Photochemical Behavior of Single‐Walled Carbon Nanotubes in the Presence of Propylamine

This report describes the photochemical behavior of single‐walled carbon nanotubes (SWNTs) in the presence of propylamine. The SWNTs are characterized by absorption and Raman spectroscopy. The spectral changes due to photoirradiation indicate that reactions occur predominantly with the metallic SWNTs and small‐diameter SWNTs. The detection of amine radicalcation species by ESR spectroscopy reveals photoinduced electron transfer from the amine to the excited SWNTs. After exposure of the photoirradiated SWNTs to air, the characteristic spectra were recovered, except for that of the small‐diameter SWNTs. The results suggest that, after photoreduction of the SWNTs, subsequent selective sidewall functionalization of the small‐diameter SWNTs occurs.     

Electrospinning of nylon-6,6 solutions into nanofibers: Rheology and morphology relationships

The relationship between the rheological properties of nylon-6,6 solutions and the morphology of their electrospun nanofibers was established. The viscosity of nylon-6,6 in formic acid(90%) was measured in the concentration range of 5 wt%-25 wt% using a programmable viscometer. Electrospinning of nylon-6,6 solutions was carried out under controlled parameters. The chemical structure, morphology and thermal properties of the obtained nanofibers were investigated using Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM) and differential scanning calorimetry(DSC), respectively. Entanglement concentration(ce) was found to be 15 wt% and a power law relationship between specific viscosity and solution concentration was observed with exponents of 2.0 and 3.3 for semi-dilute unentangled(c ce) and semi-dilute entangled(c ce) regimes, respectively. The diameter and uniformity of the nanofibers were found to be dependent on the viscosity. Moreover, the average diameter of electrospun nanofibers was found to be dependent on zero shear rate viscosity and normalized concentration(c/ce) in a power law relationship with exponents of 0.298 and 0.816, respectively. For nylon-6,6 solutions, the entanglement concentration(ce = 15 wt%) provides the threshold viscosity required for the formation of a stable polymeric jet during electrospinning and producing uniform beadless fibers. For concentrations less than ce, beaded fibers with some irregularities are formed. DSC analysis showed an increase in crystallinity of all electrospun samples compared to original polymer. Furthermore, Based on FTIR spectroscopy, α phase is dominant in electrospun nanofibers and minor amount of β and γ phases is also available.     

Bucillamine Inhibits UVB-Induced MAPK Activation and Apoptosis in Human HaCaT Keratinocytes and SKH-1 Hairless Mouse Skin

Ultraviolet B (UVB) radiation is known as a culprit in skin carcinogenesis. We have previously reported that bucillamine (N-[2-mercapto-2-methylpropionyl]-L-cysteine), a cysteine derivative with antioxidant and anti-inflammatory capacity, protects against UVB-induced p53 activation and inflammatory responses in mouse skin. Since MAPK signaling pathways regulate p53 expression and activation, here we determined bucillamine effect on UVB-mediated MAPK activation in vitro using human skin keratinocyte cell line HaCaT and in vivo using SKH-1 hairless mouse skin. A single low dose of UVB (30 mJ cm⁻²) resulted in increased JNK/MAPK phosphorylation and caspase-3 cleavage in HaCaT cells. However, JNK activation and casaspe-3 cleavage were inhibited by pretreatment of HaCaT cells with physiological doses of bucillamine (25 and 100 µm ). Consistent with these results, bucillamine pretreatment in mice (20 mg kg⁻¹) inhibited JNK/MAPK and ERK/MAPK activation in skin epidermal cells at 6–12 and 24 h, respectively, after UVB exposure. Moreover, bucillamine attenuated UVB-induced Ki-67-positive cells and cleaved caspase-3-positive cells in mouse skin. These findings demonstrate that bucillamine inhibits UVB-induced MAPK signaling, cell proliferation and apoptosis. Together with our previous report, we provide evidence that bucillamine has a photoprotective effect against UV exposure.     

A new method for estimating the relative binding free energy,derived from a free energy variational principle for the Pim-1-kinase–ligand and FKBP–ligand systems

Journal of Computer-Aided Molecular Design - In this study, a new method is proposed for calculating the relative binding free energy between a ligand and a protein, derived from a free energy...     

