Electric Birefringence Technique Research Articles

Dynamic Manipulation of Optical Anisotropy of Suspended Poly‐3‐hexylthiophene Nanofibers

Poly‐3‐hexylthiophene (P3HT) nanofibers are 1D crystalline semiconducting nanostructures, which are known for their application in photovoltaics. Due to the internal arrangement, P3HT nanofibers possess optical anisotropy, which can be enhanced on a macroscale if nanofibers are aligned. Alternating electric field, applied to a solution with dispersed nanofibers, causes their alignment and serves as a method to produce solid layers with ordered nanofibers. The transmission ellipsometry measurements demonstrate the dichroic absorption and birefringence of ordered nanofibers in a wide spectral range of 400–1700 nm. Moreover, the length of nanofibers has a crucial impact on their degree of alignment. Using electric birefringence technique, it is shown that external electric field applied to the solution with P3HT nanofibers can cause direct birefringence modulation. Dynamic alignment of dispersed nanofibers changes the refractive index of the solution and, therefore, the polarization of transmitted light. A reversible reorientation of nanofibers is organized by using a quadrupole configuration of poling electrodes. With further development, the described method can be used in the area of active optical fiber components, lab‐on‐chip or sensors. It also reveals the potential of 1D conducting polymeric structures as objects whose highly anisotropic properties can be implemented in electro‐optical applications.​

Existence of Two Different Isotropic Phases as a Reason for Bistable Phase Behavior of an LC Side‐Chain Polymethacrylate

AbstractAn isotropic melt of a chiral side‐chain polymethacrylate was studied by electric birefringence technique. A phase transition between two different isotropic phases was detected by Kerr effect and confirmed by WAXS measurements. The obtained experimental data can explain the previously reported bistable phase behavior of the polymer, as conventional Sm A phase is formed in slow cooling whereas a TGB‐like, optically isotropic mesophase in fast cooling.magnified image

Myosin motor domain lever arm rotation is coupled to ATP hydrolysis.

We have investigated coupling of lever arm rotation to the ATP binding and hydrolysis steps for the myosin motor domain. In several current hypotheses of the mechanism of force production by muscle, the primary mechanical feature is the rotation of a lever arm that is a subdomain of the myosin motor domain. In these models, the lever arm rotates while the myosin motor domain is free, and then reverses the rotation to produce force while it is bound to actin. These mechanical steps are coupled to steps in the ATP hydrolysis cycle. Our hypothesis is that ATP hydrolysis induces lever arm rotation to produce a more compact motor domain that has stored mechanical energy. Our approach is to use transient electric birefringence techniques to measure changes in hydrodynamic size that result from lever arm rotation when various ligands are bound to isolated skeletal muscle myosin motor domain in solution. Results for ATP and CTP, which do support force production by muscle fibers, are compared to those of ATPgammaS and GTP, which do not. Measurements are also made of conformational changes when the motor domain is bound to NDP's and PP(i) in the absence and presence of the phosphate analogue orthovanadate, to determine the roles the nucleoside moieties of the nucleotides have on lever arm rotation. The results indicate that for the substrates investigated, rotation does not occur upon substrate binding, but is coupled to the NTP hydrolysis step. The data are consistent with a model in which only substrates that produce a motor domain-NDP-P(i) complex as the steady-state intermediate make the motor domain more compact, and only those substrates support force production.

Electro-optic studies of polymers of varying flexibility in solution

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Transient electric birefringence of colloidal particles immersed in shear flow. Part II. The initial response under the action of a rectangular electric pulse and the behavior at a low alternating electric field

