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Real-Time High-Sensitivity Reaction Monitoring of Important Nitrogen-Cycle Synthons by 15N Hyperpolarized Nuclear Magnetic Resonance. J Am Chem Soc 2022; 144:8756-8769. [PMID: 35508182 PMCID: PMC9121385 DOI: 10.1021/jacs.2c02619] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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Here, we show how
signal amplification by reversible exchange hyperpolarization
of a range of 15N-containing synthons can be used to enable
studies of their reactivity by 15N nuclear magnetic resonance
(NO2– (28% polarization), ND3 (3%), PhCH2NH2 (5%), NaN3 (3%),
and NO3– (0.1%)). A range of iridium-based
spin-polarization transfer catalysts are used, which for NO2– work optimally as an amino-derived carbene-containing
complex with a DMAP-d2 coligand. We harness
long 15N spin-order lifetimes to probe in situ reactivity
out to 3 × T1. In the case of NO2– (T1 17.7 s
at 9.4 T), we monitor PhNH2 diazotization in acidic solution.
The resulting diazonium salt (15N-T1 38 s) forms within 30 s, and its subsequent reaction with
NaN3 leads to the detection of hyperpolarized PhN3 (T1 192 s) in a second step via the
formation of an identified cyclic pentazole intermediate. The role
of PhN3 and NaN3 in copper-free click chemistry
is exemplified for hyperpolarized triazole (T1 < 10 s) formation when they react with a strained alkyne.
We also demonstrate simple routes to hyperpolarized N2 in
addition to showing how utilization of 15N-polarized PhCH2NH2 enables the probing of amidation, sulfonamidation,
and imine formation. Hyperpolarized ND3 is used to probe
imine and ND4+ (T1 33.6 s) formation. Furthermore, for NO2–, we also demonstrate how the 15N-magnetic resonance imaging
monitoring of biphasic catalysis confirms the successful preparation
of an aqueous bolus of hyperpolarized 15NO2– in seconds with 8% polarization. Hence, we create
a versatile tool to probe organic transformations that has significant
relevance for the synthesis of future hyperpolarized pharmaceuticals.
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Contrasting Photochemical and Thermal Catalysis by Ruthenium Arsine Complexes Revealed by Parahydrogen Enhanced NMR Spectroscopy. Eur J Inorg Chem 2022. [DOI: 10.1002/ejic.202100991] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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3
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Zintl cluster supported low coordinate Rh( i) centers for catalytic H/D exchange between H 2 and D 2. Chem Sci 2022; 13:7626-7633. [PMID: 35872810 PMCID: PMC9242017 DOI: 10.1039/d2sc02552c] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2022] [Accepted: 06/08/2022] [Indexed: 12/19/2022] Open
Abstract
We describe the synthesis of the coordinatively unsaturated Zintl clusters [Rh(L){η3-Ge9(Hyp)3}] (where L = PMe3, PPh3, IMe4 or [W(Cp)2H2]). These species are active catalysts in H/D exchange and C–H bond activation reactions.
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SABRE-enhanced real-time pure shift NMR spectroscopy. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2021; 59:1244-1252. [PMID: 34405451 DOI: 10.1002/mrc.5206] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Revised: 08/04/2021] [Accepted: 08/12/2021] [Indexed: 06/13/2023]
Abstract
Pure shift nuclear magnetic resonance (NMR) methods suppress the effect of homonuclear scalar couplings to produce NMR spectra consisting solely of a single signal for each chemically distinct site. They are increasingly relied upon for analysis of complex molecules and mixtures as they overcome the extensive signal overlap that complicates proton NMR spectra of all but the simplest species. Current broadband pure shift methodologies for 1D proton spectra suffer from reduced sensitivity compared with their conventional counterparts and typically require a large amount of instrument time for low concentration samples. In this study, we demonstrate how the sensitivity limitation may be overcome by transiently increasing the bulk polarization using signal amplification by reversible exchange (SABRE) hyperpolarization. We utilize para-enriched dihydrogen to enhance the pure shift NMR resonances of pyridine by up to a factor of 60 in a single-scan experiment and extend this to propose a method to unambiguously determine mixture components based on the enhancement of their pure shift NMR signals.
