Andrey Pravdivtsev - Academia.edu (original) (raw)
Papers by Andrey Pravdivtsev
arXiv (Cornell University), Dec 13, 2021
It is well known that the association of parahydrogen (pH2) with an unsaturated molecule or a tra... more It is well known that the association of parahydrogen (pH2) with an unsaturated molecule or a transient metalorganic complex can enhance the intensity of NMR signals; the effect is known as parahydrogen-induced polarization (PHIP). During the last decades, numerous methods were proposed for converting pH2-derived nuclear spin order to the observable magnetization of protons or other nuclei of interest, usually 13 C or 15 N. Here, we analyze the constraints imposed by the topological symmetry of the spin systems on the amplitude of transferred polarization. In asymmetric systems, heteronuclei can be polarized to 100%. However, the amplitude drops to 75% in A2BX systems and further to 50% in A3B2X systems. The latter case is of primary importance for biological applications of PHIP using sidearm hydrogenation (PHIP-SAH). If the polarization is transferred to the same type of nuclei, i.e. 1 H, symmetry constraints impose significant boundaries on the spin-order distribution. For AB, A2B, A3B, A2B2, AA'(AA') systems, the maximum average polarization for each spin is 100%, 50%, 33.3%, 25%, and 0, respectively, when A and B (or A') came from pH2 We also discuss the effect of dipole-dipole induced pH2 spin-order distribution in heterogeneous catalysis or nematic liquid crystals. Practical examples from the literature illustrate our theoretical analysis.
Zero-to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is an emerging tool for precision ... more Zero-to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is an emerging tool for precision chemical analysis. In this work, we study dynamic processes and investigate the influence of chemical exchange on ZULF NMR J-spectra. We develop a computational approach that allows quantitative calculation of J-spectra in the presence of chemical exchange and apply it to study aqueous solutions of [ 15 N]ammonium ( 15 NH þ 4 ) as a model system. We show that pH-dependent chemical exchange substantially affects the J-spectra and, in some cases, can lead to degradation and complete disappearance of the spectral features. To demonstrate potential applications of ZULF NMR for chemistry and biomedicine, we show a ZULF NMR spectrum of [2-13 C]pyruvic acid hyperpolarized via dissolution dynamic nuclear polarization (dDNP). We foresee applications of affordable and scalable ZULF NMR coupled with hyperpolarization to study chemical exchange phenomena in vivo and in situations where high-field NMR detection is not possible to implement.
arXiv (Cornell University), Aug 29, 2023
In magnetic resonance, the bulk magnetization of a sample that is being measured is typically def... more In magnetic resonance, the bulk magnetization of a sample that is being measured is typically defined as a quantity proportional to spin polarization. The fact that all spins of the same type contribute equally to measurable signals is considered obvious. By focusing on nuclear spin ensembles, we prove the high-field theorem for a general case of spin-I: grouping of spins in molecules does not affect the total measurable NMR signal given thermal equilibrium at high field (ℏ𝛾𝐵 0 ≫ |𝐻 int |, where |𝐻 int | is the characteristic amplitude of internal spin-spin interactions). We demonstrate this first by analyzing equations for spin magnetization and then for a general case using the density matrix formalism. We exemplify the theorem implications by predicting NMR signal intensities for ensembles of molecules containing single, two, and three spins. The theorem is not applied in more intricate situations, such as zero-to ultralow-field conditions and far from thermodynamic equilibrium. Considering the populations of rotation levels, the thermal equilibrium polarization at HF and low temperature for H2 gas illustrate one of the intricate cases.
![Research paper thumbnail of Sensitivity-enhanced magnetic resonance reveals hydrogen intermediates during active [Fe]-hydrogenase catalysis](https://attachments.academia-assets.com/117690660/thumbnails/1.jpg)
](bioRxiv (Cold Spring Harbor Laboratory), May 11, 2023
Molecular hydrogen (H2) is considered an eco-friendly future energy-carrier and an alternative to... more Molecular hydrogen (H2) is considered an eco-friendly future energy-carrier and an alternative to fossil fuel 1 and thus, major efforts are directed towards identifying efficient and economical hydrogen catalysts. Efficient hydrogen catalysis is used by many microorganisms, some of them producing H2 from organic materials and others consuming it. To metabolize H2, these microorganisms use enzymes called hydrogenases. For the future development of efficient catalysts a detailed analysis of the catalytic mechanisms of such hydrogenases is required and existing analytical techniques could not provide a full understanding. 9 Consequently, new analytical technologies are of utmost importance to unravel natures' blueprints for highly efficient hydrogen catalysts. Here, we introduce signal-enhanced or hyperpolarized, nuclear magnetic resonance (NMR) to study hydrogenases under turnover conditions. So far undiscovered hydrogen species of the catalytic cycle of [Fe]-hydrogenases, are revealed and thus, extend the knowledge regarding this class of enzymes. These findings pave new pathways for the exploration of novel hydrogen metabolisms in vivo. We furthermore envision that the results contribute to the rational design of future catalysts to solve energy challenges of our society.
