The formation of stable unilamellar vesicles which hold great potential for biological as well as biomedical applications has been reported in the aqueous mixed solution of a surface active ionic liquid (SAIL), 1-hexadecyl-3-methylimidazolium chloride ([C16mim]Cl) and cholesterol. To make a comparison we have also shown the formation of such stable vesicles using a common cationic surfactant, benzyldimethylhexadecylammonium chloride (BHDC) which has a similar alkyl chain length but different headgroup region to that of [C16mim]Cl. It has been revealed from dynamic light scattering (DLS), transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), and other optical spectroscopic techniques that the micelles of [C16mim]Cl and BHDC in aqueous solutions transform into stable unilamellar vesicles upon increasing concentration of cholesterol. We find that, as the concentration of cholesterol increases, the solvation and rotational relaxation time of C153 in [C16mim]Cl/cholesterol solution as well as in BHDC/cholesterol solution gradually increases indicating a significant decrease in the hydration behavior around the self-assemblies upon micelle-vesicle transition. However, the extent of increase in solvation and rotational relaxation time is more prominent in the case of [C16mim]Cl/cholesterol solutions than in the BHDC/cholesterol system. This indicates that [C16mim]Cl/cholesterol vesicular membranes are comparatively less hydrated and more rigid than the BHDC/cholesterol vesicular bilayer.

The rotational dynamics and translational diffusion of a hydrophilic organic molecule, rhodamine 6G perchlorate (R6G ClO4) in small unilamellar vesicles formed by two different ionic surfactants, cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), with cholesterol have been investigated using fluorescence spectroscopic methods. Moreover, in this article the formation of vesicle using anionic surfactant, SDS at different cholesterol-to-surfactant molar ratio (expressed by Q value (Q = [cholesterol]/[surfactant])) has also been reported. Visual observation, dynamic light scattering (DLS) study, turbidity measurement, steady state fluorescence anisotropy (r0) measurement, and eventually microscopic images reveal the formation of small unilamellar vesicles in aqueous solution. Also, in this study, an attempt has been made to observe whether the cationic probe molecule, rhodamine 6G (R6G) experiences similar or different microenvironment in cholesterol-SDS and cholesterol-CTAB assemblies with increase in cholesterol concentration. The influence of cholesterol on rotational and translational diffusion of R6G molecules has been investigated by monitoring UV-vis absorption, fluorescence, time-resolved fluorescence anisotropy, and finally fluorescence correlation spectroscopy (FCS) measurements. In cholesterol-SDS assemblies, due to the strong electrostatic attractive interaction between the negatively charged surface of vesicle and cationic R6G molecules, the rotational and diffusion motion of R6G becomes slower. However, in cholesterol-CTAB aggregates, the enhanced hydrophobicity and electrostatic repulsion induces the migration of R6G from vesicle bilayer to aqueous phase. The experimental observations suggest that the surface charge of vesicles has a stronger influence than the hydrophobicity of the vesicle bilayer on the rotational and diffusion motion of R6G molecules.

It is well-known that sugars protect membrane structures against fusion and leakage. Here, we have investigated the interaction between different sugars (sucrose, trehalose, and maltose) and phospholipid membrane of 1,2-dimyristoyl-sn-glycero-3-phoshpocholine (DMPC) using dynamic light scattering (DLS), transmission electron microscopy (TEM), and other various spectroscopic techniques. DLS measurement reveals that the addition of sugar molecule results a significant increase of the average diameter of DMPC membrane. We have also noticed that in the presence of different sugars the rotational relaxation and solvation time of coumarin 480 (C480) and coumarin 153 (C153) surrounding DMPC membrane increases, suggesting a marked reduction of the hydration behavior at the surface of phospholipid membrane. In addition, we have also investigated the effect of sugar molecules on the lateral mobility of phospholipids. Interestingly, the relative increase in rotational, solvation and lateral diffusion is more prominent for C480 than that of C153 because of their different location in lipid bilayer. It is because of preferential location of comparatively hydrophilic probe C480 in the interfacial region of the lipid bilayer. Sugars intercalate with the phospholipid headgroup through hydrogen bonding and replace smaller sized water molecules from the membrane surface. Therefore, overall, we have monitored a comparative analysis regarding the interaction of different sugar molecules (sucrose, trehalose, and maltose) with the DMPC membrane through DLS, TEM, solvation dynamics, time-resolved anisotropy, and fluorescence correlation spectroscopy (FCS) measurements to explore the structural and spectroscopic aspect of lipid-sugar interaction.

In this work, we have investigated the composition dependent anomalous behavior of dimethyl sulfoxide (DMSO)-water binary mixture by collecting the ultrafast solvent relaxation response around a well known solvation probe Coumarin 480 (C480) by using a femtosecond fluorescence up-conversion spectrometer. Recent molecular dynamics simulations have predicted two anomalous regions of DMSO-water binary mixture. Particularly, these studies encourage us to investigate the anomalies from experimental background. DMSO-water binary mixture has repeatedly given evidences of its dual anomalous nature in front of our systematic investigation through steady-state and time-resolved measurements. We have calculated average solvation times of C480 by two individual well-known methods, among them first one is spectral-reconstruction method and another one is single-wavelength measurement method. The results of both the methods roughly indicate that solvation time of C480 reaches maxima in the mole fraction of DMSO XD = 0.12-0.17 and XD = 0.27-0.35, respectively. Among them, the second region (XD = 0.27-0.35) is very common as most of the thermodynamic properties exhibit deviation in this range. Most probably, the anomalous solvation trend in this region is fully guided by the shear viscosity of the medium. However, the first region is the most interesting one. In this region due to formation of strongly hydrogen bonded 1DMSO:2H2O complexes, hydration around the probe C480 decreases, as a result of which solvation time increases.

In this article, we have investigated the anomalous behavior of two alcohol-water (tert-butyl alcohol (TBA)-water and ethanol-water) binary mixtures using femtosecond fluorescence upconversion technique. Recently, Gupta and Patey (Gupta, R.; Patey, G. N. J. Chem. Phys. 2012, 137, 034509(1)-034509(12)) have used four force fields to simulate TBA-water binary mixtures. Surprisingly, two of them do not identify any aggregation of TBA molecules. We have calculated average solvation time of Coumarin 480 (C480) using two different methods. Our results indicate slowdown in solvation time in the mole fraction ranges XT = 0.09-0.15, XT = 0.40-0.46 and XE = 0.06-0.08, XE = 0.20-0.25 for TBA-water and ethanol-water binary mixtures, respectively. Additionally, we have detected another anomalous region at XT ∼ 0.03. Slow solvation responses in the ranges XT = 0.40-0.46 and XE = 0.20-0.25 are probably due to the higher shear viscosity of the medium. However, XT = 0.09-0.15 and XE = 0.06-0.08 are the manifestation of aggregation induced structural transition of alcohol molecules. Hindered rotation of C480 in the ranges XT = 0.04-0.09 and XE = 0.03-0.07 corroborates our solvation dynamics results. From temperature dependent anisotropy measurements, we have shown that aggregation of alcohol molecules increases with increase in temperature.