Dielectric relaxation measurements of 12 kbp plasmid DNA

The dielectric properties of 12 kbp plasmid DNA have been measured as a function of temperature in the range 5 degrees C to 40 degrees C. Time domain reflectometry was used to obtain dielectric data over the frequency range from 200 kHz to 3 GHz. Values of the frequency dependent polarisability per DNA macromolecule have been determined from the measurements. Possible mechanisms that could account for the dielectric dispersion are also discussed, in particular the counterion fluctuation model of Manning-Mandel-Oosawa.     

Thermographic studies of phantom and canine kidneys thawed by microwave radiation

Whole organs, such as kidneys, must be thawed quickly and uniformly to prevent damage during thawing due to excessive heating. Electromagnetic heating with microwaves thaws the kidneys quickly but frequently produces "hot spots" with heat damage. To study heat damage, phantom gelatin kidneys with different dielectric constants and canine kidneys perfused with 12.5% glycerol, ethylene glycol, or dimethyl sulfoxide before freezing were microwave thawed, and the interior temperature was measured by thermography. Phantom kidneys were thawed free standing and canine kidneys were either free standing or packed in a gel mixture. Both phantom and canine kidneys were split symmetrically and separated with a sheet of Styrofoam to facilitate immediate separation and evaluation of the halves after thawing (approximately 3 sec). All the phantoms, regardless of dielectric properties, had areas less than 0 degrees C or greater than 37 degrees C after thawing. The free-standing canine kidneys and the gel-packed ethylene glycol-perfused kidneys had frozen areas (less than 0 degrees C) and hot spots (greater than 37 degrees C). However, glycerol- and dimethyl sulfoxide-perfused kidneys packed in gel before thawing had no areas less than 0 degrees C or greater than 37 degrees C. Altering the geometry from a "kidney shape" to a cylindrical shape with increased volume improved the uniformity of thawing and was more effective than altering the dielectric constant over the range evaluated.     

Temperature-dependent dielectric properties of slightly hydrated horn keratin

With an aim to reveal the mechanism of protein-water interaction in a predominantly two phase model protein system this study investigates the frequency and temperature dependence of dielectric constant epsilon' and loss factor epsilon' in cow horn keratin in the frequency range 30 Hz to 3 MHz and temperature range 30-200 degrees C at two levels of hydration. These two levels of hydration were achieved by exposing the sample to air at 50% relative humidity (RH) at ambient temperature and by evacuating the sample for 72 h at 105 degrees C. A low frequency dispersion (LFD) and an intermediate frequency alpha-dispersion were the two main dielectric responses observed in the air-dried sample. The LFD and the high frequency arm of the alpha-dispersion followed the same fractional power law of frequency. Within the framework of percolation cluster model these dispersions, respectively have been attributed to percolation of protons between and within the clusters of hydrogen-bonded water molecules bound to polar or ionizable protein components. The alpha-dispersion peak, which results from intra-cluster charge percolation conformed to Cole-Cole modified Debye equation. Temperature dependence of the dielectric constant in the air-dried sample exhibited peaks at 120 and 155 degrees C which have been identified as temperatures of onset of release of water bound to polar protein components in the amorphous and crystalline regions, respectively. An overall rise in the permittivity was observed above 175 degrees C, which has been identified as the onset of chain melting in the crystalline region of the protein.     

Microwave properties of cryoprotectants

The values of the dielectric constant and of the loss tangent for pure samples of DMSO, ethylene glycol, and glycerol were determined over the temperature range of + 15 to −70 °C. An operating frequency range of 1.45 to 1.55 GHz was used, allowing direct application of the results of both 0.915 and 2.450 GHz studies. Strong temperature dependencies were found, with peaks and irregularities occuring at subfreezing temperatures. In order to design a suitable cryoprotective system for the long term preservation of whole organs, the effect of cryoprotectant concentration on microwave properties must be known.     

Microwave driven wood liquefaction with glycols

Wood liquefaction with glycols using p-toluenesulfonic acid as the catalyst was carried out under microwave heating. With rapid heating and temperatures in the 190–210 °C range complete liquefaction was achieved in 7 min. Liquefaction efficiency was dependent on the choice of glycol. Simple glycols such as ethylene glycol and propylene glycol were more effective than higher analogues. The use of glycerol in mixtures with glycols showed a synergistic effect. Size exclusion chromatography was used to follow the gradual emergence of liquefaction products in solution as well as the recondensation products that start forming early in the reaction and precipitate from solution when molar masses of approx. 1 × 10⁴ g/mol are reached.     

