Modeling of the θ(lower critical solution temperature) in polymer solutions using molecular connectivity indices

In this work, correlations for the estimation of the θ(lower critical solution temperature, LCST) for Polystyrene, Polyethylene, Polypropylene, Polybutene-1, Polypentene-1, Poly(4-methylpentene-1), Polydimethylsiloxane and Polyisobutylene solutions were proposed based on the molecular connectivity index. The correlations give satisfactory estimation of the θ(LCST), with the absolute error smaller than 20 K for most systems studied. Since the new correlations require only molecular connectivity indices of the solvent in the calculations, and the molecular connectivity indices can be calculated easily once the molecular structure of the substance concerned is known, they have better predictive capability and are easier to apply comparing with the existing methods and models.     

Potentiality of methyltrioctylammonium chloride ligand for selective extraction of the Uranium(VI) metal ions from selective carbonate leach liquor

In the present study, the use of 5% Aliquat-336/kerosene was evaluated in the liquid–liquid extraction of Uranium(VI) and some impurities of Thorium(IV) and rare earth elements (REEs(III)). Experiments were carried out to determine the factors affecting U(VI) and some impurities of Th(IV) and REEs(III) extraction. McCabe–Thiele diagram was constructed to define the theoretical stages for extraction mixer settler process. The effect of stripping factors from the loaded extractant was also tested. Uranium cake was finally obtained from the strip solution and a workable flow sheet was then formulated.     

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.     

Two new silver(I) complexes with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz): Preparation,characterization, crystal structure and alcohol oxidation activity in the presence of oxone

Two new silver(I) complexes ((tptz)Ag₂(NO₃)₂ and [Ag₅(tptz)₄](NO₃)₅) with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) have been synthesized and characterized by X-ray diffraction, elemental analysis, ¹H NMR, IR, fluorescence, UV–Vis spectroscopy and electrochemistry. Oxidation of alcohols to their corresponding aldehydes and ketones was conducted with one of the Ag complexes as a catalyst, soluble enough in organic solvent, using oxone (2KHSO₅·KHSO₄·K₂SO₄) as an oxidant under biphasic reaction conditions (CH₂Cl₂/H₂O) and tetra-n-butylammonium bromide as phase transfer agent under air at room temperature.     

Chemo-, regio- and stereoselective addition of triorganoindium reagents to acetates of Baylis-Hillman adducts: a new strategy for the synthesis of (E)- and (Z)-trisubstituted alkenes

The addition of several trialkyl or triarylindium reagents to the acetates of Baylis-Hillman adducts proceeds readily under the catalysis of copper and palladium derivatives. The reactions of trialkylindiums are catalyzed efficiently by CuI whereas additions of triarylindiums produce better results with Pd(PPh₃)₄. The reactions with 3-acetoxy-2-methylenealkanoates provide (E)-alkenes, whereas similar reactions with 3-acetoxy-2-methylenealkanenitriles lead to (Z)-alkenes. All the reactions are highly regio- and stereoselective and high yielding.     

1-(2-Formamidoethyl)-3-phenylurea functionalized activated carbon for selective solid-phase extraction and preconcentration of metal ions

A novel method that utilizes 1-(2-formamidoethyl)-3-phenylurea-modified activated carbon (AC-1-(2-formamidoethyl)-3-phenylurea) as a solid-phase extractant has been developed for simultaneous preconcentration of trace Cr(III), Cu(II), Fe(III) and Pb(II) prior to the measurement by inductively coupled plasma atomic emission spectrometry (ICP-AES). Experimental conditions for effective adsorption of trace levels of Cr(III), Cu(II), Fe(III) and Pb(II) were optimized using batch and column procedures in detail. The optimum pH value for the separation of metal ions simultaneously on the new sorbent was 4. And the adsorbed metal ions could be completely eluted by using 2.0 mL 2.0 mol L⁻¹ HCl solution. Common coexisting ions did not interfere with the separation and determination of target metal ions. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 39.8, 39.9, 77.8 and 17.3 mg g⁻¹ for Cr(III), Cu(II), Fe(III) and Pb(II), respectively. The detection limits of the method were found to be 0.15, 0.41, 0.27 and 0.36 ng mL⁻¹ for Cr(III), Cu(II), Fe(III) and Pb(II), respectively. The relative standard deviation (RSD) of the method was lower than 4.0% (n = 8). The method was successfully applied for the preconcentration of trace Cr(III), Cu(II), Fe(III) and Pb(II) in natural and certified samples with satisfactory results.     

