A terpyridyl-rhodamine hybrid fluorescent probe for discriminative sensing of Hg (II) and Cu (II) in water and applications for molecular logic gate and cell imaging

Sensitive and discriminative sensing of more than one analyte with a single fluorescent probe is significant and challenging. Herein a new terpyridyl-rhodamine hybrid, namely TRH, has been rationally designed and prepared with two responsive groups in the molecular structure, which facilitate the discriminative detection of Hg2+ and Cu2+ ions in water with detection limits of 4.9 and 53.3 nM by ratiometric fluorescence change (F595/F485) and fluorescence quenching, respectively. Investigations show that the selectivity to Hg2+ ions can be attributed to Hg2+-promoted spirolactam ring opening and further hydrolysis, followed by a through-bond energy transfer (TBET) process. The selective fluorescence quenching to Cu2+ ions probably can be ascribed to the binding Cu2+ to terpyridyl that triggers a ligand-to-metal charge transfer (LMCT) process, which can also efficiently inhibit the TBET process induced by Hg2+ ions and promotes the discriminative sensing of Cu (II) and Hg (II). In addition, the fluorescent responses to Hg2+ and Cu2+ ions cover a wide pH range. Moreover, a combinatorial logic gate with the functions of NOR and INHIBIT has been fabricated by using Hg2+ and Cu2+ ions as chemical input signals, and fluorescence at 485 and 595 nm as output signals. Besides, TRH also exhibits sensitive and discriminative sensing ability to Hg2+ and Cu2+ ions by the fluorescence of rhodamine fluorophore. Significantly, based on the fluorescence signal output of rhodamine moiety, TRH can be used as a tracer for the discriminative sensing of Hg2+ and Cu2+ ions by using living cells.

Analyte Detection: A Decade of Progress in the Development of Optical/Fluorescent Sensing Probes

The development of selective and sensitive chemical sensors capable of detecting metal ions, anions, neutral species, explosives and hazardous substances, selectively and sensitively has attracted considerable interest of various research groups. The presence of such analytes within the permissible limits is often beneficial, but the excess amounts may lead to lethal effects to both the environment as well as the living organisms. Owing to the toxicity of the heavy metal ions, toxic anions and nitro-aromatics which are main constituents of explosives, the timely detection of these materials is most desirable to ensure safety and security of the mankind. In this personal account, we present several classes of molecular sensors that were specifically designed in our lab during the past decade for detecting several species in solutions, solid state as well as biological media. Modulation of the optical properties in response to the presence of guest species, led to selective and sensitive detection protocols, and was supported by the theoretical studies wherever possible. We have also extended the application of some of these probes for the on-site detection of analytes by developing the paper strips, glass slides and even the wool and cotton fabrics loaded with probes. One such development represents detection of palladium in human urine and blood samples collected from clinical samples. Additionally, the sensing events in some cases have successfully been reproduced in the live cancer cells. Based on the ease and cost-effective synthesis of the molecular probes, we hope that this account shall provide significant information to researchers in understanding the structure dependent sensing capabilities of the molecular probes.

Tetraphenylethylene AIEgen bearing thiophenylbipyridine receptor for selective detection of copper(ii) ion

A new tetraphenylethylene (TPE) AIEgen appended with a thiophenylbipyridine moiety exhibits sensitivity and selectivity towards copper ions via a PET “turn on–turn off” mechanism.

Bisindolization Reaction Employing Phthalimide-N-sulfonic Acid as an Efficient Catalyst

Background:

Bis(indolyl) methanes (BIMs) have a wide spectrum of applications in biomedicine and agriculture as well as are present in natural products. These bisheterocyclic compounds possess vast pharmacological, including antifungal, antitubercular, anti-inflammatory, antibacterial, anticancer, anticonvulsant, antibiotic, antiviral, antimalarial, analgesic, and antidiabetic properties. BIMs scaffolds have also been employed as selective optical chemosensors for detection of some anions and cations with the naked eye. Because of the importance of these bisheterocycles, various methods have been reported for their synthesis through reaction of indole derivatives and aldehydes or ketones. Therefore, the synthesis of BIMs through different methodologies has received widespread attention in the field of organic synthesis and medicinal chemistry.

Objective:

In this study, the catalytic activity of phthalimide-N-sulfonic acid (PISA) as an efficient and safe solid acidic organocatalyst toward the synthesis of BIMs derivatives in ethanol is described.

Methods:

Indole derivatives (2 mmol), aryl/heteroaryl aldehydes (1 mmol), and PISA (10 mol%) were mixture in ethanol. The reaction mixture was stirred at room temperature for the appropriate times. After workup and separation of catalyst, the corresponding heterocyclic products were obtained through recrystallization from hot ethanol.

Results:

The BIMs derivatives were easily obtained via Bisindolization Reaction (BIR) of two indoles (2-methylindole and indole) with a series of aryl and heteroaryl aldehydes. The BIR was efficiently catalyzed at room temperature using PISA as an excellent organocatalyst under optimized reaction conditions.

