%0 Journal Article %J The Journal of Physical Chemistry C %D 2019 %T Indirect Detection of Short-lived Hydride Intermediates of Iridium N-Heterocyclic Carbene Complexes via Chemical Exchange Saturation Transfer (CEST) Spectroscopy %A Stephan Knecht %A Sara Hadjiali %A Danila A Barskiy %A Alexander Pines %A Grit Sauer %A Alexey Kiryutin %A Konstantin Ivanov %A Alexandra Yurkovskaya %A Gerd Buntkowsky %X

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.

%B The Journal of Physical Chemistry C %8 06/2019 %G eng %U https://pubs.acs.org/doi/10.1021/acs.jpcc.9b04179# %R https://doi.org/10.1021/acs.jpcc.9b04179 %0 Journal Article %J Review of Scientific Instruments %D 2017 %T Invited Review Article: Instrumentation for nuclear magnetic resonance in zero and ultralow magnetic field %A Tayler, MCD %A Theis, Thomas %A Tobias F. Sjolander %A John W. Blanchard %A Kentner, A %A Pustelny, S %A Pines, Alexander %A Budker, Dmitry %X

We review experimental techniques in our laboratory for nuclear magnetic resonance (NMR) in zero and ultralow magnetic field (below 0.1 μT) where detection is based on a low-cost, non-cryogenic, spin-exchange relaxation free 87Rb atomic magnetometer. The typical sensitivity is 20-30 fT/Hz1/2 for signal frequencies below 1 kHz and NMR linewidths range from Hz all the way down to tens of mHz. These features enable precision measurements of chemically informative nuclear spin-spin couplings as well as nuclear spin precession in ultralow magnetic fields.

%B Review of Scientific Instruments %V 88 %8 09/2017 %G eng %U http://aip.scitation.org/doi/abs/10.1063/1.5003347 %R https://doi.org/10.1063/1.5003347 %0 Journal Article %J ChemPhysChem %D 2015 %T Investigation of DOTA‐Metal Chelation Effects on 129Xe Chemical Shift %A Keunhong Jeong %A Clancy C. Slack %A Christophoros C. Vassiliou %A Phuong Dao %A Muller D Gomes %A Daniel J. Kennedy %A Ashley E. Truxal %A Lindsay J Sperling %A Matthew B. Francis %A David E. Wemmer %A Alexander Pines %B ChemPhysChem %G eng %0 Journal Article %J Journal of Chemical Physics %D 2010 %T Investigation of antirelaxation coatings for alkali-metal vapor cells using surface science techniques %A Seltzer, S. J. %A Michalak, D. J. %A Donaldson, M. H. %A Balabas, M. V. %A Barber, S. K. %A Bernasek, S. L. %A Bouchiat, M. A. %A Hexemer, A. %A Hibberd, A. M. %A Kimball, D. F. J. %A Jaye, C. %A Karaulanov, T. %A Narducci, F. A. %A Rangwala, S. A. %A Robinson, H. G. %A Shmakov, A. K. %A Voronov, D. L. %A Yashchuk, V. V. %A Pines, A. %A Budker, D. %K SPECTROSCOPY %X

Many technologies based on cells containing alkali-metal atomic vapor benefit from the use of antirelaxation surface coatings in order to preserve atomic spin polarization. In particular, paraffin has been used for this purpose for several decades and has been demonstrated to allow an atom to experience up to 10 000 collisions with the walls of its container without depolarizing, but the details of its operation remain poorly understood. We apply modern surface and bulk techniques to the study of paraffin coatings in order to characterize the properties that enable the effective preservation of alkali spin polarization. These methods include Fourier transform infrared spectroscopy, differential scanning calorimetry, atomic force microscopy, near-edge x-ray absorption fine structure spectroscopy, and x-ray photoelectron spectroscopy. We also compare the light-induced atomic desorption yields of several different paraffin materials. Experimental results include the determination that crystallinity of the coating material is unnecessary, and the detection of CvC double bonds present within a particular class of effective paraffin coatings. Further study should lead to the development of more robust paraffin antirelaxation coatings, as well as the design and synthesis of new classes of coating materials. (C) 2010 American Institute of Physics. [doi:10.1063/1.3489922]

