Localized pH Pulses in PBS Buffer Repeatedly Induced by Visible Light

Abstract

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 photo control of proton chemistry

“…It is worth mentioning that the pH of biological systems is often maintained by pH buffers. However, temporary and reversible pH change can be locally produced by localized mPAHs, which can be achieved by polymerizing mPAHs 44,51,52 or encapsulating mPAHs in nanomaterials. 23,38 For example, our group showed that pH pulses of ∼1.7 units can be repeatedly generated in a micrometer film of an mPAH hydrogel in PBS.…”

A Reversible Photoacid Switched by Different Wavelengths of Light

“…Photoacid 1 (PA1) was discovered during a systematic study of indazole type mPAHs. [34,37,38] Indazole mPAHs function at physiological pH and have shown potential in biomedical area. A indazole mPAH was recently utilized to change the intracellular pH environment in an anticancer study.…”

“…[34] A polymer of a indazole photoacid was shown to be able to generate pH pulses in PBS buffer under irradiation. [38] The structure, synthesis, and photoreaction of PA1 are shown in Figure 1. PA1 was conveniently synthesized by coupling a methyl benzothiazolium with a indazole aldehyde.…”

“…Photoacid 1 (PA 1 ) was discovered during a systematic study of indazole type mPAHs [34,37,38] . Indazole mPAHs function at physiological pH and have shown potential in biomedical area.…”

“…A indazole mPAH was recently utilized to change the intracellular pH environment in an anticancer study [34] . A polymer of a indazole photoacid was shown to be able to generate pH pulses in PBS buffer under irradiation [38] . The structure, synthesis, and photoreaction of PA 1 are shown in Figure 1.…”