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  1. Article ; Online: Post-acquisition correction of NMR spectra distorted by dynamic and static field inhomogeneity of cryogen-free magnets.

    Karabanov, Alexander / Kryukov, Eugeny / Langlais, Denis / Iuga, Dinu / Good, Jeremy

    Journal of magnetic resonance (San Diego, Calif. : 1997)

    2023  Volume 353, Page(s) 107494

    Abstract: Post-acquisition correction of NMR spectra is an important part of NMR spectroscopy that enables refined NMR spectra to be obtained, clean from undesirable out-phasing, broadening and noising. We describe analytical and numerical mathematical methods for ...

    Abstract Post-acquisition correction of NMR spectra is an important part of NMR spectroscopy that enables refined NMR spectra to be obtained, clean from undesirable out-phasing, broadening and noising. We describe analytical and numerical mathematical methods for post-acquisition correction of NMR spectra distorted by static and dynamic magnetic field inhomogeneity caused by imperfections of main superconducting coils and the cold head operation, typical for cryogen-free magnets. For the dynamic inhomogeneity, we apply a variant of the general reference deconvolution method, complemented with our mathematical analysis of spectral parameters. For the static inhomogeneity, we apply the method of a delayed Fourier transform, also supported with our analytical calculations. We verify our approach by correction processing of high-field experimental liquid-state
    Language English
    Publishing date 2023-06-01
    Publishing country United States
    Document type Journal Article
    ZDB-ID 1469665-4
    ISSN 1096-0856 ; 1557-8968 ; 1090-7807 ; 0022-2364
    ISSN (online) 1096-0856 ; 1557-8968
    ISSN 1090-7807 ; 0022-2364
    DOI 10.1016/j.jmr.2023.107494
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  2. Article ; Online: Cryogen-free 400 MHz (9.4 T) solid state MAS NMR system with liquid state NMR potential.

    Kryukov, Eugeny / Karabanov, Alexander / Langlais, Denis / Iuga, Dinu / Reckless, Rupert / Good, Jeremy

    Solid state nuclear magnetic resonance

    2023  Volume 125, Page(s) 101873

    Abstract: We show that the temporal magnetic field distortion generated by the Cold Head operation can be removed and high quality Solid-State Magic Angle Spinning NMR results can be obtained with a cryogen-free magnet. The compact design of the cryogen-free ... ...

    Abstract We show that the temporal magnetic field distortion generated by the Cold Head operation can be removed and high quality Solid-State Magic Angle Spinning NMR results can be obtained with a cryogen-free magnet. The compact design of the cryogen-free magnets allows for the probe to be inserted either from the bottom (as in most NMR systems) or, more conveniently, from the top. The magnetic field settling time can be made as short as an hour after a field ramp. Therefore, a single cryogen-free magnet can be used at different fixed fields. The magnetic field can be changed every day without compromising the measurement resolution.
    MeSH term(s) Magnetic Resonance Spectroscopy/methods ; Magnetic Resonance Imaging ; Magnetic Fields ; Magnets
    Language English
    Publishing date 2023-05-04
    Publishing country Netherlands
    Document type Journal Article
    ZDB-ID 1122088-0
    ISSN 1527-3326 ; 0926-2040
    ISSN (online) 1527-3326
    ISSN 0926-2040
    DOI 10.1016/j.ssnmr.2023.101873
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    In stock of ZB MED Cologne/Königswinter

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  3. Article ; Online: Heteronuclear DNP of

    Gennaro, Antonio / Karabanov, Alexander / Potapov, Alexey / Köckenberger, Walter

    Physical chemistry chemical physics : PCCP

    2020  Volume 22, Issue 15, Page(s) 7803–7816

    Abstract: This work explores the dynamic nuclear polarization (DNP) of 1H and 19F nuclei in a sample of 25/75 (% v/v) fluorobenzene/toluene containing the radical 1,3-bisphenylene-2-phenylallyl radical (BDPA) as a polarizing agent. Previously, heteronuclear ... ...

