20Binders formed through alkali-activation of slags and fly ashes, including 'fly ash 21 geopolymers', provide appealing properties as binders for low-emissions concrete production. 22However, the changes in pH and pore solution chemistry induced during accelerated 23 carbonation testing provide unrealistically low predictions of in-service carbonation resistance. 24The aluminosilicate gel remaining in an alkali-activated slag system after accelerated

The structural development of a calcium (sodium) aluminosilicate hydrate (C-(N-)A-S-H) gel system, obtained through the reaction of sodium metasilicate and ground granulated blast furnace slag, is assessed by high-resolution 29 Si and 27 Al MAS NMR spectroscopy during the first 2 yr after mixing. The cements formed primarily consist of C-(N-)A-S-H gels, with hydrotalcite and disordered alkali aluminosilicate gels also identified in the solid product assemblages. Deconvolution of the 27 Al MAS NMR spectra enables the identification of three distinct tetrahedral Al sites, consistent with the 29 Si MAS NMR data, where Q 3 (1Al), Q 4 (3Al), and Q 4 (4Al) silicate sites are identified. These results suggest significant levels of crosslinking in the C-(N-)A-S-H gel and the presence of an additional highly polymerized aluminosilicate product. The mean chain length, extent of cross-linking, and Al/Si ratio of the C-(N-)A-S-H gel decrease slightly over time. The de-crosslinking effect is explained by the key role of Al in mixed cross-linked/non-cross-linked C-(N-)A-S-H gels, because the cross-linked components have much lower Al-binding capacities than the noncross-linked components. These results show that the aluminosilicate chain lengths and chemical compositions of the fundamental structural components in C-(N-)A-S-H gels vary in a way that is not immediately evident from the overall bulk chemistry.

Effective antimicrobial peptides (AMPs) distinguish between the host and microbial cells, show selective antimicrobial activity and exhibit a fast killing mechanism. Although understanding the structure-function characteristics of AMPs is important, the impact of the peptides on the architecture of membranes with different lipid compositions is also critical in understanding the molecular mechanism and specificity of membrane destabilisation. In this study, the destabilisation of supported lipid bilayers (SLBs) by the AMP aurein 1.2 was quantitatively analysed by dual polarisation interferometry. The lipid bilayers were formed on a planar silicon oxynitride chip, and composed of mixed synthetic lipids, or Escherichiacoli lipid extract. The molecular events leading sequentially from peptide adsorption to membrane lysis were examined in real time by changes in bilayer birefringence (lipid molecular ordering) as a function of membrane-bound peptide mass. Aurein 1.2 bound weakly without any change in membrane ordering at low peptide concentration (5muM), indicating a surface-associated state without significant perturbation in membrane structure. At 10muM peptide, marked reversible changes in molecular ordering were observed for all membranes except DMPE/DMPG. However, at 20muM aurein 1.2, removal of lipid molecules, as determined by mass loss with a concomitant decrease in birefringence during the association phase, was observed for DMPC and DMPC/DMPG SLBs, which indicates membrane lysis by aurein. The membrane destabilisation induced by aurein 1.2 showed cooperativity at a particular peptide/lipid ratio with a critical mass/molecular ordering value. Furthermore, the extent of membrane lysis for DMPC/DMPG was nearly double that for DMPC. However, no lysis was observed for DMPC/DMPG/cholesterol, DMPE/DMPG and E. coli SLBs. The extent of birefringence changes with peptide mass suggested that aurein 1.2 binds to the membrane without inserting through the bilayer and membrane lysis occurs through detergent-like micellisation above a critical P/L ratio. Real-time quantitative analysis of the structural properties of membrane organisation has allowed the membrane destabilisation process to be resolved into multiple steps and provides comprehensive information to determine the molecular mechanism of aurein 1.2 action.

The membrane interactions of four antimicrobial peptides, aurein 1.2, citropin 1.1, maculatin 1.1 and caerin 1.1, isolated from Australian tree frogs, are reviewed. All four peptides are amphipathic alpha-helices with a net positive charge and range in length from 13 to 25 residues. Despite several similar sequence characteristics, these peptides compromise the integrity of model membrane bilayers via different mechanisms; the shorter peptides exhibit a surface interaction mechanism while the longer peptides may form pores in membranes.

Abeta(1-42) peptide, found as aggregated species in Alzheimer's disease brain, is linked to the onset of Alzheimer's disease. Many reports have linked metals to inducing Abeta aggregation and amyloid plaque formation. Abeta(25-35), a fragment from the C-terminal end of Abeta(1-42), lacks the metal coordinating sites found in the full-length peptide and is neurotoxic to cortical cortex cell cultures. We report solid-state NMR studies of Abeta(25-35) in model lipid membrane systems of anionic phospholipids and cholesterol, and compare structural changes to those of Abeta(1-42). When added after vesicle formation, Abeta(25-35) was found to interact with the lipid headgroups and slightly perturb the lipid acyl-chain region; when Abeta(25-35) was included during vesicle formation, it inserted deeper into the bilayer. While Abeta(25-35) retained the same beta-sheet structure irrespective of the mode of addition, the longer Abeta(1-42) appeared to have an increase in beta-sheet structure at the C-terminus when added to phospholipid liposomes after vesicle formation. Since the Abeta(25-35) fragment is also neurotoxic, the full-length peptide may have more than one pathway for toxicity.