Enhancing selectivity in oxidation catalysis with sol-gel nanocomposites

Valuable organic compounds such as alpha-hydroxy acids are easily synthesised with relevant selectivity enhancement using a sol-gel hydrophobized nanostructured silica matrix doped with the organocatalyst TEMPO: A materials science based synthetic route which cannot be achieved via classical homogeneous synthesis.     

Parallelization of three-center electron repulsion integrals

The parallelization of the three-center electron repulsion integrals arising from the variational fitting of the Coulomb potential is presented. A scheme for dynamical load balancing of the corresponding loop structure is discussed. The implementation in the density functional theory program deMon using the message passing interface is described. The efficiency of the parallelization is analyzed by selected benchmark calculations     

Oxazinins from toxic mussels: isolation of a novel oxazinin and reassignment of the C-2 configuration of oxazinin-1 and -2 on the basis of synthetic models

The analysis of a batch of toxic mussels (Mytilus galloprovincialis) from the Northern Adriatic Sea led to the isolation of a novel oxazinin, oxazinin-4. Its structure including the relative stereochemistry has been elucidated through extensive NMR analysis. A synthetic route to oxazinins has been crucial in establishing the absolute stereochemistry of oxazinin-4 and for reassigning the absolute C-2 configuration of oxazinin-1 and -2 previously isolated from toxic shellfish and stereostructurally characterized.     

A guest-induced assembly of a molecular box from methylcobaloxime and 1, 4-phenylenebisboronic acid

The guest-induced synthesis of a molecular box from methylaquacobaloxime and 1,4-phenylenebisboronic acid, with pyrazine (pz) as guest, is described. The resulting supramolecular species was characterized by X-ray structural analysis, 1H and 13C NMR spectroscopy, and low-resolution electrospray ionization (ES) mass spectrometry. The assembly was monitored by a time dependent 1H NMR experiment, which showed that the guest thermodynamically drives the assembly of the host. The effectiveness of pyrazine in this role arises from its having both the correct geometry and a sufficiently low pKa value. Several other ditopic ligands were tested, but none led to formation of an analogous product. However, a second supramolecular species was formed in the case of ethylenediamine (en). X-ray structural analysis and 1H and 13C spectroscopy revealed that this is closely related to the first, with a phenyl side removed and the pz bridge substituted by the en bridge.     

A survey on high-concentration-capability headspace sampling techniques in the analysis of flavors and fragrances

This survey critically discusses high-concentration-capacity (HCC) headspace (HS) techniques applied to sample the volatile fraction of matrices of interest in the flavors and fragrance fields. In particular, the advantages, limits, and fields of application of HS solid-phase microextraction (SPME), high-capacity HS sorptive extraction (HSSE) and HS solid-phase dynamic extraction (SPDE) are evaluated. These techniques are discussed in view of the peculiar characteristic of HCC-HS techniques, from the standpoint that these techniques are a bridge between static (S-HS) and dynamic HS (D-HS) because they are as simple, fast, easy to automate, and reliable as S-HS, yet afford analyte concentration factors comparable to those of D-HS. Moreover, the different degree of their development is a consequence of the different times in which they were introduced into the market, because the potential of HS-SPME is now well known, having been introduced approximately 12 years ago, but that of HSSE has still to be fully explored, and HS-SPDE still has to be investigated because it is very recent.     

Spectrophotometric, EPR and kinetic characterisation of the >N-O* radical from 1-hydroxybenzotriazole, a key reactive species in mediated enzymatic oxidations

Characterisation of the aminoxyl (>N-O*) radical BTNO, generated from 1-hydroxybenzotriazole (HBT) by the one-electron oxidant CAN (a Ce(IV) salt), confirms BTNO as the reactive intermediate in oxidations run with the laccase/HBT system.     

