Radicals labeled

As shown in Fig. 12-6, hydroxyl radicals primarily add to either of the carbon atoms which form the double bond. The remaining carbon atom has an unpaired electron which combines with molecular oxygen, forming an RO2 radical. There are two types of RO2 radicals labeled C3OHO2 in Fig. 12-6. Each of these RO2 radicals reacts with NO to form NO2, and an alkoxy radical reacts with O2 to form formaldehyde, acetaldehyde, and HOj. 

The radicals labeled R or R" may be the same as or different from the radicals labeled R in the same compounds. 

The reaction follows the consensus mechanism for aliphatic —H activation by oxyl-ferryl compounds (35) in which the first step is H-atom abstraction via TS1 to give a hydroxo-Fe(III) complex with a C-centered alkyl radical, labeled IN. This is followed by a rebound step via TS2 to give the final product, ethanol and the ferrous active site. Overall, this is a two-electron oxidation process where the bonding orbital serves as the electron donor and the H-atom abstraction is rate limiting. 

The 2,2,6,6-tetramethylpiperidinoxyl radical (TEMPO) was first prepared in 1960 by Lebedev and Kazarnovskii by oxidation of its piperidine precursor.18 The steric hindrance of the NO bond in TEMPO makes it a highly stable radical species, resistant to air and moisture. Paramagnetic TEMPO radicals can be employed as powerful spin probes for elucidating the structure and dynamics of both synthetic and biopolymers (e.g., proteins and DNA) by ESR spectroscopy.19 Unlike solid-phase 1H-NMR where magic angle spinning is required in order to reduce the anisotropic effects in the solid-phase environment, solid-phase ESR spectroscopy can be conducted without specialized equipment. Thus, we conducted comparative ESR studies of various polymers with persistent radical labels, and we also determined rotational correlation times as a function of... 

It has been demonstrated that it is possible to insert paramagnetic probes into nucleic acids in a site- and type-specific manner. To this end, the 2,2,6,6-tet-ramethyl-l-piperidinyloxy free radical-labelled phosphoramidites of 2-amino-2 -deoxyadenosine, 2 -deoxyadenosine, 2 -deoxycytosine and 5-methyl-2 -deoxycytosine have been prepared and used for the automatic synthesis of mono-labeled oligodeoxynucleotides which proved active by EPR. The phosphoramidites carry a nitroxide spin-label directly linked to the exocyclic amino group. Starting from appropriately protected 2 -deoxyguanosine or 2 -deoxyinosine, the precursors to (66a) and (66b) were obtained by nucleophilic... 

Suppose that we wish to treat ammonia as resulting from the collision of an H atom with the NH2 radical. Label the electronic coordinates xf, i = 1,2... 10 and the nuclear coordinates xf, i = 1,2,3,4 with the nitrogen as 4. The translationally invariant coordinates might then reasonably be chosen as... 

To date, the most commonly used spin labels for membrane proteins are pyrroline-type nitroxide radicals. Several labeling strategies and spin labels are available at present. However, the extreme specificity for the free thiol of cysteines, a stoichiometric reaction at most sites, and the relatively small size and flexibility of the modified side chain make the (l-oxyl-2,2,5,5-tetramethyl-A3-p3Troline-3-methyl) methanethiosulfonate spin label (MTSSL) the most popular choice for SDSL applications. 3 -(2-lodoacetamido)-2,2,5,5-tetramethyl-1 -pyrrolidinyloxy radical labels (lAP) are also used in combination with cysteines. The advantage of LAP vs MTSSL is that the covalent bond with the cysteine is irreversibly formed and this may be more suitable for particular situations in which the MTSSL tends to be released from the labeled sites. 

Spin Labels. - Spin labels have traditionally been a tool of ESR spectroscopy, where the ESR resonance of the free radical label (usually a nitroxide-containing species, such as TEMPO) is observed directly. However, spin labels have increasingly become a tool of NMR as T1 relaxation enhancing agents. 

Konermann, L., Tong, X., Pan, Y. (2008) Protein stmcture and dynamics studied by mass spectrometry H/D exchange, hydroxyl radical labeling, and related approaches. Journal of Mass Spectrometry, 43 (8), 1021-1036. 

Keywords Electrogenerated chemiluminescence Galvanoluminescence Hot electron Hydrated electron Hydroxyl radical Labels Lanthanoids Rare earths Sulfate radical Valve metals... 

The authors propose that the reactivity observed corresponds to a radical labelled Jt or AjTi) that does not correlate... 

The P-anisylethyl radical is oxidized with copper acetate in acetic acid predominantly to P-anisylethyl acetate. It is remarkable that radicals labeled with deuterium only in the a- and only in the P-position give the same mixture of deuterated acetates. 

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