Aurélien Bornet | Ecole Polytechnique Federale de Lausanne (original) (raw)

Papers by Aurélien Bornet

The Review of scientific instruments, 2015

To shield solutions carrying hyperpolarized nuclear magnetization from rapid relaxation during tr... more To shield solutions carrying hyperpolarized nuclear magnetization from rapid relaxation during transfer through low fields, the transfer duct can be threaded through an array of permanent magnets. The advantages are illustrated for solutions containing hyperpolarized (1)H and (13)C nuclei in a variety of molecules.

Proceedings of the National Academy of Sciences of the United States of America, Jan 14, 2014

Hyperpolarization of substrates for magnetic resonance spectroscopy (MRS) and imaging (MRI) by di... more Hyperpolarization of substrates for magnetic resonance spectroscopy (MRS) and imaging (MRI) by dissolution dynamic nuclear polarization (D-DNP) usually involves saturating the ESR transitions of polarizing agents (PAs; e.g., persistent radicals embedded in frozen glassy matrices). This approach has shown enormous potential to achieve greatly enhanced nuclear spin polarization, but the presence of PAs and/or glassing agents in the sample after dissolution can raise concerns for in vivo MRI applications, such as perturbing molecular interactions, and may induce the erosion of hyperpolarization in spectroscopy and MRI. We show that D-DNP can be performed efficiently with hybrid polarizing solids (HYPSOs) with 2,2,6,6-tetramethyl-piperidine-1-oxyl radicals incorporated in a mesostructured silica material and homogeneously distributed along its pore channels. The powder is wetted with a solution containing molecules of interest (for example, metabolites for MRS or MRI) to fill the pore c...

Chemistry - A European Journal, 2014

Hyperpolarization by dissolution dynamic nuclear polarization (D-DNP) offers a way of enhancing N... more Hyperpolarization by dissolution dynamic nuclear polarization (D-DNP) offers a way of enhancing NMR signals by up to five orders of magnitude in metabolites and other small molecules. Nevertheless, the lifetime of hyperpolarization is inexorably limited, as it decays toward thermal equilibrium with the nuclear spin-lattice relaxation time. This lifetime can be extended by storing the hyperpolarization in the form of long-lived states (LLS) that are immune to most dominant relaxation mechanisms. Levitt and co-workers have shown how LLS can be prepared for a pair of inequivalent spins by D-DNP. Here, we demonstrate that this approach can also be applied to magnetically equivalent pairs of spins such as the two protons of fumarate, which can have very long LLS lifetimes. As in the case of para-hydrogen, these hyperpolarized equivalent LLS (HELLS) are not magnetically active. However, a chemical reaction such as the enzymatic conversion of fumarate into malate can break the magnetic equivalence and reveal intense NMR signals.

Phys. Chem. Chem. Phys., 2014

Cross polarization from protons to quadrupolar 6 Li nuclei is combined with dynamic nuclear polar... more Cross polarization from protons to quadrupolar 6 Li nuclei is combined with dynamic nuclear polarization of protons at 1.2 K and 6.7 T using TEMPOL as a polarizing agent followed by rapid dissolution.

ChemMedChem, 2014

Transverse and longitudinal relaxation times (T1ρ and T1) have been widely exploited in NMR to pr... more Transverse and longitudinal relaxation times (T1ρ and T1) have been widely exploited in NMR to probe the binding of ligands and putative drugs to target proteins. We have shown recently that long-lived states (LLS) can be more sensitive to ligand binding. LLS can be excited if the ligand comprises at least two coupled spins. Herein we broaden the scope of ligand screening by LLS to arbitrary ligands by covalent attachment of a functional group, which comprises a pair of coupled protons that are isolated from neighboring magnetic nuclei. The resulting functionalized ligands have longitudinal relaxation times T1((1)H) that are sufficiently long to allow the powerful combination of LLS with dissolution dynamic nuclear polarization (D-DNP). Hyperpolarized weak "spy ligands" can be displaced by high-affinity competitors. Hyperpolarized LLS allow one to decrease both protein and ligand concentrations to micromolar levels and to significantly increase sample throughput.

