A mechanistic and kinetic study of the formation of metal nanoparticles by using synthetic tyrosine-based oligopeptides

Synthetic oligopeptides containing redox-active tyrosine residues have been employed to prepare gold and silver nanoparticles. In this reduction process an electron from the tyrosinate ion of the peptide is transferred to the metal ion at basic pH through the formation of a tyrosyl radical, which is eventually converted to its dityrosine form during the reaction. This reaction mechanism was confirmed from UV-visible, fluorescence, and EPR spectroscopy and was found to be pH-dependent. Transmission electron microscopy measurement shows that the average size and the monodispersity of gold nanoparticles increase as the number of tyrosine residues in the peptide increases. The kinetic study, based on spectrophotometric measurements of the surface plasmon resonance optical property, shows that the rate of formation of gold nanoparticles was much faster at higher pH than at lower pH and was also dependent on the number of tyrosine residues present in the peptide. The dityrosine form of the peptide was found to retain reducing properties like those of tyrosine in basic medium.     

Effect of plant-based phenol derivatives on the formation of Cu and Ag nanoparticles

The complexes formed on the reaction of various metal ions viz., Cu(II) and Cu(I) with phenol derivatives viz. catechol, chlorogenic acid (CGA), hydroquinone and n-propyl gallate (nPG) were established by UV-visible spectroscopy. The metal/ligand complexing ratio and complexation constants have been determined. Further, we showed that nanoparticles of Cu can be prepared from metal-phenol complexes in the presence of a protein (gelatin) by γ-irradiation showing that the reduction is metal ion centered. Formation of Ag nanoparticles was also observed on photo-irradiation with xenon lamp in the presence of dihydroxy benzene. The Ag and Cu nanoparticles were characterized by transmission electron microscopy (TEM) and UV-visible absorption spectroscopy. TEM technique showed the presence of Cu and Ag nanoparticles with average size of 20 and 30 nm, respectively.     

Novel Green Route of Synthesis of ZnO Nanoparticles by Using Natural Biodegradable Polymer and Its Application as a Catalyst for Oxidation of Aldehydes

ZnO nanoparticles have been synthesized by using biodegradable natural biopolymer viz. Gum Tragacanth. This single step approach is very cost effective and reproducible. The reaction time and concentration of precursor zinc acetate play a major role in the nature and growth of ZnO nanoparticles. ZnO nanoparticles were characterized by X-ray diffraction, SEM, FTIR, EDAX, UV-visible spectroscopy and TEM. ZnO nanoparticles with 20-30 nm in diameter and hexagonal morphology were found; dispersed uniformly. Raman spectrum shows the mode E₂ high at 437 cm^?1 that is related to the vibration of wurtzite Zn-O bond in crystal structure of ZnO. The space between adjacent lattice fringes is ～ sharp 2.42 Å. UV-visible absorption spectrum shows the sharp absorption band at 308 nm assigned to the intrinsic transition from valance band to conduction band. The ZnO nanoparticles display superior catalytic activity of conversion of aldehyde to acid as compared to bulk-ZnO material, because of high surface area of ZnO nanoparticles. A trace amount of ZnO nanoparticles catalyst required for organic conversion. The ZnO nanoparticles as catalyst are highly stable, recyclable and efficient in its activity.     

Anchoring Ni (II) on Fe3O4@tryptophan: A recyclable,green and extremely efficient magnetic nanocatalyst for one‐pot synthesis of 5‐substituted 1H‐tetrazoles and chemoselective oxidation of sulfides and thiols

A green, novel and extremely efficient nanocatalyst was successfully synthesized by the immobilization of Ni as a transition metal on Fe₃O₄ nanoparticles coated with tryptophan. This nanostructured material was characterized using Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, thermogravimetric analysis, inductively coupled plasma optical emission spectroscopy, vibrating sample magnetometry and X‐ray diffraction. The prepared nanocatalyst was applied for the oxidation of sulfides, oxidative coupling of thiols and synthesis of 5‐substituted 1H‐tetrazoles. The use of non‐toxic, green and inexpensive materials, easy separation of magnetic nanoparticles from a reaction mixture using a magnetic field, efficient and one‐pot synthesis, and high yields of products are the most important advantages of this nanocatalyst.     