The hyperpolarization of nuclear spins has enabled unique applications in chemistry, biophysics, ... more The hyperpolarization of nuclear spins has enabled unique applications in chemistry, biophysics, and particularly in metabolic imaging. Parahydrogen-induced polarization (PHIP) offers a fast and cost-efficient way of hyperpolarization. Nevertheless, PHIP lags behind dynamic nuclear polarization (DNP), which is already being evaluated in clinical studies. This shortcoming is mainly due to problems in the synthesis of the corresponding PHIP precursor molecules. The most widely used DNP tracer in clinical studies, particularly for the detection of prostate cancer, is 1-13 C-pyruvate. The ideal derivative for PHIP is the deuterated vinyl ester because the spin physics allows for 100% polarization. Unfortunately, there is no efficient synthesis for vinyl esters of βketocarboxylic acids in general and pyruvate in particular. Here, we present an efficient new method for the preparation of vinyl esters, including 13 C labeled, fully deuterated vinyl pyruvate using a palladium catalyzed procedure. Using 50 % enriched parahydrogen and mild reaction conditions, a 13 C polarization of 12% was readily achieved; 36% are expected with 100% pH2. Higher polarization values can be potentially achieved with optimized reaction conditions.
ChemPhysChem, Feb 1, 2021
Parahydrogen (pH2) induced polarization (PHIP) is a unique method that is used in analytical chem... more Parahydrogen (pH2) induced polarization (PHIP) is a unique method that is used in analytical chemistry to elucidate catalytic hydrogenation pathways and to increase the signal of small metabolites in MRI. PHIP is based on adding or exchanging at least one pH2 molecule with a target molecule. And thus, the spin order available for hyperpolarization is often limited to that of one pH2 molecule. To break this limit, we investigated the addition of multiple pH2 molecules to one precursor. We studied the feasibility of the simultaneous hydrogenation of three arms of trivinyl orthoacetate (TVOA) intending to obtain hyperpolarized acetate. It was found that semihydrogenated TVOA underwent a fast decomposition accompanied by several minor reactions including an exchange of geminal methylene protons of a vinyl ester with pH2. The study shows that multiple vinyl ester groups are not suitable for a fast and clean (without any side products) hydrogenation and hyperpolarization that is desired in biochemical applications.
Journal of Magnetic Resonance, Dec 1, 2018
The hyperpolarization of nuclear spins using parahydrogen is an interesting effect that allows to... more The hyperpolarization of nuclear spins using parahydrogen is an interesting effect that allows to increase the magnetic resonance signal by several orders of magnitude. Known as ParaHydrogen And Synthesis Allow Dramatically Enhanced Nuclear Alignment (PASADENA) and ParaHydrogen Induced Polarization (PHIP), the method was successfully used for in vitro analysis and in vivo imaging. In this contribution, we investigated four known and four new sequence variants of Only Parahydrogen SpectroscopY (OPSY) [J. A. Aguilar et al, ChemComm, 2007] with respect to the selective preparation of hyperpolarized NMR signal and background suppression. Depending on the method chosen, either antiphase, in-phase or a mixture of both signals are obtained: anti-phase signals are beneficial to identify hyperpolarized signals and the structure or J-coupling constants; in-phase signals are useful for imaging applications or in conditions when the lines are broad. This comprehensive overview of sequences new and old facilitates selecting the right sequence for the task at hand.
ChemPhysChem, Feb 11, 2020
Analytical Chemistry, Oct 20, 2022
Hyperpolarized (i.e., polarized far beyond the thermal equilibrium) nuclear spins can result in r... more Hyperpolarized (i.e., polarized far beyond the thermal equilibrium) nuclear spins can result in radiofrequency amplification by stimulated emission of radiation (RASER) effect. Here, we show the utility of RASER to amplify NMR signals of solute and solvent molecules in the liquid state. Specifically, parahydrogen-induced RASER was used to spontaneously enhance nuclear spin polarization of protons and heteronuclei (here 19 F and 31 P) in a wide range of molecules. The magnitude of the effect correlates with the T 1 relaxation time of the target nuclear spins. A series of control experiments validates the through-space dipolar mechanism of RASER-assisted polarization transfer between parahydrogen-polarized compound and to-be-hyperpolarized nuclei of the target molecule. Frequency-selective saturation of RASER-active resonances was used to control the RASER and the amplitude of spontaneous polarization transfer. Spin dynamics simulations support our experimental RASER studies.
PLOS ONE, Oct 1, 2020
Magnetic resonance spectroscopy (MRS) allows the analysis of biochemical processes non-invasively... more Magnetic resonance spectroscopy (MRS) allows the analysis of biochemical processes non-invasively and in vivo. Still, its application in clinical diagnostics is rare. Routine MRS is limited to spatial, chemical and temporal resolutions of cubic centimetres, mM and minutes. In fact, the signal of many metabolites is strong enough for detection, but the resonances significantly overlap, exacerbating identification and quantification. Besides, the signals of water and lipids are much stronger and dominate the entire spectrum. To suppress the background and isolate selected signals, usually, relaxation times, J-coupling and chemical shifts are used. Here, we propose methods to isolate the signals of selected molecular groups within endogenous metabolites by using long-lived spin states (LLS). We exemplify the method by preparing the LLSs of coupled protons in the endogenous molecules N-acetyl-L-aspartic acid (NAA). First, we store polarization in long-lived, double spin states, followed by saturation pulses before the spin order is converted back to observable magnetization or double quantum filters to suppress background signals. We show that LLS and zero-quantum coherences can be used to selectively prepare and measure the signals of chosen metabolites or drugs in the presence of water, inhomogeneous field and highly concentrated fatty solutions. The strong suppression of unwanted signals achieved allowed us to measure pH as a function of chemical shift difference.
