Single-Source Precursors for Alloyed Gold–Silver Nanocrystals - A Molecular Metallurgy Approach

One Pot Synthesis of PEGylated Bimetallic Gold-Silver Nanoparticles for Imaging and Radiosensitization of Oral Cancers

Background

Radiotherapy is an important treatment modality for many types of head and neck squamous cell carcinomas. Nanomaterials comprised of high atomic number (Z) elements are novel radiosensitizers enhance radiation injury by production of free radicals and subsequent DNA damage. Gold nanoparticles are upcoming as promising radiosensitizers due to their high (Z) biocompatibility, and ease for surface engineering. Bimetallic nanoparticles have shown enhanced anticancer activity compared to monometallic nanoparticles.

Materials and Methods

PEG-coated Au–Ag alloy nanoparticles (BNPs) were synthesized using facile one pot synthesis techniques. Size of ~50±5nm measured by dynamic light scattering. Morphology, structural composition and elemental mapping were analyzed by electron microscopy and SAXS (small-angle X-ray scattering). The radiosensitization effects on KB oral cancer cells were evaluated by irradiation with 6MV X-rays on linear accelerator. Nuclear damage was imaged using confocal microscopy staining cells with Hoechst stain. Computed tomography (CT) contrast enhancement of BNPs was compared to that of the clinically used agent, Omnipaque.

Results

BNPs were synthesized using PEG 600 as reducing and stabilizing agent. The surface charge of well dispersed colloidal BNPs solution was −5mV. Electron microscopy reveals spherical morphology. HAADF-STEM and elemental mapping studies showed that the constituent metals were Au and Ag intermixed nanoalloy. Hydrodynamic diameter was ~50±5nm due to PEG layer and water molecules absorption. SAXS measurement confirmed BNPs size around 35nm. Raman shift of around 20 cm⁻¹ was observed when BNPs were coated with PEG. ¹H NMR showed extended involvement of ⁻OH in synthesis. BNPs efficiently enter cytoplasm of KB cells and demonstrated potent in vitro radiosensitization with enhancement ratio ~1.5–1.7. Imaging Hoechst-stained nuclei demonstrated apoptosis in a dose-dependent manner. BNPs exhibit better CT contrast enhancement ability compared to Omnipaque.

Conclusion

This bimetallic intermix nanoparticles could serve a dual function as radiosensitizer and CT contrast agent against oral cancers, and by extension possibly other cancers as well.

Morphology Control in AgCu Nanoalloy Synthesis by Molecular Cu(I) Precursors

As nanoparticle preparation methods employing bottom-up procedures rely on the use of molecular precursors, the chemical composition and bonding of these precursors have a decisive effect on nanoparticle formation and their resulting morphology and properties. We synthesized the Cu(I) complexes [Cu(PPh₃)₂(bea)] (1, bea = benzoate) and [Cu(PPh₃)₃(Hphta)] (2, phta = phthalate) by reducing the corresponding Cu(II) mono- and dicarboxylates with triphenylphosphine. We characterized 1 and 2 by single-crystal X-ray diffraction analysis, elemental analyses, infrared and nuclear magnetic resonance spectroscopy, and mass spectrometry and obtained complete information about their structures in the solid state and in solution. Also, we examined their thermal stability in oleylamine and determined their decomposition temperatures to be used as the minimal reaction temperature in metal nanoparticle synthesis. The complexes 1 and 2 differ in the number of reducing PPh₃ ligands and the strength of carboxylate bonding to the Cu(I) center. Therefore, we employed them in combination with [Ag(NH₂C₁₂H₂₅)₂]NO₃ as molecular precursors in the solvothermal hot injection synthesis of AgCu nanoalloys in oleylamine and demonstrated their influence on the elemental distribution, phase composition, particle size distribution, shape, morphology, and optical properties of the resulting nanoparticles. The nanoalloy particles from the benzoate complex 1 were oblate and polydisperse and exhibited two surface plasmons at 393 and 569 nm, which is caused by their Janus-type structure. The nanoparticles prepared from the phthalate complex 2 were round and monodisperse and exhibited one plasmon at 413 nm, as they formed an AgCu solid solution with a random distribution of the elements in a particle.

