbon tails. Fluorometric results suggest polymer-surfactant interaction in the very low range of polymer concentrations. The relative variation in the excimer to monomer pyrene emission intensities with varying surfactant concentration reveals that initial addition of surfactant favors intramolecular preassociation until the surfactant molecules start binding with the ethylene oxide (EO) chain. With the growing number of surfactant aggregates along the EO chain, the association becomes hindered due to the polyelectrolyte effect. The results from microcalorimetric titrations in the low concentration range of PYPY solution (approximately 10(-6) M) with alkyl sulfates suggest two kinds of surfactant-polymer interactions, one with the polymer hydrophobic end groups and the other with the ethylene oxide backbone. The overall polymer-surfactant interaction starts at a much lower surfactant concentration for the hydrophobically modified polymers compared to that in the case of unsubstituted poly(ethylene oxide) homopolymer. From the experiments critical aggregation concentration values and the second critical concentration where free micelles start forming have been determined. An endeavor has been made to unveil the mechanism underlying the corresponding associations of the surfactants with the polymer.
Journal of Physical Chemistry B, 2008
Steady-state and time-resolved fluorometric techniques have been exploited to study the photophys... more Steady-state and time-resolved fluorometric techniques have been exploited to study the photophysical and distribution behavior of an efficient cancer cell photosensitizer, norharmane (NHM), in well-characterized, biomimicking nanocavities formed by cationic micelles with varying surfactant chain length. Amphiphiles like dodecyl trimethyl ammonium bromide (DTAB), tetradecyl trimethyl ammonium bromide (TTAB), and cetyl trimethyl ammonium bromide (CTAB) have been used for the purpose. Emission behavior of NHM is very much dependent on the surfactant concentration as well as their hydrophobic chain length. The binding constant (K) and free-energy change (∆G) for the interaction of NHM with the cationic micelles have been determined from the fluorescence data. Polarity of the microenvironment around the probe has been determined in the cationic micellar environments from a comparison of the variation of fluorescence properties of the two-prototropic species of the probe in water/dioxane mixture with varying composition. Experimental results demonstrate that the variation in the cationic surfactant chain length plays an important role in promoting a specific prototropic form of the probe molecule. Fluorescence decays are biexponential in all the micelles indicating that the probe molecules are distributed between the two distinct regions of the micelles. The population of the component with a longer lifetime corresponds to the probe in the head group site, while the short-lived component comes from the probe bound to the core region of the micelles. On the basis of the lifetime measurements, the partitioning behavior of the chromophore in the head group and in the core regions in the micelles has been determined. 3685 P ) [NHM] Stern /[NHM] core ) a 1 /a 2 (8)
Chemistry and Physics of Lipids, 2008
Interaction of a biologically active -carboline based non-ionic probe, 3-acetyl-4-oxo-6,7-dihydr... more Interaction of a biologically active -carboline based non-ionic probe, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), with the liposomal vesicles of dimyristoyl-l-␣-phosphatidylcholine (DMPC) and dimyristoyl-l-␣-phosphatidylglycerol (DMPG) has been demonstrated using steady-state and time-resolved fluorescence and fluorescence anisotropy techniques. Polarity sensitive intramolecular charge transfer of AODIQ shows a large hypsochromic shift along with an enhancement in the fluorescence quantum yield and fluorescence lifetime in the bilayer membranes compared to those in aqueous buffer solution. Polarity of the immediate vicinity of the probe in the lipid environments has been determined. The fluorometric, quenching and micropolarity determination studies reveal that the fluorophore penetrates deeper in the zwitterionic DMPC membrane compared to the anionic DMPG vesicle. Enhancement in the rotational relaxation time of AODIQ in liposomal membranes suggests that the fluorophore exists in motionally restricted environments.
