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Morozova O.B.,Novosibirsk State University | Fishman N.N.,International Tomography Center Institutskaya | Yurkovskaya A.V.,Novosibirsk State University
Zeitschrift fur Physikalische Chemie | Year: 2017

As a model of chemical DNA repair, intramolecular electron transfer from tryptophan to the radical of the purine base guanosine combined into a conjugate by a flexible linker was studied by time-resolved chemically induced dynamic nuclear polarization (CIDNP). The guanosyl radicals were photochemically generated in the quenching reaction of the triplet excited dye 2,2′-dipyridyl. The CIDNP kinetics was obtained by detection of NMR spectra containing anomalously enhanced signals of diamagnetic products that are formed during a variable period after excitation by a laser pulse. The kinetic data obtained for the protons located on the guanosyl and tryptophanyl moieties of the conjugate were compared to those obtained in photoreactions of the molecules containing the same linker, but with only one of the two reactive moieties of the conjugate-tryptophanyl or guanosyl. Strong differences between the CIDNP kinetics of different conjugates were revealed and explained by a rapid intramolecular electron transfer from tryptophan to the guanosyl radical in the conjugate. Model simulations of the CIDNP kinetics allowed for determination of the rate constant of intramolecular electron transfer at (1.0±0.5)×106 s-1 indicating a high potential of chemical repair of the guanosyl radical by means of electron transfer from the tryptophanyl moiety in a surrounding protein pool that can provide rather efficient protection of oxidized DNA bases from pathological damage on a submicrosecond time scale. © 2017 Walter de Gruyter GmbH, Berlin/Boston.


Bagryanskaya E.,International Tomography Center Institutskaya | Bremond P.,Aix - Marseille University | Edeleva M.,International Tomography Center Institutskaya | Marque S.R.A.,Aix - Marseille University | And 3 more authors.
Macromolecular Rapid Communications | Year: 2012

In recent work, a 15-fold increase in the C-ON bond homolysis rate constant k d of 4-pyridylethyl-SG1-based alkoxyamine was observed upon protonation of the pyridyl moiety in organic solvent. In this report, the pH dependence of k d (pK a = 4.7) is investigated in D 2O/CD 3OD (v/v 1:1). A 64-fold increase in k d is observed at acidic pH. Calculations show that the increase in k d upon protonation is due to both an increase in the stabilization of the protonated 4-pyridylethyl radical and an increase of the destabilization of the starting materials through an increase in the polarity of the alkyl fragment. This new alkoxyamine is applied to NMP of styrene and sodium styrene sulfonate. The pH effect on the C-ON bond homolysis of activable alkoxyamines is highlighted by a 64-fold increased in k d from pH 6.7 (1) to pH 3.0 (1H+). The effect of pH is investigated for the NMP of styrene and sodium styrene sulfonate. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Kochling T.,Free University of Berlin | Morozova O.B.,Novosibirsk State University | Yurkovskaya A.V.,Novosibirsk State University | Vieth H.-M.,Free University of Berlin | Vieth H.-M.,International Tomography Center Institutskaya
Journal of Physical Chemistry B | Year: 2016

Photo-oxidation of seven cyclic dipeptides containing methionine, Met, and/or S-methylcysteine, Cys(Me) by electron transfer from the sulfur atom was studied in aqueous solution by time-resolved and field dependent CIDNP (chemically induced dynamic nuclear polarization). Hyperpolarized high resolution NMR spectral patterns of the starting peptides detected immediately after pulsed laser excitation show signals of all protons that are bound to carbons neighboring the sulfur atom, thus proving the involvement of sulfur-centered cation radicals. The magnetic field dependence of CIDNP shows a pronounced maximum that is determined by the g-factors and hyperfine coupling constants of the transient radical species. From simulation of the experimental data obtained for the magnetic field dependences of CIDNP, three types of radical structures were characterized: (1) a linear sulfur-centered cation radical of the methionine (Met) residue (g = 2.0107 ± 0.0010) for cyclo-(d-Met-l-Met) (trans-configuration), cyclo-(d-Met-l-Cys(Me)) (trans-configuration), and cyclo-(Gly-Met); (2) a cyclic radical (S-O)+ (g = 2.0088 ± 0.0010) with a two-center three-electron bond (2c-3e) structure between the sulfur atom of the Cys(Me) residue and the oxygen atom of cyclo-(d-Met-l-Cys(Me)) and cyclo-(Gly-Cys(Me)); (3) a cyclic radical (S-S)+ (g = 2.013 ± 0.0020) with a two-center three-electron bond structure between the two sulfur atoms of the peptides cyclo-(l-Met-l-Met), cyclo-(l-Met-l-Cys(Me)), and cyclo-(l-Cys(Me)-l-Cys(Me)). In contrast, no indication of any type of cyclic radicals with a two-center three-electron bond between sulfur and nitrogen atoms was found. In addition, the hyperfine coupling constants (HFCCs) were determined. © 2016 American Chemical Society.