%B Journal of Chemical Physics %V 133 %P 144703 %8 October 11, 2010 %@ 0021-9606 %G English %U http://link.aip.org/link/doi/10.1063/1.3489922 %N 14 %9 Article %M WOS:000283200400049 %] 144703 %! Investigation of antirelaxation coatings for alkali-metal vapor cells using surface science techniques %& 144703 %R 10.1063/1.3489922 %0 Journal Article %J Journal of Chemical Physics %D 2005 %T Isotropic proton-detected local-field nuclear magnetic resonance in solids %A Havlin, R. H. %A Walls, J. D. %A Pines, A. %K spectra %X

A nuclear magnetic resonance method is presented which produces linear, isotropic proton-detected local-field spectra for INS spin systems in powdered samples. The method, heteronuclear isotropic evolution (HETIE), refocuses the anisotropic portion of the heteronuclear dipolar coupling frequencies by evolving the system under a series of specially designed Hamiltonians and evolution pathways. The theory behind HETIE is presented along with experimental studies conducted on a powdered sample of ferrocene, demonstrating the methodology outlined in this paper. Applications of HETIE for use in structure determination in the solid state are discussed. (C) 2005 American Institute of Physics.

%B Journal of Chemical Physics %V 122 %8 Feb 15 %@ 0021-9606 %G English %U ://WOS:000227140000043 %N 7 %M WOS:000227140000043 %! Isotropic proton-detected local-field nuclear magnetic resonance in solids %R Doi 10.1063/1.1844296 %0 Journal Article %J Journal of Chemical Physics %D 2004 %T Isotropic-liquid crystalline phase diagram of a CdSe nanorod solution %A Li, L. S. %A Marjanska, M. %A Park, G. H. J. %A Pines, A. %A Alivisatos, A. P. %K model %X

We report the isotropic-liquid crystalline phase diagram of 3.0 nm x 60 nm CdSe nanorods dispersed in anhydrous cyclohexane. The coexistence concentrations of both phases are found to be lower and the biphasic region wider than the results predicted by the hard rod model, indicating that the attractive interaction between the nanorods may be important in the formation of the liquid crystalline phase in this system. (C) 2004 American Institute of Physics.

%B Journal of Chemical Physics %V 120 %P 1149-1152 %8 Jan 15 %@ 0021-9606 %G English %U ://WOS:000188081000002 %N 3 %M WOS:000188081000002 %! Isotropic-liquid crystalline phase diagram of a CdSe nanorod solution %R Doi 10.1063/1.1640331 %0 Journal Article %J Journal of Physical Chemistry B %D 2003 %T Inclusion complexes oriented in thermotropic liquid-crystalline solvents studied with carbon-13 NMR %A Marjanska, M. %A Goodson, B. M. %A Castiglione, F. %A Pines, A. %K xe-129 %X

The inclusion complex of cryptophane-A and chloroform dissolved in two nonchiral liquid-crystalline environments was investigated via C-13 NMR. Stable solutions of oriented complexes were prepared using aromatic (ZLI 1132) and aliphatic (ZLI 1695) thermotropic nematic liquid crystals as solvents; ordering of the complexes was manifested by the H-1-C-13 dipolar splitting of the C-13 resonance of labeled chloroform. In both solutions, the dipolar splitting for the bound ligands was substantially larger than that obtained for the free ligands, indicating a significant increase in ligand ordering upon complexation despite the absence of direct contact with the oriented solvent molecules. A similar enhancement in ordering was observed for complexed ligands compared to that for free ligands in both liquid-crystalline solvents. Also, the application of heteronuclear decoupling to the ZLI 1695 solution resulted in a reduced line width for the bound C-13 chloroform resonance, suggesting that a significant component of the observed line broadening may originate from intermolecular couplings between host and guest molecules. These results demonstrate the potential for using restored dipolar couplings to investigate structural and dynamical aspects of inclusion complexes in solution.