Emission Control by Molecular Manipulation of Double‐Paddled Binuclear PtII Complexes at the Air‐Water Interface

Molecular functions depend on conformations and motions of the corresponding molecular species. An air–water interface is a suitable asymmetric field for the control of molecular conformations and motions under a small applied force. In this work, double‐paddled binuclear Pt^II complexes containing pyrazole rings linked by alkyl spacers were synthesized and their orientations and emission properties dynamically manipulated at the air–water interface. The complexes emerge from water with concurrent variation of interface orientation of the planes of the Pt^II complexes from perpendicular to parallel during mechanical compression suggesting a unique ‘submarine emission‘. Phosphorescence of the complexes is quenched at the air–water interface prior to monolayer formation with intensities subsequently rapidly increasing during monolayer compression. These results indicate that asymmetric reactions and motions might be controlled by applying mechanical force at the air–water interface.     

Photopolyaddition of dithiols to bis(alkoxyallene)s

Polyadditions of 1,4-benzenedithiol (BDT) to bis(alkoxyallene)s, such as 1,4-bis(allenyloxy)xylene (3) and 1,4-bis(allenyloxy) benzene (4) , were carried out in benzene at 25°C by irradiation with a high pressure mercury lamp. Thiol groups were added to the terminal double bonds of the allenyloxy groups selectively to afford polymers containing reactive carbon–carbon double bonds in the main chain, similar to the radical polyadditions using azobis(isobutyronitrile) (AIBN). The molecular weight of the polymer obtained from BDT and 3 was 10 times higher than that of the polymer produced in the radical polyaddition with AIBN; whereas the molecular weight of the polymer from BDT and 4 was similar to that in the radical polyaddition, probably because of poor solubility of 4 and the polymer toward benzene. The geometrical structure of carbon–carbon double bonds in the polymer isomerized from an E to Z structure with reaction time by virtue of both the addition elimination of thiyl radical to the double bonds and the UV irradiation. © 1996 John Wiley & Sons, Inc.     

A novel polyaddition of bifunctional acetylenes containing electron-withdrawing groups. III. Synthesis of polymers having β-alkoxyenoate moieties by the reaction of internal diynes with diols

Tri-n-butylphosphine-catalyzed polyadditions of activated internal diynes (bifunctional β-substituted propiolate, 1B and 1C ) with diols are described. Although a terminal bispropiolate ( 1A ) could not produce soluble polymers, with secondary diols, the polyaddition of 1B or 1C with primary as well as secondary diols gave corresponding polymers ( 3 , only composed of E isomeric units) in high yield. The rate of the present polyaddition was estimated by a model reaction of benzyl alcohol with methyl 2-heptynoate ( 4 ), from which the introduction of alkyl groups at the β-position of propiolate moieties was found to decrease the rate of the reaction by 80 times. Furthermore, the rate-determining step on this polymerization system was speculated to be a protonation step of zwitterionic intermediates with protons from diols. © 1996 John Wiley & Sons, Inc.     

First preparation and structural determination of 1,1-disubstituted dibenzo[bc,fg][1,4]silathiapentalene derivatives by x-ray crystallographic analysis and MO calculations

1,1-Dimethyldibenzo[bc,fg][1,4]silathiapentalene ( 1a ) was prepared by treatment of 1,9-bis(methyl-sulfinyl)dibenzothiophene with EtMgBr or of dibenzothiophene with n-butyllithium, and then with dimethyl dichlorosilane. The structure of 4,4-dimethyl-dibenzo[bc,fg][1,4]silathiapentalene 1-oxide ( 2 ), obtained by oxidation of compound 1a with mCPBA, was determined by X-ray crystallographic analysis. The structure of compound 2 determined experimentally was compared to the structure obtained by semiempirical molecular orbital calculations (AM1). The MO calculations of compound 1a and its phenyl analog 1b were also performed by AM1 to evaluate their structures. © 1996 John Wiley & Sons, Inc.     

Synthesis and radical ring-opening polymerization behavior of vinylcyclopropane bearing six-membered cyclic acetal moiety

Synthesis and radical ring-opening polymerization of vinylcyclopropane bearing six-membered cyclic acetal moiety, 1-vinyl-4,8-dioxaspiro[2.5]octane (1), were carried out. 1 was prepared by the reaction of 1,1-dichloro-2-vinylcyclopropane and 1,3-propanediol in DMF in the presence of a base. Radical polymerization of 1 was carried out in the presence of an appropriate initiator (3 mol % vs. 1) at 60 and 120°C in degassed sealed ampoules for 20 h. A colorless transparent viscous polymer was obtained by the isolation with preparative HPLC. The structure of poly(1) was determined to consist of two 1,5-ring-opened units and a unit bearing no olefinic moiety. The difference of the activation energies for the ring-opening reaction of the cyclopropane ring calculated by the molecular orbital method could explain the selectivity in the direction of the cleavage of the cyclopropane ring. Acid hydrolysis of poly(1) afforded the corresponding polyketone in quantitative conversion. © 1996 John Wiley & Sons, Inc.