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Magnetic field dependent long-lived spin states in amino acids and dipeptides

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Zimmermann,  Herbert
Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Max Planck Society;

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Citation

Pravdivtsev, A. N., Yurkovskaya, A. V., Zimmermann, H., Vieth, H.-M., & Ivanov, K. L. (2014). Magnetic field dependent long-lived spin states in amino acids and dipeptides. Physical Chemistry Chemical Physics, 16(16), 7584-7594. doi:10.1039/C3CP55197K.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0019-8FB0-C
Abstract
Magnetic field dependence of long-lived spin states (LLSs) of the β-CH2 protons of aromatic amino acids was studied. LLSs are spin states, which are immune to dipolar relaxation, thus having lifetimes far exceeding the longitudinal relaxation times; the simplest example of an LLS is given by the singlet state of two coupled spins. LLSs were created by means of the photo-chemically induced dynamic nuclear polarization technique. The systems studied were amino acids, histidine and tyrosine, with different isotopomers. For labeled amino acids with the α-CH and aromatic protons substituted by deuterium at low fields the LLS lifetime, TLLS, for the β-CH2 protons was more than 40 times longer than the T1-relaxation time. Upon increasing the number of protons the ratio TLLS/T1 was reduced; however, even in the fully protonated amino acids it was about 10; that is, the long-lived mode was still preserved in the system. In addition, the effect of paramagnetic impurities on spin relaxation was studied; field dependencies of T1 and TLLS were measured. LLSs were also formed in tyrosine-containing dyads; a TLLS/T1 ratio of [similar]7 was found, usable for extending the spin polarization lifetime in such systems.