Steady-state Fluorescence Anisotropy Research Articles

Solvent dependent relaxation dynamics in lithium ion battery electrolytes: Coupling to medium friction

Solution heterogeneity and dynamics of the industrially relevant electrolyte system, [9.795{xEC + (1 − x)PC} + 0.869LiClO4] with x representing mole fraction, were explored at different loadings of ethylene carbonate (EC) via temperature dependent measurements of time-resolved spectral response and physico-chemical properties. This system was chosen because polarity differed considerably on replacing propylene carbonate (PC) by EC but the solution viscosity remained nearly the same, allowing to investigate the polarity impact on solution inhomogeneity and solute dynamics. Coumarin 153 (C153) and trans‑2‑[4‑(dimethylamino)styryl]‑benzothiazole (trans-DMASBT) were used as fluorescent probes which differ widely in their excited state lifetimes. Driven by the potential for applications of these electrolyte systems in the energy sector, we have investigated them at an optimal composition with (PC + EC)/LiClO4 mole ratio of ~11.3, where direct current (DC) conductivity reaches at the maximum. Signatures of spatio-temporal heterogeneity were detected in steady state fluorescence and time-resolved anisotropy measurements with DMASBT (lifetime ~100–200 ps) but not with C153, suggesting a timescale over which the inhomogeneity density distributions persist in these electrolyte systems. Subsequent Stokes shift dynamics measurements using C153 captured a dynamic shift of ~700–900 cm−1 with an estimated missing portion of ~50%, and biphasic solvation response characterized by sub-100 ps and nanosecond components. Time-resolved fluorescence anisotropy measurements reflect partial viscosity decoupling for the short lifetime probe and bimodal frictional response in these electrolyte systems.

Studies on the Interactions of 2-Hydroxyoleic Acid with Monolayers and Bilayers Containing Cationic Lipid: Searching for the Formulations for More Efficient Drug Delivery to Cancer Cells.

Drug delivery in cationic liposomes seems to be a promising therapeutic approach in cancer treatment. The rational design of the positively charged lipid vesicles as anticancer drug carriers should be supported by a detailed analysis of the interactions of the carrier components with anticancer drugs. In the present work, 2-hydroxyoleic acid (2OHOA; Minerval), a membrane lipid therapy drug, was incorporated into positively charged mono- and bilayer membranes containing 1-palmitoyl-2-oleoyl- sn-glycero-3-ethylphosphocholine (EPOPC), the synthetic cationic lipid, and 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC). The intermolecular interactions, fluidity, and miscibility of the studied monolayers were analyzed by utilizing Langmuir balance experiments. The morphology of two-dimensional films was inspected using a Brewster angle microscopy technique. The properties of the liposomes were investigated by dynamic light scattering (DLS) and zeta potential measurements, steady-state fluorescence anisotropy experiments, and the spectrofluorimetric titration of calcein-encapsulated vesicles with a lysis-inducing agent. According to the collected results, 2OHOA intercalation into films of pure phospholipids or a binary EPOPC/DOPC film is thermodynamically favorable. Surprisingly, no significant effect of the presence of unsaturated 2OHOA chains on the EPOPC/DOPC monolayer order was observed. The experiments carried out for 2OHOA-inserted cationic EPOPC/DOPC (1:4) liposomes indicate effective incorporation of the drug into the liposome bilayer and the formation of stable vesicles without affecting their properties markedly. On the basis of the obtained results, EPOPC/DOPC/2OHOA cationic liposomes with 15% 2OHOA content in the phospholipid bilayer seem to be the most suitable for potential biomedical applications.

Behavior of the DPH fluorescence probe in membranes perturbed by drugs.

1,6-Diphenyl-1,3,5-hexatriene (DPH) is one of the most commonly used fluorescent probes to study dynamical and structural properties of lipid bilayers and cellular membranes via measuring steady-state or time-resolved fluorescence anisotropy. In this study, we present a limitation in the use of DPH to predict the order of lipid acyl chains when the lipid bilayer is doped with itraconazole (ITZ), an antifungal drug. Our steady-state fluorescence anisotropy measurements showed a significant decrease in fluorescence anisotropy of DPH embedded in the ITZ-containing membrane, suggesting a substantial increase in membrane fluidity, which indirectly indicates a decrease in the order of the hydrocarbon chains. This result or its interpretation is in disagreement with the fluorescence recovery after photobleaching measurements and molecular dynamics (MD) simulation data. The results of these experiments and calculations indicate an increase in the hydrocarbon chain order. The MD simulations of the bilayer containing both ITZ and DPH provide explanations for these observations. Apparently, in the presence of the drug, the DPH molecules are pushed deeper into the hydrophobic membrane core below the lipid double bonds, and the probe predominately adopts the orientation of the ITZ molecules that is parallel to the membrane surface, instead of orienting parallel to the lipid acyl chains. For this reason, DPH anisotropy provides information related to the less ordered central region of the membrane rather than reporting the properties of the upper segments of the lipid acyl chains.

