| 1. |
- Antzutkin, Oleg
(författare)
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Amyloidosis of Alzheimer's A peptides : solid-state nuclear magnetic resonance, electron paramagnetic resonance, transmission electron microscopy, scanning transmission electron microscopy and atomic force microscopy studies
- 2004
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 42:2, s. 231-246
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Tidskriftsartikel (refereegranskat)abstract
- Aggregation cascade for Alzheimer's amyloid-β peptides, its relevance to neurotoxicity in the course of Alzheimer's disease and experimental methods useful for these studies are discussed. Details of the solid-phase peptide synthesis and sample preparation procedures for Alzheimer's β-amyloid fibrils are given. Recent progress in obtaining structural constraints on Aβ-fibrils from solid-state NMR and scanning transmission electron microscopy (STEM) data is discussed. Polymorphism of amyloid fibrils and oligomers of the 'Arctic' mutant of Aβ(1-40) was studied by 1H,13C solid-state NMR, transmission electron microscopy (TEM) and atomic force microscopy (AFM), and a real-time aggregation of different polymorphs of the peptide was observed with the aid of in situ AFM. Recent results on binding of Cu(II) ions and Al-citrate and Al-ATP complexes to amyloid fibrils, as studied by electron paramagnetic resonance (EPR) and solid-state 27Al NMR techniques, are also presented.
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| 2. |
- Bodor, A., et al.
(författare)
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Thallium(III) coordination compounds : chemical information from Tl-205 NMR longitudinal relaxation times
- 2002
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 40:11, s. 716-722
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Tidskriftsartikel (refereegranskat)abstract
- Tl-205 longitudinal relaxation rate measurements were performed on several thallium(III) complexes with the composition Tl(OH)(n)(H2O)(6-n)((3-n)+) (n = 1,2), Tl(Cl)(n)(H2O)(m-n)((3-n)+), Tl(Br)(n)(H2O)(m-n)((3-n)+) (m = 6 for n = 1-2, m = 5 for n = 3, m = 4 for n = 4), Tl(CN)n(H2O)(m-n)((3-n)+) (m = 6 for n = 1-2, m = 4 for n = 3-4) in aqueous solution, at different magnetic fields and temperatures. C-13 and D-2 isotopic labelling and 114 decoupling experiments showed that the contribution of the dipolar relaxation path is negligible. The less symmetric lower complexes (n < 4) had faster relaxation rate dominantly via chemical shift anisotropy contribution which depended on the applied magnetic field: T, values are between 20 and 100 ms at 9.4 T and the shift anisotropy is &UDelta;σ = 1000-2000 ppm. The tetrahedral complexes, n = 4, relax slower; their T-1 is longer than 1 s and the spin-rotation mechanism is probably the dominant relaxation path as showed by a temperature dependence study. In the case of the TICl4- complex, presumably a trace amount of TICl52- causes a large CSA contribution, 300 ppm. Since the geometry and the bond length for the complexes in solution are known from EXAFS data, it was possible to establish a correlation between the CSA parameter and the symmetry of the complexes. The relaxation behaviour of the Tl-bromo complexes is not in accordance with any known relaxation mechanism.
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| 3. |
- Dvinskikh, Sergey V., et al.
(författare)
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Heating caused by radiofrequency irradiation and sample rotation in C-13 magic angle spinning NMR studies of lipid membranes
- 2004
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 42:10, s. 875-881
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Tidskriftsartikel (refereegranskat)abstract
- Application of rapid sample rotation and radiofrequency irradiation in magic angle spinning (MAS) NMR of lipid bilayers can significantly increase the sample temperature. In this work, we studied the extent of heating during the acquisition of H-1-decoupled C-13 MAS spectra of hydrated dimyristoylphosphatidyl-choline (DMPC) in the L. phase. First, we describe a simple procedure for determining the increase in temperature by observing the shift of the H-1 water signal. The method is then used to identify and assess the various factors that contribute to the sample heating. The important factors discussed in this paper include: (i) the spinning speed, (ii) the variable-temperature gas pressure, (iii) the rotor geometry, (iv) the power, duration and frequency of the radiofrequency irradiation and (v) the hydration level. A comparison of different heteronuclear decoupling schemes in terms of their ability to produce highly resolved C-13 spectra of DMPC is also reported.
