Spectroscopic Rationalization of Selective Colorimetric Chemosensing of Fe(lll) in Aqueous Medium by a New Mono-Substituted Dibenzodiaza-Crown Ether Macrocyclic Ligand Appended with Mono 2-Benzimidazole N-Pendant Side Arm

Optical chemosensor L comprising of a new mono-N-substituted derivative of dibenzodiaza-crown ether macrocyclic ligand bearing a 2-benzimidazole (2Bim) side arm was synthesized, and characterized by FT-IR, elemental microanalyses, 1H NMR, and 13C NMR, UV-visible, fluorescence (FL) spectroscopy. The colorimetric chemosensing behavior of L toward the library metal ions was examined, wherein L represented a prompt and selective yellow-to-purple color change for Fe(III) cation in a 25µM solution with LOD as 0.23 µM in ethanol:water (9:1, v/v), even in the presence of the other library metal ions (LMI). Based on the 1H NMR, UV-visible, and FL observations the coordination sphere of Fe(III) was shared with two 2-benzoimidazole (2Bim) side arms which were also confirmed by the elemental microanalyses (in the solid state) and the Job plot method (in the solution) of the complex. Moreover, the above-mentioned color change was attributed to the presence of a strong charge transfer (LMCT) band for the Fe(III)/L interaction in the solution. Furthermore, the viscosity measurement in the presence of Fe(III) uncovered an increase at 0.5-1.0 ratios for Fe(III)/L, attributable to the formation of a self-assembly in the solution. A TLC paper strip was impregnated by L for selective detection of Fe(III), demonstrating a live color change for Fe(III) at 0-5 mM in the presence of LMI.

Photoluminescent and Electrochemiluminescent Detection of Fe3+ Using Cyclometalated Iridium Complexes via Fe3+-Catalyzed Hydrolysis

Ferric ion (Fe3+) is a biologically abundant and important metal ion. We developed several cyclometalated iridium complex-based molecular sensors (1, ppy-1, 1-phen, 1 a, and 1_OMe) for the detection of Fe3+ using an acetal moiety as the reaction site. The acetal moiety in iridium complexes undergoes Fe3+-catalyzed hydrolysis and subsequent formation of a formyl group, resulting in turn-off photoluminescent and electrochemiluminescent responses. Sensor 1 showed excellent selectivity toward Fe3+ over other biologically important metal ions. Furthermore, we compared the performance of the sensors based on the structural differences of the iridium complexes, and revealed a relationship between the structure and chemical properties through electrochemical experiments and computational calculations.

Rhodamine-Anchored Polyacrylamide Hydrogel for Fluorescent Naked-Eye Sensing of Fe3

A fluorescent and colorimetric poly (acrylamide)-based copolymer probe P(AAm-co-RBNCH) has been designed via free radical polymerization of a commercial acrylamide monomer with a rhodamine-functionalized monomer RBNCH. Metal ion selectivity of RBNCH was investigated by fluorescence and colorimetric spectrophotometry. Upon addition of Fe3+, a visual color change from colorless to red and a large fluorescence enhancement were observed for the ring-opening of the rhodamine spirolactam mechanism. The monomer gives a sensitive method for quantitatively detecting Fe3+ in the linear range of 100-200 μM, with a limit of detection as low as 27 nM and exhibiting high selectivity for Fe3+ over 12 other metal ions. The hydrogel sensor was characterized by FTIR, and the effects of RBNCH amount on gel content and swelling properties were explored. According to the recipe of 1.0 mol% RBNCH to the total monomers, the fabricated hydrogel sensor displayed a good swelling property and reversibility performance and has potential for application in the imaging of Fe3+ level in industrial wastewater.

Luminescent MOFs for selective sensing of Ag+ and other ions(Fe(III) and Cr(VI))in aqueous solution

Two new title MOFs, [Zn(BTA)2]n(MOF-1), [Zn3(BTA)2(5-tbuip)2]n(MOF-2) (BTA=1H-Benzotriazole, 5-tbuip=5-tert-Butylisophthalcc Acid) have been synthesized by solvothermal method. The structures of two complexes have been determined by single-crystal X-ray diffraction analysis and further...

Photo-Induced N-N Coupling of o-Nitrobenzyl Alcohols and Indolines To Give N-Aryl-1-amino Indoles

A novel method to synthesize N-aryl-1-amino indoles was established by the photoinduced N-N coupling reaction. This protocol is by treatment of o-nitrobenzyl alcohols and indolines in the presence of TEAI and acetic acid with a 24 W ultraviolet (UV) light-emitting diode (LED) (385-405 nm) irradiation. The products bearing an aldehyde group can be further transformed to fluorescent probes based on Rhodamine 6G derivative 11, which shows a high specificity and sensitivity for Fe³⁺.