    Abstract This work explores the dynamic nuclear polarization (DNP) of 1H and 19F nuclei in a sample of 25/75 (% v/v) fluorobenzene/toluene containing the radical 1,3-bisphenylene-2-phenylallyl radical (BDPA) as a polarizing agent. Previously, heteronuclear effects in DNP were studied by analysing the shapes of DNP spectra, or by observing cross-relaxation between nuclei of different types. In this work, we report a rather specific DNP spectrum, where 1H and 19F nuclei obtain polarizations of opposite signs upon microwave (MW) irradiation. In order to explain this observation, we introduce a novel mechanism called heteronuclear thermal mixing (hn-TM). Within this mechanism the spectra of opposite signs can then be explained due to the presence of four-spin systems, involving a pair of dipolar coupled electron spins and hyperfine coupled nuclear spins of 1H and 19F, such that a condition relating their Larmor frequencies |ω1e - ω2e| ≈ ωH - ωF is satisfied. Under this condition, a strong mixing of electron and nuclear states takes place, enabling simultaneous four-spin flip-flops. Irradiation of electron spin transitions with MW followed by such four-spin flip-flops produces non-equilibrium populations of |αHβF and |βHαF states, thus leading to the enhancements of opposite signs for 1H and 19F. Signal enhancements, build-up times and DNP-spectra as a function of MW power and polarizing agent concentration, all provide additional support for assigning the observed DNP mechanism as hn-TM and distinguishing it from other possible mechanisms. We also develop a quantum mechanical model of hn-TM based on averaging of spin Hamiltonians. Simulations based on this model show very good qualitative agreement with experimental data. In addition, the system exhibits cross-relaxation between 1H and 19F induced by the presence of BDPA, which was detected by measuring the 19F signal build-up upon saturation of 1H nuclei with a train of radio-frequency pulses. We demonstrate that such cross-relaxation most likely originates due to the same electron and nuclear states mixing in the four-spin systems.
    Language English
    Publishing date 2020-04-06
    Publishing country England
    Document type Journal Article
    ZDB-ID 1476244-4
    ISSN 1463-9084 ; 1463-9076
    ISSN (online) 1463-9084
    ISSN 1463-9076
    DOI 10.1039/d0cp00892c
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  4. Article ; Online: Solid effect DNP polarization dynamics in a system of many spins.

    Wiśniewski, Daniel / Karabanov, Alexander / Lesanovsky, Igor / Köckenberger, Walter

    Journal of magnetic resonance (San Diego, Calif. : 1997)

    2016  Volume 264, Page(s) 30–38

    Abstract: We discuss the polarization dynamics during solid effect dynamic nuclear polarization (DNP) in a central spin model that consists of an electron surrounded by many nuclei. To this end we use a recently developed formalism and validate first its ... ...

    Abstract We discuss the polarization dynamics during solid effect dynamic nuclear polarization (DNP) in a central spin model that consists of an electron surrounded by many nuclei. To this end we use a recently developed formalism and validate first its performance by comparing its predictions to results obtained by solving the Liouville von Neumann master equation. The use of a Monte Carlo method in our formalism makes it possible to significantly increase the number of spins considered in the model system. We then analyse the dependence of the nuclear bulk polarization on the presence of nuclei in the vicinity of the electron and demonstrate that increasing the minimal distance between nuclei and electrons leads to a rise of the nuclear bulk polarization. These observations have implications for the design of radicals that can lead to improved values of nuclear spin polarization. Furthermore, we discuss the potential to extend our formalism to more complex spin systems such as cross effect DNP.
    Language English
    Publishing date 2016-03
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 1469665-4
    ISSN 1096-0856 ; 1557-8968 ; 1090-7807 ; 0022-2364
    ISSN (online) 1096-0856 ; 1557-8968
    ISSN 1090-7807 ; 0022-2364
    DOI 10.1016/j.jmr.2016.01.016
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  5. Article ; Online: Conversion of parahydrogen induced longitudinal two-spin order to evenly distributed single spin polarisation by optimal control pulse sequences.

