•The inclusion formation constant (K) was different in various pH values.•The inclusion stoichiometry was 1(FA):1(SCXn).•The thermal and photostability as well as the antioxidant activity of FA were all increased by formation inclusion complexes.The inclusion complexes of ferulic acid (FA) with p-Sulfonatocalix[n]arenes (SCXn, n = 4, 6, 8) were prepared and characterized both in the solid state and in solution using fluorescence spectroscopy, 1H nuclear magnetic resonance (1H NMR), attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). The results show that FA is able to form inclusion complexes with SCXn in a molar ratio of 1:1, causing a significant decrease in the fluorescence intensity of FA. The association constant of the inclusion complexes was calculated from the fluorescence titration data. 1H NMR spectroscopy analysis demonstrates that the aromatic ring and methoxy group of FA are partially covered by SCXn.Download high-res image (452KB)Download full-size image

•A novel ‘‘donor-π-acceptor’’ type fluorescence probe (PMPA) for sensing pH was facilely synthesized.•PMPA showed high response speed, selectivity and sensitivity towards pH.•PMPA had been applied successfully to imaging in vivo.A novel pH fluorescent probe 1-(pyren-1-yl)-3-(6-methoxypridin-3-yl)-acrylketone, (PMPA), which had a pyrene structure attached to methoxypyridine, was synthesized for monitoring extremely acidic and alkaline pH. The pH titrations indicated that PMPA displayed a remarkable emission enhancement with a pKa of 2.70 and responded linearly to minor pH fluctuations within the extremely acidic range of 1.26–3.97. Interestingly, PMPA also exhibited strong pH-dependent characteristics with pKa 9.32 and linear response to extreme-alkalinity range of 8.54–10.36. In addition, PMPA displayed a good selectivity, excellent photostability and large Stokes shift (167 nm). Furthermore, the probe PMPA had excellent cell membrane permeability and was applied successfully to rapidly detect pH in living cells. pH value in these organs was closely related to many diseases, so these findings suggested that the probe had potential application in pH detecting for disease diagnosis.Download high-res image (408KB)Download full-size image

•A simple tailor-made pH fluorescent probe (Probe) is facilely synthesized by the condensation reaction of 2-hydrazinobenzothiazole with N-ethylcarbazole-3-formaldehyde.•It is a useful fluorescent probe for monitoring both extremely acidic and extremely alkaline pH with different sets of fluorescence signals in the same system, quantitatively.•Fluorescent pH imaging in living E. coli cells is further successfully applied.A simple tailor-made pH fluorescent probe 2-benzothiazole (N-ethylcarbazole-3-yl) hydrazone (Probe) is facilely synthesized by the condensation reaction of 2-hydrazinobenzothiazole with N-ethylcarbazole-3-formaldehyde, which is a useful fluorescent probe for monitoring extremely acidic and alkaline pH, quantitatively. The pH titrations indicate that Probe displays a remarkable emission enhancement with a pKa of 2.73 and responds linearly to minor pH fluctuations within the extremely acidic range of 2.21–3.30. Interestingly, Probe also exhibits strong pH-dependent characteristics with pKa 11.28 and linear response to extreme-alkalinity range of 10.41–12.43. In addition, Probe shows a large Stokes shift of 84 nm under extremely acidic and alkaline conditions, high selectivity, excellent sensitivity, good water-solubility and fine stability, all of which are favorable for intracellular pH imaging. The probe is further successfully applied to image extremely acidic and alkaline pH values fluctuations in E. coli cells.Download high-res image (103KB)Download full-size image

A colorimetric and fluorescent pH probe 1-(4-methylphenyl)-3-(4-dimethylaminophenyl) acrylketone (MDAK) was facilely prepared. The probe exhibited strong pH-dependent behavior and responded linearly and rapidly to minor pH fluctuations within the range of 1.53–3.96. In addition, MDAK displayed a notably large Stokes shift of 121 nm. MDAK possessed a highly selective response to H+ over other metal ions, amion acids and displayed good photostability and excellent reversibility. Furthermore, it can be applied to visualize extreme acidity in E. coli cells.

