TY - JOUR
T1 - Transition Metal Doping Reveals Link between Electron T1 Reduction and 13C Dynamic Nuclear Polarization Efficiency
AU - Niedbalski, Peter
AU - Parish, Christopher
AU - Wang, Qing
AU - Hayati, Zahra
AU - Song, Likai
AU - Martins, André F.
AU - Sherry, A. Dean
AU - Lumata, Lloyd
N1 - Funding Information:
The authors would like to acknowledge support from the Welch Foundation, Grant Numbers AT-1877 (L.L.) and AT-584 (A.D.S.), the U.S. Department of Defense (DOD) Grant Number W81XWH-17-1-0303 (L.L.), and the NHMFL user collaboration Grants Program Award Number 5080 (L.S.). EPR was performed at NHMFL, which is supported by the National Science Foundation (NSF) Cooperative Agreement number DMR 1157490 and the State of Florida. The DNP facility at UTSW is supported by the National Institutes of Health (NIH) Grant Number 8P41-EB015908.
Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/12/7
Y1 - 2017/12/7
N2 - Optimal efficiency of dissolution dynamic nuclear polarization (DNP) is essential to provide the required high sensitivity enhancements for in vitro and in vivo hyperpolarized 13C nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI). At the nexus of the DNP process are the free electrons, which provide the high spin alignment that is transferred to the nuclear spins. Without changing DNP instrumental conditions, one way to improve 13C DNP efficiency is by adding trace amounts of paramagnetic additives such as lanthanide (e.g., Gd3+, Ho3+, Dy3+, Tb3+) complexes to the DNP sample, which has been observed to increase solid-state 13C DNP signals by 100-250%. Herein, we have investigated the effects of paramagnetic transition metal complex R-NOTA (R = Mn2+, Cu2+, Co2+) doping on the efficiency of 13C DNP using trityl OX063 as the polarizing agent. Our DNP results at 3.35 T and 1.2 K show that doping the 13C sample with 3 mM Mn2+-NOTA led to a substantial improvement of the solid-state 13C DNP signal by a factor of nearly 3. However, the other transition metal complexes Cu2+-NOTA and Co2+-NOTA complexes, despite their paramagnetic nature, had essentially no impact on solid-state 13C DNP enhancement. W-band electron paramagnetic resonance (EPR) measurements reveal that the trityl OX063 electron T1 was significantly reduced in Mn2+-doped samples but not in Cu2+-A nd Co2+-doped DNP samples. This work demonstrates, for the first time, that not all paramagnetic additives are beneficial to DNP. In particular, our work provides a direct evidence that electron T1 reduction of the polarizing agent by a paramagnetic additive is an essential requirement for the improvement seen in solid-state 13C DNP signal.
AB - Optimal efficiency of dissolution dynamic nuclear polarization (DNP) is essential to provide the required high sensitivity enhancements for in vitro and in vivo hyperpolarized 13C nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI). At the nexus of the DNP process are the free electrons, which provide the high spin alignment that is transferred to the nuclear spins. Without changing DNP instrumental conditions, one way to improve 13C DNP efficiency is by adding trace amounts of paramagnetic additives such as lanthanide (e.g., Gd3+, Ho3+, Dy3+, Tb3+) complexes to the DNP sample, which has been observed to increase solid-state 13C DNP signals by 100-250%. Herein, we have investigated the effects of paramagnetic transition metal complex R-NOTA (R = Mn2+, Cu2+, Co2+) doping on the efficiency of 13C DNP using trityl OX063 as the polarizing agent. Our DNP results at 3.35 T and 1.2 K show that doping the 13C sample with 3 mM Mn2+-NOTA led to a substantial improvement of the solid-state 13C DNP signal by a factor of nearly 3. However, the other transition metal complexes Cu2+-NOTA and Co2+-NOTA complexes, despite their paramagnetic nature, had essentially no impact on solid-state 13C DNP enhancement. W-band electron paramagnetic resonance (EPR) measurements reveal that the trityl OX063 electron T1 was significantly reduced in Mn2+-doped samples but not in Cu2+-A nd Co2+-doped DNP samples. This work demonstrates, for the first time, that not all paramagnetic additives are beneficial to DNP. In particular, our work provides a direct evidence that electron T1 reduction of the polarizing agent by a paramagnetic additive is an essential requirement for the improvement seen in solid-state 13C DNP signal.
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U2 - 10.1021/acs.jpca.7b09448
DO - 10.1021/acs.jpca.7b09448
M3 - Article
C2 - 29125294
AN - SCOPUS:85037719837
SN - 1089-5639
VL - 121
SP - 9221
EP - 9228
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 48
ER -