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Application of 1H and 31P NMR to topological description of a model of biological membrane fusion Topological description of a model of biological membrane fusion

100%
Janiak-Osajca A., Timoszyk A.
Acta Biochimica Polonica
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2012
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vol. 59
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issue 2
219-224
EN
The process of biological membrane fusion can be analysed by topological methods. Mathematical analysis of the fusion process of vesicles indicated two significant facts: the formation of an inner, transient structure (hexagonal phase - HII) and a translocation of some lipids within the membrane. This shift had a vector character and only occurred from the outer to the inner layer. Model membrane composed of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS) was studied. 31P- and 1H-NMR methods were used to describe the process of fusion. 31P-NMR spectra of multilamellar vesicles (MLV) were taken at various temperatures and concentrations of Ca2+ ions (natural fusiogenic agent). A 31P-NMR spectrum with the characteristic shape of the HII phase was obtained for the molar Ca2+/PS ratio of 2.0. During the study, 1H-NMR and 31P-NMR spectra for small unilamellar vesicle (SUV), which were dependent on time (concentration of Pr3+ ions was constant), were also recorded. The presence of the paramagnetic Pr3+ ions permits observation of separate signals from the hydrophilic part of the inner and outer lipid bilayers. The obtained results suggest that in the process of fusion translocation of phospholipid molecules takes place from the outer to the inner layer of the vesicle and size of the vesicles increase. The NMR study has showed that the intermediate state of the fusion process caused by Ca2+ ions is the HII phase. The experimental results obtained are in agreement with the topological model as well.
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Influence of acceptor functionality on charge transfer interactions in mixtures of poly(9-vinylcarbazole) with nitroaromatic compounds

100%
Grigoras A., Barboiu V.
Open Chemistry
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2012
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vol. 10
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issue 2
313-319
EN
Charge transfer interactions in mixtures of poly(9-vinylcarbazole) with three nitro compounds (4,4′dinitrodibenzyl, ethyl 3,5-dinitrobenzoate and 2,2′,4,4′-tetranitrodibenzyl) were examined. GPC shows an increase of apparent polymer weight average molecular weight (MW) in mixtures compared with pure PVK. Electron acceptors show upfield 1H-NMR shifts for all mixtures. The equilibrium association constants (k) calculated from the Benesi-Hildebrand equation are 0.511, 1.371, and 1.868 L mol−1 for PVK blends with DNDB, DNBE and TNDB, respectively. Shifts of (−NO2) stretch vibrations in mixtures support charge transfer complex formation between PVK chains and electron acceptors The ability to accept electrons decreases: TNDB>DNBE>DNDB. [...]
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Translocation of polysialic acid across model membranes: Kinetic analysis and dynamic.

86%
Janas T., Krajiński H., Timoszyk A., Janas T.
Acta Biochimica Polonica
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2001
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vol. 48
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issue 1
163-173
EN
Transmembrane translocation of polyion homopolymers takes place in the case of polyanionic polysialic acid (polySia), polyanionic polynucleotides and polycationic polypeptides. The purpose of this work was to determine the role of membrane electrical parameters on the kinetics of polyion translocation, the influence of polysialic acid on ion adsorption on positively charged membrane surface and the dynamics of the phospholipid hydrocarbon chains and choline group by using 1H-NMR. The analysis of polyion translocation was performed by using the electrical equivalent circuit of the membrane for the initial membrane potential equal to zero. The changes in polysialic acid flux was up to 75% after 1 ms in comparison with the zero-time flux. Both a decrease of membrane conductance and an increase of polyion chain length resulted in the diminution of this effect. An increase of praseodymium ions adsorption to positively charged liposomes and an increase of the rate of segmental movement of the -CH2 and -CH3 groups, and the choline headgrup of lipid molecules, was observed in the presence of polySia. The results show that the direction of the vectorial polyion translocation depends both on the membrane electrical properties and the degree of polymerization of the polymer, and that polysialic acid can modulate the degree of ion adsorption and the dynamics of membrane lipids.
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