A novel "off-on" rhodamine-based colorimetric and fluorescent chemosensor based on hydrolysis driven by aqueous medium for the detection of Fe3

A novel "off-on" colorimetric and fluorescent chemosensor N²,N⁶-bis(2-(rhodamine B amido)ethyl)pyridine-2,6-dicarboxamide (RhBEP) has been designed and synthesized, which can selectively detect the presence of Fe³⁺ with about 75-fold enhancement in fluorescence emission intensity at 585 nm over various environmentally relevant metal cations such as Hg²⁺, Cu²⁺, Cr³⁺, Li⁺, Na⁺, K⁺, Ag⁺, Zn²⁺, Mg²⁺, Ca²⁺, Ba²⁺, Fe²⁺, Cd²⁺, Ni²⁺, Mn²⁺, Al³⁺, Bi³⁺ and Au³⁺ in PBS reaction media. The remarkable color change from UV-Vis titration experiments indicates that RhBEP can be used as a colorimetric chemosensor for Fe³⁺. The ultrasensitive detection limit for Fe³⁺ in the fluorescence measurement is down to 2.0 × 10^-8 mol·L^-1. The recognition mechanism of RhBEP to Fe³⁺ was analyzed by Job's plot and mass spectrometry analysis. In addition, the data from fluorescent cell imaging experiments confirmed that the chemosensor RhBEP has a promising application for the detection of Fe³⁺ in biological systems.

Design of Multifunctional Fluorescent Hybrid Materials Based on SiO2 Materials and Core-Shell Fe3 O4 @SiO2 Nanoparticles for Metal Ion Sensing

Hybrid fluorescent materials constructed from organic chelating fluorescent probes and inorganic solid supports by covalent interactions are a special type of hybrid sensing platform that has gained much interest in the context of metal ion sensing applications owing to their excellent advantages, recyclability, and solubility/dispersibility in particular, as compared with single organic fluorescent molecules. In recent decades, SiO₂ materials and core-shell Fe₃ O₄ @SiO₂ nanoparticles have become important inorganic solid materials and have been used as inorganic solid supports to hybridize with organic fluorescent receptors, resulting in multifunctional fluorescent hybrid systems for potential applications in sensing and related research fields. Therefore, recent progress in various fluorescent-group-functionalized SiO₂ materials is reviewed, with a focus on mesoporous silica nanoparticles and core-shell Fe₃ O₄ @SiO₂ nanoparticles, as interesting fluorescent organic-inorganic hybrid materials for sensing applications toward essential and toxic metal ions. Selective examples of other types of silica/silicon materials, such as periodic mesoporous organosilicas, solid SiO₂ nanoparticles, fibrous silica spheres, silica nanowires, silica nanotubes, and silica hollow microspheres, are also mentioned. Finally, relevant perspectives of metal-ion-sensing-oriented silica-fluorescent probe hybrid materials are provided.

Recent Advances on Iron(III) Selective Fluorescent Probes with Possible Applications in Bioimaging

Iron(III) is well-known to play a vital role in a variety of metabolic processes in almost all living systems, including the human body. However, the excess or deficiency of Fe3+ from the normal permissible limit can cause serious health problems. Therefore, novel analytical methods are developed for the simple, direct, and cost-effective monitoring of Fe3+ concentration in various environmental and biological samples. Because of the high selectivity and sensitivity, fast response time, and simplicity, the fluorescent-based molecular probes have been developed extensively in the past few decades to detect Fe3+. This review was narrated to summarize the Fe3+-selective fluorescent probes that show fluorescence enhancement (turn-on) and ratiometric response. The Fe3+ sensing ability, mechanisms along with the analytical novelties of recently reported 77 fluorescent probes are discussed.

Dual-binding pyridine and rhodamine B conjugate derivatives as fluorescent chemosensors for ferric ions in aqueous media and living cells

Two new pyridine-type rhodamine B chemosensors (RBPO and RBPF) used to detect Fe3+ have been designed and synthesized, and the sensing behavior towards various metal ions was evaluated via UV-vis and fluorescence spectroscopic techniques. Both RBPO and RBPF not only have good spectral responses to Fe3+ in an EtOH/H2O solution (3 : 1, v/v, HEPES, 0.5 mM, pH = 7.33) with low detection limits and high binding constants, but also suffer from less interference from common metal cations. The two chemosensors are further proven to be practical in sensitively monitoring trace Fe3+ in real water specimens. Intracellular imaging applications demonstrated that RBPO and RBPF can be used as two fluorescent chemosensors for the detection of Fe3+ in living human breast adenocarcinoma (MCF-7) cells.

Two novel rhodamine-based fluorescent probes for the rapid and sensitive detection of Fe3+: Experimental and DFT calculations

Fe³⁺ ions play an important role in both biological and environmental field. In this work, two novel rhodamine-based colorimetric and fluorescent probes (RBA2 and RBA3) were designed and synthesized for the efficient detection of Fe³⁺. Upon the addition of Fe³⁺, the fluorescence intensity of RBA2 and RBA3 enhanced 108-fold and 222-fold, respectively. RBA2 and RBA3 exhibited a low detection limit which could achieve 12.8 nM and 11.0 nM. In addition, the binding modes of RBA2 and RBA3 with Fe³⁺ were proved to be 1:1 stoichiometry in the complexes by Job's plot, ESI-MS and ¹H NMR results. The complexing ability of RBA3 with Fe³⁺ excessed to that of RBA2 that was determined by the binding association constants, and highly consistent with DFT calculations results. Furthermore, RBA2 and RBA3 were further utilized to detect Fe³⁺ in living cells and real water samples, indicating their promising prospects in biological and environmental field.

