Enhancing Tsuji-Trost deallylation in living cells with an internal-nucleophile coumarin-based probe

In recent years, bioorthogonal uncaging reactions have been developed to proceed efficiently under physiological conditions. However, limited progress has been made in the development of protecting groups combining stability under physiological settings with the ability to be quickly removed via bioorthogonal catalysis. Herein, we present a new water-soluble coumarin-derived probe bearing an internal nucleophilic group capable of promoting Tsuji-Trost deallylation under palladium catalysis. This probe can be cleaved by a bioorthogonal palladium complex at a faster rate than the traditional probe, namely N-Alloc-7-amino-4-methylcoumarin. As the deallylation process proved to be efficient in mammalian cells, we envision that this probe may find applications in chemical biology, bioengineering, and medicine.

A fluorescent probe for the discrimination of oxidation states of palladium

Palladium-based catalysts are widely used in pharmaceutical industries, which can sometimes cause palladium contamination in pharmaceutical drug manufacture. It is important to separately quantify the different oxidation states of palladium (Pd⁰ and Pd²⁺) in pharmaceuticals as they react with scavengers differently. Although palladium sensors have been under intense investigation, oxidation state differentiators are very rare. Here, we report a simple porphyrin–coumarin conjugate, PPIX-L2, that can selectively discriminate between the oxidation states of palladium. The reaction of PPIX-L2 with Pd⁰ showed a 24-fold fluorescence increase of the coumarin emission, meanwhile, the presence of Pd²⁺ led to a 98% quenching of the porphyrin emission. Fluorescent responses of PPIX-L2 towards Pd⁰ and Pd²⁺ are specific, and its sensitivity towards both palladium species is significantly increased with a detection limit of 75 nM and 382 nM for Pd⁰ and Pd²⁺ respectively.

A simple porphyrin–coumarin conjugate PPIX-L2 was developed for the discrimination of different oxidation states of palladium (Pd⁰ and Pd²⁺), and with a significantly improved sensitivity.

α-Substituted phthalocyanines based on metal-induced H- or J-type aggregation for silver and palladium ions: synthesis, fluorescence, and antimicrobial and antioxidant properties

In this study, firstly, 3-(2,3-bis(hexadecylthio)propoxy)phthalonitrile (2) as a new phthalonitrile derivative was prepared. Then, new types of non-peripheral phthalocyanine derivatives [CuPc (3), ZnPc (4), and CoPc (5)] were synthesized by using this ligand. The synthesized new compounds were characterized by common spectroscopic methods such as FTIR, 1H-NMR, 13C-NMR, MALDI-TOF, UV-Vis and fluorescence spectroscopy. The H- or J-type aggregation behaviors of novel type metallophthalocyanines in the presence of valuable metal ions such as Ag(i) and Pd(ii) were investigated by UV-Vis and fluorescence spectroscopy. The quenching efficiency of the Ag(i) and Pd(ii) ions for ZnPc (4) was obtained using the Stern-Volmer equation and the quenching constant of ZnPc (4) towards Ag(i) and Pd(ii) ions was found to be 2.9 × 105 mol L-1 and 1.2 × 105 mol L-1, respectively. The binding constant (Ka) and binding stoichiometry (n) of Ag(i) and Pd(ii) ions for ZnPc (5) were calculated using a modified Benesi-Hildebrand equation, and were found to be 1.4 × 108 M-1 and 3.4 × 107 M-1, respectively. The binding ratio and free energy change of Ag(i) and Pd(ii) ions for ZnPc (4) were found to be 1.86, 1.54, -46.49 kJ mol-1 and -42.9 kJ mol-1, respectively. Also, the antioxidant properties of the synthesized novel type metallophthalocyanines and their Ag(i) and Pd(ii) ion doped aggregates were determined using three different methods: DPPH free radical scavenging activity, ferrous ion chelating activity and reducing power activity. Finally, the antibacterial and antifungal activities of phthalocyanine compounds synthesized within the scope of this study were determined by disc diffusion and macrobroth dilution methods and the effect of the doping of Ag(i) and Pd(ii) ions on the antibacterial activities of phthalocyanines was investigated.

