A retrievable and highly selective fluorescent probe for monitoring dihydrogen phosphate ions based on a naphthalimide framework

A highly selective and sensitive fluorescent sensor based on a 1,8-naphthalimide with a Schiff base function for Hg2+ in aqueous media

A new fluorescent sensor, N-allyl-4-[(2-(3-methoxysalicylaldimino)ethylamino]-1,8-naphthalimide (HL), for Hg2+ has been developed where the Schiff base substituent acts as a recognition group. This sensor shows a large Stokes shift of 3535–4042 cm−1 and a general fluorescence quantum yield of 0.05, 249–0.11, 866 in organic solvents of different polarity as expected. It also exhibits highly selective and a sensitive response to Hg2+ (Ф Hg+HL/Ф HL = 2.28) over other metal ions (Na+, K+, Ca2+, Mg2+, Al3+, Pb2+, Fe3+, Ni2+, Zn2+, Cu2+, Ag+, Co2+, Cr3+, Mn2+ and Cd2+) in solution (DMF/Tris-HCl buffer, 1:1, v/v, pH = 7.2). The Hg2+-induced fluorescence enhancement at 526 nm is proportional to the concentration of Hg2+ in the range of 0.5–4.0 µm with a detection limit of 0.18 µm. Based on the fluorescence titration and a Job’s plot analysis, the metal-to-ligand ratio of the complex is 2:1 with a binding constant of 1.56 × 1012 m −1.

Detection of phosphates in water utilizing a Eu3+-mediated relay mechanism

Fluorescent carboxyamidoquinolines form ensembles with Eu3+ that can be successfully leveraged in sensing of phosphates showing off–on fluorescence signaling.

Synthesis and Biological Evaluation of Some 1,8-Naphthalimide-Acridinyl Hybrids

In the present study, the synthesis of three 1,8-naphthalimide-acridinyl hybrids (2a, 2b, and 5b) using N-amido-1,8-naphthalimides (1 and 4) and acridinyl isothiocyanates is reported. The newly synthesized hybrids were evaluated for their anticancer activity in six human cancer cell lines (HL-60, MT-4, HepG2, HeLa, SK-OV-3, and MCF-7). Their inhibition activity against DNA-topoisomerase I (Topo I) and Electrophorus electricus acetylcholinesterase (AChE) was also studied. The results indicate that 2b displayed good cytotoxicity for MT-4, HepG2, HeLa, and SK-OV-3 with the IC50 values of 14.66 ± 0.31, 27.32 ± 2.67, 17.51 ± 0.34, and 32.26 ± 1.74 μM, respectively. All compounds, especially 2b, exhibited obvious bands corresponding to DNA fragments at 0.5 mM concentration, further confirming the pharmacological mechanism related to the Topo I inhibitory activities. In addition, compound 2a exhibited higher inhibition activity against AChE than 2b and 5b, with IC50 values of 0.32 ± 0.04 mM, and the acridinyl ring may contribute to the activity of 2a.

Design and applications of metal-based molecular receptors and probes for inorganic phosphate

Inorganic phosphate has numerous biomedical functions. Regulated primarily by the kidneys, phosphate reaches abnormally high blood levels in patients with advanced renal diseases. Since phosphate cannot be efficiently removed by dialysis, the resulting hyperphosphatemia leads to increased mortality. Phosphate is also an important component of the environmental chemistry of surface water. Although required to secure our food supply, inorganic phosphate is also linked to eutrophication and the spread of algal blooms with an increasing economic and environmental burden. Key to resolving both of these issues is the development of accurate probes and molecular receptors for inorganic phosphate. Yet, quantifying phosphate in complex aqueous media remains challenging, as is the development of supramolecular receptors that have adequate sensitivity and selectivity for use in either blood or surface waters. Metal-based receptors are particularly well-suited for these applications as they can overcome the high hydration enthalpy of phosphate that limits the effectiveness of many organic receptors in water. Three different strategies are most commonly employed with inorganic receptors for anions: metal extrusion assays, responsive molecular receptors, and indicator displacement assays. In this review, the requirements for molecular receptors and probes for environmental applications are outlined. The different strategies deployed to recognize and sense phosphate with metal ions will be detailed, and their advantages and shortfalls will be delineated with key examples from the literature.

