Study on the fluoride adsorption of various apatite materials in aqueous solution

The aim of this study was to evaluate the defluoridation efficiencies of various sorbents in aqueous solution. These sorbents include synthetic nano-hydroxyapatite (n-HAp), biogenic apatite (bone meal), treated biogenic apatite (bone meal prepared by H₂O₂ oxidation) and geogenic apatite (rock phosphate), which were characterized by XRD, FTIR, TEM and SEM. It has been observed that the defluoridation capacities follow the order: n-HAp > BH₂O₂ > B > rock phosphate. The controlling factors, sorbent dose, initial fluoride concentration, pH, contact time and temperature were investigated. The defluoridation capacities increased with the increase in the initial fluoride concentration and contact time, decreased with the increase in the sorbent dose. The optimum pH range for removal of fluoride on various apatite sorbents was considered to be 5.0-6.0. The fluoride adsorption can be explained by Langmuir, Freundlich isotherms, and the adsorption kinetic data follow the pseudo-second-order model. Thermodynamic parameters such as ΔH⁰, ΔS⁰ and ΔG⁰ indicated that the adsorption on various apatite sorbents was spontaneous and endothermic. These results showed that bone meal is a promising material for fluoride adsorption.     

Computed potential hypersurface (including electron correlation) of the system Li+/H2

The potential hypersurface of the system LiH₂* is calculated in the Hartree—Fock approximation and with the IEPA PNO method (including electron correlation). The basis set consists of gaussian lobes. The region of HH distances considered is 0.9 to 3 a_o (occasionally to 5 a_o) whereas the distance of the Li nucleus to the midpoint of the H₂ subunit is varied between 1 and 15 α_o. The angular dependence of the hypersurface is investigated as well. The maximum overall error (except for a parallel shift of the whole hypersurface) is estimated to be less than 0.002 au and even smaller in more limited regions of space. The role of the correlation energy is discussed and the asymptotic behaviour of the Li⁺/H₂ interaction is compared with results from perturbation theory. The results are given both as tables of numbers in the form of an analytic fit. The change of energy, equiblirium distance and force constant of the H₂ as a function of the approach of the Li⁺ is also tabulated.     

The role of internal H-bonding in the conformational preferences of some molecules of the formula CH3CHYCH2X

The conformational energies of 1-amino-2-propanol, 2-amino-1-propanol and 1,2-diaminopropane are studied using ab initio molecular orbital theory employing minimal (STO-3G) and extended (4-31G) basis sets. Calculations at both levels of theory generally favor conformations stabilized by internal H-bonding for all molecules considered. Results are first presented for conformations employing assumed geometries. Since the conformational energy differences as found by the initial set of calculations are in some cases rather small it then becomes necessary to introduce geometry optimizations into the study at the minimal STO-3G level. In addition, to get a better estimate of the energy differences of the various conformations 4-31G calculations are performed on the STO-3G optimized structures. These latter results indicate the following, (a) For 1-amino-2-propanol only one conformation that is stabilized by intramolecular H-bonding is low in energy; this has the methyl and amino groups anti. The other H-bonded conformer, where the methyl and amino groups are gauche, is predicted to be ca. 1.2 kcal mol^?1 less stable. Similar findings for this molecule have recently been provided by micro-wave spectroscopy. (b) For 2-amino-1-propanol the two H-bonded conformers are only separated by about 0.5 kcal mol^?1, with the anti conformer being more stable. Micro-wave spectroscopy again supports these calculations. (c) For 1,2-diaminopropane the gauche conformer is predicted to be of rather high energy (ca. 2.5 kcal mol^?1) compared to the corresponding anti H-bonded conformer. The value of 2.5 kcal mol^?1should be taken as an upper limit, since the geometry optimization of the gauche conformer of 1,2-diaminopropane is incomplete compared to the optimization carried out for the anti conformer.     

A Study of the Reaction of Phosphorus Trichloride with Paraformaldehyde in the Presence of Carboxylic Acids

Abstract

We investigated the mechanism of the reaction of paraformaldehyde with phosphorus trichloride in the presence of carboxylic acids (acetic, propanoic, and formic). Our results revealed that bisphosphonic acids were obtained without the use of water. The structures of the reaction products were studied by 1D and 2D homonuclear and heteronuclear ¹H-, ¹³C-, ³¹P- NMR spectroscopy.

[Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfer, and Silicon and the Related Elements for the following free supplemental files: Additional tables.]     

TGF-��-treated antigen presenting cells suppress collagen-induced arthritis through the promotion of Th2 responses

Collagen-induced arthritis (CIA) is mediated by self-reactive CD4⁺ T cells that produce inflammatory cytokines. TGF-β₂-treated tolerogenic antigen-presenting cells (Tol-APCs) are known to induce tolerance in various autoimmune diseases. In this study, we investigated whether collagen-specific Tol-APCs could induce suppression of CIA. We observed that Tol-APCs could suppress the development and severity of CIA and delay the onset of CIA. Treatment of Tol-APCs reduced the number of IFN-γ- and IL-17-producing CD4⁺ T cells and increased IL-4- and IL-5-producing CD4⁺ T cells upon collagen antigen stimulation in vitro. The suppression of CIA conferred by Tol-APCs correlated with their ability to selectively induce IL-10 production. We also observed that treatment of Tol-APCs inhibited not only cellular immune responses but also humoral immune responses in the process of CIA. Our results suggest that in vitro-generated Tol-APCs have potential therapeutic value for the treatment of rheumatoid arthritis as well as other autoimmune diseases.     

A model of macroradical recombination in dilute solutions

The dependence of exchange rate constants and diffusion coefficients of stable macroradicals (modified polydimethylsiloxane ($\text{P}\text{= 15, 29, 97}$) and polyethylenoxide ($\text{P}\text{= 25, 47, 140}$) on the length of polymer chain in various solvents is investigated. The results are compared with the rate constants for diffusive bimolecular recombination of macroradicals of various lengths. The dependence of rate constants of exchange and combination for macroradicals of different lengths obey the same law.The rate of combination for macroradical with P = 15-10⁵ is shown to depend mainly on the mobility of an active centre, limited by diffusion of the whole macromolecule. The diffusion rate constant of combination can be described by the Smoluchowski equation in which the radius of an active centre is used as the effective radius of interaction.A model of bimolecular termination of macroradicals, a model of “freely penetrating coils” (FPC), is proposed. It implies that k_ter ～ P^{?0.9 ± 0.1} (for “good” solvents). The reactivity of an active centre in recombination is independent of the length of a macroradical chain for P > 15.The exchange interaction in a radical pair broadens the ESR lines of radicals and recombination with equal effectiveness.     

Active monomeric nucleotide intermediate in the oligonucleotide synthesis

The interaction of 3′ - O - acetylthymidine - 5′ - phosphate (pT-Ac) and p - nitrophenylphosphate (pPhNO₂) with triisopropylbenzenesulphonyl chloride (TPS) in pyridine was studied by the pulsed NMR spectroscopy on ³¹P nuclei. The esters investigated were shown to convert to the corresponding disubstituted pyrophosphates, trisubstituted tripolyphosphates and compounds showing a singlet displaced 5–8 ppm from the original ester. The latter are the main final products of the interaction of nucleotide and pPhNO₂ with TPS. The investigation of the chemical conversion of a pT-Ac derivative with a 5·1 ppm shift showed that this product is a powerful phosphorylating reagent. It was shown that this active derivative contains one P atom in accordance with the structure of monomeric metaphosphoric acid ester proposed by Todd for these compounds. The reaction of monomeric metaphosphate with 5′-O-tritylthymidine results information of a compound, containing stoichiometric amounts of pT-Ac and 5′ - O - tritylthymidilyl - (3′ → 5′) - 3′ - O - acetylthymidine residues. This compound was identified as a trisubstituted P¹ - 5′ - O - trityl - P¹ - P² -bis -(3′ - O - acetylthymidine) - pyrophosph     

Thermodynamics of the formation of nickel(II) complexes with L-histidine in aqueous solutions

The heat effects of the formation of Ni(II) complexes with L-histidine in an aqueous solution are determined via direct calorimetry at 298.15 K and ionic strengths of 0.2, 0.5, and 1.0 (KNO₃). The standard thermodynamic characteristics (Δ_r H ^○, Δ_r G ^○, Δ_r S ^○) of complex formation in the investigated system are calculated. It is concluded that the resulting values are consistent with the results from studying the structure of L-histidine complexes with Ni²⁺ ions by various spectral methods.     

