New fluorinated hydroxamic acid reagents for the extraction of metal ions with supercritical CO2

Research to date on the supercritical fluid extraction (SFE) of metal ions has focused on the use of dithiocarbamates and β-diketones. Hydroxamic acids are well known as effective chelating agents for a broad range of transition metal ions. Much attention has centred in inorganic chemistry on the effect of N-substitution on metal chelate stability and selectivity, and in analytical chemistry on the immobilisation of the chelating agents to the chosen solid supports such as silica. In this paper, the synthesis of selected fluorinated mono hydroxamic acids and their N-substituted derivatives is reported. The new reagents are applied in the SFE of metal ions in particular Fe(III) using unmodified supercritical CO₂. Metal extraction is monitored using atomic absorption spectroscopy and visible spectrophotometry. The extraction efficiencies were determined as a function of pressure and temperature. The new ligands synthesised and applied were perfluorooctanohydroxamic acid (PFOHA), heptafluorobutyrichydroxamic acid (HFBHA) and their N-methylhydroxamic acid derivatives. Of the synthesised reagents, PFOHA was the most soluble and effective extractant of Fe(III) from spiked filter paper, reaching 97% extraction of the metal ion under optimised conditions. The selectivity of this ligand for Fe(III) in the presence of Cu(II), Ni(II), Pb(II) and Zn(II) is also demonstrated.     

Hg2+-交联壳聚糖配合物的合成与表征

研究了甲醛、环氧氯丙烷交联壳聚糖树脂(AECTS)对Hg2 的吸附行为和吸附Hg2 对树脂结构及性能的影响。用FT-IR、XRD、TG、DSC和SEM对吸附产物进行了结构表征,并深入分析了AECTS与Hg2 之间的作用机理。结果表明,Hg2 与AECTS中的氨基发生配位、与AECTS中的羟基形成离子键而被吸附;AECTS吸附Hg2 后,结晶度下降,总体上热稳定性变差;Hg2 对AECTS的主链分解具有明显的催化功能;Hg2 的成键使得AECTS的表面形态发生了改变。     

1-辛基壬胺从硫酸溶液中萃取铁(Ⅲ)的性能和机理

1-辛基壬胺在硫酸体系中萃取铁的能力随pH增大而增强,表明铁的水解形式有利于萃取。用饱和容量法在不同pH条件下得到的络合物,其组成各不相同;只有在pH2.3时才得到单一络合物,用UV及元素分析证实其组成为(C_(17)H_(35)NH_3)_2SO_4Fe(OH)SO_4。分子量测定表明,1-辛基壬胺硫酸盐及其铁络合物在苯中以分子间缔合状态存在。     

Synthesis and binding studies of novel thiacalixpodands and bisthiacalixarenes having O,O″-dialkylated thiacalix[4]arene unit(s) of 1,3-alternate conformation

A series of thiacalixpodands and bisthiacalixarenes with imine units have been prepared by condensation of O,O″-bis(2-aminoethyl)-O′,O?-dipropyl-p-tert-butylthiacalix[4]arene of 1,3-alternate conformation with different aromatic (di)aldehydes. The molecules derived from pyridine-2-carbaldehyde and -2,6-dicarbaldehyde quantitatively extract silver ion from aqueous into organic phase with complete selectivity over other metal ions (Na⁺, K⁺ and Cs⁺) under neutral conditions. The former compound forms a 1:2 (L:M) complex with silver ion as proved by NMR spectroscopy, Job’s plot and X-ray crystallography.     

Potentiometric study of Cd(II) and Pb(II) complexation with two high molecular weight poly(acrylic acids); comparison with Cu(II) and Ni(II)

The cadmium (II) or lead (II) complex formation with two poly(acrylic acids) of high molecular weight (Mw=2.5×10⁵ and 3×10⁶) was investigated in dilute aqueous solution (NaNO₃ 0.1 mol l⁻¹; 25°C). Potentiometric titrations were carried out to determine the stability constants of the MA and MA₂ complex species formed. Bjerrum’s method, modified by Gregor et al. (J. Phys. Chem. 59 (1955) 34–39), for the study of polymeric acids was used. The results were compared to those previously obtained in the same conditions with copper (II) and nickel (II) . It appeared that the two polymers under study present similar binding properties and that the stability constants of the complex species formed increased in the following order, depending on the metal ion: Ni(II)β₁₀₂ was found to be close to 7.0) and allowed the formation of the predominant PbA₂ species in a quite large pH domain. Finally, the greater stability of PAA complexes compared to those of their monomeric analogs, glutaric and acetic acids, was confirmed.     