The Journal of Physical Chemistry B, 2014

In deuterated molecules such as [1-13 C]pyruvate-d 3 , the nuclear spin polarization of 13 C nucl... more In deuterated molecules such as [1-13 C]pyruvate-d 3 , the nuclear spin polarization of 13 C nuclei can be enhanced by combining Hartmann−Hahn cross-polarization (CP) at low temperatures (1.2 K) with dissolution dynamic nuclear polarization (D-DNP). The polarization is transferred from remote solvent protons to the 13 C spins of interest. This allows one not only to slightly reduce build-up times but also to increase polarization levels and extend the lifetimes T 1 ( 13 C) of the enhanced 13 C polarization during and after transfer from the polarizer to the NMR or MRI system. This extends time scales over which metabolic processes and chemical reactions can be monitored.

Progress in Nuclear Magnetic Resonance Spectroscopy, 2011

Physical Review Letters, 2012

A half-century quest for improving resolution in Nuclear Magnetic Resonance (NMR) and Magnetic Re... more A half-century quest for improving resolution in Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) has enabled the study of molecular structures, biological interactions, and fine details of anatomy. This progress largely relied on the advent of sophisticated superconducting magnets that can provide stable and homogeneous fields with temporal and spatial variations below ÁB 0 =B 0 < 0:01 ppm. In many cases however, inherent properties of the objects under investigation, pulsating arteries, breathing lungs, tissue-air interfaces, surgical implants, etc., lead to fluctuations and losses of local homogeneity. A new method dubbed ''long-lived-coherence correlation spectroscopy'' (LLC-COSY) opens the way to overcome both inhomogeneous and homogeneous broadening, which arise from local variations in static fields and fluctuating dipole-dipole interactions, respectively. LLC-COSY makes it possible to obtain ultrahigh resolution two-dimensional spectra, with linewidths on the order of Á ¼ 0:1 to 1 Hz, even in very inhomogeneous fields (ÁB 0 =B 0 > 10 ppm or 5000 Hz at 9.7 T), and can improve resolution by a factor up to 9 when the homogeneous linewidths are determined by dipole-dipole interactions. The resulting LLC-COSY spectra display chemical shift differences and scalar couplings in two orthogonal dimensions, like in ''J spectroscopy.'' LLC-COSY does not require any sophisticated gradient switching or frequency-modulated pulses. Applications to in-cell NMR and to magnetic resonance spectroscopy (MRS) of selected volume elements in MRI appear promising, particularly when susceptibility variations tend to preclude high resolution.

Journal of the American Chemical Society, 2012

A new NMR method for the study of ligand−protein interactions exploits the unusual lifetimes of l... more A new NMR method for the study of ligand−protein interactions exploits the unusual lifetimes of long-lived states (LLSs). The new method provides better contrast between bound and free ligands and requires a protein−ligand ratio ca. 25 times lower than for established T 1ρ methods, thus saving on costly proteins. The new LLS method was applied to the screening of inhibitors of urokinase-type plasminogen activator (uPA), which is a prototypical target of cancer research. With only 10 μM protein, a dissociation constant (K D ) of 180 ± 20 nM was determined for the strong ligand (inhibitor) UK-18, which can be compared with K D = 157 ± 39 nM determined by the established surface plasmon resonance method.

