1,3-Cycloaddition of nitrones in ionic liquids catalyzed by Er(III): an easy access to isoxazolidines

1,3-Dipolar cycloadditions of nitrones with alkenes afforded the corresponding isoxazolidines in ionic liquids in the presence of Er(OTf)₃. The ionic liquid and the catalyst are recycled up to five times without any specific treatment or loss of activity. Extension of the procedure to the synthesis of isoxazolidinyl nucleosides has been investigated.     

Controlling the Surface Functionalization of Ultrasmall Gold Nanoparticles by Sequence-Defined Macromolecules

Ultrasmall gold nanoparticles (diameter about 2 nm) were surface-functionalized with cysteine-carrying precision macromolecules. These consisted of sequence-defined oligo(amidoamine)s (OAAs) with either two or six cysteine molecules for binding to the gold surface and either with or without a PEG chain (3400 Da). They were characterized by ¹H NMR spectroscopy, ¹H NMR diffusion-ordered spectroscopy (DOSY), small-angle X-ray scattering (SAXS), and high-resolution transmission electron microscopy. The number of precision macromolecules per nanoparticle was determined after fluorescent labeling by UV spectroscopy and also by quantitative ¹H NMR spectroscopy. Each nanoparticle carried between 40 and 100 OAA ligands, depending on the number of cysteine units per OAA. The footprint of each ligand was about 0.074 nm² per cysteine molecule. OAAs are well suited to stabilize ultrasmall gold nanoparticles by selective surface conjugation and can be used to selectively cover their surface. The presence of the PEG chain considerably increased the hydrodynamic diameter of both dissolved macromolecules and macromolecule-conjugated gold nanoparticles.     

A convenient strategy of dimerization by microwave heating and using 2,5-diketopiperazine as scaffold

A novel and convenient microwave-assisted dimerization of an active peptide compound using the DKPs as scaffold is described. The key reaction giving rise to the diketopiperazine scaffold is the intermolecular coupling. No epimerization was detected in the reactions used. Conventional and microwave heating of the reactions are compared. Synthesis by microwave irradiation gave the desired compounds in higher yields and in shorter reaction times than those obtained by conventional heating.     

New polymer structures based on vinyl ether polymerization

Sequential living cationic polymerization of octadecyl vinyl ether (ODVE) and methyl vinyl ether (MVE) was used for the preparation of amphiphilic ABA‐type block copolymers. The polymerization of ODVE was initiated with the trimethyl silyl iodide/1,1,3,3‐tetramethoxy propane/ZnI₂ system at 0°C in toluene. The living bifunctional polyODVE thus obtained was used as initiator for the polymerization of MVE. Below the LCST of polyMVE (37°C), the copolymers are amphiphiles. Above the LCST of polyMVE, the polyMVE‐blocks become hydrophobic and the amphiphilic nature of the block copolymer is lost. This was demonstrated by using the block copolymers as emulsifiers for water/decane mixtures. The emulsions were stable for several hours at room temperature, while the emulsion stability decreased to about 30 seconds at 40°C. PolyMVE‐α,ω‐bis‐methacrylates were obtained by end‐capping of living bifunctional polyMVE with 2‐hydroxyethyl methacrylate (HEMA). Copolymerization of these bis‐macromers with HEMA leads to segmented networks. The networks showed a reversible swelling/deswelling behavior in water as a function of temperature. This is caused by a change of the hydrophilicity of the polyMVE segments in the networks. Hexa(chloromethyl)melamine, combined with zinc chloride was found to be an efficient hexafunctional initiator for the living cationic polymerization of vinyl ethers. This simple initiating system opens new ways for the synthesis of endgroup‐functionalized star‐shaped poly(vinyl ethers).     

