Photolysis and Thermolysis of Platinum(IV) 2,2′‐Bipyridine Complexes Lead to Identical Platinum(II)–DNA Adducts

Two Pt^IV and two Pt^II complexes containing a 2,2′‐bipyridine ligand were treated with a short DNA oligonucleotide under light irradiation at 37 °C or in the dark at 37 and 50 °C. Photolysis and thermolysis of the Pt^IV complexes led to spontaneous reduction of the Pt^IV to the corresponding Pt^II complexes and to binding of Pt^II 2,2′‐bipyridine complexes to N7 of guanine. When the reduction product was [Pt(bpy)Cl₂], formation of bis‐oligonucleotide adducts was observed, whereas [Pt(bpy)(MeNH₂)Cl]⁺ gave monoadducts, with chloride ligands substituted in both cases. Neither in the dark nor under light irradiation was the reductive elimination process of these Pt^IV complexes accompanied by oxidative DNA damage. This work raises the question of the stability of photoactivatable Pt^IV complexes toward moderate heating conditions.     

Studies on the Formation of Catalytically Active PGM Nanoparticles from Model Solutions as a Basis for the Recycling of Spent Catalysts

The paper presents basic studies on the precipitation of platinum, palladium, rhodium, and ruthenium nanoparticles from model acidic solutions using sodium borohydride, ascorbic acid, and sodium formate as reducing agents and polyvinylpyrrolidone as a stabilizing agent. The size of the obtained PGM particles after precipitation with NaBH₄ solution does not exceed 55 nm. NaBH₄ is an efficient reducer; the precipitation yields for Pt, Pd, Ru, Rh are 75, 90, 65 and 85%, respectively. By precipitation with ascorbic acid, it is possible to efficiently separate Pt, Rh, and Ru from Pd from the two-component mixtures. The obtained Pt, Pd, and Rh precipitates have the catalytic ability of the catalytic reaction of p-nitrophenol to p-aminophenol. The morphological characteristic of the PGM precipitates was analyzed by AFM, SEM-EDS, and TEM.     

Formation of Silver Nanoparticles by Electron Transfer in Peptides and c-Cytochromes

The reduction of Ag⁺ ions to Ag⁰ atoms is a highly endergonic reaction step, only the aggregation to Ag_n clusters leads to an exergonic process. These elementary chemical reactions play a decisive role if Ag nanoparticles (AgNPs) are generated by electron transfer (ET) reactions to Ag⁺ ions. We studied the formation of AgNPs in peptides by photoinduced ET, and in c-cytochromes by ET from their Fe²⁺/hemes. Our earlier photoinduced experiments in peptides had demonstrated that histidine prevents AgNP formation. We have now observed that AgNPs can be easily synthesized with less-efficient Ag⁺-binding amino acids, and the rate increases in the order lysine<asparagine<aspartate<serine. The ability of Fe²⁺/hemes of c-cytochromes to reduce Ag⁺ to AgNPs was studied in an enzymatic experiment and with living bacteria Geobacter sulfurreducens (Gs).     

In-Situ Formation of AgCl Nanocrystallites in Films Prepared by the Sol-Gel and Silver Nanoparticles in Silica Glass Films

We are reporting on a novel preparation of silver chloride in sol-gel silica films as a precursor for nanoparticles of silver. The precipitation of silver chloride particles in-situ was achieved by the reaction of silver nitrate with trichloroacetic acid. The reaction leads to a slow release of chloride leading to a controlled precipitation of AgCl. The existence of an isotropic crystalline AgCl phase in the glass films was demonstrated by X-rays Diffraction Analysis (XRD) and Scanning Electron Microscope and Energy Dispersive Analysis of X-rays (SEM-EDAX). The resulting films are of good optical quality and exhibit a strong coloration upon irradiation with sunlight or heating to 600°C, due to the reduction of AgCl to silver nanoparticles. The absorption spectra of the films before and after irradiation are shown.     

