Dissociative Recombination of Protonated Formic Acid: Implications for Molecular Cloud and Cometary Chemistry

At the heavy ion storage ring CRYRING in Stockholm, Sweden, we have investigated the dissociative recombination of DCOOD2+ at low relative kinetic energies, from ~1 meV to 1 eV. The thermal rate coefficient has been found to follow the expression k(T) = 8.43 × 10-7 (T/300)^-0.78 cm3 s-1 for electron temperatures, T, ranging from ~10 to ~1000 K. The branching fractions of the reaction have been studied at ~2 meV relative kinetic energy. It has been found that ~87% of the reactions involve breaking a bond between heavy atoms. In only 13% of the reactions do the heavy atoms remain in the same product fragment. This puts limits on the gas-phase production of formic acid, observed in both molecular clouds and cometary comae. Using the experimental results in chemical models of the dark cloud, TMC-1, and using the latest release of the UMIST Database for Astrochemistry improves the agreement with observations for the abundance of formic acid. Our results also strengthen the assumption that formic acid is a component of cometary ices.

Rare-earth quinolinates: Infrared-emitting molecular materials with a rich structural chemistry

Near-infrared-emitting rare-earth chelates based on 8-hydroxyquinoline have appeared frequently in recent literature, because they are promising candidates for active components in near-infrared-luminescent optical devices, such as optical amplifiers, organic light-emitting diodes, .... Unfortunately, the absence of a full structural investigation of these rare-earth quinolinates is hampering the further development of rare-earth quinolinate based materials, because the luminescence output cannot be related to the structural properties. After an elaborate structural elucidation of the rare-earth quinolinate chemistry we can conclude that basically three types of structures can be formed, depending on the reaction conditions: tris complexes, corresponding to a 1:3 metal-to-ligand ratio, tetrakis complexes, corresponding to a 1:4 metal-to-ligand ratio, and trimeric complexes, with a 3:8 metal-to-ligand ratio. The intensity of the emitted near-infrared luminescence of the erbium(Ill) complexes is highest for the tetrakis complexes of the dihalogenated 8-hydroxyquinolinates.

A preliminary investigation into the use of testate amoebae for the discrimination of forensic soil samples

We present the results of an initial investigation into the efficacy of using testate amoebae for the discrimination of soils from wet ground and puddles, as little attention has been given to these organisms in forensic science. The preservation of testate amoebae in these sediments is generally good, although test concentrations are low. Statistical analysis suggests that restate amoebae assemblages are somewhat spatially distinct and have potential to be used for soil discrimination. A case study is presented where mineralogical (X-ray diffraction) and restate amoebae analyses are used in conjunction to clarify the scene of crime in a 'cold case' murder enquiry. Testate amoebae were recovered from dried sediment residues on clothing 10 years after the murder. Despite these promising results, further experimental work is crucial to examine the spatial and temporal variation of amoebae assemblages in water films, wet ground and puddles before they can be added to the armoury of methods available to the forensic biologist.

Forensic Geology in Environmental Crime: Illegal Waste Movement Burial in Northern Ireland

The illegal burial of waste often occurs in locations where loose, transferable material is abundant, allowing covert pits to be dug or filled. The transfer of waste material onto suspects and their vehicles during loading, unloading, and burial is common, as is the case during other criminal activities such as the burial of murder victims. We use two case studies to show that the established principles of using geological materials in excluding or linking suspects can be applied to illegal waste disposal. In the first case, the layering of different geological materials on the tailgate of a container used to transport toxic waste demonstrated where the vehicle had been and denied the owner's alibi, associating him with an illegal dumpsite. In the second case, an unusual suite of minerals, recovered from a suspect's trousers, provided the intelligence that led environmental law enforcement officers to an illegal waste burial site.

Fast, copper-free click chemistry: a convenient solid-phase approach to oligonucleotide conjugation

Solid-phase oligonucleotide conjugation by nitrile oxide-alkyne click cycloaddition chemistry has been successfully demonstrated; the reaction, compatible with all nucleobases, requires no metal catalyst and proceeds under physiological conditions.

