Jacek Rogowski

Chemistry of bifunctional photoprobes. 3 -- Correlation between the efficiency of CH insertion by photolabile chelating agents and lifetimes of singlet nitrenes by flash photolysis: First example of photochemical attachment of {sup 99m}Tc-complex with human serum albumin

Systematic functionalization of perfluoroaryl azides with chelating agents capable of complexing transition metals produces a new class of bifunctional photolabile chelating agents (BFPCAs). The strategy to shield the azide functionality from the electronic and steric influence of the electron-rich metal Pd through ester and amide bridges raised CH insertion efficiency to unprecedented levels (>92%) in a model solvent (cyclohexane). In contrast, perfluoroaryl azides attached to chelating agents via hydrazones show no significant CH insertion in cyclohexane upon photolysis. Measurements of the lifetimes of the singlet nitrenes derived from these agents by flash photolysis techniques correlate well with the efficiency of CH insertion by demonstrating longer lifetimes (10−50 times) for singlet nitrenes derived from azidotetrafluorinated esters and amides compared with the related hydrazones, which failed to yield significant CH insertion. A representative BFPCA 12 is chelated to diagnostic radionuclide 99mTc...

Enolization in radical cations of o-methylacetophenone and related species under cryogenic conditions

Upon radiolytic ionization of o-methylacetophenone in low temperature matrices, the radical cation of the corresponding enol is formed. The kinetics of this process indicate a significant contribution of quantum-mechanical tunnelling in the hydrogen atom transfer. The same species is also formed by ionizing 1-methyl-1,2-dihydrobenzocyclobutenol but the composition of the rotameric mixture of enol radical cations is different in this case. Analogous experiments with 5,8-dimethyl-1-tetralone demonstrate that enol radical cations are stable in their Z-conformation under cryogenic conditions in contrast to the corresponding neutrals.

Intramolecular interactions between sulfur atoms in cyclotetrathioether radical cations

Radical cations generated by low temperature steady-state and pulse radiolysis from 1,4,8,11-tetrathiocyclotetradecane (1) and derivatives bearing gem-dimethyl pairs at the 6- or at the 6- and 13-positions (2 and 3, respectively) are characterized by optical absorption spectroscopy. Despite very different conformations for the neutral compounds 1–3 their radical cations (1˙+–3˙+) possess similarly located σ→σ* transitions (about 450 nm) for structures characterized by the strongest interactions between sulfur atoms. Delayed formation of characteristic absorptions for 2˙+ and 3˙+ indicates that geometries of radical cations differ substantially from geometries of neutral molecules. In the case of 3˙+ an intermediate structure (λmax= 600 nm) was intercepted which rearranged to the most stable structure (λmax= 450 nm) both thermally or photochemically. Optimized geometries for radical cations involving multiple sulfur interactions were calculated.

Low temperature pulse radiolysis as a method to study fast isomerization processes in molecular cations

Abstract Application of the low-temperature pulse radiolysis to the studies of molecular cation transformations has been discussed. It has been shown that such parameters as: concentration of the substrate, ionization potentials of the solution components and the temperature of the matrix play important role in the charge transfer processes. These parameters have to be chosen carefully in order to secure a complete formation of the substrate radical cation prior to observation of its unimolecular transformations. A successful application of the low-temperature pulse radiolytic method to the studies of valence isomerization and conformational rotamerism of radical cations has been reviewed.