Synthesis of 3-miktoarm stars and 1st generation mikto dendritic copolymers by "living" radical polymerization and "click" chemistry

The facile synthesis of 3-miktoarm star polymers and 1st generation mikto polymeric dendrimers using atom transfer radical polymerization (ATRP) and "click" chemistry is demonstrated. ATRP was used to synthesize near uniform polymers with Br chain ends, which were easily converted into azido groups. These polymer chains were then attached to a trifunctional alkyne molecule (tripropargylamine) using click reactions in a variety of ways to make the miktoarm stars and miktoarm polymeric dendrimers.     

A microwave-heated infrared reaction cell for the in situ study of heterogeneous catalysts

A transmission infrared microreactor cell which holds a pressed disc in a controlled atmosphere and allows microwave and conventional heating up to 423 K is demonstrated using the oxidation of carbon monoxide over the standard catalyst EUROPT-1. Optical characteristics are determined by the choice of CaF2 as the window material, allowing transmission from 77,000-1000 cm(-1). An oscillating microwave power regime with a peak height of 200 W is used and time-resolved infrared spectra and mass spectrometry show oscillations in the reaction which correspond to the microwave heating.     

Tetrahydrofuran-based amino acids as library scaffolds

A furanose sugar amino acid (SAA) has been utilized as a library scaffold for the first time. Two furanose SAA scaffolds were examined to illustrate their potential for derivatization. The resulting 99-member library contained three orthogonal points of diversification that allowed easy access to ethers and carbamates from a hydroxyl moiety, a range of ureas from an azide (via an amine), and a range of amides from a methyl ester. The novel amide formation (by displacement of the methoxide from the methyl ester moiety) was achieved in good yield and purity with high structural confidence. Full characterization of several library intermediates (including a crystal structure) was obtained. The library was submitted for antibacterial screening.     

A Monte Carlo pharmacophore generation procedure: Application to the human PAF receptor

Summary A novel pharmacophore definition procedure is described, which uses a Monte Carlo method to superimpose molecules. Pharmacophore space is searched by a technique similar to high temperature annealing. Subsequent refinement of candidate pharmacophores by energy minimization produces low-energy conformations that may be involved in receptor binding. The method has been applied to compounds that bind to the human platelet-activating factor (PAF) receptor. Alternative binding site models for the PAF receptor are presented and discussed.A preliminary account of this work has been published elsewhere [1].     

Synthesis and Diels-Alder Reactions of a New Kind of Chiral Dienophiles: Cyclic Vinyl-p-tolylsulfilimines

A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group.     

Free volume and water uptake in a copolymer hydrogel series

A copolymer of 2-hydroxyethyl methacrylate (HEMA) with 2-ethoxy ethyl methacrylate (EEMA) was synthesized and the molecular mobility, free volume, and density properties examined as a function of composition. These properties were correlated with the equilibrium water uptake in order to determine which of the properties were most influential in causing high water sorption, as these materials are suitable candidates for hydrogel systems. It was found that the polar HEMA repeat unit results in a rigid, glassy sample at room temperature due to the high degree of hydrogen bonding between chains whereas high EEMA content leads to rubbery samples with subambient glass transition temperatures. The free volume properties on the molecular scale measured by positron annihilation lifetime spectroscopy (PALS) showed that higher HEMA content led to smaller, fewer holes and a lower free volume fraction than EEMA. Therefore the high water uptake of HEEMA-containing copolymers is largely related to the high polarity of the HEMA unit compared to EEMA, despite the low content of free volume into which the water can initially diffuse. Trends in density with copolymer composition, as measured on a macroscopic level, differs to that seen by PALS and indicates that the two techniques are measuring different scales of packing. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 463–471, 1998     

An ESR and NMR study of the gamma radiolysis of a bisphenol-A based polycarbonate and a phthalic acid ester

A study of the γ-radiolysis of the commercial polymers U-polymer, UP (Unitake) and polycarbonate, PC, (Aldrich) has been undertaken using ESR spectroscopy. The G-value of radical formation at 77 K has been found to be 0.31±0.01 for UP and 0.5±0.02 for PC. By using thermal annealing and spectral subtraction, the paramagnetic species formed on irradiation has been assigned. The effect of radiation on the chemical structure of UP and PC has been investigated at ambient temperature and at 423 K. The NMR results show that a new phenol type chain end is formed in the polymers on exposure to γ-radiation. The G-value of formation of the new phenol ends was estimated to be 0.7 for PC (423 K) and 0.4 for UP (300 K). © 1998 John Wiley & Sons, Ltd.