Mentioned Concentration Range Research Articles

Ferromagnetic–antiferromagnetic transition and magnetotransport properties of La0.7Sr0.3Mn1−xNixO3 perovskites

The crystal structure and magnetic properties of polycrystalline compounds La0.7Sr0.3Mn1−xNixO3 (x ⩽ 0.37) were studied by neutron powder diffraction and magnetometry measurements, and the magnetotransport properties were also investigated, focusing on the magnetic state of the compounds. The crystal structure of the compounds remains rhombohedral upon chemical doping with Ni ions in the mentioned concentration range within the temperature interval 5–300 K. Doping with nickel ions causes a decrease in magnetization, and the Curie point drops from ~290 K for x = 0.1 compound down to ~70 K for x = 0.3 wherein the electrical resistivity of the compounds increases. The compounds with the dopant concentration x < 0.2 are characterized by pronounced magnetoresistance near the Curie points; the compounds with x ⩾ 0.2 show a gradual decrease in the magnetoresistance upon temperature increase. Neutron diffraction measurements of the compounds with x ⩾ 0.25 have showed a gradual reduction in ferromagnetic component, while an antiferromagnetic component of the G-type appears and progressively strengthens with an increase in the dopant concentration. The inhomogeneous magnetic state of the compounds with 0.25 < x ⩽ 0.3, attested by magnetization and neutron diffraction measurements, is governed by a competition between positive and negative exchange interactions formed between Ni and Mn ions depending on their oxidation state and electron configuration.

Theoretical Prediction and Synthesis of CSxFy Thin Films

A new carbon-based compound: CSxFy is reported. Geometry optimizations and energy calculations were performed by density functional theory on graphene-like model systems containing sulfur and fluorine atoms. It is shown that for [S + F] concentrations in the range of 0–10 at. %, short-range ordered structural characteristics similar to graphene pieces containing ring defects are energetically favorable. The modeling predicts that CSxFy exhibiting graphite and fullerene-like characteristics may be synthesized for the mentioned concentration range. Accordingly, CSxFy thin films were synthesized from a graphite solid target and using sulfur hexafluoride as S and F source. In agreement with the theoretical prediction, transmission electron microscopy characterization and selected area electron diffraction confirmed the presence of small ordered clusters with graphitic features in a sample containing 0.4 at. % of S and 3.4 at. % of F.

Fluorescence-based selective sensing of 1,2,4-trihydroxybenzene using histidine-stabilized ZnS nanospheres

In this paper, histidine-stabilized ZnS nanospheres have been used as a fluorescent probe for the selective detection of 1,2,4 –trihydroxybenzene (1,2,4 –THB). 1,2,4 –THB quenches the fluorescence of ZnS nanospheres in the 0.2–1.0 μM concentration range. Two other isomers of the analyte (namely, 1,2,3 –THB and 1,3,5 –THB) do not quench the fluorescence of the ZnS nanospheres in the above mentioned concentration range. A charge transfer complex is formed between 1,2,4 –THB and the histidine molecules surrounding the ZnS nanospheres. Due to its electron-rich character, 1,2,4 –THB acts as an electron donor while histidine acts as an electron acceptor. The limit of detection (LOD) of 1,2,4 –THB using this method is 0.28 μM. This fluorescence-based method has the potential to be used for the detection of 1,2,4 –THB in biological samples since the experiments have been carried out in an aqueous medium at pH 7.2.

Kinetics of absorption of carbon dioxide into aqueous potassium salt of proline

The absorption of carbon dioxide (CO2) into aqueous solution of potassium prolinate (KPr) are studied at 303, 313, and 323K within the salt concentration range of 0.5–3.0kmolm−3 using a wetted wall column absorber. The experimental results are used to interpret the kinetics of the reaction of CO2 with KPr for the above mentioned concentration and temperature range. Following the reaction mechanism of CO2 with primary and secondary alkanolamies, the reaction of CO2 with KPr is also described using zwitterionic mechanism. Based on the pseudo-first-order condition for the CO2 absorption, the reaction rate parameters are determined from the kinetic measurements and presented at each experimental condition. The reaction order is found to be in between 1.36 and 1.40 with respect to KPr for the above mentioned concentration range. The second-order rate constants, k2, are obtained as 118,914, 203,851, and 317,625m3kmol−1s−1 at 303, 313, and 323K, respectively with activation energy of 36.5kJmol−1. The second-order rate constants are much higher than for alkanolamines and some other salt of amino acids.

