Dynamic nuclear polarization in inorganic solids from paramagnetic metal ion dopants

The Effect of Disorder on Endogenous MAS-DNP: Study of Silicate Glasses and Crystals

“…78 Saturation of these transitions is generally not achieved in MIDNP and is therefore a major limiting factor of signal enhancement. 16 The analytical expression for the saturation efficiency, assuming that the polarizing agent is at the same time the main source of relaxation, is related to T 1e and T 2e according to 23,49 assuming that one can replace τ 1e by T 1e . A more detailed derivation of this relation was given in previous studies.…”

“…SE DNP can occur between a nucleus coupled to a single electron upon microwave irradiation on either the zero or double quantum transition. Since these transitions are formally forbidden, the effective nutation frequency ω̃ 1 will be scaled by the strength of the dipolar coupling divided by the nuclear Larmor frequency, ω̃ 1 ≈ ω 1 ω d ω n . Saturation of these transitions is generally not achieved in MIDNP and is therefore a major limiting factor of signal enhancement . The analytical expression for the saturation efficiency, assuming that the polarizing agent is at the same time the main source of relaxation, is related to T 1e and T 2e according to , Δ p D Q / Z Q = Δ p D Q / Z Q , e q 1 + ω̃ 1 2 [ R 2 e false( 2 R 1 D Q + 2 R 1 n false) ] − 1 where normalΔ p D Q / Z Q is the polarization of the irradiated (DQ or ZQ) transition.…”

“…Common strategies for increasing the NMR sensitivity in oxide glasses include isotope enrichment, − echo train acquisition, , or the addition of small quantities of paramagnetic dopants for paramagnetic relaxation enhancement (PRE). − However, isotope labeling can require additional synthesis steps; depending on the sample composition, the enhancement from echo train acquisition might be limited by intrinsically low coherence lifetimes, and the sensitivity gain from PRE is often not sufficient to avoid long measurement times for high resolution experiments. In recent years we have shown the feasibility of obtaining large NMR signal enhancements for low sensitivity nuclei in the bulk of inorganic oxides by magic angle spinning dynamic nuclear polarization (MAS-DNP). − The approach, known as metal ions based (MI)­DNP, consists of introducing paramagnetic metal ions as dopants into the sample, which then serve as the source of polarization upon microwave irradiation. Most of the applications, however, were on crystalline oxides.…”

Polarizing agents for efficient high field DNP solid-state NMR spectroscopy under magic-angle spinning: from design principles to formulation strategies

“…Amidst the metal ions presenting an accessible EPR resonance, those which experience a strong broadening of their EPR line induced by zero eld splitting (ZFS) or spin orbit coupling (SOC) are also hampered by the subsequent inefficiency of their saturation upon microwave irradiation. 121 In a seminal study published by Corzilius and Griffin in 2011, manganese Mn(II) and gadolinium Gd(III), with S = 5/2 and S = 7/ 2 respectively, were shown to have g factors sufficiently close to that of the free electron and EPR lines sufficiently narrow to produce DNP at 5 T. 122 Thanks to their respective ground states being 6 S and 8 S, the SOC vanishes, leading to narrow central transitions in both cases. Their satellite transitions are signicantly broadened by the rst order ZFS, while the central transition is only affected at the second order, resulting in an overall narrow pseudo spin S = 1/2 EPR prole in highly symmetric highspin complexes for these two metals.…”

Dynamic Nuclear Polarization of Inorganic Halide Perovskites

“…An alternative way to introduce the paramagnetic source is to dope the material itself with high-spin metal ions, such as Mn 2+ , Gd 3+ , Cr 3+ , or Fe 3+ . ,− Under microwave irradiation, the polarization is transferred from the metal ion to nearby nuclei, typically via the solid effect. , If the metal ions are distributed throughout the sample, this naturally results in an enhancement of the bulk spectrum. However, the distribution of enhancement within the sample depends on the dopant concentration, the relaxation properties, and potentially the rate of spin diffusion. , This method, which has been successfully applied to nucleic acid, along with various oxide materials for battery ,, and fuel cell applications, , is known as endogenous DNP.…”