Computational Study of Supramolecular Bis-porphyrin “Molecular Tweezers”

A computational study of a series of space separated bis-porphyrin “molecular tweezers” using semiempirical (AM1) and DFT (B3LYP and PBE1PBE) methods has been carried out. It was found that polynorbornane bis-porphyrin systems are significantly less rigid than previously thought. The variation of the metal–metal separation distance between the two porphyrin centers does not cause a significant energy change thus enabling these molecules to easily adjust to the optimal coordination distance required for complexation by various bidentate 4-pyridyl ligands inside the cavity of these “tweezers”. Article 54, ECCC-10, April 1-30 2005, http://www.eccc.monmouth.edu     

A computer simulation — Statistical procedure for predicting complexation equilibrium constants

The complexing properties of macrocyclic ligands have been quantitatively studied by the combined use of molecular mechanics, molecular dynamics, and multiple linear regression. The dependent variables in the regression equations are experimental equilibrium constants for known macrocycle complexes in various solvents. The independent variables are theoretical simulation results on the solvent-free ligand and its complex and additional physically motivated empirical variables to describe solvent and other important effects.The systems studied were: (a) 314 metal ion-macrocycle-solvent (including 3 mixed solvents) combinations; (b) 88 ammonium ion-crown ether-solvent (including 1 mixed solvent) combinations; (c) 24 hydrogen ion-crown ether-H₂O combinations; (d) 26 Na⁺ ion-spherand-CDCl₃ combinations; (e) 78 ammonium ion-spherand-CDCl₃ combinations; and (f) 73 complicated host-guest-solvent (including 1 mixed solvent) combinations.For each system, we report the best regression equation obtained using the AMBER force field. The standard errors in logK range from 1.42 in the largest system to 0.36 in the smallest. Regression equations were determined for several of the systems using the MMP2 force field as well, and the equations are shown to be relatively insensitive to the force field.The predictive ability of the method was tested by predicting logK for 20% of the cases chosen at random using equations derived from the remaining 80%. The errors in the predicted values are shown to be consistent with the statistical assumptions of the model.Regression equations obtained with this method can be used to predict the equilibrium constants for new complexes involving some combination of new, possibly unknown macrocycle, new host and, in certain cases new solvent. No X-ray or other structural data for the macrocycle is needed.     

Polarographic Determination of Famotidine through Complexation with Nickel(II) Chloride

The present investigation describes the development of a sensitive, rapid polarographic method for the determination of famotidine in pure form and in certain dosage forms. The proposed method depends upon studying the polarographic activity of Nickel(II)‐famotidine complex in Britton Robinson buffer over the pH range 4–8 and its usefulness in the analysis of famotidine using direct current (DC_t), differential pulse (DPP), and alternating current (AC_t) polarography. The different experimental parameters affecting the cathodic waves were carefully investigated and optimized. Moreover, to check the validity of the proposed method, the standard addition method was applied by adding famotidine to the previously analyzed tablets. The recovery of the drug was calculated by comparing the concentration obtained from the spiked mixtures with those of the pure drug. The results of analysis of commercial tablets and the recovery study suggested that there is no interference from any excipients, which are present in tablets. Statistical comparison of the results was performed with regard to accuracy and precision using student's t‐test and F‐ratio at 95% confidence level. There is no significant difference between the comparison and proposed method with regard to accuracy and precision.     

Effect of Complexation on the Zeta Potential of Titanium Dioxide Dispersions

Abstract

The present paper deals with the surface charge properties and the dispersion stability of an aqueous titania suspension. Generally the titania powder surface is negatively charged. The dispersion stability of TiO₂ suspension is governed by the value of zeta potential. The zeta potential was measured as a function of barium acetate and zinc acetate concentrations, at pH 6.0, and the addition of electrolytes caused sharp decrease of surface charge. Ethylenediaminetetraacetic acid (EDTA) was used to chelate the bivalent metal ions, so that the charge of counterions was reduced. The complexation of bivalent counterions favors the increase of the negative zeta potential and the dispersion stability of aqueous TiO₂ suspension.     

Molecular Recognition Studies on Supramolecular Systems 34. Synthesis of Aromatic Diamino-bridged Bis(β-cyclodextrin)s and their Inclusion Complexation with Dye Molecules

A series of 6,6'-bis( g -cyclodextrin)s with rigid aromatic diamino tethers, i.e. p -phenylenediamino-bridged-bis(6-amino-6-deoxy- g -cyclodextrin) ( 3 ), 4,4'-bianilino-bridged-bis(6-amino-6-deoxy- g -cyclodextrin) ( 4 ) and 3,3'-bianilino-bridged-bis(6-amino-6-deoxy- g -cyclodextrin) ( 5 ), have been synthesized by the reaction of mono[6- O -( p -toluenesulfonyl)]-( g -cyclodextrin) with corresponding materials. The inclusion complexation behavior of native g -cyclodextrin ( 1 ), mono-(6-anilino-6-deoxy)- g -cyclodextrin ( 2 ), and novel bis( g -cyclodextrin) 3 - 5 with some representative dyes, i.e. ammonium 8-anilino-1-naphthalenesulfonate (ANS), Brilliant Green, Methyl Orange, Acridine Red and Rhodamine B, was investigated at 25C in aqueous phosphate buffer solution (pH 7.20) by means of fluorescence, ultraviolet, circular dichroism spectrometry as well as fluorescence lifetime measurement. The spectrophotometric titrations gave the complex stability constants ( K S ) and Gibbs free energy changes ( j G 0 ) for the stoichiometric 1:1 inclusion complexation of hosts examined with dye molecules. As compared with 1 or 2 , bridged bis( g -cyclodextrin)s displayed significantly enhanced binding abilities towards these dyes. Typically, dimer 3 showed the highest binding ability upon inclusion complexation with acridine red affording 17 times higher K S for 3 than for 1 . The molecular binding abilities and selectivities of dyes by bridged bis( g -cyclodextrin)s have been discussed from the viewpoint of induced-fit interaction and multipoint recognition mechanism.