In boron neutron capture therapy (BNCT), the intracellular localization and concentration of boron-10 atoms significantly influence therapeutic efficacy. Although various boronic-acid-targeted fluorescent probes have been developed to evaluate BNCT agents, most of these probes emit at short wavelengths and are, therefore, incompatible with common nuclear-staining reagents such as Hoechst 33342 and 4′,6-diamidino-2-phenylindole (DAPI). While our previously reported probe, BS-631, emitted fluorescence above 500 nm, it exhibited limitations in terms of reaction rate and fluorescence intensity. To address these issues, we developed a boronic-acid-targeted fluorescent probe with a longer emission wavelength, rapid reactivity, and strong fluorescence intensity. Herein, we designed and synthesized BTTQ, a probe based on a 2-(2-hydroxyphenyl)benzothiazole core structure. BTTQ exhibited immediate fluorescence upon reaction with 4-borono-L-phenylalanine (BPA), with an emission wavelength of 567 nm and a sufficiently high fluorescence quantum yield for detection. BTTQ quantitatively detected BPA with high sensitivity (quantification limit of 10.27 µM), suitable for evaluating BNCT agents. In addition, BTTQ exhibited selective fluorescence for BPA over metal cations. Importantly, BTTQ enabled fluorescence microscopic imaging of intracellular BPA distribution in living cells co-stained with Hoechst 33342. These results suggest that BTTQ is a promising fluorescent probe for the evaluation of future BNCT agents.

The chemical reaction of 2-(methylsulfinyl)naphtho[2,3-d]thiazole-4,9-dione (3) using different amines, including benzylamine (4a), morpholine (4b), thiomorpholine (4c), piperidine (4d), and 4-methylpiperazine (4e), produced corresponding new tricyclic naphtho[2,3-d]thiazole–4,9–dione compounds (5a–e) in moderate-to-good yields. The photophysical properties and antimicrobial activities of these compounds (5a–e) were then characterized. Owing to the extended π-conjugated system of naphtho[2,3-d]thiazole–4,9–dione skeleton and substituent effect, 5a–e showed fluorescence both in solution and in the solid state. The introduction of nitrogen-containing heterocycles at position 2 of the thiazole ring on naphtho[2,3-d]thiazole-4,9-dione led to large bathochromic shifts in solution, and 5b–e exhibited orange-red fluorescence with emission maxima of over 600 nm in highly polar solvents. Staphylococcus aureus (S. aureus) is a highly pathogenic bacterium, and infection with its antimicrobial-resistant pathogen methicillin-resistant S. aureus (MRSA) results in serious clinical problems. In this study, we also investigated the antimicrobial activities of 5a–e against S. aureus, MRSA, and S. epidermidis. Compounds 5c with thiomorpholine group and 5e with 4-methylpiperazine group showed potent antimicrobial activity against these bacteria. These results will lead to the development of new fluorescent dyes with antimicrobial activity in the future.

Despite the critical role of essential nutrients in maintaining overall health in freshwater organisms, the effects of nutritional deficiency remain largely unknown. This study investigated the biological and biochemical effects of single and combined deficiencies of boron (B), magnesium (Mg), and calcium (Ca), essential nutrients for physiological functions, in Daphnia magna. Biological responses included life-history parameters (survival, growth, and reproduction), while biochemical effects comprised catalase (CAT) and glutathione S-transferase (GST) activity, as markers of oxidative stress and detoxification, respectively. B deficiency conditions significantly affected survival, growth, reproduction, and CAT activity, while Mg-deficient conditions were associated with significantly reduced survival, long-term growth, reproduction, and CAT activity. Under Ca-deficient conditions, the most severe responses were observed, including reduced survival, growth, reproduction and increased GST activity. Combined B omission with Ca or Mg also produced pronounced adverse responses compared with the corresponding single-nutrient deficiency conditions. Fluorescence imaging revealed treatment-dependent differences in B-associated fluorescence, consistent with differences in B availability. Impaired life-history traits and elevated GST activity suggest cellular stress or activation of detoxification processes associated with reduced organismal performance. The findings demonstrate that nutrient deficiencies act as chronic stressors, highlighting the ecological importance of essential nutrient scarcity in freshwater ecosystems.

Photodynamic therapy (PDT) has garnered significant attention as an effective and safe method for cancer therapy, with ongoing efforts to develop new photosensitizers to enhance its efficacy. This study aimed to develop novel photosensitizers with aggregation-induced emission enhancement (AIEE) properties. A series of 3-phenyl pyrano[4,3-b]quinolizine compounds (3–10) were synthesized by reacting pyrones (1a–e) with 2-pyridylacetate (2a) or 2-pyridylacetonitrile (2b) and then evaluated for their potential as photosensitizers. Spectroscopic analyses revealed that all compounds emitted blue to green fluorescence in ethanol, with emission wavelengths ranging from 446 nm to 515 nm. Compounds 5 and 6, lacking a substituent at position 5 of pyrano[4,3-b]quinolizine, exhibited AIEE behavior in aqueous solution. Furthermore, all compounds produced reactive oxygen species upon exposure to LED light. Notably, compounds 5 and 6 demonstrate high singlet oxygen (¹O₂) generation efficiency in water-rich solvents, where they tend to aggregate, contributing to their potential to destroy cancer cells. In vitro studies using human colon cancer cells (Colo205) demonstrated that 5 and 6 exhibited potent anti-tumor activity upon exposure to LED light. These findings suggest that compounds 5 and 6, based on 3-phenyl pyrano[4,3-b]quinolizine, possessing AIEE properties, are potential new photosensitizers for PDT.