Unusual sensitivity of tween20: Cholesterol niosome structure to the presence of sodium dodecyl sulfate: A study using multiple fluorescent molecular probes

This study reports the interaction of submicellar concentrations (0 mM to 2 mM) of sodium dodecyl sulfate (SDS), a biocompatible surfactant with critical micellar concentration (CMC) value of 8 mM, with Tween20:cholesterol(1:1) niosome membranes, using the fluorescence properties of three conceptually different fluorescent probes (solvatochromic interfacial probe: 8-anilino-1-naphthalenesulfonate (ANS), fluorescence anisotropy sensitive hydrophobic probe: 1,6-diphenyl-1,3,5-hexatriene (DPH), and excited state proton transfer (ESPT) probe: 1-naphthol (1-NpOH)). Dynamic light scattering (DLS) as well as scattering intensity studies have also been used for size estimation. Interfacial polarity of the niosomal membrane increases with increase in SDS concentrations, confirmed by variation of ANS fluorescence intensity. There is an appreciable increase in microviscosity value at the niosomal interfacial domain and moderate increase at the core domain with increase in SDS concentrations, confirmed by steady state fluorescence anisotropy (rss) value of ANS and DPH (rss (ANS) 0.06 to 0.12 and rss (DPH) 0.22 to 0.26 with increase in SDS concentrations from 0 mM to 2 mM). Hydrophobicity in the niosomal core domain increases with increase in SDS concentrations as observed from the fluorescence properties of different prototropic forms of 1-NpOH.

An insight into the dependence of the deamination rate of human APOBEC3F on the length of single-stranded DNA, which is affected by the concentrations of APOBEC3F and single-stranded DNA

BackgroundAPOBEC3F (A3F), a member of the human APOBEC3 (A3) family of cytidine deaminases, acts as an anti-HIV-1 factor by deaminating deoxycytidine in the complementary DNA of the viral genome. A full understanding of the deamination behavior of A3F awaits further investigation. MethodsThe real-time NMR method and uracil-DNA glycosylase assay were used to track the activities of the C-terminal domain (CTD) of A3F at different concentrations of A3F-CTD and ssDNA. The steady-state fluorescence anisotropy measurement was used to examine the binding between A3F-CTD and ssDNA with different lengths. The use of the A3F-CTD N214H mutant, having higher activity than the wild-type, facilitated the tracking of the reactions. ResultsA3F-CTD was found to efficiently deaminate the target deoxycytidine in long ssDNA in lower ssDNA concentration conditions ([A3F-CTD] ≫ [ssDNA]), while the target deoxycytidine in short ssDNA is deaminated efficiently in higher ssDNA concentration conditions ([A3F-CTD] ≪ [ssDNA]). This property is quite different from that of the previously studied A3 family member, A3B; the concentrations of the proteins and ssDNA had no effect. ConclusionsThe concentrations of A3F-CTD and ssDNA substrates affect the ssDNA-length-dependence of deamination rate of the A3F-CTD. This unique property of A3F is rationally interpreted on the basis of its binding characteristics with ssDNA. General significanceThe discovery of the unique property of A3F regarding the deamination rate deepens the understanding of its counteraction against HIV-1. Our strategy is applicable to investigate the other aspects of the A3 activities, such as those involved in the cancer development.

Photophysical and photodynamic properties of Pyronin Y in micellar media at different temperatures.

