Controlled click-assembly of well-defined hetero-bifunctional cubic silsesquioxanes and their application in targeted bioimaging

Cage-rearranged and cage-intact syntheses of azido-functionalized larger T10 and T12 POSSs

Herein, we investigate the product type and distribution during the synthesis of azido-functionalized larger polyhedral oligomeric silsesquioxanes (POSSs) using 3-chloropropyl- and chloromethyldimethylsilylethyl-functionalized T8, T10, and T12 POSSs as precursors. Our findings indicate that cage rearrangement occurs for the 3-chloropropyl-functionalized POSS cages with a stability order of T12 > T10 > T8, while the chloromethyldimethylsilylethyl-functionalized POSS cages remain structurally intact after the nucleophilic substitution.

Synthesis of Octachloro- and Octaazido-Functionalized T8-Cages and Application to Recyclable Palladium Catalyst

Unprecedented T₈-cages bearing eight chloromethyldimethylsilylethyl substituents were obtained in excellent yield from the readily and commercially available octavinylsilsesquioxane. The chloro groups can be quantitatively substituted by azido ones to yield the corresponding octaazido T₈ without rearrangement of the cage. The syntheses of both functionalizable POSSs are scalable (gram-scale). The azido-functionalized T₈ compound constitutes a versatile building block able to undergo copper-catalyzed azide-alkyne [3 + 2] cycloaddition. As a proof of concept, it was allowed to react with 2-ethynylpyridine to give rise to a multidentate ligand bearing eight 2-pyridyl-triazole moieties (N,N-pincers). The coordination of the eight N,N-bidentate ligands to palladium(II) led to the corresponding octa-palladium complex shown to successfully promote the coupling reaction between anisole and phenylboronic acid. The low solubility of this catalytic complex in the reaction medium enabled (or facilitated or made possible) its straightforward recovery and recycling with four cycles with no loss of activity.

Acetoxymethyl-BODIPY dyes: a universal platform for the fluorescent labeling of nucleophiles

A general and robust methodology has been developed for the direct incorporation of a wide variety of C-, N-, P-, O-, S-, and halo-nucleophiles into functional BODIPY conjugates in a single reaction step.

Luminescent Neutral Cyclometalated Iridium(III) Complexes Featuring a Cubic Polyhedral Oligomeric Silsesquioxane for Lipid Droplet Imaging and Photocytotoxic Applications

New neutral iridium(III) complexes featuring a cubic polyhedral oligomeric silsesquioxane (POSS) unit, [Ir(N^∧C)₂(L1-POSS)] [HN^∧C = 2-phenylpyridine (Hppy; 1), 2-phenylbenzothioazole (Hbt; 2), and 2-(1-naphthyl)benzothiazole (Hbsn; 3); L1-POSS = (E)-4-[(2-hydroxybenzylidene)amino]benzyl 3-heptakis(isobutyl)POSS-propyl carbamate], were designed and synthesized. Their POSS-free counterparts, [Ir(N^∧C)₂(L1)] [L1 = (E)-N-(4-hydroxymethylphenyl)-1-(2-hydroxyphenyl)methanimine; HN^∧C = Hppy (1a), Hbt (2a), and Hbsn (3a)], and the poly(ethylene glycol) (PEG) derivatives [Ir(N^∧C)₂(L1-PEG)] [L1-PEG = (E)-4-[(2-hydroxybenzylidene)amino]benzyl 3-[2-[ω-methoxypoly(1-oxapropyl)]ethyl]carbamate; HN^∧C = Hppy (1b), Hbt (2b), and Hbsn (3b)] were also prepared. The photophysical, photochemical, and biological properties of the POSS complexes were compared with those of their POSS-free and PEG-modified counterparts. Upon irradiation, all of these complexes displayed orange-to-red emission and long emission lifetimes under ambient conditions. The bsn complexes 3, 3a, and 3b exhibited the highest singlet oxygen (¹O₂) generation quantum yields (Φ_Δ = 0.85-0.86) in aerated CH₃CN. Laser-scanning confocal microscopy images revealed that complexes 1-3 and 1a-3a showed exclusive lipid-droplet staining upon cellular uptake, while the PEG derivatives 1b-3b displayed lysosomal localization. Complex 3 was utilized to study various lipid-droplet-related biological events including lipid-droplet accumulation under oleic acid stimulation, the movement of lipid droplets, and preadipocyte differentiation. Notably, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays indicated that the ppy complexes 1 and 1b and the bt complexes 2 and 2b were noncytotoxic both in the dark and upon irradiation at 450 nm for 5 min (IC₅₀ > 200 μM), while the bsn complexes 3, 3a, and 3b showed low dark cytotoxicity (IC₅₀ = 52.9 to >200 μM) and high photocytotoxicity (IC₅₀ = 1.1-5.3 μM). The cellular uptake, internalization mechanisms, and cell death pathways of these complexes were also investigated. This work not only offers promising luminescent probes for lipid droplets through the structural modification of iridium(III) complexes but also paves the way to the construction of new reagents for theranostics.

