Changes in the hydration structure of imidazole upon protonation: Neutron scattering and molecular simulations

Stretchable Self-Healing Plastic Polyurethane with Super-High Modulus by Local Phase-Lock Strategy

In this work, a multiblock polyurethane (PU-Im) consisting of polyether and polyurethane segments with imidazole dangling groups is demonstrated, which can further coordinate with Ni²⁺ . By controlling the ligand content and metal-ligand stoichiometry ratio, PU-Im-Ni complex with vastly different mechanical behavior can be obtained. The elastomer PU-2Im-Ni has extraordinary mechanical strength (61MPa) and excellent toughness (420 MJ m^-3 ), but the plastic PU-4Im-Ni exhibits super-high modulus (515 MPa), strength (63 MPa), and good stretchability (≈800%). The metal-ligand interaction between polyurethane segments and Ni²⁺ is proved by Raman spectra, dynamic mechanical analysis (DMA), and transmission electron microscopy (TEM). The polyurethane segments domain formed by microphase separation is dynamically "locked" by Ni²⁺ coordinated with imidazole, revealing a local phase-lock effect. The phase-locking hard domains reinforce the PU-Im-Ni complex and maintain stimuli-responsive self-healing ability, while the free polyether segments provide stretchability. Primarily, the water environment with plasticization effect serves as an effective and eco-friendly self-healing approach for PU-Im-Ni plastic. With the excellent mechanical performance, thermal/aquatic self-healing ability, and unique damping properties, the PU-Im-Ni complexes show potential applications in self-healing engineering plastic and cushion protection fields.

Imidazole-amino acids. Conformational switch under tautomer and pH change

Replacement of the main chain peptide bond by imidazole ring seems to be a promising tool for the peptide-based drug design, due to the specific prototropic tautomeric as well as amphoteric properties. In this study, we present that both tautomer and pH change can cause a conformational switch of the studied residues of alanine (1-4) and dehydroalanine (5-8) with the C-terminal peptide group replaced by imidazole. The DFT methods are applied and an environment of increasing polarity is simulated. The conformational maps (Ramachandram diagrams) are presented and the stability of possible conformations is discussed. The neutral forms, tautomers τ (1) and π (2), adapt the conformations αRτ (φ, ψ = - 75°, - 114°) and C7eq (φ, ψ = - 75°, 66°), respectively. Their torsion angles ψ differ by about 180°, which results in a considerable impact on the peptide chain conformation. The cation form (3) adapts both these conformations, whereas the anion analogue (4) prefers the conformations C5 (φ, ψ = - 165°, - 178°) and β2 (φ, ψ ~ - 165°, - 3°). Dehydroamino acid analogues, the tautomers τ (5) and π (6) as well as the anion form (8), have a strong tendency toward the conformations β2 (φ, ψ = - 179°, 0°) and C5 (φ, ψ = - 180°, 180°). The preferences of the protonated imidazolium form (7) depend on the environment. The imidazole ring, acting as a donor or acceptor of the hydrogen bonds created within the studied residues, has a profound effect on the type of conformation.

Facile Room-Temperature Synthesis of Cerium Carbonate and Cerium Oxide Nano- and Microparticles Using 1,1'-Carbonyldiimidazole and Imidazole in a Nonaqueous Solvent

Ceria nanoparticles (CeONPs) are versatile materials due to their unique catalytic properties, and cerium carbonate particles (CeCbPs) have been widely used as precursors for cerium oxide due to their ease of production. Urea is a widely used precipitant and a source of carbonate ions for the synthesis of CeONPs and CeCbPs, and the reaction temperature is important for controlling the rate of urea decomposition. However, the precise control of the temperature is often difficult, especially in large-scale reactions. Herein, we propose a homogeneous precipitation method that uses 1,1'-carbonyldiimidazole (CDI) and imidazole in acetone without heating. The decomposition rate of CDI can be controlled by the amount of water in the reaction mixture. In the synthesis of CeCbPs, unique particle morphologies of plate-, flying-saucer-, and macaron-like shapes and a wide range of sizes from 180 nm to 13 μm can be achieved by adjusting the amount of CDI, imidazole, and water in the reaction. These CeCbPs are transformed into ceria particles by calcination while maintaining their characteristic morphology. Moreover, the direct synthesis of 130 nm spherical CeONPs was possible by decreasing the amount of CDI in the reaction and the mixing time. These nanoparticles exhibited higher production efficiency and superior reactive oxygen species (ROS) scavenging properties compared to the other CeONPs obtained from calcination. These results demonstrate a novel method using CDI and imidazole in the synthesis of CeONPs and CeCbPs without the aid of a heating process, which may be useful in the large-scale synthesis and application of CeO nanomaterials.

Combined DFT and MD simulation studies of protein stability on imidazolium–water (ImH+Wn) clusters with aromatic amino acids

The hydrated clusters of protonated imidazole (ImH⁺) can induce protein denaturation through various kinds of monovalent interactions such as cation···π (stacking), N–H⋯π (T-shaped) and water-mediated O–H⋯O H-bonds.

Hydrophilic and hydrophobic interactions in concentrated aqueous imidazole solutions: a neutron diffraction and total X-ray scattering study

A study of 5 M aqueous imidazole solutions combining neutron and X-ray diffraction with EPSR simulations shows dominance of hydrogen-bonding between imidazole and water and negligible hydrogen-bonding between imidazole molecules.

Oxalic Acid Adsorption on Rutile: Molecular Dynamics and ab Initio Calculations

Detailed analysis of the adsorption of oxalic acid ions, that is, oxalate and hydrogenoxalate, on the rutile (110) surface was carried out using molecular dynamics augmented by free energy calculations and supported by ab initio calculations. The predicted adsorption on perfect nonhydroxylated and hydroxylated surfaces with surface charge density from neutral to +0.208 C/m² corresponding to pH values of about 6 and 3.7, respectively, agrees with experimental adsorption data and charge-distribution multisite ion complexation model predictions obtained using the most favorable surface complexes identified in our simulations. We found that outer-sphere complexes are the most favorable, owing to strong hydrogen binding of oxalic acid ions with surface hydroxyls and physisorbed water. The monodentate complex, the most stable among inner-sphere complexes, was about 15 kJ/mol higher in energy, but separated by a large energy barrier. Other inner-sphere complexes, including some previously suggested in the literature as likely adsorption structures such as bidentate and chelate complexes, were found to be unstable both by classical and by ab initio modeling. Both the surfaces and (hydrogen)oxalate ions were modeled using charges scaled to 75% of the nominal values in accord with the electronic continuum theory and our earlier parameterization of (hydrogen)oxalate ions, which showed that nominal charges exaggerate ion-water interactions.

Modeling of solid–liquid interfaces using scaled charges: rutile (110) surfaces

The first application of the electronic continuum correction model with scaled charges to molecular dynamics simulations of solid–liquid interfaces.