The cellular irradiation-cross-linked polypropylene films treated by a hot-press process are corona charged to be piezoelectric. For the samples charged at room temperature, quasistatic piezoelectric d33 coefficients up to 400pC∕N are obtained. The d33 coefficients are slightly dependent on pressure in the range up to 50kPa. The d33 values decrease to 30% when the samples are exposed to 90°C for 1day; a preaging treatment improves the thermal stability of d33. The dominant drift path of the detrapped charges is from one void surface to the adjacent void surface through the bulk of the solid.
Small-molecule fluorescent probes in combination with fluorescent microscopy can be a powerful tool to provide real-time detection and high spatiotemporal resolution of transient molecules in cells and bodies. For the design of fluorescent probes for transient molecule imaging, high detection sensitivity is crucial. In this report, two new fluorescent probes, 8-(3,4-diaminophenyl)-4,4-difluoro-4-bora-3a,4a-diaza-di(1,2-dihydro)naphtho[b,g]-s-indacene (DANPBO-H) and 8-(3,4-diaminophenyl)-1,7-dimethyl-4,4-difluoro-4-bora-3a,4a-diaza-di(1,2-dihydro)naphtho[b,g]-s-indacene (DANPBO-M), have been developed for nitric oxide (NO) imaging. The detection sensitivity has been efficiently improved by use of these probes through increasing NO detection signals and decreasing background fluorescence. Fluorescence in the far-red region is enhanced by 400- and 550-fold after reaction with NO is achieved and remains stable for at least 24 h under the irradiation of xenon lamp. Excitation and emission wavelengths longer than 600 nm and excellent intracellular retention of these probes and their NO products create dark background inside and outside cells and tissues. What is more, the excellent intracellular retention of these compounds is obtained by their strong lipophilicity, which is a novel design concept diametrically opposite to the traditional approaches. The high sensitivity and dark background make DANPBO-H and DANPBO-M competitive for NO imaging in cells and tissues. The lipophilicity-based intracellular retention mechanism as a design strategy has great potential in the development of fluorescent probes for bioimaging.
We report ap hosphine-catalyzed ring opening of electron-deficient alkylidenecyclopropanes (ACPs) to generate allylic phosphonium zwitterions that resemble the well-studied phosphine-allene adducts but exhibit distinct properties.T he potent reactivity of these intermediates has been demonstrated in three types of substrate-controlled phosphine-catalyzed rearrangements of alkylidenecyclopropylketones,w hichc hemoselectively affordt ri-and tetrasubstituted furans,a nd trisubstituted dienones in good yields.Alkylidenecyclopropanes (ACPs) [1] are at ype of extremely versatile yet readily available [2] building blocks in organic synthesis.B yv irtue of significant ring strain, [3] ap lethora of ring-opening reactions of ACPs have been developed for the construction of various molecular architectures. [4] To date,the reactivity of ACPs has been predominantly unlocked by transition-metal catalysis, [1d,p] Lewis acid catalysis, [1b,i,n] radical-induced reactions, [5] and thermally induced cyclizations. [6] However,t othe best of our knowledge,t he organocatalytic activation of ACPs has not been reported.Phosphine catalysis [7] has emerged as afertile land for new reaction discovery.I np articular, electron-deficient allenes 1 exhibit remarkable reactivity in phosphine-catalyzed annulation reactions through apivotal zwitterionic intermediate A (Scheme 1). [7d,e,g,j] [3+ +2], [8] [4+ +2], [9] and [4+ +1] [10] annulations from the Lu, Kwon, and Tong groups,respectively,represent seminal advances in this area and have inspired am yriad of annulations, [11] including asymmetric variants. [12] In an effort to expand the field of phosphine catalysis,w es urmised that electron-deficient alkylidenecyclopropanes (ACPs) 2 might be av iable substrate for nucleophilic phosphine catalysis, leading to an intriguing homologue intermediate B with unexplored reactivity and potential for new reaction discovery (Scheme 1). In continuation of our research in Lewis base catalysis, [13] we report herein the phosphine-catalyzed ringopening of electron-deficient ACPs in three types of substrate-controlled rearrangements of alkylidenecyclopropylketones,w hich chemoselectively afford tri-and tetrasubstituted furans,and trisubstituted dienones in good yields.Inspired by the elegant palladium-catalyzed rearrangement reactions of alkylidenecyclopropylketones reported by Ma and co-workers, [14] we initially examined the ring-opening reactivity of alkylidenecyclopropylketone 2-1 a under aset of phosphine-catalyzed conditions (Table 1). Gratifyingly,w ith acatalytic amount of PPh 3 (20 mol %) in DMSO at 120 8 8C, 2-1a underwent af acile rearrangement to afford trisubstituted furan 3a in 78 %yield (Entry 1). [15] Arange of alkyl and aryl phosphines were examined (Entries 2-8), in which P(4-MeOC 6 H 4 ) 3 outperformed all others tested, providing 3a in 81 %yield. Anucleophilic amine DABCO also promoted the ring opening of 2-1 a but generated 3-alkylidene-2,3-dihydrofuran 3a' ' [14b] in 54 %yield (Entry 9). Among several common solvents tested (Entrie...
This paper examines the effects of nano-scale titanium coatings, and micro-groove/micro-grid patterns on cell/surface interactions on silicon surfaces. The nature of the cellular attachment and adhesion to the coated/uncoated micro-textured surfaces was elucidated by the visualization of the cells and relevant cytoskeletal & focal adhesion proteins through scanning electron microscopy and immunofluorescence staining. Increased cell spreading and proliferation rates are observed on surfaces with 50 nm thick Ti coatings. The micro-groove geometries have been shown to promote contact guidance, which leads to reduced scar tissue formation. In contrast, smooth surfaces result in random cell orientations and the increased possibility of scar tissue formation. Immunofluorescence cell staining experiments also reveal that the actin stress fibers are aligned along the groove dimensions, with discrete focal adhesions occurring along the ridges, within the grooves and at the ends of the cell extensions. The implications of the observed cell/surface interactions are discussed for possible applications of silicon in implantable biomedical systems.
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