Abstract
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.
Highlights
Cell functions are significantly affected by variation in the normal physiological pH conditions [1,2,3,4,5,6,7].The accurate determination of pH is essential for the understanding of the chemical, biological and physical processes in the living organisms
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 pyridinoyl-hydrazone moiety acts as the pH-sensitive fluorophore/chromophore probe
Summary
Cell functions are significantly affected by variation in the normal physiological pH conditions [1,2,3,4,5,6,7]. Most fluorescence/colorimetric pH probes are limited because their solubility in water and in organic phase is not sufficient for most applications Molecules possessing both hydrophilic and hydrophobic character can be employed in the biological aqueous and non-aqueous substrates [17,18]. Aryl and aroyl hydrazone structures formally contain both the Schiff base moiety and an amidic fragment [9,26,27,28] These probes, known as multitopic ligands for metal-organic architectures [29] and as sensors for cations, anions, neutral molecules [30,31,32,33], undergo keto-enol tautomeric interconversion. Molecular Dynamics (MD) simulations of PHA+ /POPC (Palmitoyl oleyl phosphocholine) system at different pH in water permitted to verify the effects on the structural parameters of the bilayer
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