Wang Xuan,Xiao Kesong,Liu Xiangnong,Wu Hao,Gao Cai
The phenomenological models based on fictive temperature and nonlinear Adam–Gibbs formulation have been widely used to describe the enthalpy relaxation kinetics. Although the parameters in Adam–Gibbs formulation are physically explicable, the reasonabilities of the parameters obtained from curve-fitting procedures have not been systematically discussed yet. In this work, differential scanning calorimetry was employed to measure the heat capacities of maltitol in both the amorphous and the crystalline states, and the data were used to generate the model parameters. Results showed that the configurational ground state plays an important role in extracting the model parameters. Selecting the crystal rather than the glass as the ground state seems to be effective to improve the reasonabilities of the fitted parameters. It suggested that even if the fit quality seems sound, the physical reasonability of the best-fit parameters still needs to be treated with caution.
Yuli Sun,Guangwen Li,Haiyan Hong,Lin Zhu,Hank F. Kung,Yan Zhang,Jinxia Zhu
Objective Diabetes mellitus (DM) is one of the major diseases in the world. Nuclear medicine imaging may be able to detect functional status of pancreatic β cells in vivo , which might elucidate the pathological mechanisms of diabetes and develop individualized treatment plans. In this study, we evaluated the ability of [ 125 I]ADAM, a serotonin transporter (SERT) imaging agent, as a probe for detecting pancreatic β-cell mass (BCM). Methods In vitro cell studies were evaluated in INS-1 cells (rat islet β cell line). Biodistribution studies were performed in male normal Sprague-Dawley rats and alloxan-induced type 1 diabetes mellitus (T1DM) rats. Distribution and expression of SERT protein in pancreas of rats were also measured by immunofluorescence staining and Western blot. Results In vitro cell studies showed that the concentration of [ 125 I]ADAM associated with the INS-1 cells was increased gradually with incubation time, and the SERT specific inhibitor, escitalopram, exhibited the inhibitory effect on this interaction. Biodistribution studies also showed that the uptake of [ 125 I]ADAM in the pancreas of normal rats was decreased in the presence of escitalopram. However, in the T1DM rat model with a significant β cells reduction, the uptake of pancreas was increased when compared with the control. Through immunofluorescence staining and Western blot, it was found that both the endocrine and exocrine cells of the normal pancreas expressed SERT protein, and the level of SERT protein in the exocrine cells was higher than islets. In the diabetic state, the expression of SERT in the exocrine cells was further increased. Conclusions The SERT imaging agent, [ 125 I]ADAM, at the present form will not be suitable for imaging β cells, specifically because there were extraordinarily high non-specific signals contributing from the exocrine cells of pancreas. In addition, we noticed that the level of SERT expression was abnormally elevated in the diabetic state, which might provide an unexpected target for studying the pathological mechanisms of diabetes.
High-Tg polymers generally exhibit high dynamic fragility (m). Here, we propose to design striking polymeric materials with low m but high Tg by introducing ionic coordination. The enthalpy relaxation of poly(vinylpyrrolidone)/metal chloride complexes was investigated to elucidate the influences of the coordination strength on Tg and m. Findings reveal that Tg increases with the addition of metallic ions, while m decreases for weakly coordinated complexes (Li+) and moderate systems (Zn2+ and Mg2+). Meanwhile, m increases continuously for strongly coordinated systems (La3+). Further experiments revealed that m is well correlated to heat capacity jump ΔCp and enthalpy hysteresis ΔHR as predicted by Adam–Gibbs theory. Ionic coordinated polymers with low m but high Tg can be achieved only when ΔHR changes more than Tg·ΔCp, suggesting that the enthalpy change plays a leading role in the activation free energy of segmental cooperative rearrangement. These results not only add new evidence of the thermodynamic link to dynamic fragility but also help clarify the mechanism of the independent tuning of Tg and m.
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