Esterase-activated two-fluorophore system for ratiometric sensing of biological zinc(II)

Intracellular ester hydrolysis by cytosolic esterases is a common strategy used to trap fluorescent sensors within the cell. We have prepared analogues of Zinpyr-1 (ZP1), an intensity-based fluorescent sensor for Zn2+, that are linked via an amido-ester or diester moiety to a calibrating fluorophore, coumarin 343. These compounds, designated Coumazin-1 and -2, are nonpolar and are quenched by intramolecular interactions between the two fluorophores. Esterase-catalyzed hydrolysis generates a Zn2+-sensitive ZP1-like fluorophore and a Zn2+-insensitive coumarin as a calibrating fluorophore. Upon excitation of the fluorophores, coumarin 343 emission relays information concerning sensor concentration whereas ZP1 emission indicates the relative concentration of Zn2+-bound sensor. This approach enables intracellular monitoring of total sensor concentration and provides a ratiometric system for sensing biological zinc ion.     

Analogues of Zinpyr-1 provide insight into the mechanism of zinc sensing

Three compounds structurally related to the fluorescent zinc sensor Zinpyr-1 (ZP1) have been synthesized and characterized. In each of these ZinAlkylPyr (ZAP) analogues, an alkyl group (methyl, benzyl) replaces one of the metal-binding picolyl moieties in ZP1. The methyl-for-picolyl substitutions in ZAP1 and ZAP2 have a negligible effect on the optical spectrum of the fluorophore but elevate the quantum yields (Phi = 0.82 (ZAP1), 0.74 (ZAP2)) to values near that of Zn2+-saturated ZP1 (Phi = 0.92). The benzyl-for-picolyl substitution in ZAP3 similarly enhances the quantum yield (Phi = 0.52) relative to that of metal-free ZP1 (Phi = 0.38). As previously observed for methylated ZP1 sensors, methylation of the 6-position of the pyridyl ring diminishes the emission by lowering both the molar extinction coefficient and the quantum yield. Although these new ZAP compounds cannot detect Zn2+ fluorimetrically at neutral pH, complexation of Zn2+ does occur, as evidenced by sizable changes in the optical spectra. The ZAP1-3 probes can detect Zn2+ fluorimetrically at pH 9, indicating that proton-induced background emission obscures any Zn2+-induced fluorescence at pH 7. The tertiary amine groups in ZAP1-3 are less basic than those in ZP1, which implies that the additional pyridine rings are responsible for the emissive response to Zn2+ at pH 7.0.     

ZP4, an improved neuronal Zn2+ sensor of the Zinpyr family

A second-generation fluorescent sensor for Zn(2+) from the Zinpyr family, ZP4, has been synthesized and characterized. ZP4 (Zinpyr-4, 9-(o-carboxyphenyl)-2-chloro-5-[2-(bis(2-pyridylmethyl)aminomethyl)-N-methylaniline]-6-hydroxy-3-xanthanone) is prepared via a convergent synthetic strategy developed from previous studies with these compounds. ZP4, like its predecessors, has excitation and emission wavelengths in the visible range ( approximately 500 nm), a dissociation constant (K(d)) for Zn(2+) of less than 1 nM and a high quantum yields (Phi = approximately 0.4), making it well suited for biological applications. A 5-fold fluorescent enhancement is observed under simulated physiological conditions corresponding to the binding of the Zn(2+) cation to the sensor, which inhibits a photoinduced electron transfer (PET) quenching pathway. The metal-binding stereochemistry of ZP4 was evaluated through the synthesis and X-ray structural characterization of [M(BPAMP)(H(2)O)(n)](+) complexes, where BPAMP is [2-(bis(2-pyridylmethyl)aminomethyl)-N-methylaniline]-phenol and M = Mn(2+), Zn(2+) (n = 1) or Cu(2+) (n = 0).     