In this study, photophysics and photodynamical properties of Pyronin Y (PyY) in different liquid media were investigated. Interactions of PyY, which is a positively charged pigment compound pertaining to the xanthene derivatives with surfactants possessing distinct charges, were determined by using the molecular absorption and fluorescence spectroscopy techniques. It was observed that band intensities of absorption and fluorescence spectra belonging to PyY increase in proportion to the water when compared to three micelle systems, cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and Triton X-100 (TX-100). This suggests that interactions in micelle systems are different from those in deionized water, and solvation and surface interactions modify. It is determined that the strongest interaction occurs between PyY dye and SDS, anionic surfactant, and this interaction arises from the electrostatic forces. Calculated photophysical parameters indicated that the microenvironment of PyY in SDS micelle is different to that of other systems. In temperature studies, it was reported that increasing the temperature of the samples increased non-radiative transitions. Steady-state fluorescence anisotropy values were calculated by using fluorescence intensities of PyY compound in pre-micellar, micellar and post-micellar systems. Once the PyY fluorescence probe is added to the surfactant containing solutions below the critical micelle concentrations, the measured anisotropy values were found to be low because the probe remains in the deionized water phase. When the surfactant concentration of the medium becomes closer to the critical micelle concentrations, the steady-state anisotropy value prominently increases. This is because of the restrictions on the rotational diffusion of the probe in micellar solution. It is observed that positively charged PyY shows a higher affinity to the negatively charged SDS compared with the positively charged CTAB and neutral TX-100 surfactants. This can be explained by Coulombic interactions.

RNA Binding Mode Regulates PKR Activation

The antiviral kinase PKR is activated by RNA. The enzyme contains two dsRNA-binding domains, dsRBD1 and dsRBD2, and a kinase domain. Co-localization of the kinase domains upon binding of two or more PKRs to a single dsRNA enhances dimerization and subsequent activation. However, multiple lines of evidence indicate that the mode of RNA binding regulates PKR activation beyond simply modulating the overall binding affinity. dsRBD2 binds RNA weakly and engagement of this domain by an RNA is correlated with enzymatic activation. In order to define the role of dsRBD2 in PKR activation we have systematically mutated residues in this domain that typically mediate dsRBD-RNA interactions and probed the consequences for PKR activation and overall binding affinity. Several mutations inhibit PKR activation and reduce RNA binding affinity in parallel. However, mutation of outward-facing residues on helix 1 that typically engages the RNA minor groove dramatically reduce PKR activation while only slightly decreasing overall RNA binding affinity. Steady-state fluorescence anisotropy analysis of PKR constructs containing a single tryptophan in either dsRBD1 or dsRBD2 indicate that both domains undergo a significant decrease in mobility upon RNA binding. These anisotropy changes are not markedly affected by the helix 1 mutations, implying that the interaction of dsRBD2 with RNA persists. We propose that instead of interacting with RNA, helix 1 in dsRBD2 engages in an intramolecular interaction that regulates kinase activity based on RNA binding mode.

Itraconazole Perturbs Behavior of Fluorescent Probes in Lipid Bilayer

1,6-diphenyl-1,3,5-hexatriene (DPH) is a frequently used fluorescence probe to study the ordering and mobility of the lipids bilayer. Here we present our studies combining molecular dynamics (MD) simulations and fluorescence anisotropy measurements in the lipid bilayer with antifungal drug Itraconazole (ITZ) added. ITZ is long, rigid, amphipathic molecule locating in the lipid bilayer below the water-membrane interface and adopting orientation parallel to the membrane surface [1]. MD simulations showed that ITZ increases the order of the hydrocarbon chains in their upper part and slightly decrease order of the lower part of the chain while steady-state fluorescence anisotropy measurement indicated substantial disordering effect of the ITZ. MD simulations of the bilayer with both ITZ and DPH showed that DPH behavior in this bilayer is determined by ITZ and not by lipids chains as assumed in traditional interpretation - DPH locates below ITZ thus its position is shifted towards bilayer center and adopt orientation parallel to the membrane surface which likely results from interactions with ITZ. These results show the limitation of the DPH in studies of lipid bilayers as DPH might report the behavior of, e.g. ITZ like molecules instead of lipids hydrocarbon chains.

The influence of the essential oil extracted from hops on monolayers and bilayers imitating plant pathogen bacteria membranes.

