Search

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

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.

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 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.

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.

Nanometal surface energy transfer (NSET) from 2-anthracene sulfonate (2-AS) to gold nanoparticles in water-soluble triblock copolymers (TBP) P123 (PEO19PPO69PEO19) and F127 (PEO100PPO65PEO100) is systematically investigated. Fluorescence lifetime and anisotropy experiments provide thorough information on the locations of the 2-AS within these micelles. Variation in the size of the micellar corona region of the TBP is found to be the prime factor for different positions of 2-AS in them. Of late, nanometal surface energy transfer (NSET) from the donor probe to the surface of the metal nanoparticles has emerged as a potential tool for sensing and biolabeling. In the present work, the quenching of emission of the water-soluble 2-AS confined in the two different triblock copolymers in the proximity of a monolayer of the gold nanoparticles has been explored. Closer agreement between the experimental and theoretical characteristic distances has been found across the full wavelength range by the NSET approach. Understanding the location of the water-soluble dye in the vicinity of a polymeric drug delivery system is of significant importance, and how altered locations can trigger different controlled energy transfer efficiency from the 2-AS to the surfaces of gold nanoparticles (GNPs) has been discussed. This strategy could offer a new prospect in designing novel optical materials for chemical sensing and light harvesting endeavors.

Sodium dicarboxylates (or Bola salts) with methylene spacers 0, 2, 4, 6, 8, and 10 were studied in aqueous solution to investigate their influence on the micellization of cetyltrimethylammonium bromide (CTAB). Since bolas with spacer length ≤12 are known not to micellize in general, the herein used sodium dicarboxylates were treated as 2:1 amphiphilic electrolytes which reduced surface tension of water (except sodium oxalate with zero spacer) without self-association. Their concentration dependent conductance was also linear without breaks. The bolas affected the micellization of CTAB but acted like salts to decrease its CMC. Their combinations did not form bilayer aggregates as found in vesicles. Nevertheless, they synergistically interacted with CTAB at the air/water interface as revealed from Rosen's thermodynamic model. Hydrodynamic radius (Rh), Zeta-potential (ζ), and electrical double layer behavior of bola interacted CTAB micelles were assessed. From SANS measurements, micelle shape, shape parameters, aggregation number (Nagg), surface charge of the bola influenced CTAB micelles were also determined. NMR study as well supported the non-mixing of bolas with the CTAB micelles. They interacted in solution like "amphiphilic electrolytes" to influence the surface and micelle forming properties of CTAB.

The detailed aggregation behavior of sodiumdodecyl sulfate (SDS) in tetrahydrofuran (Tf)-water (W) and formamide (Fa)-water (W) media at varied volume percent compositions has been investigated. Surface tension (ST), conductance (Cond), viscosity (Visc), isothermal titration calorimetry (ITC), nuclear magnetic resonance (NMR) and small angle neutron scattering (SANS) were used in this study. The presence of nonaqueous solvents affected the critical micelle concentration (CMC) of SDS, the counter-ion binding of the micelle, the energetics of the air/water interfacial adsorption and micellization of the amphiphiles in the bulk, the ion-association (ion-pair, triple-ion, quadruple, etc. between Na(+) and DS(-) ions) as well as the weakly soluble (aggregation less) amphiphile solution. Tf has been observed to produce a "dead zone" or "non-micelle formation zone" in the mixed Tf-W domain of 10-40 vol%. Fa influenced the SDS aggregation up to 70 vol%, at higher proportions (below the Krafft temperature (K(T))), instead of the micelle, "randomly arranged globular assembly" (RAGA) was formed. The correlation of the standard free energy of micellization (ΔG(m)(0)) with different solvent parameters (1) dielectric constant (ε), (2) viscosity (η0), (3) Reichardt parameter (E(T)(30)), (4) Gordon parameter (G), and (5) Hansen-Hildebrand hydrogen bonding parameter (δ(h)) has been attempted. It has been found that δ(h) produced a master correlation between ΔG(m)(0) and δ(h) for different binary mixtures such as Tf-W, Fa-W, Ml-W and Dn-W.

