The alkali cation effect on the 1H NMR chemical shifts of the indenyl carbanion

The complex character of the temperature dependence of the ¹H NMR chemical shifts of indenyl-lithium and -sodium in dimethoxyethane is explained. It is shown that the cation causes a polarisation of the C? H bonds and thus influences the proton shifts of the anion, both directly by its electric field along the bonds (the direct effect) and indirectly via its effect on the π-electron distribution (the indirect effect). The indirect effect is inferred from ¹³C NMR chemical shift data. By subtracting the temperature dependent contribution of the indirect effect from the experimental ¹H data, the direct effect is visualised. It appears that information on ion paris obtained by ¹H and ¹³C NMR on the one hand and optical spectroscopy on the other hand is complementary. Apparently, aggregation of ion pairs does not seriously affect the chemical shift data.     

Kinetic features of the adsorption of sodium oleate on talc

Kinetic features of the adsorption of sodium oleate on dispersed talc samples of Onotskoe deposit are studied. It is shown that adsorption proceeds in two steps with different rate constants of adsorption k _a and desorption k _d. It is found that at the first step, lasting for nearly one hour under experimental conditions, the process is characterized by high k _a and k _d values (1.23 × 10^?2 m²/(mol min) and 1.06 × 10^?5 m²/(L min), respectively). It is concluded that the final stage associated with the rearrangement of molecules on a talc surface lasts for a long time with k _a = 2.12 × 10^?3 m²/(mol min) and k _d = 1.82 × 10^?6 m²/(L min).     

Comprehensive ion-exchange and adsorption study of the distribution of exchanging inorganic cations over the interlayer gaps of vermiculite

The exchange of Co²⁺ ions on Na-vermiculite has been comprehensively studied by the ionexchange, adsorption, and X-ray diffraction methods. It has been shown that vermiculite is distinguished by high selectivity to Co²⁺ cations and Kielland dependence log $\tilde K_m (\theta )$ increasing with filling of ion-exchange sites with sorbed cations rather than a decreasing one that is observed for common systems. It has been established that the ion exchange is accompanied by segregation of Na+ and Co²⁺ cations in separate interlayer gaps of vermiculite with the final formation of a disordered layered “cake” composed of separate silicate layers and interlayer gaps enriched with Na⁺ and Co²⁺ ions.     

Effect of the nature of ions on the position of the absorption bands of water OH bonds in diffuse reflection spectra in the near-infrared region

The effect of the nature of anions and cations on the position of the absorption bands of free and crystallization water in inorganic salts in the near-infrared region (7400–4000 cm⁻¹) was systematically studied. It was shown experimentally that the shift of the absorption bands of free water to the high-frequency region is 100 cm⁻¹ in the region of 6900 and 62.1 cm⁻¹ in the region of 5160 cm⁻¹. It was concluded that the results on the shift of the water absorption bands in moisture-containing solid-state compounds with respect to those of pure liquid water can serve for a qualitative estimate of the bond energy of water with the substance under study and can be used to choose the wavelength for measuring the humidity of these objects and those more complicated in composition by means of near-infrared spectroscopy.     

Determination of the complete stoichiometry of Bi-Pb-Sr-Ca-Cu-O-superconductors

Summary A convenient analytical method based on complexometric and iodometric titration for determining the complete stoichiometry of Bi-Pb-Sr-Ca-Cu-O-superconductors (PBSCCO) has been developed. It is shown that the individual contents of Cu³⁺, Bi⁵⁺, Pb⁴⁺ are not required for calculating the oxygen content of such materials. It turned out that the lead content and the oxygen content of sintered samples are much lower than those of calcined powders.     

Computer simulation of the hydration of a chloride anion in a nanopore with hydrophilic walls

The hydration of a single-charged chloride anion Cl^- in a model plane nanopore with structureless hydrophilic walls in water vapor at room temperature is simulated using the Monte Carlo method. It is established that the adsorption of a fraction of associate molecules Cl^-(H₂O)_N on the walls enhances its thermodynamic stability and simulates the hydration of the ion at low vapor pressures. It is shown that a second stability crisis forms on the curve of the hydration work function in the mode of weak wall hydrophilicity.     

Study of the gadolinium sorption on the C100 ion-exchange resin for the development of the antineutrino detector targets

Adsorption of the gadolinium from H₂O and HCl solutions on the ion-exchange resin C100 is investigated. The experiments were carried out by varying the acidity of the liquid phase, the amount of sorbent, and the temperature. The maximal sorption of the ions Gd³⁺ is observed from the solution 0–0.2 M HCl under optimal conditions, the sorption reaches more than 99.5%. Sorption of Gd³⁺ on C100 from H₂O solution occurs most intensively during the first 3 min then for 30 min the system smoothly comes to equilibrium. The maximal sorption capacity of the resin C100 amounted to 1.2 ± 0.1 mmol g^?1. The thermodynamic parameters of sorption: ΔG = ? 24.20 kJ mol^?1, ΔS = ? 90.27 J mol^?1 K^?1, ?H = ? 50.93 kJ mol^?1 were evaluated. It is shown that the sorption of gadolinium on the ion-exchange resin C100 is described by models of kinetically pseudo-first and pseudo-second order. It is established that the Gd³⁺ sorption on the C100 resin is reversible second order chemical reaction.     