Investigation of the excimer dynamics in 9,10-dichloroanthracene crystals using picosecond spectroscopy

The dynamics of excimer formation, excimer migration, and excimer dissociation in β-9,10-dichloroanthracene crystals were investigated by means of picosecond time-resolved fluorescence spectroscopy. In the temperature range from T = 20 K to T = 40 K we were able to temporally resolve the relaxation into the excimer state. The excimer formation rates were determined to be k ≈ 1.8 × 10¹¹ s^?1 at T = 40 K and k ≈ 2.0 × 10¹⁰ s^?1 at T<30 K. The excimer migration was investigated by measuring the excimer annihilation rate as a function of temperature. At room temperature 20% of the excimers are dissociated. The excimer binding energy is estimated to be B = 1360 cm^?1. The experimental results are explained in terms of a kinetic scheme comprising the population and depopulation of exciton, trap, and excimer states. The nature of the trap state is identified and it is shown that thermal activation of a 25 cm^?1 librational mode induces the relaxation of the trap into the excimer state.     

First-principles relativistic calculation for 4f-5d transition energy of Ce in various fluoride hosts

In this paper, we investigated the 4f-5d transition energy of Ce³⁺ in various fluoride hosts based on the first-principles discrete-variational Dirac-Slater (DV-DS) calculations using Slater's transition-state theory. Especially, we focused on the lowest energy peak (1st peak) of 4f-5d transition for Ce³⁺ impurities. As the host crystals, we adopted the 15 fluorides, for which the experimental data of the lowest energy peak (1st peak) in 4f-5d transitions were available from literature except for NaMgF₃ and BaMgF₄. A high correlation between the experimental 1st peak energies and the theoretical ones was obtained which suggests a possibility to predict the 4f-5d transition energy of Ce³⁺ in various fluoride hosts using the first-principles calculation.     

Theoretical studies on the kinetics and mechanism of the reaction of atomic hydrogen with carbon dioxide

The potential energy surface for the reaction of hydrogen atom with carbon dioxide is explored by using various quantum chemical methods including W1BD, CBS-QB3, G4, G3B3, CCSD(T), QCISD(T), CCSD, M06-2X, and BB1K.Transition state theory and a modified strong collision/RRKM model are employed to calculate the thermal rate coefficients for the reaction. The results of calculation show that the overall rate constant for the reaction H + CO₂ are pressure-independent over the temperature range of 300 to 3500 K. By using the energies at the W1BD level, the non-Arrhenius expression k = 9.8T ^2.9exp(?74.8 kJ/mol/RT) L mol^?1 s^?1 was found for the reaction.     

The use of naphthalene derivatives in inorganic analysis : The effect of substituents in the naphthalene nucleus on the fluorimetric detection of tin

Fourteen substituted nitronaphthalene derivatives have been examined as reagents for the fluorimetric detection of tin. The compounds investigated included dinitronaphthalenes, dinitronaphthylamines, halogen substituted mononitronaphthylamines, mononitroso- and dinitro-naphthols and their sulphonic acid derivatives. Four of these reagents have been found to exhibit strong fluorescence and another four to give moderate fluorescence with stannous tin. All reagents are capable of detecting l0^-4 g stannous tin and with four of them, 10^-5 g is capable of detection in 0.01 ml of solution. The results indicate that two of the most important factors relating structure of reagent to intensity of fluorescence are (a) the position of the nitro group in the naphthalene nucleus, i.e., whether it is α- or β- or whether it is sterically hindered and (b) the electropositive or electronegative character of other substituent groups in the reagent     

Rapid and accurate amperometric determination of acetaminophen in pharmaceutical preparations and spiked human blood serum samples at cadmium pentacyanonitrosylferrate modified glassy carbon electrode

