Dielectric properties of lens tissue at microwave frequencies

The relative permittivity and conductivity of rabbit eye lens were measured in the frequency domain between 2 and 18 GHz at temperatures of 37 and 20°C. An analysis of the data suggested that a significant proportion of the bulk water in nuclear and cortical lens tissue may behave differently to pure water. In addition, the Maxwell-Fricke mixture theory was used to estimate the amount of hydrated water that relaxes far below 1 GHz.     

Microwave dielectric studies on proteins,tissues, and heterogeneous suspensions

We summarize the results of several of our recent studies on the dielectric properties of protein solutions, tissues, and nonionic microemulsions at microwave frequencies extending to 18 GHz. The data in all cases are analyzed using the Maxwell mixture theory to determine the dielectric properties of the suspending water and the amount and dielectric properties of the water of hydration associated with the suspended phase. The dielectric data from the protein solutions and tissues are broadly consistent with the results of previous studies at UHF frequencies; they indicate hydration values in the range of 0.4–0.6 g water/g protein. There is evidence of a dielectric relaxation process occurring at low-GHz frequencies that can be attributed in part to dielectric relaxation of the “bound” water in the system. The remaining solvent water appears to have dielectric properties close to, if not precisely the same as, those of pure water. The average relaxation frequency of the suspending water in the microemulsions is reduced from that of pure water, evidently reflecting an average of that of the water of hydration (～5–6 GHz) and that of pure water. This reduced average relaxation frequency implies an increased average viscosity of the water and (by Walden's rule) accounts for the unexpectedly low ionic conductivity of the preparations.     

Dielectric studies on water in solutions of purified lecithin vesicles

The complex permittivity of sonicated aqueous solutions of purified dimyristoylphosphatidylcholine has been measured as a function of frequency between 3 kHz and 40 GHz. The dielectric spectrum of the samples shows two dispersion/absorption regions, one centered at about 80 MHz the other at about 20.GHz (30°C). Otherwise than in previous studies no additional dispersion/absorption process has been found at frequencies below 10 MHz.The complex dielectric spectrum of the samples is discussed with respect to the dynamical state of solvent water in solutions of single-bilayer vesicles. The main relaxation time of the solvent water, τ₁ ((2πτ₁)^?1 ≈ 20 GHz), is smaller than that of pure water, τ_W, at the same temperature. This effect results from the action of internal depolarizing fields which obviously overcompensate and enhancement of τ₁ due to specific solute/solvent interactions (hydration) as had been previously found with micellar solutions of lysolecithins.It cannot be excluded, that some solvent water shows unusual dynamical behaviour. If there exists a substantial amount of such motionally perturbed water, however, it must be characterized by a relaxation time close to that of the phosphorylcholine zwitterions, τ₂ ((2πτ₂)^?1 ≈ 80 MHz).     

Dielectric properties of developing rabbit brain at 37 degrees C

The dielectric properties of developing rabbit brain were measured at 37 degrees C between 10 MHz and 18 GHz using time domain and frequency domain systems. The results show a variation with age of the dielectric properties of brain. An analysis of the data suggests that the water dispersion in the brain of newly born animals can be represented by a Debye equation. This dispersion increases in complexity with age, and there is evidence of a smaller additional relaxation process centered around 1 GHz. It is concluded that the principal contribution to this subsidiary dispersion region arises from water of hydration.     

Interrelationships between water and cell metabolism in Artemia cysts X. Microwave dielectric studies

Artemia cysts are composed of an inner mass of about 4000 cells surrounded by an acellular shell. This system can undergo cycles of hydration-dehydration without viability loss, and is a useful model for the study of intracellular water. We have measured the relative permittivity (ε′) of these cysts as a function of water content over the frequency range 0.8–70 GHz. Detailed analysis of the data for cysts containing close to 1 g H₂O/g dry weight indicates that a significant fraction of the total water in this system exhibits dielectric behavior different from that of pure water: the distribution parameter (α) for the dispersion analyzed by the Cole-Cole equation deviates from zero, and the permittivity of cyst water appears to be significantly lower than that of pure liquid.     