Chemical tools for detecting Fe ions

Owing to its distinctive electrochemical properties with interconvertible multiple oxidation states, iron plays a significant role in various physiologically important functions such as respiration, oxygen transport, energy production, and enzymatic reactions. This redox activity can also potentially produce cellular damage and death, and numerous diseases are related to iron overload resulting from the dysfunction of the iron regulatory system. In this case, “free iron” or “labile iron,” which refers to iron ion weakly bound or not bound to proteins, causes aberrant production of reactive oxygen species. With the aim of elucidating the variation of labile iron involved in pathological processes, some chemical tools that can qualitatively and/or quantitatively monitor iron have been utilized to investigate the distribution, accumulation, and flux of biological iron species. Since iron ions show unique reactivity depending on its redox state, i.e., Fe²⁺ or Fe³⁺ (or transiently higher oxidative states), methods for the separate detection of iron species with different redox states are preferred to understand its physiological and pathological roles more in detail. The scope of this review article covers from classical chromogenic to newly emerging chemical tools for the detection of Fe ions. In particular, chemical tools applicable to biological studies will be presented.

A novel colorimetric and turn-on fluorescent chemosensor for iron(III) ion detection and its application to cellular imaging

A novel rhodamine-based dual probe Rh-2 for trivalent ferric ions (Fe(3+)) was successfully designed and synthesized, which exhibited a highly sensitive and selective recognition towards Fe(3+) with an enhanced fluorescence emission in methanol-water media (v/v=7/3, pH=7.2). The probe Rh-2 could be applied to the determination of Fe(3+) with a linear range covering from 3.0×10(-7) to 1.4×10(-5)M and a detection limit of 1.24×10(-8)M. Meanwhile, the binding ratio of Rh-2 and Fe(3+) was found to be 1:1. Most importantly, the fluorescence and color signal changes of the Rh-2 solution were specific to Fe(3+) over other commonly coexistent metal ions. Moreover, the probe Rh-2 has been used to image Fe(3+) in living cells with satisfying results.

A reversible rhodamine 6G-based fluorescence turn-on probe for Fe3+ in water and its application in living cell imaging

A reversible fluorescent probe L based on rhodamine 6G was synthesized for the optical detection of Fe³⁺ in water.

Multifunctional Fe3O4@SiO2nanoparticles for selective detection and removal of Hg2+ion in aqueous solution

A multifunctional magnetic core–shell Fe₃O₄@SiO₂nanoparticle decorated with rhodamine-based receptor has been successfully synthesized, aiming to detect and remove Hg²⁺from aqueous media.

Multifunctional fibrous silica composite with high optical sensing performance and effective removal ability toward Hg2+ions

A multifunctional organic–inorganic hybrid sensing material (RB-KCC-1) decorated with rhodamine-based receptor has been successfully synthesized, aiming to detect and remove Hg²⁺from aqueous media.

A dual-responsive “turn-on” bifunctional receptor: a chemosensor for Fe3+ and chemodosimeter for Hg2+

Synthesis and characterization of L1–L3 along with their selective detection toward Fe³⁺ and Hg²⁺ at ppb level, exhibiting bifunctional behaviour have been presented.

One single molecule as a multifunctional fluorescent probe for ratiometric sensing of Fe3+, Cr3+ and colorimetric sensing of Cu2+

The reagent Rh-C, incorporating a rhodamine moiety and a coumarin backbone and prepared via click chemistry, was developed as the first single molecule for detecting Cu²⁺, Fe³⁺ and Cr³⁺. Its response to Cu²⁺ in different solutions is visible to the naked eye and it exhibits a ratiometric fluorescence response to Fe³⁺ in methanol and Cr³⁺ in acetonitrile.

Fluorescent, MRI, and colorimetric chemical sensors for the first-row d-block metal ions

Transition metals (d-blocks) are recognized as playing critical roles in biology, and they most often act as cofactors in diverse enzymes; however, improper regulation of transition metal stores is also connected to serious disorders. Therefore, the monitoring and imaging of transition metals are significant for biological research as well as clinical diagnosis. In this article, efforts have been made to review the chemical sensors that have been developed for the detection of the first-row d-block metals (except Cu and Zn): Cr, Mn, Fe, Co, and Ni. We focus on the development of fluorescent sensors (fall into three classes: "turn-off", "turn-on", and ratiometric), colorimetric sensors, and responsive MRI contrast agents for these transition metals (242 references). Future work will be likely to fill in the blanks: (1) sensors for Sc, Ti, and V; (2) MRI sensors for Cr, Mn, Co, Ni; (3) ratiometric fluorescent sensors for Cr(6+), Mn(2+), and Ni(2+), explore new ways of sensing Fe(3+) or Cr(3+) without the proton interference, as well as extend applications of MRI sensors to living systems.

Selectively sensing first-row transition metal ions through fluorescence enhancement

Fluorescence signaling systems that give enhancement in the presence of first-row transition metal ions are discussed.