    Bretschneider, Christian / Karabanov, Alexander / Nielsen, Niels Chr / Köckenberger, Walter

    The Journal of chemical physics

    2012  Volume 136, Issue 9, Page(s) 94201

    Abstract: Strongly enhanced spin polarization in the form of longitudinal spin order can be generated on target molecules by using parahydrogen in a catalyzed hydrogenation reaction. An optimal control algorithm was used to generate radiofrequency pulse sequences ... ...

    Abstract Strongly enhanced spin polarization in the form of longitudinal spin order can be generated on target molecules by using parahydrogen in a catalyzed hydrogenation reaction. An optimal control algorithm was used to generate radiofrequency pulse sequences which convert the arising longitudinal two-spin order into single-spin Zeeman order with high efficiency and distribute it evenly between three coupled spins within the same molecule. The pulses are designed to be very robust towards variations in the B(0) and B(1) fields. Furthermore, this strategy is applied to enhance the NMR signal in an ultrafast gradient assisted single excitation two-dimensional spectroscopy experiment.
    MeSH term(s) Hydrogen/chemistry ; Magnetic Resonance Spectroscopy ; Tomography, Optical Coherence
    Chemical Substances Hydrogen (7YNJ3PO35Z)
    Language English
    Publishing date 2012-03-07
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 3113-6
    ISSN 1089-7690 ; 0021-9606
    ISSN (online) 1089-7690
    ISSN 0021-9606
    DOI 10.1063/1.3691193
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    In stock of ZB MED Bonn / Germany

    Z 4' 49/16: Show issues

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  6. Article ; Online: Symmetries of the master equation and long-lived states of nuclear spins.

    Karabanov, Alexander A / Bretschneider, Christian / Köckenberger, Walter

    The Journal of chemical physics

    2009  Volume 131, Issue 20, Page(s) 204105

    Abstract: In terms of the master equation of relaxation, long-lived states in systems of n interacting spin-1/2 nuclei are described as those with eigenvalues much less than the characteristic T(1) rate. It is demonstrated that degeneracies of correlations between ...

    Abstract In terms of the master equation of relaxation, long-lived states in systems of n interacting spin-1/2 nuclei are described as those with eigenvalues much less than the characteristic T(1) rate. It is demonstrated that degeneracies of correlations between interacting dipole-dipole pairs are responsible for their presence. The case n=3 is considered in full detail.
    Language English
    Publishing date 2009-11-28
    Publishing country United States
    Document type Journal Article
    ZDB-ID 3113-6
    ISSN 1089-7690 ; 0021-9606
    ISSN (online) 1089-7690
    ISSN 0021-9606
    DOI 10.1063/1.3265852
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  7. Article ; Online: Dynamic nuclear polarisation by thermal mixing: quantum theory and macroscopic simulations.

    Karabanov, Alexander / Kwiatkowski, Grzegorz / Perotto, Carlo U / Wiśniewski, Daniel / McMaster, Jonathan / Lesanovsky, Igor / Köckenberger, Walter

    Physical chemistry chemical physics : PCCP

    2016  Volume 18, Issue 43, Page(s) 30093–30104

    Abstract: A theory of dynamic nuclear polarisation (DNP) by thermal mixing is suggested based on purely quantum considerations. A minimal 6-level microscopic model is developed to test the theory and link it to the well-known thermodynamic model. Optimal ... ...

    Abstract A theory of dynamic nuclear polarisation (DNP) by thermal mixing is suggested based on purely quantum considerations. A minimal 6-level microscopic model is developed to test the theory and link it to the well-known thermodynamic model. Optimal conditions for the nuclear polarization enhancement and effects of inhomogeneous broadening of the electron resonance are discussed. Macroscopic simulations of nuclear polarization spectra displaying good agreement with experiments, involving BDPA and trityl free radicals, are presented.
    Language English
    Publishing date 2016-11-02
    Publishing country England
    Document type Journal Article
    ZDB-ID 1476244-4
    ISSN 1463-9084 ; 1463-9076
    ISSN (online) 1463-9084
    ISSN 1463-9076
    DOI 10.1039/c6cp04345c
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  8. Article ; Online: Quantum mechanical simulation of solid effect dynamic nuclear polarisation using Krylov-Bogolyubov time averaging and a restricted state-space.

