Graphene Oxide Selectively Enhances Thermostability of Trypsin.

In the past few years, graphene and its derivative, graphene oxide (GO), have been extensively studied for their applications in biotechnology. In our previous work, we reported certain PEGylated GOs (GO-PEGs) can selectively promote trypsin activity and enhance its thermostability. To further explore this, here we synthesized a series of GO-PEGs with varying PEGylation degrees. Enzymatic activity assay shows that both GO and GO-PEGs can protect trypsin, but not chymotrypsin, from thermal denaturation at high temperature. Surprisingly, the lower the PEGylation degree, the better the protection, and GO as well as the GO-PEG with the lowest PEGylation degree show the highest protection efficiency (∼70% retained activity at 70 °C). Fluorescence spectroscopy analysis shows that GO/GO-PEGs have strong interactions with trypsin. Molecular Dynamics (MD) simulation results reveal that trypsin is adsorbed onto the surface of GO through its cationic residues and hydrophilic residues. Different from chymotrypsin adsorbed on GO, the active site of trypsin is covered by GO. MD simulation at high temperature shows that, through such interaction with GO, trypsin's active site is therefore stabilized and protected by GO. Our work not only illustrates the promising potential of GO/GO-PEGs as efficient, selective modulators for trypsin, but also provides the interaction mechanism of GO with specific proteins at the nano-bio interface.

Concentration-Controlled Reversible Phase Transitions in Self-Assembled Monolayers on HOPG Surfaces.

Rational control of molecular ordering on surfaces and interfaces is vital in supramolecular chemistry and nanoscience. Here, a systematic scanning tunneling microscopy (STM) study for controlling the self-assembly behavior of alkoxylated benzene (B-OC(n)) molecules on a HOPG surface is presented. Three different phases have been observed and, of great importance, they can transform to each other by modifying the solute concentration. Further studies, particularly in situ diluting and concentrating experiments, demonstrate that the transitions among the three phases are highly controllable and reversible, and are driven thermodynamically. In addition, it is found that concentration-controlled reversible phase transitions are general for different chain lengths of B-OC(n) molecules. Such controllable and reversible phase transitions may have potential applications in the building of desirable functional organic thin films and provide a new understanding in thermodynamically driven self-assembly of organic molecules on surfaces and interfaces.

The mechanism of proton translocation in respiratory complex I from molecular dynamics.

Respiratory complex I, the biggest enzyme of respiratory chain, plays a key role in energy production by the mitochondrial respiratory chain and has been implicated in many human neurodegenerative diseases. Recently, the crystal structure of respiratory complex I is reported. We perform 50 ns molecular dynamics simulations on the membrane domain of respiratory complex I under two hypothetical states (oxidized state and reduced state). We find that the density of water molecules in the trans-membrane domain under reduced state is bigger than that under oxidized state. The connecting elements (helix HL and ß-hairpins-helix element) fluctuate stronger under reduced state than that under oxidized state, causing more internal water molecules and facilitating the proton conduction. The conformational changes of helix HL and the crucial charged residue Glu in TM5 play key roles in the mechanism of proton translocation. Our results illustrate the dynamic behavior and the potential mechanism of respiratory complex I, which provides the structural basis for drug design of respiratory complex I.

Novel polymer-free iridescent lamellar hydrogel for two-dimensional confined growth of ultrathin gold membranes.

Hydrogels are generally thought to be formed by nano- to micrometre-scale fibres or polymer chains, either physically branched or entangled with each other to trap water. Although there are also anisotropic hydrogels with apparently ordered structures, they are essentially polymer fibre/discrete polymer chains-based network without exception. Here we present a type of polymer-free anisotropic lamellar hydrogels composed of 100-nm-thick water layers sandwiched by two bilayer membranes of a self-assembled nonionic surfactant, hexadecylglyceryl maleate. The hydrogels appear iridescent as a result of Bragg's reflection of visible light from the periodic lamellar plane. The particular lamellar hydrogel with extremely wide water spacing was used as a soft two-dimensional template to synthesize single-crystalline nanosheets in the confined two-dimensional space. As a consequence, flexible, ultrathin and large area single-crystalline gold membranes with atomically flat surface were produced in the hydrogel. The optical and electrical properties were detected on a single gold membrane.

Light emission in water-containing cocrystals: the influence of water molecules on the fluorescence properties of a Schiff-base molecule.

In the presence or absence of water, a Schiff-base compound, 4-amino-3-(2-(2-hydroxybenzylidene)hydrazinyl)-1H-1,2,4-triazole-5(4H)-thione (HATT), forms different crystalline states (HATT, HATT·2H2O, and a lamellar structure, m-HATT·nH2O), which show different luminescence emission properties. Herein, we investigate the emission of HATT and the role of water molecules. A water molecule, which acts as both a hydrogen-bond acceptor and -donor, enlarges the distance between adjacent HATT molecules and hinders non-radiative decay pathways.