Qingye Lu

Adhesion of mussel foot proteins to different substrate surfaces.

Mussel foot proteins (mfps) have been investigated as a source of inspiration for the design of underwater coatings and adhesives. Recent analysis of various mfps by a surface forces apparatus (SFA) revealed that mfp-1 functions as a coating, whereas mfp-3 and mfp-5 resemble adhesive primers on mica surfaces. To further refine and elaborate the surface properties of mfps, the force–distance profiles of the interactions between thin mfp (i.e. mfp-1, mfp-3 or mfp-5) films and four different surface chemistries, namely mica, silicon dioxide, polymethylmethacrylate and polystyrene, were measured by an SFA. The results indicate that the adhesion was exquisitely dependent on the mfp tested, the substrate surface chemistry and the contact time. Such studies are essential for understanding the adhesive versatility of mfps and related/similar adhesion proteins, and for translating this versatility into a new generation of coatings and (including in vivo) adhesive materials.

Understanding the molecular interactions of lipopolysaccharides during E. coli initial adhesion with a surface forces apparatus

Lipopolysaccharides (LPS) occupy 75% of the surface of Gram-negative bacteria. This work investigates the role of LPS during bacterial adhesion to solid substrates. Two model lipopolysaccharides, LPS1 and LPS2, were examined. LPS1 from E. coliJM109 has a full LPS chain consisting of lipid A, core polysaccharides, and O-antigen; LPS2 from K12 has a truncated chain without the O-antigen portion. Interactions between an LPS layer prealigned on polystyrene (PS) and three different substrates (mica, PS-coated mica, and 3-aminopropyltriethoxysilane (APTES)-functionalized mica) in 0.1 M NaCl were measured using a surface forces apparatus (SFA). The PS-supported LPS showed strong adhesion to APTES, weak adhesion to mica, and strong repulsion to PS substrate. Electrostatic interaction and steric effects contribute significantly to the interactions between the LPS and different substrates. The presence of long O-antigen chains in LPS1 reduces bacterial adhesion to various substrates because of the presence of an energetic barrier during the adsorption process, which is caused by the affinity of hydrophilic neutral O-antigen chains to water and the steric entropic barrier of LPS chains on the cell membrane surface.

Adhesion mechanism in a DOPA-deficient foot protein from green mussels

The holdfast or byssus of Asian green mussels, Perna viridis, contains a foot protein, pvfp-1, that differs in two respects from all other known adhesive mussel foot proteins (mfp): (1) instead of the hallmark L-3,4-dihydroxyphenylalanine (DOPA) residues in mfp-1, for example, pvfp-1 contains C(2)-mannosyl-7-hydroxytryptophan (Man7OHTrp). (2) In addition, pvfp-1 chains are not monomeric like mfp-1 but trimerized by collagen and coiled-coil domains near the carboxy terminus after a typical domain of tandemly repeated decapeptides. Here, the contribution of these peculiarities to adhesion was examined using a surface forces apparatus (SFA). Unlike previously studied mfp-1s, pvfp-1 showed significant adhesion to mica and, in symmetric pvfp-1 films, substantial cohesive interactions were present at pH 5.5. The role of Man7OHTrp in adhesion is not clear, and a DOPA-like role for Man7OHTrp in metal complexation (e.g., Cu(2+), Fe(3+)) was not observed. Instead, cation-π interactions with low desolvation penalty between Man7OHTrp and lysyl side chains and conformational changes (raveling and unraveling of collagen helix and coiled-coil domains) are the best explanations for the strong adhesion between pvfp-1 monomolecular films. The strong adhesion mechanism induced by cation-π interactions and conformational changes in pvfp-1 provides new insights for the development of biomimetic underwater adhesives.

In Vivo Residue‐Specific Dopa‐Incorporated Engineered Mussel Bioglue with Enhanced Adhesion and Water Resistance

Misaminoacylation of 3,4-dihydroxyphenylalanine (Dopa) molecules to tRNA(Tyr) by endogenous tyrosyl-tRNA synthetase allowed the quantitative replacement of tyrosine residues with a yield of over 90 % by an in vivo residue-specific incorporation strategy, to create, for the first time, engineered mussel adhesive proteins (MAPs) in Escherichia coli with a very high Dopa content, close to that of natural MAPs. The Dopa-incorporated MAPs exhibited a superior surface adhesion and water resistance ability by assistance of Dopa-mediated interactions including the oxidative Dopa cross-linking, and furthermore, showed underwater adhesive properties comparable to those of natural MAPs. These results propose promising use of Dopa-incorporated engineered MAPs as bioglues or adhesive hydrogels for practical underwater applications.

Probing Molecular Interactions of Asphaltenes in Heptol Using a Surface Forces Apparatus: Implications on Stability of Water-in-Oil Emulsions

The behaviors and molecular interactions of asphaltenes are related to many challenging issues in oil production. In this study, the molecular interaction mechanism of asphaltenes in Heptol solvents of varying toluene/n-heptane ratio were directly measured using a surface forces apparatus (SFA). The results showed that the interactions between asphaltene surfaces gradually changed from pure repulsion to weak adhesion as the weight ratio of toluene (ω) in Heptol decreased from ω = 1 to 0. The measured repulsion was mainly due to the steric interactions between swelling asphaltene molecules and/aggregates. The micropipet technique was applied to test the stability of two water-in-oil emulsion droplets attached to glass pipettes. A computer-controlled 4-roll mill fluidic device was also built in-house to investigate the interaction of free-suspending water-in-oil emulsions under dynamic flow conditions. Both micropipet and 4-roll mill fluidic tests demonstrate that asphaltenes adsorbed at oil/water interfaces play a critical role in stabilizing the emulsion drops, in agreement with the repulsion measured between asphaltene surfaces in toluene using SFA, and that interfacial sliding or shearing is generally required to destabilize the protective interfacial apshaltene layers which facilitates the coalescence of emulsion drops. Our results provide insights into the fundamental understanding of molecular interaction mechanisms of asphaltenes in organic solvents and stabilization/destabilization behaviors of water-in-oil emulsions with asphaltenes.

Nanocomposites of graphene oxide, Ag nanoparticles, and magnetic ferrite nanoparticles for elemental mercury (Hg0) removal

Mercury emission from combustion flue gas causes considerable environmental challenges and serious adverse health threats, and elemental mercury (Hg0) is the most challenging chemical form for removal. In this work, four types of graphene oxide (GO) based composite adsorbents were successfully synthesized by depositing Ag nanoparticles (NPs) and/or magnetic ferrite NPs on GO sheets (denoted as GO, GO–Ag, MGO and MGO–Ag), characterized and applied for the removal of Hg0 for the first time. The presence of Ag NPs on GO greatly enhances the Hg0 removal capability of GO–Ag and MGO–Ag as compared to that of pure GO, which is mainly attributed to the amalgamation of Hg0 on Ag NPs. MGO–Ag shows the best Hg0 removal performance and thermal tolerance among the four types of adsorbents developed, which can effectively capture Hg0 up to 150–200 °C in a simulated flue gas environment and can be also effectively recycled and reused. Our results indicate that the graphene oxide based composites (i.e. MGO–Ag) have significant potential applications for mercury emission control in coal-fired power plants.