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| 4. |
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| 5. |
- Furo, Istvan, et al.
(författare)
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NMR methods applied to anisotropic diffusion
- 2002
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 40, s. S3-S14
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Forskningsöversikt (refereegranskat)abstract
- The methodology of NMR experiments intended to measure anisotropic diffusion is reviewed. Experiments of this kind preferably require oriented samples and/or orientation-dependent spin coupling and/or magnetic field gradients in different directions. One strategy of diffusion experiments in anisotropic systems with broad NMR lines employs line narrowing techniques, thereby allowing for efficient gradient encoding/decoding. Depending on the nuclei, spin couplings and samples, the preferred methods vary from decoupling through echo techniques to magic angle sample orientation and spinning. Another avenue to efficient gradient encoding/decoding is through very strong magnetic field gradients. Either way, anisotropic diffusion reveals new structural features as illustrated by a few selected examples in liquid crystals and in biological tissues.
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| 6. |
- Gräfenstein, Jürgen, 1963, et al.
(författare)
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Systematic strategy for decoding the NMR spin-spin coupling mechanism: the J-OC-PSP method.
- 2004
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Ingår i: Magnetic resonance in chemistry : MRC. - : Wiley. - 0749-1581 .- 1097-458X. ; 42 Spec no
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Tidskriftsartikel (refereegranskat)abstract
- Criteria for analyzing the NMR spin-spin coupling mechanism were derived. Advantages and disadvantages of parallel- and post-processing analytical methods are discussed. An orbital decomposition into just one-orbital contributions provides less information than a decomposition into one-, two- and m-orbital effects. If just the last orbital in an orbital path leading from the perturbing to the responding nucleus is considered, the physics of the transport of spin information cannot be described. The theory of the J-OC-PSP (decomposition of J into Orbital Contributions using Orbital Currents and Partial Spin Polarization) is described to demonstrate the role of orbital contributions, orbital spin densities and orbital currents for the coupling mechanism. J-OC-PSP1 provides a decomposition into one- and two-orbital contributions with distinct physical reference (Ramsey perturbation of orbitals, steric exchange interactions, etc.) whereas J-OC-PSP2 introduces distinct orbital paths from perturbing to responding nucleus, clarifies the difference between active, passive and frozen orbitals and makes it possible to separate through-space from through-bond spin-spin coupling mechanism. Fermi contact coupling in hydrocarbons over more than two bonds is found to occur preferentially through space by tail interactions of the orbitals, as was anticipated in the early work of Barfield.
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| 7. |
- Hauksson, Jón B, et al.
(författare)
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NMR processing techniques based on multivariate data analysis and orthogonal signal correction. 13C CP/MAS NMR spectroscopic characterization of softwood kraft pulp
- 2001
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 39:5, s. 267-75
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a novel way of extracting information from a series of severely overlapped NMR spectra using multivariate data analysis techniques. A number of softwood pulps were prepared from wood chips that were subjected to kraft cooking conditions in laboratory digesters. In addition to measurements of traditional physical parameters, the pulps were characterized using standard 13C CP/MAS NMR spectroscopy. The relationship between the kappa number and both the NMR time domain and frequency domain data was modeled using multivariate data analysis techniques. The variation in the NMR spectra that was not correlated with the kappa number was removed using a new preprocessing tool, orthogonal signal correction (OSC). The resulting OSC-treated NMR spectra were used as descriptors to generate partial least-squares projections to latent structures (PLS) models for the variation of the kappa number. PLS weights were used to generate NMR sub-spectra which correspond to changes in the pulps that occur as the pulping process proceeds from high to low values of the kappa number. The sub-spectra were used to gain insight into the changes in the pulps occurring at the molecular level. Concomitant changes in cellulose crystallinity and the amounts of hemicellulose and lignin were observed in these sub-spectra. Copyright © 2001 John Wiley & Sons, Ltd.
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| 8. |
- Malliavin, TE, et al.
(författare)
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The NMR structure of [Xd(C2)]4 investigated by molecular dynamics simulations
- 2003
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 1097-458X .- 0749-1581. ; 41:1, s. 18-25
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Tidskriftsartikel (refereegranskat)abstract
- The i-motif tetrameric structure is built up from two parallel duplexes intercalated in a head-to-tail orientation, and held together by hemiprotonated cytosine pairs. Two topologies exist for the i-motif structure, one with outermost 3' extremities and the other with outermost 5' extremities, called the 3'E and 5'E topology, respectively. Since the comparison of sugar and phosphate group interactions between the two topologies is independent of the length of the intercalation motif, the relative stability of the 3'E and 5'E topologies therefore should not depend on this length. Nevertheless, it has been shown that the 3'E topology of the [d(C2)]4 is much more stable than the 5'E topology, and that the former is the only species observed in solution. In order to understand the reason for this atypical behavior, the NMR structure of the [Xd(C2)]4 was determined and analyzed by molecular dynamics simulations. In the NMR structure, the width of the narrow groove is slightly smaller than in previously determined i-motif structures, which supports the importance of phosphodiester backbone interactions in the structure stability. The simulations show that the stacking of cytosines, essential for the i-motif stability, is produced by a similar and non-negative twisting of the phosphodiester backbones. The twisting is induced by an interaction between the backbones; the [Xd(C2)]4 in 5'E topology, exhibiting very limited interaction between the phosphodiester backbones, is thus unstable. Copyright (C) 2002 John Wiley Sons, Ltd.
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| 9. |
- Mulder, Frans, et al.
(författare)
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Carbonyl 13C Transverse Relaxation Measurements to Sample Protein Backbone Dynamics.
- 2003
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 1097-458X .- 0749-1581. ; 41:10, s. 853-865
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Tidskriftsartikel (refereegranskat)abstract
- Carbonyl 13C relaxation experiments to study protein backbone dynamics have recently been developed. However, the effect of three-bond 13C-13C couplings on transverse relaxation measurements appears not to have been considered, and the potential to detect and quantify motions on the millisecond to microsecond time scale has not been fully explored. The present paper addresses these two issues. Simulations and experiments show that scalar couplings between adjacent backbone carbonyl carbon nuclei and between backbone and side-chain carbonyl/carboxyl carbon atoms in Asp and Asn residues interfere with the accurate determination of transverse relaxation rates by Carr-Purcell-Meiboom-Gill or on-resonance spin-lock measurements. The use of off-resonance radio-frequency fields avoids efficient cross-polarization, and offers a route towards accurate R1 measurements. In addition, this approach yields dispersion in the transverse relaxation rate as a function of the effective field when conformational exchange is present. In the case of calcium-bound calbindin D9k, 13C off-resonance R1 measurements yielded uniform values of R2 along the polypeptide chain, indicating homogeneous chemical shift anisotropies and restricted dynamics on the picosecond to nanosecond time scale. Variation of R2 as a function of the effective spin-lock field strength was not observed for any residue, indicating the absence of large-scale conformational changes of the protein backbone in the millisecond to microsecond time window. The absence of relaxation induced by internal motions on these wide-ranging time scales reinforces the view that calcium-loaded calbindin D9k is extremely rigid. In contrast, for the C-terminal tryptic fragment of calmodulin containing the E140Q mutation we observed widespread exchange broadening. From the carbonyl transverse relaxation dispersion profile of Asp129 the exchange rate was determined to be 28 000 s-1. Copyright © 2003 John Wiley & Sons, Ltd.
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| 10. |
- Price, W. S., et al.