Effects of small neutral osmolytes on the supercoiling free energy and intrinsic twist of p30delta DNA

Both theory and experiments are employed to investigate the effects of small neutral osmolytes on the average intrinsic twist (l0), the torsion and bending elastic constants, and the twist energy parameter (ET) that governs the supercoiling free energy. The experimental data for ethylene glycol and acetamide at 37 degrees C suggest, and are interpreted in terms of, a model wherein the DNA exhibits an equilibrium between two distinct conformational states that possess different numbers of bound water molecules and exhibit different intrinsic twists and torsion and bending elastic constants. Expressions are derived to relate the effective ET and l0 to the equilibrium constant, water activity (aw), and number (n) of bound water molecules released per cooperative domain undergoing the two-state transition. The variations of l0 and ET with -ln(aw) are similar for acetamide and ethylene glycol at 37 degrees C. Fitting the theory to those data yields the range n = 103-125 for ethylene glycol and n = 71-113 for acetamide, depending on the assumed value of ET for the dehydrated state. The cooperative domain size of the two-state transition is estimated to exceed about 25-30 base pairs (bp). Between 0 and 19.4 w/v % ethylene glycol, the torsion elastic constant, measured by time-resolved fluorescence polarization anisotropy (FPA), increases by 1.37-fold, whereas the measured ET decreases by 1.15-fold over that same range. The implied decrease in bending rigidity over that range is by a factor of about 0.7. The variations of l0 and ET with increasing -ln(aw) due to added ethylene glycol at 37 degrees C are far smaller than the corresponding variations observed previously at 14 and 15 degrees C. However, at 21 degrees C, upon adding either ethylene glycol or acetamide, l0 and ET initially decline steeply with increasing -ln(aw), with slopes possibly comparable to those seen at 14 and 15 degrees C, but then flatten out and follow curves similar to those at 37 degrees C. Possible origins of such mixed behavior are discussed. The effects of betaine at both 37 and 21 degrees C differ qualitatively and quantitatively in various respects from those of ethylene glycol and acetamide. Upon adding sucrose, l0 initially jumps to higher plateaus at both 37 and 21 degrees C, but its effects on ET cannot be reliably assessed, due to the limited range of -ln(aw).     

Surface areas and packing constraints in POPC C (12)EO (n) membranes. A time-resolved fluorescence study

The surface area occupied by nonionic detergents of the type C(12)EO(n) (n = 1-8) in POPC C (12)EO (n) mixed membranes was studied by means of time-resolved resonance energy transfer (RET) between the fluorescent probe molecules NBD-PE and rhodamine-PE. The area data were interpreted within the frame of Israelachvili's concept of packing constraints yielding the critical packing parameter, f, as a measure of the asymmetry of the molecular shape of the membrane constituents. The asymmetry of the molecular shape of the detergent increases with the ethylene oxide chain length and correlates with the potency of the detergent to solubilize the bilayers and the reduction of the DPH order parameter. For n = 1-3, the membrane surface was found to expand by 0.25-0.30 nm(2) per incorporated C(12)EO(n) molecule. This value corresponds to the cross section of one hydrocarbon chain in liquid-crystalline phases. On increasing n from n = 4 to n = 8 the net area per detergent molecule increases from 0.43 nm(2) to 1.16 nm(2). These surface requirements are consistent with a disordered, coiled conformation of the EO-chains hydrated with up to two water molecules per ethylene oxide unit. For n > 5 the limiting mole fraction of the bilayer saturation was deduced from the f-data in the two-component bilayer. DPH and NBD-PE fluorescence lifetime data are discussed to give an indication of the accessibility of the probe environment to water molecules.     

Thermal stability of proteins in the presence of poly(ethylene glycols)

Thermal unfolding of ribonuclease, lysozyme, chymotrypsinogen, and beta-lactoglobulin was studied in the absence or presence of poly(ethylene glycols). The unfolding curves were fitted to a two-state model by a nonlinear least-squares program to obtain values of delta H, delta S, and the melting temperature Tm. A decrease in thermal transition temperature was observed in the presence of poly(ethylene glycol) for all of the protein systems studied. The magnitude of such a decrease depends on the particular protein and the molecular size of poly(ethylene glycol) employed. A linear relation can be established between the magnitude of the decrease in transition temperature and the average hydrophobicity of these proteins; namely, the largest observable decrease is associated with the protein of the highest hydrophobicity. Further analysis of the thermal unfolding data reveals that poly(ethylene glycols) significantly effect the relation between delta H degrees of unfolding and temperature for all the proteins studied. For beta-lactoglobulin, a plot of delta H versus Tm indicates a change in slope from a negative to a positive value, thus implying a change in delta Cp in thermal unfolding caused by the presence of poly(ethylene glycols). Results from solvent-protein interaction studies indicate that at high temperature poly(ethylene glycol) 1000 preferentially interacts with the denatured state of protein but is excluded from the native state at low temperature. These observations are consistent with the fact that poly(ethylene glycols) are hydrophobic in nature and will interact favorably with the hydrophobic side chains exposed upon unfolding; thus, it leads to a lowering of thermal transition temperature.     

