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  • 1.
    Aski, Sahar Nikkhou
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Takacs, Zoltan
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Inclusion complexes of cryptophane–E with dichloromethane and chloroform: A thermodynamic and kinetic study using the 1D-EXSY NMR method2008In: Magnetic Resonance in Chemistry, ISSN 0749-1581, E-ISSN 1097-458X, Vol. 46, no 12, p. 1135-1140Article in journal (Refereed)
    Abstract [en]

    Complexation equilibria and kinetics of exchange of chloroform and dichloromethane molecules between the cavity of cryptophane-E and bulk solution were investigated using NMR methods. Using one dimensional magnetization transfer (1D-EXSY type sequence), chemical exchange rates were measured in different temperature ranges, limited by the equilibrium constant values of the complexes and the boiling points of the guest substances. From the kinetic data, activation energies were calculated using the Arrhenius equation. From the temperature dependence of the association constant data, the enthalpy and entropy of complexation were estimated and compared with values for similar complexes of other cryptophanes.

  • 2. Bernatowicz, P
    et al.
    Kowalewski, J
    Stockholm University.
    Szymanski, S
    Nuclear-spin relaxation in nonrigid molecules: Discrete multisite local dynamics combined with anisotropic molecular reorientation2006In: Journal of Chemical Physics, Vol. 124Article in journal (Refereed)
  • 3.
    Ghalebani, Leila
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Kotsyubynskyy, Dmytro
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    NMR relaxation interference effects and internal dynamics in γ-cyclodextrin2008In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 195, no 1, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Multiple-magnetic field (9.4, 14.1 and 21.1 T) measurements of 13C spin–lattice and spin–spin relaxation rates, the heteronuclear Overhauser enhancement and cross-correlated relaxation rates (CCRRs) in the methylene groups are reported for γ-cyclodextrin in water/dimethylsulfoxide solution at 323 and 343 K. The CCRRs are obtained from differences in the initial relaxation rates of the components of the CH2 triplet in the 13C spectra. The relaxation data are analyzed using the Lipari–Szabo approach and a novel modification of the two-site jump model. According to the latter model, inclusion of the dipolar (CH,CH) cross-correlated longitudinal and transverse relaxation is important for estimating the rate of the conformational jumps in the hydroxymethyl group. Using the dynamic information from the jump model, we have also used the differences in the initial relaxation rates for the triplet components to estimate the anisotropy of the chemical shielding tensor.

  • 4. Kaderavek, Pavel
    et al.
    Zapletal, Vojtech
    Fiala, Radovan
    Srb, Pavel
    Padrta, Petr
    Precechtelova, Jana Pavlikova
    Soltesova, Maria
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Chmelik, Josef
    Sklenar, Vladimir
    Zidek, Lukas
    Spectral density mapping at multiple magnetic fields suitable for C-13 NMR relaxation studies2016In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 266, p. 23-40Article in journal (Refereed)
    Abstract [en]

    Standard spectral density mapping protocols, well suited for the analysis of N-15 relaxation rates, introduce significant systematic errors when applied to C-13 relaxation data, especially if the dynamics is dominated by motions with short correlation times (small molecules, dynamic residues of macromolecules). A possibility to improve the accuracy by employing cross-correlated relaxation rates and on measurements taken at several magnetic fields has been examined. A suite of protocols for analyzing such data has been developed and their performance tested. Applicability of the proposed protocols is documented in two case studies, spectral density mapping of a uniformly labeled RNA hairpin and of a selectively labeled disaccharide exhibiting highly anisotropic tumbling. Combination of auto- and cross-correlated relaxation data acquired at three magnetic fields was applied in the former case in order to separate effects of fast motions and conformational or chemical exchange. An approach using auto-correlated relaxation rates acquired at five magnetic fields, applicable to anisotropically moving molecules, was used in the latter case. The results were compared with a more advanced analysis of data obtained by interpolation of auto-correlated relaxation rates measured at seven magnetic fields, and with the spectral density mapping of cross-correlated relaxation rates. The results showed that sufficiently accurate values of auto- and cross-correlated spectral density functions at zero and C-13 frequencies can be obtained from data acquired at three magnetic fields for uniformly C-13-labeled molecules with a moderate anisotropy of the rotational diffusion tensor. Analysis of auto-correlated relaxation rates at five magnetic fields represents an alternative for molecules undergoing highly anisotropic motions.

