Barry R. Jennings

The effect of neomycin and streptomycin on the electrical polarisability of aqueous suspensions of Escherichia coli

Aqueous suspensions of bacteria scatter light strongly. In addition, the bacteria exhibit strong induced dipole moments in an electric field. In this note we report how, by measuring the intensity of the scattered light, the electric polarisability (alpha) of Escherichia coli could be monitored as small quantities of antibiotics were added to the suspensions. The effect of the presence of quite small quantities of antibiotic on the electrical polarisability, which gave rise to the induced dipole, was dramatic. From the hypothesis that alpha had its origins in the bacteria-solvent interface, a theory is presented which adequately accounts for both alpha and its changes in the presence of these antibiotics. The study is taken to suggest that the antibiotic molecules were adsorbed on to the bacterial surface thereby reducing the surface charge. This in turn reduces the number of counterions and the apparent induced dipole moment. Because the electric-field scattering method is both quick and sensitive to changes in alpha, it may prove a valuable method for the study of antibiotic action on cell and microorganism surfaces.

Particle size distributions from transient electric birefringence data: II. polydisperse discs by two-parameter distribution functions

Abstract The decay of the electrically induced transient birefringence, for a dilute polydisperse suspension of ellipsoidally shaped particles of constant axial ratio, is analysed. It is shown that, for the decay process, the initial slopes of the natural logarithm of the normalised birefringence versus time curves for transients obtained under two discrete experimental conditions provide sufficient data to describe the spread in particle size in terms of two-parameter distribution functions. The procedure is described for three common skew distributions and two symmetric ones. A simple procedure for identifying the most appropriate distribution function is given.

Polarized fluorescence studies of electrically oriented DNA-dye solutions

Abstract Transient changes have been recorded in each of the four polarized components of fluorescence, when dilute solutions of dye-tagged DNA are subjected to short electric pulses. The directions of the absorption and emission transition moments, and hence of the plane of the dye molecules, relative to the DNA geometry have been estimated for eleven dyes. Data obtained for ethidium bromide and five acridine derivatives are consistent with the intercalation model generally accepted for these dyes. In addition, it is shown that neutral red, acridine red and probably auramine O also bind with their molecular planes essentially perpendicular to the long helical axis. The remaining two, hydroxystilbamidine and the bibenzimidazole derivative Hoechst 33258, give rise to effects which indicate that these molecules bind in such a manner that the absorption and emission transitions are closely associated with the grooves of the DNA helix.

Electrically induced fluorescence as a method for studying benzo[a]pyrene binding to DNA

The interaction of benzo [a] pyrene (BP) with DNA has been extensively studied as it is a known chemical carcinogen. Although the native hydrocarbon binds to DNA, current interest [ 1 ] centres on the tram-7,8dihydroxy-anti-9 ,lO epoxy-7,8,9 ,l O-tetrahydrobenzo[alpyrene derivatives (BPDE). Of these, the (t) enantiomer shown in fig.1 : (a) is the active metabolite which binds most extensively to DNA in living cells [2 1; (b) binds covalently to DNA [3]; and (c) is far the most potent carcinogenic form [4]. The majority of in vivo covalent binding is between the N-2 of guanine and the 10 carbon atom position of the(t) conformer of BPDE [5]. Synthesised racemic BPDE, reacted with native DNA, gives predominantly the same adduct [6] but with a greater degree of binding, thereby making it more convenient for in vitro experimentation. Although the sites of interaction of BPDE with DNA are known, there is much current dispute as to the binding configuration of the covalent moiety. At least 4 different models exist. The first 2 are covalent intercalations [7,8] of the hydrocarbon into the DNA with or without extensive bending of the helix. The third is the base displacement model [9] in which the diol-epoxide chromophore displaces guanine bases from the DNA which then swing into

Stiffness of aqueous sodium carboxymethyl cellulose from electric birefringence data

