Seeking Solvation: Exploring the Role of Protein Hydration in Silk Gelation

The mechanism by which arthropods (e.g., spiders and many insects) can produce silk fibres from an aqueous protein (fibroin) solution has remained elusive, despite much scientific investigation. In this work, we used several techniques to explore the role of a hydration shell bound to the fibroin in native silk feedstock (NSF) from Bombyx mori silkworms. Small angle X-ray and dynamic light scattering (SAXS and DLS) revealed a coil size (radius of gyration or hydrodynamic radius) around 12 nm, providing considerable scope for hydration. Aggregation in dilute aqueous solution was observed above 65 °C, matching the gelation temperature of more concentrated solutions and suggesting that the strength of interaction with the solvent (i.e., water) was the dominant factor. Infrared (IR) spectroscopy indicated decreasing hydration as the temperature was raised, with similar changes in hydration following gelation by freezing or heating. It was found that the solubility of fibroin in water or aqueous salt solutions could be described well by a relatively simple thermodynamic model for the stability of the protein hydration shell, which suggests that the affected water is enthalpically favoured but entropically penalised, due to its reduced (vibrational or translational) dynamics. Moreover, while the majority of this investigation used fibroin from B. mori, comparisons with published work on silk proteins from other silkworms and spiders, globular proteins and peptide model systems suggest that our findings may be of much wider significance.

Dissociation and recombination in the electrolyte flow model

We propose a one-dimensional model for the dilute aqueous solution of NaCl which is treated as an incompressible fluid placed in the external electric field. This model is based on the Poisson-Nernst-Planck system of equations, which also contains the constant flow velocity as a parameter and considers the dissociation and the recombination of ions. We study the steady-state solution analytically and prove that it is a stable equilibrium. Analyzing the numerical solutions, we demonstrate the importance of dissociation and recombination for the physical meaningfulness of the model.

A model of the growth of hydrogen bubbles in the electrolysis of water

The growth of attached bubbles during the electrochemical evolution of hydrogen at a horizontal cathode at the base of a quiescent, dilute aqueous solution is analysed using a simple model of the process that includes the Butler–Volmer reaction model, the diffusion and migration of electroactive species and a symmetry condition that approximately accounts for the presence of periodically spaced bubbles on the electrode surface. The diffusion controlled growth of a bubble approximately follows a $t^{1/2}$ law when the spacing of the bubbles on the electrode is large, departing slightly from it due to the non-uniformity of the concentration of dissolved hydrogen in the supersaturated solution into which the bubble grows, and approaches a $t^{1/3}$ law when the spacing decreases. The space- and time-averaged current density increases exponentially with the applied voltage for an alkaline solution when the consumption of water in the reaction is not taken into account. For an acidic solution, the average current density saturates to a transport limited value that depends on bubble spacing. For a given voltage, the presence of attached bubbles increases the average current density due to the decrease of the concentration overpotential caused by the bubbles. The spacing of the bubbles on the electrode surface decreases when the voltage increases if the maximum supersaturation at the electrode is imposed to be constant. The result suggests that coalescence of attached bubbles will occur above a certain voltage.

Two-dimensional monolayer salt nanostructures can spontaneously aggregate rather than dissolve in dilute aqueous solutions

It is well known that NaCl salt crystals can easily dissolve in dilute aqueous solutions at room temperature. Herein, we reported the first computational evidence of a novel salt nucleation behavior at room temperature, i.e., the spontaneous formation of two-dimensional (2D) alkali chloride crystalline/non-crystalline nanostructures in dilute aqueous solution under nanoscale confinement. Microsecond-scale classical molecular dynamics (MD) simulations showed that NaCl or LiCl, initially fully dissolved in confined water, can spontaneously nucleate into 2D monolayer nanostructures with either ordered or disordered morphologies. Notably, the NaCl nanostructures exhibited a 2D crystalline square-unit pattern, whereas the LiCl nanostructures adopted non-crystalline 2D hexagonal ring and/or zigzag chain patterns. These structural patterns appeared to be quite generic, regardless of the water and ion models used in the MD simulations. The generic patterns formed by 2D monolayer NaCl and LiCl nanostructures were also confirmed by ab initio MD simulations. The formation of 2D salt structures in dilute aqueous solution at room temperature is counterintuitive. Free energy calculations indicated that the unexpected spontaneous salt nucleation behavior can be attributed to the nanoscale confinement and strongly compressed hydration shells of ions.

Preparation of Menthol-Based Hydrophobic Deep Eutectic Solvents for Extraction of Triphenylmethane Dyes: Quantitative Properties and Extraction Mechanism

A series of natural, environmentally friendly and low-cost menthol-based hydrophobic deep eutectic solvents (DES) were synthesized to extract and concentrate solutes from dilute aqueous solution, especially triphenylmethane (TPM) dye micropollutants....

Efficient capturing of hydrogen peroxide in dilute aqueous solution by co-crystallisation with amino acids

Hydrogen peroxide (H2O2) in dilute aqueous solution can be efficiently captured by co-crystallisation with enantiomeric and racemic amino acids as evidenced by colourimetric titration and the single crystal X-ray structural...