Lifetime of Para hydrogen in Aqueous Solutions and Human Blood
ChemPhysChem, Sep 12, 2019
Molecular hydrogen has unique nuclear spin properties. Its nuclear spin isomer, parahydrogen (pH2... more Molecular hydrogen has unique nuclear spin properties. Its nuclear spin isomer, parahydrogen (pH2), was instrumental in the early days of quantum mechanics and allows to boost the NMR signal by several orders of magnitude. pH2‐induced polarization (PHIP) is based on the survival of pH2 spin order in solution, yet its lifetime has not been investigated in aqueous or biological media required for in vivo applications. Herein, we report longitudinal relaxation times (T1) and lifetimes of pH2 ( ) in methanol and water, with or without O2, NaCl, rhodium‐catalyst or human blood. Furthermore, we present a relaxation model that uses T1 and for more precise theoretical predictions of the H2 spin state in PHIP experiments. All measured T1 values were in the range of 1.4–2 s and values were of the order of 10–300 minutes. These relatively long lifetimes hold great promise for emerging in vivo implementations and applications of PHIP.
Scientific Reports, Jul 8, 2022
The setup, operational procedures and performance of a cryogen-free device for producing hyperpol... more The setup, operational procedures and performance of a cryogen-free device for producing hyperpolarized contrast agents using dissolution dynamic nuclear polarization (dDNP) in a preclinical imaging center is described. The polarization was optimized using the solid-state, DNP-enhanced NMR signal to calibrate the sample position, microwave and NMR frequency and power and flip angle. The polarization of a standard formulation to yield ~ 4 mL, 60 mM 1-13 C-pyruvic acid in an aqueous solution was quantified in five experiments to P(13 C) = (38 ± 6) % (19 ± 1) s after dissolution. The monoexponential time constant of the build-up of the solid-state polarization was quantified to (1032 ± 22) s. We achieved a duty cycle of 1.5 h that includes sample loading, monitoring the polarization build-up, dissolution and preparation for the next run. After injection of the contrast agent in vivo, pyruvate, pyruvate hydrate, lactate, and alanine were observed, by measuring metabolite maps. Based on this work sequence, hyperpolarized 15 N urea was obtained (P(15 N) = (5.6 ± 0.8) % (30 ± 3) s after dissolution). Magnetic Resonance Imaging (MRI) has revolutionized modern diagnostics by providing high resolution anatomical and functional imaging in 3D without ionizing radiation 1,2. Many of the biochemical processes in vivo, however, still elapse our best efforts, and accessing these remains a prime objective of much research. Here, hyperpolarized contrast agents hold great promise as they provide a unique window into metabolism, non-invasively and in vivo. By boosting the signal of selected, often endogenous molecules, their fate can be followed-for a limited time-with high spatial and chemical resolution. These properties have allowed the identification of cancerous tissue before a tumor was apparent, and has helped monitoring treatment response. Dissolution dynamic nuclear polarization (dDNP) 3 is the most established technique for hyperpolarizing (HP) biomolecules for in vivo imaging, and it shares the applicability to humans 4,5 only with hyperpolarized Xenon 6. Other HP techniques include brute-force 7 , parahydrogen-induced polarization 8 , chemically induced dynamic nuclear polarization 9 and, for noble gases, spin-exchange optical pumping 10,11. dDNP has allowed to polarize biomolecules to more than 50% in about 1 h 12,13. The nuclear polarization of the target is achieved by polarizing electronic spin first, using low temperatures (≈ 1.4 K) and high magnetic fields (≈ 6.7 T). Then, the electron polarization is transferred to nuclear polarization using the interactions between the electronic and nuclear spin under the action of electromagnetic waves, transmitted at a frequency corresponding to the difference in Larmor frequency of the two electron spins involved 14. The unpaired electron spins are added in the form of stable radicals: TEMPO 15 , TEMPOL, or trityl radicals 16,17 or induced by UV radiation 18. In addition, there are other types of sample formulations, for instance HYPOP 19. When the desired level of nuclear spin polarization is achieved, the frozen sample is rapidly melted, dissolved and ejected from the polarizer by pressurized overheated water, such that an injectable contrast agent results. Overall, dDNP is a complex process combining nuclear magnetic resonance (NMR) electron spin resonance (ESR), radical chemistry, high magnetic fields, fast dissolution, and cryogenictemperatures. Making this process available for biomedical research routinely is not straight forward. Over the last decades, several experimental implementations of dDNP were presented such as a cryogen-consumption-free DNP 9.4 T polarizer 20 , a 129-GHz dynamic nuclear polarizer in an ultra-wide bore superconducting magnet 21 , a Dynamic Nuclear Polarization
Chemistry: A European Journal, Mar 28, 2019
Signal amplification by reversible exchange (SABRE) with parahydrogen is a unique method to boost... more Signal amplification by reversible exchange (SABRE) with parahydrogen is a unique method to boost the NMR signal by several orders of magnitude. Many effects that govern SABRE were described before, or at least mentioned in the literature. A comprehensive model bringing together the separate pieces, however, was missing so far. This is what we did here. What prompted you to investigate this topic/problem? So far, seeing (or simulating) "the full picture" of SABRE was difficult. SABRE is complex! Many effects are intertwined, depending on each other in a non-linear way. Picking up the pieces, we came up with a single, comprehensive model, combining the linear and non-linear "chemical and physical" (CAP) effects that control SABRE. The CAP(tain) master equation was our rescue! We are particularly happy that the CAPtain is flexible with respect to the interactions and size of the spin system-it can be tailored to the problem at hand with (relative) ease!
