Chirally Twisted Ultrathin Polydopamine Nanoribbons: Synthesis and Spontaneous Assembly of Silver Nanoparticles on Them

Polydopamine (PDA) is a synthetic polymeric material with immense potential in biomedical and surface functionalization applications. Herein, we have screened self-assemblies formed by Phenylalanine-based amphiphiles (Phe-AMPs) as soft templates for preparing chiral PDA nanostructures. Our study revealed that the amphiphile 2 endowed with a primary amine residue afforded chirally-twisted ultrathin nanoribbons of PDA under optimized conditions. The chirality at the Phe residue of 2 modulated the twist-chirality of the PDA nanoribbons; the l -2 resulted in nanoribbons with right-handed twist, whereas the d -2 induced a left-handed twist to the ribbons. The racemic mixture of these two amphiphiles produced flat, achiral tapes. The PDA ribbon thickness was ≈5.86±0.40 nm, whereas its width and length were ≈133.5±3.2 nm and >5000 nm, respectively. Upon dialysis, hollow PDA nanotubes were obtained due to curling of the PDA nanoribbons. These PDA-nanoarchitectures were employed to spontaneously form and assemble Ag-nanoparticles along the edges of the PDA nanoribbons. In this work we are reporting chirality controlled synthesis of PDA nanostructures for the first time.     

Ag@SiO2@NF电化学传感器的制备及其对铅离子的检测

本文采用溶胶-凝胶法制备巯基功能化的SiO₂微球,利用银与巯基的络合作用将银负载在SiO₂微球上,利用压片法将Ag@SiO₂修饰在泡沫镍表面,制备了Ag@SiO₂@NF电化学传感器,并研究了其在水中Pb²⁺检测方面的应用。通过透射电子显微镜,扫描电镜,电子能谱等对Ag@SiO₂@NF的形貌结构进行了表征,通过差分脉冲伏安法对Ag@SiO₂@NF的电化学性能进行了检测。结果表明,制备的Ag@SiO₂微球均匀的负载在泡沫镍表面。在最佳条件下使用差分脉冲伏安法对Pb²⁺进行电化学检测。测定的线性范围为1~5×10^-4M,检测限为0.761μmol·L^-1,为在各个环境中快速、准确、灵敏的检测水中Pb²⁺的含量提供了一种新思路。     

Copper- and silver-containing heterometallic iodobismuthates(iii) with 4-(dimethylamino)-1-methylpyridinium cation: structures,thermal stability and optical properties

Reactions of BiI₃, copper or silver iodide and 4-(dimethyl-amino)-1-methylpyridinium iodide [(Me-DMAP)I] result in formation of heterometallic complexes (MeDMAP)₂{[Bi₂Cu₂I₁₀]} and (MeDMAP)₂{[Bi₂Ag₂I₁₀]}. Their crystal structures, thermal stability and optical properties have been studied. Optical band gaps calculated from diffuse reflectance spectroscopy data are 1.81 and 2.06 eV for copper- and silver-containing complexes, respectively.     

Face-Centered-Cubic Ag Nanoclusters: Origins and Consequences of the High Structural Regularity Elucidated by Density Functional Theory Calculations

Face-centered-cubic (FCC) silver nanoclusters (NCs) adopting either cubic or half-cubic growth modes have been recently reported, but the origin of these atomic assembly patterns and how they are achieved, which would inform our understanding of larger FCC silver nanomaterials, are both unknown. In this study, the cubic and half-cubic growth modes have been unified based on common structural characteristics, and differentiated depending on the starting blocks (cubic vs. half cubic). In both categories, the silver atoms adopt octahedral Ag₆, linear AgS₂ (in projection drawing), or tetrahedral AgS₃P binding modes, and the sulfur atoms adopt T-shaped SAg₃ and orthogonal SAg₄ modes. An additional T-shaped AgS₃ mode is oriented on the surface edge in cubic NCs to complete the cubic framework. Density functional theory calculations indicated that the high structural regularity originates from the strong diffusing capacity of the Ag(5d) and S(3p) orbitals, and the angular momentum distribution of the formed superatomic orbitals. The equatorial orientation of μ⁴-S or μ⁴-Ag determines whether growth stops or continues. In particular, a density-of-states analysis indicated that the octahedral silver atoms are chemically more reactive than the silver atoms in the AgS₃P motif, regardless of whether the parent NC functions as an electron donor or acceptor.     

