Highly selective sorption of small unsaturated hydrocarbons by nonporous flexible framework with silver ion

Ag2[Cr3O(OOCC2H5)6(H2O)3]2[alpha-SiW12O40] [1] is a nonporous flexible ionic crystal composed of 2D-layers of polyoxometalates ([alpha-SiW12O40](4-)) and macrocations ([Cr3O(OOCC2H5)6(H2O)3](+)) stacking along the b-axis. The silver ions are located in the vicinity of the oxygen atoms of the polyoxometalates. The sorption amounts of small unsaturated hydrocarbons such as ethylene, propylene, n-butene, acetylene, and methyl acetylene into 1 are comparable to or larger than 1.0 mol mol(-1) and large hystereses are observed, while those of paraffins and larger unsaturated hydrocarbons are smaller than the adsorption on the external surface (<0.2 mol mol(-1)). Fine crystals of 1 exhibit ethylene/ethane and propylene/propane sorption ratios over 100 at 298 K and 100 kPa, and the values are larger by 1 order of magnitude among those reported. The results of sorption kinetics, in situ IR spectroscopy, single crystal X-ray crystallography, and in situ powder XRD studies show that small unsaturated hydrocarbons penetrate into the solid bulk of 1 through the pi-complexation with Ag(+). The sorption property of 1 is successfully applied to the collection of ethylene from the gas mixture of ethane and ethylene.     

Purification of aqueous glyoxal from organic acids by ion exchange

A procedure for the purification of aqueous glyoxal (obtained by the partial oxidation of glycol) from carboxylic acids was described. Mono- and dibasic organic acids can be removed from solution without any substantial losses of glyoxal by using weakly basic EDE-10P and AN-31 anionites. A mechanism of the adsorption of carboxylic acids on weak resins was suggested based on the IR spectra recorded in a study of AN-31 anion-exchange resin. Using this method of purification also allowed the removal of the glyoxal condensation products from solution.     

Highly selective in situ metal ion determination by hybrid electrochemical "adsorption-desorption" and colorimetric methods

A novel and facile hybrid analytical method coupling electrochemical “adsorption–desorption” and colorimetric analyses was developed to detect heavy metal ions in turbid water samples. The target metal ions were deposited onto an electrode inserted into the original sample, which was referred to as the “adsorption” process. After changing the medium, the concentrated target metal ions were dissolved in a new, clean buffer (blank buffer), which was referred to as the “desorption” process. The concentrations of the target metal ions were measured by colorimetric analyses after the addition of specific indicator amounts. We demonstrated the applicability of this method by detecting Cd²⁺, Pb²⁺ and Cu²⁺ with co-depositing Bi³⁺ on portable screen-printed electrodes (SPEs). A good correlation (correlation coefficient of R = 0.997) was observed between concentrations ranging from 1 to 200 μM and absorbance values. After the multiple “desorption” process, the even better detection limits as low as 10, 10 and 100 nM were achieved for Cd²⁺, Pb²⁺ and Cu²⁺, respectively. The practicality of this hybrid method was confirmed by the detection of Cd²⁺, Pb²⁺ and Cu²⁺ in wastewater samples, and these results were in agreement with inductively coupled plasma atomic emission spectroscopy (ICP-AES). Overall, this hybrid method provides a simple, selective and effective technique for environmental pollutant analyses.     

Separation of hydroxy acids by ion exchange chromatography

Factors affecting the Chromatographic separation of hydroxy acids by means of anion exchange resins in the borate form have been studied. With the acids studied the separation factor increases for a decreased borate concentration in the eluant. With complicated mixtures it is recommended to employ stepwise elution with solutions of increasing concentration.     

Nanostructured metal sulfide surfaces by ion exchange processes

A scalable preparation procedure for structured semiconducting sulfide films from zinc oxide by means of subsequent anion and cation exchange processes is described, which is low in cost and waste production. The starting material was columnar ZnO films, which were grown in electrodeposition by O₂ reduction. Here, their detailed morphology depends on the substrate and the process parameters. These films were converted to ZnS by reaction with H₂S gas or sulfur vapour at temperatures around 450 °C. In this process the columnar morphology of the ZnO is preserved. A partial conversion is also possible and leads to tubular ZnS films. Then the ZnS films were reacted in metal salt solutions to convert them further to Ag₂S, Cu₂S, Bi₂S₃ and Sb₂S₃ films. Here the columnar or tubular morphology was, in general, also reproduced, but its outer quality depends on the interaction of the involved processes, namely dissolution, precipitation and exchange inside the solid. This was further examined by a series of Ag₂S films from modified solutions.Presented at the 3rd International Symposium on Electrochemical Processing of Tailored Materials held at the 53rd Annual Meeting of the International Society of Electrochemistry, 15–20 September 2002, Düsseldorf, Germany     

Extending the pore size of crystalline metal phosphonates toward the mesoporous regime by isoreticular synthesis

Crystalline microporous cobalt and nickel bisphosphonates with a hexagonal array of one-dimensional channels 1.8 nm in diameter have been prepared hydrothermally and provide the first example of the use of isoreticular chemistry in the synthesis of phosphonate metal-organic frameworks. The materials contain both physisorbed and coordinating water molecules in the as-prepared form, but these can be removed to give permanent extra-large microporosity, with pore volumes of up to 0.68 cm(3) g(-1), and coordinatively unsaturated sites, with concentrations up to 4.25 mmol g(-1).     

