Mixed solvent effect on lithium-coordination to poly(ethylene oxide)

This article presents a comparative study of the structure formation of poly (ethylene oxide) PEO/Li complexes in aqueous and acetonitrile solutions using small-angle neutron scattering (SANS). We demonstrate that in acetonitrile solutions, Li-cations coordinate to the ether–oxygen of the monomeric unit, and this results in charging and stretching of the polymer chains. This is found to be in contrast to aqueous solutions, where the ions remain free in solution. In particular, we demonstrate that the “binding” and “screening” regimes that were observed in case of PEO/K⁺ solutions in acetonitrile are also found in the respective PEO/Li⁺ solutions. The addition of water to solutions in acetonitrile increasingly diminishes the ion-coordination to the polymer, eventually resulting in neutral polymer chains at water contents above ϕ*_water = 30% (w/v). The preferential adsorption of water on PEO in mixtures of acetonitrile and water is evidenced by the pronounced stretching of polymer chains, in particular, at a water content of ϕ_water = 25% and 33.33% (w/v) where complete stretching of the chains is observed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3642–3650, 2006     

Trace-Level Determination of Phenol by Liquid Chromatography with On-Line Precolumn Technology and Fluorescence Detection

Abstract

A strongly basic anion-exchange resin is used for the trace enrichment and automated sample handling of phenol, with subsequent determination by reversed-phase liquid chromatography with fluorescence detection. Because of the presence of high concentrations of ionic compounds in the water samples tested, phenol is first trapped on a relatively long precolumn filled with a highly hydrophobic packing material; during this step, (in) organic anions which are not retained, are flushed to waste. In the next step, phenol is desorbed from this column at high pH and sorbed in a small zone (“peak compression”) on a short precolumn containing the anion exchanger.

In the analysis of tap and river water samples, the detection limit was found to be 10ppt (1:10¹¹).     

Supramolecular Influences on Metal Ion Coordination: Lead(II) under Eight-coordination

Crystal structure determinations on the “acid salt” of Pb(II) and dipicolinic acid (pyridine-2,6-dicarboxylic acid, dipicH²), regarded as composed of dimer entities, [Pb²(dipic)²(dipicH²)²(OH²)⁶], 1, infinitely cross-linked, and on the complex of 2,4-dinitrophenol (2,4-DNPH), a simpler coordination polymer, [Pb(2,4-DNP)²]n, 2, show both solid state structures to be influenced by π-stacking of the ligands. Although the Pb(II) coordination environment in 1 can be regarded as “hemidirected” and that in 2 as “holodirected”, it is argued that inter-dimer stacking interactions, rather than lone pair effects, are responsible for the distorted 9-coordination of Pb in 1. In 2, Pb adopts close-to-cubic 8-coordination.     

ORGANIC PERMSELECTIVE PERVAPORATION CHARACTERISTICS OF POLY(SILYLPROPYNE) AND COPOLYMER DENSE MEMBRANES

An investigation into the organic permselective separation through poly [1-trimethylsilyl-1-propyne] (PTMSP) and (1-trimethylsily1)-1-(1-penta-methyl-disilyl)-1-propyne copoly-mer (TMSP-PMDSP) dense membranes was made to gain an insight into the effect ofthe chemical structure of membrane materials on pervaporation (PV) characteristics. Theresults show that the copolymer has a higher separation factor α_(org/water) but with a rela-tively lower value of flux J_t (g/m~2·h) than pure PTMSP. This phenomenon may be at-tributed to the introduction of side chain with large bulk volume in copolymer, whichbrought about a decrease of excess free volume and the improvement of diffesion selectivityto some extent. With the same molar concentration of organic liquids in feed, THF/watersolutions have the highest value of α_(org/water) as well as J_t in comparison with ethanol/water,iso-propanol/water and THF/water mixtures.     

Determination of Organic Group Parameters: (AOCI,AOBr, AOS) in Water by Means of Ion-Chromatographic Detection. Pyrohydrolysis and Absorption

Abstract

In recent years methods have been developed to determine organic halogen at the μg/1 level in water samples by adsorbing these compounds on active carbon and by detecting the inorganic halides formed after conversion of the adsorbates by pyrohydrolysis. Applying these techniques the analysis of the so-called group parameter “Adsorbable Organic Halogen (AOX)” is performed.

The distinction of each of the halogens in the group parameter AOX and the determination of the parameter “adsorbable organic sulfur compounds (AOS)” can be realized using ion-chromatography for the detection of the anions, obtained after pyrohydrolysis of the adsorbed organic compounds.

