Periodic mesoporous organosilica from zwitterionic precursors

Novel Antifouling Coatings by Zwitterionic Silica Grafting on Glass Substrates

Zwitterionic silica coatings for surface functionalization are greatly prominent because of their simple and fast preparation, high availability, and effective antifouling properties. In this work, two zwitterionic sulfobetaine silane coatings, i.e., mono-SBSi and tris-SBSi, were deposited on glass surfaces and tested for antifouling of biological material and biofilm using human cancer cell and seawater, respectively. The used zwitterionic precursors mono-SBSi and tris-SBSi differ by the number of hydrolyzable silane groups: mono-SBSi contains one trimethoxysilane group, whereas tris-SBSi contains three of these functions. First, X-ray photoelectron spectroscopy indicates the successful grafting of zwitterionic coatings onto a glass surface. Characterization using atomic force microscopy shows the different morphologies and roughness of the two coatings. The glass surface became more hydrophilic after the grafting of zwitterionic coatings than the bare glass substrate. The antifouling properties of two coatings were evaluated via human cancer cell adsorption. Interestingly, the tris-SBSi coating displays a significantly lower level of cell adsorption compared to that of both mono-SBSi coating and the non-modified control surface. The same trend was observed for biofilm formation in seawater. Finally, the toxicity of mono-SBSi and tris-SBSi coatings was evaluated on zebrafish embryos, indicating the good biocompatibility of both coatings. Our results indicate interesting antifouling properties of zwitterionic coatings. The chemical constitution of the used precursor has an impact on the antifouling properties of the formed coating: the tris-SBSi-based zwitterionic silica coatings display improved antifouling properties compared to those of the mono-SBSi-based coating. Besides, the use of trisilylated precursors should result in the formation of more resistant and robust coatings due to the higher number of grafting functions. For all these reasons, we anticipate that tris-SBSi coatings will open new perspectives for antifouling applications for biological environments and implants.

A Brønsted acidic ionic liquid anchored to magnetite nanoparticles as a novel recoverable heterogeneous catalyst for the Biginelli reaction

In this study, simple and effective methods were used for the preparation of an ionic liquid that immobilized magnetite nanoparticles. Fe₃O₄ nanoparticles were prepared via a chemical co-precipitation method. Then, a SiO₂ shell was coated on the magnetic core via the Stober method. Finally, CPTES (chloropropyltriethoxysilane) and morpholine were coated on the SiO₂ shell. Morpholine sulfate, an acidic ionic liquid, was successfully bound to magnetite nanoparticles (Mag@Morph-AIL) and this was used as an efficient catalyst for the preparation of 3,4-dihydropyrimidinones. Compared to previous works, the easy separation of the nanocatalyst using an external magnet and the recyclability, non-toxicity, versatility, and high stability of the catalyst, combined with low reaction times and excellent yields, make the present protocol very useful for the synthesis of the title products. The synthesized products and catalyst were confirmed via ¹H-NMR, ¹³C-NMR, FT-IR, scanning electron microscope, X-ray diffraction, and elemental analysis.

Synthesis of Dihydropyrimidinones (DHPMs) and Hexahydro Xanthene Catalyzed by 1,4-Diazabicyclo [2.2.2] Octane Triflate Under Solvent-Free Condition

OBJECTIVE

DABCO salts were evaluated as catalysts for the Biginelli reaction between 4- methoxybenzaldehyde, urea and ethyl acetoacetate under solvent-free conditions. 1,4-Diazabicyclo [2.2.2] octane triflate was found to be a simple, inexpensive, highly efficient catalyst for Biginelli reaction for a variety aromatic aldehyde with urea and ethyl acetoacetate at 80°C afforded corresponding 3,4-dihydropyrimidinones in 50-99% yields after 30-120 minutes. 1,3-Cyclohexadione was used in place of ethyl acetoacetate in the absence of urea this methodology is giving hexahydro xanthene derivatives in good to excellent yields after 3-4 hours.

METHODS

DABCO salt 4 (5 mol%), 4-methoxybenzaldehyde (0.73 mmol) and urea (0.73 mmol) were stirred for 10 minutes at 80°C, then ethyl acetoacetate (1.5 equiv.) was added and reaction mixture was stirred at 80°C for specified time. The resulting solution was stirred continuously and progress of the reaction was followed by TLC. The crude reaction mixture was purified by flash column chromatography on silica gel (hexane/ethyl acetate (1:2)) to give pure desired product.

RESULTS

Reaction conditions of the Biginelli reaction were optimized using 4-methoxybenzaldehyde (0.73 mmol), urea (0.73 mmol), and ethyl acetoacetate (5 equiv.) as model substrates catalyzed by 1,4-Diazabicyclo [2.2.2] octane triflate (5 mol%) in a different solvents, screening of different catalysts and different temperatures. Neat condition was found to be the best for the Biginelli condensation and corresponding 3,4- dihydropyrimidinones was obtained in good to excellent yields. When the reaction was carried out with benzaldehyde derivatives and cyclohexane-1,3-dione in place of ethyl acetoacetate in the absence of urea, solely corresponding hexahydro xanthene derivatives were obtained in 61-91% yields.

