Regiocontrolled synthesis of enantiopure 3,3'-thiosubstituted biphenyls

Sulfenylation of 6,6'-dimethoxy-2,2'-dihydroxybiphenyl, used as a racemic mixture and single enantiomers, by phthalimidesulfenyl chloride afforded the corresponding 3,3'-N,N'-dithiophthalimide with complete regioselectivity. Simple manipulations of the latter compound allowed access to the corresponding bis-thiol or o-thioquinone as useful intermediates for the synthesis of new sulfur-containing open-chain and macrocyclic C(2) enantiopure ligands. The application of this methodology to the preparation of a biphenyl bearing two cysteine units as potential HIV-1 protease inhibitor is also described.     

Rapid access to 3-(N-substituted)-aminoquinolin-2(1H)-ones using palladium-catalyzed C-N bond coupling reaction

A series of 3-(N-substituted)-aminoquinolin-2(1H)-ones have been synthesized by the palladium-catalyzed C-N coupling reaction starting from 3-bromoquinolin-2-(1H)-ones. Various nucleophiles including amines, amides, sulfonamides, carbamates and ureas have been used successfully. In all the cases, the reactions take place rapidly in 1,4-dioxane and proceed in good to excellent yield using palladium acetate as a catalyst, Xantphos as a ligand and Cs₂CO₃ as a base.     

Phenol photonitration

This paper presents some new data on nitrophenol formation from phenol under illumination, and reviews the studies performed on phenol photonitration, from its discovery in 1988 to the very recent elucidation of its reaction pathway by the authors. Recent experimental results account for the pH effect on phenol photonitration. The nitrogen sources so far investigated are nitrate and nitrite, which undergo photolysis upon absorption of near-UV light. These studies have given a relevant information on the role of both nitrate and nitrite as environmental factors. Such processes can take place both in natural waters and in atmospheric hydrometeors.     

Binding and condensation of plasmid DNA onto functionalized carbon nanotubes: toward the construction of nanotube-based gene delivery vectors

Carbon nanotubes (CNTs) constitute a class of nanomaterials that possess characteristics suitable for a variety of possible applications. Their compatibility with aqueous environments has been made possible by the chemical functionalization of their surface, allowing for exploration of their interactions with biological components including mammalian cells. Functionalized CNTs (f-CNTs) are being intensively explored in advanced biotechnological applications ranging from molecular biosensors to cellular growth substrates. We have been exploring the potential of f-CNTs as delivery vehicles of biologically active molecules in view of possible biomedical applications, including vaccination and gene delivery. Recently we reported the capability of ammonium-functionalized single-walled CNTs to penetrate human and murine cells and facilitate the delivery of plasmid DNA leading to expression of marker genes. To optimize f-CNTs as gene delivery vehicles, it is essential to characterize their interactions with DNA. In the present report, we study the interactions of three types of f-CNTs, ammonium-functionalized single-walled and multiwalled carbon nanotubes (SWNT-NH3+; MWNT-NH3+), and lysine-functionalized single-walled carbon nanotubes (SWNT-Lys-NH3+), with plasmid DNA. Nanotube-DNA complexes were analyzed by scanning electron microscopy, surface plasmon resonance, PicoGreen dye exclusion, and agarose gel shift assay. The results indicate that all three types of cationic carbon nanotubes are able to condense DNA to varying degrees, indicating that both nanotube surface area and charge density are critical parameters that determine the interaction and electrostatic complex formation between f-CNTs with DNA. All three different f-CNT types in this study exhibited upregulation of marker gene expression over naked DNA using a mammalian (human) cell line. Differences in the levels of gene expression were correlated with the structural and biophysical data obtained for the f-CNT:DNA complexes to suggest that large surface area leading to very efficient DNA condensation is not necessary for effective gene transfer. However, it will require further investigation to determine whether the degree of binding and tight association between DNA and nanotubes is a desirable trait to increase gene expression efficiency in vitro or in vivo. This study constitutes the first thorough investigation into the physicochemical interactions between cationic functionalized carbon nanotubes and DNA toward construction of carbon nanotube-based gene transfer vector systems.     

A new type of entanglement involving one-dimensional ribbons of rings catenated to a three-dimensional network in the nanoporous structure of [Co(bix)2(H2O)2](SO4).7H2O [bix = 1,4-bis(imidazol-1-ylmethyl)benzene

Co(II) sulfate reacts with the flexible ligand 1,4-bis(imidazol-1-ylmethyl)benzene (bix) to yield the coordination network [Co(bix)2(H2O)2](SO4).7H2O, containing polymeric ribbons of rings which penetrate and catenate a 3D single frame of the CdSO4 topology, to produce an open-channel entangled architecture with nanoporous behaviour.     

Methylene‐Bridged Metallocenes with 2,2′‐Methylenebis[1H‐inden‐1‐yl] Ligands: Synthesis,Characterization, and Polymerization Catalysis of a Synthetically Simple Class of C2‐ and C2v‐Symmetric ansa‐Metallocenes