Optical acetylcholine sensor based on free base porphyrin as a chromoionophore

In this work, the possibility of application of free base porphyrin as a lipophilic pH chromoionophore for the preparation of optical cation-selective sensors was investigated. The properties of polymeric membranes, containing porphyrins of different structures, namely tetraphenylporphyrin (TPP) and octaethylporphyrin (OEP), were compared. Changes in equilibrium between protonated and deprotonated form of porphyrin, resulting from variations in ACh concentration, were evaluated. The influence of various factors (kind and quantity of anionic additive and porphyrin in the membrane phase, pH of sample solution) on initial equilibrium was studied. The best membrane composition was chosen as: TPP 3 wt.%, KTFPB 175 mol.% relative to ionophore, PVC:o-NPOE (1 : 4) and measuring buffer solution: 0.05 M MES, pH 4.5. Selectivity, response stability, reversibility and repeatability tests were carried out for chosen sensor. Developed sensor allowed for the determination of a model analyte, acetylcholine, at the concentration range of 10(-5) to 10(-2) M, both in stationary and flow-injection system. Sensor response was reversible and repeatable in the mentioned concentration range.

Kinetics of absorption of carbon dioxide into aqueous solution of 2-(1-piperazinyl)-ethylamine

The absorption of CO 2 into aqueous solution of 2-(1-piperazinyl)-ethylamine (PZEA) were studied at 303, 313, and 323 K within the amine concentration range of 0.083–1.226 kmol m −3 using a wetted wall column absorber. The experimental results were used to interpret the kinetics of the reaction of CO 2 with PZEA within the amine concentration range of 0.150–1.226 kmol m −3 for the above mentioned temperature range. Based on the pseudo-first-order condition for the CO 2 absorption, the overall second order reaction rate constants were determined from the kinetic measurements. The reaction order was found to be in between 0.99 and 1.03 with respect to amine for the later mentioned concentration range. The kinetic rate parameters were calculated and presented at each experimental condition. The second-order rate constants k 2, were obtained as 31867.6, 56354.2, and 100946 m 3 kmol –1 s –1 at 303, 313, and 323 K, respectively, with activation energy of 47.3 kJ mol −1. This new amine in the field of acid gas removal can be used as an activator by mixing with other alkanolamine solvents due to its very high rate of reaction with CO 2.

Doped and Co-doped CeO 2: Preparation and properties

Glycine/nitrate method was modified and applied to synthesize ceria solid solutions doped with rare earth cations and yttrium (Gd, Sm, Nd, Y) in the concentration range 0 ≤ x ≤ 0.25. The modification of glycine nitrate process was performed by substituting a portion of Ce-nitrate with the less expensive Ce-acetate. Nanometric size powder particles were obtained. Powder properties such as specific surface area, crystallite and particle size, dopants content and lattice parameters have been studied. The results showed that the dopants used in the mentioned concentration range formed solid solutions with host ceria. Defect model introducing anion vacancy radius can be applied to calculate lattice parameters and theoretical densities of doped and four-fold co-doped ceria nanosized solid solutions.

Surface Phase Transition of C12E1 at the Air/Water Interface: A Study by Dynamic Surface Tension, External RA FT-IR, and 2D IR Correlation Methods

The surface conformational states of the Gibbs monolayer of ethylene glycol mono-n-dodecyl ether (C(12)E(1)) at the air/water interface was studied using dynamic surface tension, external reflection-absorption FT-IR spectroscopy (ERA FT-IR), and two-dimensional infrared (2D IR) correlation methods at constant temperature. The dynamic surface tensions were measured at different bulk concentrations of C(12)E(1), and it was observed that a constant surface tension region appears at approximately 38.5 mN m(-1) in a dynamic surface tension profile at concentrations higher than 11 micromol kg(-1). This constant surface tension region corresponds to the surface phase transition from liquid expanded (LE) to liquid condensed (LC). Two sets of ERA FT-IR spectra were collected, one at different bulk concentrations but after equilibrium time (equilibrium measurements) and another at constant bulk concentration (m = 16 micromol kg(-1)) but at different times (dynamic measurements). The first set of these measurements show that the peak area increases in the range of 11 < m < or = 16 micromol kg(-1), which means the increase in the number of surfactant molecules at the air/water interface. Also, the wavenumber of antisymmetric CH(2) stretching decreases gradually from approximately 2923 cm(-1) (for 10 and 11 micromol kg(-1)) to approximately 2918 cm(-1) (for m > or = 16 micromol kg(-1)) with increasing concentration. The wavenumbers of 2923 and 2918 cm(-1) were assigned to LE and LC phases, respectively, and the decrease of wavenumber in the concentration range of 11 < m < or = 16 micromol kg(-1) were correlated to the surface phase transition (LE --> LC), or in other words, in the mentioned concentration range, two phases coexist. The dynamic ERA FT-IR measurements at 16 micromol kg(-1) also confirm the surface phase transition from LE to LC. The 2D IR correlation method was applied to the both equilibrium and dynamic IR spectra of the C(12)E(1) monolayer. The synchronous correlation maps show two strong autopeaks at approximately 2922 and approximately 2851 cm(-1) and also show a strong correlation (cross-peaks) between antisymmetric CH(2) stretching (nu(a)) and symmetric CH(2) stretching (nu(s)). The asynchronous correlation maps show that both observed bands of nu(a) and nu(s) in one-dimensional IR split into two components with the characteristic of overlapped bands, which reveals the coexistence of two phases (LE and LC) at the interface at 11 < m < or = 16 micromol kg(-1). The synchronous and asynchronous maps that were obtained from dynamic IR spectra closely resembled the equilibrium map.