A simple method for the determination of the specific activity of125I-tracer used in radioimmunoassay

Knowledge of the specific activity of the¹²⁵I-tracer is essential for optimization and for calculation of RIA parameters. The specific activity of the¹²⁵I-thyroxin used in thyroxin radioimmunoassay /RIA/ has been determined by a simple method involving combination of RIA and displacement analysis. It has been compared with the value obtained by the conventional method based on radioiodination data. Our studies indicate that even for a non-protein hormone like thyroxin the specific activity of¹²⁵I-thyroxin derived from iodination data is not reliable. The specific activities obtained by displacement analysis were consistent with the experimental findings.     

Distributions of the unperturbed dimensions of Markov-chain copolymers

This investigation shows that Markov-chain copolymers can be regarded as random copolymers the segment lengths of which depend on the copolymerization parameters. It was possible to derive simple analytical formulae for the mean-square end-to-end distance (〈r²〉), the Kuhn length, and the distribution of r² under theta-conditions. The results of these equations are in excellent agreement with data from simulations. It is shown that 〈r²〉 as well as the non-uniformity of r² increase strongly with increasing probabilities of homopropagation, i.e., with increasing mean homosequence lengths. Furthermore it is demonstrated by simulation that even chains of identical length and composition show a distribution of r² because of different arrangements of the sequences inside the chains. For chains or chain segments shorter than the average homosequences, a double-peak distribution of r² is found. The equations derived in this paper can be applied to real copolymers as well as to chains the curvature of which is altered locally by the association of ligands.     

Influence of the precipitation rate on the seasonal variation in the specific radioactivity of short-lived222Rn daughters in precipitation

Data of variations in the RaB/²¹⁴Pb/ and RaC/²¹⁴Bi/activities in precipitation obtained from observations made for a period of almost 5 years are given together with data on changes in precipitation rate measured simultaneously. It is concluded from analysis of these data that the precipitation rate variation contributes to approximately 40% to the seasonal variation in the specific activity of precipitation.     

Application of the two-body density matrix of the ground state for calculations of some excited states

It is pointed out that the density matrices of the ground state contain valuable information concerning the calculation of particle-hole excited states. As an illustration, results on the nuclei ¹⁶O, ²⁰Ne, and ²⁸Si are presented, using small model spaces.     

A new method for the direct calculation of resonance parameters with application to the quasibound states of the H2X1Σ g + system

A new method for the direct calculation of resonance parameters is presented. It is based upon searching for poles of the scattering matrix at complex energies. This search is expedited by the use of analytic derivatives of the scattering matrix with respect to the total energy. This procedure is applied initially to a single channel problem, but is generalizable to more complicated systems. Using the most accurate available potential energy data, we calculate resonance parameters for all of the physically important quasibound states of the ground electronic state of the hydrogen molecule. Corrections to the Born-Oppenheimer potential are included and assessed. The new method has no difficulty locating resonances with widths greater than about 1×10^–7 cm^–1. It is easier to find narrow resonances by monitoring the dependence of the imaginary part of the reactance matrix on the real part of a complex energy than to monitor the dependence of the eigenphase sum on energy at real energies.     

Diffusion kinetics of the ion exchange of benzocaine on sulfocationites

The theory of the ion exchange kinetics on strong acid cationites with the participation of weak electrolytes is discussed. The kinetics of desorption of benzocaine in the protonated and molecular forms from strong acid cationites, sulfonated polycalixarene, and KU-23 30/100 sulfocationite, is studied experimentally. It is shown that the flow of protonated benzocaine from cationite upon desorption proceeding by the ion-exchange mechanism is more intense than upon desorption of nonionized benzocaine molecules. It is established that the diffusion coefficient of benzocaine cations is (1.21 ± 0.23) × 10^?12 m²/s in KU-23 30/100 sulfocation and (0.65 ± 0.06) × 10^?13 m²/s in sulfonated polycalixarene, while the diffusion coefficient of benzocaine molecules is (0.65 ± 0.15) × 10^?14 m²/s in sulfonated polycalixarene.     

Features of the complexation of octadecane-2,4-dione and lanthanide ions in Langmuir monolayers

Monolayers of octadecane-2,4-dione on the surfaces of EuCl₃ and TbCl₃ solutions in the concentration range of 1 × 10^–4 to 5 × 10^–3 M at pH 5.8 are studied. It is found that the limiting area of octadecane-2,4-dione molecule in a monolayer dependence on Eu³⁺ and Tb³⁺ concentration is of extreme nature. The formation of complex compounds in the ligand monolayer is postulated, and structures are proposed for these compounds at different concentrations of metal ions.     