Microanalysis of oligodeoxynucleotides by cathodic stripping voltammetry at amalgam-alloy surfaces in the presence of copper ions

The application of gold amalgam-alloy electrode (AuAE) for a sensitive voltammetric detection of different oligodeoxynucleotides (ODNs) containing the purine units within the ODN-chains in the presence of copper is described. The detection of ODNs is based on the following procedure: (i) the first step includes an acidic hydrolysis of the ODN (ahODN) samples performing the release of the purine bases from ODN-chain; (ii) the second step includes an electrochemical accumulation of the complex of the purine base residues released from ODN-chain with copper ions Cu(I) (ahODN-Cu(I) complex) at the potential of reduction of copper ions Cu(II) on the amalgam-alloy electrode surfaces; (iii) finally followed the cathodic stripping of the electrochemically accumulated ahODN-Cu(I) complex from the electrode surface. The proposed electrochemical method was used for: (a) detection of different ODN lengths containing only adenine units (the number of adenine units within the ODN-chains was changed from 10 to 80), and (b) determination of the number of purine units within the 30-mer ODNs containing a random sequence segments involving both the purine and pyrimidine units. The intensity of the cathodic stripping current density peak (j_CSP) of the electrochemically accumulated ahODN-Cu(I) complex increased linearly with the increasing number of purine units within the ODN-chains. We observed a good correlation between the percentage content of purine units to the whole length of different 30-mer ODNs and the percentage content of the intensity of the j_CSP of the electrochemically accumulated 30-mer ahODN-Cu(I) complexes. The detection of acid hydrolysed 80-mer (A₈₀) in the bulk solution and in a 20-μl volume is possible down to 200 pM and 2 nM at the AuAE, respectively. For the shortest 10-mer (A₁₀) a detectable value of 5 nM in the bulk solution on the AuAE was observed. The sensitive detection of different ODNs containing the purine units in their chains in the presence of copper can be also performed at the platinum amalgam-alloy (PtAE) and copper amalgam-alloy (CuAE) contrary to a lower sensitivity at the silver amalgam-alloy (AgAE) electrode.     

Synthesis of ditopic ligands for the selective extraction of copper(II) nitrate and crystal structures of their Cu(II) complexes

We have synthesized two ditopic ligands for selective extraction of copper(II) nitrate. We also synthesized one cation-only binding analog for comparison. All three ligands were characterized by conventional techniques. Competitive two-phase metal ion solvent extraction experiments were performed at 25 °C over a period of 24 h. These ligands showed significant selectivity for Cu(II) ions, having the ditopic ligands extract 81 and 73% of the Cu(II) ions in a solution of different metal ions {Ni(II), Co(II), Cu(II), Zn(II), Cd(II), Pb(II)} at pH 5.09. Competitive transport experiments (water/chloroform/water) were undertaken employing each ligand separately as the ionophore in the membrane (chloroform) phase. No metal ion transport was observed, but a large concentration of Cu(II) was present in the membrane phase. Competitive anion extraction and transport were carried out with the ditopic ligands, yielding selective extraction and transport of nitrate. Furthermore, a pH isotherm of the best ditopic ligand (H₂L²) with Cu(II) was determined from pH 1.0 to 6.0, producing a pH_½ value of approximately 2.6. Finally, crystal structures of the ditopic ligands complexed with Cu(II) were determined and refined. The coordination geometry around the metal centers are distorted square planar and the Cu(II)-donor bond lengths fall within the normal range.     

Luminescent hexanuclear Cu(I)-cluster for the selective determination of copper

For the first time, the formation of a luminescent hexanuclear cluster has been used for the selective determination of copper. In aqueous solutions, the non-luminescent ligand N-ethyl-N′-methylsulfonylthiourea (EMT) forms an intensely red luminescent hexanuclear Cu(I)-cluster with an emission maximum at 663 nm only with Cu(II) ions. The intensity of the luminescence is proportional to the Cu(II) concentration and allows for selective Cu determinations in the μg l⁻¹-range. Ubiquitous metal ions such as Fe(III), Al(III), Ca(II), Mg(II), and alkaline metal ions, as well as other heavy metal ions, e.g. Co(II), Ni(II), Zn(II), Cd(II), Hg(II), and Pb(II) are tolerated in concentrations up to 50 mg l⁻¹. The detection limit for Cu(II) in aqueous solution, calculated according to Funk et al. [Qualitätssicherung in der Analytischen Chemie, Verlag Chemie, Weinheim, 1992], is 113 μg l⁻¹. The cluster formation has been used for the quantitative analysis of copper in tap water and in industrial water, as well as for the localization of copper adsorbed by activated-sludge flocs.     

