Study of the dielectric permeability in the superhigh frequency range of a degraded polyoxybutyrate biopolymer

The dielectric permeability of the degradable biopolymer polyhydroxybutyrate synthesized by hydrogen-oxidizing bacteria Alcaligenes eutrophus was investigated by the resonance method using original highly sensitive microstrip sensors. For the first time, a linear growth of dielectric permeability (delta epsilon/delta T = 7 x 10(-4) degree-1) due to the flexibility of the polymer chain in the temperature range from 10 to 70 degrees C was revealed. The energy of a bend of the nearest fragments was evaluated (E = 392 K), and its correspondence to the energies of bends of the alcyl groups of low-molecular substances like liquid crystals was established. It was shown that at low values of dielectric permeability in the high-frequency range (epsilon' = 2.25 +/- 0.02), which are stable, in a wide range of frequencies of the electromagnetic field (1 MHz - 1 Hz), polyoxybutyrate can be used in the microwave equipment.     

The dielectric increments of aqueous polyelectrolyte solutions: a scaling approach

This paper deals with dielectric dispersion curves (covering a frequency range from a few Hz to 100 MHz) of Na-poly(styrene-sulfonate) of 65,000 < or = Mw < or = 1,060,000 g mol(-1) in aqueous solutions. The values of the low frequency (dielectric increment1) and high frequency (dielectric increment2) dielectric increments, obtained from the experimental curves matched to a superposition of two Cole-Cole equations, have been analyzed in terms of their concentration and molar mass dependence. The concentrations C (g l(-1)) of the various solutions were mostly situated in the transition regime defined by Odijk [T. Odijk, Macromolecules 12 (1979) 688] between the dilute regime (C < Cg*) and the semi-dilute one (C > C**), and wherein the characteristic concentration C* marks the onset of flexibility effects on the polyion behavior. It has been shown that in the concentration range Cg* < C < C** the increments in both frequency domains satisfy a scaling relation dielectric increment(j) = Bj M(nu j) (C/C*)(mu j) with molar mass independent exponents nu j and mu j changing around C*. Their values are different for dielectric increment1 and dielectric increment2, except for mu above C* where both increments appear to become concentration-independent. Below Cg*, in the dilute regime, the two dispersion domains seem to merge. The increment dielectric increment = relative permittivity (0) - high frequency limit of relative permittivity is molar mass independent if scaled to (C/Cg*). The molar mass dependence of the increments as a function of the macromolecular concentration rhoP, dielectric increment or dielectric increment(j) approximately Mgamma (rhoP)mu, also reveals differences between the different concentration regimes. Extrapolation from above Cg* to zero concentration is thus unjustified.     

High-frequency dielectric study of side-chain dynamics in poly(lysine) aqueous solutions

The high-frequency dielectric properties of poly(lysine) of different chirality in aqueous solutions have been measured in the frequency range from 1 MHz to 1.8 GHz. The dielectric spectra show the existence of relatively small dielectric dispersions at around 100 MHz that have been attributed to internal motion in the polymer chain, due to side-chain polar groups. Our results indicate that the local structure of the chain and its possibility to undergo a conformational transition induced by pH does not modify the main feature of the side-chain dynamics, the dielectric strength being largely proportional to the concentration of charged groups. A similar behavior has been found in poly(alpha-glutamate) and in poly(gamma-glutamate) aqueous solutions, where the dielectric parameters appear to be related to the change in the charge density on the main chain, rather than to the accompanying conformational helix-coil transition.     

Microwave absorption in oligomers of ethylene glycol

The dielectric properties of biologically and pharmaceutically important low-molecular weight ethylene glycols H(-OCH2CH2-)n -OH (n = 1,2,4,6) were investigated to clarify the effect of chain length on the dielectric properties. The measurement of dielectric constant and dielectric loss was carried out over the frequency range 200 MHz to 20 GHz at temperatures of 25 degrees C to 55 degrees C. It is found that in these molecules microwave dielectric losses are significant. The dispersion behaviour of these molecules can be represented by Cole-Cole equation. The dielectric properties of these homologous ethylene glycols are discussed in terms of the effects of chain length and intermolecular hydrogen bonds regarding the molecular conformations. These wide frequency range dielectric data have also been discussed in view of the suitable selection of the oligomer of ethylene glycol for cosmetic preparations and other pharmaceutical applications with the intention of protection of the skin from weak microwave radiations present in the surrounding environment. These systematic microwave dielectric data with frequency and temperature variation are not available and are provided in this paper.     