Highly Selective and Sensitive Aggregation-Induced Emission of Fluorescein-Coated Metal Oxide Nanoparticles

We report the synthesis, characterization, and photophysical properties of novel metal oxide nanoparticles (NPs) coated with specially designed fluorescein substituents which are capped with electron-withdrawing groups. The fluorescein-coated nanoparticles were synthesized in excellent yields, and their structures were confirmed using various advanced spectroscopic, instrumental, and surface analysis techniques, revealing the formation of the target functionalized nanoparticles (FNPs) which show superior chemical and thermal stabilities. In addition, the photophysical properties of the FNPs were examined using UV-visible absorption and fluorescence spectroscopy. These latter techniques disclosed aggregation-induced emission (AIE) properties for most of the target FNPs, namely those which are soluble in common organic solvents at selective concentration ranges of water fractions in the solvent mixture.     

Dispersible polyaniline nanoparticles in aqueous poly(styrenesulfonic acid) via the interfacial polymerization route

Water-dispersible nanoparticles of polyaniline (PANI) have been conveniently synthesized via the interfacial polymerization route using chemical oxidative polymerization of aniline (ANI) with ammonium peroxodisulfate in aqueous poly(styrenesulfonic acid) (PSS). Various molar feed ratios of ANI/PSS were employed to attain highly dispersible PANI nanoparticles. PSS was used as an anionic dopant and as a template for the formation of PANI nanoparticles. The dispersed PANI nanoparticles were characterized using a Zetasizer, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS). Functional group analysis and the thermal stability of PANI particle dispersions were examined using FT-IR, UV-visible spectroscopy, and thermogravimetry analysis. The particle size of PANI-PSS nanoparticles was controlled by tuning the molar feed ratio of ANI/PSS. A uniform size distribution was obtained with the particle size of 5-15 nm for ANI/PSS ratios less than 1/1.     

Self-assembly of ordered 3D Pd nanospheres at a liquid/liquid interface

A novel route for the self-assembly of nanoparticles to nanospheres at a liquid/liquid interface has been developed to prepare palladium nanospheres. It has proved that the interface offers an excellent site and plays a key role in the self-assembly of nanoparticles to nanospheres. The palladium nanospheres are characterized by electron microscopy, energy-dispersive X-ray analysis, UV-visible spectroscopy, X-ray diffraction spectroscopy, and X-ray photoelectron spectroscopy. The mechanism of the self-assembly process is also proposed.     

四氨基酞菁锌负载二氧化硅纳米粒子的合成及其对细胞毒性的研究

通过在无极核微乳液中水解乙烯基三乙氧基硅烷(TEVS)和3-氨丙基三乙氧基硅烷(APTES),制备了疏水性光敏剂-2,9,16,23-四氨基酞菁锌负载的表面带有正电荷的二氧化硅纳米粒子(SiO2@ ZnPc( NH2)4).通过透射电镜(TEM)、Zetasizer Nano-ZS粒度仪(DLS)、紫外-可见分光光度计...     