Many plant-derived compounds possess antimicrobial, antioxidant and even anticancer activities. Therefore, they are considered as substances that can be used instead of synthetic compounds in various applications. In this work, the essential oil from hop cones was extracted and analyzed, and then its effects on model bacteria membranes were studied to verify whether the hop essential oils could be used as ecological pesticides. The experiments involved surface pressure-area measurements, penetration studies and Brewster angle microscopy (BAM) imaging of lipid monolayers as well as hydrodynamic diameter, zeta potential, steady-state fluorescence anisotropy and Cryo-Transmission Electron Microscopy (cryo-TEM) measurements of liposomes. Finally the bactericidal tests on plant pathogen bacteria Pseudomonas syringae pv. lachrymans PCM 1410 were performed. The obtained results showed that the components of the essential oils from hop cones incorporate into lipid monolayers and bilayers and alter their fluidity. However, the observed effect is determined by the system composition, its condensation and the oil concentration. Interestingly, at a given dose, the effect of the essential oil on membranes was found to stabilize. Moreover, BAM images proved that hop oil prevents the formation of a large fraction of a condensed phase at the interface. Both the studies on model membranes as well as the in vitro tests allow one to conclude that the hop essential oil could likely be considered as the candidate to be used in agriculture as a natural pesticide.

Fluorescence anisotropy analysis of comb‐type grafted poly(N,N‐diethylacrylamide‐co‐acrylic acid)‐g‐poly(N,N‐diethylacrylamide) microgels labeled by acenaphthylene

ABSTRACTTwo kinds of thermosensitive and pH sensitive comb‐type grafted poly(N,N‐diethylacrylamide‐co‐acrylicacid)‐g‐poly(N,N‐diethylacrylamide) [P(DEA‐co‐AA)‐g‐PDEA] microgels labeled by acenaphthylene (ACE) were prepared in water/methanol mixed solvent. Both of them were prepared through surfactant‐free emulsion polymerization: one was labeled in the main chain of the gel networks (B‐ACE) and the other was labeled in the grafted chains of the gel networks (G‐ACE). Steady state fluorescence anisotropy was used to study the mobility of the chains in different buffers at their lower critical solution temperature. It was found that the grafted chains moved more freely than the main chain, and the pH dependence of the mobility of the grafted chain was more pronounced. With the results obtained in the present study, we can better understand why the microgels with grafted chains have faster response rates than the ones of normal types. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46742.

Fluorescence Resonance Energy Transfer, Small-Angle Neutron Scattering, and Dynamic Light Scattering Study on Interactions of Gemini Surfactants Having Different Spacer Groups with Protein at Various Regions of Binding Isotherms.

The binding interactions of three gemini surfactants having different spacer groups (12-4-12, 12-8-12, and 12-4(OH)-12) with a high concentration (150 μM) of bovine serum albumin (BSA) at various regions of binding isotherms have been studied by means of steady-state fluorescence and fluorescence anisotropy, time-correlated single-photon counting fluorescence of trans-2-[4-(dimethylamino)styryl]benzothiazole, small-angle neutron scattering (SANS), and dynamic light scattering (DLS) measurements. The fluorescence resonance energy transfer phenomenon between the twisted intramolecular charge transfer fluorescent molecule, trans-2-[4-(dimethylamino)styryl]benzothiazole as an acceptor, and tryptophan 213 (Trp-213) of BSA as a donor has been successfully used to probe the binding interactions of gemini surfactants with protein at all regions of binding isotherms. The increasing order of energy transfer efficiency at a higher concentration range of surfactants is 12-8-12 > 12-4-12 > 12-4(OH)-12. Stronger binding of micelles of gemini surfactant molecules having a comparatively more hydrophobic spacer group with the hydrophobic segments of the protein results in closer approach of trans-2-[4-(dimethylamino)styryl]benzothiazole molecules solubilized in micelles to Trp-213. The average excited-state lifetimes become shorter with a trend of increase in contribution from the fast component and decrease in contribution from the slow component to the decay with increasing concentration of a surfactant. The nonradiative rate constant of trans-2-[4-(dimethylamino)styryl]benzothiazole increases with increasing concentration of a surfactant because the average microenvironment around it in protein–surfactant aggregates is more polar as compared to that in native protein. SANS and DLS measurements were carried out for the study of the structural deformations in the protein, on enhancement of the concentration of the gemini surfactants. The necklace and bead model has been used for the analysis of SANS data for the protein–surfactant complexes. At a higher concentration range, 12-8-12 and 12-4-12 have a slightly smaller fractal dimension and a larger correlation length as compared to 12-4(OH)-12. DLS data show that the increasing order of hydrodynamic diameter for the complexes of protein with three gemini surfactants in their high concentration range is 12-4(OH)-12 < 12-4-12 < 12-8-12.

