Photoluminescence Properties of Silica Xerogels Co‐doped with Eu3+ Ions and CdS Nanoparticles

Silica xerogels doped with Eu³⁺ ions and co‐doped with Eu³⁺ ions and CdS nanoparticles were prepared using a two‐step hydrolysis process. The effect of temperature on photoluminescence properties of Eu³⁺‐doped silica xerogel was investigated. The results showed that the photoluminescence of Eu³⁺‐doped silica xerogel was significantly dependent on the temperature of heat treatment. The study of the photoluminescence of co‐doped xerogels showed that the defect emission of silica was weakened due to competition among defects, CdS nanoparticles, and Eu³⁺ ions.     

A Novel DNA‐Enrichment Technology Based on Amino‐Modified Functionalized Silica Nanoparticles

Abstract

In this paper we report a novel DNA‐enrichment technology based on amino‐modified functionalized silica nanoparticles. The approach takes advantage of the amino‐modified silica nanoparticles that have been prepared in one step by the controlled synchronous hydrolysis of tetraethoxysilane and N‐(β‐amimoethyl)‐γ‐aminopropyltriethoxysilane in water nanodroplets of water‐in‐oil microemulsions. The functionalized silica nanoparticles display a positive surface charge at neutral pH due to the presence of amino groups on the surface of these nanoparticles. DNA‐enrichment has been realized in the form of nanoparticle–DNA complexes that is accomplished through electrostatic binding between the positive charge of the amino group and the negative charge of the phosphate groups of the nucleic acid. These nanoparticles have high affinity to bind DNA. The results show that 1 mg of nanoparticles can bind 97.2 µg of plasmid DNA with 4.3 kb. This novel DNA‐enrichment technology has been used successfully in gene delivery.     

Separation of β-Blocker Enantiomers on Silica Modified with Gold Nanoparticles with Immobilized Macrocyclic Antibiotic Vancomicin

A new chiral sorbent based on mercaptosilica modified by gold nanoparticles, then treated by 3-mercaptopropionic acid and macrocyclic antibiotic vancomycin, was obtained. The enantioseparation of isomeric β-blockers (nadolol, atenolol, metoprolol, alprenolol, oxprenolol, and pindolol) by HPLC was studied on the synthesized sorbent. The effect of the composition of the mobile phase (nature and concentration of the organic solvent, concentration and pH of the buffer solution) on retention times of β-blocker enantiomers, selectivity of separation, and resolution of chromatographic peaks were studied. The best separation was achieved for pindolol and metoprolol. The procedure was used to determine the pindolol enantiomers in the preparation “Visken,” and metoprolol in the “Vazocardin” preparation.     

Preparation of Comb‐like Styrene Grafted Silica Nanoparticles

Abstract

Comb‐like polystyrene grafted silica nanoparticles (c‐PS‐SNs) were prepared by the following steps: (a) methacryloxypropyl silica nanoparticles (MPSNs) were used as macromonomer and free radical copolymerized with 4‐vinyl benzyl chloride (VBC) by a solution polymerization method; (b) the product of (A), poly(4‐vinyl benzyl chloride) grafted silica nanoparticle (PVBC‐SN) was separated and then used as a macroinitiator for the surface‐initiated atom transfer radical polymerization (SI‐ATRP) of styrene catalyzed by the complex of Cu(I)Br and 2,2′‐bipyridyl (bipy) in toluene solutions. The structurally well‐defined polymer chains were grown from the nanoparticle surfaces to yield particles composed of a silica core and a well defined, densely grafted outer comb‐like PS layer. A percentage of grafting (PG%) (the weight ratio of the PS grafted with that of the silica charged) of more than 80% was achieved after a polymerizing time of 5?hr.     

Anodic Stripping Voltammetric Determination of Lead(II) with a 2‐Aminopyridinated‐Silica Modified Carbon Paste Electrode

Abstract

A carbon paste electrode modified with organically functionalized silica was used for the determination of lead. The measurements were carried out in three steps including an open circuit accumulation followed by electrolysis of accumulated lead at the carbon paste electrode and differential pulse voltammetric determination. The effects of several experimental variables such as carbon paste composition, pH and concentration of supporting electrolyte, electrolysis potential, and electrolysis time were studied. The resulting electrode demonstrates linear response over a wide range of Pb(II) concentration (5–1000 ng mL^?1) with an accumulation time of 60 sec. The effects of potential interfering ions were studied, and it was found that the proposed procedure is free from most interferences. Long lifetime and rapid and convenient renewal of electrode surface allows the use of a single modified electrode surface in multiple analytical determinations over at least 4 months. The prepared electrode was used for determination of lead spiked in a hair sample, and very good recovery results were obtained over a wide concentration range of lead.     

De‐agglomeration of Silica Nanoparticles in the Presence of Surfactants

The effect of the type of surfactant and pH on de‐agglomeration of a hydrophilic silica nano‐powder in a high shear mixer was investigated. It has been found that the presence of surfactant does not affect the general pattern of de‐agglomeration characterized by the transition of a single modal aggregates size distribution with the median of 10 µm, through a bi‐modal distributions with the second median of the order of 100 nm to a single modal distribution with the median of the order of 100 nm. None of the investigated surfactants enabled de‐agglomeration of the nano‐powder into a primary nanoparticle.

