Self-assembly behavior of a stimuli-responsive water-soluble [60]fullerene-containing polymer

A novel pH- and temperature-responsive water-soluble [60]fullerene-containing poly[2-(dimethylamino)ethyl methacrylate] (C60-b-PDMAEMA) was synthesized by atom transfer radical polymerization. The pH and temperature dependence of the physical properties of the aqueous C60-b-PDMAEMA solution was studied by potentiometric and conductometric titrations, UV-vis transmittance, and laser light scattering techniques. At low pH and at temperatures ranging from 25 to 55 degrees C, in addition to C60-b-PDMAEMA unimers, micelle-like aggregates are produced in the aqueous solution containing C60 hydrophobic cores and protonated PDMAEMA shells. Only unimeric C60-b-PDMAEMAs are found to exist in solution at high pH and low temperature, where PDMAEMA segments form a charge-transfer complex with C60 molecules. However, C60-b-PDMAEMA precipitates from aqueous solution at temperatures exceeding the lower critical solution temperature of PDMAEMA of approximately 45 degrees C. The pH and temperature stimuli-responsive properties of the [60]fullerene-containing polymer in aqueous solution are completely reversible.     

Structure-property behavior of polyurethanes,polyurethane ionomers,and their acrylates

Polyurethanes(PU), PU ionomers, PU ionomer acrylates, PU latex interpenetrating polymer network(LIPN), latex AB crosslinked polymers (ABCP), and uv-curable PU ionomer acrylates have been prepared and characterized in terms of structure-property relationship, together with shape memory function of PUs.     

Structure-property behavior of films containing disk spherulites: A model study

Thin films of a polyester of lactic and glycolic acid were prepared to give controlled amounts of disk spherulites. The spherulite contents ranged from zero to 100% and were accurately measured. The stress-strain properties of the films were then determined at 60°C, i.e., about 20°C above the glass transition temperature T_g. The mechanical behavior varied quite systematically with spherulite content and displayed little dependence on spherulite size. It was found that much of the mechanical data could be reasonably well described by a simple composite model. In addition, the yield strain as well as the strain to break could be principally coupled to the deformation of only the amorphous phase. SEM and optical microscopy studies supported the above conclusion, also demonstrating that the isolated spherulites adhered well to the amorphous matrix and behaved as stress concentrators in the system when the deformation temperature was above T_g.     

Synthetic studies toward the haouamines

[reaction: see text] A concise synthetic approach toward the haouamines based on Stork-Danheiser alkylation and Friedel-Crafts chemistry is described. A novel electrophilic aromatic substitution with concomitant formation of an enol triflate is reported.     

Synthetic studies toward the guanacastepenes

[reaction: see text]. An asymmetric approach toward the [6-7] ring system of the guanacastepenes is described.     

Model studies toward the synthesis of kirkine

In model studies towards the synthesis of kirkine, the carbon skeleton was constructed using a radical cascade reaction. Two different approaches towards the synthesis have been examined as well as the regioselectivity of the radical cyclisation.     

Synthetic studies toward spiroleucettadine

Synthetic hydroxydienone precursors to spiroleucettadine and to an isomer thereof resist cyclization to the orthoamide-type functionality present in the proposed structure of the natural product.     

Synthetic studies toward zoapatanol

The oxepane core of zoapatanol was efficiently synthesized from commercially available 1,2,4-butanetriol, and it was shown to be possible to introduce the angular methyl group at C2′ by the reaction of an intermediate butenolide with diazomethane.     

Structure-property relationship of polyurethane ionomer

Polyurethane (PU) ionomers were prepared using various types of polyol (PTAd, PCL, PTMG, and PPG) and isocyanate (MDI, HDI, and IPDI), together with different extender (DMPA) contents, degree of neutralization, and number average molecular weight (M _n) of polyol. Modulus (E), strength (_b), and glass transition temperature (T _g) significantly increased with the increased amount of extender and extender neutralization. Among three of the iocyanate used, PU from MDI gave the highest modulus, strength, andT _g. With regard to theM _n of PTAd (600, 1000, 2000), PU from PTAd 600M _n gave the highest modulus, strength, andT _g, due probably to the highest hard segment content and phase mixing. On the other hand, PU from PTAd 2000M _n gave significantly improved strength over PTAd 1000M _n, and the highest elongation. The results were interpreted in terms of soft-segment crystallization, and soft-hard phase separation, which was concluded from the lowered softT _g.     

Synthetic studies toward Maoecrystal V

The investigation of an intramolecular Diels-Alder reaction, en route to a projected total synthesis of maoecrystal V, is described.     

