@article {3228, title = {Indirect Detection of Short-lived Hydride Intermediates of Iridium N-Heterocyclic Carbene Complexes via Chemical Exchange Saturation Transfer (CEST) Spectroscopy}, journal = {The Journal of Physical Chemistry C}, year = {2019}, month = {06/2019}, abstract = {

For the first time, chemical exchange saturation transfer (CEST) nuclear magnetic resonance (NMR) is utilized to study short-lived hydride intermediates in the catalytic cycle of an organometallic complex [Ir(IMes)(Py)3(H)2]Cl. These complexes are typically not observable by other NMR techniques because they are low concentrated and undergo reversible ligand exchange with the main complex. The intermediatecomplexes [Ir(Cl)(IMes)(Py)2(H)2] and [Ir(CD3OD)(IMes)(Py)2(H)2]are detected, assigned, and characterized in solution, in situ and at room temperature. Understanding the spin dynamics in these complexes is necessary for enhancing the performance of the nuclear spin hyperpolarization technique signal amplification by reversible exchange. By eliminating [Ir(Cl (IMes)(Py)2(H)2] and manipulating the spin system by radiofrequency irradiation, the nuclear spin singlet lifetime of the hydride protons was increased by more than an order of magnitude, from 2.2 \± 0.1 to 27.2 \± 1.2 s. Because of its simplicity and ability to unravel unobservable chemical species, the utilized CEST NMR approach has a large application potential for studying short-lived hydride intermediates incatalytic reactions.

}, doi = {https://doi.org/10.1021/acs.jpcc.9b04179}, url = {https://pubs.acs.org/doi/10.1021/acs.jpcc.9b04179$\#$}, author = {Stephan Knecht and Sara Hadjiali and Danila A Barskiy and Alexander Pines and Grit Sauer and Alexey Kiryutin and Konstantin Ivanov and Alexandra Yurkovskaya and Gerd Buntkowsky} } @article {3230, title = {Two-Electron-Spin Ratchets as a Platform for Microwave-Free Dynamic Nuclear Polarization of Arbitrary Material Targets}, journal = {Nano Letters}, year = {2019}, month = {03/2019}, abstract = {

Optically pumped color centers in semiconductor powders can potentially induce high levels of nuclear spin polarization in surrounding solids or fluids at or near ambient conditions, but complications stemming from the random orientation of the particles and the presence of unpolarized paramagnetic defects hinder the flow of polarization beyond the defect\’s host material. Here, we theoretically study the spin dynamics of interacting nitrogen-vacancy (NV) and substitutional nitrogen (P1) centers in diamond to show that outside protons spin-polarize efficiently upon a magnetic field sweep across the NV\–P1 level anticrossing. The process can be interpreted in terms of an NV\–P1 spin ratchet, whose handedness, and hence the sign of the resulting nuclear polarization, depends on the relative timing of the optical excitation pulse. Further, we find that the polarization transfer mechanism is robust to NV misalignment relative to the external magnetic field, and efficient over a broad range of electron\–electron and electron\–nuclear spin couplings, even if proxy spins feature short coherence or spin\–lattice relaxation times. Therefore, these results pave the route toward the dynamic nuclear polarization of arbitrary spin targets brought in proximity with a diamond powder under ambient conditions.

}, doi = {10.1021/acs.nanolett.8b05114}, url = {https://pubs.acs.org/doi/full/10.1021/acs.nanolett.8b05114}, author = {Pablo R. Zangara and J. Henshaw and Daniela Pagliero and Ashok Ajoy and Jeffrey A. Reimer and Alexander Pines and Carlos A. Meriles} } @article {3193, title = {Zero-Field Nuclear Magnetic Resonance of Chemically Exchanging Systems}, journal = {Nature Communications}, volume = {10}, year = {2019}, month = {07/2019}, abstract = {

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) 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.

}, doi = {https://doi.org/10.1038/s41467-019-10787-9}, url = {https://www.nature.com/articles/s41467-019-10787-9?fbclid=IwAR1MB5nAamCMGynKRk0sjD6V8rTlZ329IvrVKrCwIO8QjrEH4wD23BV5gak}, author = {Danila Barskiy and Michael Tayler and Irene Marco-Rius and John Kurhanewicz and Daniel Vigneron and Sevil Cikrikci and Ayca Aydogdu and Moritz Reh and Andrey Pravdivtsev and Jan-Bernd H{\"o}vener and John Blanchard and Teng Wu and Dmitry Budker and Alexander Pines} } @article {2980, title = {Enhanced dynamic nuclear polarization via swept microwave frequency combs}, journal = {Proc. Natl. Acad. Sci}, year = {2018}, month = {10/2018}, abstract = {

