Fundamental understanding of the size and surface modification effects on r 1, the relaxivity of Prussian blue nanocube@m-SiO2: a novel targeted chemo-photodynamic theranostic agent to treat colon cancer

A targeted multimodal strategy on a single nanoplatform is attractive in the field of nanotheranostics for the complete ablation of cancer. Herein, we have designed mesoporous silica (m-SiO2)-coated Prussian blue nanocubes (PBNCs), functionalized with hyaluronic acid (HA) to construct a multifunctional PBNC@m-SiO2@HA nanoplatform that exhibited good biocompatibility, excellent photodynamic activity, and in vitro T 1-weighted magnetic resonance imaging ability (r 1 ∼ 3.91 mM-1 s-1). After loading doxorubicin into the as-prepared PBNC@m-SiO2@HA, the developed PBNC@m-SiO2@HA@DOX displayed excellent pH-responsive drug release characteristics. Upon irradiation with 808 nm (1.0 W cm-2) laser light, PBNC@m-SiO2@HA@DOX exhibited synergistic photodynamic and chemotherapeutic efficacy (∼78% in 20 minutes) for human colorectal carcinoma (HCT 116) cell line compared to solo photodynamic or chemotherapy. Herein, the chemo-photodynamic therapeutic process was found to follow the apoptotic pathway via ROS-mediated mitochondrion-dependent DNA damage with a very low cellular uptake of PBNC@m-SiO2@HA@DOX for the human embryonic kidney (HEK 293) cell line, illustrating its safety. Hence, it may be stated that the developed nanoplatform can be a potential theranostic agent for future applications. Most interestingly, we have noted variation in r 1 at each step of the functionalization along with size variation that has been the first time modelled on the basis of the Solomon-Bloembergen-Morgan theory considering changes in the defect crystal structure, correlation time, water diffusion rate, etc., due to varied interactions between PBNC and water molecules.

Recyclable magnetically retrievable nanocatalysts for C–heteroatom bond formation reactions

During recent years, magnetic separation has proven to be a highly indispensable and sustainable tool for facile separation of catalysts from the reaction medium with the aid of only an external magnetic force that precludes the requirement of energy intensive, solvent based centrifugation or filtration techniques. Extensive research in the area of catalysis has clearly divulged that while designing any catalyst, the foremost features that need to be paid due attention to include high activity, ready recoverability and good reusability. Fortunately, the magnetic nanocatalysts involving a superparamagnetic core material that could comprise of iron oxides such as magnetite, maghemite or hematite or mixed ferrites (CoFe2O4, CuFe2O4) have offered bright prospects of designing the ideal catalysts by proving their efficacy as strong support material that could be further engineered with various tools of nanotechnology and efficiently catalyze various C–heterobond formation reactions. This chapter provides succinct overview of all the approaches utilized for fabricating different types of magnetic nanoparticles and strategies adopted for imparting them durability. The prime forte however remains to exclusively showcase the applications of the various types of magnetic nanocatalysts in C–O, C–N, C–S and miscellaneous (C–Se, C–Te) bond formation reactions which are anticipated to benefit the synthetic community on a broad spectrum by helping them rationalize and analyze the key features that need to be taken into account, while developing these magical nanostructured catalytic systems for boosting the green bond formation reactions/transformations.

Design and Preparation of Copper(II)-Mesalamine Complex Functionalized on Silica-Coated Magnetite Nanoparticles and Study of Its Catalytic Properties for Green and Multicomponent Synthesis of Highly Substituted 4H-Chromenes and Pyridines

In the present study, a green and ecofriendly nanocatalyst was synthesized through functionalization of 2,4,6-trichloro-1,3,5-triazine (TCT) and mesalamine on silica-coated magnetic nanoparticles (MNPs), then coordination with Cu²⁺ without agglomeration, consecutively. The silica-coated MNPs functionalized with the Cu(*II)-mesalamine complex was (Fe₃O₄@SiO₂@NH₂-TCT-mesalamine-Cu(II) MNPs) completely characterized by FT-IR, XRD, EDX, FESEM, TEM, VSM, TGA, and BET analyses. Afterward, the activity of the novel catalyst was investigated in the synthesis of chromene heterocycles, which were an important group of organic compounds. The activity of Fe₃O₄@SiO₂@NH₂-TCT-mesalamine-Cu(II) MNPs as a high-performance heterogeneous nanocatalyst was evaluated for the synthesis of 2-amino-4-aryl-6-(phenylthio)pyridine-3,5-dicarbonitriles and 2-amino-4H-chromenes via aromatic aldehydes, malononitrile, and enolizable C-H acids (resorcinol, 2-hydroxynaphthalene-1,4-dione, and benzenethiol) in ethanol under reflux conditions. Fe₃O₄@SiO₂-TCT-mesalamine-Cu(II) could be quickly separated using an external magnet and reused nine times without a remarkable reduction of its catalytic activity.

