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The present contribution depicts a unique approach to generate tunable Förster resonance energy transfer (FRET) emission with variation of pH of the medium. The pH sensitive absorption of Doxorubicin leads to modification of spectral overlap between emission spectra of donor (Pyrazoline) and absorption spectra of acceptor (Doxorubicin) thereby sensing maximum FRET efficiency in an optimum pH (near pK

Photocatalysts are important milestone for harvesting chemical energy from light energy in the era of massive energy consumption. Cerium oxide nanoparticle, having wide applications from catalysis to biomedical field, has drawback as photocatalyst due to its large band gap. Herein, a conducting polymer, polyaniline has been chosen as an active catalyst support to upgrade photocatalytic activity of cerium oxide nanoparticle. In this work, at first spherical shaped cerium oxide nanoparticle was synthesized by hydrothermal method. Later, polyaniline was decorated on cerium oxide nanoparticle surface via in-situ oxidative polymerization of aniline monomer. The as synthesized polyaniline/cerium oxide nanocomposite exhibits remarkable enhanced photocatalytic efficiency in comparison to cerium oxide nanoparticle or polyaniline in the degradation of a model organic pollutant Rhodamine B in waste water under UV light irradiation. Effects of different pH, Rhodamine B concentration and polyaniline content on photocatalytic activity were also analyzed. The experimental findings demonstrate that nanocomposite with polyaniline and cerium oxide nanoparticle molar ratio 1:1 degrades 91% Rhodamine B in 2 h whereas cerium oxide nanoparticle shows only 10% degradation in same time. The first order rate constant in presence of nanocomposite increases eight fold relative to that in presence of cerium oxide nanoparticle only. The enhanced photocatalytic mechanism is attributed to the synergistic effect between polyaniline and cerium oxide nanoparticle, which reduces recombination rate of photoinduced electron hole pair. Furthermore the nanocomposite is stable upto several cycles of catalysis as evident from their activity study and Field Emission Scanning Electron Microscope images. Thus combination of a conducing polymer with a semiconductor provides an advanced pathway for achieving enhanced photocatalytic activity.

Development of stable self-assembled nanostructures (especially vesicles and liposomes), and understanding their physicochemical behaviors in aqueous solution is a long-standing topic of interest in chemical and biochemical research. In this progressive area, we report for the first-time formation of mixed micelles (at pH 12), and vesicles of anionic bolaamphiphiles (dicarboxylic acids viz. HOOC - ( CH 2 ) n - COOH , with moderate values of n 10, 11, 12, and 14) in combination with a cationic surfactant decyltrimethylammonium bromide (C10TAB) in buffered aqueous medium at different pH (6.0, 6.5, 6.8, and 8.0 for bola 10, 11, 12, and 14, respectively). Three pH dependent states of the solutions are observed: clear (high pH > 8), turbid and translucent (mid pH ≈ 6–8), and viscous inhomogeneous oil-like state (low pH

Interest in synthesizing and characterizing (IR, NMR and HRMS spectroscopic methods) a pyrimidine based Schiff-base ligand, 2-(2-(Anthracen-9-ylmethylene) hydrazinyl)-4,6-dimethyl pyrimidine (ANHP) has been developed for its application to ascertain the conformational change of protein and sensitivity towards fluorescence resonance energy transfer (FRET) process. Location of ANHP in bovine serum albumin (BSA) and human serum albumin (HSA) proteins environment has been determined using different spectroscopic techniques. Weakly fluorescent ANHP have shown greater protein induced fluorescence enhancement (PIFE) in case of HSA than BSA, though in both cases energy transfer efficiency are almost same but difference in binding constant values encourages us to find the location of ANHP within the complex protein environment. From the FRET parameter and α-helicity change, it has been found that ANHP bound with Trp-214 of HSA and surface Trp-134 of BSA. Conformational changes of proteins have been observed more for HSA than BSA in presence of ANHP, which has confirmed the location of ANHP in both the protein environments. Coupled with experimental studies, molecular docking analysis has also been done to explain the locations and distance dependent FRET process of ANHP in both proteins.

A study of the comparative drug carrier properties of cucurbituril[7] (CB7) and β-cyclodextrin (β-CD) with a naphthalimide derivative, [2-(2-aminoethyl)-1H-benzo[deisoquinoline-1,3(2H)-dione] (NAP) and its release in aqueous solution using micellar environment, is the key research interest of this work. The profound changes in the different spectroscopic behavior have been attributed to the formation of a 1:1 inclusion complex for NAP:CB7 system. Several experimental outcomes clearly interpreted that CB7 has better drug carrier properties for NAP compared to β-CD. It has been also focused on the systematic release of NAP molecule from CB7 by using different ionic and non ionic surfactants. Before releasing the drug molecules from CB7 the interaction between NAP and the three different types of surfactants has also been investigated separately. The selectivity of drug carrier and releaser has been monitored, using different spectroscopic techniques like absorbance, fluorescence, fluorescence decay life time and 1 H NMR spectroscopy. Besides, a theoretical approach has been followed for a proper geometrical optimized structure of NAP molecule and molecular arrangement of NAP:CB7 inclusion complex. From Density Functional Theory (DFT) it has been seen that NAP molecule is oriented as a t-bone like structure in its optimized form.

Research is going on to synthesize materials for acting as sensors of metal ions and are also published in different journals but the cause for sensing has not been clearly explained. In this paper, the reason for selective sensing of Cu2+ ions has been explained. A novel Schiff base fluorescent probe 3-[(2-hydroxy-naphthalen-1-ylmethylene)-hydrazono]-butan-2-one oxime (NPTH) was designed and synthesized to use as Cu2+ sensor. From our recent experiments, it has been found that only Cu2+ among different metal ions has been sensed by the synthesized ligand. The reason for selection and sensing of Cu2+ by the ligand was established by different spectroscopic techniques. The detection limit of NPTH was calculated as low as 4.11 ​× ​10-4M for Cu2+. Therefore, these results indicate that sensor NPTH has great prospective to detect Cu2+ ion in environmental analysis systems. Density functional theory (DFT) calculations have been done to ascertain the ground state geometry of NPTH.

