MECHANISM OF ORIENTATION AND LINEAR DICHROISM OF PHOTOSYNTHETIC PARTICLES IN ELECTRIC FIELDS: CHLOROPLASTS AND CHLOROPHYLL-PROTEIN COMPLEXES

Abstract— The mechanisms of orientation in pulsed and alternating electric fields of thylakoids (derived from the sonication of spinach chloroplasts) and of light-harvesting chlorophyll a/b-protein complexes (CPII) were investigated by utilizing linear dichroism techniques. Comparisons of the linear dichroism spectra of thylakoids and CPII particles suggest that the latter are oriented with their directions of largest electronic polarizabilities (and thus probably their largest dimensions) within the thylakoid membrane planes. At low electric field strengths (< 12 V cm^?1), and at low frequencies of alternating electric fields (< 0.25 Hz), thylakoid membranes tend to align with their normals parallel to the direction of the applied electric field; the mechanism of orientation involves a permanent dipole moment of the thylakoids which is oriented perpendicular to the planes of the membranes. However, at high field strengths and high frequencies of the applied alternating electric fields, the thylakoids tend to orient with their planes parallel to the applied field, thus exhibiting an inversion of the sign of the linear dichroism as the electric field strength is increased. At the higher frequencies and at higher field strengths, the orientation mechanisms of the thylakoids involve induced dipole moments related to anisotropies in the electronic polarizabilities. The polarizability is higher within the plane than along a normal to the plane, thus accounting for the inversion of the dichroism as the electric field strength is increased. The CPII particles align with their largest dimension parallel to the applied field at all field strength, indicating that the induced dipole moment dominates the orientation mechanisms in pulsed electric fields. The magnitude of the absolute linear dichroism of CPII suspensions increases with increasing dilution, indicating that aggregates of lower symmetry are formed at higher concentrations of the CPII complexes.     

ELECTRIC DICHROISM OF PURPLE MEMBRANE SUSPENSIONS

Abstract— Suspensions of purple membranes were exposed to reversing rectangular pulses of relatively low electric field (less than 100V/cm) at various frequencies. Orientation of the membranes was estimated by measuring linear dichroism at 565nm. In the electric field of frequency lower than about 10Hz the purple membranes tended to align perpendicular to the electric field. This orientation was induced mostly by permanent dipole which was perpendicular to the membrane surface. The value of permanent dipole moment was determined to be 140D per protein at pH 7.0, 25°C, in the presence of 5m M phosphate buffer.
In an electric field of frequency more than 100Hz the membrane tended to align parallel to the electric field. Electric polarizability parallel to the membrane surface was estimated to be 1 ± 10⁻¹² cm³ under the same conditions.
Electric dichroism of light-adapted and dark-adapted purple membranes was found to coincide with each other at high frequency. From this result the angle of retinal to the membrane surface was concluded to be the same between light-adapted and dark-adapted bacteriorhodopsins.     

Electrorotation of dumb-bell shaped particles: Theory and experiment

The electrorotation of symmetrical doublets was calculated in the dipole approximation as a function of the polarizability of the single spherical constituents and as a function of their distance. The result was that a doublet in parallel orientation to the electric field plane undergoes a shift of the first characteristic frequency towards higher frequencies. The second characteristic was shifted towards lower frequencies. The opposite is true for a perpendicular orientation. The theoretical predictions were confirmed with red cells and pollen. The electrical interaction was larger than theoretically possible in the dipole approximation.     

Enhanced pearl-chain formation by electrokinetic interaction with the bottom surface of vessel

Counterions in an electric double layer (EDL) around a colloidal particle accumulate on one side of the EDL and are deficient on the other side under an electric field, resulting in an imbalance of ionic concentration in the EDL, that is to say, the ionic polarization of EDL. It is well known that the ionic polarization of EDL induces electric dipole moments whereby the alignments of colloidal particles (e.g., pearl chains) are formed under alternating electric fields. In this study, we focus on the effect of the frequency of applied electric fields (100 Hz-1 kHz) on the alignment of silica particles settling at the bottom of a silica glass vessel. In digital imaging analyses for pearl chains of silica particles, it is confirmed that surface distances between two neighboring particles decrease but the number of particles in a pearl chain increases as the frequency of the applied electric field is lowered from 1 kHz to 100 Hz. More interestingly, electrical conductance measurements suggest that the induced ionic polarization of EDL around silica particles at the bottom of the silica vessel is enhanced as the frequency is lowered from 1 kHz to 100 Hz, whereas the ionic polarization around isolated silica particles in uniform dispersions is alleviated by the relaxation of ionic concentration in the EDL as a result of the diffusion of counterions. This curious phenomenon can be explained by considering that the ionic polarization of EDL of silica particles at the bottom of a vessel is affected by the electro-osmosis of the silica surface at the bottom of the vessel.     

