Diamond Light Source - Annual Review 2022/23

68 69 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 2 / 2 3 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 2 / 2 3 Fine-tuning poly-L-lysine-based antiviral nanomaterials Biochemistry – Chemistry – Biophysics – Life Science & Biotech – Nanoscience/Nanotechnology The appearance of new and lethal viruses and their potential threat urgently requires innovative antiviral systems. In addition to the most common and proven pharmacological methods, 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. The low cost of production and ease of synthesis strongly support the further development of such innovative nanomaterials as a tool for potential COVID-19 treatments and as broad-spectrum antivirals. 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. They combined these data with the results of complementary techniques, including UV–Vis, fluorescence measurements, Nuclear Magnetic Resonance, Fourier Transform Infrared Spectroscopy, and Dynamic Light Scattering. The structural analysis of the poly-L-lysine (PLL) obtained after a hydrothermal treatment (HT) at 200 °C of L-lysine showed significant 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. L-Lysine-based nanomaterials are expected to significantly impact antiviral materials as this study reveals the temperature and pH conditions under which they can be carefully engineered to modulate their size and surface properties to confer specific purposes. 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. Related publication: Stagi, L. et al. Modulating the polyLlysine structure through the control of the protonation–deprotonation state of Llysine. Scientific Reports 12 19719 (2022). DOI: 10.1038/s41598-022-24109-5 Corresponding authors: Plinio Innocenzi, University of Sassari, [email protected] Giuliano Siligardi, Diamond Light Source, [email protected] Soft CondensedMatter Group Beamline B23 Figure 2: 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. C ) CD spectra of HT-130 °C poly-L-lysine from figure 1a, overlapped to the simulated CD spectra shown as dotted lines. The simulations have been performed by adding different fractions of HT-200 °C PLL (see Fig. 3b) to the corresponding L-lysine aqueous solutions. The CD spectra of L-lysine at pH 13 is normalised because it has been measured with 0.1 cm path length instead of 0.01 cm employed in the other measurements. Figure 1: Charges of l-lysine as a function of pH.