Polyelectrolyte complexes of glycol chitosan with some mucopolysaccharides: Dielectric properties and electrical conductivity

The dielectric properties, DC electrical conductivity, and I-V characteristics of thin films of polyelectrolyte complexes formed by glycol chitosan (GlChi) with mucopolysaccharides chondroitin sulfate A (CSA), chondroitin sulfate C (CSC), and hyaluronic acid (HA) have been studied at different temperatures. The dielectric constant and the loss factor were measured at frequencies ranging from 1 to 100 kHz at all temperatures. The behavior of GlChi–CSA and GlChi–CSC complexes resembles that of the GlChi–dextran sulfate complex reported earlier. The GlChi–HA complex behaves differently and is similar to the GlChi–alginic acid complex reported [Srinivasan, R. & Kamalam, R. (1982) Biopolymers 21 , 251–263, 265–275].     

Conductivity and photoconductivity of NaDNA in the solid state

The d. c. conductivity of five samples of NaDNA in dry state was investigated. All specimens show similar behavior, with specific resistivity at 40°C of the order of 10¹³–10¹⁴ ohm-cm and an energy gap of E_c = 2.04–2.25 eV. Based on the Eley's model for conductivity mechanism, the possibility of conservation of an ordered structure in the dry state (temperature range 20–80°C) is discussed. This is ascribed to the interaction of electron systems of individual bases. From the activation energy values it may be estimated that 17–19 π-electrons take part in the interaction. Photoconductivity measurements indicated activation energies E_f of 0.88–0.96 eV in the visible region.     

Chemical enthalpy-entropy compensation effect in the hydrolysis of p-nitrophenyl carboxylates catalyzed by alkaline mesentericopeptidase

The temperature dependence of the hydrolysis of p-nitrophenyl carboxylates with general formula H(CH₂)_nCOOC₆H₄NO₂ catalyzed by alkaline mesentericopeptidase has been studied (n varying from 1 to 7, temperature range 2–30°C, pH 8.80, 5 vol% dimethylsulfoxide). The activation parameters of the deacylation step depend on the length of the hydrophobic side chain of the substrate molecule ( , , and decrease by 2.0 kcal/mol, 4.9 kcal/mol, and 10 eu, respectively, as the length of the acyl carbon chain increases from n = 1 to n = 4). The following criteria were applied to establish a chemical enthalpy-entropy compensation effect: (a) Exner's plot of log vs : (b) Petersen's plot of log, k/T vs 1/T; (c) Exner's statistical treatment in coordinates log k vs 1/T; (d) according to Krug et al. (ΔH^≠ vs ΔG_Thm^≠). By use of all the above-mentioned criteria the existence of a chemical enthalpy-entropy compensation effect was proved with an isokinetic temperature β of about 470°K, which is significantly higher than the average experimental temperature.     

Slow Organic‐to‐Inorganic Sub‐Lattice Thermalization in Methylammonium Lead Halide Perovskites Observed by Ultrafast Photoluminescence

Carrier dynamics in methylammonium lead halide (CH₃NH₃PbI_3–xCl_x) perovskite thin films, of differing crystal morphology, are examined as functions of temperature and excitation wavelength. At room temperature, long‐lived (>nanosecond) transient absorption signals indicate negligible carrier trapping. However, in measurements of ultrafast photoluminescence excited at 400 nm, a heretofore unexplained, large amplitude (50%–60%), 45 ps decay process is observed. This feature persists for temperatures down to the orthorhombic phase transition. Varying pump photon energy reveals that the fast, band‐edge photoluminescence (PL) decay only appears for excitation ≥2.38 eV (520 nm), with larger amplitudes for higher pump energies. Lower photon‐energy excitation yields slow dynamics consistent with negligible carrier trapping. Further, sub‐bandgap two‐photon pumping yields identical PL dynamics as direct absorption, signifying sensitivity to the total deposited energy and insensitivity to interfacial effects. Together with first principles electronic structure and ab initio molecular dynamics calculations, the results suggest the fast PL decay stems from excitation of high energy phonon modes associated with the organic sub‐lattice that temporarily enhance wavefunction overlap within the inorganic component owing to atomic displacement, thereby transiently changing the PL radiative rate during thermalization. Hence, the fast PL decay relates a characteristic organic‐to‐inorganic sub‐lattice equilibration timescale at optoelectronic‐relevant excitation energies.     

Optical property of bovine plasma albumin between 2 and 82 eV.

