Study of diamond film by dynamic nuclear polarization-enhanced13C nuclear magnetic resonance spectroscopy

Fang, Ke; Zhou, Jianrong; Lei, Hao; Ye, Chen; Zhan, Reggie; Fu, Hao; Zhang, X.; Yan, Entao; Liu, S.

doi:10.1007/bf03167009

Cited by 3 publications

(4 citation statements)

References 13 publications

(11 reference statements)

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“…With sufficient microwave power to overcome the unfavorable field dependence, SE can generate large DNP enhancements as shown in a trityl-doped solution in a capillary tube held in a cylindrical microwave resonator [31*]. Despite unfavorable field dependence, the option of SE can be exclusive to highly diluted paramagnetic species, such as naturally occurring electron centers in diamonds [117; 118; 119; 120], γ-ray irradiated organic solids [121] and sparsely dye-doped systems in which non-Boltzmann electron spin polarization can be obtained from photoexcited triplets [122; 123]. …”

Section: Polarizing Agents For Dnp In Dielectric Solidsmentioning

confidence: 99%

Polarizing agents and mechanisms for high-field dynamic nuclear polarization of frozen dielectric solids

2011

Solid State Nuclear Magnetic Resonance

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This article provides an overview of polarizing mechanisms involved in high-frequency dynamic nuclear polarization (DNP) of frozen biological samples at temperatures maintained using liquid nitrogen, compatible with contemporary magic-angle spinning (MAS) nuclear magnetic resonance (NMR). Typical DNP experiments require unpaired electrons that are usually exogenous in samples via paramagnetic doping with polarizing agents. Thus, the resulting nuclear polarization mechanism depends on the electron and nuclear spin interactions induced by the paramagnetic species. The Overhauser Effect (OE) DNP, which relies on time-dependent spin-spin interactions, is excluded from our discussion due the lack of conducting electrons in frozen aqueous solutions containing biological entities. DNP of particular interest to us relies primarily on time-independent, spin interactions for significant electron-nucleus polarization transfer through mechanisms such as the Solid Effect (SE), the Cross Effect (CE) or Thermal Mixing (TM), involving one, two or multiple electron spins, respectively. Derived from monomeric radicals initially used in DNP experiments, bi- or multiple-radical polarizing agents facilitate CE/TM to generate significant NMR signal enhancements in dielectric solids at low temperatures (< 100 K). For example, large DNP enhancements (~300 times at 5 T) from a biologically compatible biradical, 1-(TEMPO-4-oxy)-3-(TEMPO-4-amino)propan-2-ol (TOTAPOL), have enabled high-resolution MAS NMR in sample systems existing in submicron domains or embedded in larger biomolecular complexes. The scope of this review is focused on recently developed DNP polarizing agents for high-field applications and leads up to future developments per the CE DNP mechanism. Because DNP experiments are feasible with a solid-state microwave source when performed at <20 K, nuclear polarization using lower microwave power (< 100 mW) is possible by forcing a high proportion of biradicals to fulfill the frequency matching condition of CE (two EPR frequencies separated by the NMR frequency) using the strategies involving hetero-radical moieties and/or molecular alignment. In addition, the combination of an excited triplet and a stable radical might provide alternative DNP mechanisms without the microwave requirement.

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Section: Polarizing Agents For Dnp In Dielectric Solidsmentioning

confidence: 99%

Polarizing agents and mechanisms for high-field dynamic nuclear polarization of frozen dielectric solids

2011

Solid State Nuclear Magnetic Resonance

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“…68−71 So far, optical pumping has only been achieved for diamond single crystals. Conversely, DNP-enhanced 13 C NMR for static samples has been reported for diamond single crystals, 57,58,60−65 and chemical vapor deposited diamond films 59,66 at low static magnetic field, B 0 ≤ 1.9 T and room temperature (T), as well as for polycrystalline diamond samples of various particle sizes, including NDs, at B 0 = 3.35 T and T ≤ 1.9 K. 26,31 A DNP signal enhancement larger than 330 has also been measured for a diamond single crystal at B 0 = 9.4 T, T = 105 K and under static conditions. 72 However, low B 0 fields or static conditions do not allow the acquisition of high-resolution NMR spectra, which are required to identify surface functionalities of NDs.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Furthermore, the high polarization of unpaired electrons can be transferred via hyperfine interactions to the nearby nuclei, thus enhancing the NMR signal. In the case of diamond, this polarization transfer has been achieved either by continuous-wave or pulsed microwave (μw) irradiation near the electron paramagnetic resonance (EPR) frequency using the dynamic nuclear polarization (DNP) phenomenon ,− or by optical pumping with visible light of the electronic transition of nitrogen-vacancy (NV) centers. − So far, optical pumping has only been achieved for diamond single crystals. Conversely, DNP-enhanced 13 C NMR for static samples has been reported for diamond single crystals, ,,− and chemical vapor deposited diamond films , at low static magnetic field, B 0 ≤ 1.9 T and room temperature ( T ), as well as for polycrystalline diamond samples of various particle sizes, including NDs, at B 0 = 3.35 T and T ≤ 1.9 K. , A DNP signal enhancement larger than 330 has also been measured for a diamond single crystal at B 0 = 9.4 T, T = 105 K and under static conditions…”