(författare)
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PGSE-WATERGATE, a new tool for NMR diffusion-based studies of ligand-macromolecule binding
- 2002
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 40:6, s. 391-395
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Tidskriftsartikel (refereegranskat)abstract
- A new pulsed gradient spin-echo NMR diffusion sequence, PGSE-WATERGATE, which is based on the extremely efficient WATERGATE solvent suppression sequence, is presented. The sequence is simple to set up and particularly suited to measuring the diffusion coefficients of small ligands in aqueous solution such as is commonly required in pharmaceutical and combinatorial applications. It also affords the possibility of measuring the diffusion of exchangeable resonances, which is often impossible in conjunction with other suppression schemes. Further, a trivial modification of the sequence affords the possibility of multiple solvent suppression, thereby increasing its suitability to LC-NMR applications. The utility of the sequence is demonstrated on the salicylate-bovine serum albumin system. The dissociation constant, K-d, and the number of binding sites were found to be 0.030 M and 33, respectively. Importantly, the extremely high degree of suppression provided by the new sequence allowed the salicylate diffusion coefficients to be measured over a very wide concentration range sufficient to show that the salicylate-bovine serum albumin system is not well described by a simple two-site model. Previous studies in the literature have been based on data from a smaller concentration range, for which this model gives an apparently good fit.
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| 11. |
- Stchedroff, MJ, et al.
(författare)
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Os-187 subspectra in H-1 and P-31{H-1} spectra of triosmium carbonyl clusters
- 2002
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 1097-458X .- 0749-1581. ; 40:2, s. 107-113
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Tidskriftsartikel (refereegranskat)abstract
- A survey of the use of Os-187 satellite subspectra in H-1 and P-31{H-1} spectra of triosmium carbonyl clusters is reported. By varying evolution delays in HMQC spectra of [Os-3(mu-H)(2)(CO)(10)] we have selectively extracted the values for (1)J(Os,H) and (2)J(Os,H), respectively. An analysis of the principal modes of phosphine coordination in triosmium clusters demonstrates that P-31{H-1} Os-187 satellite subspectra are diagnostic for equatorial coordination [(1)J(Os, P) = 211-223 Hz] or for axial coordination (perpendicular to the plane of the cluster) [(1)J(Os, P) approximate to 147 Hz]. Chelating and bridging diphosphines yield Os-187 satellite subspectra which are the sum of A(2)X and AA'X spin systems. If significant P-P coupling is present, the AA'X component requires simulation. All observed (2)J(Os,P) trans-equatorial couplings fall in the range 38-65 Hz. Copyright (C) 2001 John Wiley Sons, Ltd.
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Orädd, Greger, et al.
(författare)
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Lateral diffusion studied by pulsed field gradient NMR on oriented lipid membranes
- 2004
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581. ; 42:2, s. 123-31
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Tidskriftsartikel (refereegranskat)abstract
- This mini-review focuses on the utilization of pulsed magnetic field gradients to measure diffusional motion in systems of macroscopically oriented lipid bilayers. The NMR diffusion technique is proposed to have appreciable potential for future biophysical investigations in the field of membrane biology. Topics such as transport of molecules both across and in the plane of the membrane can be successfully studied, and the formation of lipid domains and their intrinsic dynamics can also be scrutinized. First, a short introduction to the NMR technique is given together with a brief discussion on methods of obtaining a good bilayer orientation. Then, a number of recent results on biophysical/biological membrane systems of great interest is presented, in which some unique conclusions on so-called raft membranes are reached. It is shown for systems with large two-phase areas of liquid disordered and liquid ordered phases that lipid lateral diffusion is faster in the former phase and has a smaller apparent activation energy. Further, on the time-scale of the experiments (50-250 ms), exchange between the two phases is fast in the phospholipid-cholesterol-water ternary system, whereas it is slow in the sphingomyelin-dioleoylphosphatidylcholine-cholesterol-water quaternary system.
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