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Within cell plasma membranes, unsaturated lipids are asymmetrically distributed over the inner and outer leaflets, offering an attractive local structural feature. However, the mechanism to keep lipid transmembrane asymmetry and the closely related transmembrane movement (flip-flop) for unsaturated lipids remain poorly understood. Here, we applied sum frequency generation vibrational spectroscopy to investigate this lipid transmembrane asymmetry upon mimicking the cell membrane homeostatic processes. On the one hand, unsaturated lipids were found to hinder the flip-flop process and preserve lipid transmembrane asymmetry in model cell membranes, owing to the steric hindrance caused by their bent tails. On the other hand, local unsaturated lipids in the mixed unsaturated/saturated lipid bilayer were conducive to the formation of the local asymmetry. Therefore, lipid unsaturation can be recognized as an intrinsic key factor to form and maintain lipid transmembrane asymmetry in cell membranes. [ABSTRACT FROM AUTHOR]

Distinct annexin V binding behaviours in Ca2+-dependent and Ca2+-independent cases were comparatively investigated using sum frequency generation vibrational spectroscopy. It was discovered that binding affected the molecular arrangement of both membrane leaflets, and the initial Ca2+-independent binding went through a transition with annexin V reorientation to a more stable state upon adding Ca2+. [ABSTRACT FROM AUTHOR]

Development of new strategies with high antimicrobial capability against complex bacterial infections is still challenging. Herein, a three‐in‐one synergistic antimicrobial platform is presented based on gallium–carbenicillin framework coated defect‐rich hollow TiO2 nanoshells (H‐TiO2−x@MOF), for simultaneous eradicating methicillin‐resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa (PA) in complex infections, which are the two most common bacteria in wounds. The metal gallium can disrupt bacterial antioxidation system using a "Trojan horse" strategy by substituting iron in the antioxidant enzymes, and finally increase bacterial susceptibility to oxidants. Meanwhile, oxygen‐deficient hollow TiO2−x nanoshells (H‐TiO2−x NSs) can efficiently bind to the bacteria and promote local generation of abundant reactive oxygen species (ROS) under visible‐light irradiation. Thus, the combination of gallium (antioxidant enzyme inhibitor) and black H‐TiO2−x NSs (ROS generator) constitutes a photocatalyzed oxidative stress amplifier that can boost ROS accumulation to destroy pathogens thoroughly. In addition, carbenicillin (Car), as the organic ligand coordinated to gallium ion, also acts as a broad‐spectrum antibacterial agent against PA and shares the responsibility for combating complex infections simultaneously. In view of the superior antibacterial ability, accelerated healing of infected wounds, and good biosafety, the H‐TiO2−x@MOF potentially provides an alternative antibacterial agent to combat complex bacterial infections. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) are a type of metal-free fluorescent quantum dots and can be synthesized facilely and cost-effectively. In this work, we develop a one-pot solvothermal method to prepare a novel type of quaternized CDs using two commercial reagents (glycerol and dimethyloctadecyl[3-(trimethoxysilyl)propy]ammonium chloride, abbreviated as Si-QAC). The introduction of the long alkyl chain-containing quaternary ammonium compound Si-QAC endows the as-prepared CDs with the capability to interact with the negatively-charged bacterial cells via both electrostatic and hydrophobic interactions. Owning to the different surfaces of Gram-positive and Gram-negative bacteria, the CDs can selectively interact with the Gram-positive bacteria. More interestingly, once the CDs are adsorbed onto the Gram-positive bacteria, their fluorescence emission is significantly enhanced. Furthermore, the CD adsorption can further cause the bacterial cell surface destruction since the CDs may change the charge balance of the bacterial surface and can insert into the bacterial surface via the long alkyl chains, which ultimately leads to the inactivation of Gram-positive bacteria. As compared with the conventional Gram-staining method, the CD-based Gram-type differentiation approach is accurate, fast, and easy-operating. Overall, the quaternized CDs represent a metal-free nanoparticle-based nanotheranostic for imaging-guided bacterial differentiation and inhibition. Image 1 [ABSTRACT FROM AUTHOR]

[Display omitted] • The specific surface-and phase-sensitive SFG spectroscopy revealed the absolute PS structure at the buried PS/silica interface. • The PS nanolayer near the substrate gradually formed during annealing. • The dewetting occurred at the non-adsorbed PS/the flattened PS nanolayer interface due to the autophobic effect. • As the solvent quality reduced, the dewetting rate of the PS film became slower. • This study provides a molecular-level understanding of the dewetting property of the polymer thin film. Dewetting is a common phenomenon observed from polymer thin films under stimuli, such as annealing, which directly affects the applications of polymer thin films. A key to understanding such dewetting behavior is to precisely probe the molecular structure evolution at the buried polymer/substrate interface during annealing. However, non-destructively probing the buried interface is very difficult at the molecular level and in situ. In this study, the specific surface- and phase-sensitive sum frequency generation (SFG) vibrational spectroscopy was used to investigate PS thin films on silica substrates during annealing. The results showed that the absolute orientation/conformation of PS at the film surface was significantly different from that of the flattened PS nanolayer formed near the substrate by dewetting. The dynamic molecular structure evolution of the PS nanolayer (the formation process of the flattened PS nanolayer) at the buried PS/silica interface was directly observed in situ. The dewetting occurred at the non-adsorbed (bulk, free) PS/the flattened PS nanolayer interface due to the autophobic effect. Furthermore, the effects of end groups and solvents on the PS dewetting rate were also elucidated. This study provides a molecular-level understanding of the PS structure at the buried PS/silica interface and its relationship to dewetting behavior. [ABSTRACT FROM AUTHOR]