Synthesis and fluorescence properties of CdSe/CdS nanoparticles in aqueous media

On the basis of unique structural characteristics of α-cyclodextrin,α-cyclodextrin modified CdSe/CdS nanoparticles have been successfully synthesized in aqueous media.Techniques of AFM,TEM,EDS,FTIR,UV-vis absorbance and photoluminescence spectra were used to characterize the morphology,composition and optical characteristics of the synthesized nanoparticles.The results showed that the as-synthesized nanoparticles were elliptical and composed of several small particles.Their average length and diameter were ...     

Versatile phase transfer of gold nanoparticles from aqueous media to different organic media

A novel, simple, and very efficient method to prepare hydrophobically modified gold particles is presented. Gold nanoparticles of different sizes and polydispersities were prepared. The diameter of the gold particles ranges from 5 to 37 nm. All systems were prepared in aqueous solution stabilized by citrate and afterwards transferred into an organic phase by using amphiphilic alkylamine ligands with different alkyl chain lengths. The chain length was varied between 8 and 18 alkyl groups. Depending on the particle size and the alkylamine, different transfer efficiencies were obtained. In some cases, the phase transfer has a yield of about 100%. After drying, the particles can be redispersed in different organic solvents. Characterization of the particles before and after transfer was performed by using UV/Vis spectroscopy, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS) techniques. The effect of organic solvents with various refractive indices on the plasmon band position was investigated.     

Semiconductor nanoparticles for photoinitiation of free radical polymerization in aqueous and organic media

Photoinduced free radical polymerization of vinyl monomers by using semiconductor inorganic nanoparticles (NPs) is investigated. Zinc oxide and iron‐doped zinc oxide were used as photosensitive compounds to initiate the polymerization of acrylamide as a water‐soluble monomer in aqueous environment and methyl methacrylate as an oil‐soluble monomer in organic media under UV‐light irradiation. The method uses photochemically generated electrons and holes from the NPs to form initiating hydroxyl radicals in aqueous media, while tertiary amines and iodonium salt served as coinitiator in organic media. The initiation mechanism in organic media involves hydrogen abstraction or reduction processes via charge carriers, respectively. The kinetic of the polymerization in both environments was studied by means of a photo‐differential scanning calorimetry. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1500–1507     

CD inversion and fluorescence enhancement in organic nanoparticles of (R)-di-2-naphthylprolinol

The positive exciton coupling circular dichroism (ECCD) exhibited by monomer of (R)-di-2-naphthylprolinol in organic solvent is inverted to be negative upon the formation of its nanoparticles.     

Rate enhancement of PFP sulfonate ester aminolysis by chloride salts in organic and aqueous media

We report here, a method of accelerating the rate of aminolysis of PFP sulfonates to yield sulfonamides using tetrabutylammonium salts. We have previously explored the utility of employing PFP sulfonates in the formation of sulfonamides; however we demonstrate here the advantages of combining the existing methodology with a revised protocol which allows the diversity within both the sulfonate ester and the amine to be extended.     

Application of organoclays for the adsorption of recalcitrant organic molecules from aqueous media

Water purification is imperative for the welfare of a healthy population. Water is widely contaminated by recalcitrant organic chemicals such a pesticides, herbicides and hormones. One inexpensive method for purifying water from these types of molecules is through adsorption. One suite of materials for this adsorption is based upon organoclays. This paper reviews the adsorption of organics on organoclays.     

Synthesis of dendrimer-protected TiO2 nanoparticles and photodegradation of organic molecules in an aqueous nanoparticle suspension

Dendrimer-protected TiO2 nanoparticles were synthesized by hydrolysis of TiCl4 in solutions of poly(amido amine) dendrimers (64 terminals) under cooling. The morphology of dendrimers surrounding TiO2 nanoparticles depended on the terminal groups (amine, carboxyl, hydroxy) of dendrimers. The size (4.4-6.7 nm) of dendrimer-protected TiO2 nanoparticles was slightly smaller than that (7.5 nm) of bare TiO2 nanoparticles. The photodegradation of 2,4-dichlorophenoxyacetic acid revealed that dendrimer-protected TiO2 nanoparticles are more active as a photocatalyst than TiO2 nanoparticles without protectors. This suggests that the dendrimer acts as a reservoir of photoreacting reagents besides acting as a protector of nanoparticles.     