The acid‐catalyzed reaction between formaldehyde and 1H‐indene, 3‐alkyl‐ and 3‐aryl‐1H‐indenes, and six‐membered‐ring substituted 1H‐indenes, with the 1H‐indene/CH₂O ratio of 2 : 1, at temperatures above 60° in hydrocarbon solvents, yields 2,2′‐methylenebis[1H‐indenes] 1 – 8 in 50–100% yield. These 2,2′‐methylenebis[1H‐indenes] are easily deprotonated by 2 equiv. of BuLi or MeLi to yield the corresponding dilithium salts, which are efficiently converted into ansa‐metallocenes of Zr and Hf. The unsubstituted dichloro{(1,1′,2,2′,3,3′,3a,3′a,7a,7′a‐η)‐2,2′‐methylenebis[1H‐inden‐1‐yl]}zirconium ([ZrCl₂( 1′ )]) is the least soluble in organic solvents. Substitution of the 1H‐indenyl moieties by hydrocarbyl substituents increases the hydrocarbon solubility of the complexes, and the presence of a substituent larger than a Me group at the 1,1′ positions of the ligand imparts a high diastereoselectivity to the metallation step, since only the racemic isomers are obtained. Methylene‐bridged ‘ansa‐zirconocenes’ show a noticeable open arrangement of the bis[1H‐inden‐1‐yl] moiety, as measured by the angle between the planes defined by the two π‐ligands (the ‘bite angle’). In particular, of the ‘zirconocenes’ structurally characterized so far, the dichloro{(1,1′,2,2′,3,3′,3a,3′a,7a,7′a‐η)‐2,2′‐methylenebis[4,7‐dimethyl‐1H‐inden‐1‐yl]}zirconium ([ZrCl₂( 5′ )] is the most open. The mixture [ZrCl₂( 1′ )]/methylalumoxane (MAO) is inactive in the polymerization of both ethylene and propylene, while the metallocenes with substituted indenyl ligands polymerize propylene to atactic polypropylene of a molecular mass that depends on the size of the alkyl or aryl groups at the 1,1′ positions of the ligand. Ethene is polymerized by rac‐dichloro{(1,1′,2,2′,3,3′,3a,3′a,7a,7′a‐η)‐2,2′‐methylenebis[1‐methyl‐1H‐inden‐1‐yl]}zirconium ([ZrCl₂( 2′ )])/MAO to polyethylene waxes (average degree of polymerization ca. 100), which are terminated almost exclusively by ethenyl end groups. Polyethylene with a high molecular mass could be obtained by increasing the size of the 1‐alkyl substituent.     

Polycyclic aromatic hydrocarbons in the atmosphere: monitoring, sources, sinks and fate. II: Sinks and fate

This paper reviews the transformation processes that polycyclic aromatic hydrocarbons (PAHs) undergo in the atmosphere. These processes can take place both in the gas phase and in the particulate/aerosol one. Among the gas-phase processes, the most important ones are the daytime reaction with *OH and the nighttime reaction with *NO3. The relative importance of the two processes depends on the particular PAH molecule. For instance, gaseous naphthalene is mainly removed from the atmosphere upon reaction with *OH, while gaseous phenanthrene is mainly removed by reaction with *NO3. Oxy-, hydroxy-, and nitro-PAHs are the main transformation intermediates. Reaction with ozone and photolysis play a secondary role in the transformation of gaseous PAHs. The particle-associated processes are usually slower than the gas-phase ones, thus the gas-phase PAHs usually have shorter atmospheric lifetimes than those found on particulate. Due to the higher residence time on particulate when compared with the gas phase, direct or assisted photolysis plays a relevant role in the transformation of particle-associated PAHs. Among the other processes taking place in the condensed phase, nitration plays a very important role due to the health impact of nitro-PAHs, some of them being the most powerful mutagens found so far in atmospheric particulate extracts.     

LBGK method coupled to time splitting technique for solving reaction-diffusion processes in complex systems

A new approach to numerically solve a reaction-diffusion system is given, specifically developed for complex systems including many reacting/diffusing species with broad ranges of rate constants and diffusion coefficients, as well as complicated geometry of reacting interfaces. The approach combines a Lattice Boltzmann (LB) method with a splitting time technique. In the present work, the proposed approach is tested by focusing on the typical reaction process between a metal ion M and a ligand L, to form a complex ML with M being consumed at an electrode. The aim of the paper is to systematically study the convergence conditions of the associated numerical scheme. We find that the combination of LB with the time splitting method allows us to solve the problem for any value of association and dissociation rate constant of the reaction process. Also, the method can be extended to a mixture of ligands. We stress two main points: (1) the LB approach is particularly convenient for the flux computation of M and (2) the splitting time procedure is very well suited for reaction processes involving association-dissociation rate constants varying on many orders of magnitude.     

Teoremi di normalizzazione per l'omotopia regolare dei grafi

Given a metric compact spaceS and a finite graphG we show that:

Uniaxial deformation and orientation of ethylene–tetrafluoroethylene films

This study concerns the thermal and mechanical response of several commercial grades of ethylene – tetrafluoroethylene copolymer films. Differential scanning calorimetry was used to show that, although films have similar degrees of crystallinity and melting temperature, the melting endotherms and crystallisation exotherms differ between materials, suggesting small changes in composition between manufacturers. Films were deformed in tension at a range of temperatures and rates. Selected films were unloaded immediately after stretching, and measurement of the elastic recovery highlighted further differences between materials. Batches of films were pre-drawn uniaxially above the glass transition and immediately quenched. When these materials were subsequently re-drawn below the glass transition temperature, most of them exhibited much improved yield stress, modulus and tensile strength (improving by factors of 5, 5 and 4, respectively at a draw ratio of 3), but a reduced strain to failure. In most of the films, the pre-drawing, as well as the initial orientation of the films, is accounted for by a simple shift in the true strain axis. This is indicative of a material response dominated by entropic network stretch. It also suggests that, in the cases where strain superposition does not work, a different arrangement of crystalline lamellae may be present, limiting the extent to which improved properties can be achieved in some materials.