A fluorescent probe for the discrimination of oxidation states of palladium

Intelligent quantitative recognition of sulfide using machine learning-based ratiometric fluorescence probe of metal-organic framework UiO-66-NH2/Ppix

Sulfides possess either high toxicity or play crucial physiological role such as gas transmitter dependent upon dosage, hence the significant for their rapid sensitive and selective concentration determination. Herein, a machine learning enhanced ratiometric fluorescence sensor was engineered for sulfide determination by incorporating the nanometal-organic framework (UiO-66-NH2) along with protoporphyrin IX (Ppix). The blue fluorescence at 431 nm originated from the moiety of UiO-66-NH2 by 365 nm excitation serves as an internal calibration reference signal, while the red fluorescence at 629 nm from the moiety of Ppix serves as the analytical signal, and the intensity is correlated to the amount of sulfides. The fluorescence color of the sensor gradually varies from blue to red upon sequential addition of copper and sulfide ions, resulting in RGB (Red, Green, Blue) feature values for corresponding sulfide concentrations, which facilities the advanced data processing techniques using machine learning algorithms. On the basis of fluorescence image fingerprint extraction and machine learning algorithms, an online data analysis model was developed to improve the precision and accuracy of sulfide determination. The established model employed Linear Discriminant Analysis (LDA) and was subjected to rigorous cross-validation to ensure its robustness. By analyzing the correlation between RGB feature values and sulfide concentrations, the study highlighted a significant positive relationship between the red feature values and sulfide concentrations. The application of machine learning techniques on the ratiometric fluorescence signal of the UiO-66-NH2/Ppix probe demonstrated its potential for intelligent quantitative determination of sulfides, offering a valuable and efficient tool for pollution detection and real-time rapid environmental monitoring.

A sensitive ratiometric fluorescence probe with a large spectral shift for sensing and imaging of palladium

Palladium (Pd) is an important heavy metal with excellent catalytic properties and widely used in organic chemistry and the pharmaceutical industry. Efficient and convenient analytical techniques for Pd are urgently needed due to the hazardous effects of Pd on the environment and human health. Herein, we have developed five new ratiometric probes for the selective detection of Pd0 based on the Pd-catalyzed Tsuji-Trost reaction. Among them, the F-substituted probe PF-Pd showed the largest spectral shift (148 nm) and the most sensitive response (detection limit 2.11 nM). PF-Pd was employed to determine Pd0 in tap water or lake water samples, which presented satisfactory accuracy and precision. In addition, profiting from its distinct colorimetric response, visual detection of Pd0 was performed on PF-Pd loaded test strips or in field soil samples. Furthermore, fluorescence imaging of living 4T1 cells demonstrated that PF-Pd is suitable for imaging of intracellular Pd0. The good analytical performance of PF-Pd may enable it to be widely used in the convenient, rapid, sensitive and selective detection of Pd0 in environmental or biological analysis.

A Piperazine Linked Rhodamine-BODIPY FRET-based Fluorescent Sensor for Highly Selective Pd2+ and Biothiol Detection

A class of rhodamine-based fluorescent sensors for the selective and sensitive detection of Pd2+ metal ions in aqueous media has been developed. A rhodamine-based sensor PMS and a rhodamine-BODIPY Förster resonance energy transfer (FRET)-pair sensor PRS have been incorporated with a piperazine linker and an O-N-S-N podand ligand for specific recognition of Pd2+ ion. Both probes displayed colorimetric and fluorescent ratiometric changes when exposed to Pd2+ , due to their spirolactam rings opening and restoring rhodamine conjugation. PRS is highly selective to Pd2+ over 22 other metal ions, showing a 0.6-fold ratiometric difference at I600nm /I515nm . Additionally, the lactam ring in Pd2+ coordinated PRS-Pd could be switched back to the closed form in the presence of various thiols, providing a "red-green traffic light" detection mechanism between red and green emission. Furthermore, PRS showed excellent cell viability and was successfully employed to image Pd2+ and the PRS-Pd complex ensemble could interchangeably detect biothiols including glutathione (GSH) in A549 human lung cancer cells.