一种高灵敏度高选择性的荧光素基比色荧光锌传感器

本文报道了一种基于荧光素的锌离子传感器FN1,其在甲醇溶液中显示了对锌离子极高的灵敏度和选择性。随着锌离子的滴加,紫外-可见光谱中最初在371 nm处的吸收峰消失,在437 nm处出现了一个新峰。当在混合金属离子的甲醇溶液中滴加了相对于二价金属离子的等物质的量浓度的锌离子或相对于一价金属离子0.5倍物质的量浓度的锌离子后,锌离子积分荧光强度增强了近37倍（Φ=0.48,λ_max(em)=513 nm）,估算的锌离子检测限为7 μg·L^-1。基于紫外-可见光、荧光和质谱的结果,讨论了1∶1的FN1/Zn²⁺配合物的结合机理。     

A ratiometric fluorescence probe for selective visual sensing of Zn2+

A simple ratiometric fluorescence probe based on vinylpyrrole end-capped bipyridine for the visual sensing of Zn2+ under aqueous physiological pH (6.8-7.4) is described. The fluorophores 3a-c showed strong emission around 537 nm in acetonitrile with a quantum yield of 0.4. In buffered (HEPES, pH 7.2) acetonitrile-water mixture (9:1 v/v), titration of transition metal salts to 3c showed strong quenching of the emission at 547 nm except in the case of Zn2+, which resulted in a red-shifted emission at 637 nm. Alkali and alkaline earth metal salts could not induce any considerable changes to the emission behavior of 3a-c. The binding of Zn2+ was highly selective in the presence of a variety of other metal ions. Though Cu2+ quenches the emission of 3c, in the presence of Zn2+, a red emission prevails, indicating the preference of 3c toward Zn2+. Job plot and Benesi-Hildebrand analysis revealed a 1:1 complexation between the probe and the metal ion. The selective visual sensing of Zn2+ with a red emission is ideally suited for the imaging of biological specimens.     

Dendrimers as ligands. Formation of a 2:1 luminescent complex between a dendrimer with a 1,4,8,11-tetraazacyclotetradecane (cyclam) core and Zn2+

We have investigated the formation of metal complexes between Zn2+ and two derivatives, 1 and 2, of the well-known 1,4,8,11-tetraazacyclotetradecane (cyclam) ligand. Compound 1 is 1,4,8,11-tetrakis(naphthylmethyl) cyclam, and compound 2 is a dendrimer consisting of a cyclam core with appended 12 dimethoxybenzene and 16 naphthyl units. Compound 1 exhibits an emission band with a maximum around 480 nm, assigned to the formation of exciplexes between amine and excited naphthyl units. Dendrimer 2 exhibits three types of weak emission bands, assigned to naphthyl localized excited states (lambdamax = 337 nm), naphthyl excimers (lambdamax ca. 390 nm), and naphthyl-amine exciplexes (lambdamax = 480 nm). In CH3CN-CH2Cl2 1:1 v/v, titration of ligand 1 with Zn2+ causes the disappearance of the exciplex emission and the appearance of a strong naphthyl localized fluorescence; the titration plot is linear and reaches a plateau for a 1:1 stoichiometry, showing that a highly stable [Zn(1)]2+ complex is formed. In the case of 2, titration with Zn2+ causes the disappearance of the exciplex band, with a concomitant increase in the excimer and naphthyl localized emissions; the titration plot is again linear, but in this case it reaches a plateau for a 2:1 stoichiometric ratio, showing the unexpected formation of a [Zn(2)2]2+ complex. Such an unexpected stoichiometry for the complex of the dendritic ligand has been fully confirmed by 1H NMR titrations. The results obtained show that the dendrimer branches not only do not hinder, but in fact favor coordination of cyclam to Zn2+.     

A luminescence sensor of inositol 1,4,5-triphosphate and its model compound by ruthenium-templated assembly of a bis(Zn2+-cyclen) complex having a 2,2'-bipyridyl linker (cyclen = 1,4,7,10-tetraazacyclododecane)

A new supramolecular complex (Ru(Zn2L4)3) was designed and synthesized as a luminescence sensor for inositol 1,4,5-triphosphate (IP3), which is one of the important second messengers in intracellular signal transduction, and its achiral model compound, cis,cis-1,3,5-cyclohexanetriol triphosphate (CTP3), by a ruthenium(II)-templated assembly of three molecules of a bis(Zn2+-cyclen) complex having a 2,2-bipyridyl linker (Zn2L4). Single-crystal X-ray diffraction analysis of a racemic mixture of Ru(Zn2L4)3 showed that three of the six Zn2+-cyclen units are orientated to face the opposite side of the molecule with three apical ligands (Zn2+-bound HO-) of each of the three Zn2+ located on the same face. 1H NMR and UV titrations of Ru(Zn2L4)3 with CTP3 indicated that Ru(Zn2L4)3 forms a 1:2 complex with CTP3, (Ru(Zn2L4)3)-((CTP3)6-)2, in aqueous solution at neutral pH. In the absence of guest molecules, Ru(Zn2L4)3 (10 microM) has an emission maximum at 610 nm at pH 7.4 (10 mM HEPES with I = 0.1 (NaNO3)) and 25 degrees C (excitation at 300 nm). An addition of 2 equiv of CTP3 induced a 4.2-fold enhancement in the emission of Ru(Zn2L4)3 at 584 nm. In this article, we describe that Ru(Zn2L4)3 is the first chemical sensor that directly responds to CTP3 and IP3 and discriminates these triphosphates from monophosphates and diphosphates. The photodecomposition of Ru(Zn2L4)3, which is inhibited upon complexation with CTP3, and the stereoselective complexation of chiral IP3 by Ru(Zn2L4)3 are also described.     