The optical constants of bovine plasma albumin in the form of a dry solid film have been determined in the 2–82 eV region of photon energy. The extinction coefficient k was obtained by transmission measurements on thin films on a calcium fluoride substrate and on ultrathin films of polystyrene supported by mesh screen. The refractive index n was determined by a Kramers–Kronig analysis using the measured values of k. The complex dielectric function ε and the energy-loss function ?Im(1/ε) for charged particles were derived from the data of n and k. The result for k exhibit, in addition to the well-known absorptions at 4.4, 5.5, and 6.4 eV, a small peak at 7.6 eV, a shoulder around 9.7 eV, and a strong peak at 14.0 eV. A prominent peak at 22.7 eV in the energy-loss function exhibits a large degree of collective nature.     

Electrical conduction behavior of organic light‐emitting diodes using fluorinated self‐assembled monolayer with molybdenum oxide‐doped hole transporting layer

The electrical conductivity behavior of a fluorinated self‐assembled monolayer (FSAM) of a molybdenum oxide (MoOx)‐doped α‐naphthyl diamine derivative (α‐NPD) in organic light‐emitting diodes (OLEDs) was investigated. The current density of the MoOx‐doped α‐NPD/FSAM device was proportional to its voltage owing to smooth carrier injection through the FSAM and the high carrier density of its bulk. The temperature‐dependent characteristics of this device were investigated. The current density–voltage characteristics at different temperatures were almost the same owing to its very low activation energy. The activation energy of the device was estimated to be 1.056 × 10^?2 [eV] and was very low due to the inelastic electron tunneling of FSAM molecules. Copyright © 2014 John Wiley & Sons, Ltd.     

Microsolvation effect and hydrogen-bonding pattern of taurine-water TA-(H2O)n (n = 1-3) complexes

The microsolvation of taurine (TA) with one, two or three water molecules was investigated by a density functional theory (DFT) approach. Quantum theory of atoms in molecules (QTAIM) analyses were employed to elucidate the hydrogen bond (H-bond) interaction characteristics in TA-(H₂O)_n (n = 1–3) complexes. The results showed that the intramolecular H-bond formed between the hydroxyl and the N atom of TA are retained in most TA-(H₂O)_n (n = 1–3) complexes, and are strengthened via cooperative effects among multiple H-bonds from n = 1–3. A trend of proton transformation exists from the hydroxyl to the N atom, which finally results in the cleavage of the origin intramolecular H-bond and the formation of a new intramolecular H-bond between the amino and the O atom of TA. Therefore, the most stable TA-(H₂O)₃ complex becomes a zwitterionic complex rather than a neutral type. A many-body interaction analysis showed that the major contributors to the binding energies for complexes are the two-body energies, while three-body energies and relaxation energies make significant contributions to the binding energies for some complexes, whereas the four-body energies are too small to be significant.     

Temperature Dependence of Ideality Factors in Organic Solar Cells and the Relation to Radiative Efficiency

The value and temperature dependence of the ideality factor provides essential information about the dominant recombination route in solar cells. This study presents experimental results of accurate ideality factor determination for representative organic photovoltaic cells (OPV) evaluated at different temperatures over a large current density regime. It is noted that standard dark I–V curves strongly deviate from those obtained by evaluations based on short circuit current density (J _SC)–open circuit voltage (V _OC) pairs. This is attributed to the applied external voltage in a dark I–V measurement not being representative of internal chemical potential, particularly at lower temperatures. Complementary electroluminescence measurements attest that the current density dependence of the ability of the solar cell to emit light is better correlated to the series resistance free ideality factor. For the studied set of OPV devices it is observed that the ideality factors are quite low, and with very weak temperature dependence. The J _SC–V _OC method to determine ideality factors further allows good estimates of activation energies as well as recombination current prefactors J ₀₀. The findings imply that the principal OPV non‐radiative recombination mechanism is not recombination of free carriers with trapped carriers in an exponential density of tail states as previously reported.     