A simple tailor-made water-soluble broadly emitting (500–650 nm) fluorescent probe 3-methyl-2-(N-ethylcarbazole-3vinyl)-benzothiazolium iodide (IECBT) for the selective and sensitive detection of multiple analytes, including CN−, HSO3− and extremely alkaline pH, is designed and synthesized via the ethylene bridging of 3-formyl-N-ethylcarbazole and 2,3-dimethyl benzothizolium iodide, which is a useful fluorescent probe for monitoring these analytes at extremely low concentrations quantitatively. CN− and HSO3− are expected to undergo 1,4-addition reactions with the C-4 atom in the ethylene group of IECBT. This water-soluble fluorescent probe exhibits excellent sensitivity and selectivity toward CN− in DMSO, which also results in a prominent fluorescence ratiometric change and a color change. The high selectivity and sensitivity of IECBT toward HSO3− and extremely alkaline pH over other coexisting species in water are also observed. The titration experiments show that it features a remarkably large Stokes shift and good stability towards CN−, HSO3− or extremely alkaline pH with a significant fluorescence turn-off response. Importantly, we demonstrate that IECBT can be used for the real-time sensing and bioimaging of CN−, HSO3− or extremely alkaline pH in living samples.

•A highly sensitive acidic pH fluorescent probe (BLIE) is facilely synthesized.•BLIE displays high selective and large Stokes shift to extreme acidity.•BILE has been applied successfully to imaging extreme acidity in E. coli cells.A new pH fluorescent probe 3-(N-butylcarbazol-3-dicyanovinyl) pyridine (BILE), which has a carbazole structure attached to pyridine, is synthesized for extremely acidic conditions. BILE displays excellent pH-dependent performance with a pKa of 2.93 and responds linearly to minor pH changes in the range of 2.60–3.30, which can be used to quantitatively detect pH value based on regression equation, F = 2495.42 × pH – 6316.28. Moreover, BILE has good selectivity, large Stokes shift (122 nm), sensitivity and short response time. More importantly, BILE has been applied successfully to imaging extreme acidity in E. coli cells, indicating that the probe can afford practical application in biological systems.

•A ratiometric fluorescent probe (Probe) is facilely synthesized via the ethylene bridging of N-ethylcarbazole-3-formaldehyde and 1,1,2-trimethyl-3-ethyl-1H-benz[e]indolium iodide.•It is a useful fluorescent probe for monitoring cyanide ion at very low concentrations (1–2 μM), quantitatively.•The detection limit of probe for CN− is found to be 0.23 μM.•It exhibits a large Stokes shift, good selectivity, sensitivity and stability.•Fluorescent CN− imaging in living cells by this probe is further successfully applied.A ratiometric emission fluorescent probe 1,1-dimethyl-3-ethyl-2-(2-(N-ethyl-carbazol-3-yl)-vinyl)-1H-benzo[e]indolium iodide (Probe) is facilely synthesized via the ethylene bridging of N-ethylcarbazole-3-formaldehyde and 1,1,2-trimethyl-3-ethyl-1H-benz[e]indolium iodide, which is a useful fluorescent probe for monitoring cyanide ion at extremely low concentrations, quantitatively. The detection of cyanide is performed via the nucleophilic attack of cyanide toward the benzo[e]indolium group of the probe, resulting in a prominent fluorescence ratiometric change and a color change. The titration experiments for CN− show that it exhibits a large Stokes shift (92 nm), high selectivity, excellent sensitivity and good stability for CN− sensing in DMSO system. The detection limit of Probe for CN− is found to be 0.23 μM. Furthermore, the probe has excellent cell membrane permeability and is applied successfully to rapidly detect CN− in living cells.

