Hollow latex particles as submicrometer reactors for polymerization in confined geometries

A method was developed for free‐radical polymerization in the confines of a hollow latex particle. Hollow particles were prepared via the dynamic swelling method from polystyrene seed and divinylbenzene and had hollows of 500–1000 nm. So that these hollow poly(divinylbenzene) particles could function as submicrometer reactors, the particles were filled with a monomer (N‐isopropylacrylamide) via the dispersion of the dried particles in the molten monomer. The monomer that was not contained in the hollows was removed by washing and gentle abrasion. Free‐radical polymerization was then initiated by γ radiolysis in the solid state. Transmission electron microscopy showed that poly(N‐isopropylacrylamide) formed in the hollow interior of the particles, which functioned as submicrometer reactors. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5706–5713, 2004     

Moisture sorption, transport, and hydrolytic degradation in polylactide

Management of moisture penetration and hydrolytic degradation of polylactide (PLA) is extremely important during the manufacturing, shipping, storage, and end-use of PLA products. Moisture transport, crystallization, and degradation, in PLA have been measured through a variety of experimental techniques including size-exclusion chromatography, differential scanning calorimetry, and X-ray diffraction. Quartz crystal microbalance and dynamic vapor sorption experiments have also been used to measure moisture sorption isotherms in PLA films with varying crystallinity. A surprising result is that, within the accuracy of the experiments, crystalline and amorphous PLA films exhibit identical sorption isotherms.     

Chirospecific Syntheses of Conformationally Constrained 7-Azabicycloheptane Amino Acids by Transannular Alkylation

A new method is reported for the chirospecific preparation of optically pure 1-carboxy-7-azabicycloheptane amino acids for the generation of peptidomimetics as conformational probes. The method allows for the multigram preparation of these amino acid analogues through use of a thiolactam sulfide contraction and a transannular alkylation sequence as the key C-C bond-forming steps, starting from L-glutamic acid. The route provides access to two common intermediates, 7-(benzyloxycarbonyl)-1-carboxy-7-azabicyclo[2.2.1]-3-heptane and (1S,4R)-7-(benzyloxycarbonyl)-1-carboxy-7-azabicyclo[2.2.1]-3-heptanone tert-butyl ester, for elaboration to symmetrical and chiral amino acid homologues, respectively. Decarboxylation of the C-1 carboxy unit of the latter intermediate also demonstrated the applicability of the method for a short, chirospecific preparation of a (+)-epibatidine intermediate, (1S,4R)-7-(tert-butyloxycarbonyl)-1-carboxy-7-azabicyclo[2.2.1]-3-heptanone.     

Synthesis of spiro-fused (C5)-isoxazolino-(C4)-pyrazolones (1-oxa-2,7,8-triazaspiro[4,4]-2,8-dien-6-ones) via 1,3-dipolar cycloaddition and cycloelimination

An efficient and selective method for the synthesis of spiro-fused (C5)-isoxazolino-(C4)-pyrazolones (C) is reported. The process consists of utilizing the Baylis-Hillman reaction-or a quicker, stepwise MAC procedure-to give I followed by 1,3-dipolar cycloaddition and Swern oxidation to give beta-ketoesters H, which were condensed with hydrazine derivatives to provide hydrazones that underwent cycloelimination. These novel spiro-fused (C5)-isoxazolino-(C4)-pyrazolones were confirmed by spectroscopic analysis as well as single-crystal X-ray of 5. We also concluded that all condensations/cycloeliminations, except with hydrazine itself, were more effective with catalysts or higher reaction temperatures. For example, TiCl(4) was an efficient catalyst for hydrazone formation and cycloelimination with methylhydrazine, while phenyl-, benzyl-, and (4-methoxyphenyl)hydrazine reacted effectively without catalyst in refluxing xylene.     

Reversible polymerization driven by folding

Bisfunctionalized m-phenylene ethynylene imine oligomers were polymerized in the polar solvent acetonitrile, resulting in high-molecular weight poly(m-phenylene ethynylene imine)s. It is hypothesized that this polymerization, which proceeds through the reversible metathesis of imine bonds, is driven by the folding of the long m-phenylene ethynylene imine chains. Upon conducting the polymerization in a series of solvents in which the m-phenylene ethynylene oligomers exhibit different folding stabilities, it was possible to correlate the molecular weight of the resulting poly(m-phenylene ethynylene imine)s with the helical stability of the corresponding oligomers. The polymerization was also demonstrated to be reversible and responsive to solvent and temperature changes.     

Microchemical investigation of medicinal plants. XV

Summary A method is described for the determination of alkaloids in morning glory leaves by means of spectrophotofluorimetry. The total alkaloidal contents found in different batches of leaves ranged from 0.027 to 0.04%.

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Zusammenfassung Ein Verfahren zur Bestimmung der Gesamtalkaloide in den Blättern vonIpomoea violacea wurde angegeben. Spektralfluoreszenzmessungen ergaben für verschiedene Chargen solcher Blätter Gehalte von 0,027 bis 0,04%.

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For part XIV see Mikrochim. Acta [Wien]1976 I, 227.     

Comparative properties of siloxane vs phosphonate monolayers on a key titanium alloy

A direct comparison of surface loading, interface shear strength, and interface hydrolytic stability was made between a phosphonate and two siloxane monolayers formed on the native oxide surface of Ti-6Al-4V. Surface loading for the phosphonate was ca. four times greater (on a nanomole/area basis) than for the siloxanes; mechanical strengths per surface-bound molecule were comparable, but the hydrolytic stability (pH 7.5) of the siloxanes was poor. These results suggest that phosphonate monolayer interfaces are more desirable than comparable siloxane ones for applications where such interfaces contact even slightly alkaline water.     

A new tri-orthogonal strategy for peptide cyclization

A solid phase tri-orthogonal protection/cleavage strategy that uses acidic, basic, and neutral conditions is described. Strategically protected alpha-azido-gamma-9-fluorenylmethyl-L-glutamate (1) and alpha-azido-epsilon-N-Fmoc-L-lysine (2) were incorporated into growing peptides on Wang resin using a novel azide protection strategy. These residues, separated by 1-3 monomers, were deprotected at the side chains and cyclized via lactam formation. The N-terminus was further functionalized to extend the chain. This method represents a straightforward protocol for peptide cyclization on solid support.