Electroreduction of Aryldiazonium Ion at the Polar and Non-Polar Faces of ZnO: Characterisation of the Grafted Films and Their Influence on Near-Surface Band Bending

ZnO is a strong candidate for transparent electronic devices due to its wide band gap and earth-abundance, yet its practical use is limited by its surface metallicity arising from a surface electron accumulation layer (SEAL). The SEAL forms by hydroxylation of the surface under normal atmospheric conditions, and is present at all crystal faces of ZnO, although with differing hydroxyl structures. Multilayer aryl films grafted from aryldiazonium salts have previously been shown to decrease the downward bending at O-polar ZnO thin films, with Zn−O−C bonds anchoring the aryl films to the substrate. Herein we show that the Zn-polar (0001), O-polar (000 ), and non-polar m-plane (10 0) faces of ZnO single crystals, can also be successfully electrografted with nitrophenyl (NP) films. In all cases, X-ray photoelectron spectroscopy (XPS) measurements reveal that the downward surface band bending decreases after modification. XPS provides strong evidence for Zn−O−C bonding at each face. Electrochemical reduction of NP films on O-polar ZnO single crystals converts the film to a mainly aminophenyl layer, although with negligible further change in band bending. This contrasts with the large upward shifts in band bending caused by X-ray induced reduction.     

Synthesis of the methanesulfonates of α-(4-chlorophenyl)-α-[1-(2-chlorophenyl)emenyl]-1H-1,2,4-triazole-1-ethanol and α-[1-(2-chlorophenyl)ethenyl]-α-(2,4-difluorophenyl)-1H-1,2,4-triazole-1-ethanol,alpha styryl carbinol antifungal agents

The methanesulfonates of (α-(4-chlorophenyl)-α-[1-(2-chlorophenyl)ethenyl]-1H-1,2,4-triazole-1-ethanol and α-[1-(2-chlorophenyl)ethenyl]-α-(2,4-difluorophenyl)-1H-1,2,4-triazole-1-ethanol ( 1a, b ) are orally effective α-styryl carbinol derivatives developed for the treatment and prevention of systemic fungal infections. Practical new processes amenable for the large-scale production of these compounds are described. Of note is the selection of dichlorostyrene as a convenient precursor of the styryl portion, modification of a sensitive Grignard addition into a realistic preparative reaction and the use of 1,2,4-triazole simultaneously as a base transfer agent and nucleophile.     

Multilayer nitroazobenzene films covalently attached to carbon. An AFM and electrochemical study

Nitroazobenzene films have been grafted to pyrolyzed photoresist films by electrochemical reduction of the corresponding diazonium salt in acetonitrile solution. Two component films were also prepared by electrochemically grafting methylbenzene layers to preformed NAB films. Voltammetric investigation of the films in aqueous acid medium and the measurement of film thickness using atomic force microscopy (AFM) lead to new insights into film structure. In aqueous acid solution, the azobenzene groups have no detectable electroactivity and not all nitro groups in the films can be reduced. These findings point to a compact film structure in which proton diffusion is limited. There may also be spatial inhibition of the conformational changes that accompany azobenzene reduction. For increasingly thick NAB films, the peak for reduction of the nitro groups moves to more negative potentials and the peaks become more asymmetric in shape. These changes are interpreted in terms of the dielectric properties and the rate of proton diffusion in the films. Film thickness was measured by ploughing through the film with an AFM tip. When an NAB film prepared in acetonitrile solution is reduced in aqueous acid, the film thickness decreases by more than 50%. The changes can be partially reversed by treatment in acetonitrile-electrolyte solution and hence are attributed to ion-solvent induced swelling and shrinking. Thus, the large decrease in thickness detected by AFM after treatment of the film in aqueous acid is consistent with the compact film structure revealed by electrochemistry.     

