Lennart Johansson

Orientation and mobility of molecules in membranes studied by polarized light spectroscopy.

Biological membranes are composed of mainly lipids and proteins. The physical properties of the lipids, forming a bilayer structure, are of crucial importance for the living cell, since the plasma membrane is the guardian barrier towards the environment. Thus, the functioning cell needs a highly stable lipid bilayer, which depends on molecular packing and orientation properties of the various membrane components (Wieslander et al. 1980). The spatial arrangement of the membrane proteins incorporated in the lipid matrix plays an essential role for the different chemical processes occurring at or within the membrane. Information about molecular orientation and mobility is therefore necessary for unravelling the functional mechanisms of a biological membrane.

Orientation of β-carotene and retinal in lipid bilayers

The function of carotenoids in membranes of photosynthetic bacteria and plants has been intensively investigated [l-4]. In animals certain carotenoids such as p-carotene fullfil an essential physiological function as precursors of vitamin A. By enzymatic oxidation p-carotene is converted to retinol which is further oxidized to retinal i.e., vitamin A. The positioning of carotenoids in membranes is far from clear [ .5,6]. No conclusive experiment has been performed showing the orientation of any carotenoid in lipid bilayers or biological membranes. Here, we have used polarized light spectroscopy and studied the orientation of p-carotene and retinal in different types of lipid bilayers.

An ESCA investigation of some copper complexes

Abstract A series of copper complexes have been investigated by ESCA. All complexes were salts of the tetraphenylphosphonium ion. The binding energies of all the atoms in the complexes were determined. From the binding energies of the ligand atoms we estimated the effective charges on these atoms. For this purpose we used linear relations of the form Eb = kq + EbO which had been established previously within our scheme of C 1s (phenyl) as internal standard. From the data thus obtained, the effective charge on the copper atom was estimated. A linear relation between binding energy and the effective charge on the copper atom was found, i.e., Eb(Cu) = 1.52qCu + 932.2 ESCA spectra were recorded for the complexes bis(1,3-diphenyl-1,3-propanediono) copper (II) and bis(3-phenyl-2,4-pentanediono) copper (II). By a combination of the XPS binding energies and IR intensities of the νCH vibrations of the phenyl groups in the complexes with empirical relations between these entities and the effective charges of the atoms and groups, a fairly complete mapping of the charge distributions of these complexes has been achieved.

The Structure of a Lyotropic Liquid Crystalline Phase that Orients in a Magnetic Field

Abstract The structure of a lyotropic liquid crystalline phase with positive diamagnetic anisotropy (type I), that spontaneously orients in a magnetic field has been studied by means of water NMR quadrupole splittings, NMR diffusion and polarized absorption spectroscopy. It is concluded that this phase is built up of long rodlike aggregates. A preliminary study of a sample with negative diamagnetic anisotropy (type II) shows that this phase probably consists of lamellar aggregates. It is suggested that these phases are suitable as orientation matrices for studies of chromophores with polarized light spectroscopy.

Additions to the Displaced Term System of Be I

The wavelengths of 27 new lines of Be I have been measured and 24 new levels have been established, most of which belong to the displaced system 2pnl. The series 2sns 1S and 2snd 1D have been extended, the former indicating a possible disturbance from 2p2 1S0.

Circular dichroism and the configuration of deprotonated tris-tartrato chromium(III) complex

A complex with the composition Cr(THt1)3 (T = RR-tartrate2−) has been characterised in solutions with excess of tartrate by circular dichroism (CD) and potentiometric data. The CD shows peaks ϵ1 - ϵr/M−1cm−1 of +4.60 at 570 nm and −0.80 at 655 nm. Together with stereochemical considerations this strongly indicates that the complex Cr(RR-TH−1)3 takes the Λ configuration. The partially protonated forms show less pronounced stereoselectivity.

Fluorescence detected linear dichroism. A new method for studies of molecular orientation in uniaxial systems

A theoretical and experimental description of a new light spectroscopic method for determination of second rank order parameters is presented. The linear dichroism is obtained from the total fluorescent intensity, measured by using an integrating sphere. The method has been tested on a dichroic sample consisting of a stretched polymer film with an incorporated dye (2,2′‐diethyl thiocarbocyanide iodide). The main advantages of using emitted light are the high sensitivity and selectivity. With the method described the molecular orientation of a fluorophore in a mixture of other absorbing chromophores may be studied. It is also suggested that the integrating sphere should be used in determinations of excitation spectra and for measurements of fluorescence detected circular dichroism.

The distribution of lead in lead-stabilized rigid PVC pipes, as studied by scanning electron microscopy

Abstract Samples with flat, smooth surfaces were removed from rigid PVC pipes using a diamond saw, then studied in a scanning electron microscope fitted with a Robinson detector and an environmental cell, which gives an image of the back-scattered electron intensity. In such images, lead-containing particles appeared as bright spots against a dark background. This is due to the fact that the intensity of the back-scattered electrons increases with atomic number. It is shown that this method can be used to study the effect of different processing conditions on the distribution of the stabilizer in lead-stabilized rigid PVC.