%B Journal of Physical Chemistry B %V 107 %P 12558-12561 %8 Nov 20 %@ 1520-6106 %G English %U ://WOS:000186574500003 %N 46 %M WOS:000186574500003 %! Inclusion complexes oriented in thermotropic liquid-crystalline solvents studied with carbon-13 NMR %R Doi 10.1021/Jp030431e %0 Journal Article %J Solid State Nuclear Magnetic Resonance %D 2002 %T Investigations of low-amplitude radio frequency pulses at and away from rotary resonance conditions for I=5/2 Nuclei %A Logan, J. W. %A Urban, J. T. %A Walls, J. D. %A Lim, K. H. %A Jerschow, A. %A Pines, A. %K solid-state %X

Additional experimental evidence of rotary resonance effects for multiple-quantum coherence conversion in a spin-5/2 system is presented. Two-dimensional plots of the relative efficiency of MQ excitation and conversion are given as a function of radio frequency (rf) amplitude and pulse width. Data are presented for the excitation of five-quantum coherence (5QC), as well as for 5QC to three-quantum coherence (3QC) conversion, 5QC to 1QC (the central transition coherence) conversion, and 3QC to 1 QC conversion. A two-fold increase in the signal-to-noise ratio is achieved by substituting low amplitude rf pulses in place of hard rf pulses for 5QC excitation and 5QC to 3QC conversion in a mixed multiple-quantum magic angle spinning (MAS) (MMQMAS) experiment. The anisotropic line shape for the low-amplitude rf pulse version of the MMQMAS experiment was observed to be distorted from the MAS line shape. The cause and implications of the distortion are discussed. (C) 2002 Elsevier Science (USA).

%B Solid State Nuclear Magnetic Resonance %V 22 %P 97-109 %8 Sep-Nov %@ 0926-2040 %G English %U ://WOS:000179154400003 %N 2-3 %M WOS:000179154400003 %! Investigations of low-amplitude radio frequency pulses at and away from rotary resonance conditions for I=5/2 Nuclei %R Doi 10.1006/Snmr.2002.0084 %0 Journal Article %J Solid State Nuclear Magnetic Resonance %D 1998 %T Imaging of laser-polarized solid xenon %A Song, Y. Q. %A Taylor, R. E. %A Pines, A. %K gas %X

The enhanced spin polarization produced by optical pumping of gaseous rubidium/xenon samples has made possible a number of recent experiments in nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI). Here we report MRI of laser-polarized xenon in the solid phase at low temperature. Due to the high xenon density in the solid phase and the enhanced spin polarization, it is possible to achieve high intensity and spatial resolution of the image. Signals were observed from xenon films solidified onto the glass container walls and not from an enclosed chili pepper. (C) 1998 Elsevier Science B.V.

%B Solid State Nuclear Magnetic Resonance %V 10 %P 247-250 %8 Feb %@ 0926-2040 %G English %U ://WOS:000073123500009 %N 4 %M WOS:000073123500009 %! Imaging of laser-polarized solid xenon %R Doi 10.1016/S0926-2040(97)00078-7 %0 Journal Article %J Journal of Magnetic Resonance %D 1998 %T In situ NMR analysis of fluids contained in sedimentary rock %A de Swiet, T. M. %A Tomaselli, M. %A Hurlimann, M. D. %A Pines, A. %K oil %X

Limitations of resolution and absorption in standard chemical spectroscopic techniques have made it difficult to study fluids in sedimentary rocks. In this paper, we show that a chemical characterization of pore fluids may be obtained in situ by magic angle spinning (MAS) nuclear magnetic resonance (NMR), which is normally used for solid samples. H-1 MAS-NMR spectra of water and crude oil in Berea sandstone show sufficient chemical shift resolution for a straightforward determination of the oil/water ratio, (C) 1998 Academic Press.

%B Journal of Magnetic Resonance %V 133 %P 385-387 %8 Aug %@ 1090-7807 %G English %U ://WOS:000075748200020 %N 2 %M WOS:000075748200020 %! In situ NMR analysis of fluids contained in sedimentary rock %R Doi 10.1006/Jmre.1998.1459 %0 Journal Article %J Proceedings of the National Academy of Sciences of the United States of America %D 1997 %T In vivo NMR and MRI using injection delivery of laser-polarized xenon %A Goodson, B. M. %A Song, Y. Q. %A Taylor, R. E. %A Schepkin, V. D. %A Brennan, K. M. %A Chingas, G. C. %A Budinger, T. F. %A Navon, G. %A Pines, A. %K humans %X

Because xenon NMR is highly sensitive to the local environment, laser-polarized xenon could be a unique probe of living tissues. Realization of clinical and medical science applications beyond lung airspace imaging requires methods of efficient delivery of laser-polarized xenon to tissues, because of the short spin-lattice relaxation times and relatively low concentrations of xenon attainable in the body. Preliminary results from the application of a polarized xenon injection technique for in vivo Xe-129 NMR/MRI are extrapolated along with a simple model of xenon transit to show that the peak local concentration of polarized xenon delivered to tissues by injection may exceed that delivered by respiration by severalfold.

