Electric Birefringence Relaxation Research Articles

Influence of the strength of polarizing electric field on free relaxation of electric birefringence in poly(butyl-isocyanate) solutions

Free relaxation of electric birefringence in tetrachloromethane solution of high molecular weight poly(butyl-isocyanate) was studied. The effect of electric field strength on the average relaxation time was observed. The relaxation spectrum was analyzed using the Rouse and Zimm theories. With increase in the electric field strength, the contribution of fast (deformation) relaxation modes also increased significantly. It is assumed that certain changes in intramolecular mobility occur under the influence of electric field.

Aggregation Behavior of Rodlike Ionogenic Polymers in Chloroform

The rodlike ionogenic polymers poly(p-pyridylene-phenylene) and poly(p-pyridylene/phenylene-ethynylene) form polyelectrolytes when protonated with toluene sulfonic acid or ethane sulfonic acid in chloroform solution. This molecular modification, clearly indicated by a marked red shift of the UV absorption band, induces the formation of prolate, bundlelike aggregates, whose size and shape are obtained from their rotational dynamics as revealed by electric birefringence relaxation and their translational dynamics as measured by dynamic light scattering. The aggregates have a length of 400-600 nm and a high aspect ratio >15. In general, the polyelectrolyte molecules are arranged with their long axes parallel to the long axis of the aggregates. They probably attract each other through the electrostatic interaction with counterions. The counterions are not bound to specific sites but may be shifted under the action of an external electric field to account for the highly anisotropic electric polarizability. When inert salt or excess sulfonic acid is added, these compounds seem to accumulate within the aggregates and influence the attractive forces. This is generally leading to an elongation of the aggregates and, in the case of added salts, even to a marked reduction of birefringence.

Low- and High-Frequency Electric Birefringence Relaxations in Linear Polyelectrolyte Solutions

To clarify the molecular mechanism of the counterion fluctuations in linear polyelectrolyte solutions, we have studied the dependence of the low-frequency electric birefringence relaxation on the degree of polymerization N and the monomer concentration C p of sodium polystyrenesulfonate (NaPSS) in aqueous solution and the dependence of the low-frequency (LF) and high-frequency (HF) relaxations on the neutralization ratio a of polystyrenesulfonic acid (HPSS) in aqueous solution by the frequency-domain electric birefringence (FEB) method. The experimental results of the N and C p dependence of the LF relaxation definitely show that the LF relaxation strongly depends on N but is weakly dependent on or almost independent of C p , which indicates that the LF relaxation arises from the counterion fluctuation along the polyion. Also, it turns out from the experimental results of the α dependence of the LF and HF relaxations that the LF relaxation is ascribed to tightly bound counterions in the vicinity of a polyion and that the HF one is due to loosely bound counterions away from the polyion. These results support the molecular mechanism that the LF and HF relaxations come from the fluctuation of the tightly bound counterions along the polyion axis and from the fluctuation of the loosely bound counterions perpendicular to the polyion axis, respectively.

Two-dimensional spectroscopy of electric birefringence relaxation in frequency domain: Measurement method for second-order nonlinear after-effect function

A new measurement method for second-order nonlinear after-effect function has been developed. Theoretical calculation starting from a general time-evolution equation connects nonlinear responses in time domain and frequency domain and thus gives the nonlinear response to applied external field of arbitrary form. In addition, it turns out in the frequency domain that the dc component of a second-order nonlinear response function corresponds to a linear response function. For example, the dc component of the electric birefringence relaxation is equivalent to the dielectric relaxation. This simple relation indicates an advantage of a frequency-domain measurement for nonlinear responses. As an example, the electric birefringence relaxation is measured in two-dimensional frequency domain for aqueous solution of sodium poly(styrenesulfonate) to confirm the validity of the theoretical results.

Dynamics of counterions bound to linear micelles in solutions as studied by electric birefringence relaxation and high-frequency dielectric relaxation spectroscopies

The dynamics of counterions bound to linear micelles in an aqueous solution of the surfactant cetyltrimethylammonium bromide (CTAB) with sodium salicylate (NaSal) as added salts is investigated by frequency-domain electric birefringence relaxation spectroscopy (FEB method) and high-frequency (HF) dielectric relaxation spectroscopy. First, the influence of NaSal concentration Cs on the linear micelle formation is studied by the FEB method. The contour length L of linear micelles is found to increase with increasing Cs but for further increase of Cs in excess of the CTAB concentration, L decreases, i.e. linear micelles break into shorter pieces. The FEB result also indicates that the diffusion constant of Sal− ions bound to a linear micelle is nearly independent of Cs with an average value smaller than that of free Sal− ions. We also measured the dielectric increment Δε and the relaxation time τ, by HF dielectric relaxation, which showed the same concentration dependence as polyelectrolyte. These results indicate that the diffusion of Sal− ions along the chain produces a charge density fluctuation on the chain and the other counterions, Br− and Na+, are loosely bound to these charge fluctuating areas. The HF dielectric relaxation is attributed to the movement of these counterions localized in the electric potential trough on the chain.

