Retro-Brook rearrangement induces the formation of an octahedral nickel(benzamidinate) complex; synthesis, structure and catalytic activity

The neutral octahedral nickel complex (PhC(NSiMe₃)NC(Ph)CHSiMe₃)Ni(acac)(TMEDA) (7), has been synthesized and characterized including X-ray diffraction analysis. The complex was formed by the reaction of Ni(acac)₂(TMEDA) with the lithium salt of the corresponding β-diketiminate ligand. The formation of the benzamidinate motif from the corresponding β-diketiminate is a consequence of a retro-Brook isomerization that is operative only at the nickel centre. A plausible mechanism for the metal mediated isomerization is proposed. When complex 7 was activated with MAO it showed a good catalytic activity for the addition polymerization of norbornene. Furthermore, this catalytic system has been found to oligomerize ethylene to a mixture of butenes and hexenes with a high turnover frequency, η = 29,300 h⁻¹, when the reaction is performed in dichloromethane.     

Approximations of Set-Valued Functions by Metric Linear Operators

In this paper we introduce new approximation operators for univariate set-valued functions with general compact images in Rⁿ. We adapt linear approximation methods for real-valued functions by replacing linear combinations of numbers with new metric linear combinations of finite sequences of compact sets, thus obtaining "metric analogues" of these operators for set-valued functions. The new metric linear combination extends the binary metric average of Artstein to several sets and admits any real coefficients. Approximation estimates for the metric analogue operators are derived. As examples we study metric Bernstein operators, metric Schoenberg operators, and metric polynomial interpolants.     

Group 4 octahedral benzamidinate complexes: syntheses,structures, and catalytic activities in the polymerization of propylene modulated by pressure

The synthesis and structural X-ray diffraction studies for some benzamidinate ligations and several group 4 benzamidinate complexes are presented. The use of the cis-octahedral C(2)-symmetry compounds was studied to shed light on the conceptual applicability of these complexes as potential catalysts for the stereoregular polymerization of propylene. We demonstrate that the stereoregular polymerization of propylene catalyzed by early-transition metal octahedral benzamidinate complexes, activated with either MAO or B(C(6)F(5))(3) as cocatalysts, can be modulated by pressure (from atactic to isotactic through elastomers). The different effects in the polymerization process such as the nature of solvent or cocatalyst, temperature, pressure, molar ratio catalyst:cocatalyst, and the relationship between the symmetry of the complex and the polymer microstructure have been investigated. When the complex [4-CH(3)-C(6)H(4)C(NTMS)(2)](2)ZrMe(2) (9) was activated with MAO, it was found to be a good catalyst for the polymerization of propylene, at atmospheric pressure, producing an oily polymer resembling an atactic polypropylene. Being activated with B(C(6)F(5))(3), complex 9 produces a highly isotactic (mmmm = 98%) product. Likewise, when the polymerization of propylene was performed with complex 9 and MAO at high pressure (liquid propylene), a highly stereoregular polymer was also obtained. Larger activities and stereoregularities were achieved by performing the reaction in CH(2)Cl(2) as compared to toluene. Contrary to complex 9, at atmospheric pressure the complex [4-CH(3)-C(6)H(4)C(NTMS)(2)](2)TiMe(2) (10) is not active either in CH(2)Cl(2) or in toluene. At high pressure, complex 10 produces elastomeric polypropylene. Activities of the isolobal complexes [C(6)H(4)C(NTMS)(2)](2)ZrMe(2) (11) and [C(6)H(4)C(NTMS)(2)](2)TiMe(2) (12) were found to be larger than those of complexes 9 and 10, respectively. Contrary to the structures of the elastomeric polypropylenes described in the literature, the obtained elastomers are characterized by frequent alternation of the isotactic domains with stereodefects. The stereoregular errors are formed by the intramolecular epimerization of the growing chain at the last inserted unit. The epimerization reaction was corroborated through the isomerization of alkenes.     

