Raman spectra of biomarkers of relevance to analytical astrobiological exploration: hopanoids, sterols and steranes

The aim of this work is to investigate the viability and potential of three groups of organic compounds as biomarkers in a future robotic analytical exploration of Mars. The three compounds have been identified as suitable candidates for potential biomarkers for extant or extinct life from the terrestrial fossil record. The three groups of compound were all similar in structure, being either tetra- or penta-cyclic compounds. The limits of detection for a sample were also tested to estimate what concentrations it would still be amenable to Raman spectroscopic investigation. This was investigated using both solid mixtures and liquid solutions. The spectra of these compounds are characterised so that they can be added to the Raman database for future Mars missions. This involved identifying functional group characteristics, assigning peaks for each individual sample and characteristic features which would categorise the samples.     

Molecular dynamics calculation of activation volumes

We propose a novel approach toward calculating activation and reaction volumes based on MD simulations of reaction systems. The accuracy of the calculated volumes, verified by the comparison to the experimental data, is suitable for quantitative analysis of the experimental volumes of activations in terms of structural parameters of the corresponding transition states.     

Coordination chemistry of an asymmetric P,N,O tridentate ligand containing primary phosphine, amine and alcohol donors

The asymmetric, heterodonor tridentate ligand 2(S)-amino-4-phosphinobutan-1-ol, S-PNO, has been prepared from (S)-aspartic acid and some aspects of its coordination chemistry with a number of metal complexes investigated. Reaction of S-PNO with appropriate metal precursors led to the isolation of the complexes fac-Cr(CO)₃(κ³-S-PNO), 1, fac-[Mn(CO)₃(κ³-S-PNO)]PF₆, 2, and fac-[Re(CO)₃(κ³-S-PNO)]BF₄, 3. The alcohol and amine donors in fac-Cr(CO)₃(κ³-S-PNO) were substituted upon addition of trivinylphosphine to 1 to give the complex fac-Cr(CO)₃(κ¹-P-S-PNO){P(C₂H₃)₃}₂, 4. Addition of base to 4 gave a coordinated linear tridentate P₃ ligand through the formation of two new chelate rings via hydrophosphination of one vinyl group on each coordinated P(C₂H₃)₃ with the P-H bonds of the complexed S-PNO. The alcohol donor in fac-[Re(CO)₃(κ³-S-PNO)]BF₄ is labile and can be substituted with tris(2-fluorophenyl)phosphine, PAr₃^F, to give fac-[Re(CO)₃(κ²-P,N-S-PNO)(PAr₃^F)]BF₄, 5. Attempts to form a macrocyclic ligand through addition of base to fac-[Re(CO)₃(κ²-P,N-S-PNO)(PAr₃^F)]BF₄ were unsuccessful due to loss of PAr₃^F prior to any ring-closure. All the complexes have been fully characterised by spectroscopic and analytical techniques including a single-crystal X-ray structure analysis of 2.     

Laser Machined Plastic Laminates: Towards Portable Diagnostic Devices for Use in Low Resource Environments

Despite significant progress in development of bioanalytical devices cost, complexity, access to reagents and lack of infrastructure have prevented use of these technologies in resource‐limited regions. To provide a sustainable tool in the global effort to combat infectious diseases the diagnostic device must be low cost, simple to operate and read, robust, and have sensitivity and specificity comparable to laboratory analysis. In this mini‐review we describe recent work using laser machined plastic laminates to produce diagnostic devices that are capable of a wide variety of bioanalytical measurements and show great promise towards future use in low‐resource environments.     

Quadratic autocatalysis with non-linear decay

We provide a detailed, and thorough, investigation into the concentration multiplicity and dynamic stability of a prototype non-linear chemical mechanism: quadratic autocatalysis subject to non-linear decay in a continuously stirred tank reactor. This model was previously investigated in the literature using numerical path-following techniques. The contribution of this study is the application of singularity theory and degenerate Hopf-bifurcation theory to obtain analytical representations of many of the features of interest in this system. In particular, we use these presentations to identify critical values of an unfolding parameter below which specified phenomenon are no longer exhibited.     

