Quantitative determination of the spring entropy effect and its indication of the conformational change of polymer coils with varying concentration in aqueous poly(N-isopropylamide) solutions.

The lower critical solution temperature (LCST) phase separation behaviors of thermosensitive poly(N-isopropylacrylamide) (PNIPAM) aqueous solutions were investigated by power-compensation differential scanning calorimetry (DSC). The entropic effect and hence the change of swelling state of PNIPAM polymer coils in homogeneous concentrated aqueous solutions with varied solution composition was elucidated by the isothermal enthalpy demixing recovery behaviors in distinct concentration regions.

Preparation of rapamycin-loaded chitosan/PLA nanoparticles for immunosuppression in corneal transplantation.

Rapamycin-loaded chitosan/polylactic acid nanoparticles with size of about 300 nm in diameter were prepared through nanoprecipitation method using cholesterol-modified chitosan as a stabilizer. The surface coating of chitosan, which was demonstrated by zeta potential measurement, endowed the nanoparticles good retention ability at the procorneal area, facilitating the sustained release of rapamycin on the corneal. The immunosuppression in corneal transplantation of the nanoparticles was investigated using rabbit as animal model, the median survival time of the corneal allografts treated with nanoparticles was 27.2+/-1.03 days and 50% grafts still remained surviving by the end of the observation, while the group treated with 0.5% rapamycin suspension was 23.7+/-3.20 days. The median survival time of drug-free nanoparticles group and untreated groups were 10.9+/-1.45 and 10.6+/-1.26 days, respectively. The results demonstrated the excellent immunosuppression of rapamycin-loaded chitosan/polylactic acid nanoparticles in corneal transplantation.

Synthesis of switchable intelligent molecularly imprinted polymers with selective adsorption of ethyl carbamate and their application in electrochemical sensor analysis.

A cyclodextrin aldehyde based molecularly imprinted polymer with thermally responsive Diels-Alder (DA) linkages of grafted furan-type dienes was polymerized. The synthesized DA-MIP has dienophile characteristics and the specific absorption of ethyl carbamate (EC) can be switched on or off simply by thermal adjustment to 130 °C and 60 °C, respectively. The imprinting factors (α) of the MIP and rDA-MIP to EC were 6.2 and 5.0, and the selection factors (ß) were 5.2 and 4.0, respectively. The restoration of the molecular target ratio was 88%, as determined by absorption and desorption experiments. The thermal restoration ratio, determined by thermal cycling experiments, was 78%. A new electrochemical sensor was prepared using the DA-MIP and its responsiveness for detecting trace amounts of EC was investigated. The results indicate that the electrode response has good affinity and excellent specific recognition performance for template molecular chemicals.

Highly stable quantum dots with silica-poly(EGDMA-co-MAA) synergistic protection and the preliminary application in immunoassay.

For the application of biological quantitative probes, how to ameliorate chemical sensitivity and instability of quantum dots (QDs) under different environments is a longstanding issue. Here, silica and poly(EGDMA-co-MAA) as inert materials, ultrastable QD/SiO2/poly(EGDMA-co-MAA) fluorescent nanoprobes with a tri-layer core-shell structure were successfully prepared by distillation precipitation polymerization. The QD/SiO2/poly(EGDMA-co-MAA) demonstrated ultra-high chemical stability due to the synergistic combination of silica and cross-linked polymer stabilizing the fluorescence intensity of QDs under harsh chemical environments, including strong acidic solutions, which is unavailable for any of the current encapsulation technologies used alone. Immunochromatography test strips (ICTS) for the detection of human chorionic gonadotrophin (HCG) antigen was developed by using QD/SiO2/poly(EGDMA-co-MAA) as fluorescent nanoprobes. The results showed admirable reliability and sensitivity in antigen detection. What's more, reliable quantitative detection based on QD/SiO2/poly(EGDMA-co-MAA) was realized. We expect the ultrastable QDs will open up exciting opportunities in accurate quantitative analysis and imaging.

Chain length dependence of the thermodynamic properties of linear and cyclic alkanes and polymers.

The specific heat capacity was measured with step-scan differential scanning calorimetry for linear alkanes from pentane (C(5)H(12)) to nonadecane (C(19)H(40)), for several cyclic alkanes, for linear and cyclic polyethylenes, and for a linear and a cyclic polystyrene. For the linear alkanes, the specific heat capacity in the equilibrium liquid state decreases as chain length increases; above a carbon number N of 10 (decane) the specific heat asymptotes to a constant value. For the cyclic alkanes, the heat capacity in the equilibrium liquid state is lower than that of the corresponding linear chains and increases with increasing chain length. At high enough molecular weights, the heat capacities of cyclic and linear molecules are expected to be equal, and this is found to be the case for the polyethylenes and polystyrenes studied. In addition, the thermal properties of the solid-liquid and the solid-solid transitions are examined for the linear and cyclic alkanes; solid-solid transitions are observed only in the odd-numbered alkanes. The thermal expansion coefficients and the specific volumes of the linear and cyclic alkanes are also calculated from literature data and compared with the trends in the specific heats.