Arrhenius Plot Of Temperature Dependence Research Articles

Investigation on structural, dielectric and ferroelectric properties of samarium-substituted BiFeO3–PbTiO3 composites

The polycrystalline samples of 0.8BiSmxFe[Formula: see text]O3–0.2PbTiO3 ([Formula: see text] and 0.20) were prepared by using the conventional solid-state reaction technique and sintered at high temperature (850[Formula: see text]C). X-ray diffraction (XRD) confirms the distorted rhombohedral crystal structure for all the composites at room temperature. The surface morphology was checked by field-emission scanning electron microscope (FESEM) technique and homogeneous mixing of the components was confirmed by energy-dispersive analysis of X-ray (EDAX). The detailed study of dielectric properties of the composites reveals an increasing nature of dielectric constant ([Formula: see text]) and loss tangent (tan[Formula: see text]) with the increase of temperature due to thermal activation. The Arrhenius plots of temperature dependence of AC conductivity yield the activation energy within the material at high-temperature range. The ferroelectric study shows that the remnant polarization decreases with the increase of Samarium (Sm) concentration.

Nucleic acid spin labeling study of interaction between polyadenylic acid: Polyuridilic acid duplex and egg phosphatidylcholine vesicles. Involvement of terminal and internal nucleotides and sugar-phosphate backbone

Model DNA-membrane contacts were studied in the system containing polyadenylic acid (polyA): polyuridilic acid (polyU) duplex and egg phosphatidylcholine (PC) vesicles without or in the presence of MgCl2. PolyU containing O-(1-oxyl-2,2,5,5-tetramethylpyrroline-3-carbonyl) spin label at 2′-OH moiety was used for spin labeling study of nucleic acid-phospholipid interactions. For polyA labeled with the same nitroxyl radical EPR spectra from spin labels attached at terminal and at internal nucleotide units contribute into the EPR spectrum of d.s. polynucleotide without or in the presence of egg PC vesicles and Mg ions. Internal spin labels are more sensitive to the interaction with PC-MLV than terminal ones. The complexation between s.s. polynucleotide and PC-MLV was shown. The values of spin labels’ melting temperature of polyA: SL-polyU duplex at 1 mM MgCl2 reflect the changes in rotational mobility of terminal spin labels connected with duplex→triplex transition. Arrhenius plots of temperature dependence of EPR spectra parameters prove that ribose moieties of sugarphosphate backbone are involved into the interaction between polynucleotide duplex and phospholipid bilayer. Egg PC vesicles demonstrate stabilizing effect on polyA: polyU duplex at 1 mM of Mg2+ and destabilizing effect at 5 mM Mg2+.

Proton permeability and lipid dynamics of gastric and duodenal apical membrane vesicles

The passive proton permeability (Pnet) of apical membrane vesicles from rabbit parietal cells (gastric) and duodenal and renal cortical brush-border membranes (BBM) was determined by acridine orange fluorescence quenching. Values of Pnet were found to be gastric (4 x 10(-4) cm/s) less than duodenal (10(-3) cm/s) much less than renal (10(-2) cm/s). Arrhenius plots of the temperature profile of proton permeation of gastric vesicles was linear, whereas that of duodenal BBM displayed a discontinuity at 30-33 degrees C. Alcohols (octyl, benzyl, ethyl) increased Pnet in a concentration-dependent manner, with efficacy related to their oil-water partition coefficients. In a parallel series of experiments, structural parameters of the vesicle membrane lipids (fluidity) were monitored from both the steady-state and time-resolved fluorescence anisotropy of diphenylhexatriene. Fluidity of the membranes was unrelated to Pnet (renal congruent to duodenal less than gastric). Gastric vesicles demonstrated a linear Arrhenius plot of temperature dependence for fluidity, whereas duodenal BBM demonstrated a discontinuity. Membrane fluidity of gastric and duodenal vesicles was increased by alcohols, with the same potency as for Pnet, and these two variables were significantly correlated after perturbation with alcohols. Thus the fluidity of the lipid bilayer is not the major determinant of Pnet, but alteration of its structural parameters, as reflected by fluidity, produces parallel changes in Pnet.

Evidence for electrogenic sodium pumping in the ductal epithelium of rabbit salivary gland and its relationship with (Na ++K +)-ATPase.

The temperature dependence of the transepithelial potential difference (PD) of the main duct of the submaxillary gland has been measured during in vitro perfusion studies. The magnitude of the PD depends strongly on the anion composition of the perfusing and bathing fluids. The following combinations of perfusion and bathing fluids, respectively, were used: (1) Na 2SO 4/NaCl, (2) Na 2SO 4/Na 2SO 4, (3) NaCl/NaCl, (4) NaCl/Na 2SO 4. The mean transepithelial potential differences at 35 °C with these four sets of conditions were, respectively: 144, 148, 10 and −15 mV, serosal side positive with respect to lumen. From the data obtained it was possible to construct Arrhenius plots of temperature dependence of the PD for the four sets of experimental conditions. They all show a breakpoint between 16 and 19 °C. The apparent activation energies in the four situations above the breakpoint are 4.2, 1.4, 12.0 and 10.6 kcal/mol, respectively. Below the breakpoint they are 29.9, 37.5, 29.0 and 31.3 kcal/mol, respectively. The rapid change in the PD as a function of temperature (which can also be achieved by the addition of ouabain), the effects of the removal of K + on the serosal side on the PD, the decrease in the PD after the addition of ouabain or CN −, and the activation energies and breakpoints all lead to the conclusion that a large part of the PD is caused by an electrogenic sodium pump which is very probably the enzyme (Na ++K +)-ATPase. When the duct is perfused with Na 2SO 4 we find, above the breakpoint in the Arrhenius plots, alower activation energy than is found when perfusing with NaCl.