Dynamic nuclear polarization (DNP) has enabled enormous gains in magnetic resonance signals and led to vastly accelerated NMR/MRI imaging and spectroscopy. Unlike conventional cw-techniques, DNP methods that exploit the full electron spectrum are appealing since they allow direct participation of all electrons in the hyperpolarization process. Such methods typically entail sweeps of microwave radiation over the broad electron linewidth to excite DNP but are often inefficient because the sweeps, constrained by adiabaticity requirements, are slow. In this paper, we develop a technique to overcome the DNP bottlenecks set by the slow sweeps, using a swept microwave frequency comb that increases the effective number of polarization transfer events while respecting adiabaticity constraints. This allows a multiplicative gain in DNP enhancement, scaling with the number of comb frequencies and limited only by the hyperfine-mediated electron linewidth. We demonstrate the technique for the optical hyperpolarization of 13C nuclei in powdered microdiamonds at low fields, increasing the DNP enhancement from 30 to 100 measured with respect to the thermal signal at 7T. For low concentrations of broad linewidth electron radicals [e.g., TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl)], these multiplicative gains could exceed an order of magnitude.

}, doi = {1807125115}, url = {https://doi.org/10.1073/pnas.1807125115}, author = {Ashok Ajoy and Kristina Liu and Xudong Lv and Raffi Nazaryan and G.Wang and E . Druga and Jeff Reimer and Ditter Suter and C. Ramanathan and C.A Meriles and Alexander Pines} } @article {2979, title = {Orientation independent room-temperature optical 13C hyperpolarization in powdered diamond}, journal = {Science Advances}, volume = {4}, year = {2018}, month = {05/2018}, abstract = {

Dynamic nuclear polarization via contact with electronic spins has emerged as an attractive route to enhance the sensitivity of nuclear magnetic resonance beyond the traditional limits imposed by magnetic field strength and temperature. Among the various alternative implementations, the use of nitrogen vacancy (NV) centers in diamond\—a paramagnetic point defect whose spin can be optically polarized at room temperature\—has attracted widespread attention, but applications have been hampered by the need to align the NV axis with the external magnetic field. We overcome this hurdle through the combined use of continuous optical illumination and a microwave sweep over a broad frequency range. As a proof of principle, we demonstrate our approach using powdered diamond with which we attain bulk 13C spin polarization in excess of 0.25\% under ambient conditions. Remarkably, our technique acts efficiently on diamond crystals of all orientations and polarizes nuclear spins with a sign that depends exclusively on the direction of the microwave sweep. Our work paves the way toward the use of hyperpolarized diamond particles as imaging contrast agents for biosensing and, ultimately, for the hyperpolarization
of nuclear spins in arbitrary liquids brought in contact with their surface.

}, doi = {10.1126/sciadv.aar5492 }, url = {http://advances.sciencemag.org/content/4/5/eaar5492}, author = {Ashok Ajoy and Kristina Liu and Raff Nazaryan and Xudong Lv and Pablo R. Zangara and Benjamin Safvati and Guoqing Wang and Daniel Arnold and Grace Li and Arthur Lin and Priyanka Raghavan and Emanuel Druga and Siddharth Dhomkar and Daniela Pagliero and Jeffrey A. Reimer and Dieter Suter and Carlos A. Meriles and Alexander Pines} } @article {2963, title = {Rapid Catalyst Capture Enables Metal-Free para-Hydrogen-Based Hyperpolarized Contrast Agents}, journal = {The Journal of Physical Chemistry Letters}, volume = {9}, year = {2018}, month = {05/2018}, pages = {2721{\textendash}2724}, abstract = {

Hyperpolarization techniques based on the use of\ para-hydrogen provide orders of magnitude signal enhancement for magnetic resonance spectroscopy and imaging. The main drawback limiting widespread applicability of\ para-hydrogen-based techniques in biomedicine is the presence of organometallic compounds (the polarization transfer catalysts) in solution with hyperpolarized contrast agents. These catalysts are typically complexes of platinum-group metals, and their administration in vivo should be avoided. Herein, we show how extraction of a hyperpolarized compound from an organic phase to an aqueous phase combined with a rapid (less than 10 s) Ir-based catalyst capture by metal scavenging agents can produce pure\ para-hydrogen-based hyperpolarized contrast agents, as demonstrated by high-resolution nuclear magnetic resonance (NMR) spectroscopy and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The presented methodology enables fast and efficient means of producing pure hyperpolarized aqueous solutions for biomedical and other uses.

}, doi = {10.1021/acs.jpclett.8b01007}, url = {https://pubs.acs.org/doi/abs/10.1021/acs.jpclett.8b01007}, author = {Danila A Barskiy and Lucia A Ke and Xingyang Li and Vincent Stevenson and Nevin Widarman and Hao Zhang and Ashley Truxal and Alexander Pines} } @article {2698, title = {Measuring molecular parity nonconservation using nuclear-magnetic-resonance spectroscopy}, journal = {Physical Review A}, volume = {96}, year = {2017}, month = {10/2017}, abstract = {

The weak interaction does not conserve parity and therefore induces energy shifts in chiral enantiomers that should in principle be detectable in molecular spectra. Unfortunately, the magnitude of the expected shifts are small and in spectra of a mixture of enantiomers, the energy shifts are not resolvable. We propose a nuclear-magnetic-resonance (NMR) experiment in which we titrate the chirality (enantiomeric excess) of a solvent and measure the diasteriomeric splitting in the spectra of a chiral solute in order to search for an anomalous offset due to parity nonconservation (PNC). We present a proof-of-principle experiment in which we search for PNC in the 13C resonances of small molecules, and use the 1H resonances, which are insensitive to PNC, as an internal reference. We set a constraint on molecular PNC in 13C chemical shifts at a level of 10\−5 ppm, and provide a discussion of important considerations in the search for molecular PNC using NMR spectroscopy.