Dielectric relaxation spectroscopy on dimyristoylphosphatidylcholine-packaged gramicidin A

The complex permittivities of aqueous suspensions of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and of DMPC packaged gramicidin A' (DMPC-GA) have been determined over the frequency range of 1 MHz to 1 GHz and the temperature range of 0-60 degrees C. A dielectric relaxation/loss has been observed at about 66 MHz for the DMPC suspension (30 degrees C) and at about 57 MHz for the DMPC-GA suspension (30 degrees C). This dielectric relaxation/loss has been attributed to the rotational mobility of the zwitterionic group of DMPC. The temperature dependence (from 60 degrees C to 0 degrees C) of this dispersion/absorption process of the DMPC suspension indicates a sharp reduction of the dielectric relaxation at about 20 degrees C. This dielectric change is related to the conversions of shape and structure of bilayer aggregates. This sharp reduction of the dielectric relaxation disappears or broadens when GA is incorporated into the DMPC aqueous suspension. The interpretation of these results is that the GA addition into the DMPC aqueous suspension induces a small decrease of the rotational mobility of the zwitterionic group above the lipid phase transition, and a small increase of the rotational mobility of the zwitterionic group below the lipid phase transition.     

Electric polarization of polyelectrolyte and colloid media: dielectric versus electro-optic approach

The theories of dielectric dispersion and of electric birefringence as a representative of electro-optic methods are considered and it is shown that they both depend in a similar way simply on the real part of the complex electric polarizability of the macromolecules or the particles. The latter also contains the permanent dipole moment. Experimental data on dielectric dispersion, electric birefringence and electric light scattering of strongly elongated, rod-like poly(tetrafluoroethylene) particles are compared and an attempt is made to extend the dielectric dispersion curve to lower frequencies using electric birefringence and electric light scattering data. Further, the experimental data on dielectric dispersion, electric light scattering, electro-orientation and dipolophoresis for the more complicated Escherichia coli particles are compared. Again, the possibility to extend the 10 kHz-100 MHz dielectric dispersion curve down below 1 Hz by using electric light scattering data is examined. The good matching of the dielectric dispersion and electric light scattering frequency curves found in the overlapping frequency range (10 kHz-5 MHz) essentially enhances the chance that dielectric dispersion below 1 MHz is related to alpha dispersion and not to electrode polarization. Thus it is not only possible to obtain additional information on the mechanism of polarization at lower-frequency dielectric dispersion, but also to extend our knowledge about the effective dielectric properties of biological complex fluids to frequencies essentially below 1 MHz. This could be important for the understanding of the effect of low-frequency electromagnetic fields on living matter.     

Study of Bound Water of Poly-Adenine Using High Frequency Dielectric Measurements

The high frequency dielectric constant of poly-adenine (poly-A) was measured between 1 MHz and 1 GHz. The purpose of these experiments was to investigate the state of water molecules that are bound to the charged groups of the poly-A molecule. Analysis of the data using the Maxwell's mixture equation revealed the dielectric constant of bound water higher than we expected. Using Onsager's internal field in Debye's equation, we calculated the dielectric constant of water in the vicinity of a charged ion. The result of this computation demonstrates that the dielectric constant of bound water is much smaller than the normal value only in the immediate proximity of charged ions (within 2 Å). The dielectric constant increases rapidly to the normal value as the distance increases from 2 to 4 Å. This observation indicates that charged sites of polyions have only short range interactions with the surrounding water molecules. However, this conclusion pertains only to rotary diffusion of bound water since dielectric measurement is unable to detect translational diffusion.     