Journal of the American Chemical Society, 2011

Most nuclear magnetic resonance (NMR) methods employ Fourier transformations of free induction de... more Most nuclear magnetic resonance (NMR) methods employ Fourier transformations of free induction decays (FIDs). 1 Although widely used, this approach suffers from homogeneous decay and imperfect homogeneity of the static magnetic field, so that it is challenging to achieve line-widths below 1 Hz. 2 Sophisticated NMR pulse sequences have been developed to achieve reasonable line-widths (1 < Δν < 50 Hz) in moderately inhomogeneous fields, exploiting cross relaxation effects, 3 observation in the earth's magnetic field, 4 or a spatial correlation between the static and radio frequency (rf ) field profiles. 5 By combining refocusing and coherence transfer through couplings, one can obtain acceptable line-widths (1 < Δν < 50 Hz) even in very inhomogeneous fields (Δν > 2 kHz). In systems with two scalar-coupled homonuclear spins I = 1/2 and S = 1/2, one can excite long-lived coherences (LLCs) that can have very long lifetimes T LLC and hence very narrow line-widths Δν LLC = 1/(πT LLC ). 7À9 Their precession frequency is independent of offset (and hence of chemical shifts and inhomogeneous broadening) and is only determined by the sum of scalar and residual dipolar couplings (T IS = 2J IS + D IS ). So far, LLCs have only been observed indirectly in the manner of two-dimensional (2D) spectroscopy, either in combination with field cycling 7 or in high field. This work describes a one-dimensional (1D) "on-the-fly" method where the rf irradiation required to sustain the LLCs in high magnetic field is briefly interrupted at regular intervals, so that the LLCs can be temporarily observed as single-quantum coherences (SQCs). In contrast with conventional FIDs, the "sustained induction decays" (SIDs) that are observed in this manner provide line-widths as narrow as Δν LLC = 14 mHz even in poorly shimmed magnets (Δν > 20 Hz). This technique is fully compatible with signal enhancement by "dissolution" dynamic nuclear polarization (DNP). 10 ' PRINCIPLES Long-lived coherences (LLCs) constitute a class of zeroquantum coherences that can be excited by extremely low frequency fields (ELFs) in a vanishing static field. 7 LLCs can also be excited in high fields by creating a state where the coherences I x and ÀS x have opposite phases, so that they can be locked by a continuous "sustaining" rf field. This rf field in effect suppresses the chemical shifts, thus rendering the spins magnetically equivalent, so that their eigenstates can be classified according to "symmetrical" and "antisymmetrical" irreducible representations of the spin permutation group. LLCs span zeroquantum transitions between states of different symmetry. Their oscillatory decays can be subjected to a Fourier transformation, yielding doublets that are reminiscent of "J-spectroscopy". 11À13 The lifetimes T LLC of LLCs can be a factor k longer than the transverse relaxation times T 2 = T SQC of ordinary singlequantum coherences (T LLC = kT 2 ), so that the line-widths Δν LLC = 1/(πT LLC ) can be narrower by a factor Δν LLC /Δν SQC = 1/k. Depending on the role of extraneous relaxation mechanisms, 9 one can expect k e 3 in small molecules in the extreme ABSTRACT: Long-lived coherences (LLCs) in homonuclear pairs of chemically inequivalent spins can be excited and sustained during protracted radio frequency irradiation periods that alternate with brief windows for signal observation. Fourier transformation of the sustained induction decays recorded in a single scan yields NMR spectra with line-widths in the range 10 < Δν < 100 mHz, even in moderately inhomogeneous magnetic fields. The resulting doublets, which are reminiscent of J-spectra, allow one to determine the sum of scalar and residual dipolar interactions in partly oriented media. The signal intensity can be boosted by several orders of magnitude by "dissolution" dynamic nuclear polarization (DNP).

The Journal of Physical Chemistry Letters, 2013

The efficiency of dissolution dynamic nuclear polarization can be boosted by Hartmann−Hahn cross ... more The efficiency of dissolution dynamic nuclear polarization can be boosted by Hartmann−Hahn cross polarization at temperatures near 1.2 K. This enables high throughput of hyperpolarized solutions with substantial gains in buildup times and polarization levels. During dissolution and transport, the 13 C nuclear spin polarization P( 13 C) merely decreases from 45 to 40%.

Journal of Magnetic Resonance, 2010

The transverse relaxation rate R 2 of single quantum coherences, the relaxation rate R LLC of lon... more The transverse relaxation rate R 2 of single quantum coherences, the relaxation rate R LLC of long-lived coherences (LLC), and the ratio R 2 /R LLC have been studied by experiment, simulation and theory in the two-spin system formed by the Glycine aliphatic protons of the dipeptide Alanine-Glycine as a function of the correlation time of rotational diffusion.

CHIMIA International Journal for Chemistry, 2012

Although nuclear magnetic resonance (NMR) can provide a wealth of information, it often suffers f... more Although nuclear magnetic resonance (NMR) can provide a wealth of information, it often suffers from a lack of sensitivity. Dynamic Nuclear Polarization (DNP) provides a way to increase the polarization and hence the signal intensities in NMR spectra by transferring the favourable electron spin polarization of paramagnetic centres to the surrounding nuclear spins through appropriate microwave irradiation. In our group at EPFL, two complementary DNP techniques are under investigation: the combination of DNP with magic angle spinning at temperatures near 100 K ('MAS-DNP'), and the combination of DNP at 1.2 K with rapid heating followed by the transfer of the sample to a high-resolution magnet ('dissolution DNP'). Recent applications of MAS-DNP to surfaces, as well as new developments of magnetization transfer of 1 H to 13 C at 1.2 K prior to dissolution will illustrate the work performed in our group. A second part of the paper will give an overview of some 'nonenhanced' activities of our laboratory in liquid-and solid-state NMR.