Pongamia pinnata seed extract‐mediated green synthesis of silver nanoparticles: Preparation,formulation and evaluation of bactericidal and wound healing potential

Pongamia pinnata – a plant used since olden times in Ayurvedic treatment – is reported to have diverse functions including antibacterial, antidiabetic, antineurodegenerative, antiepileptic, antiulcer, etc. In this study, our objective was to prepare silver nanoparticles (AgNPs) by green synthesis mediated by methanolic seed extract of P. pinnata and to determine their antimicrobial and antioxidant potential and wound healing activity. AgNPs were characterized for particle size and shape and for antioxidant potential. Further, the AgNPs were incorporated in a gel. The wound healing activity was investigated using an excision wound healing model in Wistar rats. The AgNP‐loaded gel was applied topically to the wounded rats daily for 30 days. The wound contraction was calculated and histopathological studies of the healed tissues were conducted. Karanjin content of the extract was found to be 349 ± 2.16 mg g^?1. Formation of AgNPs was confirmed using transmission and scanning electron microscopies and X‐ray diffraction. AgNPs showed good antioxidant potential and were active against Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa. Significant wound healing activity (p < 0.05) was shown by the AgNP gel as compared to 5% Betadine ointment. Thus, the prepared AgNPs have antimicrobial and wound healing effects that may be useful in treatment of topical infections especially in wounds.     

Silver-Promoted Radical Ring-Opening/Pyridylation of Cyclobutanols with N-Methoxypyridinium Salts

The silver-promoted reaction of tertiary cyclobutanols with N-methoxypyridinium salts enables the efficient synthesis of a range of C2-substituted pyridines. The overall process likely occurs by ring-opening (via β-scission) of the cyclobutoxy radical to generate the corresponding γ-keto alkyl radical that itself adds to the pyridinium salt. A wide range of tertiary cyclobutanols and N-methoxypyridinium salts are compatible with the reaction conditions.     

Effect of the formation of silver nano‐binuclear complex on the refinement of cytotoxic and antibacterial potency of coumarin Schiff base: Spectroscopy,thermal, X‐ray diffraction analyses and density functional theory calculations

A new Schiff base (SCH) was prepared using 8‐acetyl‐7‐hydroxy‐4‐methylcoumarin and sulfaclozine. Its silver complex was also synthesized. These compounds were subjected to elemental and spectral analyses. The silver complex was also subjected to thermogravimetric analysis, molar conductance measurements, scanning electron microscopy, energy‐dispersive X‐ray analysis and X‐ray diffraction measurements. The formula of the complex was determined as [(Ag₂SCH(NO₃)₂]. The molar conductance indicates its non‐electrolyte character. The electronic structure and nonlinear optical parameters of SCH and its complex were investigated theoretically at the B3LYP/GENECP level. The geometry of the studied complex is non‐planar as indicated from the dihedral angles between central Ag metal ion and coordinated centres of SCH. Density functional theory calculations were also carried out to calculate the global properties of hardness, global softness and electronegativity. The calculated energy gap between HOMO and LUMO energies shows that charge transfer occurs within the studied complex. The total static dipole moment, the mean polarizability, the anisotropy of the polarizability and the mean first‐order hyperpolarizability were calculated and compared with those of urea as a reference material. The results of the mean first‐order hyperpolarizability showed that SCH and its silver complex are excellent candidates as nonlinear optical materials. The compounds were screened for their antimicrobial effect against various species of bacteria and fungi. Their anticancer activities were evaluated in vitro against the human cancer cell line MCF‐7 (human breast adenocarcinoma).     

