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Papers by Gabriele Stevanato

Research paper thumbnail of Long-lived states in multi-spin systems

Zenodo (CERN European Organization for Nuclear Research), Nov 1, 2015

When referring to this work, full bibliographic details including the author, title, awarding ins... more When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g.

Research paper thumbnail of Permutation Theory of LLS and Singlet To Heteronuclear Magnetization Transfer

Chapter 2 introduces a permutation symmetry theory predicting the number of LLS species. Chapter ... more Chapter 2 introduces a permutation symmetry theory predicting the number of LLS species. Chapter 10 describes some singlet-to-heteronuclear polarization transfert NMR pulse sequences.

Research paper thumbnail of Chapter 11. Converting Spin Order from Singlet to Heteronuclear Magnetisation

New Developments in NMR, 2020

Some singlet to heteronuclear polarization transfer strategies are presented. The NMR sequences a... more Some singlet to heteronuclear polarization transfer strategies are presented. The NMR sequences and relative parameters are described.

Research paper thumbnail of Dynamic Nuclear Polarization Enhancement of 200 at 21.15 T Enabled by 65 kHz Magic Angle Spinning

Solid-state nuclear magnetic resonance under magic angle spinning (MAS) enhanced with dynamic nuc... more Solid-state nuclear magnetic resonance under magic angle spinning (MAS) enhanced with dynamic nuclear polarization (DNP) is a powerful approach to characterize many important classes of materials, allowing access to previously inaccessible structural and dynamic parameters. Here, we present the first DNP MAS experiments using a 0.7 mm MAS probe, which allows us to reach spinning frequencies of 65 kHz, with microwave irradiation, at 100 K. At the highest magnetic field available for DNP today (21.1 T), we find that the polarizing agent HyTEK2 provides DNP enhancements as high as 200 at a spinning rate of 65 kHz at 100 K, and BDPA yields an enhancement of 106 under the same conditions. Fast spinning rates enable excellent DNP performance, but they also yield unprecedented 1 H resolution under DNP conditions. We report well-resolved 1 H-detected 1 H− 13 C and 1 H− 15 N correlation spectra of microcrystalline histidine•HCl•H 2 O.

Research paper thumbnail of Enhanced Intersystem Crossing and Transient Electron Spin Polarization in a Photoexcited PentaceneTrityl Radical

Identifying and characterizing systems that generate well-defined states with large electron spin... more Identifying and characterizing systems that generate well-defined states with large electron spin polarization is of high interest for applications in molecular spintronics, high-energy physics, and magnetic resonance spectroscopy. The generation of electron spin polarization on free-radical substituents tethered to pentacene derivatives has recently gained a great deal of interest for its applications in molecular electronics. After photoexcitation of the chromophore, pentacene−radical derivatives can rapidly form spinpolarized triplet excited states through enhanced intersystem crossing. Under the right conditions, the triplet spin polarization, arising from m S-selective intersystem crossing rates, can be transferred to the tethered stable radical. The efficiency of this spin polarization transfer depends on many factors: local magnetic and electric fields, excitedstate energetics, molecular geometry, and spin-spin coupling. Here, we present transient electron paramagnetic resonance (EPR) measurements on three pentacene derivatives tethered to Finland trityl, BDPA, or TEMPO radicals to explore the influence of the nature of the radical on the spin polarization transfer. We observe efficient polarization transfer between the pentacene excited triplet and the trityl radical but do not observe the same for the BDPA and TEMPO derivatives. The polarization transfer behavior in the pentacene−trityl system is also investigated in different glassy matrices and is found to depend markedly on the solvent used. The EPR results are rationalized with the help of femtosecond and nanosecond transient absorption measurements, yielding complementary information on the excited-state dynamics of the three pentacene derivatives. Notably, we observe a 2 orders of magnitude difference in the time scale of triplet formation between the pentacene−trityl system and the pentacene systems tethered with the BDPA and TEMPO radicals.