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Benchtop NMR analysis of piperazine-based drugs hyperpolarised by SABRE. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2020; 58:1151-1159. [PMID: 31945193 DOI: 10.1002/mrc.4999] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2019] [Revised: 01/09/2020] [Accepted: 01/14/2020] [Indexed: 06/10/2023]
Abstract
Piperazine-based drugs, such as N-benzylpiperazine (BZP), became attractive in the 2000s due to possessing effects similar to amphetamines. Herein, BZP, in addition to its pyridyl analogues, 2-, 3-, and 4-pyridylmethylpiperidine (2-PMP, 3-PMP, and 4-PMP respectively) was subjected to the hyperpolarisation technique Signal Amplification By Reversible Exchange (SABRE) in order to demonstrate the use of this technique to detect these piperazine-based drugs. Although BZP was not hyperpolarised via SABRE, 2-PMP, 3-PMP, and 4-PMP were, with the ortho- and meta-pyridyl protons of 4-PMP showing the largest enhancement of 313-fold and 267-fold, respectively, in a 1.4-T detection field, following polarisation transfer at Earth's magnetic field. In addition to the freebase, 4-PMP.3HCl was also appraised by SABRE and was found not to polarise, however, the addition of increasing equivalents of triethylamine (TEA) produced the freebase, with a maximum enhancement observed upon the addition of 3 equivalents of TEA. Further addition of TEA led to a reduction in the observed enhancement. SABRE was also employed to polarise 4-PMP.3HCl (~20% w/w) in a simulated tablet to demonstrate the forensic application of the technique (138-fold enhancement for the ortho-pyridyl protons). The amount of 4-PMP.3HCl present in the simulated tablet was quantified via NMR using D2 O as a solvent and compared well to complimentary gas chromatography-mass spectrometry data. Exchanging D2 O for CD3 OD as the solvent utilised for analysis resulted in a significantly lower amount of 4-PMP.3HCl being determined, thus highlighting safeguarding issues linked to drug abuse in relation to determining the amount of active pharmaceutical ingredient present.
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Spatially resolved NMR spectroscopy of heterogeneous gas phase hydrogenation of 1,3-butadiene with parahydrogen. Catal Sci Technol 2020. [DOI: 10.1039/c9cy02100k] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Glass tube reactors with Pd, Pt, Rh or Ir nanoparticles dispersed on a thin layer of TiO2, CeO2, SiO2 or Al2O3 provided mechanistic insight into the hydrogenation of 1,3-butadiene using parahydrogen.
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Quantitative In Situ Monitoring of Parahydrogen Fraction Using Raman Spectroscopy. APPLIED SPECTROSCOPY 2019; 73:88-97. [PMID: 30203662 DOI: 10.1177/0003702818798644] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Raman spectroscopy has been used to provide a rapid, noninvasive, and nondestructive quantification method for determining the parahydrogen fraction of hydrogen gas. The basis of the method is the measurement of the ratio of the first two rotational bands of hydrogen at 355 cm-1 and 586 cm-1 corresponding to parahydrogen and orthohydrogen, respectively. The method has been used to determine the parahydrogen content during a production process and a reaction. In the first example, the performance of an in-house liquid nitrogen cooled parahydrogen generator was monitored both at-line and on-line. The Raman measurements showed that it took several hours for the generator to reach steady state and, hence, for maximum parahydrogen production (50%) to be reached. The results obtained using Raman spectroscopy were compared to those obtained by at-line low-field nuclear magnetic resonance (NMR) spectroscopy. While the results were in good agreement, Raman analysis has several advantages over NMR for this application. The Raman method does not require a reference sample, as both spin isomers (ortho and para) of hydrogen can be directly detected, which simplifies the procedure and eliminates some sources of error. In the second example, the method was used to monitor the fast conversion of parahydrogen to orthohydrogen in situ. Here the ability to acquire Raman spectra every 30 s enabled a conversion process with a rate constant of 27.4×10-4 s-1 to be monitored. The Raman method described here represents an improvement on previously reported work, in that it can be easily applied on-line and is approximately 500 times faster. This offers the potential of an industrially compatible method for determining parahydrogen content in applications that require the storage and usage of hydrogen.