Conformational free energy maps for globobiose (alpha-D-Galp-(1-->4)-beta-D-Galp) in implicit and explicit aqueous solution

Four Ramachandran maps of the conformational potential of mean force (PMF) for the galactose disaccharide globobiose (alpha-D-Galp-(1-->4)-beta-D-Galp) were calculated in vacuum, explicit water, with a simple high dielectric constant and a distance-dependent dielectric coefficient, respectively. This simple model of the galactan alpha-(1-->4)-linkage is shown to be conformationally restricted, with only a small range of syn-phi/syn-psi conformations predominating at standard temperature and pressure. This has implications for the preferred conformation and chain dynamics of alpha-galactosides. In addition, comparison of the relevant PMF surfaces reveals the substitution of a high dielectric constant for explicit water solution to be a valid approximation for reproducing the minimum energy conformation of this glycosidic linkage.     

Theoretical and Numerical Approaches for Determining the Reflection and Transmission Coefficients of OPEFB-PCL Composites at X-Band Frequencies

Bio-composites of oil palm empty fruit bunch (OPEFB) fibres and polycaprolactones (PCL) with a thickness of 1 mm were prepared and characterized. The composites produced from these materials are low in density, inexpensive, environmentally friendly, and possess good dielectric characteristics. The magnitudes of the reflection and transmission coefficients of OPEFB fibre-reinforced PCL composites with different percentages of filler were measured using a rectangular waveguide in conjunction with a microwave vector network analyzer (VNA) in the X-band frequency range. In contrast to the effective medium theory, which states that polymer-based composites with a high dielectric constant can be obtained by doping a filler with a high dielectric constant into a host material with a low dielectric constant, this paper demonstrates that the use of a low filler percentage (12.2%OPEFB) and a high matrix percentage (87.8%PCL) provides excellent results for the dielectric constant and loss factor, whereas 63.8% filler material with 36.2% host material results in lower values for both the dielectric constant and loss factor. The open-ended probe technique (OEC), connected with the Agilent vector network analyzer (VNA), is used to determine the dielectric properties of the materials under investigation. The comparative approach indicates that the mean relative error of FEM is smaller than that of NRW in terms of the corresponding S₂₁ magnitude. The present calculation of the matrix/filler percentages endorses the exact amounts of substrate utilized in various physics applications.     

Complex Dielectric Properties of Sulfate-Reducing Bacteria Suspensions

Sulfate-reducing bacteria (SRB) can potentially enhance the remediation of heavy metals in the subsurface. Previous geophysical research has demonstrated the sensitivity of electrical measurements to SRB-mediated mineral transformation in porous media. However, the inherent dielectric properties of SRB and their direct contribution to the electrical properties of porous media are poorly understood. We studied the complex dielectric properties of SRB (Desulfovibrio vulgaris) suspensions at different concentrations and at different growth stages using a two-electrode dielectric spectroscopy measurement over the frequency range of 20 Hz to 1 MHz. Our results show higher dielectric responses (relative dielectric permittivity, real and imaginary conductivity) occurred with higher bacteria concentration at frequencies <10 kHz. Additionally, permittivity and conductivity both decreased as cells aged from mid-log phase to late stationary phase. Our results suggest that dielectric spectroscopy measurements can be used to noninvasively monitor biomass and various growth stages of SRB. Our work advances the interpretation of electrical signals associated with SRB observed in the subsurface.     

Comparison of dielectric response models for simulating electrostatic effects in proteins

Two recent approaches for calculating pK shifts in proteins are compared. The first of these uses Coulomb's law with a distance-dependent dielectric permittivity, epsilon (r), to model the screening effects of the environment, and the second uses a finite difference approach to solve Poisson's equation. It is shown that an explicit form of epsilon (r) which has been fitted to experimentally determined values of the dielectric permittivity in a range from 1 to 21 A can be approximated by a linear form in the functionally significant range of charge separations of approximately 3-10 A, but for distances greater than 10 A the effective permittivity is strongly nonlinear. A statistical analysis of the errors in calculated pK shifts due to electrostatic interactions between charges with separations greater than 10 A shows that there are only marginal differences in reliability between using Coulomb's law with an appropriate form of epsilon (r) or the finite difference approach for solving Poisson's equation. Thus it is concluded that pK shifts can be calculated just as well, and with considerably less effort, using Coulomb's law.     

