Mixed micelles of homologous perfluoropolyether anionic surfactants in water

The mixtures of sodium and ammonium salts of three homologous perfluoropolyether carboxylic acids having Cl-terminated perfluoroalkyl group (Cl-PFPE) and differing in the average molecular weight (MW) were examined. The surfactants, namely n2, n3 and n4, have two, three and four PFPE units, respectively. Each surfactant was studied alone and in mixture with the other surfactants with the same counterion. NMR chemical shifts were measured for each surfactant and for the mixtures in different concentrations. For a given mixture the micelle composition, X_i, can be determined from the observation of the chemical shifts of the micellar components. It was found that Cl-PFPE surfactant mixtures form in water mixed micelles which contain the surfactants in equilibrium with monomeric species. The analysis of NMR chemical shift variations allowed evaluating the partition of the various surfactants in the mixed aggregates as a function of the total concentration. Composition of mixed micelles resembles ideal mixing predictions particularly at high surfactant concentrations.     

The Effect of N-alkyl Substitution on Binding of Polycarboxylic Anions by Linear Polyammonium Cations

The interaction between three N-alkyl-substituted polyamines[1,1,4,4-tetramethylethylenediamine, 1,1,4,7,7,-pentamethyldiethylenetriamine,and 1,1,4,7,10,10-hexamethyltriethylenetetramine; general formula C_3nN_nH_(7n+2)] with fourpolycarboxylic ligands (malonate, citrate, 1,2,3-propanetricarboxylate, and1,2,3,4-butanetetracarboxylate) has been studied potentiometrically in aqueous solution at25°C. For all the systems, the species ALH_r (r = 1, 2 ... n + m – 1;n and m are the maximum degrees of protonation for the amine A and the carboxylicligand L, respectively) are formed. The stability of these species is quite high(in particular, that of species with r = n and r = n + 1) and is a linear functionof the charges involved in the formation reaction. The effect of N-alkyl substitutionis quite small: comparison with the analogous unsubstituted polyamines C_(2n–2)N_nH_(5n–2) shows only a small decrease in stability. On average we have–G ^o/n = 5.9 kJ-mol^–1 for N-alkyl-substitutedamines and 6.6 kJ-mol^–1 for unsubstituted ones (ndenoting the number of possible salt bridges). Other linear charge—stabilityrelationships are considered.     

Nanomolar inhibitors of AmpC beta-lactamase

beta-lactamases are the most widespread resistance mechanism to beta-lactam antibiotics, such as the penicillins and the cephalosporins. In an effort to combat these enzymes, a combination of stereoselective organic synthesis, enzymology, microbiology, and X-ray crystallography was used to design and evaluate new carboxyphenyl-glycylboronic acid transition-state analogue inhibitors of the class C beta-lactamase AmpC. The new compounds improve inhibition by over 2 orders of magnitude compared to analogous glycylboronic acids, with K(i) values as low as 1 nM. On the basis of the differential binding of different analogues, the introduced carboxylate alone contributes about 2.1 kcal/mol in affinity. This carboxylate corresponds to the ubiquitous C3(4)' carboxylate of beta-lactams, and this energy represents the first thermodynamic measurement of the importance of this group in molecular recognition by class C beta-lactamases. The structures of AmpC in complex with two of these inhibitors were determined by X-ray crystallography at 1.72 and 1.83 A resolution. These structures suggest a structural basis for the high affinity of the new compounds and provide templates for further design. The highest affinity inhibitor was 5 orders of magnitude more selective for AmpC than for characteristic serine proteases, such as chymotrypsin. This inhibitor reversed the resistance of clinical pathogens to the third generation cephalosporin ceftazidime; it may serve as a lead compound for drug discovery to combat bacterial resistance to beta-lactam antibiotics.     

A new standardized leaching test on stabilized wastes

A new long-term leaching test on stabilized and solidified waste material have been developed and standardized in the frame of the Standards, Measurements and Testing (SMT, formerly BCR) programme of the European Union (EU). The project was coordinated by Dr. H. A. Van der Sloot from ECN (Energy Research Foundation, The Netherlands). Twenty-five European laboratories from EU and EFTA countries participated in the intercomparison exercise. The solidification/stabilization treatment of municipal solid waste incinerator fly ashes, using cement as a matrix, was performed by INTRON B. V. (The Netherlands). The resulting solidified waste material was then used to produce the requested specimens for the intercomparison study. Before distribution to participants, specimen homogeneity was tested according to the state-of-the-art technology for physical-mechanical testing of cement samples as well as for consistency of chemical composition of the solid and stabilized waste. The results of tank leaching test for the above mentioned interlaboratory study are reported and the advantages of this new procedure for the study of the environmental impact of solidified wastes are discussed.     