Validation of methodology for determination of the mercury methylation potential in sediments using radiotracers

Experiments to determine the mercury methylation potential were performed on sediments from two locations on the river Idrijca (Slovenia), differing in ambient mercury concentrations. The tracer used was the radioactive isotope ¹⁹⁷Hg. The benefit of using this tracer is its high specific activity, which enables spikes as low as 0.02 ng Hg²⁺ g⁻¹ of sample to be used. It was therefore possible to compare the efficiency of the methylation potential experiments over a range of spike concentrations from picogram to microgram levels. The first part of the work aimed to validate the experimental blanks and the second part consisted of several series of incubation experiments on two different river sediments using a range of tracer additions. The results showed high variability in the obtained methylation potentials. Increasing Hg²⁺ additions gave a decrease in the percentage of the tracer methylated during incubation; in absolute terms, the spikes that spanned four orders of magnitude (0.019–190 pg g⁻¹ of sediment slurry) resulted in MeHg formation between 0.01 and 0.1 ng MeHg g⁻¹ in Podroteja and Kozarska Grapa. Higher spikes resulted in slightly elevated MeHg production (up to a maximum of 0.27 ng g⁻¹). The values of methylation potential were similar in both sediments. The results imply that the experimental determination of mercury methylation potential strongly depends on the experimental setup itself and the amount of tracer added to the system under study. It is therefore recommended to use different concentrations of tracer and perform the experiments in several replicates. The amount of mercury available for methylation in nature is usually very small. Therefore, adding very low amounts of tracer in the methylation potential studies probably gives results that have a higher environmental relevance. It is also suggested to express the results obtained in absolute amounts of MeHg produced and not just as the percentage of the added tracer.     

The mechanism of electroreduction of nitrobenzene and 3-nitropyridine in DMF in the presence of divalent cations

The differences in electrochemical behaviour of nitrobenzene and 3-nitropyridine connected with a change of supporting electrolyte are discussed. It is shown that in the presence of alkaline earch metal cations a deposit of composition (NB^?. Me²⁺) is formed at the electrode surface. The cations: Ba²⁺, Ca²⁺ and Mg²⁺ cause the instability of the nitrobenzene radical anion formed in the first electroreduction step. It was found that in the presence of Ba²⁺ and Ca²⁺ the NOB/NO^?. couple is stabilized.     

On the use of the Bayliss-McRae dispersion model in NMR solvent effects

The use of the Bayliss-McRae theory on the solvent induced electronic frequency shifts for NMR dispersion shifts is criticized. It is suggested that the NMR shifts should actually be proportional to the square of the Bayliss-McRae function. It is shown that the methane gas-to-liquid shifts in eleven halo-methanes as solvents are indeed proportional to this squared function; ?σ_m(CH₄) = 9.62 (n₂²?1)²/(2n₂²+1)² ppm, where n₂ is the refractive index of the solvent. The relation between this solvent factor and several existing continuum models for NMR medium shifts is discussed.     

The effect of calcination temperature on the texture of silica gel waste

In this work, the effect of temperature on the texture of silica gel waste is presented and water vapour adsorption in a different humidity is highlighted. It was found that silica gel waste is a mesoporous material with the parallel plates pores. Its specific surface area is equal to 4.61 m² g^?1, and the calculated total pore volume is equal to 9.01 × 10^?3 cm³ g^?1. The texture of silica gel waste changed during calcination in a 188–550 °C temperature interval: S_BET and ΣV_P increased to 11.32 m² g^?1 and 30.06 × 10^?3 cm³ g^?1, respectively. It was determined that the water vapour pressure influenced the mineralogical composition and the quantity of adsorbed water in the samples. The obtained results were confirmed by the differential scanning microcalorimetry, X-ray diffraction, BET and water vapour adsorption analysis data.

     

Density-functional calculations of HCN adsorption on the pristine and Si-doped graphynes

Graphyne, a lattice of benzene rings connected by acetylene bonds, is one-atom-thick planar sheet of sp- and sp²-bonded carbons differing from the hybridization of graphene (considered as pure sp²). Here, HCN adsorption on the pristine and Si-doped graphynes was studied using density-functional calculations in terms of geometric, energetic, and electronic properties. It was found that HCN molecule is weakly adsorbed on the pristine graphyne and slightly affects its electronic properties. While, Si-doped graphyne shows high reactivity toward HCN, and, in the most favorable state, the calculated adsorption energy is about ?10.1 kcal/mol. The graphyne, in which sp-carbon was substituted by Si atom, is more favorable for HCN adsorption in comparison with sp²-carbon. It was shown that the electronic properties of Si-doped graphyne are strongly sensitive to the presence of HCN molecule and therefore it may be used in sensor devices.