Stoyl P. Stoylov

Role of electrical and mechanical properties of red blood cells for their aggregation

Abstract In previous investigations using a novel electro-optical technique, we found that red blood cells (RBC) orientation and disorientation in an alternating electric field (1 kHz) is influenced by their deformability, conformational state of their glycocalyx and by the concentration and molecular weight of neutral macromolecules (dextran and polyethylene glycol) in the suspending medium. In the present study, we have altered the surface charge density of the RBC by treatment with neuraminidase and their deformability by fixing them with glutaraldehyde. We quantified these changes by means of electro-optics and observed their influence on the aggregation behaviour of the RBC in phosphate buffered saline, containing dextran 70 000 using the zeta sedimentation ratio technique (ZSR). For comparison, the electrical properties of RBC were also estimated by cell electrophoresis and by biochemical analysis of sialic acid content of their membranes. A negative linear relationship with near-equal slopes between cell electrical polarizability estimated electro-optically, membrane sialic acid content, cell electrophoretic mobility and the aggregation indices was found. The quantification of RBC deformability (rigidity) with the electro-optical method resulted in a linear relationship between aggregation indices and mechanical property. The comparison of the relative influence of mechanical and electrical factors clearly indicates the stronger influence of the electrical components on the aggregation of the RBC for the present experimental setup. The obtained results are discussed from the viewpoints of the two mechanisms proposed for dextran induced aggregation, i.e. the bridging model and the depletion model.

Transient electric light scattering: II. Determination of distribution curves for solutions of polydisperse rods☆

Abstract A method is discussed for the determination of the distribution curves for solutions of anisodiametric particles from the decay curves of the effect of variation in the intensity of the scattered light by solutions subjected to an electric field. The method works well for high electric field strengths when all particles are oriented along the electric field. The essence of the method is the geometric decomposition of the experimental decay curve into a finite number of exponential curves. The method is applied to an experiment with tobacco mosaic virus-III solution and the distribution curve obtained is compared with that obtained by the electron microscope investigation of the sample. Some questions concerning the utilization for the purpose of logarithmic representations are discussed.

Orientationally induced conservative dichroism in dilute disperse systems

Abstract The conservative dichroism induced by orientation of a disperse system in an external field is described theoretically in the Rayleigh and Rayleigh—Debye—Gans approximations. The formulas derived in the paper yield the possibility for analyzing the effect and for estimating its contribution to the total dichroism and birefringence of the system.

On the low frequency dispersion of the electrooptic effects

SummaryThe paper studies the factors which could be responsible for the difference between the high and low frequency electrooptic effects, the neglect of which could lead to erroneous conclusions about the particle electric properties. The presented considerations are illustrated by experimental data for an aqueous palygorskite suspension. New possibilities are demonstrated for the obtaining of information from the low frequency dispersion of the electrooptic effects. On the basis of the experimental data concerning the dispersion behaviour of palygorskite, the hypothesis is suggested for the existence of a slow longitudinal electric polarizability acting at frequencies of the applied field below 60 Hz.ZusammenfassungIn der Arbeit wurden die Faktoren diskutiert, welche für die Unterschiede der elektrooptischen Effekte bei hohen und niedrigen Frequenzen verantwortlich sind. Auf Grund experimenteller Daten mit wäßrigen Palygorskitsuspensionen wird eine langsam longitudinale elektrische Polarisierbarkeit postuliert, die bei den angewandten Feldstärken bei Frequenzen unter 60 cm-1 wirksam wird.

Orientational optic effects from above rayleigh particles

Abstract The general approach of van de Hulst for description of the orientationally induced optic effects in disperse systems through the components of the scattering matrix is used for the theoretical treatment and comparison of the effects from above Rayleigh particles. The orientational birefringence, dichroism, and light-scattering variation, described in the approximations of Stevenson and Ikeda, are analyzed qualitatively and the modification of some basic features of the effects is demonstrated. Some advantages of the orientational light scattering are pointed out, concerning the sensitivity of the method.

Effect of external electric fields on membrane proteins: The bacteriorhodopsin

Abstract One of the possible mechanisms of the effect of external electric fields on biological systems is through their membrane proteins. At present, contradicting reports exist about the effect of external electric fields on the behaviour of the bacteriorhodopsin, the only protein molecule in the purple membrane fragments. Complex electro-optic studies (electric light scattering; electric dichroism and electric birefringence) and detailed investigations of the electric field strength dependence of the electro-optic effects on different fractions of purple membranes provide no evidence of alterations in the behaviour of bacteriorhodopsin. The effects observed are explained well by the orientations of the whole purple membrane fragments. The faster process detected in the electric light scattering decay curve could be attributed to changes in the form and/or the volume of purple membrane aggregates. The importance of these studies in understanding the dependence of the membrane properties on the variation of the transmembrane potential, which are essential for membrane pumping and channel behaviour, is discussed. Further possibilities of the application of the methods described in the study of other membrane proteins and other membrane problems are also discussed.

A method for the determination of the particle scattering factor of rigid rodlike particles

Abstract A method for the determination of the particle scattering factor in a system of rigid rodlike particles is suggested. The particle scattering factor is determined by the relative change of the intensity of the scattered light by the colloid solution containing the particles when an electric field is applied. It is essential that the electric field strength be sufficiently high so that all particles are directed with their longest axes along the direction of the electric field (full orientation). Some preliminary experimental data are given.

Electro-optical characterization of aqueous laponite suspensions

Electric birefringence measurements have shown that 0.01 wt.% laponite suspensions are very polydisperse, including both higher size aggregates than the expected 30 nm diameter plate-like particles and smaller particles with diameter below 7 nm. Kerr constant and electric polarizabilty seems to be in reasonable agreement with the results for higher size plate-like clay particles. At higher concentrations (0.1 and 1 wt.%) anomalous signals are observed. The usefulness of this approach to elucidating the gelation properties of laponite is discussed.

Effect of the surface-active substance cetylpyridinium chloride on the electric light scattering of bentonite

Abstract The changes in the electric properties and the stability of an aqueous suspension of sodium bentonite on addition of the cationic surface-active substance cetylpyridinium chloride (CPC) is studied by electric light scattering. The CPC concentration varies from 10 −5 to 10 −3 mol l −1 , and the suspension weight concentration is 5 · 10 −6 kg l −1 . The dimensions of the bentonite particles are followed by electron microscopy and the decay of the electro-optic effect. The particle dimensions are greatest at the isoelectric point (10 −4 mol l −1 CPC), determined microelectrophoretically. The greater value of the electro-optic effect in the kHz range for suspensions to which CPC is added in comparison with untreated suspensions is explained by the increase of the particle dimensions, which leads to an increase in the particle electric polarizability. The electric polarizability per unit interfacial area of the particles decreases, which is related to CPC adsorption on the particles. The greater dispersion for suspensions with CPC at frequencies below 100 Hz, also manifest in large negative effects, is explained by the increase of the ratio of permanent dipole moment to induced dipole moment.

Electro-optical investigation of the electrical surface properties of aqueous α-Fe2O3 dispersions

Abstract Aqueous suspensions of α-Fe 2 O 3 were studied electro-optically and electrophoretically. Changes in pH led to great changes in the low-frequency behaviour of the observed electro-optical effect. The experimentally obtained relaxation time coincides with the calculated value for ellipsoids with an axial ratio of two. The isoelectric point coincides with the minimum value of the electric polarizability. a -Iron(III) oxide was found to be a suitable model for electro-optical studies of colloid stability.