Electrospray-assisted modification of proteins: a radical probe of protein structure

A new approach is described to probe the structure of proteins through their reactivity with oxygen-containing radicals. Radical-induced oxidative modification of proteins is achieved within an electrospray ion source using oxygen as a reactive nebulizer gas at high needle voltages. This method facilitates the rapid oxidation of proteins as the molecules emerge from the electrospray needle tip. Electrospray mass spectra of both ubiquitin and lysozyme reveal that over 50% of the protein can be modified under these conditions. The radical-induced oxidative modification of amino acid side chains is correlated with their solvent accessibility to obtain information on a protein's higher-order structure. The oxidation sites in hen lysozyme have been identified by proteolysis of the condensed protein solution and tandem mass spectrometry (MS/MS). Oxidation of tryptophan at positions 62 and 123 occurs exclusively over all other tryptophan residues, consistent with the relative solvent accessibilities of the residue side chains based on the NMR structure of the protein. Radical-induced oxidative modification of cysteine (Cys), methionine (Met), tryptophan (Trp), phenylalanine (Phe), tyrosine (Tyr), proline (Pro), histidine (His), and leucine (Leu) residues is also reported, providing sufficient reactive markers to span a protein sequence. This facile oxidation process could be applied to investigate the molecular mechanism by which reactive oxygen species interact with a particular protein domain as a means to investigate the onset of certain diseases.     

Amino acid sequence prerequisites for the formation of cn ions

Ammo acid sequence prerequisites are described for the formation of c, ions observed in high-energy collision-induced decomposition spectra of peptides. It is shown that the formation of c_n ions is promoted by the nature of the amino acid C-terminal to the cleavage site. A propensity for c_n cleavage preceding threonine, and to a lesser extent tryptophan, lysine, and serine, is demonstrated where fragmentation is directed N-terminally at these residues. In addition, the nature of the residue N-terminal to the cleavage site is shown to have little effect on c_n ion formation. A mechanism for c_n ion formation is proposed and its applicability to the results observed is discussed.     

Polyphenolics with Strong Antioxidant Activity from Acacia nilotica Ameliorate Some Biochemical Signs of Arsenic-Induced Neurotoxicity and Oxidative Stress in Mice

Neurotoxicity is a serious health problem of patients chronically exposed to arsenic. There is no specific treatment of this problem. Oxidative stress has been implicated in the pathological process of neurotoxicity. Polyphenolics have proven antioxidant activity, thereby offering protection against oxidative stress. In this study, we have isolated the polyphenolics from Acacia nilotica and investigated its effect against arsenic-induced neurotoxicity and oxidative stress in mice. Acacia nilotica polyphenolics prepared from column chromatography of the crude methanol extract using diaion resin contained a phenolic content of 452.185 ± 7.879 mg gallic acid equivalent/gm of sample and flavonoid content of 200.075 ± 0.755 mg catechin equivalent/gm of sample. The polyphenolics exhibited potent antioxidant activity with respect to free radical scavenging ability, total antioxidant activity and inhibition of lipid peroxidation. Administration of arsenic in mice showed a reduction of acetylcholinesterase activity in the brain which was counteracted by Acacia nilotica polyphenolics. Similarly, elevation of lipid peroxidation and depletion of glutathione in the brain of mice was effectively restored to normal level by Acacia nilotica polyphenolics. Gallic acid methyl ester, catechin and catechin-7-gallate were identified in the polyphenolics as the major active compounds. These results suggest that Acacia nilotica polyphenolics due to its strong antioxidant potential might be effective in the management of arsenic induced neurotoxicity.     

Dimetallic complexes of acyclic pyridine-armed ligands derived from 3,6-diformylpyridazine