  • 5.
    Khan, Shehryar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    A complete normal mode analysis of the Zero-Field Splitting in paramagnetic hexaaqua Mn(II) and Ni(II) complexesManuscript (preprint) (Other academic)
  • 6.
    Khan, Shehryar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kubica-Misztal, Aleksandra
    Kruk, Danuta
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Systematic theoretical investigation of the zero-field splitting in Gd(III) complexes: Wave function and density functional approaches2015In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, no 3, article id 034304Article in journal (Refereed)
    Abstract [en]

    The zero-field splitting (ZFS) of the electronic ground state in paramagnetic ions is a sensitive probe of the variations in the electronic and molecular structure with an impact on fields ranging from fundamental physical chemistry to medical applications. A detailed analysis of the ZFS in a series of symmetric Gd(III) complexes is presented in order to establish the applicability and accuracy of computational methods using multiconfigurational complete-active-space self-consistent field wave functions and of density functional theory calculations. The various computational schemes are then applied to larger complexes Gd(III)DOTA(H2O)(-), Gd(III)DTPA(H2O)(2-), and Gd(III)(H2O)(8)(3+) in order to analyze how the theoretical results compare to experimentally derived parameters. In contrast to approximations based on density functional theory, the multiconfigurational methods produce results for the ZFS of Gd(III) complexes on the correct order of magnitude.

  • 7.
    Khan, Shehryar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Peters, V.
    Stockholm University, Faculty of Science, Department of Physics.
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Zero-field splitting in the isoelectronic aqueous Gd(III) and Eu(II) complexes from a first principles analysis2018In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 503, p. 56-64Article in journal (Refereed)
    Abstract [en]

    The zero-field splitting (ZFS) of the ground state octet in aqueous Eu(II) and Gd(III) solutions was investigated through multi-configurational quantum chemical calculations and ab initio molecular dynamics (AIMD) simulations. Investigation of the ZFS of the lanthanide ions is essential to understand the electron spin dynamics and nuclear spin relaxation around paramagnetic ions and consequently the mechanisms underlying applications like magnetic resonance imaging. We found by comparing clusters at identical geometries but different metallic centres that there is not a simple relationship for their ZFS, in spite of the complexes being isoelectronic-each containing 7 unpaired f electrons. Through sampling it was established that inclusion of the first hydration shell has a dominant (over 90 %) influence on the ZFS. Extended sampling of aqueous Gd(III) showed that the 2nd order spin Hamiltonian formalism is valid and that the rhombic ZFS component is decisive.

  • 8.
    Khan, Shehryar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Pollet, Rodolphe
    Vuilleumier, Rodolphe
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    An ab initio CASSCF study of zero field splitting fluctuations in the octet ground state of aqueous [Gd(iii)(HPDO3A)(H2O)]2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, no 24, article id 244306Article in journal (Refereed)
    Abstract [en]

    In this work, we present ab initio calculations of the zero-field splitting (ZFS) of a gadolinium complex [Gd(m)(HPDO3A)(H2O)] sampled from an ab initio molecular dynamics (AIMD) simulation. We perform both post-Hartree-Fock (complete active space self-consistent field-CASSCF) and density functional theory (DFT) calculations of the ZFS and compare and contrast the methods with experimental data. Two different density functional approximations (TPSS and LC-BLYP) were investigated. The magnitude of the ZFS from the CASSCF calculations is in good agreement with experiment, whereas the DFT results in varying degrees overestimate the magnitude of the ZFS for both functionals and exhibit a strong functional dependence. It was found in the sampling over the AIMD trajectory that the fluctuations in the transient ZFS tensor derived from DFT are not correlated with those of CASSCF nor does the magnitude of the ZFS from CASSCF and DFT correlate. From the fluctuations in the ZFS tensor, we extract a correlation time of the transient ZFS which is on the sub-picosecond time scale, showing a faster decay than experimental estimates.

  • 9.
    Kotsyubynskyy, Dmytro
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tallavaara, Pekka
    Telkki, Ville-Veikko
    Jokisaari, Jukka
    Polyakov, Evgeny
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Carbon-13 NOESY and equivalent protons: methyl iodide dynamics2010In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 204, no 2, p. 239-247Article in journal (Refereed)
    Abstract [en]

    We have shown that proton-coupled carbon-13 2D NOESY experiments, performed on degenerate spin systems, can provide unique quantitative information about anisotropic reorientational motions and molecular geometry. Relevant theory for AX2 and AX3 spin systems is presented, assuming the dipole–dipole and random field relaxation mechanisms of 13C nucleus, and demonstrated on methyl iodide solution in chloroform. Agreement with experimental intensities of all the six independent peaks is very good in the whole range of mixing times (up to 45 s).

  • 10. Kotsyubynskyy, Dmytro
    et al.
    Zerbetto, Mirco
    Šoltésová, Mária
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Charles University Prague .
    Engström, Olof
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pendrill, Robert
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kowalewski, Josef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Polimeno, Antonin
    Stochastic Modeling of Flexible Biomolecules Applied to NMR Relaxation: 2. Interpretation of Complex Dynamics in Linear Oligosaccharides2012In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 116, no 50, p. 14541-14555Article in journal (Refereed)
    Abstract [en]

    A computational stochastic approach is applied to the description of flexible molecules. By combining (i) molecular dynamics simulations, (ii) hydrodynamics approaches, and (iii) a multidimensional diffusive description for internal and global dynamics, it is possible to build an efficient integrated approach to the interpretation of relaxation processes in flexible systems. In particular, the model is applied to the interpretation of nuclear magnetic relaxation measurements of linear oligosaccharides, namely a mannose-containing trisaccharide and the pentasaccharide LNF-1. Experimental data are reproduced with sufficient accuracy without free model parameters.