Dielectric Properties Based Detection of Heavy Metal Contaminated Soil in the Frequency Range from 10 MHz to 1 GHz

Physical parameters based electromagnetic methods are promising technologies to detect contaminated sites. In these methods, the dielectric property is a key parameter. In this paper, we studied the dielectric characteristics of heavy metal contaminated soil. The chromium contaminated soil was made into samples, and the open-ended coaxial line was adopted as the measurement method. Experiments were conducted in the frequency band between 10 MHz and 1 GHz. The results showed that the complex permittivity, including the real part and the imaginary part, changes as the ionic content changes. Especially, at low frequencies (<50 MHz), the complex permittivity increases significantly with the increase of ionic content. In addition, it also could be seen that the water content of the soil also affects the complex permittivity. We proposed to adopt the drying method or the Time Domain Reflection method to determine the water content. The dielectric parameters are most affected by the ionic content after knowing the water content. Therefore, it is feasible to detect heavy metal contaminated sites based on dielectric properties.     

Rotational and translational water diffusion in the hemoglobin hydration shell: dielectric and proton nuclear relaxation measurements.

The dynamic properties of water in the hydration shell of hemoglobin have been studied by means of dielectric permittivity measurements and nuclear magnetic resonance spectroscopy. The temperature behavior of the complex permittivity of hemoglobin solutions has been measured at 3.02, 3.98, 8.59, and 10.80 GHz. At a temperature of 298 K the average rotational correlation time tau of water within a hydration shell of 0.5-nm thickness is determined from the activation parameters to be 68 +/- 10 ps, which is 8-fold the corresponding value of bulk water. Solvent proton magnetic relaxation induced by electron-nuclear dipole interaction between hemoglobin bound nitroxide spin labels and water protons is used to determine the translational diffusion coefficient D(T) of the hydration water. The temperature dependent relaxation behavior for Lamor frequencies between 3 and 90 MHz yields an average value D(298K) = (5 +/- 2) x 10(-10)m2 s-1, which is about one-fifth of the corresponding value of bulk water. The decrease of the water mobility in the hydration shell compared to the bulk is mainly due to an enhanced activation enthalpy.     

The state of water in biological systems as studied by proton and deuterium relaxation.

Careful experiments on the measurement of the intensity of the deuterium NMR signal for 2-H2 O in muscle and in its distillate were performed, and they showed that all 2-H2 O muscle is "NMR visible". The spin-lattice relaxation time (T1) of the water protons in the muscle and liver of mice and in egg white has been studied at six frequencies ranging from 4.5 to 6.0 MHz over the temperature range of +37 to --70 degrees C. T1 values of deuterons in 2H2 O of gastrocnemius muscle and liver of mice have been measured at three frequencies (4.5, 9.21 and 15.35 MHz) over the temperature range of +37 to --20 degrees C. Calculations on T1 for both proton and deuteron have been made and compared with the experimental data. It is suggested that the reduction of the T1 values compared to pure water and the frequency dependence of T1 are due to water molecules in the hydration layer of the macromolecules, and that the bulk of water molecules in the biological tissues and egg white undergoes relaxation like ordinary liquid water.     

On the mechanism of dielectric relaxation in aqueous DNA solutions.

The complex dielectric response of calf thymus DNA in aqueous saline solutions has been measured from 1 MHz to 1 GHz. The results are presented in terms of the relaxation of the incremental contributions to the permittivity and conductivity from the condensed counterions surrounding the DNA molecules. Measurements of the low-frequency conductivity of the samples also lends support to the condensed counterion interpretation.     