Silver(I) and Silver(II) Complexes with Some Tetraazamacrocyclic Ligands in Aqueous Solutions

The reactions of silver(I) with isocyclam, scorpiand,trans-Me₂[14]anN₄, cis-Me₆[14]anN₄,(N-Me)Me₂py[14]anN₄ and py[12]anN₄ were investigated.The stability constant of the Ag(I) complex with py[12]anN₄ was determined. The aqueous solutions of the silver(II) complexes with the 14-membered ligands were obtained, and characterized by means of UV-VIS and CVA measurements. The Ag²⁺ ion does not form a five-coordinate complex with scorpiand. The formal potentials of the Ag(II)/Ag(I) system in the presence of scorpiand, trans-Me₂[14]anN₄, cis-Me₆[14]anN₄ and(N-Me)Me₂py[14]anN₄ were determined. The mechanism is also proposedfor the electroreduction of the silver(II) complexes with these compounds on a platinum electrode in aqueous solution.     

纳米银形状控制合成与聚合物纳米银复合材料

纳米银(Ag NPs)由于其独特的物理、化学和生物学特性备受研究人员的关注.纳米银应用性能除了受到粒子尺寸、分布、纯度等因素影响,还与纳米银的形状密切相关.纳米银的形状对纳米银的抗菌性能、光学性能以及聚合物纳米银复合材料的综合性能都会产生重要影响.纳米银的形状控制合成可以进一步发挥聚合物纳米银复合材料的性能潜力.因此,不断发展纳米银新的合成方法,研究纳米银形状控制的机理就显得尤为重要.本文综述了纳米银合成方法和不同形状纳米银的最新研究进展,合成方法重点介绍了辐射法、激光烧蚀法、电化学法、光化学法和生物合成法,评述了这些方法的优缺点;同时从模板法、动力学、热力学以及氧化刻蚀4个方面介绍了纳米银形状控制的机理.介绍了聚合物纳米银复合材料的研究进展.     

Effect of Poly(Vinyl Alcohol) on the Size,Shape, and Rate of Silver Nanoparticles Formation

The kinetics of cetyltrimethylammonium bromide (CTAB) stabilized silver nanoparticles have been studied spectrophotometrically at 425 nm (λ_max of silver sol) in the absence and presence of water soluble polymer (poly(vinyl alcohol); PVA). Transmission electron microscopy (TEM), ultraviolet-visible spectroscopy, and viscosity measurements were used to determine the size, shape, and the size distribution of the silver nanoparticles. The reaction follows the same behavior with respect to [CTAB], [tri-sodium citrate], and [Ag⁺] in both the media indicating the silver nonoparticles were formed through the same reaction path. The sigmoid nature of the kinetic curves suggests an autocatalytic path in the growth of nanoparticles. The reaction rate is increased by increasing [CTAB]. The presence of PVA inhibits nucleation and retards the rate of particle growth, absorbance and size of the particles. Polymer-surfactant interactions were analyzed based on the viscosity of the reaction mixture.     

基于银纳米粒子的生成测定痕量甲醛

在碱性溶液中甲醛能还原Ag~+得到黄色银纳米粒子,使体系的共振光散射(RLS)强度增强,从而建立起测量环境中痕量甲醛的RLS新方法. 结果表明,新建方法测定甲醛的浓度线性范围为1.0×10~(-6)～2.0×10~(-5) mol/L,检出限为1.0×10~(-7) mol/L,样品加标测定的回收率为96.26%～103.32%. 并且不同浓度的甲醛还原Ag~+得到黄色银纳米粒子的颜色明显不同,基于此建立了一种可视化半定量测定痕量甲醛的新方法,此方法简便快速、灵敏度高. 用于环境水样、室内空气中甲醛的测定,结果满意.     

Silver(I) Oxide-/DBU-Promoted Synthesis of Dihydrofuran Units through Allenyl Silver Formation

A formal [3+2] cyclization mediated by silver(I) oxide and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) is described herein. Through a broad variety of carbonyl compounds, this system can promote cyclization reactions with high yield (up to 85 %) and diastereoselectivity (up to 95:5) for a straightforward access to complex and congested dihydrofuran derivatives in one step under mild conditions. Based on DFT studies, the proposed mechanism would involve an allenyl silver intermediate.     

