Basic Fluorescent Protonation-Type pH Probe Sensitive to Small ΔpKa of Methanol and Ethanol

A novel fluorescent sensor for evaluating pH changes in organophosphorus pesticides-treated cells and C. elegans

pH plays an important role in the evaluation of the healthy status in versatile circumstances. The fluctuation of pH could be affected by complex internal and external stimuli. Especially, the abnormal pH changes is a common characteristic of organophosphorus pesticides (OPs)-caused damage owing to the irreversible inhibition of acetylcholinesterase (AChE) activity. Therefore, the rapid and efficient detection of pH changes is of great significance for predicting the OPs poisoning in living system. However, quick and convenient detecting pH levels in living cells is still limited by the lack of effective chemical tools. Here, a novel fluorescent probe TH-1 based on ESIPT mechanism was synthesized, showing specific fluorescent effects in different pH solutions. Importantly, the AChE catalyzed the hydrolysis product of acetylthiocholine iodide (ATCh) and changed the pH of solution, which influence its fluorescent intensity. Moreover, the probe TH-1 was applied to detecting the pH levels in living cells and C. elegans, providing an efficient chemical sensor for revealing the potential mechanisms of OPs in physiological and pathological processes.

Photoisomerization of "Partially Embedded Dihydropyridazine" with a Helical Structure

Herein, we report the synthesis of two "partially embedded fused-dihydropyridazine N-aryl aza[5]helicene derivatives" (PDHs) and the demonstration of their intrinsic photo-triggered multi-functional properties based on a Kekulé biradical structure. Introducing bulky electron-withdrawing trifluoromethyl or pentafluoroethyl groups into the aza[5]helicene framework (PDH-CF3 and -C2 F5 ) gives PDH axial chirality based on the helicity of the P and M forms, even at room temperature. Upon photo-irradiation of PDH-CF3 in a frozen solution, an ESR signal from the triplet biradical with zero-field splitting values, generated by N-N bond dissociation, was observed. However, when the irradiation was turned off, the ESR signal became silent, thus indicating the existence of two equilibria: between the biradical and quinoidal forms based on the Kekulé structure, and between N-N bond cleavage and recombination. The observed photo- and thermally induced behaviors indicate that T-type photochromic molecules are involved in the photoisomerization mechanism involving the two equilibria. Inspired by the photoisomerization, chirality control of PDH by photoracemization was achieved. Multiple functionalities, such as T-type photochromism, photo-excitation-mediated triplet biradical formation, and photoracemization, which are attributed to the "partially embedded dihydropyridazine" structure, are demonstrated.

Quantitative and Nondestructive Colorimetric Amine Detection Method for the Solid-Phase Peptide Synthesis as an Alternative to the Kaiser Test

Solid-phase peptide synthesis (SPPS) is an essential technique for the synthesis of peptide. For half a century, many amine detection methods have been developed to monitor coupling reactions during SPPS. Despite such efforts, to the best of our knowledge, a nondestructive and quantitative colorimetric method has not been developed. Here, we developed the first quantitative and nondestructive colorimetric amine detection method based on an acid-base reaction between HCl salt of electron donor-acceptor type dyes and amino groups on the resin. In this method, a noncolored solution of HCl salt consisting of dyes, whose pKBH+ value was carefully tuned, was deprotonated by amines, allowing the appearance of a yellow color. A good linear relationship (R2 = 0.999) between the absorption of the colored solution and the amine group quantities was confirmed. For all tested proteinogenic and nonproteinogenic amino acids, we achieved quantitative colorimetric analysis with a small relative standard deviation (RSD < 3.6%). Furthermore, during the practical synthesis of an octapeptide containing undetectable amino acids with the Kaiser test, our amine detection allowed for detailed monitoring of the coupling reaction, resulting in a significantly purer peptide in the crude form than that obtained using the Kaiser test.

Chelate-free “turn-on”-type fluorescence detection of trivalent metal ions

For the detection of trivalent ions, the chelate-free pH-responsive “Turn-ON”-type fluorescence probes based on INAs were constructed. Based on the X-ray analysis, cationic INAs formed unique outer-sphere complexes for AlIII ions.