The medium charge specific excited state behaviour of a bio-active and fluorescent 3-pyrazolyl-2-pyrazoline derivative (PYZ) was systematically monitored in aqueous solutions of ionic (CTAB, SDS) and non-ionic (Triton X-100) micelles, applying steady state and time resolved fluorescence spectroscopy in addition to theoretical molecular simulations. PYZ displays complementary emission characteristics according to the nature of the effective charge of the micelles which was rationalized on the very fundamental basis of the frontier molecular orbital approach as obtained from quantum chemical calculations involving Time Dependent Density Functional Theory (TD-DFT) in combination with B3LYP exchange correlation function using 6-31G(d,p) as the basis set. Dynamic Light Scattering (DLS) measurements provided crucial information regarding the fluorescence quenching pattern of micelle bound PYZ by quencher CpCl. This study essentially accentuates PYZ's photophysical response in different micellar media in conjunction with their individual mode of electrostatic interaction therein. The theoretically calculated HOMO–LUMO energy gap values provide adequate information about the emissive behaviour of PYZ in ionic micellar media. The variation in the lifetime values of PYZ in aqueous and micellar media act as added evidence of the fact that PYZ basically resides in different micro-environments as introduced by the respective micelles. Conclusively it was observed that, in the excited state, PYZ responded promptly and uniquely according to the nature of the micellar charge.

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.

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.

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.

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.

Physicochemistry of micellization of binary mixtures of cetylpyridinium chloride (CPC) and Triton X-100 (TX-100) have been investigated and the data collected have been analyzed and correlated. Tensiometric, conductometric, spectrophotometric, calorimetric and polarographic methods have been employed in the study. Parameters like critical micellar concentration (CMC), counter-ion binding, energetics of micellization, interfacial surfactant adsorption and minimum area of amphiphile head groups at CMC have been determined. The diffusion coefficients of pure and mixed micelles in solution have been determined by the polarographic method. The regular solution theory of Rubingh has been considered to get information on the micellar composition and their mutual interaction (synergistic for the studied system) in solution. The packing of the monomer in micelle has been estimated to witness spherical geometry for CPC and its mixtures with TX-100, whereas the later has been found to be spheroidal. Polarographic measurements have evidenced comparable diffusion coefficients of CPC and TX-100 micelles whereas their mixed micelles have shown lower values with a minimum, at equimolar composition.

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.

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.

The photophysical behavior of 3-pyrazolyl-2-pyrazoline derivative (PZ), a newly synthesized biologically active compound has been studied in micellar solutions of anionic sodium dodecyl sulfate (SDS), cationic cetyl trimethylammonium bromide (CTAB) and nonionic p- tert-octylphenoxy polyoxyethanol (Triton X-100, TX-100) micelle using steady state and time-resolved fluorescence spectroscopy technique. Influence of the micelles on the photophysics of PZ has also been investigated using different approaches. The location of the fluorophore PZ in the micelle has been identified by cetyl pyridinium chloride (CpCl) induced fluorescence quenching and micropolarity surrounding that fluorophore in micellar solution. The effect of urea on the steady state fluorescence and relaxation dynamics of the micelle bound probe has also been observed. The results have been interpreted in terms of the model that urea displaces water molecules from the micellar interface and the consequent destabilization leads to the expulsion of the probe molecules from the interfacial region. An attempt has been made to determine probe sensing microviscosities for these micellar microenvironments in the light of average reorientation times of the probe PZ.

Octadecyl-trimethyl-ammonium bromide (C18TAB) is a much less studied representative in the alkyltrimethylammonium halide surfactant series. A comprehensive study of its normal and reverse micelle (microemulsion) formation has been herein conducted by the methods of conductometry, tensiometry, fluorimetry, and microcalorimetry. The energetics of its air/liquid interfacial adsorption and self-association in aqueous solution have been examined. The phase behavior of its combinations with water, n-butanol, and n-heptane in the formation of microemulsions have been investigated with identification of a variety of phases. The energetics of formation of water dispersion in oil (w/o) has been evaluated from dilution experiments conducted at different temperatures. From the results, structural parameters of the droplets have been determined at different [water]/[surfactant] mole ratios (omega) and temperatures. The w/o dispersions have evidenced both volume- and temperature-induced conductance percolation. The results have been treated in light of the Scaling equations, and the associated parameters for the process have been determined. The activation energies for the temperature-induced percolation process of the w/o dispersion have been evaluated and assessed.

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.

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.

