Local‐field effect on the fluorescence relaxation of Tm3+:LaF3 nanocrystals immersed in liquid medium

Tm³⁺:LaF₃ nanocrystals were synthesized with hydrothermal technique. Local‐field effect on the radiative relaxation rate was studied in the system of Tm³⁺:LaF₃ nanocrystals immersed in several liquid media. The fluorescence lifetime was measured. It was found that the fluorescence decay presented the characteristics of second‐order exponential decay, for which the contribution from the ions inside the nanocrystal and ions at the interface of the nanocrystal were distinguished. Investigating the experimental results with proposed models, we found that the surface effect had to be eliminated. For rare earth doped LaF₃ nanocrystals, real‐cavity model well explains the influence of surrounding medium on the fluorescence relaxation rate. Copyright © 2009 John Wiley & Sons, Ltd.     

LLC-PK1 epithelia as a model for in vitro assessment of proximal tubular nephrotoxicity

Summary LLC-PK₁ cells, an established epithelial cell line derived from pig kidney, were used as a model system for assessment of nephrotoxic side effects of three cephalosporin antibiotics: cephaloridine, ceftazidime, and cefotaxime. Toxic effects of these xenobiotics were monitored on confluent monolayers by light and electron microscopy and by the release of cellular marker enzyme activities into the culture medium. In addition, LLC-PK₁ cells were grown on microporous supports, and cephalosporin-induced alteration of epithelial functional integrity was monitored by a novel electrophysiologic approach. For this purpose, an Ussing chamberlike experimental setup was used. The dose-dependent effects on transepithelial ionic permselectivity were monitored under conditions in which defined fractions of the apical culture medium NaCl contents were replaced iso-osmotically by mannitol. This method of determining the functional intactness of the epithelial barrier by measuring dilution potentials was found to be far more sensitive than monitoring cell injury by means of morphology or measurement of enzyme release. As expected from animal experimental data, a dose-dependent disruption of monolayer integrity was detected with all three methodologies applied. Cephaloridine was found the most toxic compound followed by ceftazidime, where a 3-fold, and cefotaxime, where a 10-fold dose of that of cephaloridine was needed to produce cell injury. Measurement of transepithelial dilution potentials was more sensitive as compared to the release of the apical plasma membrane marker enzyme activities alkaline phosphatase andγ-glutamyltranspeptidase, the cytosolic lactate dehydrogenase, or the mitochondrial glutamate dehydrogenase. The data were compared to the effects of the aminoglycoside antibiotic gentamicin, which at least with respect to its effects on LLC-PK₁ morphology and enzyme release, but not transepithelial electrical properties, was already investigated.     

Modelling of the electron transfer reactions in Photosystem I by electron tunnelling theory: The phylloquinones bound to the PsaA and the PsaB reaction centre subunits of PS I are almost isoenergetic to the iron-sulfur cluster FX

Photosystem I is a large macromolecular complex located in the thylakoid membranes of chloroplasts and in cyanobacteria that catalyses the light driven reduction of ferredoxin and oxidation of plastocyanin. Due to the very negative redox potential of the primary electron transfer cofactors accepting electrons, direct estimation by redox titration of the energetics of the system is hampered. However, the rates of electron transfer reactions are related to the thermodynamic properties of the system. Hence, several spectroscopic and biochemical techniques have been employed, in combination with the classical Marcus theory for electron transfer tunnelling, in order to access these parameters. Nevertheless, the values which have been presented are very variable. In particular, for the case of the tightly bound phylloquinone molecule A₁, the values of the redox potentials reported in the literature vary over a range of about 350 mV. Previous models of Photosystem I have assumed a unidirectional electron transfer model. In the present study, experimental evidence obtained by means of time resolved absorption, photovoltage, and electron paramagnetic resonance measurements are reviewed and analysed in terms of a bi-directional kinetic model for electron transfer reactions. This model takes into consideration the thermodynamic equilibrium between the iron-sulfur centre F_X and the phylloquinone bound to either the PsaA (A_1A) or the PsaB (A_1B) subunit of the reaction centre and the equilibrium between the iron-sulfur centres F_A and F_B. The experimentally determined decay lifetimes in the range of sub-picosecond to the microsecond time domains can be satisfactorily simulated, taking into consideration the edge-to-edge distances between redox cofactors and driving forces reported in the literature. The only exception to this general behaviour is the case of phylloquinone (A₁) reoxidation. In order to describe the reported rates of the biphasic decay, of about 20 and 200 ns, associated with this electron transfer step, the redox potentials of the quinones are estimated to be almost isoenergetic with that of the iron sulfur centre F_X. A driving force in the range of 5 to 15 meV is estimated for these reactions, being slightly exergonic in the case of the A_1B quinone and slightly endergonic, in the case of the A_1A quinone. The simulation presented in this analysis not only describes the kinetic data obtained for the wild type samples at room temperature and is consistent with estimates of activation energy by the analysis of temperature dependence, but can also explain the effect of the mutations around the PsaB quinone binding pocket. A model of the overall energetics of the system is derived, which suggests that the only substantially irreversible electron transfer reactions are the reoxidation of A₀ on both electron transfer branches and the reduction of F_A by F_X.     

