New biocompatible thermo-reversible hydrogels from PNiPAM-decorated amyloid fibrils

New biocompatible temperature-responsive hydrogels have been obtained by using unprecedented low concentration of amyloid fibril-PNiPAM hybrids. The viscoelasticity of the hydrogels can be finely controlled by tuning the PNiPAM layers without changing the structure or concentration of the amyloid fibrils.     

Antioxidant and antityrosinase activities of various extracts from the fruiting bodies of Lentinus lepideus

Lentinus lepideus is an edible mushroom currently available in Korea. The acetone, methanol and hot water extracts were prepared and assayed for their antioxidant and antityrosinase inhibitory activities. The hot water extract showed the strongest β-carotene-linoleic acid inhibition compared to the other extracts. At 8 mg/mL, the methanolic extract showed a high reducing power of 1.21. The acetone and methanol extracts were more effective in scavenging DPPH radicals than the hot water extract. The strongest chelating effect was obtained from the methanolic extract. Xanthine oxidase and tyrosinase inhibitory activities of the acetonic, methanol and hot water extracts increased with increasing concentration. Gallic acid, chlorogenic acid, vanillin, naringin, naringenin, formononetin, and biochanin-A were detected in the acetonitrile and hydrochloric acid (5:1) solvent extract. This study suggests that fruiting bodies of L. lepideus can potentially be used as a readily accessible source of natural antioxidants.     

Synthesis and thermal studies of bisphenol-A based bismaleimide

The compound 2,2-bis[4-(4-maleimidophenoxy phenyl)]propane was prepared by the imidization of bisamic acid of 2,2-bis(4-aminophenoxy phenyl)propane. Various nanoclays were blended with this bismaleimide and thermally cured. The structural characterization of the synthesized materials and the thermal properties of the bismaleimide and their blends were investigated through FTIR, ¹H and ¹³C NMR, differential scanning calorimetry and thermo gravimetric analysis. Among the various clays investigated, Cloisite 15A shows strong influence on the cure exotherm of bismaleimide. Introduction of clay mineral into bismaleimide shifts the onset of curing exotherm to higher temperature and is nearly 40 °C. The thermal stability of the clay loaded cured bismaleimide increases and the presence of clay particles in the cured bismaleimide matrix enhances the char formation.     

Hydroxyl Substituent Chemical Shift (SCS) Effects in Alcohols: The 17O NMR of Diols

The ¹⁷O NMR spectra for a series of saturated diols were investigated. From these studies both hydroxyl induced substituent chemical shift (SCS) effects of hydroxyl oxygen ¹⁷O NMR chemical shifts were determined. In addition, linear correlations between the ¹⁷O chemical shift of the hydroxyl oxygen (ROH) and the ¹³C chemical shift for the methyl group in the corresponding hydrocarbon (RCH₃) were obtained.

     

Laser Flash Photolysis of 2,2'-Dithiobls(pyridine N-oxide): Reactivity of N-Oxypyridyl-2-thio Radical

Abstract— Reaction kinetics of radicals produced by the nanosecond laser flash photolysis of 2,2'-dithiobis(pyridine N -oxide) and related compounds have been studied. The transient absorption band at 360 nm was attributed to the radical in which the unpaired electron mainly localizes on the S atom ( N -oxypyridyl-2-thio radical). The reactivities of the radical for conjugated dienes are lower than those of the pyridyl-2-thio radical, suggesting that a considerable unpaired electron density on the S atom delocalizes onto the N -oxypyridine moiety. The addition reaction rate of the radical to the conjugating diene was accelerated with hydrogen-bonding solvents and with addition of the cation, which may stabilize the N+-O^- canonical structure, increasing the unpaired electron density on the S atom. By the photolysis of N -hydroxypyridine-2-thione, the N-O bond was predominantly dissociated producing a pyr-idyl-2-thio radical. By the photolysis of its anion, photoejection took place followed by the N-O bond fission, yielding pyridine-2-thione.     

Crown ether complexes of potassium and thallium(I) 2- and 4-nitrophenoxides

18-Crown-6 and dicyclohexano-18-crown-6 complexes of potassium 2- and 4-nitrophenoxide, and 18-crown-6 complexes of thallium(I) 2- and 4-nitrophenoxide have been synthesized. Solvent effects on the visible spectra of the nitrophenoxide anions are independent of the nature of the cation and the nature of the complexing agent. The 18-crown-6 complex of thallium(I) 2-nitrophenoxide is a 1:2 complex. All the other complexes are 1:1. X-ray crystallographic examination of the potassium dicyclohexano-18-crown-6 complexes showed the potassium ion is octacoordinated in the 2-nitrophenoxide and heptacoordinated in the 4-nitrophenoxide.     

Magnetic alignment of aqueous CTAB in nematic and hexagonal liquid crystalline phases investigated by spin-1 NMR

Spin-1 NMR has been used to characterize the magnetically aligned nematic and hexagonal liquid crystalline phases of aqueous cetyltrimethylammonium bromide (CTAB). A nematic/hexagonal biphasic region has been identified for the first time in this system. The nematic phase is characterized by an order parameter of smaller magnitude and greater temperature dependence. Magnetic alignment kinetic rates of the two phases differ greatly, with the nematic phase showing magnetic alignment much faster than the hexagonal phase. Equilibration has been monitored over time by measuring the change in quadrupole splitting as a function of temperature. As the sample equilibrates the temperature dependence of the splitting decreases logarithmically. This work also demonstrates how the phase and order of the liquid crystal can be manipulated during the early part of equilibration.