ChemPhysChem, 2011

The relaxation of long-lived states (LLS) corresponds to the slow return to statistical thermal e... more The relaxation of long-lived states (LLS) corresponds to the slow return to statistical thermal equilibrium between symmetric and antisymmetric proton spin states. This process is remarkably sensitive to the presence of external spins and can be used to obtain information about partial unfolding of proteins. We detected the appearance of a destabilized conformer of ubiquitin when urea is added to the protein in its native state. This conformer shows increased mobility in the Cterminus, which significantly extends the lifetimes of proton LLS magnetisation in Ser-65. These changes could not be detected by conventional measurements of T 1 and T 2 relaxation times of protons, and would hardly be sensed by carbon-13 or nitrogen-15 relaxation measurements. Conformers with similar dynamic and structural features, as revealed by LLS relaxation times, could be observed, in the absence of urea, in two ubiquitin mutants, L67S and L69S.

Chemical Physics Letters, 2014

Dedicated to To Martial Rey, as a token of appreciation.

Chemical Physics Letters, 2011

This communication describes a three-field experiment where inequivalent scalar coupled spin pair... more This communication describes a three-field experiment where inequivalent scalar coupled spin pairs are hyperpolarized at 3.35 T and 1.2 K by dynamic nuclear polarization (DNP), rapidly transferred to high field (7 T) to prepare a suitable initial condition that is converted adiabatically into a long-lived state (LLS) by shuttling to a 'low' magnetic field (2 mT-7 T). Even without applying any rf irradiation to sustain the LLS, it has a lifetime T LLS ) T 1 in low fields. Finally, the sample is shuttled back to high field for observation under high-resolution conditions.

Chemical Physics Letters, 2012

In most applications of dissolution-DNP, the polarization of nuclei with low gyromagnetic ratios ... more In most applications of dissolution-DNP, the polarization of nuclei with low gyromagnetic ratios such as 13 C is enhanced directly by irradiating the ESR transitions of radicals with narrow ESR lines such as Trityl at low temperatures T = 1.2 K in polarizing fields B 0 6 5 T. In a field B 0 = 6.7 T at T = 1.2 K, DNP with TEMPO leads to a rapid build-up of proton polarization P( 1 H) = 91% with s DNP ( 1 H) = 150 s. CP at low temperatures yields a polarization P( 1 H ? 13 C) in excess of 70% within 20 min. After rapid dissolution to room temperature, this is 122 000 times larger than the Boltzmann polarization at 300 K and 6.7 T.

Chemical Physics Letters, 2011

Dynamic Nuclear Polarization (DNP) induced by saturation of ESR transitions of TEMPO at 1.2 K and... more Dynamic Nuclear Polarization (DNP) induced by saturation of ESR transitions of TEMPO at 1.2 K and 3.35 T is characterized by build-up rates that are typically 5 times faster for protons than for the carboxylic carbon-13 in acetate. We show that cross polarization from protons to carbon-13 allows one to achieve a polarization P( 13 C) >20% in less than 10 min, twice as much as has been previously reported, in one-fifth of the time. This should open the way to an unprecedented improvement in the efficiency of dissolution DNP.

Applied Magnetic Resonance, 2012

Cross polarization can provide significant enhancements with respect to direct polarization of lo... more Cross polarization can provide significant enhancements with respect to direct polarization of low-c nuclei such as 13 C. Substantial gains in sample throughput (shorter polarization times) can be achieved by exploiting shorter buildup times s DNP ( 1 H) \ s DNP ( 13 C). To polarize protons rather than low-c nuclei, nitroxide radicals with broad ESR resonances such as TEMPO are more appropriate than Trityl and similar carbon-based radicals that have narrow lines. With TEMPO as polarizing agent, the main Dynamic Nuclear Polarization (DNP) mechanism is thermal mixing (TM). Cross polarization makes it possible to attain higher polarization levels at 2.2 K than one can obtain with direct DNP of low-c nuclei with TEMPO at 1.2 K, thus avoiding complex cryogenic technology.

