Organic compounds present in the natural Amazonian aerosol : characterization by gas chromatography–mass spectrometry

[1] As part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA)-Cooperative LBA Airborne Regional Experiment (CLAIRE) 2001 campaign in July 2001, separate day and nighttime aerosol samples were collected at a ground-based site in Amazonia, Brazil, in order to examine the composition and temporal variability of the natural “background” aerosol. We used a high-volume sampler to separate the aerosol into fine (aerodynamic diameter, AD < 2.5 μm) and coarse (AD > 2.5 μm) size fractions and quantified a range of organic compounds in methanolic extracts of the samples by a gas chromatographic-mass spectrometric technique. The carbon fraction of the compounds could account for an average of 7% of the organic carbon (OC) in both the fine and coarse aerosol fractions. We observed the highest concentrations of sugars, sugar alcohols, and fatty acids in the coarse aerosol samples, which suggests that these compounds are associated with primary biological aerosol particles (PBAP) observed in the forest atmosphere. Of these, trehalose, mannitol, arabitol, and the fatty acids were found to be more prevalent at night, coinciding with a nocturnal increase in PBAP in the 2–10 μm size range (predominantly yeasts and other small fungal spores). In contrast, glucose, fructose, and sucrose showed persistently higher daytime concentrations, coinciding with a daytime increase in large fungal spores, fern spores, pollen grains, and, to a lesser extent, plant fragments (generally >20 μm in diameter), probably driven by lowered relative humidity and enhanced wind speeds/convective activity during the day. For the fine aerosol samples a series of dicarboxylic and hydroxyacids were detected with persistently higher daytime concentrations, suggesting that photochemical production of a secondary organic aerosol from biogenic volatile organic compounds may have made a significant contribution to the fine aerosol. Anhydrosugars (levoglucosan, mannosan, galactosan), which are specific tracers for biomass burning, were detected only at low levels in the fine aerosol samples. On the basis of the levoglucosan-to-OC emission ratio measured for biomass burning aerosol, we estimate that an average of ∼16% of the OC in the fine aerosol was due to biomass burning during CLAIRE 2001, indicating that the major fraction was associated with biogenic particles.

Regulation of human pregnane X receptor and its target gene cytochrome P450 3A4 by Chinese herbal compounds and a molecular docking study

1. The pregnane X receptor (PXR) plays a critical role in the regulation of human cytochrome P450 3A4 (CYP3A4) gene. In this study, we investigated the effect of an array of compounds isolated from Chinese herbal medicines on the activity of PXR using a luciferase reporter gene assay in transiently transfected HepG2 and Huh7 cells and on the expression of PXR and CYP3A4 in LS174T cells. Furthermore, molecular docking was performed to investigate the binding modes of herbal compounds with PXR.

2. Praeruptorin A and C, salvianolic acid B, sodium danshensu, protocatechuic aldehyde, cryptotanshinone, emodin, morin, and tanshinone IIA significantly transactivated the CYP3A4 reporter gene construct in either HepG2 or Huh7 cells. The PXR mRNA expression in LS174T cells was significantly induced by physcion, protocatechuic aldehyde, salvianolic acid B, and sodium danshensu. However, epifriedelanol, morin, praeruptorin D, mulberroside A, tanshinone I, and tanshinone IIA significantly down-regulated the expression of PXR mRNA in LS174T cells.

3. All the herbal compounds tested can be readily docked into the ligand-binding cavity of PXR mainly through hydrogen bond and aromatic interactions with Ser247, Gln285, His407, and Arg401.

4. These findings suggest that herbal medicines can significantly regulate PXR and CYP3A4 and this has important implication in herb–drug interactions.

New 'green' corrosion inhibitors based on rare earth compounds

A series of rare earth organic compounds pioneered by our group have been shown to provide a viable alternative to theuse of chromates as corrosion inhibitors for some steel and aluminium applications. For example we have shown thatthe lanthanum 4-hydroxy cinnamate offers excellent corrosion mitigation for mild steel in aqueous environments whilerare earth diphenyl phosphates offer the best protection in the case of aluminium alloys. In both cases the protectionappears to be related to the formation of a nanometre thick interphase occurring on the surface that reduces theelectrochemical processes leading to metal loss or pitting. Very recent work has indicated that we may even be able toaddress the challenging issue of stress corrosion cracking of high strength steels. Furthermore, filiform corrosion can besuppressed when selected rare earth inhibitor compounds are added as pigments to a polymer coating. There is little doubtfrom the work thus far that a synergy exists between the rare earth and organic inhibitor components in these novelcompounds. This paper reviews some of the published research conducted by the senior author and colleagues over the past10 years in this developing field of green corrosion inhibitors