The adsorption and solution behaviors of symmetrical tetramethyl-, tetraethyl-, tetrapropyl-, and tetrabutylammonium bromides (TMAB, TEAB, TPAB, and TBAB, respectively) were studied at the air/water interface and in the bulk aqueous environments. Their salts were prepared by reacting tetraalkylammonium bromide (TAAB) with sodium dodecyl sulfate (SDS) in a solution from which the products of the higher two homologues (tetrapropylammonium dodecyl sulfate (TPADS) and tetrabutylammonium dodecyl sulfate (TBADS)) could only be isolated as solids and for which detailed characterization has been performed. The interfacial behaviors of 1:1 molar mixtures of TAAB and SDS and the prepared TPADS and TBADS were examined. Micellization of the 1:1 mixtures along with the isolated species were studied in the presence and absence of NaBr salt. The energetics of the micellization process and the counterion binding of the micelles were evaluated. The interaction of the TAABs with SDS micelles was examined, and the results were evaluated in terms of single- and two-site binding interaction models. Of the formed tetraalkylammonium dodecyl sulfates (TAADSs), only TBADS evidenced clouding, which was investigated in detail along with 1:1 molar mixtures of TBAB and SDS in aqueous solution in the presence of additives such as NaBr, SDS, and TBAB. The solution behaviors of the TAADS and the clouding of TBADS have been rationalized in terms of a mixed micellar model.

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.

The fluorescence quenching of the dye Safranine T by various inorganic anions such as [Fe(CN6)]–3, [Fe(CN6)]–4, I–, Br–, NO2–, and N3– in aqueous solution and in nonionic micellar solutions of Tweens (Tween 20, Tween 40, and Tween 80) was studied. The Stern–Volmer quenching constants and quenching rate constants were evaluated. Compared to the quenching efficiency in aqueous media, that of the micellar media was found to be lower, except when iodide ion was used as a quencher. With the exception of the iodide ion, it has been established that collisional quenching plays a major role in the photophysical process. In the case of the iodide ion, both static and collisional quenching processes play a major role, owing to the complexation of iodide ion with Tween micelles. The Stern–Volmer quenching constants were found to be dependent on the ionic strength of the medium.Key words: fluorescence, static quenching, Tweens, Stern–Volmer constant, micellar media.

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.

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.

The electron donor–acceptor (EDA) interactions were studied using p -phenylenediamine as donor and polyoxyethylene–sorbitan–monolaurate (Tween 20), polyoxyethylene–sorbitan–monopalmitate (Tween 40), polyoxyethylene–sorbitan–monostearate (Tween 60) and polyoxyethylene–sorbitan–monooleate (Tween 80) as acceptor in micellar and reverse micellar environments. A charge transfer (CT) absorption band was observed and the experimental CT transition energies are well correlated (through Mulliken’s equation) with the vertical electron affinity of the acceptors. Oscillator strengths, transition dipole moments, resonance energies and formation constants of the EDA complexes have been estimated. The experimental results were explained using a theoretical model in favour of electric dipole–dipole interaction between the donor and acceptor.

The mixed micelles of sodium dodecyl sulphate (SDS) with Brij35 and Brij 97 were studied separately by fluorescence measurement using pyrene as fluorescent probe. In the range of 0–1.0 mole fraction (X) of added SDS to Brij solutions, the cmc value of the mixed micelles varies from 0.085 to 8 mmol with Brij 35 and 0.04 to 8 mmol with Brij 97. The aggregation number also changes. A measure of the stability of mixed micelles is also presented. The interaction parameter β12 and the chain–chain contribution parameter (B1) are extracted from the analysis of the results. This parameter B1 is related to the standard free energy change associated with the introduction of one ionic species into a nonionic micelle coupled with the release of one nonionic species from the micelle. The clouding behaviour of Brij 97 in the presence of SDS was investigated and the associated thermodynamic parameters of clouding were generated and discussed.

This paper has explored the quenching of fluorescence of the dye safranine T (ST) by the inorganic cations viz Cu2+, Co2+, Ni2+ and Mn2+ in micellar solutions of the surfactant dioxyethylene nonyl phenol (Igepal CO-210), pentaoxyethylene nonyl phenol (Igepal CO-520) and dodecaoxyethylene nonyl phenol (Igepal CO-720). The quenching results have been calculated in light of stern volmer equation (SV) to evaluate the extent of interaction between the fluorophore (ST) and quencher. The average concentration of the quencher ions in the micelle have been determined. The quenching efficiency of ST by inorganic ions in micellar medium is lower than that in aqueous medium. The results show that the ions get partitioned in the micellar medium. The values of the partition coefficient of the ions decrease with increase in HLB value and number of oxyethylene groups in Igepal.