Modern Manufacturing Enables Magnetic Field Cycling Experiments and Parahydrogen-Induced Hyperpolarization with a Benchtop NMR
Analytical Chemistry, Apr 5, 2023
Parawasserstoff‐induzierte Polarisation von Aminosäuren
Angewandte Chemie, Aug 13, 2021
Die Kernspinresonanz (NMR) hat sich zu einer universellen Methode für biochemische und biomedizin... more Die Kernspinresonanz (NMR) hat sich zu einer universellen Methode für biochemische und biomedizinische Studien, einschließlich Metabolomik, Proteomik und Magnetresonanztomographie (MRT), entwickelt. Durch die Vervielfachung des NMR‐Signals ausgewählter Moleküle hat die Kernspin‐Hyperpolarisation das Anwendungsspektrum von NMR und MRT bedeutsam erweitert (z. B. hyperpolarisierte Festkörper‐NMR und metabolische Bildgebung in vivo). Parawasserstoff (pH2) erlaubt es, Moleküle schnell und kostengünstig zu hyperpolarisieren. In diesem Gebiet wurden in den letzten zehn Jahren umfangreiche Fortschritte erzielt, einschließlich der Synthese neuer Tracer, Katalysatoren und Methoden für die Polarisationsübertragung. Das Portfolio an hyperpolarisierten Molekülen umfasst nunmehr Aminosäuren, die für viele Anwendungen von großem Interesse sind. In diesem Beitrag beleuchten wir die aktuelle Literatur zur Hyperpolarisation von Aminosäuren und Peptiden.
Coherent polarization transfer in chemically exchanging systems
Physical Chemistry Chemical Physics, 2020
Simulation of the interplay of coherent polarization transfer and chemical exchange described by ... more Simulation of the interplay of coherent polarization transfer and chemical exchange described by superoperators and Monte Carlo simulations alike.
Hyperpolarized (i.e., polarized far beyond the thermal equilibrium) nuclear spins can result in r... more Hyperpolarized (i.e., polarized far beyond the thermal equilibrium) nuclear spins can result in radiofrequency amplification by stimulated emission of radiation (RASER) effect. Here, we show the utility of RASER to amplify NMR signals of solute and solvent molecules in the liquid state. Specifically, parahydrogen-induced RASER was used to spontaneously enhance nuclear spin polarization of protons and heteronuclei (here 19 F and 31 P) in a wide range of molecules. The magnitude of the effect correlates with the T 1 relaxation time of the target nuclear spins. A series of control experiments validates the through-space dipolar mechanism of RASER-assisted polarization transfer between parahydrogen-polarized compound and to-be-hyperpolarized nuclei of the target molecule. Frequency-selective saturation of RASER-active resonances was used to control the RASER and the amplitude of spontaneous polarization transfer. Spin dynamics simulations support our experimental RASER studies.
Hyperpolarisierte 13C‑Magnetresonanztomographie – ein Fenster in den Stoffwechsel
Die Radiologie, May 20, 2022
Zero-to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is an emerging tool for precision ... more Zero-to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is an emerging tool for precision chemical analysis. In this work, we study dynamic processes and investigate the influence of chemical exchange on ZULF NMR J-spectra. We develop a computational approach that allows quantitative calculation of J-spectra in the presence of chemical exchange and apply it to study aqueous solutions of [ 15 N]ammonium ( 15 NH þ 4 ) as a model system. We show that pH-dependent chemical exchange substantially affects the J-spectra and, in some cases, can lead to degradation and complete disappearance of the spectral features. To demonstrate potential applications of ZULF NMR for chemistry and biomedicine, we show a ZULF NMR spectrum of [2-13 C]pyruvic acid hyperpolarized via dissolution dynamic nuclear polarization (dDNP). We foresee applications of affordable and scalable ZULF NMR coupled with hyperpolarization to study chemical exchange phenomena in vivo and in situations where high-field NMR detection is not possible to implement.
Frequency‐Selective Manipulations of Spins allow Effective and Robust Transfer of Spin Order from Parahydrogen to Heteronuclei in Weakly‐Coupled Spin Systems
ChemPhysChem, Dec 28, 2021
We present a selectively pulsed (SP) generation of sequences to transfer the spin order of parahy... more We present a selectively pulsed (SP) generation of sequences to transfer the spin order of parahydrogen (pH2) to heteronuclei in weakly coupled spin systems. We analyze and discuss the mechanism and efficiency of SP spin order transfer (SOT) and derive sequence parameters. These new sequences are most promising for the hyperpolarization of molecules at high magnetic fields. SP‐SOT is effective and robust despite the symmetry of the 1H‐13C J‐couplings even when precursor molecules are not completely labeled with deuterium. As only one broadband 1H pulse is needed per sequence, which can be replaced for instance by a frequency‐modulated pulse, lower radiofrequency (RF) power is required. This development will be useful to hyperpolarize (new) agents and to perform the hyperpolarization within the bore of an MRI system, where the limited RF power has been a persistent problem.
