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A study on the interactions of Aurein 2.5 with bacterial membranes

Aurein 2.5 (GLFDIVKKVVGAFGSL-NH₂) is an uncharacterised antimicrobial peptide. At an air/water interface, it exhibited strong surface activity (maximal surface pressure 25 mN m⁻¹) and molecular areas consistent with the adoption of α-helical structure orientated either perpendicular (1.72 nm² molecule⁻¹) or parallel (3.6 nm² molecule⁻¹) to the interface. Aurein 2.5 was strongly antibacterial, exhibiting a minimum inhibitory concentration (MIC) of 30 μM against Bacillus subtilis and Escherichia coli. The peptide induced maximal surface pressure changes of 9 mN m⁻¹ and 5 mN m⁻¹, respectively, in monolayers mimicking membranes of these organisms whilst compression isotherm analysis of these monolayers showed ΔG_Mix > 0, indicating destabilisation by Aurein 2.5. These combined data suggested that toxicity of the peptide to these organisms may involve membrane invasion via the use of oblique orientated α-helical structure. The peptide induced strong, comparable maximal surface changes in monolayers of DOPG (7.5 mN m⁻¹) and DOPE monolayers (6 mN m⁻¹) suggesting that the membrane interactions of Aurein 2.5 were driven by amphiphilicity rather than electrostatic interaction. Based on these data, it was suggested that the differing ability of Aurein 2.5 to insert into membranes of B. subtilis and E. coli was probably related to membrane-based factors such as differences in lipid packing characteristics. The peptide was active against both sessile E. coli and Staphylococcus aureus with an MIC of 125 μM. The broad-spectrum antibacterial activity and non-specific modes of membrane action used by Aurein 2.5 suggested use as an anti-biofilm agent such as in the decontamination of medical devices.     

Anionic polymerization with expansion in volume

New bicyclic and tricyclic compounds have been synthesized by the Lewis acid-catalyzed condensation of epoxides with cyclic acid anhydrides or cyclic bislactones. These materials take part in the anionic addition polymerization of amine-functional polyamides with diepoxides, and modify the shrinkage that is characteristic of the reaction. It is possible to control the extent of shrinkage by choosing an appropriate comonomer and by adjusting the concentration of this material in the reaction mixture.