Analysis of the OH bend and stretch region in the vibrational spectrum of water

A method for calculating the infrared absorption spectrum of water in a range of different physical environments is described. Calculations are based on Monte Carlo simulations together with local-mode analyses of the H₂O vibrations. Results for liquid water and amorphous ice show clearly that the major features of the OH stretching motions are reproduced with good accuracy.     

High speed analysis of underivatized drugs by gas chromatography–mass spectrometry

The technique of choice for many types of forensic drug confirmations is gas chromatography/mass spectrometry (GC/MS). Significant amounts of analytical time can be involved in a GC/MS run. The use of a 0.1 mm i.d. fused silica capillary column with hydrogen carrier gas can significantly increase the speed of an analysis without sacrificing resolution. Nanogram levels of underivatized drugs, from amphetamine to strychnine, can be eluted in less than twelve minutes. The multitasking system permits data acquisition, while performing data reduction on the previous run.     

A guide for the meaningful surface analysis of wood by XPS and ToF-SIMS

The surface analysis of wood and wood products is becoming increasingly important for reasons ranging from the investigation of molecular constituents through to the optimization of industrial processes. As with any natural product, wood analysis is not straightforward, and this review aims to provide guidance for the successful surface analysis of wood by XPS and ToF-SIMS. Through example experiments, three themes are addressed relevant to obtaining meaningful results: considerations related to heterogeneity in the composition of wood (e.g., growth rings); the impact of the chemical removal of minor wood components known as extractives, and whether such a process is necessary; and the potential for misleading or erroneous results as a result of contamination occurring during sample preparation. In addition to discussing successful sample preparation approaches, the important role to be played by MVA in surface analysis is emphasized, particularly in the analysis of ToF-SIMS data. Examples of ToF-SIMS/MVA are provided that highlight the identification of contamination in sample preparation, the quantification of wood composition in terms of cellulose and lignin, and the indication of age of softwood samples. Through consideration of the complexities that influence wood surface analysis, the design and interpretation of consequential experiments become easier and more accurate.     

Coupled-cluster study of isomers of H2SO2

A theoretical study has been made on six isomers of H2SO2 using coupled-cluster singles and doubles with noniterative triple excitations (CCSD(T)). The isomers studied are sulfoxylic acid (S(OH)2; C2 and Cs conformers), sulfinic acid (HS(=O)OH; 2 C1 conformers), dihydrogen sulfone (H2SO2; C2v), sulfhydryl hydroperoxide (HSOOH; C1), thiadioxirane (Cs), and dihydrogen persulfoxide (H2SOO; Cs). Molecular geometries, harmonic vibrational frequencies, and infrared intensities of all species were obtained using the CCSD(T) method and the 6-311++G(2d,2p) basis set. All aforementioned species were found to be local minima, with the exception of thiadioxirane, which has one imaginary frequency. A prior possible infrared observation of sulfinic acid was reassessed on the basis of the present data. In agreement with previous MP2 results, the present CCSD(T) data provide support for at most 4 of the 8 observed frequencies. The CCSD(T) frequencies and intensities should be of assistance in future identification of H2SO2 isomers by vibrational spectroscopy. Relative energies were calculated using the CCSD(T) method and several larger basis sets. As found previously, the lowest energy species is C2 S(OH)2, followed by Cs S(OH)2, HS(=O)OH, H2SO2, HSOOH, thiadioxirane, and H2SOO. Expanding the basis set significantly reduces the relative energies of HS(=O)OH and H2SO2. The CCSD(T) method was used with extended basis sets (up to aug-cc-pV(Q+d)Z) and basis set extrapolation in two reaction schemes to calculate the DeltaH degrees t (25 degrees C) of C2 S(OH)2. The two reaction schemes gave -285.8 and -282.7 kJ mol-1, which are quite close to a prior theoretical estimate (-290 kJ mol-1).     

Aryl trihydroxyborates: easily isolated discrete species convenient for direct application in coupling reactions

A conceptually and practically simple alternative approach to the use of arylboron species as the organometallic component in cross-coupling processes is described whereby trihydroxyborate salts are isolated and directly employed. The protocol derives practical benefit from the ease and convenience of the isolation and subsequent use of the discrete borate salts, eliminates the need for additional base, and aids the use of correct reaction stoichiometry.     