Synthesis and properties of novel 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-triones: methodology for synthesizing cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates

Novel condensation reaction of tropone with N-substituted and N,N′-disubstitued barbituric acids in Ac₂O afforded 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (8a-f) in moderate to good yields. The ¹³C NMR spectral study of 8a-f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-dicyanoheptafulvene. The rotational barriers (ΔG^‡) around the exocyclic double bond of mono-substituted derivatives 8a-c were obtained to be 14.51-15.03 kcal mol⁻¹ by the variable temperature ¹H NMR measurements. The electrochemical properties of 8a-f were also studied by CV measurement. Upon treatment with DDQ, 8a-c underwent oxidative cyclization to give two products, 7 and 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a-c·BF₄⁻ and 12a-c·BF₄⁻) in various ratios, while that of disubstituted derivatives 8d-f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (11d-f·BF₄⁻) in good yields. Similarly, preparation of known 5-(1′-oxocycloheptatrien-2′-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a-d) and novel derivatives 14e,f was carried out. Treatment of 14a-c with aq. HBF₄/Ac₂O afforded two kinds of novel products 11a-c·BF₄⁻ and 12a,c·BF₄⁻ in various ratios, respectively, while that of 14d-f afforded 11d-f. The product ratios of 11a-c·BF₄⁻ and 12a-c·BF₄⁻ observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a and 21a. The spectroscopic and electrochemical properties of 11a-f·BF₄⁻ and 12a-c·BF₄⁻ were studied, and structural characterization of 11c·BF₄⁻ based on the X-ray crystal analysis and MO calculation was also performed.     

Synthesis of poly(silylenephosphonate)s incorporating 2-chloroethylphosphonic acid (ethephon), a stimulant for the latex production by the Hevea brasiliensis

2-Chloroethylphosphonic acid (ethephon) is a well-known stimulant commonly used to improve the latex production by the rubber tree (Hevea brasiliensis). In order to prolong its stimulating activity, the purpose was to insert ethephon inside polymer chains which, afterwards, will be able to degrade slowly through time, and thus to release ethephon molecules. For that, linear poly(silylenephosphonate)s incorporating ethephon groups were synthesized by using a polycondensation procedure between ethephon (or one of its dialkyl phosphonate derivatives) and an α,ω-dihalogeno-silylated monomer. To make sure that polycondensation can occur, the reactivity of halogenotrimethylsilanes (X=Cl or Br) toward ethephon and its various dialkyl phosphonate derivatives, was examined first. Then, poly(silylenephosphonate) synthesis was achieved by polycondensation between diisopropyl (2-chloroethyl)phosphonate and α,ω-dichloro-silylated monomers. According to this procedure, cyclic polymers of low average molecular weights (M_n<2000) were obtained, whatever the α,ω-dihalogeno-silylated monomer used.     

Potential of ethylenediaminedi(o-hydroxyphenylacetic acid) and N,N′-bis(hydroxybenzyl)ethylenediamine-N,N′-diacetic acid for the determination of metal ions by capillary electrophoresis

Two aromatic polyaminocarboxylate ligands, ethylenediaminedi(o-hydroxyphenylacetic acid) (EDDHA) and N,N′-bis(hydroxybenzyl)ethylenediamine-N,N′-diacetic acid (HBED), were applied for the separation of transition and heavy metal ions by the ion-exchange variant of electrokinetic chromatography. EDDHA structure contains two chiral carbon centers. It makes it impossible to use the commercially available ligand. All the studied metal ions showed two peaks, which correspond to meso and rac forms of the ligand. The separation of metal–HBED chelates was performed using poly(diallyldimethylammonium) polycations in mixed acetate–hydroxide form. Simultaneous separation of nine single- and nine double-charged HBED chelates, including In(III), Ga(III), Co(II)–(III) and Mn(II)–(III) pairs demonstrated the efficiency of 40 000–400 000 theoretical plates. The separation of Co(III), Fe(III) complexes with different arrangements of donor groups and oxidation of Co(II), Mn(II), Fe(II) ions in reaction with HBED have been discussed.     