Electric birefringence relaxation spectroscopy of linear micelles in aqueous cetyltrimethylammonium bromide solutions with sodium salicylate

The influence of sodium salicylate (NaSal) concentration on the linear micelle formation in an aqueous solution of cetyltrimethylammonium bromide (CTAB) is investigated by the frequency-domain electric birefringence relaxation spectroscopy (FEB method). The contour length L of linear micelles is found to increase with increasing NaSal concentration Cs but for further increase of Cs in excess of the CTAB concentration, L decreases, i.e., linear micelles break into shorter pieces. The FEB result indicates also that the diffusion constant of salicylate ions bound to a linear micelle is nearly independent of Cs with an average value smaller than that of free salicylate ions.

Relaxation of electric birefringence near a critical consolute point.

Relaxation of electric birefringence near a critical consolute point.

Stretched-exponential relaxation of electric birefringence in complex liquids

The relaxation of electric birefringence is experimentally investigated in three distinct systems: critical binary mixtures, polydisperse micellar solutions and dilute polyelectrolyte solutions. The asymptotic behaviour is shown to be consistent with a stretched-exponential form exp(-(t/ tau )alpha ). Most of the data are quantitatively explained by a simple model of parallel relaxation of many independent processes characterized by a wide distribution of sizes.

Accessibility and Structural Role of Histone Domains in Chromatin. Biophysical and Immunochemical Studies of Progressive Digestion with Immobilized Proteases

The accessibility and role of histone regions in chromatin fibres were investigated using limited proteolysis with enzymes covalently bound to collagen membranes. The changes in chromatin conformation and condensation monitored by various biophysical methods, were correlated to the degradation of the histone proteins revealed by antibodies specific for histones and histone peptides. Upon digestion with trypsin and subtilisin, chromatin undergoes successive structural transitions. The cleavage of the C-terminal domains of H1, H2A and H2B, and of the N-terminal tail of H3 led to a decondensation of chromatin fibres, indicated by increases in electric birefringence and orientational relaxation times. It corresponds to a 15% increase in linear dimensions. The degradation of the other terminal regions of histones H3, H2A and H2B resulted in the appearance of hinge points between nucleosomes without alteration of the overall orientation of polynucleosome chains. Despite the loss of all the basic domains of H1, H3, H2A and H2B, no significant change in DNA-protein interactions occurred, suggesting that most of these protease-accessible regions interact weakly, if at all, with DNA in chromatin. Further proteolysis led to H4 degradation and other additional cleavages of H1, H2B and H3. This caused the relaxation of no more than 8% of the total DNA but resulted in changes in the ability of chromatin to condense at high ionic strength. More extensive digestion resulted in a total unravelling of nucleosomal chains which acquired properties similar to those of H1-depleted chromatin, although the globular part of H1 was still present. The data suggest that histone-histone interactions between H1 and core histone domains play a central role in stabilizing the chromatin fibres, and cuts in H3, H2A and H2B as well as H1, seem necessary for chromatin expansion. On the contrary, H4 might be involved in the stabilization of nucleosomes only.

Stretched-exponential relaxation of electric birefringence in polymer solutions.

The relaxation of electric birefringence in dilute solutions of a polyelectrolyte is shown to be consistent with a stretched-exponential form, exp[-(t/\ensuremath{\tau}${)}^{\ensuremath{\alpha}}$]. The exponent \ensuremath{\alpha} depends on polymer length L and solvent ionic strength only through the ratio x==L/${L}_{p}$, where ${L}_{p}$ is the persistence length, and crosses over from \ensuremath{\alpha}\ensuremath{\simeq}1 for stiff chains (x\ensuremath{\simeq}1) to \ensuremath{\alpha}\ensuremath{\simeq}0.44\ifmmode\pm\else\textpm\fi{}0.02 in the self-avoiding-walk regime x\ensuremath{\gg}1, the latter in accord with a simple scaling theory of polymer statistics and dynamics.

Anisotropic counterion polarizations and their dynamics in aqueous polyelectrolytes as studied by frequency-domain electric birefringence relaxation spectroscopy

Etude avec les sels de sodium du polystyrenesulfonate, de la carboxymethylcellulose et de l'ADN

Low-frequency dynamics of counterion polarization in aqueous polyelectrolyte as studied by electric birefringence relaxation methods

Abstract The low-frequency relaxation of aqueous polyelectrolytes was studied by both the time-domain electric birefringence (TEB) and the frequency-domain electric birefringence (FEB) methods. Both the methods allow us to determine the rotational relaxation time τr of the polyion as well as the dielectric relaxation time τ given as a harmonic mean of τr and the intrinsic relaxation time τr of counterion polarization. The values of the relaxation times obtained by these two methods agree very well with each other, where τr is found to be smaller than τr by an order of magnitude. The observed value of τr suggests that the translational diffusion constant of counterions along the polyion should be much smaller than that in the free medium.

