Gold‐Catalyzed Tandem Cycloisomerization–Halogenation of Chiral Homopropargyl Sulfonamides

Two new gold‐catalyzed tandem cycloisomerization–halogenation reactions of chiral homopropargyl sulfonamides have been developed. Various enantioenriched 3,3‐diiodopyrrolidin‐2‐ols and 3‐fluoropyrrolidin‐2‐ols were obtained in moderate‐to‐good yields with excellent enantio‐ and diastereoselectivity.     

An Atomically Precise Au10Ag2 Nanocluster with Red–Near‐IR Dual Emission

A red–near‐IR dual‐emissive nanocluster with the composition [Au₁₀Ag₂(2‐py?C≡C)₃(dppy)₆](BF₄)₅ ( 1 ; 2‐py?C≡C is 2‐pyridylethynyl, dppy=2‐pyridyldiphenylphosphine) has been synthesized. Single‐crystal X‐ray structural analysis reveals that 1 has a trigonal bipyramidal Au₁₀Ag₂ core that contains a planar Au₄(2‐py?C≡C)₃ unit sandwiched by two Au₃Ag(dppy)₃ motifs. Cluster 1 shows intense red–NIR dual emission in solution. The visible emission originates from metal‐to‐ligand charge transfer (MLCT) from silver atoms to phosphine ligands in the Au₃Ag(dppy)₃ motifs, and the intense NIR emission is associated with the participation of 2‐pyridylethynyl in the frontier orbitals of the cluster, which is confirmed by a time‐dependent density functional theory (TD‐DFT) calculation.     

A Hexagonal Covalent Porphyrin Framework as an Efficient Support for Gold Nanoparticles toward Catalytic Reduction of 4‐Nitrophenol

A hexagonal porphyrin‐based porous organic polymer, namely, CPF‐1, was constructed by 3+2 ketoenamine condensation of the C₂‐symmetric porphyrin diamine 5,15‐bis(4‐aminophenyl)‐10,20‐diphenylporphyrin and 1,3,5‐triformylphloroglucinol. This material exhibits permanent porosity and excellent thermal and chemical stability. CPF‐1 can be employed as a superior supporting substrate to immobilize Au nanoparticles (NPs) as a result of the strong interactions between Au NPs and the CPF support. An Au@CPF‐1 hybrid was synthesized by an interfacial solution infiltration method with NaBH₄ as reducing agent. Au NPs (5 nm) grew on CPF‐1 and were distributed without aggregation. Moreover, Au@CPF‐1 exhibits superior catalytic activity compared to many other reported Au‐based catalysts for the reduction of 4‐nitrophenol in the presence of NaBH₄. In addition, Au@CPF‐1 has excellent stability and recyclability, and it can be reused for three successive reaction cycles without loss of activity. The dense distribution of phenyl rings on the channel walls of the CPF support can reasonably be regarded as the active sites that adsorb the 4‐nitrophenol molecule through hydrogen‐bonding and C?H ??? π interactions, as was confirmed by the X‐ray structure of model compound DAPP‐Benz.     

A Gold(I)‐Catalyzed Domino Coupling of Alcohols with Allenes Enables the Synthesis of Highly Substituted Indenes

The reaction of aryl‐substituted allenes with alcohols under gold catalysis led to highly substituted indenes in good yields, with low catalyst loading and under mild conditions. During this domino transformation, two C?C bonds are formed with water as the only byproduct.     

Synthesis and investigation of dual pH‐ and temperature‐responsive behaviour of poly[2‐(dimethylamino)ethyl methacrylate]‐grafted gold nanoparticles

Gold nanoparticles (AuNPs) were synthesized by reduction of chloroauric acid (HAuCl₄) aqueous solution with hydrazine monohydrate. The AuNPs were immediately treated with cysteamine to obtain amine‐functionalized nanoparticles (Au‐NH₂). The reaction of Au‐NH₂ with epichlorohydrin and subsequent treatment with sodium hydroxide gave epoxidized AuNPs (Au‐EP). Then, thiol‐capped AuNPs (Au‐SH) were synthesized by reaction of Au‐EP with cysteamine. A ‘grafting to’ approach was utilized to graft bromine‐terminated poly(N ,N ′‐dimethylaminoethyl methacrylate), synthesized via aqueous atom transfer radical polymerization, with various molecular weights (6280, 25 800, 64 200 and 87 600 g mol⁻¹) onto Au‐SH to obtain Au‐P1, Au‐P2, Au‐P3 and Au‐P4 samples, respectively. All samples were exposed to temperature and pH variations, and Z‐average diameter was monitored using dynamic light scattering. According to the results, polymer‐grafted nanoparticles collapsed at lower temperatures with increasing solution pH for all molecular weight ranges due to deprotonation of tertiary amine groups. However, higher molecular weight polymers were more sensitive to pH variation especially in alkaline media. Also, a high degree of agglomeration was observed for Au‐P4 nanoparticles in alkaline media on increasing the temperature to 55 and 65 °C.     

Synthesis Optimization of Quaternized Chitosan and its Action as Reducing and Stabilizing Agent for Gold Nanoparticles

The optimal conditions for synthesizing quaternized chitosan (QCS) via microwave irradiation were explored. The microwave temperature, time, power, mole ratio between chitosan and 2,3-epoxypropyltrimethyl ammonium chloride (ETA), volume ratio between isopropanol and water, and pH value of the reaction system were studied to evaluate the effect on the degree of substitution (DS). The structure of QCS was characterized by means of FT-IR, NMR, XPS and XRD. TGA and DTG were used to measure its thermal stability. At last, QCS acted as a reducing and stabilizing agent to greenly synthesize gold nanoparticles without adding any other chemical reagent.     

Star-PDMAEMA-β-CD-Stabilized Colloidal Gold Nanoparticles: Synthesis,Characterization and pH-Controlled Assembly

Colloidal gold nanoparticles were prepared through in situ reduction in the presence of water-soluble star homopolymer with β-cyclodextrin core and poly[2-(dimethylamino) ethyl methacrylate] arms (star PDMAEMA-β-CD) at ambient temperature. In this process, star PDMAEMA-β-CD acted as both reducing agent and stabilizing agent for gold nanoparticles. More importantly, the optical properties and the morphology of star-PDMAEMA-β-CD-stabilized colloidal gold nanoparticles were sensitive to the solution pH due to structural changes of the polymer. Different assemblies can be formed by tuning the pH of the medium. Fourier transform infrared (FT-IR), UV-Vis absorption spectroscopy, transmission electron microscopy (TEM), dynamic laser light scattering (DLS) and X-ray diffraction (XRD) were used to characterize the synthetic gold nanoparticles and the pH-controlled assembly of gold nanoparticles.     

pH tunable self-assembly of chicoric acid and their biocompatibility studies

We report for the first time, the pH tunable self-assembly of chicoric acid, an HIV-I integrase inhibitor, which displayed a remarkable tendency to self-assemble at room temperature into varying nano- and microstructures. Furthermore, those assemblies were then functionalised with gold (Au) nanoparticles. We then investigated the biocompatibility of the materials by conducting in vitro cell attachment and cytotoxicity studies using normal rat kidney cells. The studies revealed that the biomaterials were non-toxic and biocompatible, and showed considerable adhesion to the cells. These results suggest that the assemblies could potentially be used for a variety of applications, such as carriers for targeted drug delivery as well as optoelectronics and sensors. Furthermore, the formation of highly organised nano- and microstructures of medicinally significant phytohormones such as chicoric acid is of particular interest as it might help in further understanding the supramolecular assembly mechanism of higher organised biological structures for the development of building blocks for various device fabrications.