A calcium-sensitive microelectrode suitable for intracellular measurement of calcium(II) activity

A calcium-selective microelectrode with a l-μm diameter tip suitable for impaling single neurons has been developed. The electroactive material is di[p-(1,1,3,3-tetramethyl-butyl) phenyl] phosphoric acid (t-HDOPP). The selectivity coefficients are about 5 · 10^-7 for k_Ca,K, 1–4·10^-7 for k_Ca,Na, and 10^-3 for k_Ca,Mg. Values reported previously for other calcium-selective electrodes based on long-chain phenylphosphoric acids are given for comparison. The calcium-selective microelectrodes have a linear response in 0.2 M KCl solutions over the range 10^-2–10^-XXX M CaCl₂; 10^-7 and 10^-8 M CaCl₂ solutions containing 0.2 M KCl can be detected but the response is not linear.     

Trace analysis for sulphur and phosphorus in aqueous solution by a carbon filament atom reservoir technique

The chemiluminescent emissions of S₂ and HPO are excited around a resistively heated carbon filament in a hydrogen-nitrogen diffusion flame. Detection limits of 5 · lO^-10 g and 4 · 10^-9 g were obtained, respectively, for sulphur and phosphorus for 1-μl samples of sulphuric and phosphoric acid solutions. Interference effects were studied; there are numerous cationic interferences but few anionic interferences.     

Reaction of photogenerated fluorine atoms with dopant molecules in solid argon

The products of reactions of dopant CH₄ molecules with F atoms diffusing in solid argon at 20–30 K were identified by ESR and FTIR spectroscopy. The F atoms stabilized in the matrix were generated by UV photolysis of Ar?CH₄(CD₄)?F (1000∶1∶1) samples at 13 K. Subsequent heating above 20 K results in thawing off diffusion of the F atoms and formation of products of their reaction with CH₄: radical-molecular complexes^·CH₃?HF (^·CD₃?DF) and radicals^·CH₃ (^·CD₃). The ESR spectra of the radicala are similar to those observed for matrix-isolated^·CH₃. The^·CH₃?HF complexes are characterized by the IR band of HF stetching vibration at 3764 cm^?1. Two additional splittings on the H (a _H·=2 G) and F(a _F=16G) nuclei of the HF molecule appeal in the ESR spectrum of the complex. The latter splitting is retained in the^·CD₃?DF complex, whereA _D· <0.3G The rate constant of the reaction CH₄+F→^·CH₃+HF is equal to ?10^?25 cm³s^?1 at 20 K. Its activation energy (1.7±0.2 kcal mol^?1) is ?0.5 kcal mol^?1 greater than that in the gas phase. The collinear C_3v-configuration of the^·CH₃?HF complex, which is similar to the configuration of the reagents in the transition state of the reaction considered, was established by the comparison of the exprrimental constants of hyperfine coupling with the results of the quantum-chemical calculation.     

Effect of potassium chloride on diffusion of theophylline at T = 298.15 K

Ternary mutual diffusion coefficients measured by Taylor dispersion method (D₁₁, D₂₂, D₁₂, and D₂₁) are reported for aqueous solutions of KCl + theophylline (THP) at T = 298.15 K at carrier concentrations from (0.000 to 0.010) mol · dm^?3, for each solute. These diffusion coefficients have been measured having in mind a better understanding of the structure of these systems and the thermodynamic behavior of potassium chloride and theophylline in solution. For example, from these data it will be possible to make conclusions about the influence of this electrolyte in diffusion of THP and to estimate some parameters, such as the diffusion coefficient of the aggregate between KCl and THP.     

Neutron Diffraction Study on the Structure of Aqueous LiNO3 Solutions

Neutron diffraction measurements were carried out at 25 °C for aqueous LiNO₃ heavy water solutions, (*LiNO₃) _x (D₂O)_1?x where x = 0.1, 0.05 and 0.01, in which the ⁶Li/⁷Li isotopic ratios were varied. Structural information on intermolecular nearest neighbor Li⁺···D₂O interactions in the extensive concentration range was derived from the first-order difference function, ?_Li(Q), obtained from the difference in scattering cross sections between ⁶Li- and ⁷Li-enriched sample solutions. The nearest neighbor Li⁺···O distance and coordination number for sample solution with x = 0.1 were determined to be r _LiO = 1.969 (8) Å and n _LiO = 4.12 (6), respectively, corresponding to the four-coordinated Li⁺ ion in the solution. On the other hand, those obtained for the solution with x = 0.01 are r _LiO = 2.00 (2) Å and n _LiO = 6.0 (2), respectively, indicating that hexaaqua Li⁺ is dominant in the dilute solution. These results clearly indicate that a concentration dependence of the hydration number of Li⁺ occurs in the aqueous solutions.     

