Effect of freeze-drying and rehydrating treatment on the thermo-responsive characteristics of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) microspheres

Investigations on the effect of freeze-drying and rehydrating treatment on equilibrium volume changes and on the thermo-response rate of poly(N-isopropylacrylamide) (PNIPAM) microspheres were carried out. The experimental results showed that freeze-drying and rehydrating treatment had nearly no effect on the low critical solution temperature and equilibrium volume changes of PNIPAM microspheres. Furthermore, when the PNIPAM microspheres were frozen in only liquid nitrogen through rapid cooling, the response rate of PNIPAM microspheres to environmental temperature change was nearly not affected by the treatment, which was surprisingly different from the macroscopic hydrogel. The dimension effect was responsible for this phenomenon. The micron-sized PNIPAM microsphere itself has a much quicker response rate compared with the bulky hydrogel because the characteristic time of gel deswelling is proportional to the square of a linear dimension of the hydrogel.     

Directed assembly of chiral oxidovanadium(V) methoxides into C4-symmetric metal(I) vanadate-centered quadruplexes: synergistic K+- and Ag+-specific transport

A directed assembly process to form C4-symmetric, vanadate-centered quadruplexes, for the first time, from a given chiral oxidovanadium(V) complex allows for highly efficient K+- and Ag+-specific transport from aqueous phase containing three other alkali metal cations into organic solvents, reminiscent of the K+ specific transport exerted by four homochiral glycine residues of the opening site in KcsA membrane protein.     

Facile preparation of self-assembled hydrogel-like GdPO4*H2O nanorods

Of the methods employed in the preparation of one-dimensional lanthanide phosphate (LnPO(4)) nanorods/nanowires, such as GdPO(4), the hydrothermal method has been mainly used as a synthetic route. In this study, we report a facile low-temperature solution approach to prepare GdPO 4*H(2)O nanorods by simply refluxing GdCl(3) and KH(2)PO(4) for only 15 min at 88 degrees C, an approach that can easily be scaled up by increasing the reagent amounts. We observed a highly viscous macroscopic hydrogel-like material when we mixed as-prepared GdPO(4)*H(2)O nanomaterials with H(2)O. Hydrogels are an important class of biomaterials. Their building blocks, normally formed from protein-, peptide-, polymer-, and lipid-based materials, offer three-dimensional scaffolds for drug delivery, tissue engineering, and biosensors. Our preliminary results showed that GdPO(4)*H(2)O hydrogels could be used for encapsulation and drug release, and that they were biocompatible, acting as scaffolds to foster cell proliferation. These findings suggested that they might have biomedical uses. Our findings may lead to the creation of other inorganic nanomaterial-based hydrogels apart from the organic and biomolecular protein-, peptide-, polymer-, and lipid-based building blocks.     

Flow cytometric characterization of interactions between U-937 human macrophages and positively charged catanionic vesicles

Catanionic vesicles are considered a potential alternative to liposomes for drug delivery systems because of their greater stability and lower cost. Before using catanionic vesicles in vivo, their interactions with macrophages must be fully understood because they are primarily removed from circulation by the macrophages of the mononuclear phagocyte system. Using flow cytometry, we examined the intracellular responses-reactive oxygen species (ROS) content, mitochondrial membrane potential, cell size and complexity, and cell cycle profiles-in U-937 human macrophages treated with positively charged catanionic vesicles. Kinetic hydrogen peroxide production initially increased at lower concentrations (4-10nM) but declined at higher concentrations (40 nM and 80 nM) over the entire incubation period. Superoxide content generation, however, increased over the entire concentration range and incubation period. Catanionic vesicles decreased mitochondrial membrane potential for every concentration after 4h of incubation but caused a significant fluctuation in mitochondrial membrane potential at 6h. After 6h of incubation, catanionic vesicles produced more changes in cell size and complexity than after 4h. The increase in the subG1 population of cells treated with catanionic vesicles at higher doses indicated that apoptosis progressed. Positively charged catanionic vesicles induced different activated patterns of ROS generation and changes in mitochondrial membrane potential than did cationic liposomes. The nature of the interactions between macrophages and catanionic vesicles is of great importance for the design of safer and more effective delivery systems for macrophages. Our findings contribute to a better understanding of the molecular action of catanionic vesicles in the cellular system.     

Chitosan–poly(acrylic acid) nanofiber networks prepared by the doping induction of succinic acid and its ammonia‐response studies

Chitosan–poly(acrylic acid) (CS–PAA) composite membrane with a 3D network nano‐structure was prepared using an electrostatic interaction process by adding succinic acid as a branch promoter. Variations of the final solution pH values, concentration of CS, and PAA/CS volume ratio were examined systematically for their effects on average fiber diameter size, intensity of surface charge, and tendency of network formation. It was found that nanofiber size was affected by the mixing ratio of PAA and CS, the concentration of CS, and the final pH of the CS–PAA solution. The smallest diameter size distribution of the scaffold can be obtained when the PAA/CS ratio is in the range of 2:1–1:2 in a pH 3 environment. Negative charge nanofibers prepared using PAA and CS in a ratio of 2:1 in pH 3 environments had an average diameter of 215 nm. The formation of the interconnecting 3D self‐organized network structure can be built up with limited parasitic branching by crystallized succinic acid. The gas response to ammonia, including sensitivity and response time, was evaluated using impedance spectroscopy at room temperature. The results of sensing experiments indicate that the sensitivity of nanofibrous membrane (NM)‐coated sensors was eight times higher than that of continuous film‐coated sensors. NM‐coated sensors exhibited high sensitivity towards a low concentration of ammonia, as low as 50 ppm at a relative humidity of 45%. Copyright © 2008 John Wiley & Sons, Ltd.     