Light scattering study of solubilization of organic molecules by block copolymer micelles in aqueous media

Block copolymers, when dissolved in a selective solvent, form spherical micelles. These micelles can selectively solubilize organic molecules otherwise insoluble in the pure solvent. In this study, we report solubilization of organic molecules by styrene-methacrylic acid block copolymer micelles in aqueous buffers. A light scattering technique was developed to determine the extent of micellar solubilization. Our results indicate that the extent of micellar solubilization depends on the chemical nature of organic molecules, specifically, on the interactions between the organic compound and polystyrene. A thermodynamic model has been developed to describe micellar solubilization. The theoretical calculation agrees reasonably well with the experimental results for two micellar samples examined. ©1995 John Wiley & Sons, Inc.     

Phase transfer of platinum nanoparticles from aqueous to organic solutions using fatty amine molecules

In this report we demonstrate a simple process based on amine chemistry for the phase transfer of platinum nanoparticles from an aqueous to an organic solution. The phase transfer was accomplished by vigorous shaking of a biphasic mixture of platinum nanoparticles synthesised in an aqueous medium and octadecylamine (ODA) in hexane. During shaking of the biphasic mixture, the aqueous platinum nanoparticles complex via either coordination bond formation or weak covalent interaction with the ODA molecules present in the organic phase. This process renders the nanoparticles sufficiently hydrophobic and dispersible in the organic phase. The ODA-stabilised platinum nanoparticles could be separated out from hexane in the form of a powder that is readily redispersible in weakly polar and non-polar organic solvents. The ODA-capped platinum nanoparticles show high catalytic activity in hydrogenation reactions and this is demonstrated in the efficient conversion of styrene to ethyl benzene. The nature of binding of the ODA molecules to the platinum nanoparticles surface was characterised by thermogravimetry, transmission electron microscopy (TEM), X-ray photoemission spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR)     

Electrochemical behavior of small biological molecules at organic donor—acceptor electrodes in aqueous media

The electrochemical behavior of NADH, xanthine, uric acid, 6-mercaptopurine, 6-thioxanthine, dopamine and ascorbic acid was investigated at the organic metal-like polymer paste electrodes, tetrathiafulvalene- and N-methylphenazene-tetracyanoquinodimethane. The reactivity of small biological molecules at polymer paste electrodes is generally lower than at most active graphite electrodes. Typical detection limits of about 10^?5 M and the typical upper limit of linearity of 10^?3 M are observed for the compounds studied.     

Phase transfer of silver nanoparticles from aqueous to organic solutions using fatty amine molecules

We demonstrate the phase transfer of silver nanoparticles synthesized in an aqueous medium into hexane containing the cationic surfactant octadecylamine (ODA). During vigorous shaking of the biphasic mixture, rapid phase transfer of the silver nanoparticles into the organic phase was observed. The phase transfer of the silver nanoparticles arises due to coupling of the silver nanoparticles with the ODA molecules present in organic phase via either coordination bond formation or weak covalent interaction. This process renders the nanoparticles sufficiently hydrophobic and dispersible in the organic phase. The ODA-stabilized silver nanoparticles could be separated out from the organic phase in the form of a powder and are readily redispersible in different organic solvents. The nature of binding of the ODA molecules to the silver nanoparticle surface was characterized using UV-vis spectroscopy, thermogravimetry, transmission electron microscopy, nuclear magnetic resonance spectroscopy, X-ray photoemission spectroscopy, and Fourier transform infrared spectroscopy.     

Highly sensitive fluorescence "turn-on" indicator for fluoride anion with remarkable selectivity in organic and aqueous media

A simple, convenient, and inexpensive method has been developed to quantitatively determine fluoride anion concentration in acetonitrile as well as in water. The method exhibited a high selectivity and a great sensitivity toward fluoride anions through "turn-on" chromogenic and fluorogenic dual modes. The fluoride driven silyl deprotection and the subsequent spectral changes of hydroxyl coumarin were the operating foundations for the observed selectivity and sensitivity. (1)H NMR spectral titration with F(-) revealed that complete deprotection of a triisopropylsilyl (TIPS) group needed exactly 1 equiv of TBAF. UV-vis and fluorescence titration studies exhibited the appearance of a new intense absorption band centered at 434 nm and green emission peak at 500 nm, accompanied by bright yellow color development to the naked eye. An easy-to-prepare test paper, obtained by dipping the paper into the solution of TIPS-protected coumarin derivative, was able to detect F(-) in aqueous media. The method has also shown highly promising results in detecting all kinds of fluoride salts, regardless of being organic or inorganic, and thus could be potentially useful in real applications.     

