Complexation mechanism of olefin with silver ions dissolved in a polymer matrix and its effect on facilitated olefin transport

Remarkable separation performance of olefin/paraffin mixtures was previously reported by facilitated olefin transport through silver-based polymer electrolyte membranes. The mechanism of facilitated olefin transport in solid membranes of AgCF3SO3 dissolved in poly(N-vinyl pyrrolidone) (PVP) is investigated. In silver polymer electrolyte membranes, only free anions are present up to the 2:1 mole ratio of [C=O]:[Ag], and ion pairs start to form at a ratio of 1:1, followed by higher-order ionic aggregates above a ratio of 1:2. At silver concentrations above 3:1, the propylene permeance increases almost linearly with the total silver concentration, unexpectedly, regardless of the silver ionic constituents. It was also found that all the silver constituents, including ion pairs and higher order ionic aggregates, were completely redissolved into free anions under the propylene environment; this suggests that propylene can be a good ligand for the silver cation. From these experimental findings, a new mechanism for the complexation reaction between propylenes and silver salts in silver-polymer electrolytes was proposed. The new mechanism is consistent with the linearity between the propylene permeance and the total silver concentration regardless of the kind of the silver constituents. Therefore, the facilitated propylene transport through silver-polymer electrolytes may be associated mainly with the silver cation weakly coordinated with both carbonyl oxygen atoms and propylene.     

Reaction of platinum complexes with (+)-α-pinene and (+)-limonene. Synthesis, molecular structure, and catalytic activity of dichloro(η4-[p-mentha-1,8{9}-diene])platinum(II)

The transformations of platinum(II) and platinum(IV) complexes with inner-and outer-sphere ligands by the action of (+)-α-pinene and (+)-limonene were studied. Reduction of the metal complex is the main process whose rate increases in the following outer-sphere ligand series: (Me₂SO)₂H⁺ < Et₃NH⁺ < K^? < H⁺. The reaction of K₂PtCl₄ with α-pinene gave cis-terpine monohydrate and dichloro-η⁴-[p-mentha-1,8(9)-diene]platinum(II), and their structure was proved by X-ray analysis. The complex belongs to monoclinic crystal system, the Pt-Cl and Pt-C bonds therein have different lengths, the ClPtCl angle is 85.88°, and the C=C bond plane is orthogonal to the square coordination core. Dichloro-η⁴-[p-mentha-1,8(9)-diene]-platinum(II) was tested as catalyst in the hydrosilylation of acetophenone with diphenylsilane.     

Determination of pirimicarb and endosulfan in commercial pesticide formulations by Fourier transform infrared spectrometry

A routine method based on Fourier transform infrared spectrometry was developed for the simultaneous determination of pirimicarb and endosulfan in commercially available pesticide formulations. The method is based on peak area absorbance measurements between 1362 and 1352 cm(-1), corrected with a baseline fixed at 1338 cm(-1), for pirimicarb and peak area absorbance measurements between 919 and 909 cm(-1) with a baseline fixed at 931 cm(-1) for endosulfan; chloroform solutions for analysis were obtained by direct dilution of emulsifiable concentrates or by solvent extraction from solid samples. Various extraction conditions and appropriate band selection were investigated, and interference studies were performed. Under the experimental conditions selected, limits of detection of 13 microg/g for pirimicarb and 150 microg/g for endosulfan were obtained that correspond to 0.13 and 1.6% (w/w), respectively, in commercial samples. Results from analyses of commercial samples by the developed method compared well with those obtained by a liquid chromatography reference method.     

