Understanding the significant role of Si O Si bonds: Organosilicon materials as powerful platforms for bioimaging

Fluorescent probes for detecting and imaging mitochondrial hydrogen sulfide

Hydrogen sulfide (H2S) is a potent redox-active signaling molecule commonly dysregulated in disease states. The production of H2S and its involvement in various pathological conditions associated with mitochondrial dysfunction have extensively documented. During stress, cystathionine gamma-lyase and cystathionine beta-synthase in cytosol are copiously translocated into the mitochondria to boost H2S production, confirming its pivotal role in mitochondrial activities. However, little study has been done on H2S levels in tissues, cells and organelles, mainly due to the absence of precise and accurate detection tools. Thus, there is an urgent need to determine and monitor the levels of H2S in these important organelles. Fluorescent probes are efficient tools for detecting and monitoring various important biomolecules including biological thiols. The development of fluorescent probes is a multi-pronged approach which involves coupling fluorophores with responsive sites. The use of fluorescent probes for monitoring mitochondrial H2S levels has recently received widespread attention, resulting in numerous publications depicting their synthesis, mechanism of action, application, and potential challenges. Fluorescent probes offer precise and timely results, high sensitivity and selectivity, low biotoxicity, and minimal background interference. In this review, we aim to report designs of such probes, reaction mechanisms and their application in detecting mitochondrial H2S levels. Fluorescent probes can help uncover physio/pathological levels of H2S in essential organelles, its interactions with various biomarkers and associated consequences in biological systems.

A Crystalline Mesoionic Diazasilole Featuring Low-Valent Silicon

A 1,4,2-diazasilole containing a low-valent silicon atom has been synthesized employing a bulky imino N-heterocyclic carbene ligand. This molecular structure is characterized by a mesoionic C2N2Si five-membered ring, notable for its delocalized π electrons, intrinsic charge-separated zwitterionic properties, and a distinctly nucleophilic silicon center, culminating in 6π aromaticity. This compound manifests either mesoionic silylene or silylone characteristics upon coordination with transition metals. Demonstrating extraordinary versatility, this compound engages in diverse reactions such as coordination with iron or iridium, oxidation by S8, intramolecular ring saturation under the coordination influence of iridium, silicon atom transfer facilitated by Ph2Se2, ring contraction induced by Ph2Te2, and skeletal rearrangement triggered by Et3N•HCl. These reactions culminate in the formation of a variety of unprecedented silicon-based heterocycles, which are typically formidable to achieve using conventional methods. This study unveils previously unexplored facets of low-valent 1,4,2-diazasilole, positioning it as a promising foundational building block for future innovations in unique silicon compounds.

Design, Synthesis and Application of 1,4-disubstituted 1,2,3-triazole Based Chemosensors: A Promising Avenue

The 1,2,3-triazole-based chemosensors, synthesized through Cu(I)-catalyzed azide-alkyne cycloaddition via 'click chemistry', offer a straightforward yet highly effective method for detecting metal cations and anions with remarkable accuracy, selectivity and sensitivity, making them invaluable across various fields such as chemistry, pharmacology, environmental science and biology. The selective recognition of these ions is crucial due to their significant roles in biological and physiological processes, where even slight concentration variations can have major consequences. The article reviews literature from 2017 to 2024, highlighting advancements in the synthesis of 1,2,3-triazole-based ligands and their application (along with sensing mechanism) for detection of various ions causing health and environmental hazards. The detection aspects have been discussed sequentially for the transition-, inner transition-, and the metals from the s or p block of the periodic table.

Organo-photocatalytic dearomative hydrosilylation of indoles with silanes

A photocatalytic dearomative hydrosilylation reaction of indole derivatives with silanes has been accomplished for the synthesis of valuable indolinyl silanes through a carbon-silyl radical coupling process with the cooperation of photoredox and hydrogen atom transfer catalytic systems composed of 3DPA2FBN (2,4,6-tris(diphenylamino)-3,5-difluorobenzonitrile), (i-Pr)3SiSH, and base additives. This protocol is featured by a broad substrate scope, transition metal-free conditions, high diastereoselectivities and applications in natural product derivatives.

