Naphthol‐modified β‐cyclodextrins as fluorescent sensors for detecting contaminants in drinking water

The naphthol‐modified β‐cyclodextrins 1 and 2 have been synthesized as novel chemosensors for detecting contaminants in drinking water. They exhibit a broad fluorescence band with a peak around 505 nm for 1 and 485 nm for 2 , arising from anion species of the excited naphthol unit. Upon the addition of contaminant guests, the fluorescence intensity of 2 decreased, while that of 1 increased. These fluorescence changes may be related to the guest‐induced location change of the naphthol moiety from the inside to the outside of the cyclodextrin cavity. They exhibited high sensitivities for carbon tetrachloride, among several alkyl halides, as well as for odorants such as geosmin and 2‐methylisoborneol. These results demonstrate that 1 and 2 will be useful for monitoring the purity of drinking water.     

Fast swelling/deswelling kinetics of comb-type grafted poly(N-isopropylacrylamide) hydrogels

The synthesis and characterization of comb-type grafted thermo-sensitive hydrogels is presented. These hydrogels were synthesized by polymerization of N-isopropylacrylamide (IPAAm) with a PIPAAm macromonomer. This process leads to a crosslinked IPAAm backbone polymer, copolymerized with highly mobile comb-type PIPAAm chains. These new thermo-responsive copolymers displayed higher equilibrium swellings at lower temperatures and rapid deswelling kinetics at elevated temperatures. The swelling/deswelling for comb-type gels is dependent on the graft chain lengths, in contrast to normal PIPAAm gel lacking the graft chains. As the temperature is increased above the critical temperature, the dehydrated graft chains aggregated due to hydrophobic attraction. Rapid and reversible kinetics of the graft-type gel were observed in response to stepwise temperature changes within short time cycles: phenomena not observed in normal crosslinked thermo-sensitive gels. The influence of freely mobile graft chains on both the equilibrium and dynamic properties of comb-type PIPAAm gel is demonstrated. Possible application of graft-type gel is discussed for actuator systems.