Hydration of Hydroxyl and Amino Groups Examined by Molecular Dynamics and Neutron Scattering

Low vaporization enthalpy of modified chitosan hydrogel for high performance solar evaporator

The high vaporization enthalpy of water attributed to the strong hydrogen bonds between water molecules is limiting the performance of solar evaporators. This work demonstrates a deliberate attempt to significantly reduce the vaporization enthalpy of water through the introduction of weak water-amine hydrogen bond interactions in hydrogel evaporators. In this article, bio-based chitosan-agarose/multiwalled carbon nanotube hydrogel film evaporators (CAMFEs) exhibit larger vaporization enthalpy reduction with the presence of primary amine groups in chitosan. An interplay between vaporization enthalpy reduction and water diffusivity leads to an optimal ratio of chitosan to agarose = 7:1 (CAMFE7) showing an impressive evaporation rate of 4.13 kg m-2 h-1 under 1 sun irradiation. CAMFE7 also exhibits excellent salt resistance, with a stable water evaporation rate, using brine water of up to 10 % salinity under continuous 1 sun irradiation. The high mechanical robustness together with its scalability makes CAMFE7 a highly promising material for practical drinking water production.

Efficient Strategy for U(VI) Photoreduction: Simultaneous Construction of U(VI) Confinement Sites and Water Oxidation Sites

Reduction of hexavalent uranium [U(VI)] by the photocatalytic method opens up a novel way to promote the selectivity, kinetics, and capacity during uranium removal, where organic molecules act as the sacrificial agents. However, the addition of sacrificial agents can cause a secondary environmental pollution and increase the cost. Here, a UiO-66-based photocatalyst (denoted as MnO_x/NH₂-UiO-66) simultaneously with efficient U(VI) confinement sites and water oxidation sites was successfully developed, achieving excellent U(VI) removal without sacrificial agents. In MnO_x/NH₂-UiO-66, the amino groups served as efficient U(VI) confinement sites and further decreased the U(VI) reduction potential. Besides, MnO_x nanoparticles separated the photogenerated electron-hole pairs and provided water oxidation sites. The U(VI) confinement sites and water oxidation sites jointly promoted the U(VI) photoreduction performance of MnO_x/NH₂-UiO-66, resulting in the removal ratio of MnO_x/NH₂-UiO-66 for U(VI) achieving 97.8% in 2 h without hole sacrifice agents. This work not only provides an effective UiO-66-based photocatalyst but also offers a strategy for effective U(VI) photoreduction.

On the mechanism of predominant urea formation from thermal degradation of CO2-loaded aqueous ethylenediamine

This study attempts to explain the well-known experimental observation that 1,3-bis(2-aminoethyl)urea (urea) is preferentially formed over the other major product, 2-imidazolidone (IZD), from thermal degradation of aqueous ethylenediamine (EDA) during the CO₂ capture process. This is in direct contrast to the case of monoethanolamine (MEA), preferentially forming oxazolidinone (OZD), rather than urea, which undergoes further reactions leading to more stable products. Given their similar molecular structures, the different preferred degradation pathways of EDA and MEA impose an intriguing question regarding the underlying mechanism responsible for the distinct difference. Thermal degradation of both EDA and MEA tends to proceed mainly via formation of an isocyanate intermediate that may further undergo either cyclization to IZD (or OZD) or a reaction with EDA (or MEA) forming urea. For the EDA case, our first-principles simulations clearly demonstrate that the urea formation reaction is kinetically more, but thermodynamically less, favorable than the cyclization reaction; the opposite is true for the MEA case. Our further analysis shows that EDA-isocyanate is less prone to cyclization than MEA-isocyanate, which in turn allows for more facile urea formation. The reconfiguration dynamics of isocyanate is found to be governed by the dynamic nature of the interaction between its terminal group and surrounding solvent molecules. Our work highlights the importance of kinetic effects associated with the local structure and dynamics of solvent molecules around the intermediates that may significantly alter the degradation process of amine solvents.

