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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 99mTc−Complex with Human Serum Albumin
journal contribution
posted on 1998-10-30, 00:00 authored by Raghoottama S. Pandurangi, Przemyslaw Lusiak, Robert R. Kuntz, Wynn A. Volkert, Jacek Rogowski, Matthew S. PlatzSystematic 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 and covalently attached to human serum albumin
via photochemical activation extending the favorable bimolecular insertion characteristics of BFPCA
to tracer level concentrations in buffer conditions. Flash photolysis experiments correlate singlet
nitrene lifetimes with the efficiency of intermolecular insertion reactions. This work provides new
photo-cross-linking technology, useful in radiodiagnostics and radiotherapy in nuclear medicine.
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Photolabile Chelating Agentsrepresentative BFPCA 12chelating agentscomplexing transition metalsradionuclide 99 m TcHuman Serum Albumin Systematic functionalizationflash photolysis techniquesbifunctional photolabile chelating agentsCH insertionperfluoroaryl azidesCH insertion efficiencysinglet nitrenestracer level concentrationsFlash photolysis experimentssinglet nitrene lifetimes
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