Surface and structural properties of pt/ceo2catalyst under preferential co oxidation in hydrogen (PROX)

Summary Preferential oxidation of CO in the presence of excess hydrogen was studied on Pt/CeO₂with 5% metal loading. Catalytic data were similar to those observed on 1% Pt/CeO₂earlier [16]. The optimum temperature region is T￡373 K; conversion and selectivity of CO oxidation strongly decreased at higher temperatures. High-pressure XPS indicated CO adsorbed on platinum particles and significant amount of water on the ceria surface. The top-most ceria surface re-oxidized as small amount of oxygen (3%) was introduced into the H₂/CO feed. Despite this surface re-oxidation, high-resolution TEM after reaction indicated oxygen deficient ceria bulk structure, in which the defects formed a super-cell, with CeO_1.695structure. The defective ceria is suggested to play an important role stabilizing the hydrogen bonded surface water, which (i) suppresses further hydrogen oxidation and (ii) reacts at the metal/support interface with linearly adsorbed CO in a low temperature water-gas-shift type reaction to produce CO₂.</o:p>     

Application of Imidazolylazo Resin : Separation of Palladium(II), Silver(I) from Synthetic Mixtures,Medicinal and Geological Samples

ABSTRACT

A resin (I) containing imidazolylazo functional group has been used for the separation and preconcentration of palladium(II) and silver(I) from other metal ions in synthetic mixture, ores, alloys and medicinal samples. No interference could be observed from alkali and alkaline earth metal. Palladium(II) is quantitatively separated from ores and platinum wire without interferences.     

Electron Transfer in Peptides: On the Formation of Silver Nanoparticles

Some microorganisms perform anaerobic mineral respiration by reducing metal ions to metal nanoparticles, using peptide aggregates as medium for electron transfer (ET). Such a reaction type is investigated here with model peptides and silver as the metal. Surprisingly, Ag⁺ ions bound by peptides with histidine as the Ag⁺‐binding amino acid and tyrosine as photoinducible electron donor cannot be reduced to Ag nanoparticles (AgNPs) under ET conditions because the peptide prevents the aggregation of Ag atoms to form AgNPs. Only in the presence of chloride ions, which generate AgCl microcrystals in the peptide matrix, does the synthesis of AgNPs occur. The reaction starts with the formation of 100 nm Ag@AgCl/peptide nanocomposites which are cleaved into 15 nm AgNPs. This defined transformation from large nanoparticles into small ones is in contrast to the usually observed Ostwald ripening processes and can be followed in detail by studying time‐resolved UV/Vis spectra which exhibit an isosbestic point.     

银纳米粒子的一步合成与表征

在水和乙醇溶液中,以对巯基苯胺作为还原剂,利用一步法合成了银纳米微粒,并利用拉曼光谱仪考察了对巯基苯胺在银纳米微粒表面的自组装行为.结果表明,合成的银纳米微粒的形貌与介质的pH值密切相关;对巯基苯胺可在银纳米微粒表面自组装.     

Facile Synthesis of Catalytically Active Platinum Nanosponges,Nanonetworks, and Nanodendrites

Facile synthesis : Pt nanosponges, nanonetworks, and nanodendrites (see figure) are synthesized through a unique galvanic replacement reaction between Te nanowires and PtCl₆^2? ions in the presence of sodium dodecyl sulfate. The three Pt nanomaterials all have large active surface areas and highly electrocatalytic activities for the oxidation of methanol.

     

Gold(I) and Silver(I) Complexes of Diphosphacyclobutadiene Cobaltate Sandwich Anions

The synthesis and structural characterization of the first coordination compounds of bis(diphosphacyclobutadiene) cobaltate anions [M(P₂C₂R₂)₂]^? is described. Reactions of the new potassium salts [K(thf)₃{Co(η⁴‐P₂C₂tPent₂)₂}] ( 1 ) and [K(thf)₄{Co(η⁴‐P₂C₂Ad₂)₂}] ( 2 ) with [AuCl(tht)] (tht=tetrahydrothiophene), [AuCl(PPh₃)] and Ag[SbF₆] afforded the complexes [Au{Co(P₂C₂tPent₂)₂}(PMe₃)₂] ( 3 ), [Au{Co(P₂C₂Ad₂)₂}]_x ( 4 ), [Ag{Co(P₂C₂Ad₂)₂}]_x ( 5 ), [Au(PMe₃)₄][Au{Co(P₂C₂Ad₂)₂}₂] ( 6 ), [K([18]crown‐6)(thf)₂][Au{Co(P₂C₂Ad₂)₂}₂] ( 7 ), and [K([18]crown‐6)(thf)₂][M{Co(P₂C₂Ad₂)₂}₂] ( 8 : M=Au 9 : M=Ag) in moderate yields. The molecular structures of 2 and 3 , and 6 – 9 were elucidated by X‐ray crystallography. Complexes 4 – 9 were thoroughly characterized by ³¹P and ¹³C solid state NMR spectroscopy. The complexes [Au{Co(P₂C₂Ad₂)₂}]_x ( 4 ) and [Ag{Co(P₂C₂Ad₂)₂}]_x ( 5 ) exist as coordination polymers in the solid state. The linking mode between the monomeric units in the polymers is deduced. The soluble complexes 1 – 3 , 6 , and 7 were studied by multinuclear ¹H‐, ³¹P{¹H}‐, and ¹³C{¹H} NMR spectroscopy in solution. Variable temperature NMR measurements of 3 and 6 in deuterated THF reveal the formation of equilibria between the ionic species [Au(PMe₃)₄]⁺, [Au(PMe₃)₂]⁺, [Co(P₂C₂R₂)₂]^?, and [Au{Co(P₂C₂R₂)₂}₂]^? (R=tPent and Ad).     

