Selective recognition of homocysteine and cysteine based on new ruthenium(II) complexes

Research progress of auxiliary groups in improving the performance of fluorescent probes

In the design work of fluorescent probes, it is important to consider not only the factors of fluorescence properties but also the environment in which the fluorescent molecule works. This requires the design of auxiliary groups to refine the fluorescent molecule. Nowadays, more and more fluorescent molecules are not limited to the traditional fluorescent probe consisting of a fluorophore, linker arm and recognition group, but integrate the three into one, and introduce auxiliary groups where possible. Auxiliary groups are "catalytic groups" that do not interact with the substrate, or "catalyze" the interaction of the recognition group with the substrate. The introduced auxiliary groups can improve the sensitivity and selectivity of the detection to some extent, which has attracted great interest from researchers. Although previous work has focused on this aspect, no one has summarized it systematically and comprehensively. So this review summarizes the role of auxiliary groups that are classified into three categories according to the different mechanisms between the auxiliary groups and the substance, in improving the performance of fluorescent probes in recent years (2012-2022). In particular, we generalize the mechanisms of the auxiliary groups in improving the sensitivity and selectivity of fluorescent probes. Also, the fundamental principles of auxiliary groups to improve the sensitivity and selectivity of fluorescent probes are discussed and future research directions in this field are proposed.

Three-Photon AIE Pt(II) Complexes as Cysteine-Targeting Theranostic Agents for Tumor Imaging and Chemotherapy

Herein, we have synthesized a series of three-photon fluorescent Pt(II) complexes targeting a tumor-associated biothiol, cysteine (Cys), which allows it to be detected without any interference from other intracellular proteins. We focused on how to significantly improve the fluorescence response of Cys via regulating the recognition units in probes. The reaction of K₂PtCl₄ with L-CH₃ or L-COOEt in DMSO solution gave Lyso-Pt-CH₃ and Lyso-Pt-COOEt, respectively, which present four-coordinated square-planar geometries in mononuclear structures. Lyso-Pt-CH₃ consists of a Cys aptamer labeled with typical aggregation-induced emission (AIE) characteristics, which shows strong three-photon absorption cross section (3PA) only in the presence of Cys. It was found that Lyso-Pt-CH₃ displayed a perfect signal-to-noise ratio for imaging lysosomes and for rapid detection of Cys. Using Lyso-Pt-CH₃, Cys-related cellular mechanisms were proposed. We confirm that cystine (Cyss) could be absorbed in cells through cystine/glutamate antiporters (system x_c^-) and is then converted to Cys under the effect of enzymes. All of these suggest that Lyso-Pt-CH₃ might be a potential candidate as a simple and straightforward biomarker of lysosome-related Cys in vitro. Lyso-Pt-CH₃ can effectively identify tumor tissues with excessive levels of Cys. Lyso-Pt-CH₃ also showed excellent antitumor activity than cisplatin. This work provides a novel strategy for the rational design of controllably activated and Cys-targeted Pt(II) anticancer prodrugs for clinical diagnosis and treatment.

Determination and Imaging of Small Biomolecules and Ions Using Ruthenium(II) Complex-Based Chemosensors

Luminescence chemosensors are one of the most useful tools for the determination and imaging of small biomolecules and ions in situ in real time. Based on the unique photo-physical/-chemical properties of ruthenium(II) (Ru(II)) complexes, the development of Ru(II) complex-based chemosensors has attracted increasing attention in recent years, and thus many Ru(II) complexes have been designed and synthesized for the detection of ions and small biomolecules in biological and environmental samples. In this work, we summarize the research advances in the development of Ru(II) complex-based chemosensors for the determination of ions and small biomolecules, including anions, metal ions, reactive biomolecules and amino acids, with a particular focus on binding/reaction-based chemosensors for the investigation of intracellular analytes' evolution through luminescence analysis and imaging. The advances, challenges and future research directions in the development of Ru(II) complex-based chemosensors are also discussed.

Chemistry of Substituted Thiazinanes and Their Derivatives

Thiazinanes and its isomeric forms represent one of the most important heterocyclic compounds, and their derivatives represented a highly potent drug in disease treatment such as, 1,1-dioxido-1,2-thiazinan-1,6-naphthyridine, which has been shown to have anti-HIV activity by a mechanism that should work as anti-AIDS treatment, while (Z)-methyl 3-(naphthalen-1-ylimino)- 2-thia-4-azaspiro[5 5]undecane-4-carbodithioate showed analgesic activity, cephradine was used as antibiotic and chlormezanone was utilized as anticoagulants. All publications were interested in the chemistry of thiazine (partially or fully unsaturated heterocyclic six-membered ring containing nitrogen and sulfur), but no one was dealing with thiazinane itself which encouraged us to shed new light on these interesting heterocycles. This review was focused on the synthetic approaches of thiazinane derivatives and their chemical reactivity.