A novel microfluidic driver via AC electrokinetics

A novel ac electrokinetic microfluidic driver based on alternating current electro-osmosis flow induced by asymmetrically capacitance/chemistry-modulated microelectrode arrays has been successfully developed and demonstrated. Asymmetric capacitance modulation (ACM) is made of comb electrode arrays and parts of individual electrode surfaces are modulated/deposited with a SiO(2) dielectric layer. This proposed design can be utilized to shift the optimal operation frequency of maximum velocity to a higher frequency to minimize electrolytic bubble generation and enhance micropumping performance. The pumping velocity, described in this paper, is measured via the tracing of microbeads and is a function of applied potential, signal frequency, buffer concentration, and dielectric layer thickness. A maximum pumping velocity up to 290 microm s(-1) in 5 mM buffer solution with the applied potential of 10 Vpp is observed in our prototype device, and the estimated maximum flow rate is up to 26.1 microl h(-1). This is the first successful demonstration regarding bubble-free ac electrokinetic micropumping via such asymmetrically capacitance-modulated electrode arrays. Design, simulation, microfabrication, experimental result, and theoretical model are described in this paper to characterize and exhibit the performance of the proposed novel bubble-free ac electrokinetic microfluidic driver.     

Design, synthesis, and biological evaluation of novel alkenylthiophenes as potent and selective CB1 cannabinoid receptor antagonists

A novel class of (5-(pent-1-enyl)thiophen-2-yl)pyrazole antagonists was discovered, many of which exhibited potent CB1 activity and good CB1/2 selectivity, suggesting that along with a 1,3-transposition of the carbonyl of the pyrazole 3-carboxamide, bioisosteric replacement of the conventional pyrazole 5-aryl group with a thienyl ring substituted with an appropriate alkenyl moiety is viable.     

Dinickel complexes of disubstituted benzoate polydentate ligands: mimics for the active site of urease

Two dinickel mimics, [LNi2(DMF)4](ClO4)3 () and [L'Ni2(CH3CN)4](ClO4)3 (), for the active site of urease supported by a disubstituted benzoate polydentate ligand were synthesized and fully characterized, subsequently addition of urea afforded two urea adducts, [LNi2(urea)4](ClO4)3 () and [L'Ni2(urea)4](ClO4)3 ().     

A novel thermoresponsive hydrogel with ion-recognition property through supramolecular host-guest complexation

A novel thermoresponsive hydrogel with ion-recognition property was prepared via free-radical cross-linking copolymerization of N-isopropylacrylamide (NIPAM) with benzo-18-crown-6-acrylamide (BCAm) as host receptor. Both chemical structures and stimuli-sensitive properties of the prepared poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) P(NIPAM-co-BCAm) hydrogel were characterized. The smart hydrogel could respond to both temperature and ion stimuli. When the crown ether units captured Ba2+ and formed stable BCAm/Ba2+ host-guest complexes, the lower critical solution temperature (LCST) of the hydrogel increased due to the repulsion among charged BCAm/Ba2+ complex groups and osmotic pressure within the hydrogel. Whereas crown ethers captured Cs+, the LCST shifted to a lower temperature because of the formation of 2:1 sandwich complexes. Unexpectedly, the LCST of the cross-linked P(NIPAM-co-BCAm) hydrogel in K+ solution did not shift to a higher temperature, which was definitely different from the previously reported linear P(NIPAM-co-BCAm) copolymer in K+ solution. The results of this work provide valuable information for development of dual thermo- and ion-responsive hydrogels which have potential applications in drug controlled-release systems or biomedical fields.     

Real-Time In Situ Volatile Organic Compound Sensing by a Dual-Emissive Polynuclear Ln-MOF with Pronounced LnIII Luminescence Response

Lanthanide metal–organic frameworks (Ln-MOFs) are promising for luminescence detection of volatile organic compound (VOC) vapors, but usually suffer from the silent or quenched Ln³⁺ emission. Herein, we report a new dual-emissive Eu-MOF composed of the coordinatively unsaturated Eu₉ clusters that afford abundant open metal sites to form a confined “binding pocket” to facilitate the preconcentration and recognition of VOCs. Single-crystal structural analyses reveal that specific analytes can replace the OH oscillators in the first coordination sphere of Eu³⁺ and form a unique hydrogen-bonding second-sphere adduct tying adjacent Eu₉ clusters together to minimize their nonradiative vibrational decay. With the promoted Eu³⁺ luminescence, the MOF realizes real-time in situ visual sensing of THF vapor (<1 s) and shows a quantitative ratiometric response to the vapor pressure with a limit of detection down to 17.33 Pa. Also, it represents a top-performing ratiometric luminescent thermometer.