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  • 1
    Electronic Resource
    Electronic Resource
    Magnetic Field Effects Observed upon Photolysis of Para-Substituted Diphenyl Disulfides in Micellar Solutions (1994)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 4069-4075 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100066a027
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  • 2
    Electronic Resource
    Electronic Resource
    Electron–electron–nuclear three-spin mixing in spin-correlated radical pairs (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 10072-10086 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron–electron–nuclear three-spin mixing occurs in radical pairs in solid-state matrices if the radicals feature a significant electron–electron spin coupling and an anisotropic hyperfine coupling. The perturbation of nuclear frequencies by the electron–electron spin coupling and the three-spin mixing have to be generally considered in the calculation of transition frequencies and probabilities in such radical pairs. Analytical descriptions of three-spin mixing for different ratios of the spin Hamiltonian parameters are introduced. It is found that nuclear frequencies are strongly perturbed if the difference of the Zeeman energies of the two electron spins is matched to half the hyperfine coupling and that three-spin mixing is maximum, if also the nuclear Zeeman frequency matches the former two interactions. Such double matching situations may be encountered for pairs of organic radicals under the conditions where transient electron spin resonance (ESR) experiments are usually performed. If three-spin mixing is significant, spin-correlated radical pairs are born in a state that features nuclear coherence in addition to the electron spin zero-quantum coherence that is created irrespective of this mixing. The possibility is discussed to detect such chemically induced nuclear coherence (CINC) in transient electron spin resonance experiments by selective microwave irradiation. It is shown that subsequent electron transfer reactions can yield chemically induced dynamic nuclear coherence (CIDNC) in isolated radicals and chemically induced dynamic nuclear polarization (CIDNP) in diamagnetic products if three-spin mixing is significant. The novel CINC, CIDNC, and CIDNP effects in the solid state might be used in the structure determination of spin-correlated radical pairs with applications to photosynthesis research. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474063
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  • 3
    Electronic Resource
    Electronic Resource
    Spin locking of I=3/2 nuclei in static and spinning samples: A description by abstract spins and Floquet formalism (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 907-917 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Abstract spin formalism is introduced to simplify the quantum mechanical description of spins I=3/2. The approach is based on a factorization of Hilbert space that can be applied to any spin for which 2I+1 is not a prime number. For I=3/2, a description in terms of two coupled abstract spins 1/2 is obtained that allows one to make use of the well-established product operator formalism. This approach is applied to the analysis of spin lock of the central transition in a static sample. The treatment is extended to the case of magic angle sample spinning by using Floquet operator formalism [A. Schmidt and S. Vega, J. Chem. Phys. 96, 6895 (1987)]. It is demonstrated that a proper spin lock requires a sample spinning frequency that is larger than the radio frequency field strength. The theoretical results are confirmed by numerical simulations and experiments. The concept of spin locking in the fast-spinning, low-power regime is utilized in a cross polarization experiment on sodium nitrite. Cross polarization from 23Na to 15N at a distance of more than 2.6 Å results in an about sevenfold better signal-to-noise ratio than direct polarization. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475454
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  • 4
    Electronic Resource
    Electronic Resource
    Hyperfine decoupling in electron spin resonance (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 9979-9991 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new class of experiments is introduced to electron spin resonance (ESR) spectroscopy that utilizes hyperfine decoupling for resolution enhancement and spectrum simplification, and that provides a basis for correlation techniques. A general framework is provided for the discussion of pulse ESR experiments on systems with arbitrary effective electron spin S and an arbitrary number of coupled nuclear spins and is used to describe spin decoupling in pulse ESR and ENDOR spectroscopy. Analytical expressions are given for the hyperfine-decoupled nuclear frequencies and the residual hyperfine splittings of spin-1/2 nuclei during strong decoupling. Pulse sequences are proposed for hyperfine-decoupled electron spin echo envelope modulation (ESEEM) and electron nuclear double resonance (ENDOR) experiments as well as for the correlation of the hyperfine-decoupled ESEEM spectrum with two-pulse and three-pulse ESEEM spectra and of hyperfine-decoupled ENDOR with the hyperfine splittings. It is shown that hyperfine-decoupled ESEEM and ENDOR spectra can reveal information on the magnetic quantum numbers involved in an ESR observer transition, and that choosing a transition mS↔mS+1 with mS≠−1/2 can improve the resolution of a nuclear frequency spectrum. In addition, such experiments can be used to determine the relative signs of hyperfine couplings. The potential of the two-dimensional DECENT (decoupled ESEEM correlated to nuclear transition frequencies) experiment is demonstrated on weakly coupled 14N nuclei in both an ordered and a disordered system and on the hexaquo manganese (II) complex (S=5/2) in a single crystal. It is also shown that for the ESR observer transition mS=(−3/2↔−5/2) the S=5/2 system yields highly resolved hyperfine-decoupled ENDOR spectra which allow for a complete assignment of the ENDOR lines. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474073
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  • 5
    Electronic Resource
    Electronic Resource