Nanorods of vanadium compounds: synthesis, characterisation, and application in electrochemical energy storage

The synthesis and characterisation of nanorods of vanadium pentoxide, V(2)O(5), vanadium trioxide, V(2)O(3), vanadium dioxide, VO(2)(B), and vanadium nitride, VN, are presented, and their application in electrochemical supercapacitors and lithium-ion batteries is outlined. Specifically, a novel method for the preparation of V(2)O(5) nanorods is discussed. It involves ball milling as a first step and controlled annealing as a second step. Nanorods of V(2)O(5) can be converted into those of other vanadium-related phases by simple chemical reduction treatments. Such chemical transformations are pseudomorphic and often topotactic, that is, the resulting nanorods belong to a different chemical phase but tend to retain the original morphology and preferential crystal orientation dictated by parent V(2)O(5) crystals.

The corresponding properties of nanorods for their prospective application in electrochemical energy storage (lithium-ion batteries and electrochemical supercapacitors) are discussed. The synthesised V(2)O(5) nanorods possess a stable cyclic behaviour when they are used in a cathode of a lithium-ion battery and are suitable for use in an anode. VN nanorods synthesised by NH(3) reduction of V(2)O(5) were found to possess pseudocapacitive properties in aqueous electrolytes.

New series of intramolecularly coordinated diaryltellurium compounds. Rational synthesis of the diarylhydroxytelluronium triflate [(8-Me 2NC 10H 6) 2Te(OH)](O 3SCF 3)

The reaction of 8-dimethylaminonaphthyllithium etherate with the tellurium(II) bis(dithiocarbamate) Te(S₂CNEt₂)₂ provided the diaryltelluride (8-Me₂NC₁₀H₆)₂Te (1). The oxidation of 1 with an excess of H₂O₂ did not afford the expected diaryltellurium(IV) oxide (8-Me₂NC₁₀H₆)₂TeO (2), but the diaryltellurium(VI) dioxide (8-Me₂NC₁₀H₆)₂TeO₂ (3). The preparation of 2 was achieved by the comproportionation reaction of 1 and 3. The protonation of 2 using triflic acid gave rise to the formation of diarylhydroxytelluronium triflate [(8-Me₂NC₁₀H₆)₂Te(OH)](O₃SCF₃) (4), which features the protonated diaryltellurium oxide [(8-Me₂NC₁₀H₆)₂Te(OH)]+ (4a). Compounds 1, 3·H₂O·H₂O₂, 3·2H₂O, and 4 were characterized by X-ray crystallography. The experimentally obtained molecular structures were compared to those calculated for 1–3, 4a, and (8-Me₂NC₁₀H₆)₂Te(OH)₂ (5) as well as the related diphenyltellurium compounds Ph₂Te (6), Ph₂TeO (7), Ph₂TeO₂ (8), [Ph₂Te(OH)]+ (9a), and Ph₂Te(OH)₂ (10) at the DFT/B3PW91 level of theory.

Electronic structure of the azide group in 3′-Azido-3′- deoxythymidine (AZT) compared to small azide compounds

Theoretical calculations for some structural and electronic properties of the azide moiety in the nucleoside reverse transcriptase (RT) inhibitor 3′-azido-3′- deoxythymidine (AZT) are reported. These properties, which include geometrical properties in three dimensional space, Hirshfeld charges, electrostatic potential (MEP), vibrational frequencies, and core and valence ionization spectra, are employed to study how the azide group is affected by the presence of a larger fragment. For this purpose, two small but important organic azides, hydrazoic acid and methyl azide, are also considered. The general features of trans Cs configuration for RNNN fragments[1] is distorted in the large AZT bio-molecule. Hirshfeld charge analysis shows charges are reallocated more evenly on azide when the donor group R is not a single atom. Infrared and photoelectron spectra reveal different aspects of the compounds. In conclusion, the electronic structural properties of the compounds depend on the specific property, the local structure and chemical environment of a species.

π-Selective stationary phases: (II) Adsorption behaviour of substituted aromatic compounds on n-alkyl-phenyl stationary phases

The frontal analysis method was used to measure the adsorption isotherms of phenol, 4-chlorophenol, p-cresol, 4-methoxyphenol and caffeine on a series of columns packed with home-made alkyl-phenyl bonded silica particles. These ligands consist of a phenyl ring tethered to the silica support via a carbon chain of length ranging from 0 to 4 atoms. The adsorption isotherm models that fit best to the data account for solute–solute interactions that are likely caused by π–π interactions occurring between aromatic compounds and the phenyl group of the ligand. These interactions are the dominant factor responsible for the separation of low molecular weight aromatic compounds on these phenyl-type stationary phases. The saturation capacities depend on whether the spacer of the ligands have an even or an odd number of carbon atoms, with the even alkyl chain lengths having a greater saturation capacity than the odd alkyl chain lengths. The trends in the adsorption equilibrium constant are also significantly different for the even and the odd chain length ligands.