Study on Dynamic Interfacial Tension of 3‐Dodecyloxy‐2‐hydroxypropyl Trimethyl Ammonium Chloride at n‐Decane/Water Interface

Dynamic interfacial tension (DIT) and interface adsorption kinetics at the n‐decane/water interface of 3‐dodecyloxy‐2‐hydroxypropyl trimethyl ammonium chloride (R₁₂TAC) were measured using spinning drop method. The effects of R_nTAC concentration and temperature on DIT have been investigated, the reason of the change of DIT with time has been discussed. The effective diffusion coefficient, D _a, and the adsorption barrier, ?_a, have been obtained with extended Word‐Tordai equation. The results show that the higher the concentration of surfactants is, and the smaller will be the DIT and the lower will be the curve of the DIT, and the R₁₂TAC solutions follow a mixed diffusion‐activation adsorption mechanism in this investigation. With increase of concentration in bulk solution of R₁₂TAC from 8×10^?4 mol · dm^?3 to 4×10^?3 mol · dm^?3, D _a decreases from 2.02×10^?10 m^?2 · s^?1 to 1.4×10^?11 m^?2 · s^?1 and ? _a increases from 2.60 kJ · mol^?1 to 9.32 kJ · mol^?1, while with increase of temperature from 30°C to 50°C, D _a increases from 2.02×10^?10 m^?2 · s^?1 to 5.86×10^?10 m^?2 · s^?1 and ε_a decreases from 2.60 kJ · mol^?1 to 0.73 kJ · mol^?1. This indicates that the diffusion tendency becomes weak with increase strength of the interaction between surfactant molecules and that the thermo‐motion of molecules favors interface adsorption.     

Neutron diffraction study of uranyl oxalate [UO2(C2O4)(D2O)] · 2D2O

A powdered sample of uranyl oxalate [UO₂(C₂O₄)(D₂O)] · 2D₂O (compound I) is studied using neutron diffraction. The crystals are monoclinic, space group P2₁/c, with a = 5.608(1) Å, b = 17.016(3) Å, c = 9.410(2) Å, β = 98.9369(2)°, Z = 4, R _f = 0.042, R _I = 0.054, x ² = 1.5. The main structural units of the crystals are [UO₂(C₂O₄)(D₂O)] chains. These chains, which belong to the AK⁰²M¹ (A = UO ₂ ²⁺ ) crystal-chemical group of the uranyl complexes, lie parallel to [101]. The water molecules in the crystals of I are hydrogen-bonded into zigzag chains running along [100]. Since each third oxygen atom of the chain formed of water molecules is coordinated to the uranium atom, the uranyl oxalate chains are linked into {[UO₂(C₂O₄)(D₂O)] · 2D₂O} layers that lie normal to [010]. The layers are linked into the framework through interlayer hydrogen bonds (D₂O)O-D···O (oxalate).     

A kinetic study of diffusion in the electrothermal atomizer with a graphite filter by laser excited atomic fluorescence

Laser excited atomic fluorescence-electrothermal atomizer (LEAFS-ETA) was used to study atomization and diffusion mechanisms in a novel diffusive graphite tube atomizer. The atomizer design included a hollow graphite cylinder mounted between two graphite rods which served as electrodes. One of the rods had a small graphite insert with a sampling hollow and could move backwards and forwards. After the sample was introduced into the hollow, the electrodes tightly sealed the graphite cylinder ensuring that the insert was directly in the center of the furnace. The furnace assembly was then heated and the vaporized sample diffused through the hot graphite wall. The atomic fraction of the sample vapor was excited by a laser beam which was directed along the graphite tube surface so that no gap remained between the beam and the tube surface. Fluorescence vs. time profiles for three elements — Cu, Ag and Ni — were obtained within the temperature range of 1400–2600 K. The rate constants of specific processes were measured from the decay portions of the fluorescence signals under the assumption of first-order kinetics. The Arrhenius plots were constructed and the activation energies, E_a were evaluated from their slopes. The plots obtained for Cu and Ag consisted of two linear parts, the corresponding values of E_a were: 195 kJ/mol and 77 kJ/mol for Cu (1550 K < T < 2600 K) and 238 kJ/mol and 97 kJ/mol for Ag (1430 K < T < 2280 K). The Arrhenius plot for Ni was linear within the temperature range of 1770–2530 K resulting in an E_a equal to 161 kJ/mol. The diffusion coefficients were evaluated on the basis of a steady-state diffusion model out of a hollow cylinder. The values for the diffusion coefficients were: 3.7·10⁻⁴−2.0·10⁻³ cm²/s (1750–2600 K) for Cu, 6.5·10⁻³−1.4·10⁻³ cm²/s (1750–2280 K) for Ag and 5.6·10⁻⁵−1.5·10⁻³ cm²/s (1770–2530 K) for Ni.     

