Low-temperature dynamic nuclear polarization at 9.4 T with a 30 mW microwave source.
Dynamic nuclear polarization (DNP) can provide large signal enhancements in nuclear magnetic resonance (NMR) by transfer of polarization from electron spins to nuclear spins. We discuss several aspects of DNP experiments at 9.4 T (400 MHz resonant frequency for (1)H, 264 GHz for electron spins in organic radicals) in the 7-80K temperature range, using a 30 mW, frequency-tunable microwave source and a quasi-optical microwave bridge for polarization control and low-loss microwave transmission. In experiments on frozen glycerol/water doped with nitroxide radicals, DNP signal enhancements up to a factor of 80 are observed (relative to (1)H NMR signals with thermal equilibrium spin polarization). The largest sensitivity enhancements are observed with a new triradical dopant, DOTOPA-TEMPO. Field modulation with a 10 G root-mean-squared amplitude during DNP increases the nuclear spin polarizations by up to 135%. Dependencies of (1)H NMR signal amplitudes, nuclear spin relaxation times, and DNP build-up times on the dopant and its concentration, temperature, microwave power, and modulation frequency are reported and discussed. The benefits of low-temperature DNP can be dramatic: the (1)H spin polarization is increased approximately 1000-fold at 7 K with DNP, relative to thermal polarization at 80K.
Thurber
Kent R
KR
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, USA.
Yau
Wai-Ming
WM
Tycko
Robert
R
D003080:Cold Temperature; D005990:Glycerol / Q000737:chemistry* / Q000528:radiation effects*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008872:Microwaves; D013696:Temperature; D014867:Water / Q000737:chemistry*
D014867:Water; D005990:Glycerol
Solid State Nucl Magn Reson. 2004 Jan;25(1-3):138-41
14698400
J Am Chem Soc. 2004 Apr 21;126(15):4979-90
15080704
Proc Natl Acad Sci U S A. 2005 Mar 1;102(9):3284-9
15718283
J Magn Reson. 2009 Jan;196(1):74-7
18926750
J Magn Reson. 2000 May;144(1):134-41
10783283
J Am Chem Soc. 2010 Jan 13;132(1):24-5
20000466
J Magn Reson. 2011 Dec;213(2):404-9
22152358
Nat Struct Biol. 1999 Feb;6(2):141-5
10048925
J Am Chem Soc. 2009 Oct 7;131(39):13902-3
19743849
J Am Chem Soc. 2009 May 6;131(17):6090-2
19361195
J Magn Reson. 1999 Sep;140(1):293-9
10479576
J Magn Reson. 2008 Dec;195(2):179-86
18922715
Biochemistry. 2007 Mar 20;46(11):3586-93
17311419
J Chem Phys. 2008 Feb 7;128(5):052211
18266416
J Mol Biol. 2009 Oct 2;392(4):1055-73
19647001
J Chem Phys. 2007 Jan 28;126(4):044512
17286492
J Mol Biol. 2001 Nov 2;313(4):845-59
11697908
J Magn Reson. 2007 Dec;189(2):251-79
17942352
Angew Chem Int Ed Engl. 2009;48(27):4996-5000
19492374
J Am Chem Soc. 2006 Sep 6;128(35):11385-90
16939261
J Magn Reson. 2007 Aug;187(2):242-50
17524687
J Chem Phys. 2008 Jun 28;128(24):241102
18601309
J Magn Reson. 2009 Apr;197(2):167-75
19162518
Phys Rev Lett. 1993 Nov 22;71(21):3561-3564
10055008
Phys Rev Lett. 2007 Jun 1;98(22):220501
17677824
J Phys Chem B. 2008 Mar 13;112(10):2818-28
18284225
J Chem Phys. 2008 Feb 7;128(5):052302
18266419
J Am Chem Soc. 2001 Feb 7;123(5):1010-1
11456650
J Magn Reson. 2009 Aug;199(2):159-65
19447055
Methods Enzymol. 2005;394:350-82
15808228