Electrodeposition and stripping voltammetry of arsenic(III) and arsenic(V) on a carbon black–polyethylene composite electrode in the presence of iron ions

In this work, a new sensor is proposed for the stripping voltammetric determination (anodic stripping voltammetry—ASV) of total arsenic(V) or arsenic(III). The sensor is based on an Fe-modified carbon composite electrode containing 30 % carbon black–high-pressure polyethylene (CB/PE). The modification with iron is achieved by the addition of Fe(III) or Fe(II) ions to the sample solution and co-electrodeposition of iron and arsenic on the CB/PE electrode. In anodic stripping voltammetry, two peaks are observed: an Fe peak at ?0.45 or ?0.29 V and a peak at 0.12?±?0.07 V which depends on the arsenic concentration and corresponds to the As(0) → As(III) oxidation, as is the case with other solid electrodes. The optimum conditions proposed for ASV determination of As(V) and As(III) in solutions in the presence of dissolved oxygen are the following: the background electrolyte is 0.005 M HCl containing 0.5–1 mg/?L Fe(III) for As(V) and containing 1.0–1.5 mg/?L Fe(III) for As(III), respectively; E _dep?=??2.3 V; rest period at ?0.10 V for 3–5 s before the potential sweep from ?0.2 to +0.4 V; scan rate is 120 mV/?s. The detection limit (LOD, t?=?120 s) for As(III) and As(V) is 0.16 and 0.8 μg/?L, respectively. Various hypotheses on the effect of Fe ions and atoms on the electrodeposition and dissolution of arsenic are considered. The new method of determination of As(III) and As(V) differs from known analogues by its simplicity, low cost, and easy accessibility of the electrode material. It allows the voltammetric determination of total arsenic after chemical reduction of all its forms to As(III) or after their oxidation to As(V).     

Moduli of smoothness of vector valued functions of a real variable and applications

Moduli of smoothness of Banach space valued functions of a real argument are defined and studied. The classical Whitney's theorem on the error of polynomial approximation [7] is extended to this case. Estimates for quadrature formulae and numerical treatment of abstract differential equations are presented.

Applications to the numerical analysis of set-valued maps, differential inclusions and interval functions are made.     

Effects of metal and the phytyl chain on chlorophyll derivatives: physicochemical evaluation for photodynamic inactivation of microorganisms

Chlorophyll compounds and their derivatives containing metal or phytyl chain can be used as photosensitizer in photodynamic inactivation of microorganisms (PDI). So, the physicochemical properties and antimicrobial effect of chlorophyll derivatives were investigated: Mg‐chlorophyll (Mg‐Chl), Zn‐chlorophyll (Zn‐Chl), Zn‐chlorophyllide (Zn‐Chlde), Cu‐chlorophyll (Cu‐Chl), pheophytin (Pheo) and pheophorbide (Pheid). The photobleaching experiments showed photostability according to Cu‐Chl > Pheo ∼ Pheid ≫ Zn‐Chl ∼ Zn‐Chlde > Mg‐Chl. This order was discussed in terms of metal and the phytyl chain presences. Pheid and Zn‐Chl in aqueous Tween 80 solution exhibited highest singlet oxygen yield compared with the other derivatives. Chlorophyll derivatives (CD) with phytyl chain was limited by the self‐aggregation phenomenon at high concentrations, even in micellar systems (Tween 80 and P‐123). The antimicrobial effect of CD derivatives was investigated against Staphylococcus aureus, Escherichia coli, Candida albicans and Artemia salina. Pheid showed the best results against all organisms tested, Zn‐Chlde was an excellent bactericide in the dark and Cu‐Chl had no PDI effect. No correlation with CD uptake by microorganisms and darkness cytotoxicity was found. The physicochemical properties allied to bioassays results indicate that Mg‐Chl, Pheo, Zn‐Chl and Pheid are good candidates for PDI.     