The time-dependent rotational diffusion equation for rigid macromolecules in solution has been approximately solved for two cases in order to extend the electric birefringence technique to streaming-electric birefringence. One is for the initial period through the application of a rectangular electric pulse to the solution immersed in a low shear flow. The purpose of this is expansion of the distribution function into a function series made by the product of the powers of reduced time (= Θt) and hydrodynamic field α ( = G Θ , G: velocity gradient, Θ: rotary diffusion constant) and a surface harmonic P i j cos jφ. The solution for the build-up process at arbitrary electric field strength is found, but is limited to low hydrodynamic fields. The other is for the response when an alternating electric field is applied to the solution in a shear flow. Here, instead of reduced time, the maximum electric field E 0 is chosen as a parameter for the expansion. The expressions for the intensity of the transmitted light through crossed Nicols are derived in two optical systems where the polarizer is set at an angle of 45° and 0° to the direction of the electric field. The results in the former case show that we can determine four parameters, the ratio of velocity gradient to rotary diffusion constant, the axial ratio of a particle, the anisotropy of electric polarizability, and the optical anisotropy factor, from four values observed in two optical systems, namely, two light intensities before applying an electric field and two initial slopes of the build-up after applying an electric field. On the other hand, when a low alternating electric field with extremely high frequency is applied, the build-up of the light intensity in the former case is the same as that of electric birefringence for pure induced dipole orientation. The build-up for the latter optical system is the same as the expression for pure induced dipole orientation of Eq. (38) shown in a previous work.

Electric Birefringence Study of Reaction-Limited Colloidal Aggregation

The kinetics of slow irreversible aggregation of monodisperse polystyrene latex spheres is investigated by means of the transient electric birefringence (TEB) technique. The amplitude of the TEB signal is connected with the anisotropy of fractal clusters; the decay of the signal after the electric field is switched off contains information about average cluster size and size distribution. The TEB results are compared with static and dynamic light scattering data.

Nucleutide- and temperature- induced changes in myosin subfragment-1 structure

The effects of nucleotide binding and temperature on the internal structural dynamics of myosin subfragment 1 (S1) were monitored by intrinsic tryptophan phosphorescence lifetime and fluorescence anisotropy measurements. Changes in the global conformation of S1 were monitored by measuring its rate of rotational diffusion using transient electric birefringence techniques. At 5°C, the binding of MgADP, MgADP,P and MgADP,V (vanadate) progressively reduce the rotational freedom of S1 tryptophans, producing what appear to be increasingly more rigidified S1-nucleotide structures. The changes in the luminescence properties of the tryptophans suggest that at least one is located at the interface of two S1 subdomains. Increasing the temperature from 0 to 25°C increases the apparent internal mobility of S1 tryptophans in all cases and, in addition, a reversible temperature-dependent transition centered near 15°C was observed for S1,S1-MgADP and S1-MgADP,P, but not for S1-MgADP,V. The rotational diffusion constants of S1 and S1-MgADP were measured at temperatures between 0 and 25°C. After adjusting for the temperature and viscosity of the solvent, the data indicate that the thermally induced transition at 15°C comprises local conformational changes, but no global conformational change. Structural features of S1-MgADP,P, which may relate to its role in force generation while bound to actin, are presented.

Solution behavior of random copolymers of styrene with sodium‐2‐acrylamido‐2‐methylpropane sulfonate

AbstractThe nonaqueous solution behavior of random copolymers of styrene (ST) with sodium‐2‐acrylamido‐2‐methylpropane sulfonate (Na‐AMPS) [poly(ST‐Na‐AMPS)] has been investigated using the transient electric birefringence (TEB) technique. The copolymers with varying high sulfonate contents (about 30–70 mol%), bridging the gap between conventional ionomers and classical polyelectrolytes, were dissolved in the solvent methylformamide (MFA) with a high permittivity ϵ of ca. 190. The solutions showed a negative birefringence at electric field strength E of the order of kV/cm. A typical Kerr effect was observed at low polymer concentrations C of ca. 10−3g/mL and electric field strengths of the order of kV/cm. However, the detailed, TEB studies demonstrated different behavior at two concentration regimes in dilute solution. At a low concentration regime (e.g., C ≤ 1 × 10−3g/mL for the copolymer with a 66.7 mol % sulfonate content) where the reduced viscosity exhibited a pronounced polyelectrolyte effect, the birefringence signal pattern showed a maximum before reaching a steady value. Additionally, during the rise at an applied electric field strength beyond a threshold value, it was observed that the nonexponential field‐free decay was slower than the single exponential field‐induced rise. The observed anomalous behavior was similar to those of a polyelectrolyte [sodium poly (styrene sulfonate)] in aqueous solution and might be attributed to the perturbation of the molecular shape by the applied electric field. At the higher concentration regime (e.g., C ≥ 4 × 10−3g/mL for the same copolymer with a 66.7 mol % sulfonate content) where the polyelectrolyte effects started to diminish as indicated by the viscosity study, the birefringence shape showed no variation with an increased electric field strength and the field‐free decay turned out to be faster than the single exponential rise. The dissociation of ionic aggregates was tentatively interpreted to be responsible for this observation. It seems that by simply varying the polymer concentration, poly (ST‐Na‐AMPS) could behave either as a polyelectrolyte or as an ionomer in a single polar organic solvent.

