The first ruthenium-alkyne-dihydride reported is now recognized as an intermediate in the homogeneous hydrogenation of diphenylacetylene: Crystal structure of (μ-H)2Ru3(CO)9(μ3-η2-∥-C2Ph2)

The title complex (complex1) was the first alkyne-substituted triruthenium dihydrido cluster to be reported and was characterized by spectroscopy as a triangular cluster with the alkyne parallel to a Ru-Ru edge. Recently, we have found that1 is a key intermediate in the homogeneous hydrogenation of diphenylacetylene catalyzed by tetrahedral Ru₄ and FeRu₃ clusters. Since the discovery of1, a great number of complexes with alkynes parallel to a cluster edge have been reported; at present this is the more common bonding mode for alkynes on trinuclear clusters. The structural features of1 allow a comparison with those of other ruthenium-containing derivatives and help to draw suggestions of the role of1 in hydrogenation catalysis.     

Concise asymmetric synthesis of (−)-halosaline and (2R,9aR)-(+)-2-hydroxy-quinolizidine by ruthenium-catalyzed ring-rearrangement metathesis

A ruthenium-catalyzed ring opening-ring closing metathesis reaction serves as the key step in the stereoselective synthesis of a new enantiopure 2-substituted-4,5-dehydropiperidine skeleton, a valuable intermediate for the synthesis of piperidine alkaloids (such as (−)-halosaline) and of hydroxylated quinolizidines (such as (2R,9aR)-(+)-2-hydroxy-quinolizidine).     

Longitudinally detected electron spin resonance: Recent developments

Multiple-quantum spectroscopies are reviewed in the frame of electron paramagnetic resonance. Some properties of different nonlinear techniques are discussed for both transverse and longitudinal detection. The connections of effects recently presented with the procedure of longitudinal detection of electron paramagnetic resonance (LODESR) in presence of double transverse irradiation are stressed. Peculiarities of LODESR spectroscopy and its capabilities in facing problems related to relaxations in presence of very slow dynamic processes are evidentiated. Recent results show the vitality of the LODESR technique, that in the future could be applied to new fields, owing to experimental updating.     

Frequency stability of an optically pumped cesium beam frequency standard

Results obtained in an experimental optically pumped cesium beam frequency standard in which a single semiconductor laser is used for the state selection and the atom detection are reported. The separation between the two interaction regions is equal to 21 cm. This gives a 500 Hz linewidth which is observed with a signal to noise ratio equal to 10,000 in a 1 Hz noise bandwidth. A quartz crystal oscillator is frequency controlled by the atomic transition. The measured short term frequency stability is given by _y()=2×10^–12–1/2 for 1 s<500 s. Prospects for improvement of this frequency stability are discussed.     

Phenomenological and neural-network modeling of cephalosporin C production bioprocess

Cephalosporin C production process withCephalosporium acremonium ATCC 48272 in synthetic medium was investigated and the experimental results allowed the development of a mathematical model describing the process behavior. The model was able to explain fairly well the diauxic phenomenon, higher growth rate during the glucose-consumption phase, and the production occurring only in the sucrose-consumption phase. Moreover, the process was simulated utilizing the neural-networks technique. Two feed-forward neural-networks with one hidden layer were employed. Both models, phenomenological and neural-networks based, satisfactorily describe the bioprocess. The difficulties in determining kinetic parameters are avoided when neural networks are utilized.     

Cyclopentene-regioselective palladium-catalyzed cycloisomerization under neutral and bis-cationic reaction conditions

A series of 1,6-dienes is cyclized to cyclopentene derivatives under neutral conditions with palladium chloride in ethanol or with in situ generated LPd²⁺ in acetonitrile.     

Solid-state equilibrium relations in the Ternary Systems TeO2?MoO3?MoO2 and TeO2?MoO3?Te

In a study of the solid-state reactions in the ternary systems TeO₂? MoO₃? MoO₂ and TeO₂? MoO₃? Te, approximately 70 selected compositions were sintered at 550°C to attain equilibrium conditions, and solid-state equilibrium relations were characterized by x-ray diffraction. In a large composition range, the interaction of TeO₂ and MoO₃ with the reducing agents MoO₂ or Te leads to the reduced ternary oxide TeMo₄O₁₃ (m. p. 748°C), in addition to Te₂MoO₇, Te and (intermediate) molybdenum oxides. The compatibility relations for the binary systems TeO₂? MoO₂ and MoO₃? Te are presented for the first time. In the TeO₂? MoO₂ system, three-phase regions are found: (Te₂MoO₇? TeO₂? Te) on the TeO₂? and (TeMo₄O₁₃? MoO₂? Te) on the MoO₂-rich sides with (TeMo₄O₁₃? Te₂MoO₇? Te) in the intermediate region. In the MoO₃? Te system, three-phase regions (TeMo₄O₁₃? MoO₂? Te), (TeMo₄O₁₃? Mo₄O₁₁? MoO₂) and (TeMo₄O₁₃? MoO₃? Mo₄O₁₁) were detected. TeMo₄O₁₃ presents two allotropic forms (α′ for T < 450°C, α for T > 450°C). Both structures have been characterized by I.R. and optical reflectance spectroscopy. Unit cell dimensions are also given.     

Application of ZrC-coated tubes to the determination of aluminum in serum by graphite furnace atomic absorption spectroscopy

An improved method for the determination of aluminum in serum by atomic absorption spectrometry with a graphite furnace is presented. The method is suitable for the analysis of serum samples having normal and elevated aluminum content. The serum sample can be analyzed diluted or undiluted because the selected temperatures program minimizes the matrix interferences. High temperatures are made possible by the use of graphite Zr-coated tubes. The detection limit is 0.7 μg Al/liter. The coefficient of variation is 3.2% for serum concentration of 5 μg Al/liter and 1% for serum concentration of 50 μg Al/liter.