Effects of natural environmental factors on delta13C of lichens

This preliminary study was designed to determine the extent to which the carbon isotope ratio in four species of lichens was influenced by such features as humidity, rainfall, radioactivity, and air quality. The sampling sites were selected to be at a great distance from any pollution. At the time of sampling, field data (temperature, relative humidity, average monthly precipitation, and radioactivity) were recorded. delta(13)C in whole lichen specimens were determined using standard mass spectrometric techniques with a standard deviation of+/-0.3 per thousand. We have found a weak but negative correlation between delta(13)C and relative humidity, and a positive correlation between delta(13)C and average monthly precipitation at the studied sites. The effects were minor, of the order of 1.5 per thousand for all the lichens. We have examined the correlation between (137)Cs activity concentration of the studied lichens and delta(13)C of these lichens, and we have suggested that fixation of radiocesium does not alter photosynthesis rate. There was a delta(13)C variation with the altitude gradient with less negative delta(13)C values at higher altitude. It is possible that this difference is caused by the ozone and occurred at the high elevations.     

Biofunctionalized, ultrathin coatings of cross-linked star-shaped poly(ethylene oxide) allow reversible folding of immobilized proteins

Dense, ultrathin networks of isocyanate terminated star-shaped poly(ethylene oxide) (PEO) molecules, cross-linked at their chain ends via urea groups, were shown to be extremely resistant to unspecific adsorption of proteins while at the same time suitable for easy biocompatible modification. Application by spin coating offers a simple procedure for the preparation of minimally interacting surfaces that are functionalized by suitable linker groups to immobilize proteins in their native conformations. These coatings form a versatile basis for biofunctional and biomimetic surfaces. We have demonstrated their advantageous properties by using single-molecule fluorescence microscopy to study immobilized proteins under destabilizing conditions. Biotinylated ribonuclease H (RNase H) was labeled with a fluorescence resonance energy transfer (FRET) pair of fluorescent dyes and attached to the surface by a biotin-streptavidin linkage. FRET analysis demonstrated completely reversible denaturation/renaturation behavior upon exposure of the surface-immobilized proteins to 6 M guanidinium chloride (GdmCl) followed by washing in buffer. A comparison with bovine serum albumin (BSA) coated surfaces and linear PEO brush surfaces yielded superior performance in terms of chemical stability, inertness and noninteracting nature of the star-polymer derived films.     

A new non-destructive method for chemical analysis of particulate matter filters: the case of manganese air pollution in Vallecamonica (Italy)

Total Reflection X-ray Fluorescence (TXRF) is a well-established technique for chemical analysis, but it is mainly employed for quality control in the electronics semiconductor industry. The capability to analyze liquid and uniformly thin solid samples makes this technique suitable for other applications, and especially in the very critical field of environmental analysis. Comparison with standard methods like inductively coupled plasma (ICP) and atomic absorption spectroscopy (AAS) shows that TXRF is a practical, accurate, and reliable technique in occupational settings. Due to the greater sensitivity necessary in trace heavy metal detection, TXRF is also suitable for environmental chemical analysis. In this paper we show that based on appropriate standards, TXRF can be considered for non-destructive routine quantitative analysis of environmental matrices such as air filters. This work has been developed in the frame of the EU-FP6 PHIME (Public Health Impact of long-term, low-level Mixed element Exposure in susceptible population strata) Integrated Project (www.phime.org). The aim of this work was to investigate Mn air pollution in the area of Vallecamonica (Italy).     

Synthesis of new 3‐(trifluoromethyl)‐1H‐indoles by reduction of trifluoromethyloxoindoles

This work describes the synthesis of new 3‐trifluoromethylindoles. Different isatins were trifluoromethylated using (trifluoromethyl) trimethylsilane (Me₃SiCF₃) as a nucleophilic agent giving new 3‐hydroxy‐3‐(trifluoromethyl)indolin‐2‐one. Different “one‐step” procedures to transform the latter compounds into the reduced indoles were attempted, but failed. For the synthesis of the new trifluoromethylindoles the corresponding 2‐oxo‐3‐(trifluoromethyl)indoles were reduced using borane/THF complex to furnish 3‐(trifluoromethyl)indolin‐3‐ol that additionally were dehydrated using thionyl chloride in pyridine to give excellent yields of the desired products.