Solvation Dynamics in Different Phases of the Lyotropic Liquid Crystalline System

Abstract

Reverse hexagonal (HII) liquid crystalline material based on glycerol monooleate (GMO) is considered as a potential carrier for drugs and other important biomolecules due to its thermotropic phase change and excellent morphology. In this work, the dynamics of encapsulated water, which plays important role in stabilization and formation of reverse hexagonal mesophase, has been investigated by time dependent Stokes shift method using Coumarin-343 as a solvation probe. The formation of the reverse hexagonal mesophase (HII) and transformation to the L2 phase have been monitored using small-angle X-ray scattering and polarized light microscopy experiments. REES studies suggest the existence of different polar regions in both HII and L2 systems. The solvation dynamics study inside the reverse hexagonal (HII) phase reveals the existence of two different types of water molecules exhibiting dynamics on a 120-900 ps time scale. The estimated diffusion coefficients of both types of water molecules obtained from the observed dynamics are in good agreement with the measured diffusion coefficient collected from the NMR study. The calculated activation energy is found to be 2.05 kcal/mol, which is associated with coupled rotational-translational water relaxation dynamics upon the transition from "bound" to "quasi-free" state. The observed ∼2 ns faster dynamics of the L2 phase compared to the HII phase may be associated with both the phase transformation as well as thermotropic effect on the relaxation process. Microviscosities calculated from time-resolved anisotropy studies infer that the interface is almost ∼22 times higher viscous than the central part of the cylinder. Overall, our results reveal the unique dynamical features of water inside the cylinder of reverse hexagonal and inverse micellar phases.

Behavior of PPI-G2 Dendrimer in a Microemulsion

“…The vibrational band of OH stretching can be split to three Gaussians that are centered at 3600, 3400, and 3250 cm –1 . − Strongly bound water stretching vibrations that appear at 3600 cm –1 show a progressive shift to lower wavenumbers with increasing concentration of solubilized PPI-G2. Its frequency decreases gradually from 3526 to 3508 cm –1 (Figure A), indicating stronger hydrogen bonding between water molecules and solubilized PPI-G2 .…”

Probing of Reorganization Dynamics within the Different Phases of Themotropic Liquid Crystals

“…Recently Hazra and his coworkers studied the solvation dynamics in a lyotropic liquid crystalline phase using an external probe molecule Coumarin 343 (C343). They observed the presence of two different types of water molecules within a glycerol mono‐oleate based reverse hexagonal liquid crystalline phase . In a seminal work by Fayer and his coworkers, using 2D IR vibrational echo spectroscopy, they observed the presence of long range isotropic phase within the anisotropic nematogenic liquid crystalline phase.…”

Dynamics of different steps of the photopyrolytic cycle of an eminent anticancer drug topotecan inside biocompatible lyotropic liquid crystalline systems

“…[57][58][59] In one of our previous works, we have shown that the average solvation dynamics inside lipid base H II phase is $6674 ps, which is several order magnitude slower than that of bulk water. 53 Bhattacharyya and co-workers also observed very slow solvation dynamics of $4500 ps inside Pluoronic-123 based cubic phase (Ia3d space group). 60 Kim et al reported slow dynamics of encapsulated water molecules inside lipidic cubic (Pn3m space group) phases.…”

“…[57][58][59] However, the number of available free water molecules vastly reduces inside the lipid based LLC phases due to the presence of 'bound water' molecules as a result of H-bonding with the -OH groups of GML. 53 Hence, the reduction of free water molecules inside liquid crystalline phases leads to slowing down of the ESPT dynamics of TPT. Thirdly, the decreased polarity (dielectric constant) inside the LLC phases slows down the ESPT dynamics of TPT.…”

“…52 Interestingly, dielectric constant inside LLC phases is lower (ethylene glycol type) as evidenced from steady state and literature results, 53 and the excited state lifetime of the conjugate base (Z*) is $6 ns inside LLC phases (s 3 in Table 1), which is long enough to re-encounter the solvent separated geminate ion-pair. Generally, geminate recombination process gives rise to a non-exponential long time decay tail in the time-resolved decay prole of the probe.…”