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Autoperoxidácia chromatograficky čistého fosfatidylcholínu izolovaného z vaječných žĺtkov (EYPC)sa sledovala prostredníctvom vzniku konjugovaných diénov (CD) a produktov reagujúcich s kyselinou tiobarbiturovou (TBARS) metódou UV-VIS spektrofotometrie. V propagačnej fáze autoperoxidácie n-dekán (C10) a n-oktadekán (C18) inhibujú peroxidáciu EYPC do mólových pomerovC10:EYPC = 0,2, resp. C18:EYPC = 1. Pri vyšších mólových pomeroch výťažok autoperoxidačnejreťazovej reakcie rastie. Pri najvyššom študovanom mólovom pomere (alkán:EYPC = 2:1) koncentrácie CD a TBARS presahovali pôvodné koncentrácie u kontrolných vzoriek bez prítomnostialkánov. Na základe zmeny hrúbky lipidovej dvojvrstvy unilamelárnych lipozómov z dioleoylfosfatidylcholínu (DOPC) určenej pomocou malouhlového rozptylu neutrónov predpokladáme, že prinízkych koncentráciách alkánu (C10:DOPC Ł 0,4) je C10 lokalizovaný v hydrofóbnej oblasti dvojvrstvy paralelne s acylovými reťazcami fosfolipidu. Pri vyšších mólových pomeroch (0,6 Ł C10:DOPCŁ 1,0) alkán mení svoju lokalizáciu do stredu hydrofóbnej oblasti dvojvrstvy, medzi monovrstvylipidu. Alkán lokalizovaný paralelne s polynenasýtenými acylovými reťazcami mastných kyselínRH separuje tieto rešazce a znižuje pravdepodobnosš ich zrážok, čo zníži výšažok radikálovýchreakcií ROO L +RH -> ROOH+R L , 2 ROOH -> RO L +ROO L +H2O, RO L +RH -> R L +ROH a následnepoklesne autoperoxidácia. Redistribúcia alkánu do stredu hydrofóbnej oblasti lipidovej dvojvrstvyvráti hodnotu autoperoxidácie na úroveň kontrolnej vzorky. 1 H dekaplované 31 P NMR spektrávodných disperzií EYPC+C10 ukazujú, že pri mólových pomeroch C10:EYPC > 1:1 sa lipidovádvojvrstva reštrukturalizuje do nelamelárnych fáz. Inverzná hexagonálna fáza H II s C10 (alebo C18)lokalizovanými v intersticiálnych oblastiach elementárnych buniek HII vykazuje vyiiiu autoperoxidáciu než kontrolná vzorka, čo je výsledkom väčiej pohybovej voľnosti RH reťazcov v HII fáze.
Conjugated dienes (CD) and thiobarbituric acid reactive substances (TBARS) have been estimatedduring the autoperoxidation of chromatographically pure phosphatidylcholine from hen eggs(EYPC) in multilamellar liposomes by UV-VIS spectrophotometry. During the propagation phaseof autoperoxidation reaction, n-decane (C10) and n-octadecane (C18) gradually inhibit EYPCperoxidation up to 0:2:1 and 1:1 alkane:EYPC molar ratios, respectively. At higher molar ratios, theyield of estimated autoperoxidation products increases. At the highest molar ratio studied (alkane:EYPC = 2:1), the CD and TBARS concentrations exceed their levels in control sample without alkane added. The changes in the lipid bilayer thickness estimated from the small-angle neutronscattering (SANS) curves of unilamellar dioleoylphosphatidylcholine (DOPC) liposomes have indi-cated that C10 is located in the bilayer hydrophobic region parallel to the DOPC acyl chains at lowmolar ratios (C10:DOPC £ 0.4). At higher molar ratios (0.6 £ C10:DOPC £ 1.0), the alkane changesits location into the center of the bilayer between the apposing monolayers. The alkane locationparallel to polyunsaturated lipid fatty acyl chains RH separates these chains resulting in a decreased frequency of their encounters, in decreased yields of ROO L +RH -> ROOH+R L , 2 ROOH ->RO L +ROO L +H2O and RO L +RH -> R L +ROH free radical reactions, and consequently, in decreasedautoperoxidation. Autoperoxidation returns to the control values due to alkane redistribution intothe bilayer center. 1 H decoupled 31 P NMR spectra of EYPC+C10 aqueous dispersions have shownthat the lipid bilayer transforms into nonbilayer phases at C10:EYPC > 1:1 molar ratios. Theinverted hexagonal HII phase with C10 (or C18) preferentially located in the interstitial regions ofthe HII unit cell displays higher autoperoxidation than the control bilayer sample due to greatermotional freedom of RH chains in the HII phase.
The agar working electrode as a hydrogel support for bilayer lipid membranes (BLM) was studied by electrochemical impedance spectroscopy. The aim was to study the influence of dc bias voltage on the formation of a stable supported bilayer lipid membrane (s-BLM) on the electrode tip. It was concluded that the hydrogel support is sufficiently stable in the applied range of bias voltages. The agar electrode provides satisfactory results in the frequency range 1–1?104 Hz. The electrode properties suggest applicability in deposition of s-BLM. Electric properties of s-BLM significantly depend on the dc bias voltage. The specific membrane capacitance of s-BLM at ?0.4 V was comparable with that of a conventional planar BLM. However, a shift to negative bias voltages led to a significant change of membrane resistance, possibly due to the increasing number of pores or defective structures in the lipid bilayer.
Lipid bilayer properties are quantified with a variety of arbitrary selected parameters such as molecular packing and dynamics, electrostatic potentials or permeability. In the paper we determined the effect of phloretin and 6-ketocholestanol (dipole potential modifying agents) on the membrane hydration and efficiency of the trans-membrane water flow. The dynamics of water molecules within the lipid bilayer interface was evaluated using solvent relaxation method, whereas the osmotically induced trans-membrane water flux was estimated with the stopped-flow method using the liposome shrinkage kinetics. The presence of phloretin or 6-ketocholestanol resulted in a change of both, the interfacial hydration level and osmotically driven water fluxes. Specifically, the presence of 6-ketocholestanol reduced the amount and mobility of water in the membrane interface. It also slows the osmotically induced water flow. The interfacial hydration change caused by phloretin was much smaller and the effect on osmotically induced water flow was opposite to that of 6-ketocholestanol.
- MeSH
- floretin chemie MeSH
- fluorescenční barviva chemie MeSH
- ketocholesteroly chemie MeSH
- lipidové dvojvrstvy chemie metabolismus MeSH
- liposomy chemie metabolismus MeSH
- permeabilita MeSH
- simulace molekulární dynamiky * MeSH
- voda chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH