Synthesis of end‐functionalized poly(methyl methacrylate) by ruthenium‐catalyzed living radical polymerization with functionalized initiators

A series of functionalized 2‐bromoisobutyrates and 2‐chloro‐2‐phenylacetates led to α‐end‐functionalized poly(methyl methacrylate)s in Ru(II)‐catalyzed living radical polymerization; the terminal functions included amine, hydroxyl, and amide. These initiators were effective in the presence of additives such as Al(Oi‐Pr)₃ and n‐Bu₃N. The chlorophenylacetate initiators especially coupled with the amine additive gave polymers with well‐controlled molecular weights (M_w/M_n = 1.2–1.3) and high end functionality (F_n ～ 1.0). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1937–1944, 2002     

Iron‐catalyzed living radical polymerization of acrylates: Iodide‐based initiating systems and block and random copolymerizations

A half‐metallocene iron iodide complex [Fe(Cp)I(CO)₂] induced living radical polymerization of methyl acrylate (MA) in conjunction with an iodide initiator [(CH₃)₂C(CO₂Et)I, 1 ] and Al(Oi‐Pr)₃ to give polymers of controlled molecular weights and narrow molecular weight distributions (MWDs) (M_w/M_n < 1.2). With the use of chloride and bromide initiators, the MWDs were broader, whereas the molecular weights were similarly controlled. Other acrylates such as n‐butyl acrylate (nBA) and tert‐butyl acrylate (tBA) can be polymerized with 1 /Fe(Cp)I(CO)₂ in the presence of Ti(Oi‐Pr)₄ and Al(Oi‐Pr)₃, respectively, to give living polymers. The 1 /Fe(Cp)I(CO)₂ initiating system is applicable for the synthesis of block and random copolymers of acrylates (MA, nBA, and tBA) and styrene of controlled molecular weights and narrow MWDs (M_w/M_n = 1.2–1.3). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2033–2043, 2002     

Human neural stem cell growth and differentiation in a gradient-generating microfluidic device

This paper describes a gradient-generating microfluidic platform for optimizing proliferation and differentiation of neural stem cells (NSCs) in culture. Microfluidic technology has great potential to improve stem cell (SC) cultures, whose promise in cell-based therapies is limited by the inability to precisely control their behavior in culture. Compared to traditional culture tools, microfluidic platforms should provide much greater control over cell microenvironment and rapid optimization of media composition using relatively small numbers of cells. Our platform exposes cells to a concentration gradient of growth factors under continuous flow, thus minimizing autocrine and paracrine signaling. Human NSCs (hNSCs) from the developing cerebral cortex were cultured for more than 1 week in the microfluidic device while constantly exposed to a continuous gradient of a growth factor (GF) mixture containing epidermal growth factor (EGF), fibroblast growth factor 2 (FGF2) and platelet-derived growth factor (PDGF). Proliferation and differentiation of NSCs into astrocytes were monitored by time-lapse microscopy and immunocytochemistry. The NSCs remained healthy throughout the entire culture period, and importantly, proliferated and differentiated in a graded and proportional fashion that varied directly with GF concentration. These concentration-dependent cellular responses were quantitatively similar to those measured in control chambers built into the device and in parallel cultures using traditional 6-well plates. This gradient-generating microfluidic platform should be useful for a wide range of basic and applied studies on cultured cells, including SCs.     

Colorimetric anion chemosensor based on 2-aminobenzimidazole: naked-eye detection of biologically important anions

We synthesized a novel colorimetric anion chemosensor bearing benzimidazole motifs as recognition sites in the pods of the receptor. The addition of tetrabutylammonium salts of F⁻ or AcO⁻ to the solution of receptor caused dramatic color changes from colorless to yellow, which was clearly visible to the naked eye. The receptor showed no significant changes on addition of other anions such as Cl⁻, Br⁻, I⁻, NO₃⁻, and H₂PO₄⁻.     

Adsorption of atomic hydrogen on single-walled carbon nanotubes

We have investigated atomic and electronic structures of hydrogen-chemisorbed single-walled carbon nanotubes (SWCNTs) by density functional calculations. We have searched for relative stability of various hydrogen adsorption geometries with coverage. The hydrogenated SWCNTs are stable with coverage of H/C, theta >/= 0.3. The circular cross sections of nanotubes are transformed to polygonal shapes with different symmetries upon hydrogen adsorption. We find that the band gap in carbon nanotubes can be engineered by varying hydrogen coverage, independent of the metallicity of carbon nanotubes. This is explained by the degree of sp(3) hybridization.     

Role of sphingomyelin-MAPKs pathway in heat-induced apoptosis

The role of sphingomyelinase (SMase) activation and mitogen activated protein kinases (MAPKs) activation in cellular apoptosis was investigated during the hyperthermic treatment of HL-60 human leukemia cells. Treating the cells for 1 h at 43(o)C caused more than 50% of cellular apoptosis within several hours. The neutral-SMase activity in the cells treated for 1 h at 42(o)C was slightly increased but decreased in the cells treated at 43(o)C or 44(o)C for the same period whereas the acid SMase activity was slightly increased after heating the cells at 42(o)C and 43(o)C and markedly increased at 44(o)C for 1 h. Treatment of cells with inhibitors of SMase activation and ceramide formation significantly reduced the heat-induced apoptosis. Three major families of mitogen-activated protein kinases (MAPKs), i.e. ERK1/2, p38 and JNK, were activated by the hyperthermic treatment of cells. Inhibition of ERK1/2 with PD98059 exerted little effect on the heat-induced apoptosis and p38 inhibition with SB203580 slightly lessened apoptosis whereas, inhibition of JNK with SP600125 markedly suppressed the heat-induced apoptosis. These results indicate that heat-shock induced the activation of SMase, particularly acid-SMase, thereby causing apoptosis and that JNK played a pivotal role in heat-induced apoptosis in HL-60 leukemia cells.     

Pretilt angle generation by UV exposure during imidization of polyimide

We investigated pretilt angle generation and liquid crystal (LC) alignment by ultraviolet exposure during the imidization of polyimide (PI). The generated pretilt angle of a nematic (N) LC using an in situ photo-alignment method is smaller than that using a conventional photo-alignment method on a surface of PI having side chains. The NLC pretilt angles using an in situ photo-alignment method injected at isotropic phase increased with annealing were observed.     

A micro/nanocasting method for replicating soft micro/nanosurface structures using a dynamic electrical field

We propose a new electric field-induced micro/nanocasting method to replicate soft patterns using micro/nanocasting techniques without pressure. The process uses an alternating current (AC) electrical field and rotation of one electrode, generating a dynamic electrical field that induces electrokinetic flow motion in a dielectric solution (polydimethylsilane, PDMS). We used a lotus leaf as a replication template and characterised the PDMS flow motion to observe the effects of various process parameters (e.g., electrical field strength, rotation speed of an electrode, and electrode shape). The unstable flow motion was significantly dependent on the processing parameters, especially the rotation speed of the electrode. Using the optimised processing conditions, the replication efficiency was about 88%. We believe that this method has potential for fabricating soft micro/nanosized structures.