Research paper thumbnail of Alternating Delays Achieve Polarization Transfer (ADAPT) to heteronuclei in PHIP experiments

Journal of Magnetic Resonance, 2017

A new methodology for producing hyperpolarized 13 C nuclei in small organic systems via parahydro... more A new methodology for producing hyperpolarized 13 C nuclei in small organic systems via parahydrogen induced polarization (PHIP) is proposed: ADAPT (Alternating Delays Achieve Polarization Transfer). The theoretical foundation of the process is investigated in some detail and experimental examples demonstrating the viability of the approach are provided as well. The number of adjustable parameters is fewer than most of other conversion schemes. The achieved theoretical heteronuclear polarization is close to unity for any examined magnetic equivalence regime. The duration of the pulse sequence, which was successfully implemented, can be shorter than other established methods reducing possible relaxation losses. The conversion scheme is robust to B 1 inhomogeneities, but more sensitive to off-resonance RF irradiation.

Research paper thumbnail of Long-Lived Nuclear Spin States in Methyl Groups and Quantum-Rotor-Induced Polarization

Journal of the American Chemical Society, 2013

B. 4-Methyl-13 C-pyridine (3) To a suspension of Mg turnings (170 mg, 7.00 mmol) in dry Et 2 O (3... more B. 4-Methyl-13 C-pyridine (3) To a suspension of Mg turnings (170 mg, 7.00 mmol) in dry Et 2 O (3.5 mL) was added 1 crystal of I 2 followed by 13 CH 3 I (1) (1 g, 7.00 mmol) drop-wise. After addition of a few drops of 13 CH 3 I (1) the reaction initiated spontaneously and the remaining was added drop-wise over 15 min with occasional cooling in an ice bath to maintain ambient temperature. After the addition was complete, the solution was stirred for a further 30 min at rt. The Grignard solution was then added drop-wise to a mixture of 4-iodopyridine (1.43 g, 7.00 mmol) and NiCl 2 (dppp) (265 mg, 0.49 mmol) in THF (15 mL) at 0 • C. The resulting suspension was stirred at 0 • C for 1 h before being warmed to rt and stirred for 24 h. The reaction was quenched by slow addition of aqueous 2M HCl (10 mL). The mixture was extracted with Et 2 O (2 x 15 mL) and the extracts discarded. The aqueous layer was then basified with aqueous 3M NaOH (10 mL) and extracted with Et 2 O (4 x 20 mL). The combined extracts were washed with brine (40 mL) and dried (Na 2 SO 4) before the solvent was removed by careful distillation at atmospheric pressure. Chromatography on silica gel (Et 2 O:pentane 1:9 to 1:1), followed by evaporation of the solvent by careful distillation under atmospheric pressure, afforded 4-methyl-13 C-pyridine (3)(Ref. (1)) (89 mg, 14 %) as a colourless liquid:

Research paper thumbnail of Theory and simulations of homonuclear three-spin systems in rotating solids NMR Raw Data

<strong>The NMR raw data is in both jcamp and topspin format. The data folders are separate... more <strong>The NMR raw data is in both jcamp and topspin format. The data folders are separated in experimental and simulation folders.</strong> <strong>Folders containing all the simulated MAS spectra acquired at variable MAS rates for two-spin systems single crystal for Figures 2, 5 and 6: </strong>(topspin format) 1) two_spin_different_alphas_and_betas_sc (Figure 2) 2) two_spin_different_alphas_and_betas_sc_increase_chemdiff (Figure 5) 3) two_spin_different_alphas_and_betas_sc_increase_dipolar (Figure 6) 4) mas_slowintermediate_regime_chemdiff (Figure S6) 5) mas_slowtointermed_regime_mas (Figure S7) <strong>Folders containing all the simulated MAS spectra acquired at variable MAS rates for two-spin systems single crystal for Figures 2, 5 and 6: </strong>(jcamp format) 1) two_spin_different_alphas_and_betas_sc_jcamp (Figure 2) 2) two_spin_different_alphas_and_betas_sc_increase_chemdiff_jcamp (Figure 5) 3) two_spin_different_alphas_and_betas_sc_increase_dipolar_jcamp (Figure 6) 4) mas_slowintermediate_regime_chemdiff_jcamp (Figure S6) 5) mas_slowtointermed_regime_mas_jcamp (Figure S7) <strong>Folders containing all the simulated MAS spectra acquired at variable MAS rates for three-spin single crystal systems for Figure 7: </strong>(topspin format) 1) three_spin_different_alphas_and_betas_sc <strong>Folders containing all the simulated MAS spectra acquired at variable MAS rates for three-spin single crystal systems for Figure 7: </strong>(jcamp format) 1) three_spin_different_alphas_and_betas_sc_jcamp <strong>Folders containing all the simulated MAS spectra acquired at variable MAS rates for two-spin and three-spin powder systems for Figure 10, 11 and 12: </strong>(topspin format) 1) two_spin_different_alphas_and_betas_rep_2ang_200pts_sph 2) three_spin_powder_800pts <strong>Folders containing all the simulated MAS spectra acquired at variable MAS rates for two-spin and three-spin powder systems for Figure 10, 11 and 12: </strong>(camp format) 1) two_spin_different_alphas_and_betas_rep_2ang_200pts_sph_jcamp 2) three_ [...]