At pH=4, breakage of large secondary aggregates was enhanced by the addition of PEG and PVP, whereas the addition of SDS slowed down de‐agglomeration. The final aggregates were larger in all suspensions containing surfactant than in surfactant free suspensions. At pH=9 all surfactants drastically reduced de‐agglomeration rate without affecting the size of the primary aggregates. PEG induced bridge flocculation of the primary aggregates leading to a drastic change of the rheology of suspension.     

Unraveling the Origin of Differentiable ‘Turn-On’ Fluorescence Sensing of Zn2+ and Cd2+ Ions with Squaramides

A squaramide ring conjugated with Schiff-bases decorated with hydroxy and methoxy functional groups differentially senses zinc and cadmium ions, which turn on the fluorescence. The feebly emitting free ligands light up in the presence of zinc and cadmium acetates, with the acetate ion playing a pivotal role as a conjugate anion. The selective and differentiable emission responses for zinc and cadmium ions make these ligands efficient multi-analyte sensing agents. Furthermore, these ligands could be used to differentially sense zinc and cadmium ions even in aqueous environments. The NMR investigations reveal marginal differences in the binding of zinc and cadmium ions to the ligands, whereas density functional theory calculations suggest the different extent of ligand-to-metal charge transfer (LMCT) contributes to the differential behavior. Finally, comparison of the excited-state dynamics of free ligand and the metal complexes reveal the appearance of longer lifetime (about 500–700 ps) component with complexation, due to rigidified molecular skeleton, thereby impeding the non-radiative processes.     

Sorption Properties of α-Aluminum Oxide Modified with Decationized Silica Sol

The method of sorption of tetrachloromethane vapor at the solid/gas interface was applied to study the sorption and structural properties of a mesoporous aluminum oxide material obtained by deposition of amorphous hydrated silicon(IV) oxide onto -aluminum oxide particles submerged in decationized silica sol.     

Synthesis of 2′‐Amino‐2′‐deoxyuridine Modified by 1,8‐Naphthalimide

A simple and efficient synthetic route of 2′‐amino‐2′‐deoxyuridine was studied. 2′‐Amino‐2′‐deoxyuridine was incorporated into 1,8‐naphthalimides in the 2′‐position of 2′‐sugar via linking arms of different lengths. A convenient method for the synthesis of the conjugates was adopted.     

Preparation of CdO Thin Films by Annealing Cd2+‐Dithiol Self‐Assembled Films

Cadmium oxide thin films were prepared by annealing the alternating multilayer films of cadmium ion and 1, 6‐hexanedithiol at 1073 K, which were built up by using the layer‐by‐layer self‐assembly technique. The result of EDX confirms the formation of CdO. The CdO film has a high average transmittance over 90% in visible of the region. The mean surface roughness was measured by AFM to be 3.267 nm.     

Oxidative Cleavage of Oximes with Silica‐Gel‐Supported Chromic Acid in Nonaqueous Media

A simple procedure for a clean and high‐yielding oxidative deoximation of benzaldoximes and ketoximes using a silica‐gel‐supported chromic acid reagent has been developed. This solid‐supported reagent allows us to carry out this reaction in nonaqueous dichloromethane reaction media.     

Pyrene-Based “Turn-Off” Probe with Broad Detection Range for Cu2+, Pb2+ and Hg2+ Ions

Detection of metals in different environments with high selectivity and specificity is one of the prerequisites of the fight against environmental pollution with these elements. Pyrenes are well suited for the fluorescence sensing in different media. The applied sensing principle typically relies on the formation of intra- and intermolecular excimers, which is however limiting the sensitivity range due to masking of e. g. quenching effects by the excimer emission. Herein we report a highly selective, structurally rigid chemical sensor based on the monomer fluorescence of pyrene moieties bearing triazole groups. This sensor can quantitatively detect Cu²⁺, Pb²⁺ and Hg²⁺ in organic solvents over a broad concentrations range, even in the presence of ubiquitous ions such as Na⁺, K⁺, Ca²⁺ and Mg²⁺. The strongly emissive sensor's fluorescence with a long lifetime of 165 ns is quenched by a 1 : 1 complex formation upon addition of metal ions in acetonitrile. Upon addition of a tenfold excess of the metal ion to the sensor, agglomerates with a diameter of about 3 nm are formed. Due to complex interactions in the system, conventional linear correlations are not observed for all concentrations. Therefore, a critical comparison between the conventional Job plot interpretation, the method of Benesi-Hildebrand, and a non-linear fit is presented. The reported system enables the specific and robust sensing of medically and environmentally relevant ions in the health-relevant nM range and could be used e. g. for the monitoring of the respective ions in waste streams.     

