| 1. |
- Gogoll, Adolf, et al.
(författare)
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Chemical shift assignment of geminal protons in 3,7-diazabicyclo [3.3.1]nonanes : An unexpected deviation from the axial/equatorial chemical shift order
- 1997
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Ingår i: Magnetic Resonance in Chemistry. - : John Wiley & Sons. - 0749-1581 .- 1097-458X. ; 35:1, s. 13-20
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Tidskriftsartikel (refereegranskat)abstract
- The chemical shift order of axial and equatorial methylene protons in 1,5-disubstituted 3,7-diazabicyclo[3.3.1]nonan-9-ones may be altered by substituents in the 1,5-positions, but the corresponding alcohols behave differently. Unambiguous signal assignments for a series of the title compounds are provided, based on 3JCH coupling constants and on {1H} 13C heteronuclear Overhauser effects. Substituent anisotropy effects as a source of the chemical shift changes are discussed.
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| 2. |
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| 3. |
- Altaib, Mohamed S., et al.
(författare)
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Synthesis and NMR elucidation of novel pentacycloundecane-based peptides
- 2010
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 48:6, s. 435-442
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and NMR elucidation of two novel pentacycloundecane (PCU)-based peptides are reported. The PCU cage amino acids were synthesised as racemates and the incorporation of the cage amino acid with (S)-natural amino acids produced diastereomeric peptides. The diastereomeric 'cage' peptides were separated using preparative HPLC and the NMR elucidation of these PCU containing peptides are reported for the first time. The H-1 and C-13 NMR spectra showed series of overlapping signals of the cage skeleton and that of the peptide, making it extremely difficult to resolve the structure using one-dimensional NMR techniques only. The use of two-dimensional NMR techniques proved to be a highly effective tool in overcoming this problem.
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| 4. |
- 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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| 5. |
- Arkhipov, Victor, et al.
(författare)
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Micelle structure and molecular self-diffusion in isononylphenol ethoxylate–water systems
- 2013
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 51:7, s. 424-430
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Tidskriftsartikel (refereegranskat)abstract
- The structure and dynamic properties of micellar solutions of nonionic surfactants of a series of isononylphenol ethoxylates, C9H19C6H4O(C2H4O)nH (where n = 6,8,9,10, and 12), were studied by NMR diffusometry, dynamic light scattering, and viscosimetry. The sizes of the micelles were determined for different surfactants and at different surfactant concentrations. The numbers of water molecules bound by a micelle and by one oxyethylene group of the surfactant were estimated
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| 6. |
- Arkhipov, Victor P., et al.
(författare)
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Dynamic and molecular association in premicellar aqueous solutions of dicarboxylate amino acid-based surfactant as studied by 1H NMR
- 2022
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Ingår i: Magnetic Resonance in Chemistry. - : John Wiley & Sons. - 0749-1581 .- 1097-458X. ; 60:3, s. 359-368
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Tidskriftsartikel (refereegranskat)abstract
- We examined a series of amino acid-based surfactants with two carboxylic groups separated by a spacer of one, two, or three carbon atoms with sodium and calcium counterions in the premicellar concentration region near the CMC. 1H NMR spectroscopy and NMR diffusometry techniques were used to study the local environment, association and translational dynamics of the surfactant’s molecules. We measured the self-diffusion coefficients of the micelles, calculated the effective hydrodynamic radii, and determined the temperature region in which the premicelles exist. With an increase in temperature from 295 to 335 K, the premicellar state of the surfactant is replaced by the monomeric state.
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| 7. |
- Arkhipov, Victor P., et al.
(författare)
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Micellar and solubilizing properties of rhamnolipids
- 2023
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Ingår i: Magnetic Resonance in Chemistry. - : John Wiley & Sons. - 0749-1581 .- 1097-458X. ; 61:6, s. 345-355
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Tidskriftsartikel (refereegranskat)abstract
- We studied the micellar and solubilizing properties of aqueous solutions of unfractionated rhamnolipids produced by Pseudomonas aeruginosa. We used nuclear magnetic resonance (NMR) diffusometry, dynamic light scattering, and conductometry to measure the critical micelle concentration (CMC) of rhamnolipid solutions and determined the effective hydrodynamic radii of rhamnolipid monomers and micelles. Based on selective measurements of the self-diffusion coefficients of molecules, performed by NMR diffusometry, the solubilizing properties of rhamnolipids were studied depending on their concentration in solution; aromatic hydrocarbons, benzene, toluene, ethylbenzene, and para-xylene were taken as solubilizates. On the basis of the measurement results, we estimated the distribution coefficient of the solubilizate between the micellar (solubilized) and free (in the aqueous phase) states and the solubilizing capacity of rhamnolipid micelles.
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| 8. |
- Arkhipov, Victor P., et al.
(författare)
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Study of the premicellar state in aqueous solutions of sodium dodecyl sulfate by nuclear magnetic resonance diffusion
- 2021
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Ingår i: Magnetic Resonance in Chemistry. - : John Wiley & Sons. - 0749-1581 .- 1097-458X. ; 59:11, s. 1126-1133
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Tidskriftsartikel (refereegranskat)abstract
- Self‐diffusion coefficients of sodium dodecyl sulfate (SDS) were measured in aqueous solutions in the premicellar range of the SDS concentrations 7‐34.7 mM and temperatures 30‐900C. Average effective hydrodynamic radii and aggregation numbers of SDS in the premicellar region were determined. At C < CMC at all temperatures, the SDS solution is the solution of monomers. At C > CMC the increase of temperature leads to decrease in the effective hydrodynamic radii and the average aggregation numbers. At C >> CMC, it is impossible to reach the monomeric state by increasing the temperature.