Human skin permittivity determined by millimeter wave reflection measurements

Millimeter wave reflection from the human skin was studied in the frequency range of 37-74 GHz in steps of 1 GHz. The forearm and palm data were used to model the skin with thin and thick stratum corneum (SC), respectively. To fit the reflection data, a homogeneous unilayer and three multilayer skin models were tested. Skin permittivity in the mm-wave frequency range resulted from the permittivity of cutaneous free water which was described by the Debye equation. The permittivity increment found from fitting to the experimental data was used for determination of the complex permittivity and water content of skin layers. Our approach, first tested in pure water and gelatin gels with different water contents, gave good agreement with literature data. The homogeneous skin model fitted the forearm data well. Permittivity of the forearm skin obtained with this model was close to the skin permittivity reported by others. To fit reflection from the palmar skin with a thick SC, a skin model containing at least two layers was required. Multilayer models provided better fitting to both the forearm and palmar skin reflection data. The fitting parameters obtained with different models were consistent with each other.     

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.     

Ultrasonic and dielectric study of nonequilibrium monosaccharide solutions in water

Based on broadband acoustical (10 kHz < or = nu < or = 2 GHz) and dielectric (1 MHz < or = nu < or = 40 GHz) spectrometry, time-resolved ultrasonic attenuation coefficient and static permittivity measurements have been performed on nonequilibrium tautomer solutions of d-arabinose and d-fructose in water. Via the chair-chair ring inversion the ultrasonic attenuation measurements display the decrease in the content of beta-arabinopyranoside and the increase of the alpha-fructopyranoside concentration during the establishment of the tautomer equilibrium. For the arabinose solutions, the mutarotation decay constant (m=(0.027+/-0.004) min(-1), 20 degrees C) from the ultrasonic measurements almost agrees with that from optical activity observations. For d-fructose the ultrasonic decay constant (m=(0.043+/-0.007) min(-1), 20 degrees C) is smaller than that from rotary polarization (m=0.054 min(-1), 20 degrees C) and dielectric permittivity (m=(0.058+/-0.007) min(-1), 20 degrees C), likely because the latter methods probe parallel pathways in the tautomer equilibrium whereas the former one reflects only one pathway.     

Dielectric study of low-molecular weight mannan triacetate in chloroform

The permittivity ϵ′ and dielectric loss ϵ′' of low-molecular weight mannan triacetate in chloroform in the frequency range 1 kHz to 10 MHz at 20°C are reported. Deviations from a rod-like configuration are suggested to account for the observed behaviour of the dielectric relaxation time as a function of the degree of polymerization.     

A Study of Dielectric Properties of Proteinuria between 0.2 GHz and 50 GHz

This paper investigates the dielectric properties of urine in normal subjects and subjects with chronic kidney disease (CKD) at microwave frequency of between 0.2 GHz and 50 GHz. The measurements were conducted using an open-ended coaxial probe at room temperature (25°C), at 30°C and at human body temperature (37°C). There were statistically significant differences in the dielectric properties of the CKD subjects compared to those of the normal subjects. Statistically significant differences in dielectric properties were observed across the temperatures for normal subjects and CKD subjects. Pearson correlation test showed the significant correlation between proteinuria and dielectric properties. The experimental data closely matched the single-pole Debye model. The relaxation dispersion and relaxation time increased with the proteinuria level, while decreasing with the temperature. As for static conductivity, it increased with proteinuria level and temperature.     

The effect of protein relaxation on charge-charge interactions and dielectric constants of proteins.

