Bis(2-quinolylmethyl)ethylenediaminediacetic acids (BQENDAs), TQEN–EDTA hybrid molecules as fluorescent zinc sensors

Abstract

Molecular hybrids of TQEN (N,N,N',N'-tetrakis(2-quinolylmethyl)ethylenediamine) and EDTA (ethylenediamine-N,N,N',N'-tetraacetic acid) were examined as fluorescent Zn(2+) sensors. Upon the addition of Zn(2+), N,N-BQENDA (N,N-bis(2-quinolylmethyl)ethylenediamine-N',N'-diacetic acid, 1a) exhibits a 30-fold emission enhancement at 456 nm (λex = 315 nm, ϕZn = 0.018) in buffer (HEPES, pH = 7.5, 100 mM KCl). The fluorescence enhancement is Zn(2+)-specific as Cd(2+) induces much smaller increases (ICd/I0 = 5 and ICd/IZn = 16%). These spectroscopic properties, as well as the excellent water-solubility, represent a significant improvement compared to the parent TQEN sensor (ϕZn = 0.007, ICd/IZn = 64%). The isoquinoline analog N,N-1-isoBQENDA (N,N-bis(1-isoquinolylmethyl)ethylenediamine-N',N'-diacetic acid, 1b) possesses a similar Zn(2+) fluorescence response to the parent 1-isoTQEN (N,N,N',N'-tetrakis(1-isoquinolylmethyl)ethylenediamine) sensor, but exhibits diminished fluorescence intensity. Apo 1a and 1b extract more than 50% of the Zn(2+) from an equimolar amount of [Zn(TPEN)](2+) (TPEN = N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine) or [Zn(EDTA)](2-), whereas TPEN and EDTA cannot effectively remove Zn(2+) from [Zn(1a)] and [Zn(1b)]. The reduction of steric crowding in [Zn(TQEN)](2+) resulting from the substitution of two quinolines with carboxylates enhances the interaction between the metal ion and the remaining quinoline nitrogen atoms. The stronger bonding interaction results in enhanced emission intensity, Zn(2+) selectivity and metal ion affinity. This is in contrast to [Zn(1-isoTQEN)](2+) where the isoquinoline-carboxylate replacement does not relieve any coordination distortion, therefore no significant changes in fluorescence or metal binding properties are observed.

N,N,N′,N′‐Tetrakis(3‐isoquinolylmethyl)‐2,6‐lutidylenediamine (3‐isoTQLN): A Fluorescent Zn2+/Cd2+ Dual Sensor as a Hybrid of 2‐Quinolyl/1‐Isoquionolyl Counterparts TQLN/1‐isoTQLN

“…Our previous investigation revealed that the long fluorescence lifetime were suggestive of excimer emission. [37][38][39][40][41] As discussed in our previous communication, [36] the long lifetime of TQLNÀ Zn 2 + is an indication of intramolecular excimer emission and short lifetime of 1-isoTQLNÀ Cd 2 + complex suggests the monomer emission based on CHEF and inhibition of PeT. [42] Table summarizes the data from fluorescence lifetime measurement and other fluorescence properties of TQLN derivatives.…”

“…The present results provide valuable information for future molecular design of fluorescent probes for specific metal ions and other small molecules. Development of water-soluble derivatives [33,40,45] is also under investigation in our laboratory.…”

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

“…stronger metal bonding affinity, the sensor has higher selectivity towards Zn 2+ detection [84]. It is crucial to keep in mind that fluorescent groups with lone pairs of electrons like nitrogen will be quenching the emission.…”

“…Figure 4c showed, under the same condition, the emission of N, N-BQENDA-Zn is more enhanced than the emission of TQEN-Zn. With the stronger metal bonding affinity, the sensor has higher selectivity towards Zn 2+ detection [84].…”

A highly selective multi-responsive fluorescence sensor for Zn2+ based on a diarylethene with a 4,6-dimethylpyrimidine unit

“…In order to deeply understand the crucial role of Zn 2+ in important life processes, large amounts of Zn 2+ uorescent sensors have been accepted and effectively applied in vivo. [19][20][21][22][23][24] Among the reported uorescent chemosensors for detecting Zn 2+ , [25][26][27][28] diarylethenes are considered one of the most potential candidates due to their remarkable fatigue resistance, excellent thermal stability, rapid response and multi-responsively photoswitchable properties under various stimulations. [29][30][31][32] To date, numerous diarylethene-based uorescent sensors with various functional groups have been developed for the detection of Zn 2+ .…”