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| 9. |
- Arkhipov, Victor P., et al.
(författare)
-
The efficiency of micellar solubilization of naphthalene from aqueous solutions using rhamnolipid as a biological surfactant according to NMR diffusometry
- 2024
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Ingår i: Magnetic Resonance in Chemistry. - : John Wiley & Sons. - 0749-1581 .- 1097-458X.
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic Resonance in Chemistry published by John Wiley & Sons Ltd.The micellar solubilization of naphthalene from its saturated aqueous solutions using the biosurfactant rhamnolipid was studied. Using the NMR diffusion method, selective measurements of the self-diffusion coefficients of molecules of all components of the solution—naphthalene, rhamnolipid, and water—were carried out at various rhamnolipid concentrations from 0.06 to 100 g/L. Based on the results of diffusometry, the distribution of naphthalene molecules between the states free in solution and states bound by micelles was found. With an increase in the concentration of rhamnolipids, the proportion of bound naphthalene molecules increases from 50% at CRL = 2 g/L to 100% at CRL ≥ 50 g/L. The micelle-water partition coefficient Km and the molar solubilization ratio MSR were calculated.
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| 10. |
- Aski, Sahar Nikkhou, et al.
(författare)
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Inclusion complexes of cryptophane–E with dichloromethane and chloroform : A thermodynamic and kinetic study using the 1D-EXSY NMR method
- 2008
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 46:12, s. 1135-1140
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 11. |
- Banyai, Istvan, et al.
(författare)
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Simple O-17 NMR method for studying electron self-exchange reaction between UO22+ and U4+ aqua ions in acidic solution
- 2016
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Ingår i: Magnetic Resonance in Chemistry. - : WILEY-BLACKWELL. - 0749-1581 .- 1097-458X. ; 54:6, s. 444-450
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Tidskriftsartikel (refereegranskat)abstract
- O-17 NMR spectroscopy is proven to be suitable and convenient method for studying the electron exchange by following the decrease of O-17-enrichment in (UOO2+)-O-17 ion in the presence of U4+ ion in aqueous solution. The reactions have been performed at room temperature using I=5MClO(4)(-) ionic medium in acidic solutions in order to determine the kinetics of electron exchange between the U4+ and UO22+ aqua ions. The rate equation is given as R = a[H+](-2) + R, where R is an acid independent parallel path. R depends on the concentration of the uranium species according to the following empirical rate equation: R = k(1)[UO2+](1/2)[U4+](1/2) + k(2)[UO2+](3/2)[U4+](1/2). The mechanism of the inverse H+ concentration-dependent path is interpreted as equilibrium formation of reactive UO2+ species from UO22+ and U4+ aqua ions and its electron exchange with UO22+. The determined rate constant of this reaction path is in agreement with the rate constant of UO22+-UO2+, one electron exchange step calculated by Marcus theory, match the range given experimentally of it in an early study. Our value lies in the same order of magnitude as the recently calculated ones by quantum chemical methods. The acid independent part is attributed to the formation of less hydrolyzed U(V) species, i.e. UO3+, which loses enrichment mainly by electron exchange with UO22+ ions. One can also conclude that O-17 NMR spectroscopy, or in general NMR spectroscopy with careful kinetic analysis, is a powerful tool for studying isotope exchange reactions without the use of sophisticated separation processes. Copyright (C) 2015 John Wiley amp; Sons, Ltd.
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| 12. |
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| 13. |
- Batta, Gy., et al.
(författare)
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C‐19 configurational assignments in some morphine derivatives by homonuclear NOE
- 1992
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 30:13, s. S96-S104
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Tidskriftsartikel (refereegranskat)abstract
- Azidolysis‐thermolysis of C‐19 diastereomer tosyl esters of morphine derivatives resulted in the formation of a new substituted 4‐azatetracyclo [4.4.02,4.03,8] decane ring system. As the course of such transformations depends on the chirality of C‐19, its relative configuration was determined both in the starting materials and in the new compounds. To this end a semiquantitative 1H{1H} NOE interpretation was combined with MMX molecular mechanics. Interestingly, both in the starting materials with a rotating C‐7—C‐19 bond and in the fairly rigid aziridine ring‐containing products, the same (H‐8α{19‐Me}) NOE effects were the most informative on the stereochemistry. In addition full a priori 1H and 13C assignments of 13 compounds are presented.
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| 14. |
- 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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| 15. |
- Carvalho, José P., et al.
(författare)
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Separation of quadrupolar and paramagnetic shift interactions with TOP-STMAS/MQMAS in solid-state lighting phosphors
- 2020
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 58:11, s. 1055-1070
-
Tidskriftsartikel (refereegranskat)abstract
- A new approach for processing satellite-transition magic-angle spinning(STMAS) and multiple-quantum magic-angle spinning (MQMAS) data, basedon the two-dimensional one-pulse (TOP) method, which separates thesecond-rank quadrupolar anisotropy and paramagnetic shift interactions viaa double shearing transformation, is described. This method is particularlyrelevant in paramagnetic systems, where substantial inhomogeneous broadeningmay broaden the lineshapes. Furthermore, it possesses an advantage overthe conventional processing of MQMAS and STMAS spectra because it overcomesthe limitation on the spectral width in the indirect dimension imposedby rotor synchronization of the sampling interval. This method was appliedexperimentally to the 27Al solid-state nuclear magnetic resonance of a seriesof yttrium aluminum garnets (YAGs) doped with different lanthanide ions,from which the quadrupolar parameters of paramagnetically shifted and bulkunshifted sites were extracted. These parameters were then compared withdensity functional theory calculations, which permitted a better understandingof the local structure of Ln substituent ions in the YAG lattice.
