Jitendriya Swain

Study of aqueous phase aggregation of FTY720 (fingolimod hydrochloride) and its effect on DMPC liposomes using fluorescent molecular probes

This work focuses on the study of aqueous phase aggregation of the recently FDA approved oral drug molecule FTY720 (fingolimod hydrochloride) and its effect on dimyristoylphosphatidylcholine (DMPC) liposomes using different fluorescent molecular probes and fluorescence parameters. The variation of the steady state fluorescence intensity of 8-anilino-1-naphthalene sulfonic acid (ANS) with FTY720 in water shows an efficient micellar aggregation with the critical micellar concentration (CMC) at ~75 μM. The aggregation number calculation from steady state fluorescence quenching of pyrene shows the formation of small micellar aggregates in aqueous solution having an aggregation number of 42 ± 3 with the free energy of micellization ~-23 kJ mol(-1). Fluorescence intensity and lifetime decay analysis of the molecular probe 1-naphthol indicate that the interaction of FTY720 with the DMPC lipid bilayer membrane prevents partitioning of small molecules such as 1-naphthol to the membrane in both solid gel (SG) and liquid crystalline (LC) phases. Temperature dependent fluorescence intensity studies of 1-naphthol and fluorescence anisotropy measurements of 1,6-diphenyl-1,3,5-hexatriene (DPH) have shown that above the CMC of FTY720, the SG to LC main phase transition temperature (T(M)) of the lipid bilayer membrane decreases from 23 °C to 21 °C in the aqueous medium.

Characterization and phase transition study of a versatile molecular gel from a glucose-triazole-hydrogenated cardanol conjugate

The synthesis and gelation properties of a structurally simple, renewable-resource-based glucose-triazole-hydrogenated cardanol conjugate (GTHCC) are reported. The conjugation of hydrogenated cardanol and glucose was done using a triazole linker employing copper(I) mediated acetylene azide cycloaddition ‘click’ chemistry in the key step. The GTHCC was found to form four different classes of gels; namely, (i) hydrogel from aqueous-protic solvents, (ii) organogel from non-polar solvents, (iii) gel from vegetable oil and (iv) gel from petroleum oil. In a water–methanol (1 : 1) mixture, the conjugate acted as a stable thermoreversible supergelator, even at a very low gelator concentration of 0.03% w/v. Unlike glycoside-based gels derived from hydrogenated cardanol and glucose, the GTHCC is stable under acidic as well as basic conditions, owing to the covalent linkages in the tether. The intrinsic fluorescence of the hydrogel was found to be sensitive towards a gel–sol transition.

Thermotropic gelation induced changes in micropolarity and microviscosity of hydrogel derived from glucose-triazole-hydrogenated cardanol conjugate: a study using fluorescent molecular probe

Glucose triazole cardanol conjugate (GTHCC) is a supergelator in water–methanol (1:1) solvent mixture. Environmental scanning electron microscopy (ESEM) and fluorescence molecular probe based techniques were employed to understand the thermotropic gelation induced changes in micropolarity and microviscosity of GTHCC hydrogel in water–methanol (1:1) solvent mixture. ESEM analysis has shown the formation of spongy sheet like structures having micrometer size pores inside it. The fluorescence intensity and fluorescence anisotropy measurements of the polarity sensitive probe 8-anilino-1-naphthalene sulfonic acid (ANS) revealed a significant increase in the micropolarity and a significant decrease in the microviscosity of GTHCC hydrogel between the gel and sol phases. Time resolved fluorescence decay analysis of ANS has shown the presence of two different microenvironments in the system and thermotropic microenvironmental changes between gel and sol phases of GTHCC hydrogels.

Study on binding and fluorescence energy transfer efficiency of Rhodamine B with Pluronic F127-gold nanohybrid using optical spectroscopy methods

This work focuses on the binding efficiency and fluorescence resonance energy transfer (FRET) of fluorescent dye Rhodamine B (Rh B) to Pluronic F127-gold nanohybrid. The formation of gold nanoparticles inside Rh B doped Pluronic F127 copolymer have been characterized using dynamic light scattering study, HR-TEM images, UV-visible spectra and fluorescence studies. Fluorescence quenching and the constant fluorescence lifetime of the Rhodamine B present in the cavity of Pluronic F127-gold nanohybrid suggested a strong binding ability (3.5×103Lmol-1), static nature of quenching and better energy transfer efficiency of fluorescent dye towards Pluronic F127-gold (Au) nanohybrids.

