Aminoquinoline‐Salicylaldimine Dyads as Highly Selective Turn‐On Fluorescent Sensors for Zinc (II) Ions

Abstract

Four new derivatives of 8-aminoquinolines are successfully synthesized by extension of the p-conjugated system on the quinoline ring and incorporation of either the salicylaldimine or its reduced amino form. These compounds show selective fluorescence enhancement by Zn 2 + ion, attributing to the chelation-enhanced fluorescence (CHEF) effects, in which the deprotonation of the amido -NH and phenolic -OH causes the internal charge transfer (ICT) process. The fluorescent signals of these compounds are shifted from the range of 391-562 nm to 535-590 nm upon addition of Zn 2 + . The sensing mechanism is investigated by 1 H NMR titration, mass spectrometry, and single crystal X-ray diffraction analysis which suggests a 1:1 binding stoichiometry between the sensor and Zn 2 + . The detection limits of 0.024 to 0.431 mM and the association constants ranging between 7.0 3 10 3 and 1.2 3 10 4 M À1 can be estimated for these four sensors. One of these compounds is fabricated on wax-patterned filter paper and used as a probe for Zn 2 + in aqueous solution with a naked-eye detection limit at 10 mM.The zinc ion is the second most abundant transition metal ions in living organism after iron. It plays crucial roles in many important biological processes like structural and catalytic cofactors, neural signal transmitters or modulators, and regulator of gene expression and apoptosis. [1] Moreover, it is known that a disorder of zinc metabolism is closely associated with many severe neurological diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), Parkinson's disease, hypoxia-ischemia, and epilepsy. [2] In the environment, an excessive concentration of zinc may reduce the soil microbial activity resulting in a phytotoxic effect. [3] The development of detection methods for zinc ion such as inductively coupled plasma mass spectroscopy, [4] atomic absorption spectroscopy, [5] gel electrophoresis, [6] and reverse-phase liquid chromatography have been widely reported. [7] Nevertheless, these techniques rely on expensive instruments, complicated procedures, and skillful users. Fluorescence spectroscopy has then become a preferred method of choice due to its high sensitivity and selectivity with simple instrument operation. A number of fluorescent sensors based on various fluorophores such as quinolone, [8] fluorescein, [9] coumarin, [10] naphthalimide, [11] BODI-PY, [12] and others were developed for detection of zinc ions. [13] However, the development of new zinc-selective fluorescent sensors with high affinity and good selectivity over other relevant metal ions, especially Cd 2 + is still highly desirable.During our work on the development of new fluorescent chemosensors, we recently became interested in the sensing properties of 8-aminoquinoline derivatives, especially their highly selective binding with glucosamine and several transition metals. [14] They have been used as ionophores for detection of Zn 2 + , [8b,15] and other metal ions such as Cu 2 + , Al 3 + , Cr 3 + , and Hg 2 + . [8c,d,16]...

Synthesis and photophysical, thermal and antimycobacterial properties of novel 6-amino-2-alkyl(aryl/heteroaryl)-4-(trifluoromethyl) quinolines

“…16 In recent years, the synthesis and fluorescent properties of a series of 6-aminoquinolines were reported. [17][18][19][20][21][22] As an example, this kind of molecule has shown luminescent properties, with potential applications in organic solar cells (OSCs), biomolecular markers, organic light-emitting diodes (OLEDs), molecular probes and switches. 17,19 Application of 6-aminoquinolines in photoluminescent sensors to detect different metals in solution has also been highlighted.…”

“…17,19 Application of 6-aminoquinolines in photoluminescent sensors to detect different metals in solution has also been highlighted. This is possible through complex formation between quinoline with chelating groups attached and these species, [19][20][21] which leads to high quantum yield results and easier detection of these metal species in living organisms. 22 Therefore, considering the importance of the studies involving aminoquinolines containing the trifluoromethyl substituent and alkyl(aryl/heteroaryl) substituents -which are rarely reported together -our research group decided to perform the synthesis of a series of 6-amino-2-alkyl(aryl/heteroaryl)-4-(trifluoromethyl)quinolines, and evaluate their photophysical and thermal properties, allied with an antimycobacterial evaluation.…”

A Phenyl Thioether‐Based Probe: Zn2+ Ion Sensor, Structure Determination and Live Cell Imaging†

“…Herein we report, a diformyl thioether based fluorescent chemosensor, H 2 ‐SAP , prepared by simple Schiff base condensation procedure ( Scheme S1 ) which displays selective fluorescence sensitivity towards Zn 2+ by chelation enhancement fluorescence effect (CHEF) process in presence of large number of ions and could identify Zn 2+ in nM level, much lower than so far reported results . The composition of the complex formed between Zn 2+ and H 2 ‐SAP has been supported by spectroscopic data (Mass, Job's plot) and single crystal X‐ray crystallography.…”

“…Chemical sensing via fluorescence signal recognition has been first established during 1980s . Since then researchers are engaged to design various types of fluorogenic sensors to detect Zn 2+ in different environment including intracellular measurements, Fluorogenic motifs like naphthyl, Diformyl derivative, terpyridyl, quinoline,, imidazoylpyridyl,, bipyridyl,, pyrenyl derivatives, terphenyl‐based motif, pyrimidinyl attached Schiff‐base, pyrazolyl,, BINOL, rhodamine,, catechol appended Schiff base, coumarinyl Schiff base, thiazolyl derivative etc. have successfully been used.…”

The Role of 8-Amidoquinoline Derivatives as Fluorescent Probes for Zinc Ion Determination

“…However, the emission was at different wavelength (Al 3+ = 439 nm, Zn 2+ = 550 nm). Figure 15b) displayed fluorescence enhancement ratios of sensors 1-4 in 9 EtOH: 1 H2O in the presence of different metal ions, respectively [147]. However, some limitations still exist for these compounds as Zn fluorophores.…”