Metastable-State NH Photoacids and Organic Photo Carbon Monoxide Releasing Materials
Abeyrathna, Aluthwatte Rallage Nawodi Madhusanka
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The recently discovered metastable-state photoacids (mPAHs) can produce a large proton concentration with high efficiency and good reversibility upon irradiation with visible light with moderate intensity. Therefore, mPAHs can be conveniently incorporated in to different systems to control various proton-transfer processes. Recently, several applications of mPAHs have been demonstrated. However, none of the previously reported mPAHs can function at a pH 7.4. Thus, biological applications of mPAHs are limited. In this work, mPAHs that can reversibly release a proton in PBS buffer (pH = 7.4) under visible light are designed and synthesized. NH-PAH-1 is the first of this type of photoacids. The design is based on the dual acid−base property and tautomerization of indazole. The activity of the proton released from the mPAH is demonstrated by protonation of an acridine dye both in solution and polymer. Further, a pH pulse is photogenerated using a NH-PAH-polymer at pH 7.4. This type of mPAH is promising to control proton transfer processes in physiological conditions and may find applications in biomedical areas. Protonated merocyanines (MEHs) are the mostly used mPAHs to control various chemical, material, and biological processes using visible light. Photoactivity, reversibility and stability of MEHs in aqueous and polymeric media have been a concern. In this work, a series of experiments investigating the photoactivity, reversibility and stability of MEHs in polymer films and stability in aqueous solution are demonstrated. The outcome of these experiments provides insight into most of the concerns regarding MEHs, when it comes to real applications. Design and synthesis of cyclic-α-diketone (DK) based organic carbon monoxide releasing molecules (CORMs) under visible light and an approach to generate a novel tissue engineered scaffold as a delivery system for CORMs in vascular tissue engineering is demonstrated. The results revealed that CORM-loaded, electrospun poly(ε-caprolactone) based scaffolds can be photoactivated and release CO. The released CO can be monitored via fluorescence imaging techniques. This is the first use of a CORM for tissue engineering. These novel organic photoresponsive materials may provide a promising platform to investigate new applications to control chemical and biological processes using visible light.