A new fluorescent probe for zinc(II): an 8-hydroxy-5-N,N-dimethylaminosulfonylquinoline-pendant 1,4,7,10-tetraazacyclododecane

A new fluorescent probe for Zn2+, namely, 8-hydroxy-5-N,N-dimethylaminosulfonylquinolin-2-ylmethyl-pendant cyclen (L8), was designed and synthesized (cyclen=1,4,7,10-tetraazacyclododecane). By potentiometric pH, 1H NMR, and UV spectroscopic titrations, the deprotonation constants pKa1-pKa6 of L(8)4 HCl were determined to be <2, <2, <2 (for amino groups of the cyclen and quinoline moieties), 7.19+/-0.05 (for 8-OH of the quinoline moiety), 10.10+/-0.05, and 11.49+/-0.05, respectively, at 25 degrees C with I=0.1 (NaNO3). The results of 1H NMR, potentiometric pH, and UV titrations, as well as single-crystal X-ray diffraction analysis, showed that L8 and Zn2+ form a 1:1 complex [Zn(H-1L8)], in which the 8-OH group of the quinoline ring of L8 is deprotonated and coordinates to Zn2+, in aqueous solution at neutral pH. On addition of one equivalent of Zn2+ and Cd2+, the fluorescence emission of L8 (5 microM) at 512 nm in aqueous solution at pH 7.4 [10 mM HEPES with I=0.1 (NaNO3)] and 25 degrees C increased by factors of 17 and 43, respectively. We found that the cyclen moiety has the unique property of quenching the fluorescence emission of the quinolinol moiety when not complexed with metal cations, but enhancing emission when complexed with Zn2+ or Cd2+. In addition, the Zn2+-L8 complex [Zn(H-1L8)] is much more thermodynamically and kinetically stable (Kd{Zn(H-1L8)}=[Zn2+]free[L8]free/[Zn(H-1L8)]=8 fM at pH 7.4) than the Zn2+ complexes of our previous Zn2+ fluorophores ([Zn(H-1L2)] and [Zn(L3)]). Furthermore, formation of [Zn(H-1L8)] is much faster than those of [Zn(H-1L2)] and [Zn(L3)]. The staining of early-stage apoptotic cells with L8 is also described.     

Ratiometric and selective fluorescent sensor for CuII based on internal charge transfer (ICT)

A Cu(II)-sensing, ratiometric, and selective fluorescent sensor 1, N-butyl-4,5-di[(pyridin-2-ylmethyl)amino]-1,8-naphthalimide, was designed and synthesized on the basis of the mechanism of internal charge transfer (ICT). In aqueous ethanol solutions of 1, the presence of Cu(II) induces the formation of a 1:1 metal-ligand complex, which exhibits a strong, increasing fluorescent emission centered at 475 nm at the expense of the fluorescent emission of 1 centered at 525 nm. [structure: see text]     

基于羟苯基苯并咪唑的Zn2+比率荧光探针

通过羰基将两分子2-(4-氨基-2-羟苯基)苯并咪唑(4-AHBI)连接,合成了结构高度对称的新化合物N,N′-二-[3-羟基-4-(2-苯并咪唑)苯基]脲(C27H20N6O3,1),测试了不同溶剂条件下1的紫外吸收和荧光发射光谱,研究了1对Zn2+的选择性识别作用。结果表明,随着溶剂极性的增大,1的紫外吸收峰发生蓝移,激发态分子内质子转移(ESIPT)荧光发射峰明显增强。与4-AHBI相比,1在乙腈溶液中的紫外吸收强度增强约3.5倍,最大吸收峰红移8 nm,荧光发射增强8倍多。1在乙腈溶液中的Zn2+荧光响应行为表明1与Zn2+的结合将导致1在445 nm处的荧光强度不断降低,而在395 nm处出现的新峰的荧光强度不断增强,具有比率荧光探针的特点,而且检测范围较宽,可达1×10-6-1×10-2 mol.L-1。     

