An electroactive nickel containing polymeric film obtained by electrochemical reduction of an aryl-nickel derivative

The electrochemical reduction of [Ni(PPh₃)₂(p-C₆H₄Br)Br] in acetonitrile results in a polymeric coating of a nickel-containing poly-p-phenylene, formulated as [-Ni(p-C₆H₄)_n-] (n=6?7) on the basis of elemental analysis, IR, UV, MS and ESCA measurements. This coating is found to undergo a two-electron reversible reduction and a one-electron reversible oxidation with a large potential window (3.6 V), without the polymeric film being destroyed. Moreover, the polymer obtained is shown to be electroactive towards dissolved reactants via permeation or mediated electron transfer, depending on the molecular size of the electroactive species employed.     

Meromorphic singular foliations on complex projective surfaces

Here we show that many numerical computations and bounds on the degrees of the algebraic leaves for singular meromorphic foliations on ² may be extended to large classes of foliations and complex projective surfaces.The author was partially supported by MURST and GNSAGA of CNR (Italy)     

Cathodic behaviour of nickel(II) in acetonitrile in the presence of carbon monoxide and substituted phosphines

Summary The reduction of nickel perchlorate in the presence of carbon monoxide and substituted phosphines or diphosphines has been studied in acetonitrile by cyclic voltammetry. The results show that only mono- and bis-carbonylphosphinenickel(O) complexes are formed, while no evidence for the formation of carbonyl-nickel(I) and -nickel(II) species was obtained. Although the oxidation processes are not reversible, a good correlation between the anodic peak potentials relative to nickel(O) complexes and the -donor--acceptor abilities of the phosphines employed was observed.     

Ion chromatographic separation of car☐ylic acids prediction of retention data

The retention behavior of biologically relevant monovalent (formic, acetic, propionic, lactic and pyruvic) and divalent (oxalic, malonic, succinic, fumaric, maleic and tartaric acids) car☐ylic acids together with inorganic analytes (chloride and sulphate) has been studied. The separation was performed on a latex-based strong anion-exchange resin using carbonate buffer systems in suppressed IC. The retention behaviour of analytes was investigated at different pH values and [HCO₃⁻]+[CO₃²⁻] concentrations. A theoretical model, involving ion-exchange equilibria of sample and eluent anions, was derived and applied to the chromatographic data obtained. Chromatographic ion exchange selectivity values were determined and retention data were calculated for the anions using different carbonate eluent conditions. The average of errors between the predicted and the measured retention volumes of the analytes studied does not exceed 4.0%. The study effectively characteristics the behaviour of different analytes under elution conditions of practical importance.     

In situ infrared study of SBA-15 functionalized with carboxylic groups incorporated by a co-condensation route

Two samples of SBA-15 mesoporous silica with a different content of carboxylic groups (-COOH) were prepared by a co-condensation route, using 4-(triethoxysilil)butyronitrile as the organosilane agent, then treating the samples with sulfuric acid, which removes the template and simultaneously hydrolyses the -CN to -COOH groups, as shown by IR spectroscopy. Both incorporation of organosilane agents and subsequent acid treatment do not affect the ordered SBA-15 structure. The proton-donor ability of carboxylic groups, as well their accessibility to reactants, has been studied in the IR by dosing ammonia, which forms reversibly COO- groups and NH4+ ions. The related equilibrium constants have been determined by elaboration of IR data. Outgassing the samples at progressively increasing temperatures destabilizes to an increasing extent the ammonium/carboxylate ion pair, because of the decrease in surface polarity brought about by dehydration: this decreases the related equilibrium constants. The amount of carboxylic groups undergoing reaction appears instead to be constant with dehydration, and to coincide with the whole population of COOH groups. Titration with alkali solutions yielded surface concentrations for the two samples of ca. 1.0 and 0.45 COOH/nm2. Proportionality between the surface concentrations and the intensities of the C=O IR band is observed: this suggests that COOH groups are noninteracting with each other and allows the computation of the related extinction molar coefficient.     

Microbial products. II. Granaticinic acid,a new antibiotic from a thermophilic streptomycete

Streptomyces sp. XT-11989 produces a mixture of two antibiotics with litmus-like indicator properties. One of them was shown to be identical with granaticin, the other was identified as [1S,3S,4S,7R,9R,10S,13R]-4,7,9,10-tetrahydro-5,12-dioxo-4, 6,10,11,13-pentahydroxy-1,9-dimethyl-(1H,3H)-7,10-ethanonaphtho[2,3-c: 6,7-c]dipyran-3-acetic acid and termed granaticinic acid. Microbial production and nuclear magnetic resonance data of these antibiotics are discussed and the antibacterial properties of the antibiotics are compared.