Rapid and selective detection of biothiols by novel ruthenium(II) complex-based phosphorescence probes

Considering the excellent photochemical properties of ruthenium(II) complexes, two new ruthenium(II) complexes, RuL¹-DNBS and RuL²-DNBS, have been developed as phosphorescence probes for detection of biothiols in 100:1 (v/v) Hepes buffer (20 mM, pH = 7.2)/CH₃CN solution. The response rate was highly improved of these two probes toward biothiols because the steric interactions between 1H-imidazo [4, 5-f] [1,10] phenanthroline group and ortho-2, 4-dinitrobenzensulfonate resulted in a relatively rapid thiol-induced S_NAr substitution reaction. RuL¹-DNBS and RuL²-DNBS were weakly phosphorescent owing to the effectual photoinduced electron transfer from ruthenium(II) luminophore to the sensing group, 2,4-dinitrobenzenesulfonyl. After reacting with biothiols, the 2,4-dinitrobenzenesulfonyl group of RuL¹-DNBS and RuL²-DNBS were cleavaged and the RuL¹ and RuL² were obtained. Meanwhile, the phosphorescence were "turn-on". Both of these two probes can detect biothiols sensitively and selectively under physiological conditions with submicromolar detection limits. Furthermore, application of RuL²-DNBS for detecting of intracellular biothiols has been successfully performed in living Glioma cells.

An efficient ruthenium(ii) tris(bipyridyl)-based chemosensor for the specific detection of cysteine and its luminescence imaging in living zebrafish

A water-soluble, red emissive and cysteine-specific probe has been achieved through 1,4-addition of cysteine to α,β-unsaturated ketones.

Selective Targeting of the Zinc Finger Domain of HIV Nucleocapsid Protein NCp7 with Ruthenium Complexes

Nucleocapsid protein 7 (NCp7) is an attractive target for anti-HIV drug development. Here we found that ruthenium complexes are reactive to NCp7 and various Ru-agents exhibit significantly different reactivity. Interestingly, the zinc-finger domains of NCp7 also demonstrate different affinity to Ru-complexes; the C-terminal domain is much more reactive than the N-terminal domain. Each zinc-finger domain of NCp7 binds up to three Ru-motifs, and the ruthenium binding causes zinc-ejection from NCp7 and disrupts the protein folding. Therefore, ruthenium complexes interfere with the DNA binding of NCp7 and interrupt the protein function. The different reactivity of Ru-agents suggests a feasible strategy for improving the targeting of NCp7 by ligand design. This work provides an insight into the mechanism of ruthenium complex with NCp7, and suggests more potential application of ruthenium drugs.

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.

Safranin and cysteine capped gold nanoparticles: spectroscopic qualitative and quantitative studies

The interaction between cysteine and safranin with citrate capped gold nanoparticles was studied.

Synthesis of cross-linked polymers via multi-component Passerini reaction and their application as efficient photocatalysts

Cross-linked polymers containing Ru complexes synthesized via multi-component Passerini reaction were shown to be highly effective and recyclable heterogeneous photocatalysts.

Colorimetric and luminescent bifunctional Ru(ii) complexes for rapid and highly sensitive recognition of cyanide

Four novel ruthenium(ii) complexes have been characterized for the colorimetric and luminescent bi-functional sensing of cyanide ions. The structure of one complex is also determined by single crystal X-ray diffraction.

Core cross-linked micelle-based nanoreactors for efficient photocatalysis

Stable nanoscale cross-linked polymer micelles containing Ru complexes (Ru-CMs) were prepared from monomethoxy[poly(ethylene glycol)]-block-poly(L-lysine) (MPEG-PLys) and [(bpy)2Ru(fmbpy)](PF6)2 (bpy=bipyridine, fmbpy=5-formy-5'-methyl-2,2'-bipyridine). To stabilize the micelles, bifunctional glutaraldehyde was used as a cross-linker to react with the free amino groups of the PLys block. After that, the Ru-CMs showed very good stability in common solvents. The Ru-CMs showed photocatalytic activity and selectivity in the oxidation of sulfides that were as high as those of the well-known [Ru(bpy)3(PF6)2] complex, because the micelles were swollen in the methanol-sulfide mixture. Moreover, because of the nanoscale size of the particles and their high stability, the Ru-CM photocatalysts can be readily recovered by ultrafiltration and reused without loss of photocatalytic activity. This work highlights the potential of using cross-linked micelles as a platform for developing highly efficient heterogeneous photocatalysts for a number of important organic transformations.

Colorimetric and luminescent dual-signaling responsive probing of thiols by a ruthenium(II)-azo complex

A dinuclear ruthenium(II) complex linked via a reducible azo group [Ru(bpy)2(azobpy)Ru(bpy)2]Cl4 (Ru2azo, bpy=2,2'-bipyridine, azobpy=4,4″-azobis (2,2'-bipyridine)) was adopted as a probe for thiols. Results showed that Ru2azo could selectively and effectively react with biological thiols (such as cysteine, homocysteine and glutathione) with a 10(-7)M detection limit. After it reacted with thiols, the original gray color of Ru2azo solution immediately turned yellow and the luminescence significantly enhanced, showing "naked-eye" colorimetric and "off-on" luminescent dual-signaling response for thiols. Mechanism studies demonstrated that Ru2azo reacted with thiols undergoing a two-electron transfer process, forming the azo(2-) anion product.