Electric parameters of photosystem II particles — electric light scattering study

Electric light scattering and microelectrophoresis were applied to investigate the electric moments (permanent dipole moment and electric polarizability and electrophoretic mobility of envelope-free chloroplasts and photosystem II (PS II particles. The effect of the removal of the extrinsic polypeptides (18, 24 and 33 kDa) on the electric moments was also studied. A significant difference was observed between the orientation behaviour of chloroplasts and PS II preparations. The data indicate that the permanent and induced dipole moments contribute to the orientation of the PS II particles, whereas chloroplasts possess induced dipole moment only.

NaCl and Tris treatments of PS II preparations influence both the transverse permanent dipole moment and the electric polarizability of PS II particles. The increase in the electrophoretic mobility of PS II particles on removal of the extrinsic proteins corresponds to an increase in the electric polarizability value, demonstrating its interfacial nature.     

On the electric polarizability of purple membrane

The permanent dipole moment and electric polarizability of purple membrane have been found using electrooptic methods. Comparison of the results with those for other inorganic or biological disperse particles as well as the observed effects and dynamics for a large range of applied electric field strengths support the proposal of a surface origin for the electric polarizability of purple membrane.     

Contribution of LHC II complex to the electric properties of thylakoid membranes: an electric light scattering study of Chl b-less barley mutant

Electric light scattering measurements demonstrate a strong decline in the permanent electric dipole moment and electric polarizability of both thylakoid membranes and photosystem II-enriched particles of the Chlorina f2 mutant which has severely reduced levels of light-harvesting chlorophyll a/b-binding proteins compared to the wild type barley chloroplasts. The shift in the electric polarizability relaxation to higher frequencies in thylakoids and photosystem II particles from Chlorina f2 reflects higher mobility of the interfacial charges of the mutant than that of the wild type membranes. The experimental data strongly suggest that the major light-harvesting complex of photosystem II directly contribute to the electric properties of thylakoid membranes.     

The ripple phase in a DMPC-water mixture. A dielectric investigation

The dielectric behaviour of a DMPC-water mixture has been investigated in the frequency range from 1 kHz to 10 MHz and in the temperature interval from 0 to 40°C over the crystalline-liquid crystalline phase transition temperatures. A model to explain the dielectric characteristics of the DMPC-water mixture as a function of frequency, and in general for each DPL-water mixture which displays a ripple phase, is proposed. The model is based on the assumption that a particular contribution to the total polarizability comes from the ripple deformation of the bilayer. This contribution is evaluated supposing strong interactions between the lipid head groups with the formation of in-phase domains of correlated electric dipoles. A further assumption relates the extension of the domains to a set of spatial modes, called ripplons, thermally activated in the ripple phase. By the ripplon dispersion relation, the dipole domain extensions (hence the polarizability), were made frequency dependent. The final result shows that the anomalous peak which appears in the permittivity at the ripple phase temperature interval is qualitatively well fitted by our model.     

Electrochromism and Solvatochromism

The position and the intensity of electronic bands are influenced by an electric field. Pronounced changes in the position of absorption bands are mainly due to the dipole moment of the molecule in the ground state and the change in the dipole moment during the excitation process, and pronounced changes in intensity are due to the field dependence of the transition moment, which can be described by the transition polarizability. The effect of an external electric field on the optical absorption (electrochromism) of suitable molecules can be used to determine the dipole moment in the ground state, the change in dipole moment during the excitation process, the direction of the transition moment of the electronic band, and certain components of the transition polarizability tensor. These data largely determine the strong solvatochromism (solvent-dependence of the position and intensity of electronic bands), which is observed in particular with molecules having large dipole moments. Smaller contributions to solvatochromism result from dispersion interactions, which predominate in the case of nonpolar molecules. The models developed have been experimentally checked and verified by a combination of electro-optical absorption measurements (influence of an external electric field on absorption) and investigation of the solvent-dependence of the electronic bands.     

The ripple phase in a DMPC-water mixture. A dielectric investigation

Abstract

The dielectric behaviour of a DMPC-water mixture has been investigated in the frequency range from 1 kHz to 10 MHz and in the temperature interval from 0 to 40°C over the crystalline-liquid crystalline phase transition temperatures. A model to explain the dielectric characteristics of the DMPC-water mixture as a function of frequency, and in general for each DPL-water mixture which displays a ripple phase, is proposed. The model is based on the assumption that a particular contribution to the total polarizability comes from the ripple deformation of the bilayer. This contribution is evaluated supposing strong interactions between the lipid head groups with the formation of in-phase domains of correlated electric dipoles. A further assumption relates the extension of the domains to a set of spatial modes, called ripplons, thermally activated in the ripple phase. By the ripplon dispersion relation, the dipole domain extensions (hence the polarizability), were made frequency dependent. The final result shows that the anomalous peak which appears in the permittivity at the ripple phase temperature interval is qualitatively well fitted by our model.     