Nile red fluorescence for quantitative monitoring of micropolarity and microviscosity of pluronic F127 in aqueous media

The photophysical behaviour and excited state decay kinetics of the fluorescent probe Nile red were used for quantitative monitoring of micropolarity, microviscosity and the sol-gel transition temperature of a copolymer hydrogel, pluronic F127. There was considerable enhancement of the emission intensity with a large blue shift in emission and an absorption maximum at and above the sol-gel transition temperature (20 °C), showing the sensitivity of Nile red fluorescence to the sol-gel transition. The estimation of micropolarity by comparing the Nile red emission maximum in dioxane-water mixtures suggested a considerable decrease in the polarity of the PF127 microenvironment from less polar (20% dioxane-water) in its sol phase to almost non-polar (90% dioxane-water) microenvironments in the gel phase. The thermotropic response of the wavelength dependent fluorescence lifetime of the probe with a rise time in the longer wavelength region has enabled monitoring of the microheterogeneity of the gel medium. With an increase in temperature, the microviscosity progressively increases from ∼10 mPa s (sol state) to ∼23 mPa s (gel state). The mismatch between microviscosity as estimated by the Nile red and the corresponding bulk viscosity reflected the microheterogeneity of the pluronic medium and its sensitivity towards PF127 microenvironments.

Molecular Level Understanding of Sodium Dodecyl Sulfate (SDS) Induced Sol–Gel Transition of Pluronic F127 Using Fisetin as a Fluorescent Molecular Probe

The thermoreversible sol-gel transition of pluronic F127 is markedly altered even with addition of submicellar concentration of sodium dodecyl sulfate (SDS) surfactant. Multiple fluorescence parameters like fluorescence intensity, fluorescence anisotropy and fluorescence lifetime of both the prototropic forms (anion (A-*) and phototautomer FT*) of the photoprototropic fluorescent probe fisetin has been efficiently used to understand the molecular level properties like polarity and microviscosity of the PF127-SDS system as a function of temperature. The SDS-induced increase in the interfacial hydrophobicity level is seen to affect the sol-gel phase transition of PF127 (21-18 °C). The ET(30) polarity parameter value of anionic emission of fisetin suggests that there is a considerable decrease in the polarity of the PF127 medium with increase in temperature and with the addition of SDS. The microviscosity progressively increases from ∼5 mPa s (sol state, 10 °C) to ∼22.01 mPa s (gel state 35 °C) in aqueous solution of PF127. The variation in microviscosity with addition of SDS in PF127-SDS mixed system is significant in sol phase whereas in gel phase this variation is significantly less. Temperature dependent fluorescence lifetime of FT* indicates that there is heterogeneity in distribution of fisetin molecules at different domains of PF127. This work also show-cases the sensitivity of fisetin toward change in polarity and change in sol-gel transition temperature of copolymer PF127 with variation in temperature (both forward and reverse directions) and SDS.

Temperature-dependent water penetration in Tween20:cholesterol niosome membrane: a study using excited state prototropism of 1-naphthol

This work uses the dynamics of the excited state proton transfer of 1-naphthol to water as a basis for understanding the temperature-dependent changes in the water accessibility of the niosome membrane domain. The decrease in the neutral form fluorescence intensity of membrane bound 1-naphthol, the significant drop in the membrane-bound anion form fluorescence lifetime, and the changes in the fluorescence lifetime distribution plots of the two prototropic forms of 1-naphthol indicate a regular increase in the water penetration in the interfacial region of the niosome membrane domain, whereas the dry core regions appear unaffected with increasing temperature (10–60 °C). Unlike some liposomes and niosomes, these niosomes do not show thermotropic phase transition behavior.

Molecular level investigation on the interaction of pluronic F127 and human intestinal bile salts using excited state prototropism of 1-naphthol.

Pluronic F127 (PF127), a surfactant polymer is used as a drug delivery system and has been introduced recently in the food research to delay lipid digestion process. In this context study the interaction of this polymer with human intestinal bile salts assumes important. The studies involving interaction of PF127 with human intestinal bile salts sodium taurocholic acid (NaTC) and sodium cholate acid (NaC) by using differential scanning calorimetry (DSC) and 1-naphthol as a fluorescent molecular probe show that the bile salts induce decrease of sol-gel phase transition temperature of the PF127 to lower temperature, from ~21°C to ~18°C. Variation of neutral form fluorescence intensity of 1-naphthol with bile salts in water confirmed efficient micellar aggregation with critical micellar concentration (CMC) values of 12.6mM for NaTC and 12.7mM for NaC. Fluorescence parameters like fluorescence intensity and fluorescence lifetime of the two excited state prototropic forms {neutral form emission (λem=370nm), anion form emission (λem=470nm)} of 1-naphthol suggested that the NaTC (below critical micellar concentration 12mM) and NaC (above critical micellar concentration 12mM) induce appreciable dehydration of the hydrophilic corona as well as core region PF127 hydrogel. The micropolarity of the hydrogel microenvironment decreases with increase in concentration of both the bile salts.