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| 16. |
- Danielsson, J, et al.
(författare)
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15N relaxation study of the amyloid beta-peptide structural propensities and persistence length.
- 2006
-
Ingår i: Magn Reson Chem. - : Wiley. - 0749-1581. ; 44:S1, s. S114-21
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of monomeric Alzheimer A(1-40) in aqueous solution was studied using heteronuclear NMR experiments. 15N NMR relaxation rates of amide groups report on the dynamics in the peptide chain and make it possible to estimate structural propensities from temperature-dependent relaxation data and chemical shifts change analysis. The persistence length of the polypeptide chain was determined using a model in which the influence of neighboring residue relaxation is assumed to decay exponentially as a function of distance. The persistence length of the A(1-40) monomer was found to decrease from eight to three residues when temperature was increased from 3 to 18 °C. At 3 °C the peptide shows structural propensities that correlate well with the suggested secondary structure regions of the peptide to be present in the fibrils, and with the -helical structure in membrane-mimicking systems. Our data leads to a structural model for the monomeric soluble -peptide with six different regions of secondary structure propensities. The peptide has two regions with -strand propensity (residues 16-24 and 31-40), two regions with high PII-helix propensity (residues 1-4 and 11-15) and two unstructured regions with higher mobility (residues 5-10 and 25-30) connecting the structural elements. Copyright © 2006 John Wiley & Sons, Ltd.
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| 17. |
- 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
-
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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| 18. |
- Elwinger, Fredrik, et al.
(författare)
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C-13 SPE MAS measurement of ligand concentration in compressible chromatographic beads
- 2015
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 53:8, s. 572-577
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Tidskriftsartikel (refereegranskat)abstract
- A method for measuring the ligand concentration in heterogeneous materials like chromatography media is described. In this method, C-13 single pulse excitation magic angle spinning NMR experiment with broadband H-1 decoupling is used to determine the peak integrals for a butyl ligand in the spectrum of a dried chromatography medium. Within a carefully controlled protocol, those integrals compared with that of the internal reference compound dimethyl sulfone provide the required volume concentration with an accuracy of ca 2%. The effects of temperature, degree of hydration, and other experimental parameters are discussed. Copyright (C) 2015 The Authors. Magnetic Resonance in Chemistry published by John Wiley & Sons Ltd.
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| 19. |
- Elwinger, Fredrik, et al.
(författare)
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High-resolution magic angle spinning H-1 NMR measurement of ligand concentration in solvent-saturated chromatographic beads
- 2016
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley-Blackwell. - 0749-1581 .- 1097-458X. ; 54:4, s. 291-297
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Tidskriftsartikel (refereegranskat)abstract
- A method based on H-1 high-resolution magic angle spinning NMR has been developed for measuring concentration accurately in heterogeneous materials like that of ligands in chromatography media. Ligand concentration is obtained by relating the peak integrals for a butyl ligand in the spectrum of a water-saturated chromatography medium to the integral of the added internal reference. The method is fast, with capacity of 10min total sample preparation and analysis time per sample; precise, with a reproducibility expressed as 1.7% relative standard deviation; and accurate, as indicated by the excellent agreement of derived concentration with that obtained previously by C-13 single-pulse excitation MAS NMR. The effects of radiofrequency field inhomogeneity, spin rate, temperature increase due to spinning, and distribution and re-distribution of medium and reference solvent both inside the rotor during spinning and between bulk solvent and pore space are discussed in detail.
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| 20. |
- Engdahl, Carin, et al.
(författare)
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Long‑Range Deuterium Isotope Effects on 13C NMR Shifts of Intramolecularly Hydrogen‑Bonded 9‑Hydroxyphenalen‑1‑ones
- 1991
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 29:1, s. 54-62
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Tidskriftsartikel (refereegranskat)abstract
- The 1H and 13C NMR spectra of 9-hydroxyphenalenone (1) and 9-hydroxy-2-methylphenalenone (2) have been completely assigned. Primary and secondary deuterium isotope effects were determined in three solvents (chloroform, acetone and dimethyl sulphoxide), including the effect of temperature on the secondary isotope effects. Both negative and large long-range secondary isotope effects were found for both 1 and 2. The average secondary isotope effects for corresponding carbons follow the same sign and magnitude pattern in both compounds.
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| 21. |
- Fang, Yuan, et al.
(författare)
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Assessing the potential of 2D electrophoretic mobility spectroscopy (2D MOSY) for analytical applications
- 2017
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Ingår i: Magnetic Resonance in Chemistry. - : John Wiley & Sons. - 0749-1581 .- 1097-458X. ; 55:6, s. 584-588
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Tidskriftsartikel (refereegranskat)abstract
- Electrophoretic displacement of charged entity phase modulates the spectrum acquired in electrophoretic NMR experiments, and this modulation can be presented via 2D FT as 2D mobility spectroscopy (MOSY) spectra. We compare in various mixed solutions the chemical selectivity provided by 2D MOSY spectra with that provided by 2D diffusion-ordered spectroscopy (DOSY) spectra and demonstrate, under the conditions explored, a superior performance of the former method. 2D MOSY compares also favourably with closely related LC-NMR methods. The shape of 2D MOSY spectra in complex mixtures is strongly modulated by the pH of the sample, a feature that has potential for areas such as in drug discovery and metabolomics.
