The pH of biological systems is important for the activity of enzymes, and abnormal cellular pH is related to many diseases. Spatial and temporal modulation of pH with light will be useful for studying the pH effects on enzymatic functions and disease mechanisms and may lead to new drug delivery and therapeutic methods. However, the pH of biological systems is maintained by pH buffers, which implies that only temporary pH change (pH pulse) can be induced in an open system. A key fundamental problem is whether a photoinduced pH pulse can be strong and long enough to generate a significant effect. In this work, a photoinduced pH pulse in a micrometer hydrophilic film in PBS buffer has been demonstrated. The thin film was made of an metastable-state photoacid (mPAH) polymer. It is an open system that allows exchange of protons. A quick release of the protons from the mPAHs and the proton exchange between the film and PBS resulted in a pH pulse generated by moderate visible-light irradiation. The magnitude of the pulse is 1.4−1.9 units with maximum pH change occurring after ∼18 s of the irradiation. Since the mPAH is a reversible photoacid, the pH pulse could be repeatedly generated after the photoacid recovered in the dark. This work shows that photochemical modulation of pH is possible even in buffered solutions.
Reversible photoacids have been widely used in different areas for control of proton-driven processes with light. Previously reported reversible photoacids rely on thermal relaxation to return to the low-acidity ground state. Herein we report a photoacid that can be switched between low-acidity and highacidity states by different wavelengths of light. The photoacid can be converted into a high-acidity metastable state by 470 nm irradiation. The thermal relaxation of the metastable state is very slow and its half-life in DMSO is 55 h. Irradiation with 365 nm light quickly induced the reverse reaction and reached a photostationary state. UV/Vis absorption spectra of the forward and reverse processes induced by 470 nm and 365 nm irradiation, respectively, have well-matched isosbestic points. No decomposition was observed after the photoacid was switched by the two wavelengths of light for many cycles. Reversible patterning with both writing and erasing steps performed with light was demonstrated using a polymer thin film containing the photoacid and chlorophenol red as the proton acceptor.
A new organic photoCORM encapsulated in a poly(butyl cyanoacrylate) nanoparticle showed nearly quantitative CO release under visible light and low cytotoxicity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.