Conclusion:

The reactions were implemented in simple manner and were completed within acceptable reaction times. The expected BIM products were obtained in satisfactory yields. The catalyst can be recovered and reused several times in the template reaction. This approach provides the benefits of convenience, simple operational procedure, no use of hazardous organic solvents, cheapness and ease of preparation of catalyst.

Helquats as Promoters of the Povarov Reaction: Synthesis of 1,2,3,4-Tetrahydroquinoline Scaffolds Catalyzed by Helicene-Viologen Hybrids

Helquats (HQs) are structurally linked to helicenes and viologens, and they represent an attractive field of research in chemistry and medicinal chemistry. In the present work they were used as catalysts for the synthesis of 1,2,3,4-tetrahydroquinolines in good yields by the Povarov reaction. The substrate scope and the capability of different helquats to promote Povarov reactions are demonstrated. Studies to elucidate mechanistic details revealed that helquats act as single-electron transfer oxidants through a cation-radical mechanism. The screening of the catalytic activity of HQs confirmed that an active HQ must have a LUMO energy below -8.67 eV and the standard redox potential higher (less negative) than -1.2 V vs. the ferrocene/ferrocenium redox couple.

A Fluorescent and Colorimetric Chemosensor for Hg2+ Based on Rhodamine 6G With a Two-Step Reaction Mechanism

A fluorescent and colorimetric chemosensor L based on rhodamine 6G was designed, synthesized, and characterized. Based on a two-step reaction, the chemosensor L effectively recognized Hg²⁺. The interaction between the chemosensor and Hg²⁺ was confirmed by ultraviolet–visible spectrophotometry, fluorescence spectroscopy, electrospray ionization–mass spectrometry, Fourier-transform infrared spectroscopy, and frontier molecular orbital calculations. The chemosensor L was also incorporated into test strips and silica gel plates, which demonstrated good selectivity and high sensitivity for Hg²⁺.

Spectral studies on anthracene based dual sensor for Hg2+ and Al3+ ions with two distinct output modes of detection

A simple and easily synthesized colorimetric and fluorescent chemosensor 1, based on aromatic OH and imine moieties as a binding and anthracene as signaling unit, has been synthesized in a one-step procedure. The chemosensor 1 is developed as a dual chemosensor for detection of Hg²⁺ and Al³⁺ ions in CH₃OH, which exhibited a color change from light yellow to dark yellow with Hg²⁺ ions, enabling 1 a suitable "bare eye" indicator for Hg²⁺ ions. On the other hand, fluorescent enhancement with blue shift along with brilliant cyan fluorescence was observed upon binding with Al³⁺ ions. A possible sensing mechanism has been proposed by means of Job's plot and ¹H NMR titration.

A highly selective chemosensor for naked-eye sensing of nanomolar Cu(ii) in an aqueous medium

A colorimetric chemosensor was developed for the sensitive detection and quantification of Cu²⁺with a short response time in an aqueous medium.

An efficient solvent-free synthesis of bis(indolyl)methane-based naked eye chemosensor for Cu2+ion from β-chloro-α,β-unsaturated aldehydes using PMA-Cellulose as a solid phase reusable catalyst

A green one pot synthesis of novel bis(indolyl)methanes as naked eye chemosensors towards Cu²⁺ion has been developed from β-chloro-α,β-unsaturated aldehydes using new reusable solid acid support/catalyst PMA-Cellulose.

Benzodithieno-imidazole based π-conjugated fluorescent polymer probe for selective sensing of Cu2+

A benzodithieno-imidazole based π-conjugated fluorescent polymer probe shows excellent selectivity towards Cu²⁺ions through fluorescence quenching.

Two and three input molecular logic operations mediated by a novel azo-azomethine based chromogenic probe through intramolecular charge transfer processes

A novel azo-azomethine based chromogenic receptor has been successfully designed and synthesized for the construction of multifunctional molecular logic circuits.

Highly selective fluorimetric sensor for Cu2+and Hg2+using a benzothiazole-based receptor in semi-aqueous media and molecular docking studies

A new chemosensor (Z)-ethyl 2-((Z)-2-(benzo[d]thiazol-2-ylimino)-4-oxo-3-phenylthiazolidin-5-ylidene)acetate (receptor1) was designed and synthesized under catalyst-free conditions.

Recent advances in heterobimetallic catalysis across a “transition metal–tin” motif

This review focuses on the efficacy of catalysts, based on a transition metal–tin (TM–Sn) motif and crafted on a single scaffold, in mediating a wide variety of organic transformations.

A multiaddressable photochromic bisthienylethene with sequence-dependent responses: construction of an INHIBIT logic gate and a keypad lock

A photochromic bisthienylethene derivative (BIT) containing two imidazole units has been synthesized and fully characterized. When triggered by chemical ions (Ag(+)), protons, and light, BIT can behave as an absorbance switch, leading to a multiaddressable system. BIT exhibits sequence-dependent responses via efficient interaction of the specific imidazole unit with protons and Ag(+). Furthermore, an INHIBIT logic gate and a keypad lock with three inputs are constructed with the unimolecular platform by employing an absorption mode at different wavelengths as outputs on the basis of an appropriate combination of chemical and photonic stimuli.