Two tri-block copolymers P123 (PEO19PPO69PEO19) and F127 (PEO100PPO65PEO100) have been employed to form polymeric nanomicelles and function as potential nanocarriers for an anticancer pyrazoline derivative (PYZ) in aqueous buffer solution for biological studies. Encapsulation within these nanomicelles considerably enhanced the fluorescence of the PYZ compared to its low fluorescence in aqueous buffer medium. The effect of the micellar structures on the photophysical properties of PYZ have been demonstrated by means of steady state and time resolved fluorescence spectroscopy. Variation in hydrophilicity of the corona region was found to be a prime factor in modulating the location of the PYZ within the micelles which in turn influenced its corresponding enhanced emission and cytotoxicity. These drug encapsulated nanomicelles were found to be successfully internalized into the MCF-7 cells to demonstrate high-quality fluorescent images. The location of PYZ within the polymeric micelles influenced the CAC (Critical Aggregation Concentration)/CMC (Critical Micellar Concentration) ratio which modulated their drug release capacity resulting in a variation in their cytotoxicity.

The present work reveals the study of interaction of a promising chemotherapeutic drug ciprofloxacin (CFX) with a model transport protein bovine serum albumin (BSA). The occurrence of the drug-protein interaction is found to result in significant modulations of the fluorescence excitation and emission spectroscopic properties of CFX following interaction with BSA. However, the major focus of the study underlies a critical insight into the quantitation of the drug-protein interaction phenomenon. To this end, we have exploited the isothermal titration calorimetric (ITC) technique to quantify the affinity constant (K a ) and stoichiometry (n) of the CFX-BSA interaction with simultaneous revelation of the accompanying thermodynamics of the interaction process. In this context, our discussion also sheds light on the lacuna surrounding various experimental methodologies for evaluation of drug-protein binding parameters. Our endeavor also extends to elucidation of the kinetic parameters and energy of activation (E a ) of the CFX-BSA interaction. The present study also delineates the modulation of the dynamical aspects of CFX following interaction with BSA. The rotational relaxation dynamics of the protein-bound drug reveals the not-so-common “ dip-rise-dip ” anisotropy decay. Furthermore, the effect of drug binding on the native protein conformation has been evaluated from circular dichroism (CD) spectroscopy which reveals partial rupture of the protein secondary structure.

Significant Fluorescence Resonance Energy Transfer (FRET) process was observed between Naproxen (NPX) and a pharmaceutically important 3-pyrazolyl-2-pyrazoline derivative (PYZ) in bulk aqueous and heterogeneous cyclodextrin medium. The FRET efficacy of NPX-PYZ pair varied considerably in different cyclodextrin environments. Variation in the FRET efficacy mainly occurs due to a change in microenvironment of the fluorophores from bulk to a confined one. The structures of the FRET-pair and their interactions with cyclodextrins invoke a change in their spatial arrangement and proximity, which noticeably affects the FRET efficacy. The plausible explanations for this modulation in FRET efficacy has been established by employing steady state and time resolved fluorescence techniques in which simultaneous time–correlated analysis of the donor decay was observed to be reduced through FRET rather than some other relaxation pathway. Molecular Docking Analysis provided evidence of the possible modes of spatial orientation of the FRET pair in different cyclodextrin nano-cavities. Further TD-DFT calculations using B3LYP/6-31G/(d,p) method provided an intriguing insight about the medium dependent changes in the energies of the frontier molecular orbitals (HOMO-LUMO) associated with the corresponding FRET pair.

Gold Nanomaterials (GNMs) interact with fluorophores via electromagnetic coupling under excitation. In this particular work we carried out (to the best of our knowledge for the first time) a comprehensive study of systematic quenching of a blue emitter 2-Anthracene Sulfonate (2-AS) in the presence of gold nanoparticles of different size and shape. We synthesized gold nanomaterials of four different dimensions [nanoparticle (0D), nanorod (1D), nanotriangle (2D) and nanobipyramids (3D)] and realized the underlying effect on the emitting dipole in terms of steady and time resolved fluorescence. Nanometal Surface Energy Transfer (NSET) has already been proved to be the best long range spectroscopic ruler so far. Many attempts have been made to understand the interaction between a fluorescent molecule and gold nanomaterials. But not a single model can interpret alone the interaction phenomena. We have opted three different models to compare the experimental and theoretical data. Due to the presence of size dependent absorptivity and dielectric function, modified CPS-Kuhn model was proved to be the worthiest to comprehend variance of behavior of an emitting dipole in close proximity to nanometal surface by coupling with the image dipole of gold nanomaterials.

Molecules capable of inducing self-structure in poly(A) may arrest protein synthesis by preventing poly(A) chain elongation thereby inhibiting the function of mRNA. We examined whether new methylene blue can induce such structural organization in single stranded poly(A) and compared the results with those of the phenothiazinium dyes thionine and toluidine blue O. Strong association between the dyes and poly(A) was revealed from the spectroscopy and cyclic voltammetry. Thionine has a higher affinity compared to toluidine blue O and new methylene blue at 50 mM and 100 mM, but at 200 mM [Na + ] new methylene blue exhibited the highest binding affinity. Negative enthalpy and positive entropy changes, and enthalpy-entropy compensation behaviour were characteristic features for the complexation. Involvement of hydrophobic forces in the binding process is correlated to the negative heat capacity changes. Differential scanning calorimetry and circular dichroism results revealed that the dyes bind poly(A) and induce a stable secondary structure with a melting temperature of 333.15 K. The binding constants increased in the range of 50–200 mM [Na + ]. Molecular docking results revealed that not only van der Waals forces of attraction but hydrogen bonding also plays a crucial role in dye-poly(A) binding. Recognition and binding of small molecules to single stranded poly(A) may present a new avenue for therapeutic intervention.

