Document Detail

Trityl biradicals and 13C dynamic nuclear polarization.
MedLine Citation:
PMID:  20458385     Owner:  NLM     Status:  MEDLINE    
The objective of this study is to investigate if trityl biradicals could lead to more efficient dynamic nuclear polarization (DNP) for low gamma nuclear spins at low temperature (approximately 1 K) than a trityl monoradical. Three novel trityl biradicals of different size are synthesized, characterized and employed for hyperpolarization of [1-(13)C]pyruvic acid at 3.35 T and 4.64 T. Intramolecular electron-electron distances are obtained via dipolar couplings from electron paramagnetic resonance (EPR) spectroscopy at X-band and W-band that match well with calculated molecular structures. Steady-state DNP levels and build-up times are measured as function of radical concentration, magnetic field strength and microwave frequency for each biradical. Similar maximal DNP is obtained with all studied biradicals whereas a twice as high polarization is achievable with the monoradical. Both the biradicals and the monoradical show approximately a doubling of the polarization when increasing the field strength from 3.35 T to 4.64 T. Biradical concentrations at maximum polarization are several times lower than the optimum monoradical concentration, but the penalty is a much longer build-up time. Adding a small amount of Gd(3+) to the samples (molar fraction of typically 100 ppm) has the same effect on DNP with the biradicals as with the monoradical. The electron longitudinal relaxation time T(1e) is found to be independent of the radical type and the field strength in this study. The same dependence of T(1e) on the trityl concentration is observed for all radicals. A considerable shortening of the (13)C longitudinal relaxation time is observed for biradicals which agrees with the shortened build-up time compared to the monoradical at the same trityl concentration. This is probably the reason for lower DNP levels with trityl biradicals.
Sven Macholl; Haukur Jóhannesson; Jan Henrik Ardenkjaer-Larsen
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Publication Detail:
Type:  Journal Article     Date:  2010-05-10
Journal Detail:
Title:  Physical chemistry chemical physics : PCCP     Volume:  12     ISSN:  1463-9084     ISO Abbreviation:  Phys Chem Chem Phys     Publication Date:  2010 Jun 
Date Detail:
Created Date:  2010-05-27     Completed Date:  2010-08-25     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  100888160     Medline TA:  Phys Chem Chem Phys     Country:  England    
Other Details:
Languages:  eng     Pagination:  5804-17     Citation Subset:  IM    
GE Healthcare, Medical Diagnostics, The Grove Centre, GC/18, Amersham HP7 9LL, UK.
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MeSH Terms
Carbon Isotopes / chemistry
Free Radicals / chemistry*
Gadolinium / chemistry
Magnetic Resonance Spectroscopy / methods*
Pyruvic Acid / chemistry
Reg. No./Substance:
0/Carbon Isotopes; 0/Free Radicals; 127-17-3/Pyruvic Acid; 7440-54-2/Gadolinium

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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