Solution-State 2D NMR Spectroscopy of Mixtures HyperpolarizedUsing Optically Polarized Crystals.

The HYPNOESYS method (Hyperpolarized NOE System), which relies on the dissolution of optically polarized crystals, has recently emerged as a promising approach to enhance the sensitivity of NMR spectroscopy in the solution state. However, HYPNOESYS is a single-shot method that is not generally compatible with multidimensional NMR. Here we show that 2D NMR spectra can be obtained from HYPNOESYS-polarized samples, using single-scan acquisition methods. The approach is illustrated with a mixture of terpene molecules and a benchtop NMR spectrometer, paving the way to a sensitive, information-rich and affordable analytical method.

Long-Lived, Transportable Reservoir of Nuclear Polarization Used to Strongly Enhance Solution-State NMR Signals.

There is a fundamental issue with the use of dynamic nuclear polarization (DNP) to enhance nuclear spin polarization: the same polarizing agent (PA) needed for DNP is also responsible for shortening the lifetime of the hyperpolarization. As a result, long-term storage and transport of hyperpolarized samples is severely restricted and the apparatus for DNP is necessarily located near or integrated with the apparatus using the hyperpolarized spins. In this paper, we demonstrate that naphthalene single crystals can serve as a long-lived reservoir of proton polarization that can be exploited to enhance signals in benchtop and high-field NMR of target molecules in solution at a site 300 km away by a factor of several thousand. The naphthalene protons are polarized using short-lived optically excited triplet states of pentacene instead of stable radicals. In the absence of optical excitation, the electron spins remain in a singlet ground state, eliminating the major pathway of nuclear spin-lattice relaxation. The polarization decays with a time constant of about 50 h at 80 K and 0.5 T or above 800 h at 5 K and 20 mT. A module based on a Halbach array yielding a field of 0.75 T and a conventional cryogenic dry shipper, operating at liquid nitrogen temperature, allows storage and long distance transport of the polarization to a remote laboratory, where the polarization of the crystal is transferred after dissolution to a target molecule of choice by intermolecular cross-relaxation. The procedure has been executed repeatedly and has proven to be reliable and robust.

Scalable and Tunable Diamond Nanostructuring Process for Nanoscale NMR Applications.

Nanostructuring of a bulk material is used to change its mechanical, optical, and electronic properties and to enable many new applications. We present a scalable fabrication technique that enables the creation of densely packed diamond nanopillars for quantum technology applications. The process yields tunable feature sizes without the employment of lithographic techniques. High-aspect-ratio pillars are created through oxygen-plasma etching of diamond with a dewetted palladium film as an etch mask. We demonstrate an iterative renewal of the palladium etch mask, by which the initial mask thickness is not the limiting factor for the etch depth. Following the process, 300-400 million densely packed 100 nm wide and 1 µm tall diamond pillars were created on a 3 × 3 mm2 diamond sample. The fabrication technique is tailored specifically to enable applications and research involving quantum coherent defect center spins in diamond, such as nitrogen-vacancy (NV) centers, which are widely used in quantum science and engineering. To demonstrate the compatibility of our technique with quantum sensing, NV centers are created in the nanopillar sidewalls and are used to sense 1H nuclei in liquid wetting the nanostructured surface. This nanostructuring process is an important element for enabling the wide-scale implementation of NV-driven magnetic resonance imaging or NV-driven NMR.

Hyperpolarized Solution-State NMR Spectroscopy with Optically Polarized Crystals.

Nuclear spin hyperpolarization provides a promising route to overcome the challenges imposed by the limited sensitivity of nuclear magnetic resonance. Here we demonstrate that dissolution of spin-polarized pentacene-doped naphthalene crystals enables transfer of polarization to target molecules via intermolecular cross-relaxation at room temperature and moderate magnetic fields (1.45 T). This makes it possible to exploit the high spin polarization of optically polarized crystals, while mitigating the challenges of its transfer to external nuclei. With this method, we inject the highly polarized mixture into a benchtop NMR spectrometer and observe the polarization dynamics for target 1H nuclei. Although the spectra are radiation damped due to the high naphthalene magnetization, we describe a procedure to process the data to obtain more conventional NMR spectra and extract the target nuclei polarization. With the entire process occurring on a time scale of 1 min, we observe NMR signals enhanced by factors between -200 and -1730 at 1.45 T for a range of small molecules.

Shimming Halbach magnets utilizing genetic algorithms to profit from material imperfections.

In recent years, permanent magnet-based NMR spectrometers have resurfaced as low-cost portable alternatives to superconducting instruments. While the development of these devices as well as clever shimming methods have yielded impressive advancements, scaling the size of these magnets to miniature lengths remains a problem to be addressed. Here we present the results of a study of a discrete shimming scheme for NMR Mandhalas constructed from a set of individual magnet blocks. While our calculations predict a modest reduction in field deviation by a factor of 9.3 in the case of the shimmed ideal Mandhala, a factor of 28 is obtained in the case of the shimmed imperfect Mandhala. This indicates that imperfections of magnet blocks can lead to improved field homogeneity. We also present a new algorithm to improve the homogeneity of a permanent magnet assembly. Strategies for future magnet construction can improve the agreement between simulation and practical implementation by using data from real magnets in these assemblies as the input to such an algorithm to optimize the homogeneity of a given design.

Halogen bonding in DNA base pairs.

Halogen bonding (R-X···Y) is a qualitative analogue of hydrogen bonding that may prove useful in the rational design of artificial proteins and nucleotides. We explore halogen-bonded DNA base pairs containing modified guanine, cytosine, adenine and thymine nucleosides. The structures and stabilities of the halogenated systems are compared to the normal hydrogen bonded base pairs. In most cases, energetically stable, coplanar structures are identified. In the most favorable cases, halogenated base pair stabilities are within 2 kcal mol(-1) of the hydrogen bonded analogues. Among the halogens X = Cl, Br, and I, bromine is best suited for inclusion in these biological systems because it possesses the best combination of polarizability and steric suitability. We find that the most stable structures result from a single substitution of a hydrogen bond for a halogen bond in dA:dT and dG:dC base pairs, which allows 1 or 2 hydrogen bonds, respectively, to complement the halogen bond.

Oligonucleotide incorporation and base pair stability of 9-deaza-2'-deoxyguanosine, an analogue of 8-oxo-2'-deoxyguanosine.

9-Deaza-2'-deoxyguanosine (CdG) is a C-nucleoside and an analogue of the abundant promutagen 8-oxo-2'-deoxyguanosine (OdG). Like 2'-deoxyguanosine (dG), CdG should form a stable base pair with dC, but similar to OdG, CdG contains an N7-hydrogen that should allow it to also form a relatively stable base pair with dA. In order to further investigate the base pairing of CdG, it was incorporated into DNA and paired with either dC or dA. Melting studies revealed CdG:dC base pairs are less stable than dG:dC base pairs, while CdG:dA base pairs are less stable than OdG:dA base pairs. In order to gain a deeper understanding of these results, quantum studies on model structures of nucleoside monomers and base pairs were performed, the results of which indicate that (i) CdG:dC base pairs are likely destabilized relative to dG:dC as a result of structural constraints imposed by the C-nucleotide character of CdG, and (ii) CdG:dA base pairs may be less stable than OdG:dA base pairs, at least in part, because of a third long-range interaction that is possible in OdG:dA but not in CdG:dA.