Exploring the Role of Coinage Metalates in Trifluoromethylation: A Combined Experimental and Theoretical Study

Despite the known nucleophilic nature of [M(CF₃ )₂ ]^- (M=Cu, Ag, Au) complexes, their participation in trifluoromethylation reactions of aryl halides remains unexplored. Here, for the first time, selective access to a [Cu(CF₃ )₂ ]^- species is reported, which is ubiquitous in Cu-mediated trifluoromethylations, and we rationalize its complex mechanistic scenario as well as its behavior compared to its silver and gold congeners through a combination of experimental and computational approaches.

Gold Difluorocarbenoid Complexes: Spectroscopic and Chemical Profiling

Gold carbenes of the general type [LAu=CR₂ ]⁺ are sufficiently long-lived for spectroscopic inspection only if the substituents compensate for the largely missing stabilization of the carbene center by the [LAu]⁺ fragment. π-Donation by two fluorine substituents (R=F) is insufficient; rather, difluorocarbene complexes are so deprived in electron density that they sequester even "weakly coordinating" anions such as triflate or triflimide. This particular bonding situation translates into unmistakable carbenium ion chemistry upon reaction with stilbene as a model substrate.

Molecularly Engineered Lithium–Chromium Alkoxide for Selective Synthesis of LiCrO2 and Li2CrO4 Nanomaterials

Achieving control over the phase-selective synthesis of mixed metal oxide materials remains a challenge to the synthetic chemist due to diffusion-driven growth, which necessitates the search for new compounds with pre-existent chemical bonds between the phase-forming elements. We report here a simple solvothermal process to fabricate LiCrO2 and Li2CrO4 nanoparticles from bimetallic single-source precursors, demonstrating the distinctive influence of molecular design and calcination conditions on the resulting nanomaterials. The chemical identity of [Li2Cr(OtBu)4Cl(THF)2] (1) and [LiCr(OtBu)2(PyCH=COCF3)2(THF)2] (2) was unambiguously established in the solid state by single-crystal X-ray diffraction, revealing the formation of a coordination polymeric chain in compound 1, whereas electron paramagnetic resonance spectroscopy (EPR) studies revealed a monomeric structure in solution. TEM analysis of synthesized LiCrO2 nanoparticles showed nearly uniform particles size of approximately 20 nm. The sensitivity of the LiCrO2 phase towards oxidation was investigated by X-ray diffraction, revealing the formation of the stable Li2CrO4 after calcination in air.

Unequal coordination environment in complexes of the type [Au2Ag2(R)4(L)2]n. An immiscible solvent mixture as a key point in the control of ligand replacement

Following an acid-base strategy, based on the reaction between gold(i) basic fragments and acid silver salts, it is possible to obtain heterometallic polymers of the general formula [Au₂Ag₂(R)₄(L)₂]_n (R = C₆Cl₂F₃; L = pyrimidine). Using this new heterometallic complex [Au₂Ag₂(C₆Cl₂F₃)₄(pym)₂]_n (1) as a starting material, and a good coordinating solvent such as acetonitrile, it is possible to modify the arrangement of the ligands connected to the silver centres and to obtain three different tetranuclear Au₂Ag₂ building blocks leading to the new polymer [Au₆Ag₆(C₆Cl₂F₃)₁₂(μ₂-pym)₂(NCMe)₆]_n (2). Both complexes display very intense luminescence emission. Structural, experimental and computational studies have been carried out in order to identify the origin of these properties and the factors that can affect them, such as, the presence of metallophilic interactions as well as different coordination environments for the metallic centres.