Green and Mechanochemical One-Pot Multicomponent Synthesis of Bioactive 2-amino-4H-benzo[b]pyrans via Highly Efficient Amine-Functionalized SiO2@Fe3O4 Nanoparticles

An ecofriendly, magnetically retrievable amine-functionalized SiO2@Fe3O4 catalyst was successfully synthesized and affirmed by several physicochemical characterization tools, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM), energy-dispersive X-ray spectroscopy (EDX), and powder X-ray diffraction. Thereafter, the catalytic performance of this environmentally benign NH2@SiO2@Fe3O4 catalyst was investigated in the one-pot multicomponent synthesis of 2-amino-4H-benzo[b]pyran derivatives. The reaction was simply achieved by grinding of various substituted aromatic aldehydes, dimedone, and malononitrile at room temperature under solvent and waste-free conditions with excellent yields and high purity. Moreover, the developed catalyst not only possesses immense potential to accelerate the synthesis of bioactive pyran derivatives but also exhibits several remarkable attributes like broad functional group tolerance, durability, improved yield, reusability, and recyclability. Besides, various other fascinating advantages of this protocol are milder reaction conditions, cost effectiveness, short reaction time, and simple work up procedures.

Expanding the Horizon of Multicomponent Oxidative Coupling Reaction via the Design of a Unique, 3D Copper Isophthalate MOF-Based Catalyst Decorated with Mixed Spinel CoFe2O4 Nanoparticles

This work discloses the first ever magnetically retrievable copper isophthalate-based metal-organic framework (MOF) decorated with surface-modified cobalt ferrite (CoFe2O4) nanoparticles that have been utilized as catalytic reactors for obtaining a relatively large number of biologically active benzimidazole scaffolds. A facile one-pot solvothermal approach was employed for obtaining spherical and monodisperse CoFe2O4 nanoparticles, which were subsequently modified using suitable protecting and functionalizing agents. Finally, these functionalized magnetic nanoparticles were anchored onto the three-dimensional copper isophthalate MOF via a covalent immobilization methodology. The exploitation of advanced microscopic tools such as transmission electron microscopy and scanning electron microscopy provided valuable insights into the morphology of the immobilized MOF. These results indicated that the surface-modified magnetic nanoparticles had grown onto the surface of copper-5-nitroisophthalic acid MOF. A greener C-H functionalization strategy that involves the multicomponent oxidative cross-coupling between two different set of amines (sp2-hybridized nitrogen-containing anilines and sp3-hybridized nitrogen-containing alkyl/aryl amine derivatives) and sodium azide has been incorporated to provide access to a broad spectrum of the value-added target benzimidazole moieties. It is interesting to note that this magnetic MOF-catalyzed protocol not only replaces toxic solvents with water, which is a green solvent, but also enhances the economic competitiveness since the magnetic catalyst can be readily recovered and recycled for eight consecutive runs.

Fabrication of Core-Shell-Structured Organic-Inorganic Hybrid Nanocatalyst for the Expedient Synthesis of Polysubstituted Oxazoles via Tandem Oxidative Cyclization Pathway

The quest for designing efficient heterogeneous catalytic systems for tandem oxidative cyclization reactions has provided a great impetus to research efforts, as it enables the step-economic construction of complex heterocyclic molecules as well as confers the benefits of a facile catalytic recovery. In the present study, we disclose a new core-shell-structured organic-inorganic hybrid copper nanocatalyst fabricated via the covalent grafting of 2,2'-dipyridyl ketone ligand on amine-functionalized silica-encapsulated magnetite nanoparticles, followed by its metallation with cupric acetate for the tandem oxidative cyclization of amines and β-ketoesters, leading to the production of biologically active polysubstituted oxazole moieties. This programmed catalytic protocol proceeds via the formation of intermolecular C-C and C-N bonds by single-step synthesis and accommodates a broad combination of reaction coupling partners.