Relativistically parameterized extended Hückel calculations. 10. Lanthanide trihalides

The REX relativistically parameterized extended Hückel method is used to study the electronic structure of lanthanide trihalide molecules. All valence orbitals are described in terms of double-zeta Slater functions, with the atomic orbital parameters being determined by a least-squares fitting to published relativistic (Dirac- Fock) radial densities. Comparisons of orbital energies to experimental values are made and various trends are discussed. Ab initio all-electron calculations at the self-consistent field level and as a function of molecular geometry are reported for LaH₃, LaF₃, and LaCl₃. While LaH₃ and LaF₃ are calculated to be pyramidal, LaCl₃ is calculated to be planar.     

Monte Carlo simulation of the adsorption of C2–C7 linear alkanes in aluminophosphate AlPO4-11

The adsorption behaviors of linear alkanes ranging in length from C₂ to C₇ in AlPO₄-11 have been simulated by using configurational-bias Monte Carlo technique at 313 K. The calculated heats of adsorption at zero coverage for linear alkanes, estimated by Henry coefficients, are consistent well with previously reported experimental and simulation results. The simulated isotherms for n-hexane in AlPO₄-11 at 298 K agree with the experimental data. The isotherms of C₂–C₇ linear alkane were predicted, in which butane presents a substep. The adsorbed alkane molecules are only localized in 10-membered ring channels, and adsorbed phase structures for each alkane were investigated. Total potentials for individual alkane molecule decrease with increasing number of carbon atoms. A linear change in total potential is observed for each linear alkane with increasing loading per unit cell, except that an increasing trend is found in the total potential curve of butane as the loading per unit cell is higher than two molecules.     

Influence of soil water potential on respiration and nitrogen fixation ofAzotobacter vinelandii

Summary Respiration and N₂-fixation (acetylene reduction) ofAzotobacter vinelandii have been studied at a variety of soil water potentials. Both processes were strictly linked and strongly reduced at water potentials between –0.6 and –1.3 MPa. Complete inhibition occurred below –2.1MPa. Osmotic potentials in soil compared to matric potentials of the same value were less inhibitory to respiration and acetylene reduction by Azotobacter. The N₂-fixing efficiency (mg N/g glucose) was not influenced by water potentials ranging from –0.1 to –2.1 MPa.     

The correlation of cathodic peak potentials of vitamin K3 derivatives and their calculated electron affinities : The role of hydrogen bonding and conformational changes

2-methyl-1,4-naphtoquinone 1 (vitamin K₃, menadione) derivatives with different substituents at the 3-position were synthesized to tune their electrochemical properties. The thermodynamic midpoint potential (E_1/2) of the naphthoquinone derivatives yielding a semi radical naphthoquinone anion were measured by cyclic voltammetry in the aprotic solvent dimethoxyethane (DME). Using quantum chemical methods, a clear correlation was found between the thermodynamic midpoint potentials and the calculated electron affinities (E_A). Comparison of calculated and experimental values allowed delineation of additional factors such as the conformational dependence of quinone substituents and hydrogen bonding which can influence the electron affinities (E_A) of the quinone. This information can be used as a model to gain insight into enzyme-cofactor interactions, particularly for enzyme quinone binding modes and the electrochemical adjustment of the quinone motif.     

First-principles investigation on structural,elastic, electronic and thermodynamic properties of filled skutterudite PrFe4P12 compound for thermoelectric applications

Filled skutterudite compound PrFe₄P₁₂ is studied using the full potential linear muffin-tin orbital method with the local density approximation for the exchange correlation potential to investigate the systematic trends for structural and elastic properties of the cubic PrFe₄P₁₂ skutterudite. The calculated ground state quantities such as the lattice constant and internal free parameters are in fairly good agreement with the available experimental data. The elastic constants and their pressure dependence are obtained by calculating the total energy versus volume-conserving strains using the Mehl model. Pressure and temperature effects on the lattice constant, bulk modulus, thermal expansion coefficient, Debye temperature and heat capacity are obtained in the range of 0–30 GPa and 0–1000 K. Reduction of bulk modulus and Debye temperature with temperature essentially indicates the thermal softening of the rare earth-filled skutterudites lattice.     

