Cassia fistula galactomannan stabilized copper nanocatalyst as an efficient, recyclable heterogeneous catalyst for the fast clickable [3+2] Huisgen cycloadditions in water

In this study, we have first time investigated the synthesis of copper nanocatalyst by using biopolymer galactomannan, naturally extracted from Cassia fistula pods. The methodology involved for the preparation of copper nanocatalyst is economical, efficient, environment friendly, and did not involve further processing for stabilization or reduction of copper nanoparticles. The morphology and structural characterization of the nanocatalyst was performed by using different techniques such as FT-IR, 1H NMR, SEM, EDX, HR-TEM, XRD, XPS, ICP-MS, BET, and TGA analysis. The prepared copper nanocatalyst is applied for the click [3+2] Huisgen cycloadditions of various azides and alkynes, employing water as environmentally benign solvent. In comparison to earlier reported methods, our method requires lowest catalyst loading, less reaction time, excellent yields and have wide substrate scope. Additionally, the catalyst was easily recovered by simple filtration and recycled at least ten consecutive times without any appreciable loss of efficiency and selectivity. The effect of mannose and galactose (Man/Gal) ratio of Cassia fistula galactomannan on the catalytic activity were also investigated.

Mesoporous epoxidized soybean oil-supported copper-based magnetic nanocatalyst and amberlite-supported azide as a green and efficient catalytic system for 1,2,3-triazole synthesis

A new green mesoporous magnetically heterogeneous catalyst was prepared by the copper immobilization onto magnetic epoxidized soybean oil as a nano bio-support and was utilized for the synthesis of 1,4-disubstituted-1,2,3-triazole derivatives in the presence of amberlite supported azide. A great range of triazole derivatives were synthesized from benzyl halides or epoxides halides in high yields at the room temperature. The catalyst was characterized by various techniques such as FT-IR, XRD, VSM, FE-SEM, EDX, TEM, BET, TGA, and ICP analysis. This catalytic system can be reused for five times without any significant decrease in the catalytic activity. Fe3O4@SiO-ESBO/CuO nanocatalyst and amberlite supported azide as a green catalytic system has been used for the regioselective synthesis of triazole derivatives in water. A large range of triazole derivatives were synthesized from benzyl halides or epoxides in high yields.

Supported Metal Catalysts for the Synthesis of N-Heterocycles

Nitrogen-containing heterocycles are important scaffolds for a large number of compounds with biological, pharmaceutical, industrial and optoelectronic applications. A wide range of different methodologies for the preparation of N-heterocycles are based on metal-catalyzed cyclization of suitable substrates. Due to the growing interest in Green Chemistry criteria over the past two decades, the use of supported metal catalysts in the preparation of N-heterocycles has become a central topic in Organic Chemistry. Here we will give a critical overview of all the solid supported metal catalysts applied in the synthesis of N-heterocycles, following a systematic approach as a function of the type of support: (i) metal catalysts supported on inorganic matrices; (ii) metal catalysts supported on organic matrices; (iii) metal catalysts supported on hybrid inorganic-organic matrices. In particular, we will try to emphasize the effective heterogeneity and recyclability of the described metal catalysts, specifying which studies were carried out in order to evaluate these aspects.

CuO-decorated magnetite-reduced graphene oxide: a robust and promising heterogeneous catalyst for the oxidative amidation of methylarenes in water via benzylic sp3 C–H activation

CuO-decorated magnetite-reduced graphene oxide: a heterogeneous catalyst for the oxidative amidation of methylarenes in water at room temperature.

A Study of Graphene-Based Copper Catalysts: Copper(I) Nanoplatelets for Batch and Continuous-Flow Applications

The use of graphene derivatives as supports improves the properties of heterogeneous catalysts, with graphene oxide (GO) being the most frequently employed. To explore greener possibilities as well as to get some insights into the role of the different graphenic supports (GO, rGO, carbon black, and graphite nanoplatelets), we prepared, under the same standard conditions, a variety of heterogeneous Cu catalysts and systematically evaluated their composition and catalytic activity in azide-alkyne cycloadditions as a model reaction. The use of sustainable graphite nanoplatelets (GNPs) afforded a stable Cu^I catalyst with good recyclability properties, which are compatible with flow conditions, and able to catalyze other reactions such as the regio- and stereoselective sulfonylation of alkynes (addition reaction) and the Meerwein arylation (single electron transfer process).