The association of polyoxyethylene nonyl phenol (Igepal) in four different organic solvents such as chloroform, carbon tetrachloride, cyclohexane, and heptane has been studied. The critical micellar concentration of the reverse micelle (RM) formed in different nonaqueous media has been determined using four different techniques: UV-visible spectroscopy, fluorescence spectroscopy, Stokes shift, and NMR spectroscopic studies. From the correlation of cmc with hydrophile-lipophile balance (HLB), we have found that cmc decreases with decrease in HLB. The obtained cmc values using different methods have been found to be consistent and facilitate the determination of DeltaG values associated with the micellization. The association constant of the dye molecule Safranine T (ST) with the reverse micelle, aggregation number of the surfactant monomer, and location of fluorophore in the RM have been determined. The vertical ionization potential of Igepal, electron affinity of the dye, and the degree of charge transfer have been estimated by the theoretical AM1 calculations. A linear relationship has been obtained between cmc(s) and the ionization potential of the solvents. The polarity of the micelle solubilization sites has been determined from the solvatochromic shift, Kosower Z value, and ET(30) value.

The fluorescence characteristics of Safranine T (ST) (3,6-diamino-2,7-dimethyl-5 phenyl phenazinium chloride) in presence of thiourea have been studied in reverse micelles of Aerosol–O–T in heptane and in presence of alkanols. From the results of the fluorescence quenching of ST by thiourea the occupancy number of the quencher in the reverse micelle (RM), and the binding constant of the quencher with the RM have been determined using Encinas–Lissi equation. The alkanols added are found to affect the quenching process.

The fluorescence quenching of Safranine T (ST) by [Fe(CN)6]3−, [Fe(CN)6]4−, Fe2+, Co2+ and Cu2+ was studied in Aerosol orange T (AOT) reverse micelles in n-heptane. The quenching process was exploited to calculate the Stern Volmer quenching constants (KSV) using Stern Volmer equation, the aggregation number of AOT reverse micelles at different ω values. Upon progressive addition of water to ST/AOT/n-heptane solution, the quenching efficiency increases. The results are interpreted in terms of the variations in the microenvironments of ST which depend in a sensitive manner on the water / Surfactant (ω) molar ratio.

The absorption and fluorescence extents of the dye Safranine T (ST) are influenced by micellar solution. The critical micellar concentration (CMC), aggregation number and micelle-ST binding constant of ionic surfactant, sodium dodecylsulphate (SDS) and nonionic surfactants polyoxyethylene (20) sorbitan -monolaurate, -monopalmitate, -monostearate and -monooleate (Tween-20, Tween-40, Tween-60 and Tween-80) respectively have been determined by exploiting the spectral behaviours of ST in presence of urea and thiourea. The CMC and the aggregation number of the micelles have been found to increase and decrease respectively in presence of the additives urea and thiourea. While thiourea has greater CMC increasing effect than urea, it diminishes the aggregation number of the micelles efficiently than urea. The dye-micelle binding constant has been found to decrease in presence of urea and thiourea. Thiourea also quenches the fluorescence of ST in aqueous as well as in micellar medium.

The results of quenching of fluorescence of the dye Safranine T (ST) by the inorganic ions [Fe(CN)6]3−, [Fe(CN)6]4−, Cu2+, Co2+, Ni2+ and Mn2+ in aqueous micellar solutions of the surfactants diethylene glycol hexadecyl ether (Brij 52), decaethylene glycol hexadecyl ether (Brij 56) and cicosaethylene glycol hexadecyl ether (Brij 58) are presented. The quenching results have been processed in the light of Stern-Volmer (SV) equation and its modified forms to evaluate the extents of interaction between the fluorophore (ST) and the quencher. The magnitudes of the Stern-Volmer constant (KSV) in quencher micelles follow the trend [Fe(CN)6]3− > [Fe(CN)6]4− > Co2+ > Cu2> Ni2+> Mn2+ in all the Brij media; for each ion the trend in terms of the surfactants is Brij 52> Brij 56> Brij 58, which is the order of the polarity of the Brij environment. The ion Co2+ appears to partly quench the emission process by the static mode. The solvent parameters of the Brij micellar media like the Kosower Z value, the transition energy for the intramolecular charge transfer, ET30 and the dielectric constant, D, have been estimated from the shift between the absorption and emission frequencies. A comparison of the quenching behaviours of inorganic ions on ST fluorescence in different media viz., aqueous, aqueous polyethylene glycol and aqueous micellar solutions of Tweens and Brijs has been presented.