Carbon chemistry in Galactic bulge planetary nebulae

Galactic bulge planetary nebulae show evidence of mixed chemistry with emission from both silicate dust and polycyclic aromatic hydrocarbons (PAHs). This mixed chemistry is unlikely to be related to carbon dredge-up, as third dredge-up is not expected to occur in the low-mass bulge stars. We show that the phenomenon is widespread and is seen in 30 nebulae out of 40 of our sample, selected on the basis of their infrared flux. Hubble Space Telescope (HST) images and Ultraviolet and Visual Echelle Spectrograph (UVES) spectra show that the mixed chemistry is not related to the presence of emission-line stars, as it is in the Galactic disc population. We also rule out interaction with the interstellar medium (ISM) as origin of the PAHs. Instead, a strong correlation is found with morphology and the presence of a dense torus. A chemical model is presented which shows that hydrocarbon chains can form within oxygen-rich gas through gas-phase chemical reactions. The model predicts two layers, one at A_V~ 1.5, where small hydrocarbons form from reactions with C+, and one at A_V~ 4, where larger chains (and by implication, PAHs) form from reactions with neutral, atomic carbon. These reactions take place in a mini-photon-dominated region (PDR). We conclude that the mixed-chemistry phenomenon occurring in the Galactic bulge planetary nebulae is best explained through hydrocarbon chemistry in an ultraviolet (UV)-irradiated, dense torus.

Antioxidants in health and disease

Free radical production occurs continuously in all cells as part of normal cellular function. However, excess free radical production originating from endogenous or exogenous sources might play a role in many diseases. Antioxidants prevent free radical induced tissue damage by preventing the formation of radicals, scavenging them, or by promoting their decomposition. This article reviews the basic chemistry of free radical formation in the body, the consequences of free radical induced tissue damage, and the function of antioxidant defence systems, with particular reference to the development of atherosclerosis.

A click chemistry approach to C3 symmetric, G-quadruplex stabilising ligands.

Described is the structure-based design and synthesis of a series of tris-triazole G-quadruplex binding ligands utilising the copper catalysed azide–alkyne ‘click’ reaction. The results of G-quadruplex stabilisation by the ligands are reported and discussed.

Targeting telomerase and telomeres: a click chemistry approach towards highly selective G-quadruplex ligands.

Maintenance of telomeres—specialized complexes that protect the ends of chromosomes, is undertaken by the enzyme complex telomerase, which is a key factor that is activated in more than 80% of cancer cells, but is absent in most normal cells. Targeting telomere maintenance mechanisms could potentially halt tumour growth across a broad spectrum of cancer types, with little cytotoxic effect outside cancer cells. Here, we describe in detail a new class of G-quadruplex binding ligands synthesized using a click chemistry approach. These ligands comprise a 1,3-di(1,2,3-triazol-4-yl)benzene pharmacophore, and display high levels of selectivity for interaction with G-quadruplex DNA vs. duplex DNA. The ability of these ligands to inhibit the enzymatic activity of telomerase correlates with their ability to stabilize quadruplex DNA, and with estimates of affinity calculated by molecular modeling.

Forensic examination of multilayer white paint by lateral scanning Raman spectroscopy

Multilayer samples of white architectural paint potentially have very high evidential value in forensic casework, because the probability that two unrelated samples will have the same sequence of layers is extremely low. However, discrimination between the different layers using optical microscopy is often difficult or impossible. Here, lateral scanning Raman spectroscopy has been used to chemically map the cross-sections of multilayer white paint chips. It was found that the spectra did allow the different layers to be delineated on the basis of their spectral features. The boundaries between different layers were not as sharp as expected, with transitions occurring over length scales of > 20 µm, even with laser spot diameters <4 µm. However, the blurring of the boundaries was not so large as to prevent recording and identification of spectra from each of the layers in the samples. This method clearly provides excellent discrimination between different multilayer white paint samples and can readily be incorporated into existing procedures for examination of paint transfer evidence.