Development of calixarene-based host molecules for peptides in aqueous media

We synthesized a peptidocalix[4]arene library consisting of 1000 members that was suitable for peptide recognition in aqueous media. Some peptidocalix[4]arenes in the library were host molecules for guest peptides. Electrostatic interaction between the host and guest molecules was the most important factor for binding in aqueous media.     

Modulation of fluorescence through coassembly of molecules in organic nanostructures

This paper describes the fluorescence of bimolecular coassemblies that form one-dimensional nanostructures. One molecule is a fluorescent peptide amphiphile containing its branched stilbene chromophore covalently linked to the hydrophilic end of the amphiphile, and the second molecule is a shorter, nonfluorescent peptide amphiphile of complementary charge. Using circular dichroism we observe that mixing both molecules results in coassemblies that exhibit a beta-sheet signature in the peptide region indicative of these types of nanostructures. The nature of the coassembly is dependent on the molar ratio of each component, and the changing CD spectra suggest the formation of domains along the length of the nanofibers with decreasing concentrations of the fluorescent component. In coassemblies with dilute concentrations of the fluorophore, we observe an increase in fluorescence intensity and quantum yield, as well as chiral transfer to the achiral segment of the fluorescent peptide amphiphile. The coassemblies studied containing a fluorescent component at a low molar ratio exhibit fluorescence resonance energy transfer to fluorescent acceptors in solution. When the nonfluorescent peptide amphiphile component is designed to bind the important bioactive polysaccharide heparin, a selective transfer of energy is observed between fluorescein-tagged heparin and the coassemblies in both dilute solution and in macroscopic gels.     

Ligand-free CuCl-catalyzed C-N bond formation in aqueous media

CuCl-catalyzed N-arylation of alkyl amines and N-heterocycles with substituted aryl iodides and bromides can be carried out in 40% ⁿBu₄N⁺OH⁻ aqueous solution without any ligands.     

Radical formation during phenol oxidation in aqueous media

Kinetics of oxygen consumption, reaction product formation, and chemiluminescence during polyphenol oxidation by molecular oxygen in alkaline aqueous media with additions of l ‐ascorbic acid (AscH₂) and homocysteine (HCys) has been investigated. In these processes, AscH₂ and HCys have been shown to act as typical radical‐reaction inhibitors that can be used for determinations of the radical formation rates. The rates of radical formation during oxidation of hydroquinone (p‐QH₂), chlorohydroquinone (Cl‐QH₂), 2,5‐dichlorohydroquinone (2,5Cl‐QH₂), catechol (PK), 4‐methylcatechol (4CH₃‐PK), pyrogallol (PG), gallic acid (GK) have been estimated. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 414–422, 2012     

Vapor-phase extraction of organic substances from aqueous media

A method for the vapor-phase extraction of dissolved organic substances from an aqueous medium into an organic solvent was developed. This method allowed us to introduce hydrophilic extractants into extraction. The experimental results were discussed in terms of the kinetic model proposed for the mechanism of vapor-phase extraction. The analytical capabilities of this method were demonstrated using the study of sulfide mineral waters as an example.     

Rates of ionic reactions with charged nanoparticles in aqueous media

A theory is developed to evaluate the electrostatic correction for the rate of reaction between a small ion and a charged ligand nanoparticle. The particle is assumed to generally consist of an impermeable core and a shell permeable to water and ions. A derivation is proposed for the ion diffusion flux that includes the impact of the equilibrium electrostatic field distribution within and around the shell of the particle. The contribution of the extra- and intraparticulate field is rationalized in terms of a conductive diffusion factor, f(el), that includes the details of the particle geometry (core size and shell thickness), the volume charge density in the shell, and the parameters defining the electrostatic state of the particle core surface. The numerical evaluation of f(el), based on the nonlinear Poisson-Boltzmann equation, is successfully complemented with semianalytical expressions valid under the Debye-Hückel condition in the limits of strong and weak electrostatic screening. The latter limit correctly includes the original result obtained by Debye in his 1942 seminal paper about the effect of electrostatics on the rate of collision between two ions. The significant acceleration and/or retardation possibly experienced by a metal ion diffusing across a soft reactive particle/solution interphase is highlighted by exploring the dependence of f(el) on electrolyte concentration, particle size, particle charge, and particle type (i.e., hard, core/shell, and entirely porous particles).