Amphoteric Properties Research Articles

Cation exchange properties of charcoal impregnated with tin(IV) oxide from nitrate media

New charcoal impregnated with tin(IV) oxide ion exchanger was prepared and characterized by IR spectroscopy, X-ray diffraction measurements and thermal analysis methods. The material shows good stability towards HNO 3, HCl, NaOH and their salt solutions. It exhibits amphoteric properties. acting as a monofunctional anion exchanger and a polyfunctional cation exchanger containing weakly acidic groups. Apparent capacities of 1.3–2.7 meq Na + ions per gram of exchanger were obtained in the pH range 1.3–11.5. The adsorption behaviour of some alkali and alkaline earth metal cations and Ce 3+ ions from nitrate media on the exchanger has been investigated by batch equilibration and chromatographic column breakthrough techniques. Based on selective sorption on the adsorbent, the separation of alkali metal cations from each other and from cations of alkaline earth metals on small columns of the exchanger have been achieved.

Study on the vaporisation of sulphur-containing amino acids in a hydrogen flame by use of molecular emission cavity analysis and liquid chromatography

Peak splitting of the S 2 emission response from sulphur-containing amino acids in molecular emission cavity analysis is investigated. The primary reaction of the compounds in a hydrogen flame is found to be desulphurization by the determination of non-volatile products remaining in a cavity, using liquid chromatography. The mechanism of peak-splitting is suggested on the basis of the rapidity of the desulphurization and the amphoteric property of the amino acids. It is discussed that the desulphurization is hydrodesulphurization rather than the radical cleavage due to the weakness of the C-S bond.

Zinc metallochemistry in biochemistry.

The chemically stable but stereochemically flexible, non-toxic nature of zinc combined with its amphoteric properties has permitted it to orchestrate a number of zinc-binding motifs critical to life processes. For zinc enzymes, catalytic, cocatalytic, and structural zinc sites exist. DNA-binding proteins have zinc fingers, twists, and clusters exist.

Study on S 2 emission response from sulphur-containing amino acids in molecular emission cavity analysis

Several factors which affect S 2 emission response from sulphur-containing amino acids are investigated by molecular emission cavity analysis. It is found that multi-peaked responses observed from the amino acids result from heterogeneous gasification of the sample rather than formation of non-volatile compounds. A portion of the sample in a cavity is rapidly gasified by contact with flame gases and the others are slowly and thermally decomposed with temperature rise of the cavity. Thus, sample gasification processes are mainly discussed on the basis of several effects on the emission response, such as sample location within the cavity, addition of acids or bases, cavity temperature and flame composition. It is suggested that the amphoteric property of amino acids suppresses the rapid gasification process by contact with flame gases. Temporary condensed water on the cavity surface on introduction into a flame significantly affects the emission response from the amino acids and a mechanism for the effect is discussed.

Effects of Vacancies on the Electrical Characteristics of Metal/GaAs Schottky Contacts “A Quantitative Model”

An analytical method, proceeding by solving the Poisson equations both in the metal and in the GaAs substrate, is proposed to study the effects of the vacancies on the electrical characteristics of metal/GaAs contacts. A quantitative model used to calculate the effective charges contributed by the vacancies is developed here for the first time. From this analysis, it is found that the phenomenon of the Fermi level pinning in metal/GaAs contacts can be explained by the existence of vacancies at the metal/GaAs interface. Because of the amphoteric property of the vacancies in GaAs, the Fermi level is pinned at a level, called the “neutral level” of the vacancy, at which the effective charge introduced by the vacancies is zero. The change of the Fermi level pinning positions observed in previous experimental results for p and n GaAs can be ascribed to the change of vacancy types due to the nonstoichiometry in the GaAs substrate.

Synthesis of 2,3,4,5-Tetra(2-thienyl)cyclopentadienone Exhibiting Considerable Substituent Effects and Synthetic Utility

Abstract 2,3,4,5-Tetra(2-thienyl)cyclopentadienone and the related compounds, here first synthesized, show large bathochromic shift of visible absorptions and appreciably higher amphoteric redox properties than tetraphenylcyclopentadienone; 2-thienyl groups at 2,5-positions exert stronger substituent effects than those at 3,4-positions.

Novel Amphoteric 2,5-Furoquinonoid-Containing p-Terphenoquinone Analogues Giving Both a Stable Radical Anion and a Stable Radical Cation

Abstract Novel p-terphenoquinone analogues incorporating a central dihydrofurandiylidene skeleton have been synthesized. These quinones gave a stable radical cation and a stable radical anion on one-electron redox reactions showing an amphoteric property even though they do not contain any sulfur atom as an integral component. The radical cation and the radical anion of the tetra-t-butyl derivative have been characterized by EPR spectroscopy.

Preparation of fibre-entrapped enzyme using cellulose acetate-titanium-iso-propoxide composite as gel matrix

Enzyme (uricase or invertase) was entrap-immobilized in gel fibre of cellulose acetate-TiO 2 by using a gel formation of cellulose acetate and titanium iso-propoxide. The fibre is stable in common solvents, phosphate solution and electrolyte solution over a wide range of pH 4–10. The pH maximum of activity shifts to a more alkaline side compared to free enzyme, reflecting an amphoteric property of TiO 2.

