Two series of homopolyimides based on oxydiphthalic anhydride and bisphenol A bisether-4-diphthalic anhydride were synthesized with 12 kinds of aromatic diamines. Several thermo-processable homopolyimides were the focus of further investigation. The structureproperty relationships of these homopolyimides were examined as functions of the glass transition temperature (T g ), melting point (T m ), thermal decomposition temperature (T d ), and meltflowability. The effects of the chemical and higher-order structures on these properties were discussed in this work to obtain an indication for the molecular design of high-performance thermoprocessable polyimides. A series of thermoplastic copolyimides were prepared to achieve higher T g and T d without sacrificing thermo-processability. The copolyimides investigated exhibited a comparable or lower melt viscosity, higher T g and T d , and higher long-term thermo-oxidative stability than those of ULTEM type polyimides. One of them exhibited a low melt viscosity (4700 poise at 400 • C), a high T g (224 • C), and excellent thermo-oxidative stability.

Aromatic copolyimides were prepared using 2,3,3′,4′-biphenyltetracarboxylic dianhydride (asymmetric BPDA or a-BPDA) and several aromatic diamines with flexible ether linkages to obtain melt-processable polyimides (PIs) with balanced properties, i.e. high Tg, high thermo-oxidative stability, low melt viscosity, and sufficient toughness. The use of a-BPDA for the present purpose is based on our previous results which showed that a-BPDA-based PIs always show both higher Tg and much higher thermoplasticity than the corresponding symmetric BPDA-derived PIs. On the basis of the structure–property relationship, a copolyimide system was focused upon as a promising candidate. The molecular weight of the selected copolyimide was controlled using an end-capping reagent to balance between Tg, the melt viscosity, and toughness. The effect of the polymerization route (one-pot and two-step) on the properties was also discussed. An a-BPDA-based copolyimide accomplished a high Tg at 249 °C, a low melt viscosity of 8200 Poise at 400 °C, and high thermo-oxidative stability concurrently with considerably high film toughness (elongation at break = 66%).

No abstract

Fish and marine invertebrates constitute an important part of the human diet worldwide, and their muscles are the major edible parts. The muscles are a rich source of proteins, which in other terms determines the nutritional value and the quality of seafood products. Though the fish skeletal muscle proteins share many similarities with their mammalian counterparts, there exist great differences in their biological activity and structural stability. While the muscles of shellfish or aquatic invertebrates share many properties and general structural features with their vertebrate counterparts, they have unique characteristics. Therefore, understanding the biochemical and physicochemical properties of their major protein components is needed from the viewpoint of effective utilization of aquatic bioresources. Thus, in this review, we aimed to assemble the basis of such differences and also to understand the benefits of these proteins as the targets for studies on the structure–stability relationship of proteins.

No abstract

No abstract

No abstract

The striated and smooth adductor muscle tropomyosins (TMs) of Yesso scallop Mizuhopecten yessoensis have been known to express different isoforms, but have not been characterized in detail to date. In the present study, TMs from both muscles of Yesso scallop were purified and their stabilities were compared by circular dichroism (CD) spectrometry and differential scanning calorimetry (DSC). From the CD data, the apparent melting temperature and the apparent free energy of folding at 20 degrees C were calculated to be 30.5 degrees C and -13.4 kJ/mol, and 36.0 degrees C and -31.9 kJ/mol for the striated and smooth muscle TMs, respectively. From the DSC data, DeltaH values were calculated to be 1.87 x 10(3) and 2.19 x 10(3) kJ/mol for striated and smooth muscle TMs. These results suggest that smooth muscle TM has higher thermostability than striated muscle TM. The amino acid residues responsible for such stability difference were considered to be the six amino acid substitutions in the middle region of the TM molecules.