Shedding Light Onto the Nature of Iron Decorated Graphene and Graphite Oxide Nanohybrids for CO2 Conversion at Atmospheric Pressure

We report on the design and testing of new graphite and graphene oxide-based extended π-conjugated synthetic scaffolds for applications in sustainable chemistry transformations. Nanoparticle-functionalised carbonaceous catalysts for new Fischer Tropsch and Reverse GasWater Shift (RGWS) transformations were prepared: functional graphene oxides emerged from graphite powders via an adapted Hummer's method and subsequently impregnated with uniform-sized nanoparticles. Then the resulting nanomaterials were imaged by TEM, SEM, EDX, AFM and characterised by IR, XPS and Raman spectroscopies prior to incorporation of Pd(II) promoters and further microscopic and spectroscopic analysis. Newly synthesised 2D and 3D layered nanostructures incorporating carbon-supported iron oxide nanoparticulate pre-catalysts were tested, upon hydrogen reduction in situ, for the conversion of CO₂ to CO as well as for the selective formation of CH₄ and longer chain hydrocarbons. The reduction reaction was also carried out and the catalytic species isolated and fully characterised. The catalytic activity of a graphene oxide-supported iron oxide pre-catalyst converted CO₂ into hydrocarbons at different temperatures (305, 335, 370 and 405 °C), and its activity compared well with that of the analogues supported on graphite oxide, the 3-dimensional material precursor to the graphene oxide. Investigation into the use of graphene oxide as a framework for catalysis showed that it has promising activity with respect to reverse gas water shift (RWGS) reaction of CO₂ to CO, even at the low levels of catalyst used and under the rather mild conditions employed at atmospheric pressure. Whilst the γ-Fe₂O₃ decorated graphene oxide-based pre-catalyst displays fairly constant activity up to 405 °C, it was found by GC-MS analysis to be unstable with respect to decomposition at higher temperatures. The addition of palladium as a promoter increased the activity of the iron functionalised graphite oxide in the RWGS. The activity of graphene oxide supported catalysts was found to be enhanced with respect to that of iron-functionalised graphite oxide with, or without palladium as a promoter, and comparable to that of Fe@carbon nanotube-based systems tested under analogous conditions. These results display a significant step forward for the catalytic activity estimations for the iron functionalised and rapidly processable and scalable graphene oxide. The hereby investigated phenomena are of particular relevance for the understanding of the intimate surface morphologies and the potential role of non-covalent interactions in the iron oxide-graphene oxide networks, which could inform the design of nano-materials with performance in future sustainable catalysis applications.     

Mild persubstitution of di- and tetrabrominated arenes with arylthiolate nucleophiles

A mild selective protocol was used to prepare tetrakis(2-chlorophenylthio)anthracene from tetrabromoanthracene and sodium 2-chlorobenzenethiolate avoiding the thiolate self-attack. The uncatalyzed nucleophilic substitution of a series of mono-, di-, and tetrabrominated arenes by arylthiolate ions was attempted in mild conditions to investigate the scope of the substitution reaction regarding the size of the aromatic system as well as the number of bromine atoms. Successful reactions afforded only the persubstituted products in good purity and yield after a simple workup and chemoselectivity of Br versus Cl substituents was achieved for the tetrabromide.     

Sul movimento di un punto pesante sopra una superficie di rivoluzione

Rendiconti del Circolo Matematico di Palermo Series 1 -     

On a class of hyperbolic 3-orbifolds of small volume and small heegaard genus associated to 2-bridge links

We consider a class of hyperbolic 3-orbifoldsO(α/β); the underlying topological space of such an orbifold is the 3-sphere and the singular set is obtained by adding the two standard (upper and lower) unknotting tunnels to a 2-bridge linkL(α/β) (and associating branching order two to both unknotting tunnels). These 3-orbifolds are extremal with respect to the notion of Heegaard genus or Heegaard number of 3-orbifolds; it is to be expected that they are also extremal with respect to the volume, that is the smallest volume hyperbolic 3-orbifolds should belong to this or some closely related class. We show that an orbifoldO(α/β) has a uniqueD ₂-covering by an orbifoldℒ _n(α/β) wose space is the 3-sphere and whose singular set is the same 2-bridge linkL(α/β) used for the construction ofO(α/β); moreoverO(α/β) is hyperbolic if and only ifℒ _n(α/β) is hyperbolic. As the volumes of the orbifoldsℒ _n(α/β) are known resp. can be computed, this allows to compute the volumes of the orbifoldsO(α/β). The problem of computation of volumes remains open for some closely related classes of 3-orbifolds which are also extremal with respect to the Heegaard genus (for example associating a branching order bigger than two to one or both unknotting tunnels).     

