A bifunctional acridine-based fluorescent sensor: ratiometric sensing of H2PO4− and obvious fluorescence quenching towards HSO4− through a synergistic binding effect of benzimidazolium and urea moieties

Hydrogen bond regulated hydrogen sulfate ion recognition: an overview

Hydrogen sulfate possesses substantial biological importance, having a colossal impact on physiological and environmental events. Therefore, several scientific groups have devoted serious effort to the development of versatile colorimetric and fluorimetric HSO4- sensors. Along with the scope, challenges, and significance, this review emphasizes the advancement of the optical recognition of HSO4- based on hydrogen bonding during the past two decades. Moreover, hydrogen-bond-driven proton transfer, ESIPT, ICT, PET, CHEF, and TBET mechanisms that allow for the optical detection of HSO4- are also discussed concisely. The foundation of this review includes the key points of the sensing process, like the nature of spectroscopic changes, selectivity and sensitivity, naked-eye color changes, the reusability of sensors, and the in vivo detection of HSO4-, if any. Special attention is focused on the correlation between the photophysical changes and the underlying interaction mechanisms that triggered the recognition aspect.

Revisiting imidazolium receptors for the recognition of anions: highlighted research during 2010-2019

Imidazolium based receptors selectively recognize anions, and have received more and more attention. In 2006 and 2010, we reviewed the mechanism and progress of imidazolium salt recognition of anions, respectively. In the past ten years, new developments have emerged in this area, including some new imidazolium motifs and the identification of a wider variety of biological anions. In this review, we discuss the progress of imidazolium receptors for the recognition of anions in the period of 2010-2019 and highlight the trends in this area. We first classify receptors based on motifs, including some newly emerging receptors, as well as new advances in existing receptor types at this stage. Then we discuss separately according to the types of anions, including ATP, GTP, DNA and RNA.

Synthesis of new chromogenic sensors containing thiourea and selective detection for F–, H2PO4–, and Ac– anions

Two new chromogenic sensors 1-(2-hydroxyphenyl)-3-(4-nitrophenyl)thiourea 1 and 1-(3-hydroxypyridin-2-yl)-3-(4-nitrophenyl)thiourea 2 bearing nitrophenyl and thiourea groups were designed and synthesized by one-step procedure and characterized through 1H NMR, 13C NMR, FTIR, and MS. The anion recognition property of the receptors was studied via naked-eye detection, UV–vis, and 1H NMR. Based on the existence of amino gen and hydroxyl moieties in receptors, receptors 1 and 2 exhibit obvious selectivity by the redshift of UV–vis signals, colour changes through naked-eye detection, and binding effects for F–, H2PO4–, and Ac–. Surprisingly, the detection limits of receptor 1 for F– and Ac– were calculated to be 5.45 × 10−7 and 2.11 × 10−7 (mol/L)−1, respectively, which indicated that F– and Ac– can be identified with high sensitivity by receptor 1. Besides, simple “test strips” were developed and were used as sensors for recognition of F–, H2PO4–, or Ac– in DMSO solution. Lastly, the mechanisms of the recognition process were studied through DFT calculation and 1H NMR titration.

Exploration of highly selective fluorogenic 'on-off' chemosensor for H2 PO4 - ions: ICT-based sensing and ATPase activity profiling

In this study, the recognition contour of Chemosensor 1 was investigated using semiaqueous methanol (X_H , mole fraction = 0.31) for a range of anions and bioactive species. Host-receptor signalling based on the internal charge transfer mechanism for Chemosensor 1 was explored and reported. Structure of Chemosensor 1 and its plausible anion coordination based on hydrogen bonding is complemented with density functional theory. Consequently, we investigated the applicability of the synthesized probe in blood plasma, urine, tap water samples, and for monitoring of ATP in lysosomes by apyrase enzyme.

Traditional hydrogen bonding donors controlled colorimetric selective anion sensing in tripodal receptors: First-naked-eye detection of cyanide by a tripodal receptor via fluoride displacement assay

Here in we report tris (3-aminopropyl) amine based tripodal receptors L, L¹ and L² which were functionalized with 4-nitrophenyl moieties having thio-urea, amide and sulfonamide as hydrogen bonding moieties respectively, shows a strong selectivity towards cyanide. A competitive colorimetric assay with L in the presence of fluoride ion suggests that the cyanide ion is much capable of displacing the bound fluoride, showing a sharp distinguishable color change. To the best of our knowledge, this is the first example of a naked-eye detection of cyanide via fluoride displacement assay by a tripodal receptor and such a displacement phenomenon is not observes in the cases of L¹ and L², instead the receptor L¹ binds nitrate and cyanide; L² binds dihydrogen phosphate and cyanide. Using this assay, we have proposed an AND logic gate using L·F^- and CN^-.