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| 22. |
- Filippov, Andrei, et al.
(författare)
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Aggregation of amyloid Aβ(1-40) peptide in perdeuterated 2,2,2-trifluoroethanol caused by ultrasound sonication
- 2010
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 48:6, s. 427-434
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Tidskriftsartikel (refereegranskat)abstract
- Ultrasound sonication of protein and peptide solutions is routinely used in biochemical, biophysical, pharmaceutical and medical sciences to facilitate and accelerate dissolution of macromolecules in both aqueous and organic solvents. However, the impact of ultrasound waves on folding/unfolding of treated proteins, in particular, on aggregation kinetics of amyloidogenic peptides and proteins is not understood. In this work, effects of ultrasound sonication on the misfolding and aggregation behavior of the Alzheimer's Aβ(1–40)-peptide is studied by pulsed-field gradient (PFG) spin–echo diffusion NMR and UV circular dichroism (CD) spectroscopy. Upon simple dissolution of Aβ(1–40) in perdeuterated trifluoroethanol, CF3-CD2-OD (TFE-d3), the peptide is present in the solution as a stable monomer adopting α-helical secondary structural motifs. The self-diffusion coefficient of Aβ(1–40) monomers in TFE-d3 was measured as 1.35 × 10−10 m2 s−1, reflecting its monomeric character. However, upon ultrasonic sonication for less than 5 min, considerable populations of Aβ molecules (ca 40%) form large aggregates as reflected in diffusion coefficients smaller than 4.0 × 10−13 m2 s−1. Sonication for longer times (up to 40 min in total) effectively reduces the fraction of these aggregates in 1H PFG NMR spectra to ca 25%. Additionally, absorption below 230 nm increased significantly upon sonication treatment, an observation, which also clearly confirms the ongoing aggregation process of Aβ(1–40) in TFE-d3. Surprisingly, upon ultrasound sonication only small changes in the peptide secondary structure were detected by CD: the peptide molecules mainly adopt α-helical motifs in both monomers and aggregates formed upon sonication.
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| 23. |
- Filippov, Andrei, et al.
(författare)
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Disordering of phospholipid headgroups induced by a small amount of polyethylene oxide
- 2013
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 51:1, s. 1-3
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Tidskriftsartikel (refereegranskat)abstract
- We present a 31P NMR spectroscopy study of planar glass-plate-oriented multi-bilayers of dimyristoylphosphatidylcholine (DMPC) with addition of polyethylene oxide (PEO). This work revealed the presence of a new component in the spectra that appeared only with addition of a small fraction of PEO (up to one PEO segment per dimyristoylphosphatidylcholine molecule) and disappeared when larger amounts of PEO were added. We explained this phenomenon as an effect of an inhomogeneous force field induced by the PEO molecules located at a certain depth in the lipid membrane interface region
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| 24. |
- Filippov, Andrei, et al.
(författare)
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Dynamic Properties of Imidazolium Orthoborate Ionic Liquids Mixed with Polyethylene Glycol Studied by NMR Diffusometry and Impedance Spectroscopy
- 2018
-
Ingår i: Magnetic Resonance in Chemistry. - : John Wiley & Sons. - 0749-1581 .- 1097-458X. ; 56:2, s. 113-119
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Tidskriftsartikel (refereegranskat)abstract
- We used 1H pulsed field gradient (PFG) NMR to study the self-diffusion of polyethylene glycol (PEG) with average molecular mass of 200 and ions in mixtures of PEG with imidazolium bis(mandelato)borate (BMB) and imidazolium bis(oxalato)borate (BOB) ionic liquids (ILs). The ionic liquid was mixed with PEG in the concentration range of 0–100 wt%. Within the temperature range of 295 to 353 K, the diffusion coefficient of BMB is slower than that of the imidazolium cation. The diffusion coefficients of PEG, as well as the imidazolium cation and BMB anions, differ under all experimental conditions tested. This demonstrates that the IL in the mixture is present in at least a partially dissociated state. Generally, increasing the concentration of PEG leads to an increase in the diffusion coefficients of PEG and both the ions, and decreases their activation energy for diffusion. NMR chemical shift alteration analysis showed that the presence of PEG changes the chemical shifts of both ions but in different directions. Impedance spectroscopy was used to measure the ionic conductivity of the ionic liquids mixed with PEG.
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| 25. |
- Filippov, Andrei, et al.
(författare)
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Lateral diffusion in sphingomyelin bilayers
- 2010
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 48:12, s. 945-950
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Tidskriftsartikel (refereegranskat)abstract
- Sphingomyelin (SM) is an important lipid of eukaryotic cellular membranes and neuronal tissues. We studied lateral diffusion in macroscopically oriented bilayers of synthetic palmitoylSM (PSM) and natural sphingomyelins of egg yolk (eSM), bovine brain (bSM) and bovine milk (mSM) by NMR pulsed field gradient (NMR PFG) in the temperature range of 50-60oC. We found that the mean values of lateral diffusion coefficients (LDCs) of SMs are 1.9-fold lower in comparison with dipalmitoylphosphatidylcholine, which is similar in molecular structure. This discrepancy could be explained by the characteristics of intermolecular SM interactions. The LDCs of different SMs differ: egg SM is most similar to PSM, both of them have a 10% higher LDC value in comparison with the two other natural SMs. Besides, all natural SMs show a complicated form of the spin-echo diffusion decay, which is an indicator of a distribution of LDC values in bilayers. This peculiarity was explained by broad distributions of fatty acid lengths of the natural SMs studied here, especially mSM and bSM. We confirmed the relationship between chain length and the LDC in bilayers by computer analysis of a set of 1H NMR spectra obtained by scanning the value of the pulsed field gradient: there is a correlation between lower LDC values and SM molecules with longer acyl chains. The most probable mechanisms by which long-chain SM molecules decrease their lateral diffusion relative to the average value are protrusion into the other side of the bilayer or lateral separation into areas that diverge with their LDCs.