Recent Advances in Silica-Based Nanomaterials for Enhanced Tumor Imaging and Therapy

Cancer remains a formidable challenge, inflicting profound physical, psychological, and financial burdens on patients. In this context, silica-based nanomaterials have garnered significant attention for their potential in tumor imaging and therapy owing to their exceptional properties, such as biocompatibility, customizable porosity, and versatile functionalization capabilities. This review meticulously examines the latest advancements in the application of silica-based nanomaterials for tumor imaging and therapy. It underscores their potential in enhancing various cancer imaging modalities, including fluorescence imaging, magnetic resonance imaging, computed tomography, positron emission tomography, ultrasound imaging, and multimodal imaging approaches. Moreover, the review delves into their therapeutic efficacy in chemotherapy, radiotherapy, phototherapy, immunotherapy, gas therapy, sonodynamic therapy, chemodynamic therapy, starvation therapy, and gene therapy. Critical evaluations of the biosafety profiles and degradation pathways of these nanomaterials within biological environments are also presented. By discussing the current challenges and prospects, this review aims to provide a nuanced perspective on the clinical translation of silica-based nanomaterials, thereby highlighting their promise in revolutionizing cancer diagnostics, enabling real-time monitoring of therapeutic responses, and advancing personalized medicine.

Molecular orbital breaking in photo-mediated organosilicon Schiff base ferroelectric crystals

Ferroelectric materials, whose electrical polarization can be switched under external stimuli, have been widely used in sensors, data storage, and energy conversion. Molecular orbital breaking can result in switchable structural and physical bistability in ferroelectric materials as traditional spatial symmetry breaking does. Differently, molecular orbital breaking interprets the phase transition mechanism from the perspective of electronics and sheds new light on manipulating the physical properties of ferroelectrics. Here, we synthesize a pair of organosilicon Schiff base ferroelectric crystals, (R)- and (S)-N-(3,5-di-tert-butylbenzylidene)-1-((triphenylsilyl)oxy)ethanamine, which show optically controlled phase transition accompanying the molecular orbital breaking. The molecular orbital breaking is manifested as the breaking and reformation of covalent bonds during the phase transition process, that is, the conversion between C = N and C-O in the enol form and C-N and C = O in the keto form. This process brings about photo-mediated bistability with multiple physical channels such as dielectric, second-harmonic generation, and ferroelectric polarization. This work further explores this newly developed mechanism of ferroelectric phase transition and highlights the significance of photo-mediated ferroelectric materials for photo-controlled smart devices and bio-sensors.

Advances in disilylation reactions to access cis/trans-1,2-disilylated and gem-disilylated alkenes

Organosilane compounds are widely used in both organic synthesis and materials science. Particularly, 1,2-disilylated and gem-disilylated alkenes, characterized by a carbon-carbon double bond and multiple silyl groups, exhibit significant potential for subsequently diverse transformations. The versatility of these compounds renders them highly promising for applications in materials, enabling them to be valuable and versatile building blocks in organic synthesis. This review provides a comprehensive summary of methods for the preparation of cis/trans-1,2-disilylated and gem-disilylated alkenes. Despite notable advancements in this field, certain limitations persist, including challenges related to regioselectivity in the incorporation and chemoselectivity in the transformation of two nearly identical silyl groups. The primary objective of this review is to outline synthetic methodologies for the generation of these alkenes through disilylation reactions, employing silicon reagents, specifically disilanes, hydrosilanes, and silylborane reagents. The review places particular emphasis on investigating the practical applications of the C-Si bond of disilylalkenes and delves into an in-depth discussion of reaction mechanisms, particularly those reactions involving the activation of Si-Si, Si-H, and Si-B bonds, as well as the C-Si bond formation.

Polarity responsive polysiloxanes with twisting intramolecular charge transfer effect for monitoring lipophagy process and the detection of volatile organic compounds

Polarity plays a critical role in biology and materials science, serving as a complex parameter. Imbalances in polarity within subcellular organelles are closely associated with various diseases. Moreover, volatile organic compounds (VOC) with low polarity pose significant health and safety risks, therefore, researchers have shown great interest in accurately detecting polarity. However, precise observation of polarity changes within organisms and identification of low-polarity volatile organic solvents are formidable challenges. To overcome these difficulties, we developed a versatile polymeric twisting intramolecular charge transfer (TICT) effect Polysiloxane-n (PDMS-n), utilizing polysiloxane molecular chains as "smart guides" to connect TICT molecules, inspired by the concept of "threading a needle." With the aid of PDMS-n, the process of polarity changes during cellular lipophagy was monitored in situ with high accuracy. Remarkably, the polarity changes of the local microstructure of the PDMS films were successfully visualized. PDMS-Films were also constructed, which enabled the recognition of Dichloromethane (DCM) gas during swelling. This work will contribute to the understanding of changes in cellular physiological processes, and facilitate the sensitive detection of VOCs.