The visible and fluorescence spectra of the dye safranine T were studied in micellar solutions of non-ionic surfactants in different concentration ranges. The complexing strengths (1 : 1 dye : micelle charge transfer complex formed between the dye and micelle) of the non-ionic micelles increase with increasing concentration of the surfactant in the micellar solution. The aggregation number and several solvent parameterss, i.e. the Kosower z value, intramolecular charge transfer energy E T 30 , dielectric constant of the micellar medium and viscosity of the micellar solution, were evaluated. These values remain constant over certain concentration ranges, but vary in different concentration regions of a surfactant.

The visible spectra of safranine T (ST) in micellar solutions of Brij 52, Brij 56 and Brij 58 indicate 1 : 1 charge transfer complex formation of ST with non-ionic Brij micelles. The complexing strength follows the order Brij 52 > Brij 56 > Brij 58. The fluorescence spectra of ST in micellar solutions of Brij also support 1 : 1 ST-micelle complex formation as in the ground state. The equilibrium constant of the dye—micelle complex is directly proportional to the micellar aggregation number and inversely proportional to the surfactant critical micellar concentration (CMC). The solvent parameters, i.e. the Kosower Z value, intramolecular charge transfer energy E T 30 and dielectric constant of the micellar medium, were evaluated. The binding constant, micellar aggregation number and solvent parameters remain constant over a certain range of Brij concentration, but vary beyond this range.

Self-aggregation of MEGA-9 (N-nonanoyl-N-methyl-D-glucamine), a nonionic sugar-based surfactant, was studied with respect to the effect of salt (NaCl) and ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) on its critical micelle concentration (cmc), aggregation number, hydrodynamic dimensions, energetics of micellization, and micellar microenvironment. Fluorimetry (both steady state and time resolved) was used to understand the microenvironments under the influence of additives. NaCl was found to decrease cmc, increase aggregation number (N), increase micellar size, and decrease enthalpy of micelle formation; the IL effect on the parameters was mostly opposite. The microscopic properties of micelles were probed using two fluorophores: one nonpolar C-153 (2,3,5,6-1H,4H-tetrahydro-8-trifluormethylquinolizino-(9,9a,1-gh)coumarin) and the other fairly polar ANS (8-anilinonaphthalene-1-sulfonate); they delivered information on the palisade layer and the peripheral region of the micelle interface, respectively. Energy of activation and entropy of activation of the dynamics of the probes were evaluated from their decay time, lifetime, and rotational movements in the regions of residency in the micelles. Density functional theory (DFT) calculations showed that the ternary combination MEGA-9/IL/H2O had the maximum interaction energy compared to any of the binary combinations. Thus, the ionic liquid reduced MEGA-9 self-association to a large extent.

The visible spectra of Safranine T in reverse micelles indicate 1:1 (dye:reverse micelle) charge transfer complex formation with the non-ionic surfactants Triton X-100, Tween 20, Tween 40, Tween 60 and Tween 80. The complexing strength follows the order Tween 80 > Tween 60 > Triton X-100 > Tween 40 > Tween 20. The fluorescence spectrum of the dye is also enhanced by the reverse micellar solution confirming the formation of 1:1 complex having comparable complexing strength as revealed from the ground state spectra. The equilibrium constants of the dye-reverse micelle complex are directly proportional to the carbon number of the non-polar tail of Tweens and their aggregation number. The latter has been determined together with the critical micelle concentrations of the reverse micelles as well as their core polarities.

The fluorescence quenching of Safranine T by [Fe(CN)6]3−, [Fe(CN)6]4−, Fe2+, Co2+, Cu2+, Ni2+ and Mn2+ was studied in aqueous solutions as well as in solutions of non-ionic micelles of Triton X-100 and Tweens (20, 40, 60, and 80). The rate constant of quenching were calculated using the Stern-Volmer equation. In a micellar medium, the quenching efficiency is less compared with that in an aqueous medium. It has been established that the quenching phenomenon is not affected by the transfer of electrons from the quencher to the dye molecule, and that collisional plays the main role in this photochemical process.

