Construction of microscale structures in enclosed microfluidic networks by using a magnetic beads based method

A large number of microscale structures have been used to elaborate flowing control or complex biological and chemical reaction on microfluidic chips. However, it is still inconvenient to fabricate microstructures with different heights (or depths) on the same substrate. These kinds of microstructures can be fabricated by using the photolithography and wet-etching method step by step, but involves time-consuming design and fabrication process, as well as complicated alignment of different masters. In addition, few existing methods can be used to perform fabrication within enclosed microfluidic networks. It is also difficult to change or remove existing microstructures within these networks. In this study, a magnetic-beads-based approach is presented to build microstructures in enclosed microfluidic networks. Electromagnetic field generated by microfabricated conducting wires (coils) is used to manipulate and trap magnetic beads on the bottom surface of a microchannel. These trapped beads are accumulated to form a microscale pile with desired shape, which can adjust liquid flow, dock cells, modify surface, and do some other things as those fabricated microstructures. Once the electromagnetic field is changed, trapped beads may form new shapes or be removed by a liquid flow. Besides being used in microfabrication, this magnetic-beads-based method can be used for novel microfluidic manipulation. It has been validated by forming microscale dam structure for cell docking and modified surface for cell patterning, as well as guiding the growth of neurons.     

氢化物发生-原子荧光光谱法同时测定水中砷和锑

建立在硝酸介质中用氢化物发生-原子荧光光谱法同时测定水中砷和锑的方法。优化了仪器工作条件、酸度、硼氢化钾及还原剂浓度。砷、锑的线性范围为0～10．0μg／L;检出限分别为0．02,0．01μg／L;测定结果的相对标准偏差分别为1．77％～3．72％,2．95％～4．87％（n=6）;加标回收率分别为98％106％,96％105％。该法操作简便,灵敏度高,快速,便于推广,适用于水中砷和锑的同时测定。     

Determination of antazoline hydrochloride in rat plasma and excreta by reversed‐phase ion‐pair chromatography and its application to pharmacokinetics

A reversed‐phase ion pair chromatography method with liquid–liquid extraction analytical method was developed and validated for the determination of antazoline hydrochloride in plasma and excreta of rat. The aim of our study was to characterize the preclinical pharmacokinetics and excretion profiles of antazoline hydrochloride in rats after intravenous injection at the dose of 10 mg/kg. Plasma and excreta samples were extracted with ethyl acetate, and phenacetin was used as the internal standard. The result showed that the method is suitable for the quantification of antazoline hydrochloride in plasma and excreta samples. Analysis of accuracy (90.89–112.33%), imprecision (<7.1%) and recovery (>82.5%) showed adequate values. After a single intravenous administration at 10 mg/kg to rats, plasma concentration profile showed a relative fast elimination proceeding with a terminal elimination half‐life of 3.53 h. Approximately 61.8 and 14.2% of the administered dose were recovered in urine and bile after 72 and 24 h post‐dosing respectively; 5.9% of the administered dose was recovered in feces after 72 h post‐dosing. The above results show that the major elimination route is urinary excretion. Copyright © 2013 John Wiley & Sons, Ltd.     

Alternating DNA and pi-conjugated sequences. Thermophilic foldable polymers

Foldable polymers with alternating single-strand deoxyribonucleic acid and planar conjugated organic perylene tetracarboxylic diimide units were found to self-organize into loosely folded nanostructures. Upon heating, the loosely folded structures become more ordered as evidenced by pi-stacking in the perylene segments. The folding and unfolding processes driven by the molecular interactions of adjacent perylenes were monitored in both aqueous and organic solutions. Heat-promoted folding, or inverse temperature behavior, which originates from positive enthalpy changes, was only observed in water. Therefore, we attributed this inverse temperature dependence to hydrophobic effects rather than pi-pi molecular orbital overlap between the perylene planes. These findings shed light on the design of new thermophiles in protein engineering as well as the construction of macromolecular-based nanodevices with actuator and sensory properties.     