CONCLUSION

In conclusion, we have applied salts of 1,4-Diaza-bicyclo [2.2.2] octane as catalysts in the Biginelli condensation and corresponding 3,4-dihydropyrimidinones were obtained in 50- 99% yields under solvent free conditions. This methodology is having advantages like simple work-up; low loading of catalyst and reaction was performed at moderate temperature under solvent-free conditions.

Biginelli Reaction: Polymer Supported Catalytic Approaches

The Biginelli product, dihydropyrimidinone (DHPM) core, and its derivatives are of immense biological importance. There are several methods reported as modifications to the original Biginelli reaction. Among them, many involve the use of different catalysts. Also, among the advancements that have been made to the Biginelli reaction, improvements in product yields, less hazardous reaction conditions, and simplified isolation of products from the reaction predominate. Recently, solid-phase synthetic protocols have attracted the research community for improved yields, simplified product purification, recyclability of the solid support, which forms a special economic approach for Biginelli reaction. The present Review highlights the role of polymer-supported catalysts in Biginelli reaction, which may involve organic, inorganic, or hybrid polymers as support for catalysts. A few of the schemes involve magnetically recoverable catalysts where work up provides green approach relative to traditional methods. Some research groups used polymer-catalyst nanocomposites and polymer-supported ionic liquids as catalyst. Solvent-free, an ultrasound or microwave-assisted Biginelli reactions with polymer-supported catalysts are also reported.

Polyampholytic graft copolymers based on polydehydroalanine (PDha) – synthesis, solution behavior and application as dispersants for carbon nanotubes

We herein introduce a versatile platform of graft copolymers featuring a polyampholytic backbone and side chains of varying length and polarity using post-polymerization modification of polydehydroalanine (PDha).

Pd/APTPOSS@KCC-1 as a new and efficient support catalyst for C–H activation

In this study, KCC-1 was functionalized with APTPOSS groups acting as the strong performers so that the Pd NPs were well-dispersed on the fibers of the KCC-1 microspheres.

Nickel containing ionic liquid based ordered nanoporous organosilica: a powerful and recoverable catalyst for synthesis of polyhydroquinolines

The synthesis, characterization and catalytic application of a novel nickel containing ionic liquid based ordered mesoporous organosilica are demonstrated.

Amine-functionalized ionic liquid-based mesoporous organosilica as a highly efficient nanocatalyst for the Knoevenagel condensation

A novel aminopropyl-containing ionic liquid-based mesoporous organosilica was prepared and characterized and its catalytic performance was studied in the Knoevenagel condensation.

Ionosilicas as efficient adsorbents for the separation of diclofenac and sulindac from aqueous media

Mesoporous and nanostructured ionosilica material containing ammonium groups was successfully applied for diclofenac and sulindac adsorption via ion exchange.

Surface modification strategies on mesoporous silica nanoparticles for anti-biofouling zwitterionic film grafting

In the past decade, zwitterionic-based anti-biofouling layers had gained much focus as a serious alternative to traditional polyhydrophilic films such as PEG. In the area of assembling silica nanoparticles with stealth properties, the incorporation of zwitterionic surface film remains fairly new but considering that silica nanoparticles had been widely demonstrated as useful biointerfacing nanodevice, zwitterionic film grafting on silica nanoparticle holds much potential in the future. This review will discuss on the conceivable functional chemistry approaches, some of which are potentially suitable for the assembly of such stealth systems.

Anion selectivity in ion exchange reactions with surface functionalized ionosilicas

Mesoporous imidazolium functionalized ionosilicas have been investigated as anion exchange materials for the adsorption of oxo-anions in aqueous media. Pertechnetate exchange in the presence of competing anionic species revealed Hofmeister selectivity.

Periodic mesoporous organosilica with ionic-liquid framework supported manganese: an efficient and recyclable nanocatalyst for the unsymmetric Hantzsch reaction

We have described the catalytic application of a manganese containing ionic liquid-based ordered mesoporous organosilica in the synthesis of polyhydroquinolines.

A general method for preparing bridged organosilanes with pendant functional groups and functional mesoporous organosilicas

New organosilica precursors containing two triethoxysilyl groups suitable for the organosilica material formation through the sol-gel process were designed and synthesised. These precursors display alkyne or azide groups for attaching targeted functional groups by copper-catalysed azide-alkyne cycloaddition (CuAAC) and can be used for the preparation of functional organosilicas following two strategies: 1) the functional group is first appended by CuAAC under anhydrous conditions, then the functional material is prepared by the sol-gel process; 2) the precursor is first subjected to the sol-gel process, producing porous, clickable bridged silsesquioxanes or periodic mesoporous organosilicas (PMOs), then the desired functional groups are attached by means of CuAAC. Herein, we show the feasibility of both approaches. A series of bridged bis(triethoxysilane)s with different pending organic moieties was prepared, demonstrating the compatibility of the first approach with many functional groups. In particular, we demonstrate that organic functional molecules bearing only one derivatisation site can be used to produce bridged organosilanes and bridged silsesquioxanes. In the second approach, clickable PMOs and porous bridged silsesquioxanes were prepared from the alkyne- or azide-containing precursors, and thereafter, functionalised with complementary model azide- or alkyne-containing molecules. These results confirmed the potential of this approach as a general methodology for preparing functional organosilicas with high loadings of functional groups. Both approaches give rise to a wide range of new functional organosilica materials.

