Adsorption of citrate ions on hydroxyapatite synthetized by various methods

The specific adsorption of citric acid ions at hydroxyapatite interface was investigated by the means of radioisotope method (¹⁴C) as a function of citric acid ions concentration, NaCl concentration and pH. Application of the hydroxyapatite has become wide in the biomaterial field as the Ca₁₀(OH)₂(PO₄)₆ possess biocompatibility with human hard tissue. Hydroxyapatite was synthesized using three different methods. The physical properties of the resulting powder were characterized by DTA/TG, XRD, AFM and SEM microscopy. Physicochemical qualities characterizing the electrical double layer of the hydroxyapatite/NaCl solution interface were determined. The zeta potential and the adsorption of citric acid molecule were studied as a function of pH. The point of zero charge and the isoelectric point of samples were determined. Electrical double layer parameters of hydroxyapatite/NaCl interface are influenced by a synthesis method. The points pH_pzc and pH_IEP for sample 1 are pH_pzc 7.5 and pH_IEP 3; for sample 2 pH_pzc 7.05 and pH_IEP 3, for smaple 3 pH_pzc 6.7 and pH_IEP 3. Temperature has weak influence both on pure substance and with citric acid adsorbed, as derivatographic analysis has shown, and characterization of hydroxyapatite structure may be carried out by this thermal analysis. Two phenomena are responsible for citric acid adsorption: phosphate group’s replacement at hydroxyapatite surface by citric ions parallel to intraspherical complexes formation.     

Electrochemical reduction of nitrate using various anodes and a Cu/Zn cathode

Electrochemical reduction of nitrate was studied using a Cu/Zn cathode and Ti/Pt, Ti/IrO₂–Pt and Ti/RuO₂–Pt anodes in an undivided and unbuffered cell. A novel condition for performing both cathodic reduction of nitrate and anodic oxidation of the ammonia and nitrite by-products was achieved using Ti/Pt and Ti/IrO₂–Pt anodes in the presence of NaCl, especially with Ti/IrO₂–Pt anode. Nitrate could be completely removed using the Ti/IrO₂–Pt and Ti/Pt anode, with neither ammonia nor nitrite detected in the treated solution. A low nitrate reduction rate was observed when using a Ti/RuO₂–Pt anode in the presence of NaCl. However, in the absence of NaCl, all anodes showed good performance for nitrate reduction, with the Ti/Pt anode having the highest selectivity for reducing nitrate to nitrogen.     

Comparative study of pertechnetate reduction by thiourea using spectrophotometric,solvent extraction and ion-exchange methods

The results of a comparative study of pertechnetate reduction by thiourea in mineral acid (HCl, HNO₃, HClO₄, H₂SO₄) media using spectrophotometric, solvent extraction and ion-exchange chromatographic methods are presented. Changes of spectral characteristics of redox systems and distribution characteristics of reduced technetium (cationic) forms on extraction with bis(1,2-dicarbollide)cobaltic acid and on ion exchange on Dowex 50WX8 were established as a function of time and either aqueous or organic phase composition. Thiourea was tested as a reagent for reduction back-extraction of technetium from organic phases containing the amines Aliquat 336 and trilaurylmethylammonium as convenient extraction reagents for pertechnetate.     