  • 11.
    Kowalewski, Josef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nuclear spin relaxation in liquids and gases2014In: Nuclear Magnetic Resonance: Volume 43 / [ed] K. Kamienska-Trela, Royal Society of Chemistry, 2014, p. 230-285Chapter in book (Refereed)
    Abstract [en]

    The review covers the progress in the field of NMR relaxation in fluids during the period from June 2012 through May 2013. The emphasis is on comparatively simple liquids and solutions of physico-chemical and chemical interest, in analogy with the previous periods, but selected biophysics-related topics and relaxation-related work on more complex systems (macromolecular solutions, liquid crystalline systems, glassy and porous materials) are also covered. The first part of the chapter is concerned with general, physical and experimental aspects of nuclear spin relaxation, while the second part is concentrated on applications.

  • 12.
    Kowalewski, Josef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nuclear spin relaxation in liquids and gases2012In: Nuclear Magnetic Resonance: Volume 41 / [ed] Krystyna Kamienska-Trela, Jacek Wojcik, Royal Society of Chemistry, 2012, Vol. 40, p. 196-243Chapter in book (Refereed)
  • 13.
    Kowalewski, Josef
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Kruk, Danuta
    Paramagnetic Relaxation in Solution2011In: Encyclopedia of Magnetic Resonance / [ed] R.K. Harris and R.E. Wasylishen, John Wiley & Sons, 2011Chapter in book (Other academic)
    Abstract [en]

    Relaxation theory for paramagnetic systems is reviewed in a historical perspective and different principal aspects covered. The emphasis is on the post-Solomon–Bloembergen–Morgan developments of the last two decades. Experimental methods and protocols are presented briefly. Illustrative examples of experimental spin-lattice and spin-spin relaxation rates as a function of temperature and magnetic field are provided for transition metal and lanthanide complexes. Novel experiments and applications for metalloproteins are also mentioned. Finally, some joint investigations of variable-field paramagnetic relaxation enhancement and ESR spectral lineshapes are presented

  • 14.
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    From J-Coupling Theory to Paramagnetic Relaxation: 40 Years of NMR Research at Stockholm University2010In: Encyclopedia of Magnetic Resonance, Wiley , 2010, 1Chapter in book (Other academic)
  • 15.
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nuclear spin relaxation in liquids and gases2015In: Nuclear Magnetic Resonance: A Specialist Periodical Report / [ed] K. Kamienska Trela, Royal Society of Chemistry, 2015, Vol. 44, p. 235-293Chapter in book (Refereed)
    Abstract [en]

    The review covers the progress in the field of NMR relaxation in fluids during the period from June 2013 through May 2014. The emphasis is on comparatively simple liquids and solutions of physico-chemical and chemical interest, in analogy with the previous periods, but selected biophysics-related topics and relaxation-related work on more complex systems (macromolecular solutions, liquid crystalline systems, glassy and porous materials) are also covered. The first part of the chapter is concerned with general, physical and experimental aspects of nuclear spin relaxation, while the second part is concentrated on applications.

  • 16. Kruk, D.
    et al.
    Hoffmann, S. K.
    Goslar, J.
    Lijewski, S.
    Kubica-Misztal, A.
    Korpala, A.
    Oglodek, I.
    Kowalewski, Josef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Roessler, E. A.
    Moscicki, J.
    ESR lineshape and H-1 spin-lattice relaxation dispersion in propylene glycol solutions of nitroxide radicals - Joint analysis2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 139, no 24, p. 244502-Article in journal (Refereed)
    Abstract [en]

    Electron Spin Resonance (ESR) spectroscopy and Nuclear Magnetic Relaxation Dispersion (NMRD) experiments are reported for propylene glycol solutions of the nitroxide radical: 4-oxo-TEMPO-d(16) containing N-15 and N-14 isotopes. The NMRD experiments refer to H-1 spin-lattice relaxation measurements in a broad frequency range (10 kHz-20 MHz). A joint analysis of the ESR and NMRD data is performed. The ESR lineshapes give access to the nitrogen hyperfine tensor components and the rotational correlation time of the paramagnetic molecule. The NMRD data are interpreted in terms of the theory of paramagnetic relaxation enhancement in solutions of nitroxide radicals, recently presented by Kruk et al. [J. Chem. Phys. 138, 124506 (2013)]. The theory includes the effect of the electron spin relaxation on the H-1 relaxation of the solvent. The H-1 relaxation is caused by dipole-dipole interactions between the electron spin of the radical and the proton spins of the solvent molecules. These interactions are modulated by three dynamic processes: relative translational dynamics of the involved molecules, molecular rotation, and electron spin relaxation. The sensitivity to rotation originates from the non-central positions of the interacting spin in the molecules. The electronic relaxation is assumed to stem from the electron spin-nitrogen spin hyperfine coupling, modulated by rotation of the radical molecule. For the interpretation of the NMRD data, we use the nitrogen hyperfine coupling tensor obtained from ESR and fit the other relevant parameters. The consistency of the unified analysis of ESR and NMRD, evaluated by the agreement between the rotational correlation times obtained from ESR and NMRD, respectively, and the agreement of the translation diffusion coefficients with literature values obtained for pure propylene glycol, is demonstrated to be satisfactory.