}, doi = {https://doi.org/10.1103/PhysRevA.96.042119}, url = {https://journals.aps.org/pra/abstract/10.1103/PhysRevA.96.042119}, author = {John W. Blanchard and J. Ellis and Bougas, L and M. G. Kozlov and Alexander Pines and Dmitri Budker} } @article {2391, title = {An optimized microfabricated platform for the optical generation and detection of hyperpolarized 129Xe}, journal = {Scientific Reports }, year = {2017}, url = {http://www.nature.com/articles/srep43994}, author = {Daniel J. Kennedy and Scott J. Seltzer and Ricardo Jimenez-Martinez and Hattie L. Ring and Nicholas Malecek and Svenja Knappe and Elizabeth Donley and John Kitching and Vikram S. Bajaj and Alexander Pines} } @article {1867, title = {129Xe NMR Relaxation-Based Macromolecular Sensing}, journal = {JACS Communication}, volume = {138}, year = {2016}, month = {07/2016}, chapter = {9747}, author = {Muller Gomes and Phuong Dao and Keunghong Jeong and Clancy Slack and Christophoros Vassiliou and Matthew B. Francis and David Wemmer and Alexander Pines} } @article {1941, title = {Rotaxane-mediated suppression and activation of cucurbit[6]uril for molecular detection by 129Xe hyperCEST NMR}, journal = {ChemComm}, year = {2016}, author = {Joel A. Finbloom and Clancy C. Slack and Carson J. Bruns and Keunhong Jeong and David E. Wemmer and Alexander Pines and Matthew B. Francis} } @article {2074, title = {Targeted Molecular Imaging of Cancer Cells using MS2-Based 129Xe NMR}, journal = {Bioconjugate Chemistry}, volume = {27}, year = {2016}, month = {07/2016}, chapter = {1796}, doi = {10.1021/acs.bioconjchem.6b00275}, url = {http://pubs.acs.org/doi/abs/10.1021/acs.bioconjchem.6b00275}, author = {Keunhong Jeong and Chawita Netirojjanakul and Henrik K Munch and Jinny Sun and Joel A Finbloom and David E Wemmer and Alexander Pines and Matthew B Francis} } @article {1863, title = {Decoherence-protected transitions of nitrogen-vacancy centers in 99\% 13C-enriched diamond}, journal = {arXiv:1506.05484}, year = {2015}, month = {06/2015}, author = {Anna J. Parker and Hai-Jing Wang and Yiran Li and Alexander Pines and Jonathan P. King} } @article {1866, title = {Investigation of DOTA-Metal Chelation Effects on 129Xe Chemical Shift}, journal = {ChemPhysChem}, year = {2015}, author = {Keunhong Jeong and Clancy C. Slack and Christophoros C. Vassiliou and Phuong Dao and Muller D Gomes and Daniel J. Kennedy and Ashley E. Truxal and Lindsay J Sperling and Matthew B. Francis and David E. Wemmer and Alexander Pines} } @article {1924, title = {~Measurement of untruncated nuclear spin interactions via zero-to ultralow-field nuclear magnetic resonance}, journal = {Physical Review B}, year = {2015}, author = {John W. Blanchard and Tobias F. Sjolander and Jonathan P. King and Micah Ledbetter and Emma H. Levine and Vikram S. Bajaj and Dmitri Budker and Alexander Pines} } @article {1875, title = {Room temperature in situ nuclear spin hyperpolarization from optically pumped nitrogen vacancy centers in diamond}, journal = {Nature Communications}, year = {2015}, author = {Jonathan P. King and Keunhong Jeong and Christophoros C. Vassiliou and Chang S. Shin and Ralph H. Page and Claudia E. Avalos and Hai-Jing Wang and Alexander Pines} } @article {1474, title = {Genetically encoded reporters for hyperpolarized xenon MRI}, journal = {Nature Chemistry}, volume = {6}, year = {2014}, month = {04/2014}, pages = {629-634}, chapter = {629}, doi = {10.1038/nchem.1934 }, author = {Mikhail G. Shapiro and R. Matthew Ramirez and Lindsay J. Sperling and George Sun and Jinny Sun and Alexander Pines and David V. Schaffer and Vikram S. Bajaj} } @article {1925, title = {Non-disruptive dissolution of hp-129Xe in viscou aqueous and organic liquid crystalline environments}, author = {Ashley E. Truxal and Clancy C. Slack and Muller D. Gomes and Christophoros C. Vassiliou and David E. Wemmer and Alexander Pines} }