Aqueous Lubrication with the Molecularly Confined Films of Silicone-Based Amphiphilic Block Copolymer Aggregates

The confined film structures and tribological properties of the dilute aqueous solution of a silicone-based amphiphilic block copolymer, bis-isobutyl poly(ethylene glycol) (PEG)-14/amodimethicone (BIPA) copolymer, between mica surfaces were investigated. The BIPA copolymer existed as positively charged water-soluble aggregates in the solution. The adsorption behavior of the BIPA copolymer aggregates on a mica surface from solution was studied using an atomic force microscope (AFM); the result showed the immediate formation of a uniform adsorbed BIPA copolymer layer, followed by the gradual deposition of BIPA aggregates on the top of the adsorbed layer. Friction measurements were carried out using the surface forces apparatus (SFA) for the confined films of BIPA copolymer solution between mica surfaces, which revealed two different sliding film structures depending on the elapsed time after surface preparation. The sliding film consisting of two adsorbed BIPA copolymer layers was obtained for a relatively short elapsed time (not longer than 3 h), which had an extremely low friction coefficient μ (of the order of 10^-5). The sliding film on the following day (elapsed time of approximately 24 h) had the structure of a deposited/kinetically trapped BIPA aggregate layer confined between the opposing adsorbed layers, and the μ values were within the range from 10^-4 to 10^-3. Our results suggest that the different elapsed time ranges and resulting absence or presence of the intervening layer of trapped aggregates between the absorbed layers determine the tribological properties of the confined films. Molecular friction mechanisms are discussed for the two sliding structures, which give insight into using amphiphilic block copolymer aggregates for a new class of aqueous lubrication system to design extremely low friction interfaces.

Ice-Nucleating and Antifreeze Proteins Recognize Ice through a Diversity of Anchored Clathrate and Ice-like Motifs

Cold-adapted organisms produce antifreeze and ice-nucleating proteins to prevent and promote ice formation. The crystal structure of hyperactive bacterial antifreeze protein (AFP) MpAFP suggests that this protein binds ice through an anchored clathrate motif. It is not known whether other hyperactive AFPs and ice-nucleating proteins (INPs) use the same motif to recognize or nucleate ice. Here we use molecular simulations to elucidate the ice-binding motifs of hyperactive insect AFPs and a model INP of Pseudomonas syringae. We find that insect AFPs recognize ice through anchored clathrate motifs distinct from that of MpAFP. By performing simulations of ice nucleation by PsINP, we identify two distinct ice-binding sites on opposite sides of the β-helix. The ice-nucleating sequences identified in the simulations agree with those previously proposed for the closely related INP of Pseudomonas borealis based on the structure of the protein. The simulations indicate that these sites have comparable ice-nucleating efficiency, but distinct binding motifs, controlled by the amino acid sequence: one is an anchored clathrate and the other ice-like. We conclude that anchored clathrate and ice-like motifs can be equally effective for binding proteins to ice and promoting ice nucleation.

On the structure of prilocaine in aqueous and amphiphilic solutions

The solvation of prilocaine has been investigated in pure water and in amphiphilic solutions using a combination of neutron diffraction and simulations.

Design, discovery, modelling, synthesis, and biological evaluation of novel and small, low toxicity s-triazine derivatives as HIV-1 non-nucleoside reverse transcriptase inhibitors

A set of top-ranked compounds from a multi-objective in silico screen was experimentally tested for toxicity and the ability to inhibit the activity of HIV-1 reverse transcriptase (RT) in cell-free assay and in cell-based assay using HIV-1 based virus-like particles. Detailed analysis of a commercial sample that indicated specific inhibition of HIV-1 reverse transcription revealed that a minor component that was structurally similar to that of the main compound was responsible for the strongest inhibition. As a result, novel s-triazine derivatives were proposed, modelled, discovered, and synthesised, and their antiviral activity and cellular toxicity were tested. Compounds 18a and 18b were found to be efficient HIV-1 RT inhibitors, with an IC50 of 5.6±1.1μM and 0.16±0.05μM in a cell-based assay using infectious HIV-1, respectively. Compound 18b also had no detectable toxicity for different human cell lines. Their binding mode and interactions with the RT suggest that there was strong and adaptable binding in a tight (NNRTI) hydrophobic pocket. In summary, this iterative study produced structural clues and led to a group of non-toxic, novel compounds to inhibit HIV-RT with up to nanomolar potency.

Atomic scale insights into urea–peptide interactions in solution

Investigations on the β-turn forming peptide, GPG, suggest that urea denatures proteins by replacing water molecules and subsequently weakening the peptide bonds as a possible mechanism of protein denaturation by urea.

On the atomic structure of cocaine in solution

A combination of neutron diffraction and computation has been used to investigate the atomic scale structure of cocaine in aqueous solutions.