Electrochemical synthesis and characterization of conducting polymers in supercritical carbon dioxide

This contribution reports the first synthesis of conducting polymers (CPs), specifically, polyaniline (PAn) and polypyrrole (PPy), in supercritical carbon dioxide (scCO2). CPs synthesized electrochemically in scCO2 were characterized with cyclic voltammetry (CV), four-point probe conductivity, scanning electron microscopy (SEM), and UV-vis spectroscopy. Preliminary data indicate that CPs synthesized by this method exhibit novel morphology and high conductivity comparable to that synthesized by traditional methods.     

Tumour cell identification by means of Raman spectroscopy in combination with optical traps and microfluidic environments

Raman spectroscopy has been recognized to be a powerful tool for label-free discrimination of cells. Sampling methods are under development to utilize the unique capabilities to identify cells in body fluids such as saliva, urine or blood. The current study applied optical traps in combination with Raman spectroscopy to acquire spectra of single cells in microfluidic glass channels. Optical traps were realized by two 1070 nm single mode fibre lasers. Microflows were controlled by a syringe pump system. A novel microfluidic glass chip was designed to inject single cells, modify the flow speed, accommodate the laser fibres and sort cells after Raman based identification. Whereas the integrated microchip setup used 514 nm for excitation of Raman spectra, a quartz capillary setup excited spectra with 785 nm laser wavelength. Classification models were trained using linear discriminant analysis to differentiate erythrocytes, leukocytes, acute myeloid leukaemia cells (OCI-AML3), and breast tumour cells BT-20 and MCF-7 with accuracies that are comparable with previous Raman experiments of dried cells and fixed cells in a Petri dish. Implementation into microfluidic environments enables a high degree of automation that is required to improve the throughput of the approach for Raman activated cell sorting.     

Hydrolysis of a sulfonamide by a novel elimination mechanism generated by carbanion formation in the leaving group

The alkaline hydrolysis of N-alpha-methoxycarbonyl benzyl-beta-sultam occurs 10(3) times faster than the corresponding carboxylate and with rapid D-exchange at the alpha-carbon: the pH rate profile indicates pre-equilibirum CH ionisation and together with formation of benzoyl formate as a product this suggests a novel mechanism for hydrolysis.     

Intramolecular fluorine migration via four-member cyclic transition states

Gaseous CF(3)(+) interchanges F(+) for O with simple carbonyl compounds. CF(3)(+) reacts with propionaldehyde in the gas phase to produce (CH(3))(2)CF(+) via two competing pathways. Starting with 1-(13)C-propionaldehyde, the major pathway (80%) produces (CH(3))(2)CF(+) with the carbon label in one of the methyl groups. The minor pathway (20%) produces (CH(3))(2)CF(+) with the carbon label in the central position. The relative proportions of these two pathways are measured by (19)F NMR analysis of the neutral CH(3)CF=CH(2) produced by deprotonation of (CH(3))(2)CF(+) at <10(-)(3) Torr in an electron bombardment flow (EBFlow) reactor. Formation of alkene in which carbon is directly bonded to fluorine means that (in the minor product, at least) an F(+) for O transposition occurs via adduct formation followed by 1,3-atom transfer and then isomerization of CH(3)CH(2)CHF(+) to the more stable (CH(3))(2)CF(+). Use of CF(4) as a chemical ionization (CI) reagent gas leads to CF(3)(+) adduct ions for a variety of ketones, in addition to isoelectronic transposition of F(+) for O. Metastable ion decompositions of the adduct ions yield the metathesis products. Decompositions of fluorocycloalkyl cations formed in this manner give evidence for the same kinds of rearrangements as take place in CH(3)CH(2)CHF(+). Density functional calculations confirm that F(+) for O metathesis takes place via addition of CF(3)(+) to the carbonyl oxygen followed by transposition via a four-member cyclic transition state. A computational survey of the effects of different substituents in a series of aldehydes and acyclic ketones reveals no systematic variation of the energy of the transition state as a function of thermochemistry, but the Hammond postulate does appear to be obeyed in terms of progress along the reaction coordinate. Bond lengths corresponding to the central barrier correlate with overall thermochemistry of the F(+) for O interchange, but in a sense opposite to what might have been expected: the transition state becomes more product-like as the metathesis becomes increasingly exothermic. This reversal of the naive interpretation of the Hammond postulate is accounted for by the relative positions of the potential energy wells that precede and follow the central barrier.     