Further investigations have shown good adsorption capacity of a newly developed nearly chlorine- and sulfur-free active carbon for organic model substances. This report presents the examinations concerning pyrohydrolysis of the organic solutes and absorption of the formed inorganic species.

The conditions for complete conversion of the model substances and high recovery rates in inorganic anions have been proved successfully. The optimization of the pyrohydrolysis apparatus and of the combustion conditions have been performed and proved with good results.     

Complexation‐Induced Supramolecular Assembly Drives Metal‐Ion Extraction

Combining experiment with theory reveals the role of self‐assembly and complexation in metal‐ion transfer through the water–oil interface. The coordinating metal salt Eu(NO₃)₃ was extracted from water into oil by a lipophilic neutral amphiphile. Molecular dynamics simulations were coupled to experimental spectroscopic and X‐ray scattering techniques to investigate how local coordination interactions between the metal ion and ligands in the organic phase combine with long‐range interactions to produce spontaneous changes in the solvent microstructure. Extraction of the Eu³⁺–3(NO₃^?) ion pairs involves incorporation of the “hard” metal complex into the core of “soft” aggregates. This seeds the formation of reverse micelles that draw the water and “free” amphiphile into nanoscale hydrophilic domains. The reverse micelles interact through attractive van der Waals interactions and coalesce into rod‐shaped polynuclear Eu^III‐containing aggregates with metal centers bridged by nitrate. These preorganized hydrophilic domains, containing high densities of O‐donor ligands and anions, provide improved Eu^III solvation environments that help drive interfacial transfer, as is reflected by the increasing Eu^III partitioning ratios (oil/aqueous) despite the organic phase approaching saturation. For the first time, this multiscale approach links metal‐ion coordination with nanoscale structure to reveal the free‐energy balance that drives the phase transfer of neutral metal salts.     

Solvent effect on the rate of metal deposition reactions: Investigations of the kinetics of Ni(II) discharge at the mercury in mixed water methanol solvents

The kinetics of Ni²⁺ deposition at the mercury electrode, from non-complexing electrolytes in mixed water methanol solvents has been investigated. The rate of this reaction, in the whole composition range, at large overpotentials is controlled by a limiting “chemical” process. The rate constants of the limiting process when plotted as a function of the solvent composition display a relationship similar to those observed for the large organic, bidendate ligands substitution reactions, believed to the controlled by the Ni(II)-solvent bond rupture. Hence, the limiting “chemical” process in Ni²⁺ discharge can be identified as the slow solvent dissociation step. These results confirm the mechanism of Ni²⁺ dischrage already proposed by Gierst and Dandoy on the basis of investigations performed in aqueous solutions.     

Spectrophotometric Determination of Palladium with Sodium Ethylene-Bis-Selendglycollate

Abstract

SUMMARY

Palladium was determined spectrophotometrically with sodium ethylene-bis-selenoglycollate in acid medium. The system obeys Beer' law in the range 0.25–0, 3 5 μg.ml^?1 and the molar absorptivity is 2.4 × 10⁴ 1. mol^?1 .cm^?1. Determination of palladium in the presence of many ions is reported.

In spite of the fact that selenium compounds have rarely been used as organic analytical reagents and one finds many palladium determination methods in the literature, this paper fits into the general Purpose reported before ^1,2 :systematic comparison of organic sulphur, sellenium and tellurium compounds as analytical reagents in agreement with propositions made some years agp ^3,4

In previous work⁵ the behaviour of the ethylseleno glycollic (L₁), selenodiglycollic (L₂) and ethylene-bis-selenoglycollic (L₃) anions in acidic solutions of some “soft”, “borderline” and “hard” cations was studied.

The results obtained for Pd(II) afforded evidences that its determination could be run with the three mentioned ligands.

Nevertheless, L₃ was selected because it provides the most sensitive signal and its synthesis is very simple and its overall yield is excellent⁶

From the qualitative study⁵ the foreseen selectivity could present some restrictions, but there is little doubt about the usefulness of the method that will be proposed, in various schemes of determination. Similar comments Beamish have been made about EDTA method for Pd(II) determination⁸     

REACTION OF α-CHLOROTOLUENE WITH ELEMENTAL SULFUR IN LIQUID AMMONIA

Abstract

α-Chlorotoluene (1) reacts with elemental sulfur in liquid ammonia affording dibenzyl disulfide (2), dibenzyl trisulfide (3), dibenzyl tetrasulfide (4), dibenzyl pentasulfide (5) and benzylidene benzylimide (6) at a low temperature such as 20°C. This reaction is presumed to be initiated by the nucleophilic attack of ammonium thioaminohydroxylate, “H₂NS^-NH₄ ⁺,” or dithioaminohydroxylate, “H₂NSS^-NH₄,” formed upon treating elemental sulfur in liquid ammonia, on α-chlorotoluene (1). Benzylidene benzylimide (6) is presumed to be formed from benzylamine, which can be formed by treatment of α-chlorotoluene (1) with ammonia.     