Morozova O.B.,International Tomography Center Institutskaya | Yurkovskaya A.V.,International Tomography Center Institutskaya
Angewandte Chemie - International Edition | Year: 2010

Invisible to other methods, reactions of the histidyl radical could be followed by NMR spectroscopic detection of the histidine signal through the use of time-resolved chemically induced dynamic nuclear polarization (CIDNP). CIDNP decay of the His signal during photooxidation of the peptides His-Tyr and Tyr-His pointed to electron transfer from the tyrosine residue to the histidyl radical (see scheme for Tyr-His). © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Korchak S.,Free University of Berlin | Ivanov K.,Free University of Berlin | Ivanov K.,International Tomography Center Institutskaya | Yurkovskaya A.,Free University of Berlin | And 2 more authors.
Journal of Chemical Physics | Year: 2010

Effects of scalar spin-spin interactions on the nuclear magnetic relaxation dispersion (NMRD) of coupled multispin systems were analyzed. Taking spin systems of increasing complexity we demonstrated pronounced influence of the intramolecular spin-spin couplings on the NMRD of protons. First, at low magnetic fields where there is strong coupling of spins the apparent relaxation times of the coupled spins become equal. Second, there are new features, which appear at the positions of the nuclear spin level anticrossings. Finally, in coupled spin systems there can be a coherent contribution to the relaxation kinetics present at low magnetic fields. All these peculiarities caused by spin-spin interactions are superimposed on the features in NMRD, which are conditioned by changes of the motional regime. Neglecting the effects of couplings may lead to misinterpretation of the NMRD curves and significant errors in determining the correlation times of molecular motion. Experimental results presented are in good agreement with theoretical calculations. © 2010 American Institute of Physics.


Krumkacheva O.A.,International Tomography Center Institutskaya | Gorelik V.R.,International Tomography Center Institutskaya | Bagryanskaya E.G.,International Tomography Center Institutskaya | Lebedeva N.V.,University of North Carolina at Chapel Hill | Forbes M.D.E.,University of North Carolina at Chapel Hill
Langmuir | Year: 2010

A systematic investigation of the photochemistry and ensuing radical chemistry of three guest ketones encapsulated in randomly methylated β-cyclodextrin (β-CD) hosts is reported. Dibenzyl ketone (DBK), deoxybenzoin (DOB), and benzophenone (BP) triplet states are rapidly formed after photolysis at 308 nm. Time-resolved electron paramagnetic resonance (TREPR) spectroscopy, steady-state NMR spectroscopy, and time-resolved chemically induced nuclear polarization (TR-CIDNP) experiments were performed on the ketone/CD complexes and on the ketones in free solution for comparison. The major reactivity pathways available from these excited states are either Norrish I α-cleavage or H-atom abstraction from the interior of the CD capsule or the solvent. The DOB triplet state undergoes both reactions, whereas the DBK triplet shows exclusively α-cleavage and the BP triplet shows exclusively H-atom abstraction. Radical pairs are observed in β-CDs by TREPR, consisting of either DOB or BP ketyl radicals with sugar radicals from the CD interior. The TREPR spectra acquired in CDs are substantially broadened due to strong spin exchange. The electron spin polarization mechanism is mostly due to S-T0 radical pair mechanism (RPM) in solution but changes to S-T-RPM. in the CDs due to the large exchange interaction. The TR-CIDNP results confirm the reactivity patterns of all three ketones, and DOB shows strong nuclear spin polarization from a novel rearrangement product resulting from the α-cleavage reaction. © 2010 American Chemical Society.


Morozova O.B.,International Tomography Center Institutskaya | Yurkovskaya A.V.,Novosibirsk State University
Journal of Physical Chemistry B | Year: 2015

