A Computer Experiment in Physical Chemistry: Linear Dichroism in Nematic Liquid Crystals

1996 ◽  
Vol 73 (6) ◽  
pp. 586 ◽  
Author(s):  
Erhan Demirbas ◽  
Robin Devonshire
Keyword(s):  
Physical Chemistry ◽  
Liquid Crystals ◽  
Nematic Liquid Crystals ◽  
Computer Experiment ◽  
Linear Dichroism

Localization and preferred orientations of ubiquinone homologs in model bilayers

1992 ◽  
Vol 70 (6) ◽  
pp. 504-514 ◽  
Author(s):  
Giorgio Lenaz ◽  
Bruno Samori ◽  
Romana Fato ◽  
Maurizio Battino ◽  
Giovanna Parenti Castelli ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Fluorescence Quenching ◽  
Coenzyme Q ◽  
Nematic Liquid Crystals ◽  
Lateral Diffusion ◽  
Linear Dichroism ◽  
Two Dimensions ◽  
Phospholipid Bilayer ◽  
Guest Molecules ◽  
Site Distribution

The localization of ubiquinone has been investigated in phospholipid bilayer vesicles in studies of fluorescence quenching of membrane-bound probes by ubiquinone homologs (Qn, where n is the number of the isoprenoid units of the chain). Fluorescence-quenching data obtained by using a set of anthroylstearate probes, having the fluorophore located at different depths, revealed that ubiquinone-3 is located throughout the whole bilayer thickness. From the bimolecular quenching constants in the membrane, lateral diffusion coefficients in two dimensions were calculated to span values of 10−7–10−6 cm2∙s−1. This suggests that ubiquinones laterally diffuse in a very fluid environment. On this basis, it is proposed that their translational diffusion in the bilayer takes place in two dimensions, with the quinone ring oscillating between the two bilayer surfaces within a hydrophobic environment not extending beyond the glycerol region. This model implies that the quinonic head is both settled near the polar surface of the bilayer and buried into the host hydrocarbon interior. This two-site distribution was confirmed for all Qn, except Q0, by their linear dichroism spectra in the bilayers provided by disc-like lyotropic nematic liquid crystals. These spectra also provided detailed information on the preferential orientations of the quinonic head of the different derivatives within the two sites. The mechanism by which the localization and orientation of Qn guest molecules inside the host bilayer is modulated by the isoprenoid chain length is discussed on a thermodynamical basis. Being that Qn is expected to be also widely contained in the highly curved cristae of the mitochondrial inner membrane, by using rod-like lyotropic nematic liquid crystals we searched out effects of the curvature of the host bilayer on those Qn distributions. The linear dichroism measurements reveal that Qn guest molecules are no longer obliged to find a partition between two different types of localizations when the host bilayer is highly curved. In this case all Qn, even the longest Q10, were found to stay parallel to the amphiphilic chains with a single site localization of the head near the polar interface. By the same linear dichroism technique, the local ordering of all Qn derivatives was also evaluated. The order parameters were found to be basically the same for all derivatives. This result is justified on the basis of the relaxation, caused by the surface curvature, of the lateral compression of the host chains.Key words: coenzyme Q (ubiquinone), fluorescence quenching, lateral diffusion, linear dichroism, model bilayers.

The electrohydrodynamic instability in twisted nematic liquid crystals

1994 ◽  
Vol 4 (2) ◽  
pp. 239-252 ◽  
Author(s):  
A. Hertrich ◽  
A. P. Krekhov ◽  
O. A. Scaldin
Keyword(s):  
Liquid Crystals ◽  
Nematic Liquid Crystals ◽  
Electrohydrodynamic Instability ◽  
Twisted Nematic

Surface disclinations in nematic liquid crystals

1975 ◽  
Vol 36 (1) ◽  
pp. 59-67 ◽  
Author(s):  
V. Vitek ◽  
M. Kléman
Keyword(s):  
Liquid Crystals ◽  
Nematic Liquid Crystals
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