•A ratiometric fluorescence pH probe ECBT is developed by ethylene bridging of N-ethyl-3-carbazolecarboxaldehyde and benzothiazole.•It is a useful fluorescent probe for strongly acidic pH sensing.•It exhibits good selectivity, sensitivity, photostability and reversibility.•The probe is further applied successfully to imaging extreme acidity in Escherichia coli cells.A ratiometric fluorescence pH probe 2-(N-ethylcarbazole-3-vinyl)-benzothiazole (ECBT) is facilely developed by ethylene bridging of N-ethyl-3-carbazolecarboxaldehyde and benzothiazole, which is a useful fluorescent probe for strongly acidic pH sensing. The pH titration indicates remarkable fluorescence enhancement effect and an emission red-shift of 87 nm with pH decreasing from 7.00 to 1.00. Furthermore, the solution color changes from light blue to orange under a UV lamp illumination. A pKa value of 1.62 and a good linearity in the pH range of 1.23–2.10 indicate that the probe can be used in quantitative fluorescence imaging under strongly acidic condition. In addition, ECBT exhibits high selectivity and sensitivity, good photostability and excellent reversibility for pH sensing. The probe is further applied successfully to imaging extreme acidity in Escherichia coli cells without influence of autofluorescence in biological systems.In this paper, a ratiometric fluorescence pH probe ECBT is facilely developed by ethylene bridging of N-ethyl-3-carbazolecarboxaldehyde and benzothiazole, which is a useful fluorescent probe for strongly acidic pH sensing. The pH titration experiments show that it exhibits high selectivity and sensitivity, good photostability and excellent reversibility for pH sensing and can be used in quantitative fluorescence imaging. In addition, laser scanning confocal microscopy of Escherichia coli cells demonstrated that this probe might be used to monitor the minor pH fluctuations in biological systems under strongly acidic condition.

•The inclusion interaction of SCXn with Caffeic acid was studied.•Fluorescence, DSC, SEM, FT-IR, NMR were applied to characterize the complex.•CA is able to form inclusion complexes with SCXn in a molar ratio of 1:1.•The thermal stability and photostability of CA were increased.•The antioxidant activity of CA on complexation with SCXn was increased.In this work the inclusion complex formation of Caffeic acid (CA) with p-sulfonatocalix[n]arenes (SCXn, n = 4, 6, 8) is reported aiming to improve the antioxidant activity, thermal stability and photostability properties of CA. Evidence for the formation was obtained using fluorescence spectroscopy, nuclear magnetic resonance spectroscopy (NMR), pulsed field gradient NMR (PFG-NMR), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and scanning electron microphotographs (SEM). Experimental conditions including concentrations of SCXn and pH were investigated for the inclusion formation in detail. The results showed that CA was able to form inclusion complexes with SCXn in a molar ratio of 1:1, and the formation constants were varied with the pH conditions. NMR spectroscopy indicated that both the aromatic ring and the vinyl group of CA were partially covered by SCXn.Graphical abstractSCX4 was more suitable than any other SCXn for inclusion of the CA molecule in acidic media, whereas SCX8 had a higher capacity to form an inclusion complex with CA in basic media. The antioxidant activity of CA on complexation with SCXn and the thermal stability and photostability of the system were increased.

•The inclusion behaviors of SCXn–NPP complexes were studied by spectroscopy.•The K values of SCXn–NPP complexes decreased with the increasing of pH value.•The inclusion mechanism was explored by 1H NMR and molecular modeling studies.The inclusion behaviors of 4-Sulfonatocalix[n]arenes (SCXn) (n = 4, 6, 8) with 1-(4-nitrophenyl)piperazine (NPP) were investigated by UV spectroscopy and fluorescence spectroscopy at different pH values (pH = 3.05, 6.50, 8.40). The UV absorption and fluorescence intensity of NPP remarkably increased in presence of SCXn revealing formation of the inclusion complexes between NPP and SCXn. Moreover, the formation constants (K) of inclusion complexes were also determined by the non-linear fitting method, and the obtained data showed that the formation constants decreased gradually with the increasing of the pH value. When the pH value was 3.05, the formation constant of NPP with SCX8 reached a maximum of 1.7 × 107 L mol−1. The stoichiometric ratio was verified to be 1:1 by the continuous variation method. Meanwhile FT-IR and DSC analysis also indicated that NPP could form the inclusion complex with SCXn. In order to explore the inclusion mechanism of NPP with SCXn, 1H NMR and molecular modeling studies were carried out and experimental results showed that the part of benzene ring of NPP penetrated into the hydrophobic cavity of SCXn.Graphical abstract

A coumarin-based dye, Fluorescent Red GK, was developed for the detection of bisulfite anions. The probe has exhibited high selectivity and sensitivity against other anions at room temperature. Upon addition of HSO3−, the strong fluorescence of Fluorescent Red GK was severely quenched and its color changed significantly from orange to colorless under illumination with a UV lamp. The color of the solution was also changed from pink to colorless. As a result, it can be used as a specific colorimetric and fluorescent probe for bisulfite anions. In addition, the detection limit was as low as 1.76 μM. The results showed that the Fluorescent Red GK could be used in the design of the fluorescent probe for detecting HSO3− in aqueous solution. Furthermore, the probe has been used for determination of bisulfite in sugar samples with satisfactory results.

