Doubly-destabilized carbocations. Detection and trapping of aryl-biscarboethoxycarbocations

Diethyl bromo(aryl)malonates undergo ionization in superacids at −78°C to give the corresponding cations. These doubly destabilized cations can be trapped with benzene or toluene to give the corresponding Friedel-Crafts adducts.     

Irreversible trapping of DNA during crossed-field gel electrophoresis.

Using an original protocol with a rotating gel electrophoresis apparatus, it is shown that duplex DNA undergoing crossed-field electrophoresis in agarose gets trapped in the gel when the field is increased above a threshold value which decreases with the chain length and depends on the angle between the fields in a non-monotonous manner. This trapping is irreversible, i.e. once trapped at a high field strength, chains are unable to resume their motion when the field is returned to a lower value at which they moved prior to trapping. A model of trapping by "tight knots" is proposed. It predicts a trapping threshold proportional to the inverse square of the electric field, in qualitative agreement with the data. The implications of our results for the separation of large DNA molecules are discussed.     

Productive trapping of NAD-type radicals. Non-biomimetic reduction of pyridinium salts

One-electron reduction of pyridinium salts (NAD+ analogues) generates dihydropyridyl radicals which may then be engaged in radical addition processes to regioselectively form gamma-substituted dihydropyridines.     

Spin trapping with phosphonothionesters. Part VI. * Phosphoryl- and thiophosphoryl-thionformates

Ethyl (diethoxyphosphoryl)thionformate, ethyl (diethoxythiophosphoryl) thionformate, ethyl (diethoxyphosphoryl)thiolformate, and ethyl (diethoxythiophosphoryl)thiolformate have been allowed to react with a variety of in situ generated free radicals. Spin adducts were observed by EPR with the two thionesters but not with thiolesters; even the former compounds, however, exhibited a remarkably lower reactivity than similarly substituted dithioesters.     

The trapping of sulfenic acids from penicillin sulfoxides - use of 2,5-dimercapto-1,3,4-thiadiazole and 2,4-dimercaptopyrimidine as trapping agents.

2,5-Dimercapto-1,3,4-thiadiazole and 2,4-dimercaptopyrimidine were used to trap sulfenic acids from penicillin sulfoxides.     

Spin trapping reactions with nitric oxides II. Acylalkyl nitroxides

Radical trapping by nitric oxide in the presence of oxygen has been studied by ESR spectroscopy. The oxygen was found to react much faster with alkyl radicals than nitric oxide, it suppresses formation of dialkyl nitroxides and initiates creation of acyl nitroxides through reactions between peroxy radicals and nitric oxide.     

Deprotonation-electrophile trapping of terminal epoxides

Organolithium-induced deprotonation of terminal epoxides in the presence of appropriate diamine ligands allows trapping with a range of electrophiles, yielding functionalised di- and tri-substituted epoxides in good yields and with control of stereochemistry at the epoxide.     

Spin trapping reactions with nitric oxides,I. Dialkyl nitroxides

Dialkyl-nitroxide radicals formed from nitric oxide, which trapped two alkyl radicals in consecutive steps, have been detected by Electron Spin Resonance spectroscopy. The structure of radicals was found independent of the way of alkyl radical generation. Stereoselectivity of radical trapping was observed for secondary alkyl radicals with chiral carbons.     

Diels–Alder trapping vs. amidoalkylation of cyclopentadiene with polychloroacetaldehyde sulfonylimines

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The trapping of sulfenic acids from penicillin sulfoxides. Ethyl 2-mercaptoacetate

The thermolysis of trichloroethyl 6-phenoxyacetamido penicillanate sulfoxide and ethyl 2-mercaptoacetate in toluene gave the unsym-azetidinone disulfide(β,γ-isomer) in 65% yield. With added catalytic amounts of N,N-dimethylaniline the α,β-isomer was the major product (60%), along with a $\text{new}$ β-lactam cleaved product, $\text{8}$ (5–6%).     

Single DNA molecule isolation and trapping in a microfluidic device.

This paper presents a systematic method to isolate and trap long single DNA segments between integrated electrodes in a microfluidic environment. Double stranded lambda-DNA molecules are introduced in a microchip and are isolated by electrophoretic force through microfluidic channels. Downstream, each individual molecule is extended and oriented by ac dielectrophoresis (900 kHz, 1 MV m(-1)) and anchored between aluminium electrodes. With a proper design, a long DNA segment (up to 10 microm) can be instantly captured in stretched conformation, opening way for further assays.     

Physical electron trapping in boric acid glass in competition with the H+ chemical trapping. A study by recombination delayed fluorescence

Tryptophan and naphthalene in boric acid glass at 77 K give rise to a delayed fluorescence under U.V. excitation and to a photostimulated delayed fluorescence under visible light excitation of an irradiated sample. It is shown that these emissions are due to electron-cation recombination and that, beside the chemical trapping of electrons by protons which is the main process, a physical electron trapping occurs in this strongly acidic medium. This unexpected property is related to the inhomogeneous structure of boric acid glasses which plays an important role in the unique properties of this medium for photoionization studies of aromatic compounds.     

Efficient trapping of HNO by deoxymyoglobin

Nitrosyl hydride, HNO, also commonly termed nitroxyl, is a transient species that has been implicated in the biological activity of nitric oxide, NO. Herein, we report the first generation of a stable HNO-metal complex by direct trapping of free HNO. Deoxymyoglobin (Mb-Fe(II)) rapidly reacts with HNO produced from the decomposition of methylsulfonylhydroxylamine (MSHA) or Angeli's salt (AS) in aqueous solutions from pH 7 to pH 10, forming an adduct, Mb-HNO. The unique 1H NMR signal of the Fe-bound HNO at 14.8 ppm allows definitive proof of its formation. The generation of Mb-HNO and quantification of various myoglobin byproducts were accomplished by correlation of 1H NMR, UV-vis, and EPR spectroscopies. Typically, the maximum Mb-HNO yield obtained is 60-80%; competitive side reactions with byproducts as well as the further reactivity of the Mb-HNO decrease the overall yield. At pH 10, the observed rate of Mb-HNO generation by trapping HNO from MSHA is close to that for MSHA decomposition; kinetic simulations give a lower limit to the bimolecular rate of trapping as 1.4 x 10(4) M(-1) s(-1). The binding of HNO to deoxymyoglobin is rapid and essentially irreversible, which suggests that the biological activity of nitroxyl may be mediated by its reactivity with ferrous heme proteins such as myoglobin and hemoglobin.