Activity-Based Sensing: A Synthetic Methods Approach for Selective Molecular Imaging and Beyond

Emerging from the origins of supramolecular chemistry and the development of selective chemical receptors that rely on lock-and-key binding, activity-based sensing (ABS)-which utilizes molecular reactivity rather than molecular recognition for analyte detection-has rapidly grown into a distinct field to investigate the production and regulation of chemical species that mediate biological signaling and stress pathways, particularly metal ions and small molecules. Chemical reactions exploit the diverse chemical reactivity of biological species to enable the development of selective and sensitive synthetic methods to decipher their contributions within complex living environments. The broad utility of this reaction-driven approach facilitates application to imaging platforms ranging from fluorescence, luminescence, photoacoustic, magnetic resonance, and positron emission tomography modalities. ABS methods are also being expanded to other fields, such as drug and materials discovery.

Direct fluorogenic detection of palladium and platinum organometallic complexes with proteins and nucleic acids in polyacrylamide gels

Allyl- and propargyl ethers of umbelliferone are sensitive probes for palladium and platinum, including anticancer compounds cisplatin, carboplatin and oxaliplatin, and effective for direct visualization of protein and DNA complexes with organometallic compounds in polyacrylamide gels allowing easy detection of interactions with analyzed protein or nucleic acid. Both probes can be used for fast evaluation of Pd/Pt binding to nanocarriers relevant in drug targeted therapy or specific clinically relevant target macromolecules.

CO Sense and Release Flavonols: Progress toward the Development of an Analyte Replacement PhotoCORM for Use in Living Cells

Carbon monoxide (CO) is a signaling molecule in humans. Prior research suggests that therapeutic levels of CO can have beneficial effects in treating a variety of physiological and pathological conditions. To facilitate understanding of the role of CO in biology, molecules that enable fluorescence detection of CO in living systems have emerged as an important class of chemical tools. A key unmet challenge in this field is the development of fluorescent analyte replacement probes that replenish the CO that is consumed during detection. Herein, we report the first examples of CO sense and release molecules that involve combining a common CO-sensing motif with a light-triggered CO-releasing flavonol scaffold. A notable advantage of the flavonol-based CO sense and release motif is that it is trackable via fluorescence in both its pre- and postsensing (pre-CO release) forms. In vitro studies revealed that the PdCl₂ and Ru(II)-containing CORM-2 used in the CO sensing step can result in metal coordination to the flavonol, which minimizes the subsequent CO release reactivity. However, CO detection followed by CO release is demonstrated in living cells, indicating that a cellular environment mitigates the flavonol/metal interactions.

A BODIPY-based fluorescent sensor for the detection of Pt2+ and Pt drugs

A novel BODIPY-based fluorescent sensor PS was designed for imaging Pt2+, cisplatin and nedaplatin in aqueous medium and biological environments, providing great potential for studying the Pt-drug metabolism and the development of new platinum drugs.

A fluorescent probe based on novel fused four ring quinoxalinamine for palladium detection and bio-imaging

An “off–on” fluorescent probe was designed to detect palladium of all the typical oxidation states (0, +2, +4) without additional additives.

Intracellular Catalysis with Selected Metal Complexes and Metallic Nanoparticles: Advances toward the Development of Catalytic Metallodrugs

Platinum-containing drugs (e.g., cisplatin) are among the most frequently used chemotherapeutic agents. Their tremendous success has spurred research and development of other metal-based drugs, with notable achievements. Generally, the vast majority of metal-based drug candidates in clinical and developmental stages are stoichiometric agents, i.e., each metal complex reacts only once with their biological target. Additionally, many of these metal complexes are involved in side reactions, which not only reduce the effective amount of the drug but may also cause toxicity. On a separate note, transition metal complexes and nanoparticles have a well-established history of being potent catalysts for selective molecular transformations, with examples such as the Mo- and Ru-based catalysts for metathesis reactions (Nobel Prize in 2005) or palladium catalysts for C-C bond forming reactions such as Heck, Negishi, or Suzuki reactions (Nobel Prize in 2010). Also, notably, no direct biological equivalent of these transformations exists in a biological environment such as bacteria or mammalian cells. It is, therefore, only logical that recent interest has focused on developing transition-metal based catalytic systems that are capable of performing transformations inside cells, with the aim of inducing medicinally relevant cellular changes. Because unlike in stoichiometric reactions, a catalytically active compound may turn over many substrate molecules, only very small amounts of such a catalytic metallodrug are required to achieve a desired pharmacologic effect, and therefore, toxicity and side reactions are reduced. Furthermore, performing catalytic reactions in biological systems also opens the door for new methodologies to study the behavior of biomolecules in their natural state, e.g., via in situ labeling or by increasing/depleting their concentration at will. There is, of course, an art to the choice of catalysts and reactions which have to be compatible with biological conditions, namely an aqueous, oxygen-containing environment. In this review, we aim to describe new developments that bring together the far-distant worlds of transition-metal based catalysis and metal-based drugs, in what is termed "catalytic metallodrugs". Here we will focus on transformations that have been performed on small biomolecules (such as shifting equilibria like in the NAD⁺/NADH or GSH/GSSG couples), on non-natural molecules such as dyes for imaging purposes, or on biomacromolecules such as proteins. Neither reactions involving release (e.g., CO) or transformation of small molecules (e.g., ¹O₂ production), degradation of biomolecules such as proteins, RNA or DNA nor light-induced medicinal chemistry (e.g., photodynamic therapy) are covered, even if metal complexes are centrally involved in those. In each section, we describe the (inorganic) chemistry involved, as well as selected examples of biological applications in the hope that this snapshot of a new but quickly developing field will indeed inspire novel research and unprecedented interactions across disciplinary boundaries.