The fluorescent property of the aqueous solution of a metal organic framework (MOF) of Mn(II), having a sedimentary rocks like microstructure in solid-state, has been investigated. The luminescent feature of the the aqueous solution of MOF has been employed for studying the interactions of MOF with different surfactants including neutral, cationic, and anionic types in water medium. Interestingly, the MOF can very selective sense Triton X-100 based micelle in water medium. During the sensing process the fluorescent monomer of the MOF gets accommodated at the palisade layer of Triton X-100 in water medium and this has also been justified by simple fluorescence spectral and FE-SEM microstructural analysis. Thus, a MOF of Mn(II) can act as a selective fluorescent sensor for Triton X-100 based organized medium in water.

We have studied the effect of interaction of surfactants on the FRET process in aqueous solution from transport proteins, BSA and HSA to the probe molecule, sodium salt of anthracene 1,5-disulphonate (1,5-AS). Cationic surfactant CTAB and gemini, anionic surfactant SDS and nonionic surfactant igepal-630 have been used for our investigation as surfactants and micellar solution. In organized media denaturation of protein occurs. Denaturation of protein has also been observed in presence of 1,5-AS. This has been established from steady state, time resolved fluorescence and circular dichroism (CD) studies in homogeneous and heterogeneous environments. Helecity calculations from CD spectra have also supported the results. Nonionic and ionic micellar solutions have been found to directly affect the protein helicity and the FRET parameters. The FRET parameters and denaturation of proteins in homogeneous and heterogeneous media have been compared.

Accumulation of amyloid fibrils of proteins in different organs is a pathological indication for various neurogenerative disorders. Recently nanotechnology is at the centre of interest to tackle with those disorders. In this study we have chosen hen egg white lysozyme as our model protein which is responsible for hereditary systemic Amyloidosis disease. Here we have reported effect of cerium oxide nanoparticle (CeONP), folic acid functionalized CeONP (FA-CeONP) and polyacrylic acid functionalized CeONP (PAA-CeONP) (all of them having size ∼18 nm) on fibrillation of hen egg white lysozyme (Lyz). The amyloid growth is monitored by Thioflavin T (ThT), Congo Red (CR), 8-anilinonapthalene-1-sulfonic acid (ANS) assay, time resolved fluorescence anisotropy, intrinsic fluorescence, circular dichroism, atomic force microscopy and fluorescence microscopy study. Results demonstrate that all nanoparticle (NP) shows antiamyloid activity by broadening lag phase and suppressing growth phase of Lyz amyloid growth, but PAA-CeONP shows maximum inhibitory effect. These bare and functionalized CeONP shows dose dependent antiamyloid activity. We have also demonstrated that such inhibition of amyloid formation is associated with reduction of β-sheet content of protein. The inhibition efficiency is quantified by half maximal inhibition concentration IC50 values. A mechanistic pathway is explained on the basis of electrostatic interaction between NP and Lyz by ζ- potential measurement. This interaction is also analyzed theoretically by docking analysis. Thus our study provides a basis for use of CeONP as a promising candidate in therapeutic application in amyloid related disorders.

Interaction between the anionic double tail AOT (sodium bis (ethylhexyl) sulfosuccinate) and the zwitterionic single tail TPS ( N -tetradecyl- N , N -dimethyl-3-ammoino-1-propane sulfonate) in water and at the air/water interface has been studied. The surfactants synergistically interact with the solution as well as at the air/water interface forming mixed assemblies. The physicochemical properties of the free amphiphile monomers up to the point of their critical micelle concentration (CMC) have been evaluated and discussed. The interactions between the two amphiphiles in the mixed micelles in the bulk, and the adsorbed mixed assemblies at the air/solution interface have been analyzed using Rubingh and Rosen formalisms. The mixed systems have been found to undergo composition dependent salt induced micelle → vesicle → micelle forming transitions (MVMT). This has been supported by the fluorescence anisotropy measurements of the DPH probe, and the hydrodynamic diameter determined by the DLS method. Stable vesicle formation has been confirmed from the calcein dye encapsulation experiments, and the high resolution transmission electron microscopy (HRTEM) measurements. Nano-structured gold particles (GNPs) have been synthesized in the pure and mixed micelles of the AOT and TPS by the reduction of the HAuCl 4 by NaBH 4 . The morphology of the nano-structured materials was characterized from the UV and HRTEM measurements.

For high-fidelity selective and sensitive fluorescent detection of zinc ions (Zn2+), a new pyrimidine based Schiff-base ligand PyMD (2,2′-((1Z, 1′Z)-(2,2′-(pyrimidine-2,4-diyl)bis(hydrazin-2-yl-1-ylidene))bis(ethan-1-yl-1-ylidene))diphenol) was designed and synthesized. In 4:1 methanol (MeOH)–water mixture, zinc (Zn2+) binding was found to promote ∼23 fold fluorescence enhancement of PyMD at wavelength 469 nm. The limit of detection (LOD) of Zn2+ was calculated to be 6.9 × 10−7 M according to fluorometric titration. The 1:1 binding mode of the metal complex was established by combined UV–vis, fluorescence, NMR and HRMS spectroscopic methods. Photophysical investigations including steady-state and time resolved analysis suggested a mechanism for the fluorescent zinc response that involved a ligand-to-metal charge transfer (LMCT) pathway. The experimental observations were further confirmed by DFT (Density Functional Theory) calculations of the free sensor molecule (i.e., PyMD) and the complex structure (PyMD-Zn2+). Finally, newly synthesized PyMD was applied for detection of free zinc in real samples, e.g., cabbage, banana, banana stem juice and commercial fruit juice. Besides, fluorescence behavior of PyMD-Zn2+ complex was also employed for Escherichia coli bacterial cell imaging study.