Synthesis of Silsesquioxanes with Substituted Triazole Ring Functionalities and Their Coordination Ability

A synthesis of a series of mono-T8 and difunctionalized double-decker silsesquioxanes bearing substituted triazole ring(s) has been reported within this work. The catalytic protocol for their formation is based on the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) process. Diverse alkynes were in the scope of our interest-i.e., aryl, hetaryl, alkyl, silyl, or germyl-and the latter was shown to be the first example of terminal germane alkyne which is reactive in the applied process' conditions. From the pallet of 15 compounds, three of them with pyridine-triazole and thiophenyl-triazole moiety attached to T8 or DDSQ core were verified in terms of their coordinating properties towards selected transition metals, i.e., Pd(II), Pt(II), and Rh(I). The studies resulted in the formation of four SQs based coordination compounds that were obtained in high yields up to 93% and their thorough spectroscopic characterization is presented. To our knowledge, this is the first example of the DDSQ-based molecular complex possessing bidentate pyridine-triazole ligand binding two Pd(II) ions.

Fluorescent-Labeled Octasilsesquioxane Nanohybrids as Potential Materials for Latent Fingerprinting Detection

The recent demand for fluorescent-labeled materials (FLMs) in forensic security concepts such as latent fingerprints (LFs) that encode information for anti-counterfeiting and encryption of confidential data makes necessary the development of building new and innovative materials. Here, novel FLMs based on polyhedral oligomeric silsesquioxanes (POSS) functionalized with fluorophores via "click" reactions have been successfully synthesized and fully characterized. A comprehensive study of their photophysical properties has displayed large Stokes's shift together with good photostability in all cases, fulfilling the fundamental requisites for any legible LF detection on various surfaces. The excellent performance of the hetero-bifunctional FLM in the visualization of LF is emphasized by their legibility, selectivity, sensitivity and temporal photostability. In this study, development mechanisms have been proposed and the overall concept constitute a novel approach for vis-à-vis forensic investigations to trace an individual's identity.

Formation of Bifunctional Octasilsesquioxanes via Silylative Coupling and Cross-Metathesis Reaction

Bifunctional silsesquioxanes create an attractive group of compounds with a wide range of potential applications, and recently they have gained much interest. They are known to be obtained mainly via hydrosilylation, but we disclose novel synthetic protocols based on different but complementary reactions, i.e., cross-metathesis (CM) and silylative coupling (SC). A series of cubic T₈ type silsesquioxane derivatives with a broad scope of styryl substituents were synthesized in a one-pot procedure and characterized by spectroscopic and spectrometric methods. All of the new compounds can be obtained in a one-pot manner, which has an attractive impact on the synthetic procedure, as it is economic in terms of the isolation of intermediate products. Additionally, the methodology disclosed here enables the (E)-stereoselective introduction of styrenes derivative to the cubic T₈ type core. The presented compounds can be interesting precursors for a further functionalization that may significantly increase the possibility of their application in the design and synthesis of new functional materials.

Synthesis of Bifunctional Silsesquioxanes and Spherosilicates with Organogermyl Functionalities

In this paper we present the synthesis of mixed bifunctional compounds of T₈ H₈ silsesquioxane and spherosilicate (HSiMe₂ O)₈ Si₈ O₁₂ derivatives via platinum-catalyzed hydrosilylation of alkenylgermanes and olefins. To the best of our knowledge, this is the first literature example of bifunctional compounds with organogermyl functionalities. Eleven mixed systems with a variety of substituents (Si-H, alkyl, germyl, epoxy, and hydroxy) were prepared and fully characterized by NMR spectroscopy. Additionally, our research includes a real-time FT-IR study of the synthesis of these bifunctional compounds of the general formula (R)_8-m (GeR'₃ (CH₂ )_n+2 R)_m Si₈ O₁₂ . and (R''(CH₂ )₂ R)_8-m (GeR'₃ (CH₂ )₂ R)_m Si₈ O₁₂ where m∼4.

Cage-like silsesquioxanes-based hybrid materials

Cage-like silsesquioxanes are considered to be ideal and versatile building blocks of hybrid materials due to their unique structures and excellent performance. This Perspective highlights recent advances in the field of cage-like silsesquioxane-based hybrid materials, ranging from monomer functionalization and materials preparation to application. The existing issues are reviewed and the challenges and prospects in this field are also discussed for further development and exploitation.

