Bending contours in silver nanoprisms

A detailed electron microscopy analysis is reported on the structure of silver nanoprisms synthesized by controlled photoinduced aggregation of Ag nanoparticles. Bending of the nanoprism (111) face is directly revealed in the presence of fringes in both bright and dark field TEM images, which are unequivocally assigned to bending contours. Such contours can be individually imaged through shifting of the objective aperture and selectively allowing transmission of the corresponding diffraction spot. The assignment of a bent structure is supported by images of the lateral sides of the prisms, and high-resolution images where apparent changes in the lattice constant are observed.     

Selectively colorimetric detection of cysteine with triangular silver nanoprisms

Triangular silver nanoprisms were prepared and applied to make colorimetric detection of cysteine based on our findings that cysteine could lead to the blue shift of the dipole plasmon resonance absorption,but other 19 kinds of natural amino acids could not.Cysteine with a concentration 160 nmol/L can result in a color change that can be discerned with naked eyes.     

Solubility studies in formamide: III. Solubility product of silver bromate and standard electrode potential of silver—silver bromate electrode in formamide

The solubility and solubility product of silver bromate in formamide in sodium perchlorate solutions have been determined at 25, 30 and 35°C. At these temperatures, the solubilities in pure formamide are found to be 1.837 × 10^?2, 1.967 × 10^?2, and 2.092 × 10^?2 moll^?1, respectively, and the corresponding solubility products are 3.375 × 10^?4, 3.869 × 10^?4, and 4.377 × 10^?4 mol² l^?2. The standard potentials of the Ag(s)/AgBrO₃(s)/BrO^?₃ electrode have been calculated and found to be 0.4997, 0.4948, and 0.4892 V, at 25, 30, and 35°C, respectively. The mean activity coefficients of silver bromate at various rounded molarities of sodium perchlorate solutions, and the standard thermodynamic quantities for the process AgBrO₃(s) → Ag⁺(solvated) + BrO^?₃(solvated) have been calculated at these three temperatures and compared with those for the process AgIO₃(s) → Ag⁺(solvated) + IO^?₃(solvated) in formamide.     

Solubility studies in formamide: II. Solubility product of silver iodate and standard electrode potential of silver—silver iodate electrode in formamide

The solubility and solubility product of silver iodate in formamide in sodium perchlorate solutions have been determined at 25, 30 and 35°C. The solubilities in pure formamide are found to be 2.169 × 10^?4, 2.488 × 10^?4, and 2.943 × 10^?4 mole I^?1, respectively, at these temperatures, and the corresponding solubility products are 4.609 × 10^?8, 6.053 × 10^?8, and 8.448 × 10^?8 mole² 1^?2. The standard potential of the Ag_(s)/AgIO_3(s)/IO₃^? electrode has been calculated and found to be 0.2562 V at 25°C. The mean activity coefficients of silver iodate at various rounded molarities of sodium perchlorate solutions, and the standard thermodynamic quantities for the process AgIO_3(s)åAg⁺ (solvated) + IO₃^? (solvated) have been calculated at these three temperatures.     

Effective chemical route for the synthesis of silver nanostructures in formamide

Poly(N-vinyl-2-pyrrolidone) (PVP) and gelatin protected silver nanostructures are prepared in formamide by simple chemical route. Both PVP and gelatin stabilized silver nanoparticles in formamide lead to the formation of nanostructures of various definite geometric shapes and sizes. The effect of anisotropy on the surface plasmon absorption band is analyzed by monitoring the UV-Visible absorption spectra of gelatin stabilized silver nanoparticles. The particles were characterized by UV-Visible absorption spectra and TEM.     

Preparation, characterization, and surface modification of silver nanoparticles in formamide

