Justin B. Davies

Silver nanoparticles prepared by gamma irradiation across metal–organic framework templates

In this study, we demonstrate for the first time the successful fabrication of well-dispersed ultrafine silver nanoparticles inside metal–organic frameworks through a single step gamma irradiation at room temperature. HKUST-1 crystals are soaked in silver nitrate aqueous solution and irradiated with a Cobalt 60 source across a range of irradiation doses to synthesize highly uniformly distributed silver nano-particles. The average size of the silver nanoparticles across the Ag@HKUST-1 materials is found to vary between 1.4 and 3 nm for dose exposures between 1 and 200 kGy, respectively. The Ag@HKUST-1 hybrid crystals exhibit strong surface plasmon resonance and are highly durable and efficient catalytic materials for the reduction of 4-nitrophenol to 4-aminophenol (up to 14.46 × 10−3 s−1 for 1 kGy Ag@HKUST-1). The crystals can be easily recycled for at least five successive cycles of reaction with a conversion efficiency higher than 99.9%. The gamma irradiation is demonstrated to be an effective and environmental friendly process for the synthesis of nano-particles across confined metal–organic frameworks at room temperature with potential applications in environmental science.

Formation and detection of oxidant-generated tryptophan dimers in peptides and proteins

Abstract Free radicals are produced during physiological processes including metabolism and the immune response, as well as on exposure to multiple external stimuli. Many radicals react rapidly with proteins resulting in side‐chain modification, backbone fragmentation, aggregation, and changes in structure and function. Due to its low oxidation potential, the indole ring of tryptophan (Trp) is a major target, with this resulting in the formation of indolyl radicals (Trp•). These undergo multiple reactions including ring opening and dimerization which can result in protein aggregation. The factors that govern Trp• dimerization, the rate constants for these reactions and the exact nature of the products are not fully elucidated. In this study, second‐order rate constants were determined for Trp• dimerization in Trp‐containing peptides to be 2–6 × 108 M−1 s−1 by pulse radiolysis. Peptide charge and molecular mass correlated negatively with these rate constants. Exposure of Trp‐containing peptides to steady‐state radiolysis in the presence of NaN3 resulted in consumption of the parent peptide, and detection by LC‐MS of up to 4 different isomeric Trp‐Trp cross‐links. Similar species were detected with other oxidants, including CO3•‐ (from the HCO3‐ ‐dependent peroxidase activity of bovine superoxide dismutase) and peroxynitrous acid (ONOOH) in the presence or absence of HCO3‐. Trp‐Trp species were also isolated and detected after alkaline hydrolysis of the oxidized peptides and proteins. These studies demonstrate that Trp• formed on peptides and proteins undergo rapid recombination reactions to form Trp‐Trp cross‐linked species. These products may serve as markers of radical‐mediated protein damage, and represent an additional pathway to protein aggregation in cellular dysfunction and disease. Graphical abstract No caption available. HighlightsTryptophan‐derived indolyl radicals (Trp•) have been implicated in protein dimerization.Trp• formed on Trp‐containing peptides dimerize with high rate constants: k2 2–6 × 108 M−1 s−1.Multiple carbon‐carbon and carbon‐nitrogen Trp‐Trp dimers detected by LC‐MS analyses.Trp‐Trp dimers formed by multiple oxidants, including N3•, ONOOH + bicarbonate, and CO3•‐.Trp‐Trp dimers detected after alkaline hydrolysis of oxidized lysozyme.

Low Dose Gamma Irradiation Does Not Affect the Quality or Total Ascorbic Acid Concentration of "Sweetheart" Passionfruit (Passiflora edulis)

Passionfruit (Passiflora edulis, Sims, cultivar “Sweetheart”) were subject to gamma irradiation at levels suitable for phytosanitary purposes (0, 150, 400 and 1000 Gy) then stored at 8 °C and assessed for fruit quality and total ascorbic acid concentration after one and fourteen days. Irradiation at any dose (≤1000 Gy) did not affect passionfruit quality (overall fruit quality, colour, firmness, fruit shrivel, stem condition, weight loss, total soluble solids level (TSS), titratable acidity (TA) level, TSS/TA ratio, juice pH and rot development), nor the total ascorbic acid concentration. The length of time in storage affected some fruit quality parameters and total ascorbic acid concentration, with longer storage periods resulting in lower quality fruit and lower total ascorbic acid concentration, irrespective of irradiation. There was no interaction between irradiation treatment and storage time, indicating that irradiation did not influence the effect of storage on passionfruit quality. The results showed that the application of 150, 400 and 1000 Gy gamma irradiation to “Sweetheart” purple passionfruit did not produce any deleterious effects on fruit quality or total ascorbic acid concentration during cold storage, thus supporting the use of low dose irradiation as a phytosanitary treatment against quarantine pests in purple passionfruit.

