[en] Recent developments in the understanding of the biosynthesis of the active site of the nitrogenase enzyme, the structure of the iron centre of [Fe]-hydrogenase and the structure and biomimetic chemistry of the [FeFe] hydrogenase H-cluster as deduced by application of X-ray spectroscopy are reviewed. The techniques central to this work include X-ray absorption spectroscopy either in the form of extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES) and nuclear resonant vibrational spectroscopy (NRVS). Examples of the advances in the understanding of the chemistry of the system through integration of a range of spectroscopic and computational techniques with X-ray spectroscopy are highlighted. The critical role played by ab initio calculation of structural and spectroscopic properties of transition-metal compounds using density functional theory (DFT) is illustrated both by the calculation of nuclear resonance vibrational spectroscopy (NRVS) spectra and the structures and spectra of intermediates through the catalytic reactions of hydrogenase model compounds.

[en] Thiolate-bridged diiron compounds that are related to the active site of the [Fe-Fe] hydrogenase enzyme have been shown to act as electrocatalysts for reduction of protons. The use of XAFS for clarification of the structures of intermediates formed following reduction of related diiron carbonyl compounds is described. These measurements allow the determination of Fe-Fe and Fe-S bond lengths with good reliability and when used in conjunction with the standard bonding models this provides a means of validating the structures proposed for longer-lived (t_1/2>20s at -50deg. C) reaction intermediates

[en] A combined Fourier transform infrared (FTIR) spectra of ferrocene (Fc) and density functional theory (DFT) based quantum mechanical calculations confirmed the dominance of the eclipsed Fc conformer in the fingerprint region of 400–500 cm⁻¹ in solutions. Solution IR spectra of Fc measured in acetonitrile (ACN, ε = 35.69), dichloromethane (DCM, ε = 8.93), tetrahydrofuran (THF, ε = 7.43) and dioxane (DOX, ε = 2.21) show two well-defined bands in the 480-500 cm⁻¹ region with the higher-wavenumber band higher in intensity. The band profile agrees well with the earlier IR spectra of Lippincott and Nelson (1958) in tetrachloromethane solution as well as more recent measurement in dichloromethane solution of Duhović and Diaconescu (2013). DFT based quantum mechanical calculations predict that the eclipsed (D_5h) Fc conformer is lower in energy than the staggered (D_5d) conformer and that the room-temperature solution spectrum of Fc is dominated by that of the D_5h form (Best et al., 2016). The present study confirms that solvent effects enhanced the dominance of the D_5h Fc conformer which resulted in switch of the IR profile patterns in 400–500 cm⁻¹, from low-wavenumber band higher in intensity pattern in gas phase to higher-wavenumber band higher in intensity in solutions. It further suggests that the effects of solvents on the IR spectra of Fc in this region are small and the solvent model effects are also small for the IR spectrum in the region of 400–500 cm⁻¹ of Fc.

[en] The suitability of IRGANOX^®1076 in paraffin wax as a near-tissue equivalent radiation dosimeter was investigated for various radiotherapy beam types; kV and MV X-rays, electrons and protons over clinically-relevant doses (2 −20 Gy). The radical formed upon exposure to ionising radiations was measured by Electron Paramagnetic Resonance (EPR) spectroscopy, and the single peak signal obtained for solid solutions of IRGANOX^®1076 in wax is attributed to the phenoxyl radical obtained by net loss of H^• . Irradiation of solid IRGANOX^®1076 gives a doublet consistent with the formation of the phenol cation radical, obtained by electron loss. Solid solutions of IRGANOX^®1076 in paraffin wax give a linear dose response for all types of radiations examined, which was energy independent for MV, electron and proton beams, and energy-dependent for kV X-ray irradiation. Reliable dose measurements were obtained with exposures as low as 2 Gy, and comparisons with alanine wax-pellets containing the same amount of dosimeter material (w/w) gave similar responses for all beam types investigated. Post-irradiation measurements (up to 77 days for proton irradiation for samples stored in the dark and at room temperature) indicate good signal stability with minimal signal fading (between 1.6 to 3.8%). Relative to alanine dosimeters, solid solutions of IRGANOX^®1076 in wax give EPR signals with better sensitivity at low dose and do not significantly change with the orientation of the sample. Solid solutions of IRGANOX^®1076 are ideal for applications in radiotherapy dosimetry for X-rays and charged particles, as IRGANOX^®1076 is relatively cheap, can easily and reproducibly prepared in wax and be moulded to different shapes. - Highlights: • Homogenous solid solutions of IRGANOX/wax irradiated with X-rays and charged particles. • The phenoxyl radical gave reliable dose measurements with exposures as low as 2 Gy. • The EPR signal is energy independent for MV X-rays, electrons and protons, and energy dependent for kV X-rays. • Post-irradiation measurements show good signal stability with minimal fading. • IRGANOX shows minimal EPR angular response when rotated within the EPR cavity.