Synthesis and Characterization of Thieno[3,4-c][1,2,5]thiadiazoles

Thieno[3,4-c][1,2,5]thiadiazoles (1a-b) were synthesized and characte- rized based on the spectral and structural data. The most notable structural feature of this «nonclassical» condensed thiophene is the small HOMO-LUMO separation leading to the highly amphoteric redox properties compared with the related «classical» thiophenes. The X-ray structure analysis suggested that this heterocycle has the character of a thiocarbonyl ylide. Short intermolecular S---N contacts were found in the crystal

Influence of membrane-solution interface on the performance of zirconia ultrafiltration membrane

The amphoteric and complexation properties of a zirconia powder formed in a sol—gel process in order to prepare ultrafiltration membranes were studied. In NaCl solutions, the point of zero charge was observed for a pH value of 7.5 and the intrinsic acidity constants were determined to be p K a1 int = 4.8 and p K a2 int = 10.4. Quantitative data on interfacial equilibria were also measured, such as the stability constants of the ZrO −Na +, ZrO −Ca 2+, and ZrOH 2 +Cl − complexes. The results are in good agreement with the triple-layer theory at the oxide solution interface. Using the zirconia membrane in an ultrafiltration process showed that the flux is influenced by interfacial properties of the material in the dynamic range of the experiments.

Perthienyl analogues of chichibabin's hydrocarbon. A new stable, highly amphoteric multistage redox system with low oxidation potentials.

Perthienyl analogues of Chichibabin's hydrocarbon have been first synthesized as fairly stable substances, showing highly amphoteric multistage redox properties with considerably low oxidation potentials.

Specific features of selective fluorination of bromosubstituted esters by halogen fluorides and the system

ClF, BrF 3 and hexachloromelamine (HCM)/HF system are effective reagents for selective substitution of covalently bonded bromine atoms by fluorine. BrF 3 demonstrates marked amphoteric properties; therefore esters, being weak Lewis bases, lower BrF 3 reactivity in the reactions of substitutive fluorination. For this reason, reaction rate of BrF 3 with bromine containing esters depends not only on the electron properties of substituents at the reaction center, but on ester basicity as well. ClF is far less amphoteric than BrF 3, so its reactivity is not deactivated by the ester function. The HCM/HF system with respect to bromosubstituted esters is effective only with a considerable excess of HF, which protonates the nitrogen atoms in the HCM nucleus, due to the high acidity of the reaction medium. Concrete examples, illustrating the preparative abilities of halogen fluorides in nonpolar media, and of the system HCM/HF will be discussed in the report.

The effect of second-phase oxides on the catalytic properties of dispersed metals: Cobalt supported on 12% WO 3/Al 2O 3

The differences in the amphoteric properties Of WO 3 and Al 2O 3 were exploited and cobalt precursors were selectively mounted on the tungsten oxide phase of a 12% WO 3/Al 2O 3 composite. Temperature-programmed reduction (TPRd), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and catalyst performance testing using H 2/CO methanation as a test reaction revealed that this composite-supported catalyst's properties were significantly different from cobalt supported on alumina. Cobalt crystallites as well as a CoAl 2O 4 type of surface species are formed on the Al 2O 3 support. The presence of WO 3 as a second-phase oxide offers the possibility for a greater number of surface compounds to be formed on the composite. Specifically, cobalt-tungsten interaction species are formed. We provide evidence that strongly suggests the active catalytic center in the conversion of H 2 and CO to methane is a (cobalt-tungsten) interaction species. These active centers. are present on CO/WO 3, Co/12% WO 3/Al 2O 3, and a commercial cobalt/tungsten oxide compound. A portion of the cobalt: in these active centers is not reduced to the metallic state.

Simple Method of Calculating Octanol/Water Partition Coefficient.

A simple method of calculating log P (partition coefficient in octanol/water) has been developed based on the quantitative structure-log P relationship for 1230 organic molecules having a wide variety of structures. The 1230 organic compounds investigated included general aliphatic, aromatic, and heterocyclic molecules together with various drugs and agrochemicals. The predictive structure-log P model obtained by multiple regression analysis involved only 13 parameters for hydrophobic atoms, hydrophilic atoms, their proximity effects, unsaturated bonds, amphoteric property, and several specific functionalities. A saturation effect was recognized in the parameters for hydrophobic and hydrophilic atoms, and unsaturated bonds. The structure-log P relationship was highly significant as the F-statistics=900.4. This simple method appears accurate enough for semiquantitative uses in structure-activity rating studies, especially for quantitative structure-activity relationship in toxicity.