Emerging Trends in the Syntheses of Heterocycles Using Graphene-based Carbocatalysts: An Update

Graphene-based carbocatalysts owing to numerous amazing properties such as large specific surface area, high intrinsic mobility, excellent thermal and electrical conductivities, chemical stability, ease of functionalization, simple method of preparation, effortless recovery and recyclability have gained a superior position amongst the conventional homogeneous and heterogeneous catalysts. In this review, an endeavor has been made to highlight the syntheses of diverse heterocyclic compounds catalyzed by graphene-based catalysts. Further, the study also reveals that all the catalysts could be reused several times without significant loss in their catalytic activity. Additionally, most of the reactions catalyzed by graphene-based carbocatalysts were carried out at ambient temperature and under solvent-free conditions. Thus, the graphene-based catalysts do not merely act as efficient catalysts but also serve as sustainable, green catalysts. This review is divided into various sub-sections, each of which comprehensively describes the preparation of a particular heterocyclic scaffold catalyzed by graphene-derived carbocatalyst in addition to synthesis of graphene oxide and reduced graphene oxide, functionalization, and structural features governing their catalytic properties. Synthesis of heterocycles catalyzed by graphene-based carbocatalysts.

Chemical Waltz of Organic Molecules "On Water": Saline-Assisted Sustainable Regioselective Synthesis of Fluorogenic Heterobioconjugates via Click Reaction

A new sustainable green protocol for obtaining highly fluorogenic heterobioconjugates by a well-known copper-mediated azide-alkyne cycloaddition click reaction of nonfluorescent 3-azidocoumarins/benzyl azides (2a-f) and terminal alkynes (1a-e) using aqueous NaCl as a cheap and nontoxic salting-out agent under ultrasonication at ambient temperature is described. The presence of aqueous NaCl significantly influences the reaction by disturbing the water kosmotropes and augments the hydrophobic interaction of water-insoluble reactants, thus making the reaction feasible in water at neutral pH. The "beauty" of the presented ecofriendly approach is further boosted up by recycling the aqueous filtrate of the reaction mixture without further addition of NaCl, CuSO₄·5H₂O, and Na ascorbate up to seven cycles, resulting in effectively low copper loading (100 ppm) with excellent turn-over number (4850) and turn-over frequency (88.18 min^-1). A gram-scale synthesis was also successfully achieved with 92% yield, further elaborating the scope of this methodology.

Cellulose‑copper as bio-supported recyclable catalyst for the clickable azide-alkyne [3 + 2] cycloaddition reaction in water

Naturally-occurring cellulose has been employed as a bio-support macromolecule for the immobilization of either copper(I) or copper(II) ions in order to click azide and alkyne derivatives in water. Under such a click regime, 1,4-disubstitued-1,2,3-triazoles were obtained regioselectively in excellent yields at room temperature. The reaction work-up is simple and the bio-heterogeneous catalyst that has been fully characterized by AAS, SEM, EDX and FT-IR can be easily separated and reused at least five times without any significant decrease in its activity and selectivity, particularly in the case of the very stable CuI-Cellulose.

Carnosine-graphene oxide conjugates decorated with hydroxyapatite as promising nanocarrier for ICG loading with enhanced antibacterial effects in photodynamic therapy against Streptococcus mutans

Antimicrobial photodynamic therapy (aPDT) has been emerged as a noninvasive strategy to remove bacterial contaminants such as S. mutans from the tooth surface. Photosensitizer (PS), like indocyanine green (ICG), plays a key role in this technique which mainly suffers from the poor stability and concentration-dependent aggregation. An appropriate nanocarrier (NC) with enhanced antibacterial effects could overcome these limitations and improve the efficiency of ICG as a PS. In this study, various ICG-loaded NCs including graphene oxide (GO), GO-carnosine (Car) and GO-Car/Hydroxyapatite (HAp) were synthesized and characterized by Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Filed Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), Zeta Potential and Ultraviolet-Visible spectrometry (UV-Vis). The colony forming unit and crystal violet assays were performed to evaluate the antimicrobial and anti-biofilm properties of PSs against S. mutans. The quantitative real-time PCR approach was also applied to determine the expression ratio of the gtfB gene in S. mutans. The zeta potential analysis and UV-Vis spectrometry indicated successful loading of ICG onto/into NCs. GO-Car/HAp showed highest amount of ICG loading (57.52%) and also highest aqueous stability after one week (94%). UV-Vis spectrometry analyses disclosed a red shift from 780 to 800 nm for the characteristic peak of ICG-loaded NCs. In the lack of aPDT, GO-Car@ICG showed the highest decrease in bacterial survival (86.4%) which indicated that Car could significantly promote the antibacterial effect of GO. GO@ICG, GO-Car@ICG and GO-Car/HAp@ICG mediated aPDT, dramatically declined the count of S. mutans strains to 91.2%, 95.5% and 93.2%, respectively (P < 0.05). The GO@ICG, GO-Car@ICG, GO-Car/HAp@ICG significantly suppressed the S. mutans biofilm formation by 51.4%, 63.8%, and 56.8%, respectively (P < 0.05). The expression of gtfB gene was considerably reduced to 6.0, 9.0 and 7.9-fold after aPDT in the presence of GO@ICG, GO-Car@ICG, GO-Car/HAp@ICG, respectively (P < 0.05). It could be concluded that the multi-functionalized GO as a novel nanocarrier could significantly enhance the ICG loading, stability, and improve its inhibitory effects as a photosensitizer in aPDT against S. mutans. These findings might provide opportunity for efficient treatment of local dental infections.