Flow injection determination of bismuth in urine by successive retention of Bi(III) and tetrahydroborate(III) on an anion-exchange resin and hydride generation atomic absorption spectrometry

Bismuth as BiCl₄⁻ and BH₄⁻ ware successively retained in a column (150 mm × 4 mm, length × i.d.) packed with Amberlite IRA-410 (strong anion-exchange resin). This was followed by passage of an injected slug of hydrochloric acid resulting in bismuthine generation (BiH₃). BiH₃ was stripped from the eluent solution by the addition of a nitrogen flow and the bulk phases were separated in a gas–liquid separator. Finally, bismutine was atomized in a quartz tube for the subsequent detection of bismuth by atomic absorption spectrometry. Different halide complexes of bismuth (namely, BiBr₄⁻, BiI₄⁻ and BiCl₄⁻) were tested for its pre-concentration, being the chloride complexes which produced the best results. Therefore, a concentration of 0.3 mol l⁻¹ of HCl was added to the samples and calibration solutions. A linear response was obtained between the detection limit (3σ) of 0.225 and 80 μg l⁻¹. The R.S.D.% (n = 10) for a solution containing 50 μg l⁻¹ of Bi was 0.85%. The tolerance of the system to interferences was evaluated by investigating the effect of the following ions: Cu²⁺, Co²⁺, Ni²⁺, Fe³⁺, Cd²⁺, Pb²⁺, Hg²⁺, Zn²⁺, and Mg²⁺. The most severe depression was caused by Hg²⁺, which at 60 mg l⁻¹ caused a 5% depression on the signal. For the other cations, concentrations between 1000 and 10,000 mg l⁻¹ could be tolerated. The system was applied to the determination of Bi in urine of patients under therapy with bismuth subcitrate. The recovery of spikes of 5 and 50 μg l⁻¹ of Bi added to the samples prior to digestion with HNO₃ and H₂O₂ was in satisfactory ranges from 95.0 to 101.0%. The concentrations of bismuth found in six selected samples using this procedure were in good agreement with those obtained by an alternative technique (ETAAS). Finally, the concentration of Bi determined in urine before and after 3 days of treatment were 1.94 ± 1.26 and 9.02 ± 5.82 μg l⁻¹, respectively.     

Final elucidation of the absolute configuration of the signal metabolite hormaomycin

The complete absolute configuration of hormaomycin 1 a has been established by HPLC and HPLC/MS experiments with appropriately derivatized 4-propylprolines, (2S,4S)-6 and (2R,4R)-6, as well as 4-(Z)-propenylprolines, cis-5 and trans-5, and also feeding experiments with enantiomerically pure samples of the deuterium-labeled 3-(2'-nitrocyclopropyl)alanine, (2S)-3,3-[D2]15 and (2S)-2,2'-[D2]15, and 4-(Z)-propenylproline 2',4-[D2]-(2S,4R)-5. The latter five amino acids were prepared for the first time and allowed one to unequivocally assign the hitherto unknown absolute configurations of the last four stereocenters in hormaomycin 1 a. As a bonus, some new information about the biosynthesis of this molecule has also been gathered.     

Enantioselective approaches to potential MetAP-2 reversible inhibitors

[reaction: see text] Enantioselective deprotonation of 4-substituted cyclohexanones and highly stereoselective conjugate addition of higher order mixed cuprates were the key steps in a concise synthesis of fumagalone-related molecules. The origin of the (low) biological activity of the new compounds as compared to fumagalone is briefly discussed.     

On-line preconcentration of mercury by sorption on an anion-exchange resin loaded with 1,5-bis[(2-pyridyl)-3-sulphophenyl methylene] thiocarbonohydrazide and determination by cold-vapour inductively coupled plasma atomic emission

1,5-Bis[(2-pyridyl)-3-sulphophenyl methylene] thiocarbonohydrazide (PSTH) immobilized on an anion-exchange resin (Dowex) has been used for the on-line preconcentration of mercury from biological samples and waters prior to its determination by inductively coupled plasma atomic emission spectroscopy. The metal was eluted from the column using a solution of 2 M HNO(3) and mixed on-line with SnCl(2). The optimum experimental conditions were evaluated for the continuous preconcentration of Hg, the direct generation of mercury vapour and the final determination of this element by ICP-AES. The enrichment, together with low blank levels of the optimized procedure, allow the simple determination of this toxic element at concentrations down to a few nanograms per milliliter. The proposed method has a linear calibration range 5-1000 ng ml(-1) of mercury, with a detection limit of 4 ng ml(-1) (S/N=3) and a sampling rate of 40 h(-1), investigated with a 9 ml sample volume. The precision of the method (evaluated as the relative standard deviation obtained after analyzing ten series of ten replicates) was +/-3.6% at the 10 ng ml(-1) level of Hg(II) and +/-1.3% at the 100 ng ml(-1) level. The accuracy of the method was examined by the analysis of certified reference materials.     