Transient electric birefringence study of highly dilute agarose solutions

AbstractIn order to characterize the first step of agarose gelation, highly dilute solutions (2·10−3 to 0.5 g/L) have been studied by means of the transient electric birefringence technique. The field‐free decay curves of the birefringence are well described by a stretched‐exponential B(t) ≈ exp(−t/τ)β; the value of the exponent β is close to 0.5 whatever the agarose concentration. The suspended particles observed by electron microscopy present a rod‐like shape with a constant diameter (∼50 Å), without any branching; they are polydisperse with a distribution of lengths approximately exponential. The mean length of these fibers, deduced from their mean rotational diffusion coefficient, is proportional to the 0.37 power of the agarose concentration in the solution. Furthermore, these particles possess a strong permanent electrical dipole confirming the side‐to‐side arrangement of helices into bundles; this dipole is roughly proportional to the particle length, indicating a self‐similarity in the unidirectional growth of the agarose fibers, even when approaching the gelling concentration.

The measurement of the rotational diffusion coefficient of bovine plasma fibronectin by electric birefringence technique

Although the conformation of fibronectin has been widely investigated by various techniques, there has not yet been any determination of its rotational diffusion coefficient. We report here this determination by the transient electric birefringence study of solutions of bovine plasma fibronectin at physiological ionic strength. The solutions showed a positive birefringence. A linear relationship was observed between the intensity of the birefringence at equilibrium and the square of the electric field within the range of fields applied (up to 12.5 kV.cm-1). The field-independent decay of the induced birefringence was described by a single exponential with a relaxation time of 0.76 (+/- 0.08) microsecond at 23 degrees C. This establishes fibronectin in solution as a globally rigid structure with a rotational diffusion coefficient, at 20 degrees C, of 202,000 s-1. This result allows the first rigorous determination of the low-resolution structure of fibronectin. It is important to notice that the analysis combines only results obtained in physiological conditions on native molecules and follows a strict hydrodynamic interpretation. The conclusion of this work is that a hollow sphere of about 20 nm external diameter can be proposed as a model for the three-dimensional structure of the fibronectin molecule in solution. This new model suggests the fibronectin could have the structure of a carrier protein.

Study of large DNA fragments in agarose gels by transient electric birefringence

The pulsed-field gel electrophoresis (PFG) is a newly developing technique used in the fractionation of large DNA fragments. Advances in PFG demand a better understanding in the corresponding mechanisms of DNA dynamics in the gel network. Detailed experiments are needed to verify and to extend existing theoretical predictions as well as to find optimum conditions for efficient separation of large DNA fragments. In the present study, deformation of large DNA fragments (40-70 kilobase pairs) imbedded in agarose gels were investigated by using the transient electric birefringence (TEB) technique under both singular polarity and bipolarity electric pulses at low applied electric field strengths (E less than or equal to 5 V/cm). The steady-state optical retardation (delta s) of DNA molecules is linearly proportional to E2. At a given E, the amplitude of optical retardation [delta(t)] increases monotonically with the pulse width (PW) and then reaches a plateau value [delta(t = 0) = delta s] where t = 0 denotes the time when the applied field is turned off or reversed. The field-free decay time (tau-a few minutes) is several orders of magnitudes slower than that from previous TEB observations using high electric field strengths (E-kV/cm) and short pulse widths (PW-ms). The degree of deformation (stretching and orientation) and the time of restoration to the equilibrium conformation of overall DNA chains have been related to delta and tau. In field inversion measurements, exponentially rising and linearly falling of birefringence signals in the presence of forward/inverse applied fields were observed. The rising and falling of birefringence signals were reproducible under a sequence of alternating pulses. Comparison of our results with literature findings and discussions with theories are presented.

