Relaxation dynamics of liposomes in an aqueous solution.

The gel-liquid crystal phase transition has been studied by the temperature and frequency dependent dielectric relaxation behavior of liposomes in an aqueous solution (40 g L(-1) DPPC-water mixture). Four relaxation processes were observed in the frequency range from 40 Hz to 30 GHz which were ascribed to different molecular mechanisms, related to the structural units of the system. The gel-liquid crystal phase transition was also described very accurately from the temperature-dependent dielectric relaxation strength, relaxation time and symmetric shape parameter of the relaxation functions obtained from the fitting procedure. Relaxation process 3, obtained from the dielectric fitting procedure, was confirmed by dielectric modulus analysis. A comparison of the lipid membrane with non-biological systems like liquid crystals was performed. It was determined that the lipid membrane has a ferroelectric liquid crystal like behavior. Process 3 is comparable to the soft mode relaxation process observed in ferroelectric liquid crystals which was detected close to the smectic-C*-smectic-A phase transition. Differential scanning calorimetry was also used to confirm the gel-liquid crystal phase transition of this mixture.

The glass transition and dielectric secondary relaxation of fructose-water mixtures.

Broad-band dielectric measurements for fructose-water mixtures with fructose concentrations between 70.0 and 94.6 wt% were carried out in the frequency range of 2 mHz to 20 GHz in the temperature range of -70 to 45 degrees C. Two relaxation processes, the alpha process at lower frequency and the secondary beta process at higher frequency, were observed. The dielectric relaxation time of the alpha process was 100 s at the glass transition temperature, T(g), determined by differential scanning calorimetry (DSC). The relaxation time and strength of the beta process changed from weaker temperature dependences of below T(g) to a stronger one above T(g). These changes in behaviors of the beta process in fructose-water mixtures upon crossing the T(g) of the mixtures is the same as that found for the secondary process of water in various other aqueous mixtures with hydrogen-bonding molecular liquids, polymers, and nanoporous systems. These results lead to the conclusion that the primary alpha process of fructose-water mixtures results from the cooperative motion of water and fructose molecules, and the secondary beta process is the Johari-Goldstein process of water in the mixture. At temperatures near and above T(g) where both the alpha and the beta processes were observed and their relaxation times, tau(alpha) and tau(beta), were determined in some mixtures, the ratio tau(alpha)/tau(beta) is in accord with that predicted by the coupling model. Fixing tau(alpha) at 100 s, the ratio tau(alpha)/tau(beta) decreases with decreasing concentration of fructose in the mixtures. This trend is also consistent with that expected by the coupling model from the decrease of the intermolecular coupling parameter upon decreasing fructose concentration.

Broadband dielectric study of dynamics of polymer and solvent in poly(vinyl pyrrolidone)/normal alcohol mixtures.

Broadband dielectric measurements of poly(vinyl pyrrolidone) (PVP)-monohydroxyl alcohol mixtures of various normal alcohols with the number of carbon atoms per molecule ranging from 1 to 9 were made in the frequency range of 20 Hz to 20 GHz at 25 degrees C. Two relaxation processes due to the reorientation of dipoles on the PVP and alcohol molecules were observed. The relaxation process at frequencies higher than 100 MHz is the primary process of alcohols, and that at frequencies lower than 10 MHz is attributed to the local chain motion of PVP. For mixtures of alcohol molecules that are smaller than propanol, the relaxation time of the alcohol increases with increasing PVP concentration, whereas for mixtures of alcohol molecules larger than butanol, the relaxation time of the alcohol decreases with increasing PVP concentration. The increase in the density of hydrogen-bonding sites upon the addition of PVP reduces the relaxation time of alcohol in the mixture, and vice versa. The relaxation time of the local chain motion of PVP increases with PVP concentration and solvent viscosity. Different time scales of the molecular motions of polymer and solvent coexist in homogeneous mixtures with hydrogen-bonded polar solvent and polymer.

Broadband dielectric study of dynamics of poly(vinyl pyrrolidone)-ethylene glycol oligomer blends.

Broadband dielectric measurements for blends of poly(vinyl pyrrolidone) (PVP) and ethylene glycol oligomer (EGO) from 0 to 40 wt % PVP were carried out at 25 degrees C in the frequency range from 20 Hz to 20 GHz. The EGOs used in this study were ethylene glycol (EG), diethylene glycol (2EG), and PEG400 (MW = 400). For the PVP-EG, -2EG, and -PEG400 blends, relaxation processes caused by the motion of EGO in the GHz range and the micro-Brownian motion of the PVP chain at 10 kHz-1 MHz were observed. Although the PVP-EGO blend is miscible, relaxation processes caused by the molecular motion of EGO and the local chain motion of PVP were observed individually. The relaxation time of the local chain motion of PVP showed a strong PVP concentration dependence and a solvent viscosity dependence, which are similar to those reported so far for the solutions in nonpolar solvents.

Broadband dielectric study of the glass transition in poly(ethyleneglycol)-water mixture.

