Efficient synthesis of an imidazole-substituted delta-amino acid by the integration of chiral technologies

Two methods to produce (2S)-5-amino-2-(1-n-propyl-1H-imidazol-4-ylmethyl)-pentanoic acid were investigated. Diastereoisomeric salt resolution, using the quinidine salt, gave the desired intermediate in 98% ee and 33% yield. Asymmetric hydrogenation of various substrates gave high conversions, with up to 83% ee. Integration of these two approaches via asymmetric hydrogenation of a quinidine salt substrate followed by crystallization provided the desired intermediate in 94% ee and 76% yield.     

The ligand, the metal and the 'Holey'-host: Synthesis, structural and magnetic characterisation of Co(II), Ni(II) and Mn(II) metal-organic frameworks incorporating 4,4'-dicarboxy-2,2'-bipyridine

We report herein the single crystal structures of four metal-organic framework complexes incorporating the 4,4'-dicarboxy-2,2'-bipyridine ligand, H(2)dcbp: alpha-[Co(dcbp)(H(2)O)(2)], 1; beta-[Co(dcbp)(H(2)O)(2)], 2, [Ni(dcbp)(H(2)O)(2)], and [[Mn(dcbp)].1/2DEF], 4 (DEF = diethylformamide). In each complex the ligand is deprotonated giving neutral species with 1:1 stoichiometry that form three-dimensional coordination polymers. Supramolecular isomerism (polymorphism) in 1 and 2 arises from the different ligand connectivity around the octahedral Co(II) centres. The two coordinated water molecules in 1 occupy cis positions, which are trans to the chelating bipyridine nitrogen atoms, leaving the carboxylate oxygen atoms in axial trans positions. In 2 all like donors occupy cis positions. Different modes of carboxylate coordination in 1 and 2 give dissimilar network topologies. A rare example of two interpenetrating 6(4)8(2)-b (quartz-like) chiral networks in 1 results from both dcbp carboxylate groups coordinating in a monodentate fashion to adjacent Co(II) centres, whereas in 2 only one carboxylate group bridges between adjacent Co(II) centres giving rise to a single chiral (10,3)-a net. In 1 and 2 the coordinated water molecules hydrogen bond to the non-coordinated carboxylate oxygen atoms. These interactions give rise to water-carboxylate double helices in , and support the coordination network in 2. Strikingly for a pair of dimorphs the crystal densities of 1 and 2 differ by ca. 0.3 g cm(-3)(1.654 vs. 1.940 g cm(-3), respectively). Compound 3 is isomorphous with 1 and likewise features two chiral interpenetrating nets of quartz topology. In 4, chelating bipyridine nitrogen atoms and four carboxylate oxygen atoms from a total of five adjacent dcbp ligands provide distorted octahedral geometry around Mn(II). The carboxylate groups bridge adjacent Mn(II) centres to produce bis-carboxylato chains which cross-link and generate a 3D network that is perforated with channels. The channels are occupied with disordered DEF molecules. The network topology in 4 is quite different to 1-3 and has a (4.6(2))(4(2).6)(4(3).6(6).8(6)) Schlafli notation. Magnetic susceptibility studies performed on 1, 2, [[Mn(dcbp)].1/2DMF] 5 (DMF = dimethylformamide) and [[Mn(dcbp)].2H(2)O] 6 reveal very weak antiferromagnetic coupling between the metal centres in each case.     

Influence of precursor solvent extraction on stable isotope signatures of methylamphetamine prepared from over-the-counter medicines using the Moscow and Hypophosphorous routes

A number of methods of clandestine manufacture of methylamphetamine involve the extraction and subsequent reaction of pseudoephedrine hydrochloride with other essential chemicals. The precursor can be easily extracted from over-the-counter medication widely available in the UK and elsewhere. Essential chemicals such as iodine and red phosphorous are also readily available and can be extracted from iodine tinctures and matchboxes, respectively. This work reports the repetitive preparation of methylamphetamine using two popular routes (the Moscow and Hypophosphorous synthesis). The focus was on the extraction solvent used for isolation of the precursor chemical and any consequential isotopic variation which may arise in the final product. Six batches of methylamphetamine were prepared under precisely controlled conditions for each synthetic route and for each of three different precursor extraction solvents. Synthesis of the final product from laboratory grade precursor using the synthetic methods described was used as a template for comparison. The resultant IRMS data from all 48 prepared samples suggests some underlying trends in the identification of the synthetic route which may aid in the interpretation of IRMS data derived from clandestine samples.     

Eine Regulirungsvorrichtung

Ohne Zusammenfassung     

The increasing importance of carbon nanotubes and nanostructured conducting polymers in biosensors

The growing need for analytical devices requiring smaller sample volumes, decreased power consumption and improved performance have been driving forces behind the rapid growth in nanomaterials research. Due to their dimensions, nanostructured materials display unique properties not traditionally observed in bulk materials. Characteristics such as increased surface area along with enhanced electrical/optical properties make them suitable for numerous applications such as nanoelectronics, photovoltaics and chemical/biological sensing. In this review we examine the potential that exists to use nanostructured materials for biosensor devices. By incorporating nanomaterials, it is possible to achieve enhanced sensitivity, improved response time and smaller size. Here we report some of the success that has been achieved in this area. Many nanoparticle and nanofibre geometries are particularly relevant, but in this paper we specifically focus on organic nanostructures, reviewing conducting polymer nanostructures and carbon nanotubes.     

Über Diffusion von Tanninlösungen in Gelatinegele

Ohne Zusammenfassung     

Efficient Regioselective Ring Opening of Activated Aziridine-2-Carboxylates with [18F]Fluoride

Aziridines can undergo a range of ring-opening reactions with nucleophiles. The regio- and stereochemistry of the products depend on the substituents on the aziridine. Aziridine ring-opening reactions have rarely been used in radiosynthesis. Herein we report the ring opening of activated aziridine-2-carboxylates with [¹⁸F]fluoride. The aziridine was activated for nucleophilic attack by substitution of various groups on the aziridine nitrogen atom. Fluorine-18 radiolabelling was followed by ester hydrolysis and removal of the activation group. Totally regioselective ring opening and subsequent deprotection was achieved with tert-butyloxycarbonyl- and carboxybenzyl-activated aziridines to give α-[¹⁸F]fluoro-β-alanine in good radiochemical yield.     

Investigating the provenance of un-dyed spun cotton fibre using multi-isotope profiles and chemometric analysis

The analysis of un-dyed spun cotton fibres can be challenging within a forensic science context where discrimination of one fibre from another is of importance. Conventional microscopic and chemical analysis of these fibres is generally unsuccessful because of their similar morphology. In this work we have explored the potential of isotope ratio mass spectrometry (IRMS) as a tool for spun cotton fibre analysis in an attempt to reveal any discriminatory information available. Seven different batches of un-dyed spun cotton fibre from four different countries were analysed. A combination of the hydrogen and oxygen isotopic data facilitated the correct association of the samples, demonstrating, for the first time, the applicability of IRMS to fibre analysis in this way.