[en] Highlights: • Dosimeters were ‘spiked’ with large radiation doses then smaller doses; 0.5–10 Gy. • Subtraction of the ^spike signal gave reliable measurements for doses below 2 Gy. • Spiking is easy to perform and requires no complex EPR signal analysis. • The method is not susceptible to EPR signal baseline distortions at doses • Spiking can extend the use of alanine/ other epr dosimeters in radiotherapy. - Abstract: Alanine dosimeters are limited in radiotherapy by poor sensitivity at low doses (< 5 Gy). A set of alanine dosimeters were ‘spiked’ with a large dose of radiation, (~30 Gy, 6 MV X-rays) and additional doses ranging between 0.5 and 10 Gy. The radical yield was measured by Electron Paramagnetic Resonance (EPR) spectroscopy, and after subtraction of the contribution from the ^spike dose, a linear correlation between the radiation dose and the area of the central EPR signal was obtained for doses between 0.5 and 10 Gy (regression value of 0.9890), and for the central peak's amplitude (regression value of 0.9895). Overall, this method is easy to perform, requires no complex EPR signal analysis, and offers much potential to extend the current usage of alanine dosimeters in radiotherapy.

[en] The main aims of this research was to employ alanine doped with gold-nanoparticles “AuNPs” to determine the levels of dose enhancement caused by these particles when irradiated with proton beams, low and high energy X-rays and electrons. DL-alanine was impregnated with 5 nm gold-nanoparticles (3% by weight) and added as a uniform layer within a wax pellet of dimensions 10 × 5 × 5 mm. Control pellets, containing DL-Alanine were also produced, and placed within a phantom, and exposed to various types of radiations: low energy (kV ranges) X-rays were obtained from a superficial machine, high energy (MV) X-rays and electrons derived from a linear accelerator, and protons were produced by the Hyogo Ion Beam Centre in Japan. Nominal doses received ranged from 2 to 20 Gy (within clinical range). The Electron Paramagnetic Resonance (EPR) spectra of the irradiated samples were recorded on a BRUKER Elexsys 9.5 MHz. The dose enhancement caused by gold nanoparticles for 80 kV x-rays was found to be more than 60% at about 5 Gy. Smaller dose enhancements (under the same measurement conditions) were observed for megavoltage x-ray beams (up to 10%). Dose enhancement caused by charged particles indicated minimal values for 6 MeV electrons (approximately 5%) whilst less than that is obtained with protons of 150 MeV. The proton results validate the latest simulation results based on Monte Carlo calculations but the dose enhancement is significantly less than that reported in cell and animal model systems, (about 20%). We attribute this difference to the fact that alanine only measures the levels of free radicals generated by the inclusion of nanoparticles and not the redox type radicals (such as reactive oxygen species) generated from aqueous media in cells. Dose enhancement caused by 5 nm gold-nanoparticles with radiotherapy type proton beams has been found to be less than 5% as determined when using alanine/wax as both a phantom and dosimeter. This agrees well with the latest Monte Carlo simulation results for similar sized gold-nanoparticles. Furthermore, our results for both low and high energy x-rays are validated against published data for in vitro studies. - Highlights: • Dose enhancement by 5 nm AuNPs (3% within alanine) determined for various beam types • Alanine/3% AuNPs composites show potential as low dose radiotherapy dosimeters (kV) • Alanine doped with AuNPs gave ∼60% dose enhancement for kV and ∼10% for MV X-rays • Alanine doped with AuNPs gave ≤5% dose enhancement for electron and proton beams • Good agreement with results for dose enhancement in cell and simulation studies