Diamond Annual Review 2023/24

53 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 3 / 2 4 Fine-tuning poly-L-lysine-based antiviral nanomaterials​ Nanomaterials can represent alternative resources to fight viruses at different stages of infection by selective action or in a broad spectrum. A fundamental requirement is non-toxicity. However, biocompatible nanomaterials often have little or no antiviral activity, preventing their practical use. Carbon-based nanomaterials have displayed encouraging results and can present the required mix of biocompatibility and antiviral properties. Researchers at the University of Sassari recently synthesised a polymeric nanomaterial, derived from the amino acid L-lysine, with an antiviral activity against SARS-CoV-2 and a good safety profile in vitro. ​ As the polymer structure is highly dependent on the starting pH conditions and hydrothermal temperature, there is a need to study the polymerisation process of L-lysine as a function of pH growing conditions.​ The research group is developing a new generation of lysine-based nanostructures by modifying the lysine branched structure with other amino acids, such as arginine and glycine, whose structure is not yet understood. They used synchrotron radiation circular dichroism (SRCD) on Diamond’s B23 beamline to understand the supramolecular structure of this peculiar class of biomaterials.​ The structural analysis of the poly-L-lysine (PLL) obtained after a hydrothermal treatment (HT) at 200 °Cof L-lysine showedsignificant differences in the homopeptide architecture as a function of pH. The polylysine synthesised at low pH is a hyperbranched cross-linked polymer, whereas a high pH allows the formation of linear structures. It is, therefore, possible to tune the synthesis process to obtain cross-linked or linear lysine polymers by modulating the pH of the starting solution.​ The knowledge acquired in this study has enabled the design of very specific L-lysine-based nanosystems that can inhibit the replication of different types of viruses with potential broad-spectrum responses.​ Stagi, L. et al. DOI: 10.1038/s41598-022-24109-5​ Cooking residues can cling on to indoor pollutants Aerosols contribute to ambient air pollution and, via processes such as cloud droplet formation, affect air quality and climate. Organic compounds often play a major role in aerosol composition, varying with time, location, season, and environment. Cooking food releases fatty acids into the air, and cooking emissions contribute around 10% to UK emissions of PM2.5 (aerosols up to two and a half microns wide). These aerosol particles can be deposited onto surfaces such as windows. A thin, layered film of material builds up over time, creating a persistent crust that is only slowly broken down by other chemicals in the atmosphere. In work recently selected as the best 2022 paper in Environmental Science: Atmospheres, a teamledby researchers at theUniversityof Birminghamcreated ultra-thin films, just a few tens of nanometres in thickness, approximating real- world pollution samples. They used a combination of optical microscopy, neutron reflectometry (NR) (at ISIS and ILL) and grazing-incidence small-angle X-ray scattering (GI-SAXS) on Diamond’s I22 beamline to study changes in the surface structure of the films as they aged. Commonly used to determine the self- assembly and self-organisation of thin films at the nanoscale, GISAXS can measure X-ray scattering over a larger angular range and off-specular scattering (in the y-direction). In this work, it allowed the research team to determine the orientation of the layered stacks. The researchers found that the self-organised layered structure can trap toxic pollutants and form a barrier that can prevent their breakdown. Identifying the conditions under which these persistent films form will also improve our understanding of aerosol behaviour in the atmosphere, feeding into the models scientists use to investigate air quality, cloud formation and climate. Milsom, A. et al. DOI:10.1039/D2EA00011C. Figure: A) CD spectra of HT-130 °C poly-l-lysine prepared from l-lysine aqueous solutions at different pHs (2.5, green line; 7.3, sky blue line; 9.7, red line; blue, 13). The samples have been measured at 20 °C. B) CD spectra of HT-200 °C poly-l-lysine prepared from l-lysine aqueous solutions at different pHs (2.5, green line; 7.3, sky blue line; 9.7, red line; blue, 13). The samples have been measured at 20 °C. The CD spectra of pure L-lysine in aqueous solutions at different pH are the dashed lines. Schematic representations of grazing-incidence small-angle X-ray scattering (GI-SAXS) experiments. The GI-SAXS data presented are from a film coated on a silicon wafer at 2000 rpm.