Theoretical study of isomerization and decomposition of propenal

We investigated the dynamics of isomerization and multi-channel dissociation of propenal (CH(2)CHCHO), methyl ketene (CH(3)CHCO), hydroxyl propadiene (CH(2)CH(2)CHOH), and hydroxyl cyclopropene (cyclic-C(3)H(3)-OH) in the ground potential-energy surface using quantum-chemical calculations. Optimized structures and vibrational frequencies of molecular species were computed with method B3LYP∕6-311G(d,p). Total energies of molecules at optimized structures were computed at the CCSD(T)∕6-311+G(3df,2p) level of theory. We established the potential-energy surface for decomposition to CH(2)CHCO + H, CH(2)CH + HCO, CH(2)CH(2)∕CH(3)CH + CO, CHCH∕CH(2)C + H(2)CO, CHCCHO∕CH(2)CCO + H(2), CHCH + CO + H(2), CH(3) + HCCO, CH(2)CCH + OH, and CH(2)CC∕cyclic-C(3)H(2) + H(2)O. Microcanonical rate coefficients of various reactions of trans-propenal with internal energies 148 and 182 kcal mol(-1) were calculated using Rice-Ramsperger-Kassel-Marcus and Variational transition state theories. Product branching ratios were derivable using numerical integration of kinetic master equations and the steady-state approximation. The concerted three-body dissociation of trans-propenal to fragments C(2)H(2) + CO + H(2) is the prevailing channel in present calculations. In contrast, C(3)H(3)O + H, C(2)H(3) + HCO and C(2)H(4) + CO were identified as major channels in the photolysis of trans-propenal. The discrepancy between calculations and experiments in product branching ratios indicates that the three major photodissociation channels occur mainly on an excited potential-energy surface whereas the other channels occur mainly on the ground potential-energy surface. This work provides profound insight in the mechanisms of isomerization and multichannel dissociation of the system C(3)H(4)O.     

Hydrogen‐Bonding Induced Cooperative Effect on the Energy Transfer in Helical Polynorbornenes Appended with Porphyrin‐Containing Amidic Alanine Linkers

Polynorbornenes appended with porphyrins containing a range of different linkers are synthesized. The use of bisamidic chiral alanine linkers between the pending porphyrins and the polymeric backbone has been shown to bring the adjacent porphyrin chromophores to more suitable orientation for exciton coupling owing to hydrogen bonding between the adjacent linkers. The hydrogen bonding between the adjacent pendants in these polymers may induce a cooperative effect and therefore render single‐handed helical structures for these polymers. Such a cooperative effect is reflected in the enhancement of FRET efficiencies between zinc–porphyrin and free base porphyrin in random copolymers.     

Surface‐initiated atom transfer radical polymerization from porous poly(tetrafluoroethylene) membranes using the C?F groups as initiators

This work reports the surface‐initiated atom transfer radical polymerization (ATRP) from hydrogen plasma‐treated porous poly(tetrafluoroethylene) (PTFE) membranes using the C? F groups as initiators. Hydrogen plasma treatment on PTFE membrane surfaces changes their chemical environment through defluorination and hydrogenation reactions. With the hydrogen plasma treatment, the C? F groups of the modified PTFE membrane surface become effective initiators of ATRP. Surface‐initiated ATRP of poly(ethylene glycol) methacrylate (PEGMA) is carried out to graft PPEGMA chains to PTFE membrane surfaces. The chain lengths of poly(PEGMA) (PPEGMA) grafted on PTFE surfaces increase with increasing the reaction time of ATRP. Furthermore, the chain ends of PPEGMA grown on PTFE membrane surfaces then serve as macroinitiators for the ATRP of N‐isopropylacrylamide (NIPAAm) to build up the PPEGMA‐b‐PNIPAAm block copolymer chains on the PTFE membrane surfaces. The chemical structures of the modified PTFE membranes are characterized using X‐ray photoelectron spectroscopy. The modification increases the surface hydrophilicity of the PTFE membranes with reductions in their water‐contact angles from 120° to 60°. The modified PTFE membranes also show temperature‐responsive properties and protein repulsion features owing to the presence of PNIPAAM and PPEGMA chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2076–2083, 2010     

Compatible and tearing properties of poly(lactic acid)/poly(ethylene glutaric‐co‐terephthalate) copolyester blends