ATP competes with PIP2 for binding to gelsolin.

Gelsolin is a severing and capping protein that targets filamentous actin and regulates filament lengths near plasma membranes, contributing to cell movement and plasma membrane morphology. Gelsolin binds to the plasma membrane via phosphatidylinositol 4,5-bisphosphate (PIP2) in a state that cannot cap F-actin, and gelsolin-capped actin filaments are uncapped by PIP2 leading to filament elongation. The process by which gelsolin is removed from PIP2 at the plasma membrane is currently unknown. Gelsolin also binds ATP with unknown function. Here we characterize the role of ATP on PIP2-gelsolin complex dynamics. Fluorophore-labeled PIP2 and ATP were used to study their interactions with gelsolin using steady-state fluorescence anisotropy, and Alexa488-labeled gelsolin was utilized to reconstitute the regulation of gelsolin binding to PIP2-containing phospholipid vesicles by ATP. Under physiological salt conditions ATP competes with PIP2 for binding to gelsolin, while calcium causes the release of ATP from gelsolin. These data suggest a cycle for gelsolin activity. Firstly, calcium activates ATP-bound gelsolin allowing it to sever and cap F-actin. Secondly, PIP2-binding removes the gelsolin cap from F-actin at low calcium levels, leading to filament elongation. Finally, ATP competes with PIP2 to release the calcium-free ATP-bound gelsolin, allowing it to undergo a further round of severing.

Revealing cardiolipins influence in the construction of a significant mitochondrial membrane model

Cardiolipins are essential for the integrity and the dynamics of the mitochondria membrane, where they exclusively exist in eukaryotes. Changes in cardiolipins membrane levels have been related to several cardiac health disorders. To evaluate cardiolipins impact on membrane properties a physico-chemical study was conducted using steady-state fluorescence anisotropy, dynamic light scattering and Nuclear Magnetic Resonance (1H and 31P NMR). Different binary and ternary mixtures of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and a natural extract of bovine heart cardiolipin were used as models of mitochondrial membrane. The main transition temperatures, obtained by the first two techniques, revealed to be cardiolipins dependent. Cardiolipins also showed to act as a bidirectional regulator of membrane fluidity. 1H and 31P NMR results revealed that cardiolipins affects the conformation, mobility and structural order of the phospholipid molecules. According to 1H NMR results, cardiolipins disturbs the overall structure and packing order of membrane demonstrated with the decrease of the line broadening and shift of all resonances. The 31P NMR line shape analysis confirmed that, at distinct temperatures, different lipid phases coexist in the systems, and their type and quantitative distribution are cardiolipins dependent. In summary, cardiolipins presence/absence dramatically changes the membrane properties and has a major impact in the construction of a mitochondrial membrane model.

Photophysics and rotational diffusion dynamics of large prolate non-polar laser dyes

The present work deals with experimental determination of steady state fluorescence anisotropies, fluorescence lifetimes and consequentially the rotational reorientation times of three large, nonpolar laser dyes that are modelled as prolate ellipsoids. Steady state and time resolved fluorescence spectroscopic measurements on Exalite 404 (E404), Exalite 417 (E417) and Exalite 428 (E428) dyes in series of alkane and alcohol solutions are discussed. All the three probes are observed to exhibit significantly shorter reorientation times in series of alcohols as compared to alkanes. The experimental results are explained in light of SED hydrodynamic and quasihydrodynamic theories. It is for the first time DKS theory is found to correctly predict the experimental results in alkanes with precision for all the three probes. Particularly in case of E417 DKS theory correlates exceptionally well with predictions of slip hydrodynamics. Interestingly, the largest probe (E428) being reported for the first time, exhibits slip behaviour in alkanes and alcohols; behaviour in higher alcohols as well as alkanes. This suggests the existence of nonhydrodynamic forces and speculates that the straightforward relation between the probe size and the nature of their behaviour may not be appropriate. Further, the nature and geometries of probes were fully explored and characterized using NBO and DFT studies employing Gaussian09 program. Optimized geometries, energy band gap and HOMO-LUMO levels were determined from DFT exchange-correlation function B3LYP with 6-311g basis set. Inter and intra hyper-conjugative interactions were estimated from NBO analysis. A very strong interactions between π(C19C21) → π⁎(C24C25), π(C1C6) → π⁎(C2C3) and π(C33C34) → π⁎(C28C30) with E(2) energies 21.44, 21.75 and 22.75 kcal/mol were observed for E404, E417 and E428, respectively. Electron occupancies and p-character were also determined for these molecules.

