Understanding the activity of nanomaterials at the lipid bilayer surface can provide key information for the feasible design of functional bioactive agents. Herein, we used micro-and nanoscopic imaging techniques to evaluate the activity of nanometer-sized inorganic clusters and report that destruction of the lipid membrane is induced by a cluster-induced morphological change on the membrane surface. As model experiments, we used the Keggin-type polyoxometalate (POM) SiW 12 O 40 4− for the inorganic cluster and a 1,2-dimyristoyl-sn-glycerol-3-phosphatidylcholine (DMPC) and egg phosphatidylcholine (EPC) bilayer for the cell membrane. Imaging experiments revealed vigorous desorption of the lipid bilayer from solid substrate by the formation of POM−lipid assembly through a supramolecular-type assembly process in which electrostatic and hydrophobic interactions between the POM and lipid determine the efficiency and dynamics of assembly formation and thereby determine lipid desorption. Furthermore, maximum efficiency of lipid desorption was found at the phase-transition temperature. This phase dependency was explained by the formation of a "leaky interface" between the gel and fluid domains, in which freedom in the conformational change of lipids during the formation of the POM−lipid assemblies becomes maximal.

Polyoxometalate (POM) is rapidly emerging as an attractive antimicrobial inorganic cluster that exhibits its antimicrobial activity by attacking the cell membrane. Precise understanding and control of the antimicrobial activity of POM can allow us to design novel functional nanomedicines with high stability, high selectivity, and low cost. Therefore, in this study, we investigated the interaction between POM and a model cell membrane through single-molecule observation and found that the presence of POM causes macroscopic morphological changes in the microbial membrane, and these changes were detectable as modulations in the diffusivity of the membrane. Numerical analyses based on mean square displacement and diffusion length histogram revealed the reduction in the fluidity of the membrane in the presence of POM. Further analysis from single-molecule tracking revealed the formation of pores in the membrane, along with the formation of POM–lipid assemblies. The pores were found to act as diffusion barriers and diffusion trap sites and thus contributed to the reduction in the fluidity of the membrane. Furthermore, pore formation also led to the loss of important functions of the cell membrane. Based on this ability of POM to induce pore formation and form assemblies with membrane lipids, we believe that POM is a promising candidate for use as a membrane-targeting bioactive nanomedicine.

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rings with 7 or more members rings with 7 or more members Q 0050 -077Synthesis and Reactions of 1,1-Trimethylene-1H-azulenium Ion.--(ODA, M.; SAKAMOTO, A.; MIYATAKE, R.; KURODA, S.; Tetrahedron Lett. 39 (1998) 34, 6195-6198; Dep. Appl. Chem., Fac. Eng., Toyama Univ.,

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