| 1. |
- 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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| 2. |
- 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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| 3. |
- 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
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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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| 4. |
- 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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| 5. |
- 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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| 6. |
- Filippov, Andrei, et al.
(författare)
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Self-diffusion in a hyaluronic acid–albumin–water system as studied by NMR
- 2012
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 50:2, s. 114-119
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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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| 7. |
- Jonsson, K. Hanna M., et al.
(författare)
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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
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 49:3, s. 117-124
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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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| 8. |
- Kleinmaier, Roland, et al.
(författare)
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Solvent effects on 15N NMR coordination shifts
- 2013
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Ingår i: Magnetic resonance in chemistry : MRC. - : Wiley. - 1097-458X .- 0749-1581. ; 51:1, s. 46-53
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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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| 9. |
- Maneval, J. E., et al.
(författare)
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Magnetic resonance analysis of capillary formation reaction front dynamics in alginate gels
- 2011
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 1097-458X .- 0749-1581. ; 49:10, s. 627-640
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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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| 10. |
- 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
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 49, s. 584–591-
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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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