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Pulsed dynamic nuclear polarization (DNP) enhances the nuclear magnetic resonance sensitivity by coherently transferring electron spin polarization to dipolar coupled nuclear spins. Recently, many new pulsed DNP techniques such as NOVEL, TOP, XiX, TPPM, and BEAM have been introduced. Despite significant progress, numerous challenges remain unsolved. The electron–electron (e–e) interactions in these sequences can severely disrupt the efficiency of electron–nuclear (e–n) polarization transfer. In order to tackle this issue, we propose the magic-NOVEL DNP method, utilizing Lee–Goldburg decoupling to counteract e–e coupling effects. Our theoretical analysis and quantum mechanical simulations reveal that magic-NOVEL significantly improves the transfer efficiency of DNP, even at shorter e–e distances. This method offers a new perspective for advancing pulsed DNP techniques in systems with dense electron spin baths. Furthermore, we demonstrate the effectiveness of phase-modulated Lee–Goldburg sequences in improving pulsed DNP transfer. [ABSTRACT FROM AUTHOR]

A simplified theoretical description of multiple-quantum excitation and mixing for nuclear magnetic resonance of half-integer quadrupolar nuclei is presented. The approach recasts the multiple-quantum nutation behavior in terms of reduced excitation and mixing curves through a scaling of the first-order offset frequency by the quadrupolar coupling constant. The two-dimensional correlation of the static first-order anisotropic line shape to the second-order anisotropic magic-angle-spinning (MAS) line shape is utilized to transform the three-dimensional integral over the three Euler angles into a single integral over the dimensionless first-order offset parameter. These transformations lead to a highly efficient algorithm for simulating the multiple-quantum (MQ)-MAS spectrum for arbitrary excitation and mixing radio frequency (RF) field strengths, pulse durations, and MAS rates within the static limit approximation, which is defined in terms of the rotation period, pulse duration, RF field strength, and quadrupolar coupling parameters. This algorithm enables a more accurate determination of the relative site populations and quadrupolar coupling parameters in a least-squares analysis of MQ-MAS spectra. Furthermore, this article examines practical considerations for eliminating experimental artifacts and employing affine transformations to improve least-squares analyses of MQ-MAS spectra. The optimum ratio of RF field strength to the quadrupolar coupling constant and the corresponding pulse durations that maximize sensitivity within experimental constraints are also examined. [ABSTRACT FROM AUTHOR]

An integral procedure in every coherent multidimensional spectroscopy experiment is to suppress undesired background signals. For that purpose, one can employ a particular phase-matching geometry or phase cycling, a procedure that was adapted from nuclear magnetic resonance (NMR) spectroscopy. In optical multidimensional spectroscopy, phase cycling has been usually carried out in a "nested" fashion, where pulse phases are incremented sequentially with linearly spaced increments. Another phase-cycling approach that was developed for NMR spectroscopy is "cogwheel phase cycling," where all pulse phases are varied simultaneously in increments defined by so-called "winding numbers." Here we explore the concept of cogwheel phase cycling in the context of population-based coherent multidimensional spectroscopy. We derive selection rules for resolving and extracting fourth-order and higher-order nonlinear signals by cogwheel phase cycling and describe how to perform a numerical search for the winding numbers for various population-detected 2D spectroscopy experiments. We also provide an expression for a numerical search for nested phase-cycling schemes and predict the most economical schemes of both approaches for a wide range of nonlinear signals. The signal selectivity of the technique is demonstrated experimentally by acquiring rephasing and nonrephasing fourth-order signals of a laser dye by both phase-cycling approaches. We find that individual nonlinear signal contributions are, in most cases, captured with fewer steps by cogwheel phase cycling compared to nested phase cycling. [ABSTRACT FROM AUTHOR]

Signal amplification by reversible exchange (SABRE) employs the non-equilibrium spin order of parahydrogen as a source of strong nuclear magnetic resonance (NMR) signal enhancement, with the objective of increasing NMR sensitivity. In SABRE, a parahydrogen molecule and a substrate form a transient polarization transfer complex. Performed within the high magnetic field of an NMR spectrometer, SABRE enables the hyperpolarization of nuclear spins without additional polarizers. Nevertheless, it requires thorough pulse sequence design. The high-field polarization transfer strategy strongly depends on the type of the spin system formed by the parahydrogen-nascent protons in the SABRE complex: chemically equivalent or non-equivalent. SABRE hyperpolarization in chemically equivalent spin systems has been the subject of considerable attention, even after being relevant only for a limited number of substrates. Efficient hyperpolarization in chemically non-equivalent complexes remained a key challenge, hindering the full potential of high-field SABRE and the ability to polarize a broader range of SABRE substrates. This work reports the multinuclear 1H–15N pulse sequence for efficient 15N hyperpolarization in chemically non-equivalent SABRE complexes. This approach relies on the simultaneous 1H and 15N radiofrequency excitation of the complex-bound nuclei with weak continuous wave magnetic fields. The proposed pulse sequence enabled the hyperpolarization of the 15N nuclei in a mixture of the antimicrobial drugs containing a 5-nitroimidazol moiety at their natural 15N isotopic abundance (0.76% of 15N polarization). Furthermore, it permitted the precise assignment of the SABRE complexes responsible for the polarization transfer. [ABSTRACT FROM AUTHOR]

The open-source Python package, MRSimulator, is presented as a simple-to-use, fast, versatile, and extendable package capable of simulating one- and higher-dimensional Nuclear Magnetic Resonance (NMR) spectra under static, magic-angle, and variable-angle conditions. High benchmarks in spectral simulations are achieved by assuming that there are no degeneracies in the energy eigenstates, i.e., all dipolar couplings are in the weak limit and that there are no rotational resonances during evolution periods. Under these assumptions, the symmetry pathway formalism is exploited to reduce an NMR method applied to a spin system into a sum of individual transition pathways, whose signals are more efficiently calculated individually than as part of a full-density matrix simulation. To increase numerical efficiencies further, our approach restricts coherence transfer among transitions to pure rotations about an axis in the x–y plane of the rotating frame or through an artificial total mixing operation between selected transitions of adjacent free evolution periods. The assumptions used in this approach are valid for most commonly used solid-state NMR methods. Details of the implementation, along with example code usage, are given, including a least-squares spectral analysis. [ABSTRACT FROM AUTHOR]