Studies on the Critical Micellar Concentration and Phase Transitions of Stearoylcarnitine

The critical micellar concentration (CMC) of stearoylcarnitine was determined at different pH values at room temperature by fluorescence spectroscopy, monitoring the spectral changes of 8-anilinonaphthalene-1-sulfonate (ANS). The CMC was found to vary with pH, increasing from about 10 μM at pH 3.0 to ca. 25 μM at pH 7.0, but decreasing slightly with further increase in pH to approximately 19 μM at pH 10.0. Differential scanning calorimetry (DSC) shows that stearoylcarnitine dispersed in water at low concentration undergoes a broad thermotropic phase transition at 44.5°C, with a transition enthalpy of 15.0 kcal/mol. The transition temperature (T _t) shifts to ca. 50.5°C in the presence of 1 mM EDTA or when the concentration is increased significantly. The turbidity of aqueous dispersions of stearoylcarnitine was found to be considerably high at low temperatures, which decreases quite abruptly over a short temperature range, indicating that a transition occurs from a phase of large aggregates to one of much smaller aggregates, most likely micelles. The phase transition temperature was determined as 29.1°C at pH 3.0, which increased with increasing pH up to a value of 55.3°C at pH 8.6 and remains nearly constant thereafter up to pH 11.2. The pH dependence of CMC and T _t suggest that the pK _a of the carboxyl group of long chain acylcarnitines shifts to higher temperatures upon aggregation (micelles or bilayer membranes).     

Power law dispersion in animal horn

The dielectric response of sheep horn has been measured in the frequency range from 10^–3–10⁵ Hz and over temperatures in the range 304–500 K. The dynamic behaviour of the conductance and capacitance in sheep horn has been observed to follow fractional power law dependences on frequency. It is shown that the over all dielectric response of these dead cells correspond to a dispersive imperfect bulk in series with a dispersive barrier region. It is further shown that the increase in temperature influences the reponse by eliminating the room temperature dc conductance and affecting the magnitude of the dispersion in capacitance. The magnitudes of activation energies are found as 0.33±0.02 eV for conductance, 0.40±0.02 eV for relaxation and 0.33±0.02 eV for the frequency shift.     

Nutrients and temperature additively increase stream microbial respiration

Rising temperatures and nutrient enrichment are co‐occurring global‐change drivers that stimulate microbial respiration of detrital carbon, but nutrient effects on the temperature dependence of respiration in aquatic ecosystems remain uncertain. We measured respiration rates associated with leaf litter, wood, and fine benthic organic matter (FBOM) across seasonal temperature gradients before (PRE) and after (ENR1, ENR2) experimental nutrient (nitrogen [N] and phosphorus [P]) additions to five forest streams. Nitrogen and phosphorus were added at different N:P ratios using increasing concentrations of N (~80–650 μg/L) and corresponding decreasing concentrations of P (~90–11 μg/L). We assessed the temperature dependence, and microbial (i.e., fungal) drivers of detrital mass‐specific respiration rates using the metabolic theory of ecology, before vs. after nutrient enrichment, and across N and P concentrations. Detrital mass‐specific respiration rates increased with temperature, exhibiting comparable activation energies (E, electronvolts [eV]) for all substrates (FBOM E = 0.43 [95% CI = 0.18–0.69] eV, leaf litter E = 0.30 [95% CI = 0.072–0.54] eV, wood E = 0.41 [95% CI = 0.18–0.64] eV) close to predicted MTE values. There was evidence that temperature‐driven increased respiration occurred via increased fungal biomass (wood) or increased fungal biomass‐specific respiration (leaf litter). Respiration rates increased under nutrient‐enriched conditions on leaves (1.32×) and wood (1.38×), but not FBOM. Respiration rates responded weakly to gradients in N or P concentrations, except for positive effects of P on wood respiration. The temperature dependence of respiration was comparable among years and across N or P concentration for all substrates. Responses of leaf litter and wood respiration to temperature and the combined effects of N and P were similar in magnitude. Our data suggest that the temperature dependence of stream microbial respiration is unchanged by nutrient enrichment, and that increased temperature and N + P availability have additive and comparable effects on microbial respiration rates.     

The Presence of Novel Plant Growth Regulators in Leaves of Distylium racemosum Sieb et Zucc

The scaling law derived from the percolation theory was applied to the concentration dependence of mechanical properties of polyacrylamide measured near the sol–gel transition point. The critical concentration of the sol–gel transition, ?_g, was estimated from the plot of concentration (?) vs. the reciprocal of viscosity (η) by extrapolating 1/η to zero. The critical exponent for the sol viscosity, s, which was estimated from the slope of the log(?_g–?) vs. log η plot was about 0.7. The estimated value of s was similar to the value predicted by the percolation theory based on the superconductor–normal conductor mixture model. The critical exponent for the gel elasticity, t, as estimated from the slope of the log(?–?_g) vs. log G′ plot, where G′ was the dynamic shear modulus of the gel at a frequency of 2Hz. The value of t was about 2, which was also similar to the value predicted by the percolation theory. These results indicated the at the concentration dependences of η and G′ of polyacrylamide near the sol–gel transition point were described by the percolation theory.     