A near-infrared study of the hydration of various ions and nonelectrolytes

The differential infrared absorption spectra of H₂O at 1200 nm and HOD/D₂O at 1450 nm have been recorded as function of temperature between 2 and 55°C. Following earlier investigations in the 1000 nm region,^(1,2) the data were interpreted on the basis of a hydrogen-bonding equilibrium invoking two states of the OH oscillators which are found to differ by a van't Hoff heat of formation of 2–3 kcal-mole^–1. The spectral changes induced by various non-electrolytes (1.0m) on the 1000 nm band have been recorded at 25°C for the following: tetrahydrofuran, tetrahydropyran, dioxane, dimethoxyethane, dimethyl sulfoxide, acetone, methyl acetate, propylene carbonate, dimethylformamide, dimethylacetamide, tetramethylurea, acetonitrile, and nitromethane. The specific influence of hydrocarbon chains on the near-IR absorption spectrum of water was further studied using a series of homologous sodiumn-alkyl carboxylates (formate to octanoate). The differential solvation spectra of three azoniaspiroalkane bromides have been obtained to compare the relative effects of cyclic and linear alkyl substituents. Finally, the study of ionic hydration effects has been extended to include the following electrolytes: NaPF₆, NaClO₄, NaBF₄, NaClO₃, NaNO₃, NaBrO₃, NaCN, NaSCN, Na₂SO₄, Na₂SO₃, Na₂CO₃, Na₂S₂O₃, MgCl₂, CaCl₂, BaCl₂, and SrCl₂. These data are discussed in terms of perturbations of the hydrogen-bonding equilibrium in water originating from one of the following: (1) direct OH... [polar group or anion] interactions, (2) structure-breaking effects due to weak OH... solute interactions, and (3) water-structure-promoting effects by alkyl groups.     

生物质再燃异相还原NO的分子模拟

基于密度泛函理论和过渡态理论,在分子水平上对焦炭异相还原NO以及碱金属钠的作用机理进行探究。结合单点能的零点能校正以及过渡态的虚频验证,发现钠能够有效促进焦炭对于第一个NO分子的吸附。尽管钠不能改变反应步骤,但可将焦炭异相还原NO决速步的活化能由121.04 kJ/mol降至100.62 kJ/mol;钠的存在使焦炭异相还原NO的指前因子增大且反应速率加快,增加了焦炭边缘的活性位点,强化了焦炭对于NO的异相还原性能。     

Comparative investigation of zein isolated from gluten by various methods

A comparative study has been made on zein preparations isolated from gluten by extraction with 70% ethanol and precipitation under various conditions; by dialysis, and by the addition of a 0.1 M solution of sodium sulfate or of acetone. An investigation of absorption spectra and of electrophoresis in polyacrylamide gel has shown the advantage of the method using acetone for precipitating the protein preparation.Scientific-Research Institute of Biology, Dnepropetrovsk State University. Translated from Khimiya Priorodnykh Soedinenii, No. 5, pp. 695–699, September–October, 1989.     

Comparative investigation of zein isolated from gluten by various methods

A comparative study has been made on zein preparations isolated from gluten by extraction with 70% ethanol and precipitation under various conditions; by dialysis, and by the addition of a 0.1 M solution of sodium sulfate or of acetone. An investigation of absorption spectra and of electrophoresis in polyacrylamide gel has shown the advantage of the method using acetone for precipitating the protein preparation.     

On the assessment of electrocatalysts for nitrate reduction

The electrochemical reduction of nitrate is attracting attention in the context of producing ammonia, besides the traditional removal to harmless N₂. To make progress in this complex reaction and facilitate the search for active and selective catalysts, we need to establish generalized testing protocols which will enable to compare and complement data from different laboratories. The purpose of this article is to raise awareness on the importance of (i) solution processes that involve products of the electrode reaction, (ii) determination of products with appropriate, product-specific quantitative methods, (iii) the strong sensitivity of the reaction on experimental parameters, (iv) the cell design for the separation of anode from cathode processes, and (v) the increase in the interfacial and solution pH that occurs during the electrolysis at high current densities.     

Comparative analysis of structural parameters of the nearest surrounding of nitrate and perchlorate ions in aqueous solutions of electrolytes

Data on structural parameters of the nearest surrounding of nitrate and perchlorate ions in aqueous solutions under standard conditions have been generalized. Hydration numbers, interparticle distances, and ionic association types have been discussed and compared. The major difference between the ions is that nitrate ion tends to form ion pairs, whereas perchlorate ion does not.     

Comparative study of O2 dissociation on various metalloporphyrins

We investigate O(2) interaction with various metalloporphyrins (MnP, FeP, CoP, and NiP) using ab initio calculations based on density-functional theory. We discuss the trends in the activation barriers for the O-O bond cleavage in relation to the geometric, vibrational, electronic, and energetic properties of the systems. Whether the lowest unoccupied molecular orbital-highest occupied molecular orbital (LUMO-HOMO) levels of the metalloporphyrins involve the corresponding metal centers depends on the d orbital occupancies of the metals. We found that activation barriers for the O(2) dissociation can be mainly determined from the LUMO-HOMO characters of the metalloporphyrins, and consequently the FeP is the best catalyst with respect to the O(2) interaction from adsorption to dissociation.     