Selective azide–alkyne cycloaddition reactions of azidoalkylated calixarenes

Reaction of calixarene oligo(azides) with alkynes taken in deficiency lead selectively to oligo(triazoles) under Cu(i) catalysis. Same azides react with alkynes intramolecularly under copper-free conditions forming 1,5-substituted triazole bridges.

A facile approach for the synthesis of novel silsesquioxanes with mixed functional groups

An efficient pathway for the synthesis of novel organofunctional silsesquioxanes with varied functional groups.

Anion identification using silsesquioxane cages

Anthracene-conjugated octameric silsesquioxane cages thermodynamically display intramolecular excimer formation, which can be used to identify anions through the change of fluorescence.

Anthracene-conjugated octameric silsesquioxane (AnSQ) cages, prepared via Heck coupling between octavinylsilsesquioxane (OVS) and 9-bromoanthracene, thermodynamically display intramolecular excimer emissions. More importantly, these hosts are sensitive to each anionic guest, thereby resulting in change of anthracene excimer formation, displaying the solvent-dependent fluorescence and allowing us to distinguish up to four ions such as F^–, OH^–, CN^– and PO₄^3– by fluorescence spectroscopy. Depending on the solvent polarity, for example, both F^– and CN^– quenched the fluorescence emission intensity in THF, but only F^– could enhance the fluorescence in all other solvents. The presence of PO₄^3– results in fluorescence enhancements in high polarity solvents such as DMSO, DMF, and acetone, while OH^– induces enhancements only in low polarity solvents (e.g. DCM and toluene). A picture of the anion recognizing ability of AnSQ was obtained through principal component analysis (PCA) with NMR and FTIR confirming the presence of host–guest interactions. Computational modeling studies demonstrate the conformation of host–guest complexation and also the change of excimer formation. Detection of F^–, CN^– and OH^– by AnSQ hosts in THF is noticeable with the naked eye, as indicated by strong color changes arising from charge transfer complex formation upon anion addition.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

The use of azide-alkyne click chemistry in recent syntheses and applications of polytriazole-based nanostructured polymers

The rapid development of efficient organic click coupling reactions has significantly facilitated the construction of synthetic polymers with sophisticated branched nanostructures. This Feature Article summarizes the recent progress in the application of efficient copper-catalyzed and copper-free azide-alkyne cycloaddition (CuAAC and CuFAAC) reactions in the syntheses of dendrimers, hyperbranched polymers, star polymers, graft polymers, molecular brushes, and cyclic graft polymers. Literature reports on the interesting properties and functions of these polytriazole-based nanostructured polymers are also discussed to illustrate their potential applications as self-healing polymers, adhesives, polymer catalysts, opto-electronic polymer materials and polymer carriers for drug and imaging molecules.

BODIPY Dye, the Most Versatile Fluorophore Ever?

BODIPY laser dyes constitute a fascinating topic of research in modern photochemistry due to the large variety of options its chromophore offers, which is ready available for a multitude of synthetic routes. Indeed, in the literature one can find a huge battery of compounds based on the indacene core. The possibility of modulating the spectroscopic properties or inducing new photophysical processes by the substitution pattern of the BODIPY dyes has boosted the number of scientific and technological applications for these fluorophores. Along the following lines, I will overview the main results achieved in our laboratory with BODIPYs oriented to optoelectronic as well to biophotonic applications, stressing the more relevant photophysical issues to be considered in the design of a tailor-made BODIPY for a certain application and pointing out some of the remaining challenges.

Efficient multi-click approach to well-defined two-faced octasilsesquioxanes: the first perfect Janus nanocube

A symmetry-controlled multi-click reaction of a cubic octa-azido silsesquioxane gives access to the first nanocube with a perfect Janus-type structure.

A simple approach to a new T8-POSS based MRI contrast agent

A simple synthesis of a new nanoglobular T₈-silsesquioxane based contrast agent for the application in MRI is reported.

Synthesis and isolation of non-chromophore cage-rearranged silsesquioxanes from base-catalyzed reactions

Carbonate (CO₃²⁻) anion as a stronger base but poorer in nucleophilicity gives rise exclusively to a cage expansion of unsubstituted products.