The photophysical (visible and fluorescence) behavior of the dye safranine T has been studied in several polar and non-polar solvents and in micellar solution (non-ionic and ionic surfactants). The change in the dipole moment of the dye between the ground and excited states has been estimated using approximate sovent-induced spectral shift (Stokes shift) theories based on non-specific interactions. The dependence of the dye behaviour on the nature of the micellar interface is shown by the Strokes shift which exhibits an inverse dependence on the average aggregation number of the surfactant micelles. A reasonables estimation of the dielectric constant of the micellar interface has been attempted.

Spectroscopic studies of Naproxen (NP), a nonsteroidal drug have been carried out in well characterized, micellar media of cationic surfactants of a homologous series having general formula CnTAB (alkyl trimethyl ammonium bromide) and of nonionic surfactants of Igepal (Ig) series (poly(oxyethylene) nonyl phenol). The fluorescence behavior of the drug molecule in CnTAB micelles has been found to be opposite to that in Igepal micelles. The binding constants during probe micelle binding have been evaluated from relevant fluorescence data. Location and nature of the surrounding medium of the probe in micellar media have been ascertained from fluorescence quenching study. Fluorescence anisotropy parameter has been monitored for exploring the imposed motional restriction of the microenvironment around the probe. Contrasting behavior of the drug molecule has been observed in two different types of micelles. Based on the experimental and theoretical studies, an attempt has been made to explain the different behavior of the probe in different media.

The physicochemistry of interaction of the cationic polymer poly(diallyldimethylammonium chloride) (PDADMAC) with the anionic surfactants sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and sodium N-dodecanoylsarcosinate was studied in detail using tensiometry, turbidimetry, calorimetry, viscometry, dynamic light scattering (DLS), and scanning electron microscopy (SEM). Fair interaction initially formed induced small micelles of the surfactants and later on produced free normal micelles in solution. The interaction process yielded coacervates that initially grew by aggregation in the aqueous medium and disintegrated into smaller species at higher surfactant concentration. The phenomena observed were affected by the presence of isopropyl alcohol (IP) in the medium. The hydrodynamic sizes of the dispersed polymer and its surfactant-interacted species were determined by DLS measurements. The surface morphologies of the solvent-removed PDADMAC and its surfactant-interacted complexes from water and IP-water media were examined by the SEM technique. The morphologies witnessed different patterns depending on the composition and the solvent environment. The head groups of the dodecyl chain containing surfactants made differences in the interaction process.

The visible spectra of safranine T in micellar solutions indicate 1:1 (dye to micelle) charge transfer complex formation with the non-ionic surfactants Triton X 100 (TX 100), Tween 20, Tween 40, Tween 60 and Tween 80 as well as with the anionic surfactant sodium dodecyl sulphate (SDS). The non-ionic surfactant micelles show stronger interaction than the ionic micelle SDS, the complexing strengths of the non-ionic micelles following the order Tween 80>Tween 60>TX 100>Tween 40>Tween 20. The fluorescence spectrum of the dye is also affected (intensified) by the surfactant micelles. The results confirm a 1:1 complex and comparable complexing strengths (except the position of TX 100) as revealed by the ground state spectra. Thermodynamic analysis shows that the increased stability of the dye—micelle complex is associated with a systematic increase in exothermic enthalpy and decrease in entropy which compensate each other. The equilibrium constants of the dye—micelle complex are directly proportional to the carbon numbers of the Tweens and inversely proportional to the critical micelle concentration (CMC) of the surfactants.

The results of the fluorescence quenching of 2-anthracene sulphonate by cetylpyridinium chloride in ionic and non-ionic micellar environments are presented. The static quenching process (lifetime, 4.5 ns) was exploited to estimate the bimolecular quenching rate constants and binding constants between the probe and the quencher from the Stern—Volmer equation, the aggregation number of the surfactant micelles, and the occupancy number of the quencher in the micelle and the binding constant of the quencher with the micelle from the Encinas—Lissi equation. Both ionic and non-ionic micelles, i.e. cetyltrimethylammonium bromide, sodium dodecylsulphate, Triton X-100, Tween-20, Tween-40, Tween-60 and Tween-80, were employed. In the Tween series (Tween-20 to Tween- 80), the micellar aggregation numbers systematically varied. The average occupancy number of the quencher in the micelle and the binding constant of the quencher with the micelle showed a linear correlation with the aggregation number of the micelles.