%B Proceedings of the National Academy of Sciences of the United States of America %V 94 %P 14725-14729 %8 Dec 23 %@ 0027-8424 %G English %U ://WOS:000071182800090 %N 26 %M WOS:000071182800090 %! In vivo NMR and MRI using injection delivery of laser-polarized xenon %R Doi 10.1073/Pnas.94.26.14725 %0 Journal Article %J Journal of Chemical Physics %D 1996 %T Isotropic second-order dipolar shifts in the rotating frame %A Ernst, M. %A Kolbert, A. C. %A Schmidt-Rohr, K. %A Pines, A. %K spins %X

An experiment is described that utilizes the truncation of the Hamiltonian in the rotating frame by a radio-frequency field designed to yield an isotropic shift for the dipolar coupling. This approach allows the measurement of a normally orientation-dependent coupling constant by a single isotropic value. The dipolar isotropic shift is closely related to the field-dependent chemical shift in solids due to the second-order dipolar perturbation observed in magic-angle spinning experiments. In the rotating frame, larger shifts of up to 1000 Hz can be observed for the case of a one-bond C-H coupling compared to a shift of a few Hertz in the laboratory-frame experiment. In addition to the isotropic shift, a line broadening due to the P-4(cos beta) terms is observed when the experiment is carried out under magic-angle sample spinning (MAS) conditions, leading to the requirement of higher-order averaging such as double rotation (DOR) for obtaining narrow lines. As an application of this new experiment the separation of CH, CH2, and CH3 groups in a 2D spectrum under MAS is demonstrated. Implemented under DOR it could be used as a technique to select carbon atoms according to the number of directly attached protons. (C) 1996 American Institute of Physics.

%B Journal of Chemical Physics %V 104 %P 8258-8268 %8 Jun 1 %@ 0021-9606 %G English %U ://WOS:A1996UM90900008 %N 21 %M WOS:A1996UM90900008 %! Isotropic second-order dipolar shifts in the rotating frame %R Doi 10.1063/1.471579 %0 Journal Article %J Journal of Physical Chemistry %D 1992 %T Isotropic Chemical-Shifts and Quadrupolar Parameters for O-17 Using Dynamic-Angle Spinning Nmr %A Mueller, K. T. %A Baltisberger, J. H. %A Wooten, E. W. %A Pines, A. %K zeolites %X

Several oxygen-17-enriched silicates were studied using dynamic-angle spinning (DAS) NMR spectroscopy at two magnetic field strengths. The DAS method averages second-order quadrupolar interactions by reorienting a sample about a time-dependent axis, thereby yielding high-resolution spectra for half-odd integer spin quadrupolar nuclei such as oxygen-17. A narrow spectral line is observed for each distinct oxygen site in a powdered sample at the sum of the isotropic chemical shift and the field-dependent isotropic second-order quadrupolar shift. Using equations for the total shift observed at two field strengths, the chemical shift is uniquely determined together with a product of the quadrupolar coupling constant (C(Q) = e2qQ/h) and the quadrupolar asymmetry parameter (eta). For one silicate, we demonstrate aa computer program that uses the isotropic shifts and quadrupolar products as constraints and provides simulations of overlapped magic-angle spinning line shapes. In this way the quadrupolar parameters, C(Q) and eta, are determined separately for each crystallographic site. The silicates studied include the discrete orthosilicates larnite (Ca2SiO4) and forsterite (Mg2SiO4), as well as diopside (CaMgSi2O6), wollastonite (CaSiO3), and clinoenstatite (MgSiO3), which are minerals composed of chains of silicon-oxygen tetrahedra.