Synthesis of Benzazepine Analogues of Noscapine

The synthesis of benzazepine analogues of the opium alkaloid noscapine ( 1 ) is described. The benzazepines 2 and 3 were prepared starting from nornarceine ethyl ester ( 4 ; readily available from 1 ) in several steps. X-Ray analysis of compound 2 revealed that it is not a diastereosisomer mixture but a racemate of the threo-form and thus has the same configuration as 1 .     

Luminescent Labels—More than Just an Alternative to Radioisotopes?

Chemical, chromatographic, or spectrometric methods are generally unsuitable for the detection of molecules in the nano and subnanogram region because of their low sensitivity. The radioimmunoassay (RIA) developed by Yalow and Berson in 1959 combined the high sensitivity of radioactively labeled substances with the high specificity of immunological reactions for the first time. In this way it was possible to detect quantitatively the tiniest traces of substances in the presence of an excess of other, in some cases, similar foreign substances without prior enrichment. Immunoassays have certainly developed to become the most valuable analytical tool of in vitro diagnostics and are today routinely employed for the detection of endogenous and exogenous substances (e.g. hormones, tumor-associated proteins, bacteria, viruses, toxins, drugs, etc). The many disadvantages of radioactivity such as the required handling licenses, disposal costs, precautions necessary to prevent risks to health, short shelf-life, and limited sensitivity soon led to the search for other nonradioactive labeling methods. Encouraged by the development of light measuring techniques and the commercial availability of highly sensitive apparatus, radioactive isotopes as labels are today being replaced increasingly by enzymes, fluorophores, or luminophores. Some of the new luminescent labels have, however, not only facilitated replacement of radioisotopes, but also a breakthrough into what has until now been unattainable levels of sensitivity. The following article reviews the methods of luminescent labeling and their applications mainly in the area of immunoassays.     

Silyl stabilized azanes: Reactions of mono- and dilithium bis(trimethylsilyl)hydrazide with dichloro- and tetrachlorostannane

SnCl₄ acts primarily as an oxidant and oxidizes monolithium bis(trimethylsilyl) hydrazide 1 to mainly bis(trimethylsilyl)amine, BSA and tris(trimethylsilyl)hydrazine, TrSH and itself get reduced to SnCl₂. Similarly, reaction of SnCl₄ with dilithiumbis(trimethylsilyl) hydrazide 2, oxidizes it to lithium tris(trimethylsilyl)hydrazide, Li-TrSH. Reaction of dichlorostannane (reduction of oxidation state of tin from +4 to +2) with 1 gives a simple substitution reaction and give a pale yellow solid, 1,4-bis(trimethylsilyl)-1,2,4,5-tetraza-3,6-distannacyclohexane, 3b. Whereas, in reaction of 2 with SnCl₂ intermediate stannimine [(Me₃Si)₂N-NSn], tetramerizes and further loses tetrakis(trimethylsilyl)tetrazene, TST to give a cubane compound [(Me₃Si)N-Sn]₄, 4.     

Antihydrophobic cosolvent effects in organic displacement reactions

[formula: see text] Rates of reactions in water can be modified by the presence of antihydrophobic cosolvents such as ethanol and DMSO, which lower the energies of nonpolar surfaces. The rate effects reflect changes both in the solvation of nonpolar surfaces and also in the solvation of polar groups. The effects have been sorted out for some displacement reactions, revealing the geometry of an interesting branching reaction whose two paths show different antihydrophobic effects.