ABSTRACT
Rotational-translational decoupling in systems near Tg, in which translational diffusion is apparently enhanced relative to rotation, has been observed in ensemble and single molecule experiments and has been linked to dynamic heterogeneity. Here, simulations of single molecules experiencing homogeneous diffusion and static and dynamic heterogeneous diffusion are performed to clarify the contributions of heterogeneity to such enhanced translational diffusion. Results show that time-limited trajectories broaden the distribution of diffusion coefficients in the presence of homogeneous diffusion but not when physically reasonable degrees of static heterogeneity are present. When dynamic heterogeneity is introduced, measured diffusion coefficients uniformly increase relative to input diffusion coefficients, and the widths of output distributions decrease, providing support for the idea that dynamic heterogeneity can drive apparent translational enhancement. Among simulations with dynamic heterogeneity, when the frequency of dynamic exchange is correlated with the initial diffusion coefficient, the measured diffusion coefficient behavior as a function of observation time matches that seen experimentally, the only set of simulations explored in which this occurs. Taken together with experimental results, this suggests that enhanced translational diffusion in glassy systems occurs through dynamic exchange consistent with wide underlying distributions of diffusion coefficients and exchange coupled to local spatiotemporal dynamics.
ABSTRACT
BACKGROUND: Weight gain is a common adverse effect of sodium valproic acid (VPA) in children with epilepsy. Several mechanisms of VPA-induced obesity have been suggested such as increased appetite, facultative thermogenesis, and elevated insulin and leptin levels. In this study, we aimed to investigate the role of Insulin and Leptin in the pathogenesis of weight gain caused by VPA. MATERIALS AND METHODS: Body mass index (BMI) was calculated, and serum insulin and leptin levels were measured in 45 consecutive patients and 45 controls. RESULTS: The mean BMI of the cases and control group was 22.97 kg/m2 and 19.4 kg/m2, respectively, and it was significantly higher in cases (P < 0.001). Fasting serum insulin levels were higher in VPA group (26.3 µU/ml) than in controls (15.83 µU/ml), which was statistically significant (P < 0.001). Serum leptin levels were also found to be elevated significantly in VPA group (7.9 ng/ml) than in controls (1.6 ng/ml). CONCLUSION: Sodium VPA is associated with significant rise of BMI, hyperinsulinemia, raised insulin resistance, and increased leptin levels in children with epilepsy.