The Review of scientific instruments, 2015

To shield solutions carrying hyperpolarized nuclear magnetization from rapid relaxation during tr... more To shield solutions carrying hyperpolarized nuclear magnetization from rapid relaxation during transfer through low fields, the transfer duct can be threaded through an array of permanent magnets. The advantages are illustrated for solutions containing hyperpolarized (1)H and (13)C nuclei in a variety of molecules.

Proceedings of the National Academy of Sciences of the United States of America, Jan 14, 2014

Hyperpolarization of substrates for magnetic resonance spectroscopy (MRS) and imaging (MRI) by di... more Hyperpolarization of substrates for magnetic resonance spectroscopy (MRS) and imaging (MRI) by dissolution dynamic nuclear polarization (D-DNP) usually involves saturating the ESR transitions of polarizing agents (PAs; e.g., persistent radicals embedded in frozen glassy matrices). This approach has shown enormous potential to achieve greatly enhanced nuclear spin polarization, but the presence of PAs and/or glassing agents in the sample after dissolution can raise concerns for in vivo MRI applications, such as perturbing molecular interactions, and may induce the erosion of hyperpolarization in spectroscopy and MRI. We show that D-DNP can be performed efficiently with hybrid polarizing solids (HYPSOs) with 2,2,6,6-tetramethyl-piperidine-1-oxyl radicals incorporated in a mesostructured silica material and homogeneously distributed along its pore channels. The powder is wetted with a solution containing molecules of interest (for example, metabolites for MRS or MRI) to fill the pore c...

Chemistry - A European Journal, 2014

Hyperpolarization by dissolution dynamic nuclear polarization (D-DNP) offers a way of enhancing N... more Hyperpolarization by dissolution dynamic nuclear polarization (D-DNP) offers a way of enhancing NMR signals by up to five orders of magnitude in metabolites and other small molecules. Nevertheless, the lifetime of hyperpolarization is inexorably limited, as it decays toward thermal equilibrium with the nuclear spin-lattice relaxation time. This lifetime can be extended by storing the hyperpolarization in the form of long-lived states (LLS) that are immune to most dominant relaxation mechanisms. Levitt and co-workers have shown how LLS can be prepared for a pair of inequivalent spins by D-DNP. Here, we demonstrate that this approach can also be applied to magnetically equivalent pairs of spins such as the two protons of fumarate, which can have very long LLS lifetimes. As in the case of para-hydrogen, these hyperpolarized equivalent LLS (HELLS) are not magnetically active. However, a chemical reaction such as the enzymatic conversion of fumarate into malate can break the magnetic equivalence and reveal intense NMR signals.

Phys. Chem. Chem. Phys., 2014

Cross polarization from protons to quadrupolar 6 Li nuclei is combined with dynamic nuclear polar... more Cross polarization from protons to quadrupolar 6 Li nuclei is combined with dynamic nuclear polarization of protons at 1.2 K and 6.7 T using TEMPOL as a polarizing agent followed by rapid dissolution.

ChemMedChem, 2014

Transverse and longitudinal relaxation times (T1ρ and T1) have been widely exploited in NMR to pr... more Transverse and longitudinal relaxation times (T1ρ and T1) have been widely exploited in NMR to probe the binding of ligands and putative drugs to target proteins. We have shown recently that long-lived states (LLS) can be more sensitive to ligand binding. LLS can be excited if the ligand comprises at least two coupled spins. Herein we broaden the scope of ligand screening by LLS to arbitrary ligands by covalent attachment of a functional group, which comprises a pair of coupled protons that are isolated from neighboring magnetic nuclei. The resulting functionalized ligands have longitudinal relaxation times T1((1)H) that are sufficiently long to allow the powerful combination of LLS with dissolution dynamic nuclear polarization (D-DNP). Hyperpolarized weak "spy ligands" can be displaced by high-affinity competitors. Hyperpolarized LLS allow one to decrease both protein and ligand concentrations to micromolar levels and to significantly increase sample throughput.

