Use of solid-phase micro-extraction as a sampling technique in the determination of volatiles emitted by flowers,isolated flower parts and pollen

The volatiles emitted by fresh whole flowers or isolated flower parts of mandarin, Citrus deliciosa Ten. (Rutaceae), were sampled using solid-phase micro-extraction (SPME). This technique offers several advantages over dynamic headspace sampling techniques used in previous investigations. In particular, SPME requires smaller sample sizes and very short sampling times, which can minimize the formation of artifacts due to damage to the plant, and contaminations or loss of compounds. This was especially applicable to the collection of volatiles from pollen.     

Iron-Iridium Mixed-Metal Carbonyl Clusters: A Mössbauer Study of the Structure and of the Adsorption of [Fe2Ir2(CO)12]2− on MgO

¹⁹³Ir and ⁵⁷Fe Mössbauer spectroscopy was used to investigate the structure of the [Fe₂Ir₂(CO)₁₂]^2- cluster compound and the adsorption of this cluster on hydrated MgO. Supported samples were prepared by impregnation of the magnesia with solutions of [Et₄N]₂[Fe₂Ir₂(CO)₁₂] in acetone. The Mössbauer and FT-IR spectra of the MgO-supported cluster confirm that the bimetallic carbonyl is molecularly physisorbed onto MgO without undergoing any transformation or decomposition. The easy solvent extraction of the intact cluster from the oxide surface excludes ion pairing between the cluster anion and the Mg²⁺ surface sites. Mössbauer spectra are in agreement with the refined structure of the molecular cluster and the temperature dependence of the ⁵⁷Fe Mössbauer spectra above 80 K is consistent with the low degree of interaction of the cluster with the support. This technique, therefore, appears to be promising in order to infer structural information when X-ray determination fails.     

Mechanism of formation and decay of the compound nuclei150Gd produced by two entrance channels (16O+134Ba) and (40Ar+110Pd)

Excitation functions have been drawn for evaporation residues issued from¹⁵⁰Gd, a compound nucleus produced either by¹⁶O ions on¹³⁴Ba, or by⁴⁰Ar on¹¹⁰Pd. Absolute cross sections were measured for^145–147Gd,^145–147Eu,^141m Sm,^143m Sm,^140m Pm and^139m Nd. Complete fusion cross sections have been obtained and compared to calculated estimations based, at low energies, on the simple expressionσ _CF=πR _Fuss ² (1?V _Fus/E) whereR _Fus andV _Fus are respectively the distance and the potential for fusion atdV/dr=0. For high energies σ_CF=πR _cr ² (1?V_cr/E) with the model of critical distanceR _cr and critical potentialV _cr. Thresholds energies have been determined with a particular care. The analysis of the shape and the width of excitation functions, particularly for the emission of 4 and 5 neutrons, has been carried out and compared to calculated values. The difference between argon and oxygen induced reactions has been attributed to the difference inl population in the entrance channel.     

Improvement of plant parameters of the ROBO gamma irradiation facility due to design modification

Two industrial scale, “ROBO” type ⁶⁰Co gamma irradiation facilities have recently been put into operation in Syria and Peru, and the dosimetry commissioning of both plants have been carried out to determine dose distribution within products and to calculate plant parameters such as efficiency, dose uniformity ratio and throughput. There are some design modifications between the two plants in connection with the location of the carriers with respect to the source plaque and also to each other. The effect of these construction modifications on the plant parameters is discussed in the analysis of the dose distribution data measured in the carriers with depth and height among the four irradiation rows on both sides of the source plaque. The plant parameters were also calculated for different product densities using the technical data of the facilities, and the calculated and measured results were compared to each other.     

Sequential injection system with higher dimensional electrochemical sensor signals Part 1. Voltammetric e-tongue for the determination of oxidizable compounds

A sequential injection analysis (SIA) system was developed with the aim of obtaining an automatic and versatile way to prepare standards needed in the study of systems with higher dimensional sensor signals. To illustrate this, different analytical techniques were used in determinations of several analytes. Automated potentiometric calibrations of different potentiometric sensors, with and without interference, were carried out. Useful determinations of selectivity coefficients with two degrees of freedom were obtained. Simultaneous voltammetric determinations have also been done. Firstly, simultaneous determinations of lead and cadmium, using epoxy-graphite composite as the working electrode, have enabled a separate calibration for each metal to be obtained. Next, a voltammetric electronic tongue was designed and applied to the determination of oxidizable species. The use of artificial neural networks has solved the overlapped signal of ascorbic acid, 4-aminophenol and 4-acetamidophenol (paracetamol). A set of 63 data points was prepared automatically and has facilitated the training of an electronic tongue for these three analytes. Accurate predictions of test solutions, in the range of 12–410 μM for ascorbic acid, 17–530 μM for 4-aminophenol and 10–420 μM for paracetamol, have been achieved with RMSEs lower than 0.10 μM.     