l-Proline-catalyzed three-component domino reactions for the synthesis of highly functionalized pyrazolo[3,4-b]pyridines

A series of novel N,3-dimethyl-5-nitro-1-aryl-1H-pyrazolo[3,4-b]pyridin-6-amines was obtained in good yields from the domino reactions of N-methyl-1-(methylthio)-2-nitroprop-1-en-1-amine, aromatic aldehydes, and 3-methyl-1-aryl-1H-pyrazol-5-amines in ethanol in the presence of green catalyst, l-proline. This transformation involves the formation of two C–C and one C–N bonds leading to the creation of a six-membered ring in a one-pot operation.     

Proteomic platform for the identification of proteins in olive (Olea europaea) pulp

The nutritional and cancer-protective properties of the oil extracted mechanically from the ripe fruits of Olea europaea trees are attracting constantly more attention worldwide. The preparation of high-quality protein samples from plant tissues for proteomic analysis poses many challenging problems. In this study we employed a proteomic platform based on two different extraction methods, SDS and CHAPS based protocols, followed by two precipitation protocols, TCA/acetone and MeOH precipitation, in order to increase the final number of identified proteins.     

Temperature-dependent interfacial properties of hydrophobically end-modified poly(2-isopropyl-2-oxazoline)s assemblies at the air/water interface and on solid substrates

We describe herein the properties at the air/water (A/W) interface of hydrophobically end-modified (HM) poly(2-isopropyl-2-oxazoline)s (PiPrOx) bearing an n-octadecyl chain on both termini (telechelic HM-PiPrOx) or on one chain end (semitelechelic HM-PiPrOx) for different subphase temperatures and spreading solvents using the Langmuir film balance technique. The polymer interfacial properties revealed by the π–A isotherms depend markedly on the architecture and molecular weight of the polymer. On cold water subphases (14 °C), diffusion of PiPrOx chains onto water takes place for all polymers in the intermediate compressibility region (5 mN m⁻¹). At higher subphase temperatures (36 and 48 °C), the HM-PiPrOx film exhibited remarkable stability with time. Brewster angle microscopy (BAM) imaging of the A/W interface showed that the polymer assembly was not uniform and that large domains formed, either isolated grains or pearl necklaces, depending on the polymer structure, the concentration of the spreading solution and the subphase temperature. The Langmuir films were transferred onto hydrophilic substrates (silica) by the Langmuir–Blodgett (LB) technique and onto hydrophobic substrates (gold) by Langmuir–Schaefer (LS) film deposition, resulting in the formation of adsorbed particles ranging in size from 200 to 500 nm, depending on the polymer architecture and the substrate temperature. The particles presented “Janus”-like hydrophilic/hydrophobic characteristics.     

A simple route for the synthesis of 3,3,3′,3′-tetramethyl-2,3,3′,4′-tetrahydro-1H,1′H-[4,9′-bixanthene]-1,1′(2′H,9′H)-dione and its derivatives catalyzed by Mn and other transition metal cations

A simple and efficient unusual coupling reaction of 9-(2-hydroxy-4,4-dimethyl-6-oxocyclohex-1-en-1-yl)-3,3-dimethyl-2,3,4,9-tetrahydro-1H-xanthen-1-one and its derivatives was accomplished in the presence of Mn²⁺, Cu²⁺, Cd²⁺, Hg²⁺, Fe³, or La³⁺. The structure elucidation was accomplished by IR, ¹H NMR, ¹³C NMR, X-ray crystallography, UV-Visible and elemental analysis. A reaction mechanism is proposed.     

Au(I)/Ag(I)-catalyzed annulation of sugar aldehyde tethered with 3-phenylprop-2-yn-1-yl ether with aryl amines for the pyrano[4,3-b]quinoline derivatives

Aryl amines undergo smooth annulation with O-phenylpropynyl sugar aldehyde in the presence of the Ph₃PAuCl (10 mol %)/AgSbF₆ (10 mol %) catalytic system to afford the corresponding tetrahydro-3aH-spiro[[1,3]dioxolo[4″,5″:4′,5′]furo[3′,2′:5,6]pyrano[4,3-b]quinoline-2,1′-cyclohexane] derivatives in good yields and selectivity.