Reversing‐pulse electric birefringence of poly(γ‐benzyl‐L‐glutamate). III. The temperature dependence of the transient and steady‐state behavior in cyclohexanone

AbstractThe reversing‐pulse electric birefringence (RPEB) technique was applied to the study of the temperature effect on the electrooptical and hydrodynamic properties of a fractionated [Glu(OBzl)]n sample, which is molecularly dissolved in cyclohexanone. The aim was to develop a standard analytical method for thermal denaturation and temperature‐induced conformational transitions. The field‐on reverse and steady‐state signal, and the field‐off decay signal, were measured at 535 nm and at a constant low field strength (ca. 3 kV/cm) over a wide temperature range (5–90°C). The steady‐state birefringence and the relaxation time in the decay process were also measured at two constant temperatures (5 and 70°C) over a wide field strength range (E ≤ 20 kV/cm). By the combination of these two different sets of RPEB measurements, the unwanted effect of the high pulse field on polymer conformation at elevated temperatures could be minimized. Together with the density and viscosity of cyclohexanone measured between 5 and 95°C, the following quantities could be evaluated: the weight‐average permanent dipole moment and polarizability anisotropy, the reduced optical anisotropy factor (Δg/n), the weight‐average length, and the degree of polydispersity. All these quantities, except for Δg/n, were found to be almost independent of temperature (5–90°C) and concentration (1.54–4.27 mM).

Structural aspects and orientation mechanism of mitochondrial F1 adenosinetriphosphatase. Evidence for a negative electric birefringence due to a permanent moment perpendicular to the long axes of the particle.

The electric birefringence technique was used to investigate the steady-state birefringence, the orientational relaxation time, and the orientation mechanism of pig heart mitochondrial F1 adenosine-5'-triphosphatase (F1-ATPase). The electrooptical properties of this enzyme in solution were studied as functions of pH, protein concentration, and applied electric field. The F1-ATPase exhibits a surprising negative electric birefringence with a specific Kerr constant of -1.5 X 10(-3) esu cgs. The field-independent relaxation time was found to be 0.65 +/- 0.05 microseconds, corresponding to a rotational diffusion constant of 2.55 X 10(5) s-1. The overall size and shape of F1-ATPase have been calculated from both translational and rotational diffusion constants. The enzyme may be assumed to be an oblate ellipsoid of revolution with dimensions of about 170 X 170 X 70 A. The orientation mechanism of F1-ATPase was analyzed by fitting experimental birefringence rising curves with theoretical rising functions. The ratio of the permanent to induced dipole moment is found to be very high; therefore, the birefringence of F1-ATPase is due to a strong permanent dipole moment in a direction perpendicular to the long axes of the particle. These particular electric properties can be explained by the oligomeric structure of the protein and seem likely to play a role in its mechanism of functioning.

Cation effects on the nonlinear electrical properties of DNA solutions.

AbstractThe nonlinear electrical properties of DNA solutions were measured when different monovalent cations were added to DNA. The influence of different parameters has been examined: fundamental frequency, field strength, and concentration. A linear relationship between the harmonic current Ih and the DNA concentration is shown, even for higher concentration values (400 mg/l.). The frequency dispersion of Ih has the same shape for all the cations and the low‐frequency amplitude of Ih increases in the following order: Li+ < Na+ < K+ < NH < Cs+. The nonlinear polarizability values are compared with the linear ones determined using the very low field electric birefringence technique. Both linear and nonlinear values are of the same order of magnitude. It is thought that the nonlinear electrical property of high‐molecular‐weight DNA mainly results from the deformation of the DNA coils by the electric field.

Nucleosomes arrangement in chromatin.

The spatial arrangement of nucleosomes in rat liver chromatin has been examined using the electric birefringence technique. All chromatin subunits studied (up to 9 consecutive nucleosomes) contain their full complement of the five histone types associated with about 200 base pairs repeat length DNA. From the relaxation times and the orientation mechanisms, the nucleosome may be assimilated to an oblate ellipsoid of dimensions about 140 x 140 x 70 A, and the DNA superhelical axis is parallel to its shorter axis. The most important result is a sharp transition in the electro-optical properties of subunits when the number of nucleosomes in the chain is greater than 6 : the initial negative birefringence, as for DNA, becomes positive and the relaxation time is multiplied by ten. The hexanucleosome, which presents no birefringence, has an helical symmetrical structure without preferential orientation axis. This structure is approximatively spherical of about 250 A diameter and the chromatin appears as a periodic array of such a structure.