Reduction of Trivalent Chromium Ions on Stationary Mercury Electrode in Concentrated LiCl Solutions

The effect of supporting-electrolyte (LiCl) concentration on the first stage Cr(III) + e → Cr(II) of Cr(III) reduction on a stationary mercury electrode is studied by linear voltammetry. It is found that an increase in the LiCl molar concentration m from 0.4 to ≈7 weakly affects the position of the cathodic current peak potential EP1 corresponding to this process. In the mentioned concentration range, [Cr(H2O)6 – nCln]3 – n (0 ≤ n < 3) ions are preferentially reduced. The further increase in m up to 19.1 results in a substantial positive shift of EP1, which is associated with the formation (upon passing the complete hydration limit) of the [Cr(H2O)3Cl3] (n = 3) complex, which is followed by its reduction.

Changing the composition of Ag–As–S amorphous films using photo-induced solid state reaction

The technique of step-by-step optically-induced solid state reaction of Ag into As 33S 67 amorphous films, which has allowed the design of films with known silver concentrations, is reported. The host, As 33S 67 films, were photo-doped by consecutive dissolution of a 10 nm layer of silver, which resulted in a single layer film of optical quality as measured by optical transmissivity. The silver concentration of the samples ranged between 1 and 41 at.%. Such Ag containing films cannot be prepared directly by vacuum evaporation from AgAsS glasses due to the phase separation during evaporation process. We analyzed the affect of the silver doping in the host material on optical, thermal properties, and its structure by means of optical spectroscopy, temperature-modulated differential scanning calorimetry, and Raman spectroscopy, respectively. Optically-induced silver dissolution led to a formation of the solid solutions in above mentioned concentration range, connected with a decrease of –S–S– bonds due to their solid state reaction with migrating silver ions. The films with a silver content close to 25 at.% had the structure of stoichiometric AgAsS 2. There is evidence of As–As bond formation in photo-doped materials with a silver content >40 at.%. Results of all analytical techniques we used have helped to understand the processes taking place during silver photo-dissolution.

Einfluß verschiedener flavonole auf das lamellarsystem der chloroplasten in vitro

The influence of various flavonoles on light triggered reactions of isolated chloroplasts was examined in order to receive some more detailed information about the problem just in discussion, wether those substances of the secondary metabolism are involved in reactions of primary metabolism of plants. Among the substances examined kaempferol was the most active one. 1. ATP synthesis is inhibited by kaempferol at a concentration of about 8 · 10 −5 M. Inhibition is due to an influence on the chloroplast membrane itself. 2. Calcium dependent, trypsin activated ATPase is stimulated at the mentioned concentration range, whereas magnesium dependent light triggered ATPase is inhibited as cyclic photophosphorylation too. 3. Electron transfer, measured with various Hill-reagents, is neither inhibited severely nor stimulated. 4. Kaempferol inhibits the methylamine uncoupled electron transfer up to 40 0/o. These results suggest that kaempferol does not act as an energy transfer inhibitor according to Good. Though kaempferol does not stimulate electron transport, it is assumed that kaempferol acts more like an uncoupling substance influencing a reaction site near electron transport chain, preventing the energy transfer from electron transport chain to ATPase. 5. Bovine serum albumine prevents the kaempferol inhibition up to 50%, if it is adjected to the medium before kaempferol. Polyvinylpyrrolidon, which is an usefull reactivator of tannin inhibited reactions, does not reactivate kaempferol inhibited membrane bound enzyme reactions. 6. Flavonole glucosides inhibit pseudocyclic photophosphorylation at the same concentration range up to 40 %. From these results it is concluded, that a part of the measurable kaempferol inhibition is due to a more specific reaction, whereas a second part seems to be due to an unspecific reaction between a protein and kaempferol. Nevertheless it is clear that flavonoles do have an influence on the primary metabolism of chloroplasts. But it seems to be impossible to postulate a corresponding effect of flavonoles in vivo, since kaempferol was not found in spinach chloroplasts.