Sensitive detection of strong acidic condition by a novel rhodamine-based fluorescent pH chemosensor.

A novel rhodamine-based fluorescent pH probe responding to extremely low pH values has been synthesized and characterized. This probe showed an excellent photophysical response to pH on the basis that the colorless spirocyclic structure under basic conditions opened to a colored and highly fluorescent form under extreme acidity. The quantitative relationship between fluorescence intensity and pH value (1.75-2.62) was consistent with the equilibrium equation pH = pKa + log[(Imax - I)/(I - Imin)]. This sensitive pH probe was also characterized with good reversibility and no interaction with interfering metal ions, and was successfully applied to image Escherichia coli under strong acidity.

A novel "off-on" colorimetric and fluorescent rhodamine-based pH chemosensor for extreme acidity.

A novel "off-on" colorimetric and fluorescent rhodamine analogue was synthesized and characterized, and used to monitor extreme acidity (below pH 3.5) via the photophysical response to pH. The colorless spirocyclic structure at high pH (pH⩾7.0) opened to the colored and highly fluorescent form at very low pH (pH<3.0). This sensitive pH probe was characterized with short response time, good reversibility and no interaction with interfering metal ions, and the quantitative relationship between the fluorescence intensity and pH value was consistent with the equilibrium equation pH=pKa-log[(Imax-I)/(I-Imin)]. The fluorescent response to strong acidity was further verified by fluorescent imaging of bacteria, Escherichia coli, which contributed to the development of more useful colorimetric and fluorescent sensors based on the rhodamine platform for measuring intracellular pH in extremely acidic conditions.

1,4-Benzoxazine-3(4H)-ones as potent inhibitors of platelet aggregation: design, synthesis and structure-activity relations.

A series of novel potentially platelet aggregation-inhibiting 1,4-benzoxazine-3(4H)-one derivatives was designed and synthesized through Smiles rearrangement, reduction and acetylation reactions. The antiaggregatory activities of the target molecules on arterial blood samples from rabbits, expressed by IC50 values (µM), were then evaluated in vitro against ADP induced platelet aggregation. The favorable IC50 values of compound 8c (IC50=8.99 µM) and 8d (IC50=8.94 µM) indicated that these two compounds were the most potent molecules among all the synthesized compounds. A detailed molecular docking study to explore the interaction of compounds 8c and 8d with GP IIb/IIIa receptor showed that they these two compounds were docked into the active site of GPIIb/IIIa receptor. These results suggest that the 1,4-benzoxazine-3(4H)-one derivatives are promising lead compounds to develop new platelet aggregation inhibitors.