A simple benzimidazole styryl-based colorimetric chemosensor for dual sensing application

A new colorimetric styryl-benzimidazole based receptor to recognize more than one analyte trans-2-[4'-(dimethylamino)styryl]benzimidazole) (L1) has been synthesized and fully characterized by ¹³C and ¹H NMR, elemental analysis, UV-vis spectroscopy, and HRMS. Investigation of sensing ability of receptor L1 was carried out in presence of multiple anions (Br^-, CN^-, Cl^-, ClO₄^-, F^-, HSO₄^-, PF₆^-, NO₃^-, S^2-, OH^-, AcO^- and H₂PO₄^-) and cations (Cu²⁺, Cr³⁺, Al³⁺, Mg²⁺, Cd²⁺, Ni²⁺, Fe³⁺, K⁺, Fe²⁺, Mn²⁺, Ag⁺, Hg²⁺, Ca²⁺, Co²⁺, Pb²⁺, Na⁺, and Zn²⁺) by using UV-vis spectroscopy. Receptor L1 showed colorimetric response towards only for HSO₄^- ion. Receptor L1-HSO₄^- interaction confirmed with the help of ¹H NMR titration. Among various cations, L1 selectively sense the Cu²⁺ and Al³⁺ with the drastic colour change from yellow to green and dark yellow respectively. The stoichiometric binding ratio of L1 with HSO₄^-, Cu²⁺, and Al³⁺ found to be 1:1 by jobs method and HRMS data proved the complex formation between L1 and Cu²⁺/Al³⁺ with very low detection limit. In addition to explore practical applicability of L1, paper strips have been made and used to detect HSO₄^- and Cu²⁺ ions, respectively, up to 10 ppm level.

Medicinal chemistry of acridine and its analogues

'Acridine' along with its functional analogue 'Acridone' is the most privileged pharmacophore in medicinal chemistry with diverse applications ranging from DNA intercalators, endonuclease mimics, ratiometric selective ion sensors, and P-glycoprotein inhibitors in countering the multi-drug resistance, enzyme inhibitors, and reversals of neurodegenerative disorders. Their interaction with DNA and ability of selectively identifying numerous biologically useful ions has cemented exploitability of the acridone nucleus in modern day therapeutics. Additionally, most derivatives and salts of acridine are planar, crystalline, and stable displaying a strong fluorescence which, when coupled with their marked bio selectivity and low cytotoxicity, enables the studying and monitoring of several biochemical, metabolic, and pharmacological processes. In this review, a detailed picture covering the important therapeutic aspects of the acridone nucleus and its functional analogues is discussed.

Selective Recognition of Fluoride by using a Benzobisimidazolium Derivative through Aggregation-Induced Fluorescence

A new benzobisimidazolium derivative (1) bearing four naphthalene moieties was synthesized and demonstrated as an F- ion-selective fluorescent chemosensor. The fluorescence of 1 in acetonitrile (CH3CN) is significantly stronger with F- and acetate (CH3CO2-), but not with other anions (Cl-, Br-, I-, HSO4-, and H2PO4-). The fluorescence of 1 is enhanced selectively with F- in the presence of a small amount of water. Our DFT calculations indicate that the electrostatic interactions between the positively charged benzobisimidazolium moieties and F- play an important role in the formation of stable aggregates. The formation of stable aggregates of 1 with F- in CH3CN is a key step for the selective sensing of F-, and the fluorescence of the aggregates is further enhanced in a mixture of 95 % CH3CN and 5 % water, which can be attributed to the aggregation-induced emission.

Imidazolium Based Probes for Recognition of Biologically and Medically Relevant Anions

The imidazolium derivatives due to their positive charge possess one of the most polarized and positively charged proton at C2-H to form strong ionic hydrogen bond (also termed as double ionic hydrogen bond) with anions and also provide opportunities for anion - π interactions with electron-deficient imidazolium ring. In the present review article, imidazolium based molecular probes for their ability to recognize inorganic anions like halides, cyanide, perchlorate, carboxylic acids, phosphate, sulfate etc. and their derived molecules viz. nucleotides, DNA, RNA, surfactants, proteins, etc have been discussed. The review covers the literature published after year 2009 and has > 130 references. The previous literature has already been discussed by Yoon et al. in two review articles published in Chem. Soc. Rev. 2006 and 2010.

Hydrogen sulfate ion sensing in aqueous media based on a fused pyrimido benzothiazole derivative

The receptor 3-cyano-4-imino-2-methylthio-4H-pyrimido[2,1-b][1,3]benzothiazole (SVK-1) was employed for the selective sensing of HSO₄⁻ ions in aqueous media.

The synthesis of UDP-selective fluorescent probe and its imaging application in living cells

A perylene-based probe was developed for uridine diphosphate (UDP) sensing and cell imaging. The probe presented about 4-fold fluorescence enhancement in the presence or absence of 100equiv UDP. The selectivity toward UDP over other phosphor-containing anions was observed. The selective UDP sensing was speculated to be related to the binding affinities of Zn(2+) ions in sensor with the uridine and phosphate moieties of UDP. Furthermore, this probe was also applied to image of UDP in living cells.

Recent advances in H2PO4− fluorescent sensors

The recent advances in H₂PO₄⁻ fluorescent sensors were thoroughly reviewed.