π-Selective stationary phases: (III) Influence of the propyl phenyl ligand density on the aromatic and methylene selectivity of aromatic compounds in reversed phase liquid chromatography

The retention characteristics of phenyl type stationary phases for reversed phase high performance liquid chromatography are still largely unknown. This paper explores the retention process of these types of stationary phases by examining the retention behaviour of linear PAHs and n-alkylbenzenes on a series of propyl phenyl stationary phases that have changes in their ligand density (1.23, 1.31, 1.97, 2.50 μmol m⁻²). The aromatic and methylene selectivities increased with increasing ligand density until a point where a plateau was observed, overall the propyl phenyl phases had a higher degree of aromatic selectivity than methylene selectivity indicating that these columns are suitable for separations involving aromatic compounds. Also, retention characteristics relating to the size of the solute molecule were observed to be influenced by the ligand density. It is likely that the changing retention characteristics are caused by the different topologies of the stationary phases at different ligand densities. At high ligand densities, the partition coefficient became constant.

π-Selective stationary phases: (I) Influence of the spacer chain length of phenyl type phases on the aromatic and methylene selectivity of aromatic compounds in reversed phase high performance liquid chromatography

Phenyl type stationary phases of increasing spacer chain length (phenyl, methyl phenyl, ethyl phenyl, propyl phenyl and butyl phenyl, with 0–4 carbon atoms in the spacer chain, respectively) were synthesised and packed in house to determine the impact that the spacer chain length has on the retention process. Two trends in the aromatic selectivity, q_aromatic, were observed, depending on whether the number of carbon atoms in the spacer chain is even or odd. Linear log k′ vs ϕ plots were obtained for each stationary phase and the S coefficient was determined from the gradient of these plots. For the phenyl type phases, the S vs n_c plots of the retention factors of linear polycyclic aromatic hydrocarbons vs the number of rings exhibit a distinct discontinuity that between 3 and 4 rings, which increases with increasing spacer chain length for even phases but decreases for odd phases. Accordingly, we suggest that the retention factors depend differently on the number of carbon atoms in the spacer chain depending on whether this number is even or odd and that this effect is caused by different orientations of the aromatic ring relative to the silica surface.

Recent developments in corrosion inhibitors based on rare earth metal compounds

Rare earth organic compounds can provide an environmentally safe and non-toxic alternative to chromates as corrosion inhibitors for some steel and aluminium applications. For steel lanthanum 4-hydroxy cinnamate offers corrosion protection and reduces the susceptibility to hydrogen embrittlement. Recent work has also indicated that it inhibits the corrosion of steel in environments containing high levels of carbon dioxide. For aluminium alloys, cerium diphenyl phosphate provides excellent corrosion inhibition in chloride environments, and reduces susceptibly to stress corrosion cracking. Furthermore, for both steel and aluminium alloys filiform corrosion can be suppressed when rare earth inhibitor compounds are added as pigments to polymer coatings. The levels of inhibition observed are thought to be due to synergistic effects between the rare earth and organic parts of these novel compounds, and are related to the various species that may be present in the complex chemical conditions that develop in solution close to a metal surface. This paper reviews some of the published research conducted by the group at Deakin University over recent years.

Inhibiting localized corrosion of aluminum and aluminum alloy by rare earth metal compounds : behaviors and characteristics observed using an electrochemically integrated multi-electrode array

An electrochemically integrated multi-electrode array namely the wire beam electrode (WBE) has been used to characterize the behavior of cerium chloride (CeCl3) and lanthanum chloride (LaCl3) in inhibiting localized corrosion of AA2024-T3 and AA1100. CeCl3 has been found to inhibit AA2024-T3 corrosion in 0.005 M sodium chloride (NaCl) solution by suppressing galvanic corrosion activities and by creating a large number of insignificant anodes. It has also been shown to inhibit localized corrosion of AA1100 in 0.5 M NaCl solution by promoting the random distribution of minor anodes. LaCl3 has been found to inhibit localized corrosion of AA2024-T3 at 1000 ppm, although its efficiency dropped significantly when its concentration decreased to 500 ppm. The addition of CeCl3 and LaCl3 to corrosion testing cells at later stages was unable to effectively suppress existing corrosion anodes.