Two cyanine-based fluorescent probes, ( E)-2-(4-(diethylamino)-2-hydroxystyryl)-3-ethyl-1,1-dimethyl-1 H-benzo[ e]indol-3-ium iodide (L) and ( E)-3-ethyl-1,1-dimethyl-2-(4-nitrostyryl)-1 H-benzo[ e]indol-3-ium iodide (L), have been designed and synthesized. Of these two probes, the twisted-intramolecular-charge-transfer (TICT)-based probe, L, can preferentially self-assemble to form nanoaggregates. L displayed a selective turn-on fluorescence response toward human and bovine serum albumin (HSA and BSA) in ∼100% aqueous PBS medium, which is noticeable with the naked eye, whereas L failed to sense these albumin proteins. The selective turn-on fluorescence response of L toward HSA and BSA can be attributed to the selective binding of probe L with HSA and BSA without its interfering with known drug-binding sites. The specific binding of L with HSA led to the disassembly of the self-assembled nanoaggregates of L, which was corroborated by dynamic-light-scattering (DLS) and transmission-electron-microscopy (TEM) analysis. Probe L has a limit of detection as low as ∼6.5 nM. The sensing aptitude of probe L to detect HSA in body fluid and an artificial-urine sample has been demonstrated.
A new water soluble and fluorogenic probe (L) that can demonstrate a specific ratiometric detection of a SO derivative (SO) in 100% aqueous medium and live cells has been designed and synthesized. The detection process can be visualized by the naked eye, as the orange-red fluorescence of L turns into a strong blue fluorescence upon interaction with SO. L displayed several beneficial attributes such as detection in complete aqueous medium, extremely fast response time along with high selectivity and sensitivity. The ratiometric sensing was attributed to the selective nucleophilic addition reaction of SO with L. The probe was further used to develop a low cost microfluidic sensor device (μPAD). The probe was biocompatible and its potential to sense SO in mitochondria was captured in live HeLa cells.
Over the past few decades, the tren [tris(2-aminoethyl)amine] skeleton has materialized as one of the supreme anion binding building blocks demonstrating a strong interplay among topology, complementarity, cooperativity, and coordination. However, anion recognition by modest tren-based unsubstituted aromatic urea has been underexplored, mainly due to the deficiency of π-acidic or electronwithdrawing aryl terminals. This report establishes an infrequent hexameric neutral receptor-anion-water molecular self-assembly, where a conformationally flexible C 3v -symmetric halide (F − /Cl − ) encapsulated electron-rich naphthyl group containing N-bridged tripodal urea receptor effectively entraps a chair-shaped ice-like neutral cyclic water hexamer within the hexameric cavity of a neutral receptor-halide host−guest assembly.
For a comprehensive analysis of host–guest
binding propensity in their neutral form, three linear flexible bis-urea
) with different terminal substituents have
been synthesized. It has been established that, with the existence
of electron-withdrawing or π-acidic phenyl substituents, they
act as a possible system that can proficiently coordinate with anions
of diverse dimensions constantly initiated by the size of the countercations.
The 3,5-bis(trifluoromethyl)phenyl-derived isomer (L
) can readily form cooperative neutral self-assemblies
irrespective of the size the monovalent halides (viz. chloride, bromide,
and iodide anions) and noncooperative neutral self-assemblies with
planar divalent carbonate anion. The meta isomer L
captures spherical halides, i.e. chloride and
bromide, in an isostructural way, forming a 1:2 host–guest
assembly, whereas the isomeric para receptor L
shows cooperative binding with chloride anions, having
coordination number 3. However, due to the greater flexibility and
lesser hydrophobicity of receptor L
to receptor L
, successful crystallization
of any oxyanion complexes through the meta and para isomers was not
Judiciously designed cyanine based fluorogenic probe (L) can exhibit interesting solvent polarity induced isomerization. The probe displayed a highly selective TURN-ON fluorescence response towards hypochlorite among various reactive oxygen species (ROS) and analytes in a mixed aqueous medium. The sensing process was attributed to the formation of a probe-OCl adduct which results in restricting the donoracceptor extended conjugation. The detection limit was found to be as low as 3 μM. The proposed sensing mechanism is supported by mass spectrometric analysis and HPLC study.
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