  • 17. Kruk, D.
    et al.
    Korpala, A.
    Kowalewski, Josef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Roessler, E. A.
    Moscicki, J.
    H-1 relaxation dispersion in solutions of nitroxide radicals: Effects of hyperfine interactions with N-14 and N-15 nuclei2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 4, p. 044512-Article in journal (Refereed)
    Abstract [en]

    H-1 relaxation dispersion of decalin and glycerol solutions of nitroxide radicals, 4-oxo-TEMPO-d(16)-N-15 and 4-oxo-TEMPO-d(16)-N-14 was measured in the frequency range of 10 kHz-20 MHz (for H-1) using STELAR Field Cycling spectrometer. The purpose of the studies is to reveal how the spin dynamics of the free electron of the nitroxide radical affects the proton spin relaxation of the solvent molecules, depending on dynamical properties of the solvent. Combining the results for both solvents, the range of translational diffusion coefficients, 10(-9)-10(-11) m(2)/s, was covered (these values refer to the relative diffusion of the solvent and solute molecules). The data were analyzed in terms of relaxation formulas including the isotropic part of the electron spin - nitrogen spin hyperfine coupling (for the case of N-14 and N-15) and therefore valid for an arbitrary magnetic field. The influence of the hyperfine coupling on H-1 relaxation of solvent molecules depending on frequency and time-scale of the translational dynamics was discussed in detail. Special attention was given to the effect of isotope substitution (N-14/N-15). In parallel, the influence of rotational dynamics on the inter-molecular (radical - solvent) electron spin - proton spin dipole-dipole coupling (which is the relaxation mechanism of solvent protons) was investigated. The rotational dynamics is of importance as the interacting spins are not placed in the molecular centers. It was demonstrated that the role of the isotropic hyperfine coupling increases for slower dynamics, but it is of importance already in the fast motion range (10(-9)m(2)/s). The isotope effects is small, however clearly visible; the H-1 relaxation rate for the case of N-15 is larger (in the range of lower frequencies) than for N-14. It was shown that when the diffusion coefficient decreases below 5 x 10(-11) m(2)/s electron spin relaxation becomes of importance and its role becomes progressively more significant when the dynamics slows done. As far as the influence of the rotational dynamics is concerned, it was show that this process is of importance not only in the range of higher frequencies (like for diamagnetic solutions) but also at low and intermediate frequencies.

  • 18. Kruk, D.
    et al.
    Korpala, A.
    Kubica, A.
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Roessler, E. A.
    Moscicki, J.
    H-1 relaxation dispersion in solutions of nitroxide radicals: Influence of electron spin relaxation2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, no 12, p. 124506-Article in journal (Refereed)
    Abstract [en]

    The work presents a theory of nuclear (H-1) spin-lattice relaxation dispersion for solutions of N-15 and N-14 radicals, including electron spin relaxation effects. The theory is a generalization of the approach presented by Kruk et al. [J. Chem. Phys. 137, 044512 (2012)]. The electron spin relaxation is attributed to the anisotropic part of the electron spin-nitrogen spin hyperfine interaction modulated by rotational dynamics of the paramagnetic molecule, and described by means of Redfield relaxation theory. The H-1 relaxation is caused by electron spin-proton spin dipole-dipole interactions which are modulated by relative translational motion of the solvent and solute molecules. The spectral density characterizing the translational dynamics is described by the force-free-hard-sphere model. The electronic relaxation influences the H-1 relaxation by contributing to the fluctuations of the inter-molecular dipolar interactions. The developed theory is tested against H-1 spin-lattice relaxation dispersion data for glycerol solutions of 4-oxo-TEMPO-d(16)-N-15 and 4-oxo-TEMPO-d(16)-N-14 covering the frequency range of 10 kHz-20 MHz. The studies are carried out as a function of temperature starting at 328 K and going down to 290 K. The theory gives a consistent overall interpretation of the experimental data for both N-14 and N-15 systems and explains the features of H-1 relaxation dispersion resulting from the electron spin relaxation.