    Matched two-pulse electron spin echo envelope modulation spectroscopy (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 2199-2211 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The theory of nonideal microwave pulses acting on electron–nuclear spin systems is extended and applied to optimize the two-pulse electron spin echo envelope modulation (ESEEM) experiment. A superoperator approach for a computationally efficient simulation of experiments involving non-ideal pulses is introduced and the corresponding unitary transformation superoperator is given analytically for a system consisting of one electron spin S=1/2 and one nuclear spin I=1/2. Density operator single-element transfers are divided into allowed and forbidden ones and are classified according to their functioning in pulse ESR. By increasing the efficiency of forbidden transfers by Hartmann–Hahn matching during prolonged pulses, the sensitivity of the conventional two-pulse ESEEM experiment may drastically be improved and discrimination between basic, hyperfine, and combination frequencies becomes possible. The implications of the theory for spin systems with an arbitrary number of nuclear spins 1/2 are investigated by deriving and discussing a general condition for Hartmann–Hahn matching of forbidden transitions. It is shown that the product rule valid for two-pulse echo modulations caused by more than one nucleus does not hold for nonideal pulses. A method is developed that allows one to reduce the thus arising large dimensionality of the diagonalization problem in numerical simulations. The theoretical conclusions are verified by experiments on two transition metal complexes in single crystals and on a spin-label-doped polymer sample. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472087
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  • 6
    Electronic Resource
    Electronic Resource
    The generalized hyperfine sublevel coherence transfer experiment in one and two dimensions (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2172-2184 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The generalized hyperfine sublevel coherence transfer pulsed ESR experiment is described that consists of a nuclear coherence generator, a first evolution period, a nonselective microwave π pulse, a second evolution period, and a nuclear coherence detector. Several incrementation schemes to perform one-dimensional experiments are discussed, namely, a four-pulse electron spin echo envelope modulation scheme for measuring combination frequencies, two types of nuclear coherence transfer echo experiments (DEFENCE) to record dead time free electron spin echo envelope modulation spectra of disordered systems, and a new hyperfine spectroscopy experiment for the direct measurement of hyperfine frequencies. The one-dimensional experiments can be combined to four two-dimensional schemes. In addition to hyperfine sublevel correlation spectroscopy (HYSCORE) where two nuclear frequency dimensions are correlated, three new two-dimensional experiments are introduced that correlate the hyperfine with the nuclear frequency, the combination frequency with the nuclear frequency, and the combination frequency with the hyperfine frequency. With a properly selected two-dimensional incrementation scheme the digital resolution and signal-to-noise ratio of the spectra can be improved and artifacts can be suppressed. The predicted features of the one- and two-dimensional experiments are verified experimentally for both ordered and disordered systems using echo and coherent Raman beat detection. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470973
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  • 7
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    Role of the nucleotidyl cyclase helical domain in catalytically active dimer formation (2017)
    National Academy of Sciences
    Details
    Publication Date: 2017-10-30
    Description: Nucleotidyl cyclases, including membrane-integral and soluble adenylyl and guanylyl cyclases, are central components in a wide range of signaling pathways. These proteins are architecturally diverse, yet many of them share a conserved feature, a helical region that precedes the catalytic cyclase domain. The role of this region in cyclase dimerization has been a subject of debate. Although mutations within this region in various cyclases have been linked to genetic diseases, the molecular details of their effects on the enzymes remain unknown. Here, we report an X-ray structure of the cytosolic portion of the membrane-integral adenylyl cyclase Cya from Mycobacterium intracellulare in a nucleotide-bound state. The helical domains of each Cya monomer form a tight hairpin, bringing the two catalytic domains into an active dimerized state. Mutations in the helical domain of Cya mimic the disease-related mutations in human proteins, recapitulating the profiles of the corresponding mutated enzymes, adenylyl cyclase-5 and retinal guanylyl cyclase-1. Our experiments with full-length Cya and its cytosolic domain link the mutations to protein stability, and the ability to induce an active dimeric conformation of the catalytic domains. Sequence conservation indicates that this domain is an integral part of cyclase machinery across protein families and species. Our study provides evidence for a role of the helical domain in establishing a catalytically competent dimeric cyclase conformation. Our results also suggest that the disease-associated mutations in the corresponding regions of human nucleotidyl cyclases disrupt the normal helical domain structure.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 8
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    Multiple Pathway Relaxation Enhancement in the System Composed of Three Paramagnetic Species: Nitroxide Radical–Ln3+–O2 (2012)
    American Chemical Society
    Details
    Publication Date: 2012-05-04
    Electronic ISSN: 1948-7185
    Topics: Physics
    Published by American Chemical Society
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  • 9
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    RIDME Spectroscopy with Gd(III) Centers (2014)
    American Chemical Society
    Details
    Publication Date: 2014-11-03
    Electronic ISSN: 1948-7185
    Topics: Physics
    Published by American Chemical Society
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  • 10
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    Linear and Kinked Oligo(phenyleneethynylene)s as Ideal Molecular Calibrants for Förster Resonance Energy Transfer (2019)
    American Chemical Society
    Details
    Publication Date: 2019-10-21
    Electronic ISSN: 1948-7185
    Topics: Physics
    Published by American Chemical Society
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