Synthesis and properties of poly(acrylamide)s containing both long chain alkyl groups and phosphatidylcholine analogues in the side chains

A series of new phospholipid analogous acrylamide monomers ( 4a–e ) containing long alkyl chains as hydrophobic groups and containing phosphatidylcholine analogues as hydrophilic group were synthesized in high yields. The homopolymerizations and copolymerization ( 4b with 4e ) were carried out in the presence of a radical initiator. The structures and thermal properties of these polymers were investigated by x-ray diffraction analysis, DSC, and polarizing microscopy measurements. It has been revealed that these homopolymers ( 5b, 5c , and 5d ) which bear saturated long-hydrocarbon chains in the side chains exhibited not only orderly stacked bilayer structures at room temperature but also clear liquid crystalline behavior within a wide temperature range. The viscosity behavior of all polymers was found similar to usual polyelectrolytes in porlar solvent. The polymers obtained were also characterized by ¹H-NMR, IR, and melting point, respectively. © 1996 John Wiley & Sons, Inc.     

Theoretical study on decomposition of γ-halo allylalkoxide and β-halo acrylate ions

β, γ-Substituted γ-halo allylalkoxide ions decompose to form a halogen ion, formaldehyde, and an alkyne under mild conditions, for example at room temperature. The E isomer does not differ from the Z isomer in terms of activation energy. We attempted to shed light on the mechanism of the reaction by using ab initio molecular orbital calculations. The observed propensity was confirmed by the present calculation on model molecules, γ-chloro allylalkoxide ions. We conducted further calculations and compared the alkoxide results with a similar reaction of β-haloacrylate ions that release carbon dioxide instead of formaldehyde. This similar reaction needs heating as high as 150°C. The activation energy of the acrylate ions (36–39 kcal mol⁻¹) was calculated to be about 10 kcal mol⁻¹ higher than that of the alkoxide ions. The activation energy of the E acrylate ion is smaller by 0.8 kcal mol⁻¹ than that of the Z isomer at the MP2/6-31+G**//RHF/6-31+G* level of theory. This is consistent with experimental results. While the ready deprotonation from the carboxylic group does not activate the acrylate ion very much, the alkoxide ion is destabilized to a great degree in the process of anion formation. The difficulty in deprotonation that proceeds from the neutral molecule is seen in the difference in the activation energies for the decomposition of the corresponding anions. Therefore, the pK _a of a hydroxy or a carboxylic group plays the leading role in determining the magnitude of activation energies of allyl halides with a negatively charged fragment. Received: 2 July 1998 / Accepted: 9 September 1998 / Published online: 8 February 1999     

Study on thermal degradation mechanisms of comb polyacrylates containing long fluorocarbon side chains by TG/FTIR

Thermal degradation of two series of polyacrylates containing long fluorocarbon chains [abbr.: PF_nA {HCF₂(CF₂)_n−1  CH₂ O C(O) , n = 4, 6, 8, 10} and abbr.: PFF_nEA {CF₃(CF₂)_n−1  CH₂CH₂ O C(O) , n = 6, 8, 10}] was investigated by TG /FTIR. Thermal degradation behavior of polymers changed depending on the type of tie groups, which link the fluorocarbon chains to the main chain, and also on the length of fluorocarbon chains. It was clarified that the apparent activation energies (ΔE_a ) of PF_nA series obtained by Ozawa's method varied in the order of PF₄A > PF₆A > PF₈A > PF₁₀A, while those of PFF_nEA series having tie group of  CH₂ CH₂ O C(O) were almost constant. The results for PF_nA series (tie group:  CH₂ O C(O) ) are attributable to the shield effect of long fluorocarbon chains on the back‐biting reaction in the thermal degradation of comb polymers rather than the change of C C bond dissociation energy in the main chain. It was found that TG curves of PFF_nEA series were shifted to the lower temperature region than those of PF_nA. This result can be attributable to the scission of side groups followed by the evaporation of fluorocarbon compounds and carbon dioxide. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2794–2803, 2000     

Characterization of poly(styrene‐co‐methacrylonitrile)s obtained by low‐temperature radiation polymerization and thermal degradation behavior measured by Py‐GC and CRTG

Poly(styrene‐co‐methacrylonitrile)s were polymerized in solutions with different polarities (n‐hexane and THF) by low‐temperature γ‐ray irradiation polymerization in a temperature range of −83.6–30 °C. It was found by IR measurement that the composition of the copolymers changed remarkably due to the effects of the polarity of solvents and the polymerization temperature. The thermal degradation behavior in the flash pyrolysis and in the continuous heating pyrolysis of these copolymers was measured by Py‐GC and controlled rate thermogravimetry (CRTG). The effects of the copolymer composition and sequence distribution on the thermal degradation behavior were investigated. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3569–3577, 2000     

An Optochemical Oxygen Scavenger Enabling Spatiotemporal Control of Hypoxia

We present an optochemical O₂ scavenging system that enables precise spatiotemporal control of the level of hypoxia in living cells simply by adjusting the light intensity in the illuminated region. The system employs rhodamine containing a selenium or tellurium atom as an optochemical oxygen scavenger that rapidly consumes O₂ by photochemical reaction with glutathione as a coreductant upon visible light irradiation (560–590 nm) and has a rapid response time, within a few minutes. The glutathione-consuming quantum yields of the system were calculated as about 5 %. The spatiotemporal O₂ consuming in cultured cells was visualized with a hypoxia-responsive fluorescence probe, MAR. Phosphorescence lifetime imaging was applied to confirmed that different light intensities could generate different levels of hypoxia. To illustrate the potential utility of this system for hypoxia research, we show that it can spatiotemporally control calcium ion (Ca²⁺) influx into HEK293T cells expressing the hypoxia-responsive Ca²⁺ channel TRPA1.