Perturbative vibration of the coupled hydrogen-bond (O:H-O) in water

Hydrogen Bonding Polarization Strengthening the Peptide-Based Hydrogels

Peptide-based hydrogels form a kind of promising material broadly used in biomedicine and biotechnology. However, the correlation between their hydrogen bonding dynamics and mechanical properties remains uncertain. In this study, we found that the adoption of β-sheet and α-helix secondary structures by ECF-5 and GFF-5 peptides, respectively, could further form fiber networks to immobilize water molecules into hydrogels. Increasing the peptide concentrations improvethe solidity of these hydrogels, as evidenced by their higher storage modulus (G') values determined by a frequency sweep. Raman and FTIR spectroscopies probed a blue shift in the O-D stretching vibration in both ECF-5 and GFF-5 hydrogels, indicating the D-O bond contraction and stiffness gain. This finding provides valuable insight and offers an efficient means of modulating the mechanism of mechanical properties.

Local and global expansivity in water

The supra-molecular structure of a liquid is strongly connected to its dynamics, which in turn control macroscopic properties such as viscosity. Consequently, detailed knowledge about how this structure changes with temperature is essential to understand the thermal evolution of the dynamics ranging from the liquid to the glass. Here, we combine infrared spectroscopy (IR) measurements of the hydrogen (H) bond stretching vibration of water with molecular dynamics simulations and employ a quantitative analysis to extract the inter-molecular H-bond length in a wide temperature range of the liquid. The extracted expansivity of this H-bond differs strongly from that of the average nearest neighbor distance of oxygen atoms obtained through a common conversion of mass density. However, both properties can be connected through a simple model based on a random loose packing of spheres with a variable coordination number, which demonstrates the relevance of supra-molecular arrangement. Furthermore, the exclusion of the expansivity of the inter-molecular H-bonds reveals that the most compact molecular arrangement is formed in the range of ∼316-331K (i.e., above the density maximum) close to the temperature of several pressure-related anomalies, which indicates a characteristic point in the supra-molecular arrangement. These results confirm our earlier approach to deduce inter-molecular H-bond lengths via IR in polyalcohols [Gabriel et al. J. Chem. Phys. 154, 024503 (2021)] quantitatively and open a new alley to investigate the role of inter-molecular expansion as a precursor of molecular fluctuations on a bond-specific level.

Interfacial Phenomena in Nanostructured Systems with Various Materials

Interfacial phenomena linked to the behavior of bound water, organic solvents (co-sorbates, dispersion media), hydrogen, methane, acids/bases, and salts bound to various silicas, polymers, and carbon materials were analyzed vs. temperature and concentrations using 1 H NMR spectroscopy, differential scanning calorimetry (DSC) and other methods. The material characteristics were studied using microscopy, infrared spectroscopy (IR), small angle X-ray scattering (SAXS), and nitrogen adsorption. Confined space effects (CSE) result in enhanced freezing point depression (FPD) and stronger diminution of solvent activity and colligative properties of liquid mixtures in narrower pores. Short hydrophobic functionalities (≡Si-CH3 , =Si(CH3 )2 ) at a silica surface and the presence of nanopores result in differentiation of bound water into weakly (WAW, δH =0.2-2.0 ppm) and strongly (SAW, δH =4-6 ppm) associated waters of smaller solvent activity in smaller clusters located in narrower pores and unfrozen below a bulk freezing point. These effects are enhanced in hydrophobic dispersion media. Hydrophobic liquids could displace bound water into narrower pores inaccessible for their molecules larger than water and/or into broader pores to reduce contact area between immiscible liquids. The observed phenomena depend on sorbent/sorbate kinds and play an important role on practical applications of various sorbents.