| 1. |
- Kaderavek, Pavel, et al.
(författare)
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Spectral density mapping at multiple magnetic fields suitable for C-13 NMR relaxation studies
- 2016
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Ingår i: Journal of magnetic resonance. - : Elsevier. - 1090-7807 .- 1096-0856. ; 266, s. 23-40
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Kotsyubynskyy, Dmytro, et al.
(författare)
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Stochastic Modeling of Flexible Biomolecules Applied to NMR Relaxation : 2. Interpretation of Complex Dynamics in Linear Oligosaccharides
- 2012
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 116:50, s. 14541-14555
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Kowalewski, Josef
(författare)
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Nuclear spin relaxation in liquids and gases
- 2014
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Ingår i: Nuclear Magnetic Resonance: Volume 43. - Cambridge : Royal Society of Chemistry. - 9781849739559 - 9781849738125 - 9781782621607 ; , s. 230-285
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Bokkapitel (refereegranskat)abstract
- 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.
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| 4. |
- Kowalewski, Josef
(författare)
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Nuclear spin relaxation in liquids and gases
- 2012
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Ingår i: Nuclear Magnetic Resonance: Volume 41. - : Royal Society of Chemistry. - 9781849733731 - 9781849734851 ; , s. 196-243
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Bokkapitel (refereegranskat)
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| 5. |
- Kowalewski, Josef, et al.
(författare)
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Paramagnetic Relaxation in Solution
- 2011
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Ingår i: Encyclopedia of Magnetic Resonance. - Chichester, UK : John Wiley & Sons.
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- 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
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| 6. |
- Kruk, D., et al.
(författare)
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ESR lineshape and H-1 spin-lattice relaxation dispersion in propylene glycol solutions of nitroxide radicals - Joint analysis
- 2013
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 139:24, s. 244502-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Kruk, D., et al.
(författare)
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H-1 relaxation dispersion in solutions of nitroxide radicals : Effects of hyperfine interactions with N-14 and N-15 nuclei
- 2012
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 137:4, s. 044512-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Kruk, D., et al.
(författare)
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Joint analysis of ESR lineshapes and (1)H NMRD profiles of DOTA-Gd derivatives by means of the slow motion theory
- 2011
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:2, s. 024508-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Maliniak, Arnold, et al.
(författare)
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NUCLEAR-SPIN RELAXATION STUDY OF HYDROGEN-BONDING IN SOLUTIONS OF QUINUCLIDINE
- 1984
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Ingår i: Journal of Physical Chemistry. - 0022-3654. ; 88:23, s. 5628-5631
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Tidskriftsartikel (refereegranskat)abstract
- The intermolecular hydrogen bonds formed by quinuclidine together with different solvents (benzene, chloroform, methanol, trifluoroacetic acid) are studied by using NMR relaxation measurements. The carbon-1 3 and nitrogen-I4 relaxation rates are determined and Woessner's model for dipole relaxation in a symmetric rotor is applied. The different values for the ratio between the rotational diffusion constants RII and R, in different solvents and at different temperatures are discussed in terms of molecular reorientation anisotropy due to hydrogen bonds formed by quinuclidine and the solvent. From the nitrogen-14 relaxation rates the quadrupole coupling constants (QCC) are evaluated and compared with the results of quantum-chemical calculations of electric field gradients performed on model systems.
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| 10. |
- Takacs, Zoltan, et al.
(författare)
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Host-Guest Complexes between Cryptophane-C and Chloromethanes Revisited
- 2013
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 51:1, s. 19-31
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 11. |
- Takács, Zoltan, et al.
(författare)
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NMR Investigation of Chloromethane Complexes of Cryptophane-A and Its Analogue with Butoxy Groups
- 2014
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 118:8, s. 2134-2146
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 12. |
- Tosner, Zdenek, 1976-
(författare)
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NMR Investigations of Host-Guest Complexes and Their Dynamic Properties
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis discusses several different methods offered by solution and solid state nuclear magnetic resonance for investigation of host-guest complexes and their constituents. The presented methods were used especially (but not exclusively) to address rotational dynamics of the bound guest in different molecular systems.The main part of this thesis presents results of a project that combines and compares solution and solid state NMR investigations of inclusion complexes of a spherical, cage-like molecule of cryptophane-E with small neutral guest molecules like chlorinated methanes. Strong and weak bonding of these host--guest systems is studied in solution using C-13 NMR relaxation and in the crystalline form, using advanced dipolar recoupling methods as well as deuterium NMR lineshape and spin relaxation analysis. Comparison of the results from all the techniques suggests very similar guest behaviour regardless of the physical state of the system. Residing inside the cavity, CHCl3 behaves almost as an integral part of cryptophane-E, whereas the reorientation of CH2Cl2 is influenced only slightly by weak interactions with its host. Molecular flexibility of thiacalix[4]arenes, a new class of the very popular calixarene family, was also studied by C-13 NMR relaxation in solution. Calixarenes are widely used in supramolecular chemistry as building blocks of receptors to many guest molecules.The thesis is completed with examination of a β-cyclodextrin (β-CD) inclusion complex with adamantanecarboxylic acid (AdCA) where changes of translational and rotational diffusion properties of the guest were monitored during complexation with the host. By means of C-13 NMR relaxation it was found that despite the high association constant (which suggests strong interactions between the two molecules) AdCA rotates fast around the β-CD symmetry axis inside the cavity. This motion is made possible by the spherical shape of the adamantyl moiety and the whole system resembles to a "molecular bearing".
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