Electrical conductivity of single crystals of lysozyme

The dc electrical conductivity of large single crystals of hen egg-white lysozyme has been measured. The samples were grown from aqueous solution and dried in air with silica gel. The temperature dependence of the conductivity obeyed the relation σ = σ₀ exp(? ΔE/kT), with ΔE = 1.2 eV. The ΔE value agreed with most of the previous results for various proteins in the form of lyophilized powder. On the other hand, log σ₀, being between 7 and 11, was much larger than the previously reported values and differed among the samples. An irreversible decrease in σ₀, without affecting ΔE, was observed on heating the samples above 85°C. It was shown that the set of results can be explained if the charge carriers responsible for the observed conduction are regarded as protons, originating from residual water molecules. Photoresponse of the samples to uv radiation below 305–315 nm was also observed. Reproducible and reliable results were obtained relatively easily in the present experiments, which is thought to be the main advantage of using single-crystalline samples.     

Using temperature‐dependent changes in leaf scaling relationships to quantitatively account for thermal acclimation of respiration in a coupled global climate–vegetation model

The response of plant respiration (R) to temperature is an important component of the biosphere's response to climate change. At present, most global models assume that R increases exponentially with temperature and does not thermally acclimate. Although we now know that acclimation does occur, quantitative incorporation of acclimation into models has been lacking. Using a dataset for 19 species grown at four temperatures (7, 14, 21, and 28 °C), we have assessed whether sustained differences in growth temperature systematically alter the slope and/or intercepts of the generalized log–log plots of leaf R vs. leaf mass per unit leaf area (LMA) and vs. leaf nitrogen (N) concentration. The extent to which variations in growth temperature account for the scatter observed in log–log R–LMA–N scaling relationships was also assessed. We show that thermal history accounts for up to 20% of the scatter in scaling relationships used to predict R, with the impact of thermal history on R–LMA–N generalized scaling relationships being highly predictable. This finding enabled us to quantitatively incorporate acclimation of R into a coupled global climate–vegetation model. We show that accounting for acclimation of R has negligible impact on predicted annual rates of global R, net primary productivity (NPP) or future atmospheric CO₂ concentrations. However, our analysis suggests that accounting for acclimation is important when considering carbon fluxes among thermally contrasting biomes (e.g. accounting for acclimation decreases predicted rates of R by up to 20% in high‐temperature biomes). We conclude that acclimation of R needs to be accounted for when predicting potential responses of terrestrial carbon exchange to climatic change at a regional level.     

Microsolvation of aminoethanol: a study using DFT combined with QTAIM

The microsolvation of aminoethanol (AE) with one, two, three or four water molecules was investigated using a density functional theory (DFT) approach. Quantum theory of atoms in molecules (QTAIM) analyses were employed to elucidate the hydrogen-bonding characteristics of AE–(H₂O) _n (n = 1–4) complexes. The results showed that AE tends to break its intramolecular OH^AE···N^AE hydrogen bond (H-bond) upon microsolvation and form intermolecular H-bonds with water molecules, while complexes that retain the intramolecular OH^AE···N^AE H-bond show reduced stabilities. The intermolecular H-bond that forms between the nitrogen atom of AE and the hydroxyl of a water molecule is the strongest one for the most stable AE–(H₂O) _n (n = 1–4) complexes, and as n increases from 1 to 4 they grow stronger. The partial covalent character of this H-bond was confirmed by QTAIM analyses. Many-body interaction analysis showed that the relaxation energies and two- and three-body energies make significant contributions to the binding energies of the complexes.     

Development of urea biosensor using non-covalent complexes of urease with aldehyde derivative of PEG and analysis on serum samples