The reduction of silver ions in formamide is shown to take place spontaneously at room temperature without addition of any reductant. The growth of Ag particles was found to be dependent on Ag+ ion concentration. In the absence of any stabilizer, deposition of silver film on the glass walls of the container takes place. However, in the presence of poly(N-vinyl-2-pyrrolidone) (PVP) or colloidal silica (SiO2), which are capable of stabilizing silver nanoparticles by complexing and providing support, a clear dispersion was obtained. The formation of the silver nanoparticles under different conditions was investigated through UV-visible absorption spectrophotometry, gas chromatography, and also electron and atomic force microscopic techniques. Atomic force microscopy results for silver films prepared in the absence of any stabilizer showed the formation of polygonal particles with sizes around 100 nm. Transmission electron microscopy results showed that the prepared silver particles in the presence of PVP were around 20 nm. The Ag nanoparticles get oxidized in the presence of chloroform and toluene. Surface modification of silver film was done in the presence of the tetrasodium salt of ethylenediaminetetraaceticacid (Na4EDTA). It was shown that the reactivity of the silver film increased in its presence. The Fermi potential of silver particles in the presence of Na4EDTA seems to lie between -0.33 and -0.446 V vs NHE.     

Photovoltage mechanism for room light conversion of citrate stabilized silver nanocrystal seeds to large nanoprisms

We investigate the photoconversion of aqueous 8 nm Ag nanocrystal seeds into 70 nm single crystal plate nanoprisms. The process relies on the excitation of Ag surface plasmons. The process requires dioxygen, and the transformation rate is first-order in seed concentration. Although citrate is necessary for the conversion, and is consumed, the transformation rate is independent of citrate concentration. We propose a mechanism that accounts for these features by coupling the oxidative etching of the seed and the subsequent photoreduction of aqueous Ag(+). The reduced Ag deposits onto a Ag prism of specific size that has a cathodic photovoltage resulting from plasmon "hot hole" citrate photo-oxidation. This photovoltage mechanism also explains recent experimental results involving single and dual wavelength irradiation and the core/shell synthesis of Ag layers on Au seeds.     

Formation of silver nanoparticles in formamide:water mixtures: a radiolytic study

The pulse radiolysis of FA and FA:water solutions was studied in the absence and presence of redox indicator 1,1′-dimethyl-4,4′-bipyridinium dichloride (methyl viologen, MV²⁺). The experiments performed in the presence of MV²⁺ have provided strong support to the idea that the first species obtained from the reaction of e_sol⁻ and ^•OH with FA produces radicals that show reactivity towards the MV²⁺. Both the radicals on reaction with MV²⁺ results in the appearance of the well-known intense blue MV^•+ radical absorption signal (λ_max = 395 nm, λ_max = 605 nm). The intermediate radicals formed during radiolysis were used to generate silver nanoparticles.     

Solubility product and related thermodynamic quantities of silver and barium chromates in formamide

The values of ΔG⁰, ΔH⁰, and ΔS⁰ for the dissolution process, M₂(CrO₄)_x + solvent — 2 M^x+ (solvated) + xCrO₄^2? (solvated), where M is Ag or Ba, and x is 1 or 2, have been determined in formamide from solubility studies. The negative value of ΔS⁰ indicates that there is more order in the dissolved state than in the undissolved state.     

Multipolar excitation in triangular nanoprisms

Theoretical studies on the optical properties of gold triangular prisms in solution are presented to determine how structural modifications affect the extinction spectrum. Well-defined trends in the particle extinction are found to depend on the triangular edge length and the prism thickness. Calculations performed on large, thin triangular prisms indicate multipolar excitation and display numerous peaks in the extinction spectrum. The dominant peaks are assigned to different in-plane modes corresponding to the lowest three orders of a multipole expansion. Vector polarization plots are presented to support the peak assignments. Altering the prisms by snipping off the points of the triangular cross section significantly blueshifts the dipole peak, but the higher-order modes are only slightly affected. Snipping off large volumes can lead to the suppression of high-order multipoles in the extinction spectrum.     

Ultrasensitive visual and colorimetric determination of dopamine based on the prevention of etching of silver nanoprisms by chloride

The authors describe a selective and sensitive colorimetric method for determination of dopamine (DA) in serum. It is based on the protection of silver nanoprisms (AgNPRs) from being etched by chloride ion in the presence of DA. In the absence of DA, the shape of the AgNPRs is changed from triangle nanoplates to round nanodisk due to etching by chloride. This is accompanied by a stepwise color change from blue via purple and red to yellow. It is found that DA is strongly adsorbed on the surface of AgNPRs and thereby acts as a protective agent. As a result, etching by chloride is prevented and the color changes do not occur. This finding ease exploited to design a method for optical quantification of DA with either bare eyes or UV-vis spectrophotometry. The wavelength shift of the in-plane dipole surface plasmon band of the AgNPRs is linearly related to the DA concentration in the range from 0.5 to 100 nM. The detection limit is 0.16 nM (at an S/N ratio of 3) which is lower than that of most existing methods. Uric acid, ascorbic acid and other coexisting species do not interfere. The sensor is reproducible and stable and was applied to the determination of DA in spiked serum samples where it gave recoveries that ranged from 97.4 to 104.3%.