Organosilicon-Based Carbon Dots and Their Versatile Applications

Carbon dots (CDs) are a newly discovered type of fluorescent material that has gained significant attention due to their exceptional optical properties, biocompatibility, and other remarkable characteristics. However, single CDs have some drawbacks such as self-quenching, low quantum yield (QY), and poor stability. To address these issues, researchers have turned to organosilicon, which is known for its green, economical, and abundant properties. Organosilicon is widely used in various fields including optics, electronics, and biology. By utilizing organosilicon as a synthetic precursor, the biocompatibility, QY, and resistance to self-quenching of CDs can be improved. Meanwhile, the combination of organosilicon with CDs enables the functionalization of CDs, which significantly expands their original application scenarios. This paper comprehensively analyzes organosilicon in two main categories: precursors for CD synthesis and matrix materials for compounding with CDs. The role of organosilicon in these categories is thoroughly reviewed. In addition, the paper presents various applications of organosilicon compounded CDs, including detection and sensing, anti-counterfeiting, optoelectronic applications, and biological applications. Finally, the paper briefly discusses current development challenges and future directions in the field.

Designing of efficient two-armed colorimetric and fluorescent indole appended organosilicon sensors for the detection of Al(III) ions: Implication as paper-based sensor

Metal ions have significant roles in diagnosis, industry, human health, and the environment. To design and develop new lucid molecular receptors for the selective detection of metal ions is important for environmental and medical applications. In the present work, two-armed indole appended Schiff bases conjoined with 1,2,3-Triazole bis-organosilane and bis-organosilatrane skelton sensors for naked eye colorimetric and fluorescent detection sensors for Al(III) are developed. The introduction of Al(III) in sensor 4 and 5 show red shift in UV-visible spectra, changes in fluorescence spectra and immediate color change from colorless to dark yellow. Furthermore, the pH and time response studies were explored for both sensors 4 & 5. The sensors 4 and 5 exhibited significantly low detection limit (LOD) in nano-molar range 1.41 × 10-9 M and 0.17 × 10-9 M respectively from emission titration. The LOD form absorption titration was found to be 0.6 × 10-7 M for sensor 4 and 0.22 × 10-7 M for sensor 5. In addition, the sensing model is developed as paper based sensor for its practical applicability. The theoretical calculations were performed on Gaussian 03 program by relaxing the structures using Density functional theory.

Disilane-bridged architectures: an emerging class of molecular materials

Disilanes are organosilicon compounds that contain saturated Si-Si bonds. The structural characteristics of Si-Si single bonds resemble those of C-C single bonds, but their electronic structure is more similar to that of C[double bond, length as m-dash]C double bonds, as Si-Si bonds have a higher HOMO energy level. These organosilicon compounds feature unique intramolecular σ electron delocalization, low ionization potentials, polarizable electronic structure, and σ-π interaction. It has been demonstrated that the employment of disilane units (Si-Si) is a versatile and effective approach for finely adjusting the photophysical properties of organic materials in both solution and solid states. In this review, we present and discuss the structure, properties, and relationships of novel σ-π-conjugated hybrid architectures with saturated Si-Si σ bonds. The application of disilane-bridged σ-conjugated compounds as optoelectronic materials, multifunctional solid-state emitters, CPL, and non-linear optical and stimuli-responsive materials is also reviewed.

Polysiloxane-Based Molecular Logic Gate for Dual-Channel Visualizing Mitochondrial pH and Sulphite Changes during Cuproptosis

Intracellular Cu-induced regulated cell death, characterized by the aggregation of lipidizing mitochondrial enzymes, is called cuproptosis. Mitochondria play a vital role in the metabolic regulation of cell injury and stressful immune responses. The pH levels and sulfur dioxide (SO2) content in mitochondria have important indicative roles in the regulation of cuproptosis. However, fluorescent probes that simultaneously detect changes in pH and SO2 in mitochondria during cuprotosis have not been reported. To fill this blank, in this study, we dexterously used functional polysiloxane as a fluorescent platform to propose a molecular logic gate probe P0-pH-SO2 for detecting changes in intramitochondrial pH and SO2 content through a dual-channel mode. In addition, we defined a new function to reflect the cellular state of the elesclomol-induced cuproptosis process based on the input and output of the relevant logic relationship. This new fluorescent molecular logic gate probe P0-pH-SO2 can be rapidly activated by mitochondrial sulfites to induce green fluorescence, while the red fluorescence is quenched with the proton in the mitochondria. Overall, this study developed a novel logic-gated molecular probe that provided a versatile strategy for monitoring the role played by intramitochondrial sulfites and H+ in cuproptosis. This work will open the way to broaden the applications of molecular logic gates and fluorescent polysiloxanes.