%B Journal of Physical Chemistry %V 96 %P 7001-7004 %8 Aug 20 %@ 0022-3654 %G English %U ://WOS:A1992JK80700028 %N 17 %M WOS:A1992JK80700028 %! Isotropic Chemical-Shifts and Quadrupolar Parameters for O-17 Using Dynamic-Angle Spinning Nmr %R Doi 10.1021/J100196a028 %0 Journal Article %J Journal of Physical Chemistry %D 1990 %T Investigations of Adsorbed Organic-Molecules in Na-Y Zeolite by Xe-129 Nmr %A Demenorval, L. C. %A Raftery, D. %A Liu, S. B. %A Takegoshi, K. %A Ryoo, R. %A Pines, A. %B Journal of Physical Chemistry %V 94 %P 27-31 %8 Jan 11 %@ 0022-3654 %G English %U ://WOS:A1990CH53200006 %N 1 %M WOS:A1990CH53200006 %! Investigations of Adsorbed Organic-Molecules in Na-Y Zeolite by Xe-129 Nmr %R Doi 10.1021/J100364a006 %0 Journal Article %J Journal of Magnetic Resonance %D 1988 %T Iterative Carr-Purcell Trains %A Shaka, A. J. %A Rucker, S. P. %A Pines, A. %B Journal of Magnetic Resonance %V 77 %P 606-611 %8 May %@ 0022-2364 %G English %U ://WOS:A1988N456100022 %N 3 %M WOS:A1988N456100022 %! Iterative Carr-Purcell Trains %R Doi 10.1016/0022-2364(88)90022-4 %0 Journal Article %J Journal of Magnetic Resonance %D 1988 %T Iterative Schemes for Bilinear Operators - Application to Spin Decoupling %A Shaka, A. J. %A Lee, C. J. %A Pines, A. %B Journal of Magnetic Resonance %V 77 %P 274-293 %8 Apr %@ 0022-2364 %G English %U ://WOS:A1988N164700006 %N 2 %M WOS:A1988N164700006 %! Iterative Schemes for Bilinear Operators - Application to Spin Decoupling %R Doi 10.1016/0022-2364(88)90178-3 %0 Journal Article %J Journal of Chemical Physics %D 1987 %T Iterative Maps for Broad-Band Excitation of Transverse Coherence in 2 Level Systems %A Cho, H. %A Pines, A. %B Journal of Chemical Physics %V 86 %P 6591-6601 %8 Jun 15 %@ 0021-9606 %G English %U ://WOS:A1987H766500003 %N 12 %M WOS:A1987H766500003 %! Iterative Maps for Broad-Band Excitation of Transverse Coherence in 2 Level Systems %R Doi 10.1063/1.452405 %0 Journal Article %J Journal of Chemical Physics %D 1987 %T Iterative Maps with Multiple Fixed-Points for Excitation of 2 Level Systems %A Cho, H. %A Baum, J. %A Pines, A. %B Journal of Chemical Physics %V 86 %P 3089-3106 %8 Mar 15 %@ 0021-9606 %G English %U ://WOS:A1987G442400004 %N 6 %M WOS:A1987G442400004 %! Iterative Maps with Multiple Fixed-Points for Excitation of 2 Level Systems %R Doi 10.1063/1.452020 %0 Journal Article %J Physical Review Letters %D 1986 %T Indirect Phase Detection of Nmr Spinor Transitions %A Suter, D. %A Pines, A. %A Mehring, M. %B Physical Review Letters %V 57 %P 242-244 %8 Jul 14 %@ 0031-9007 %G English %U ://WOS:A1986D125600022 %N 2 %M WOS:A1986D125600022 %! Indirect Phase Detection of Nmr Spinor Transitions %R Doi 10.1103/Physrevlett.57.242 %0 Journal Article %J Physical Review Letters %D 1986 %T Iterative Maps for Bistable Excitation of 2-Level Systems %A Cho, H. M. %A Tycko, R. %A Pines, A. %A Guckenheimer, J. %B Physical Review Letters %V 56 %P 1905-1908 %8 May 5 %@ 0031-9007 %G English %U ://WOS:A1986C111400006 %N 18 %M WOS:A1986C111400006 %! Iterative Maps for Bistable Excitation of 2-Level Systems %R Doi 10.1103/Physrevlett.56.1905 %0 Journal Article %J Chemical Physics Letters %D 1984 %T Iterative Schemes for Broad-Band and Narrow-Band Population-Inversion in Nmr %A Tycko, R. %A Pines, A. %B Chemical Physics Letters %V 111 %P 462-467 %@ 0009-2614 %G English %U ://WOS:A1984TU81300031 %N 4-5 %M WOS:A1984TU81300031 %! Iterative Schemes for Broad-Band and Narrow-Band Population-Inversion in Nmr %R Doi 10.1016/0009-2614(84)85541-4