arXiv subjects

Yuanyan Wu

Publications and source records attributed to Yuanyan Wu.

3 recordsLinked to original sources

arXiv2021

Unexpected Hydrophobicity on Self-Assembled Monolayers Terminated with Two Hydrophilic Hydroxyl Groups

Current major approaches to access surface hydrophobicity include directly introducing hydrophobic nonpolar groups/molecules into surface or elaborately fabricating surface roughness. Here, for the first time, molecular dynamics simulations show an unexpected hydrophobicity with a contact angle of $82^o$ on a flexible self-assembled monolayer terminated only with two hydrophilic OH groups ($(OH)_2\!-\!SAM$). This hydrophobicity is attributed to the formation of a hexagonal-ice-like H-bonding structure in the OH matrix of $(OH)_2\!-\!SAM$, which sharply reduces the hydrogen bonds between surface and water molecules above. The unique simple interface presented here offers a significant molecular-level platform for examining the bio-interfacial interactions ranging from biomolecules binding to cell adhesion.

physics.app-ph↗

arXiv2020

Remarkable antibacterial activity of reduced graphene oxide functionalized by copper ions

Despite long-term efforts for exploring antibacterial agents or drugs, it remains challenging how to potentiate antibacterial activity and meanwhile minimize toxicity hazards to the environment. Here, we experimentally show that the functionality of reduced graphene oxide (rGO) through copper ions displays selective antibacterial activity significantly stronger than that of rGO itself and no toxicity to mammalian cells. Remarkably, this antibacterial activity is two orders of magnitude greater than the activity of its surrounding copper ions. We demonstrate that the rGO is functionalized through the cation-$π$ interaction to massively adsorb copper ions to form a rGO-copper composite in solution and result in an extremely low concentration level of surrounding copper ions (less than ~0.5 $μM$). These copper ions on rGO are positively charged and strongly interact with negatively charged bacterial cells to selectively achieve antibacterial activity, while rGO exhibits the functionality to not only actuate rapid delivery of copper ions and massive assembly onto bacterial cells but also result in the valence shift in the copper ions from Cu$^{2+}$ into Cu$^{+}$ which greatly enhances the antibacterial activity. Notably, this functionality of rGO through cation-$π$ interaction with copper ions can similarly achieve algaecidal activity but does not exert cytotoxicity against neutrally charged mammalian cells. The remarkable selective antibacterial activity from the rGO functionality as well as the inherent broad-spectrum-antibacterial physical mechanism represents a significant step toward the development of a novel antibacterial material and reagent without environmental hazards for practical application.

physics.app-ph↗

arXiv2018

Water-phospholipid interactions at the interface of lipid membranes: comparison of different force fields

Water-phospholipid interactions at the lipid bilayer/water interfaces are of essential importance for the dynamics, stability and function of biological membrane, and are also strongly associated with numerous biological processes at the interfaces of lipid bilayers. Various force fields, such as the united-atom Berger force field, its two improved versions by Kukol and by Poger, and the all-atom Slipid force field developed recently, can be applied to simulating the structures of lipid bilayer, with their structural predictions in good agreement with experimental data. In this work, we show that despite the similarity in structural predictions of lipid bilayers, there are observable differences in formation of hydrogen bonds and the interaction energy profiles between water and phospholipid groups at the lipid bilayer/water interfaces, when four force fields for dipalmitoylphosphatidylcholine (DPPC) phospholipids are employed in molecular dynamics simulations. In particular, the Slipid force field yields more hydrogen bonds between water and phospholipids and more symmetrical interaction energy distributions for the two carboxylic groups on their respective acyl tails, compared to the Berger and its two improved force fields. These differences are mainly attributed to the different interfacial water distributions and ability to form hydrogen bonds between interfacial water and oxygen atoms of the DPPC lipids using different force fields. These results would be helpful in understanding the behaviors of water as well as its interaction with phospholipids at the lipid bilayer/water interfaces, and provide a guide for making the appropriate choice on the force field in simulations of lipid bilayers.

cond-mat.soft↗