    Karabanov, Alexander / van der Drift, Anniek / Edwards, Luke J / Kuprov, Ilya / Köckenberger, Walter

    Physical chemistry chemical physics : PCCP

    2012  Volume 14, Issue 8, Page(s) 2658–2668

    Abstract: A strategy is described for simulations of solid effect dynamic nuclear polarisation that reduces substantially the dimension of the quantum mechanical problem. Averaging the Hamiltonian in the doubly rotating frame is used to confine the active space to ...

    Abstract A strategy is described for simulations of solid effect dynamic nuclear polarisation that reduces substantially the dimension of the quantum mechanical problem. Averaging the Hamiltonian in the doubly rotating frame is used to confine the active space to the zero quantum coherence subspace. A further restriction of the Liouville space is made by truncating higher spin order states, which are weakly populated due to the presence of relaxation processes. Based on a dissipative transport equation, which is used to estimate the transport of the magnetisation starting from single spin order to higher spin order states, a minimal spin order for the states is calculated that needs to be taken into account for the spin dynamics simulation. The strategy accelerates individual spin calculations by orders of magnitude, thus making it possible to simulate the polarisation dynamics of systems with up to 25 nuclear spins.
    Language English
    Publishing date 2012-02-28
    Publishing country England
    Document type Journal Article
    ZDB-ID 1476244-4
    ISSN 1463-9084 ; 1463-9076
    ISSN (online) 1463-9084
    ISSN 1463-9076
    DOI 10.1039/c2cp23233b
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  9. Article: Two-level systems with relaxation.

    Rourke, David E / Khodarinova, Larisa / Karabanov, Alexander A

    Physical review letters

    2004  Volume 92, Issue 16, Page(s) 163003

    Abstract: A method is presented for the coherent control of two-level systems when T2 relaxation is significant. The Bloch equations are rewritten as an equation of motion of the stereographic projection, Gamma, of the spin vector. This allows a Schur-type ... ...

    Abstract A method is presented for the coherent control of two-level systems when T2 relaxation is significant. The Bloch equations are rewritten as an equation of motion of the stereographic projection, Gamma, of the spin vector. This allows a Schur-type iteration used for the design of shaped pulses in magnetic resonance and coherent optics to be extended to include the effect of T2. In general, the effect of T2 on Gamma cannot be completely compensated for, although in practice it can be to a high degree. An example is presented of a driving field that produces a coherent superposition (no on-diagonal elements of the density matrix) over a chosen band of frequencies, in the presence of relaxation.
    Language English
    Publishing date 2004-04-23
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.92.163003
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    In stock of ZB MED Bonn / Germany

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  10. Article ; Online: On the accuracy of the state space restriction approximation for spin dynamics simulations.

    Karabanov, Alexander / Kuprov, Ilya / Charnock, G T P / van der Drift, Anniek / Edwards, Luke J / Köckenberger, Walter

    The Journal of chemical physics

    2011  Volume 135, Issue 8, Page(s) 84106

    Abstract: We present an algebraic foundation for the state space restriction approximation in spin dynamics simulations and derive applicability criteria as well as minimal basis set requirements for practically encountered simulation tasks. The results are ... ...

    Abstract We present an algebraic foundation for the state space restriction approximation in spin dynamics simulations and derive applicability criteria as well as minimal basis set requirements for practically encountered simulation tasks. The results are illustrated with nuclear magnetic resonance (NMR), electron spin resonance (ESR), dynamic nuclear polarization (DNP), and spin chemistry simulations. It is demonstrated that state space restriction yields accurate results in systems where the time scale of spin relaxation processes approximately matches the time scale of the experiment. Rigorous error bounds and basis set requirements are derived.
    Language English
    Publishing date 2011-08-28
    Publishing country United States
    Document type Journal Article
    ZDB-ID 3113-6
    ISSN 1089-7690 ; 0021-9606
    ISSN (online) 1089-7690
    ISSN 0021-9606
    DOI 10.1063/1.3624564
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