  • 19. Kruk, D.
    et al.
    Kowalewski, Josef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Tipikin, S.
    Freed, J. H.
    Moscicki, M.
    Mielczarek, A.
    Port, M.
    Joint analysis of ESR lineshapes and (1)H NMRD profiles of DOTA-Gd derivatives by means of the slow motion theory2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 2, p. 024508-Article in journal (Refereed)
    Abstract [en]

    The Swedish slow motion theory [Nilsson and Kowalewski, J. Magn. Reson. 146, 345 (2000)] applied so far to Nuclear Magnetic Relaxation Dispersion (NMRD) profiles for solutions of transition metal ion complexes has been extended to ESR spectral analysis, including in addition g-tensor anisotropy effects. The extended theory has been applied to interpret in a consistent way (within one set of parameters) NMRD profiles and ESR spectra at 95 and 237 GHz for two Gd(III) complexes denoted as P760 and P792 (hydrophilic derivatives of DOTA-Gd, with molecular masses of 5.6 and 6.5 kDa, respectively). The goal is to verify the applicability of the commonly used pseudorotational model of the transient zero field splitting (ZFS). According to this model the transient ZFS is described by a tensor of a constant amplitude, defined in its own principal axes system, which changes its orientation with respect to the laboratory frame according to the isotropic diffusion equation with a characteristic time constant (correlation time) reflecting the time scale of the distortional motion. This unified interpretation of the ESR and NMRD leads to reasonable agreement with the experimental data, indicating that the pseudorotational model indeed captures the essential features of the electron spin dynamics.

  • 20. Kruk, D
    et al.
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    General treatment of paramagnetic relaxation enhancement associated with translational diffusion2009In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 130, p. -174104Article in journal (Refereed)
    Abstract [en]

    A theory of nuclear spin relaxation in isotropic liquids for nuclear spins interacting with electron spins, residing in other molecules (the outer-sphere relaxation), is presented. The approach, valid outside of the Redfield limit for electron spin relaxation, is an extension of the Swedish slow motion theory [ Benetis et al., Mol. Phys. 48, 329 (1983) ; Nilsson and Kowalewski, J. Magn. Reson. 146, 345 (2000) ] for inner-sphere relaxation. It is demonstrated that the outer-sphere relaxation rate can be expressed as an integral of a product of a translational diffusion correlation function and a function analogous to the inner-sphere spectral density. A numerical implementation of the theory is described and applied to a large number of realistic parameter sets for S = 7/2 and S = 1, which may correspond to Gd(III) and Ni(II) systems. It is shown that the outer-sphere contribution is relevant and should be included into the analysis of nuclear magnetic relaxation dispersion relaxation profiles, especially for slow relative translational diffusion and fast molecular tumbling

  • 21. Kubica, A.
    et al.
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kruk, D.
    Odelius, Michel
    Stockholm University, Faculty of Science, Department of Physics.
    Zero-field splitting in nickel(II) complexes: A comparison of DFT and multi-configurational wavefunction calculations2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, no 6, p. 064304-Article in journal (Refereed)
    Abstract [en]

    The zero-field splitting (ZFS) is an important quantity in the electron spin Hamiltonian for S = 1 or higher. We report calculations of the ZFS in some six- and five-coordinated nickel(II) complexes (S = 1), using different levels of theory within the framework of the ORCA program package [F. Neese, Wiley Interdiscip. Rev.: Comput. Mol. Sci. 2, 73 (2012)]10.1002/wcms.81. We compare the high-end ab initio calculations (complete active space self-consistent field and n-electron valence state perturbation theory), making use of both the second-order perturbation theory and the quasi-degenerate perturbation approach, with density functional theory (DFT) methods using different functionals. The pattern of results obtained at the ab initio levels is quite consistent and in reasonable agreement with experimental data. The DFT methods used to calculate the ZFS give very strongly functional-dependent results and do not seem to function well for our systems.

  • 22. Petrov, Oleg
    et al.
    Tosner, Zdenek
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Csöregh, Ingeborg
    Kowalewski, Jozef
    Sandström, Dick
    Dynamics of Chloromethanes in Cryptophane-E Inclusion Complexes: A H-2 Solid State NMR and X-ray Diffraction Study2005In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 109, no 20, p. 4442-4451Article in journal (Refereed)
    Abstract [en]

    In this paper, we present a variable temperature 2H solid-state NMR investigation of cryptophane-E:chloroform and cryptophane-E:dichloromethane inclusion complexes. The 2H line shapes and nuclear spin relaxation rates were analyzed in terms of the distribution of C−D bond orientations and the time scale of the guest dynamics. It was found that encaged chloroform produces broad 2H spectra, and that its reorientation is relatively slow with a correlation time of 0.17 μs at 292 K. In contrast, the 2H line shapes of encaged dichloromethane are narrow and the motion of this guest molecule is fast with a correlation time of 1.4 ps at 283 K. The 2H NMR data were complemented by an X-ray diffraction study of the cryptophane-E:dichloromethane structure, which was utilized in the analysis of the NMR parameters.

