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Abstract: AC electrochemical processes have found applications in controlled surface roughening of aluminium (AC electrograining), fine-tip sharpening for field ion microscopy (AC machining) and thin film anodising (AC anodising). The formation of a surface layer and copious amounts of hydrogen gas are inherent in these AC processes. The presence of a resistance is observed in these processes but it is the source of the resistance that is important to the understanding of ionic transport through the surface film.The AC electrograining process is chosen here, as the annual worldwide production of aluminium plate for high quality lithographic printing and for energy storage super-capacitors is in excess of 800 km(2). In this study, a method to detect gas in the surface layer (smut) in-situ with Small Angle X-ray Scattering (SAXS) is proposed. The total scattering from the in-situ SAXS is used with knowledge of the total volume of smut to explain how a gas fraction can be determined by comparing two samples. Results suggest that a gas fraction can be retained in smut during AC electrograining, the degree to which varies with smut properties. (C) 2010 Elsevier B.V. All rights reserved.
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Mar 2010
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Diamond Proposal Number(s):
[316]
Open Access
Abstract: The mechanism by which nucleotide-binding domains (NBDs) of ABC transporters power the transport of substrates across cell membranes is currently unclear. Here we report the crystal structure of an NBD, FbpC, from the Neisseria gonorrhoeae ferric iron uptake transporter with an unusual and substantial domain swap in the C-terminal regulatory domain. This entanglement suggests that FbpC is unable to open to the same extent as the homologous protein MalK. Using molecular dynamics we demonstrate that this is not the case: both NBDs open rapidly once ATP is removed. We conclude from this result that the closed structures of FbpC and MalK have higher free energies than their respective open states. This result has important implications for our understanding of the mechanism of power generation in ABC transporters, because the unwinding of this free energy ensures that the opening of these two NBDs is also powered.
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Sep 2009
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Abstract: The group 13 monoalkoxometallanes [Me_{2}Ga(OC(CH_{3})_{2}CH_{2}OMe)]_{2} (1) and [Me_{2}In(OCH(CH_{3})CH_{2}OMe)]_{2} (2), incorporating donor functionalised alkoxides, were synthesised from the reaction of GaMe_{3} or InMe_{3} with ROH (R=C(CH_{3})_{2}CH_{2}OMe (1); R=CH(CH_{3})CH_{2}OMe (2)) in toluene. X-ray crystallography showed that both compounds adopt dimeric structures with a planar M_{2}O_{2} ring, and each group 13 atom is coordinated in a distorted trigonal bipyramidal geometry. The AACVD reaction of GaMe_{3} and ROH (R =C(CH_{3})_{2}CH_{2}OMe, CH_{2}CH_{2}OMe, CH_{2}CH_{2}NMe_{2}) resulted in the formation of thin films of Ga_{2}O_{3} on glass substrates at 450°C. The gallium oxide films were analyzed by scanning electron microscopy, X-ray powder diffraction, energy dispersive analysis of X-rays, wavelength dispersive analysis of X-rays and X-ray photoelectron spectroscopy. This CVD technique offers a rapid, convenient route to Ga_{2}O_{3}, which involves the in situ formation of dimethylgallium alkoxides, of the type [Me_{2}Ga(?-OR)]_{2} similar to compound 1.
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Mar 2010
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Abstract: We have determined the structure of a complex rhodium carbonyl chloride [Rh(CO)2Cl] molecule adsorbed on the TiO2(110) surface by the normal incidence x-ray standing wave technique. The data show that the technique is applicable to reducible oxide systems and that the dominant adsorbed species is undissociated with Rh binding atop bridging oxygen and to the Cl found close to the fivefold coordinated Ti ions in the surface. A minority geminal dicarbonyl species, where Rh-Cl bond scission has occurred, is found bridging the bridging oxygen ions forming a high-symmetry site.
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Feb 2007
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Abstract: The metal cofactor determines the thermal stability in cupredoxins, but how the redox state of copper modulates their melting points remains unknown. The metal coordination environment is highly conserved in cyanobacterial plastocyanins. However, the oxidised form is more stable than the reduced one in thermophilic Phormidium, but the opposite occurs in mesophilic Synechocystis. We have performed neutral amino-acid substitutions at loops of Phormidium plastocyanin far from the copper site. Notably, mutation P49G/G50P confers a redox-dependent thermal stability similar to that of the mesophilic plastocyanin. Moreover, X-ray absorption spectroscopy reveals that P49G/G50P mutation makes the electron density distribution at the oxidised copper site shift towards that of Synechocystis plastocyanin.
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Jun 2010
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Abstract: This editorial serves as the preface to a special issue of New Journal of Physics, which collects together solicited papers on a common subject, x-ray beams with high coherence. We summarize the issue's content, and explain why there is so much current interest both in the sources themselves and in the applications to the study of the structure of matter and its fluctuations (both spontaneous and driven). As this collection demonstrates, the field brings together accelerator physics in the design of new sources, particle physics in the design of detectors, and chemical and materials scientists who make use of the coherent beams produced.
