Facile hydrometalation of alkynes by nido-1,2-(CpRuH)(2)B(3)H(7) yielding novel Ru-B edge-bridging alkylidenes. Stepwise conversion of HCtbd1;CC(O)OMe into nido-1,2-(CpRuH)(2)-3-HOB-4-MeC-5-MeOC-BH(3), Cp = eta(5)-C(5)Me(5)

The reaction of the alkyne HCCC(O)OMe with 7 sep 1,2-(Cp*RuH)2B3H7 leads to hydroboration plus hydroruthenation to produce nido-1,3-mu-Me{C(O)OMe}C-1,2-(Cp*Ru)2B3H7, a compound with an exocluster ruthenium-boron mu-alkylidene that exists in two isomeric forms. Both isomers undergo rearrangement with intramolecular chelation of the carbonyl oxygen at a boron site, thereby opening the cluster and generating arachno-2,3,-mu(C)-5-eta1(O)-Me{C(O)OMe}C-1,2-(Cp*Ru)2B3H7. Further heating leads to deoxygenation of the carbonyl fragment by a boron center concurrent with insertion of the carbon atom into the metallaborane cage to give nido-1,2-(Cp*RuH)2-3-HOB-4-MeC-5-MeOC-BH3.     

不对称Fe-Fe双金属化合物[Cp*Fe(dppe)(C≡CFc))[PF6]n(n=0，1)的合成、结构及光谱性质的研究(英)

A biased bimetallic Fe-Fe complex Cp^*Fe(dppe)(C≡CFc) (1) was synthesized from FcC≡CH (Fc=C₅H₄FeC₅H₅) and Cp^*Fe(dppe)Cl (Cp^*=C₅Me₅). Its one-electron oxidation species [Cp^*Fe(dppe)(C≡CFc)][PF₆] (1a) was also prepared and the spectroscopic properties of 1a was studied. The single-crystal X-ray diffraction analysis of 1 shows that ferrocenylacetylene is bonded at the terminal carbon to the iron center in the Cp^*Fe(dppe) part. Crystallographic data for 1: monoclinic, space group C2/c, with a=4.067 65(14) nm, b=1.260 74(4) nm, c=1.649 89(5) nm, β=104.387(10)°, V=8.195 7(5) nm³, Z=8, D_c=1.354 g·cm^-3, F(000)=3512, μ=0.822 mm^-1. The structure was refined to R₁=0.038 4, wR₂=0.100 0. CCDC: 234893.     

Prediction of the behaviour of organic pollutants using cloud point extraction

A preconcentration study based on the cloud point phenomenon was carried out for a set of triazine herbicides, three of them chloro-substituted and three of them methylthio-substituted. Concentration factors and recoveries were calculated as function of the percentage of the non-ionic surfactant Triton X-114 employed. From these values, obtained from a cloud point extraction (CPE) procedure, the distribution coefficient between the Triton X-114 micelles and water, Kc, prior to CPE was calculated for each triazine and related to the corresponding octanol-water partition coefficient, Kow. In order to confirm the results obtained with the triazine herbicides, two sets of data from chemically different organic pollutants--organophosporous and chlorophenols--obtained from the literature were assessed, concluding that they display a similar behaviour to that of the triazine herbicides. This can be used to predict the CPE behaviour of other organic pollutants from their octanol-water partition coefficients. The Kc values were compared with the analyte concentration ratio in the surfactant-rich phase and aqueous phase (Ksa) with a view to obtaining a link between the analyte behaviour prior to and after cloud point extraction procedures.     