A new turn-on fluorescent probe for the detection of palladium(0) and its application in living cells and zebrafish

A new “turn-on” fluorescent probe 1 for the detection of Pd⁰ has been designed and synthesized.

Use of rhodamine-allyl Schiff base in chemodosimetric processes for total palladium estimation and application in live cell imaging

An allyl-rhodamine Schiff base shows excellent palladium sensitivity (LOD, 95 nM) irrespective of Pd(0,ii,iv) and practical applicability is judged in living cells of RAW 264.7 (macrophage) cells.

Noneffervescent Method for Catalysis-Based Palladium Detection with Color or Fluorescence

Palladium is a highly valuable metal in automobile, chemical, and pharmaceutical industries. The metal is generally quantified by atomic absorption spectrometry or inductively coupled plasma mass spectrometry. These techniques are tedious and require expensive instruments that are operated mostly off site. As cost-effective and user-friendly alternatives to these techniques, we previously reported two practical fluorometric or colorimetric methods to quantify palladium. Both methods rely on the use of NaBH₄, which cannot be stored in solution for more than 10 days. Commercially available solutions of NaBH₄ are partially or fully degraded to di- or triborohydride species and cannot be used for palladium(0)-catalyzed allylic C-O bond cleavage for quantification purposes. Here, we report a new method that replaces NaBH₄ with NH₂NH₂ for the palladium-catalyzed deallylation of fluorogenic and colorimetric chemodosimeter resorufin allyl ether. This method is slower but as sensitive as the most recent method from our laboratory. The method is selective for palladium and depends on the presence of tri(2-furyl)phosphine as a palladium ligand and NH₂NH₂ as a palladium-reducing reagent.

A two-photon ratiometric ESIPT probe for fast detection and bioimaging of palladium species

A two-photon ratiometric ESIPT probe for fast detection of palladium species, which can be used for bioimaging has been designed.

Development and application of bond cleavage reactions in bioorthogonal chemistry

Bioorthogonal chemical reactions are a thriving area of chemical research in recent years as an unprecedented technique to dissect native biological processes through chemistry-enabled strategies. However, current concepts of bioorthogonal chemistry have largely centered on 'bond formation' reactions between two mutually reactive bioorthogonal handles. Recently, in a reverse strategy, a collection of 'bond cleavage' reactions has emerged with excellent biocompatibility. These reactions have expanded our bioorthogonal chemistry repertoire, enabling an array of exciting new biological applications that range from the chemically controlled spatial and temporal activation of intracellular proteins and small-molecule drugs to the direct manipulation of intact cells under physiological conditions. Here we highlight the development and applications of these bioorthogonal cleavage reactions. Furthermore, we lay out challenges and propose future directions along this appealing avenue of research.

A water-soluble colorimetric two-photon probe for discrimination of different palladium species and its application in bioimaging

A novel water-soluble colorimetric two-photon chemodosimeter for discrimination of different palladium species and its application in bioimaging.

An efficient non-reaction based colorimetric and fluorescent probe for the highly selective discrimination of Pd0 and Pd2+ in aqueous media

A novel anthraquinone-imidazole based colorimetric and fluorogenic probe 1 discriminates the oxidation states of Pd⁰ and Pd²⁺ by naked eye with high selectivity in aqueous media due to the difference in coordination in the pocket of probe molecule.

