Papers by Alexandra Yurkovskaya
The Journal of Physical Chemistry A, 1998
The transient absorption spectrum of the tert-butoxyl radical in the UV region was obtained by th... more The transient absorption spectrum of the tert-butoxyl radical in the UV region was obtained by the laser flash photolysis technique. The rate constants for-scission and self-termination reactions of tert-butoxyl radicals were measured in five solvents; the Arrhenius parameters of the rate constant for-scission k were determined. It was shown that both the solvent polarity and ability for hydrogen bonding accelerate the reaction of-scission. The solvent effect on the rate constant of the-scission reaction is discussed in terms of a simple Onzager-Betcher model, a point dipole model, and a model of the H-bonded complex of the radical with the solvent molecule.
Kinetics and mechanism of the photochemical reaction of Octacyanomolybdate (IV) and Diethylenetriamine
International Journal of Chemical Kinetics, 1999
... (18) Saini, RD; Dhanya, S.; Bhattacharyya, PK J. Photochem. Photobiol. A: Chem. 1988, 43, 91−... more ... (18) Saini, RD; Dhanya, S.; Bhattacharyya, PK J. Photochem. Photobiol. A: Chem. 1988, 43, 91−103. ...
Chemically induced dynamic nuclear polarization during thermal decomposition of peroxides and azo compounds
Accounts of Chemical Research, 1969
Marcus Cross-Relationship Probed by Time-Resolved CIDNP
The time-resolved CIDNP method can provide information about degenerate exchange reactions (DEE) ... more The time-resolved CIDNP method can provide information about degenerate exchange reactions (DEE) involving short-lived radicals. In the temperature range from 8 to 65°C, the DEE reactions of the guanosine-5’-monophosphate anion GMP(-H)- with the neutral radical GMP(-H)•, of the N-acetyl tyrosine anion NacTyrO- with a neutral radical NacTyrO• and of the tyrosine anion TyrO- with a neutral radical TyrO• were studied. In all the studied cases, the radicals were formed in the reaction of quenching triplet 2,2’-dipyridyl. The reorganization energies were obtained from Arrhenius plots. The rate constant of the reductive electron-transfer reaction in pair GMP(-H)•/TyrO- was determined at T = 25°C. Rate constants of GMP(-H)• radical reduction reactions with TyrO- and NacTyrO- anions calculated by the Marcus cross relation differ from the experimental ones by two orders of magnitude. The rate constants of several other electron transfer reactions involving GMP(-H)-/•, NacTyrO-/•, and TyrO-/•...
Physical Chemistry Chemical Physics
Photo-chemically induced nuclear polarization yields to NMR signal-to-noise enhancement and can b... more Photo-chemically induced nuclear polarization yields to NMR signal-to-noise enhancement and can be tuned by chemical modification of one of the radical-pair partners.
Two‐Dimensional Methods and Zero‐ to Ultralow‐Field ( <scp>ZULF</scp> ) <scp>NMR</scp>
Two‐Dimensional (2D) NMR Methods, Apr 14, 2023
Over the past decade, azobenzene-based molecular photoswitches have emerged as promising control ... more Over the past decade, azobenzene-based molecular photoswitches have emerged as promising control devices in a range of fields, including chemistry, biology, materials science, physics, energy storage and pharmacology. Previous studies revealed that cis isomer of azobenzene gains strong nonequilibrium polarization (called hyperpolarization) of 15N nuclear spins through interaction with parahydrogen molecules (i.e., a dihydrogen isomer with protons having zero total spin, pH2) in the reversible exchange with Ir-complex. This technique, known as SABRE (Signal Amplification by Reversible Exchange), enhances inherently weak NMR signals by several orders of magnitude at relatively low operational cost. We demonstrate that performing SABRE in the presence of light irradiation allows to hyperpolarize trans-azobenzene, which direct coordination with the SABRE Ir-complex is sterically hindered. The proposed approach, which we called photo-SABRE, is robust and efficient, as well as non-destruc...
Disproportionation and Dimerisation of Kynurenic Acid Under Uv Light
SSRN Electronic Journal
RSC Advances
This review provides a short introduction to the parahydrogen-based hyperpolarization (PHIP) tech... more This review provides a short introduction to the parahydrogen-based hyperpolarization (PHIP) techniques in NMR and MRI and then reviews the current literature on method developments and applications of various flavors of them.
Applied Magnetic Resonance
Photo-CIDNP (photo-chemically induced dynamic nuclear polarization) refers to nuclear polarizatio... more Photo-CIDNP (photo-chemically induced dynamic nuclear polarization) refers to nuclear polarization created by the spin-chemical evolution of spin-correlated radical pairs (SCRPs). This phenomenon occurs in gases, liquids and solids. Based on the solid-state photo-CIDNP effect observed under magic-angle spinning (MAS), photo-CIDNP MAS NMR has been developed as analytical method. Here we report the origin, the theory and the state of the art of this method.