Genetic differentiation and subspecies development of the giant panda as revealed by DNA fingerprinting

Over the last 100 years giant pandas (Ailuropoda melanoleuca) have been separated into six completely isolated mountain ranges. DNA fingerprinting revealed different differentiation patterns in giant pandas, including early-stage, late-stage, recent divergence and recent genetic depression. A separation around 10 000 years ago resulted in highly significant differences in DNA fingerprints and morphological characteristics between Qinling and Sichuan populations. Supported by morphological differences, the genetic data were used to classify the Qinling population as a new subspecies, A. m. qinlingensis, while the Sichuan populations were classified into the original subspecies, A. m. melanoleuca. Thus, the Qinling population deserves management as a separate unit. In the Sichuan populations, two management units were defined, including Qionglai-Minshan and Daxiangling-Xiaoxiangling-Liangshan. Our data suggest urgent measures are needed to establish green corridors between subpopulations in each mountain range to increase gene flow and genetic variation to ensure long-term survival.     

Excited-state intramolecular proton transfer in o-hydroxybiaryls: a new route to dihydroaromatic compounds

An excited-state intramolecular proton transfer (ESIPT) from the phenol OH to the 7'-carbon on the naphthyl ring in o-(1-naphthyl)phenol (3) and 1-(1'-naphthyl)-2-naphthol (4) leads to efficient (Phi = 0.1-0.2) formation of the corresponding dihydrobenzoxanthenes (5 and 7) via quinone methide intermediates. This new reaction represents a clean, efficient, and high-yielding route to benzoxanthenes and dihydrobenzoxanthenes. A related ESIPT of similar efficiency has been detected at the 2'-aromatic position in these systems, by deuterium labeling studies.     

Photohydration and photosolvolysis of biphenyl alkenes and alcohols via biphenyl quinone methide-type intermediates and diarylmethyl carbocations

Evidence is presented for the photochemical generation of novel biphenyl quinone methide (BQM)-type intermediates on photolysis of hydroxybiphenyl alkenes 7 and 8 and hydroxybiphenyl alcohols 9 and 10. Mechanistic investigations utilizing product, fluorescence, and nanosecond laser flash photolysis (LFP) studies indicate two distinct pathways for the formation of these BQMs depending upon the functional groups of the progenitor. Formal excited-state intramolecular proton transfer (ESIPT) between the phenol and the alkene led to BQMs upon irradiation of the hydroxybiphenyl alkenes 7 and 8, while excited-state proton transfer (ESPT) to solvent followed by dehydroxylation was responsible for BQM formation from the hydroxybiphenyl alcohols 9 and 10. Photolysis of 7 and 8 in aqueous CH(3)CN gave photohydration products via attack of water on the respective BQMs, while photolysis of the analogous methyl ethers (of the phenolic moiety) gave only carbocation intermediates. Hydroxybiphenyl alcohols 9 and 10 yielded the corresponding photomethanolysis products in aqueous methanol, through attack of CH(3)OH on the respective BQMs. Although no evidence was found for BQM formation in LFP studies of 8 and 10, due to its suspected short lifetime, the respective diaryl carbocation (lambda(max) 420 nm, tau = 8.5 micros) has been observed upon irradiation of 8 in 2,2,2-trifluoroethanol. A BQM (lambda(max) 580 nm) was observed for 9 but not for 10, the latter having more complex chemistry on laser excitation, resulting in a transient that appears to mask any BQM absorption. Significant quenching of fluorescence from the hydroxybiphenyl alkenes at low water content implies that H(2)O is directly involved in reaction from the singlet excited state. The decrease in fluorescence intensity of 8 was found to depend on [H(2)O](3); however, the distance required for ESIPT in these systems is too large to be bridged by a water trimer. The nonlinear quenching has been attributed to deprotonation of the phenol by two water molecules, with concerted protonation at the alkene by another molecule of water. Fluorescence quenching of the hydroxybiphenyl alcohols required much higher water content, implying a different mechanism of reaction, consistent with the proposal of ESPT (to solvent water) followed by dehydroxylation.     