A new 1,8-naphthalimide-based fluorescent “turn-off” sensor for detecting Cu2+ and sensing mechanisms

In this article, a new “turn-off” fluorescent sensor N- n-butyl-4-{2-[(ethylimino)methyl]phenol}-1,8-naphthalimide (HL) for CuII ions is synthesized, which contains a 1,8-naphthalimide moiety as the fluorophore and a Schiff base as the recognition group. As expected, it exhibits high selectivity and sensitivity for detecting CuII ions over other common metal ions in acetonitrile–2-(4-(2-hydroxyethyl)-1-piperazinyl)-ethanesulfonic acid (HEPES) (1:1 v/v, pH = 7.4) solution. In addition, the fluorescence intensity for HL showed a good linearity with the concentration of CuII ions in the range of 0.5–5.0 μM. The 2:1 binding stoichiometry between HL and CuII ions was established on the basis of combined fluorescence titrations, a Job’s plot, single-crystal X-ray analysis and mass spectrometry. The quenching response of HL toward CuII ions is attributed to the reverse photoinduced electron transfer mechanism. The proposed sensor HL is preliminarily applied to quantify CuII ions in water samples from the Yellow River and tap water.

Three-in-one type fluorescent sensor based on a pyrene pyridoxal cascade for the selective detection of Zn(ii), hydrogen phosphate and cysteine

A novel fluorescent receptor L was developed for the selective detection of important bioactive analytes.

A fluorescence turn-on chemosensor for hydrogen sulfate anion based on quinoline and naphthalimide

A new fluorescence turn-on chemosensor 1 based on quinoline and naphthalimide was prepared and its anion sensing toward various anions behavior was explored in this paper. Sensor 1 exhibited a highly selective fluorescent response toward HSO4(-) with an 8-fold fluorescence intensity enhancement in the presence of 10equiv. of HSO4(-) in DMSO-H2O (1/1, v/v) solution. The sensor also displayed high sensitivity to hydrogen sulfate and the detection limit was calculated to be 7.79×10(-7)M. The sensing mechanism has been suggested to proceed via a hydrolysis process of the Schiff base group. The hydrolysis product has been isolated and further identified by (1)H NMR and MS.

A highly selective fluorescent chemosensor based on naphthalimide and Schiff base units for Cu2+ detection in aqueous medium

A new Schiff base, 4-allylamine-N-(N-5-methylsalicylidene)-1,8-naphthalimide (1), has been designed and synthesized by combining a 1,8-naphthalimide moiety as a fluorophore and a Schiff base as a recognition group. Its photophysical properties were investigated by absorption and fluorescence spectroscopy, and this sensor exhibits a high fluorescence quantum yield of 0.75–0.91 inorganic solvents of different polarity. It also shows high selectivity for Cu2+ over other ions with fluorescence quenching in aqueous medium (pH=7.2). The reason for this phenomenon (fluorescence quenching) is attributed to the formation of a 1:1 complex between 1 and Cu2+ according to the Job plot and fluorescence titration. The sensor can be applied to the quantification of Cu2+ in a linear fashion from 0.5 to 5 μM with a detection limit of 0.23 μM. Additionally, the association constant (K a) between Cu2+ and 1 is 1.328×106 M− 1 in aqueous media.

A highly fluorescent zinc complex of a dipodal N-acyl hydrazone as a selective sensor for H2PO4− ions and application in living cells

A dipodal N-acyl hydrazone receptor (R1) was synthesized in a single step, and utilized as a test probe for the selective sensing of metal ions as well as anions.

Recent advances in H2PO4− fluorescent sensors

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