Influence of Cationic Phosphatidylcholine Derivative on Monolayer and Bilayer Artificial Bacterial Membranes.

An increasing number of bacterial infections and the rise in antibiotic resistance of a number of bacteria species forces one to search for new antibacterial compounds. The latter facts motivate the investigations presented herein and are aimed at studying the influence of a cationic lipid, 1-palmitoyl-2-oleoyl- sn-glycero-3-ethylphosphocholine (EPOPC), on model (mono- and bilayer) membranes. The monolayer experiments involved the analysis of the interactions of EPOPC with bacterial membrane lipids in one component and mixed systems as well as Brewster angle microcopy studies. The properties of liposomes were analyzed based on the results of dynamic light scattering (DLS) and zeta potential measurements as well as on the experiments concerning the release of calcein entrapped in liposomes after titration with surfactant solution and steady-state fluorescence anisotropy of DPH. The obtained results evidenced that EPOPC, even at low concentrations, strongly changes organization of model systems making them less condensed. Moreover, EPOPC decreases the hydrodynamic diameter of liposomes, increases their zeta potential, and destabilizes model membranes, increasing their fluidity and permeability. Also, the in vitro tests performed on Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) strains prove that EPOPC has some bacteriostatic properties which seem to be stronger toward Gram-negative than Gram-positive bacteria. All these findings allow one to conclude that EPOPC mode of action may be directly connected with the interactions of EPOPC molecules with bacterial membranes.

Pharmacokinetic interaction of diosmetin and silibinin with other drugs: Inhibition of CYP2C9-mediated biotransformation and displacement from serum albumin

Diosmin and silibinin (SIL) are polyphenolic compounds which are the active components of several drugs and dietary supplements. After the oral administration of diosmin (flavonoid glycoside), only its aglycone diosmetin (DIO) reaches the systemic circulation. Both DIO and SIL form complexes with serum albumin and are able to inhibit several cytochrome P450 enzymes. Therefore, it is reasonable to hypothesize that these polyphenols may displace some drugs from serum albumin and inhibit their biotransformation, potentially leading to the disruption of drug therapy. In this study, the inhibitory action of DIO and SIL on CYP2C9-catalyzed metabolism of diclofenac to 4′-hydroxydiclofenac was examined, using warfarin as a positive control. Furthermore, interaction of DIO and SIL with human and bovine serum albumins as well as the displacement of warfarin from albumin by DIO and SIL were tested, employing steady-state fluorescence spectroscopy, fluorescence anisotropy, ultrafiltration, and molecular modeling. It is demonstrated that DIO and SIL are potent inhibitors of CYP2C9 enzyme and are able to displace the Site I ligand warfarin from human serum albumin. Because DIO and SIL may interfere with the pharmacokinetics of several drugs through both ways, we need to consider the potentially hazardous consequences of the consumption of diosmin or SIL together with other drugs.

Effect of Urea on Solvation Dynamics and Rotational Relaxation of Coumarin 480 in Aqueous Micelles of Cationic Gemini Surfactants with Different Spacer Groups.

The present work highlights the effect of urea on solvation dynamics and the rotational relaxation of Coumarin 480 (C-480) in the Stern layer of aqueous micelles of cationic gemini surfactants, 12-4(OH)n-12 (n = 0, 1, 2). UV–visible absorption, steady-state fluorescence and fluorescence anisotropy, time-resolved fluorescence and fluorescence anisotropy, and dynamic light scattering measurements have been carried out for this study. The formation of micelles becomes disfavored in the presence of urea at high concentration. Solvation dynamics is bimodal in nature with fast solvation as a major component. The average solvation time increases, reaches a maximum, and then decreases with increasing concentration of urea because the degree of counterion dissociation also follows the same order with the addition of urea in the micellar solution. With increased degree of counterion dissociation, the extent of clustering of water molecules is increased, resulting in slower solvation process. The −OH group present in the spacer group of gemini surfactant controls the rate of solvation by shielding the water molecules from the probe molecules forming hydrogen bond. The microviscosity of micelles is decreased with increasing concentration of urea, as a result of which the rotational relaxation process becomes faster. In the presence of the −OH group in the spacer group, the microviscosity of micelles is enhanced, resulting in longer rotational relaxation time. Rotational relaxation process is bimodal in nature with the major contribution from the fast component to the fluorescence depolarization. Slow rotational relaxation is mainly due to the lateral diffusion of C-480 molecules along the surface of the micelle. The tumbling motion of the micelle as a whole is much slower than the lateral diffusion of C-480. Wobbling motion of C-480 becomes faster with increasing concentration of urea as a result of decreased microviscosity of micelles. The alignment of C-480 molecules in micelles might change with changing microviscosity.

