Metal-Salen Schiff base complexes in catalysis: practical aspects

Schiff base ligands are considered "privileged ligands" because they are easily prepared by the condensation between aldehydes and imines. Stereogenic centres or other elements of chirality (planes, axes) can be introduced in the synthetic design. Schiff base ligands are able to coordinate many different metals, and to stabilize them in various oxidation states, enabling the use of Schiff base metal complexes for a large variety of useful catalytic transformations. Practical guidelines for the preparation and use of different Schiff base metal complexes in the field of catalytic transformations are discussed in this tutorial review.     

Differential pulse polarographic determination of inorganic and organic arsenic in natural waters

Summary As(III), As(V) and organic arsenic in water are determined by differential pulse polarography. As (III) is directly determined in 2M HCl as supporting electrolyte. Total inorganic arsenic [As (III) + As(V)] is measured after reduction of electro-inactive As(V) with sodium sulphite. Total arsenic is determined after oxidative treatment of the water residue with potassium permanganate and magnesium nitrate, and reduction of arsenic with sodium sulphite. Organic arsenic is evaluated by difference. The efficiency of the whole procedure is 78–80% and its detection limit is 1g/l. The relative standard deviation is better than ±1.5% at 50g/l. Interferences due to heavy metals are overcome by removing them by anionexchange or pre-electrolysis with a mercury cathode.

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Differential-puls-polarograpbische Bestimmung von anorganischem und organischem Arsen in natürlichen Wässern

Zusammenfassung As (III), As(V) und organisches Arsen in Wässern wurden differentialpuls-polarographisch bestimmt. As (III) wurde direkt in 2 M HCl als Trägerelektrolyt bestimmt. Das anorganische Gesamtarsen [As(III) und As(V)] wurde nach Reduktion des elektro-inaktiven As(V) mit Natriumsulfit gemessen. Nach der oxydativen Behandlung des Wasserrückstandes mit KMnO₄ und Magnesiumnitrat und nach Reduktion des Arsens mit Natriumsulfit wurde das Gesamtarsen bestimmt, und das organisch gebundene Arsen durch Differenzbildung ermittelt. Die Ausbeute des gesamten Verfahrens beträgt 78–80%, seine Erfassungsgrenze 1g/l Die relative Standardabweichung ist besser als ±1,5% bei 50g/l. Störungen durch Schwermetalle werden entweder durch deren Entfernung mittels Anionen-austauscher oder durch vorhergehende Elektrolyse mit einer Quecksilberelektrode beseitigt.

     

Two-dimensional molecular profiling of mantle cell lymphoma

The present research establishes standard two-dimensional (2-D) maps for control, reactive lymph node and non-Hodgkin's lymphoma (mantle cell lymphoma, MCL). Medium sensitivity, mass spectrometry compatible colloidal Coomassie has revealed a total of ca. 750 spots in each of the maps. Comparison of 2-D maps by statistical packages, such as the PDQuest, established up- and downregulation of a total of ca. 145 spots, with positive variations of up to 10-folds and negative variations of up to 13-folds in both MCL biopsies' protein extracts. Qualitative and quantitative variations in the two lymphoma samples are consistent. More than 20 proteins have been so far identified by matrix assisted laser desorption/ionisation-time of flight (MALDI-TOF)-mass spectrometry, with an additional five spots, which gave very good spectra but could not be matched to any of the presently available databases. Some of the spots, such as the 78 kDa glucose-regulated protein precursor and the glutathione S-transferase P, appear to be in common with other tumors, such as lung adenocarcinoma. Others may simply reflect overall changes in cellular metabolism and growth rate that occur during malignancy and thus might turn out to be in common with any cell population receiving any kind of stress. Some (notably T-cell leukemia/lymphoma protein 1A, TCL1, found to be 10-fold overexpressed) appear to be specific of the non-Hodgkin's lymphoma here studied. Western blot and immunohistochemical analyses were applied to obtain further information about stathmin (Op18) and TCL1, respectively.     

Me2Zn-mediated addition of acetylenes to aldehydes and ketones

[reaction: see text] Contrary to expectations, commercially available 2 M Me2Zn in toluene is able to promote the addition of phenylacetylene to aldehydes and ketones. This reactivity is determined by a new, unprecedented mechanism, which involves activation of the zinc reagent via coordination with carbonyl substrates that behave "ligand like". Broad scope, high tolerance to functional groups, and a simple procedure make this new method highly interesting for the synthetic chemist.     

Capillary electrophoresis of DNA for molecular diagnostics

A number of applications of capillary zone electrophoresis (CZE) in sieving liquid polymers (notably linear polyacrylamides and cellulose) for the analysis of polymerase chain reaction (PCR) products of clinically relevant, diagnostic DNA, are reviewed. The fields covered are: human genetics, quantitative gene dosage, microbiology and virology, forensic medicine and therapeutic DNA (notably, antisense nucleotides). Some unique, novel developments are highlighted, such as: (i) nonisocratic CZE, i.e., temperature-programmed CZE for detection of DNA point mutations; (ii) the synthesis of novel N-substituted acrylamides, offering extreme resistance to alkaline hydrolysis coupled to high hydrophilicity. In the field of denaturing gradient gel electrophoresis (DGGE), as routinely performed in gel slabs, a novel methodology is described in CZE: double-gradient DGGE. In this technique, two gradients are simultaneously applied along the migration direction: a chemical (or thermal) denaturing gradient, for partially unwinding homo- and hetero-duplexes of DNA, and a porosity gradient, for recompacting diffuse bands melting over a broader range of denaturing conditions. It is thus demonstrated that chemical gradients, in addition to temperature gradients, can be easily implemented even in a capillary format.     