Synthesis,Characterization, and crystallographic analysis of some benzoimidazole derivatives

A number of benzenesulfonyl derivatives of benzoimidazol-2-ylamine and 1-methyl-benzoimidazol-2-ylamine were synthesized, their synthesis reactions under different experimental conditions being monitored by hptlc. The crystal and molecular structures of N-(1-benzenesulfonyl-1,3-dihydrobenzoimidazol-2-ylidene)benzenesulfonamide (4) and N-(1-benzenesulfonyl-3-methyl-1,3-dihydro-benzoimidazol-2-ylidene)-benzenesulfonamide (7) were determined by X-ray diffraction analysis. The structure of compound 4 is made up of two crystallographically independent molecules and that of compound 7 of one molecule. In both cases, the structure contains the imido form of the molecules. There are strong conjugative effects between the imido groups and the imidazolic rings. Weak intramolecular C? H···O hydrogen bonding interactions could influence the molecular conformations.     

Selective acetylation of substituted (E)-4(1H)-hydroxyimino-2,3-dihydro-1,8-naphthyridine

We report a selective acetylation of compounds 2 in 1-, 4- or 1,4-position. The treatment of 2 with acetic anhydride gave the compounds 3 and with acetyl chloride the compounds 4 . The 1-acetyl derivatives were obtained starting from 5 via the oxime derivatives 6, 7 and 8 . Tests on phytoiatric antimycotic activity and on reactivation of phosphylated acetylcholinesterase and inhibition of acetylcholinesterase were performed.     

Gas-phase ion chemistry in the ternary SiH(4)-C(3)H(6)-PH(3) system

Propene-phosphine and the silane-propene-phosphine gaseous mixtures were studied by ion trap mass spectrometry. For the binary mixture the variation of ion abundances under different partial pressures and the mechanisms of ion-molecule reactions are reported. Moreover, the rate constants of the main processes were measured and compared with the collisional rate constants to determine the reaction efficiencies. In the ternary silane-propene-phosphine mixture the mechanisms of formation of Si(m)C(n)P(p)H(+)(s) ion clusters were elucidated, but the complexity of the system and the low abundances of the ions usually isolated by successive steps prevented the determination of rate constants. The hydrogenated ternary ions are mainly formed by reactions of Si(r)P(s)H(+)(t) ions with propene, whereas a minor contribution comes from reactions of Si(m)C(n)H(+)(p) ions with phosphine. The C(v)P(w)H(+)(z) ions show very low reactivity with silane. The formation processes of these species are discussed in relation to their possible role as precursors of amorphous silicon carbides doped with phosphorus obtained by deposition from properly activated silane-propene-phosphine mixtures.     

The fractionation and determination procedures for the speciation of Pb and Po in soil samples

A method for speciation and determination of ²¹⁰Pb and ²¹⁰Po in soil samples was developed. The speciation was carried out by fractionating the soil samples into five fractions which are water soluble or exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and bound to residue. After mineralisation, 10% solution of each fraction was used to spontaneously deposit polonium on a silver disk at 85-90 °C and pH 1.5, and ²¹⁰Po was measured by α-spectrometry; the remain solution was used to separate lead by anion-exchange resin and purified by precipitation as PbS and PbSO₄, and ²¹⁰Pb was determined by a low background β-counter. The IAEA-327 reference material (soil) was studied for ²¹⁰Pb and ²¹⁰Po speciation. The results show that: (1) the average yields are 88.7 ± 6.4% for ²¹⁰Pb and 93.8 ± 8.2% for ²¹⁰Po; (2) if compared to the total ²¹⁰Pb activity in the sample, ²¹⁰Pb fractions are 0.95% in exchangeable form, 10.6% bound to carbonates, 14.3% bound to Fe-Mn oxides, 7.0% bound to organic matter and 67.2% bound to residue or acid soluble, and the corresponding values for ²¹⁰Po are 0.17%, 0.97%, 21.0%, 0.47% and 77.4%, respectively; and (3) the obtained ²¹⁰Pb concentration is in good agreement with the recommended value given by the IAEA.     

On the hydrolysis of the dioxouranium(VI) ion in oxalate solutions

The complex formation between the dioxouranium (VI) and the oxalate ions has been investigated by measuring the potential of a glass electrode, at 25.00 degrees C, in 1 and 3 M NaClO4, at lower acidities than 10(-4.5) M, in order to favour the formation of (mixed) ternary species. The upper limits of concentration of all the analytical parameters have been imposed by the modest solubility of Na2C2O4 in the ionic media. The experimental measurements at different ionic strengths have been treated by means of the computerised least square programme LETAGROP - ETITR. Ternary complexes of general composition (p, q, r) are formed according to reaction (1), in addition to the already reported binary complexes. pUO2(2+) + qH2O + rC2O4(2-) <==> (UO2)p(OH)q(C2O4)r(2p-q-2r)(+) + qH+ (1). The stoichiometric compositions of the ternary species are (1, 1, 1), (2, 4, 2), (2, 2, 4). Their formation constants, expressed in molality, obtained in the two ionic media, are listed below. [table: see text]. For reasons discussed in the present work in the last column only the value of the constant in 1 M ionic medium is reported for the species (2, 4, 2). Additional evidence on the stoichiometric composition of the species formed is afforded by the mass-spectrometric measurements, collected in solutions of known composition.