Preparation and Application of La(OH)3 Nanoparticles Self‐Assembled Film Modified Electrode

Abstract

La(OH)₃ nanoparticles were successfully prepared with the sol‐gel method, and the preparation of a glassy carbon electrode modified by La(OH)₃ nanoparticles was investigated. The modified electrode shows an excellent electrocatalytic activity for hydroquinone. The anodic and cathodic overpotentials are reduced by ca. 143 mV and 83 mV, respectively, compared with those obtained with a bare glassy carbon electrode. According to the electrochemistry response, we set up a new method to determinate hydroquinone. The catalytic anodic current response of differential pulse voltammogram increases linearly with hydroquinone concentrations from 2.7×10^?7 to 6.5×10^?4 mol L^?1 with a detection limit of 6.0×10^?8 mol L^?1. The recovery of hydroquinone in a simulative sample is satisfactory, especially for its elimination of the interference of 1,2‐benzenediol (pyrocatechol) and 1,3‐benzenediol (m‐dihydroxybenzene). The method is simple, quick, and sensitive.     

Low-Temperature Adsorption–Luminescence Determination of Gold Using Silica Gel Chemically Modified with Mercapto Groups

Silica gel with mercaptopropyl groups covalently bonded to the surface extracts gold(III) from its hydrochloric solutions in a wide acidity range (from 6 M HCl to pH 8). An adsorption equilibrium is attained in no more than 5 min. The distribution ratio is 1.65 × 10⁴–1 × 10⁵ cm³/g. The intense yellow–orange luminescence (_max = 575 nm) appearing in the adsorbent phase under UV irradiation of wet liquid-nitrogen cooled adsorbates (77 K) is used for the low-temperature adsorption–luminescence determination of gold. The calibration plot is linear in the range of 1–100 g of gold per 0.1 g of adsorbent. The detection limit is 0.05 g/0.1 g of adsorbent. The relative standard deviation for the determination of more than 10 g of gold is no more than 5%.     

A Gas Chromatographic Analysis of Light Hydrocarbons on a Column Packed with Modified Silica Gel

IntroductionAnalysis of light hydrocarbons achieved by gas-solid chromatography is important in petrochemical industry, environmental protection and some other areas. A variety of columns have been used, including conventional packed column1, Al2O3 and graphitized carbon black PLOT column2, 3 and silica gel SCOT column4. Al2O3 PLOT column is excellent for the analysis of light hydrocarbons. Conventional packed column also has its own advantages, such as easy column preparation, resistanc…     

Highly Efficient and Stable Palladium Nanoparticles Supported on an Ionic Liquid Silica Sol?Gel Modified Electrode

A carbon ionic liquid electrode modified with a thin layer of silica sol? gel containing phosphinite ionic liquid was prepared for deposition of palladium nanoparticles. Palladium nanoparticles were formed easily by simple contact of the modified electrode with palladium chloride solution. The novel material overcomes the shortcomings of conventionally modified electrodes with a thin layer of silica sol? gel, due to the existence of ionic liquid in silica matrix. A crack‐free sol? gel matrix was obtained and also, the uniform porous structure of the ionic liquid‐sol? gel matrix resulted in a fast mass transport and increased ionic conductivity. The electrode exhibits high electrocatalytic effects towards hydrazine and ascorbic acid. It is very stable against repetitive cycling in the applied potential window.     

Highly Sensitive Electrogenerated Chemiluminescence Isoniazid with NiO Nanoparticles‐modified Graphite Electrode

Abstract

NiO nanoparticles (NiO NPs) were prepared with chemical precipitation method and modified on the surface of vaseline‐impregnated graphite electrode with chitosan. It was found that, based on the catalysis of the NiO NPs for the chemiluminescent reaction of the ECL process, the enhancing effect of isoniazid on the weak electrogenerated chemiluminescence (ECL) signal of luminol at a NiO NPs‐chitosan modified electrode was stronger than that at a bare graphite electrode. Under the optimum experimental conditions, the relative ECL intensity was linear with isoniazid concentration over the range 3.0×10^?10～1.0×10^?6 g/ml at the NiO NPs‐chitosan modified electrode with a detection limit of 1.0×10^?10 g/ml.     

Self‐assembly of Functionalized Gold Nanoparticles with Rigid and Flexible Multifunctional Linkers

The interparticle spacing of carboxyl functionalized gold nanoparticles (Au‐COOH) were mediated by rigid crosslinkers, octa(3‐aminopropyl)octasilsesquioxane (POSS‐NH₃ ⁺) and poly(amidoamine) dendrimer terminated with hydroxyl groups (PAMAM‐OH), and a flexible polymeric linker, poly(hexanul viologen) (6‐VP). Regular interparticle spacing was achieved by utilizing POSS‐NH₃ ⁺ and PAMAM‐OH dendrimer as cross linkers, whereas size growth of Au‐COOH was observed featuring no interparticle spacing by utilizing 6‐VP as the crosslinker.     

Microwave‐Promoted Ullmann Condensation of 2‐Aminopyridines with 2‐Chlorobenzoic Acids

A new efficient synthetic method of microwave‐promoted Ullmann condensation of 2‐aminopyridines with 2‐chlorobenzoic acids to yield various substituted 11H‐pyrido[2,1‐b]quinazolin‐11‐ones in dry media is presented. Results were compared with those obtained following the classical heating.