Synthetic studies toward ecteinascidin 743

An efficient synthesis of a fully functionalized tetracycle (A-B-C-H) 7 containing a 1,4-bridged 10-membered lactone was developed. Phenolic aldol condensation between 2-methylsesamol (15) and Garner's aldehyde provided the protected amino diol 16, which was converted to free amine 11 in excellent yield. A Pictet-Spengler reaction between 11 and ethyl glyoxylate under carefully controlled conditions (LiCl, toluene, 1,1,1,3,3,3-hexafluoro-2-propanol, room temperature) provided the acid-sensitive tetrahydroisoquinoline (18) in high yield, which was converted to the amino alcohol 9. Enantioselective alkylation of a glycine template in the presence of a catalytic amount of chiral cinchonidium salt was the key step for the access of enantiomerically pure amino aldehyde 10. Union of the two fragments 9 and 10 via oxazolidine intermediate afforded amino nitrile 39, which upon esterification of the primary alcohol with (R)-N-(S-4,4',4' '-trimethoxyltrityl) Cys (42) afforded 43. Cyclization of 43 (1% trifluoroacetic acid in trifluoroethanol) provided compound 44 by a domino process involving (a) unmasking of the S-trimethoxytrityl group, (b) fragmentation of dioxane assisted by an electron-rich aromatic ring, and (c) formation of a 1,4-bridged 10-membered lactone via formation of a sulfide linkage. Treatment of 7, obtained in two steps from 44b, under acidic conditions (0.5% methyl sulfonic acid in acetonitrile) afforded the pentacyclic compound 51 via fragmentation of the 10-membered cyclic sulfide followed by an intramolecular Pictet-Spengler reaction.     

Synthetic studies toward melotenine A

Attempts to the construction of B/C ring and E ring in melotenine A are described. Based on para-dienone chemistry, a tactical application of tandem aminolysis/aza-Michael addition reaction was made to access highly functionalized building blocks with the pyrrolo[2,3-d]carbazole tetracyclic unit (A/B/C/D ring). Albeit negative results for assembling the dihydroazepine unit (E ring) by using the proposed fragmentation reaction of gem-dihalocyclopropanes, an alternative strategy based on ring closing metathesis was evolved to forge the E ring possessing a twisted 1,3-diene unit embedded in the rigid skeleton of melotenine A.     

Synthetic studies toward A-74528

A potentially biomimetic approach toward the complex polyketide A-74528 is described. It is based on highly substituted biaryl compounds, synthesized using advanced cross-coupling and condensation methodologies.     

Synthetic studies toward phenoxan analogs

We developed two reactions needed for a total synthesis of phenoxan, a naturally occurring compound with anti-HIV activity. In this Note, we further examined these two issues: metallation of a 2-methyl-oxazole and formation of a pyran-4-one. We employed these methods for the preparation of a phenoxan analog.     

Double stimuli-responsive behavior of aliphatic poly(urethane-amine)s derived from supercritical carbon dioxide

Copolymeric products from 2-methylaziridine and carbon dioxide showed sharp and rapid phase transitions in response to both temperature and pH; the responsive property can be controlled by varying the reaction conditions whilst maintaining the supercritical state.     

On the mechanism of peripentacene formation from pentacene: computational studies of a prototype for graphene formation from smaller acenes

The formation of peripentacene during the high-temperature vacuum sublimation of pentacene (P) in the presence of trace amounts of 6,13-dihydropentacene (DHP) has been studied computationally with density functional theory. Computational and kinetic analyses indicate that competing mechanisms involving a series of H atom transfers initiated by hydrogen transfer from DHP to P can account for the formation of peripentacene. The overall reaction is predicted to proceed with a free energy barrier of 36.1 kcal/mol and to be autocatalytic. Kinetic modeling supports the proposed mechanism.     

Organization of acenes with a cruciform assembly motif

This study explores the assembly in the crystalline state of a class of pentacenes that are substituted along their long edges with aromatic rings forming rigid, cruciform molecules. The crystals were grown from the gas phase, and their structures were compared with DFT-optimized geometries. Both crystallographic and computed structures show that a planar acene core is the exception rather than the rule. In the assembly of these molecules, the phenyl groups block the herringbone motif and further guide the arrangement of the acene core into higher order structures. The packing for the phenyl-substituted derivatives is dictated by close contacts between the C-H's of the pendant aromatic rings and the carbons at the fusions in the acene backbone. Using thiophene substituents instead of phenyls creates cofacially stacked acenes. In thin films, the thiophene-substituted derivative forms devices with good electrical properties: relatively high mobility, high ON/OFF ratios, and low threshold voltage for device activation. An unusual result is obtained for the decaphenyl pentacene when devices are fabricated on its crystalline surface. Although its acene cores are well isolated from each other, this material still exhibits good electrical properties.     

Structure-property relationship of acceptor-substituted oligothiophenes

A series of oligothiophenes that are end-capped with dicyanovinyl (DCV) and 1,3,2-(2H)-dioxaborine (DOB) moieties has been prepared using standard procedures. Their optoelectronic properties have been investigated by cyclic voltammetry and optical absorption. The optical absorption has been measured both in solution and thin film state.     

Cycloaddition studies directed toward the strychnos alkaloid minfiensine

The thermolysis of several imidofuranyl carbamates delivers products derived from an intramolecular [4+2]-cycloaddition reaction. In the case of the ortho-azido aryl carbamate 13, the preferred path proceeds by an electrocyclization of a nitrene intermediate to produce a 3-substituted indole. Attempts to reduce the azido group resulted in a novel intramolecular aza-Wittig reaction with the neighboring imido group.