Section: Introductionmentioning

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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“…Therefore, the major obstacle for iMQC methods is the sensitivity. Higher magnetic field and the combination with dynamic nuclear polarization-enhanced high-resolution NMR methods are potential solutions [58] . Despite its major drawback of the inherently low sensitivity, line narrowings are observed along a specific direction in the 2D iMQC spectrum in inhomogeneous fields, where it is not possible to obtain relevant spectral information by conventional 1D technique.…”

Section: Discussionmentioning

confidence: 99%

Advances in high-resolution nuclear magnetic resonance methods in inhomogeneous magnetic fields using intermolecular multiple quantum coherences

Chen

Lin

Chen

et al. 2009

Sci. China Ser. G-Phys. Mech. Astron.

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Strong and extremely homogeneous static magnetic field is usually required for high-resolution nuclear magnetic resonance (NMR).However, in the cases of in vivo and so on, the magnetic field inhomogeneity owing to magnetic susceptibility variation in samples is unavoidable and hard to eliminate by conventional methods such as shimming. Recently, intermolecular multiple quantum coherences (iMQCs) have been employed to eliminate inhomogeneous broadening and obtain high-resolution NMR spectra, especially for in vivo samples. Compared to other high-resolution NMR methods, iMQC method exhibits its unique feature and advantage. It simultaneously holds information of chemical shifts, multiplet structures, coupling constants, and relative peak areas. All the information is often used to analyze and characterize molecular structures in conventional one-dimensional NMR spectroscopy. In this work, recent technical developments including our results in this field are summarized; the high-resolution mechanism is analyzed and comparison with other methods based on interactions between spins is made; comments on the current situation and outlook on the research directions are also made.nuclear magnetic resonance, high-resolution, inhomogeneous magnetic fields, intermolecular multiple quantum coherence Nuclear magnetic resonance (NMR) has revolutionized modern science by its precision, selectivity and non-invasiveness. From complicated biomolecules to materials, from living organisms to nanoparticles, magnetic resonance imaging (MRI) and spectroscopy have provided a wealth of invaluable information. Line widths and shapes are key criteria determining the utility of a NMR spectrum. The line widths of conventional NMR signals are directly proportional to overall static magnetic field homogeneity across samples. Considerable effort is usually expended in maximizing spectral resolution, including careful shimming, sample spinning, rigorous exclusion of paramagnetic or particulate impurities from samples, and the use of magnetic susceptibility matched glasses for the sample container.Even if external shims can be used to acquire necessary homogeneity of static magnetic field, typically on the order of 1 ppb/cm 3[1] , there are many circumstances, such as in vivo, ex situ, and in situ NMR, where the spatial and temporal homogeneity of magnetic fields is degraded, and cannot be avoided by fundamental shims. Inhomogeneous line broadening owing to magnetic susceptibility gradients leads to severe problems of signal overlaps [2] . Although improvements in spectral line shapes and widths are achieved by spinning samples, some types of NMR experiments are not performed with this method. Obvious examples are in vivo specimens, whole animals and perfused organs. All these preclude NMR spectral analyses based on the interpretation of familiar NMR information of chemical shifts, scalar

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Study of diamond film by dynamic nuclear polarization-enhanced13C nuclear magnetic resonance spectroscopy

Cited by 3 publications

References 13 publications

Polarizing agents and mechanisms for high-field dynamic nuclear polarization of frozen dielectric solids

Polarizing agents and mechanisms for high-field dynamic nuclear polarization of frozen dielectric solids

NMR and EPR Characterization of Functionalized Nanodiamonds

Advances in high-resolution nuclear magnetic resonance methods in inhomogeneous magnetic fields using intermolecular multiple quantum coherences

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