High-Performance Recognition, Cell-Imaging, and Efficient Removal of Carbon Monoxide toward a Palladium-Mediated Fluorescent Sensing Platform

Novel high-performance fluorescent approaches have always significant demand for room-temperature detection of carbon monoxide (CO), which is highly toxic even at low concentration levels and is not easy to recognize due to its colorless and odorless nature. In this paper, we constructed a palladium-mediated fluorescence turn-on sensing platform (TPANN-Pd) for the recognition of CO at room temperature, revealing simultaneously quick response speed (<30 s), excellent selectivity, superior sensitivity, and low detection limit (∼160 nM for CORM-3, ∼1.7 ppb for CO vapor). Moreover, rapid detection and efficient removal (24%) from the air by naked-eye vision has been successfully realized based on TPANN-Pd supramolecular gels. Furthermore, the developed sensing platform was elucidated with low cytotoxicity and high cellular uptake, and it was successfully applied to CO imaging in living cells, providing real-time monitoring of potential CO-involved reactions in biological systems.

Visible-light-driven oxidation of organosilanes by a charge-transfer complex

Direct oxidation of organosilanes is one of the most straightforward ways to access silanols. Herein, we describe a novel photo-induced strategy for oxidation of organosilanes to access silanols, promoted by a photoactive charge-transfer complex (CTC) between sodium benzenesulfinate and molecular O₂. A streamlined sequence transformation of organosilanes to silyl ethers was also readily achieved. This developed protocol represents the first example of CTC-based oxidation of organosilanes, offering a facile approach to access a series of silanol and silyl ether products.

Hyperbranched polysiloxane-based probe with enhanced lipophilicity for visualizing ONOO- fluctuations in endoplasmic reticulum

The endoplasmic reticulum, a cellular signaling regulator, participates in the synthesis and secretion of many proteins, glycogen, lipids and cholesterol substances. Peroxynitrite (ONOO^-) is a highly oxidative and nucleophilic agent. Abnormal fluctuations of ONOO^- induce oxidative stress in the endoplasmic reticulum, further disrupting the normal function of protein folding and transport and glycosylation modification, ultimately leading to neurodegenerative diseases, cancer and Alzheimer's disease. Up to now, most probes have tended to achieve targeting functions by introducing specific targeting groups. However, this approach increased the difficulty of the construction process. Therefore, a simple and efficient construction strategy for fluorescent probes with excellent specificity targeting the endoplasmic reticulum is lacking. To overcome this difficulty and put forward an efficient design strategy for the endoplasmic reticulum targeted probes, in this paper, we constructed alternating rigid and flexible polysiloxane-based hyperbranched polymeric probes (Si-Er-ONOO) by bonding perylenetetracarboxylic anhydride and silicon-based dendrimers for the first time. Efficient and specific targeting of the endoplasmic reticulum was successfully achieved by the excellent lipid solubility of Si-Er-ONOO. Furthermore, we observed different effects of metformin and rotenone on the changes of ONOO^- volatility in the cellular and zebrafish internal environment by Si-Er-ONOO. We believe that Si-Er-ONOO will expand the application of organosilicon hyperbranched polymeric materials in bioimaging and provide an excellent indicator of reactive oxygen species fluctuations in biological systems.

Versatile Switchable Targeted Polysiloxanes for High-Resolution Visualization of Mitochondrial and Lysosomal Interactions during Ferroptosis

Ferroptosis is an iron-dependent process that regulates cell death and is essential for maintaining normal cell and tissue survival. The explosion of reactive oxygen species characterizes ferroptosis in a significant way. Peroxynitrite (ONOO^-) is one of the endogenous reactive oxygen species. Abnormal ONOO^- concentrations cause damage to subcellular organelles and further interfere with organelle interactions. However, the proper conduct of organelle interactions is critical for cellular signaling and the maintenance of cellular homeostasis. Therefore, investigating the effect of ONOO^- on organelle interactions during ferroptosis is a highly attractive topic. To date, it has been challenging to visualize the full range of ONOO^- fluctuations in mitochondria and lysosomes during ferroptosis. In this paper, we constructed a switchable targeting polysiloxane platform. During the selective modification of NH₂ groups located in the side chain, the polysiloxane platform successfully constructed fluorescent probes targeting lysosomes and mitochondria (Si-Lyso-ONOO, Si-Mito-ONOO), respectively. Real-time detection of ONOO^- in lysosomes and mitochondria during ferroptosis was successfully achieved. Remarkably, the occurrence of autophagy during late ferroptosis and the interaction between mitochondria and lysosomes was observed via the differentiated responsive strategy. We expect that this switchable targeting polysiloxane functional platform will broaden the application of polymeric materials in bioimaging and provide a powerful tool for further deeper understanding of the ferroptosis process.