  • 23.
    Steiner, Emilie
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Brotin, Thierry
    Takacs, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Chemical Shielding Anisotropies for Chloroform Exchanging between a Free Site and a Complex with Cryptophane-D: A Cross-Correlated NMR Relaxation Study2015In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 119, no 35, p. 11760-11767Article in journal (Refereed)
    Abstract [en]

    The case of C-13-labeled chloroform exchanging between a free site in solution and the encaged site within the cryptophane-D cavity is investigated using the measurements of longitudinal cross-correlated relaxation rates, involving the interference of the dipole-dipole and chemical shielding anisotropy interactions. A compact theoretical expression is provided, along with an experimental protocol, based on INEPT (insensitive nuclei enhanced by polarization)enhanced double-quantum-filtered inversion recovery measurements. The analysis of the build-up curves results in a set of cross-correlated relaxation rates for both the C-13 and H-1 spins at the two sites. It is demonstrated that the results can be given a consistent interpretation in terms of molecular-level properties, such as rotational correlation times, the Lipari-Szabo order parameter, and interaction strength constants. The analysis yields the bound-site carbon-13 chemical shielding anisotropy, Delta sigma(C) = -58 +/- 8 ppm, in good agreement with most recent liquid-crystal measurements and the corresponding proton shielding anisotropy, Delta sigma(H) = 14 +/- 2 ppm.

  • 24.
    Steiner, Emilie
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mathew, Renny
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zimmermann, Iwan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Brotin, Thierry
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Investigation of chloromethane complexes of cryptophane-A analogue with butoxy groups using C-13 NMR in the solid state and solution along with single crystal X-ray diffraction2015In: Magnetic Resonance in Chemistry, ISSN 0749-1581, E-ISSN 1097-458X, Vol. 53, no 8, p. 596-602Article in journal (Refereed)
    Abstract [en]

    Host-guest complexes between cryptophane-A analogue with butoxy groups (cryptophane-But) and chloromethanes (chloroform, dichloromethane) were investigated in the solid state by means of magic-angle spinning C-13 NMR spectroscopy. The separated local fields method with C-13-H-1 dipolar recoupling was used to determine the residual dipolar coupling for the guest molecules encaged in the host cavity. In the case of chloroform guest, the residual dipolar interaction was estimated to be about 19kHz, consistent with a strongly restricted mobility of the guest in the cavity, while no residual interaction was observed for encaged dichloromethane. In order to rationalize this unexpected result, we performed single crystal X-ray diffraction studies, which confirmed that both guest molecules indeed were present inside the cryptophane cavity, with a certain level of disorder. To improve the insight in the dynamics, we performed a C-13 NMR spin-lattice relaxation study for the dichloromethane guest in solution. The system was characterized by chemical exchange, which was slow on the chemical shift time scale but fast with respect to the relaxation rates. Despite these disadvantageous conditions, we demonstrated that the data could be analyzed and that the results were consistent with an isotropic reorientation of dichloromethane within the cryptophane cavity.

  • 25.
    Takacs, Zoltan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Brotin, Thierry
    Chloromethane complexes of cryptophane-A and its analogue with butoxy groupsManuscript (preprint) (Other academic)
    Abstract [en]

    Host-guest complexes between cryptophane-A as host and dichloromethane and chloroformas guests are investigated using 1H and13C NMR spectroscopy. Moreover, a relatedcryptophane, with the methoxy groups replaced by butoxy units (cryptophane-But), and itscomplexes with the same guests were also studied. Variable temperature spectra showedeffects of chemical exchange between the free and bound guests, as well as of conformationalexchange of the host. The guest exchange was studied quantitatively by exchangespectroscopy or line shape analysis. In the case of CHCl3@cryptophane-A, carbon-13relaxation of the guest was also investigated. Structural information was obtained throughmeasurements of cross-relaxation rates, both within the host and between the host and guestprotons. The NMR results were supported by DFT calculations.1

  • 26.
    Takacs, Zoltan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Šoltésová, Mária
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Charles University Prague .
    Kotsyubynskyy, Dmytro
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lang, Jan
    Brotin, Thierry
    Dutasta, Jean-Pierre
    NMR Investigation of Guest–Host Complex between Chloroform and Cryptophane C2010In: Magnetic Resonance in Chemistry, ISSN 0749-1581, E-ISSN 1097-458X, Vol. 48, no 8, p. 623-629Article in journal (Refereed)
    Abstract [en]

    Guest–host complex between cryptophane C, possessing two non-equivalent caps, and chloroform is investigated by NMR spectroscopy. The kinetics of the chloroform exchange between the bound and free sites is determined by 1H exchange spectroscopy. Moreover, the preferential orientation of chloroform molecule with respect to the cryptophane C frame is examined by the NOESY and ROESY experiments. The experimental findings are compared to the results of quantum chemical calculations.

  • 27.
    Takacs, Zoltan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Šoltésová, Mária
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Charles University Prague .
    Kowalewski, Josef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lang, Jan
    Host-Guest Complexes between Cryptophane-C and Chloromethanes Revisited2013In: Magnetic Resonance in Chemistry, ISSN 0749-1581, E-ISSN 1097-458X, Vol. 51, no 1, p. 19-31Article in journal (Refereed)
    Abstract [en]

    Cryptophane-C is composed of two nonequivalent cyclotribenzylene caps, one of which contains methoxy group substituents on the phenyl rings. The two caps are connected by three OCH2CH2O linkers in an anti arrangement. Host-guest complexes of cryptophane-C with dichloromethane and chloroform in solution were investigated in detail by nuclear magnetic resonance techniques and density functional theory (DFT) calculations. Variable temperature proton and carbon-13 spectra show a variety of dynamic processes, such as guest exchange and host conformational transitions. The guest exchange was studied quantitatively by exchange spectroscopy measurements or by line-shape analysis. The conformational preferences of the guest-containing host were interpreted through cross-relaxation measurements, providing evidence of the gauche+2 and gauche-2 conformations of the linkers. In addition, the mobility of the chloroform guest inside the cavity was studied by carbon-13 relaxation experiments. Combining different types of evidence led to a detailed picture of molecular recognition, interpreted in terms of conformational selection.