Research paper thumbnail of Theory of long-lived nuclear spin states in methyl groups and quantum-rotor induced polarisation

The Journal of chemical physics, Jan 28, 2015

Long-lived nuclear spin states have a relaxation time much longer than the longitudinal relaxatio... more Long-lived nuclear spin states have a relaxation time much longer than the longitudinal relaxation time T1. Long-lived states extend significantly the time scales that may be probed with magnetic resonance, with possible applications to transport and binding studies, and to hyperpolarised imaging. Rapidly rotating methyl groups in solution may support a long-lived state, consisting of a population imbalance between states of different spin exchange symmetries. Here, we expand the formalism for describing the behaviour of long-lived nuclear spin states in methyl groups, with special attention to the hyperpolarisation effects observed in (13)CH3 groups upon rapidly converting a material with low-barrier methyl rotation from the cryogenic solid state to a room-temperature solution [M. Icker and S. Berger, J. Magn. Reson. 219, 1 (2012)]. We analyse the relaxation properties of methyl long-lived states using semi-classical relaxation theory. Numerical simulations are supplemented with a ...

Research paper thumbnail of Long-lived states in multi-spin systems

Zenodo (CERN European Organization for Nuclear Research), Nov 1, 2015

When referring to this work, full bibliographic details including the author, title, awarding ins... more When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g.

Research paper thumbnail of Permutation Theory of LLS and Singlet To Heteronuclear Magnetization Transfer

Chapter 2 introduces a permutation symmetry theory predicting the number of LLS species. Chapter ... more Chapter 2 introduces a permutation symmetry theory predicting the number of LLS species. Chapter 10 describes some singlet-to-heteronuclear polarization transfert NMR pulse sequences.

Research paper thumbnail of Chapter 11. Converting Spin Order from Singlet to Heteronuclear Magnetisation

New Developments in NMR, 2020

Some singlet to heteronuclear polarization transfer strategies are presented. The NMR sequences a... more Some singlet to heteronuclear polarization transfer strategies are presented. The NMR sequences and relative parameters are described.

Research paper thumbnail of Dynamic Nuclear Polarization Enhancement of 200 at 21.15 T Enabled by 65 kHz Magic Angle Spinning

Solid-state nuclear magnetic resonance under magic angle spinning (MAS) enhanced with dynamic nuc... more Solid-state nuclear magnetic resonance under magic angle spinning (MAS) enhanced with dynamic nuclear polarization (DNP) is a powerful approach to characterize many important classes of materials, allowing access to previously inaccessible structural and dynamic parameters. Here, we present the first DNP MAS experiments using a 0.7 mm MAS probe, which allows us to reach spinning frequencies of 65 kHz, with microwave irradiation, at 100 K. At the highest magnetic field available for DNP today (21.1 T), we find that the polarizing agent HyTEK2 provides DNP enhancements as high as 200 at a spinning rate of 65 kHz at 100 K, and BDPA yields an enhancement of 106 under the same conditions. Fast spinning rates enable excellent DNP performance, but they also yield unprecedented 1 H resolution under DNP conditions. We report well-resolved 1 H-detected 1 H− 13 C and 1 H− 15 N correlation spectra of microcrystalline histidine•HCl•H 2 O.