We performed broadband dielectric measurements of a polyethyleneglycol-water mixture in the frequency range between 10 GHz and 1 microHz and the temperature range between 300 and 133 K. One relaxation process is observed throughout the whole temperature range. The temperature dependence of the relaxation time clearly obeys the Vogel-Fulcher law above 183 K, and the Arrhenius law below 183 K. This observed relaxation process is the secondary process, and the primary process related to the glass transition is masked by the low-frequency ionic contribution below 183 K. The glass transition concerned with the masked primary process leads to the Vogel-Fulcher to Arrhenius transition of the secondary process.

Globule-coil transition of denatured globular protein investigated by a microwave dielectric technique.

A mechanism for the gel-glass transition of denatured globular protein has been explained from the viewpoint of the globule-coil transition with microwave dielectric measurements using a time domain reflectometry (TDR) method. Boiled egg white, which is an aqueous gel of egg white prepared by heat treatment at 100 degrees C, becomes a glass on drying. In the gel state, the relaxation processes corresponding to the orientation of bulk water and the micro-Brownian motion of peptide chains of denatured protein were observed around 10 GHz and 10 MHz, respectively. When the gel-glass transition occurred, the relaxation strength for bulk water decreased rapidly as evaporation and breaking of water structure occurred. Simultaneously, the relaxation strength for micro-Brownian motion increased abruptly, as the structure of globular protein varied from globule state to coiled state. It is considered that the protein molecule spreads out and takes up a coiled state by reductions of hydrophobic and hydrophilic interactions of the globular protein. These reductions occur through a decrease in the amount of water.

Molecular dynamics of hinge-bending motion of IgG vanishing with hydrolysis by papain.

We have performed dielectric relaxation measurements via a time domain reflectometry (TDR) method to study dynamic behaviors of the segmental flexibility of immunoglobulin G (IgG) in aqueous solution without antigen binding. In general, an intermediate relaxation process due to bound water is observed around 100 MHz at 25 degrees C for common proteins between two relaxation processes due to overall rotation and reorientation of free water. However, the intermediate process observed around 6 MHz for IgG was due to both bound water and hinge-bending motion. The apparent activation energy of 33 kJ/mol was larger than 27 kJ/mol for only bound water, and the relaxation strength was about five times as large as expected for bound water. The shape of the relaxation curve was very broad and asymmetric. These characteristic differences arising from the hinge-bending motion of IgG disappeared for fragments decomposed from IgG hydrolyzed by papain, since the hinge-bending motion did not exist in this case. We have separated the relaxation processes due to hinge-bending motion and bound water for IgG and obtained the Fab-Fab angle of IgG as about 130 degrees by Kirkwood's correlation parameter and the activation energy of 34 kJ/mol for hinge-bending motion.

Microwave dielectric analysis of human stratum corneum in vivo.

The dielectric properties of the human skin stratum corneum (SC) in the frequency range higher than 107 Hz are not well understood because of the difficulty in selective scanning of the SC area in vivo. The present study was carried out to make clear factors responsible for the dielectric properties using a measuring system specially developed for the study of SC [S. Naito, M. Hoshi, S. Mashimo, Anal. Biochem. 251 (1997) 163-172]. We found that the dielectric properties of SC can be expressed by the linear combination of two relaxation processes and d.c. conduction. The faster relaxation is that of free water. The slower relaxation and d. c. conduction were analyzed using a model assuming interfacial polarization between dissimilar materials. We concluded that the polarization is the origin of the slower relaxation process because the experimental data could be well interpreted according to the above mechanism. We also concluded that the polarization of swelled SC locates at the interface between SC cells and the intercellular lipid layer, or at the interface between the lipophilic and the hydrophilic part of the lamellar structured intercellular lipid layer.

Microwave dielectric study on hydration of moist collagen.

Two dielectric relaxation peaks were found in moist collagen by the time domain reflectometry. The low-frequency peak around 100 MHz moves little as the water content is varied. Its relaxation strength depends on the content and vanishes for completely dried collagen. This process is concluded to be due to water molecules strongly bound to the tropocollagen. Amount of the bound water is estimated as 0.12 g water/g collagen. Twenty-one water molecules are bound to one repeat of the triple helix. The existence of stringlike water chains is suggested. If the water content is less than 0.5 g water/g collagen, the high frequency peak locates between those of bound and bulk water. Water among the tropo-collagen is weakly bound to the collagen. In the higher region it does not change much with the content, being close to that of bulk water. The bulk water appears in this region.

Dielectric study on hydration of B-, A-, and Z-DNA.

Dielectric relaxation peak due to bound water was found around 100 MHz in poly(dG-dC).poly(dG-dC) and calf thymus DNA in water-ethanol mixtures with NaCl buffer. Relaxation time and strength show a transition for poly(dG-dC).poly(dG-dC) at an ethanol composition Cw = 0.45 (w/w) where the structural transition from B- to Z-DNA takes place. It has been suggested that the transition is caused by removal of the bound water molecules preferentially from the phosphate groups. If the bound water molecules are removed equally from the phosphate groups and the grooves, the structural transition from B to A takes place. By analogy with hydration of tropocollagen, it was found that 19 water molecules per one nucleotide are at least necessary to keep B-DNA. Thirteen molecules are bound to A-DNA and 9 molecules to Z-DNA. Stringlike multimers are proposed as available structures of the bound water.