High selectivity and fluorescence sensitivity of a well-recognized antiexcitotoxic and anticonvulsant drug, kynurenic acid (KA), toward Cd II ion has been demonstrated by UV–vis, fluorescence, 1 H NMR spectroscopy in combination with computational calculations. Upon complexation with Cd II , KA exhibits a distinct excimer emission at 528 nm along with monomer emission at 402 nm. The sensing ability of drug KA toward Cd II ion is distinctly different from sensing for Hg II or Cu II ion. KA can form dimer by intermolecular O–H⋯O hydrogen bonding between the –COOH groups. Presence of Cd II metal ions promotes dimer formation in the excited state which exhibits excimer fluorescence.

In the present contribution, we have explored ground and excited state spectroscopic properties of an antiexcitotoxic and anticonvulsant drug, Kynurenic acid (KA), through steady-state absorption, emission and time-resolved emission spectroscopy and quantum chemical calculations. The main focus of this article is to illustrate the effects of various parameters such as the nature of the solvents and pH of the medium on the spectral properties of KA which confirms the presence of different neutral and ionic species in the ground and excited states. The molecule KA exists mainly as keto- or anionic form in the ground state, whereas the main contribution of its emission is arising from the keto tautomer in the excited state. Quantum chemical calculations by Density Functional Theory (DFT) method has been effectively employed to correlate the experimental findings. The ground and excited state properties of KA ascertained by means of experimental and theoretical method reveal that it resembles well with other two compounds, 4-hydroxyquinoline and xanthurenic acid formed by the decomposition of UV filters.

In this work, a pyridine containing Schiff-base, 1-((anthracen-10-yl)methylene)-2-(pyridin-2-yl)hydrazine (AP) and a pyrimidine containing Schiff-base 2-(2-(Anthracen-9-ylmethylene) hydrazinyl)-4, 6-dimethyl pyrimidine (ANHP) have been synthesized and characterized by IR, NMR, HRMS and different spectroscopic methods. Two different tri block co polymers (P-123 and F-127) have been used as delivering system of this poor water soluble drug molecule AP and ANHP which are the main investigation of this work. To find out which one is the better delivering systems of AP and ANHP, spectroscopic studies have been carried out in P-123 and F-127 polymeric media. From the interactions of AP and ANHP with P-123 and F-127 polymers individually, binding constant values have been determined. The drug delivering efficiency of block co polymers has been investigated by using different spectroscopic techniques like absorbance, fluorescence, DLS and time resolved fluorescence measurements. All these experimental results indicate that P-123 is the better AP and ANHP delivering system than F-127 polymer. In addition, the structural properties like bond length, bond angles etc. of AP have been calculated by using density functional theory (DFT).

Entrapping of a drug molecule having prospective therapeutic activity in microhetrogeneous environments and modulating important photophysical properties is of immense importance in various potential applications. The photophysical properties of a newly synthesized bioactive 7-oxy(5-selenocyanato-pentyl)-2H-1-benzopyran-2-one (PCM) has been studied in micellar solutions of anionic sodium dodecyl sulfate (SDS), cationic cetyl trimethyl ammonium bromide (CTAB) and nonionic p-tert-octylphenoxy polyoxyethanol (TX-100) micelle using steady state, time resolved fluorescence and fluorescence anisotropy techniques. The present effort illustrates the degree of accessibility of the fluorophore toward the heavy ion quencher in the presence of micelles of different surface charge characteristics. Iodide induced quenching leads to a decrease in the fluorescence intensity in case of SDS and TX-100 micelles, where as in CTAB micelles enhancement of fluorescence intensity is observed. Quantitative estimation of the micropolarity at the binding site of the probe has been determined. The imposed motional restriction of the microenvironment around the probe has been established from environment dependent fluorescence parameter, fluorescence anisotropy (r) value.

Interaction of bovine serum albumin (BSA) with the solvent spread monolayer of a catanionic surfactant, octadecyltrimethylammonium dodecylsulfate, (C18TA+DS−) at the air–buffer interface was investigated by measuring the surface pressure with time and change in surface area. Dipalmitoylphosphatidylcholine (DPPC) was used as reference. Kinetics of BSA desorption from the interface to the buffer subphase, that of C18TA+DS− and DPPC through their interaction with BSA, were also studied at different BSA concentrations (in the subphase) and surface pressures. Surface pressure (π)–area (A) isotherms (at pH = 5.4, μ = 0.01, T = 298 K) revealed that the coacervate/DPPC monolayer becomes expanded in the presence of BSA at low π while their protein bound species are released into the subphase at high π. Film morphology, studied by epifluorescence microscopy (EFM) and atomic force microscopy (AFM), reveals that the sizes of the domains of both DPPC and coacervate decrease in the presence of BSA. Presence of BSA in the coacervate and DPPC monolayer was supported from AFM data analysis.