Journal of Physical Chemistry B, 2007
A steady-state and time-resolved photophysical study of a cationic phenazinium dye, phenosafranin... more A steady-state and time-resolved photophysical study of a cationic phenazinium dye, phenosafranin (PSF), has been investigated in well-characterized biomimetic micellar nanocavities formed by anionic surfactants of varying chain lengths, namely, sodium decyl sulfate (S(10)S), sodium dodecyl sulfate (S(12)S), and sodium tetradecyl sulfate (S(14)S). In all these micellar environments, the charge transfer fluorescence of PSF shows a large hypsochromic shift along with an enhancement in the fluorescence quantum yield as compared to that in aqueous medium. A reduction in the nonradiative deactivation rate within the hydrophobic interior of micelles led to an increase in the fluorescence yield and lifetime. The present work shows the degree of accessibility of the fluorophore toward the ionic quencher in the presence of surfactants of different surfactant chain lengths. The fluorometric and fluorescence quenching studies suggest that the fluorophore resides at the micelle-water interfacial region. The enhancements in the fluorescence anisotropy and rotational relaxation time of the probe in all the micellar environments from the pure aqueous solution suggest that the fluorophore binds in motionally restricted regions introduced by the micelles. Polarity and viscosity of the microenvironments around the probe in the micellar systems have been determined. The work has paid proper attention to the hydrophobic effect of the surfactant chain length on photophysical observations.
Langmuir, 2007
A photophysical study of norharmane (NHM), an efficient cancer cell photosensitizer, has been und... more A photophysical study of norharmane (NHM), an efficient cancer cell photosensitizer, has been undertaken in well-characterized biomimetic micellar nanocavities formed by anionic surfactants of varying chain length, namely, sodium decyl sulfate (S10S), sodium dodecyl sulfate (S12S), and sodium tetradecyl sulfate (S14S), using steady-state and time-resolved fluorescence spectroscopy. The effect of the hydrophobic chain length on the structural dynamism of the fluorophore has been reported. Experimental results demonstrate that the equilibrium of this dynamism is sensitive to the environment. Variation in the surfactant chain length plays an important role in promoting a specific prototropic form of the probe molecule. A striking feature of the present study is that an increase in the surfactant chain length (hydrophobicity) favors the cationic species of NHM. This has been rationalized on the basis of changes in the local pH and the aggregation number of the micelles. A fluorescence quenching study of the micelle-bound probe using ionic quencher Cu2+ corroborates this.
Journal of Chemical Sciences, 2007
The interaction between a bioactive molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quino... more The interaction between a bioactive molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), with human serum albumin (HSA) has been studied using steady-state absorption and fluorescence techniques. A 1:1 complex formation has been established and the binding constant (K) and free energy change for the process have been reported. The AODIQ-HSA complex results in fluorescence resonance energy transfer (FRET) from the tryptophan moiety of HSA to the probe. The critical energy-transfer distance (R 0) for FRET and the Stern-Volmer constant (K sv) for the fluorescence quenching of the donor in the presence of the acceptor have been determined. Importantly, K SV has been shown to be equal to the binding constant itself, implying that the fluorescence quenching arises only from the FRET process. The study suggests that the donor and the acceptor are bound to the same protein at different locations but within the quenching distance.
Journal of Physical Chemistry B, 2007
Interaction of a beta-carboline based biologically active molecule, 3-acetyl-4-oxo-6,7-dihydro-12... more Interaction of a beta-carboline based biologically active molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), with alpha-, beta-, and gamma-cyclodextrins (CDs) in aqueous solution has been studied using steady state and time-resolved fluorescence and steady-state fluorescence anisotropy techniques. Polarity dependent intramolecular charge transfer (ICT) process is responsible for the remarkable sensitivity of this biological fluorophore to the CD environments. Upon encapsulation, the CT fluorescence exhibits hypsochromic shift along with enhancements in the fluorescence yield, fluorescence anisotropy (r), and fluorescence lifetime. The reduction in the nonradiative deactivation rate of the fluorophore within the CD nanocavities leads to an increase in both fluorescence yield and lifetime. Among the three CDs, gamma-CD shows the most spectacular confinement effect. The results establish the formation of 1:1 AODIQ:CD inclusion complexes in alpha- and beta-CDs. In aqueous gamma-CD solutions, however, depending on the concentration of the gamma-CD, formation of both 1:1 and 1:2 complexes have been revealed. Hydrodynamic radii of the 1:1 and 1:2 probe-gamma-CD supramolecular complexes have also been determined.