Intra-molecular Electronic Energy Transfer in Mono- and Di-nuclear Zinc(II) Supramolecular Complexes

Intra-molecular electronic energy transfer processes have been investigated in systems containing two distinct fluorophores Fl 1 (absorbing photonic energy) and Fl 2 (coumarin 343, brought at a close distance through coordinative interactions, emitting). Fl 1 is covalently linked or incorporated in a polyamine platform containing one or two Zn II ions, while Fl 2 coordinates the Zn II centre(s) through a carboxylate group. Zn II has been chosen for its photophysical inactivity and quick reversibility of the interaction with Fl 2 .     

A ratio-metric fluorescent sensor design platform with red emission of Europium(III) as built-in fluorescence correction

A Eu^III-containing single molecule BCR-Eu as design platform for ratio-metric fluorescent sensor which includes a blue-emitting coumarin dye, a green-emitting BODIPY fluorophore and a Eu^III moiety as the origin of red light has been designed and synthesized. The compound BCR shows only green emission with large stoke shift when excited in 400 nm due to good fluorescence resonance energy transfer from coumarin to BODIPY. After embedding Eu^III complexes in the molecule, BCR-Eu exhibits dual emission which is equal in magnitude and independent of each other, when excited at the range of 305–365 nm. An emission from Lanthanide complexes as the stable built-in standard fluorescence peak offers a promising opportunity to enhance the precision of bioimaging and also an ideal design platform for future ratio-metric fluorescent sensor.     

Solvent dependent fluorescent properties of a 1,2,3-triazole linked 8-hydroxyquinoline chemosensor: tunable detection from zinc(II) to iron(III) in the CH3CN/H2O system

A triazole-containing 8-hydroxyquinoline (8-HQ) ether 2 was efficiently synthesized in two steps from the "click" strategy. Compound 2 gave a strong fluorescence (Φ = 0.21) in nonprotic solvent like CH(3)CN, and a weak fluorescence (Φ = 0.06) in protic solvent like water. In water, a more than 100 nm red shift of the fluorescence maximum was observed for compound 2 in comparison with that in CH(3)CN. This fluorescence difference may be attributed to the intermolecular photoinduced proton transfer (PPT) process involving the protic solvent water molecules. Similarly, this intermolecular PPT process was also observed in the high-water-content CH(3)CN aqueous solution (e.g., CH(3)CN/H(2)O = 5/95, v/v). The water content in the CH(3)CN/H(2)O binary solvent mixture greatly affected the fluorescence intensity (e.g., Φ = 0.06 and 0.25 when CH(3)CN/H(2)O = 5/95 and 95/5, v/v, respectively) and emission wavelength. Using this interesting property, by simple variation of the water content in the CH(3)CN aqueous solution, compound 2 was tuned from a selective "turn-on" fluorescent sensor for Zn(2+) (CH(3)CN/H(2)O = 5/95, v/v) to a ratiometric one for Zn(2+) and a selective "turn-off" one for Fe(3+) (CH(3)CN/H(2)O = 95/5, v/v) over a wide range of pH value. In high-water-content (CH(3)CN/H(2)O = 5/95, v/v) aqueous solution compound 2 shows a selective "turn-on" response toward Zn(2+), with a 10-fold enhancement in the fluorescence intensity at 428 nm and a 62 nm blue shift of the emission maximum (490 to 428 nm) due to the inhibition of intermolecular PPT process upon chelating with Zn(2+). However, in a less polar solvent (CH(3)CN/H(2)O = 95/5, v/v) in which compound 2 has high fluorescence (quantum yield =0.25), it shows a ratiometric response toward Zn(2+), with a continuous decrease of the fluorescence intensity at 399 nm and an increase at 423 nm. More interestingly, in this case, it also exhibits a very sensitive, selective, and ratiometric fluorescence quenching in the presence of Fe(3+), with an 81 nm red shift of the emission maximum (399 to 480 nm) in a wide range of pH through a metal ligand charge transfer (MLCT) effect.     

