A natural antibacterial peptide, cecropin B (CB), and designed analogs, CB-1 and CB-3, were synthesized. The three peptides have different structural characteristics, with CB having one hydrophobic and one amphipathic ␣-helix, CB-1 having two amphipathic ␣-helices, and CB-3 having two hydrophobic ␣-helices. These differences were used as the rationale for a study of their efficacy in breaking liposomes with different combinations of phosphatidic acid and phosphatidylcholine. Biosensor binding measurements and encapsulating dye leakage studies showed that the higher binding affinity of CB and CB-1 to the polar heads of lipids is not necessary for the peptides to be more effective at lysing lipid bilayers, especially when liposomes have a higher phosphatidic acid content. Kinetic studies, by intrinsic and extrinsic fluorescence stopped-flow measurements, revealed two transitional steps in liposome breakage by CB and CB-1, although only one kinetic step was found for CB-3. Circular dichroism stopped-flow measurements, monitoring the formation of secondary structure in the peptides, found one kinetic step for the interaction of all of the peptides with the liposomes. Also, the ␣-helical motif of the peptides was maintained after interacting with the liposomes. Based on these results, the mechanisms of liposome lysis by CB, CB-1, and CB-3 are discussed.

Si-based Er-doped Si nanostructures were fabricated for exploring efficient light emission from Er ions and Si nanocrystallites. High-resolution transmission electron microscopy observations reveal that Si nanocrystallites are spherically embedded in the SiO 2 matrix. Energy-dispersive x-ray analysis indicates that the Er centers are distributed at the surfaces of nanocrystallites surrounded by the SiO 2 matrix. Lowfrequency Raman scattering investigation shows that Lamb's theory can be adopted to exactly calculate the surface vibration frequencies from acoustic phonons confined in spherical Si nanocrystallites and the matrix effects are negligible.

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