Trivalent rare‐earth activated hexagonal lanthanum fluoride (LaF3:RE3+, where RE = Tb,Sm, Dy and Tm) nanocrystals: Synthesis and optical properties

The LaF₃ nanocrystals through a facile hydrothermal route with hexagonal structures have been synthesized via doping of trivalent rare earth (RE³⁺) ions – RE = Tb, Sm, Dy and Tm – with rod‐like and perforated morphologies using NH₄F as fluorine precursor. Hexagonal phase formation was confirmed by powder X‐ray diffraction. The crystalline sizes were calculated by the Scherrer equation where found to have an average crystalline size of 12 to 35 nm. The morphological studies of the nanocrystals were carried out by means of transmission electron microscopy (TEM). The LaF₃:Tm³⁺,Sm³⁺ ions show the characteristic emission of Tb³⁺ and Tm³⁺ respectively. In Sm³⁺‐doped LaF₃, three prominent emission peaks at 561, 597 and 641 nm were found, which belong to ⁴G_5/2 → ⁶H_5/2, ⁴G_5/2 → ⁶H_7/2 (magnetic dipole) and ⁴G_5/2 → ⁶H_9/2 (electric dipole) transitions, respectively. The Dy³⁺ activated LaF₃ shows blue and yellow emission and the corresponding CIE color coordinate show white light emission (CCT value 10650 K).     

Molecular dynamics simulation of the Al2O3 film structure during atomic layer deposition

Based on an understanding of atomic layer deposition (ALD) from prior experimental and computational results, all-atom molecular dynamics (MD) simulations are used to model the Al₂O₃ film structure and composition during ALD processing. By separating the large time-scale surface reactions from the small time-scale structural relaxation, we have focused on the growth dynamics of amorphous Al₂O₃ films at the atomic scale. The simulations are able to reproduce some important properties and growth mechanisms of Al₂O₃ ALD films, and hence provide a bridge between atomic-level information and experimental measurements. Information about the evolution of the microscopic structures of the Al₂O₃ films is generated, and the influence of operation parameters on the Al₂O₃ ALD process. The simulations predict a strong influence of the initial surface composition and process temperature on the surface roughness, growth rate and growth mode of the deposited films.     

Application of a Novel Technique for Clinical Evaluation of Nitric Oxide-Induced Free Radical Reactions in ICU Patients

1. We recently developed a new technique for measuring serum NO₂ and NO₃ levels precisely, and we examined these parameters in severely brain-injured ICU patients who could not take nutrition intestinally.2. Our results demonstrated that NO increased rapidly after stroke, trauma, and the occurrence of infection in all ICU patients. Elevation of NO₂/NO₃ was most pronounced 24 to 48 hr after trauma or ischemic stroke. This dysregulation of free radical elimination closely correlated with hemoglobin levels.3. In most ICU patients,with the exception of those with complications of infection, the free radical potentials were maximal at 24 to 48 hr and continued to remain high for 4 to 5 days after trauma or stroke. The level of free radical potentials was closely correlated with the severity and prognosis of critically injured patients. None with radical potential values higher than 0.4 M survived.4.Clinically, the maintenance of hemoglobin at >12 g/dl and lower body temperature were demonstrated to be successful in the management of these free radical reactions.     

Electronic structure,mechanical and thermodynamic properties of BaPaO<Subscript>3</Subscript> under pressure

Density functional theory (DFT)-based investigations have been put forward on the elastic, mechanical, and thermo-dynamical properties of BaPaO₃. The pressure dependence of electronic band structure and other physical properties has been carefully analyzed. The increase in Bulk modulus and decrease in lattice constant is seen on going from 0 to 30 GPa. The predicted lattice constants describe this material as anisotropic and ductile in nature at ambient conditions. Post-DFT calculations using quasi-harmonic Debye model are employed to envisage the pressure-dependent thermodynamic properties like Debye temperature, specific heat capacity, Grüneisen parameter, thermal expansion, etc. Also, the computed Debye temperature and melting temperature of BaPaO₃ at 0 K are 523 K and 1764.75 K, respectively.     

