A versatile rhodamine B-derived fluorescent probe for selective copper(II) sensing

Highly selective Cu2+ detection with a naphthalimide-functionalised pillar[5]arene fluorescent chemosensor

Ligand 1, a rim-differentiated pillar[5]arene macrocycle modified with five naphthalimide groups through click chemistry, serves as an effective ratiometric fluorescent chemosensor for Cu2+. In contrast to the monomeric naphthalimide control compound 2, which shows only monomer emission, ligand 1 demonstrates dual emission characteristics encompassing both the monomer and excimer of the naphthalimide moieties. The binding properties of ligand 1 toward 15 different metal ions were systematically investigated in CH2Cl2/CH3CN (v/v, 1 : 1) by UV-vis and fluorescence spectroscopy. Remarkably, ligand 1 exhibits exceptional selectivity for Cu2+ ions. Upon complexation with Cu2+, the excimer emission of ligand 1 diminishes, concomitant with an enhancement of its monomer emission. The binding ratio for 1·Cu2+ was determined to be 1 : 1, with an association constant of (3.39 ± 0.40) × 105 M-1 calculated using a nonlinear least-squares curve-fitting method. Furthermore, the limit of detection (LOD) was found to be 185 ± 7 nM. Our results from 1H NMR titration, high-resolution mass spectrometry analysis and density functional theory calculations of 1·Cu2+ suggest synergistic coordination between Cu2+ and the triazole groups on ligand 1.

Rhodamine hydrazide-linked naphthalimide derivative: Selective naked eye detection of Cu2+, S2- and understanding the therapeutic potential of the copper complex as an anti-cervical cancer agent

A naphthalimide-labeled rhodamine hydrazone derivative HL has been synthesized, characterized and examined in metal ion recognition. It shows selective colorimetric detection of Cu2+ over a number of other metal ions with a detection limit of 1.66 × 10-7 M in CH3CN/HEPES buffer (v/v = 2:1, pH = 6.8). The spirolactam ring of rhodamine and the imino-phenol motif of naphthalimide in HL are involved in complexation of Cu2+ as shown by single crystal X-ray. Single crystal of the copper-complex is prepared by utilizing NaSCN and it is characterized as CuL(SCN). The emergence of new absorption at 550 nm in UV-vis and the pink color of the solution reveal the selective interaction toward Cu2+. HL is characterized as a fluorescence resonance energy transfer (FRET) system that remains 'turned OFF' while spirolactam ring exists. In the presence of Cu2+, FRET is 'turned ON' via the opening of spirolactam ring to give emission at 580 nm which is less intense due to the quenching effect of Cu2+ ion. The complexation is reversible and the ensemble of Cu2+.HL selectively recognizes S2- over a series of different anions involving a color change from pink to colorless via the formation of spirolactam ring. The copper complex CuL(SCN) is further employed to understand its efficacy as a therapeutic agent. The complex is cytotoxic to high-risk HPV positive cervical cancer cell lines like SiHa and HeLa and is efficient in the generation and accumulation of reactive oxygen species (ROS). The complex also initiates nuclear blebbing and shows DNA degradation as understood by DNA laddering assay.

Robust Optical Detection of Ga3+ by a Rhodamine- and Coumarin-Based Proficient Probe: Theoretical Investigations and Biological Applications

The present investigation highlights a rhodamine-B- and coumarin-based efficient probe that selectively detects Ga3+ over other metal ions. The active pocket of the ligand for trapping the metal ions and the binding stoichiometry of its Ga3+ complex were discovered by single-crystal X-ray diffraction (SC-XRD) analysis. This binding stoichiometry was further confirmed in the solution state by mass spectrometry and Job's plot. The detection limit was found to be at the nanomolar level. Pyrophosphate being a well-known quencher could easily quench the fluorescence intensity of the RC in the presence of Ga3+ and reversibly recognize Ga3+ in the solution. The spiro ring opening of the ligand after Ga3+ insertion is proposed to be the principal mechanism for the turn-on fluorescence response. This ring opening was confirmed by SC-XRD data and nuclear magnetic resonance (NMR) titration experiments. Both ground- and excited-state calculations of the ligand and complex have been carried out to obtain information about their energy levels and to obtain the theoretical electronic spectra. Furthermore, the live-cell imaging of the probe only and the probe after the addition of Ga3+ have been carried out in HaCaT cells and satisfactory responses were observed. Interestingly, with the help of this probe, Ga3+ can be tracked inside the intracellular organelle such as lysosomes along with other regions of the cell. The article highlights a rhodamine-coumarin-based probe for the detection of Ga3+ over other metal ions with a nanomolar level detection limit. Structural characterization of the ligand and its Ga3+ complex was investigated by SC-XRD. Density functional theory (DFT) and time-dependent DFT (TD-DFT) studies were carried out to explore the excited-state energies and electronic spectra. The application of the probe for the detection of Ga3+ in live cells has been explored, and positive responses were observed.

