Open Access

Show Abstract ▼

Abstract: Hexavalent chromium contamination of groundwater is a worldwide problem caused by anthropogenic and natural processes. We report the rate of Cr(VI) removal by two humic acids (extracted from Miocene age lignite and younger peat soil) in aqueous suspensions across a pH range likely to be encountered in terrestrial environments. Cr(VI) was reduced to Cr(III) in a first-order reaction with respect Cr(VI) concentration, but exhibited a partial order (~ 0.5) with respect to [H+]. This reaction was more rapid with the peat humic acid, where Cr(VI) reduction was observed at all pH values investigated (3.7 ≤ pH ≤ 10.5). 13C NMR and pyrolysis GC-MS spectroscopy indicate that the reaction results in loss of substituted phenolic moieties and hydroxyl groups from the humic acids. X-ray absorption spectroscopy indicated that at all pH values the resulting Cr(III) was associated with the partially degraded humic acid in an inner-sphere adsorption complex. The reaction mechanism is likely to be controlled by ester formation between Cr(VI) and phenolic/hydroxyl moieties, as this initial step is rapid in acidic systems but far less favourable in alkaline conditions. Our findings highlight the potential of humic acid to reduce and remove Cr(VI) from solution in a range of environmental conditions.

Open Access

Show Abstract ▼

Abstract: Bacteria acquire phosphate (Pi) by maintaining a periplasmic concentration below environmental levels. We recently described an extracellular Pi buffer which appears to counteract the gradient required for Pi diffusion. Here, we demonstrate that various treatments to outer membrane (OM) constituents do not affect the buffered Pi because bacteria accumulate Pi in the periplasm, from which it can be removed hypo-osmotically. The periplasmic Pi can be gradually imported into the cytoplasm by ATP-powered transport, however, the proton motive force (PMF) is not required to keep Pi in the periplasm. In contrast, the accumulation of Pi into the periplasm across the OM is PMF-dependent and can be enhanced by light energy. Because the conventional mechanism of Pi-specific transport cannot explain Pi accumulation in the periplasm we propose that periplasmic Pi anions pair with chemiosmotic cations of the PMF and millions of accumulated Pi pairs could influence the periplasmic osmolarity of marine bacteria.

Show Abstract ▼

Abstract: The complexity and heterogeneity of bone chemistry makes it difficult to discern information on physiological and taphonomic processes stored within the bone matrix. Analysis of archaeological and palaeontological bone becomes more difficult because in many cases the most pivotal specimens are too scientifically valuable for destructive analysis. This problem is further escalated by the fact that the heterogeneity of the bone may cause small “pockets” of preservation that can be missed during sampling. Therefore, a non-destructive technique that can spatially resolve such heterogeneity within the bone is needed. Here we use microfocus, non-destructive synchrotron-based X-Ray Fluorescence (XRF) imaging and X-ray Absorption Spectroscopy (XAS) to map the organic constituents within extant and fossil bovid bones. XAS analysis of sulfur allowed organic sulfur (within collagen as methionine) to be distinguished from inorganic sulfate (within bone apatite). Mapping and quantification of organic sulfur within the samples were made by setting the beam to the methionine resonance, allowing for the detection, distribution and quantification of collagen present by using organic sulfur as an internal marker. Results show organic sulfur to be distributed in small “pockets” throughout the bone matrix in both extant and fossil specimens. Significant loss of collagen (organic sulfur) was seen in specimens between 100 ka and 650 ka with little organic sulfur preservation persisting after this date. Comparison of residual organic sulfur concentrations as a function of sample age revealed a second order rate law for organic sulfur oxidation (k ≈ 1 × 10−5 y−1) within bone. These results show that non-destructive, synchrotron-based XRF mapping of organic sulfur is a useful tool for not only calculating rates of collagen degradation through time, but also identifying areas of potential collagen preservation for other paleobiological applications such as proteomics and stable isotope analyses.

Open Access

Show Abstract ▼

Abstract: This thesis focuses on the Aerosol Assisted Chemical Vapour deposition (AACVD) of titanium dioxide (TiO2) thin films using titanum (IV) isopropoxide (TTIP) and also reports the deposition of tungsten oxide via AACVD using tungsten hexacarbonyl [W(CO)6] in different solvents including methanol and ethanol. Chapter 1 of this thesis gives an overview of TiO2, including its properties and functions and the motivation for this project. In chapter 2 brief descriptions are provided of the main characterisation techniques used throughout this thesis. The substrate and solvent effect on the phase of TiO2 obtained by AACVD is outlined in chapter 3 and 4. TiO2 was deposited via the AACVD of TTIP in different solvents including methanol, ethanol and other solvents. The films deposited showed some substrate dependent morphology and properties. In particular at 550°C the films on steel show needle and rod like particles. XRD and Raman spectra of the TiO2 films showed that on steel or titanium substrates only the rutile form could be obtained, whereas on glass either anatase, anatase-rutile mixtures or rutile could be obtained depending on substrate temperature. Using methanol as the carrier solvent produced exclusively the rutile films on steel and predominantly rutile on glass substrates while the use of the other solvents produced exclusively the anatase phase on the steel under the same conditions. TiO2 was also deposited by AACVD from a mixture of ethanol and methanol solvents. As little as 15% of methanol in ethanol produces rutile as the predominant phase. The photocatalytic properties and the hydrophilicity of the films deposited are also reported. X-ray absorption spectroscopy (XAS) was used to map across the surface of the TiO2 films deposited as described in chapter 5. The X-ray absorption near edge structure (XANES) was used to determine the phase of TiO2 present at each point on the substrate. The AACVD deposition tungsten oxide using tungsten hexacarbonyl (W(CO)6) in methanol and ethanol is reported in chapter 6. Preferred orientation was observed when using either ethanol or methanol as the carrier solvent. In chapter 7 insitu work was attempted to investigate the mechanism of the deposited titania and tungsten oxide films. A new reactor vessel was designed, constructed and tested to allow synchrotron radiation in and out using a kapton window. The XANES pattern recorded during in-situ deposition were not of high enough to resolve the mechanism. The in-situ work carried out has great potential in the growth study of thin film deposition and can in the future help control the phase and composition of deposited films to produce more desirable properties.

Open Access

Show Abstract ▼

Abstract: Brain  senescence  is  a  complex  process  affecting  a  multitude  of  molecular  and   structural  mechanisms  culminating  in  perturbed  cognitive  and  motor  abilities.     •Dysfunctional  mitochondria  driven  by  oxidative  stress  mechanisms  and  potential   increases  in  iron  have  been  postulated  as  potential  key  mediators  of  senescent   mechanisms.     •Magnetic  resonance  imaging  relaxometry  is  a  well-­documented  iron-­sensitive   technique  that  has  been  used  to  demonstrate  elevations  in  brain  iron  during   ageing,  most  notably  in  the  basal  ganglia.     •To  date,  no  study  has  demonstrated  age-­related  changes  in  MR  relaxometry  with   direct  and  quantitative  measures  of  brain  iron  levels.