The effect of gamma-irradiation conditions on the immunogenicity of whole-inactivated Influenza A virus vaccine

Gamma-irradiation, particularly an irradiation dose of 50kGy, has been utilised widely to sterilise highly pathogenic agents such as Ebola, Marburg Virus, and Avian Influenza H5N1. We have reported previously that intranasal vaccination with a gamma-irradiated Influenza A virus vaccine (γ-Flu) results in cross-protective immunity. Considering the possible inclusion of highly pathogenic Influenza strains in future clinical development of γ-Flu, an irradiation dose of 50kGy may be used to enhance vaccine safety beyond the internationally accepted Sterility Assurance Level (SAL). Thus, we investigated the effect of irradiation conditions, including high irradiation doses, on the immunogenicity of γ-Flu. Our data confirm that irradiation at low temperatures (using dry-ice) is associated with reduced damage to viral structure compared with irradiation at room temperature. In addition, a single intranasal vaccination with γ-Flu irradiated on dry-ice with either 25 or 50kGy induced seroconversion and provided complete protection against lethal Influenza A challenge. Considering that low temperature is expected to reduce the protein damage associated with exposure to high irradiation doses, we titrated the vaccine dose to verify the efficacy of 50kGy γ-Flu. Our data demonstrate that exposure to 50kGy on dry-ice is associated with limited effect on vaccine immunogenicity, apparent only when using very low vaccine doses. Overall, our data highlight the immunogenicity of influenza virus irradiated at 50kGy for induction of high titre antibody and cytotoxic T-cell responses. This suggests these conditions are suitable for development of γ-Flu vaccines based on highly pathogenic Influenza A viruses.

Superoxide radicals react with peptide-derived tryptophan radicals with very high rate constants to give hydroperoxides as major products.

ABSTRACT Oxidative damage is a common process in many biological systems and proteins are major targets for damage due to their high abundance and very high rate constants for reaction with many oxidants (both radicals and two‐electron species). Tryptophan (Trp) residues on peptides and proteins are a major sink for a large range of biological oxidants as these side‐chains have low radical reduction potentials. The resulting Trp‐derived indolyl radicals (Trp•) have long lifetimes in some circumstances due to their delocalized structures, and undergo only slow reaction with molecular oxygen, unlike most other biological radicals. In contrast, we have shown previously that Trp• undergo rapid dimerization. In the current study, we show that Trp• also undergo very fast reaction with superoxide radicals, O2•−, with k 1–2 × 109 M−1 s−1. These values do not alter dramatically with peptide structure, but the values of k correlate with overall peptide positive charge, consistent with positive electrostatic interactions. These reactions compete favourably with Trp• dimerization and O2 addition, indicating that this may be a major fate in some circumstances. The Trp• + O2•− reactions occur primarily by addition, rather than electron transfer, with this resulting in high yields of Trp‐derived hydroperoxides. Subsequent degradation of these species, both stimulated and native decay, gives rise to N‐formylkynurenine, kynurenine, alcohols and diols. These data indicate that reaction of O2•− with Trp• should be considered as a major pathway to Trp degradation on peptides and proteins subjected to oxidative damage. Graphical abstract Figure. No caption available. HighlightsTryptophan (Trp) residues are a major sink for oxidants on peptides and proteins.Trp radicals in peptides undergo fast reactions with O2•− (k ˜ 109 M−1 s−1).Trp hydroperoxides are major products of Trp• + O2•− reactions in peptides.Hydroperoxide degradation gives N‐formylkynurenine, kynurenine and alcohols.Hydroperoxide formation competes favourably with dimerization and O2 addition.

Organic bioelectronic plasma polymerised polyterpenol thin films: Preservation of properties relevant to biomedical and organic electronic applications following exposure to sterilising doses of gamma radiation

Plasma polymers such as polyterpenol have been investigated for use as biofunctional coatings, insulating/dielectric layers in electronics, and adhesion promoting interlayers in organic electronics. The commercialisation of plasma polymers in these and other biomaterial-related applications is contingent upon their ability to resist degradation in response to sterilising and potentially damaging ionising radiation, such as gamma rays. Hence, this study focusses on the stability of plasma polymerised polyterpenol thin films following exposure to gamma radiation doses ranging from 0 to 100xa0kGy. Irradiated films were subjected to ellipsometry, current–voltage, dielectric, Fourier transform infrared, and atomic force microscopy characterisation. Stability of polyterpenol was evidenced by the observed lack of radiation-induced variation in its complex refractive index, optical band gap, relative permittivity, dc conductivity, surface chemical functionalities, and surface morphology.