title: Towards redox active liquid crystalline phases of lipids: a monoolein/water system with entrapped derivatives of ferrocene.
abstract: The phase and electrochemical behavior of the aqueous mixtures of monoolein (MO) and synthetic ferrocene (Fc) derivatives containing long alkyl chains-(Z)-octadec-9-enoylferrocene (1), (Z)-octadecen-9-ylferrocene (2), and ferrocenylmethyl (Z)-octadec-9-enoate (3)-were studied. At low hydration, the reversed micelles (L(2) phase) and cubic Q(230) phase of MO can accommodate relatively high amounts (>6 wt.%) of the Fc-derivative 2, whereas at high hydration, the pseudoternary cubic phase Q(224) is destabilized even at about 2 wt.% of this Fc. Increasing the Fc-derivative content induces L(alpha)-->L(2) and L(alpha)-->reversed bicontinuous cubic phase (Q(II))-->H(II) transitions depending upon hydration. A rough study of the MO system containing compounds 1 and 3 indicates very similar phase behavior to that of the MO/2/H(2)O system. Compound 2 apparently has no effect on the lipid monolayer thickness in the pseudoternary L(alpha), H(II) and Q(II) liquid crystalline phases of MO. Within a 3D-structure of the Q(224) phase, derivatives 1-3 exhibit electrochemical activity on the gold electrode. The one-electron redox conversion processes are electrochemically quasi-reversible and controlled by diffusion. The values of apparent diffusion coefficient (D(app)) and heterogeneous electron-transfer rate constant (k(s)) of Fcs are significantly lower in the cubic phase matrix when compared to the acetonitrile solution. By contrast, the MO H(II) phase with entrapped Fc-derivatives does not exhibit electrochemical activity on the electrode surface. It is suggested that the diffusional anisotropy and/or localized aggregation of compounds 1-3 within a 2D-structure of the H(II) phase account(s) for the latter observation.
authors.affiliation: Department of Bioelectrochemistry and Biospectroscopy, Institute of Biochemistry, Mokslininkucedil, 12, LT-2600 Vilnius, Lithuania.
authors.forename: Justas
authors.initials: J
authors.lastname: Barauskas
authors.forename: Valdemaras
authors.initials: V
authors.lastname: Razumas
authors.forename: Zita
authors.initials: Z
authors.lastname: Talaikyte
authors.forename: Arūnas
authors.initials: A
authors.lastname: Bulovas
authors.forename: Tommy
authors.initials: T
authors.lastname: Nylander
authors.forename: Daiva
authors.initials: D
authors.lastname: Tauraite
authors.forename: Eugenijus
authors.initials: E
authors.lastname: Butkus
mesh_terms: D003460:Crystallization / Q000379:methods*; D003461:Crystallography; D004058:Diffusion; D004563:Electrochemistry; D004579:Electron Transport; D005296:Ferrous Compounds / Q000737:chemistry* / Q000145:classification; D005989:Glycerides / Q000737:chemistry*; D046911:Macromolecular Substances; D000075163:Metallocenes; D008823:Micelles; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D012996:Solutions; D014867:Water / Q000737:chemistry*
chemical_list: D005296:Ferrous Compounds; D005989:Glycerides; D046911:Macromolecular Substances; D000075163:Metallocenes; D008823:Micelles; D012996:Solutions; D014867:Water; C005953:monoolein; C004998:ferrocene