Cation exchange and sorption properties of crystalline alpha-titanium(IV) phosphate

The ion-exchange and sorption properties of alpha-titanium bis(monohydrogen orthophosphate) monohydrate of composition Ti(HPO(4))(2).H(2)O was studied in aqueous electrolyte solutions of KCl over the temperature range of 300-320 K, varying the pH and metal ion concentration in the solution. The data were explained on the basis of the law of chemical equilibrium and the metal ion sorption data were fitted to Langmuir parameters. Further, the extent of sorption was found to increase with increasing temperature and metal ion concentration in the selectivity order Fe(3+)>Cu(2+)>Co(2+)>Mn(2+)>Cr(3+)>Ni(2+). The values of Langmuir constants were used to calculate the various thermodynamic parameters, such as DeltaG(0), DeltaH(0), and DeltaS(0), during the sorption process.     

Highly selective complexation of metal ions by the self-tuning tetraazacalixpyridine macrocycles

By means of UV-vis and ¹H NMR titrations and X-ray crystallography, complexation of tetramethylazacalix[4]pyridine L1 and tetramethylazacalix[2]arene[2]pyridine L2 with metal ions was studied. While no interaction was observed with alkali and alkaline earth metal ions, both ligands have been found to act as powerful and selective macrocyclic hosts to complex a number of transition and heavy metal ions. Due to the intrinsic nature of the bridging nitrogen atoms that can adopt different electronic configurations and form varied degrees of conjugations with their adjacent pyridine rings, tetramethylazacalix[4]pyridine L1 regulated its conformation and cavity structure to best fit the guest metal ion species, yielding a 1:1 square planar L1-Mⁿ⁺ complex with binding constants log K_1:1 ranging from 2.7(1) to 8.2(8).     

Highly accurate radiochemical neutron activation analysis of arsenic in biological materials involving selective isolation of arsenic by hybrid and conventional ion exchange

A highly accurate (definitive) radiochemical neutron activation analysis (RNAA) method was developed for the determination of traces of arsenic (As) in biological materials. It consists of the following steps: (a) irradiation in the nuclear reactor; (b) microwave-assisted sample digestion; (c) quantitative and selective radiochemical separation of arsenates on hydrated ferric oxide nanoparticles dispersed in a macroporous cation exchanger, preceded by a conventional strongly acidic cation exchanger column, and (d) gamma-ray spectrometric measurement of ⁷⁶As. The suitability and accuracy of the method was demonstrated by analysing several certified reference materials. The detection limit is 8 ng g^?1. The standard uncertainty in the determination of As in oriental tobacco leaves is around 3.4%. This, together with its compliance with several other formal requirements, makes the method comparable to primary methods based on isotope dilution mass spectrometry.     

Transition metal phosphonates with pyridyl-based phosphonic acids: synthesis,characterization and luminescence properties

Two transiton metal phosphonates, Cd₂[OOCC₅H₃NPO₃H]₂·H₂O (1) and Zn[OOCC₅H₄NPO₃]·H₂O (2), were synthesized by hydrothermal reactions. Single-crystal X-ray diffraction analyses show that both have a 3-D framework. In 1, the asymmetric [Cd–NO₅] octahedron is connected to the [P–CO₃] tetrahedron through corner sharing and two neighboring [Cd–NO₅] octahedra are bridged via a mutual plane [O1–O2–O3]. Compound 2 has a scales-like multilayer structure viewing from b and c. [Zn–O₄] tetrahedra linked [P–CO₃] tetrahedra through corner O sharing. The thermogravimetric properties and luminescence spectra of 1 and 2 were investigated. Compound 2 emitted a purple-blue light upon 323 nm excitation. Above 100 nm, red shifts in both compounds make them candidates for luminescent materials.     