A bis(pyridine-armed) acyclic Schiff base ligand L1 has been synthesised from 3,6-diformylpyridazine and two equivalents of 2-(2-aminoethyl)pyridine. Reduction of this ligand using NaBH(4) resulted in the formation of the amine analogue L2. Complexes of the form [M(2)L1(mu-X)]Y(2)ClO(4)[where: M = Cu(II), X = OH(-) and Y = ClO(4)(-) 1, Cl(-) 2, Br(-) 3 or I(-) 4; M = Co(II), X = OH(-) and Y = ClO(4)(-) 5; M = Ni(II), X = SCN(-) 6 or X = N(3)(-) 7 and Y = ClO(4)(-)], and [Cu(2)L2(mu-OH)](ClO(4))(3) 8 were prepared and characterised. The complexes 1 and 5-7 have been characterised by single-crystal X-ray diffraction. The acyclic L1 ligand provides three nitrogen donor atoms per metal centre, including a pyridazine bridge between the metal centres, and the anion X also bridges the two metal centres. As required, coordinating solvent molecules or additional anions make up the remainder of the coordination sphere. The two copper centres of 1 are very strongly antiferromagnetically coupled (2J=-1146 cm(-1))via the pyridazine and hydroxide ion bridges, whereas the competing antiferromagnetic pyridazine bridging pathway and ferromagnetic 1,1-bridging azide pathway resulted in the observation of weak antiferromagnetic exchange in the dinickel(II) complex 7 (2J=-14 cm(-1)). Electrochemical examination of L1, L2 and complexes 1 and 5-8 revealed multiple redox processes. These have been tentatively assigned to a mixture of metal centred and ligand centred redox processes on the basis of cyclic voltammetry and coulometry results and comparisons with literature examples.     

Design of robust binary film onto carbon surface using diazonium electrochemistry

The electroreduction of functionalized aryldiazonium salts combined with a protection-deprotection method was evaluated for the fabrication of organized mixed layers covalently bound onto carbon substrates. The first modification consists of the grafting of a protected 4-((triisopropylsilyl)ethynyl)benzene layer onto the carbon surface on which the introduction of a second functional group is possible without altering the first grafted functional group. After deprotection, we obtained an ultrathin robust layer presenting high densities of both active ethynylbenzene groups (available for "click" chemistry) and the second functional group. The strategy was successfully demonstrated using azidomethylferrocene to react with ethynyl moieties in the binary film by "click" chemistry, and NO(2)-phenyl as the second functional group. Two possible modification pathways with different orderings of the various steps were considered to show the influence and importance of the protection-deprotection process on the final surface obtained. Using mild conditions for the grafting of the second layer maintains a concentration of active ethynyl groups similar to that obtained for a one-component monolayer while achieving a high surface concentration of the second modifier. Considering the wide range of functional aryldiazonium salts that could be electrodeposited onto carbon surfaces and the versatility and specificity of the "click" chemistry, this approach appears very promising for the preparation of mixed layers in well-controlled conditions without altering the reactivity of either functional group.     

A history of mass spectrometry in Australia

An interest in mass spectrometry in Australia can be traced back to the 1920s with an early correspondence with Francis Aston who first visited these shores a decade earlier. The region has a rich tradition in both the development of the field and its application, from early measurements of ionization and appearance potentials by Jim Morrison at the Council for Scientific and Industrial Research (CSIR) around 1950 to the design and construction of instrumentation including the first use of a triple quadrupole mass spectrometer for tandem mass spectrometry, the first suite of programs to simulate ion optics (SIMION), the development of early TOF/TOF instruments and orthogonal acceleration and the local design and construction of several generations of a sensitive high-resolution ion microprobe (SHRIMP) instrument. Mass spectrometry has been exploited in the study and characterization of the constituents of this nation's unique flora and fauna from Australian apples, honey, tea plant and eucalyptus oil, snake, spider, fish and frog venoms, coal, oil, sediments and shale, environmental studies of groundwater to geochronological dating of limestone and granite, other terrestrial and meteoritic rocks and coral from the Great Barrier Reef. Peter Jeffery's establishment of geochronological dating techniques in Western Australia in the early 1950s led to the establishment of geochronology research both at the Australian National University and at what is now the Curtin Institute of Technology in the 1960s. This article traces the history of mass spectrometry in its many guises and applications in the island continent of Australia. An article such as this can never be complete. It instead focuses on contributions of scientists who played a major role in the early establishment of mass spectrometry in Australia. In general, those who are presently active in the field, and whose histories are incomplete, have been mentioned at best only briefly despite their important contributions to the field.