In Situ Formation of a Uniform Distribution of Silver Nanoparticles in PVDF: Kinetics of Formation and Resulting Properties

Hybrid organic/silver nanoparticle thermoplastic films have been prepared using a single step process where the silver nanoparticles were formed during a cure cycle applied to the film. Figure 1 is a TEM demonstrating the ability of our technique to produce silver nanoparticles in the semi-crystalline polymer Poly(vinylidene fluoride) (PVDF). The current laboratory focus is on characterizing kinetics and particularly the diameter growth and inter-particle distance as a function of time and temperature using the techniques of small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). Using the Beaucage model, the SAXS data demonstrates that the particle size reaches equilibrium after approximately 70 minutes of curing at 240 °C. This result is also observed in the XRD results where the half width of the diffraction peaks becomes smaller quickly during the initial hour. In a parallel experiment using DSC, the exothermic heat flow increases rapidly during the first hour but does not reach completion until almost 150 minutes.     

Characterization and Evaluation of Antimicrobial Potential of Trigonella incise (Linn) Mediated Biosynthesized Silver Nanoparticles

The goal of the research was to explore a new green method used to synthesize silver nanoparticles (Ag NPs) from an aqueous extract of Trigonella incise, which serves as a reducing and stabilizing agent. The obtained results showed an 85% yield of nanoparticles by using 2:5 (v/v) of 5% plant extract with a 0.5 M solution of AgNO₃. Different techniques were used to characterize the synthesized Ag NPs, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and UV–visible spectroscopy. The UV–visible spectra of green synthesized silver nanoparticles showed maximum absorption at a wavelength of 440 nm. The FT-IR studies revealed the stretching oscillation frequency of synthesized silver nanoparticles in the absorption band near 860 cm⁻¹. Similarly, the bending and stretching oscillation frequencies of the NH function group were assigned to the band in the 3226 cm⁻¹ and 1647 cm⁻¹ regions. The bending vibration of C-O at 1159 cm⁻¹ confirmed the carbonyl functional group that was also assigned to the small intensity band in the range of 2361 cm⁻¹. The X-ray diffraction analysis of Ag NPs revealed four distinct diffraction peaks at 2θ of 38°, 45°, 65° and 78°, corresponds to (111), (200), (220) and (311) of the face-centered cubic shape. The round shape morphology of Ag NPs with a mean diameter in the range 20–80 nm was analyzed via SEM images. Furthermore, the nanoparticles showed more significant antimicrobial activity against Salmonella typhi (S. typhi) and Staphylococcus aureus (S. aureus) with an inhibition zone of 21.5 mm and 20.5 mm at 6 μg/mL concentrations, respectively, once compared to the standard reference. At concentrations of 2 µg/mL and 4 µg/mL, all of the bacterial strains showed moderate activity, with inhibition zones ranging from 11 mm to 18.5 mm. Even at high concentrations of AgNPs, S. typhi showed maximum resistance. The best antifungal activity was observed by synthesized Ag NPs against Candida albicans (C. albicans) with 21 mm zone of inhibition, as compared to a standard drug which gives 22 mm of inhibition. Therefore, we conclude that the antibacterial and antifungal activities showed satisfactory results from the synthesized Ag NPs.