Fluorescence recognition and sensing of aqueous anionic species is a challenging task and is being increasingly appreciated as far as potential biological and environmental issues of such systems are concerned. In the present contribution, we introduce for the first time fluorescence amplified recognition of a naphthalimide derivative (NAP) being embedded in a cationic alkyl trimethyl ammonium bromide micellar (CnTAB) units by various anions applying steady state and time resolved fluorescence techniques. Strongly quenched NAP emission in micellar framework has been effectively recovered upon intervention of various anions (such as H2PO4−, HPO42−, PO43−, SO42−, Cl−, etc.) with different sensitivities. The sensing process based on ion displacement mechanism, which principally governs a proficient fluorescence enhancement to various anions in a simple and efficient way, has been demonstrated. Optimization of sensor is achieved by altering surfactant chain length. The intermolecular approach used here seems to be rather flexible and appealing to design interface oriented fluorescent sensors to convene different analytic purposes for a wide variety of anion targets.

A novel fluorescent probe and pharmaceutically significant: 3-pyrazolyl-2-pyrazoline derivative (PYZ) has been selected as an acceptor molecule for fluorescence resonance energy transfer (FRET) interaction with serum albumins. Steady state and time resolved fluorescence techniques were applied to elucidate the nature of interaction of PYZ with serum albumins (BSA and HSA). Negligible FRET mediated emission occurred in the case of HSA but an efficient FRET mediated emission resulted in case of BSA. To gain further insight into the FRET selectivity of PYZ with the proteins, FRET from L-tryptophan (donor; native tryptophan) to PYZ (acceptor) was performed with the aim of getting an idea about the steric restrictions imposed on PYZ by the other groups present in BSA and HSA. The studies revealed that the surface bound Trp-134 in BSA allows an efficient FRET process with PYZ while the buried Trp-214 in HSA does not. The unusual selectivity for FRET in case of PYZ and the serum albumins has also been attributed to the complex structure of PYZ due to the presence of bulkier phenyl moieties in it. The complex nature of the excited state photophysics of tryptophan (Trp) in proteins also accounts for this FRET selectivity of PYZ with BSA and HSA.

Entrapping of a fluorogenic material comprising prospective therapeutic activity in microhetrogeneous environments and modulating important photophysical properties is highly desirable as far as potential applications of such systems are concerned. The present work demonstrates the interesting photobehavior of a newly synthesized antioxidative naphthalimide (isoquinolinedione) derivative (ANAP) in micellar solutions of anionic sodium dodecyl sulphate (SDS), cationic cetyl trimethylammonium bromide (CTAB) and nonionic p-tert-octylphenoxy polyoxyethanol (TX-100) surfactants using steady-state, time-resolved fluorescence and fluorescence anisotropy techniques. The remarkable sensitivity of the fluorescence properties of ANAP to the polarity of the media is attributed to the existence of a fluorescent intramolecular charge transfer (ICT) state. ANAP is found to be an excellent fluorescence sensor for following the micellar aggregation process. Fluorometric studies suggest that the probe resides at the micelle–water interface in all these systems. The present effort endeavors the degree of accessibility of the fluorophore toward the metal ion quencher in the presence of micelles of different surface charge characteristics. The enhancements in the steady-state anisotropy and rotational relaxation time in the micellar media compared to that in pure aqueous solution reflect that the fluorophore resides in a motionally restricted environment introduced by the micelles.

The synthesis and solvatochromic behavior of the compound, 7-oxy(5-selenocyanato-pentyl)-2H-1-benzopyran-2-one (PCM), a pervasive, bioactive coumarin derivative, which is expected to possess antioxidative properties and other important therapeutic activities of significant potency with low systematic toxicity, have been reported employing steady state and time resolved fluorescence techniques. Spectroscopic studies reveal that the solvatochromic behavior of the probe depends not only on the polarity of the medium but also on the hydrogen bonding properties of the solvents. Specific hydrogen bonding interaction of PCM in polar solvents modulated the order of the two close-lying lowest singlet states. The photophysical response of PCM in different solvents has been explained considering solute-solvent interactions. To corroborate these results, we performed the ground-state geometry, lowest energy transition and the UV–vis spectrum of PCM using the density functional theory (DFT) and the time-dependent density functional theory (TD–DFT) at B3LYP/6-31G ⁎ level. We found excellent correlation between the predicted and experimental spectral data, providing a useful tool in the design of new fluorogenic probes having potential therapeutic activity.

Interactions of luminescence, water soluble ZnS nanoparticles (NPs) with flavins and glucose oxidase have been thoroughly investigated through optical spectroscopy. The photoluminescence of ZnS nanoparticles was quenched severely (∼60%) by riboflavin while other flavins such as flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) show quenching to different extents under analogous conditions. However, interestingly no effect in luminescence intensity of ZnS NPs was observed with protein bound flavins such as in glucose oxidase. Fluorescence lifetime measurement confirmed the quenching to be static in nature. Scavenging of photo-generated electron of ZnS nanoparticles by the flavin molecules may be attributed to the decrease in luminescence intensity. Quenching of ZnS nanoparticles with flavins follows the linear Stern–Volmer plot. The Stern–Volmer constants decreased in the following order: K S−V (Riboflavin)> K S−V (FAD)> K S−V (FMN). This interaction study could generate useful protocol for the fluorimetric determination of riboflavin (vitamin B 2 ) content and also riboflavin status in biological systems.

This present investigation has revealed that steady state as well as time-resolved fluorescence techniques can serve as highly sensitive monitors for exploring the interaction of fluorescent probe 1-anthracene sulphonate (1-AS) with model transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA).We have focused on fluorescence resonance energy transfer (FRET) between excited tryptophan in transport proteins to 1-AS, for the study of relaxation dynamics of biological molecules.