Microwave dielectric relaxation in muscle. A second look.

The dielectric permittivity and conductivity of muscle fibers from the giant barnacle, Balanus nubilus, have been measured at 1, 25, and 37 degrees C, between 10 MHz and 17 GHz. The dominant microwave dielectric relaxation process in these fibers is due to dipolar relaxation of the tissue water, which shows a characteristic relaxation frequency equal to that of pure water, ranging from 9 GHz (1 degree C) to 25 GHz (37 degree C). The total permittivity decrease, epsilon 0 -- epsilon infinity, due to this process accounts for approximately 95% of the water content of the tissue; thus, the major fraction of tissue water is dielectrically identical to the pure fluid on a picosecond time scale. A second dielectric process contributes significantly to the tissue dielectric properties between 0.1 and 1--5 GHz, and arises in part form Maxwell-Wagner effects due to the electrolyte content of the tissue, and in part from dielectric relaxation of the tissue proteins themselves.     

The structure of water absorbed in collagen. I. The dielectric properties

The dielectric constant and the loss factor of water in collagen are measured for various water, NaCl, and HCl contents at frequencies ranging from 10² to 10⁵ Hz and at temperatures ranging from ?70° to +23°C. For all measurements, both the dielectric constant and the loss decrease monotonically as the frequency increases, or the temperature decreases; the absence of a maximum in the loss curves as a function of temperature and frequency indicates an extremely broad spectrum of relaxation times. By shifting the curves obtained for the dielectric constant and the loss factor along the log–frequency axis, all data, obtained at different temperatures, can be represented on master curves valid for 23°C. In order to explain these results, water molecules are assumed to be hydrogen bonded to each other in long chains. All water molecules in a chain can, cooperatively, be oriented in two different directions along the channel, resulting in large, reversible, dipole moments. These chains are not rigid, but are flexible liquid-like structures. Diffusion of chains as entities is assumed to be the rate-limiting step for dipole reorientation. Although the rate of diffusion decreases inversely proportional to chain length, the activation energy is independent of chain length. At lower temperatures, diffusion becomes slower, until at the glass point, approximately ?100°C, it ceases.     

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 effect of different methods of cross-linking of collagen on its dielectric properties

This paper reports on the effect of different methods of collagen cross-linking on its dielectric properties. In order to obtain collagen-hyaluronic acid (HA) scaffolds, collagen was first dehydrated by a combination of thermal and vacuum drying (DHT) and then treated with the chemical reagent carbodiimide (EDC/NHS) for final cross-linking. The measurements of the relative permittivity varepsilon' and the dielectric loss varepsilon' for all materials were carried over the frequency range of 10 Hz-100 kHz and at temperatures from 22 to 260 degrees C. The results for these samples reveal distinct relaxation processes at low temperatures, below 140 degrees C and at higher temperatures as broad peak around 230 degrees C. The first and second relaxation are associated with changes in the secondary structure of collagen accompanied by the release of water and with the denaturation of dry collagen, respectively. The influence of cross-linking on the permittivity of collagen is significant over the entire temperature range.     

Molecular mobility of elastin: effect of molecular architecture

The thermal and dielectric properties of elastin and two soluble derivatives (kappa-elastin and derived elastin peptides from enzymatic elastolysis) were investigated in the freeze-dried state in a wide temperature range (from -180 to +220 degrees C). The glass transition of these amorphous proteins was studied by differential scanning calorimetry (DSC). The dielectric relaxations of both proteins were followed by thermally stimulated currents (TSC), an isochronal dielectric spectrometry running at variable temperature, analogous to a low-frequency spectroscopy (10(-3)-10(-2) Hz) and by dynamic dielectric spectroscopy (DDS), performed isothermally with the frequency varying from 10(-2) to 3 x 10(6) Hz. The combination of TSC and DDS experiments and the determination of the activation parameters of the relaxation times inform about the molecular mobility of the proteins, both in the glassy state and in the liquid state. Major differences between the relaxation behavior of elastin and its soluble derivatives have been discussed and correlated with the molecular architecture of the proteins.     

