Alignment Of Water Molecules Research Articles

Role of hydrophobic side chain in urea induced protein denaturation at interface

The molecular mechanism of denaturing ability of urea is still a subject of considerable debate due to two opposing mechanisms: direct and indirect. In the direct mechanism, urea directly disrupts hydrogen bonding and hydrophobic interactions within proteins. On the other hand, the indirect mechanism suggests that urea alters the properties of water and disrupts protein-protein interactions. Our aim is to unravel the denaturing mechanism of urea by studying its interaction with the side chain of octadecylphosphonic acid (ODPA)) as a mimicking surface of a protein. We employ vibrational sum frequency generation (VSFG) spectroscopy to examine the interaction between urea, the side chain of ODPA, and water molecules at the interface. Our findings suggest that urea interacts with the side chain of ODPA, effectively reducing the hydrophobic barriers provided by the long hydrophobic chain of the ODPA molecules for the water molecules at the interface. The interaction of the urea with the side chain of the ODPA molecules results in the alignment of water molecules, increasing their SFG intensity. Our findings indicate that the interaction of urea with the side chain plays a crucial role in governing the interaction between water and ODPA molecules. These outcomes help us understand the side chain's role in urea-induced protein denaturation at the interface.

Lateral growth of xenon hydrate films on mica

<abstract> <p>In this paper, we report an <italic>in situ</italic> optical microscopy study of lateral growth of xenon (Xe) hydrate thin films on mica at sub-zero temperatures. The interactions between a solid surface and water molecules can strongly affect the alignment of water molecules and induce ice-like ordered structures within the water layer at the water-surface interface. Mica was chosen as a model surface to study the surface effect of hydrophilic sheet silicates on the lateral growth of Xe hydrate films. Under the experimental conditions, the lateral growth of Xe hydrate films was measured to be at an average rapid rate of ~200 μm/s and 400 μm/s under two different pressures of Xe. Mass transfer estimation of the Xe-water system revealed that the increasing trend of lateral film growth rates followed the increase in the net mass flux and aqueous solubility of Xe. However, as the supercooling temperature increased, the trend of lateral film growth rates attained a plateau region where little change in the rate was observed. This unique feature in the lateral film growth trend, the fast lateral growth kinetics, and the short induction time for hydrate film growth hinted at the assistance of the mica surface to aid the lateral growth process of Xe hydrate films at low Xe mass flux and at a low degree of subcooling. A mechanism based on the reported structured water layer at the interface on mica was proposed to rationalize a postulated surface-promotional effect of mica on the nucleation and lateral growth kinetics of Xe hydrate films.</p> </abstract>

Affinity of Hydrated Protons at Intrinsic Water/Vapor Interface Revealed by Ion-Induced Water Alignment.

Protons at the water/vapor interface are relevant for atmospheric and environmental processes, yet characterizing their surface affinity on the quantitative level is still challenging. Here we utilize phase-sensitive sum-frequency vibrational spectroscopy to quantify the surface density of protons (or their hydronium form) at the intrinsic water/vapor interface through inspecting the surface-field-induced alignment of water molecules in the electrical double layer of ions. With hydrogen halides in water, the surface adsorption of protons is found to be independent of specific proton-halide anion interactions and to follow a constant adsorption free energy, ΔG ≈ -3.76 (±0.79) kJ/mol, corresponding to a partitioning coefficient of the surface with respect to bulk water by 3.3∼6.2, for bulk ion concentrations up to 0.3 M. Our spectroscopic study not only is of importance in atmospheric chemistry but also offers a microscopic-level basis to develop advanced quantum-mechanical models for molecular simulations.

Polarized Water Wires under Confinement in Chiral Channels.

The alignment of water molecules along chiral pores may activate proton/ion conduction along dipolar hydrophilic pathways. Here we show that a simple synthetic "T-channel" forms a directional pore with its carbonyl moieties solvated by chiral helical water wires. Atom-scale simulations and experimental crystallographic assays reveal a dynamical structure of water and electrolyte solutions (alkali metal chlorides) confined in these organic T-channels. Oscillations in the dipole orientation, which correspond to alternative ordering (dipole up-dipole down) of the water molecules with a period of about 4.2 Å (imposed by the distance between two successive carbonyl groups) are observed. When ions are added to the system, despite the strong Coulombic water/ion interaction, confined water remains significantly ordered in the T-channel and still exhibits surface-induced polarization. Cation permeation can be achieved through alternated hydration-dehydration occurring along strongly oriented water wires. The T-channel, which exhibits chirality with strong water orientation, provides an opportunity to unravel novel water-channel systems that share many interesting properties of biomolecular systems.

Structural and Transport Properties of an SPC/E Electrolyte in a Nanopore

Equilibrium (EMD) and nonequilibrium molecular dynamics (NEMD) simulations were conducted to investigate the effects of confinement on the structural and transport properties of an electrolyte in a nanopore. The extended simple point charge (SPC/E) model was used to model water molecules in a 0.5 M KCl electrolyte. The cylindrical nanopore was smooth, structureless, and hydrophobic with a radius that varied from 4.75 to 15.8 Å. Changes in energies and structures were observed as the nanopore radius varied. The ion−ion, ion−water, and water−water interaction energies, the ion−ion and ion−water pair distribution functions, the density profiles of H and O atoms, and the water orientation about the vertical axis and around an ion were calculated in the simulations. Because of confinement in the radial direction in a narrow pore, there was incomplete solvation of ions, evidenced by less negative ion−water energy and less alignment of water molecules with the field of the ion. With a stronger confinement, H-bonding decreased, whereas the external field had a stronger influence on the orientation of the water molecules. Both EMD and NEMD results showed a decrease of ionic conductivity with decreasing pore radius, but there was an appreciable discrepancy between the conductivities obtained by the two methods for the cases of smaller pore diameters.