Homopolymer poly(N,N-dimethylacrylamide) (PDMA) is soluble in water, but poly(N,Ndiethylacrylamide) (PDEA) and poly(N-ethylacrylamide) (PEA) are soluble only in cold water. The copolymers made of DEA and DMA or DEA and EA are hydrophilic at T < ∼32 °C, but become amphiphilic in the higher temperature range. The synthesis of two series of P(DEA-co-DMA) and P(DEA-co-EA) copolymers with a similar chain length, but different compositions (30 and 50 mol % of DMA and 40, 60, and 80 mol % of EA, respectively), enabled us to study the composition dependence of their association in water by laser light scattering. Our results showed that a limited number of these neutral copolymer chains could associate together to form stable mesoglobules existing between single-chain collapsed globules and macroscopic precipitation. Besides thermodynamical consideration, the formation of such mesoglobules can also be attributed to the competition between intrachain contraction and interchain association as well as the viscoelastic effect. Increasing the hydrophilic DMA or EA content leads to a larger average aggregation number, but increasing the heating rate results in smaller, but less dense, mesoglobules consisting of many loosely associated small single-or pauci-chain globules. For the copolymers with higher EA contents, we unexpectedly found that interchain association can gradually relax to intrachain association as time elapses.

Background/Objectives: Skeletal muscle plays important role in the regulation of whole-body metabolism. In skeletal muscle, uptakes of glucose and fatty acid from circulation are facilitated by transmembrane substrate transporters GLUT4 and FAT/ CD36, respectively. The aim of this study was to determine the effect of dietary glycemic index (GI) on GLUT4 and FAT/CD36 gene expressions in human skeletal muscle after a single bout of exercise. Subjects/Methods: Eight male subjects completed a 60-min cycling exercise at 75% maximal oxygen consumption (VO 2 max ), and were immediately fed an isocaloric meal containing either high-GI (HGI) or low-GI (LGI) diets, with similar proportions of carbohydrate, fat and protein in a crossover design. Muscle samples from deep vastus lateralis were taken by needle biopsy immediately after exercise and 3 h after exercise. Results: After exercise, the HGI diet produced significantly greater glucose and insulin responses compared with the LGI diet, as indicated by the greater area under the curves. Both diets resulted in rapid reductions in plasma fatty acid and glycerol below fasting level. GLUT4 mRNA was downregulated by both HGI and LGI diets to a comparable extent, whereas GLUT4 protein levels were not changed during this short period. FAT/CD36 mRNA and protein levels were substantially decreased with the HGI diet below baseline, but not with the LGI diet. Conclusion: This study found a significant dietary GI effect on post-exercise FAT/CD36 gene expression in human skeletal muscle. This result implicates that the differences in dietary GI are sufficient to alter fat metabolism.