Role of LHCII organization in the interaction of substituted 1,4-anthraquinones with thylakoid membranes

The chlorophyll fluorescence, photochemical activity and surface electric properties of thylakoid membranes with different stoichiometry of pigment-protein complexes and organization of the light-harvesting chlorophyll a/b protein complex of photosystem II (LHCII) were studied in the presence of substituted 1,4-anthraquinones. Data show strong dependence of the quenching of the chlorophyll fluorescence on the structural organization of LHCII. The increase of the LHCII oligomerization, which is associated with significant reduction of the transmembrane electric charge asymmetry and electric polarizability of the membrane, correlates with enhanced quenching effect of substituted 1,4-athraquinones. Crucial for the large quinone-induced changes in the membrane electric dipole moments is the structure of the quinone molecule. The strongest reduction in the values of the dipole moments is observed after interaction of thylakoids with 3-chloro-9-hydroxy-1,4-anthraquinone (TF33) which has the highest quenching efficiency. The quinone induced changes in the photochemical activity of photosystem II (PSII) correlate with the total amount of the supramolecular LHCII-PSII complex and depend on the number of substituents in the 1,4-anthraquinone molecule.     

Molecular dynamics in liquid-crystalline side chain polymers studied by dielectric relaxation spectroscopy: A comparative study

A series of liquid-crystalline side chain copolymers with different main chains have been studied by the dielectric method in a maximum frequency range of 9 decades. Oriented samples were used throughout. The data were analysed in terms of the Havriliak-Negami and Fuoss-Kirkwood formulae for the relaxation functions. Two well separated dispersion regions with their strengths depending strongly on the macroscopic orientation were found. The low frequency or δ-relaxation shows a marked change in its curve form and width with different main chain structure, its strength being determined by the longitudinal dipole moment of the mesogenic unit. The high frequency relaxation shows a more complicated dependence of its characteristic parameters on the molecular structure. In some cases a decomposition into two underlying relaxations was successfully attempted. We discuss the models for molecular motions developed for low molecular weight liquid crystals and for amorphous polymers, in order to explain the behaviour of the different dispersions found.     

ROLE OF ELECTRIC POLARIZATION IN THE THERMOLUMINESCENCE OF CHLOROPLASTS

Abstract Effect of an external electric field on thermoluminescence and thermodepolarization currents were studied in suspensions and dry films of pea chloroplasts. The external electric field was applied either during interrupted heating at a given temperature ("direct effect") or was "stored" in the sample during cooling in the range –25°C and –70°C ("electret effect").
It is shown that in chloroplast suspension both the luminescence burst upon "direct effect" and the new band peaking between –40°C and –50°C induced by the "electret effect" are accompanied by a preferential decrease in the intensity of the thermoluminescence band around +10°C.
A correlation was established between the polarized state of thylakoids and the thermoluminescence burst induced by the external field. In electret samples of chloroplast suspension the intensity of field induced low temperature thermoluminescence band under different experimental conditions varied in parallel with the intensity of thermodepolarization current. In dry films of chloroplasts, in addition to parallel changes in intensities of thermoluminescence and thermodepolarization current, also the peak positions shifted in the same manner when either humidity of samples or temperature of illumination and of application of external field were varied.
We conclude that the polarization state of thylakoid membrane, which can be governed by an external electric field, plays an important role in determining charge stabilization and recombination properties of photosynthetic units. Our results implicate that electric field induces conformational changes in the membranes which increases the frequency factor ascribed to the recombination processes.     

Polarizabilities and dipole moments of benzaldehyde, benzoic acid and oxalic acid in polar and nonpolar solvents

The purpose of this report is to calculate the orientation polarizability of benzaldehyde, benzoic acid and oxalic acid in polar and nonpolar solvents. The calculations are based on the knowledge of permanent dipole moment of the solutions. Other important physical quantities such as refractive index, density, specific volume, dielectric constant, molar polarization and molar refractivity are also calculated. Dipole moments of the solutions are calculated by using measured dielectric constants of the solutions. The dielectric constant measurements were made at 100 kHz. Relationships between the polarizability and concentration, specific volume, dielectric constant and dipole moment of the solutions are suggested.     