Biomacromolecules, 2007
A photophysical study on the binding interaction of an efficient cancer cell photosensitizer, nor... more A photophysical study on the binding interaction of an efficient cancer cell photosensitizer, norharmane (NHM), with model transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA), has been performed using a combination of steady-state and time-resolved fluorescence techniques. The emission profile undergoes a remarkable change upon addition of the proteins to the buffered aqueous solution of the photosensitizer. The polarity-dependent prototropic transformation is responsible for the remarkable sensitivity of this biological fluorophore to the protein environments. A marked increase in the fluorescence anisotropy in the proteinous environments indicates that the albumin proteins introduce motional restriction on the drug molecule. Light has been thrown on the denaturing action of urea on the probe-bound protein. The probable binding site of the drug in proteins has also been assessed from the combination of denaturation study, micropolarity measurement, and fluorescence resonance energy transfer (FRET) study. The present study suggests that the stability of serum albumins is enhanced upon binding with the drug.
Journal of Photochemistry and Photobiology B-biology, 2009
Steady state and time resolved fluorometric and circular dichroism (CD) techniques have been expl... more Steady state and time resolved fluorometric and circular dichroism (CD) techniques have been exploited to explore the binding interaction of a ketocyanine dye, namely, 2-[3-(N-methyl-N-phenylamino)-2-propenylidene] indanone (MPAPI) with transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA). The emission spectrum of buffered solution of the dye is found to be perturbed remarkably upon binding with the proteins. An explicit study with respect to modification of fluorescence and fluorescence anisotropy upon binding, effect of denaturant, fluorescence lifetime and CD measurements reveal that the dye binds with both BSA and HSA; the binding being stronger with the latter. Denaturation and CD studies reveal that stability of the proteins increases upon binding with the dye. The probable binding sites of the dye in the proteinous environments have been assessed from fluorescence resonance energy transfer (FRET) study. The probe is argued to be located in the inter domain cleft region of HSA (near Trp-214). From the similarity in the fluorescence behavior of the dye in BSA and HSA it is inferred that in BSA environment the probe is located near Trp-212 rather than Trp-132.
Journal of Physical Chemistry C, 2008
Time-resolved fluorescence anisotropy decay analysis, dynamic light scattering (DLS), and transmi... more Time-resolved fluorescence anisotropy decay analysis, dynamic light scattering (DLS), and transmission electron microscopy (TEM) techniques have been exploited to substantiate and characterize the formation of a substrateanchored γ-cyclodextrin nanotubular suprastructure in aqueous medium, the diameter and the length of the entity being ∼250 nm and a few micrometers, respectively. Similar aggregation is not observed with Rand -cyclodextrins. Dimensions of the substrate and the cyclodextrin cavity have been ascribed to control the formation of the substrate-induced elongated aggregates. The report projects a simple way to design nanotubes of variable dimensions with a proper choice of the anchoring probe and the cyclodextrin.
Journal of Physical Chemistry B, 2008
Absorption, steady-state fluorescence, steady-state fluorescence anisotropy, and intrinsic and in... more Absorption, steady-state fluorescence, steady-state fluorescence anisotropy, and intrinsic and induced circular dichroism (CD) have been exploited to explore the binding of calf thymus DNA (ctDNA) with three cationic phenazinium dyes, viz., phenosafranin (PSF), safranin-T (ST), and safranin-O (SO). The absorption and fluorescence spectra of all the three dyes reflect significant modifications upon interaction with the DNA. A comparative study of the dyes with respect to modification of fluorescence and fluorescence anisotropy upon binding, effect of urea, iodide-induced fluorescence quenching, and CD measurements reveal that the dyes bind to the ctDNA principally in an intercalative fashion. The effect of ionic strength indicates that electrostatic attraction between the cationic dyes and ctDNA is also an important component of the dye-DNA interaction. Intrinsic and induced CD studies help to assess the structural effects of dyes binding to DNA and confirm the intercalative mode of binding as suggested by fluorescence and other studies. Finally it is proposed that dyes with bulkier substitutions are intercalated into the DNA to a lesser extent.
Chemical Physics Letters, 2009
Excited state proton transfer (ESPT) and fluorescence resonance energy transfer (FRET) have been ... more Excited state proton transfer (ESPT) and fluorescence resonance energy transfer (FRET) have been linearly coupled, leading to an efficient pH-sensitive energy transfer from carbazole to a potentially bioactive ketocyanine dye, 2-[3-(N-methyl-N-phenylamino)-2-propenylidene]indanone (MPAPI). The prototropic product produced exclusively from the photoexcited carbazole in the presence of alkali serves as the energy donor. The efficiency of the energy transfer process has been enhanced through the introduction of cyclodextrins of suitable dimensions. The imperative feature of the present model system involving the linear coupling of ESPT and FRET processes lies in its simplicity for designing pH sensitive molecular switches.
