Investigation of the Ribbon Structure of a Lyotropic Liquid Crystal by Deuterium Nuclear Magnetic Resonance

Chidichimo, Giuseppe; Vaz, Nuno A.; Yaniv, Z.; Doane, J. William

doi:10.1103/physrevlett.49.1950

Cited by 50 publications

(25 citation statements)

References 5 publications

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“…In other cases mixtures of different amphiphiles give rise to phases not formed by the individual components in similar conditions (12). Intermediate phases have been classified according to the fraction of planar interface W present in the amphiphile aggregate (13,14). A layered structure has W Ͼ 0.33, e.g., C 22 EO 6 (7), while a cubic phase has W ϭ 0 and a rhombohedral structure has W Ͻ 0.33 [C 30 EO 9 (9)].…”

mentioning

confidence: 99%

A continuous topological change during phase transitions in amphiphile/water systems

Funari

Rapp²

1999

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

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Amphiphiles are molecules such as surfactants or lipids that have a polar head group (hydrophilic) attached to nonpolar hydrophobic alkyl chains. Because of this characteristic they self-assemble in water and give rise to a wide range of phases with different structures and properties. Aqueous dispersions of amphiphiles are present in every aspect of day-to-day life-e.g., forming biological cell membranes, stabilizing emulsified food, or being used as soap. Time-resolved x-ray diffraction has been used to study the hexadecylhexa(oxyethylene glycol) ether (C 16 EO 6 )͞water system, which shows an intermediate phase whose structure depends on the thermal path between lamellar and hexagonal structures. Heating the hexagonal phase from room temperature leads to a lamellar phase via an Ia3d cubic structure. Cooling from the lamellar phase initially leads epitaxially to an intermediate R3 m before the hexagonal phase is reached. Both cubic and R3 m phases are formed by very similar rod units, but the overall structures differ because of their spatial distribution and they both bridge morphologically the hexagonal and lamellar phases. The Ia3d does so on heating, whereas the R3 m does on cooling. The structural path during the phase transitions is determined by topological similarities between the forming phase and the one from which it originates. Although the estimated curvature energies for these two phases are similar, on cooling, kinetics and topology are initial factors determining the path for the phase transitions, whereas on heating energy is the dominant factor.Aqueous suspensions of nonionic surfactants of the type poly(oxyethylene glycol) alkyl ether, C n EO m , are widely used in, e.g., extraction of membrane proteins, oil recovery, and cleaning processes. They show a rich polymorphism governed by the hydrophobic effect (1), forming among others lamellar, hexagonal, and cubic phases. In some cases the cubic phase is replaced by the so-called intermediate (or fluid) phases whose structures are still controversial. Characterization of these structures and their building units is important for the understanding of lyotropism. Moreover, these phases are also believed to occur as intermediate structures during biological processes-e.g., cell fusion (2).The mesogenic units can have different sizes and shapes, and from their organization different phases originate. They can range from disordered (liquid) to ordered structures in one (lamellar), two (hexagonal), and three dimensions (cubic). The most common cubic phases are formed by bicontinuous networks of rods (3). Gel and lamellar phases are stacked bilayers of amphiphiles and water, as shown in Fig. 1. The transition between these phases can be induced by, e.g., change in temperature or concentration. Most important, during such process there are significant changes in the curvature and morphology of the units (4).From the different amphiphile͞water systems studied it has been found that C n EO m molecules having long alkyl chains form stable intermed...

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mentioning

confidence: 99%

A continuous topological change during phase transitions in amphiphile/water systems

Funari

Rapp²

1999

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

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“…There are two significant features of these data: (1) Magnitude of the motionally induced asymmetry parameter 11 is noticeably different for KP-a-CD 2 and KL-a-CD 2 • This will be shown later to be a direct result of segregation of the compounds in different regions of aggregate. (2) Within experimental error the value of 11 is not temperature dependent for KP-a-C~ but is weakly temperature dependent for KLa-CD 2 in this region. Below 36°C the spectral patterns for the a position abruptly change to one in which 11 ~ 0 and with a width which is reduced from that of the La phase.…”

Section: Deuterium Spectral Patternsmentioning

confidence: 84%

“…Such a system is known to produce elongated ribbon shaped aggregates which are amenable to study with deuterium NMR. 2 A cross section of the ribbon aggregates illustrated in Fig. 1 consists of a lamellar-like central region capped on the edges by semicylinders.…”

Section: Introductionmentioning

confidence: 99%

Molecular distribution among regions of different curvature in aggregates of a lyotropic ternary system: A NMR measurement

Chidichimo

Golemme

Doane

et al. 1985

The Journal of Chemical Physics

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A lyotropic phase consisting of elongated ribbon aggregates on a rectangular lattice is induced when a small amount ( -1 mol %) of potassium laurate (KL) is added to a potassium palmitate (KP)/water mixture. By selective deuteration it is shown that the KL and KP molecules are not uniformly distributed throughout the ribbon aggregate. The less abundant KL molecules with the shorter hydrocarbon chain are more concentrated at the edges of the ribbons where there is high curvature, whereas the more abundant KP molecules are more concentrated in the central lamellar region of the aggregates. A quantitative measurement is described. The deuterium spectra also show how the KP and KL lipids are distributed among coexisting phases when an uneven distribution also occurs. The KP molecules prefer the lamellar structures, whereas the KL molecules prefer the aggregate structures.

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“…There are also other modes of motion that could be alternative ways to understand spectra taken for liquid crystals. These could include other internal rotations (42), the collective fluctuations of molecules in the bilayer, and even the diffusion over a curved surface (48) or ribbon phase (49), across defects in the bilayer structure, and uniform diffusive wobbling in a cone (28). The latter can be used to gain information on the extent of the head groups restriction.…”

Section: Motions Of Head Group In Simis 16mentioning

confidence: 99%

Molecular Motions of the Head Group of SHBS in Lamellar Liquid Crystals

Duke¹,

Funchess²,

Blum³

1991

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Investigation of the Ribbon Structure of a Lyotropic Liquid Crystal by Deuterium Nuclear Magnetic Resonance

Cited by 50 publications

References 5 publications

A continuous topological change during phase transitions in amphiphile/water systems

A continuous topological change during phase transitions in amphiphile/water systems

Molecular distribution among regions of different curvature in aggregates of a lyotropic ternary system: A NMR measurement

Molecular Motions of the Head Group of SHBS in Lamellar Liquid Crystals

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