Centrifugal Partition Chromatography. V. Octanol-Water Partition Coefficients,Direct and Indirect Determination

Abstract

Octanol-water partition coefficients (K_oct) are one of the accepted physico-chemical parameters for predicting the biological effects of organic chemicals. It is demonstrated that centrifugal partition chromatography (CPC) can be used to determine directly the K_oct values from about 0.003 to 300. The mobile phase must be water and the stationary phase must be octanol for accurate determination of the larger K_oct values. To reduce retention times and volumes, the stationary phase volume can be decreased. This can be done using an original mode: the “underload” mode. The “underloading” procedure is described. To extend the K_oct range which can be determine by CPC, the system hexane (60%) octanol (40%)-water was used. A single linear relationship between log K in this system and log K_oct was established allowing to determine the K_oct values up to 1000 (log K_oct=3).     

REACTIVITY OF MACROMONOMERS IN FREE RADICAL POLYMERIZATION

Abstract

Macromonomers are linear polymeric o r oligomeric species which, because of the presence of a reactive end group, have the potential either to polymerize with themselves or with comonomers. The reactive group is most commonly a vinyl group that can participate in free radical polymerization, but any polymerizable end group, such as epoxy, bis-hydroxy, etc., is sufficient for the molecule to be classified as a macromonomer. The words “macromer” and “macromonomer” are often used interchangeably, although the former term was introduced originally as a trademark of CPC International to describe the macromonomers discovered by Milkovich [1].     

Perylene as a visible light photoredox catalyst for photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of MMA

Abstract

The organic photocatalyst, perylene, was used to mediate photoinduced electron transfer (PET) reversible addition-fragmentation chain transfer polymerization (RAFT) of methyl methhacrylate (MMA) under light irradiation in N,N-dimethylformamide (DMF) at 25°C with 4-cyanopentanoic acid dithiobenzoate (CPADB) as chain transfer agent (CTA). Kinetic studies confirmed that the polymerization obeyed the first order kinetic m'odel. The production of PMMAs with a good control of molecular weights (M_n,GPC) and narrow polymer molecular weight distribution (M_w/M_n) were obtained. It is found that well-controlled PET RAFT polymerization of MMA can be manipulated even with the amount of perylene decreasing to ppm level. No polymer was obtained in the absence of light irradiation, implying that the model of PET RAFT polymerization of MMA is an ideal light “on”-“off” switchable system. Furthermore, the speed of PET RAFT polymerization of MMA was also finely tunable by the external light irradiation intensity. The resultant PMMA macro-CTA was characterized by ¹H nuclear magnetic resonance spectrum (¹H NMR) and gel permeation chromatography (GPC). The accessibility of the high end group fidelity was further demonstrated by chain extension experiments.     

A reversible fluorescence “ON–OFF–ON” sensor for sequential detection of F− and Cu2+ ions and its application as a molecular-scale logic device and security keypad lock

A new azoimine receptor, R₁, was synthesized by Schiff base condensation of 4-(4-butylphenyl) azophenol and 2,6-diaminopyridine and acts as a colorimetric and fluorometric chemosensor for F^? and also toward Cu²⁺ ions in aqueous environment. UV–Vis absorption and fluorescent emission spectra were employed to study the sensing process. Emission study was performed to examine the dual sensing ability of the obtained probe with sequential addition of F^? followed by Cu²⁺ and vice versa. The receptor is an efficient “ON–OFF” fluorescent probe for the fluoride ion. Also, R₁ + F^? operated as an “OFF–ON” fluorescent sensor for Cu²⁺ ions. Considering emission intensity and absorption wavelength for F^? and Cu²⁺ ions, a molecular system was developed with the ability to mimic the functions of XNOR logic gating on the molecular level. In addition, R₁ behaved as a molecular security keypad lock with F^? and Cu²⁺ inputs. The keypad lock operation is particularly important, as the output of the system depends not only on the proper combination but also on the order of input signals, creating the correct password that can be used to “open” this molecular keypad lock through strong fluorescence emission at 460?nm.     