Supramolecular host-guest interaction of antibiotic drug ciprofloxacin with cucurbit[7]uril macrocycle: Modulations in photophysical properties and enhanced photostability

Supramolecularly assisted modulations in the photophysical properties of the well known and practised antibiotic drug ciprofloxacin (Cpf) with versatile macrocyclic cavitand molecule cucurbit[7]uril (CB7) has been explored under different pH conditions. Both the cationic (Cpf-H+) and neutral (Cpf) forms of the drug exhibits strong binding interaction with CB7. Ground state absorption, steady-state fluorescence, time-resolved emission and fluorescence anisotropy decay measurements documented the host assisted intriguing changes in the photophysical properties of the drug, occurred through the successive formations of the 1:1 and 1:2 (drug to host) inclusion complexes, and thereby causing the intriguing small initial enhancement in fluorescence intensity at lower host concentrations and subsequently leading to a strong fluorescence quenching at higher CB7 concentration. Inferences drawn from the photophysical studies are nicely supported by the results obtained from the 1H NMR measurements. Investigations on the photodegradation studies involving the Cpf-H+ and Cpf forms of the drug, both in the absence and in the presence of CB7 host, revealed that there is a large enhancement in the photostability for both the prototropic forms of the drug, by about 3 times, on their inclusion complex formation with the CB7 host. Observed results from the supramolecular interactions of the ciprofloxacin drug with CB7 macrocycle are suggested to have implications in improving drug stability and in the possible deployments in drug formulations and drug delivery systems.

Electronic Nature of Nonlinear Optical Properties of a Symmetrical Two-Photon Absorbing Fluorene Derivative: Experimental Study and Theoretical Modeling

A comprehensive experimental and theoretical study of linear photophysical properties, such as excited-state relaxation, two-photon absorption, and stimulated emission spectra of the symmetrical fluorene derivative 2,2′-((1E,1′E)-(9,9-diethyl-9H-fluorene-2,7-diyl)bis(ethene-2,1-diyl))bis(1-methyl-1H-pyrrole) (1), is presented. The steady-state absorption, fluorescence, excitation, and excitation anisotropy spectra of 1 in organic solvents of different polarities are investigated experimentally and modeled. The fluorescence solvatochromism of 1 suggests the occurrence of symmetry breaking in the first excited state. The nature of fast relaxation processes in the excited state of 1, with the characteristic times of several picoseconds, is investigated by transient absorption femtosecond pump–probe spectroscopy. The spectral properties of 1 are satisfactorily described by an essential-state model that, accounting for electron–vibration coupling and for polar solvation, addresses spectroscopic features not on...

Unveiling the pH dependent interaction between bolaamphiphiles (dicarboxylic acids) and C10TAB (decyltrimethylammonium bromide) in aqueous medium

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-(CH2)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 < 6). The micelle size varies from 6.24 to 7.43 nm at pH 12, for vesicles the values are large (220–296 nm), and small (∼30–70 nm) in the pH range of 6.0–8.0. The self-assembly formation properties of their mixtures are herein investigated using different techniques viz. UV–vis spectroscopy, fluorescence spectroscopy, dynamic light scattering, laser confocal scanning microscopy, and isothermal titration calorimetry. The formed vesicles are fairly polydisperse, and show overall spherical shape. Formation of the bilayer assemblies, and their conversion to mixed micelles by the temperature effect are observed from steady state fluorescence anisotropy measurements. Micellization of the mixed bola-C10TAB species is endothermic and fairly entropy controlled; their formation/deformation is pH sensitive. They have spherical morphologies, and once formed at the right pH they are found to be very stable in terms of time. Thus, these vesicles have prospects for encapsulation and delivery of materials like drugs, and other substrates by controling the acid-base conditions of the system environment. The formed mixed micelles, and vesicles are expected to be low toxic, and thus green materials in nature with wider application possibilites.