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131.
Wedel T Gehring T Podlech J Kordel E Bihlmeier A Klopper W 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(15):4631-4639
Conjugate additions of nucleophiles (e.g. enolates, amines and malonate anions) to bis(p-tolylsulfinyl)alkenes, alkylidene-1,3-dithiane-1,3-dioxides and alkylidene-1,3-dithiolane-1,3-dioxides have recently been published. Reasons for different selectivities and reaction rates will be discussed by consideration of steric and electronic effects. The preferred mode of attack can be explained by stereoelectronic effects (hyperconjugation) in the primarily carbanion, which is stabilized by n-->S-O-sigma* interaction with an antiperiplanar S=O group. Calculation of the transition states [BP86/aug-TZVP] for the addition of acetone enolate to the dithiane-derived alkylidene bis(sulfoxide) revealed that 6.6-7.3 kJ mol(-1) more energy is needed for an attack leading to a less-stabilized carbanion. Two axial S=O groups in dithiolane-derived alkylidene bis(sulfoxides) lead to a higher reactivity towards nucleophiles. 相似文献
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Ahonen P Laaksonen T Schiffrin DJ Kontturi K 《Physical chemistry chemical physics : PCCP》2007,9(35):4898-4901
The influence of conformational and electrical properties of azobenzene molecules on the electron transfer barrier properties of their SAMs was studied by SECM and ellipsometry. 相似文献
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Strong electrogenerated chemiluminescence (ECL) of fluorescein is generated during cathodic pulse polarization of oxide-covered
aluminum electrodes and the resulting decay of emission is so sluggish that time-resolved detection of fluorescein is feasible.
The present ECL in aqueous solution is based on the tunnel emission of hot electrons into the aqueous electrolyte solution,
which probably results in the generation of hydrated electrons and hydroxyl radicals acting as redox mediators. The successive
one-electron redox steps with the primary radicals result in fluorescein in its lowest excited singlet state. The method allows
the detection of fluorescein (or its derivatives containing usable linking groups to biomolecules) over several orders of
magnitude of concentration with detection limits well below nanomolar concentration level. The detection limits can still
be lowered, e.g., by addition of azide or bromide ions as coreactants. The results suggest that the derivatives of fluorescein,
such as fluorescein isothiocyanate (FITC), can be detected by time-resolved measurements and thus be efficiently used as electrochemiluminescent
labels in bioaffinity assays. 相似文献
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