Branched Polyhedral Oligomeric Silsesquioxane Nanoparticles Prepared via Strain-Promoted 1,3-Dipolar Cycloadditions

Conjugation of small organic molecules and polymers to polyhedral oligosilsesquioxane (POSS) cores results in novel hybrid materials with unique physical characteristics. We report here an approach in which star-shaped organic-inorganic scaffolds bearing eight cyclooctyne moieties can be rapidly functionalized via strain-promoted azide-alkyne cycloaddition (SPAAC) to synthesize a series of nearly monodisperse branched core-shell nanoparticles with hydrophobic POSS cores and hydrophilic arms. We established that SPAAC is a robust method for POSS core octafunctionalization with the reaction rate constant of 1.9 × 10(-2) M(-1) s(-1). Functionalization with poly(ethylene glycol) (PEG) azide, fluorescein azide, and unprotected lactose azide gave conjugates which represent different classes of compounds: polymer conjugates, fluorescent dots, and bioconjugates. These resulting hybrid compounds were preliminarily tested for their ability to self-assemble in solution and at the air-water interface. We observed the formation of robust smooth Langmuir monolayers with diverse morphologies. We found that polar lactose moieties are completely submerged into the subphase whereas the relatively hydrophobic fluorescein arms had extended conformation at the interface, and PEG arms were partially submerged. Finally, we observed the formation of stable micelles with sizes between 70 and 160 nm in aqueous solutions with size and morphology of the structures dependent on the molecular weight and the type of the peripheral hydrophilic moieties.

T10 Polyhedral Oligomeric Silsesquioxane-Based Shape Amphiphiles with Diverse Head Functionalities via "Click" Chemistry

Head diversification of shape amphiphiles not only broadens the scope of supramolecular engineering for new self-organizing materials but also facilitates their potential applications in high technologies. In this letter, T₁₀ azido-functionalized polyhedral oligomeric silsesquioxane (POSS) nanoparticle was used to construct new shape amphiphiles via sequential "click" chemistry for addressing two issues: (1) new symmetry of T₁₀ POSS head could enrich the self-assembly behaviors of shape amphiphiles, and (2) copper-catalyzed azide-alkyne cycloaddition (CuAAC)-based head functionalization strategy allows the introduction of diverse functionalities onto POSS heads, including bulky ligands (i.e., isobutyl POSS) and UV-attenuating ones (i.e., ferrocene and 4-cyano-4'-biphenyl). This study expands the library of POSS-based shape amphiphiles with numerous possibilities for head manipulations, offering an important step toward new shape amphiphiles beyond traditional hydrophobic/hydrophilic nature for potential applications in giant molecule-based nanoscience and technology.

Rapid access to novel 1,2,3-triazolo-heterocyclic scaffolds via tandem Knoevenagel condensation/azide-alkyne 1,3-dipolar cycloaddition reaction in one pot

An operationally simple, one-pot, two-step cascade method has been developed to afford biologically important fused 1,2,3-triazolo-heterocyclic scaffolds from 2-alkynyl aryl(heteroaryl) aldehydes and phenacyl azides. This unique atom economical transformation engages four reactive centers (aldehyde, alkyne, active methylene, and azide) under metal-free catalysis.

Preparation of a sulfo-group-containing rod-like polysilsesquioxane with a hexagonally stacked structure and its proton conductivity

A sulfo-group-containing rod-like polysilsesquioxane with a hexagonally stacked structure (PSQ-SO3H) was successfully prepared by oxidation and hydrolytic polycondensation of 3-mercaptopropyltrimethoxysilane (MPTMS) in a mixed aqueous solution of NaOH and H2O2. The X-ray diffraction pattern of the PSQ-SO3H film exhibited three diffraction peaks with a d-value ratio of 1:1/√3:1/2, indicating the formation of a hexagonally stacked structure. In addition, the transmission electron microscopy image of PSQ-SO3H exhibited a striped pattern, indicating that the rod-like PSQs were stacked in a parallel fashion. The presence of ionic side-chains composed of the sulfonate anions and sodium cations during the hydrolytic polycondensation of MPTMS was found to be essential for the formation of this regularly structured PSQ. Finally, the proton conductivity of the PSQ-SO3H film, determined by using complex impedance spectroscopy, was relatively high (>10(-2) S cm(-1)) at 80 °C and 30-90 % relative humidity.

Tuning “thiol-ene” reactions toward controlled symmetry breaking in polyhedral oligomeric silsesquioxanes

A facile method toward polyhedral oligomeric silsesquioxane-based nano-building blocks with controlled symmetry breaking was reported by using thiol-ene chemistry.

Cascading One-Pot Synthesis of Single-Tailed and Asymmetric Multitailed Giant Surfactants

Rapid and precise synthesis of macromolecules has been a grand challenge in polymer chemistry. In this letter, we describe a convenient, rapid, and robust strategy for a one-pot synthesis of various precisely defined giant surfactants based on polyhedral oligomeric silsesquioxane (POSS). The method combines orthogonal oxime ligation, strain-promoted azide-alkyne cycloaddition (SPAAC), and thiol-ene "click" coupling. The process is usually completed within 0.5-2 h and does not require chromatography methods for purification. With near quantitative conversion efficiency, the method yields giant surfactants with distinct topologies, including single-tailed and asymmetric, multitailed giant surfactants. Both polymer tail composition and POSS surface chemistry are controlled precisely and tuned independently, enabling the design and preparation of new classes of giant surfactants.