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Reduced texaphyrin: A ratiometric optical sensor for heavy metals in aqueous solution
Harrison D. Root, Gregory Thiabaud, Jonathan L. Sessler
Front. Chem. Sci. Eng.. 2020, 14 (1 ): 19-27.
https://doi.org/10.1007/s11705-019-1888-y
We report here a water-soluble metal cation sensor system based on the as-prepared or reduced form of an expanded porphyrin, texaphyrin. Upon metal complexation, a change in the redox state of the ligand occurs that is accompanied by a color change from red to green. Although long employed for synthesis in organic media, we have now found that this complexation-driven redox behavior may be used to achieve the naked eye detectable colorimetric sensing of several number of less-common metal ions in aqueous media. Exposure to In(III), Hg(II), Cd(II), Mn(II), Bi(III), Co(II), and Pb(II) cations leads to a colorimetric response within 10 min. This process is selective for Hg(II) under conditions of competitive analysis. Furthermore, among the subset of response-producing cations, In(III) proved unique in giving rise to a ratiometric change in the ligand-based fluorescence features, including an overall increase in intensity. The cation selectivity observed in aqueous media stands in contrast to what is seen in organic solvents, where a wide range of texaphyrin metal complexes may be prepared. The formation of metal cation complexes under the present aqueous conditions was confirmed by reversed phase high-performance liquid chromatography, ultra-violet-visible absorption and fluorescence spectroscopies, and high-resolution mass spectrometry.
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Diporphyrin tweezer for multichannel spectroscopic analysis of enantiomeric excess
Daniel T. Payne, Mandeep K. Chahal, Václav Březina, Whitney A. Webre, Katsuhiko Ariga, Francis D’Souza, Jan Labuta, Jonathan P. Hill
Front. Chem. Sci. Eng.. 2020, 14 (1 ): 28-40.
https://doi.org/10.1007/s11705-019-1869-1
Chiral 1,1’-binaphthyl-linked diporphyrin ‘tweezers’ (R )-1 /(S )-1 and the corresponding zinc(II) complexes (R )-2 /(S )-2 were prepared as chiral host molecules, and their utility for chiral analyses (especially enantiomeric excess (ee ) determinations) were evaluated. Tris(1-n -dodecyl)porphyrins were used for the first time as the interacting units. Host capabilities of the diporphyrin tweezers were investigated by titrations with (R ,R )- and (S ,S )-cyclohexane-1,2-diamine (CHDA). The host molecules could be used as multichannel probes of ee by using UV-vis, circular dichroism (CD), fluorescence emission and 1 H nuclear magnetic resonance (1 H-NMR) methods. Chiral configurations could also be differentiated using CD or 1 H-NMR spectroscopy. All three optical techniques give good resolution of ee with reasonable sensitivity considering the low concentrations used (ca. 10−6 mol·L−1 ). The ee determination of CHDA enantiomers using NMR spectroscopy is also possible because of the reasonably well separated resonances in the case of (R ,R )- and (S ,S )-CHDA. Non-metallated (R )-1 /(S )-1 hosts could not be used to detect chiral information in a strongly acidic chiral guest. This work demonstrates the utility of 1,1’-binapthyl-linked chiral hosts for chiral analysis of ditopically interacting enantiomers.
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Near-infrared fluorescent probe for fast track of cyclooxygenase-2 in Golgi apparatus in cancer cells
Bhaskar Gurram, Miao Li, Jiangli Fan, Jingyun Wang, Xiaojun Peng
Front. Chem. Sci. Eng.. 2020, 14 (1 ): 41-52.