The effect of the reorganization of the protein polar groups on charge-charge interaction and the corresponding effective dielectric constant (epsilon(eff)) is examined by the semimicroscopic version of the Protein Dipole Langevin Dipoles (PDLD/S) method within the framework of the Linear Response Approximation (LRA). This is done by evaluating the interactions between ionized residues in the reaction center of Rhodobacter sphaeroides, while taking into account the protein reorganization energy. It is found that an explicit consideration of the protein relaxation leads to a significant increase in epsilon(eff) and that semimicroscopic models that do not take this relaxation into account force one to use a large value for the so-called "protein dielectric constant," epsilon(p), of the Poisson-Boltzmann model or for the corresponding epsilon(in) in the PDLD/S model. An additional increase in epsilon(eff) is expected from the reorganization of ionized residues and from changes in the degree of water penetration. This finding provides further support for the idea that epsilon(in) (or epsilon(p)) represents contributions that are not considered explicitly. The present study also provides a systematic illustration of the nature of epsilon(eff), supporting our previously reported view that charge-charge interactions correspond to a large value of this "dielectric constant," even in protein interiors. It is also pointed out that epsilon(eff) for the interaction between ionizable groups in proteins is very different from the effective dielectric constant, epsilon'(eff), that determines the free energy of ion pairs in proteins (epsilon'(eff) reflects the effect of preoriented protein dipoles). Finally, the problems associated with the search for a general epsilon(in) are discussed. It is clarified that the epsilon(in) that reproduces the effect of protein relaxation on charge-charge interaction is not equal to the epsilon(in) that reproduces the corresponding effect upon formation of individual charges. This reflects fundamental inconsistencies in attempts to cast microscopic concepts in a macroscopic model. Thus one should either use a large epsilon(in) for charge-charge interactions and a small epsilon(in) for charge-dipole interactions or consider the protein relaxation microscopically.     

Observation of unfreezable water in aqueous solution of globule protein by microwave dielectric measurement

A freezing process analyzed by the dielectric method on aqueous solution of albumin has revealed water structure around protein molecule. A relaxation peak due to bound water attached on the protein surface around 100 MHz at room temperature was found. It could be seen commonly in globule proteins. Another peak due to a different kind of unfreezable water was found around 1 GHz at ?6°C. The amount of this water is estimated as 0.36 g water/g protein and in good agreement with that obtained by differential scanning calorimetry and nmr measurements. The water molecules form a shell layer around the protein molecule. © 1995 John Wiley & Sons, Inc.     

Boundary-element calculations for dielectric behavior of doublet-shaped cells

In order to simulate dielectric relaxation spectra (DRS) of budding yeast cells (Saccharomyces cerevisiae) in suspension, the complex polarization factor (Clausius-Mossotti factor) beta for a single cell and the complex permittivity of a cell suspension epsilon(sus)* were calculated with a doublet-shaped model (model RD), in which two spheres were connected with a part of a ring torus, using the boundary element method. The beta values were represented by a diagonal tensor consisting of components beta(z) parallel to the rotation axis (z axis) and beta(h) in a plane (h plane) perpendicular to the axis. The epsilon(sus)* values were calculated from the complex permittivity of the suspending medium epsilon(a)* and the components of beta. The calculation was compared with that of a conventional prolate spheroid model (model CP). It was found that model CP could be used as a first approximation to model RD. However, differences existed in beta(z) between models RD and CP; beta(z) showed three relaxation terms in the case of model RD in contrast with two terms in model CP. Narrowing the junction between the two spheres in model RD markedly decreased the characteristic frequency of one of the relaxation terms in beta(z). This suggests that the structure of the junction can be estimated from DRS. Effects of the shape change from model RD to a two-sphere model (model RD without the junction) were also examined. The behavior of beta(z) in the two-sphere model, the relaxation intensity of which was much lower than model RD, was quite similar to that in a single-sphere model. These simulations were consistent with the experimental observations of the dielectric behavior of the yeast cells during cell cycle progression.     

The influence of cholesterol on head group mobility in phospholipid membranes.

The dielectric dispersion in the MHz range of the zwitterionic dipolar phosphocholine head groups has been measured from 0--70 degrees C for various mixtures of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and cholesterol. The abrupt change in the derived relaxation frequency f2 observed for pure DPPC at the gel-to-liquid crystalline phase transition at 42 degrees C reduces to a more gradual increase of frequency with temperature as the cholesterol content is increased. In general the presence of cholesterol increases the DPPC head group mobility due to its spacing effect. Below 42 degrees C no sudden changes in f2 are found at 20 or 33 mol% cholesterol, where phase boundaries have been suggested from other methods. Above 42 degrees C, however, a decrease in f2 at cholesterol contents up to 20--30 mol% is found. This is thought to be partly due to an additional restricting effect of the cholesterol on the number of hydrocarbon chain conformations and consequently on the area occupied by the DPPC molecules.