Time-resolved chemically induced dynamic nuclear polarization (CIDNP) was used to investigate reversible intramolecular electron transfer (IET) in short-lived oxidized peptides, which had different structures and contained tryptophan and tyrosine residues, in an acidic aqueous solution with a pH below the pKa of the tryptophanyl cation radical. The CIDNP kinetic data were obtained at the microsecond scale and were analyzed in detail to calculate the rate constants for electron transfer in both directions: from the tyrosine residue to the tryptophanyl cation radical, kf, and from the tryptophan residue to the neutral tyrosyl radical, kr. The charge of the terminal amino group and the presence of glycine and proline spacers were shown to strongly affect the rate constants of the reaction under study. Among these functional groups, the presence and the location of the positive charge on the amino group in close proximity to the cationic indolyl radical had the strongest effect on the rate constant of the forward IET from the tyrosine residue to the tryptophanyl radical cation, kf. This effect was manifested as an increase of 2 orders of magnitude in kf for a change in the linkage order between residues in the dipeptide: kf = 4 × 103 s-1 for the oxidized Tyr-Trp increased to kf = 5.5 × 105 s-1 in oxidized Trp-Tyr. The reverse rate constant for IET was less sensitive to the amino group charge. Moreover, the presence of glycine or proline spacers in the peptides with a tryptophan residue at the N-terminus not only reduced the IET rate constant but also shifted the equilibrium of the IET in the reaction under study toward the formation of tyrosyl radicals with respect to the peptide Trp-Tyr. That is, the glycine or proline spacers affected the difference in the reduction potential of the tryptophanyl and tyrosyl radicals. (Graph Presented). © 2014 American Chemical Society.


Morozova O.B.,International Tomography Center Institutskaya | Ivanov K.L.,International Tomography Center Institutskaya | Kiryutin A.S.,International Tomography Center Institutskaya | Sagdeev R.Z.,International Tomography Center Institutskaya | And 3 more authors.
Physical Chemistry Chemical Physics | Year: 2011

Chemically Induced Dynamic Nuclear Polarization (CIDNP) of the diamagnetic products of radical reactions is exploited for the purpose of determination of the hyperfine coupling constants (HFCCs) of the radical intermediates. A simple proportionality relation between geminate CIDNP of a nucleus and its HFCC at the radical stage is established. The applicability range of this relation is determined: the relation is fulfilled in the case of a large difference in g-factor between the radicals involved and for the situation where the number of magnetic nuclei in the system is sufficiently large. The validity of the relation was confirmed by CIDNP experiments on radical pairs with precisely known HFCCs. Using the proportionality relation we were able to measure the HFCCs in various short-lived radicals of the amino acids histidine and tryptophan and of the S-N-centered cyclic radical of methionine derived from the methionine-glycine dipeptide in aqueous solution. © 2011 the Owner Societies.


PubMed | Free University of Berlin and International Tomography Center Institutskaya
Type: Journal Article | Journal: The journal of physical chemistry letters | Year: 2015

A method is proposed to transfer spin order from para-hydrogen, that is, the H2 molecule in its singlet state, to spin-1/2 heteronuclei of a substrate molecule. The method is based on adiabatic passage through nuclear spin level anticrossings (LACs) in the doubly rotating frame of reference; the LAC conditions are fulfilled by applying resonant RF excitation at the NMR frequencies of protons and the heteronuclei. Efficient conversion of the para-hydrogen-induced polarization into net polarization of the heteronuclei is demonstrated; the achieved signal enhancements are about 6400 for (13)C nuclei at natural abundance. The theory behind the technique is described; advantages of the method are discussed in detail.


PubMed | Free University of Berlin and International Tomography Center Institutskaya
Type: Journal Article | Journal: The journal of physical chemistry. B | Year: 2016

Photo-oxidation of seven cyclic dipeptides containing methionine, Met, and/or S-methylcysteine, Cys(Me) by electron transfer from the sulfur atom was studied in aqueous solution by time-resolved and field dependent CIDNP (chemically induced dynamic nuclear polarization). Hyperpolarized high resolution NMR spectral patterns of the starting peptides detected immediately after pulsed laser excitation show signals of all protons that are bound to carbons neighboring the sulfur atom, thus proving the involvement of sulfur-centered cation radicals. The magnetic field dependence of CIDNP shows a pronounced maximum that is determined by the g-factors and hyperfine coupling constants of the transient radical species. From simulation of the experimental data obtained for the magnetic field dependences of CIDNP, three types of radical structures were characterized: (1) a linear sulfur-centered cation radical of the methionine (Met) residue (g = 2.0107 0.0010) for cyclo-(d-Met-l-Met) (trans-configuration), cyclo-(d-Met-l-Cys(Me)) (trans-configuration), and cyclo-(Gly-Met); (2) a cyclic radical (SO)(+) (g = 2.0088 0.0010) with a two-center three-electron bond (2c-3e) structure between the sulfur atom of the Cys(Me) residue and the oxygen atom of cyclo-(d-Met-l-Cys(Me)) and cyclo-(Gly-Cys(Me)); (3) a cyclic radical (SS)(+) (g = 2.013 0.0020) with a two-center three-electron bond structure between the two sulfur atoms of the peptides cyclo-(l-Met-l-Met), cyclo-(l-Met-l-Cys(Me)), and cyclo-(l-Cys(Me)-l-Cys(Me)). In contrast, no indication of any type of cyclic radicals with a two-center three-electron bond between sulfur and nitrogen atoms was found. In addition, the hyperfine coupling constants (HFCCs) were determined.

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