Luminescence and Palladium: The Odd Couple

The synthesis, photophysical properties, and applications of highly fluorescent and phosphorescent palladium complexes are reviewed, covering the period 2018–2022. Despite the fact that the Pd atom appears closely related with an efficient quenching of the fluorescence of different molecules, different synthetic strategies have been recently optimized to achieve the preservation and even the amplification of the luminescent properties of several fluorophores after Pd incorporation. Beyond classical methodologies such as orthopalladation or the use of highly emissive ligands as porphyrins and related systems (for instance, biladiene), new concepts such as AIE (Aggregation Induced Emission) in metallacages or in coordination-driven supramolecular compounds (CDS) by restriction of intramolecular motions (RIM), or complexes showing TADF (Thermally Activated Delayed Fluorescence), are here described and analysed. Without pretending to be comprehensive, selected examples of applications in areas such as the fabrication of lighting devices, biological markers, photodynamic therapy, or oxygen sensing are also here reported.

Imaging mitochondrial palladium species in living cells with a NIR iridium(III) complex

The wide use of palladium (Pd) raises the concern about environmental pollution and human diseases, evoking the need for the development of detection methods for Pd species. However, the development of near-infrared (NIR) luminescence probes for subcellular Pd species remains challenging. In this work, we presented a NIR iridium(III) complex-based luminescence probe for the detection of Pd⁰ species through incorporating an allyl group and amino group into the N^N ligand. We found that the probe was capable of detecting Pd⁰ species with a limit of detection (LOD) of 0.5 μM. Importantly, cell imaging experiments showed that the probe is applicable for visualizing mitochondrial Pd⁰ ions in living cells, which are also suitable for Pd(II) species. To the best of our knowledge, this is the first NIR luminescence imaging probe for the detection of mitochondria Pd species in living cells, paving the way for studying subcellular distributions and related toxicity analysis of exogenous Pd species in living cells.

An effective approach to develop targetable and responsive fluorescent probes for imaging of organelles based on cresyl violet scaffold

Fluorescent probes combined with confocal microscopy are recognized as a powerful tool for imaging living cells and even organelles due to their high sensitivity and resolution. However, many of analyte-activatable and organelle-targetable fluorescent probes are developed via tedious attempts, and a relatively predictable method to design such probes is still lacking. Herein, we put forward an effective synthetic strategy to construct both targetable and responsive probes for organelles based on the cresyl violet scaffold. The approach allows access to a variety of organelle-targeting fluorescent probes for an analyte of interest via introducing the corresponding targeting and recognition groups to the 5- and 9-positions of cresyl violet, respectively. The potency of the approach is exemplified by its application to develop four cresyl violet-based fluorophores with different organelle-targeting groups, and a mitochondrion-targeting ratiometric probe capable of imaging Pd⁰ in living cells.

Synthesis, Characterization, and Spectroscopic Studies of Bis-(meso-4-methoxyphenyl)-Benziporphyrin and Its Pd-Metal Complex

Benziporphyrin systems are widely explored, yet alternative improved synthetic routes towards these systems are needed. Here, a fairly and efficient synthesis of the free base and its metal complex is well designed. Dimethoxybenzene dicarbinol intermediate was prepared in excellent yields by reacting 4-methoxyphenylmagnesium bromide with isophthaladehyde in diethyl ether. Reaction with equivalent pyrrole and pentafluorobenzaldehyde in the presence of trifluoroacetic acid (TFA), followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), provided good yields of bis-(meso-4-methoxyphenyl)-benziporphyrin. Metalation of the free base was performed using palladium(II) acetate salt in acetonitrile. All intermediates and the final products are fully characterized using NMR, HMRS, and UV-Vis spectroscopies and briefly discussed.