Association of methyl viologen and its cation radical with dihexadecyl phosphate vesicles

Lukac, Sava; Harbour, John R.

doi:10.1021/ja00351a022

Cited by 11 publications

(6 citation statements)

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“…Results reported recently in the literature also agree with the present picture: methylviologen MV2+ itself associates o 0' e P o' N strongly with sodium dihexadecyl phosphate vesicles (33) and diffuses through the membrane above 30'C (34); lipophilic derivatives of MV2" dissolve in membranes and may act as transmembrane electron carriers (35,36); long, terminal aliphatic diquaternary ammonium cations may span anionic vesicle membranes (37).…”

Section: Methodssupporting

confidence: 92%

Molecular devices: Caroviologens as an approach to molecular wires—synthesis and incorporation into vesicle membranes

Arrhenius

Blanchard‐Desce

Dvolaïtzky

et al. 1986

Proc. Natl. Acad. Sci. U.S.A.

124

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Molecular wires, which would allow electron flow to take place between different components, are important elements in the design of molecular devices. An approach to such species would be molecules possessing an electron-conducting conjugated chain, terminal electroactive polar groups, and a length sufficient to span a lipid membrane. To this end, bispyridinium polyenes of different lengths have been synthesized and their incorporation into the bilayer membrane of sodium dihexadecyl phosphate vesicles has been studied. Since they combine the features of carotenoids and of viologens, they may be termed caroviologens. Vesicles containing the caroviologen whose length approximately corresponds to the thickness of the sodium dihexadecyl phosphate bilayer display temperature-dependent changes of its absorption spectrum reflecting the gel --liquidcrystal phase transition of the membrane. The data agree with a structural model in which the caroviologens of sufficient length span the bilayer membrane, the pyridinium sites being close to the negatively charged outer and inner surfaces of the sodium dihexadecyl phosphate vesicles and the polyene chain crossing the lipidic interior of the membrane. These membranes may now be tested in processes in which the caroviologen would function as a continuous, transmembrane electron channel-i.e., as a molecular wire. Various further developments may be envisaged along these lines.Molecular devices may be defined as structurally organized and functionally integrated chemical systems built into supramolecular architectures. The development of such devices requires the design of molecular components performing a given function (e.g., photoactive, electroactive, ionoactive, thermoactive, or chemoactive) and suitable for assembly into an organized array. A major requirement is that these components and the devices that they build up should perform their function(s) at the molecular and supramolecular (1) levels, as distinct from the level of the bulk material.

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Section: Methodssupporting

confidence: 92%

Molecular devices: Caroviologens as an approach to molecular wires—synthesis and incorporation into vesicle membranes

Arrhenius

Blanchard‐Desce

Dvolaïtzky

et al. 1986

Proc. Natl. Acad. Sci. U.S.A.

124

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“…The photoreduction of methyl viologen has been studied in vesicular and micellar suspensions. [21][22][23] This molecule has also been used as an electron acceptor in zeolites. [24][25][26] There is considerable interest in the use of microporous materials, such as zeolites, as hosts for photoinduced charge separation.…”

Section: Introductionmentioning

confidence: 99%

Photoreduction of Methyl Viologen in Zeolite X

Koodali

Kevan

2002

J. Phys. Chem. B

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The photoreduction of methyl viologen (MV2+) was examined in zeolite X. A series of alkali metal ion-exchanged zeolite X materials with ion-exchanged methyl viologen was photoionized with 320 nm light at room temperature in the absence of any reducing counteranion. Photoreduction of methyl viologen containing alkali metal ion-exchanged zeolite X results in the formation of methyl viologen cation radicals (MV•+). The radicals were identified by electron spin resonance (ESR). Upon irradiation at room temperature the samples turn light blue in color and a single line ESR spectrum characteristic of the methyl viologen radical cation is observed. The photoyield depends on the nature of the alkali metal ion-exchanged into the zeolite framework. The photoyield increases in the order Li−X/MV2+ < Na−X/MV2+ < K−X/MV2+ < Rb−X/MV2+ < Cs−X/MV2+. The donor strength of the zeolite framework increases in the order Li−X < Na−X < K−X < Rb−X < Cs−X. Thus, the electron donor is suggested to be the anionic aluminosilicate framework of the host zeolite. This is supported by a linear correlation of the photoyields of alkali metal ions exchanged into zeolite X with Sanderson's partial charges on the framework oxygens.

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“…In 20 mM Tris, pH 8.0, binding varied from 80% to 43% as the MV2+/ DHP ratio increased from 0.026 to 0.10; in 20 mM glycine, pH 9.5, with MV2+/DHP E 0.05, binding was 8696, and in H20 using DHP vesicles whose phosphate group headgroup were neutralized with sodium hydroxide, MV2+ binding has been reported as essentially complete. 19 These effects can be understood qualitatively in terms of changes in electrostatic binding forces. Specifically, decreasing the solution ionic strength and increasing in alkalinity should increase the effective negative surface charge density of the anionic DHP Vesicles, enhancing electrostatic attraction of the dications.…”

Section: Respltsmentioning

confidence: 99%

Pathways of viologen-mediated oxidation-reduction reactions across dihexadecyl phosphate bilayer membranes

Patterson¹,

Hurst²

1993

J. Phys. Chem.

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Transmembrane reduction of methylviologen (N, MV2+) and several n-alkylmethyl analogs, i.e., N-alkyl-N'-methyl-4,4/-bipyridinium (C,MV+, n I lo), entrapped within dihexadecyl phosphate (DHP) vesicles by S202-or CrEDTAZ-located in the bulk aqueous phase occurred only when viologens were also initially present on the same side of the membrane as the reductant. Viologen radical cation formation was biphasic, with reduction of the externally bound viologen dications preceding reduction of the entrapped viologen. For MV2+, the rate law was dwhere the subscripts i and o refer to viologens bound at the vesicle inner and outer interfaces, respectively. Transmembrane reduction was accompanied by comigration of a viologen radical cation with each electron transferred across the bilayer. The MV+ ion formed on the external surface was monomeric, but the MV+ formed internally was aggregated (or multimeric); from the wavelength dependence of the kinetic curves, it was shown that aggregation coincided with or rapidly followed the rate-limiting transmembrane redox step. For the C,MV2+ ions, the reaction dynamics were qualitatively similar but were complicated by the simultaneous presence of both monomeric and multimeric forms of C,MV+ at the outer vesicle interface. When n > 10, reduction of external C,MVZ+ ions was biphasic. For C16MV2+, only about one-third of the entrapped viologen was reducible unless the reaction medium also contained lipophilic ions, under which conditions all of the internal ions could be reduced.Correspondingly, only one-third of the external Cl6MVZ+ translocated to the inner vesicle surface. Computer simulations of the complex kinetic waveforms required inclusion of two independent transmembrane redox steps to obtain adequate data fits. There were interpreted in terms of two distinct reaction pathways involving (i) transverse diffusion of interfacially bound reactants and (ii) electron tunneling between the viologen radical cations and dications juxtaposed in the opposite bilayer leaflets. Possible alternative molecular mechanisms corresponding to the two pathways are discussed.

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Association of methyl viologen and its cation radical with dihexadecyl phosphate vesicles

Cited by 11 publications

References 0 publications

Molecular devices: Caroviologens as an approach to molecular wires—synthesis and incorporation into vesicle membranes

Molecular devices: Caroviologens as an approach to molecular wires—synthesis and incorporation into vesicle membranes

Photoreduction of Methyl Viologen in Zeolite X

Pathways of viologen-mediated oxidation-reduction reactions across dihexadecyl phosphate bilayer membranes

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