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| 26. |
- Filippov, Andrei, et al.
(författare)
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Self-diffusion and interactions in mixtures of imidazolium bis(mandelato)borate ionic liquids with polyethylene glycol : H-1 NMR study
- 2015
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 53:7, s. 493-497
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Tidskriftsartikel (refereegranskat)abstract
- We used H-1 nuclear magnetic resonance pulsed-field gradient to study the self-diffusion of polyethylene glycol (PEG) and ions in a mixture of PEG and imidazolium bis(mandelato)borate ionic liquids (ILs) at IL concentrations from 0 to 10 wt% and temperatures from 295 to 370 K. PEG behaves as a solvent for these ILs, allowing observation of separate lines in H-1 NMR spectra assigned to the cation and anion as well as to PEG. The diffusion coefficients of PEG, as well as the imidazolium cation and bis(mandelato) borate (BMB) anion, differ under all experimental conditions tested. This demonstrates that the IL in the mixture is present in at least a partially dissociated state, while the lifetimes of the associated states of the ions and ions with PEG are less than similar to 30ms. Generally, increasing the concentration of the IL leads to a decrease in the diffusion coefficients of PEG and both ions. The diffusion coefficient of the anion is less than that of the cation; the molecular mass dependence of diffusion of ions can be described by the Stokes-Einstein model. NMR chemical shift alteration analysis showed that the presence of PEG changes mainly the chemical shifts of protons belonging to imidazole ring of the cation, while chemical shifts of protons of anions and PEG remain unchanged. This demonstrated that the imidazolium cation interacts mainly with PEG, which most probably occurs through the oxygen of PEG and the imidazole ring. The BMB anion does not strongly interact with PEG, but it may be indirectly affected by PEG through interaction with the cation, which directly interacts with PEG. Copyright (C) 2015 John Wiley & Sons, Ltd.
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| 27. |
- Filippov, Andrei, et al.
(författare)
-
Self-diffusion in a hyaluronic acid–albumin–water system as studied by NMR
- 2012
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 50:2, s. 114-119
-
Tidskriftsartikel (refereegranskat)abstract
- In the presence of even a small amount of hyaluronic acid, the self-diffusion coefficient of albumin decreases. Three hypotheses were proposed and analyzed. The most likely one is that BSA and HA molecules form complex. The state of the BSA molecules in the BSA-HA-D2O system corresponds to a ‘fast exchange’ condition from the NMR point of view: BSA molecules reside in the ‘free’ and ‘bound’ states for much shorter time than the diffusion time of the PFG NMR experiment. Hyaluronic acid (HA) is an anionic biopolymer that is present in many tissues and can be involved in cancerous neoformations. HA can form complexes with proteins (particularly, serum albumin) in the body. However, HA structures and processes involving HA have not been extensively studied by NMR because the molecule's rigid structure makes these studies problematic. In the current work, self-diffusion of HA and bovine serum albumin (BSA), and water in solutions was measured by 1H pulsed field gradient NMR (PFG NMR) with a focus on the HA-BSA-D2O systems at various concentrations of BSA and HA. It was shown that in the presence of even a small amount of HA, the self-diffusion coefficient (SDC) of BSA decreases. To explain this fact, three hypotheses were proposed and analyzed. The first one was based on the effect of slowing down of water mobility in the presence of HA. The second hypothesis suggested an effect of mechanical collisions of BSA with HA molecules. The third hypothesized that BSA and HA molecules form a complex where BSA molecules reduced in mobility. It was shown that the third mechanism is the most likely. The state of the BSA molecules in the BSA-HA-D2O system corresponds to a ‘fast exchange’ condition from the NMR point of view: BSA molecules reside in the ‘free’ and ‘bound’ (with HA) states for much shorter time than the diffusion time of the PFG NMR experiment, 7 ms. The fractions of ‘bound’ BSA molecules in the BSA-HA complex were estimated.
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| 28. |
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| 29. |
- Furo, Istvan, et al.
(författare)
-
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
-
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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| 30. |
- Galvosas, P., et al.
(författare)
-
Rheo-NMR in food science - Recent opportunities
- 2019
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 57:9, s. 757-765
-
Tidskriftsartikel (refereegranskat)abstract
- For over 25years, nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques have been used to study materials under mechanical deformation. Collectively, these methods are referred to as Rheo-NMR. In many cases, it provides spatially and temporally resolved maps of NMR spectra, intrinsic NMR parameters (such as relaxation times), or motion (such as diffusion or flow). Therefore, Rheo-NMR is complementary to conventional rheological measurements. This review will briefly summarize current capabilities and limitations of Rheo-NMR in the context of material science and food science in particular. It will report on recent advances such as the incorporation of torque sensors or the implementation of large amplitude oscillatory shear and point out future opportunities for Rheo-NMR in food science. © 2019 John Wiley & Sons, Ltd.
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| 31. |
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| 32. |
- Gogoll, Adolf, 1957-, et al.