Comparative study of breakthrough volumes BTV on various sorbents

Summary Breakthrough volumes on ten sorbents (Chromosorb 102, 104, 105 and 106, Porapak R and S, XAD-2, XAD-7, Tenax GC and Carbosphere) have been determined for vapours of 15 volatile organic compounds (halogenated hydrocarbons, alcohols, etc.). The volumes were determined by an indirect method employing typical chromatographic parameters such as retention volume and peak width.The method seems to be useful for preliminary estimation of adsorption capacity of various sorbents. It is not suitable, however, for the investigation of the effect of various parameters on the breakthrough volume.

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Vergleichende Untersuchung des Durchbruchsvolumens an verschiedenen Sorbentien

Zusammenfassung An 10 verschiedenen Sorbentien (Chromosorb 102, 104, 105, 106; Porapak R und S; XAD-2; XAD-7; Tenax GC; Carbosphere) wurden für 15 flüchtige organische Verbindungen (halogenierte Kohlenwasserstoffe, Alkohole u. a.) die Durchbruchsvolumina bestimmt. Es wurde dafür ein indirektes Verfahren mit typischen chromatographischen Parametern (Retentionsvolumen, Peakbreite) benutzt. Die Methode erscheint nützlich für die vorläufige Abschätzung der Adsorptionskapazität von Sorbentien, eignet sich jedoch nicht für die Untersuchung des Einflusses verschiedener Parameter auf das Durchbruchsvolumen.

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Part of this research was supported by Institute of Oceanology, Polish Academy of Sciences, Gdask, grant MR. I-15.     

On the induced reduction of chlorate ions

The induced reduction of chlorate ions can be carried out only by 1-equivalent oxidising agents. As^IV is formed by these, and this reduces chlorate very rapidly. The properties and mechanism of the induced reduction are discussed in detail.

For the determination of chlorate ions a reliable method is given, based on this induced reduction.     

A density functional study of the various forms of UN4O12 containing uranyl nitrate

In this paper we report the computational results of a density functional study of 73 UN4O12 isomers containing uranyl nitrate, UO2(NO3)2, as a component. The isomers are grouped into three categories and 19 types. Forty-four isomers of 14 types are dinitrogen tetroxide adducts of uranyl nitrate, UO2(NO3)2.N2O4, 22 are nitrosonium salt adducts of uranyl nitrate, NO+UO2(NO3)3-, NO+UO2(NO3)2O(NO2)-, NO+UO2(NO3)2(ONOO)-, or (NO+)2UO2(NO3)2O22-, and 7 are bis(nitrogen dioxide) adducts of uranyl nitrate, UO2(NO3)2.2NO2. The 22 most stable isomers in solution, representing the 20 most stable gas-phase isomers, were selected for analysis. Of these selected structures only two categories and six types were represented. Structures, frequencies, gas-phase and solution energetics, atomic charges, dipole moments, and the bonding within the N2O4 unit and between NO+ and UO2(NO3)3- components have been analyzed in detail. On the basis of relative Gibbs free energy calculations five isomers (the N2O4 adducts a1, a2, and a3 and the nitrosonium salts b1 and b2) were identified as strong candidates to exist and possibly predominate in the gas phase, with a1 and a2 being the strongest candidates. Similarly, four isomers (a6, a5, a8, and a1, all of them N2O4 adducts) were identified as strong candidates to exist and possibly predominate in a nonaqueous solution of nitromethane/dinitrogen tetroxide. Of these, a6 was determined to be the most likely candidate to predominate in solution. The possibility of dissociation in solution has been addressed briefly. In addition, computational evidence for the existence of four new N2O4 isomers 20, 22, 27, and 28 in both the gas and the solution phases is presented for the first time.