Rapid quantitative analysis of calcium in infant formula powder assisted by long short-term memory with variable importance using laser-induced breakdown spectroscopy

Calcium is the main mineral responsible for healthy bone growth in infants. Laser-induced breakdown spectroscopy (LIBS) was combined with a variable importance-based long short-term memory (VI-LSTM) for the quantitative analysis of calcium in infant formula powder. First, the full spectra were used to establish PLS (partial least squares) and LSTM models. The R2 and root-mean-square error (RMSE) of the test set (R P2 and R M S E _P) were 0.1460 and 0.0093 in the PLS method, respectively, and 0.1454 and 0.0091 in the LSTM model, respectively. To improve the quantitative performance, variable selection based on variable importance was introduced to evaluate the contribution of input variables. The variable importance-based PLS (VI-PLS) model had R P2 and R M S E _P of 0.1454 and 0.0091, respectively, whereas the VI-LSTM model had R P2 and R M S E _P of 0.9845 and 0.0037, respectively. Compared with the LSTM model, the number of input variables in the VI-LSTM model was reduced to 276, R P2 was improved by 114.63%, and R M S E _P was reduced by 46.38%. The mean relative error of the VI-LSTM model was 3.33%. We confirm the predictive ability of the VI-LSTM model for the calcium element in infant formula powder. Thus, combining VI-LSTM modeling and LIBS has great potential for the quantitative elemental analysis of dairy products.

Dual-mode colorimetric/fluorescent chemosensor for Cu2+/Zn2+ and fingerprint imaging based on rhodamine ethylenediamine bis(triazolyl silsesquioxane)

A novel dual functional and visual rhodamine ethylenediamine bis(triazolyl silsesquioxane) (RBS) chemosensor was successfully synthesized using "click" chemistry. The results have unambiguously demonstrated that RBS can act in fluorescent and colorimetric sensing of Cu²⁺ and Zn²⁺ by their respective coordination with triazole structures and, more importantly, it has also been found that triazole-amide of RBS could turn on chelation-enhanced fluorescence (CHEF) of Cu²⁺. Remarkably, the addition of Cu²⁺ triggered an enhanced fluorescent emission by 63.3-fold (ϕ_F = 0.41), while Zn²⁺ enhanced it 48.3-fold (ϕ_F = 0.29) relative to the original RBS (ϕ_F = 0.006) in acetonitrile (MeCN) solvent. The fluorescent limit of detection for Cu²⁺ and Zn²⁺ is similar and fall within 3.0 nM, while under colorimetric sensing the responses were 2.14 × 10^-8 and 4.0 × 10^-8 mol L^-1, respectively. Moreover, the effective sensing profile of RBS and extended applications of RBS-Cu²⁺ and RBS-Zn²⁺ for fingerprinting detection and imaging were observed with adequate sensitivity, stability and legibility under the dual visual responses.

Microwave-assisted synthesis for a highly selective rhodamine 6G-derived fluorescent sensor and bioimaging

A new rhodamine 6G derivative R1 has been synthesized by condensation of rhodamine hydrazide and 6-hydroxymethyl-pyridine using microwave-assisted reaction. Naked-eye colorimetric and photo physical studies show the synthesized compound is selectively sensing Cu2+ in CH3CN/H2O (9:1, v/v) solution. Upon coordination with Cu2+ ion, the spirolactam of R1 is opened, which results in a formation of highly fluorescent complex and change in color of the solution. The Job's plot indicates 1:2 binding stoichiometry between Cu2+ ion and R1. Limit of detection for Cu2+ was determined to be 1.23 μM. The sensor was successfully applied to fluorescent imaging of Cu2+ ion in living cells.

Copper (II)-Catalyzed Oxidation of Ascorbic Acid: Ionic Strength Effect and Analytical Use in Aqueous Solution

Copper is an important metal both in living organisms and in the industrial activity of humans, it is also a distributed water pollutant and a toxic agent capable of inducing acute and chronic health disorders. There are several fluorescent chemosensors for copper (II) determination in solutions; however, they are often difficult to synthesize and solvent-sensitive, requiring a non-aqueous medium. The present paper improves the known analytical technique for copper (II) ions, where the linear dependence between the ascorbic acid oxidation rate constant and copper (II) concentration is used. The limits of detection and quantification of the copper (II) analysis kinetic method are determined to be 82 nM and 275 nM, respectively. In addition, the selectivity of the chosen indicator reaction is shown: Cu2+ cations can be quantified in the presence of the 5–20 fold excess of Co2+, Ni2+, and Zn2+ ions. The La3+, Ce3+, and UO22+ ions also do not catalyze the ascorbic acid oxidation reaction. The effect of the concentration of the common background electrolytes is studied, the anomalous influence for chloride-containing salts is observed and discussed.

A highly selective chromogenic and fluorogenic chemodosimeter for dual detection of Cu2+ based on a redox-active calix[4]arene with isoxazolylchloroanthracene

Calix[4]arene 1 with 25,27-diisoxazolylchloroanthryl groups is a chromogenic and fluorogenic sensor for Cu2+ with a LOD of 1.67 μM by fluorescence. Calix[4]diquinone was obtained in high yield through the redox reaction of ligand 1 with Cu(ClO4)2.