A surface-enhanced Raman scattering method for detection of trace glutathione on the basis of immobilized silver nanoparticles and crystal violet probe

Unsatisfactory sensitivity and stability for molecules with low polarizability is still a problem limiting the practical applications of surface-enhanced Raman scattering (SERS) technique. By preparing immobilized silver nanoparticles (Fe₃O₄/Ag) through depositing silver on the surface of magnetite particles, a highly sensitive and selective SERS method for the detection of trace glutathione (GSH) was proposed on the basis of a system of Fe₃O₄/Ag nanoparticles and crystal violet (CV), in which the target GSH competed with the CV probe for the adsorption on the Fe₃O₄/Ag nanoparticles. Raman insensitive GSH replaced the highly Raman sensitive CV adsorbed on the surface of Fe₃O₄/Ag particles. This replacement led to a strong decrease of the CV SERS signal, which was used to determine the concentration of GSH. Under optimal conditions, a linear response was established between the intensity decrease of the CV SERS signal and the GSH concentration in the range of 50–700 nmol L⁻¹ with a detection limit of 40 nmol L⁻¹. The use of a Fe₃O₄/Ag substrate provided not only a great SERS enhancement but also a good stability, which guarantees the reproducibility of the proposed method. Its use for the determination of GSH in practical blood samples and cell extract yielded satisfactory results.     

Synthesis and antifungal activity of chitosan-silver nanocomposite synergize fungicide against Phytophthora capsici

Fungicides are important tools for preventing pathogens and maintaining crop quality; however, their effectiveness was directly affected by high-priced, toxicity, and environmental pollution. As a result, it is necessary to get a safe and efficient antimicrobial agent against agricultural pathogens. In this study, silver-incorporated chitosan nanocomposites (Ag@CS) were first prepared in which CS was used as reducing and stabilizing agent and then these nanocomposites was synergized with fungicide Antracol (An), Ag@CS/An, against Phytophthora capsici causing Phytophthora blight in pepper. The obtained nanocomposites were characterized by Fourier transform infrared (FTIR), X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), dynamic light scattering (DLS), and transmission electron microscopy (TEM). These results showed that Ag@CS and Ag@CS/An were successfully synthesized with spherical shape AgNPs having diameter of 20.3?±?0.7?nm and 44.6?±?0.3?nm, respectively. More importantly, Ag@CS/An was found to have significantly stronger antifungal ability than each component alone, analyzed by agar diffusion method. It might be anticipated that Ag@CS/An has a promising future as nano-antibiotic materials for agriculture.     

Organophosphine/phosphite‐stabilized silver(I) complexes bearing N‐hydroxysuccinimide ligand: synthesis,solid state structure and their potential use as MOCVD precursors

Six organophosphine/phosphite‐stabilized silver(I) N‐hydroxysuccinimide complexes of type [C₄H₄NO₃Ag?L_n] (L = PPh₃; n = 1, 2a; n = 2, 2b; L = P(OEt)₃; n = 1, 2c; n = 2, 2 d; L = P(OMe)₃; n = 1, 2e; n = 2, 2f) were prepared. These complexes were obtained in high yields and characterized by elemental analysis, ¹H NMR, ¹³ C{¹H} NMR and IR spectroscopy, respectively. The molecular structure of 2b has been determined by X‐ray single‐crystal analysis in which the silver atom is in a distorted tetrahedral geometry. An interstitial methanol solvent molecule is hydrogen bonded to the oxygen atom of N‐hydroxysuccinimide molecule. Complex 2f was used to deposit silver films by metal‐organic chemical vapor deposition (MOCVD) for the first time. The silver film obtained at 480 °C is dense and homogeneous, which is composed of many well‐isolated, granular particulates spreading all over the substrate surface. Copyright © 2012 John Wiley & Sons, Ltd.