Motional narrowing of the 2H NMR spectra near the chain melting transition of phospholipid/D2O mixtures

The reduction in spectral splitting, or motional narrowing, of the deuterium spectra of D₂O/phos-pholipid mixtures near the main chain melting phase transition was studied for palmitoyloleoylphosphatidylcholine (POPC), palmitoyloleoylphosphatidylethanolamine (POPE) and equimolar mixtures of the two at 10% hydration. For POPC the splitting was about 1700 Hz in both the fluid and gel phases, dropping to zero near the phase transition (as reported previously). For POPE the splitting remained approximately constant above the phase transition. Below the phase transition the spectrum showed a single broad line whose linewidth varied between 100 Hz and 800 Hz. This was interpreted as being due to small domains of water within a weakly hydrated crystal. POPC:POPE (1:1) samples exhibited motional narrowing behaviour similar to that for POPC except that the splitting above the phase transition was approximately twice that below the transition. The relatively broad temperature range (20 K) of the transition is explained using a simple physical model involving lipid fluctuations near the phase transition.Abbreviations NMR Nuclear Magnetic Resonance - PC phosphatidylcholine - PE phosphatidylethanolamine - POPC Palmitoyloleoylphosphatidylcholine - POPE Palmitoyloleoylphosphatidylethanolamine - H_II Inverse hexagonal phase     

Dielectric properties of BaTiO3 by molecular dynamics simulations using a shell model

We calculated the susceptibilities of BaTiO₃ by molecular dynamics (MD) simulations using an isotropic shell model of Tinte et al. (S. Tinte, M.G. Stachiotti, S.R. Phillpot, M. Sepliarsky, D. Wolf, and R.L. Migoni, Ferroelectric properties of BaxSr1-xTiO₃ solid solutions obtained by molecular dynamics simulation. J Phys Condens Matter, 16, pp. 3495–3506, 2004). The anisotropy of the susceptibilities was reproduced for the ferroelectric phases. However, the susceptibilities were significantly underestimated with respect to experimental ones especially for the a direction. The densities of probabilities of the local polarisations in this model for both the macroscopically polarised and not polarised directions were strongly localised around their average values, leading to the small fluctuation of the total dipole moment of the MD cell and resulting in the underestimated susceptibilities. The order–disorder character was found to be stronger in this model than in the effective Hamiltonian based on the first principles calculations.     

Below-canopy CO2 flux and its environmental response characteristics in a coniferous and broad-leaved mixed forest in Dinghushan, China

Accurate estimation of below-canopy CO₂ flux (Fcb) in typical forest ecosystems is of great importance to validate terrestrial carbon balance models. Continuous eddy covariance measurements of Fcb were conducted in a coniferous and broad-leaved mixed forest located in Dinghushan Nature Reserve of South China. Using year-round data, Fcb dynamics and its environmental response were analyzed, and the results mainly showed that: (1) Fcb decreased during daytime which indicated that the understory of the forest continued photosynthesis throughout the year; however, understory and soil acted as CO₂ source as a whole. (2) Using soil temperature (Ts) as a dependent variable, all of Van’t Hoff equation, Arrhenius equation and Lloyd-Taylor equation can explain a considerable variation of Fcb. Among those three equations Lloyd-Taylor equation is the best to reflect the relationship between soil respiration and temperature for its ability in revealing the variation of Q₁₀ with temperature. (3) Fcb derived from Lloyd-Taylor equation is utterly determined by Ts, while Fcb derived from the multiplicative model is driven by Ts and soil moisture (Ms). The multiplicative model can reflect the synthetic effect of Ts and Ms; therefore it explains more Fcb variations than Lloyd-Taylor equation does. (4)Fcb derived from the multiplicative model was higher than that from Lloyd-Taylor equation when Ms was relatively high; on the contrary, Fcb derived from the multiplicative model was lower than that from Lloyd-Taylor equation when Ms was low, indicating that Ms might be a main factor affecting Fcb when the ecosystem is stressed by low-moisture. (5) Annual Fcb of the forest in 2003 was estimated as (787.4±296.8) gCm^-2a^-1, which was 17% lower than soil respiration measured by statistic chamber method. CO₂ flux measured by eddy covariance is often underestimated, and further study therefore calls for emphasis on methods quantifying Fcb components of respiration of soil, as well as respiration and photosynthesis of understory vegetations.     

