42 research outputs found
Essential Tools of Linear Algebra for Calculating Nuclear Spin Dynamics of Chemically Exchanging Systems
In this work, we describe essential tools of linear algebra necessary for
calculating the effect of chemical exchange on spin dynamics and polarization
transfer in various nuclear magnetic resonance (NMR) experiments. We show how
to construct Hamiltonian, relaxation, and chemical exchange superoperators in
the Liouville space, as well as demonstrate corresponding code in Python.
Examples of applying the code are given for problems involving chemical
exchange between NH3 and NH4+ at zero and high magnetic field and polarization
transfer from parahydrogen relevant in SABRE (signal amplification by
reversible exchange) at low magnetic field (0-20 mT). The presented methodology
finds utility for describing the effect of chemical exchange on NMR spectra and
can be extended further by taking into account non-linearities in the master
equation
Theoretical description of hyperpolarization formation in the SABRE-relay method
SABRE (Signal Amplification By Reversible Exchange) has become a widely used method for hyper-polarizing nuclear spins, thereby enhancing their Nuclear Magnetic Resonance (NMR) signals by orders of magnitude. In SABRE experiments, the non-equilibrium spin order is
transferred from parahydrogen to a substrate in a transient organometallic complex. The applicability of SABRE is expanded by the methodology of SABRE-relay in which polarization can be relayed to a second substrate either by direct chemical exchange of hyperpolarized nuclei
or by polarization transfer between two substrates in a second organometallic complex. To understand the mechanism of the polarization
transfer and study the transfer efficiency, we propose a theoretical approach to SABRE-relay, which can treat both spin dynamics and chemical kinetics as well as the interplay between them. The approach is based on a set of equations for the spin density matrices of the spin
systems involved (i.e., SABRE substrates and complexes), which can be solved numerically. Using this method, we perform a detailed study of
polarization formation and analyze in detail the dependence of the attainable polarization level on various chemical kinetic and spin dynamic
parameters. We foresee the applications of the present approach for optimizing SABRE-relay experiments with the ultimate goal of achieving
maximal NMR signal enhancements for substrates of interest
Possible Applications of Dissolution Dynamic Nuclear Polarization in Conjunction with Zero- to Ultralow-Field Nuclear Magnetic Resonance
The combination of a powerful and broadly applicable nuclear
hyperpolarization technique with emerging (near-)zero-field modalities offer
novel opportunities in a broad range of nuclear magnetic resonance spectroscopy
and imaging applications, including biomedical diagnostics, monitoring
catalytic reactions within metal reactors and many others. These are discussed
along with a roadmap for future developments.Comment: 12 pages, 5 figure
Recommended from our members
Zero-field nuclear magnetic resonance of chemically exchanging systems.
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 [15N]ammonium (15N[Formula: see text]) 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 [2-13C]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
Symmetry Constraints on Spin Order Transfer in Parahydrogen-Induced Polarization (PHIP)
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 recent decades, numerous methods were proposed for converting pH2-derived nuclear spin order to the observable magnetization of protons or other nuclei of interest, usually 13C or 15N. Here, we analyze the constraints imposed by the topological symmetry of the spin systems on the amplitude of transferred polarization. We find that 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., 1H, 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, (where A and B (or A’) came from pH2). Remarkably, if the polarization of all spins in a molecule is summed up, the total polarization grows asymptotically with ~1.27N and can exceed 2 in the absence of symmetry constraints (where N is the number of spins). 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
Efficient Synthesis of Nicotinamide-1-<sup>15</sup>N for Ultrafast NMR Hyperpolarization Using Parahydrogen
Nicotinamide (a vitamin B<sub>3</sub> amide) is one of the key
vitamins as well as a drug for treatment of M. tuberculosis, HIV, cancer, and other diseases. Here, an improved Zincke reaction
methodology is presented allowing for straightforward and scalable
synthesis of nicotinamide-1-<sup>15</sup>N with an excellent isotopic
purity (98%) and good yield (55%). <sup>15</sup>N nuclear spin label
in nicotinamide-1-<sup>15</sup>N can be NMR hyperpolarized in seconds
using parahydrogen gas. NMR hyperpolarization using the process of
temporary conjugation between parahydrogen and to-be-hyperpolarized
biomolecule on hexacoordinate iridium complex via the Signal Amplification
By Reversible Exchange (SABRE) method significantly increases detection
sensitivity (e.g., >20 000-fold for nicotinamide-1-<sup>15</sup>N at 9.4 T) as has been shown by Theis T. et al. (<i>J. Am.
Chem. Soc.</i> <b>2015</b>, <i>137</i>, 1404),
and hyperpolarized in this fashion, nicotinamide-1-<sup>15</sup>N
can be potentially used to probe metabolic processes in vivo in future
studies. Moreover, the presented synthetic methodology utilizes mild
reaction conditions, and therefore can also be potentially applied
to synthesis of a wide range of <sup>15</sup>N-enriched N-heterocycles
that can be used as hyperpolarized contrast agents for future in vivo
molecular imaging studies