Characterisation of botulinum toxins type C, D, E, and F by matrix-assisted laser desorption ionisation and electrospray mass spectrometry

In a follow-up of the earlier characterisation of botulinum toxins type A and B (BTxA and BTxB) by mass spectrometry (MS), types C, D, E, and F (BTxC, BTxD, BTxE, BTxF) were now investigated. Botulinum toxins are extremely neurotoxic bacterial toxins, likely to be used as biological warfare agent. Biologically active BTxC, BTxD, BTxE, and BTxF are comprised of a protein complex of the respective neurotoxins with non-toxic non-haemagglutinin (NTNH) and, sometimes, specific haemagglutinins (HA). These protein complexes were observed in mass spectrometric identification. The BTxC complex, from Clostridium botulinum strain 003-9, consisted of a 'type C1 and D mosaic' toxin similar to that of type C strain 6813, a non-toxic non-hemagglutinating and a 33 kDa hemagglutinating (HA-33) component similar to those of strain C-Stockholm, and an exoenzyme C3 of which the sequence was in full agreement with the known genetic sequence of strain 003-9. The BTxD complex, from C. botulinum strain CB-16, consisted of a neurotoxin with the observed sequence identical with that of type D strain BVD/-3 and of an NTNH with the observed sequence identical with that of type C strain C-Yoichi. Remarkably, the observed protein sequence of CB-16 NTNH differed by one amino acid from the known gene sequence: L859 instead of F859. The BTxE complex, from a C. botulinum isolated from herring sprats, consisted of the neurotoxin with an observed sequence identical with that from strain NCTC 11219 and an NTNH similar to that from type E strain Mashike (1 amino acid difference with observed sequence). BTxF, from C. botulinum strain Langeland (NCTC 10281), consisted of the neurotoxin and an NTNH; observed sequences from both proteins were in agreement with the gene sequence known from strain Langeland. As with BTxA and BTxB, matrix-assisted laser desorption/ionisation (MALDI) MS provided provisional identification from trypsin digest peptide maps and liquid chromatography-electrospray (tandem) mass spectrometry (LC-ES MS) afforded unequivocal identification from amino acid sequence information of digest peptides obtained in trypsin digestion.     

The Crystal Structure of Ba3Cu2Al2F16: a Relative of Ba4Cu2Al3F21

Ba₃Cu₂Al₂F₁₆ is monoclinic: a = 7.334(1)Å, b = 5.320(2)Å, c = 16.022(1)Å, β = 96.34(1)°, Z = 2. Its crystal structure was solved in the space group P2₁ (No. 4) from synchrotron X‐ray single crystal data using 2685 unique reflections (2639 with F_o/σ(F_o) > 4). The final R factor is 0.044. The structure consists of a succession along the c‐axis of the cell of three layers of two different kinds of sheets developing in the (a, b) plane. The first one, formulated [(AlF₅)₂]_∞^4— and hereafter named A, is built up from infinite cis‐chains of aluminium‐fluorine octahedra [AlF₆], linked by two vertices and distanced by a. The second one, formulated [Cu₂AlF₁₁]_∞^4— and named B, is bidimensional. It is constituted of distorted copper‐fluorine octahedra [CuF₆], linked by edges, which form infinite chains interconnected by three vertices of isolated [AlF₆] octahedra. The stacking sequence of the sheets is (A, B, B)_∞. The barium ions, 12‐coordinated, are inserted between the sheets. The crystal structure of Ba₃Cu₂Al₂F₁₆ is closely related to that of Ba₄Cu₂Al₃F₂₁. Only the proportion and the stacking sequence of the two kinds of sheets in the c‐direction differ, according to two different compositions and two different symmetries.