https://doi.org/10.1007/s11705-019-1796-1
Cyclooxygenase-2 (COX-2) has been used as an excellent traceable biomarker, and exists maximally in Golgi apparatus (Cancer cells). Celecoxib (CCB) is a selective inhibitor for COX-2, and has been used as one of non-steroidal anti-inflammatory drug. Herein we report the conjugation of nile blue (NB) with CCB via a six-carbon linkage to form a fluorescence probe NB-C6-CCB for the detection of COX-2. NB-C6-CCB displays strong fluorescence with the emission peak centered at near-infrared wavelength (700 nm) in tumor cells or tumor tissues with high expression of COX-2. Importantly, NB-C6-CCB can discriminate cancer cells (MCF-7) fluorescence intensity from normal ones (COS-7) in the co-culture medium under confocal microscope. Subcellular localization of the NB-C6-CCB preferentially points to the Golgi apparatus and increases the fluorescent intensity. The competitive analysis (with CCB) and Native-PAGE analysis confirmed that NB-C6-CCB shows selective binding affinity towards COX-2 enzyme. Competitive analysis with CCB (flow cytometry assay) revealed the fluorescence intensity fluctuation due to pretreatment of CCB with different concentrations, indicating that the NB-C6-CCB is a precise or sensitive probe for the COX-2. Tumor tissue (depth: 500 µm), organs and mice imaging tests show excellent near-infrared visualization, specific localization and identification of tumors.
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Structural effect of fluorophore on phenylboronic acid fluorophore/cyclodextrin complex for selective glucose recognition
Takeshi Hashimoto, Mio Kumai, Mariko Maeda, Koji Miyoshi, Yuji Tsuchido, Shoji Fujiwara, Takashi Hayashita
Front. Chem. Sci. Eng.. 2020, 14 (1 ): 53-60.
https://doi.org/10.1007/s11705-019-1851-y
Based on the design of the fluorescent site of a fluorescent probe, we have created a unique system that changes its twisting response to sugar. Two probes were synthesized, in which phenylboronic acid and two kinds of aromatic fluorescent site (pyrene or anthracene) were conjugated by an amide bond. In the fluorescence measurement of pyrene-type probe 1 , dimer fluorescence was observed at high pH. In induced circular dichroism (ICD) experiments, a response was observed only in the presence of glucose and γ -cyclodextrin, and no response was seen with fructose. On the other hand, in the fluorescence measurement of anthracene-type probe 2 , dimer fluorescence was observed in the presence of both glucose and galactose, and the fluorescence was different from the case of fructose. When the ICD spectra of these inclusion complexes were measured, an inversion of the Cotton effect, which indicates a change in the twisted structure, was observed in galactose and glucose. These differences in response to monosaccharides may originate in the interaction between the fluorescent site and the cyclodextrin cavity.
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4-Amino-1,8-naphthalimide based fluorescent photoinduced electron transfer (PET) pH sensors as liposomal cellular imaging agents: The effect of substituent patterns on PET directional quenching
Miguel Martínez-Calvo, Sandra A. Bright, Emma B. Veale, Adam F. Henwood, D. Clive Williams, Thorfinnur Gunnlaugsson
Front. Chem. Sci. Eng.. 2020, 14 (1 ): 61-75.
https://doi.org/10.1007/s11705-019-1862-8
Four new fluorescent sensors (1 -4 ) based on the 4-amino-1,8-naphthalimide fluorophores (Naps ) have been synthesized based on the classical fluorophore-spacer-receptor model. These four compounds all gave rise to emission bands centred at ca. 535 nm, which were found to be highly pH dependent, the emission being ‘switched on’ in acidic media, while being quenched due to PET from the amino moieties to the excited state of the Nap at more alkaline pH. The luminescent pH dependence for these probes was found to be highly dependent on the substitution on the imide site, as well as the polyamine chain attached to the position 4-amino moiety. In the case of sensor 2 the presence of the 4-amino-aniline dominated the pH dependent quenching. Nevertheless, at higher pH, PET quenching was also found to occur from the polyamine site. Hence, 2 is better described as a receptor1 -spacer1 -fluorophore-spacer2 -receptor2 system, where the dominant PET process is due to (normally less favourable) ‘directional’ PET quenching from the 4-amino-aniline unit to the Nap site. Similar trends and pH fluorescence dependences were also seen for 3 and 4 . These compounds were also tested for their imaging potential and toxicity against HeLa cells (using DRAQ5 as nuclear stain which does now show pH dependent changes in acidic and neutral pH) and the results demonstrated that these compounds have reduced cellular viability at moderately high concentrations (with IC50 values between ca. 8–30 µmol∙L− 1 ), but were found to be suitable for intracellular pH determination at 1 µmol∙L− 1 concentrations, where no real toxicity was observed. This allowed us to employ these as lysosomal probes at sub-toxic concentrations, where the Nap based emission was found to be pH depended, mirroring that seen in aqueous solution for 1-4 , with the main fluorescence changes occurring within acidic to neutral pH.