A study of paramyosin aggregation using transient electric birefringence techniques.

AbstractThe aggregation of several forms of the molluscan muscle protein paramyosin at low concentration and at low ionic strength was studied in the pH range 6–10 using transient electric birefringence techniques. In the lower part of this pH range, the aggregates exhibit negative birefringence, but this changes to positive birefringence when the pH increases. Analysis of the field‐free birefringence decay transients of the paramyosin solutions showed that all aggregates coexisted with paramyosin monomer and allowed a determination of the rotational diffusion constant of the aggregates present at each pH. The size and shape of these aggregates were estimated from their rotational diffusion constants and were compared with the known characteristics of larger aggregates such as paracrystals. The positively birefringent aggregates appear to be staggered dimers at certain values of pH; at other pH values, these aggregates appear to be higher aggregates, probably formed by lateral aggregation of monomer or dimer onto one of these staggered dimers. The staggered dimers are formed by overlap of 200–600 Å along each cylindrical paramyosin molecule, in agreement with the 530‐Å overlap distance found in paramyosin paracrystals by Cohen et al. (1971) J. Mol. Biol. 56, 223–237. Some speculations are presented about the nature of the negatively birefringent species.

Length and dipole moment of TMV by laser signal‐averaging transient electric birefringence

AbstractTransient electric birefringence experiments have been performed on well‐characterized highly monodisperse samples of tobacco mosaic virus (TMV). Experiments and calculations are presented that show that the sensitivity and accuracy of the traditional transient electric birefringence technique can be enhanced by several orders of magnitude through the use of a low‐powered laser and crystal polarizing optics, signal averaging, and digital data processing. Measurements of the field‐free decay of the birefringence yield for the rotational diffusion coefficient, DR = 318 ± 3 sec−1. The length of the rodlike virion, calculated from the Broersma equation with this value of DR and a rod diameter of 15 nm, is 292.5 ± 1.0 nm. Measurements of the growth of the birefringence when an electric field is applied across the sample yield μ2/kT(α∥ − α⊥) = 0.47 ± 0.07, where μ is the permanent dipole moment (assumed parallel to the symmetry axis of the virus) and α∥ − α⊥ is the electrical polarizability anistropy of the virus. Using the value of α∥ − α⊥ measured by O'Konski et al., we then obtain μ = 2.5 × 10−14 esu cm.

Dielectric measurements in the presence of a rectangular electric pulse and their comparison with electric birefringence

An apparatus for the measurement of the effect of high electric fields on the dielectric constant of liquids has been modified to accept rectangular voltage pulses with rise and fall times of less than 50 μs. The mode of operation of this apparatus is compared with that for the pulsed electric birefringence technique. The limitations of the technique are discussed with reference to Joule heating and bandwidth considerations.

The anisotropy of the aliphatic C-C bond

In the conformational analysis of organic molecules by electric birefringence and Rayleigh scattering techniques, the value assigned to the aliphatic C-C bond, γC-C, is of fundamental importance. Thiscommunication discusses the implications of recent changes in the experimental parameters used to derive γC-C.

14] Electric birefringence

Publisher Summary The electric-birefringence technique takes advantage of effect to study the characteristics of macromolecular suspensions as they respond to an electric field that is usually in the form of a square-wave pulse. In this way, it is possible to measure two characteristic electric birefringence constants, rotatory diffusion constant, permanent and induced dipole moments, electric polarizability, and optical anisotropy, as well as to determine whether a given macromolecular suspension is monodisperse. By extending the techniques described in the chapter, electric birefringence should also prove useful in investigating the distribution of polymeric species in a suspension, aggregation phenomena, charge patterns of macromolecules, and particle-particle interaction. The electric birefringence technique is not limited to simple square-wave pulsed fields. Other shapes that have been used include alternating positive and negative square waves and alternating sine waves.