Batch versus Flow Photochemistry: A Revealing Comparison of Yield and Productivity

The use of flow photochemistry and its apparent superiority over batch has been reported by a number of groups in recent years. To rigorously determine whether flow does indeed have an advantage over batch, a broad range of synthetic photochemical transformations were optimized in both reactor modes and their yields and productivities compared. Surprisingly, yields were essentially identical in all comparative cases. Even more revealing was the observation that the productivity of flow reactors varied very little to that of their batch counterparts when the key reaction parameters were matched. Those with a single layer of fluorinated ethylene propylene (FEP) had an average productivity 20 % lower than that of batch, whereas three‐layer reactors were 20 % more productive. Finally, the utility of flow chemistry was demonstrated in the scale‐up of the ring‐opening reaction of a potentially explosive [1.1.1] propellane with butane‐2,3‐dione.     

The Direct Synthesis of Hydrogen Peroxide Using Platinum‐Promoted Gold–Palladium Catalysts

The direct synthesis of hydrogen peroxide offers a potentially green route to the production of this important commodity chemical. Early studies showed that Pd is a suitable catalyst, but recent work indicated that the addition of Au enhances the activity and selectivity significantly. The addition of a third metal using impregnation as a facile preparation method was thus investigated. The addition of a small amount of Pt to a CeO₂‐supported AuPd (weight ratio of 1:1) catalyst significantly enhanced the activity in the direct synthesis of H₂O₂ and decreased the non‐desired over‐hydrogenation and decomposition reactions. The addition of Pt to the AuPd nanoparticles influenced the surface composition, thus leading to the marked effects that were observed on the catalytic formation of hydrogen peroxide. In addition, an experimental approach that can help to identify the optimal nominal ternary alloy compositions for this reaction is demonstrated.     

Age-dependent photoionization thresholds of melanosomes and lipofuscin isolated from human retinal pigment epithelium cells

Melanosomes and lipofuscin were isolated from 14-, 59-, and 76-year-old, human retinal pigment epithelium specimens and examined. The morphological features of these samples were studied by scanning electron microscopy and atomic force microscopy, and the photoionization properties were examined by photoelectron emission microscopy. Ovoid- and rod-shaped melanosomes were observed. The size of the granules and the distribution between the two shapes show no significant age-dependent change. However, there is a higher occurrence of irregularly shaped aggregates of small round granules in older samples which suggests degradation or damage to melanosomes occurs with age. The melanosomes from the 14-year-old donor eye are well characterized by a single photoionization threshold, 4.1 eV, while the two older melanosomes exhibit two thresholds around 4.4 and 3.6 eV. Lipofuscin from both young and old cells show two thresholds, 4.4 and 3.4 eV. The similarity of the potentials observed for aged melanosomes and lipofuscin suggest that the lower threshold in the melanosome sample reflects lipofuscin deposited the surface of the melanosome. The amount, however, is not sufficient to alter the density of the melanosome, and therefore these granules do not separate in a sucrose gradient at densities characteristic of the typical melanolipofuscin granule. These data suggest that thin deposits of lipofuscin on the surface of retinal pigment epithelium melanosomes are common in the aged eye and that this renders the melanosomes more pro-oxidant.     

On the mechanism of the selenolactonization reaction with selenenyl halides

The mechanism of selenocyclization reactions of beta,gamma-unsaturated acids and their derivatives has been studied. The reactions of (E)-4-phenyl-3-butenoic acid 10 and its silyl and alkyl esters with benzeneselenenyl chloride (PhSeCl) and bromide (PhSeBr) have been examined by VT-NMR and in situ IR spectroscopic methods. Whereas the reactions of the acid 10 in the presence of a base were irreproducible and complicated, reactions of the silyl esters were clean and spontaneously and quantitatively afforded a chloroselenylation adduct at -70 degrees C as a single (Markovnikov) isomer. This adduct underwent three processes as the temperature was raised: (1) reversal to the starting materials, (2) isomerization to the anti-Markovnikov product, and (3) cyclization to the selenolactone 12. All of these processes are believed to proceed via a seleniranium ion the intermediacy of which was established by independent synthesis and spectroscopic identification. The reversible formation of chloro selenide adducts was unambiguously established by crossover experiments. The reaction of 10 with PhSeBr was found to be rapid but thermodynamically unfavorable at room temperature.