Reversible fluorous phase-switching of pyridyl-tagged porphyrins: Application to the sensing of histamine in water

Upon stirring a chloroform/perfluorodecalin biphasic system, the 5,10,15,20-tetrapyridyl porphyrin (TPyP) solubilized in the organic phase was almost quantitatively extracted (∼99.9%) into the fluorous phase containing an excess of the “heavy fluorous” copper(II)-carboxylate complex 1. The porphyrin was quantitatively and almost instantaneously released into the chloroform after addition of excess tetrahydrofuran (THF), which successfully competed with the pyridine ligand for binding sites on complex 1. Metallation of TPyP by copper(II) ions was never observed during the “catch-and-release” process. With the 5,10,15-tripyridyl-20-phenylporphyrin (TPyMPP) or the 5,15-dipyridyl-10,20-diphenylporphyrin (trans-DPyDPP) both efficient extraction (98%) and metallation occurred simultaneously leading to the immobilization of the metallated copper(II)-porphyrins in the fluorous phase. The metalloporphyrins were quantitatively released in the organic phase by addition of THF. With the 5-pyridyl-10,15,20-triphenylporphyrin (MPyTPP) no extraction but rapid metallation was observed under biphasic stirring leading to the quantitative recovery of the Cu²⁺-metalloporphyrin in the organic phase. The “catch-and-release” methodology of TpyP was exploited to develop a triphasic C₆F₁₄/DCM/water indicator displacement assay (IDA) for histamine in which the receptor–indicator complex is compartimentalized in the perfluorocarbon. It has been shown that in such IDA methodology the fluorous phase can play the role of a membrane impervious to water, allowing the detection of histamine in water at micromolar concentrations.     

Reaction Species in the Aqueous Solution and Interfacial Synthesis of Zirconium Polyethers

The following tentative identifications are made from the study of variations in pH and substituted hydroquinones in the synthesis of zirconium polyethers: active species for aqueous solution systems, CP₂Zr²⁺ and RO η active species for interfacial systems, Cp₂ ZrCl₂ and R-OH with reaction occurring near the interface or in the organic phase. Yield increases as stirring rate increases throughout the stirring range of 13,000 to 24,500 rpm. Decent yields can also be obtained utilizing “inverse interfacial” systems where the Cp₂ ZrCl₂ is originally contained in water and the diol and added base in the organic layer. No product is found utilizing organic solution systems.     

Stable Oxypyridinium Triflate (OPT) Salts for the Synthesis of Halobenzyl Ethers

A collection of new oxypyridinium triflate reagents (1a–d) for the synthesis of halobenzyl ethers from alcohols under “mix‐and‐heat” conditions is described. The reagents are stable organic salts that can be stored indefinitely and handled without special precautions, making them attractive for general use in organic synthesis. Halobenzylation of representative alcohols occurs in good to excellent yield.     

Kinetic Analysis Applied to Iron in a Natural Water Model Containing Ions,Organic Complexes,Colloids, and Particles

Abstract

Kinetic analysis using complex formation reactions is applied to “mixtures” containing (variously), Fe³⁺, Fe²⁺, iron complexed to a fulvic acid, hydrous oxide colloids, and non-settleable particulate iron. Such mixtures can be directly resolved if the kinetics of complex formation reactions are pseudo first order and differences among rate constants are large enough. At pH = 4, it is found that fulvic acid causes substantial reduction of Fe³⁺ to Fe²⁺ and that it causes complete dissolution and depolymerization of colloidal and particulate iron at 1:1 ratio. Addition of one equivalent of phosphate causes precipitation of ferric phosphate even in the presence of fulvic acid. This system is very useful for modeling natural water because the kinetic technique allows convenient analysis of components of varying particle size. The present results are strongly indicative of the role of fulvic acid in mediating metal ion chemistry in natural water.     

Mechanistic Insight into the Reaction of Organic Acids with SO3 at the Air–Water Interface

The gas‐phase reaction of organic acids with SO₃ has been recognized as essential in promoting aerosol‐particle formation. However, at the air–water interface, this reaction is much less understood. We performed systematic Born–Oppenheimer molecular dynamics (BOMD) simulations to study the reaction of various organic acids with SO₃ on a water droplet. The results show that with the involvement of interfacial water molecules, organic acids can react with SO₃ and form the ion pair of sulfuric‐carboxylic anhydride and hydronium. This mechanism is in contrast to the gas‐phase reaction mechanisms in which the organic acid either serves as a catalyst for the reaction between SO₃ and H₂O or reacts with SO₃ directly. The distinct reaction at the water surface has important atmospheric implications, for example, promoting water condensation, uptaking atmospheric condesation species, and incorporating “SO₄^2?” into organic species in aerosol particles. Therefore, this reaction, typically occurring within a few picoseconds, provides another pathway towards aerosol formation.