Damage and molecular changes under a laser beam in SEM‐EDX/MRS interface: a case study on iron‐rich particles

The control of damage to individual environmental particles by a laser beam during Raman spectroscopy carried out in ambient air is generally well understood. The nature and control of damage under vacuum conditions (e.g. in the scanning electron microscopy with energy X‐ray detection combined with micro‐Raman spectroscopy—interfaced SEM‐EDX/MRS) are more complex and less well comprehended. The physical and chemical processes that affect the damage caused to small particles by lasers still remain somewhat unclear, but certainly the atmosphere (vacuum/air) and the beam intensity have very significant influences. Furthermore, it has been determined that some particles (e.g. haematite), although stable under an electron beam, are damaged by the laser beam, hampering their analysis. Additionally, when simultaneous analyses by SEM/EDX and MRS are considered, the correct choice of the collection surface plays a crucial role. As a result, the following collection substrates were tested to determine their influence on the laser beam damage process to the particle: silver and aluminium foils and silicon wafers. A test study was performed using artificial examples of haematite (Fe₂O₃) particles. Exposure of Fe₂O₃ particles in vacuum to 514‐ and 785‐nm laser radiation often leads to their melting, transformation and evaporation. The dependence of the damage caused by the laser beam on the particle structure is reported here. Molecular and crystallographic changes have also been revealed. Formation of magnetite (as an effect of re‐crystallisation) and Raman inactive structures was detected. Copyright © 2010 John Wiley & Sons, Ltd.     

The Henry reaction: spectroscopic studies of nitrile and hydroxylamine by-products formed during synthesis of psychoactive phenylalkylamines

A clandestine two-step route to psychoactive racemic phenylalkylamines utilises the Henry reaction. In the first step an aromatic aldehyde reacts with a nitroalkane to give the nitrostyrene intermediate. In the second step the nitrostyrene is reduced to the phenylalkylamine. An impurity profile of both steps was evaluated through the synthesis and analysis of common street derivatives. The formation of nitrile impurities in the nitroaldol reaction and hydroxylamine impurities in the reduction step were shown by NMR spectroscopy and GC-MS. A selection of reducing agents has been used to give the phenylalkylamines, together with variable quantities of the partially reduced hydroxylamine product. GC-MS analysis of the hydroxylamines showed heat-induced disproportionation which led to the detection of the corresponding oximes.      

Selective binding of L-glutamate derivative in aqueous solvents

A chiral bisguanidinium macrocycle binds N-Boc-L-glutamate in a 1 : 1 stoichiometry with significant selectivity in competitive solvent (DMSO-H(2)O).     

Exciplex and excimer molecular probes: detection of conformational flip in a myo-inositol chair

2-O-tert-Butyldimethylsilyl-4,6-bis-O-pyrenoyl-myo-inositol-1,3,5-orthoformate (6) and 2-O-tert-butyldimethylsilyl-4-O-[4-(dimethylamino)benzoyl]-6-O-pyrenoyl-myo-inositol-1,3,5-orthoacetate (10) adopt conformationally restricted unstable chairs with five axial substituents. In the symmetrical diester 6, the two pi-stacked pyrenoyl groups are electron acceptor-donor partners, giving a strong intramolecular excimer emission. In the mixed ester 10, the pyrenoyl group is the electron acceptor and the 4-(dimethylamino)benzoyl ester is the electron donor, giving a strong intramolecular exciplex emission. The conformation of the mixed ester 10 was assessed using 1H NMR spectroscopy (1H-NOESY) and computational studies. which showed the minimum inter-centroid distance between the two aromatic systems to be approximately 3.9 A. Upon addition of acid, the orthoformate/orthoacetate trigger in 6 and 10 was cleaved, which caused a switch of the conformation of the myo-inositol ring to the more stable penta-equatorial chair, leading to separation of the aromatic ester groups and loss of excimer and exciplex fluorescence, respectively. This study provides proof of principle for the development of novel fluorescent molecular probes.     

