Portable Diagnosis Method of Hyperkalemia Using Potassium-Recognizable Poly(<i>N</i>‑isopropylacrylamide-<i>co</i>-benzo-15-crown-5-acrylamide) Copolymers

A novel, simple, portable, and low-cost method for diagnosis of hyperkalemia by using K⁺-recognizable poly­(<i>N</i>-isopropylacrylamide-<i>co</i>-benzo-15-crown-5-acrylamide) [poly­(NIPAM-<i>co</i>-B15C5Am)] linear copolymer as indicator is presented in this work. The pendent 15-crown-5 units in the linear copolymers can selectively and specifically recognize K⁺ to form stable 2:1 “sandwich” host–guest complexes, which cause the copolymer chains to change from the hydrophilic state to the hydrophobic state isothermally, whereas other tested metal ions (e.g., Li⁺, Na⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Cu²⁺, Fe³⁺, Pb²⁺, Cd²⁺, Cr³⁺) cannot be recognized. With increasing the 15-crown-5 content or the K⁺ concentration, the poly­(NIPAM-<i>co</i>-B15C5Am) linear copolymers exhibit higher sensitivity to K⁺. The hyperkalemia can be simply diagnosed by observing the K⁺-induced optical transmittance change of human blood samples with poly­(NIPAM-<i>co</i>-B15C5Am) linear copolymer as an indicator. Normal blood samples with low potassium level containing the poly­(NIPAM-<i>co</i>-B15C5Am) linear copolymer are almost transparent since the copolymer is hydrophilic and soluble at the operating temperature. However, severe hyperkalemia samples with high potassium level become completely cloudy since the copolymer is hydrophobic and insoluble at this temperature. The presented diagnosis method with poly­(NIPAM-<i>co</i>-B15C5Am) linear copolymer as indicator is quite simple and low-cost, and it would bring a new candidate material to design simple and portable tools for diagnosis of hyperkalemia in the general population. Moreover, the results in this work provide valuable guidance for building novel poly­(NIPAM-<i>co</i>-B15C5Am)-based artificial K⁺-recognizable “smart” or “intelligent” systems in various application fields

Insights into the Effects of 2:1 “Sandwich-Type” Crown-Ether/Metal-Ion Complexes in Responsive Host–Guest Systems

In-depth investigations of the specific ion-responsive characteristics based on 2:1 “sandwich” structures and effects of crown ether cavity sizes on the metal-ion/crown-ether complexation are systematically performed with a series of PNIPAM-based responsive copolymers containing similar contents of crown ether units with different cavity dimensions (12-crown-4 (12C4), 15-crown-5 (15C5), 18-crown-6 (18C6)). The lower critical solution temperature (LCST) values of copolymers in deionized water shift to lower temperatures gradually when the crown ether contents increase or the ring sizes decrease from 18C6 to 12C4. With increasing the concentrations of alkali metal ions (Na⁺, K⁺, Cs⁺) or the contents of pendent crown ether groups, the copolymers with different crown ether cavity sizes exhibit higher selectivity and sensitivity to corresponding cations. Importantly, the ion sensitivities of the copolymers in response to corresponding alkali metal ions increase dramatically with an increase in the crown ether cavity size. Interestingly, a linear relationship between the crown ether cavity size and the diameter of corresponding cation for the formation of stable 2:1 “sandwich” complexes is found for the first time, from which the size of metal ions or other guests that able to form 2:1 “sandwich” complexes with crown ethers can be deduced. The results in this work are valuable and useful for further developments and practical applications of various crown-ether-based smart materials