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Mechanistic Insight into the Heterogeneous Hydrogenation of Furan Derivatives with the use of Parahydrogen. ChemCatChem 2018. [DOI: 10.1002/cctc.201701653] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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9
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High-resolution hyperpolarized in vivo metabolic 13C spectroscopy at low magnetic field (48.7mT) following murine tail-vein injection. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 281:246-252. [PMID: 28651245 PMCID: PMC5544012 DOI: 10.1016/j.jmr.2017.06.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Revised: 06/12/2017] [Accepted: 06/14/2017] [Indexed: 05/20/2023]
Abstract
High-resolution 13C NMR spectroscopy of hyperpolarized succinate-1-13C-2,3-d2 is reported in vitro and in vivo using a clinical-scale, biplanar (80cm-gap) 48.7mT permanent magnet with a high homogeneity magnetic field. Non-localized 13C NMR spectra were recorded at 0.52MHz resonance frequency over the torso of a tumor-bearing mouse every 2s. Hyperpolarized 13C NMR signals with linewidths of ∼3Hz (corresponding to ∼6ppm) were recorded in vitro (2mL in a syringe) and in vivo (over a mouse torso). Comparison of the full width at half maximum (FWHM) for 13C NMR spectra acquired at 48.7mT and at 4.7T in a small-animal MRI scanner demonstrates a factor of ∼12 improvement for the 13C resonance linewidth attainable at 48.7mT compared to that at 4.7T in vitro. 13C hyperpolarized succinate-1-13C resonance linewidths in vivo are at least one order of magnitude narrower at 48.7mT compared to those observed in high-field (≥3T) studies employing HP contrast agents. The demonstrated high-resolution 13C in vivo spectroscopy could be useful for high-sensitivity spectroscopic studies involving monitoring HP agent uptake or detecting metabolism using HP contrast agents with sufficiently large 13C chemical shift differences.
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The effect of oxidative and reductive treatments of titania-supported metal catalysts on the pairwise hydrogen addition to unsaturated hydrocarbons. Catal Today 2017. [DOI: 10.1016/j.cattod.2016.02.030] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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11
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Parahydrogen enhanced NMR reveals correlations in selective hydrogenation of triple bonds over supported Pt catalyst. Phys Chem Chem Phys 2015; 17:26121-9. [PMID: 26376759 DOI: 10.1039/c5cp04223b] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Parahydrogen induced polarization using heterogeneous catalysis can produce impurity-free hyperpolarized gases and liquids, but the comparatively low signal enhancements and limited scope of substrates that can be polarized pose significant challenges to this approach. This study explores the surface processes affecting the disposition of the bilinear spin order derived from parahydrogen in the hydrogenation of propyne over TiO2-supported Pt nanoparticles. The hyperpolarized adducts formed at low magnetic field are adiabatically transported to high field for analysis by proton NMR spectroscopy at 400 MHz. For the first time, the stereoselectivity of pairwise addition to propyne is measured as a function of reaction conditions. The correlation between partial reduction selectivity and stereoselectivity of pairwise addition is revealed. The systematic trends are rationalized in terms of a hybrid mechanism incorporating non-traditional concerted addition steps and well-established reversible step-wise addition involving the formation of a surface bound 2-propyl intermediate.
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12
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A Mechanistic Study of Thiophene Hydrodesulfurization by the Parahydrogen-Induced Polarization Technique. ChemCatChem 2015. [DOI: 10.1002/cctc.201500691] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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13
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Production of Catalyst-Free Hyperpolarised Ethanol Aqueous Solution via Heterogeneous Hydrogenation with Parahydrogen. Sci Rep 2015; 5:13930. [PMID: 26349543 PMCID: PMC4642547 DOI: 10.1038/srep13930] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Accepted: 08/12/2015] [Indexed: 01/02/2023] Open
Abstract
An experimental approach for the production of catalyst-free hyperpolarised ethanol solution in water via heterogeneous hydrogenation of vinyl acetate with parahydrogen and the subsequent hydrolysis of ethyl acetate was demonstrated. For an efficient hydrogenation, liquid vinyl acetate was transferred to the gas phase by parahydrogen bubbling and almost completely converted to ethyl acetate with Rh/TiO2 catalyst. Subsequent dissolution of ethyl acetate gas in water containing OH(-) ions led to the formation of catalyst- and organic solvent-free hyperpolarised ethanol and sodium acetate. These results represent the first demonstration of catalyst- and organic solvent-free hyperpolarised ethanol production achieved by heterogeneous hydrogenation of vinyl acetate vapour with parahydrogen and the subsequent ethyl acetate hydrolysis.
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Shaped Ceria Nanocrystals Catalyze Efficient and Selective Para-Hydrogen-Enhanced Polarization. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201506045] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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15
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Shaped Ceria Nanocrystals Catalyze Efficient and Selective Para‐Hydrogen‐Enhanced Polarization. Angew Chem Int Ed Engl 2015; 54:14270-5. [DOI: 10.1002/anie.201506045] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2015] [Indexed: 11/08/2022]
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16
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Investigating pyridazine and phthalazine exchange in a series of iridium complexes in order to define their role in the catalytic transfer of magnetisation from para-hydrogen. Chem Sci 2015; 6:3981-3993. [PMID: 29218168 PMCID: PMC5707471 DOI: 10.1039/c5sc00756a] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Accepted: 04/27/2015] [Indexed: 11/22/2022] Open
Abstract
Reaction of [Ir(IMes)(COD)Cl] with pyridazine (pdz) or phthalazine (phth) and H2 results in the formation of the para-hydrogen magnetisation transfer catalysts [Ir(H)2(IMes)(pdz)3]Cl and [Ir(H)2(IMes)(phth)3]Cl.