The Journal of Physical Chemistry B, 2014

In deuterated molecules such as [1-13 C]pyruvate-d 3 , the nuclear spin polarization of 13 C nucl... more In deuterated molecules such as [1-13 C]pyruvate-d 3 , the nuclear spin polarization of 13 C nuclei can be enhanced by combining Hartmann−Hahn cross-polarization (CP) at low temperatures (1.2 K) with dissolution dynamic nuclear polarization (D-DNP). The polarization is transferred from remote solvent protons to the 13 C spins of interest. This allows one not only to slightly reduce build-up times but also to increase polarization levels and extend the lifetimes T 1 ( 13 C) of the enhanced 13 C polarization during and after transfer from the polarizer to the NMR or MRI system. This extends time scales over which metabolic processes and chemical reactions can be monitored.

Progress in Nuclear Magnetic Resonance Spectroscopy, 2011

Physical Review Letters, 2012

A half-century quest for improving resolution in Nuclear Magnetic Resonance (NMR) and Magnetic Re... more A half-century quest for improving resolution in Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) has enabled the study of molecular structures, biological interactions, and fine details of anatomy. This progress largely relied on the advent of sophisticated superconducting magnets that can provide stable and homogeneous fields with temporal and spatial variations below ÁB 0 =B 0 < 0:01 ppm. In many cases however, inherent properties of the objects under investigation, pulsating arteries, breathing lungs, tissue-air interfaces, surgical implants, etc., lead to fluctuations and losses of local homogeneity. A new method dubbed ''long-lived-coherence correlation spectroscopy'' (LLC-COSY) opens the way to overcome both inhomogeneous and homogeneous broadening, which arise from local variations in static fields and fluctuating dipole-dipole interactions, respectively. LLC-COSY makes it possible to obtain ultrahigh resolution two-dimensional spectra, with linewidths on the order of Á ¼ 0:1 to 1 Hz, even in very inhomogeneous fields (ÁB 0 =B 0 > 10 ppm or 5000 Hz at 9.7 T), and can improve resolution by a factor up to 9 when the homogeneous linewidths are determined by dipole-dipole interactions. The resulting LLC-COSY spectra display chemical shift differences and scalar couplings in two orthogonal dimensions, like in ''J spectroscopy.'' LLC-COSY does not require any sophisticated gradient switching or frequency-modulated pulses. Applications to in-cell NMR and to magnetic resonance spectroscopy (MRS) of selected volume elements in MRI appear promising, particularly when susceptibility variations tend to preclude high resolution.

Journal of the American Chemical Society, 2012

A new NMR method for the study of ligand−protein interactions exploits the unusual lifetimes of l... more A new NMR method for the study of ligand−protein interactions exploits the unusual lifetimes of long-lived states (LLSs). The new method provides better contrast between bound and free ligands and requires a protein−ligand ratio ca. 25 times lower than for established T 1ρ methods, thus saving on costly proteins. The new LLS method was applied to the screening of inhibitors of urokinase-type plasminogen activator (uPA), which is a prototypical target of cancer research. With only 10 μM protein, a dissociation constant (K D ) of 180 ± 20 nM was determined for the strong ligand (inhibitor) UK-18, which can be compared with K D = 157 ± 39 nM determined by the established surface plasmon resonance method.