Fourier transform infrared and nuclear magnetic resonance results suggest that the carboxylic acid groups of poly(lactic acid) (PLA) molecules react with the hydroxyl groups of FePol (FP) molecules during the melt‐blending of PLA_xFP_y specimens. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) experiments of PLA and PLA/FP specimens suggest that only small amounts of poor PLA and/or FP crystals are present in their corresponding melt crystallized specimens. In fact, the percentage crystallinity, peak melting temperature, and onset re‐crystallization temperature values of PLA/FP specimens reduce gradually as their FP contents increase. However, the glass transition temperatures of PLA molecules found by DSC and DMA reduce to a minimum value as the FP contents of PLA_xFP_y specimens reach 6 wt %. Further DMA and morphological analysis of PLA/FP specimens reveal that FP molecules are compatible with PLA molecules at FP contents equal to or less than 6 wt %, as no distinguished phase‐separated FP droplets and tan δ transitions were found on fracture surfaces and tan δ curves of PLA/FP specimens, respectively. In contrast to PLA, the FP specimen exhibits highly deformable and tearing properties. After blending proper amounts of FP in PLA, the inherent brittle deformation and poor tearing behavior of PLA were successfully improved. Possible reasons accounting for these interesting crystallization, compatible and tearing properties of PLA/FP specimens are proposed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 913–920, 2010     

Toll-like receptor 9-mediated inhibition of apoptosis occurs through suppression of FoxO3a activity and induction of FLIP expression

Synthetic oligodeoxynucleotides (ODN) with a CpG-motif are recognized by Toll-like receptor 9 (TLR9) and pleiotropic immune responses are elicited. Stimulation of macrophages with TLR9 agonist prevented apoptosis induced by serum deprivation through increased expression of FLICE-like inhibitory protein (FLIP). CpG ODN-mediated anti-apoptosis depended on the TLR9-Akt-FoxO3a signaling pathway. Inhibition of TLR9 by small interfering (si) RNA or an inhibitor suppressed CpG ODN-mediated anti-apoptosis. Analysis of signaling pathways revealed that the anti-apoptotic effect of CpG ODN required phosphorylation of FoxO3a and its translocation from the nucleus to the cytosol. Overexpression of FoxO3a increased apoptosis induced by serum deprivation and CpG ODN blocked these effects through FLIP expression. In contrast, siRNA knock-down of FoxO3a decreased apoptosis by serum deprivation. In addition, Akt activation was involved in CpG ODN-induced phosphorylation of FoxO3a, expression of FLIP, and anti-apoptosis. Taken together, these results demonstrate the involvement of Akt-FoxO3a in TLR9-mediated anti-apoptosis and indicate that FoxO3a is a distinct regulator for FLIP expression.     

Challenges associated with the synthesis of unusual o-carboxamido stilbenes by the Heck protocol: Intriguing substituent effects, their toxicological and chemopreventive implications

The syntheses of fourteen unusual o-carboxamido stilbenes by the Heck protocol revealed surprising complexity related to intriguing substituent effects with mechanistic implications. The unexpected cytotoxic and chemopreventive properties also seem to be substituent dependent. For example, although stilbene 15d (with a 4-methoxy substituent) showed cytotoxicity on HT29 colon cancer cells with an IC(50) of 4.9 μM, the 3,4-dimethoxy derivative (15c) is inactive. It is interesting to observe that the 3,5-dimethoxy derivative (15e) showed remarkable chemopreventive activity in WRL-68 fetal hepatocytes, surpassing the gold standard, resveratrol. The resveratrol concentration needed to be 5 times higher than that of 15e to produce comparable elevation of NQO1.     

Characterization of cellulose fibers electrospun using ionic liquid

Nonwoven fibers of cellulose were obtained by electrospinning of cellulose in an ionic liquid, 1-butyl-3-methylinmidazolium chloride (BMIMCl), which is known to be one of the non-volatile solvents. The electrospinning setup was modified in such a way that the syringe was contained in a constant-temperature chamber because of the high melting point of BMIMCl, and the electrospun fibers were collected on the water, which immediately removed the remnant solvent from the electrospun cellulose fibers. The effect of the viscosity of the cellulose solution in BMIMCl on the size and the structure of the fibers was investigated. The crystalline structure of cellulose was examined by X-ray diffraction. Also, the effect of dimethyl sulfoxide, which was expected to induce swelling of cellulose, was studied. The minimum diameter of the continuous electrospun cellulose fibers obtained in this work ranged between 500 and 800 nm.     

Temperature and humidity aging of poly(p-phenylene-2,6-benzobisoxazole) fibers: Chemical and physical characterization

In recent years, poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers have become prominent in high strength applications such as body armor, ropes and cables, and recreational equipment. The objectives of this study were to expose woven PBO body armor panels to elevated temperature and moisture, and to analyze the chemical, morphological and mechanical changes in PBO yarns extracted from the panels. A 30% decrease in yarn tensile strength, which was correlated to changes in the infrared peak absorbance of key functional groups in the PBO structure, was observed during the 26 week elevated temperature/elevated moisture aging period. Substantial changes in chemical structure were observed via infrared spectroscopy, as well as changes in polymer morphology using microscopy and neutron scattering. When the panels were removed to an ultra-dry environment for storage for 47 weeks, no further decreases in tensile strength degradation were observed. In a follow-on study, fibers were sealed in argon-filled glass tubes and exposed to elevated temperature; less than a 4% decrease in tensile strength was observed after 30 weeks, demonstrating that moisture is a key factor in the degradation of these fibers.