The reaction of [Ir(IMes)(COD)Cl], [IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, COD = 1,5-cyclooctadiene] with pyridazine (pdz) and phthalazine (phth) results in the formation of [Ir(COD)(IMes)(pdz)]Cl and [Ir(COD)(IMes)(phth)]Cl. These two complexes are shown by nuclear magnetic resonance (NMR) studies to undergo a haptotropic shift which interchanges pairs of protons within the bound ligands. When these complexes are exposed to hydrogen, they react to form [Ir(H)2(COD)(IMes)(pdz)]Cl and [Ir(H)2(COD)(IMes)(phth)]Cl, respectively, which ultimately convert to [Ir(H)2(IMes)(pdz)3]Cl and [Ir(H)2(IMes)(phth)3]Cl, as the COD is hydrogenated to form cyclooctane. These two dihydride complexes are shown, by NMR, to undergo both full N-heterocycle dissociation and a haptotropic shift, the rates of which are affected by both steric interactions and free ligand pKa values. The use of these complexes as catalysts in the transfer of polarisation from para-hydrogen to pyridazine and phthalazine via signal amplification by reversible exchange (SABRE) is explored. The possible future use of drugs which contain pyridazine and phthalazine motifs as in vivo or clinical magnetic resonance imaging probes is demonstrated; a range of NMR and phantom-based MRI measurements are reported.
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Single-atom gold catalysis in the context of developments in parahydrogen-induced polarization. Chemistry 2015; 21:7012-5. [PMID: 25754067 DOI: 10.1002/chem.201406664] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2014] [Indexed: 01/04/2023]
Abstract
A highly isolated monoatomic gold catalyst, with single gold atoms dispersed on multiwalled carbon nanotubes (MWCNTs), has been synthesized, characterized, and tested in heterogeneous hydrogenation of 1,3-butadiene and 1-butyne with parahydrogen to maximize the polarization level and the contribution of the pairwise hydrogen addition route. The Au/MWCNTs catalyst was found to be active and efficient in pairwise hydrogen addition and the estimated contributions from the pairwise hydrogen addition route are at least an order of magnitude higher than those for supported metal nanoparticle catalysts. Therefore, the use of the highly isolated monoatomic catalysts is very promising for production of hyperpolarized fluids that can be used for the significant enhancement of NMR signals. A mechanism of 1,3-butadiene hydrogenation with parahydrogen over the highly isolated monoatomic Au/MWCNTs catalyst is also proposed.
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Parahydrogen-Induced Polarization by Pairwise Replacement Catalysis on Pt and Ir Nanoparticles. J Am Chem Soc 2015; 137:1938-46. [DOI: 10.1021/ja511476n] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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19
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Probing signal amplification by reversible exchange using an NMR flow system. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2014; 52:358-69. [PMID: 24801201 PMCID: PMC4190690 DOI: 10.1002/mrc.4073] [Citation(s) in RCA: 75] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Revised: 02/21/2014] [Accepted: 03/20/2014] [Indexed: 05/16/2023]
Abstract
Hyperpolarization methods are used in NMR to overcome its inherent sensitivity problem. Herein, the biologically relevant target nicotinamide is polarized by the hyperpolarization technique signal amplification by reversible exchange. We illustrate how the polarization transfer field, and the concentrations of parahydrogen, the polarization-transfer-catalyst and substrate can be used to maximize signal amplification by reversible exchange effectiveness by reference to the first-order spin system of this target. The catalyst is shown to be crucial in this process, first by facilitating the transfer of hyperpolarization from parahydrogen to nicotinamide and then by depleting the resulting polarized states through further interaction. The 15 longitudinal one, two, three and four spin order terms produced are rigorously identified and quantified using an automated flow apparatus in conjunction with NMR pulse sequences based on the only parahydrogen spectroscopy protocol. The rates of build-up of these terms were shown to follow the order four~three > two > single spin; this order parallels their rates of relaxation. The result of these competing effects is that the less-efficiently formed single-spin order terms dominate at the point of measurement with the two-spin terms having amplitudes that are an order of magnitude lower. We also complete further measurements to demonstrate that (13)C NMR spectra can be readily collected where the long-lived quaternary (13)C signals appear with significant intensity. These are improved upon by using INEPT. In summary, we dissect the complexity of this method, highlighting its benefits to the NMR community and its applicability for high-sensitivity magnetic resonance imaging detection in the future.