Electric birefringence and conformation of polychlorohexylisocyanate in solutions

Electric birefringence was investigated for solutions of polychlorohexylisocyanate fractions for molecular weights 30·6 × 10⁴–1·2 × 10⁴ in tetrachloromethane.Experimentally found dispersion of the Kerr effect is used for estimating the coefficients of rotatory diffusion D_r of molecules. A comparison of rotatory diffusion D_r values with molecular weights M and intrinsic viscosities [η] of fractions shows that the value of D_rM[η] decreases with M. This illustrates the change in the conformation of molecules from a random coil to a rod.On the basis of experimental dependences of D_r and the Kerr constants K on M, the main structural parameters of the polymer investigated were determined: the number of monomer units in a segment, the projection of the length of the monomer unit on the axis of the molecule, the value of the dipole moment μ₀ of the monomer unit and the angle formed by μ₀ and the chain direction.     

Influence of composition and ionizing radiation on kinetics of reduction of mixed CdO-ZnO oxides with hydrogen

The reduction of cadmium oxide and zinc oxide mixtures of various compositions with hydrogen at 410–450° was studied with thermogravimetry. The reduction kinetics, which depends markedly on the composition in the whole composition range, can be described by the equation (α+0.3)/(1?α)=A·e ^kt. Preliminary irradiation of the samples with⁶⁰Coγ-rays (applied doseD _γ=10⁵ Gy) causes an increase in the rate of reduction of samples containing an excess of CdO and decrease in the rate of reduction in the region with excess of non-reducible ZnO. Fast neutron irradiation with a flux density of 1.18·10¹⁷ n/m² (total doseD _n=4.5·10² Gy) from a²⁵²Cf source retards the reduction in the whole range of composition. The probable mechanism of mutual interaction of both components and of the applied ionizing radiation is discussed.     

Separation of no-carrier-added 113,117mSn and 113m,114mIn from alpha particle irradiated natural cadmium target

A natural cadmium foil was irradiated by 42 MeV α-particles to produce ^113,117mSn, ^{111,113m,114m}In simultaneously in the target matrix. After the complete decay of short lived radionuclides, long-lived NCA products were separated sequentially from the bulk cadmium by liquid–liquid extraction using di-(2-ethylhexyl)phosphoric acid (HDEHP) dissolved in cyclohexane as organic phase and HCl as aqueous phase. At the optimum condition, 10^?2 M HCl and 5 % HDEHP, NCA In along with NCA Sn radionuclides (75 %) were separated from the bulk Cd resulting to high separation factors of 2.7 × 10⁴ (D _In/D _Cd) and 500 (D _Sn/D _Cd), respectively. The NCA In was stripped back completely to the aqueous phase by 6 M HCl leaving NCA Sn in the HDEHP phase with a separation factor (D _Sn/D _In) of 3.94 × 10⁶.     

Transport of U(VI) from sulphuric acid medium across supported liquid membrane (SLM) containing di-(2-ethylhexyl) phosphoric acid (D2EHPA)/n-dodecane as a carrier

This paper reports on the supported liquid membrane (SLM) based transport studies of U(VI) from sulphate medium using di-(2-ethylhexyl) phosphoric acid/n-dodecane as carrier. Polytetrafluoroethylene membrane was used as solid support and H₂SO₄ as receiver phase. The effects of various parameters such as receiver phase concentration, feed acidity, carrier concentration, U(VI) concentration, membrane thickness and membrane pore size on U(VI) transport had been investigated. With increase in H₂SO₄ concentrations and pH of feed solution there is an increase in U(VI) transport across the SLM. Similarly with increase in membrane thickness the U(VI) transport decrease whereas in case of pore size variation reverse results are obtained. The membrane thickness variation results showed that the U(VI) transport across the SLM is entirely diffusion controlled and the diffusion coefficient the D _(o) was calculated as 1.36 × 10^?7 cm² s^?1. Based on optimized condition, a scheme had been tested for selective recovery of U(VI) from ore leach solution containing a large number of other metal ions.     