Temperature dependence of DNA dielectric dispersion at radiofrequency

We have studied the dielectric behavior of DNA aqueous solutions at various ionic strengths and in the presence of the specific DNA ligand ethidium bromide, in the frequency range 1 MHz-1 GHz, at different temperatures ranging from 5 to 40 degrees C. The activation enthalpies of the dielectric relaxations studied were obtained by Arrhenius plots of In(tau T)-1 vs. T-1. The results are consistent with a counterion fluctuation model as previously developed by Mandel and colleagues.     

Hydration dependence of conformational dielectric relaxation of lysozyme

Dielectric response of hen egg white lysozyme is measured in the far infrared (5-65 cm-1, 0.15-1.95 THz, 0.6-8.1 meV) as a function of hydration. The frequency range is associated with collective vibrational modes of protein tertiary structure. The observed frequency dependence of the absorbance is broad and glass-like. For the entire frequency range, there is a slight increase in both the absorbance and index of refraction with increasing hydration for <0.27 h (mass of H2O per unit mass protein). At 0.27 h, the absorbance and index begin to increase more rapidly. This transition corresponds to the point where the first hydration shell is filled. The abrupt increase in dielectric response cannot be fully accounted for by the additional contribution to the dielectric response due to bulk water, suggesting that the protein has not yet achieved its fully hydrated state. The broad, glass-like response suggests that at low hydrations, the low frequency conformational hen egg white lysozyme dynamics can be described by a dielectric relaxation model where the protein relaxes to different local minima in the conformational energy landscape. However, the low frequency complex permittivity does not allow for a pure relaxational mechanism. The data can best be modeled with a single low frequency resonance (nu approximately 120 GHz=4 cm-1) and a single Debye relaxation process (tau approximately .03-.04 ps). Terahertz dielectric response is currently being considered as a possible biosensing technique and the results demonstrate the required hydration control necessary for reliable biosensor applications.     

The properties of liquid water in electric and magnetic fields

A new model of liquid water is proposed, which involves the liquid-crystalline phase, namely, the presence of linearly ordered chains of water molecules and large clusters of these molecules. The presence of linearly ordered chains and clusters in liquid water makes itself evident after the exposure of water to low-frequency electromagnetic radiation. The kinetics of the linearly ordered chains is described by nonlinear excitations (solitons). A hydrodynamic equation describing the behavior of this model system was derived. On the basis of the model, the dimensions of clusters were determined (approximately 600 A). The calculated values of dielectric permeability in the range of low frequencies appeared to be close to their experimentally obtained values. A tenfold increase in the stationary value of dielectric permeability compared with the known value of the dielectric constant in the frequency range of 10(4)-10(6) Hz was predicted. The frequency dependence of dielectric permeability in this range was studied.     

Effect of ions on counterion fluctuation in low-molecular weight DNA dielectric dispersions

The dielectric permittivity of aqueous solutions of low-molecular weight DNA (Mr = 3.2 X 10(5) ) in the presence of MgCl2 and AgNO3 has been measured in the frequency range from 5 kHz to 30 MHz, at a temperature of 25 degrees C. The DNA concentration was 3.5 X 10(-4) M in terms of phosphate and the salt concentration was varied from 1 X 10(-5) to 2 X 10(-4) M. The dielectric results have been analyzed in terms of two contiguous dielectric dispersions, and characteristic parameters have been discussed on the basis of polyelectrolyte theories which deal with counterion fluctuation. Some molecular parameters of the DNA molecule in electrolyte solutions are estimated.     

