A Multiparametric Fluorescence Probe to Understand the Physicochemical Properties of Small Unilamellar Lipid Vesicles in Poly(ethylene glycol)-Water Medium.

FDAPT (2-formyl-5-(4'-N,N-dimethylaminophenyl)thiophene) efficiently senses the minimum alteration of lipid bilayer microenvironment with all six different fluorescence parameters namely emission wavelength, fluorescence intensity, steady-state anisotropy, and their corresponding time-dependent parameters (Sahu et al., J. Phys. Chem. B 2018, 122, 7308-7318). In the present work, the effect of poly(ethylene glycol) on the small unilamellar vesicle is demonstrated with the emission behavior of the FDAPT probe. A medium and a high molecular weight PEG were chosen to perturb the lipid vesicles. The alteration of the bilayer polarity, water content inside bilayer, lipid packing density in the perturbed vesicles reflect significant changes in different fluorescence parameters of FDAPT probe. The effect of PEG on the unilamellar vesicle was rationalized with the alteration of the emission behavior, fluorescence lifetime, steady-state anisotropy and anisotropy decay of the probe. The simple and convenient fluorescence measurements provide new insights into the effect of PEG on the packing density, water volume, micro polarity, and microviscosity of the small unilamellar vesicle. The physiological understanding was extended to rationalize the cryoprotecting behavior of PEG.

Swollen liquid crystalline mesophase assisted synthesis of GO-PANI nanocomposite as a fluorescent probe for purines.

This article focuses on the use of graphene oxide-polyaniline (GO-PANI) nanocomposite as fluorescent probe for sensing of adenine (A) and guanine (G). Swollen liquid crystalline mesophase were used for the synthesis of graphene oxide-polyaniline nanocomposite. GO-PANI nanocomposite showed enhanced fluorescent at 441 nm (ƛ excitation = 361 nm) on interaction of purines viz A and G solutions in dimethyl sulfoxide, GO exhibited quenching at 540 nm (ƛ excitation = 261 nm). The fluorescence emission spectra of GO-PANI nanocomposite and GO were recorded in the the pressence of A and G concentrations upto 1.2 × 10-4 M. The limits of detection (LOD) calculated from the concentration dependence study for GO-PANI nanocomposite and GO are 7.5 × 10-6 M and 13.4 × 10-6 M respectively. The LOD in the case of GO is identical for both A (13.0 × 10-6) and G (13.6 × 10-6 M). The binding constant (Kb) determined for GO-PANI with purines are in the range of 0.05-0.08 × 103 M-1 which is higher in the case of GO (2.42-7.52 × 103 M-1). The lifetime measurement demonstrates, an excited state interaction of GO-PANI nanocomposite and GO with purines. This is evident from the increasing lifetime from 4.3 ns to 29.2 ns for GO-PANI nanocomposite, while 17.5 ns to 37.2 ns for GO respectively. The relatively short lifetime of the GO-PANI nanocomposite in comparison with GO suggest an electronic charge dissipation of the excited state between polyaniline and graphene oxide possibly due to the alignment of polyaniline on the graphene oxide sheet. The photopysical properties of GO-PANI nanocomposite and GO observed in this study is new and has potential for application as fluorescent probe for the detection of purines.

Physicochemical characterization of solid lipid nanoparticles comprised of glycerol monostearate and bile salts.

Successful applications of solid lipid nanoparticles (SLNs) rely on their physicochemical properties which are mainly governed by their comprising materials (e.g., lipids, emulsifiers) and preparation methods. We have prepared biocompatible solid lipid nanoparticles with glycerol monostearate as lipid and varying combinations of bile salts sodium deoxycholate and sodium cholate (bile salts to lipid ratio 8% w/w) as emulsifiers. The detailed characterization of solid lipid nanoparticles was performed using a combination of light scattering, microscopic, calorimetric, and spectroscopic techniques. It was seen that different compositions of bile salts yield nanoparticles with different sizes. The use of only sodium deoxycholate (8% w/w) produces nanoparticles with average sizes ∼487 nm. The average particle size increases with increasing cholate fraction. A higher average particle size around ∼652 nm is obtained with 8% (w/w) sodium cholate. All the SLNs show good physical stability at room temperature and do not show polymorphic transformation during the storage. In order to study the microenvironments, solid lipid nanoparticles are loaded with an external fluorescent-probe fisetin (probe to lipid ratio 1% w/w). Photophysical properties of fisetin loaded SLNs indicate the micro-heterogenicity inside the nanoparticles.

Thermodynamic insights into drug-surfactant interactions: Study of the interactions of naporxen, diclofenac sodium, neomycin, and lincomycin with hexadecytrimethylammonium bromide by using isothermal titration calorimetry.

The success of drug delivery depends on the efficiency of the route of administration, which in turn relies on properties of the drug and its transport vehicle. A quantitative knowledge of association of drugs with transport vehicles is lacking when the latter are in the category of self assembled structures. The work reported in this manuscript addresses the mechanism of partitioning of naproxen, diclofenac sodium, neomycin and lincomycin in the micelles of hexadecytrimethylammonium bromide and that is quantitatively based on the measurement of thermodynamic parameters of interactions by using isothermal titration calorimetry. The addressed mechanism of partitioning is based on the identification of the type of interactions of these drugs with the surfactant micelles and monomers, along with the effect of the former on the micellization properties of the surfactant. The conclusions are based on the interpretation of the values of partitioning constant, standard molar enthalpy change, standard molar entropy change and the stoichiometry of the interaction. The results of this study have implications for deriving guidelines for the target oriented synthesis of new drugs that are to be used for effective delivery via micellar media.