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[Display omitted] The attachment and dissociation of a proton from a water molecule and the proton transfers at solid–liquid interfaces play vital roles in numerous biological, chemical processes and for the development of sustainable functional materials for energy harvesting and conversion applications. Using first-principles computational methodologies, we investigated the protonated forms of polyhedral oligomeric silsesquioxane (POSS-H+) interacting with water clusters (W n , where n = 1–6) as a model to quantify the proton conducting and localization ability at solid–liquid interfaces. Successive addition of explicit water molecules to POSS-H+ shows that the assistance of at least three water molecules is required to dissociate the proton from POSS with the formation of an Eigen cation (H 9 O 4 +), whereas the presence of a fourth water molecule highly favors the formation of a Zundel ion (H 5 O 2 +). Reaction pathway and energy barrier analysis reveal that the formation of the Eigen cation requires significantly higher energy than the Zundel features. This confirms that the Zundel ion is destabilized and promptly converts in to Eigen ion at this interface. Moreover, we identified a Grotthuss-type mechanism for the proton transfer through a water chain close to the interface, where symmetrical and unsymmetrical arrangements of water molecules around H+ of protonated POSS-H+ are involved in the conduction of proton through water wires where successive Eigen-to-Zundel and Zundel-to-Eigen transformations are observed in quick succession. [ABSTRACT FROM AUTHOR]

Hypothesis Silanol groups at the silica–water interface determine not only the surface charge, but also have an important role in the binding of ions and biomolecules. As the pH is increased above pH 2, the silica surface develops a net negative charge primarily due to deprotonation of the silanol group. An improved understanding of the energetics and mechanisms of this fundamentally important process would further understanding of the relevant dynamics. Simulations Density Functional Theory ab initio molecular dynamics and geometry optimisations were used to investigate the mechanisms of surface neutralisation and charging in the presence of OH - and H 3 O + respectively. This charging mechanism has received little attention in the literature. Findings The protonation or deprotonation of isolated silanols in the presence of H 3 O + or OH - , respectively, was shown to be a highly rapid, exothermic reaction with no significant activation energy. This process occurred via a concerted motion of the protons through ‘water wires’. Geometry optimisations of large water clusters at the silica surface demonstrated proton transfer to the surface occurring via the rarely discussed ‘proton holes’ mechanism. This indicates that surface protonation is possible even when the hydronium ion is distant (at least 4 water molecules separation) from the surface. [ABSTRACT FROM AUTHOR]

Abstract: Water is clearly important for the functioning of Photosystem II (PSII). Apart from being the very substrate that needs to be transported in this water oxidation enzyme, water is also vital for the transport of protons to and from the catalytic center as well as other important co-factors and key residues in the enzyme. The latest crystal structural data of PSII have enabled detailed analyses of the location and possible function of water molecules in the enzyme. Significant progress has also been made recently in the investigation of channels and pathways through the protein complex. Through these studies, the mechanistic significance of water for PSII is becoming increasingly clear. An overview and discussion of key aspects of the current research on water in PSII is presented here. The role of water in three other systems (aquaporin, bacteriorhodopsin and cytochrome P450) is also outlined to illustrate further points concerning the central significance that water can have, and potential applications of these ideas for continued research on PSII. It is advocated that water be seen as an integral part of the protein and far from a mere solvent. [Copyright &y& Elsevier]

Abstract: 1H NMR was performed on the ceramic proton conductor (NaS)xGe(OH)4−x·yH2O for x=2, 3 and y~1–4 over the temperature range of −100°C to 400°C. NMR spectra, nuclear spin–lattice relaxation rates (R1), spin–spin relaxation rates (R2), and rotating frame relaxation rates (R1ρ) were obtained for both hydrated and dehydrated samples. It was found that the low temperature NMR spectra were consistent with simulated H2O lineshapes, and the presence of H3O+ at low temperature was not detected within the experimental uncertainty. Short- and long-range hydrogen motion occurred together, a signature of Grotthuss conduction mechanisms. The long range motion was a combination of H+ and H2O diffusion, with H2O motion limiting H+ dynamics as the onset temperature was approached. [Copyright &y& Elsevier]