Green Synthesis and Characterization of Zinc Oxide Using Carica papaya Leaf Extract

Environmental methodologies are gaining recognition in this modern world. Environmental nanotechnology plays a major role in improving modern fields of environmental engineering and science. Metal oxide nanoparticles have exceptional properties due to their small size, including quantum confinement, surface-to-volume ratio, plasmon excitation, high biocompatibility, and surface modifiability. The biosynthesis of nanoparticles using fungi, bacteria, and plants through various biotechnological techniques is currently a new paradigm for environmental protection. Synthesis of nanoparticles through plant extract is good because it eliminates the dangers of toxic chemicals, it is environmentally friendly, simpler, and safer as the reaction time is reduced and it can also be increased in size for higher operation. The present study is based on the development of zinc oxide nanoparticles from papaya leaf extract where zinc nitrate is used as a precursor. The biosynthesized nanoparticles are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, electron microscopy, energy-dispersive X-ray analysis, UV-visible spectroscopy, and dynamic light scattering analysis. The crystalline phase determination of the zinc oxide nanoparticles is analyzed by X-ray diffraction and the formation of polycrystalline zinc oxide nanoparticles is confirmed. FT-IR spectrum reveals the main functional groups and chemical information in zinc oxide nanostructures. Morphological analysis is performed using SEM at different magnification levels. EDAX analysis shows the purity of the composite samples. Optical characterization is performed using a UV–vis spectrophotometer. DLS analysis shows that the nanoparticles formed have a relatively well-defined dimension.     

First row transition metal ion-assisted ammonia-borane hydrolysis for hydrogen generation

Ammonia-borane (AB) hydrolysis for the generation of hydrogen has been studied using first row transition metal ions, such as Co (2+), Ni (2+), and Cu (2+). In the cases of cobalt- and nickel-assisted AB hydrolysis, amorphous powders are formed that are highly catalytically active for hydrogen generation. Annealing of these amorphous powders followed by powder X-ray diffraction measurements revealed the presence of Co(0) and Co 2B and Ni(0) and Ni 3B, respectively. On the other hand, copper-assisted AB hydrolysis was catalyzed by in situ generated H (+) and Cu(0) nanoparticles. The reduction ability of AB for the realization of coinage metal nanoparticles from the respective metal salts has also been studied. These reduction reactions were found to be facile, affording colloids of pure metal nanoparticles. Nanoparticles prepared in this manner were characterized by UV-visible spectroscopy and high-resolution electron microscopy.     

Microbial synthesis of gold nanoparticles: Current status and future prospects

Gold nanoparticles have been employed in biomedicine since the last decade because of their unique optical, electrical and photothermal properties. Present review discusses the microbial synthesis, properties and biomedical applications of gold nanoparticles. Different microbial synthesis strategies used so far for obtaining better yield and stability have been described. It also includes different methods used for the characterization and analysis of gold nanoparticles, viz. UV–visible spectroscopy, Fourier transform infrared spectroscopy, X ray diffraction spectroscopy, scanning electron microscopy, ransmission electron microscopy, atomic force microscopy, electron dispersive X ray, X ray photoelectron spectroscopy and cyclic voltametry. The different mechanisms involved in microbial synthesis of gold nanoparticles have been discussed. The information related to applications of microbially synthesized gold nanoparticles and patents on microbial synthesis of gold nanoparticles has been summarized.     

Synthesis,Characterization, and Assessment of Anti-Cancer Potential of ZnO Nanoparticles in an In Vitro Model of Breast Cancer

Advanced innovations for combating variants of aggressive breast cancer and overcoming drug resistance are desired. In cancer treatment, ZnO nanoparticles (NPs) have the capacity to specifically and compellingly activate apoptosis of cancer cells. There is also a pressing need to develop innovative anti-cancer therapeutics, and recent research suggests that ZnO nanoparticles hold great potential. Here, the in vitro chemical effectiveness of ZnO NPs has been tested. Zinc oxide (ZnO) nanoparticles were synthesized using Citrullus colocynthis (L.) Schrad by green methods approach. The generated ZnO was observed to have a hexagonal wurtzite crystal arrangement. The generated nanomaterials were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV-visible spectroscopy. The crystallinity of ZnO was reported to be in the range 50–60 nm. The NPs morphology showed a strong absorbance at 374 nm with an estimated gap band of 3.20 eV to 3.32 eV. Microscopy analysis proved the morphology and distribution of the generated nanoparticles to be around 50 nm, with the elemental studies showing the elemental composition of ZnO and further confirming the purity of ZnO NPs. The cytotoxic effect of ZnO NPs was evaluated against wild-type and doxorubicin-resistant MCF-7 and MDA-MB-231 breast cancer cell lines. The results showed the ability of ZnO NPs to inhibit the prefoliation of MCF-7 and MDA-MB-231 prefoliation through the induction of apoptosis without significant differences in both wild-type and resistance to doxorubicin.     