arXiv (Cornell University), Dec 13, 2021
It is well known that the association of parahydrogen (pH2) with an unsaturated molecule or a tra... more It is well known that the association of parahydrogen (pH2) with an unsaturated molecule or a transient metalorganic complex can enhance the intensity of NMR signals; the effect is known as parahydrogen-induced polarization (PHIP). During the last decades, numerous methods were proposed for converting pH2-derived nuclear spin order to the observable magnetization of protons or other nuclei of interest, usually 13 C or 15 N. Here, we analyze the constraints imposed by the topological symmetry of the spin systems on the amplitude of transferred polarization. In asymmetric systems, heteronuclei can be polarized to 100%. However, the amplitude drops to 75% in A2BX systems and further to 50% in A3B2X systems. The latter case is of primary importance for biological applications of PHIP using sidearm hydrogenation (PHIP-SAH). If the polarization is transferred to the same type of nuclei, i.e. 1 H, symmetry constraints impose significant boundaries on the spin-order distribution. For AB, A2B, A3B, A2B2, AA'(AA') systems, the maximum average polarization for each spin is 100%, 50%, 33.3%, 25%, and 0, respectively, when A and B (or A') came from pH2 We also discuss the effect of dipole-dipole induced pH2 spin-order distribution in heterogeneous catalysis or nematic liquid crystals. Practical examples from the literature illustrate our theoretical analysis.
Zero-to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is an emerging tool for precision ... more Zero-to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is an emerging tool for precision chemical analysis. In this work, we study dynamic processes and investigate the influence of chemical exchange on ZULF NMR J-spectra. We develop a computational approach that allows quantitative calculation of J-spectra in the presence of chemical exchange and apply it to study aqueous solutions of [ 15 N]ammonium ( 15 NH þ 4 ) as a model system. We show that pH-dependent chemical exchange substantially affects the J-spectra and, in some cases, can lead to degradation and complete disappearance of the spectral features. To demonstrate potential applications of ZULF NMR for chemistry and biomedicine, we show a ZULF NMR spectrum of [2-13 C]pyruvic acid hyperpolarized via dissolution dynamic nuclear polarization (dDNP). We foresee applications of affordable and scalable ZULF NMR coupled with hyperpolarization to study chemical exchange phenomena in vivo and in situations where high-field NMR detection is not possible to implement.
arXiv (Cornell University), Aug 29, 2023
In magnetic resonance, the bulk magnetization of a sample that is being measured is typically def... more In magnetic resonance, the bulk magnetization of a sample that is being measured is typically defined as a quantity proportional to spin polarization. The fact that all spins of the same type contribute equally to measurable signals is considered obvious. By focusing on nuclear spin ensembles, we prove the high-field theorem for a general case of spin-I: grouping of spins in molecules does not affect the total measurable NMR signal given thermal equilibrium at high field (ℏ𝛾𝐵 0 ≫ |𝐻 int |, where |𝐻 int | is the characteristic amplitude of internal spin-spin interactions). We demonstrate this first by analyzing equations for spin magnetization and then for a general case using the density matrix formalism. We exemplify the theorem implications by predicting NMR signal intensities for ensembles of molecules containing single, two, and three spins. The theorem is not applied in more intricate situations, such as zero-to ultralow-field conditions and far from thermodynamic equilibrium. Considering the populations of rotation levels, the thermal equilibrium polarization at HF and low temperature for H2 gas illustrate one of the intricate cases.
bioRxiv (Cold Spring Harbor Laboratory), May 11, 2023
Molecular hydrogen (H2) is considered an eco-friendly future energy-carrier and an alternative to... more Molecular hydrogen (H2) is considered an eco-friendly future energy-carrier and an alternative to fossil fuel 1 and thus, major efforts are directed towards identifying efficient and economical hydrogen catalysts. Efficient hydrogen catalysis is used by many microorganisms, some of them producing H2 from organic materials and others consuming it. To metabolize H2, these microorganisms use enzymes called hydrogenases. For the future development of efficient catalysts a detailed analysis of the catalytic mechanisms of such hydrogenases is required and existing analytical techniques could not provide a full understanding. 9 Consequently, new analytical technologies are of utmost importance to unravel natures' blueprints for highly efficient hydrogen catalysts. Here, we introduce signal-enhanced or hyperpolarized, nuclear magnetic resonance (NMR) to study hydrogenases under turnover conditions. So far undiscovered hydrogen species of the catalytic cycle of [Fe]-hydrogenases, are revealed and thus, extend the knowledge regarding this class of enzymes. These findings pave new pathways for the exploration of novel hydrogen metabolisms in vivo. We furthermore envision that the results contribute to the rational design of future catalysts to solve energy challenges of our society.
