Ordered self-assembled monolayers of Peptide nucleic acids with DNA recognition capability

We report on the formation of ordered self-assembled monolayers (SAMs) of single-stranded peptide nucleic acids (ssPNA). In spite of their remarkable length (7 nm) thiolated PNAs assemble standing up on gold surfaces similarly to the SAMs of short alkanethiols. SAMs of ssPNA recognize complementary nucleic acids, acting as specific biosensors that discriminate even a point mutation in target ssDNA. These results are obtained by surface characterization techniques that avoid labeling of the target molecule: x-ray photoemission, x-ray absorption and atomic force microscopy.     

Oxorhenium complexes as aldehyde-olefination catalysts

Several oxorhenium compounds in the formal oxidation states V and VII are examined as catalysts for the aldehyde-olefination starting from diazo compounds, phosphines, and aldehydes. Of these, [ReMeO2(eta2-alkyne)] complexes provide the simplest catalysts to study, although [ReOCl3(PPh3)2] still remains the most efficient rhenium catalyst for aldehyde-olefination described to date. Prior to the reaction with the Re catalysts the phosphine and the diazo compound react to form a phosphazine. No catalytic reaction occurs in cases where no phosphazine formation is observed. The first step of the catalytic cycle involves the formation of a carbene intermediate by the reaction of phosphazine and catalyst under extrusion of phosphine oxide and dinitrogen. In a second step the carbene reacts with aldehyde under olefin formation and catalyst regeneration. Excess of alkyne as well as the presence of ketones slows down the catalytic reaction. The olefination of 4-nitrobenzaldehyde with diazomalonate is possible with these Re catalysts. In contrast, this reaction does not take place either in the classical Wittig fashion from Ph3P=C(CO2Et)2 and aldehyde or by use of all other catalysts for aldehyde olefination reactions reported to date. Catalytic ylide formation from diazo compounds seems therefore not to be the only pathway through which catalytic aldehyde-olefination reactions can proceed.     

Thermogravimetric investigations in dynamical regime on some tetramolybdates or organic bases

A systematic study about the thermal decomposition kinetics in function ofthe substituted bases in (BH)₂Mo₄O₁₃ type compounds shows a decomposition pattern with three or two steps which are controlled by a random nucleation mechanism.The thermal stability as well as the activation energy is studied as a function of the nature of the base, its symmetry and its pK_a.     

The determination of stable scandium in plants,animals, sediments,sands, soils,rocks and minerals by neutron-activation analysis

A method is described for the determination of stable scandium in samples of plants, animals, sediments, soils, rocks and minerals. The samples and comparator standards were irradiated in a neutron flux of 5·10¹² n/cm²/sec for 4 h and dissolved and the scandium quantitatively precipitated from 2N nitric acid as scandium phytate; contaminants were rinsed from the precipitate with nitric and hydrochloric acids. The limit of detection was 0.005μg(±10% at the 95% confidence level). The activated ⁴⁶Sc was counted by γ-spectrometry.     

Nickel(0)-induzierte CC-verknüpfung zwischen kohlendioxid und alkinen sowie alkenen

CO₂ and alkynes or alkenes undergo a 1/1 coupling in the presence of (Lig)Ni⁰ complexes to give five-membered cyclic nickela complexes of types V and XVII. The influence of temperature and of the ligands upon the regioselectivity of the CC coupling in the case of monosubstituted olefins is reported, and the significance of these ring systems in preparative chemistry is emphasized. Oxanickelacyclopentenones (V) react with alkynes to form oxanickelacycloheptadienones (XIII). The structure of one of the compounds of this class has been determined by X-ray crystallography. Special features of these novel compounds, which can be readily prepared from CO₂, are discussed together with the probable reaction mechanisms.     

Radical copolymerization of acrylic monomers—III stereochemical configuration of methyl methacrylate-phenyl acrylate copolymers

The kinetics of the copolymerization of methyl methacrylate with phenyl acrylate in solution at low conversions have been examined. The ¹[H]NMR spectra of copolymers show some special features which are explained by taking into account the composition and the stereochemical configuration of copolymer sequences in terms of methyl methacrylate centered triads.     

Thermal decomposition of molybdenum(IV) dialkyldithiocarbamates: application of a new method to kinetic studies

Summary We describe the application of a new method (differential scanning calorimetry, d.s.c.) to the kinetic analysis of the thermal decomposition under dinitrogen of several adducts with pyridine of Mo^IV dialkyldithiocarbamates. The adducts are of the form [Mo₂(dtc)₄(py)₂] (dtc=Et₂,n-Pr₂,i-Pr₂,t-Bu₂, orN-methyl-cyclo-hexyldithiocarbamate and py). From d.s.c. curves, the activation energies for the loss of two pyridine molecules were calculated, and the mechanism was determined. A relationship between activation energies and the steric requirements of the ligands was also determined.