Preconcentration and selective metal ion separation using chelating micelles

Chelating aggregates consisting of Triton X100 host micelles and hydrophobic derivatives of PAN have been examined as suitable candidates for preconcentration and selective separation of transition metal ions through micellar-enhanced ultrafiltration. The effective accumulation in the surfactant-rich retentate of nickel(II), copper(II), cobalt(II), manganese(II) and zinc(II), present at trace levels in aqueous samples, has been achieved by operating at pH ca. 6 with a ligand having a binding constant to the host micelles higher than 2000 l./mol. The efficient separation of micelle-bound metal chelates from unreactive ions has been assessed, together with the feasibility of selective enrichment and purification of the investigated metal ions present in mixtures through a multistage process.     

Highly efficient and selective olefination of acyl phosphonates with ethyl diazoacetate catalyzed by a cobalt(II) porphyrin complex

The cobalt(II) porphyrin complex (CoTPP) was found to be an efficient catalyst for the Wittig type olefination of acyl phosphonates with ethyl diazoacetate (EDA) in the presence of triphenylphosphine (Ph₃P). By using this one pot methodology under mild conditions, densely functionalized vinyl phosphonates were obtained in high yields and high E/Z selectivities in relatively short reaction times. A rather broad substrate spectrum and steric influence on the reaction rate were observed.     

Highly selective synthesis of pyrazole and spiropyrazoline phosphonates via base-assisted reaction of the Bestmann-Ohira reagent with enones

Novel carbonylated pyrazole phosphonates have been synthesized as single regioisomers by treating conjugated enones, dienones, tropone, and quinone with the Bestmann-Ohira reagent under KOH/EtOH conditions at room temperature. Through an "interrupted" version of the above reaction, carbonylated spiropyrazoline phosphonates have been synthesized from arylidenecycloalkanones under similar conditions (K(2)CO(3)/EtOH) with absolute regio- and diastereoselectivity. The key structures were confirmed by detailed spectroscopic analysis and X-ray crystallography.     

Highly fructose selective transport promoted by boronic acids based on a pentaerythritol core

We have designed and synthesized a highly lipophilic boronic acid (11) with a molecular shape that makes it much more effective at carrying sugars through organic membranes than a previously used steroidal boronic acid. The corresponding diboronic acid (12) was also found to transport fructose ahead of glucose with a very high selectivity (7.6:1.0). Modeling suggests that 12 is able to carry two fructose molecules at once in a complex stabilized through hydrogen bonding and ion pairing.     

镝促进下醛、酮与炔丙基溴及苯基炔丙基溴的高 选择性反应

在金属镝的促进下,醛、酮可与炔丙基溴反应,高选择性高产率地得到相应的高炔丙醇,没有发现连二烯醇的存在。当用苯基炔丙基溴代替炔丙基溴与醛、酮反应时,主要得到了相应的连二烯醇,而没有发现高炔丙醇的存在,由此提出了六元环过渡态的反应机理。     

螯合金属离子亲和色谱法分离α-氨基酸和肽

 以ＳｅｐｈａｄｅｘＧ１０为基质螯合二价铜离子的亲和色谱法分离α－氨基酸和肽，使之得以完全分离。对分离过程的原理进行了讨论。     

Calcium binding by fulvic acids studied by an ion selective electrode an ultrafiltration method

The interaction between Ca(2+) and two well-characterized fulvic acids (Armadale and Laurentide FA) has been studied at 0.100 and 0.010M sodium nitrate using a fixed concentration of fulvic acid (100 ppm) and varying amounts of calcium (0.005-0.020 mmoles). Free calcium concentration was determined by in situ measurements employing a calcium electrode. For Armadale FA, free calcium was additionally determined via an ultrafiltration technique followed by atomic absorption measurements. For both fulvic acids, Ca(2+) binding was observed to be decreased by an increase in the ionic strength of the system. At the lower ionic strength the tendency for binding is dependent on the fulvic acid-to-metal ratio while at the higher ionic strength, the binding is insensitive to changes in the fulvic acid-to-metal ratio (an observation corroborating the contention that calcium binding to humic substances is primarily electrostatic). Comparison of the computed overall complex formation functions shows that values obtained from the ultrafiltration method were higher than those obtained using the calcium electrode. The binding of calcium was similar for the two fulvic acids.     

Label-free selective DNA detection with high mismatch recognition by PNA beacons and ion exchange HPLC

Two 11mer peptide nucleic acid (PNA) beacons were synthesized and tested for the detection of full-matched or single mismatched DNA. Fluorescent measurements carried out in solution showed only partial discrimination of the mismatched sequence, while using anion-exchange HPLC, in combination with fluorimetric detection, allowed DNA analysis to be performed with high sensitivity and extremely high sequence selectivity. Up to >90 : 1 signal discrimination in the presence of one single mismatched base was observed. The analysis was tested on both short and long DNA oligomers. Detection of DNA obtained from PCR amplification was also performed allowing the selective detection of the target sequence in complex mixtures. Label free detection of the DNA with high sequence selectivity is therefore possible using the present approach.