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Demonstration of heterogeneous parahydrogen induced polarization using hyperpolarized agent migration from dissolved Rh(I) complex to gas phase. Anal Chem 2014; 86:6192-6. [PMID: 24918975 PMCID: PMC4079322 DOI: 10.1021/ac5013859] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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Parahydrogen-induced polarization
(PHIP) was used to demonstrate
the concept that highly polarized, catalyst-free fluids can be obtained
in a catalysis-free regime using a chemical reaction with molecular
addition of parahydrogen to a water-soluble Rh(I) complex carrying
a payload of compound with unsaturated (C=C) bonds. Hydrogenation
of norbornadiene leads to formation of norbornene, which is eliminated
from the Rh(I) complex and, therefore, leaves the aqueous phase and
becomes a gaseous hyperpolarized molecule. The Rh(I) metal complex
resides in the original liquid phase, while the product of hydrogen
addition is found exclusively in the gaseous phase based on the affinity.
Hyperpolarized norbornene 1H NMR signals observed in situ were enhanced by a factor of approximately 10 000
at a static field of 47.5 mT. High-resolution 1H NMR at
a field of 9.4 T was used for ex situ detection of
hyperpolarized norbornene in the gaseous phase, where a signal enhancement
factor of approximately 160 was observed. This concept of stoichiometric
as opposed to purely catalytic use of PHIP-available complexes with
an unsaturated payload precursor molecule can be extended to other
contrast agents for both homogeneous and heterogeneous PHIP. The Rh(I)
complex was employed in aqueous medium suitable for production of
hyperpolarized contrast agents for biomedical use. Detection of PHIP
hyperpolarized gas by low-field NMR is demonstrated here for the first
time.
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Evaluation of the Mechanism of Heterogeneous Hydrogenation of α,β-Unsaturated Carbonyl Compounds via Pairwise Hydrogen Addition. ACS Catal 2014. [DOI: 10.1021/cs500426a] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Low-field permanent magnets for industrial process and quality control. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2014; 76:1-60. [PMID: 24360243 DOI: 10.1016/j.pnmrs.2013.09.001] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Revised: 09/19/2013] [Accepted: 09/19/2013] [Indexed: 05/13/2023]
Abstract
In this review we focus on the technology associated with low-field NMR. We present the current state-of-the-art in low-field NMR hardware and experiments, considering general magnet designs, rf performance, data processing and interpretation. We provide guidance on obtaining the optimum results from these instruments, along with an introduction for those new to low-field NMR. The applications of lowfield NMR are now many and diverse. Furthermore, niche applications have spawned unique magnet designs to accommodate the extremes of operating environment or sample geometry. Trying to capture all the applications, methods, and hardware encompassed by low-field NMR would be a daunting task and likely of little interest to researchers or industrialists working in specific subject areas. Instead we discuss only a few applications to highlight uses of the hardware and experiments in an industrial environment. For details on more particular methods and applications, we provide citations to specialized review articles.
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Abstract
Ir(COD)(NHC)Cl complexes provide significant insight into the catalytic processes underpinning SABRE hyperpolarization.
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Para-hydrogen perspectives in hyperpolarized NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 235:130-142. [PMID: 23932399 DOI: 10.1016/j.jmr.2013.07.010] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Revised: 07/11/2013] [Accepted: 07/15/2013] [Indexed: 06/02/2023]
Abstract
The first instance of para-hydrogen induced polarization (PHIP) in an NMR experiment was serendipitously observed in the 1980s while investigating a hydrogenation reaction (Seldler et al., 1983; Bowers and Weitekamp, 1986, 1987; Eisenschmid et al., 1987) [1-4]. Remarkably a theoretical investigation of the applicability of para-hydrogen as a hyperpolarization agent was being performed in the 1980's thereby quickly providing a theoretical basis for the PHIP-effect (Bowers and Weitekamp, 1986) [2]. The discovery of signal amplification by a non-hydrogenating interaction with para-hydrogen has recently extended the interest to exploit the PHIP effect, as it enables investigation of compounds without structural alteration while retaining the advantages of spectroscopy with hyperpolarized compounds [5]. In this article we will place more emphasis of the future applications of the method while only briefly discussing the efforts that have been made in the understanding of the phenomenon and the development of the method so far.