The solvatochromic behavior of 3-pyrazolyl 2-pyrazoline derivative (PYZ), a newly synthesized molecular probe having pharmaceutical importance, has been studied in various solvents of different polarity. The Kamlet and Taft solvatochromic comparison method was utilized to rationalize the solute–solvent interactions from absorption and emission measurements. Spectroscopic studies reveal that the solvatochromic behavior of the dye depends not only on the polarity of the medium but also on the hydrogen-bonding properties of the solvents. The non-radiative relaxation process is facilitated by an increase in the polarity of the media. The photophysical response of PYZ in different solvents has been explained considering solute–solvent interactions.

Fluorescence resonance energy transfer (FRET) between anionic probe 1-anthracene sulphonate (1-AS) and transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA) solubilized in reverse micelles of sodium 1,4-bis (2-ethylhexyl) sulphosucccinate (AOT) in heptane was studied where the donor and acceptor pair comes in close proximity within the smaller water pools. The mechanism of fluorescence quenching of transport proteins by 1-AS in reverse micelles has been ascribed to the non-radiative energy transfer process. The probable binding site of the probe with proteins has been ascertained from FRET study. Circular dichroism study suggests that the number of folding of the protein increases markedly due to binding of the proteins with 1-AS.

The association of a non-ionic surfactant of polyoxyethylene-p-(1,1,3,3-tetramethylbutyl)phenyl ether (Triton X) series with 2-AS in aqueous solution has been studied by means of steady-state, time-resolved fluorescence and fluorescence anisotropy techniques. 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. The association constant of the probe molecule with the non-ionic micelles of Triton X (TX), location of the probe in the micellar environment, have been determined from the change in emission characteristics of the probe as a function of surfactant concentration. The rate constant of quenching and mode of quenching of probe in micellar media have been ascertained. Quantitative estimates of the micropolarity at the binding sites of the probe molecule have been determined. Some of the environment-dependent relevant fluorescence parameters, fluorescence anisotropy (r), have been monitored for exploring the imposed motional restriction of the microenvironment around the probe. An attempt has been made to correlate the steady-state results with time resolved study.

Nanoparticles of cerium tungstate have been prepared in the nanodomain water pools of water/AOT [sodium bis(2-ethylhexyl)sulphosuccinate]/n-heptane, water in oil microemulsion at various [water]/[AOT] mole ratio (ω) by double displacement reaction of cerium nitrate with sodium tungstate adapting intermixing two microemulsions technique. The formation of cerium tungstate in the dispersion has been established by UV–vis, X-ray diffraction and Fourier transform infrared measurements. Thermal stability of the products has been determined by thermogravimetric/differential thermal analyzer. The hydrodynamic diameter of the nanoparticles formed at different ω has been determined by the dynamic light scattering method. The size and shape of the isolated particles have been examined by the transmission electron microscope. Size of the nanoparticles increases with increase in ω. The fluorescent property and the magnetic behaviour of the synthesized product have been observed. The nanoparticles do not undergo any chemical change in HCl medium but unstable in KOH.

The aggregation of surfactant of polyoxyethylene-p-(1,1,3,3-tetramethylbutyl)phenyl ether (Triton X) series in chloroform has been studied. The critical micellar concentration (cmc) of the reverse micelles formed has been determined by four different techniques. The determined cmc values by various techniques are close to each other and facilitate determination of the free energy change (Δ G ) values associated with the micellization. From the correlation of cmc with hydrophile–lipophile balance (HLB) it was found that cmc decreases with decrease in HLB values. The association constant of the reverse micelle with fluorescent probe 1-anthracene sulphonate (1-AS) and micellar aggregation number has been evaluated. The location of the fluorophore in the reverse micelle and the polarity of the micelle solubilized sites have been determined from the E T (30), Kosower Z , and dielectric constant values. The pH of the aqueous region of reverse micelles has been estimated by comparison method.

In this work, three newly synthesized derivatives of thiazolidinediones, with potential for application as drugs in pharmaceutical industry and free radical scavenging activity, have been taken up to investigate their behaviour in different homogeneous solvents. The purpose of this work is to study the solvation characteristics in ground and excited states of the derivatives by monitoring the absorbance and fluorescence band maxima. The steady state and time resolved fluorescence studies in protic and aprotic solvents have been rationalized on the basis of solute–solvent interaction and substituent effect on these photophysical processes have been analyzed. Substituents at different positions of the aryl moiety affect the hydrogen bond formation ability of the probes.

The optical absorption spectra of 3.6 MeV 12 C ions irradiated low-density polyethylene (LDPE) show the gradual increase in the optical absorption and the shift from the near UV to the visible region with increase in ion fluence. The increase in absorption may be attributed to the generation of a conjugated system of bonds, which are also corroborated by FTIR. Scanning electron microscopic (SEM) studies reveal that the formation of linear network structure occurred at relatively lower ion fluence of 5×10 13 ions/cm 2 .

Thiazolidinedione (TZD) derivatives have been found to possess potent immunostimulatory properties as well as antiarthritic, antidiabetic and oncostatic activities. These compounds are free radical scavengers. Photophysical properties of the compounds have been studied in different aqueous micellar environments using steady state and time resolved emission spectroscopy. Appreciable hypsochromic shifts with enhancement in the fluorescence intensities have been observed in the ionic micellar media. The binding constants and energy changes during probe-micelle binding have been evaluated from relevant fluorescence data. Polarity of the microenvironment surrounding the probe molecules has been determined in the micellar systems.

How solvent conditions such as solvent polarity and hydrogen-bonding affect the fluorescence of a newly synthesized 3-pyrazolyl 2-pyrazoline derivative (Pyz) having pharmaceutical activity has been explored. The solvatochromic effect of Pyz is due to a change in dipole moment of the compound in the excited state. The relaxation of S1 state is perturbed in hydrogen-bonding solvents. The fluorescence properties of the systems are strongly dependent on the polarity of the media. The non-radiative relaxation process is facilitated by an increase in the polarity of the media. The photophysical response of Pyz in different solvents has been explained considering solute-solvent interactions.

