Polarization inscription in ferroelectric (111) PZT and (100) SBT films

Ferroelectric thin films form an equilibrium domain structure compatible with their respective crystallographic symmetry. In tetragonal (111) PZT, 90° domains prevail; in (pseudo-tetragonal) (100) SBT both 90° and 180° domains are present. The size of 90° domains has been measured for e.g., PZT as slabs of 15 nm width. Domain size is a result of stress minimization in the film during the paraelectric (PE) → ferroelectric (FE) transition. A precise and regular domain pattern for (111) PZT and (100) SBT films has been investigated in detail by TMSFM. Single domains can be addressed mechanically with the tip of an AFM. Such single domain switching corresponds to a data storage density of 200 Gbit/inch². Applications of ferroelectric and high- paraelectric materials for e.g., non-volatile data storage replacing DRAM devices or as sensors in infrared cameras are increasingly becoming popular.     

Rh(i)-catalyzed stereoselective desymmetrization of prochiral cyclohexadienones via highly exo-selective Huisgen-type [3 + 2] cycloaddition

A Rh(i)-catalyzed highly stereoselective desymmetrization of 2-alkynylbenzaldehyde-tethered cyclohexadienones triggered by intramolecular Huisgen-type [3 + 2] cycloaddition has been developed. This method enables convergent construction of complex epoxy-bridged polycyclic ring systems with five contiguous stereocenters with excellent exo-selectivity and broad substrate scope. The highly atom-economical process involves 6-endo-dig cyclization of carbonyl oxygen onto an activated alkyne resulting in a highly reactive metal–benzopyrylium intermediate, which readily undergoes intramolecular [3 + 2] annulation/hydration. Asymmetric induction is also achieved for the first time in Rh(i)-catalyzed 1,3-dipolar cycloaddition using an easily accessible chiral diene as the ligand.

A Rh(i)-catalyzed highly stereoselective desymmetrization of 2-alkynylbenzaldehyde-tethered cyclohexadienones triggered by intramolecular Huisgen-type [3 + 2] cycloaddition has been developed.     

Ni+Pd+Ga and Ni+Pd+in liquid alloys: Enthalpies of formation

In order to fill the evident gap in the thermodynamic data of nickel-palladium-gallium and nickel-palladium-indium ternary alloys, the enthalpies of formation of these systems in the liquid state have been determined. This was achieved by means of a very high temperature calorimeter (T<1800 K), using the direct drop method, and based on analogous measurements of the respective binary alloys previously published. Complete automation of the calorimeter led to a good precision even at the highest temperatures. The enthalpies of formation of the ternary liquid alloys were measured between 1400 and 1600 K on the whole composition range. As in the limiting binary systems, enthalpies of formation are negative and non temperature dependent at any composition.

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Zusammenfassung Um die Lücke hinsichtlich thermodynamischer Daten von Nickel-Palladium-Gallium und Nickel-Palladium-Indium Legierungen zu füllen, wurden die Bildungsenthalpien dieser ternÄren Systeme im flüssigen Zustand bestimmt. Dies erfolgte mittels eines Kalorimeters für sehr hohe Temperaturen (T<1800 K), unter Verwendung der direkten Einwurfmethode auf der Basis früher veröffentlichter Messungen an den entsprechenden binÄren Systemen. Die Bildungsenthalpien der flüssigen ternÄren Legierungen wurden zwischen 1400 und 1600 K über den gesamten Zusammensetzungsbereich bestimmt. VollstÄndige Automation des Kalorimeters bewirkte hohe PrÄzision selbst bei den höchsten Temperaturen. Wie in den begrenzenden binÄren Systemen sind die Bildungsenthalpien negativ und bei allen Zusammensetzungen nicht temperaturabhÄngig.