Carboxylic acid adsorption on NiO(100) characterized by X-ray photoelectron and high resolution electron energy loss spectroscopies

Formic, acetic and propionic acids have been adsorbed onto NiO(100) at 300 K and the resulting species characterized by X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS). As do many ionic solids, nickel oxide possesses a strong series of Fuchs-Kliewer multiple phonon losses, which obscures the weaker adsorbate vibrational structure. A novel phonon deconvolution procedure that removes multiple phonons has, therefore, been used in analyzing the HREELS data. NiO(100) exhibits amphoteric chemisorptive properties, dissociatively adsorbing the acids as carboxylates and surface hydroxyls. Adsorption saturates after approximately 10000 langmuir to yield one carboxylate for every two nickel sites. By stoichiometry, one half of all surface oxygen sites are assumed to be hydroxylated. A tilted carboxylate geometry is evident in the high value of thev s(COO) vibrational mode observed in the HREEL spectra.

Tetra(2-thienyl)butatrienes: new butatriene derivatives with highly amphoteric multistage redox properties and a short central double bond

Tetra(2-thienyl)butatrienes 2a–c show highly amphoteric redox properties; an X-ray structure of the tetrakistrimethylsilyl derivative 2b reveals a short bond length for the central double bond.

Surface complexation of calcium minerals in aqueous solution: 1. Surface protonation at fluorapatite—water interfaces

The amphoteric properties of hydrous fluorapatite surfaces have been investigated. The measurements were performed as potentiometric titrations in 0.1 M NaCl medium at 25°C using a glass electrode. The experimental data could be explained by a model that assumes the surface equilibria PO −+H +=POH logβ s 101( int.)=6.6±0.1(3σ) CAOH 2 +−H +=CAOH logβ s -101( int.)=-9.7±0.1(3σ) The equilibrium constants were evaluated using the computer program FITEQL by Westall (Report 82-01, Department of Chemistry, Oregon State University, Corvallis, 1982), assuming a constant capacitance model for the electric double layer. The acidity constants result in a value of log[H +] pzc = −8.15, which shifts to log[H +] pzc = −7.13 upon exposure to atmospheric carbon dioxide.

Surface reactions in aqueous metal sulfide systems: 2. Ion exchange and acid/base reactions at the ZnS [sbnd]H 2O interface

The amphoteric properties of hydrous ZnS surfaces as well as an ion exchange reaction between surface coordinated Zn 2+ ions and H + ions of the aqueous phase have been established. The measurements were performed as potentiometric titrations in 0.1 M NaClO 4 medium at 25°C. Besides measuring −log[H +] by using a glass electrode, −log[S 2−] was recorded (Ag/Ag 2S selective electrode). In addition, the total concentrations of H +, Zn 2+, and S were analyzed as a function of −log[H +] of the bulk solution. Synthetically prepared ZnS and the mineral sphalerite were studied. Bro¨nsted acidity constants pK 1 s = 6.91 and pK 2 s = 10.28 for synthetic ZnS, and pK 1 s = 7.14 and pK 2 s = 10.29 for sphalerite, were established, which implies −log[H +] of zero proton condition equal to 8.60 and 8.72, respectively. Furthermore, the ion exchange reaction SZn + 2H + ⇆ SH 2 + Zn 2+ was characterized within the range 4 ⩽ −log[H +] ⩽ 7, with log K = 9.59 and 9.65. Experimental data were evaluated on the basis of the constant capacitance model by using the computer program FITEQL. The “best” fit to experimental data was obtained by assuming no charge dependence of K 1 s and K 2 s.

A novel [3]radialene derivative with an amphoteric redox property. A dihydrothiophenediylidene-extended trisbenzoquinocyclopropane

1,2-Bis(3,5-di- t-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-3-[5-(3,5-di- t-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-2,5-dihydrothiophen-2-ylidene] cyclopropane, a new near-infrared dye, has been synthesized and characterized as the first radialene derivative exhibiting an amphoteric multi-stage redox property.

The adsorption of copper to chitin in seawater

The interaction of metal ions with particulate matter is important in limiting their concentration in seawater. Chitin is one of the constituents of the natural particulate organic matter than can interact with metal ions and therefore may serve as a reasonable model for natural organic solids. The adsorption of Cu 2+ on the chitin surface has been studied in seawater as a function of pH, temperature, and salinity. The amphoteric properties of the surface of chitin were characterized in 0.7 M NaCl in terms of a two-protic acid-base system ( pH PZC = 5.4) with acidity constants p ∗K a1 s = 4.4 ± 0.2 and p ∗K a2 s = 6.4 ± 0.2 . The maximum proton exchange capacity of chitin was found to be 2.3 ± 0.3 mol kg −1, broadly similar to other solids. The rates of the adsorption were quite rapid ( t 1 2 = 8 min ) and not strongly affected by the presence of other metals such as Cd 2+ and Pb 2+. The adsorption equilibrium data have been found to correlate well with surface complex-formation equilibria or the mathematically equivalent Langmuir- type adsorption equilibria. The value for the stability constant of Cu 2+ on chitin was found to be log ∗K H s = 8.95 ± 0.01 , and the complexing capacity of chitin was found to be 6.9 and 5.9 μmol g −1, respectively, in the absence and in the presence of Cd 2+ and Pb 2+. An increase in the salinity and a decrease in the temperature result in greater adsorption of Cu 2+ to chitin