Does Confinement Modify Preferential Solvation and H-Bond Fluctuation Dynamics? A Molecular Level Investigation through Simulations of a Bulk and Confined Three-Component Mixture

Abstract

Exploring the local environment around a dissolved solute in a bulk aqueous solution of alcohol and assessing the impact of confinement on the solvation structure is an important topic yet is much less studied. Such a study is important because it can provide critical information regarding the miscibility of an amphiphilic drug after delivery at a designated nanoscopic site and the subsequent release. The present molecular dynamics simulation study reports an in-depth investigation of the composition-dependent solvation structure around a dissolved hydrophobic solute, coumarin 153 (C153), in ambient binary mixtures of methanol and water in both bulk and under confinement. The confinement is a spherical sodium bis­(2-ethylhexyl) sulfosuccinate (AOT) reverse micelle with a diameter of 55 Å. Inter- and intraspecies H-bond fluctuation dynamics have been monitored and compared with those from the corresponding bulk binary mixtures. A systematic comparison of both solvation structure and H-bond dynamics between confined and bulk binary mixtures reveals modulation of both preferential solvation and H-bond relaxation times inside a nanoscopic environment. More specifically, confinement accentuates the preferential solvation phenomenon and facilitates di-mixing of mixture components. In addition, the present study reveals that the tetrahedral H-bond network of neat liquid water becomes severely affected upon addition of methanol, which becomes further distorted under confinement. Confinement severely affects the interspecies hydrogen bonds and makes the corresponding continuous hydrogen bonds much shorter-lived. Interestingly, structural hydrogen bond relaxation timescales become longer in confined binary mixtures than those in bulk binary mixtures.

Facile Preparation of Drug-Releasing Supramolecular Hydrogel for Preventing Postoperative Peritoneal Adhesion

“…Notably, the reversible H-bonds that formed between PVA and QUE in the hydrogel may cause some of the drug molecules to be released, with the hydrogel three-dimensional network limiting the release rate. − In addition, hydrophobic drugs that are not involved in cross-linking in the gel should also be considered. Drug release behavior mainly includes physical diffusion and connection or dynamic cross-linking of polymers.…”

The Role of Hydrogen Bonding in the Preferential Solvation of 5-Aminoquinoline in Binary Solvent Mixtures

“…The study of solvation dynamics has been an area of intense activity over the last few decades and has provided insight into solute–solvent interactions at the molecular level. This field has been enriched by rigorous theoretical calculations and simulations − on one hand and state-of-the-art spectroscopic experiments − on the other. Synergy between experiments and theory has provided deep insight into the process. , Time-dependent fluorescence Stokes shift (TDFSS) is the most popular experimental technique in this context, ,− which makes use of fluorescent probes like coumarin dyes that are significantly more dipolar in their excited state than in their ground state. , TDFSS has been used, for example, to study protein–surface interactions, biological water dynamics, and hydrogen bonding networks .…”

Dynamical Anomaly of Aqueous Amphiphilic Solutions: Connection to Solution H-Bond Fluctuation Dynamics?

“…Note that these structural H-bond relaxation times (⟨τ C HB ⟩) are easily experimentally accessible, unlike continuous H-bond relaxation times (⟨τ S HB ⟩). This ⟨τ C HB ⟩ are known 79 , 80 , 87 , 88 , 98 − 100 to be strongly coupled to the translational diffusion of H-bonded molecules. Significant fluctuations in structural H-bond relaxation of water–water and TBA–water H bonds at x TBA ∼0.15 have been found where anomalies have been reported in experiments for various aqueous amphiphilic solutions.…”

“…Our earlier works have already revealed substantial disruption of water tetrahedrality in the presence of simple alcohol like methanol in bulk aqueous binary mixtures and for confined water molecules near a charged interface. 87 , 88 …”

“…This has been reported already in a number of simulation studies that involve aqueous binary mixtures of alcohols. 14 , 87 What has not been examined in those studies, however, is the rate of change of water tetrahedrality as a function of the alcohol mole fraction. This composition-dependent slope, , is shown in the inset of Figure 5 , which clearly indicates appreciable changes in the water tetrahedrality at two TBA mole fractions: one is around 0.04 and the other is ∼0.12.…”