  • 28.
    Takács, Zoltan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Brotin, Thierry
    Dutasta, Jean-Pierre
    Lang, Jan
    Todde, Guido
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Inclusion of Chloromethane Guests Affects Conformation and Internal Dynamics of Cryptophane-D Host2012In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 116, no 27, p. 7898-7913Article in journal (Refereed)
    Abstract [en]

    Cryptophane-D is composed of two nonequivalent cyclotribenzylene caps bound together by three OCH2CH2O bridges in a syn arrangement. Host-guest complexes with chloroform and dichloromethane were investigated in solution by NMR spectroscopy. Variable temperature NMR. H-1 and C-13 spectra showed effects of chemical exchange between the free and bound guest and of conformational exchange for the host, strongly and specifically affected by guest binding. We found in particular that the carbon-13 chemical shifts for the linkers connecting the two cyclotribenzylene units are very informative. The NMR results were supported by DFT calculations. The guest exchange was also studied quantitatively, either by EXSY measurements (for chloroform as guest) or by line-shape analysis (for dichloromethane as guest). In the case of chloroform guest, we also investigated cross relaxation between the guest and host protons, as well as carbon 13 longitudinal relaxation and heteronuclear NOE at three different fields. The results were interpreted in terms of orientation and dynamics of the guest inside the host cavity. Putting together various types of evidence resulted in remarkably detailed insight into the process of molecular recognition of the two guests by cryptophane-D host.

  • 29.
    Takács, Zoltan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Steiner, Emelie
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kowalewski, Josef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Brotin, T.
    NMR Investigation of Chloromethane Complexes of Cryptophane-A and Its Analogue with Butoxy Groups2014In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 118, no 8, p. 2134-2146Article in journal (Refereed)
    Abstract [en]

    Host guest complexes between cryptophane-A as host and dichloromethane and chloroform as guests are investigated using H-1 and C-13 NMR spectroscopy. Moreover, a related cryptophane, with the methoxy groups replaced by butoxy units (cryptophane-But), and its complexes with the same guests were also studied. Variable temperature spectra showed effects of chemical exchange between the free and bound guests, as well as of conformational exchange of the host. The guest exchange was studied quantitatively by exchange spectroscopy or line shape analysis. Extraction of kinetic and thermodynamic parameters led to the characterization of the affinity between guests and hosts. On the other hand, the host exchange was investigated by means of C-13 Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion which aims at the determination of the transverse relaxation rate R-2, the inverse of the transverse relaxation time T-2, as a function of the repetition of the pi pulses in a CPMG train. The variation of the measured transverse relaxation rate with the repetition rate nu(CPMG) indicated conformational exchange occurring on the microsecond millisecond time scale. Structural information was obtained through measurements of cross-relaxation rates, both within the host and between the host and the guest protons. The NMR results were supported by DFT calculations.

  • 30. Tosner, Z
    et al.
    Aski, SN
    Kowalewski, J
    Stockholm University.
    Rotational dynamics of adamantanecarboxylic acid in complex with beta-cyclodextrin2006In: Journal of Inclusion Phenomena and Macrocyclic Chemistry, Vol. 55, p. 59-70Article in journal (Refereed)
  • 31. Tosner, Zdenek
    et al.
    Skoch, Antonin
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Behavior of Two Almost Identical Spins during the CPMG Pulse Sequence2010In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 11, no 3, p. 638-645Article in journal (Refereed)
    Abstract [en]

    Multiple-spin-echo experiments have found wide use in nuclear magnetic resonance spectroscopy. In particular, the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence is used to determine transverse relaxation times T-2. Herein it is demonstrated, both theoretically and experimentally, that for a pair of almost identical spins-1/2 the experimental setup can have a profound effect on the observed spin dynamics. It is shown that, in the case of dipolar relaxation, the measured T-2 values can roughly vary between the limits of identical and unlike spins, just depending on the repetition rate of pi pulses with respect to chemical shift separation. Such an effect can, in the extreme narrowing regime, amount to a 50% difference.

  • 32. Tošner, Zdeněk
    et al.
    Škoch, Antonín
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Behavior of two almost identical spins during CPMG pulse sequence2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, no 3, p. 638-645Article in journal (Refereed)
    Abstract [en]

    Multiple-spin-echo experiments have found wide use in nuclear magnetic resonance spectroscopy. In particular, the Carr–Purcell–Meiboom–Gill (CPMG) pulse sequence is used to determine transverse relaxation times T2. Herein it is demonstrated, both theoretically and experimentally, that for a pair of almost identical spins-1/2 the experimental setup can have a profound effect on the observed spin dynamics. It is shown that, in the case of dipolar relaxation, the measured T2 values can roughly vary between the limits of identical and unlike spins, just depending on the repetition rate of π pulses with respect to chemical shift separation. Such an effect can, in the extreme narrowing regime, amount to a 50 % difference.