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Mar 2010
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S.
Arai
,
I.
Yamato
,
A.
Saijo
,
Y.
Kakinuma
,
Y.
Ishizuka-katsura
,
M.
Toyama
,
T.
Terada
,
M.
Shirouzu
,
S.
Yokoyama
,
S.
Iwata
,
T.
Murata
Diamond Proposal Number(s):
[316]
Abstract: Enterococcus hirae vacuolar ATPase (V-ATPase) is composed of a soluble catalytic domain (V1; NtpA3-B3-D-G) and an integral membrane domain (V0; NtpI-K10) connected by a central and peripheral stalk(s) (NtpC and NtpE-F). Here we examined the nucleotide binding of NtpA monomer, NtpB monomer or NtpD-G heterodimer purified by using Escherichia coli expression system in vivo or in vitro, and the reconstitution of the V1 portion with these polypeptides. The affinity of nucleotide binding to NtpA was 6.6 ?M for ADP or 3.1 ?M for ATP, while NtpB or NtpD-G did not show any binding. The NtpA and NtpB monomers assembled into NtpA3-B3 heterohexamer in nucleotide binding-dependent manner. NtpD-G bound NtpA3-B3 forming V1 (NtpA3-B3-D-G) complex independent of nucleotides. The V1 formation from individual NtpA and NtpB monomers with NtpD-G heterodimer was absolutely dependent on nucleotides. The ATPase activity of reconstituted V1 complex was as high as that of native V1-ATPase purified from the V0V1 complex by EDTA treatment of cell membrane. This in vitro reconstitution system of E. hirae V1 complex will be valuable for characterizing the subunit-subunit interactions and assembly mechanism of the V1-ATPase complex.
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Dec 2009
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Abstract: The X-ray standing wave technique is used for a site specific analysis of the valence band of SrTiO3. The determined partial photoelectron yields reveal the hybridization of metal and oxygen derived states. Fitting ab initio calculated density of states to the data yields solid state photoelectric cross sections, which are much larger than for corresponding atomic states for Ti 4s and Sr 5s. Valence band features are significantly broader than predicted by single particle band structure calculations in particular for oxygen derived states. This can, at least in part, be explained by correlation effects. (C) 2010 Elsevier Ltd. All rights reserved.
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Jan 2010
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Abstract: Controlling a phase of matter by coherently manipulating specific vibrational modes has long been an attractive (yet elusive) goal for ultrafast science. Solids with strongly correlated electrons, in which even subtle crystallographic distortions can result in colossal changes of the electronic and magnetic properties, could be directed between competing phases by such selective vibrational excitation. In this way, the dynamics of the electronic ground state of the system become accessible, and new insight into the underlying physics might be gained. Here we report the ultrafast switching of the electronic phase of a magnetoresistive manganite via direct excitation of a phonon mode at 17-THz. A prompt, five-order-of-magnitude drop in resistivity is observed, associated with a non-equilibrium transition from the stable insulating phase to a metastable metallic phase. In contrast with light-induced1, 2, 3 and current-driven4 phase transitions, the vibrationally driven bandgap collapse observed here is not related to hot-carrier injection and is uniquely attributed to a large-amplitude Mn-O distortion. This corresponds to a perturbation of the perovskite-structure tolerance factor, which in turn controls the electronic bandwidth via inter-site orbital overlap5, 6. Phase control by coherent manipulation of selected metal-oxygen phonons should find extensive application in other complex solids-notably in copper oxide superconductors, in which the role of Cu-O vibrations on the electronic properties is currently controversial.
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Sep 2007
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Abstract: The self-assembly of a hydrophobically modified fragment of the amyloid b (Ab) peptide has been studied in methanol. The peptide FFKLVFF is based on Ab(16-20) extended at the N terminus by two phenylalanine residues. The formation of amyloid-type fibrils is confirmed by Congo Red staining, thioflavin T fluorescence and circular dichroism experiments. FTIR points to the formation of b-sheet structures in solution and in dried films and suggests that aggregation occurs at low concentration and is not strongly affected by further increase in concentration, i.e. the peptide is a strong fibril-former in methanol. UV fluorescence experiments on unstained peptide and CD point to the importance of aromatic interactions between phenylalanine groups in driving aggregation into b-sheets. The CD spectrum differs from that usually observed for b-sheet assemblies formed by larger peptides or proteins and this is discussed for solutions in methanol and also trifluoroethanol. The fibril structure is imaged by transmission electron microscopy and scanning electron microscopy on dried samples and is confirmed by small-angle X-ray scattering experiments in solution.
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Aug 2007
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