Modulation of amyloid-β aggregation by metal complexes with a dual binding mode and their delivery across the blood–brain barrier using focused ultrasound

One of the key hallmarks of Alzheimer''s disease is the aggregation of the amyloid-β peptide to form fibrils. Consequently, there has been great interest in studying molecules that can disrupt amyloid-β aggregation. While a handful of molecules have been shown to inhibit amyloid-β aggregation in vitro, there remains a lack of in vivo data reported due to their inability to cross the blood–brain barrier. Here, we investigate a series of new metal complexes for their ability to inhibit amyloid-β aggregation in vitro. We demonstrate that octahedral cobalt complexes with polyaromatic ligands have high inhibitory activity thanks to their dual binding mode involving π–π stacking and metal coordination to amyloid-β (confirmed via a range of spectroscopic and biophysical techniques). In addition to their high activity, these complexes are not cytotoxic to human neuroblastoma cells. Finally, we report for the first time that these metal complexes can be safely delivered across the blood–brain barrier to specific locations in the brains of mice using focused ultrasound.

We report a series of non-toxic cobalt(iii) complexes which inhibit Aβ peptide aggregation in vitro; these complexes can be safely delivered across the blood–brain barrier in mice using focused ultrasound.     

Fragmentations and reactions of the organophosphate insecticide Diazinon and its oxygen analog Diazoxon studied by electrospray ionization ion trap mass spectrometry

The fragmentations and reactions of Diazinon and related compounds have been studied by electrospray ionization ion trap mass spectrometry. Several novel fragmentation and rearrangements have been observed, including an intramolecular thiono-thiolo rearrangement. The stability, in the gas-phase, of the protomers of 2-isopropyl-4-methyl-6-pyrimidinol has been demonstrated. The complexity of the gas phase ion processes observed suggest that, at present, caution should be exercised in using this approach for the analysis of environmental and other samples until our understanding of these processes increases considerably.     

Collection and Identification of Trace Organic Compounds in Atmospheric Deposition from a Semi-Rural Site in the U.K.

Abstract

The collection of rainwater, aerosol and vapour samples at a semi-rural site in the UK was achieved using a PTFE-lined wet-only rainfall collector and a high-volume filter/adsorption trap air sampler, respectively. Analysis of atmospheric deposition revealed the presence of several hundred compounds, many of which were of anthropogenic origin, e.g.: PAH, phenols and alkylbenzenes. Amounts of compounds varied from low nanograms to tens of micrograms per litre in rainwater samples and from low picograms to high nanograms per cubic metre in aerosols. Phenolic compounds were the most abundant group of organics identified in rainwater and were present at total concentrations of >20μg1^?1 in some of the samples analysed. In the high-volume air samples most anthropogenic compounds were detected in the adsorbent rather than the filter extract. Seasonal variations in the PAH content of the adsorbent extracts were observed. The presence of siloxanes in the air samples was thought to be the result of contamination.     

Differential stable isotope labeling of peptides for quantitation and de novo sequence derivation.

We have demonstrated the use of per-methyl esterification of peptides for relative quantification of proteins between two mixtures of proteins and automated de novo sequence derivation on the same dataset. Protein mixtures for comparison were digested to peptides and resultant peptides methylated using either d0- or d3-methanol. Methyl esterification of peptides converted carboxylic acids, such as are present on the side chains of aspartic and glutamic acid as well as the carboxyl terminus, to their corresponding methyl esters. The separate d0- and d3-methylated peptide mixtures were combined and the mixture subjected to microcapillary high performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). Parent proteins of methylated peptides were identified by correlative database searching of peptide tandem mass spectra. Ratios of proteins in the two original mixtures could be calculated by normalization of the area under the curve for identical charge states of d0- to d3-methylated peptides. An algorithm was developed that derived, without intervention, peptide sequence de novo by comparison of tandem mass spectra of d0- and d3-peptide methyl esters.     

A review of oxygen-17 solid-state NMR of organic materials--towards biological applications

¹⁷O solid state NMR of organic materials is developing rapidly. This article provides a snapshot of the current state of development of this field. The NMR techniques and enrichment protocols that are driving this progress are outlined. The ¹⁷O parameters derived from solid-state NMR experiments are summarized and the structural sensitivity of the approach to effects such as hydrogen bonding highlighted. The prospects and challenges for ¹⁷O solid-state NMR of biomolecules are discussed.