Ramping of pH Across the Water-Pool of a Reverse Micelle.

In this work, we have addressed the problem of "acidity" of the water-pool of a reverse micelle (RM) through the well-known inversion of sucrose reaction as a tool of investigation. This reaction has been performed inside positively and negatively charged RM and the rates are compared with that in bulk water. We propose that the buffer-like action in a water-pool is much stronger than expected earlier. The rate of sucrose hydrolysis slowed down in the negatively charged AOT reverse micelle while it sped up for the positively charged CTAB reverse micelle. However, temperature-dependent measurements showed that the activation energy remained the same for all the cases. It has been concluded that a proton gradient exists inside the water-pool of the reverse micelle and it determines the buffer-like action of the water-pool that persists until about 2 N of HCl in AOT RM of w(0) = 10.5.

Synthesis and Aggregation Studies of a Pyridothiazole-Based AIEE Probe and Its Application in Sensing Amyloid Fibrillation.

We report the aggregation and photophysical properties of a pyridothiazole-based, aggregation-induced, emission-enhancement (AIEE) luminogen 4-(5-methoxy-thiazolo[4,5-b]pyridin-2-yl)benzoic acid (PTC1) and its application for the sensitive detection and monitoring of amyloid fibrillation. The aggregation properties of the AIEE probe were extensively studied by atomic force microscopy (AFM) and dynamic light scattering (DLS), and it was noted that as aggregation increases the fluorescence of PTC1 also was increased. The fluorescence of PTC1 was quenched upon the addition of cupric (Cu2+) ions, while the fluorescence is regenerated in the presence of amyloid fibers. AFM studies reveal that the PTC1 molecules self-associate/aggregate to hairy micelle-like structures, which dissociate or disrupt in the presence of the Cu2+ ions and again reassemble in the presence of amyloid fibers. Hence, the quenching and regeneration of PTC1 fluorescence may be attributed to the disaggregation and aggregation-induced emission (AIE), respectively. Further, a comparative analysis of the performance of PTC1 was done with conventional Thioflavin T, which confirms it to be a more sensitive probe for the detection of the amyloid, both in the presence and absence of Cu2+ ions. The experimental results were also validated theoretically via molecular docking and simulation studies. Of note, a very simple, facile, and cost-effective methodology for the detection of the amyloid fibers is presented, wherein fluorescence quenching/enhancement can be visualized under the UV light without the use of sophisticated instrumentation techniques. The AIEE probe was designed using an unusual pyridothiazole scaffold unlike commonly used archetypal AIE scaffolds based on tetraphenylethene (TPE) and hexaphenylsilole (HPS). Hence, the work also has implications in designing future AIEE dyes based on the pyridothiazole scaffold reported.

Ornamentation of Triskelion Peptide Nanotori to Produce Gold Nanoparticle (AuNP)-Embedded Peptide Nanobangles.

We report the formation of gold nanoparticle (AuNP)-biotinylated triskelion peptide hybrid nanostructures. These structures were created by using self-organization and mimicking strategies to develop AuNP-ornamented peptide nanobangles with predetermined properties on biocompatible surfaces. Such intelligent and fascinating nanomaterials can be used for several bio-nanotechnological applications.

Dynamics of solvent response in methanol-chloroform binary solvent mixture: a case of synergistic solvation.

Steady-state absorption, emission, and femtosecond transient absorption spectroscopies were used to ascertain the static and dynamic nature of the solvent response of methanol-chloroform binary solvent mixtures of different stoichiometric ratios using 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) as the probe molecule. The appearance of synergistic solvation behavior in the steady-state absorption measurements can be explained in terms of solvent-solvent interactions through an extended hydrogen-bonding network. The disappearance of such synergistic behavior in the excited state of the DCM dye was recently proposed by us to be due to the weak nature of the intermolecular interactions present in binary solvent mixtures (J. Phys. Chem. B 2012, 116, 1345). It was anticipated and subsequently confirmed by the dynamics of the solvent response that the disruption of the weak interactive solvent network is the main reason for the absence of the synergism in the excited state. As expected, we observed the slowest dynamics for the mixture with X(MeOH) = 0.45, with an average solvation time of 12.03 ps, which is much higher than the values for the pure bulk counterparts (⟨τ(s)⟩(Methanol) = 4.32 ps and ⟨τ(s)⟩(Chloroform) = 1.32 ps). The unprecedented slowing of solvation for DCM is probably due to the rigid interactive methanol-chloroform solvent system in the first solvation shell, followed by solvent rearrangements around the solute dipole. Overall interactions present within the methanol-chloroform binary solvent mixture furnish clear evidence of solvent association through weak hydrogen bonding.

Origin of strong synergism in weakly perturbed binary solvent system: a case study of primary alcohols and chlorinated methanes.

A strong synergistic solvation was observed for the mixtures of hydrogen bond donating and accepting solvent pairs. The nature of the interactions between two solvent pairs was investigated with different dye molecules viz. coumarin 480, coumarin 153, 4-aminophthalimide, and p-nitroaniline. Coumarin 480 in differenet alcohols-CHCl(3) (alcohols: MeOH, EtOH, BuOH) binary mixture shows a strong synergism, which is explained in the backdrop of solvent-solvent interactions. Fluorescence quenching of C480 by 1,2-phenylenediamine in the binary solvent mixture exhibited the maximum deviation in quenching constant corresponding to ~0.45 mol fraction of MeOH in MeOH-CHCl(3) binary mixture and hence suggested the maximum extent of hydrogen-bonding interactions prevailing at this proportion of mixture. The solvation behavior of MeOH-CHCl(3) mixture shows strong probe dependence with no synergism observed in p-nitroaniline, which is ascribed to its higher ground state dipole moment (8.8 D) relative to C480 (6.3 D). Interestingly, the strong synergistic signature observed through spectrophotometric measurement of C480 in alcohol-CHCl(3) binary mixture is absent when studied by fluorescence measurement. The higher excited state dipole moment of coumarin 480 (13.1 D) is considered to be the driving force for the absence of synergism in the excited state. In such strongly perturbed systems (due to high dipole moment values) the dominant phenomenon is preferential solvation. Analysis of proton NMR of MeOH-CHCl(3) binary solvent mixture indicates the existence of MeOH-CHCl(3) clusters in the stoichiometric ratio of 1:2.15. Refractive index measurement also infers the existence of hydrogen bonded network structure between MeOH and CHCl(3). A modified Bosch solvent exchange model has been used to determine the feasibility of synergistic behavior and polarity parameter of the mixed solvent structure of MeOH-CHCl(3) binary solvent mixture.