Linear dichroism spectroscopy as a tool for studying molecular orientation in model membrane systems

• Ordinary linear dichroism (LD) spectroscopy with rectangular optics is not applicable to thin uniaxial sampleshaving the optical axis perpendicular to the plane of the sample. A method has been developed to study suchsamples at inclined optical incidence and a general relation derived between the LD (corrected for polarizedreflection) and the average orientation of the absorbing transition dipole. For molecules of C2”, D2h, or highersymmetry the usual order parameters can be obtained. The method has been tested on anthracene in apolyethylene standard slab of perfectly axial symmetry. The estimated orientation agreed with previous reportson anthracene in stretched polyethylene sheets. A number of chromophoric molecules solubilized in macroscopicallyaligned lamellar mesophases of the systems sodium octanoate/decanol/water and sodium di-2-ethylhexylsulfosuccinate (Aerosol OT)/water have also been studied. In the first system rodlike molecules(diphenylethyne, anthracene, retinal) are oriented with their long axes parallel to the hydrocarbon chains ofthe amphiphile, while an extremely long molecule (&carotene) as well as water-soluble planar cationic dyesare on the average oriented parallel to the lamellar planes. In the Aerosol OT system all molecules studiedwere oriented parallel to the lamellar planes.

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NATURVETENSKAP  -- Kemi -- Fysikalisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Physical Chemistry (hsv//eng)

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