Journal of Physical Chemistry A, 2008
Absorption, fluorescence, and fluorescence excitation spectral studies of two planar, cationic ph... more Absorption, fluorescence, and fluorescence excitation spectral studies of two planar, cationic phenazinium dyes, namely, phenosafranin (PSF) and safranin-T (ST), have been performed in protic and aprotic polar solvents. The studies reveal the formation of both J-and H-aggregates in concentrated solutions. The planarity of the phenazinium skeleton and the presence of a positive charge are attributed to be the driving force for this aggregation behavior. The aggregates are established to be dimers only. The positive inductive effect of the methyl substituents in safranin-T augments the aggregation process. The experiments reveal that for both dyes, the polar protic solvent favors the aggregation process more than the aprotic solvent.
Journal of Physical Chemistry B, 2009
Effect of variation of length of nonionic surfactants in terms of the headgroup as well as the ta... more Effect of variation of length of nonionic surfactants in terms of the headgroup as well as the tail part on the photophysical and rotational dynamical properties of a -carboline analogue, 3-acetyl-4-oxo-6,7-dihydro-12H-indolo-[2,3-a]quinolizine (AODIQ) has been investigated. Steady-state and time-resolved fluorescence and fluorescence anisotropy have been exploited for the purpose. The experiments revealed modification of the photophysics of AODIQ by the conjugate effect of polarity and rigidity of the micellar environments with varying poly(ethylene oxide) chain length in the case of Triton X series and the alkyl chain length in the case of Tween series surfactants. Fluorometric studies suggest that the fluorophore resides at the micelle-water interface in all these systems. The enhancements in the steady-state anisotropy in all the micellar media compared to those in pure aqueous solution reflect that the fluorophore is located in motionally restricted regions introduced by the nonionic micelles. Contrary to the single exponential nature of the fluorescence anisotropy decay of AODIQ in aqueous medium, they were found to be biexponential in the micellar environments. The rotational relaxation of AODIQ in the micellar environments has been discussed in light of the two-step and wobbling in a cone model. The model helps to evaluate different rotational parameters and to ascertain the location of the fluorophore in the micellar media. The significant feature is that the motional restriction decreases with an increase in the poly(ethylene oxide) chain length while it increases with an increase in the alkyl chain length. The difference in the extent of water penetration due to variation in the thickness of the palisade layer and therefore a variation in the micellar polarity with a variation of the length of poly(ethylene oxide) and alkyl chain has been argued to be responsible. * Corresponding
Journal of The American Chemical Society, 2006
Tuning of the sensory capability of a potentially bioactive indoloquinolizine system, namely, 3-a... more Tuning of the sensory capability of a potentially bioactive indoloquinolizine system, namely, 3-acetyl-4-oxo-6,7-dihydro-12Hindolo-[2,3-a]-quinolizine (AODIQ), is described in a biomimicking micellar nanocage. It has been shown that surfactant concentration dictates the sensing behavior of the fluorophore toward physiologically essential trace metals, such as Cu 2+ . This is a simple and efficient technique that allows one to utilize the sensor to its maximum efficiency.
Journal of The American Chemical Society, 2006
Tuning of the sensory capability of a potentially bioactive indoloquinolizine system, namely, 3-a... more Tuning of the sensory capability of a potentially bioactive indoloquinolizine system, namely, 3-acetyl-4-oxo-6,7-dihydro-12Hindolo-[2,3-a]-quinolizine (AODIQ), is described in a biomimicking micellar nanocage. It has been shown that surfactant concentration dictates the sensing behavior of the fluorophore toward physiologically essential trace metals, such as Cu 2+ . This is a simple and efficient technique that allows one to utilize the sensor to its maximum efficiency.
Journal of Molecular Liquids, 2007
The interaction between a bioactive molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quino... more The interaction between a bioactive molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), with human serum albumin (HSA) has been studied using steady-state absorption and fluorescence techniques. A 1 : 1 complex formation has been established and the binding constant (K) and free energy change for the process have been reported. The AODIQ-HSA complex results in fluorescence resonance energy transfer (FRET) from the tryptophan moiety of HSA to the probe. The critical energy-transfer distance (R 0 ) for FRET and the Stern-Volmer constant (K sv ) for the fluorescence quenching of the donor in the presence of the acceptor have been determined. Importantly, K SV has been shown to be equal to the binding constant itself, implying that the fluorescence quenching arises only from the FRET process. The study suggests that the donor and the acceptor are bound to the same protein at different locations but within the quenching distance.