All-solid-state potentiometric sensors sensitive to nonionic surfactants based on ionophores containing ethoxylate units

Earlier work of potentiometric Ion-selective electrodes (ISEs) sensitive to nonionic surfactants of the polyethoxylate type is further extended. The ISEs constructed were all-solid-state sensors with plasticized PVC membranes. The sensing material was a tetraphenylborate salt of the barium complex with a polyethoxylate nonionic surfactant. As membrane component, the combinations of two polyethoxylates of the nonylphenoxy type, which differed in the number of oxyethylene units (5 or 12), and two different plasticizers, (o-nitrophenyloctyl ether and o-nitrophenylphenyl ether), were tested. The response of these electrodes to different nonionic surfactants and the interference effect of several species has been evaluated. For all the types of tested electrodes, the sensitivities shown were ca. 30.0 mV dec(-1) and the limit of detection, ca. 10(-5) M, when a nonylphenoxyde with 12 oxyethylene units was used as standard. The membrane with the best response characteristics was then applied in potentiometric titrations of this kind of surfactants in the presence of Ba(2+) ion and using tetraphenylborate as the titrant.     

Activation of the carbon—nitrogen triple bond of benzonitrile in the presence of triosmium clusters and acetic acid. Crystal structure of (μ-H)Os3(CO)10(μ-O2CCH3), a product of the reaction

The activation of the CN triple bond of benzonitrile in the presence of acetic acid and of Os₃(CO)₁₂ or H₂Os₃(CO)₁₀ has been studied. When Os₃(CO)₁₂ reacts with PhCN and acetic acid in refluxing n-octane the three main products are (μ-H)Os₃(CO)₁₀(μ-O₂CCH₃) (I), (μ-H)Os₃(CO)₁₀(μ-NCHPh) (II) and (μ-H)Os₃(CO)₁₀(μ-NHCH₂Ph) (III); II and III are analogues of (μ-H)Ru₃(CO)₁₀(μ-NCHPh) and (μ-H)Ru₃(CO)₁₀(μ-NHCH₂Ph) obtained from PhCN, Ru₃(CO)₁₂ or H₄Ru₄(CO)]₁₂, and acetic acid. In contrast to the reaction with ruthenium clusters, Os₃(CO)₁₂ and H₂Os₃(CO)₁₀ also give the adduct Os₃(CO)₁₀(CH₃COOH) (I). The structure of I has been fully elucidated by X-ray diffraction. Crystals of I are monoclinic, space group P2₁/m, with unit cell parameters a 7.858(6), b 12.542(8), c 9.867(6) Å, β 109.92(2)°, Z = 2. In I an edge of the triangular cluster of osmium atoms is doubly bridged by a hydride and an acetate ligand. Ten terminal carbonyl groups are bonded to the metal atoms.     

Affinity capillary electrophoresis study of the linkage existing between proton and zinc ion binding to bacitracin A1

Measurements by capillary electrophoresis (CE) of bacitracin A(1) effective mobility at different pH values permitted to estimate the five acidic dissociation constants and the Stokes radii at different protonation stages of the macrocyclic dodecapeptide. The pK(a) values were 3.6 and 4.4 for the two carboxylic groups of the lateral chains of D-Asp-11 and D-Glu-4, respectively, 6.4 for the aza-atom of the imidazole ring of His-10, 7.6 for the amino group of N-terminal Ile-1 and 9.7 for the delta-amino group of D-Orn-7, very close to the values obtained by other researchers by titration experiments. In agreement with a rigid macrocyclic structure the Stokes radii of different protonated forms ranged only between 14.3 and 14.8 A. Best fitting procedures performed on experimental mobility measured at two different pH values (5.50 and 6.72) in the presence of increasing Zn(+2) concentration allowed confirming the model that assumes the binding of Zn(+2) to P(0) peptide form with a 1.5 x 10(3) M(-1) intrinsic association constant. Following to Zn(+2) binding, the pK(a) of the amino group of N-terminal Ile-1 is shifted from 7.6 to 5.9 and the Stokes radius is reduced of about 3 A. The mean charge of the bacitracin A(1)-Zn(+2) complex resulted +1.67 and +1.12 at pH 5.50 and 6.72, respectively. These results suggest that the amino group of N-terminal Ile-1 is not essential for Zn(+2) binding.     

New Nitrogenous Bisabolene‐Type Sesquiterpenes from a Hainan Sponge Axinyssa aff. variabilis

Two new uncommon nitrogenous sesquiterpenes, 11‐ethoxy‐3‐formamidotheonellin ( 1 ) and 7‐ethoxy‐3‐formamidobisabolane‐8,10‐diene ( 2 ), together with two known related sesquiterpenes, 3‐formamidotheonellin (=theonellin formamide; 3 ) and theonellin isothiocyanate ( 4 ), were isolated from the Hainan sponge Axinyssa aff. variabilis. Their structures were determined on the basis of extensive spectroscopic analysis and by comparison of their NMR data with those of known compounds.     

Reaction of thiete 1,1-dioxide with α-chlorobenzalphenylhydrazine and methyl phenylhydrazonochloroacetate

Thiete 1,1-dioxide reacts with 2 moles of α-chlorobenzalphenylhydrazine and methyl phenylhydrazonochloroacetate in the presence of triethylamine leading to the pyrazole derivatives 6 and 7 whose structure and mechanism of formation are discussed.