Spontaneous Formation of Vesicles by Self-Assembly of Nicotinyl Amino Acid Amphiphiles: Application as “Turn-On” Fluorescent Sensors for the Selective Detection of Trace-Level Hg(II) in Water

A Water Soluble 2-Phenyl-5-(pyridin-3-yl)-1,3,4-oxadiazole Based Probe: Antimicrobial Activity and Colorimetric/Fluorescence pH Response

The growing demand of responsive tools for biological and biomedical applications pushes towards new low-cost probes easy to synthesize and versatile. Current optical probes are theranostic tools simultaneously responsive to biological parameters/analyte and therapeutically operating. Among the optical methods for pH monitoring, simple small organic molecules including multifunctional probes for simultaneous biological activity being highly desired by scientists and technicians. Here, we present a novel pH-responsive probe with a three-ring heteroaromatic pattern and a flexible cationic chain. The novel molecule shows real-time naked-eye colorimetric and fluorescence response in the slightly acidic pH range besides its excellent solubility both in the organic phase and in water. In addition, the small probe shows significant antibacterial activity, particularly against Escherichia coli. Single-crystal X-ray study and density functional theory (DFT) calculations rationalize the molecule spectroscopic response. Finally, molecular dynamics (MD) elucidate the interactions between the probe and a model cell membrane.

Amphiphilic Diazapyrenes with Multiple Stimuli-Responsive Properties

A series of amphiphilic diazapyrenes exhibiting switchable fluorescence under the stimulus of mechanical force or water vapor are reported for the first time. Comprehensive studies of their photophysical properties in different states based on UV-Vis absorption, FL emission, FT-IR spectroscopy, and XRD analysis have revealed a stimuli-induced excimer-based sensing mechanism. The relationship between molecular structures and optical responsive properties of these diazapyrene derivatives is illustrated. Moreover, the unique fluorescent, stimuli-responsive behaviors of these diazapyrene compounds in the solid state are used to fabricate sensory films for successively and orthogonally sensing mechanical force and water vapor. In contrast to the well-established knowledge on the transformation between the pyrene monomer and excimer, our study offers valuable information about the unknown diazapyrene excimers and demonstrates their potential applications in biocompatible force sensors, data storage, and humidity sensors.

An Amphiphilic Pyridinoyl-hydrazone Probe for Colorimetric and Fluorescence pH Sensing

A new pH sensor based on a substituted aroylhydrazide with a flexible side chain and a terminal trimethyl ammonium group (PHA⁺) was designed and synthesized. The terminal quaternary ammonium guarantees excellent solubility in water. At the same time, the probe is very soluble in hydrophobic envirornments. The pyridinoyl-hydrazone moiety acts as the pH-sensitive fluorophore/chromophore probe. Extensive physicochemical characterization has been performed on the bromide salt PHABr. DFT calculations, based on single-crystal X-ray data, permitted to rationalize the optical behavior. Molecular dynamics simulations permitted to clarify the mode of interaction with lipid membrane. The ability of the probe to change color and fluorescence in response to different pH and media of different polarity has been investigated. PHABr shows a remarkable pH-dependent behavior in both absorption and fluorescence spectra with high sensitivity and strong on-off switch effect at neutral pH, perceptible even to the naked eye.