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.     

Dielectric spectroscopy of Tobacco Mosaic Virus

The dielectric properties of the Tobacco Mosaic Virus (TMV) have been measured using time domain dielectric spectroscopy (TDDS) in the temperature range from 1 to 40 degrees C. A single dielectric dispersion is observed in the MHz range. The activation energy of the process is found to be in the range 1-2 kcal/mol. The experimental data could not be completely accounted for by current theoretical models, but evidence indicates that the dielectric loss arises from polarisation of charge on and around the virus.     

Temperature dependence of the microwave properties of aqueous solutions of ethylene glycol between +15 degrees C and -70 degrees C.

The values of the dielectric constant and of the loss tangent for samples of 0 m (distilled H₂O), 1 m, 2 m, 3 m, 4 m, 5 m, 10 m, and 100% ethylene glycol were determined over the temperature range of +15 °C to ?70 °C. An operating frequency of 1.40 GHz to 1.55 GHz was used, allowing the results to be applied directly to both 0.915 GHz and 2.450 GHz studies. Strong temperature and concentration dependencies were found; low concentration solutions tended to behave similarly to water, while higher concentration solutions were more independent. Peak values and discontinuities occurred at different temperatures, depending on concentration. Five molar ethylene glycol was indicated as a near optimum concentration based on toxicity, cryoprotection, and microwave power absorption considerations. A study of blends of cryoprotectants is suggested.     

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.     

Effect of cryoprotectors on the structural state of liposomes cooled to minus 25 degrees C

Cryoprotectors (propylene glycol), ethylene glycol, polyethylene glycol-1500 and dimethyl sulphoxide) are studied for their effect on permeability of liposomes for incorporated molecules of 5,5-dithiobis-2-nitrobenzoic acid (DTNB) under cooling within a temperature range from 0 degree C to -25 degrees C. A similarity is found in the way of ethylene glycol and propylene glycol, dimethyl sulphoxide and polyethylene glycol-1500 effect on the liposome permeability way. Cooling in the presence of ethylene glycol and propylene glycol causes changes in liposome permeability with a local maximum at -18 degrees C. In the medium with 2M NaCl and ethylene glycol, liposomes were resistant to cooling. Dimethyl sulphoxide and polyethylene glycol-1500 induced a two-phase kinetics of changes in liposome permeability, the first phase being within the 0 = -9 degrees C and the second--within -9--25 degrees C temperature ranges. The found differences are supposed to be associated with the effect of the cryoprotective compounds on the lipid crystallization in a lower-temperatures range.     

Dielectric properties of muscle and liver from 500 MHz–40 GHz

Dielectric properties are the most important parameters determining energy deposition when biological tissues are exposed to radio frequency and microwave fields. Energy absorption is determined by the specific absorption rate (SAR). SAR distributions can be computed accurately only if the complex relative permittivity of the target tissue is known to a sufficiently high accuracy, and currently there is a lack of data on the dielectric properties of biological tissues at high frequencies. In this study, tissue dielectric properties are measured using an open-ended coaxial probe technique from 500 MHz up to 40 GHz. We present dielectric data for ex vivo bovine and porcine muscle and liver tissues at 37 °C. One-pole Cole–Cole model is used to fit the measured data as a function of frequency and the dispersion parameters are presented. This data is supported by an accurate study on reference liquids such as methanol and ethanediol.     

Temperature dependence of the dielectric properties of blood

The aim of the work was to investigate the temperature effect in physiological range on the dielectric properties of a fish (Cyprinus carpio) blood. By applying an empirical non-damaging method and statistical analysis of the dielectric data, it is observed that a heating of carp blood induces an almost linear value variation of the electrical conductivity and permittivity of the intracellular matter of carp red blood cells. The dielectric data, however, reveal anomalous behaviour for conductivity and permittivity of the interior of carp erythrocytes at 23 degrees C and 23 degrees, 37 degrees C, respectively and for both volume fraction and dielectric loss factor tg delta at 30 degrees, 35 degrees, 37 degrees C. For the presented dielectric parameters the temperature coefficient and the Arrhenius activation energy were estimated. Moreover, this work led to conclusion that the changes of the volume fraction of carp erythrocytes induce corresponding variations of the maximum of the dielectric loss factor tg delta determined for a whole blood.