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Graphical abstract A simple and sensitive colorimetric assay for dopamine is presented. It is based on the protection of Ag nanoprism from being etched by halide ion in the presence of dopamine.

     

Anisotropic assembly of Ag nanoprisms

The Ag nanoprisms with controlled arrangements show distinct optical, crystallographic, and surface-enhanced Raman scattering properties depending on their orientation in the assemblies, demonstrating that the controlled assembly of anisotropic nanostructures can be utilized as a powerful tool for studying their physicochemical properties and for the creation of new classes of functional materials.     

2-氨基-4,6-二氯-5-甲酰氨基嘧啶的合成

以丙二酸二乙酯和盐酸胍为起始原料,经环合、亚硝化、还原、氯化、水解得到2-氨基4,6-二氯-5-甲酰氨基嘧啶,总收率20％,其结构经61HNMR和IR表征。     

Synthesis and applications of silver nanoparticles

Over the past few decades, nanoparticles of noble metals such as silver exhibited significantly distinct physical, chemical and biological properties from their bulk counterparts. Nano-size particles of less than 100 nm in diameter are currently attracting increasing attention for the wide range of new applications in various fields of industry. Such powders can exhibit properties that differ substantially from those of bulk materials, as a result of small particle dimension, high surface area, quantum confinement and other effects. Most of the unique properties of nanoparticles require not only the particles to be of nano-sized, but also the particles be dispersed without agglomeration. Discoveries in the past decade have clearly demonstrated that the electromagnetic, optical and catalytic properties of silver nanoparticles are strongly influenced by shape, size and size distribution, which are often varied by varying the synthetic methods, reducing agents and stabilizers. Accordingly, this review presents different methods of preparation silver nanoparticles and application of these nanoparticles in different fields.     

Synthesis of silver nanoclusters in starch aqueous solutions

The capability of aqueous starch solution for reduction of Ag⁺ ions and stabilization of metallic silver nanoparticles was examined. Kinetic parameters of formation of Ag nanoparticles were determined.     

Synthesis and degradation of nucleic acid components by formamide and iron sulfur minerals

We describe the one-pot synthesis of a large panel of nucleic bases and related compounds from formamide in the presence of iron sulfur and iron-copper sulfur minerals as catalysts. The major products observed are purine, 1H-pyrimidinone, isocytosine, adenine, 2-aminopurine, carbodiimide, urea, and oxalic acid. Isocytosine and 2-aminopurine may recognize natural nucleobases by Watson-Crick and reverse Watson-Crick interactions, thus suggesting novel scenarios for the origin of primordial nucleic acids. Since the major problem in the origin of informational polymers is the instability of their precursors, we also investigate the effects of iron sulfur and iron-copper sulfur minerals on the stability of ribooligonucleotides in formamide and in water. All of the iron sulfur and iron-copper sulfur minerals stimulated degradation of RNA. The relevance of these findings with respect to the origin of informational polymers is discussed.     

Synthesis of uniform gold nanoparticles using non-pathogenic bio-control agent: evolution of morphology from nano-spheres to triangular nanoprisms

Green synthesis of gold nanospheres with uniform diameter and triangular nanoprisms with optically flat surface was carried out using a non-pathogenic bio-control agent Trichoderma asperellum for reduction of HAuCl(4). Kinetics of the reaction was monitored by UV-Vis absorption spectroscopy. No additional capping/complexing agent was used for stabilizing the gold nanoparticles. Evolution of morphology from pseudospherical nanoparticles to triangular nanoprisms was studied by transmission electron microscopy (TEM). It revealed that three or more pseudospheres fused to form nanoprisms of different shapes and sizes. Slow rate of reduction of HAuCl(4) by constituents of cell-free fungal extract was instrumental in producing such exotic morphologies. Isolation of gold nanotriangles from the reacting masses was achieved by differential centrifugation.