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A simple, azulene-based colorimetric probe for the detection of nitrite in water
Lloyd C. Murfin, Carlos M. López-Alled, Adam C. Sedgwick, Jannis Wenk, Tony D. James, Simon E. Lewis
Front. Chem. Sci. Eng.. 2020, 14 (1 ): 90-96.
https://doi.org/10.1007/s11705-019-1790-7
We describe the synthesis and evaluation of an azulene-based chemodosimeter for nitrite. The probe was found to undergo two distinct color changes upon introduction of aqueous nitrite ion. A near-instant formation of a grey color provides a qualitative indication of the presence of nitrite, followed by the formation of a deep-yellow/orange color, the endpoint from which quantitative data can be derived. The azulene probe exhibits 1:1 stoichiometry of reaction with nitrite in water, and is selective for nitrite over other anions. The azulene probe was applied to determine nitrite content in cured meat, and compared with the British Standard testing procedure (Griess test). The value obtained from the azulene-based probe agreed closely with the standard test. Our procedure only requires the preparation of one standard solution, instead of the three required for the standard Griess test.
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A boronic acid-based fluorescent hydrogel for monosaccharide detection
Suying Xu, Adam C. Sedgwick, Souad A. Elfeky, Wenbo Chen, Ashley S. Jones, George T. Williams, A. Toby A. Jenkins, Steven D. Bull, John S. Fossey, Tony D. James
Front. Chem. Sci. Eng.. 2020, 14 (1 ): 112-116.
https://doi.org/10.1007/s11705-019-1812-5
A boronic acid-based anthracene fluorescent probe was functionalised with an acrylamide unit to incorporate into a hydrogel system for monosaccharide detection. In solution, the fluorescent probe displayed a strong fluorescence turn-on response upon exposure to fructose, and an expected trend in apparent binding constants, as judged by a fluorescence response where D-fructose>D-galactose>D-mannose>D-glucose. The hydrogel incorporating the boronic acid monomer demonstrated the ability to detect monosaccharides by fluorescence with the same overall trend as the monomer in solution with the addition of D-fructose resulting in a 10-fold enhancement (≤0.25 mol/L).
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Dual enzyme activated fluorescein based fluorescent probe
Maria L. Odyniec, Jordan E. Gardiner, Adam C. Sedgwick, Xiao-Peng He, Steven D. Bull, Tony D. James
Front. Chem. Sci. Eng.. 2020, 14 (1 ): 117-121.
https://doi.org/10.1007/s11705-018-1785-9
A simple dual analyte fluorescein-based probe (PF3-Glc ) was synthesised containing β -glucosidase (β -glc) and hydrogen peroxide (H2 O2 ) trigger units. The presence of β -glc, resulted in fragmentation of the parent molecule releasing glucose and the slightly fluorescent mono-boronate fluorescein (PF3 ). Subsequently, in the presence of glucose oxidase (GOx), the released glucose was catalytically converted to D-glucono-δ -lactone, which produced H2 O2 as a by-product. The GOx-produced H2 O2, resulted in classic H2 O2 -mediated boronate oxidation and the release of the highly emissive fluorophore, fluorescein. This unique cascade reaction lead to an 80-fold increase in fluorescence intensity.
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