Fingerprint analysis of thermolytic decarboxylation of tryptophan to tryptamine catalyzed by natural oils

A number of N,N-dialkylated tryptamines show psychoactive properties in man which resulted in a renewed interest in psychopharmacological research. Attempts to manufacture these derivatives are increasing within a clandestine environment, where literature procedures are adapted and information is exchanged on the Internet. One such example is based on the thermolytic decarboxylation of tryptophan to tryptamine as the precursor to psychoactive derivatives. This procedure was proposed to make use of household solvents such as turpentine substitute and white spirit to facilitate decarboxylation. Discussions on websites also suggested the catalytic use of natural oils in order to accelerate these reactions. In this research, the analytical characterization of this preparation procedure was carried out using gas chromatography-ion trap single and tandem stage mass spectrometry in electron and chemical ionization mode that led to the identification of previously unreported 1-mono and 1,1-disubstituted tetrahydro-beta-carboline (THBCs) by-products. The tryptamine product and several THBC by-products were determined quantitatively and a "fingerprint" analysis of the crude products allowed for the differentiation between the essential oil catalysts involved as indicated by the presence of tetrahydro-beta-carbolines and their imine intermediates.     

Factors influencing tetranuclear [2 x 2] grid vs dinuclear side-by-side structures for silver(I) complexes of pyridazine-based bis-bidentate ligands

Silver(I) complexes of five bis-bidentate Schiff-base ligands, derived from 3,6-diformylpyridazine and substituted anilines (2,4-dimethylaniline L ( o,p - Me ); 3,5-dichloroaniline L ( m,m - Cl ); 2-aminobiphenyl L ( o - Ph ); p-toluidine L ( p - Me ); 4-aminophenol L ( p - OH ); p-anisidine L ( p - OMe )), have been prepared. The ligands have a wide range of steric and electronic properties due to variation in the extent and nature of the substitution of the aniline rings. Four of the resulting complexes were structurally characterized by X-ray crystallography: three of the four, [Ag 2( L ( o,p - Me )) 2](BF 4) 2, [Ag 2( L ( m,m - Cl )) 2](BF 4) 2 and [Ag 2( L ( o - Ph )) 2](BF 4) 2 formed dinuclear side-by-side complexes, while [Ag 4( L ( p - Me )) 4](BF 4) 4 gave a tetranuclear [2 x 2] grid. The previously reported tetranuclear [2 x 2] grid [Ag 4( L ( p - OMe )) 4](BF 4) 4 was recrystallized in the presence of benzene to see if this would alter the architecture of this complex. It did not: the [2 x 2] grid architecture was retained despite the benzene molecules of solvation. Given the flexibility of silver(I) with regard to coordination geometry, the molecular structure of these complexes is influenced mostly by the ligand rather than the metal ion. In each case, the factors which influence the molecular architecture are presented and discussed. Substituent effects on the electrostatics of the intramolecular ligand-ligand pi-pi interactions (XED2.8) account for some of the differences observed in the structures.     

Non-fouling microfluidic chip produced by radio frequency tetraglyme plasma deposition

This Technical Note presents the direct surface modification of a glass/PTFE hybrid microfluidic chip, via radio frequency glow discharge plasma polymerisation of tetraethlylene glycol dimethylether (tetraglyme), to produce hydrophilic, non-fouling, PEO-like surfaces. We use several techniques including X-ray photoelectron spectroscopy (XPS), direct enzyme-linked immunosorbent assays (ELISA) and immunofluorescent imaging to investigate the channel coatings. Our results indicate the successful deposition of a PEO-like coating onto microchannel surfaces that has both solution and shelf stability (>3 months) and is capable of preventing fibrinogen adsorption to the microchannel surfaces.     

Synthesis and characterization of immobilized PAMAM dendrons

This communication describes the synthesis and characterization of immobilized PAMAM dendrons onto a surface modified silicon wafer substrate (functionalized using plasma polymerized PAA) using a "growing from" strategy.