Search

The recently observed temperature-dependent quasiphase transition of the single-file water chain confined within a carbon nanotube in experiments has been validated by the simple lattice theory and molecular dynamics simulations. It has been pointed out that the atomic charges in water models are important, yet how the values will affect the structural details and thermodynamic properties of the quasiphase transition has not been fully revealed. In this work, we perform orientational-biased replica exchange Monte Carlo simulations in the canonical ensemble to explore the effect of atomic charges in the SPC/E water model on the quasiphase transition of a single-file water chain. Based on the atomic charge values reported in literature, three distinct quasiphases are reproduced, comprising a fully hydrogen-bonded water chain at lower temperatures, a more ordered dipolar orientation along the tube axis at intermediate temperatures, and a completely disordered structure at higher temperatures. Then by increasing the atomic charge values, we find that the fragmentation of the entire water chain into shorter water segments, the orientational ordering of water dipoles along the tube axis, and the transition towards complete disorder are all inhibited. Consequently, the transition temperatures between three quasiphases have been shifted to higher temperatures. The thermodynamic analysis demonstrates that the increased atomic charge values enhance the hydrogen bonding between neighbouring water molecules also the electrostatic attraction within the water chain, leading to a longer water dipole correlation length even at higher temperatures. These findings highlight the vital role of atomic charges in water models also the electrostatic interaction in regulating the orientational ordering of water molecules under nanoconfinement., Comment: 14 pages and 7 figures in Main text, 5 figures in Appendix

The hydroxyl-terminated self-assembled monolayer (OH-SAM), as a surface resistant to protein adsorption, exhibits substantial potential in applications such as ship navigation and medical implants, and the appropriate strategies for designing anti-fouling surfaces are crucial. Here, we employ molecular dynamics simulations and alchemical free energy calculations to systematically analyze the factors influencing resistance to protein adsorption on the SAMs terminated with single or double OH groups at three packing densities ({\Sigma} = 2.0 nm-2, 4.5 nm-2, and 6.5 nm-2), respectively. For the first time, we observe that the compactness and order of interfacial water enhance its physical barrier effect, subsequently enhancing the resistance of SAM to protein adsorption. Notably, the weak spatial hindrance effect of SAM leads to the embedding of protein into SAM, resulting in a lack of resistance of SAM towards protein. Furthermore, the number of hydroxyl groups per unit area of double OH-terminated SAM at {\Sigma} = 6.5 nm-2 is approximately 2 to 3 times that of single OH-terminated SAM at {\Sigma} = 6.5 nm-2 and 4.5 nm-2, consequently yielding a weaker resistance of double OH-terminated SAM towards protein. Meanwhile, due to the structure of SAM itself, i.e., the formation of a nearly perfect ice-like hydrogen bond structure, the SAM exhibits the weakest resistance towards protein. This study will complement and improve the mechanism of OH-SAM resistance to protein adsorption, especially the traditional barrier effect of interfacial water.