Magnetically separable graphene oxide anchored sulfonic acid: a novel, highly efficient and recyclable catalyst for one-pot synthesis of 3,6-di(pyridin-3-yl)-1H-pyrazolo[3,4-b]pyridine-5-carbonitriles in deep eutectic solvent under microwave irradiation

A magnetic separable sulfonic acid catalyst was prepared and applied for the synthesis of 3,6-di(pyridin-3-yl)-1H-pyrazolo[3,4-b]pyridine-5-carbonitriles via three-component reaction of 1-phenyl-3-(pyridin-3-yl)-1H-pyrazol-5-amine, β-ketonitrile and aldehydes in DES.

When CuAAC 'Click Chemistry' goes heterogeneous

Within the green chemistry context, heterogeneous catalysis is more and more applied to organic synthesis. The well known ‘click chemistry’ and especially its flagship, the copper-catalyzed azide–alkyne cycloaddition reaction (CuAAC), is now catch up by such heterogenisation process and copper ions or metals have been grafted or deposited on or into various solids, such as (bio)polymers, charcoal, silica, zeolites, POM or MOF.

Graphene oxide decorated with Cu(i)Br nanoparticles: a reusable catalyst for the synthesis of potent bis(indolyl)methane based anti HIV drugs

A reusable nanocatalytic system comprising Cu(i)Br decorated on graphene oxide has been prepared, and successfully applied for an efficient synthesis of bis(indolyl)methanes. The synthesized compound 3d shows significant anti-HIV-1 activity.

An efficient CuI/DBU-catalyzed one-pot protocol for synthesis of 1,4-disubstituted 1,2,3-triazoles

A convenient CuI/DBU catalyzed one-pot method has been developed for the synthesis of 1,4-disubstituted 1,2,3-triazoles from aryl iodides, sodium azide and phenylacetaldehyde derivatives or from aryl iodides, sodium azide and alkynes in DMSO.

Fe3O4 magnetic nanoparticles (MNPs) as an efficient catalyst for selective oxidation of benzylic and allylic C–H bonds to carbonyl compounds with tert-butyl hydroperoxide

Fe₃O₄ MNP as an eco-friendly catalyst was prepared, characterized and applied for oxidation of benzylic and allylic C–H bonds.

Copper-catalysed azide-alkyne cycloadditions (CuAAC): an update

The reactions of organic azides and alkynes catalysed by copper species represent the prototypical examples of click chemistry. The so-called CuAAC reaction (copper-catalysed azide-alkyne cycloaddition), discovered in 2002, has been expanded since then to become an excellent tool in organic synthesis. In this contribution the recent results described in the literature since 2010 are reviewed, classified according to the nature of the catalyst precursor: copper(I) or copper(II) salts or complexes, metallic or nano-particulated copper and several solid-supported copper systems.

A metal–organic framework as a highly efficient and reusable catalyst for the solvent-free 1,3-dipolar cycloaddition of organic azides to alkynes

A new highly efficient and reusable Cu-MOF has been developed for the regioselective synthesis of 1,2,3-triazoles via the 1,3-dipolar cycloaddition of organic azides to terminal alkynes under solvent-free conditions.

One-pot three-component synthesis of 1,2,3-triazoles using magnetic NiFe2O4–glutamate–Cu as an efficient heterogeneous catalyst in water

A magnetic NiFe₂O₄ supported glutamate–copper catalyst is prepared and applied for the synthesis of a wide variety of 1,2,3-triazoles in water at room temperature.

Magnetic nano-Fe3O4@TiO2/Cu2O core–shell composite: an efficient novel catalyst for the regioselective synthesis of 1,2,3-triazoles using a click reaction

An efficient and recoverable core–shell nanomagnetic composite was developed for regioselective synthesis of 1,2,3-triazoles using a green procedure.