Pd nanoparticles encapsulated in magnetic carbon nanocages: an efficient nanoenzyme for the selective detection and multicolor imaging of cancer cells

Rapid and simple molecular recognition based techniques for the identification of the subtypes of cancer cells are essential in molecular medicine. However, improving the sensitivity and accuracy of the early diagnosis of this disease remains a major challenge. Herein, we develop a novel approach for the in situ growth of palladium nanoparticles in magnetic carbon nanocages (PdNPs/MCNCs). The confined Pd NPs, which have excellent dispersion in magnetic carbon nanocages, show superior catalytic performance for the cleavage reaction of N-butyl-4-NHAlloc-1,8-naphthalimide (NNPH), thereby producing significant changes in both color (from colorless to jade-green) and fluorescence (from blue to green) through the ICT process. Based on the abovementioned results, a novel sensing platform utilizing the PdNPs/MCNC nanocatalyst as an artificial enzyme and NNPH as a fluorescent and color change reporter molecule for the multicolor imaging and colorimetric detection of cancer cells was developed. We envision that this nanomaterial can be used as a power tool for a wide range of potential applications in biotechnology and medicine.

A simple and effective fluorescent probe based on rhodamine B for determining Pd2+ ions in aqueous solution

It is demonstrated that the mechanism of the probe to Pd²⁺ and images under a UV lamp.

Synthesis and characterization on novel fluorescent sensors for Pd2+/Pd0 with high selectivity

Novel chemosensors based on triaryl 1H-imidazo[4,5-b]pyrazine with high selectivity for palladium (Pd⁰/Pd²⁺) detection have been synthesized simply.

A sensitive and selective chemiluminogenic probe for palladium

Palladium triggered removal of a propargyl group leads to the cleavage of the 1,2-dioxetane ring, leading to bright chemiluminescence.

A colorimetric and ratiometric fluorescent probe for detection of palladium in the red light region

We synthesized a colorimetric and ratiometric red-light emissive chemosensor with high selectivity and sensitivity towards palladium species.

Fluorometric imaging methods for palladium and platinum and the use of palladium for imaging biomolecules

Palladium and platinum metals have been used to facilitate novel bioimaging methods.

A catalytic chemodosimetric approach for detection of nanomolar cyanide ions in water, blood serum and live cell imaging

The nano-molar detection of cyanide in live cell imaging and blood serum has been achieved through cyanide catalysed fluorescence enhancement with a TON between 70 and 360.

A new fluorogenic probe for the selective detection of carbon monoxide in aqueous medium based on Pd(0) mediated reaction

A coumarin-based fluorogenic probe, PCO-1, detects carbon monoxide selectively in buffer at pH 8.0 through the intramolecular cyclization–elimination pathway based on Pd(0) mediated reaction.

An azodye–rhodamine-based fluorescent and colorimetric probe specific for the detection of Pd2+ in aqueous ethanolic solution: synthesis, XRD characterization, computational studies and imaging in live cells

An azodye–rhodamine hybrid colorimetric fluorescent probe (L) has been designed and synthesized.

Highly selective fluorescence detection of Pd2+/4+ species based on a catalyzed aromatic Claisen rearrangement

A highly selective chemodosimeter based on 1,8-naphthalimide for Pd^2+/4+ species via a Claisen rearrangement was developed with a detection limit of 1.4 μM.

‘Turn-on’ coordination based detection of Pd2+and bioimaging applications

A BODIPY based molecular probe recognises Pd²⁺via off–ontype fluorescence enhancement which could be correlated to the restricted PET on the basis of DFT/TD-DFT calculations.

Colourimetric and fluorescent probes for the optical detection of palladium ions

In recent years, the development of optical probes to analyse trace palladium ions (Pd(2+)) has attracted great attention because of the residual palladium released by catalytic converters or from various Pd-catalysed reactions. These residual palladium ions may cause potential health hazards. This review provides a brief introduction to the new methods used to determine trace amounts of Pd(2+), which then mainly focuses on the different reporting systems and unique mechanisms of the colourimetric and fluorescent probes used to detect Pd(2+), including Pd(2+) complex formation or Pd-catalysed reactions.

Reaction-based small-molecule fluorescent probes for chemoselective bioimaging

The dynamic chemical diversity of elements, ions and molecules that form the basis of life offers both a challenge and an opportunity for study. Small-molecule fluorescent probes can make use of selective, bioorthogonal chemistries to report on specific analytes in cells and in more complex biological specimens. These probes offer powerful reagents to interrogate the physiology and pathology of reactive chemical species in their native environments with minimal perturbation to living systems. This Review presents a survey of tools and tactics for using such probes to detect biologically important chemical analytes. We highlight design criteria for effective chemical tools for use in biological applications as well as gaps for future exploration.