Solvent-Free Dynamic Nuclear Polarization of Amorphous and Crystalline <i>ortho</i>-Terphenyl

Ong, Ta‐Chung; Mak‐Jurkauskas, Melody L.; Walish, Joseph J.; Michaelis, Vladimir K.; Corzilius, Björn; Smith, Albert A.; Clausen, Ashley; Cheetham, Janet; Swager, Timothy M.; Griffin, Robert G.

doi:10.1021/jp311237d

Cited by 72 publications

(65 citation statements)

References 60 publications

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“…However, in polycrystalline samples, it is well known that radical spins are forced to accumulate at the boundaries between different crystalline grains, as already suggested by NMR measurements reported in Ref. [24]. Inside these boundary regions, an anomalously high radical concentration is responsible for a suppression of hyperpolarization as confirmed by experimentally [25] and theoretically [12,20].…”

Section: Discussionmentioning

confidence: 61%

Evidence of spin-temperature in dynamic nuclear polarization: an exact computation of the EPR spectrum

Caracciolo

Filibian

Carretta

et al. 2016

Phys. Chem. Chem. Phys.

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In dynamic nuclear polarization (DNP) experiments, the compound is driven out-of-equilibrium by microwave (MW) irradiation of the radical electron spins. Their stationary state has been recently probed via electron double resonance (ELDOR) techniques showing, at low temperature, a broad depolarization of the electron paramagnetic resonance (EPR) spectrum under microwave irradiation. In this theoretical manuscript, we develop a numerical method to compute exactly the EPR spectrum in presence of dipolar interactions. Our results reproduce the observed broad depolarisation and provide a microscopic justification for spectral diffusion mechanism. We show the validity of the spin-temperature approach for typical radical concentration used in dissolution DNP protocols. In particular once the interactions are properly taken into account, the spin-temperature is consistent with the non-monotonic behavior of the EPR spectrum with a wide minimum around the irradiated frequency.

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Section: Discussionmentioning

confidence: 61%

Evidence of spin-temperature in dynamic nuclear polarization: an exact computation of the EPR spectrum

Caracciolo

Filibian

Carretta

et al. 2016

Phys. Chem. Chem. Phys.

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“…Since the paramagnetic label is covalently attached to the biomolecule, separation of the polarizing agent and protein in different phases—which reportedly inhibits DNP 51 —cannot occur. DNP enhancement factors improved three-fold to about −9 while at the same time strong line broadening occurs.…”

Section: Resultsmentioning

confidence: 99%

Gd(iii) and Mn(ii) complexes for dynamic nuclear polarization: small molecular chelate polarizing agents and applications with site-directed spin labeling of proteins

Kaushik

Bahrenberg

Can

et al. 2016

Phys. Chem. Chem. Phys.

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109

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We investigate complexes of two paramagnetic metal ions Gd3+ and Mn2+ to serve as polarizing agents for solid-state dynamic nuclear polarization (DNP) of 1H, 13C, and 15N at magnetic fields of 5, 9.4, and 14.1 T. Both ions are half-integer high-spin systems with a zero-field splitting and therefore exhibit a broadening of the mS = −½ ↔ +½ central transition which scales inversely with the external field strength. We investigate experimentally the influence of the chelator molecule, strong hyperfine coupling to the metal nucleus, and deuteration of the bulk matrix on DNP properties. At small Gd-DOTA concentrations the narrow central transition allows us to polarize nuclei with small gyromagnetic ratio such as 13C and even 15N via the solid effect. We demonstrate that enhancements observed are limited by the available microwave power and that large enhancement factors of >100 (for 1H) and on the order of 1000 (for 13C) can be achieved in the saturation limit even at 80 K. At larger Gd(III) concentrations (≥ 10 mM) where dipolar couplings between two neighboring Gd3+ complexes become substantial a transition towards cross effect as dominating DNP mechanism is observed. Furthermore, the slow spin-diffusion between 13C and 15N, respectively, allows for temporally resolved observation of enhanced polarization spreading from nuclei close to the paramagnetic ion towards nuclei further removed. Subsequently, we present preliminary DNP experiments on ubiquitin by site-directed spin-labeling with Gd3+ chelator tags. The results hold promise towards applications of such paramagnetically labeled proteins for DNP applications in biophysical chemistry and/or structural biology.