The interaction of DNA bases and corresponding nucleotides with CdS nanoparticles (NPs), biofunctionalized by cysteine, has been investigated by absorption and fluorescence spectroscopy. Unique enhancement effect of adenine, in contrast to other nucleobases, on the luminescence of cysteine capped CdS (cys-CdS) NPs at both pH 7.5 and 10.5 was found, the extent of enhancement being much higher at pH 10.5. At the latter pH, the difference optical absorption spectra show development of new peak at 278 nm with corresponding decrease in the absorption of adenine at 260 nm, which is attributed to binding of adenine anion to the CdS surface through N7 of the purine ring. Appearance of a new band at 478 cm−1 and concomitant shift in the C8–N7 vibrations to 1610 cm−1 in the FTIR spectra of cys-CdS NPs with adenine also suggest Cd–N7 binding on the particle surface. Amongst various nucleotides, ATP exhibited maximum luminescence enhancement on CdS NPs for a given change in concentration in the micro-molar range at physiological pH. A quantitative correlation between ATP concentration and PL enhancement of CdS NPs has been established, a step which in future might assist in developing new protocols for fluorescence sensing of adenine nucleotides under certain pathological conditions.

Quenching of fluorescence of the dye 3,7-diamino-2,8-dimethyl-5-phenyl Phenazinium Chloride (Safranine T) has been investigated by AgCl nanoparticles in the W/O microemulsion medium at different [H 2 O]/[AOT] ratios ( ω ) and with Ag nanoparticles and Ag + in aqueous medium. A simple straightforward method has been introduced to prepare AgCl nanoparticles in well-characterized, monodispersed biomimicking nanocavities formed by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in heptane. Experimental results reveal that the size of the AgCl nanoparticles increases with increase in hydration. The results of the quenching experiment were analysed in the light of Stern Volmer equation. Quenching of fluorescence of the dye has been found to decrease with decrease in the size of the nanoparticles of AgCl and the variation of Stern Volmer quenching constants ( K SV ) with particle size is different for two different size regimes.

The absorption and steady-state fluorescence of a non-amphiphilic derivative of pyrene, Pyrene-1-Carboxaldehyde (1-PyCHO) is sensitive to the probe’s environment. Association of the surfactants in aqueous medium as micelles and mixed micelles has been studied from the photophysical changes of 1-PyCHO in these media. The physicochemical characteristics of the micelles, i.e. CMC, aggregation number have been determined. The obtained CMC values from different methods are close to each other. The association constants of the 1-PyCHO molecules with the non-ionic micelle of Igepal and location of the fluorophore in the micellar environment have been determined. Micropolarity of Igepal micelle and Igepal/Igepal mixed micelle surrounding 1-PyCHO has been ascertained comparing the shift in fluorescence maximum with ET(30) values of standard solutions. © 2007 Elsevier B.V. All rights reserved.

S 0 → S 1 and S 0 → S 2 electronic transitions have been observed in UV–Visible absorption spectroscopy of 3-pyrazolyl-2-pyrazoline (PZ) in different homogeneous solvents. Radiative emissions and relaxation processes from S 1 and S 2 states of PZ have been resolved in water, ethylene glycol and glycerol whereas in polar aprotic and protic solvents the radiative transitions have been observed from S 1 state. The S 2 –S 1 electronic energy spacing has been calculated from the absorption maxima of the S 0 → S 2 transitions and fluorescence maxima of the S 1 → S 0 transitions. Solute–solvent interactions have been established to rationalize the photophysical modification of PZ in H-bonding solvents.

The growth mechanism of CdTe nanocrystals (NCs) vis-a-vis CdS with stabilizing shell of cysteine has been examined. The nucleation and growth were found to be well separated for CdS NCs whereas there is partial overlap of the two events for CdTe NCs. The initial growth rate (d r /d t ) of CdS NCs was higher than that of CdTe NCs. As the reflux time was increased, the growth rate showed a linear decline with increasing particle size. Three distinct stages of growth were identified with respect to particle size distribution: focusing, defocusing and equilibrium. The extent of focusing for CdTe NCs (49%) was much larger than that of CdS NCs (23%). With increasing time of reflux, photoluminescence quantum efficiency (PLQE) rose initially and started decreasing after reaching a peak value. A maximum PLQE of 0.13 and 0.16 was observed for CdS and CdTe NCs, respectively, for the same size of 3.4 nm. The particle size increased with increasing concentration of the capping ligand, cysteine and maximum PLQE was obtained at an optimum molar ratio of Cd 2+ :cysteine. Interestingly, on increasing the ionic strength of the initial synthetic mixture, photoluminescence (PL) intensity of CdS NCs was substantially enhanced while the particle size remained unaffected.

Interaction of 1-hydroxy-pyrene-3,6,8-trisulphonate (HPTS) has been investigated in well-characterized, monodispersed, micellar media of cationic surfactants of a homologous series having the general formula C n TAB and with trisodium citrate, employing absorption and fluorescence spectroscopy. The interaction of HPTS with cationic micelles depends on the hydrophobic chain length of the cationic surfactants. The binding constant of HPTS with C n TAB micelles decreases with decreasing n . Micelles have strong effect on the interaction of HPTS with trisodium citrate. Fluorescence of HPTS is quenched by citrate ion at the surface of the micelle and the rate of fluorescence quenching decreases with decreasing alkyl chain length of cationic surfactants.

