¹³C Dynamic Nuclear Polarization Using a Trimeric Gd³⁺ Complex as an Additive.

Area of Science:

• Magnetic Resonance Spectroscopy
• Hyperpolarization Techniques
• Lanthanide Chemistry

Background:

• Dissolution dynamic nuclear polarization (DNP) amplifies Nuclear Magnetic Resonance (NMR) signals, addressing sensitivity limitations.
• Lanthanide complexes, particularly monomeric gadolinium (Gd3+), are known additives that enhance DNP polarization.
• Optimizing DNP efficiency requires exploring novel polarizing agents and dopants.

Purpose of the Study:

• To investigate the efficacy of a trimeric gadolinium complex as a dopant for enhancing 13C DNP signals.
• To compare the performance of the trimeric Gd3+ complex with established monomeric Gd3+ complexes in DNP.
• To elucidate the mechanism by which the trimeric Gd3+ complex influences DNP efficiency.

Main Methods:

• Solid-state DNP experiments at 3.35 T and 1.2 K using a trityl OX063 radical and the trimeric Gd3+ complex.
• Dissolution of DNP-polarized samples for liquid-state 13C NMR spectroscopy at 9.4 T and 298 K.
• W-band electron paramagnetic resonance (EPR) measurements to assess electron spin relaxation times (T1).

Main Results:

• The trimeric Gd3+ complex improved solid-state 13C DNP polarization by a factor of 3.4, comparable to monomeric complexes.
• This enhancement was achieved at approximately one-fifth the concentration of monomeric Gd3+ complexes.
• Liquid-state NMR signal enhancements reached ~20,000-fold post-dissolution, a threefold increase over control samples.
• Electron T1 of the trityl radical was reduced by 3-Gd doping, with minimal changes to the EPR spectrum.

Conclusions:

• The trimeric Gd3+ complex is a highly effective additive for 13C DNP, offering superior concentration efficiency.
• The observed DNP enhancement aligns with the thermal mixing mechanism, similar to monomeric Gd3+ complexes.
• This finding presents a promising avenue for further improving NMR/MRI sensitivity through optimized lanthanide dopants.