Green synthesis of well-dispersed gold nanoparticles using Macrotyloma uniflorum

The synthesis of metal nanoparticles of different sizes, shapes, chemical composition and controlled monodispersity is an important area of research in nanotechnology because of their interesting physical properties and technological applications. Present work describes an eco-friendly method for the synthesis of spherical gold nanoparticles using aqueous extract of Macrotyloma uniflorum. The effects of quantity of extract, temperature and pH on the formation of nanoparticles are studied. The nanoparticles are characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and FTIR analysis. The high crystallinity of nanoparticles with fcc phase is evident from HRTEM images, SAED and XRD patterns. Synthesized nanoparticles have size in the range 14-17nm. FTIR spectrum indicates the presence of different functional groups present in the bio-molecule capping the nanoparticles. The possible mechanism leading to the formation of gold nanoparticles is suggested.     

One‐step Hydrothermal Synthesis and Assembly of Copper and Silver Nanoparticles to Aggregates in Glyoxal Reduction System

A simple hydrothermal process has been developed for the synthesis and assembly of copper and silver nanoparticles to aggregates. The reduction of Cu²⁺ and Ag⁺ ions to the zerovalent metal was performed by glyoxal in the absence of any external agent. The produced glyoxylic acid (GA) in the redox process stabi‐ lized metallic copper and silver particles and rendered them oxidation resistant for several months and dispersible in polar organic solvents and water. Detailed nanostructures of synthesized products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD). The results demonstrated that assembly of nanoparticles to aggregates and their regularity were dependent on the reaction conditions such as temperature and concentration of the starting material. The Ostwald ripening process was proposed to explain the formation of copper nanoparticles by TEM observation at several times during the reaction. The existence of the surface stabilizing agent was identified by Fourier Transform infrared spectroscopy (FT‐IR) and thermogravimetric analyses (TGA).     

In situ synthesis of gold and silver nanoparticles by using redox-active amphiphiles and their phase transfer to organic solvents

An in situ reduction approach to synthesizing gold and silver nanoparticles by using a series of newly designed, redox-active amphiphiles at basic pH is described. These amphiphiles are the conjugates of a fatty acid (e.g., oleic acid, stearic acid, and lauric acid) and a redox-active amino acid (e.g., tryptophan or tyrosine). The amphiphile-coated nanoparticles are then efficiently transferred from water to different nonpolar organic media (such as benzene, toluene, xylene, cyclohexane, and hexane) simply by acid treatment. The phase-transfer process was monitored by UV/visible spectroscopy and transmission electron microscopy, and the results showed that the average particle size and size distribution remain almost unchanged after transferring to the organic media. The anchoring of the amphiphile to the nanoparticle surface was confirmed by FTIR spectroscopy and thermogravimetric analysis. A mechanism is proposed to describe the stability of colloidal Au and Ag nanoparticles formed in situ and their phase transfer to organic solvents. The presence of the amphiphile increases the thermal stability of the colloidal gold nanoparticle conjugates in organic solvents.     