Differences in the condensation of chromatin by individual subfractions of histone H1: implications for the role of H1.degree. in the structural organization of chromatin

The effectiveness of histone H1 subfractions H1-1 and H1(0) in inducing the ordered condensation of chromatin was examined by thermal denaturation, circular dichroism, electric birefringence, orientation mechanism, and orientational relaxation time measurements. Soluble rat liver chromatin was stripped of H1 by dissociation in 500 mM NaCl and long fragments of chromatin were subsequently reassociated with purified individual H1 subfractions for ratios of 1 and 2 mol of H1 per nucleosome. H1 subfractions behave differently with respect to their interactions with DNA in chromatin: although the orientation mechanisms of reconstituted chromatins are identical, H1(0) induces a less efficient protection of DNA than H1-1, as shown by nuclease digestion and by the length of free extended linker DNA determined by electric birefringence. This corresponds to a more extended structure of H1(0)-reconstituted chromatin as judged by the value of relaxation time. One can imagine that the replacement of H1 by H1(0) leads to a different structure or stability of the chromatin, confering a certain degree of flexibility of this region. This may be related to the functional role of H1(0) in DNA replication or transcription and may explain metabolic and evolutionary differences among H1 subfractions as recently suggested by Lennox [Lennox, R. W. (1984) J. Biol. Chem. 259, 669-672]. The extent of condensation when H1-depleted chromatin is overloaded with histones is probably a function of the electrostatic interactions between the basic C-terminal tails of histones and chromatin. Electric birefringence also reveals differences between native and reconstituted chromatins that are overlooked by several other criteria.

An electro-optical study of the mechanisms of DNA condensation induced by spermine

Condensation of DNA by spermine has been studied by electric dichroism, electric birefringence and rotational relaxation times at 1 mM ionic strength. Using Manning's theory, we found that condensation occurs for a fraction of neutralized phosphate charges ( r) equal to 0.90, in good agreement with previous studies using spermidine, synthetic polyamines and trivalent cations (e.g. Co(NH 3) 3+ 6, Tb 3+). Our results are compatible with the presence in solution of torus-shaped condensed structures in a narrow range of spermine concentration; further addition of the polyamine produced precipitation due to the self-aggregation of several toroids. For spermine concentrations lower than that required for collapse, important changes of the orientation mechanism in the electric field and of DNA stiffness were observed. Whereas free DNA was mainly oriented by a fast-induced polarizability mechanism, DNA-spermine complexes displayed an important permanent dipole component, in the spermine concentration range where extension of the DNA molecules was present. The birefringence relaxation times suggested that, in the first step, the stiffness of the DNA molecules increased, and then, at higher spermine concentration, bending of the DNA molecules occurred so that condensation into toroidal particles became possible.

Electric birefringence of eukaryotic ribosomes

Eukaryotic 60S ribosomal subunits were studied by transient electric birefringence. Conformations of subunits in active and inactive states upon changes in magnesium concentration were compared by electric birefringence and orientational relaxation time measurements. Active subunits exhibit a positive birefringence and a relaxation time of the order of 8 μs. In the presence of EDTA, inactive subunits show no birefringence. When Mg 2+ is reverted in the cold to its initial level, the electro-optical properties of the subunits are partially restored although the particles remain biologically inactive.

Interaction of ethidium bromide with DNA. Optical and electrooptical study.

AbstractThe binding of ethidium bromide to DNA has been studied by various optical methods. From fluorescence polarization studies, and film, electric linear dichroism, and circular dichroism spectra, we propose assignments of the absorption bands of the dye, which are discussed in connection with wave‐mechanical calculations recently reported.The optical activity induced in the dye absorption bands upon binding to DNA was attributed to various origins depending on the electronic transition considered. The visible absorption band displayed a circular dichroism due to the asymmetry of the binding site and independent of the amount of binding. The transition identified at 378 nm from the circular dichroism and electric dichroism observations was thought to be due to a magnetic‐dipole transition. It remained constant with increasing amounts of dye bound. The main ultraviolet band showed circular dichroism characteristics corresponding to exciton interactions between dye molecules bound to neighboring sites.The electric dichroism observed for the strongly bound dye molecules indicated that the phenanthridinium ring of ethidium bromide was probably not perfectly parallel to the DNA base planes. When the amount of dye bound to DNA exceeded the maximum amount compatible with the exclusion of adjacent binding sites, the electric dichroism decreased owing to the appearance of externally bound dye molecules with no contribution to the dichroism.Sonicated DNA was used to study the lengthening of the DNA molecule upon complexation. Although the viscosity of the complexes increased with the amount of binding, the rotational diffusion coefficient measured by the electric birefringence relaxation was not detectably affected. The absence of variation in the electric birefringence with the binding indicated that the DNA base stacking remained unaltered.

Estimation of particle dimensions from the relaxation of transient electric birefringence of suspensions.

Estimation of particle dimensions from the relaxation of transient electric birefringence of suspensions.