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Nuclear spin isomers of guest molecules in H₂@C₆₀, H₂O@C₆₀ and other endofullerenes. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2013; 371:20110628. [PMID: 23918710 DOI: 10.1098/rsta.2011.0628] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Spectroscopic studies of recently synthesized endofullerenes, in which H₂, H₂O and other atoms and small molecules are trapped in cages of carbon atoms, have shown that although the trapped molecules interact relatively weakly with the internal environment they are nevertheless susceptible to appropriately applied external perturbations. These properties have been exploited to isolate and study samples of H₂ in C₆₀ and other fullerenes that are highly enriched in the para spin isomer. Several strategies for spin-isomer enrichment, potential extensions to other endofullerenes and possible applications of these materials are discussed.
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The theory and practice of hyperpolarization in magnetic resonance using parahydrogen. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2012; 67:1-48. [PMID: 23101588 DOI: 10.1016/j.pnmrs.2012.03.001] [Citation(s) in RCA: 253] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2012] [Accepted: 03/05/2012] [Indexed: 05/03/2023]
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Conversion of parahydrogen induced longitudinal two-spin order to evenly distributed single spin polarisation by optimal control pulse sequences. J Chem Phys 2012; 136:094201. [DOI: 10.1063/1.3691193] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Abstract
Parahydrogen-induced polarization of nuclear spins provides enhancements of NMR signals for various nuclei of up to four to five orders of magnitude in magnetic fields of modern NMR spectrometers and even higher enhancements in low and ultra-low magnetic fields. It is based on the use of parahydrogen in catalytic hydrogenation reactions which, upon pairwise addition of the two H atoms of parahydrogen, can strongly enhance the NMR signals of reaction intermediates and products in solution. A recent advance in this field is the demonstration that PHIP can be observed not only in homogeneous hydrogenations but also in heterogeneous catalytic reactions. The use of heterogeneous catalysts for generating PHIP provides a number of significant advantages over the homogeneous processes, including the possibility to produce hyperpolarized gases, better control over the hydrogenation process, and the ease of separation of hyperpolarized fluids from the catalyst. The latter advantage is of paramount importance in light of the recent tendency toward utilization of hyperpolarized substances in in vivo spectroscopic and imaging applications of NMR. In addition, PHIP demonstrates the potential to become a useful tool for studying mechanisms of heterogeneous catalytic processes and for in situ studies of operating catalytic reactors. Here, the known examples of PHIP observations in heterogeneous reactions over immobilized transition metal complexes, supported metals, and some other types of heterogeneous catalysts are discussed and the applications of the technique for hypersensitive NMR imaging studies are presented.
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Process and reaction monitoring by low-field NMR spectroscopy. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2012; 60:52-70. [PMID: 22293399 DOI: 10.1016/j.pnmrs.2011.11.003] [Citation(s) in RCA: 131] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2011] [Accepted: 11/29/2011] [Indexed: 05/31/2023]
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Z-Selective Semihydrogenation of Alkynes Catalyzed by a Cationic Vanadium Bisimido Complex. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201007876] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Z-Selective Semihydrogenation of Alkynes Catalyzed by a Cationic Vanadium Bisimido Complex. Angew Chem Int Ed Engl 2011; 50:3900-3. [DOI: 10.1002/anie.201007876] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Revised: 02/07/2011] [Indexed: 11/07/2022]
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New Perspectives for Parahydrogen-Induced Polarization in Liquid Phase Heterogeneous Hydrogenation: An Aqueous Phase and ALTADENA Study. Chemphyschem 2010; 11:3086-8. [DOI: 10.1002/cphc.201000407] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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The spin chemistry and magnetic resonance of H2@C60. From the Pauli principle to trapping a long lived nuclear excited spin state inside a buckyball. Acc Chem Res 2010; 43:335-45. [PMID: 19902960 DOI: 10.1021/ar900223d] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