Synthesis of a stable gold hydrosol by the reduction of chloroaurate ions by the amino acid, aspartic acid

Development of reliable protocols for the synthesis of nanoparticles of well-defined sizes and good monodispersity is an important aspect of nanotechnology. In this paper, we present details of the synthesis of gold nanoparticles of good monodispersity by the reduction of aqueous chloroaurate ions by the amino acid, aspartic acid. The colloidal gold solution thus formed is extremely stable in time, indicating electrostatic stabilization via nanoparticle surface-bound amino acid molecules. This observation has been used to modulate the size of the gold nanoparticles in solution by varying the molar ratio of chloroaurate ions to aspartic acid in the reaction medium. Characterization of the aspartic acid-reduced gold nanoparticles was carried out by UV-visible spectroscopy, thermogravimetric analysis and transmission electron microscopy. The use of amino acids in the synthesis and stabilization of gold nanoparticle in water has important implications in the development of new protocols for generation of bioconjugate materials.     

酪氨酸与色氨酸间电子转移——氧化还原活性及电子跃迁能的从头算研究

在HF/6-31G和GASSCF/6-31G水平上对色氨酸和酪氨酸间的电子转移进行了理论 研究。用类导体屏蔽模型考察体系的溶剂效应。通过对给、受体几何构型的优化, 计算了孤立的给、受体之间电子转移反应的内重组能和反应能差。分别用 Koopmans定理和CASSCF/6-31G方法计算了色氨酸和酪氨酸的电离能。计算了此两种 氨基酸从基态到最低激发态的跃迁能。理论计算结果很好地解释了N_3~·高选择性 地氧化色氨酸残基,并诱发电子从酪氨酸残基向色氨酸残基转移的实验现象。     

A simple method for measuring the size of metal nanoclusters in solution

The connection between quantum size effects and the surface plasmon resonance of metal nanoclusters is introduced and the pros and cons of in situ and ex situ cluster analysis methods are outlined. A new method for estimating the size of nanoclusters is presented. This method combines core/shell cluster synthesis, UV-visible spectroscopy, and Mie theory. The core/shell approach enables the estimation of metal cluster sizes directly from the UV-visible spectra, even for transition metal nanoclusters such as Pd that have no distinct surface-plasmon peak in UV-visible region. Pd/Au and Au/Pd core/shell clusters as well as Au-Pd alloy clusters are synthesized and used as test cases for simulations and spectroscopic measurements. The results of the simulations and UV-visible spectroscopy experiments are validated with transmission electron microscopy.     

Promising anticancer mono- and dinuclear ruthenium(III) dithiocarbamato complexes: systematic solution studies

During the last decade, our research group has prepared a number of metal dithiocarbamato derivatives of Pt, Pd and Au that were expected to resemble the main features of cisplatin together with higher activity, improved selectivity and bioavailability, and lower side-effects. Furthermore, we have already published the synthesis, characterization and in vitro cytotoxicity studies of novel ruthenium(III) dithiocarbamato complexes such as [RuL(3)] monomers (11) and α-[Ru(2)L(5)]Cl dimers (12) with five different dithiocarbamate ligands. As both the monomer and the dinuclear complexes have shown significant antitumor activity in different human tumor cell lines, we decided to widen the characterization studies and to analyse thoroughly their behavior in physiological-like medium by UV-visible and CD spectroscopy. In the present paper we report on the crystal structure of [Ru(DMDT)(3)], [Ru(PDT)(3)] and [Ru(ESDT)(3)] complexes and we determine the spin state of the paramagnetic Ru(III) by means of Evans' method. Then, we discuss in detail the UV-visible spectral data of the complexes in different medium. All the studied complexes are stable in dimethyl sulfoxide, and show low solubility in phosphate buffered saline solution, particularly the monomer species, even at low concentration, while increased solubility for both types of complexes have been found in the presence of bovine serum albumin (BSA). Moreover, no changes on the coordination sphere of the metal, as well as no direct interaction between the BSA protein and the complex have been identified by UV-visible spectroscopy. However, some conformational changes on the BSA structure, induced by the ruthenium(III) complexes have been confirmed by CD spectroscopy, indicating a probable secondary electrostatic interaction between the metal complex and the peptide. In addition, no significant interaction has been demonstrated with the components of Dulbecco's Modified Eagle's Medium, used for the in vitro assays.     

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.