The present work describes a rapid and accurate amperometric technique for the determination of acetaminophen (ACT) in pharmaceutical preparations and human blood serum, based on electrocatalytic oxidation of ACT at a glassy carbon electrode modified by cadmium pentacyanonitrosylferrate (CdPCNF) film. The electrocatalytic response of the modified GC electrode was linear over the concentration of 1.64-52.90 μM. The limit of detection was found to be 2.04 μM by amperometric technique. The method was successfully utilized for the determination of ACT in various pharmaceutical preparations and the results have been statistically compared with those obtained by the official method. The interference of some pharmaceutical and biological compounds was investigated. The results of interference study showed that the Nafion-coated CdPCNF|GC electrode can be utilized as a selective amperometric sensor for acetaminophen determination in human blood serum. The mean value of rate constant k for catalytic reaction, and the diffusion coefficient of ACT (D) in the phosphate buffer solution of pH 7.2 were found to be 4.27 × 10² M?¹ s?¹, and (4.25 ± 0.33) × 10^?6 cm² s^?1, respectively.     

Rheological properties of the methylcellulose gels in N,N-dimethyl formamide: Validity of scaling laws

The rheological behavior of the methylcellulose (MC) gels in N,N-dimethylformamide (DMF) was studied under dynamic compression with respect to the presence of various concentrations c (1, 2, 2.5 and 3 wt %) and different molecular weight M (4.1 × 10⁴, 6.3 × 10⁴ and 8.8 × 10⁴) of MC in the gels. The temperature scan for the 1 wt % MC gel (M = 8.8 × 10⁴) in DMF shows double crossover of the storage modulus E′ with the loss modulus E″. This indicates that two types of transitions namely the phase separated MC-DMF mixture to MC-DMF gel and MC-DMF gel to solution are present. The plot of storage modulus E′ with temperature shows almost plateau like behavior. This plateau like behavior may reflect the equilibrium between the core formation and core disintegration. In the frequency scan of MC gels, the modulus increases with an increase in the concentration. This can be explained by the increase in core structure of the gel. The core formation in the MC-DMF gel is a concentration dependent parameter. While comparing the different molecular weight grades of MC, it is observed that the storage modulus increases with an increase in the molecular weight of the MC. The validity of three scaling laws is also investigated with respect to various concentration of MC-88.000. The modified scaling law in terms of relative frequency and modulus $\left( {\eta '_r = \frac{{\left| {\frac{{E''}} {\omega } - \left( {\frac{{E''}} {\omega }} \right)_c } \right|}} {{\left( {\frac{{E''}} {\omega }} \right)_c }}andE'_r = \frac{{\left| {E' - E'_c } \right|}} {{E'_c }}} \right) $ is seemed to be applicable.     

Non-empirical calculations on the conformational structure of azobenzene and benzylideneaniline

The conformational structures of cis- and trans-azobenzene and benzylideneaniline have been investigated by means of ab initio SCF calculations. Contrary to semiempirical results, the equilibrium molecular geometries are correctly accounted for in the non-empirical SCF-formalism. Trans-azobenzene is found to be planar, or at least peri-planar, while the phenyl rings of the cis-isomer are twisted by 56° out-of-plane. Both isomers of benzylideneaniline are non-planar, with rotational angles θ₁ (C-N) = 48°, θ₂(C-C) = 0° and θ₁ = θ₂ = 75° for the trans and cis form, respectively. Trans-azobenzene is calculated to be more stable by 10.4 kcal mol^?1 than the cis isomer, which is in good accord with the experimental value of 10 kcal mol^?1. The energy of isomerization of benzylideneaniline amounts to 13.0 kcal mol^?1.     

Unusual influences of temperature and medium on the tacticity of radically polymerised poly(n-vinyl imidazole)

The tacticities of radical poly(N-vinyl imidazole)s prepared in several organic solvents, in water and at various values of pH and temperature have been investigated by ¹H and ¹³C-NMR. It seems most likely that high temperatures favour racemic placements over meso placements but that, at low pH, meso placements are favoured. Thus the changes in polymerisation rate with pH noted by others for this system are accompanied by changes in the stereochemistry of the resulting polymer.     