Acidic range titration of HEWL using a constant-pH molecular dynamics method

In this work, we present the first application to a protein of the stochastic constant-pH molecular dynamics (MD) method with the inclusion of proton tautomerism. The acidic titration of HEWL was performed under different conditions. Both generalized reaction field (GRF) and particle mesh Ewald (PME) methods were used in the treatment of the long range electrostatics and, even though the PME simulations revealed to be more stable, the better results were obtained using GRF (pK(a) RMSD of 0.82 for GRF and 1.13 for PME). The results using PME at different dielectric constants (2, 4, and 8) also revealed that there was no significant improvement in pK(a)'s prediction upon increasing the dielectric constant. The secondary structure analysis of HEWL revealed a remarkably stable protein in the acidic pH range. The beta-sheet strands (unlike the alpha-helices) seem to be destabilized upon pH decrease, suggesting that the beta-domain is less stable than the alpha-domain. The four principal alpha-helices were also ordered according to their stability in the acidic pH range and the results (4 < 1 < 2 approximately = 3) were consistent with the ones obtained in thermal denaturation studies.     

Dielectric spectroscopy of L-alpha-lysolecithin-packaged gramicidin A

The complex permittivities of L-alpha-lysolecithin in the absence and presence of the gramicidin A ion channel were measured over the temperature range 0-60 degrees C and over the frequency range 1-1000 MHz. One dielectric relaxation/loss has been observed. It is located at 103.3 MHz (1.54 ns) for a micellar 0.4 M L-alpha-lysolecithin solution at 20 degrees C, whereas it is shifted to 71.7 MHz (2.22 ns) for a lamellar L-alpha-lysolecithin-gramicidin A aqueous solution (0.4 M L-alpha-lysolecithin, 0.0308 M gramicidin A) at 20 degrees C. The dielectric relaxation decreases and the relaxation time increases when gramicidin A is incorporated into L-alpha-lysolecithin. These dielectric changes are related, in part, to the micellar-to-lamellar lipid phase transition induced by the incorporation of gramicidin A into lysolecithin. We suggest that the diffuse rotational motion of the polar head group of L-alpha-lysolecithin contributes to the dielectric relaxation/loss at around 100 MHz.     

Dielectric analysis for estimation of oil content in the mycelia of Mortierella alpina.

The dielectric behavior of the filamentous fungi Mortierella alpina SAM2104 and 1S-4, which produce polyunsaturated fatty acid enriched oil in the mycelia, was investigated. During the cultivation carried out in a 10-kL fermentor for 12-15 days, the relative permittivity and conductivity of the broth were measured in the frequency range of 100 kHz to 30 MHz. The dielectric parameters, i.e., the amplitude of dielectric relaxation (Deltaepsilon) and the characteristic frequency (f(c)), were obtained by fitting the Cole-Cole equation to the observed dielectric relaxation, and the conductivity of the medium (kappa(a)) was also measured. The value of Deltaepsilon gradually increased from the second day through the end of cultivation, suggesting that volume fraction of the cell increased with oil accumulation. The conductivity of the cytoplasm (kappa(i)) was calculated from the experimental values of f(c) and kappa(a), using a theoretical equation based on an ellipsoidal cell model. As a result, good correlation between the calculated kappa(i) and the oil content was obtained. These findings indicate that dielectric analysis enables us to estimate the oil content in the mycelia of oleaginous fungi and also provides a useful tool for monitoring cell growth and for controlling the cultivation process.     

Electrochromic shift of chlorophyll absorption in photosystem I from Synechocystis sp. PCC 6803: a probe of optical and dielectric properties around the secondary electron acceptor

Nanosecond absorption dynamics at approximately 685 nm after excitation of photosystem I (PS I) from Synechocystis sp. PCC 6803 is consistent with electrochromic shift of absorption bands of the Chl a pigments in the vicinity of the secondary electron acceptor A(1). Based on experimental optical data and structure-based simulations, the effective local dielectric constant has been estimated to be between 3 and 20, which suggests that electron transfer in PS I is accompanied by considerable protein relaxation. Similar effective dielectric constant values have been previously observed for the bacterial photosynthetic reaction center and indicate that protein reorganization leading to effective charge screening may be a necessary structural property of proteins that facilitate the charge transfer function. The data presented here also argue against attributing redmost absorption in PS I to closely spaced antenna chlorophylls (Chls) A38 and A39, and suggest that optical transitions of these Chls, along with that of connecting chlorophyll (A40) lie in the range 680-695 nm.