Abstract

Non-covalent complexes of urease/polyethylene glycol (PEG)-aldehyde were synthesized using regular molar ratios of urease and PEG-aldehyde at room temperature. The physical properties of the non-covalent complexes were analyzed in order to investigate the impact of coupling ratio, temperature, pH, storage stability, and thermal stability. Urease activity was analyzed by UV–Vis spectrophotometer at 630?nm. The results showed that the strongest thermal resistance was obtained using n_U/n_PEG:1/1 (mg/mL) complex within all molar ratios tested. The enzymatic activity of n_U/n_PEG:1/1 complex doubled the activity of the free enzyme. Therefore, this complex was chosen to be used in the analyses. When coupled with PEG-aldehyde, urease exhibited improved activity between pH 4.0–9.0 and the optimum pH was found to be 7.0. The thermal inactivation results of the complex demonstrated that higher activity remained (40%) when compared with the free enzyme (10%) at 60?°C. The storage stability of the non-covalent complex was 4 weeks which was greater than the storage stability of the free enzyme. A kinetic model was suggested in order to reveal the mechanism of enzymatic conversion. Potentiometric urea biosensor was prepared using two different membranes: carboxylated poly vinyl chloride (PVC) and palmitic acid containing PVC. The potentiometric responses of both sensors were tested against pH and temperature and the best results were obtained at pH 7.0 and 20–30?°C. Also, selectivity of the suggested biosensors toward Na⁺, Li⁺ Ca²⁺, and K⁺ ions was evaluated and the reproducibility responses of the urea biosensors were measured with acceptable results.     

Reversing-pulse electric birefringence of poly(γ-benzyl-L-glutamate). III. The temperature dependence of the transient and steady-state behavior in cyclohexanone

The reversing-pulse electric birefringence (RPEB) technique was applied to the study of the temperature effect on the electrooptical and hydrodynamic properties of a fractionated [Glu(OBzl)]_n sample, which is molecularly dissolved in cyclohexanone. The aim was to develop a standard analytical method for thermal denaturation and temperature-induced conformational transitions. The field-on reverse and steady-state signal, and the field-off decay signal, were measured at 535 nm and at a constant low field strength (ca. 3 kV/cm) over a wide temperature range (5–90°C). The steady-state birefringence and the relaxation time in the decay process were also measured at two constant temperatures (5 and 70°C) over a wide field strength range (E ≤ 20 kV/cm). By the combination of these two different sets of RPEB measurements, the unwanted effect of the high pulse field on polymer conformation at elevated temperatures could be minimized. Together with the density and viscosity of cyclohexanone measured between 5 and 95°C, the following quantities could be evaluated: the weight-average permanent dipole moment and polarizability anisotropy, the reduced optical anisotropy factor (Δg/n), the weight-average length, and the degree of polydispersity. All these quantities, except for Δg/n, were found to be almost independent of temperature (5–90°C) and concentration (1.54–4.27 mM).     

An Investigation of Electrical Conductivity of Steroids

The electrical conductivity of sixteen steroids in the solid state was measured as a function of temperature. While too small to measure at room temperature, the exponential increase in conductivity with temperature can be determined at elevated temperatures (70° - 130°C). Most steroids tested had a conductivity of 10^-13 to 10^-15 ohm^-1 cm^-1 at 100°C and an activation energy of 2 to 4 ev. It it concluded that the observed conductivity is due to impurities. Exposure of keto steroids to iodine vapor results in unstable colored compounds, probably charge transfer complexes, which in some cases have a conductivity as high as 10^-4 ohm^-1 cm^-1.     

Optical spectroscopic studies of light-harvesting by pigment-reconstituted peridinin-chlorophyll-proteins at cryogenic temperatures

Low temperature, steady-state, optical spectroscopic methods were used to study the spectral features of peridinin-chlorophyll-protein (PCP) complexes in which recombinant apoprotein has been refolded in the presence of peridinin and either chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll d (Chl d), 3-acetyl-chlorophyll a (3-acetyl-Chl a) or bacteriochlorophyll a (BChl a). Absorption spectra taken at 10 K provide better resolution of the spectroscopic bands than seen at room temperature and reveal specific pigment–protein interactions responsible for the positions of the Q_y bands of the chlorophylls. The study reveals that the functional groups attached to Ring I of the two protein-bound chlorophylls modulate the Q_y and Soret transition energies. Fluorescence excitation spectra were used to compute energy transfer efficiencies of the various complexes at room temperature and these were correlated with previously reported ultrafast, time-resolved optical spectroscopic dynamics data. The results illustrate the robust nature and value of the PCP complex, which maintains a high efficiency of antenna function even in the presence of non-native chlorophyll species, as an effective tool for elucidating the molecular details of photosynthetic light-harvesting.     

Dielectric relaxation in synthetic melanin

The charging and discharging currents were investigated in a synthetic melanin sample. The presence of long-lasting dielectric relaxation was established. The steady state was reached after a long time, from 10³ to 10⁵ s, which depends both on temperature and voltage. The temperature dependence of polarization was of an activation character (E_α = 0.67 eV). The kind of electrode material did not influence the current curves.