The Journal of Chemical Physics, 2021
A detailed experimental study on reversible photo-induced intramolecular charge separation is pre... more A detailed experimental study on reversible photo-induced intramolecular charge separation is presented based on nuclear magnetic resonance detection of chemically induced dynamic nuclear polarization. From variation of such polarization with the external magnetic field, the coupling constants of isotropic and anisotropic hyperfine interactions at individual 13C sites are measured in the short-lived charge separated state of dyad molecules composed of donor–bridge–acceptor parts. The objects of study were rigid donor–bridge–acceptor dyads, consisting of triarylamine as a donor, naphthalene diimide as an acceptor, and a meta-conjugated diethynylbenzene fragment as a bridge. By systematic variation of side groups in the bridging moiety, their influence on the electron withdrawing strength is traced. In combination with similar data for the 1H positions obtained previously for the same compounds [I. Zhukov et al., J. Chem. Phys. 152, 014203 (2020)], our results provide a reliable basis...
Physical Chemistry Chemical Physics, 2021
In SABRE experiments at a high magnetic field, the spin order of molecular hydrogen is not just t... more In SABRE experiments at a high magnetic field, the spin order of molecular hydrogen is not just the singlet order, but a combination of singlet and central triplet ones. Additional proton pulse in some cases increases enhancement more than 10-fold.
Multidimensional Nuclear Magnetic Resonance (NMR) is based on the combination of well-established... more Multidimensional Nuclear Magnetic Resonance (NMR) is based on the combination of well-established building blocks for polarization transfer. These blocks are used to design correlation experiments through one or a few chemical bonds or through space. Here, we introduce a building block that enables polarization transfer across all NMR-active nuclei in a coupled network of spins: isotropic mixing at Zero and Ultra-Low Field (ZULF). Exploiting mixing under ZULF-NMR conditions, heteronuclear TOtal Correlation SpectroscopY (TOCSY) experiments were developed to highlight coupled spin networks. We demonstrate 1H-13C and 1H-15N correlations in ZULF-TOCSY spectra of labelled amino acids, which allow one to obtain cross-peaks among all hetero-nuclei belonging to the same coupled network, even when the direct interaction between them is negligible. We also demonstrate the interest of ZULF-TOCSY to analyze complex mixtures on the supernatant of ISOGRO, a growth medium of isotope-labelled biomo...
Nucleic acids research, Jan 5, 2018
DNA damage can affect various regulatory elements of the genome, with the consequences for DNA st... more DNA damage can affect various regulatory elements of the genome, with the consequences for DNA structure, dynamics, and interaction with proteins remaining largely unexplored. We used solution NMR spectroscopy, restrained and free molecular dynamics to obtain the structures and investigate dominant motions for a set of DNA duplexes containing CpG sites permuted with combinations of 5-methylcytosine (mC), the primary epigenetic base, and 8-oxoguanine (oxoG), an abundant DNA lesion. Guanine oxidation significantly changed the motion in both hemimethylated and fully methylated DNA, increased base pair breathing, induced BI→BII transition in the backbone 3' to the oxoG and reduced the variability of shift and tilt helical parameters. UV melting experiments corroborated the NMR and molecular dynamics results, showing significant destabilization of all methylated contexts by oxoG. Notably, some dynamic and thermodynamic effects were not additive in the fully methylated oxidized CpG, i...
Journal of magnetic resonance (San Diego, Calif. : 1997), 2018
A method is proposed for significant improvement of NMR pulse sequences used in high-field SABRE ... more A method is proposed for significant improvement of NMR pulse sequences used in high-field SABRE (Signal Amplification By Reversible Exchange) experiments. SABRE makes use of spin order transfer from parahydrogen (pH, the H molecule in its singlet spin state) to a substrate in a transient organometallic Ir-based complex. The technique proposed here utilizes "re-polarization", i.e., multiple application of an NMR pulse sequence used for spin order transfer. During re-polarization only the form of the substrate, which is bound to the complex, is excited by selective NMR pulses and the resulting polarization is transferred to the free substrate via chemical exchange. Owing to the fact that (i) only a small fraction of the substrate molecules is in the bound form and (ii) spin relaxation of the free substrate is slow, the re-polarization scheme provides greatly improved NMR signal enhancement, ε. For instance, when pyridine is used as a substrate, single use of the SABRE-INEPT...