Sedimentation rate in the Sungai Linggi estuary using excess 210Pb and 137Cs

The purpose of this study was to estimate the sedimentation rate in the Sungai Linggi estuary using the constant initial concentration of unsupported or excess ²¹⁰Pb model and verified with ¹³⁷Cs method. Five sediment cores were collected on 25 January 2011 using gravity corer with the inner tube of 50 cm length and 7.5 cm diameter. The total ²¹⁰Pb activities in the sediment cores profile at all sampling stations were varied and upper than those obtained for supported ²¹⁰Pb i.e. ²²⁶Ra, indicated disequilibrium among ²¹⁰Pb and its grandparents in the ²³⁸U decay series. Meanwhile, the lower ¹³⁷Cs activities were observed at all sampling stations due to no significant sources of ¹³⁷Cs releases were transferred into Malaysian marine. The estimation of sedimentation rate indicated the agreement of ²¹⁰Pb and ¹³⁷Cs method with a general presence of deep mixing in the Sungai Linggi estuary. Therefore, the apparent sedimentation rates calculated from ²¹⁰Pb profiles generally reflect the true value with the range from 0.70 to 1.97 cmyr^?1. High sedimentation rate was observed at some sampling stations which are located in river channel, estuary and closer to mainland. This suggested that land-use development, agriculture activities, channelization etc. introduced a large amount of sediment loaded into those areas.     

Modelling and measuring the thermal conductivity of multi-metallic Zn/Cu nanofluid

A metallic nanofluid is a suspension of metallic nanoparticles in a base fluid. Multi-metallic nanoparticles are a combination of two or more types of metallic particles. Such multi-metallic nanoparticles were suspended in water using an ultrasonic vibrator for different total volume fractions and different ratios of metallic/metallic nanoparticles. A transient hot wire setup was built to measure the thermal conductivity of the nanofluid at different temperatures. The experimental results were in good agreement with the results in the literature. Then, the experimental results were used as input data for an adaptive neural fuzzy inference system (ANFIS) to predict the thermal conductivity of the multi-metallic nanofluid. The maximum deviation between the ANFIS results and experimental measurements was 1 %. The predicted results and the experimental data were compared with other models. The ANFIS model was found to have good ability to predict the thermal conductivity of the multi-metallic nanofluid over the range of the experimental results.     

Evaluating a four-directional benzene-centered aliphatic polyamine curing agent for epoxy resins

A four-directional benzene-centered aliphatic polyamine, MXBDP, with high functionality and low volatility, is used to cure epoxy resin (DGEBA). Herein we originally report the isothermal cure kinetics and dynamic mechanical properties of DGEBA/MXBDP. Differential scanning calorimetry confirms that MXDBP is more reactive than commercial linear metaxylenediamine and branched Jeffamine T-403 and the isothermal curing reaction is autocatalytic. The Kamal model is found to be able to well describe the curing rate up to the onset of diffusion control, and the excellent match over the whole conversion range is achieved using the extended Kamal model. Interestingly, the isoconversional kinetic analysis indicates that the effective reaction activation energy (E _α ) changes substantially with conversion, and ultimately decreases to a very small value (<10 kJ mol^?1) because of the diffusion-controlled reaction kinetics. Then, dynamic mechanical analysis reveals that DGEBA/MXBDP exhibits the higher α- and β-relaxation temperatures and the much higher crosslink density than DGEBA/metaxylenediamine. Our experiment results support that MXBDP has the high reactivity and improved thermal resistance in combination with the advantages of the high functionality, low volatility and decreased CO₂ absorption. Therefore, MXBDP may be especially suitable for room temperature-cure epoxy coatings and adhesives.