Journal of the American Chemical Society, 2011

Most nuclear magnetic resonance (NMR) methods employ Fourier transformations of free induction de... more Most nuclear magnetic resonance (NMR) methods employ Fourier transformations of free induction decays (FIDs). 1 Although widely used, this approach suffers from homogeneous decay and imperfect homogeneity of the static magnetic field, so that it is challenging to achieve line-widths below 1 Hz. 2 Sophisticated NMR pulse sequences have been developed to achieve reasonable line-widths (1 < Δν < 50 Hz) in moderately inhomogeneous fields, exploiting cross relaxation effects, 3 observation in the earth's magnetic field, 4 or a spatial correlation between the static and radio frequency (rf ) field profiles. 5 By combining refocusing and coherence transfer through couplings, one can obtain acceptable line-widths (1 < Δν < 50 Hz) even in very inhomogeneous fields (Δν > 2 kHz). In systems with two scalar-coupled homonuclear spins I = 1/2 and S = 1/2, one can excite long-lived coherences (LLCs) that can have very long lifetimes T LLC and hence very narrow line-widths Δν LLC = 1/(πT LLC ). 7À9 Their precession frequency is independent of offset (and hence of chemical shifts and inhomogeneous broadening) and is only determined by the sum of scalar and residual dipolar couplings (T IS = 2J IS + D IS ). So far, LLCs have only been observed indirectly in the manner of two-dimensional (2D) spectroscopy, either in combination with field cycling 7 or in high field. This work describes a one-dimensional (1D) "on-the-fly" method where the rf irradiation required to sustain the LLCs in high magnetic field is briefly interrupted at regular intervals, so that the LLCs can be temporarily observed as single-quantum coherences (SQCs). In contrast with conventional FIDs, the "sustained induction decays" (SIDs) that are observed in this manner provide line-widths as narrow as Δν LLC = 14 mHz even in poorly shimmed magnets (Δν > 20 Hz). This technique is fully compatible with signal enhancement by "dissolution" dynamic nuclear polarization (DNP). 10 ' PRINCIPLES Long-lived coherences (LLCs) constitute a class of zeroquantum coherences that can be excited by extremely low frequency fields (ELFs) in a vanishing static field. 7 LLCs can also be excited in high fields by creating a state where the coherences I x and ÀS x have opposite phases, so that they can be locked by a continuous "sustaining" rf field. This rf field in effect suppresses the chemical shifts, thus rendering the spins magnetically equivalent, so that their eigenstates can be classified according to "symmetrical" and "antisymmetrical" irreducible representations of the spin permutation group. LLCs span zeroquantum transitions between states of different symmetry. Their oscillatory decays can be subjected to a Fourier transformation, yielding doublets that are reminiscent of "J-spectroscopy". 11À13 The lifetimes T LLC of LLCs can be a factor k longer than the transverse relaxation times T 2 = T SQC of ordinary singlequantum coherences (T LLC = kT 2 ), so that the line-widths Δν LLC = 1/(πT LLC ) can be narrower by a factor Δν LLC /Δν SQC = 1/k. Depending on the role of extraneous relaxation mechanisms, 9 one can expect k e 3 in small molecules in the extreme ABSTRACT: Long-lived coherences (LLCs) in homonuclear pairs of chemically inequivalent spins can be excited and sustained during protracted radio frequency irradiation periods that alternate with brief windows for signal observation. Fourier transformation of the sustained induction decays recorded in a single scan yields NMR spectra with line-widths in the range 10 < Δν < 100 mHz, even in moderately inhomogeneous magnetic fields. The resulting doublets, which are reminiscent of J-spectra, allow one to determine the sum of scalar and residual dipolar interactions in partly oriented media. The signal intensity can be boosted by several orders of magnitude by "dissolution" dynamic nuclear polarization (DNP).

The Journal of Physical Chemistry Letters, 2013

The efficiency of dissolution dynamic nuclear polarization can be boosted by Hartmann−Hahn cross ... more The efficiency of dissolution dynamic nuclear polarization can be boosted by Hartmann−Hahn cross polarization at temperatures near 1.2 K. This enables high throughput of hyperpolarized solutions with substantial gains in buildup times and polarization levels. During dissolution and transport, the 13 C nuclear spin polarization P( 13 C) merely decreases from 45 to 40%.

Journal of Magnetic Resonance, 2010

The transverse relaxation rate R 2 of single quantum coherences, the relaxation rate R LLC of lon... more The transverse relaxation rate R 2 of single quantum coherences, the relaxation rate R LLC of long-lived coherences (LLC), and the ratio R 2 /R LLC have been studied by experiment, simulation and theory in the two-spin system formed by the Glycine aliphatic protons of the dipeptide Alanine-Glycine as a function of the correlation time of rotational diffusion.

CHIMIA International Journal for Chemistry, 2012

Although nuclear magnetic resonance (NMR) can provide a wealth of information, it often suffers f... more Although nuclear magnetic resonance (NMR) can provide a wealth of information, it often suffers from a lack of sensitivity. Dynamic Nuclear Polarization (DNP) provides a way to increase the polarization and hence the signal intensities in NMR spectra by transferring the favourable electron spin polarization of paramagnetic centres to the surrounding nuclear spins through appropriate microwave irradiation. In our group at EPFL, two complementary DNP techniques are under investigation: the combination of DNP with magic angle spinning at temperatures near 100 K ('MAS-DNP'), and the combination of DNP at 1.2 K with rapid heating followed by the transfer of the sample to a high-resolution magnet ('dissolution DNP'). Recent applications of MAS-DNP to surfaces, as well as new developments of magnetization transfer of 1 H to 13 C at 1.2 K prior to dissolution will illustrate the work performed in our group. A second part of the paper will give an overview of some 'nonenhanced' activities of our laboratory in liquid-and solid-state NMR.