     

Non-covalent assemblies of negatively charged boronated porphyrins with different cationic moieties

A unique approach to non-covalent electron and energy transfer is described that is based on the formation of salt bridges between oppositely charged porphyrin units. A new class of electrostatically linked dimeric and pentameric porphyrins was synthesized by interaction of novel anionic boron containing porphyrins such as 5-(benzamidodecahydro-closo-dodecaborate)-10,15,20-triphenylporphyrin (N1) and meso-tetrakis-benzamidodecahydro-closo-dodecaborate)porphyrin (N2) and a variety of cationic meso-tetraarylporphyrin units. A bipyridine linked dimer (N1 · bpy · N1) was also prepared by employing N,N′-dimethyl-4,4′-bipyridinium (bpy) as a spacer between two mono-anionic species. A quinone-porphyrin dyad was also prepared for electron or energy transfer demonstration. All the synthesized assemblies were characterized by NMR, IR, UV-Vis, and mass spectroscopy. Significant spectral changes occurred in the absorption spectra of these non-covalent porphyrin assemblies compared to those of the reference monomers, indicating the presence of electronic interaction between the adjacent porphyrin units. Resonance light scattering was also used to study the formation of these assemblies in solution.     

Synthesis and characterization of a novel functionalized azanonaborane cluster for boron neutron capture therapy

The reactivity of an azanonaborane cluster containing free amino groups {H2N(CH2)4H2NB8H11NH(CH2)4NH2} towards ketones and aldehydes is investigated. In a one step reaction, the reductive amination of some ketones and aldehydes (namely acetone, benzaldehyde, 3-hydroxybenzaldehyde, 4-hydroxybenzaldehyde, 4-nitrobenzaldehyde, 4-acetoxybenzaldehyde, and 4-acetamidobenzaldehyde) with an azanonaborane cluster in the presence of H3BNH2(CH2)4NH2 gives monoalkylamino derivatives of the azanonaborane cluster {RHN(CH2)4H2NB8H11NH(CH2)4NHR} where (R =(Me)2CH-, C6H5CH2-, 3-OHC6H4CH2-, 4-OHC6H4CH2-, 4-NO2C6H4CH2-, 4-MeOCOC6H4CH2-, or 4-NH2COC6H4CH2-). The functionalized derivatives of the {B8N} cluster can be used in boron neutron capture therapy for tumors (BNCT). Similarly, the reductive amination of 5-(4"-formylphenyl)-10,15,20-triphenylporphyrin with the {B8N} cluster gave a porphyrin bearing azanonaborane cluster, while a porphyrin dimer linked by an azanonaborane moiety was obtained following the same method, starting with a 2:1 molar ratio of porphyrin:{B8N} cluster. 5,10,15,20-Tetraformylphenylporphyrin gave the chance to increase the percentage of boron in the resulting boronated porphyrin, which is considered an important factor for a BNCT delivery agent. With these compounds, the cell toxicity using V79 cells was carried out to determine whether these compounds would have favorable biological properties.     

The chemistry of the azanonaborane cluster RNH2---B8H11NHR

The preparation and properties of the R¹R²NH---B₈H₁₁NHR cluster are described. The cluster is stable to aqueous solutions and can be made water-soluble by the introduction of a few hydrophilic groups. This makes the cluster a good candidate as the boron moiety in compounds for boron neutron capture therapy. The chemistry of the cluster preparation, the stability of the cluster, and conditions for reactions of the organic moieties are reviewed. Pyridine derivatives of the cluster show electronic interaction between the cluster and the pyridine.     