•The inclusion interaction of p-sulfonatocalix[6]arene with triamterene was studied by spectroscopic methods.•The inclusion constant is obtained by the nonlinear curve fitting method.•The results showed that p-sulfonatocalix[6]arene preferred to form 1:1 inclusion complexes with triamterene at pH 6.50.•The water solubility of triamterene were obviously increased through complexation with p-sulfonatocalix[6]arene.The inclusion complexation behavior of p-sulfonatocalix[6]arene (SCX6) with triamterene (TA) was investigated by fluorescence spectroscopy, UV–Vis spectroscopy, 1H and 2D NMR, FT-IR, SEM and DSC. The results indicate that TA is able to form an inclusion complex with SCX6. The inclusion complex has a stoichiometry of 1:1 at pH 6.50. In addition, the water solubility of TA was obviously increased in the inclusion complex with SCX6.Graphical abstract

The inclusion behavior of Solvent Violet 9 (SV9) with 4-sulfonatocalix[n]arenes (SCXn) (n = 4, 6, 8) was investigated at various pH values by ultraviolet–visible spectroscopy. SV9 is able to form an inclusion complex with calixarenes. Different absorption behaviors were observed for the dye with the various host calixarenes. The molecular binding abilities were affected by the configuration of the calixarene cavities and the solution pH. Various experimental conditions, including calixarenes concentrations, were investigated and the results suggested that the three calixarene were most suitable for inclusion of the dye at pH = 3.05. The formation constant could be calculated. The inclusion behavior of the complexes was studied in detail using nuclear magnetic resonance spectroscopy. Finally, the interactions of SV9 with Salmon testes DNA in SCXn supramolecular system were studied by UV–Vis absorption spectroscopy. The UV–Vis absorption show that the interaction of SV9 with DNA depends on the concentration ratio of SV9 to DNA and the pH values. The binding constants of inclusion complexes with DNA are calculated. It was observed that SCXn can affect the interactive mode of SV9 with DNA.Graphical abstractThe figure propose complexation of Solvent Violet 9 and 4-sulfonatocalix[4]arene. The results of all experiments suggested that the host formed a cap on the guest during inclusion.Highlights► At various pH values, the inclusion of SV9 with SCXn has different absorption. ► The pHs have an effect on the binding of SV9 to DNA in SCXn supramolecular system. ► The NMR spectra suggested that the host formed a cap on guest during inclusion.

To investigate the inclusion ability of γ-cyclodextrin (γ-CD) for caffenic acid (CA). The conditions for the formation of inclusion complex and the binding constant between γ-CD and CA were determined by fluorescent and ultraviolet spectroscopic methods. The behavior of CA as a free radical scavenger before and after its inclusion was investigated. In addition, solid samples of the inclusion complex, prepared through the co-precipitation and grinding methods, were characterized via IR spectroscopy and differential scanning calorimetry. The inclusion complex was further characterized with 1H NMR spectroscopy. By using fluorescent and ultraviolet spectroscopy, the conditions for the formation of inclusion complex between γ-CD and CA were optimized and the binding constant determined. It was observed that the guest molecule behaves as a better anti-oxidant after its inclusion into γ-CD.

The formation of the complexes of BG with β-CD and HP-β-CD was studied by UV–vis absorption spectroscopy, fluorescence spectra, Phase-solubility measurements and nuclear magnetic resonance spectroscopy (NMR) in solution. The formation constants (K) of complexes were determined by fluorescence method and Phase-solubility measurements. The results showed that the inclusion ability of β-CD and its derivatives was the order: HP-β-CD > β-CD. In addition, the experimental resulted confirmed the existence of 1:1 inclusion complex of BG with CDs.The antioxidant ability studies of BG and CDs complexes were done. The results obtained indicated that the BG/HP-β-CD complex was the most reactive form, and then was the BG/β-CD complex; the last was BG. Special configuration of complex has been proposed on NMR technique.