The hyperpolarization of nuclear spins has enabled unique applications in chemistry, biophysics, ... more The hyperpolarization of nuclear spins has enabled unique applications in chemistry, biophysics, and particularly in metabolic imaging. Parahydrogen-induced polarization (PHIP) offers a fast and cost-efficient way of hyperpolarization. Nevertheless, PHIP lags behind dynamic nuclear polarization (DNP), which is already being evaluated in clinical studies. This shortcoming is mainly due to problems in the synthesis of the corresponding PHIP precursor molecules. The most widely used DNP tracer in clinical studies, particularly for the detection of prostate cancer, is 1-13 C-pyruvate. The ideal derivative for PHIP is the deuterated vinyl ester because the spin physics allows for 100% polarization. Unfortunately, there is no efficient synthesis for vinyl esters of βketocarboxylic acids in general and pyruvate in particular. Here, we present an efficient new method for the preparation of vinyl esters, including 13 C labeled, fully deuterated vinyl pyruvate using a palladium catalyzed procedure. Using 50 % enriched parahydrogen and mild reaction conditions, a 13 C polarization of 12% was readily achieved; 36% are expected with 100% pH2. Higher polarization values can be potentially achieved with optimized reaction conditions.
ChemPhysChem, Feb 1, 2021
Parahydrogen (pH2) induced polarization (PHIP) is a unique method that is used in analytical chem... more Parahydrogen (pH2) induced polarization (PHIP) is a unique method that is used in analytical chemistry to elucidate catalytic hydrogenation pathways and to increase the signal of small metabolites in MRI. PHIP is based on adding or exchanging at least one pH2 molecule with a target molecule. And thus, the spin order available for hyperpolarization is often limited to that of one pH2 molecule. To break this limit, we investigated the addition of multiple pH2 molecules to one precursor. We studied the feasibility of the simultaneous hydrogenation of three arms of trivinyl orthoacetate (TVOA) intending to obtain hyperpolarized acetate. It was found that semihydrogenated TVOA underwent a fast decomposition accompanied by several minor reactions including an exchange of geminal methylene protons of a vinyl ester with pH2. The study shows that multiple vinyl ester groups are not suitable for a fast and clean (without any side products) hydrogenation and hyperpolarization that is desired in biochemical applications.
Journal of Magnetic Resonance, Dec 1, 2018
The hyperpolarization of nuclear spins using parahydrogen is an interesting effect that allows to... more The hyperpolarization of nuclear spins using parahydrogen is an interesting effect that allows to increase the magnetic resonance signal by several orders of magnitude. Known as ParaHydrogen And Synthesis Allow Dramatically Enhanced Nuclear Alignment (PASADENA) and ParaHydrogen Induced Polarization (PHIP), the method was successfully used for in vitro analysis and in vivo imaging. In this contribution, we investigated four known and four new sequence variants of Only Parahydrogen SpectroscopY (OPSY) [J. A. Aguilar et al, ChemComm, 2007] with respect to the selective preparation of hyperpolarized NMR signal and background suppression. Depending on the method chosen, either antiphase, in-phase or a mixture of both signals are obtained: anti-phase signals are beneficial to identify hyperpolarized signals and the structure or J-coupling constants; in-phase signals are useful for imaging applications or in conditions when the lines are broad. This comprehensive overview of sequences new and old facilitates selecting the right sequence for the task at hand.
ChemPhysChem, Feb 11, 2020
Analytical Chemistry, Oct 20, 2022
Hyperpolarized (i.e., polarized far beyond the thermal equilibrium) nuclear spins can result in r... more Hyperpolarized (i.e., polarized far beyond the thermal equilibrium) nuclear spins can result in radiofrequency amplification by stimulated emission of radiation (RASER) effect. Here, we show the utility of RASER to amplify NMR signals of solute and solvent molecules in the liquid state. Specifically, parahydrogen-induced RASER was used to spontaneously enhance nuclear spin polarization of protons and heteronuclei (here 19 F and 31 P) in a wide range of molecules. The magnitude of the effect correlates with the T 1 relaxation time of the target nuclear spins. A series of control experiments validates the through-space dipolar mechanism of RASER-assisted polarization transfer between parahydrogen-polarized compound and to-be-hyperpolarized nuclei of the target molecule. Frequency-selective saturation of RASER-active resonances was used to control the RASER and the amplitude of spontaneous polarization transfer. Spin dynamics simulations support our experimental RASER studies.
PLOS ONE, Oct 1, 2020
Magnetic resonance spectroscopy (MRS) allows the analysis of biochemical processes non-invasively... more Magnetic resonance spectroscopy (MRS) allows the analysis of biochemical processes non-invasively and in vivo. Still, its application in clinical diagnostics is rare. Routine MRS is limited to spatial, chemical and temporal resolutions of cubic centimetres, mM and minutes. In fact, the signal of many metabolites is strong enough for detection, but the resonances significantly overlap, exacerbating identification and quantification. Besides, the signals of water and lipids are much stronger and dominate the entire spectrum. To suppress the background and isolate selected signals, usually, relaxation times, J-coupling and chemical shifts are used. Here, we propose methods to isolate the signals of selected molecular groups within endogenous metabolites by using long-lived spin states (LLS). We exemplify the method by preparing the LLSs of coupled protons in the endogenous molecules N-acetyl-L-aspartic acid (NAA). First, we store polarization in long-lived, double spin states, followed by saturation pulses before the spin order is converted back to observable magnetization or double quantum filters to suppress background signals. We show that LLS and zero-quantum coherences can be used to selectively prepare and measure the signals of chosen metabolites or drugs in the presence of water, inhomogeneous field and highly concentrated fatty solutions. The strong suppression of unwanted signals achieved allowed us to measure pH as a function of chemical shift difference.