Graphite catalyzed solvent free synthesis of dihydropyrimidin-2(1H)-ones/thiones and their antidiabetic activity

A solvent free three component condensation reaction between an aldehyde, ethyl acetoacetate and urea catalyzed by graphite, a green catalyst is described for the synthesis of dihydropyrimidin-2(1H)-ones. This protocol is scalable and the catalyst is reusable. This method is also applied for the synthesis of dihydropyrimidin-2(1H)-thiones. α-Amylase, a key enzyme in carbohydrate metabolism is generally targeted for management of type 2 diabetes. The therapeutic potential of the dihydropyrimidinones and dihydropyrimidinthiones to inhibit α-amylase activity was evaluated by in vitro assay. Of the synthesized compounds 3,4-dihydropyrimidin-2(1H)-thione (1k) demonstrated highest inhibition of α-amylase activity.

Precursor Mediated Synthesis of Nanostructured Silicas: From Precursor-Surfactant Ion Pairs to Structured Materials

The synthesis of nanostructured anionic-surfactant-templated mesoporous silica (AMS) recently appeared as a new strategy for the formation of nanostructured silica based materials. This method is based on the use of anionic surfactants together with a co-structure-directing agent (CSDA), mostly a silylated ammonium precursor. The presence of this CSDA is necessary in order to create ionic interactions between template and silica forming phases and to ensure sufficient affinity between the two phases. This synthetic strategy was for the first time applied in view of the synthesis of surface functionalized silica bearing ammonium groups and was then extended on the formation of materials functionalized with anionic carboxylate and bifunctional amine-carboxylate groups. In the field of silica hybrid materials, the “anionic templating” strategy has recently been applied for the synthesis of silica hybrid materials from cationic precursors. Starting from di- or oligosilylated imidazolium and ammonium precursors, only template directed hydrolysis-polycondensation reactions involving complementary anionic surfactants allowed accessing structured ionosilica hybrid materials. The mechanistic particularity of this approach resides in the formation of precursor-surfactant ion pairs in the hydrolysis-polycondensation mixture. This review gives a systematic overview over the various types of materials accessed from this cooperative ionic templating approach and highlights the high potential of this original strategy for the formation of nanostructured silica based materials which appears as a complementary strategy to conventional soft templating approaches.

Phosphonic acid functionalized ordered mesoporous material: a new and ecofriendly catalyst for one-pot multicomponent Biginelli reaction under solvent-free conditions

We report a new ordered 2D hexagonal mesoporous organosilica material (PAFMS-1) bearing phosphonic acid functionality at the surface. This hybrid material showed high Brunauer-Emmett-Teller surface area (565 m(2) g(-1)) and ordered assembly of mesoporoes with an average pore diameter of ca. 2.1 nm. This novel hybrid mesoporous material has been synthesized via cocondensation of (triethoxysilyl)(propyliminomethyl)biphenylmethyl phosphoester (PEFOS) and tetraethyl orthosilicate (TEOS) in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) at 373 K. The phosphoester-functionalized organosilane (PEFOS) precursor has been synthesized for the first time by a simple SN2 reaction followed by Suzuki coupling and a Mannich reaction. The material has been characterized by powder X-ray diffraction, N2 sorption, and transmission electron microscopy image analysis, whereas the presence of organic moieties (an aromatic biphenyl ring and an aliphatic side chain), phosphrous, and silicon in the pore wall of the material have been characterized by solid-state magic-angle-spinning NMR, X-ray photoelectron, and Fourier transform infrared (FT-IR) spectroscopic tools. Further, the surface acid strength of the hybrid material has been determined by FT-IR analysis of the samples via temperature-programmed pyridine adsorption studies. The material has been utilized as a reusable heterogeneous catalyst for the synthesis of biologically important and value added multifunctionalized 3,4-dihydropyridin-2-1H-(ones)/3,4-dihydropyridin-2-1H-(thiones) (DHPMs) through a multicomponent Biginelli condensation reaction under solvent-free conditions at 333 K. The phosphonic acid functionalized 2D hexagonal mesoporous material showed much higher catalytic activity in this multicomponent condensation reaction over sulfonic acid functionalized mesoporous silica (MCM-41-SO3H) bearing an aliphatic chain in the hybrid framework.