Mechanisms of carbon and nutrient release and retention in beech forest gaps

Fluxes of CO₂ and N₂O were measured along a microclimatic gradient stretching from the centre of a gap into a mature beech stand using an automated chamber method. Simultaneously the regulating factors like soil water tensions, soil temperatures, nitrate concentrations were measured along the gradient. The daily mean values of the fluxes of CO₂ and N₂O were divided into classes of temperature and furthermore subdivided into classes of soil water tension to assess the significance of each regulating factor.Soil respiration at the centre of the gap was 40% lower compared to the rooted mature stand. The difference was explained by root respiration. At both sites soil respiration was primarily controlled by the soil temperature with an average Q₁₀ value of 2.3 over the different classes of temperature and soil water tension. Soil water tension reduced the soil respiration by up to 20% only by soil water tension above 400–600 hPa at the mature stand. The formation of N₂O was reduced when the soil temperature was below 10°C or the soil water tension exceeded 200 hPa. Therefore the N₂O emission was 6 times higher at the unrooted centre of the gap due to the high moisture content in the growing season. Higher nitrate concentration doubled the N₂O emission at the unrooted edge of the canopy and resulted in losses of 6.4 kg N ha^-1 within six months. Above 10°C and below 200 hPa the N₂O emission depended strongly upon the temperature with varying Q₁₀ values over the different classes of temperature and soil water tension. High Q₁₀ values up to 14.4 have been calculated below 14°C and were explained by several processes with synergetic effects.     

On the origin of the temperature dependence of the supercoiling free energy.

Monte Carlo simulations using temperature-invariant torsional and bending rigidities fail to predict the rather steep decline of the experimental supercoiling free energy with increasing temperature, and consequently fail to predict the correct sign and magnitude of the supercoiling entropy. To illustrate this problem, values of the twist energy parameter (E(T)), which governs the supercoiling free energy, were simulated using temperature-invariant torsion and bending potentials and compared to experimental data on pBR322 over a range of temperatures. The slope, -dE(T)/dT, of the simulated values is also compared to the slope derived from previous calorimetric data. The possibility that the discrepancies arise from some hitherto undetected temperature dependence of the torsional rigidity was investigated. The torsion elastic constant of an 1876-bp restriction fragment of pBR322 was measured by time-resolved fluorescence polarization anisotropy of intercalated ethidium over the range 278-323 K, and found to decline substantially over that interval. Simulations of a 4349-bp model DNA were performed using these measured temperature-dependent torsional rigidities. The slope, -dE(T)/dT, of the simulated data agrees satisfactorily with the slope derived from previous calorimetric measurements, but still lies substantially below that of Duguet's data. Models that involve an equilibrium between different secondary structure states with different intrinsic twists and torsion constants provide the most likely explanation for the variation of the torsion constant with T and other pertinent observations.     

Identification of a V-type proton pump in the outer mantle epithelium of Anodonta cygnea

The dissected outer mantle epithelium (OME) of Anodonta cygnea, when mounted in Ussing type chambers, generated a spontaneous potential difference of 22.0±12.6 mV and, when short-circuited, a positive current (I_sc) of 30.0±11 μA/cm² towards the shell side and a conductance of 1.1±0.4 mS/cm². When in contact with the shell side, Bafilomycin A₁ and Concanamycin A, specific inhibitors of V-proton pumps, induced 90% inhibition of I_sc in 5 and 35 min, respectively. They had no effect in the current from the hemolymph side. Both drugs induced a dramatic fall in conductance from the shell side. Tributyltin oxide (TBTO) inhibited 90% of the I_sc in 3 min and induced a fall in conductance only from the shell side. Two observations suggest a direct effect on the proton pump: it was effective only from the shell side and the time course of the effect was identical to that of Bafilomicyn A₁. Dicyclohexycarbodiimide (DCCD) and N-ethylmaleimide (NEM) inhibited I_sc from both sides but very slowly and there was a delay of the effect from the hemolymph side in relation to the shell side. Taken together, the results suggest the presence of a V-type proton pump located at the apical (shell side) barrier of the OME.     

Predicting ultimate methane yields of Jatropha curcus and Morus indica from their chemical composition

In this study, all the components of Jatropha curcus and Morus indica were chemically characterized and their biochemical methane potentials (BMP) were determined. From the variables that showed strong influence on the ultimate methane yield (B_o) of J. curcus, a multiple regression Jatropha model was developed. This model comprised of total carbohydrates, protein, lipid, acid-detergent fiber (ADF), cellulose and ash in ADF as independent variables, with r² value of 0.943. The Jatropha model was validated on 7 samples of M. indica parts and wastes from silkworm rearing trays of this study and 13 samples of heterogeneous organic wastes of earlier studies, to judge the prediction quality. It was found that most of the predicted values differed by less than 15% of their experimental B_o.