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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]

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]