Shundrina I.K.,Novosibirsk State University |
Bukhtoyarova A.D.,RAS Institute of Organic Chemistry |
Russkikh V.V.,RAS Institute of Organic Chemistry |
Parkhomenko D.A.,International Tomography Center Institutskaya |
Shelkovnikov V.V.,RAS Institute of Organic Chemistry
Polymer Bulletin | Year: 2015
New piperazine-based polymerizable monomers were synthesized to modify adhesive properties of fluoromethacrylic copolymer. The new monomers showed good ability to radical copolymerization with fluoroalkylmethacrylates. Amorphous glassy terpolymers were prepared with random distribution units in the macromolecules and weight-average molecular weight (Mw) 110,000–130,000. The ratio of monomer units in the obtained copolymer is close to the ratio of the monomers in the starting mixture. The terpolymers exhibited excellent solubility in tetrahydrofuran (THF), acetone and α,α,α-trifluorotoluene (TFT). The introduction of new monomers to the macromolecules increased the glass-transition temperatures (Tg) of terpolymers, significantly improved their thermal stability and adhesion to the aluminum substrate. © 2015, Springer-Verlag Berlin Heidelberg.
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.
Krumkacheva O.,Novosibirsk State University |
Tanabe M.,Tohoku University |
Yamauchi S.,Tohoku University |
Fedin M.,International Tomography Center Institutskaya |
And 2 more authors.
Applied Magnetic Resonance | Year: 2012
The triplet states of deoxybenzoin (DOB) and benzophenone (BP) molecules in randomly methylated β-cyclodextrin (CD) cavity are studied by time-resolved (TR) and pulse electron paramagnetic resonance (EPR). The observed TR EPR spectrum of DOB in β-CD at 30 K is close to the spectrum measured in polar solvent trifluoroethanol, revealing strong hydration by water molecules. At the same time, TR EPR spectrum of BP in β-CD corresponds to nonpolar surrounding of the CO-group. The electron spin relaxation times T 1 and T 2 of triplet BP at 30 K measured by pulse EPR are found to be different in β-CD compared to nonpolar toluene glass. The observed increase of T 2 by up to a factor of four in β-CD is caused by the lower vibration amplitude of CO-bond of BP due to the confinement in β-CD. The influence of β-CD with covalently attached nitroxide on the triplet states of DOB and BP is principally different: the excited triplet states could not be observed by TR EPR due to the efficient quenching of the excited states by nitroxide. © 2011 Springer-Verlag.
Korchak S.E.,Free University of Berlin |
Kiryutin A.S.,Free University of Berlin |
Kiryutin A.S.,International Tomography Center Institutskaya |
Ivanov K.L.,Free University of Berlin |
And 6 more authors.
Applied Magnetic Resonance | Year: 2010
Dynamic nuclear polarization (DNP) effects in aqueous solutions of stable 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) radicals were studied in a pulsed mode of pumping the electron paramagnetic resonance (EPR) transitions. Our fast field cycling setup allowed us to perform the EPR pumping at low magnetic fields and to detect the enhanced nuclear magnetic resonance signals at 7 T with high spectral resolution. Pumping was performed at two different frequencies, 300 MHz and 1.4 GHz, corresponding to magnetic fields around 10 and 48.6 mT, respectively. For both frequencies, the DNP enhancements were close to the limiting theoretical values of -110 (14N TEMPOL) and -165 (15N TEMPOL). Our pulsed experiments exploit coherent motion of the electronic spins in the radio-frequency field as seen by an oscillatory component in the dependence of the DNP effect on the radio-frequency pulse duration. The DNP enhancement was studied in detail as a function of the pulse length, duty cycle, delay between the pulses, and applied power. The analysis of the results shows that pulsed DNP experiments provide an opportunity to achieve enhancements of about -110 with relatively low applied power as compared to the standard continuous-wave DNP experiments. An adequate theoretical approach to the problem under study is suggested. © Springer 2009.
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.