Coumarin-based two-photon AIE fluorophores: Photophysical properties and biological application

Based on the coumarin skeleton, we deliberately designed two groups of fluorophores, termed as Coum-R and Naph-Coum-R, using the diphenylamino group as the electron donor, which displayed long-wavelength emissions (red spectral region), large Stokes shift (up to 204 nm), superior AIE performance, and large two-photon absorbance cross-sections (as high as 365 GM). The electron-withdrawing substituents at the 3-position of these dyes could induce a significant red-shift in their emission spectra. Preliminary imaging experiments demonstrated the capability of these dyes as two-photon fluorophores for specifically staining lipid droplets in living cells.     

8-Hydroxyquinoline derivative as a fluorescent chemosensor for zinc ion.

8-Hydroxyquinoline derivative 1 as a fluorescent chemosensor for Zn2+ was synthesized. Because Cd2+ is often found with Zn2+ in the environment and can form fluorescent complexes with chelating fluorophores, a potentially important property of chemosensors for Zn2+ is their selectivity for Zn2+ over Cd2+. The Zn2+ or Cd2+ complexes of 1 gave an emission band from the 1:1 complex, but the fluorescence intensity for Cd2+ was a half of that for Zn2+. Ligand 1 is suited for use as a fluorescent chemosensor for Zn2+.     

6-methylpyridyl for pyridyl substitution tunes the properties of fluorescent zinc sensors of the Zinpyr family

To prepare fluorescent zinc sensors with binding affinities lower than that of the parent 9-(o-carboxyphenyl)-2,7-dichloro-4,5-bis(bis(2-pyridylmethyl)methylaminomethyl)-6-hydroxy-3-xanthenone (ZP1), dimethylated and tetramethylated derivatives were synthesized having either two or four of the pyridyl subunits methylated at the 6-position. Like the parent ZP1, both Me(2)ZP1 and Me(4)ZP1 exhibit increased fluorescence in the presence of Zn(2+). The integrated emission of Me(2)ZP1 increases 4-fold in the presence of excess zinc, whereas Me(4)ZP1 displays 2.5-fold enhanced fluorescence for Zn(2+). Methylating the 6-positions of the pyridyl rings raises the dissociation constant of the sensors and lowers the pK(a) values associated with the tertiary amine ligands in a systematic manner. The properties of the dimethylated Me(2)ZP1 dye resemble those of ZP1, but the tetramethylated Me(4)ZP1 differs greatly from ZP1 in terms of its brightness, affinity toward Zn(2+), exchange kinetics, and metal sensitivity. Both Me(2)ZP1 and Me(4)ZP1 can enter HeLa cells and signal the presence of Zn(2+). Staining caused by both dyes is punctate, with localization patterns resembling that observed for ZP1.     

5,5-二乙烯基-2,2-联吡啶:可能的新型锌离子荧光探针(英文)

生物体系里微量元素锌在发育、新陈代谢和疾病的发生等多个领域扮演了重要的角色,定性和定量测量锌的含量将帮助我们理解锌的生物学意义。我们偶然发现5,5-二乙烯基-2,2-联吡啶(DVBP)在二氧六环里对锌离子呈现出类似比例计量型荧光探针的特性:即有2个荧光发射峰而且长波长峰随锌离子的增加按比例增长。但DVBP难溶于水而且2个荧光发射峰距离太近从而相互干扰,我们尝试利用硅氢反应将DVBP固定在多孔硅上制备感应锌离子的光极,我们发现多孔硅固相载体上的联吡啶通过与锌离子的螯合后荧光增强约8倍,比DVBP在溶液里与锌离子螯合后的荧光增强(约4.5倍)还要多,联吡啶对锌离子的荧光响应是一个值得继续探索的领域。     

From model compounds to protein binding: syntheses, characterizations and fluorescence studies of [RuII(bipy)(terpy)L]2+ complexes (bipy = 2,2'-bipyridine; terpy = 2,2':6',2''-terpyridine; L = imidazole, pyrazole and derivatives, cytochrome c)