High frequency electric polarizability of bacteria E. coli: dependence on the medium ionic strength

There are two main kinds of electric polarizability of bacteria: surface charge dependent (SChD) and Maxwell-Wagner (MW) polarizability. The aim of this article is to distinguish SChD and MW components on the external bacteria surface. An electro-optic method (electric turbidity) was used to study the polarizability of E. coli fixed by formaldehyde at the frequency range 20kHz to 20MHz. According to the literature the SChD polarization disappears at such high frequencies and MW one gives the main contribution. However we found unexpected dependence on the outer medium electrolyte concentration, which cannot be explained by MW polarization. The results show that the polarizability decreases by ionic strength increasing in the same way as the double electric layer thickness does. Such behaviour is a characteristic for SChD polarizability, which allows us to conclude that this component has the main contribution on the external bacteria surface at the experimental frequencies mentioned.     

Comment on a sum rule for vibrational raman optical activity

The expressions for the sum of vibrational Raman optical activity (ROA) intensities indicate that the ROA intensity sum for chiral molecules is non-zero for those with an anisotropic electric dipole polarizability. The non-zero sum depends upon the electric dipole, magnetic dipole and electric quadrupole polarizability components and moments of inertia at equilibrium geometry.     

Size- and shape-dependent polarizabilities of sandwich and rice-ball Co(n)Bz(m) clusters from density functional theory

The dipole polarizabilities of Co(n)Bz(m), (n, m = 1-4, m = n, n + 1) clusters are studied by means of an all-electron gradient-corrected density functional theory and finite field method. The dipole moments are relatively large for most of the clusters, implying their asymmetric structures. The total polarizability increases rapidly as cluster size, whereas the average polarizability shows "odd-even" oscillation with relatively large values at (n, n + 1). The polarizabilities exhibit clear shape-dependent variation, and the sandwich structures have systematically larger polarizability and anisotropy than the rice-ball isomers. The dipole polarizabilities are further analyzed in terms of the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap, ionization potential, and electron delocalization volume. We conclude that the polarizability variations are determined by the interplay between the geometrical and electronic properties of the clusters.     

Dynamic polarizability of many-electron systems within a time-dependent density-functional theory

Using the time-dependent extension, proposed by us recently, of the Hohenberg—Kohn—Sham density-functional theory, in the presence of an oscillating electric field, we suggest a Karplus—Kolker-type variation—perturbation method for the calculation of dynamic 2^L-pole polarizability of many-electron systems. As an illustration of the present density-functional formalism, the frequency-dependent dipole polarizability of He atom has been calculated in the frequency range 0 ? ω ? 0.65 au, using local density forms of the exchange and correlation potentials. For ω = 0, the results are numerically better than recent density-functional calculations of the static dipole polarizability of He. The corresponding hydrodynamical formulation, which employs the single-particle density as a basic variable, is also presented.     

External electric field effects on absorption, fluorescence, and phosphorescence spectra of diphenylpolyynes in a polymer film

External electric field effects on absorption, fluorescence, and phosphorescence spectra of a series of unsubstituted diphenylpolyynes have been examined in a PMMA film. The analysis of the electroabsorption spectra indicates that the shorter diphenylpolyynes exhibit only the change in molecular polarizability, whereas the longer ones exhibit the change both in dipole moment and in molecular polarizability following absorption. The finding of the change in dipole moment following absorption of centrosymmetric diphenylpolyynes is interpreted in terms of the symmetry distortion upon doping a polymer film. When the external electric field is applied, the fluorescence yield is reduced and enhanced, respectively, in diphenylacetylene and diphenyloctatetrayne, indicating that the rate of the nonradiative process from the fluorescence state is accelerated in diphenylacetylene and decelerated in diphenyloctatetrayne by an external electric field. All of the diphenylpolyynes used in the present study exhibit the change in molecular polarizability following the phosphorescence process.     

In situ conductance measurements for alignments of silica particles under alternating electric fields

The alignments of silica particles formed in sinusoidal electrical fields of 1 kHz were assessed using an optical microscope with measuring the electric conductance of a silica dispersion between two Pt electrodes in a vitreous silica glass cell. We confirmed that the electric conductance of the silica dispersion between the two electrodes in the cell reflected the surface conductance of the silica particles settling at the bottom of the cell. More interestingly, we observed that the electric conductance of the silica dispersion in the cell increased when pearl chains of the silica particle were formed along the direction of the electric field. However, no clear change in the electric conductance of the dispersion was observed at higher electric field strengths where a transition from pearl chains to zigzag band patterns and circulating movements of the silica particles in the zigzag bands formed.