---

Mikrobielle produkte. II. Granaticinsäure, ein neues Antibiotikum von einem thermophilen Streptomyceten

Zusammenfassung Der Streptomycetenstamm XT-11989 produziert eine Mischung von zwei Antibiotika mit Lakmus-ähnlichen Indikatoreigenschaften. Eines dieser Antibiotika erwies sich als Granaticin, das andere wurde als [1S,3S,4S,7R,9R,10S,13R]-4,7,9,10-tetrahydro-5,12-dioxo-4,6,10,11,13-pentahydroxy-1,9-dimethyl-(1H,3H)-7,10-ethanonaphto[2,3-c: 6,7-c]dipyran-3-essigsäure identifiziert und Granaticinsäure benannt. Mikrobiologische Produktion und Kernresonanzdaten dieser antibiotika werden besprochen und ihre antibakteriellen Eigenschaften verglichen.

     

Design and self-assembly of ditopic and tetratopic cavitand complexes

The self-assembly of open ditopic and tetratopic cavitand complexes has been investigated by using monofunctionalized cavitand ligands and suitable metal precursors. In the case of ditopic complexes, self-assembly protocols, leading exclusively to the formation of both thermodynamically stable cis-Pt square-planar complexes 8 and 9 and the kinetically inert fac-Re octahedral complex 14, have been elaborated. The use of cis-[Pt(CH3)CN)2Cl2] as metal precursor led to the formation of monotopic trans-10 and ditopic trans-11 cavitand complexes, while cis-[Pt(dmso)2Cl2] afforded both cis-13 and trans-11 isomers. The self-assembly of tetratopic cavitand complexes has been achieved by using mononuclear [Pd(CH3CN)4(BF4)2] and dinuclear [M2(tppb)(OTf)4] (19: M = Pt; 20: M = Pd) metal precursors. Only the tetratopic dinuclear complexes 21 and 22 were stable. The ligand configuration with two phosphorus and two cavitand ligands at the metal centers is the most appropriate to build tetratopic cavitand complexes with sufficient kinetic stability.     

Blood lead monitoring in Italy: Assessment of the quality of results obtained between 1992 and 1994

Between 1992 and 1994, a new screening campaign for blood Pb monitoring in the Italian general population was carried out. Since the first campaign (started in 1978, in accomplishment of the European Community Directive 77/312/EEC) a working group of the Laboratory of Clinical Biochemistry at the Italian National Institute of Health (Istituto Superiore di Sanità), as the Reference Centre (RC), has coordinated the activity of various laboratories spread over the national territory. Appropriate quality assurance procedures, including an external quality assessment scheme (EQAS), were elaborated. Within the EQAS, three or four trials were carried out every year. Each laboratory participating in the trial analyzed eight control samples prepared from cow blood at different Pb concentrations. The results obtained by each peripheral laboratory and the RC between 1992 and 1994 have been compared by regression analysis. The same statistical method was adopted to compare the results obtained by each peripheral laboratory and the RC in the duplicate analysis of about 10 per cent of the human samples collected during the 1992–1994 monitoring campaign. There was no evidence of systematic differences between the regression lines obtained on control and human samples. In spite of the lower Pb concentration in the control samples analyzed during the 1992–1994 campaign, the analytical performance of the laboratories was better than that obtained in the previous screening campaign (1985–1986). Blood Pb levels observed in human samples collected between 1992 and 1994, confirm the downward time trend observed in the campaigns carried out in 1978–1979, 1980–1981 and 1985–1986. This study confirms that the results obtained in an EQAS are representative of the actual performance in the analysis of real (human) samples.     

Synthesis and molecular and extended structures for a diaminonaphthalene-derived bis(amido)stannylene

The cyclic bis(amido)tin(II) compound Sn[1,8-((iPrN)2C10H6] (2) was isolated from the reaction of Li2[1,8-((iPrN)2C10H6] (1) and SnCl2. Solid-state structural analysis of 2 showed it to be a mononuclear species with a pyramidal Sn center as part of a nonplanar metallaheterocycle. The packing diagram of 2 revealed an extended one-dimensional head-to-tail chain structure with short intermolecular Sn/arene-C interactions. Computational examination of 2 (DFT/PW91 and MP2 with 6-31G* and 6-311G** basis functions) indicated that the optimum gas-phase structure of 2,which displays a Sn center in the plane of the naphthyl backbone with a slightly twisted metallaheterocycle, is approximately 24 kcal/mol lower in energy than the X-ray structure. The solid-state geometry of 2 is attributed to the intermolecular donation of the naphthalene pi-electrons to a Lewis acidic Sn center, which leads to the observed supramolecular structure. The crystal structure of 1 is also reported.     

Erratum: Separability between valence and conduction bands in transition metal clusters

Density Functional Theory (DFT) and direct ab initio molecular dynamics (MD) calculations were applied to the hydrogen molecule trapped in a water cluster composed of 12 water molecules (H₂O)₁₂. The static DFT calculation showed that the H₂ molecule is trapped in the center of mass of (H₂O)₁₂. The vibrational frequency of the H–H stretching mode of the H₂ molecule trapped in the water cluster was blueshifted from that in vacuo. On the other hand, the vibrational frequency of H₂ in water‐hydrogen 1:1 complex (H₂O–H₂) was redshifted. A direct ab initio MD calculation of H₂(H₂O)₁₂ at 50 K indicated that the H₂ molecule is rotated freely around the center of mass of the water cluster. The origin of the spectral shift of H₂ in water ice is discussed on the basis of the theoretical results. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005