The effect of Ho³⁺ doping on ¹³C dynamic nuclear polarization at 5 T

Abstract

Dissolution dynamic nuclear polarization was introduced in 2003 as a method for producing hyperpolarized C solutions suitable for metabolic imaging. The signal to noise ratio for the imaging experiment depends on the maximum polarization achieved in the solid state. Hence, optimization of the DNP conditions is essential. To acquire maximum polarization many parameters related to sample preparation can be modulated. Recently, it was demonstrated that Ho, Dy, Tb, and Gd complexes enhance the polarization at 1.2 K and 3.35 T when using the trityl radical as the primary paramagnetic center. Here, we have investigated the influence of Ho-DOTA on C solid state DNP at 1.2 K and 5 T. We have performedC DNP on [1-C] sodium acetate in 1 : 1 (v/v) water/glycerol with 15 mM trityl OX063 radicals in the presence of a series of Ho-DOTA concentrations (0, 0.5, 1, 2, 3, 5 mM). We have found that adding a small amount of Ho-DOTA in the sample preparation not only enhances the C polarization but also decreases the buildup time. The optimum Ho-DOTA concentration was 2 mM. In addition, the microwave sweep spectrum changes character in a manner that suggests both the cross effect and thermal mixing are active mechanisms for trityl radical at 5 T and 1.2 K.

The influence of Ho3+ doping on 13C DNP in the presence of BDPA

“…Our group performed the same experiment in 5 T (1.2 K) system and found B 1.5 times better enhancement on sodium [1- 13 C]acetate nuclear polarization. 19 Several other groups reported a small beneficial effect on 13 C solid state polarization for Gd 3+ doped DNP samples with trityl in different magnetic fields, with temperature ranges from 1.4 to 3.7 K 7,17,26,39 .…”

“…Therefore, optimization of DNP conditions are warranted. The DNP enhancement is affected by several factors that include sample composition and concentration, types of radicals used, glassing agents with or without deuteration, 10,18 lanthanide as a relaxation agent, 7,9,10,13,[19][20][21] microwave power and frequency, temperature, and magnetic field. [22][23][24][25] So far, several radicals with either wide or narrow ESR linewidths have been reported to enhance polarization of different types of targeted nuclei.…”

“…7,20,35 Inclusion of 1 to 2 mM Gd 3 + in DNP samples containing 15 mM trityl as a radical is a well-established protocol for many groups. 7,9,[19][20][21]36 Holmium has recently gained attention for producing polarizations in excess of those achieved with Gd 3 +, presumably because of modulation of T1e. 9,19,20 If the source of divergent results between BDPA and trityl is related to the T1e, a proper choice of relaxation agent should be able to produce congruent polarization between the two agents.…”

“…7,9,[19][20][21]36 Holmium has recently gained attention for producing polarizations in excess of those achieved with Gd 3 +, presumably because of modulation of T1e. 9,19,20 If the source of divergent results between BDPA and trityl is related to the T1e, a proper choice of relaxation agent should be able to produce congruent polarization between the two agents. The goal of this project was to determine if an optimal mixture of BDPA and a holmium based relaxation agent could produce enhancements similar to those of trityl.…”

Effects of glassing matrix deuteration on the relaxation properties of hyperpolarized 13C spins and free radical electrons at cryogenic temperatures

“…43,44 In addition, inclusion of trace amounts of paramagnetic additives such as lanthanides and certain transition metal complexes or nanoparticles in the DNP samples could significantly boost the DNP enhancement. [45][46][47][48][49][50][51][52] Furthermore, isotopic labeling of the other component of the DNP sample, the glassing solvents, could either boost or adversely affect the DNP signal in the frozen state depending upon the EPR linewidth of the free radical polarizing agent used. [53][54][55] Previous studies 54,55 have found that glassing matrix deuteration could boost the FIG.…”