Research output: Contribution to journal › Article › peer-review
Electron spin echo detection of stochastic molecular librations : Non-cooperative motions on solid surface. / Golysheva, Elena A.; Samoilova, Rimma I.; De Zotti, Marta et al.
In: Journal of Magnetic Resonance, Vol. 309, 106621, 01.12.2019.Research output: Contribution to journal › Article › peer-review
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TY - JOUR
T1 - Electron spin echo detection of stochastic molecular librations
T2 - Non-cooperative motions on solid surface
AU - Golysheva, Elena A.
AU - Samoilova, Rimma I.
AU - De Zotti, Marta
AU - Toniolo, Claudio
AU - Formaggio, Fernando
AU - Dzuba, Sergei A.
N1 - Copyright © 2019 Elsevier Inc. All rights reserved.
PY - 2019/12/1
Y1 - 2019/12/1
N2 - In frozen biological media and molecular glasses only restricted motions exist; because of the weakness and disorder of intermolecular bonds these motions may have stochastic nature. Electron spin echo (ESE) spectroscopy of spin-labeled molecules allows detecting their restricted stochastic rotations (stochastic molecular librations). As in molecular disordered media motions may be highly cooperative, it would be desirable to investigate their spectroscopic manifestation also in the systems where cooperative effects would be certainly ruled out. In this work, ESE of spin-labeled molecules adsorbed on inorganic SiO2 surface was investigated in a wide temperature range. The rate of motion-induced spin relaxation was found to become measurable above 130 K, increasing with temperature and attaining then a saturating behavior with a well-defined maximum near 250 K. For two types of molecules differing remarkably in their size and polarity (a small highly-polar nitroxide radical and a large spin-labeled peptide), quite similar results were obtained. This saturating behavior was quantitatively reproduced in simulations within a simple model of jump between two close orientations. Comparison with experiment allowed estimate that at 250 K the correlation time of the motion τc is of the order of several tens of nanoseconds and the angle α between two orientations is around 0.02 rad. As the found saturating behavior is a property of individual motions, for any other molecular system an excess of the spin relaxation rate above the maximum found here for adsorbed molecules may be ascribed to cooperative motions. Comparison with literature data on molecular systems of different origin has shown that effects of cooperativity indeed are present and, moreover, may be very essential.
AB - In frozen biological media and molecular glasses only restricted motions exist; because of the weakness and disorder of intermolecular bonds these motions may have stochastic nature. Electron spin echo (ESE) spectroscopy of spin-labeled molecules allows detecting their restricted stochastic rotations (stochastic molecular librations). As in molecular disordered media motions may be highly cooperative, it would be desirable to investigate their spectroscopic manifestation also in the systems where cooperative effects would be certainly ruled out. In this work, ESE of spin-labeled molecules adsorbed on inorganic SiO2 surface was investigated in a wide temperature range. The rate of motion-induced spin relaxation was found to become measurable above 130 K, increasing with temperature and attaining then a saturating behavior with a well-defined maximum near 250 K. For two types of molecules differing remarkably in their size and polarity (a small highly-polar nitroxide radical and a large spin-labeled peptide), quite similar results were obtained. This saturating behavior was quantitatively reproduced in simulations within a simple model of jump between two close orientations. Comparison with experiment allowed estimate that at 250 K the correlation time of the motion τc is of the order of several tens of nanoseconds and the angle α between two orientations is around 0.02 rad. As the found saturating behavior is a property of individual motions, for any other molecular system an excess of the spin relaxation rate above the maximum found here for adsorbed molecules may be ascribed to cooperative motions. Comparison with literature data on molecular systems of different origin has shown that effects of cooperativity indeed are present and, moreover, may be very essential.
KW - Antibiotic peptide
KW - Biological media
KW - Cooperative motions
KW - EPR
KW - ESE
KW - ESR
KW - Glassy media
KW - Neutron scattering
KW - Spin label
KW - Spin relaxation
KW - PHOTOSYNTHETIC REACTION CENTERS
KW - HIGH-FIELD EPR
KW - NITROXIDES
KW - DYNAMICAL TRANSITION
KW - LABELED LIPIDS
KW - PROTEIN DYNAMICS
KW - PARAMAGNETIC-RESONANCE
KW - PROBE MOLECULES
KW - IONIC LIQUIDS
KW - ORIENTATIONAL MOTION
UR - http://www.scopus.com/inward/record.url?scp=85073758261&partnerID=8YFLogxK
U2 - 10.1016/j.jmr.2019.106621
DO - 10.1016/j.jmr.2019.106621
M3 - Article
C2 - 31669794
AN - SCOPUS:85073758261
VL - 309
JO - Journal of Magnetic Resonance
JF - Journal of Magnetic Resonance
SN - 1090-7807
M1 - 106621
ER -
ID: 21937611