(författare)
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Complete 1H and 13C NMR spectral assignment of venturicidin A by 2D NMR spectroscopy
- 1989
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 27:9, s. 863-871
-
Tidskriftsartikel (refereegranskat)abstract
- After correlation of the majority of signals by COSY and one-bond heteronuclear correlation, the complete assignment of the 1H and 13C NMR spectra of the macrolide antibiotic venturicidin A required the application of long-range CH coupling information. This was accessible by the COLOC-S and selective INEPT experiments, and the sensitivity of these experiments is discussed. Steric information was obtained from a NOESY spectrum, and the solution structure compared with that in the crystal.
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| 33. |
- Gogoll, Adolf, et al.
(författare)
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Structural Assignment of σ-π-Palladium Complexes by 2D NMR
- 1993
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 31:10, s. 954-959
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Tidskriftsartikel (refereegranskat)abstract
- A series of (σ-π)palladium complexes derived from cyclooctadiene were investigated by 1H, 13C and 19F NMR. The stereochemical assignment was based on intramolecular NOEs in conjunction with molecular modelling and semi-empirical methods, and confirmed by interligand NOEs in nitrogen chelate complexes derived from the title compounds. The nitrogen chelating ligands are involved in a rotation with respect to the ligand-palladium axis.
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| 34. |
- 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
-
Ingår i: Magnetic resonance in chemistry : MRC. - : Wiley. - 0749-1581 .- 1097-458X. ; 42 Spec no
-
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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| 35. |
- Hakkarainen, Birgit, et al.
(författare)
-
NMR study of hydroxy protons of di- and trimannosides, substructures of Man-9
- 2007
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 45:12, s. 1076-1080
-
Tidskriftsartikel (refereegranskat)abstract
- The chemical shifts, temperature coefficients and inter-residual rotating-frame Overhauser effect (ROE)s for the hydroxy protons of some alpha-(1,2)-, alpha-(1,3)- and alpha-(1,6)linked di- and trimannosides have been measured for samples in 85% H2O/15% acetone-d(6) solution. These mannosides, Man alpha(1 -> 2)Man alpha OMe (1) Man alpha(1 -> 3)Man alpha OMe (2), Man alpha(1 -> 6)Man alpha OMe (3), Man alpha(1 -> 2)Man alpha(1 -> 2)Man alpha OMe (4), Man alpha(1 -> 2)Man alpha(1 -> 3)Man alpha OMe (5), Man alpha(1 -> 2)Man alpha(1 -> 6)Man alpha OMe (6) and Man alpha(1 -> 3)[Man alpha 1 -> 6]Man alpha OMe (7), are substructures of the N-glycan Man-9. The NMR data show that the hydration of each individual hydroxyl group in the di- and trisaccharides is very similar to the hydration of the corresponding hydroxyl in the monomeric methyl alpha-D-mannoside. No hydrogen-bond interactions were found to stabilize the conformations of the alpha-(1,2)- and alpha-(1,6)-linkages and the chemical shifts for the hydroxy proton resonances of the alpha-(1,6)-linkage indicated high-conformational flexibility. For the alpha-(1,3)-linkage, however, the downfield shift for the signal of O(2)H of the 3-substituted residue together with the ROE between this proton and H5' on the next residue suggest some weak inter-residue interactions.
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| 36. |
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| 37. |
- Hauksson, Jón B, et al.
(författare)
-
NMR processing techniques based on multivariate data analysis and orthogonal signal correction. 13C CP/MAS NMR spectroscopic characterization of softwood kraft pulp
- 2001
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 39:5, s. 267-75
-
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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| 38. |
- Jonsson, K. Hanna M., et al.
(författare)
-
NMR analysis of conformationally dependent nJC,H and nJC,C in the trisaccharide α-L-Rhap-(1→2)[α-L-Rhap-(1→3)]-α-L-Rhap-OMe and a site-specifically labeled isotopologue thereof
- 2011
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 49:3, s. 117-124
-
Tidskriftsartikel (refereegranskat)abstract
- An array of NMR spectroscopy experiments have been carried out to obtain conformationally dependent 1H,13C- and 13C,13C-spin–spin coupling constants in the trisaccharide α-L-Rhap-(1 → 2)[α-L-Rhap-(1 → 3)]-α-L-Rhap-OMe. The trisaccharide was synthesized with 13C site-specific labeling at C2′ and C2″, i.e. in the rhamnosyl groups in order to alleviate 1H spectral overlap. This facilitated the measurement of a key trans-glycosidic proton–proton cross-relaxation rate using 1D 1H,1H-T-ROESY experiments as well as a 3JC, H coupling employing 1D 1H,13C-long-range experiments, devoid of potential interference from additional J coupling. By means of both the natural abundance compound and the 13C-labeled sample 2D 1H,13C-J-HMBC and 1H,13C-HSQC-HECADE NMR experiments, total line-shape analysis of 1H NMR spectra and 1D 13C NMR experiments were employed to extract 3JC, H, 2JC, H, 3JC, C, and 1JC, C coupling constants. The 13C site-specific labeling facilitates straightforward determination of nJC, C as the splitting of the 13C natural abundance resonances. This study resulted in eight conformationally dependent coupling constants for the trisaccharide and illustrates the use of 13C site-specific labeling as a valuable approach that extends the 1D and 2D NMR methods in current use to attain both hetero- and homonuclear spin–spin coupling constants that subsequently can be utilized for conformational analysis.
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| 39. |
- Kazimierczuk, Krzysztof, et al.