Comparative study of separation and determination of triazines by micellar electrokinetic capillary chromatography and nonaqueous capillary electrophoresis: application to residue analysis in natural waters

The separation and determination of a mixture of chloro- and methylthiotriazines in water samples by both micellar electrokinetic capillary chromatography (MEKC) and nonaqueous capillary zone electrophoresis (NA-CZE) were compared. The characteristics of both methods proved to be very similar in terms of separation efficiency and analysis times, but application of these methods for the analysis of triazines in natural waters, with a prior preconcentration step, revealed significant differences. A preconcentration step by solid-phase extraction (SPE) with Oasis HLB cartridges was accomplished for the determination of triazines at sub-ppb levels in drinking and river waters; when NA-CZE was used after this SPE step, electropherograms with fewer interferences and more stable baselines were obtained than when separation was carried out using MEKC. Another aspect related to the application to real samples was the lack of precision encountered upon evaluating the electrophoretic signals generated when using SPE coupled with NA-CZE. Here, we demonstrate the importance of choosing an appropriate internal standard for analyte quantification. It is recommended that a triazine belonging to the same family as that of the triazine to be determined should be used as internal standard.     

Analytical characterization of diterpenoid resins present in pictorial varnishes using pyrolysis-gas chromatography-mass spectrometry with on line trimethylsilylation

A procedure based on the technique of the pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) has been applied, in this work, in order to determine the composition of diterpenoid resin employed in art works. The method is based on the on line derivatization of these resins using hexamethyldisilazane (HMDS). Results obtained were compared with those previously reported in literature from Venice turpentine, Strasbourg turpentine, colophony, sandarac and Manila copal using this same method and with those others from in situ thermally assisted hydrolysis and methylation with tetramethylammonium hydroxide (TMAH). Canada balsam, copper resinate and Copaiba balsam have been also analyzed extending the scope of this method in the field of the analysis of artwork materials. Several non-reported trimethylsilylated derivatives of compounds present in the diterpenoid resins have been identified. An improvement in sensitivity has been obtained by using HMDS as derivatizing reagent, together with a better resolution of the most representative peaks. Additionally, this method reduces the number of pyrolytic fragmentation, recombination, dehydration and isomerization products formed during the pyrolysis process and, in consequence, more simplified chromatograms are obtained. Finally, the reported procedure has been successfully used for characterizing two diterpenoid resin-based varnishes present in the canvas painting "The Betrothal of the Virgin" (Anonymous, 17th century) which is included in the pictorial collection of Saint Joseph Church in Taormina (Italy) and the Magdalena Tryptich (Master of Alzira, 16th century, Valencia, Spain).     

Holo- and hemidirected lead(II) in the polymeric [Pb(4)(mu-3,4-TDTA)2(H2O)2]*4H2O complex. N,N,N',N'-tetraacetate ligands derived from o-phenylenediamines as sequestering agents for lead(II)

The coordinating ability of the ligands 3,4-toluenediamine-N,N,N',N'-tetraacetate (3,4-TDTA), o-phenylenediamine-N,N,N',N'-tetraacetate (o-PhDTA), and 4-chloro-1,2-phenylenediamine-N,N,N',N'-tetraacetate (4-Cl-o-PhDTA) (H4L acids) toward lead(II) is studied by potentiometry (25 degrees C, I = 0.5 mol x dm(-3) in NaClO4), UV-vis spectrophotometry, and 207Pb NMR spectrometry. The stability constants of the complex species formed were determined. X-ray diffraction structural analysis of the complex [Pb4(mu-3,4-TDTA)4(H2O)2]*4H2O (1) revealed that 1 has a 2-D structure. The layers are built up by the polymerization of centrosymmetric [Pb4L2(H2O)2] tetranuclear units. The neutral layers have the aromatic rings of the ligands pointing to the periphery, whereas the metallic ions are located in the central part of the layers. In compound 1, two types of six-coordinate lead(II) environments are produced. The Pb(1) is coordinated to two nitrogen atoms and four carboxylate oxygens from the ligand, whereas Pb(2) has an O6 trigonally distorted octahedral surrounding. The lead(II) ion is surrounded by five carboxylate oxygens and a water molecule. The carboxylate oxygens belong to four different ligands that are also joined to four other Pb(1) ions. The selective uptake of lead(II) was analyzed by means of chemical speciation diagrams as well as the so-called conditional or effective formation constants K(Pb)eff. The results indicate that, in competition with other ligands that are strong complexing agents for lead(II), our ligands are better sequestering agents in acidic media.     