The inclusion complexation behavior of caffeic acid (CA) with hydroxypropyl-β-cyclodextrin (HP-β-CD) was studied by UV–vis, fluorescence spectroscopy and nuclear magnetic resonance spectroscopy (NMR). Experimental conditions including the concentration of HP-β-CD and media acidity were investigated in detail. The result suggested HP-β-CD was more suitable for including CA in acidity solution. The binding contants (K) of the inclusion complexes were determined by linear regression analysis and the inclusion ratio was found to be 1:1. The water solubility of CA was increased by inclusion with HP-β-CD according to the phase-solubility diagram. The spatial configuration of complex has been proposed based on 1H NMR and two-dimensional (2D) NMR, the result suggested that CA was entrapped inside the hydrophobic core of HP-β-CD with the lipophilic aromatic ring and the portion of ethylene.

The formation of the complexes of Norfloxacin with 2-methyl-β-cyclodextrin (Me-β-CD) was studied by UV-Vis absorption spectroscopy, fluorescence and nuclear magnetic resonance spectroscopy (NMR). Experimental conditions including Me-β-CD concentration and media acidity were investigated in detail at room temperature. The results suggest that Norfloxacin exists in three molecular forms in aqueous solution at different pH values, namely, the acidic form, the neutral form and the alkaline form). Me-β-CD was more suitable for inclusion of Norfloxacin in the acidic medium. The binding constant (K) of the inclusion complex was determined by fluorescence measurement, and the complexation ratio was determined as 1:1 in the concentration range used in this study. A mechanism was proposed to explain the inclusion process based on the experimental NMR data.

The interaction of cloxacillin sodium with β-cyclodextrin (β-CD) has been studied by several analytical techniques, including 1H NMR, fluorescence spectroscopy, infrared spectroscopy. In this paper, solid inclusion complex of cloxacillin sodium with β-CD was synthesized by the coprecipitation method. In addition, the characterization of the inclusion complex has been proved by fluorimetry, infrared spectroscopy and 1D, 2D NMR. The experimental results confirmed the existence of 1:1 inclusion complex of cloxacillin sodium with β-CD. The formation constant of complex was determined by fluorescence method and 1H NMR. Spacial configuration of complex has been proposed on 2D NMR technique.

The nuclear magnetic resonance (NMR) spectroscopy demonstrated that the inclusion complexes of meso-tetrakis- (p-sulfonatophenyl) porphyrin (TPPS) with β-, Hydroxypropyl-β- and Methyl-β-cyclodextrin (β-, HP-β- and Me-β-CD) are formed, which resulted in the dissociation of TPPS J-aggregates efficiently under certain acidity. There are no significant differences in binding affinities and basic complexation mechanisms between TPPS and β-cyclodextrin (β-CD) or hydroxypropyl-β-cyclodextrin (HP-β-CD), i.e. porphyrin is included through the wide side of the cavity of β-CD or HP-β-CD. Alternatively, porphyrin is included through the narrow side of the Me-β-CD cavity.

A simple tailor-made water-soluble broadly emitting (500–650 nm) fluorescent probe 3-methyl-2-(N-ethylcarbazole-3vinyl)-benzothiazolium iodide (IECBT) for the selective and sensitive detection of multiple analytes, including CN−, HSO3− and extremely alkaline pH, is designed and synthesized via the ethylene bridging of 3-formyl-N-ethylcarbazole and 2,3-dimethyl benzothizolium iodide, which is a useful fluorescent probe for monitoring these analytes at extremely low concentrations quantitatively. CN− and HSO3− are expected to undergo 1,4-addition reactions with the C-4 atom in the ethylene group of IECBT. This water-soluble fluorescent probe exhibits excellent sensitivity and selectivity toward CN− in DMSO, which also results in a prominent fluorescence ratiometric change and a color change. The high selectivity and sensitivity of IECBT toward HSO3− and extremely alkaline pH over other coexisting species in water are also observed. The titration experiments show that it features a remarkably large Stokes shift and good stability towards CN−, HSO3− or extremely alkaline pH with a significant fluorescence turn-off response. Importantly, we demonstrate that IECBT can be used for the real-time sensing and bioimaging of CN−, HSO3− or extremely alkaline pH in living samples.