Lifetime of Para hydrogen in Aqueous Solutions and Human Blood
ChemPhysChem, Sep 12, 2019
Molecular hydrogen has unique nuclear spin properties. Its nuclear spin isomer, parahydrogen (pH2... more Molecular hydrogen has unique nuclear spin properties. Its nuclear spin isomer, parahydrogen (pH2), was instrumental in the early days of quantum mechanics and allows to boost the NMR signal by several orders of magnitude. pH2‐induced polarization (PHIP) is based on the survival of pH2 spin order in solution, yet its lifetime has not been investigated in aqueous or biological media required for in vivo applications. Herein, we report longitudinal relaxation times (T1) and lifetimes of pH2 ( ) in methanol and water, with or without O2, NaCl, rhodium‐catalyst or human blood. Furthermore, we present a relaxation model that uses T1 and for more precise theoretical predictions of the H2 spin state in PHIP experiments. All measured T1 values were in the range of 1.4–2 s and values were of the order of 10–300 minutes. These relatively long lifetimes hold great promise for emerging in vivo implementations and applications of PHIP.
Scientific Reports, Jul 8, 2022
The setup, operational procedures and performance of a cryogen-free device for producing hyperpol... more The setup, operational procedures and performance of a cryogen-free device for producing hyperpolarized contrast agents using dissolution dynamic nuclear polarization (dDNP) in a preclinical imaging center is described. The polarization was optimized using the solid-state, DNP-enhanced NMR signal to calibrate the sample position, microwave and NMR frequency and power and flip angle. The polarization of a standard formulation to yield ~ 4 mL, 60 mM 1-13 C-pyruvic acid in an aqueous solution was quantified in five experiments to P(13 C) = (38 ± 6) % (19 ± 1) s after dissolution. The monoexponential time constant of the build-up of the solid-state polarization was quantified to (1032 ± 22) s. We achieved a duty cycle of 1.5 h that includes sample loading, monitoring the polarization build-up, dissolution and preparation for the next run. After injection of the contrast agent in vivo, pyruvate, pyruvate hydrate, lactate, and alanine were observed, by measuring metabolite maps. Based on this work sequence, hyperpolarized 15 N urea was obtained (P(15 N) = (5.6 ± 0.8) % (30 ± 3) s after dissolution). Magnetic Resonance Imaging (MRI) has revolutionized modern diagnostics by providing high resolution anatomical and functional imaging in 3D without ionizing radiation 1,2. Many of the biochemical processes in vivo, however, still elapse our best efforts, and accessing these remains a prime objective of much research. Here, hyperpolarized contrast agents hold great promise as they provide a unique window into metabolism, non-invasively and in vivo. By boosting the signal of selected, often endogenous molecules, their fate can be followed-for a limited time-with high spatial and chemical resolution. These properties have allowed the identification of cancerous tissue before a tumor was apparent, and has helped monitoring treatment response. Dissolution dynamic nuclear polarization (dDNP) 3 is the most established technique for hyperpolarizing (HP) biomolecules for in vivo imaging, and it shares the applicability to humans 4,5 only with hyperpolarized Xenon 6. Other HP techniques include brute-force 7 , parahydrogen-induced polarization 8 , chemically induced dynamic nuclear polarization 9 and, for noble gases, spin-exchange optical pumping 10,11. dDNP has allowed to polarize biomolecules to more than 50% in about 1 h 12,13. The nuclear polarization of the target is achieved by polarizing electronic spin first, using low temperatures (≈ 1.4 K) and high magnetic fields (≈ 6.7 T). Then, the electron polarization is transferred to nuclear polarization using the interactions between the electronic and nuclear spin under the action of electromagnetic waves, transmitted at a frequency corresponding to the difference in Larmor frequency of the two electron spins involved 14. The unpaired electron spins are added in the form of stable radicals: TEMPO 15 , TEMPOL, or trityl radicals 16,17 or induced by UV radiation 18. In addition, there are other types of sample formulations, for instance HYPOP 19. When the desired level of nuclear spin polarization is achieved, the frozen sample is rapidly melted, dissolved and ejected from the polarizer by pressurized overheated water, such that an injectable contrast agent results. Overall, dDNP is a complex process combining nuclear magnetic resonance (NMR) electron spin resonance (ESR), radical chemistry, high magnetic fields, fast dissolution, and cryogenictemperatures. Making this process available for biomedical research routinely is not straight forward. Over the last decades, several experimental implementations of dDNP were presented such as a cryogen-consumption-free DNP 9.4 T polarizer 20 , a 129-GHz dynamic nuclear polarizer in an ultra-wide bore superconducting magnet 21 , a Dynamic Nuclear Polarization
Chemistry: A European Journal, Mar 28, 2019
Signal amplification by reversible exchange (SABRE) with parahydrogen is a unique method to boost... more Signal amplification by reversible exchange (SABRE) with parahydrogen is a unique method to boost the NMR signal by several orders of magnitude. Many effects that govern SABRE were described before, or at least mentioned in the literature. A comprehensive model bringing together the separate pieces, however, was missing so far. This is what we did here. What prompted you to investigate this topic/problem? So far, seeing (or simulating) "the full picture" of SABRE was difficult. SABRE is complex! Many effects are intertwined, depending on each other in a non-linear way. Picking up the pieces, we came up with a single, comprehensive model, combining the linear and non-linear "chemical and physical" (CAP) effects that control SABRE. The CAP(tain) master equation was our rescue! We are particularly happy that the CAPtain is flexible with respect to the interactions and size of the spin system-it can be tailored to the problem at hand with (relative) ease!