Ternary mutual diffusion coefficients of aqueous {l-dopa (1) + β-CD (2)} solutions at T = 298.15 K

Ternary mutual diffusion coefficients (D₁₁, D₂₂, D₁₂ and D₂₁) measured by the Taylor dispersion method are reported for aqueous solutions of {levodopa (l-dopa) + β-cyclodextrin (β-CD)} solutions at T = 298.15 K and concentrations up to 0.007 mol · dm⁻³. Significant effects on the diffusion were observed, suggesting interactions between this carbohydrate and l-dopa. Support for this came from ¹H NMR spectroscopy, which shows that these effects are due to formation of 1:1 (β-CD:l-dopa) complexes.     

Analysis of asymmetry of the Mössbauer bands of FexZn1−x(4-amino-1,2,4-Triazole)3(NO3)2 complexes with the spin transition1 A 1 ⇄5 T 2 proof of anisotropy of iron atom vibrationsproof of anisotropy of iron atom vibrations

This paper analyzes the nature of asymmetry of quadrupole doublets in the Mössbauer spectra of the high-spin (HS) and low-spin (LS) forms ofFe _x Zn _1?x (ATr) ₃(NO ₃)₂ complexes possessing a polynuclear chain structure. It is assumed that the quantization axis z is directed along the polymer chain. The asymmetric character of bands in the spectra is explained by the anisotropy of iron atom vibrations along the z axis or perpendicular to it, i.e., by Goldanskii-Karyagin's effect. The quadrupole splitting is theoretically analyzed and compared with experiment the electric field gradient on the iron nuclei is negative for the HS form and positive for the LS form. The standard deviations of iron atoms are 2>=2.78·10^?18 cm², 2>=0.72·10^?18 cm² for the HS form and 2>=1.63·10^?18 cm², 2>=0.72·10^?18 cm² for the LS form at 295 K; 2>=2>=0.26·10^?18 cm² for the LS form at 78 K.     

Electrochemical Study on the Interaction of Irinotecan with Calf Thymus Double Stranded DNA

Voltammetric behavior of Irinotecan (CPT‐11) was studied in a phosphate buffer (0.002 mol·L^?1, pH 7.5) solution at the hanging mercury drop electrode (HMDE) using cyclic voltammetry (CV). CPT‐11 showed two irreversible cathodic peaks at ?1.01 V and ?1.09 V which involved two electrons and two protons in each reduction step. In addition, the interaction of Irinotecan with double‐stranded calf thymus DNA (ds‐DNA) was studied by CV at the HMDE employing an irreversible electrochemical equation. As a result of the reaction with ds‐DNA, the reduction peaks related to CPT‐11 were shifted in a negative direction and the peak currents were decreased. The diffusion coefficients of CPT‐11 in the absence (D_f) and presence (D_b) of ds‐DNA were calculated as 2.8×10^?5 cm²·s^?1 and 1.6×10^?5 cm²·s^?1 respectively. The binding constant (K=1.0×10⁴ L·mol^?1), and binding site size (s=0.60) of CPT‐11 interacting with ds‐DNA were obtained simultaneously by non‐linear fit analysis. The results demonstrate that the main interaction mode of CPT‐11 with ds‐DNA is electrostatic.     

Population and deactivation of lowest lying barium levels by collisions with He,Ar, Xe and Ba ground state atoms