ChemPhysChem, 2011

The relaxation of long-lived states (LLS) corresponds to the slow return to statistical thermal e... more The relaxation of long-lived states (LLS) corresponds to the slow return to statistical thermal equilibrium between symmetric and antisymmetric proton spin states. This process is remarkably sensitive to the presence of external spins and can be used to obtain information about partial unfolding of proteins. We detected the appearance of a destabilized conformer of ubiquitin when urea is added to the protein in its native state. This conformer shows increased mobility in the Cterminus, which significantly extends the lifetimes of proton LLS magnetisation in Ser-65. These changes could not be detected by conventional measurements of T 1 and T 2 relaxation times of protons, and would hardly be sensed by carbon-13 or nitrogen-15 relaxation measurements. Conformers with similar dynamic and structural features, as revealed by LLS relaxation times, could be observed, in the absence of urea, in two ubiquitin mutants, L67S and L69S.

Chemical Physics Letters, 2014

Dedicated to To Martial Rey, as a token of appreciation.

Chemical Physics Letters, 2011

This communication describes a three-field experiment where inequivalent scalar coupled spin pair... more This communication describes a three-field experiment where inequivalent scalar coupled spin pairs are hyperpolarized at 3.35 T and 1.2 K by dynamic nuclear polarization (DNP), rapidly transferred to high field (7 T) to prepare a suitable initial condition that is converted adiabatically into a long-lived state (LLS) by shuttling to a 'low' magnetic field (2 mT-7 T). Even without applying any rf irradiation to sustain the LLS, it has a lifetime T LLS ) T 1 in low fields. Finally, the sample is shuttled back to high field for observation under high-resolution conditions.

Chemical Physics Letters, 2012

In most applications of dissolution-DNP, the polarization of nuclei with low gyromagnetic ratios ... more In most applications of dissolution-DNP, the polarization of nuclei with low gyromagnetic ratios such as 13 C is enhanced directly by irradiating the ESR transitions of radicals with narrow ESR lines such as Trityl at low temperatures T = 1.2 K in polarizing fields B 0 6 5 T. In a field B 0 = 6.7 T at T = 1.2 K, DNP with TEMPO leads to a rapid build-up of proton polarization P( 1 H) = 91% with s DNP ( 1 H) = 150 s. CP at low temperatures yields a polarization P( 1 H ? 13 C) in excess of 70% within 20 min. After rapid dissolution to room temperature, this is 122 000 times larger than the Boltzmann polarization at 300 K and 6.7 T.

Chemical Physics Letters, 2011

Dynamic Nuclear Polarization (DNP) induced by saturation of ESR transitions of TEMPO at 1.2 K and... more Dynamic Nuclear Polarization (DNP) induced by saturation of ESR transitions of TEMPO at 1.2 K and 3.35 T is characterized by build-up rates that are typically 5 times faster for protons than for the carboxylic carbon-13 in acetate. We show that cross polarization from protons to carbon-13 allows one to achieve a polarization P( 13 C) >20% in less than 10 min, twice as much as has been previously reported, in one-fifth of the time. This should open the way to an unprecedented improvement in the efficiency of dissolution DNP.

Applied Magnetic Resonance, 2012

Cross polarization can provide significant enhancements with respect to direct polarization of lo... more Cross polarization can provide significant enhancements with respect to direct polarization of low-c nuclei such as 13 C. Substantial gains in sample throughput (shorter polarization times) can be achieved by exploiting shorter buildup times s DNP ( 1 H) \ s DNP ( 13 C). To polarize protons rather than low-c nuclei, nitroxide radicals with broad ESR resonances such as TEMPO are more appropriate than Trityl and similar carbon-based radicals that have narrow lines. With TEMPO as polarizing agent, the main Dynamic Nuclear Polarization (DNP) mechanism is thermal mixing (TM). Cross polarization makes it possible to attain higher polarization levels at 2.2 K than one can obtain with direct DNP of low-c nuclei with TEMPO at 1.2 K, thus avoiding complex cryogenic technology.