Zn(II) coordination to polyamine macrocycles containing dipyridine units. New insights into the activity of dinuclear Zn(II) complexes in phosphate ester hydrolysis

Zn(II) binding by the dipyridine-containing macrocycles L1-L3 has been analyzed by means of potentiometric measurements in aqueous solutions. These ligands contain one (L1, L2) or two (L3) 2,2'-dipyridine units as an integral part of a polyamine macrocyclic framework having different dimensions and numbers of nitrogen donors. Depending on the number of donors, L1-L3 can form stable mono- and/or dinuclear Zn(II) complexes in a wide pH range. Facile deprotonation of Zn(II)-coordinated water molecules gives mono- and dihydroxo-complexes from neutral to alkaline pH values. The ability of these complexes as nucleophilic agents in hydrolytic processes has been tested by using bis(p-nitrophenyl) phosphate (BNPP) as a substrate. In the dinuclear complexes the two metals play a cooperative role in BNPP cleavage. In the case of the L2 dinuclear complex [Zn(2)L2(OH)(2)](2+), the two metals act cooperatively through a hydrolytic process involving a bridging interaction of the substrate with the two Zn(II) ions and a simultaneous nucleophilic attack of a Zn-OH function at phosphorus; in the case of the dizinc complex with the largest macrocycle L3, only the monohydroxo complex [Zn(2)L3(OH)](3+) promotes BNPP hydrolysis. BNPP interacts with a single metal, while the hydroxide anion may operate a nucleophilic attack. Both complexes display high rate enhancements in BNPP cleavage with respect to previously reported dizinc complexes, due to hydrophobic and pi-stacking interactions between the nitrophenyl groups of BNPP and the dipyridine units of the complexes.     

Radium,uranium and thorium concentrations in low specific activity scales and in waters of some oil and gas production plants

Low specific activity scales consisting of alkaline earth metal carbonates and sulfates are often present in some gaseous and liquid hydrocarbon plants; these scales contain a certain concentration of radium, uranium and thorium, which can cause a risk of -irradiation and of internal radiocontamination when they must be mechanically removed. That being stated,²³⁸U,²³²Th and²²⁶Ra were determined in scales, sludges and waters coming from different plants.²³⁸U and²³²Th concentrations were found very low; the isotopes²³⁸U and²³⁴U resulted in radioactive equilibrium, whilst²³²Th and²²⁸Th were not always in equilibrium.²²⁶Ra concentration was higher in scales and sludges than in waters.     

Microstructured cocultures of cardiac myocytes and fibroblasts: a two-dimensional in vitro model of cardiac tissue.

Cardiac myocytes and fibroblasts are essential elements of myocardial tissue structure and function. In vivo, myocytes constitute the majority of cardiac tissue volume, whereas fibroblasts dominate in numbers. In vitro, cardiac cell cultures are usually designed to exclude fibroblasts, which, because of their maintained proliferative potential, tend to overgrow the myocytes. Recent advances in microstructuring of cultures and cell growth on elastic membranes have greatly enhanced in vitro preservation of tissue properties and offer a novel platform technology for producing more in vivo-like models of myocardium. We used microfluidic techniques to grow two-dimensional structured cardiac tissue models, containing both myocytes and fibroblasts, and characterized cell morphology, distribution, and coupling using immunohistochemical techniques. In vitro findings were compared with in vivo ventricular cyto-architecture. Cardiac myocytes and fibroblasts, cultured on intersecting 30-microm-wide collagen tracks, acquire an in vivo-like phenotype. Their spatial arrangement closely resembles that observed in native tissue: Strands of highly aligned myocytes are surrounded by parallel threads of fibroblasts. In this in vitro system, fibroblasts form contacts with other fibroblasts and myocytes, which can support homogeneous and heterogeneous gap junctional coupling, as observed in vivo. We conclude that structured cocultures of cardiomyocytes and fibroblasts mimic in vivo ventricular tissue organization and provide a novel tool for in vitro research into cardiac electromechanical function.