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“…However, no DNP enhancement of 1 H and 13 C NMR signals was measured for ND C18 dispersed in 16 mM TOTAPOL aqueous solution. This absence of enhancement must stem from (i) the formation of ice crystals, which leads to phase separation between ice, ND C18 , and TOTAPOL, 112 1 H and 13 C NMR signals were enhanced by μw irradiation, but the 13 C signal of [ 2 H 6 ]-DMSO at ∼40 ppm overlaps with those of ND C18 . The mixture ND C18 -TCE* was sonicated during 10 min, just before being placed in 3.2 mm sapphire rotors.…”

Section: ■ Experimental Detailsmentioning

confidence: 99%

NMR and EPR Characterization of Functionalized Nanodiamonds

Presti

Thankamony²,

Alauzun

et al. 2015

J. Phys. Chem. C

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We investigated the potential of solid-state NMR using magic angle spinning (MAS) with and without dynamic nuclear polarization (DNP) and electron paramagnetic resonance (EPR) for the characterization of functionalized nanodiamonds (NDs). We showed that conventional 1 H, 31 P, and 13 C solid-state NMR spectra allow differentiating in a straightforward way NDs from commercial sources and custom-made NDs bearing aromatic or aliphatic phosphonate moieties at their surface. Besides, the short nuclear relaxation times prove the close proximity between the endogenous paramagnetic centers of NDs and the grafted organic moieties. EPR spectra confirmed the presence of these paramagnetic centers in functionalized NDs, which are centered on dangling bonds as well as a few N 0 defects, corresponding to the substitution of carbon atoms by nitrogen ones. Hyperfine sublevel correlation spectroscopy indicates that the N 0 paramagnetic centers are mostly located in the disordered shell of NDs. Preliminary DNP-enhanced NMR experiments at 9.4 T and 100 K under MAS have shown a lack of significant DNP enhancement, which can be attributed to the short relaxation times of the unpaired electrons and the nuclei in NDs. When using exogenous polarizing agents, the endogenous unpaired electrons contribute to a leakage of polarization. Furthermore, low temperatures lead to a broadening of NMR signals. It therefore appears that conventional direct excitation remains the NMR method of choice for the characterization of functionalized NDs. ■ INTRODUCTIONNanodiamonds (NDs), that is, diamond particles with a diameter smaller than 100 nm, are receiving considerable attention due to their remarkable hardness and thermal conductivity, luminescence properties, chemical inertness, and biocompatibility. 1−6 For instance, they have been proposed as fillers to reinforce the mechanical properties of polymers and ceramics, 7,8 as catalyst supports for metal nanoparticles (NPs), 9 or as nanovectors for various drugs. 4,6,10 Depending on the preparation and purification methods used, the surface of NDs can be terminated by a variety of functional groups, including carboxylic groups, hydroxyls, ketones, and lactone moieties. 5,11−14 To attain the targeted properties, the surface of nanodiamonds most often needs to be functionalized, so that the interactions between the NPs and their environment are optimal. Several methods have been proposed to tune the surface properties of NDs by covalent grafting of organic moieties. 14−20To date, the characterization of NDs functionalized by organic fragments has involved a variety of methods, such as X-ray photoelectron, 21 UV, 22 and FTIR 16,20,23−26 spectroscopies. Solid-state NMR spectroscopy has been attempted, 27−29 but the use of this technique is still limited despite the high specific surface area of NDs (∼150−300 m 2 ·g −1 ), which should be favorable for detecting the surface functional groups. So far, solidstate NMR studies of NDs have mainly focused on the investigation of the core and surface structure of N...

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Solvent-Free Dynamic Nuclear Polarization of Amorphous and Crystalline ortho-Terphenyl

Cited by 72 publications

References 60 publications

Evidence of spin-temperature in dynamic nuclear polarization: an exact computation of the EPR spectrum

Evidence of spin-temperature in dynamic nuclear polarization: an exact computation of the EPR spectrum

Gd(iii) and Mn(ii) complexes for dynamic nuclear polarization: small molecular chelate polarizing agents and applications with site-directed spin labeling of proteins

NMR and EPR Characterization of Functionalized Nanodiamonds

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