Synthesis and Characterization of pH and Temperature-Sensitive Semi-IPN Hydrogels

A series of novel cross-linked poly N-isopropylacrylamide (PNIPAM)/poly diallyl dimethyl ammonium chloride (PDMDAAC) semi-IPN hydrogels were synthesized through free radical solution polymerization in water at 30°C. FTIR was used to characterize the structure of resultant hydrogels. The pH and temperature sensitivity of hydrogels were systematicly studied, and the swelling properties of hydrogels were also explored. The results show that the semi-IPN hydrogels have both temperature and pH sensitivities. The hydrogels exhibit fast swelling rate and excellent stimuli-responsive behavior.

Synthesis and Characteristics of Thermo-and pH-Sensitive PNIPAAm/PVP Hydrogels

Poly (N-isopropylacrylamide)(PNIPAAm)/Poly (N-vinylpyrrolidone)(PVP) hydrogels were prepared by irradiating the aqueous solution mixture of NIPAAm and PVP with electron beam. The effects of feed ratio, pH, and temperature on the swelling ratio of the hydrogels were investigated. It appeared that the hydrogels possessed both pH and temperature sensitivity, the lower critical solution temperature (LCST) of PNIPAAm/PVP hydrogels increased with the increasing of PVP content in the copolymers. The experimental results also showed that the hydrogels were ionic strength sensitivity, the swelling ratio decreased sharply when the ionic strength of the solution arrived to a certain critical value.

pH-, temperature- and ion-dependent oligomerization ofSulfolobus solfataricusrecombinant amidase: a study with site-specific mutants

Recombinant amidase fromSulfolobus solfataricusoccurred as a dimer of 110 kDa comprising identical subunits. Only dimers were present at pHs above 7.0, but with decreasing pH, dimers associated into octamers, with complete oligomerization occurring at pH 3.0. Oligomerization showed reversible temperature-dependence, with octamer formation increasing with temperature from 36 °C to between 70 and 80° C. Increasing salt concentrations, favored dissociation of the octamers. Among the three investigated factors affecting the dimer–octamer equilibrium, the most important was pH. Among four mutants obtained by site-specific mutagenesis and selection for pH and temperature sensitivity, the T319I and D487N mutant amidases, like that of the nativeSulfolobus solfataricus, responded to changes in pH and temperature with a conformational change affecting the dimer–octamer equilibrium. The Y41C and L34P mutant amidases were unaffected by pH and temperature, remaining always in the dimeric state. The differences among mutants in protein conformation must be related to the position of the introduced mutation. Although the L34P and Y41C mutations are located in the helical region 33–48 (LLKLQLESYERLDSLP), which is close to the amino-terminal segment of the protein, the T319I mutation is located in a strand on the surface of the protein, which is far from, and opposite to, the amino-terminal segment. The D487N mutation is located in the center of the protein, far distant from the 33–48 segment. These observations suggest that the segment of the protein closest to the amino-terminus plays a key role in the association of dimers into octamers.