  • 33. Wyrwal, J
    et al.
    Schroeder, G
    Kowalewski, J
    Stockholm University.
    Aski, SN
    The effects of pendant-arm modification and ring size on the dynamics of cyclic polyamines2006In: Journal of Molecular Structure, Vol. 792, p. 274-279Article in journal (Refereed)
  • 34. Zerbetto, Mirco
    et al.
    Kotsyubynskyy, Dmytro
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Widmalm, Goran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Polimeno, Antonino
    Stochastic Modeling of Flexible Biomolecules Applied to NMR Relaxation: I. Internal Dynamics of Cyclodextrins; y-Cyclodextrin as a Case Study2012In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 116, no 44, p. 13159-13171Article in journal (Refereed)
    Abstract [en]

    In this work, we address the description of the dynamics of cyclodextrins in relation with nuclear magnetic resonance (NMR) relaxation data collected for hydroxymethyl groups. We define an integrated computational approach based on the definition and parametrization of a stochastic equation able to describe the relevant degrees of freedom affecting the NMR observables. The computational protocol merges molecular dynamics simulations and hydrodynamics approaches for the evaluation of most of the molecular parameters entering the stochastic description of the system. We apply the method to the interpretation of the C-13 NMR relaxation of the -CH2OH group of cyclodextrins. We use gamma-cyclodextrin as a case study. Results are in agreement with quantitative and qualitative analyses performed in the past with simpler models and molecular dynamics simulations. The element of novelty in our approach is in the treatment of the coupling of the relevant internal (glucopyranose ring twisting/tilting and hydroxymethyl group jumps) and global (molecular tumbling) degrees of freedom.

  • 35. Zerbetto, Mirco
    et al.
    Polimeno, Antonino
    Kotsyubynskyy, Dmytro
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Ghalebani, Leila
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Department of Physical Chemistry.
    Meirovitch, Eva
    Olsson, Ulrika
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    An integrated approach to NMR spin relaxation in flexible biomolecules: Application to β-D-glucopyranosyl-(1→6)-α-D-mannopyranosyl-OMe2009In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, no 23, p. p234501-Article in journal (Refereed)
    Abstract [en]

    The description of the reorientational dynamics of flexible molecules is a challenging task, in particular when the rates of internal and global motions are comparable. The commonly used simple mode-decoupling models are based on the assumption of statistical independence between these motions. This assumption is not valid when the time scale separation between their rates is small, a situation that was found to arise in oligosaccharides in the context of certain internal motions. To make possible the interpretation of NMR spin relaxation data from such molecules, we developed a comprehensive approach generally applicable to flexible rotators with one internal degree of freedom. This approach integrates a stochastic description of coupled global tumbling and internal torsional motion, quantum chemical calculations of the local potential and the local geometry at the site of the restricted torsion, and hydrodynamics-based calculations of the diffusive properties. The method is applied to the disaccharide -D-Glcp-(16)--D-[6-13C]-Manp-OMe dissolved in a DMSO-d6/D2O cryosolvent. The experimental NMR relaxation parameters, associated with the 13CH2 probe residing at the glycosidic linkage, include 13C T1 and T2 and 13C-{1H} nuclear Overhauser enhancement (NOE) as well as longitudinal and transverse dipole-dipole cross-correlated relaxation rates, acquired in the temperature range of 253–293 K. These data are predicted successfully by the new theory with only the H–C–H angle allowed to vary. Previous attempts to fit these data using mode-decoupling models failed.

  • 36.
    Šoltésová, Mária
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Charles University in Prague.
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Dynamics of exocyclic groups in the Escherichia coli O91 O-antigen polysaccharide in solution studied by carbon-13 NMR relaxation2013In: Journal of Biomolecular NMR, ISSN 0925-2738, E-ISSN 1573-5001, Vol. 57, no 1, p. 37-45Article in journal (Refereed)
    Abstract [en]

    Carbon-13 relaxation data are reported for exocyclic groups of hexopyranosyl sugar residues in the repeating unit within the Escherichia coli O91 O-antigen polysaccharide in a dilute D2O solution. The measurements of T 1, T 2 and heteronuclear nuclear Overhauser enhancements were carried out at 310 K at two magnetic fields (16.4 T, 21.1 T). The data were analyzed using the standard and extended Lipari–Szabo models, as well as a conformational jump model. The extended version of the Lipari–Szabo and the two-site jump models were most successful for the hydroxymethyl groups of Gal and GlcNAc sugar residues. Different dynamics was found for the hydroxymethyl groups associated with different configurations (d-gluco, d-galacto) of the sugar residues, the latter being faster than the former.

1 - 36 of 36
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