Growth of colloidal ZnS nanoparticles in aqueous solution has been extensively investigated in presence of two water-soluble thiols, cysteine and mercaptoethanol. In addition to controlling the particle size by duration of heating, an effective control over growth rate (dr/dt) was also obtained just by altering the functional groups of thiol-surfactants, even without changing heating rate or temperature. The growth rate was found to vary linearly with the average radius of growing nanoparticles. Higher growth rate for cysteine-capped ZnS NPs was observed which could be attributed to greater specific surface energy at the solvent–NP interface as compared to mercaptoethanol capped ones. Photoluminescence of these nanoparticles was found to be influenced by the concentration and nature of the surfactant molecules. Maximum PLQY of 2.3% and 2.0% was obtained for mercaptpethanol and cysteine capped NPs, respectively at an optimum Zn2+:surfactant molar ratio, 1:1.5. For given particle size, mercaptoethanol-capped ZnS NPs show greater PLQY as compared to cysteine-capped ones. The lower PLQY of cysteine-capped ZnS NPs is attributed to the sulfur vacancy defects, which was not found in case of mercaptoethanol-capped ZnS nanoparticles.

Ground and excited state properties of newly synthesized N-substituted naphthalimide derivatives (3a–c) have been investigated in protic and aprotic solvents of varying polarity. These studies focused identification of the π, π* and charge transfer to solvent (CTTS) transitions. Excited state properties have been rationalized in terms of photoinduced intramolecular charge transfer (PICT) process. Effect of protic solvent and aprotic solvent on the PICT process has also been determined. Excited state PICT process of the compounds has also been studied in aqueous solution of H-bonding agent reduced l -glutathione (GSH).

Solubilization and conductivity studies are carried out with AOT/Brijs (Brij-30, Brij-35, Brij-52, Brij-56, Brij-58, Brij-72, Brij-76, Brij-78)/isooctane/water mixed reverse micellar systems. Replacement of AOT molecules with large head group Brij molecules (Brij-30, Brij-35, Brij-56, Brij-58, Brij-76, Brij-78) decreases the solubilization capacity, whereas those with smaller polar head groups (Brij-52 and Brij-72) increases it. The former blends assist the conductance percolation whereas the latter retard it. An attempt has been taken to obtain more insight on the interfacial composition of the mixed interface with the help of spectrophotometric studies using 7-hydroxycoumarin as the fluorophore. The results obtained from the solubilization and conductometric studies have been correlated with those obtained from the spectroscopic studies.

Visible spectra of Safranine T (ST) in anionic reverse micelle (AOT/cyclohexane/water), non-ionic reverse micelle (Igepal CO720/cyclohexane/water) and mixed reverse micelles of AOT/Igepal CO720/cyclohexane/water at different compositions and different ω (=[water]/[surfactant]) have been studied. Charge transfer band of Safranine T in reverse micellar and mixed reverse micellar medium has been isolated both in ground and excited state. Iodide ion induced dynamic quenching at low quencher concentration becomes a combination of both the dynamic and static quenching at high quencher concentration. Iodide ion induced quenching study has been used as a tool to identify the altered interface of AOT/Igepal CO720/cyclohexane/water mixed reverse micelle compared to AOT/cyclohexane/water reverse micelle. Absorption and fluorescence spectra of ST in polyethylene glycol coated interface of AOT reverse micelle has been observed to identify the role of poly(oxyethylene) group of Igepal CO720 on spectral behavior of ST in mixed reverse micelle.

A steady-state fluorescence quenching study has been undertaken to estimate aggregation numbers, N, and the average occupancy number ( n ¯ ) of quencher per micelle and the water pool size, rw, of nonionic surfactant Igepal (polyoxyethylene nonyl phenol), carbon tetrachloride and water reverse micelles at a different [water]/[Igepal] ratio. For the purpose, Safranine T (3,7-diamino-2,8-dimethyl-5-phenyl phenazinium chloride) has been employed as fluorescent probe and iodide, bromide and azide ions as static quencher. The fluorescence quenching data has been exploited to determine the nature and properties of water in the core of reverse micelles (RM), size of the water pool, association of quencher molecule with the RM, the localization of the probe and the distribution of quencher molecule in the quenching sphere. The demarcation of reverse micelles and microemulsion has also been determined.

Para-aminophenol, N-methyl para-aminophenol sulfate and pyrogallol are used as photographic developer and their fluorescence intensity has been quenched in presence of acid, base, KCl, KBr, KI and oxygen. In presence of sodium sulfite fluorescence intensity of the compounds gradually increases with time. It has been established that in the steady-state fluorescence of these photographic developers the role of sodium sulfite is oxygen scavenger. In presence of β cyclodextrin, fluorescence intensity of these photographic developers increases due to steric restriction. Location and nature of the surrounding medium of the photographic developers in cyclodextrin have been ascertained from quenching study. The presence of two rotamers of aminophenols and substituted aminophenols has been established from fluorescence anisotropy study. The relative stability of the rotamers and the attachment of the compounds in the cavity of β cyclodextrin have been established on the basis of semiempirical AM1-SCI calculation.

Energy transfer by dipole–dipole interaction between anionic dye Fluorescein and cationic dye Safranine T (3,6 diamino-2,7-dimethyl-5-phenyl phenazinium chloride) solubilised in aqueous solution and micellar solution of cetyl trimethyl ammonium bromide (CTAB) was studied where donor–acceptor Forster critical radius ( R 0 ) is larger than the micellar diameter ( d m ). The mechanism of quenching of fluorescence of Fluorescein by Safranine T in aqueous solution and in normal micellar medium has been related to the non-radiative energy transfer processes. The value of overlap integral and critical energy transfer distance is higher in CTAB micellar medium compared to that in the aqueous solution. The variation of quantum yield and efficiency of energy transfer between two dyes in micellar medium and aqueous solution has been compared. Effect of viscosity on the fluorescence resonance energy transfer (FRET) between the dye pairs has been determined from fluorescence anisotropy study.