Dynamic nuclear polarization of 13C in aqueous solutions under ambient conditions.

The direct enhancement of the (13)C NMR signal of small molecules in solution through Overhauser-mediated dynamic nuclear polarization (DNP) has the potential to enable studies of systems where enhanced signal is needed but the current dissolution DNP approach is not suitable, for instance if the sample does not tolerate a freeze-thaw process or if continuous flow or rapid re-polarization of the molecules is desired. We present systematic studies of the (13)C DNP enhancement of (13)C-labeled small molecules in aqueous solution under ambient conditions, where we observe both dipolar and scalar-mediated enhancement. We show the role of the three-spin effects from enhanced protons on (13)C DNP through DNP experiments with and without broadband (1)H decoupling and by comparing DNP results with H(2)O and D(2)O. We conclude that the efficiency of (13)C Overhauser DNP in small molecules strongly depends on the distance of closest approach between the electron and (13)C nucleus, the presence of a scalar contribution to the coupling factor, and the magnitude of the three-spin effect due to adjacent polarized protons. The enhancement appears to depend less on the translational dynamics of the (13)C-labeled small molecules and radicals.

[1]  W. Müller-Warmuth,et al.  Intermolecular interactions of benzene and carbon tetrachloride with selected free radicals in solution as studied by 13C and 1H dynamic nuclear polarization , 1976 .

[2]  J. Ardenkjær-Larsen,et al.  Increase in signal-to-noise ratio of > 10,000 times in liquid-state NMR , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[3]  Brandon D. Armstrong,et al.  Hyperpolarized water as an authentic magnetic resonance imaging contrast agent , 2007, Proceedings of the National Academy of Sciences.

[4]  F. Reinbold,et al.  Dynamic polarisation in a three-spin system☆ , 1962 .

[5]  Jan H. Ardenkjær-Larsen,et al.  Molecular imaging with endogenous substances , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[6]  D. Singel,et al.  High frequency (140 GHz) dynamic nuclear polarization: Polarization transfer to a solute in frozen aqueous solution , 1995 .

[7]  Richard D. Bates,et al.  Use of nitroxide spin labels in studies of solvent–solute interactions , 1999 .

[8]  R. Wind,et al.  Applications of dynamic nuclear polarization in 13C NMR in solids , 1985 .

[9]  Michael P. Williamson,et al.  The Nuclear Overhauser Effect , 2008 .

[10]  R. Bryant,et al.  NMR relaxation dispersion in an aqueous nitroxide system , 1981 .

[11]  M. Thaning,et al.  Real-time metabolic imaging. , 2006, Proceedings of the National Academy of Sciences of the United States of America.

[12]  Robert G Griffin,et al.  Dynamic nuclear polarization at high magnetic fields. , 2008, The Journal of chemical physics.

[13]  R. Vold,et al.  Magnetic resonance measurements of proton exchange in aqueous urea , 1970 .

[14]  Brandon D Armstrong,et al.  A new model for Overhauser enhanced nuclear magnetic resonance using nitroxide radicals. , 2007, The Journal of chemical physics.

[15]  D. Bethune,et al.  The nature of fullerene solution collisional dynamics. A 13C DNP and NMR study of the C60/C6D6/TEMPO system , 1993 .

[16]  R. A. McAllister,et al.  The viscosity of acetone‐water solutions up to their normal boiling points , 1958 .

[17]  R. Griffin,et al.  Solution-state dynamic nuclear polarization at high magnetic field. , 2002, Journal of the American Chemical Society.

[18]  Ray Freeman,et al.  Broadband heteronuclear decoupling , 1982 .

[19]  J. Shea,et al.  Overhauser dynamic nuclear polarization and molecular dynamics simulations using pyrroline and piperidine ring nitroxide radicals. , 2009, Journal of magnetic resonance.

[20]  Songi Han,et al.  Spin-labeled gel for the production of radical-free dynamic nuclear polarization enhanced molecules for NMR spectroscopy and imaging. , 2008, Journal of magnetic resonance.

[21]  H. Dorn,et al.  A model for establishing the ultimate enhancements (A∞) in the low to high magnetic field transfer dynamic nuclear polarization experiment , 1990 .

[22]  G. Guiochon,et al.  The role of the temperature in reversed-phase high-performance liquid chromatography using pyrocarbon-containing adsorbents , 1978 .

[23]  Brandon D Armstrong,et al.  Portable X-band system for solution state dynamic nuclear polarization. , 2008, Journal of magnetic resonance.

[24]  G. Iglesias-Silva,et al.  Densities and Viscosities of (N,N-Dimethylformamide + Water) at Atmospheric Pressure from (283.15 to 353.15) K , 2008 .

[25]  J. E. Tanner.  Use of the Stimulated Echo in NMR Diffusion Studies , 1970 .

[26]  David Neuhaus,et al.  The Nuclear Overhauser Effect in Structural and Conformational Analysis , 1989 .

[27]  John A. Weil,et al.  Electron paramagnetic resonance : elementary theory and practical applications , 1995 .

[28]  R. Mills,et al.  A Study of Diffusion in the Ternary System, Labeled Urea-Urea-Water, at 25° by Measurements of the Intradiffusion Coefficients1 of Urea2 , 1965 .

[29]  S. Stevenson,et al.  13C Dynamic Nuclear Polarization: A Detector for Continuous-Flow, Online Chromatography , 1994 .

[30]  Dietmar Stehlik,et al.  Dynamic Nuclear Polarization in Liquids , 1968 .

[31]  Songi Han,et al.  Dynamic nuclear polarization enhanced nuclear magnetic resonance and electron spin resonance studies of hydration and local water dynamics in micelle and vesicle assemblies. , 2008, Langmuir : the ACS journal of surfaces and colloids.

[32]  John A. Weil,et al.  Electron Paramagnetic Resonance , 2006 .

[33]  C. Tanford,et al.  Viscosity and density of aqueous solutions of urea and guanidine hydrochloride. , 1966, The Journal of biological chemistry.