(författare)
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Non-uniform sampling: Post-Fourier era of NMR data collection and processing
- 2015
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 53:11, s. 921-926
-
Tidskriftsartikel (refereegranskat)abstract
- The invention of multidimensional techniques in the 1970s revolutionized NMR, making it the general tool of structural analysis of molecules and materials. In the most straightforward approach, the signal sampling in the indirect dimensions of a multidimensional experiment is performed in the same manner as in the direct dimension, i.e. with a grid of equally spaced points. This results in lengthy experiments with a resolution often far from optimum. To circumvent this problem, numerous sparse-sampling techniques have been developed in the last three decades, including two traditionally distinct approaches: the radial sampling and non-uniform sampling. This mini review discusses the sparse signal sampling and reconstruction techniques from the point of view of an underdetermined linear algebra problem that arises when a full, equally spaced set of sampled points is replaced with sparse sampling. Additional assumptions that are introduced to solve the problem, as well as the shape of the undersampled Fourier transform operator (visualized as so-called point spread function), are shown to be the main differences between various sparse-sampling methods. Copyright © 2015 John Wiley & Sons, Ltd.
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| 40. |
- Kleinmaier, Roland, et al.
(författare)
-
Solvent effects on 15N NMR coordination shifts
- 2013
-
Ingår i: Magnetic resonance in chemistry : MRC. - : Wiley. - 1097-458X .- 0749-1581. ; 51:1, s. 46-53
-
Tidskriftsartikel (refereegranskat)abstract
- (15)N NMR chemical shift became a broadly utilized tool for characterization of complex structures and comparison of their properties. Despite the lack of systematic studies, the influence of solvent on the nitrogen coordination shift, Δ(15)N(coord), was hitherto claimed to be negligible. Herein, we report the dramatic impact of the local environment and in particular that of the interplay between solvent and substituents on Δ(15)N(coord). The comparative study of CDCl(3) and CD(3)CN solutions of silver(I)-bis(pyridine) and silver(I)-bis(pyridylethynyl)benzene complexes revealed the strong solvent dependence of their (15)N NMR chemical shift, with a solvent dependent variation of up to 40ppm for one and the same complex. The primary influence of the effect of substituent and counter ion on the (15)N NMR chemical shifts is rationalized by corroborating Density-Functional Theory (nor discrete Fourier transform) calculations on the B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d) level. Cooperative effects have to be taken into account for a comprehensive description of the coordination shift and thus the structure of silver complexes in solution. Our results demonstrate that interpretation of Δ(15)N(coord) in terms of coordination strength must always consider the solvent and counter ion. The comparable magnitude of Δ(15)N(coord) for reported transition metal complexes makes the principal findings most likely general for a broad scale of complexes of nitrogen donor ligands, which are in frequent use in modern organometallic chemistry.
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| 41. |
- Knoll, Kevin, et al.
(författare)
-
A supramolecular and liquid crystalline water-based alignment medium based on azobenzene-substituted 1,3,5-benzenetricarboxamides
- 2022
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 60:6, s. 563-571
-
Tidskriftsartikel (refereegranskat)abstract
- A supramolecular, lyotropic liquid crystalline alignment medium based on an azobenzene-containing 1,3,5-benzenetricarboxamide (BTA) building block is described and investigated. As we demonstrate, this water-based system is suitable for the investigation of various water-soluble analytes and allows for a scaling of alignment strength through variation of temperature. Additionally, alignment is shown to reversibly collapse above a certain temperature, yielding an isotropic solution. This collapse allows for isotropic reference measurements, which are typically needed in addition to those in an anisotropic environment, to be performed using the same sample just by varying the temperature. The medium described thus provides easy access to anisotropic NMR observables and simplifies structure elucidation techniques based thereon.
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| 42. |
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| 43. |
- Kuhn, Stefan, et al.
(författare)
-
NMReDATA : Tools and applications
- 2021
-
Ingår i: Magnetic Resonance in Chemistry. - : John Wiley & Sons. - 0749-1581 .- 1097-458X. ; 59:8, s. 792-803
-
Tidskriftsartikel (refereegranskat)abstract
- The nuclear magn etic resonance extracted data (NMReDATA) format has beenproposed as a way to store, exchange, and disseminate nuclear magneticresonance (NMR) data and physical and chemical metadata of chemical com-pounds. In this paper, we report on analytical workflows that take advantageof the uniform and standardized NMReDATA format. We also give access to arepository of sample data, which can serve for validating software packagesthat encode or decode files in NMReDATA format.
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| 44. |
- Liebau, Jobst, et al.
(författare)
-
Characterization of fast-tumbling isotropic bicelles by PFG diffusion NMR
- 2017
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 55:5, s. 395-404
-
Forskningsöversikt (refereegranskat)abstract
- Small isotropic bicelles are versatile membrane mimetics, which, in contrast tomicelles, provide a lipid bilayer and are at the same time suitable for solution-state NMR studies. The lipid composition of the bilayer is flexible allowing for incorporation of various head groups and acyl chain types. In bicelles, lipids are solubilized by detergents, which are localized in the rimof the disk-shaped lipid bilayer. Bicelles have been characterized by a broad array of biophysical methods, pulsed-field gradient NMR (PFG NMR) being one of them. PFG NMR can readily be used to measure diffusion coefficients of macromolecules. It is thus employed to characterize bicelle size and morphology. Even more importantly, PFG NMR can be used to study the degree of protein association to membranes. Here, we present the advances that have been made in producing small, fast-tumbling isotropic bicelles from a variety of lipids and detergents, together with insights on the morphology of such mixtures gained from PFG NMR. Furthermore, we review approaches to study protein-membrane interaction by PFG NMR.