ViscosityB-coefficients for lithium perchlorate in ethylene glycol-water mixtures

Viscosities and densities of lithium perchlorate solutions in different ethylene glycol-water compositions have been measured at 25.0 and 35.0 °C. From these data, the correspondingB-coefficients of theJones-Dole equation have been determined. TheB-value depends on the solvent composition and it reaches a maximum in the water-rich region. This behaviour is analysed in terms of ionic solvation and solvent structure.

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Viskositäts-B-Koeffizienten für Lösungen von Lithiumperchlorat in Ethylenglykol-Wasser-Mischungen

Zusammenfassung Es wurden die Dichten und Viskositäten für Lösungen von Lithiumperchlorat in verschieden zusammengesetzten Ethylenglykol-Wasser-Mischungen bei 25 °C und 35 °C gemessen. Auf Grund der erhaltenen Daten wurden dieB-Koeffizienten in den entsprechendenJones-Dole-Gleichungen für die relative Viskosität bestimmt. DieB-Werte hängen von der Zusammensetzung des Lösungsmittels ab und erreichen im wasserreichen Konzentrationsgebiet ein Maximum. Dieses Verhalten wird in Hinblick auf die Ionensolvatation und die Struktur des Lösungsmittels analysiert.

     

Crystal engineering: Supramolecular structures by cocrystallization ofMeso-1,2-diphenyl-1,2-ethanediol and bisimines,simple cases of molecular recognition

The crystal structures of molecular complexes betweenmeso- 1,2-diphenyl-1,2-ethanediol and two bisimines (N,N-(dibenzylidene)-ethylenediamine and glyoxylidene-bis(2,4-dimethyl-3-pentyl-amine) are reported at different temperatures. The structure-determining motif of the cocrystalline arrangement is one single O-H . N hydrogen bond resulting in infinite ladderlike polymers. The supramolecular structure is formed by recognition of fitting species: Thed- orl-isomers do not arrange in such structures.¹H NMR experiments show that no prearrangements take place by forming complexes in solution.     

Rose Bengal‐Sensitized Photooxidation of the Dipeptides l‐Tryptophyl‐l‐Phenylalanine,l‐Tryptophyl‐l‐Tyrosine and l‐Tryptophyl‐l‐Tryptophan: Kinetics,Mechanism and Photoproducts¶

The Rose Bengal‐sensitized photooxidations of the dipeptides l ‐tryptophyl‐l ‐phenylalanine (Trp‐Phe), l ‐tryptophyl‐l ‐tyrosine (Trp‐Tyr) and l ‐tryptophyl‐l ‐tryptophan (Trp‐Trp) have been studied in pH 7 water solution using static photolysis and time‐resolved methods. Kinetic results indicate that the tryptophan (Trp) moiety interacts with singlet molecular oxygen (O₂(¹Δ_g)) both through chemical reaction and through physical quenching, and that the photooxidations can be compared with those of equimolecular mixtures of the corresponding free amino acids, with minimum, if any, influence of the peptide bond on the chemical reaction. This is not a common behavior in other di‐ and polypeptides of photooxidizable amino acids. The ratio between chemical (k_r) and overall (k_t) rate constants for the interaction O₂(¹Δ_g)‐dipeptide indicates that Trp‐Phe and Trp‐Trp are good candidates to suffer photodynamic action, with k_rlk_t values of 0.72 and 0.60, respectively (0.65 for free Trp). In the case of Trp‐Tyr, a lower k_rlk_t value (0.18) has been found, likely as a result of the high component of physical deactivation of O₂(¹Δ_g) by the tyrosine moiety. The analysis of the photooxidation products shows that the main target for O₂(¹Δ_g) attack is the Trp group and suggests a much lower accumulation of kynurenine‐type products, as compared with free Trp. This is possibly because of the occurrence of another accepted alternative pathway of oxidation that gives rise to 3a‐oxidized hydrogenated pyrrolo[2,3‐b]indoles.