Oxygen electrodes in fused salts: Investigation and mechanistic remarks on the system (Ni)O2, H2O/OH− in the (Na,K)NO3 eutectic melt

A potentiometric investigation on the system (Ni)O₂, H₂O/OH^? was carried out within the temperature range 513?T?636 K in the (Na, K)NO₃ equimolar mixture containing OH^? ions in the concentration range 5×10^?6<[OH^?]<10^?1m and flushed with a mixture of O₂ and H₂O at variable partial pressures. The system has been found to behave reversibly in all hydroxide concentration and temperature intervals studied with respect to all the species involved in the over-all electrode reaction ½ O₂+H₂O+2e^?=2OH^? so that the following nernstian relationship could be written E=E_O2,H₂O/OH^?+RT/Fln{[O₂]^1/4[H₂O]^1/2/[OH^?]} This potentiometric behaviour was tentatively interpreted on the basis of mechanistic models involving, in some steps, solid nickel oxides formed on the electrode surface by contact with the melt. The actual formation and existence of these compounds on the electrode surface under the given experimental conditions was proved by a proper XPS investigation.     

Synthesis of [SCo3(CO)7(S2COMe)] and the structure of its PPh3 derivative

Summary The title compound has been prepared in reasonable yield by reaction of a methanolic solution of CoCl₂ and MeOCS₂K with CO. I.r. spectra have been analyzed both in the C-O stretching region and in the region of the main vibrations of the xanthate ligand: an explanation of the appearance of only 4 out of 7 i.r.-active (CO) modes is proposed. The structure of the triphenylphosphine derivative has been solved by x-ray diffraction analysis: [SCo₃(CO)₆(PPh₃)(S₂COMe)] crystallizes in the triclinic space group P¯1, witha = 10.710(3),b = 10.199(3) andc = 16.208(4) Å, = 113.57(2)°, = 98.14(2)°, = 104.32(2)°, Z = 2, (MoK) = 0.7107 Å. The final R value is 0.045 [4461 reflections with F > 6 (F)]. The molecule is formed by an SCo₃ cluster, in which each Co atom coordinates two CO groups. The chelating xanthate ligand is equatorially bonded to two cobalt atoms forming a nonplanar pentaatomic ring; the phosphine is equatorially bonded to the other cobalt atom.     

Analytical characterization of poly(pyrrole-3-carboxylic acid) films electrosynthesised on Pt, Ti and Ti/Al/V substrates

With the aim of developing a polymeric multilayer film for application in advanced biomaterials, as a first step poly(pyrrole-3-carboxylic acid) films (abbreviated as PPy-3-carbox) were electropolymerised from pyrrole-3-carboxylic acid solutions by cyclic voltammetry and chronoamperometry on platinum, titanium and Ti90Al6V4 substrates and characterised both electrochemically (cyclic voltammetry) and spectroscopically (X-Ray Photoelectron Spectroscopy, XPS). Electrochemical experiments showed that the potential range adopted for electropolymerization affects the polymer electroactivity, by analogy with unsubstituted polypyrrole. The combination of conventional and chemical derivation-XPS provided information on PPy-3-carbox surface structure, showing no significant difference between films grown on different substrates and an increase of the COOH groups amount (one group over three pyrrole rings, as an average) with respect to unsubstituted polypyrrole (PPy), as expected. Finally, a preliminary Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) investigation was performed in order to get further information on the polymer structure and electroactivity.     

Potential binding of borate ions to mono- and oligonucleotides: a capillary electrophoresis investigation

The potential binding of borate to oligonucleotides and DNA fragments is here investigated. In case of free nucleotides, such as AMP, there appears to be a weak binding, although no free versus complexed species could ever be separated under any experimental condition. The binding was suggested by the strong peak asymmetry and by the fact that, at progressively lower borate molarities in the background electrolyte, the peak shape suddenly switched from fronting to tailing. This indicated, as also confirmed by theoretical simulations, that the AMP-borate complex was the slow, not the fast moving species. On the contrary, in the case of free adenosine, strong binding ensued, since in Tris-acetate buffer this compound was only eluted with the electroendoosmotic flux, being neutral, whereas in Tris-borate it had a much higher mobility, comparable to, although lower than, that of AMP. When running oligonucleotides, at standard borate molarities (ca. 45 mM), and under strict iso-ionic strength conditions, no binding to borate could be demonstrated, since the free mobility of a 24-mer DNA was identical in TA and TB buffers. However, at very high borate molarities (200 mM) and high pH values (pH 8.92), some binding to oligonucleotides could occur, since in these latter conditions the mobility of a 24-mer was seen to be ca. 20% lower than at pH 7.69, a pH value that should discourage any complex formation.