Split‐Ugi Reaction with Chiral Compounds: Synthesis of Piperazine‐ and Bispidine‐Based Peptidomimetics

A simple, one‐step, stereoconservative synthesis of diamine‐based peptidomimetics is described, by split‐Ugi multicomponent reaction, involving chiral N‐protected amino acids and α‐substituted isocyanoacetate. In particular, piperazine and bispidine (3,7‐diazabicyclo[3.3.1]nonane) are exploited as diamine components, bispidine being the first example of a sterically demanding bicyclic system employed in a split‐Ugi reaction.     

Soft,Oxidative Stripping of Alkyl Thiolate Ligands from Hydroxyapatite‐Supported Gold Nanoclusters for Oxidation Reactions

A strategy for the mild deprotection of alkyl‐thiolated (6‐mercaptohexanoic acid, MHA, and 3‐mercaptopropanoic acid, MPA) gold nanoclusters (Au NCs) supported on hydroxyapatite (HAP) has been developed by employing a peroxide (tert‐butyl hydroperoxide, TBHP, or hydrogen peroxide, H₂O₂) as an oxidant. The thiol ligands on the supported Au NCs were removed after oxidation, and the size and integrity of the supported clusters were well‐preserved. The bare gold clusters on HAP after removal of the ligands were catalytically effective for the epoxidation of styrene and the aerobic oxidation of benzyl alcohol. These two reactions were also investigated on calcined Au NCs that were supported on HAP for comparison, and the resulting Au NCs that were prepared by using this new strategy showed superior catalytic activity.     

Thermodynamics and kinetics of PNA-DNA quadruplex-forming chimeras

PNA-DNA chimeras present the interesting properties of PNA, such as the high binding affinity to complementary single-strand (DNA or RNA), and the resistance to nuclease and protease degradation. At the same time, the limitations of an oligomer containing all PNA residues, such as low water solubility, self-aggregation, and low cellular uptake, are effectively overcome. Further, PNA-DNA chimeras possess interesting biological properties as antisense agents. We have explored the ability of PNA-DNA chimeric strands to assemble in quadruplex structures. The rate constant for association of the quadruplexes and their thermodynamic properties have been determined by CD spectroscopy and differential scanning calorimetry (DSC). Thermal denaturation experiments indicated higher thermal and thermodynamic stabilities for chimeric quadruplexes in comparison with the corresponding unmodified DNA quadruplex. Singular value decomposition analysis (SVD) suggests the presence of kinetically stable intermediate species in the quadruplex formation process. The experimental results have been discussed on the basis of molecular dynamic simulations. The ability of PNA-DNA chimeras to form stable quadruplex structures expands their potential utility as therapeutic agents.     

Determination of phenolic compounds in dietary supplements and tea blends containing Echinacea by liquid chromatography with coulometric electrochemical detection

Analytical methodologies with ultrasonic extraction and liquid chromatography (LC) were developed for the determination of phenolic compounds in dietary supplements containing Echinacea. The phenolic compounds determined by these methods included caftaric acid, chlorogenic acid, cynarin, echinacoside, and cichoric acid. Samples from tablets, capsules, and bags of tea blends were extracted by sonication for < or = 30 min with methanol-water (60 + 40). The extracts were centrifuged and filtered, and the filtrates were diluted and analyzed by LC using a reversed-phase column and coulometric electrochemical (EC) detection. The mobile phase was acetonitrile-ammonium formate buffer, pH 3.5 (15.3 + 84.7) containing tetrabutyl ammonium hydrogen sulfate as an ion-pairing reagent. Extraction conditions (e.g., composition of the extraction solvent and sonication time) were optimized for different types of samples. Intra- and interday analytical variations were determined, and intraday analyses were performed by 2 independent analysts using 2 different LC systems. Results were generally comparable. The LC method with EC detection showed better sensitivity and selectivity when compared with LC with ultraviolet detection, although results were similar for the 2 methods for major compounds, i.e., caftaric acid, echinacoside, and cichoric acid. The identities of these major compounds found in samples were confirmed by LC/electrospray ionization mass spectrometry.