One of the early triumphs of quantum mechanics was Heisenberg's prediction, based on the Pauli principle and wave function symmetry arguments, that the simplest molecule, H(2), should exist as two distinct species-allotropes of elemental hydrogen. One allotrope, termed para-H(2) (pH(2)), was predicted to be a lower energy species that could be visualized as rotating like a sphere and possessing antiparallel ( upward arrow downward arrow) nuclear spins; the other allotrope, termed ortho-H(2) (oH(2)), was predicted to be a higher energy state that could be visualized as rotating like a cartwheel and possessing parallel ( upward arrow upward arrow) nuclear spins. This remarkable prediction was confirmed by the early 1930s, and pH(2) and oH(2) were not only separated and characterized but were also found to be stable almost indefinitely in the absence of paramagnetic "spin catalysts", such as molecular oxygen, or traces of paramagnetic impurities, such as metal ions. The two allotropes of elemental hydrogen, pH(2) and oH(2), may be quantitatively incarcerated in C(60) to form endofullerene guest@host complexes, symbolized as pH(2)@C(60) and oH(2)@C(60), respectively. How does the subtle difference in nuclear spin manifest itself when hydrogen allotropes are incarcerated in a buckyball? Can the incarcerated "guests" communicate with the outside world and vice versa? Can a paramagnetic spin catalyst in the outside world cause the interconversion of the allotropes and thereby effect a chemical transformation inside a buckyball? How close are the measurable properties of H(2)@C(60) to those computed for the "quantum particle in a spherical box"? Are there any potential practical applications of this fascinating marriage of the simplest molecule, H(2), with one of the most beautiful of all molecules, C(60)? How can one address such questions theoretically and experimentally? A goal of our studies is to produce an understanding of how the H(2) guest molecules incarcerated in the host C(60) can "communicate" with the chemical world surrounding it. This world includes both the "walls" of the incarcerating host (the carbon atom "bricks" that compose the wall) and the "outside" world beyond the atoms of the host walls, namely, the solvent molecules and selected paramagnetic molecules added to the solvent that will have special spin interactions with the H(2) inside the complex. In this Account, we describe the temperature dependence of the equilibrium of the interconversion of oH(2)@C(60) and pH(2)@C(60) and show how elemental dioxygen, O(2), a ground-state triplet, is an excellent paramagnetic spin catalyst for this interconversion. We then describe an exploration of the spin spectroscopy and spin chemistry of H(2)@C(60). We find that H(2)@C(60) and its isotopic analogs, HD@C(60) and D(2)@C(60), provide a rich and fascinating platform on which to investigate spin spectroscopy and spin chemistry. Finally, we consider the potential extension of spin chemistry to another molecule with spin isomers, H(2)O, and the potential applications of the use of pH(2)@C(60) as a source of latent massive nuclear polarization.
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Current concepts on hyperpolarized molecules in MRI. Curr Opin Chem Biol 2010; 14:90-6. [DOI: 10.1016/j.cbpa.2009.10.021] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2009] [Revised: 10/13/2009] [Accepted: 10/14/2009] [Indexed: 10/20/2022]
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Spontaneous transfer of parahydrogen derived spin order to pyridine at low magnetic field. J Am Chem Soc 2010; 131:13362-8. [PMID: 19719167 DOI: 10.1021/ja903601p] [Citation(s) in RCA: 145] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The cationic iridium complex [Ir(COD)(PCy(3))(py)]BF(4) (1) is shown to react with dihydrogen in the presence of pyridine (py) to form the dihydride complex fac,cis-[Ir(PCy(3))(py)(3)(H)(2)]BF(4) (2). Complex 2 undergoes rapid exchange of the two bound pyridine ligands which are trans to hydride with free pyridine; the activation parameters for this process in methanol are DeltaH(double dagger) = 97.4 +/- 9 kJ mol(-1) and DeltaS(double dagger) = 84 +/- 31 J K(-1) mol(-1). When parahydrogen is employed as a source of nuclear spin polarization, spontaneous magnetization transfer proceeds in low magnetic field from the two nascent hydride ligands of 2 to its other NMR active nuclei. Upon interrogation by NMR spectroscopy in a second step, signal enhancements in excess of 100 fold are observed for the (1)H, (13)C and (15)N resonances of free pyridine after ligand exchange. The degree of signal enhancement in the free substrate is increased by employing electronically rich and sterically encumbered phosphine ligands such as PCy(3), PCy(2)Ph, or P(i)Pr(3) and by optimizing the strength of the magnetic field in which polarization transfer occurs.
