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CIDNP study of photo-chemically generated short-lived radical intermediates of biologically important molecules

Final Activity Report Summary - CIDNP_OF_BM (CIDNP study of photochemically generated short lived radical intermediates of biologically important molecules)

The research activity focussed on experimental study of the structural and dynamic properties of short-lived intermediates of biologically important molecular systems and photoprocesses using novel techniques of magnetic resonance spectroscopy.

They were based on the effects of electron and nuclear spins in particular and on magnetic interaction in general, on the rates and yields of chemical and biological reactions. The work involved the application of the nuclear magnetic resonance (NMR) technique termed Chemically induced dynamic nuclear polarisation (CIDNP) that allowed for high sensitivity and spectral resolution in crowded spectra combined with optical initiation of chemical intermediates. The technique had high potential for determining the structural and magnetic resonance properties and the reactivity of the radicals of proteins, nucleic acids and their building blocks.

The research activity was associated with the following:
1. study of photochemical reactions involving proteins and protein related molecules. There was linear correlation between hyperfine coupling constants and polarisation amplitude for the geminate reaction products yielding the sign and value of hyperfine coupling constants (HFCC) while the position and coupling in NMR spectrum provided assignment of individual nuclear spins in the molecule. Determining the structure and magnetic resonance parameters of radicals formed in this way, as well as the kinetics of multistep reactions of peptides and oligonucleotides.
2. investigation of structure, i.e. surface accessibility and confinement, and dynamic processes, i.e. intermolecular electron and proton transfer, in native and ill defined partly folded and denatured states of proteins as promising new applications. We proposed to utilise CIDNP kinetics in proteins to determine the paramagnetic nuclear relaxation times and use them for site-specific determination of correlation times of intramolecular mobility of residues in different conformational states on the nanosecond time scale.
3. modelling of non-enzymatic Deoxyribonucleic acid (DNA) repair via electron transfer from amino acids to the oxidised purine nucleotides that we recently found as a prototype of fast chemical repair of radiation induced damages of DNA and extending the findings to systems with increased complexity within the frame of proteomic research on peculiarities of recognition and processing of DNA substrate.
4. dynamic nuclear polarisation (DNP) experiments with stable radicals utilising fast magnetic field cycling with high resolution NMR detection with the aim to increase the sensitivity of NMR studies of biomolecules that did not participate in photoreactions.
5.the detailed mechanism of photooxidation of a number of peptides, such as gly-gly, met-gly, gly-met, by tripled excited 4-carboxybenzophenone (CBP) was established. The oxidation channel via electron transfer from the amino group was revealed. This reaction pathway led to the formation of triplet spin-correlated radical pair of anion radical of CBP and N-centered aminium cation radical which deprotonated within tens of nanoseconds.
6. it was also shown that spin-spin interaction induced polarisation transfer in diamagnetic states and essentially affected field dependences of hyperpolarisation when the condition of strong coupling was fulfilled.