The Journal of chemical physics, Jan 21, 2015
A method for precise manipulation of non-thermal nuclear spin polarization by switching a RF-fiel... more A method for precise manipulation of non-thermal nuclear spin polarization by switching a RF-field is presented. The method harnesses adiabatic correlation of spin states in the rotating frame. A detailed theory behind the technique is outlined; examples of two-spin and three-spin systems prepared in a non-equilibrium state by Para-Hydrogen Induced Polarization (PHIP) are considered. We demonstrate that the method is suitable for converting the initial multiplet polarization of spins into net polarization: compensation of positive and negative lines in nuclear magnetic resonance spectra, which is detrimental when the spectral resolution is low, is avoided. Such a conversion is performed for real two-spin and three-spin systems polarized by means of PHIP. Potential applications of the presented technique are discussed for manipulating PHIP and its recent modification termed signal amplification by reversible exchange as well as for preparing and observing long-lived spin states.
Long-lived spin states as a source of contrast in magnetic resonance spectroscopy and imaging
Journal of Magnetic Resonance, 2015
A method is proposed to create Long-Lived spin States (LLSs) from longitudinal spin magnetization... more A method is proposed to create Long-Lived spin States (LLSs) from longitudinal spin magnetization, which is based on adiabatic switching of a Radio-Frequency (RF) field with proper frequency. The technique is simple to implement with standard Nuclear Magnetic Resonance (NMR) equipment, providing an excellent conversion of population from the triplet T+ (or T-) state to the singlet state of a pair of spins and back. The method has been tested for the amino acid tyrosine and its partially deuterated isotopomer; for the deuterated compound, we have achieved a LLS lifetime, which exceeds the longitudinal relaxation time by a factor of 21. Furthermore, by slightly modifying the method, an enhanced contrast with respect to LLSs in NMR spectra is achieved; contrast enhancements of more than 1200 are feasible. This enables efficient suppression of longitudinal spin magnetization in NMR allowing one to look selectively at LLSs. Using this method we have demonstrated that not only spectral but also spatial contrast can be achieved: we have obtained spatial NMR images with strongly improved contrast originating from the difference of LLS lifetimes at different positions in the sample.
Journal of Magnetic Resonance, 2015
We have investigated the magnetic field dependence of Signal Amplification By Reversible Exchange... more We have investigated the magnetic field dependence of Signal Amplification By Reversible Exchange (SABRE) arising from binding of para-hydrogen (p-H 2) and a substrate to a suitable transition metal complex. The magnetic field dependence of the amplification of the 1 H Nuclear Magnetic Resonance (NMR) signals of the released substrates and dihydrogen, and the transient transition metal dihydride species shows characteristic patterns, which is explained using the theory presented here. The generation of SABRE is most efficient at low magnetic fields due to coherent spin mixing at nuclear spin Level Anti-Crossings (LACs) in the SABRE complexes. We studied two Ir-complexes and have shown that the presence of a 31 P atom in the SABRE complex doubles the number of LACs and, consequently, the number of peaks in the SABRE field dependence. Interestingly, the polarization of SABRE substrates is always accompanied by the para-to-ortho conversion in dihydride species that results in enhancement of the NMR signal of free (H 2) and catalyst-bound H 2 (Ir-HH). The field dependences of hyperpolarized H 2 and Ir-HH by means of SABRE are studied here, for the first time, in detail. The field dependences depend on the chemical shifts and coupling constants of Ir-HH, in which the polarization transfer takes place. A negative coupling constant of À7 Hz between the two chemically equivalent but magnetically inequivalent hydride nuclei is determined, which indicates that Ir-HH is a dihydride with an HH distance larger than 2 Å. Finally, the field dependence of SABRE at high fields as found earlier has been investigated and attributed to polarization transfer to the substrate by cross-relaxation. The present study provides further evidence for the key role of LACs in the formation of SABRE-derived polarization. Understanding the spin dynamics behind the SABRE method opens the way to optimizing its performance and overcoming the main limitation of NMR, its notoriously low sensitivity.
The journal of physical chemistry. B, Jan 14, 2015
The paramagnetic relaxation times of the aromatic and protons of Tyr59 and His68 residues of th... more The paramagnetic relaxation times of the aromatic and protons of Tyr59 and His68 residues of the native ubiquitin and of Tyr59 residue of the non-native ubiquitin were determined from an analysis of Chemically Induced Dynamic Nuclear Polarization (CIDNP) kinetics obtained during the photoreaction of the protein and 2,2-dipyridyl excited in the triplet state. Using the paramagnetic relaxation times determined earlier for the radicals of free amino acids as an internal standard and assuming that the hyperfine interaction (HFI) anisotropy is very similar for the radicals of free amino acids and the corresponding radicals of amino acid residues in the proteins, we determined parameters that characterize the intramolecular mobility of different protons in native and two non-native states of ubiquitin. The latter are denatured at pH 2 and 57 (○)C, and the A-state at pH 2 in a 60%/40% methanol/water mixture. The determination of the two parameters of intramolecular mobility (i.e., the c...
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Papers by Alexandra Yurkovskaya