Research paper thumbnail of Enhanced Intersystem Crossing and Transient Electron Spin Polarization in a Photoexcited PentaceneTrityl Radical

Identifying and characterizing systems that generate well-defined states with large electron spin... more Identifying and characterizing systems that generate well-defined states with large electron spin polarization is of high interest for applications in molecular spintronics, high-energy physics, and magnetic resonance spectroscopy. The generation of electron spin polarization on free-radical substituents tethered to pentacene derivatives has recently gained a great deal of interest for its applications in molecular electronics. After photoexcitation of the chromophore, pentacene−radical derivatives can rapidly form spinpolarized triplet excited states through enhanced intersystem crossing. Under the right conditions, the triplet spin polarization, arising from m S-selective intersystem crossing rates, can be transferred to the tethered stable radical. The efficiency of this spin polarization transfer depends on many factors: local magnetic and electric fields, excitedstate energetics, molecular geometry, and spin-spin coupling. Here, we present transient electron paramagnetic resonance (EPR) measurements on three pentacene derivatives tethered to Finland trityl, BDPA, or TEMPO radicals to explore the influence of the nature of the radical on the spin polarization transfer. We observe efficient polarization transfer between the pentacene excited triplet and the trityl radical but do not observe the same for the BDPA and TEMPO derivatives. The polarization transfer behavior in the pentacene−trityl system is also investigated in different glassy matrices and is found to depend markedly on the solvent used. The EPR results are rationalized with the help of femtosecond and nanosecond transient absorption measurements, yielding complementary information on the excited-state dynamics of the three pentacene derivatives. Notably, we observe a 2 orders of magnitude difference in the time scale of triplet formation between the pentacene−trityl system and the pentacene systems tethered with the BDPA and TEMPO radicals.

Research paper thumbnail of Alternating Delays Achieve Polarization Transfer (ADAPT) to heteronuclei in PHIP experiments

Journal of Magnetic Resonance, 2017

A new methodology for producing hyperpolarized 13 C nuclei in small organic systems via parahydro... more A new methodology for producing hyperpolarized 13 C nuclei in small organic systems via parahydrogen induced polarization (PHIP) is proposed: ADAPT (Alternating Delays Achieve Polarization Transfer). The theoretical foundation of the process is investigated in some detail and experimental examples demonstrating the viability of the approach are provided as well. The number of adjustable parameters is fewer than most of other conversion schemes. The achieved theoretical heteronuclear polarization is close to unity for any examined magnetic equivalence regime. The duration of the pulse sequence, which was successfully implemented, can be shorter than other established methods reducing possible relaxation losses. The conversion scheme is robust to B 1 inhomogeneities, but more sensitive to off-resonance RF irradiation.

Research paper thumbnail of Long-Lived Nuclear Spin States in Methyl Groups and Quantum-Rotor-Induced Polarization

Journal of the American Chemical Society, 2013

B. 4-Methyl-13 C-pyridine (3) To a suspension of Mg turnings (170 mg, 7.00 mmol) in dry Et 2 O (3... more B. 4-Methyl-13 C-pyridine (3) To a suspension of Mg turnings (170 mg, 7.00 mmol) in dry Et 2 O (3.5 mL) was added 1 crystal of I 2 followed by 13 CH 3 I (1) (1 g, 7.00 mmol) drop-wise. After addition of a few drops of 13 CH 3 I (1) the reaction initiated spontaneously and the remaining was added drop-wise over 15 min with occasional cooling in an ice bath to maintain ambient temperature. After the addition was complete, the solution was stirred for a further 30 min at rt. The Grignard solution was then added drop-wise to a mixture of 4-iodopyridine (1.43 g, 7.00 mmol) and NiCl 2 (dppp) (265 mg, 0.49 mmol) in THF (15 mL) at 0 • C. The resulting suspension was stirred at 0 • C for 1 h before being warmed to rt and stirred for 24 h. The reaction was quenched by slow addition of aqueous 2M HCl (10 mL). The mixture was extracted with Et 2 O (2 x 15 mL) and the extracts discarded. The aqueous layer was then basified with aqueous 3M NaOH (10 mL) and extracted with Et 2 O (4 x 20 mL). The combined extracts were washed with brine (40 mL) and dried (Na 2 SO 4) before the solvent was removed by careful distillation at atmospheric pressure. Chromatography on silica gel (Et 2 O:pentane 1:9 to 1:1), followed by evaporation of the solvent by careful distillation under atmospheric pressure, afforded 4-methyl-13 C-pyridine (3)(Ref. (1)) (89 mg, 14 %) as a colourless liquid:

Research paper thumbnail of Theory and simulations of homonuclear three-spin systems in rotating solids NMR Raw Data

<strong>The NMR raw data is in both jcamp and topspin format. The data folders are separate... more <strong>The NMR raw data is in both jcamp and topspin format. The data folders are separated in experimental and simulation folders.</strong> <strong>Folders containing all the simulated MAS spectra acquired at variable MAS rates for two-spin systems single crystal for Figures 2, 5 and 6: </strong>(topspin format) 1) two_spin_different_alphas_and_betas_sc (Figure 2) 2) two_spin_different_alphas_and_betas_sc_increase_chemdiff (Figure 5) 3) two_spin_different_alphas_and_betas_sc_increase_dipolar (Figure 6) 4) mas_slowintermediate_regime_chemdiff (Figure S6) 5) mas_slowtointermed_regime_mas (Figure S7) <strong>Folders containing all the simulated MAS spectra acquired at variable MAS rates for two-spin systems single crystal for Figures 2, 5 and 6: </strong>(jcamp format) 1) two_spin_different_alphas_and_betas_sc_jcamp (Figure 2) 2) two_spin_different_alphas_and_betas_sc_increase_chemdiff_jcamp (Figure 5) 3) two_spin_different_alphas_and_betas_sc_increase_dipolar_jcamp (Figure 6) 4) mas_slowintermediate_regime_chemdiff_jcamp (Figure S6) 5) mas_slowtointermed_regime_mas_jcamp (Figure S7) <strong>Folders containing all the simulated MAS spectra acquired at variable MAS rates for three-spin single crystal systems for Figure 7: </strong>(topspin format) 1) three_spin_different_alphas_and_betas_sc <strong>Folders containing all the simulated MAS spectra acquired at variable MAS rates for three-spin single crystal systems for Figure 7: </strong>(jcamp format) 1) three_spin_different_alphas_and_betas_sc_jcamp <strong>Folders containing all the simulated MAS spectra acquired at variable MAS rates for two-spin and three-spin powder systems for Figure 10, 11 and 12: </strong>(topspin format) 1) two_spin_different_alphas_and_betas_rep_2ang_200pts_sph 2) three_spin_powder_800pts <strong>Folders containing all the simulated MAS spectra acquired at variable MAS rates for two-spin and three-spin powder systems for Figure 10, 11 and 12: </strong>(camp format) 1) two_spin_different_alphas_and_betas_rep_2ang_200pts_sph_jcamp 2) three_ [...]

Research paper thumbnail of Theory of long-lived nuclear spin states in methyl groups and quantum-rotor induced polarisation

The Journal of chemical physics, Jan 28, 2015

Long-lived nuclear spin states have a relaxation time much longer than the longitudinal relaxatio... more Long-lived nuclear spin states have a relaxation time much longer than the longitudinal relaxation time T1. Long-lived states extend significantly the time scales that may be probed with magnetic resonance, with possible applications to transport and binding studies, and to hyperpolarised imaging. Rapidly rotating methyl groups in solution may support a long-lived state, consisting of a population imbalance between states of different spin exchange symmetries. Here, we expand the formalism for describing the behaviour of long-lived nuclear spin states in methyl groups, with special attention to the hyperpolarisation effects observed in (13)CH3 groups upon rapidly converting a material with low-barrier methyl rotation from the cryogenic solid state to a room-temperature solution [M. Icker and S. Berger, J. Magn. Reson. 219, 1 (2012)]. We analyse the relaxation properties of methyl long-lived states using semi-classical relaxation theory. Numerical simulations are supplemented with a ...