The use of nonendcapped C18 columns in the cleanup of clenbuterol and a new adrenergic agonist from bovine liver by gas chromatography-tandem mass spectrometry analysis

More specific official methodology is needed to survey the illegal use of clenbuterol in animal production plus the synthesis of new compounds that currently elude routine analytical methods. The identification of a new adrenergic agonist, N1-(2-(4-amino-3,5-dichlorophenyl)-2-hydroxyethyl)-N1-isopropyl-propanamide (known as compound A) in animal feed has prompted studies to verify if the existing cleanup procedures developed for clenbuterol are really effective. This study considers the ion-exchange mechanism on cyanopropyl (CN), sulfonic cation exchange (SCX), mixed phase (MPH) (C8 + SCX), and nonendcapped C18 (C18NE) solid-phase extraction (SPE) columns. Results indicate that compound A (by contrast with clenbuterol) is not efficiently retained on the CN, SCX, and MPH SPE columns (recovery <10%). This finding thus leads to the development of a gas chromatography-tandem mass spectrometry procedure based on C18NE SPE that is able to purify both agonists from bovine livers spiked at 0.5, 1.0, and 2.0 ppb with a mean recovery of 93% for clenbuterol and 92% for compound A.     

Photoconvertible fluorescent protein EosFP: biophysical properties and cell biology applications

EosFP is a fluorescent protein from the coral Lobophyllia hemprichii that changes its fluorescence emission from green to red upon irradiation with near-UV light. Here we present the spectroscopic properties of wild-type EosFP and a variety of monomeric and dimeric mutants and provide a structural interpretation of its oligomerization and photoconversion, which is based on X-ray structure analysis of the green and red species that we reported recently. Because functional expression of the monomeric EosFP variant is limited to temperatures of 30 degrees C, we have developed a tandem dimer. This construct, in which two EosFP subunits are connected by a flexible 12 amino acid linker, expresses well after fusion with the androgen and endothelin A receptors at 37 degrees C. A variety of applications in cellular imaging, developmental biology and automated high-content screening applications are presented, which demonstrate that EosFP is a powerful tool for in vivo monitoring of cellular processes.     

N,O-Nucleoside Analogues: Metabolic and Apoptotic Activity

Two new families of N,O-nucleoside analogues containing the anthracene moiety introduced through the nitrosocarbonyl ene reaction with allylic alcohols were prepared. The core structure is an isoxazolidine heterocycle that introduces either atom either a phenyl ring or dimethyl moiety at the C3 carbon. Different heterobases were inserted at the position 5 of the heterocyclic ring. One of the synthesized compounds demonstrated a good capacity to induce cell death and an appreciable nuclear fragmentation was evidenced in treated cells.     

Fracture behavior and mechanical,thermal, and rheological properties of biodegradable films extruded by flat die and calender

The development of biodegradable materials for tailored applications, particularly in the field of polymeric films and sheets, is a challenging technological goal as well as a contribution to help protect the environment. Poly(lactic) acid (PLA) is a promising substitute for several oil-based polymers; however, to overcome its thermal and mechanical drawbacks, researchers have developed solutions such as blending PLA with polybutylene adipate terephthalate (PBAT), which is capable of increasing the ductility of the final material. In this study, PLA/PBAT binary blends, with minimum possible content of nonrenewable materials, were examined from processing, thermal, morphological, and rheological perspective. An optimized PLA/PBAT ratio was chosen as the polymeric basis to obtain a biodegradable formulation by adding a biobased plasticizer and appropriate fillers to produce a micrometer film with tailored flexibility and tear resistance. The processing technology involved flat-die extrusion, followed by calendering. The tearing resistance of the produced film was investigated, and the results were compared with literature data. A study on the essential work of fracture was implemented to explore the mode III out-of-plane fracture resistance starting from a trouser tear test.     

One of the most complex "small molecule structures" ever reported: 16 independent molecules in the asymmetric unit for an ortho-palladated primary amine

The presumably "small molecule structure" of the organopalladium complex rac-PdCl(C(6)H(3)-4-OMe-CHMeNH(2))(py) crystallizes with 16 molecules in the asymmetric unit, a highly unusual situation according to the CSD database. The symmetrically independent residues differ with respect to soft conformational degrees of freedom. Packing in the acetonitrile solvate of the same compound is unexceptional.