Excitation transfer between the barium low lying excited states 6s6p ³ P ₁ ⁰ , 6s5d ¹ D ₂ and 6s5d ³ D _J by collisions with He,Ar,Xe and Ba has been investigated. The population densities in all levels involved were probed by absorption or by fluorescence usingcw lasers. The depopulation cross sections of the Ba³ P ₁ ⁰ state by collisions with noble gases were found to be σ_He(³ P ₁ ⁰ )=5.5·10^?16 cm², σ_Ar(³ P ₁ ⁰ )=4.6·10^?16 cm², and σ_Xe(³ P ₁ ⁰ )=1.7·10^?16 cm². For Ar, the collisional depopulation of the³ P ₁ ⁰ level is exclusively due to the transition to the¹ D ₂ state. Under the assumption that the³ D _J metastable states are populated collisionally by¹ D ₂ →³ D _J transfer only, we have deduced the upper limit for the corresponding cross section σ ₁₃ ^Ar =1.5·10^?18 cm². From the Ba¹ D ₂ and Ba³ D _J steady-state diffusion distributions, collisional relaxation rates of the¹ D ₂ and³ D _J levels were evaluated. The collisional relaxation rates by Ar and Ba yielded total cross sections for the depopulation of metastable levels: σ_Ar(¹ D ₂)=1.5·10^?17 cm², σ_Ba(¹ D ₂)?1·10^?13 cm², σ_Ar(³ D _J)=7·10^?21 cm², and σ_Ba(³ D _J)=1·10^?15 cm². Furthermore, it was found that the main contribution of the collisional depopulation of the¹ D ₂ state by Ar is related to back transfer to the³ P _J ⁰ state, whereas the deactivation of the³ D _J metastable state is due to back transfer to the¹ D ₂ state. Taking into account other cross sections reported in literature we can conclude that collisional deactivation of both metastable levels by Ba ground state atoms can be attributed to their mutual collisional mixing.     

Thermal and calorimetric investigations of M(IO3)2·2H2O forM 2+=Ni2+ and Zn2+ and their deuterated analogues

The thermal dehydration and decomposition of M(IO₃)₂·2H₂O (M ²⁺=Ni²⁺ and Zn²⁺) and their deuterates were investigated by DTA and DSC methods. The data obtained confirm their onestage dehydration and their decomposition to the respective oxides. Ni(IO₃)₂·2H₂O and Ni(IO₃)₂·2D₂O, were more stable than Zn(IO₃)₂·2H₂O and Zn(IO₃)₂·2D₂O. A considerable isotope effect was observed in relation toT _deh for Ni(IO₃)₂·2H₂O and Ni(IO₃)₂·2D₂O, which was explained by the presence of structural changes well differentiated from the dehydration process for the deuterate. The data obtained for both pairs of dihydrates were used to determine ΔH _f ^o for Ni(IO₃)₂·2H₂O and Ni(IO₃)₂·2D₂O.     

Evaluation of sorption and diffusion behavior of selenium in crushed granite by through-diffusion column tests

Distribution coefficients (K _d), apparent diffusion coefficients (D _a) and retardation factor (Rf) in this work obtained by batch and through-diffusion experiments have been performed, respectively. The accumulative concentration method developed by Crank (The mathematics of diffusion, 12) was applied to realize apparent and effective diffusion coefficient (D _a and D _e) of Se. Besides, a non-reactive radionuclide, HTO, was initially conducted in through-diffusion experiment for assessing the ability of radionuclide retardation. The distribution coefficients (K _d) obtained by batch tests in 14 days under aerobic and anaerobic systems were 6.98 ± 0.35 and 5.21 ± 0.25 mL/g. Moreover, Rf^cal and K _d ^cal of Se obtained from accumulative concentration’s method in through-diffusion test showed an obvious discrepancy with the increase of length/diameter (L/D) ratio. However, it presented an agreement of Rf^H/Se and K _d ^H/Se in a various L/D ratio by comparison of apparent diffusion coefficient’s (D _a) between HTO and Se. It appears that the Rf^H/Se and K _d ^H/Se obtained from the through-diffusion experiments are lower than those derived from the batch experiments. Therefore, it demonstrates that reliable Rf and K _d of Se by through-diffusion experiments could be achieved at a non-reactive radiotracer (HTO) prior to tests and will be more confident in long-term performance assessment of disposal repository.     

Diffusion of levodopa in aqueous solutions of hydrochloric acid at 25 °C

Ternary mutual diffusion coefficients (D₁₁, D₂₂, D₁₂ and D₂₁) measured by the Taylor dispersion method are reported for aqueous solutions of {levodopa (l-dopa) + HCl} solutions at 25 °C and HCl concentrations up to 0.100 mol · dm⁻³. The coupled diffusion of l-dopa (1) and HCl (2) is significant, as indicated by large negative cross-diffusion coefficients. D₂₁, for example, reaches values that are larger than D₁₁, the main coefficient of l-dopa. Combined Fick and Nernst–Planck equations are used to analyze the proton coupled diffusion of l-dopa and HCl in terms of the binding of H⁺ ions to l-dopa and ion migration in the electric field generated by l-dopa and HCl concentration gradients.