Palladium-catalyzed addition of acylsilanes across alkynes via the activation of a C-Si bond

Palladium-catalyzed addition of a C-Si bond in acylsilanes across the triple bonds in an alkyne bearing a carbonyl group at one terminal is reported. The reaction proceeds with excellent regioselectivity, in which a silyl group is incorporated into the carbon α to the carbonyl group, allowing for straightforward access to a variety of functionalized alkenylsilane derivatives. Catalytic synthesis of indanones by annulation between acylsilanes and alkynes with an identical catalytic system is also reported.

An unusual autocatalysis with an air-stable Pd complex to promote enantioselective synthesis of Si-stereogenic enynes

Given the powerful potential of chiral-at-silicon chemistry, enantioselective synthesis of Si-stereogenic centers has attracted substantial research interest in recent years. However, the catalytic asymmetric synthesis of Si-stereogenic organosilicon compounds remains an appealing venture and is a challenging subject because of the difficulty in achieving high reactivity and stereoselectivity for "silicon-center" transformations. Herein, we disclose a highly enantioselective palladium-catalyzed hydrosilylation of 1,3-diynes with dihydrosilanes, which enables the facile preparation of Si-stereogenic enynes and an enyne-linked chiral polymer (polyenyne) in good yields and excellent ees (up to >99%) by desymmetrization. The unusual stereoselectivity in this reaction is achieved by precisely controlling the steric hindrance and electronic effect of the newly developed chiral ligands, resulting in a wide range of chiral silanes and a Si-containing polymer bearing a Si-stereogenic center which is otherwise difficult to access. The key to the high enantioselectivity relies on catalyst aggregation-induced non-covalent interaction, which exerts a remarkably positive influence on the Si-H bond activation and enhancement of enantioselectivity, in which the palladium/P-ligand complex was proved to be air-stable and moisture-insensitive in this reaction.

Organosilicon Fluorescent Materials

In the past few decades, organosilicon fluorescent materials have attracted great attention in the field of fluorescent materials not only due to their abundant and flexible structures, but also because of their intriguing fluorescence properties, distinct from silicon-free fluorescent materials. Considering their unique properties, they have found broad application prospects in the fields of chemosensor, bioimaging, light-emitting diodes, etc. However, a comprehensive review focusing on this field, from the perspective of their catalogs and applications, is still absent. In this review, organosilicon fluorescent materials are classified into two main types, organosilicon small molecules and polymers. The former includes fluorescent aryl silanes and siloxanes, and the latter are mainly fluorescent polysiloxanes. Their synthesis and applications are summarized. In particular, the function of silicon atoms in fluorescent materials is introduced. Finally, the development trend of organosilicon fluorescent materials is prospected.

Copper-Catalyzed Reaction of 2,3-Allenols with Silylzinc Reagents: Access to 2-Silyl-1,3-butadienes

Reaction of 2,3-allenols with PhMe₂SiZnCl or Ph₂MeSiZnCl under catalysis of IPrCuCl or SIPrCuCl was carried out, affording 2-silyl-1,3-butadienes. Secondary and tertiary 2,3-allenols could be used as coupling partners. Reaction of secondary 2,3-allenols gave (E)-2-silyl-1,3-butadienes as the only products.

Cascade cyclization of alkene-tethered acylsilanes and allylic sulfones enabled by unproductive energy transfer photocatalysis

Developing photo-induced cascade cyclization of alkene-tethered acylsilanes is challenging, because acylsilanes are unstable under light irradiation. Herein, we report that the energy transfer from excited acylsilanes to a photocatalyst that possesses lower triplet energy can inhibit the undesired decomposition of acylsilanes. With neutral Eosin Y as the photocatalyst, an efficient synthesis of cyclopentanol derivatives is achieved with alkene-tethered acylsilanes and allylic sulfones. The reaction shows broad substrate scope and the synthetic potential of this transformation is highlighted by the construction of cyclopentanol derivatives which contain fused-ring or bridged-ring.

Acylsilanes decompose under light irradiation, and this limits their use in light-induced organic transformations. Here the authors report a strategy to inhibit the light-induced decomposition of acylsilanes, enabling the photochemical synthesis of cyclopentanol derivatives from alkene-tethered acylsilanes and allylic sulfones.