Fused quinoline heterocycles VI: Synthesis of 5H‐1‐thia‐3,5,6‐triazaaceanthrylenes and 5H‐1‐thia‐3,4,5,6‐tetraazaaceanthrylenes

Ethyl 3‐amino‐4‐chlorothieno[3,2‐c]quinoline‐2‐carboxylate ( 4 ) is a versatile synthon, prepared by reacting an equimolar amount of 2,4‐dichloroquinoline‐3‐carbonitrile ( 1 ) with ethyl mercaptoacetate ( 2 ). Ethyl 5‐alkyl‐5H‐1‐thia‐3,5,6‐triazaaceanfhrylene‐2‐carboxylates 9a‐c , novel perianellated tetracyclic heteroaro‐matics, were prepared by refluxing 4 with excess of primary amines 7a‐c to yield the corresponding amino‐thieno[3,2‐c]quinolines 8a‐c . Subsequent reaction with an excess of triethyl orthoformate (TEO) furnished 9a‐c . Reaction of 4 with TEO in Ac₂O at reflux, gave the simple acetylated compounds, thieno[3,2‐c]‐quinolines 12 and 13 . Refluxing 4 with benzylamine ( 7d ) gave 10 , and subsequent treatment with TEO gave the tetracyclic compound 11 . Refluxing 13 with an excess of alkylamines 7a‐d gave the fhieno[3,2‐c]quino‐lines 15 . Refluxing the aminothienoquinolines 8b with an excess of triethyl orthoacetate gave thieno[3,2‐c]quinoline 17 , while heating with Ac₂O gave 18 and 19 , with small amounts of 16 . Reaction of 8a,b with ethyl chloroformate and phenylisothiocyanate generated the new 1‐thia‐3,5,6‐triazaaceanthrylenes 20a,b and 21a,b , respectively. Diazotization of 8a‐c afforded the novel tetracyclic ethyl 5‐alkyl‐5H‐1‐fhia‐3,4,5,6‐tetraazaaceanthrylene‐2‐carboxylates 22a‐c in good yields.     

Buffer layer effect in nanostructured tin electrodeposition on insulating and conducting substrates

The electroplating techniques for metal aggregates and films deposition commonly use an electric current to reduce metal ions in solution, but are restricted to conducting substrate. This new electrochemical technique permits coating of insulating or conducting substrates with metals having controlled aggregate size and growth speed. The basis of our approach is the progressive outward growth of the metal from an electrode in contact with the substrate, with the cell geometry chosen in such a way that the electron current providing the reduction passes through the growing deposit. The nanostructured deposit is composed of branched nanoaggregates from a quasi-continuous film to a more dendritic morphology dependant on current conditions. This approach has been used to elaborate tin electrodeposited thin films composed of a homogeneous distribution of nanoparticles on conducting or insulating substrates. In our works, when a non-continuous buffer gold coating is used, spontaneous mixing of tin atoms into AuSn nanoparticles takes place even at room temperature forming a nanostructured fractal film, if the substrate is conducting or insulating. Without a gold buffer layer, the deposit is composed of large pure tin micro-crystals with a large size distribution, less adapted to tin oxide nanoparticle formation. Indeed, from these tin metal deposits, the final goal is to elaborate functional nanostructured tin oxide films by oxidation for gas sensor applications.     

Electrochemical characterization and stress corrosion cracking behavior of α-brass in molybdate-containing electrolytes

One of the major challenges in material design is the achievement of reasonable operational efficiency through understanding the factors affecting the material’s performance particularly strength and service lifetime characteristics. In this work, the electrochemical behavior of 72Cu–28Zn α-brass alloy in Na₂MoO₄-containing electrolytes was investigated using potentiodynamic polarization and electrochemical frequency modulation techniques complemented with scanning electron microscopy. Also, stress corrosion cracking behavior of the alloy under both open-circuit potential and anodic applied potentials, using the slow strain rate technique, was evaluated. The results drawn from the different techniques are comparable.     

Stereoselective total synthesis of (−)-zeylenol,a key intermediate for the synthesis of (+)-pipoxide, (−)-uvarigranol G and (−)-tonkinenin A

Total synthesis of (?)-zeylenol, a key intermediate for the synthesis of (+)-pipoxide, (?)-uvarigranol G and (?)-tonkinenin A was achieved from commercially available starting material d-mannose. The key steps are mixed aldol condensation, Grignard reaction, ring closing metathesis and regioselective benzoylation.