The micellization behavior of cetylammonium bromide and its mono-, di-, and trihydroxyethylated head group analogues and water/oil (w/o) microemulsion formation with them have been studied with detailed thermodynamic and structural considerations. The critical micellar concentration, micellar aggregation number, and behavior of the surfactants at the air/solution interface have been studied in detail. The results have been analyzed and discussed. The formation of the w/o microemulsion stabilized by the aforesaid surfactants in conjunction with the cosurfactant n-hexanol in isooctane has been investigated by the dilution method. The energetics of the transfer of cosurfactant from oil to the interface has been estimated. The structural parameters, namely, droplet dimension, droplet number, and population of surfactant and cosurfactant on the droplet surface, have also been estimated. The efficacy of the surfactants in respect to water dispersion in oil and cosurfactant concentration level at the oil/water interface has been worked out. Such microemulsions are prospective compartmentalized systems to assist enzyme activities. In this respect, the trihydroxyethylated head group analogue in the above series has been found to be a better performer for the preparation and stabilization of microemulsions that has correlated well with its performance than the others in the hydrolysis of p-nitrophenyl-n-hexanoate by the enzyme Chromobacterium viscosum lipase.

Spectroscopic studies of newly synthesized bioactive compound 2-(2-bromo-ethyl)-6-nitro-benzo[de]isoquinolene-1,3-dione (BNBIO) have been carried out in polar aprotic solvent, viz. acetonitrile, tetrahydrofuran, 1,4-dioxan, ethylene glycol, dimethyl formamide, and polar protic solvent, viz. methanol, ethanol, propanol, water. Variation in absorbance of BNBIO in water–methanol, water–ethanol and water–propanol mixtures at their different compositions have been observed. Absorption behaviour of the dye has been studied in poly(oxyethylene) nonylphenol surfactants Igepal CO 630, Igepal CO 720 and Igepal CO 890 containing same hydrophobic tail and different numbers of poly(oxyethylene) groups. Experimental results of the BNBIO nonionic micelles have been explained in terms of 1:1 electron donor–acceptor (EDA) complexation and the complexation equilibrium becomes suppressed with increasing number of poly(oxyethylene) residue on the Igepal surfactant. Variation in binding constant of dye–micelle complexation has been rationalized considering a competitive equilibrium process between the BNBIO–water interactions.

The visible spectra of Safranine T (ST) in micellar solution of Brij 58, Tween 20 and Tween 40 and mixed micellar solution of Brij 58/Tween 20 and Brij 58/Tween 40 indicate formation of 1:1 charge transfer (CT) complex between acceptor ST and donor nonionic micelles and mixed micelles. The experimental CT transition energies are well correlated (through Mulliken's equation) with the vertical ionization potential of the donors. The solvent parameters, i.e. the intramolecular charge transfer energy ET(30) have been determined from the Stokes spectral shift. Variations of ionization potential and micropolarity in the mixed micellar region have been investigated as a function of surfactant composition and the obtained results in mixed micellar medium has been compared to the normal micelles. The critical micelle concentration (CMC) values determined at various surfactant compositions are lower than the ideal values indicating a synergistic interaction. The interaction parameter (β) and micellar stability has been calculated using regular solution theory.

The interaction of 3,7-diamino-2,8-dimethyl-5-phenyl phenazinium chloride (Safranine T) with the aqueous as well as reverse micellar solution of a phospholipid 1,2-diacyl-sn-glycero-3-phosphocholine (Azolecithin), a major structural phospholipid in brain, comprising approx 15% of total lipid, primarily localized in grey matter have been studied by absorption and fluorescence spectroscopic studies. The results show the evidence of complex formation of the dye in the ground and in the excited state. The interaction of the dye with the lipid in reverse micellar state is more compared to that in liposomes. An attempt has been made to determine the polarity of the microenvironment of the dye in liposomes or reverse micelles from the spectral studies of the dye in different solvents of known polarity. The polarity functions of the phosphatidylcholine (PC) liposomes are slightly lower compared to that of PC reverse micelles.