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Parahydrogen-induced polarization in alkyne hydrogenation catalyzed by Pd nanoparticles embedded in a supported ionic liquid phase. Chem Commun (Camb) 2010; 46:5764-6. [DOI: 10.1039/c0cc01411g] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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39
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Para-hydrogen induced polarization without incorporation of para-hydrogen into the analyte. Inorg Chem 2009; 48:663-70. [PMID: 19072592 DOI: 10.1021/ic8020029] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The cationic iridium complexes [Ir(COD)(PR3)2]BF4 (1a-c) (a, R = Ph; b, R = p-tolyl; c, R = p-C6H4-OMe) react with parahydrogen in the presence of pyridine to give trans, cis, cis-[Ir(PR3)2(py)2(H)2]+ (2a-c) and small amounts of fac, cis-[Ir(PR3)(py)3(H)2]+ (3a-c), each of which exhibit polarized hydride resonances due to the magnetic inequivalence associated with the resultant AA"XX" spin system when 15N-labeled pyridine is employed. The pyridine ligands in 2 are labile, exchanging slowly into free pyridine with a rate constant of 0.4 s(-1) for 2a at 335 K in a dissociative process where DeltaH(double dagger) = 134 +/- 1 kJ mol(-1) and DeltaS(double dagger) = 151 +/- 5 J mol(-1) K(-1). Pyridine ligand exchange in 2 proves to be slower than that determined for 3. Parahydrogen induced polarization (PHIP) based on the hydride ligands of 2 and 3 is transferred efficiently to the 15N nuclei of the bound pyridine ligand by suitable insensitive-nuclei-enhanced-by-polarization-transfer (INEPT) based procedures. Related methods are then used to facilitate the sensitization of the free pyridine 15N signal by a factor of 120-fold through ligand exchange even though this substrate does not contain parahydrogen. This therefore corresponds to the successful polarization of an analyte by parahydrogen induced polarization methods without the need for the actual chemical incorporation of any parahydrogen derived nuclei into it.
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An NMR study of cobalt-catalyzed hydroformylation using para-hydrogen induced polarisation. Dalton Trans 2009:2496-509. [DOI: 10.1039/b815853c] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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41
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Para-hydrogen induced polarisation effects in liquid phase hydrogenations catalysed by supported metal nanoparticles. Dalton Trans 2009:5074-6. [DOI: 10.1039/b906449d] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Observation of Parahydrogen-Induced Polarization in Heterogeneous Hydrogenation on Supported Metal Catalysts. Angew Chem Int Ed Engl 2008; 47:1492-5. [DOI: 10.1002/anie.200704881] [Citation(s) in RCA: 161] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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44
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Observation of Parahydrogen-Induced Polarization in Heterogeneous Hydrogenation on Supported Metal Catalysts. Angew Chem Int Ed Engl 2008. [DOI: 10.1002/ange.200704881] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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45
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Palladium catalysed alkyne hydrogenation and oligomerisation: a parahydrogen based NMR investigation. Dalton Trans 2008:4270-81. [DOI: 10.1039/b804162h] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Detection of platinum dihydride bisphosphine complexes and studies of their reactivity through para-hydrogen-enhanced NMR methods. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2008; 46 Suppl 1:S107-S114. [PMID: 18855330 DOI: 10.1002/mrc.2342] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
In-situ NMR studies on the reactions of Pt{CH2 = CHSi(Me)2}2O)(PCy3) with phosphines, HSiEt3 and--hydrogen or Pt(L)(L')(Me)(2) alone enable the detection of cis-Pt(L)(L')(H)2 [L = PCy3 and L' = PCy2H, PPh3 or PCy3] which then undergo hydride site interchange and H2 reductive elimination on the NMR timescale.
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A DFT Study on the Mechanism of Palladium-Catalyzed Alkyne Hydrogenation: Neutral versus Cationic Pathways. Organometallics 2007. [DOI: 10.1021/om700307c] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Para-Hydrogen-Enhanced Hyperpolarized Gas-Phase Magnetic Resonance Imaging. Angew Chem Int Ed Engl 2007; 46:4064-8. [PMID: 17455180 DOI: 10.1002/anie.200700830] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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50
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Contrasting photochemical and thermal reactivity of Ru(CO)2(PPh3)(dppe) towards hydrogen rationalised by parahydrogen NMR and DFT studies. Dalton Trans 2006:2072-80. [PMID: 16625251 DOI: 10.1039/b510616h] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The synthesis, characterisation and thermal and photochemical reactivity of Ru(CO)2(PPh3)(dppe) 1 towards hydrogen are described. Compound proved to exist in both fac (major) and mer forms in solution. Under thermal conditions, PPh3 is lost from 1 in the major reaction pathway and the known complex Ru(CO)2(dppe)(H)2 2 is formed. Photochemically, CO loss is the dominant process, leading to the alternative dihydride Ru(CO)(PPh3)(dppe)(H)2 3. The major isomer of 3, viz. 3a, contains hydride ligands that are trans to CO and trans to one of the phosphorus atoms of the dppe ligand but a second isomer, 3b, where both hydride ligands are trans to distinct phosphines, is also formed. On the NMR timescale, no interconversion of 3a and 3b was observed, although hydride site interchange is evident with activation parameters of DeltaH(double dagger) = 95 +/- 6 kJ mol(-1) and DeltaS(double dagger) = 26 +/- 17 J K(-1) mol(-1). Density functional theory confirms that the observed species are the most stable isomeric forms, and suggests that hydride exchange occurs via a transition state featuring an eta2-coordinated H2 unit.
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