Modern Manufacturing Enables Magnetic Field Cycling Experiments and Parahydrogen-Induced Hyperpolarization with a Benchtop NMR
Analytical Chemistry, Apr 5, 2023
Parawasserstoff‐induzierte Polarisation von Aminosäuren
Angewandte Chemie, Aug 13, 2021
Die Kernspinresonanz (NMR) hat sich zu einer universellen Methode für biochemische und biomedizin... more Die Kernspinresonanz (NMR) hat sich zu einer universellen Methode für biochemische und biomedizinische Studien, einschließlich Metabolomik, Proteomik und Magnetresonanztomographie (MRT), entwickelt. Durch die Vervielfachung des NMR‐Signals ausgewählter Moleküle hat die Kernspin‐Hyperpolarisation das Anwendungsspektrum von NMR und MRT bedeutsam erweitert (z. B. hyperpolarisierte Festkörper‐NMR und metabolische Bildgebung in vivo). Parawasserstoff (pH2) erlaubt es, Moleküle schnell und kostengünstig zu hyperpolarisieren. In diesem Gebiet wurden in den letzten zehn Jahren umfangreiche Fortschritte erzielt, einschließlich der Synthese neuer Tracer, Katalysatoren und Methoden für die Polarisationsübertragung. Das Portfolio an hyperpolarisierten Molekülen umfasst nunmehr Aminosäuren, die für viele Anwendungen von großem Interesse sind. In diesem Beitrag beleuchten wir die aktuelle Literatur zur Hyperpolarisation von Aminosäuren und Peptiden.
Coherent polarization transfer in chemically exchanging systems
Physical Chemistry Chemical Physics, 2020
Simulation of the interplay of coherent polarization transfer and chemical exchange described by ... more Simulation of the interplay of coherent polarization transfer and chemical exchange described by superoperators and Monte Carlo simulations alike.
Hyperpolarized (i.e., polarized far beyond the thermal equilibrium) nuclear spins can result in r... more Hyperpolarized (i.e., polarized far beyond the thermal equilibrium) nuclear spins can result in radiofrequency amplification by stimulated emission of radiation (RASER) effect. Here, we show the utility of RASER to amplify NMR signals of solute and solvent molecules in the liquid state. Specifically, parahydrogen-induced RASER was used to spontaneously enhance nuclear spin polarization of protons and heteronuclei (here 19 F and 31 P) in a wide range of molecules. The magnitude of the effect correlates with the T 1 relaxation time of the target nuclear spins. A series of control experiments validates the through-space dipolar mechanism of RASER-assisted polarization transfer between parahydrogen-polarized compound and to-be-hyperpolarized nuclei of the target molecule. Frequency-selective saturation of RASER-active resonances was used to control the RASER and the amplitude of spontaneous polarization transfer. Spin dynamics simulations support our experimental RASER studies.
Hyperpolarisierte 13C‑Magnetresonanztomographie – ein Fenster in den Stoffwechsel
Die Radiologie, May 20, 2022
Zero-to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is an emerging tool for precision ... more Zero-to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is an emerging tool for precision chemical analysis. In this work, we study dynamic processes and investigate the influence of chemical exchange on ZULF NMR J-spectra. We develop a computational approach that allows quantitative calculation of J-spectra in the presence of chemical exchange and apply it to study aqueous solutions of [ 15 N]ammonium ( 15 NH þ 4 ) as a model system. We show that pH-dependent chemical exchange substantially affects the J-spectra and, in some cases, can lead to degradation and complete disappearance of the spectral features. To demonstrate potential applications of ZULF NMR for chemistry and biomedicine, we show a ZULF NMR spectrum of [2-13 C]pyruvic acid hyperpolarized via dissolution dynamic nuclear polarization (dDNP). We foresee applications of affordable and scalable ZULF NMR coupled with hyperpolarization to study chemical exchange phenomena in vivo and in situations where high-field NMR detection is not possible to implement.
Frequency‐Selective Manipulations of Spins allow Effective and Robust Transfer of Spin Order from Parahydrogen to Heteronuclei in Weakly‐Coupled Spin Systems
ChemPhysChem, Dec 28, 2021
We present a selectively pulsed (SP) generation of sequences to transfer the spin order of parahy... more We present a selectively pulsed (SP) generation of sequences to transfer the spin order of parahydrogen (pH2) to heteronuclei in weakly coupled spin systems. We analyze and discuss the mechanism and efficiency of SP spin order transfer (SOT) and derive sequence parameters. These new sequences are most promising for the hyperpolarization of molecules at high magnetic fields. SP‐SOT is effective and robust despite the symmetry of the 1H‐13C J‐couplings even when precursor molecules are not completely labeled with deuterium. As only one broadband 1H pulse is needed per sequence, which can be replaced for instance by a frequency‐modulated pulse, lower radiofrequency (RF) power is required. This development will be useful to hyperpolarize (new) agents and to perform the hyperpolarization within the bore of an MRI system, where the limited RF power has been a persistent problem.