Acid-catalyzed aza-Diels-Alder versus 1,3-dipolar cycloadditions of methyl glyoxylate oxime with cyclopentadiene

The acid-catalyzed 1,4- and 1,3-cycloadditions between methyl glyoxylate oxime (1) and cyclopentadiene were investigated using various Lewis and/or Bronsted acids at different temperatures in dichloromethane as solvent. Besides the expected new adducts, (±)-methyl [(3-exo)-2-hydroxy-2-azabicyclo[2.2.1]hept-5-ene]-3-carboxylate (2) and (±)-methyl [(3-endo)-2-hydroxy-2-azabicyclo[2.2.1]hept-5-ene]-3-carboxylate (3), a third adduct, (±)-methyl (1R,4R,5R)-(2-oxa-3-azabicyclo[3.3.0]oct-7-ene)-4-carboxylate (4), whose formation can be explained by a 1,3-dipolar cycloaddition, was obtained. Yields and product ratios were found to be more dependent on the catalyst than on the temperature; these results and the stereochemistry of the adducts, confirmed by spectroscopic data (¹H and ¹³C NMR) and by X-ray crystallography, were used to analyze and propose a mechanistic explanation for both cycloadditions.     

Benchmarking the Fluxional Processes of Organometallic Piano-Stool Complexes

The correlation consistent Composite Approach for transition metals (ccCA-TM) and density functional theory (DFT) computations have been applied to investigate the fluxional mechanisms of cyclooctatetraene tricarbonyl chromium ((COT)Cr(CO)₃) and 1,3,5,7-tetramethylcyclooctatetraene tricarbonyl chromium, molybdenum, and tungsten ((TMCOT)M(CO)₃ (M = Cr, Mo, and W)) complexes. The geometries of (COT)Cr(CO)₃ were fully characterized with the PBEPBE, PBE0, B3LYP, and B97-1 functionals with various basis set/ECP combinations, while all investigated (TMCOT)M(CO)₃ complexes were fully characterized with the PBEPBE, PBE0, and B3LYP methods. The energetics of the fluxional dynamics of (COT)Cr(CO)₃ were examined using the correlation consistent Composite Approach for transition metals (ccCA-TM) to provide reliable energy benchmarks for corresponding DFT results. The PBE0/BS1 results are in semiquantitative agreement with the ccCA-TM results. Various transition states were identified for the fluxional processes of (COT)Cr(CO)₃. The PBEPBE/BS1 energetics indicate that the 1,2-shift is the lowest energy fluxional process, while the B3LYP/BS1 energetics (where BS1 = H, C, O: 6-31G(d′); M: mod-LANL2DZ(f)-ECP) indicate the 1,3-shift having a lower electronic energy of activation than the 1,2-shift by 2.9 kcal mol⁻¹. Notably, PBE0/BS1 describes the (CO)₃ rotation to be the lowest energy process, followed by the 1,3-shift. Six transition states have been identified in the fluxional processes of each of the (TMCOT)M(CO)₃ complexes (except for (TMCOT)W(CO)₃), two of which are 1,2-shift transition states. The lowest-energy fluxional process of each (TMCOT)M(CO)₃ complex (computed with the PBE0 functional) has a ΔG^‡ of 12.6, 12.8, and 13.2 kcal mol⁻¹ for Cr, Mo, and W complexes, respectively. Good agreement was observed between the experimental and computed ¹H-NMR and ¹³C-NMR chemical shifts for (TMCOT)Cr(CO)₃ and (TMCOT)Mo(CO)₃ at three different temperature regimes, with coalescence of chemically equivalent groups at higher temperatures.     

Analysis and predictions of the vibronic spectrum of the ethynyl radical C2H by ab initio methods

A purely ab initio study of the vibronic structure of the C₂H spectrum in the region up to 7000 cm^?1, which is complicated by the coupling of theX ²Σ⁺ andA ² II systems, is presented. The potential surfaces for the three lowest-lying electronic states 1² A′, 2² A′ and 1² A″ correlating withX ²Σ⁺ andA ² II at the linear molecular geometry are calculated for the various geometrical distortions by means of the multireference configuration interaction (MRD-CI) method. These adiabatic surfaces are transformed into suitable diabatic counterparts. An approach is developed for a simultaneous treatment of three electronic states coupled via the bending and C-C stretching vibrations. Spin-orbit splitting of the vibronic levels and the vibronically averaged values for the hyperfine coupling constants are computed. The results obtained in this study enable a reliable explanation of the available experimental findings of the C₂H spectrum and predict a number of features to be verified by future experiments.