Novel functionalised imidazo-benzocrown ethers bearing a thiophene spacer as fluorimetric chemosensors for metal ion detection

Abstract

Novel phenylalanine derivatives bearing benzimidazole and crown ethers as coordinating/reporting units and thiophene as spacer unit were synthesized, and their evaluation as fluorimetric chemosensors was carried out in acetonitrile and acetonitrile/water solutions. 15-Crown-5 benzimidazolyl phenylalanine methyl ester, 15-crown-5 thienylbenzimidazolyl phenylalanine methyl ester and 18-crown-6 thienylbenzimidazolyl phenylalanine methyl ester were tested for alkaline, alkaline-earth and transition metal ions (such as Na + , Ca 2+ , Cd 2+ , Co 2+ , Cr 3+ , Cu 2+ , Fe 2+ , Fe 3+ , Hg 2+ , Ni 2+ , Pd 2+ and Zn 2+). The different crown ether binding moieties as well as the electronic nature and the length of the π-bridge linked to the benzimidazole heterocycle allowed the fine tuning of the sensory properties as seen by spectrofluorimetric titrations. Therefore, 15-crown-5 benzimidazolyl phenylalanine methyl ester is a fluorimetric chemosensor, being selective and sensitive for Cu 2+ and Pd 2+ in aqueous solutions (ACN/H2O; 80:20). On the other hand, the metal cation sensing properties displayed by 15-crown-5 thienylbenzimidazolyl phenylalanine methyl ester bearing an arylthienyl spacer showed that this is a promising candidate as fluorimetric chemosensor for Fe 3+ , Pb 2+ and Pd 2+ in acetonitrile solution.

Organic–inorganic hybrid sol–gel materials doped with a fluorescent triarylimidazole derivative

“…51 In addition, they are also used as optical chemosensors in organic solvents and aqueous solutions, and as bioimaging probes for the detection of anions, neutral molecules and metal ions with biological/medical relevance. 49,[52][53][54][55][56][57][58][59][60][61] Several imidazole derivatives have been used as pH sensors. Ge et al reported the synthesis of a 4-phenyl-pyrido[1,2-a] benzimidazole-3-carboxylic acid (PPBI-1), which exhibits a uorescence quantum yield of 0.96 and is sensitive to pH values between 4.2 and 6.4.…”

Crown Ether Benzoxazolyl-Alanines as Fluorimetric Chemosensors for the Detection of Palladium in Aqueous Environment

“…For the sensing of metallic cations, there are reports on fluorescent sensors based on amino acids containing different heterocyclic fluorescent and/or coordination units at the side chain [7][8][9][10][11][12][13]. Metal cations are known to be complexed through electron donor atoms at the main/side chains in amino acids, and the insertion of heterocycles at the side chain of natural amino acids yields novel unnatural amino acids with added functionality.…”

“…Bearing these facts in mind, and considering the research group´s experience on the design, synthesis and characterization of fluorescent chemosensors [7][8][9][10][11][12], we report herein the evaluation of two benzoxazolyl-alanine derivatives bearing a crown ether moiety as potential fluorimetric chemosensors for Pd 2+ detection in aqueous media. Preliminary chemosensory studies for these unnatural amino acids in the presence of selected metal cations, with biological and environmental relevance, were performed in acetonitrile solution and in aqueous mixtures of SDS (20 mM, pH 7.5) solution with acetonitrile, 90:10 v/v.…”

Heterocyclic Aldehydes Based on Thieno[3,2-b]thiophene Core: Synthesis and Preliminary Studies as Ion Optical Chemosensors

“…An electrophilic aromatic substitution of the substrate takes place, followed by hydrolysis to yield the heterocyclic carbaldehyde [3]. -Conjugated heterocyclic aldehydes can also be prepared through Suzuki cross coupling reaction using the appropriate coupling components [6][7][8][9].…”

“…Carrying on the research group's investigation on optical chemosensors [7,9,[19][20][21][22], this work reports the synthesis and characterization of two heterocyclic aldehydes by Suzuki coupling of 5-bromothieno [3,2-b]thiophene-2-carbaldehyde with two different phenylboronic acids. The synthesis and the characterization of the thieno [3,2-b]thiophene precursors is also included.…”