Journal of Photochemistry and Photobiology C-photochemistry Reviews, 2010
The photobehavior of norharmane (9H-pyrido[3,4-b]-indole) (NHM), one of the vastly used skeleton ... more The photobehavior of norharmane (9H-pyrido[3,4-b]-indole) (NHM), one of the vastly used skeleton of drugs in therapeutic applications, has recently been the subject of increasing interest due to the finding of their phototoxic and photocarcinogenic properties. Its absorption and fluorescence behavior from different prototropic species show remarkable sensitivity towards the polarity, viscosity and local pH, exhibited by various microheterogeneous bio and biomimetic environments like micelles, reverse micelles, proteins, etc. The significant results obtained for NHM in homogeneous and a series of microheterogeneous environments is reviewed in this account. Much attention has been given to the properties of the excited states, location and biodistribution of NHM in different biological environments. The results can help in understanding the photophysics of the probe in biological environments and in assessing the correlation between different prototropic forms and biological activity.
Langmuir, 2006
Steady-state fluorescence measurements and isothermal titration calorimetric experiments have bee... more Steady-state fluorescence measurements and isothermal titration calorimetric experiments have been performed to study the interaction between a telechelic polymer, pyrene-end-capped poly(ethylene oxide) (PYPY), and sodium alkyl sulfate surfactants having decyl, dodecyl, and tetradecyl hydrocarbon tails. Fluorometric results suggest polymer-surfactant interaction in the very low range of polymer concentrations. The relative variation in the excimer to monomer pyrene emission intensities with varying surfactant concentration reveals that initial addition of surfactant favors intramolecular preassociation until the surfactant molecules start binding with the ethylene oxide (EO) chain. With the growing number of surfactant aggregates along the EO chain, the association becomes hindered due to the polyelectrolyte effect. The results from microcalorimetric titrations in the low concentration range of PYPY solution (approximately 10(-6) M) with alkyl sulfates suggest two kinds of surfactant-polymer interactions, one with the polymer hydrophobic end groups and the other with the ethylene oxide backbone. The overall polymer-surfactant interaction starts at a much lower surfactant concentration for the hydrophobically modified polymers compared to that in the case of unsubstituted poly(ethylene oxide) homopolymer. From the experiments critical aggregation concentration values and the second critical concentration where free micelles start forming have been determined. An endeavor has been made to unveil the mechanism underlying the corresponding associations of the surfactants with the polymer.
Journal of Physical Chemistry B, 2008
Steady-state and time-resolved fluorometric techniques have been exploited to study the photophys... more Steady-state and time-resolved fluorometric techniques have been exploited to study the photophysical and distribution behavior of an efficient cancer cell photosensitizer, norharmane (NHM), in well-characterized, biomimicking nanocavities formed by cationic micelles with varying surfactant chain length. Amphiphiles like dodecyl trimethyl ammonium bromide (DTAB), tetradecyl trimethyl ammonium bromide (TTAB), and cetyl trimethyl ammonium bromide (CTAB) have been used for the purpose. Emission behavior of NHM is very much dependent on the surfactant concentration as well as their hydrophobic chain length. The binding constant (K) and free-energy change (∆G) for the interaction of NHM with the cationic micelles have been determined from the fluorescence data. Polarity of the microenvironment around the probe has been determined in the cationic micellar environments from a comparison of the variation of fluorescence properties of the two-prototropic species of the probe in water/dioxane mixture with varying composition. Experimental results demonstrate that the variation in the cationic surfactant chain length plays an important role in promoting a specific prototropic form of the probe molecule. Fluorescence decays are biexponential in all the micelles indicating that the probe molecules are distributed between the two distinct regions of the micelles. The population of the component with a longer lifetime corresponds to the probe in the head group site, while the short-lived component comes from the probe bound to the core region of the micelles. On the basis of the lifetime measurements, the partitioning behavior of the chromophore in the head group and in the core regions in the micelles has been determined. 3685 P ) [NHM] Stern /[NHM] core ) a 1 /a 2 (8)