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| 45. |
- Maliarik, Mikhail, et al.
(författare)
-
The solvation of the mercury(II) ion - A 199Hg NMR study
- 2005
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 43:10, s. 835-842
-
Tidskriftsartikel (refereegranskat)abstract
- The solvation of the mercury(II) ion in solvents with different solvation properties, water, dimethylsulfoxide, N,N-dimethylthioformamide, and liquid ammonia, has been studied by means of 199Hg NMR. The 199Hg chemical shift shows a pronounced dependence on the coordination number of the mercury(II) ion in the solvates resulting in a difference of over 1200 ppm between basically tetrahedral and octahedral complexes. The chemical shifts can furthermore be associated with electron-pair donor properties of the solvents. The spin-lattice relaxation times of the 199Hg nucleus in the solvates have been measured at different applied magnetic fields, concentrations, temperatures, and isotope substitutions. Possible mechanisms for the 199Hg relaxation were proposed and the chemical shielding anisotropy in the solvates has been estimated. The 199Hg relaxation rates and the anisotropy are correlated with the structure of the solvate complexes in solution obtained from recent LAXS and EXAFS studies. Copyright © 2005 John Wiley & Sons, Ltd.
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| 46. |
- Malliavin, TE, et al.
(författare)
-
The NMR structure of [Xd(C2)]4 investigated by molecular dynamics simulations
- 2003
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 1097-458X .- 0749-1581. ; 41:1, s. 18-25
-
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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| 47. |
- Malmodin, Daniel, 1974, et al.
(författare)
-
Robust and versatile interpretation of spectra with coupled evolution periods using multi-way decomposition.
- 2006
-
Ingår i: Magnetic resonance in chemistry : MRC. - : Wiley. - 0749-1581 .- 1097-458X. ; 44 Spec No
-
Tidskriftsartikel (refereegranskat)abstract
- Coupling of evolution periods in NMR experiments is a very promising approach that has recently attracted much attention for its substantial savings in measurement time. Another novel concept, which has already proved useful in many types of NMR applications is multi-way decomposition. The PRODECOMP tool described here addresses the combination of these two modern tools in protein NMR. The following properties of this approach are described and illustrated. Highly similar information to what would be found in a corresponding full-dimensional spectrum is extracted from a set of projected spectra. All experimental spectra are used simultaneously, avoiding sensitivity loss associated with individual examination of the spectra. Aliasing caused by the linear combinations of individual shifts in the projected spectra is automatically resolved, allowing for better resolution due to smaller spectral widths. Reconstructions of various high-dimensional spectra, including the corresponding full-dimensional spectrum become straightforward. Spectral overlap is efficiently resolved. The capabilities of PRODECOMP are illustrated for a 14 kD protein, for which 12 projections of a 5-dimensional spectrum with the nuclei N, HN, CO, Calpha and Halpha are analysed.
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| 48. |
- Maneval, J. E., et al.
(författare)
-
Magnetic resonance analysis of capillary formation reaction front dynamics in alginate gels
- 2011
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 1097-458X .- 0749-1581. ; 49:10, s. 627-640
-
Tidskriftsartikel (refereegranskat)abstract
- The formation of heterogeneous structures in biopolymer gels is of current interest for biomedical applications and is of fundamental interest to understanding the molecular level origins of structures generated from disordered solutions by reactions. The cation-mediated physical gelation of alginate by calcium and copper is analyzed using magnetic resonance measurements of spatially resolved molecular dynamics during gel front propagation. Relaxation time and pulse-field gradient methods are applied to determine the impact of ion front motion on molecular translational dynamics. The formation of capillaries in alginate copper gels is correlated to changes in translational dynamics.
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| 49. |
- Morssing Vilén, Eric, et al.
(författare)
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Application of diffusion-edited NMR spectroscopy for selective suppression of water signal in the determination of monomer composition in alginates
- 2011
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 49, s. 584–591-
-
Tidskriftsartikel (refereegranskat)abstract
- Alginate is a linear copolymer of 1-4 linked β-d-mannuronic acid (M) and 1-4 linked α-l-guluronic acid (G). The physical properties of these polysaccharides such as gel properties and viscosity are largely correlated to the monomer composition (M/G ratio), the sequence of the polymer and the molecular weight. Determination of the M/G ratio is therefore important and NMR spectroscopy is among the most common methods used to accurately obtain this ratio. Instead of using time consuming, possibly sample altering, acid hydrolysis to reduce the viscosity of the alginate sample prior to analysis, samples of low concentrations can be used. However, this results in a water peak in the NMR spectrum that is several orders of magnitude larger than the alginate signals and water suppression is required. In this article, a diffusion-edited NMR experiment that suppresses the water peak while retaining the signals of interest has been used to enable correct M/G ratio determination. This approach exploits the difference in translational diffusion between the larger alginate molecules and the smaller water molecules. Using this method, the monomer composition of 20 different alginate powders was determined. The diffusion parameters were optimized to allow measurement for samples covering a large range of M/G ratios and viscosities. Thus, such method should be useful for analyzing large numbers of unknown alginate samples using, for example, automation procedures
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| 50. |
- Mulder, Frans, et al.
(författare)
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Carbonyl 13C Transverse Relaxation Measurements to Sample Protein Backbone Dynamics.
- 2003
-
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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