Abstract Electric birefringence studies have been made on some five samples of sodium carboxymethyl cellulose of different molecular weights (M) in water. The orientational relaxation times were evaluated from the decay rates of pulsed field experiments. These were analysed in terms of theories for rigid rods, weakly bending rods and worm-like chains. At M less than 5 × 103, the rod model appeared to be representative of the molecular conformation. The optical anisotropy factor (g3 − g1) and the electrical polarizability anisotropy (α3 − α1) were also evaluated at each molecular weight and in terms of the rod model. It appears that, the electrical polarizability anisotropy when reduced to unit length is a sensitive parameter which is constant in the rod-like region but deviates rapidly with the onset of flexibility. It is suggested that this parameter may be of value (a) to indicate the molecular weight at which the flexibility is significant, and (b) as an indicator of the relative flexibility of different members of the polysaccharide family.

A simple apparatus for the measurement of the Cotton-Mouton effect in particulate suspensions

An apparatus has been constructed for the practical realization of the Cotton-Mouton effect in colloidal suspensions. Measurements of the magnetically induced birefringence in such media, using a medium power argon-ion laser operating at a wavelength of 515 nm, have been made for variable magnetic field intensities up to 2.5 T. Data have been recorded on the four pure liquids-nitrobenzene, carbon disulphide, acetone, and benzene. The system has been primarily designed for studies on colloidal media for which the Cotton-Mouton effect can be large, thereby requiring relatively low intensity magnetic fields. Data for bentonite and vermiculite are reported, which demonstrate the ease and validity of such measurements for colloid characterization. These are the first known data on suspensions of vermiculite clay. Furthermore, the influence of any stray Faraday effect is examined.

Electric birefringence as a means of studying the effect of anaesthetics on liposomes

Birefringence can be induced in liposome suspensions using electric fields. The fields interact predominantly with anisotropic electrical polarisabilities which give rise to induced dipole moments. Using pulsed electric fields, the optical and electrical polarisabilities and the geometrical size of the liposomes can be measured simultaneously. These parameters have been found to be very sensitive to the presence of small amounts of fluidising additives of polar and ionic nature. Illustrative data are presented for the influence of the amines ammonium chloride, methyl ammonium chloride and lignocaine and of benzyl alcohol on phosphatidylcholine/serine liposomes. Structural changes in the vesicle membranes were detected, which appeared to correlate with the biological functions, thus indicating that electric birefringence is a rapid and useful method for studying interactive phenomena in lipid membrane systems.

The effect of antibiotics on the electrical polarisability of aqueous suspensions of bacteria.

The orientation of washed Escherichia coli bacteria in suspension induced by applied a.c. electric fields has been monitored by observing the accompanying changes in the intensity of light scattered by the suspension. The data enable the anisotropy of electrical polarisability deltaalpha to be determined. Changes in deltaalpha due to the addition of various antibiotics to the suspension have been measured as a function of both the antibiotic concentration and the temperature of the suspension. The results are taken to indicate that there is an accumulation of the antibiotic molecules at the bacterial surface.

Transient scattering from absorbing solutions

Abstract Although light scattering has become a standard method for determining the geometric parameters of macromolecular solutes in solution, it has serious theoretical and experimental limitations when the solutions partly absorb the incident light. When subjected to pulsed electric fields, electrically anisotropic molecules orientate. This changes the scattered intensity. By making measurements of the relative scattered intensity changes as the molecules revert to a random array after the electric pulse has ceased, the molecular relaxation times, and hence the molecular dimensions, may be evaluated whether or not the material is absorbing. Typical measurements are made on vanadium pentoxide and benzopurpurine suspensions and tobacco mosaic virus solutions at a variety of wavelengths to demonstrate the method.

Polydisperse particle size analysis by pulsed electric birefringence

Abstract The birefringence decay following the application of an electric pulse to a sol or solution is analysed. By considering the response to pulses of variable duration, size distributions can be evaluated for rigid particles of various shapes without presupposing the form of the distribution function. The method is able to deal with multimodal distributions. Generalized expressions are given that are applicable whatever the dipolar characteristics of the particles, and systems which experience surface-induced polarization, as is commonly encountered in aqueous and conducting media, are described in detail.