Compounds [RuII(bipy)(terpy)L](PF6)2 with bipy = 2,2'-bipyridine, terpy = 2,2':6',2"-terpyridine, L = H2O, imidazole (imi), 4-methylimidazole, 2-methylimidazole, benzimidazole, 4,5-diphenylimidazole, indazole, pyrazole, 3-methylpyrazole have been synthesized and characterized by 1H NMR, ESI-MS and UV/Vis (in CH3CN and H2O). For L = H2O, imidazole, 4,5-diphenylimidazole and indazole the X-ray structures of the complexes have been determined with the crystal packing featuring only few intermolecular C-H...pi or pi-pi interactions due to the separating action of the PF6-anions. Complexes with L = imidazole and 4-methylimidazole exhibit a fluorescence emission with a maximum at 662 and 667 nm, respectively (lambdaexc= 475 nm, solvent CH3CN or H2O). The substitution of the aqua ligand in [Ru(bipy)(terpy)(H2O)]2+ in aqueous solution by imidazole to give [Ru(bipy)(terpy)(imi)]2+ is fastest at a pH of 8.5 (as followed by the increase in emission intensity). Coupling of the [Ru(bipy)(terpy)]2+ fragment to cytochrome c(Yeast iso-1) starting from the Ru-aqua complex was successful at 35 degrees C and pH 7.0 after 5 d under argon in the dark. The [Ru(bipy)(terpy)(cyt c)]-product was characterized by UV/Vis, emission and mass spectrometry. The location where the [Ru(bipy)(terpy)] complex was coupled to the protein was identified as His44 (corresponding to His39 in other numbering schemes) using digestion of the Ru-coupled protein by trypsin and analysis of the tryptic peptides by HPLC-high resolution MS.     

Ratiometric fluorescent sensor based on inhibition of resonance for detection of cadmium in aqueous solution and living cells

Although cadmium has been recognized as a highly toxic heavy metal and poses many detrimental effects on human health, the Cd(2+)-uptake and nosogenesis mechanisms are still insufficiently understood, mainly because of the lack of facile analytical methods for monitoring changes in the environmental and intracellular Cd(2+) concentrations with high spatial and temporal reliability. To this end, we present the design, synthesis, and photophysical properties of a cadmium sensor, DQCd1 based on the fluorophore 4-isobutoxy-6-(dimethylamino)-8-methoxyquinaldine (model compound 1). Preliminary investigations indicate that 1 could be protonated under neutral media and yield a resonance process over the quinoline fluorophore. Upon excitation at 405 nm, 1 shows a strong fluorescence emission at 554 nm with a quantum yield of 0.17. Similarly, DQCd1 bears properties comparable to its precursor. It exhibits fluorescence emission at 558 nm (Φ(f) = 0.15) originating from the monocationic species under physiological conditions. Coordination with Cd(2+) causes quenching of the emission at 558 nm and simultaneously yields a significant hypsochromic shift of the emission maximum to 495 nm (Φ(f) = 0.11) due to inhibition of the resonance process. Thus, a single-excitation, dual-emission ratiometric measurement with a large blue shift in emission (Δλ = 63 nm) and remarkable changes in the ratio (F(495 nm)/F(558 nm)) of the emission intensity (R/R(0) up to 15-fold) is established. Moreover, the sensor DQCd1 exhibits very high sensitivity for Cd(2+) (K(d) = 41 pM) and excellent selectivity response for Cd(2+) over other heavy- and transition-metal ions and Na(+), K(+), Mg(2+), and Ca(2+) at the millimolar level. Therefore, DQCd1 can act as a ratiometric fluorescent sensor for Cd(2+) through inhibition of the resonance process. Confocal microscopy and cytotoxicity experiments indicate that DQCd1 is cell-permeable and noncytotoxic under our experimental conditions. It can indeed visualize the changes of intracellular Cd(2+) in living cells using dual-emission ratiometry.     

N-芳基香豆素甲基酮缩氨基硫脲对Cu2+的选择性比色识别

设计合成了2种新型N-芳基香豆素甲基酮缩氨基硫脲受体分子S1和S2, 利用紫外-可见(UV-Vis)吸收光谱考察了其对Fe3+, Hg2+, Ag+, Ca2+, Cu2+, Zn2+, Pb2+, Cd2+, Ni2+, Cr3+和Mg2+等阳离子的识别作用. 结果表明, 当加入Cu2+时, 溶液颜色立刻由无色变为黄色, 而加入其它阳离子则无变化, 从而实现了对Cu2+的裸眼检测, 具有专一选择性比色识别效果. 通过计算可知, 受体分子S2对Cu2+的络合常数大于S1, 且主客体间形成1: 1的配合物. 受体分子S2对Cu2+的检出限为2.0×10-7 mol/L, 稳定常数Ks=1.02×105 L/mol. 另外, 在EDTA存在时, 配合物可以释放出Cu2+, 与EDTA结合, 表现出对Cu2+的"off-on"模式.