Synthesis of silver nanowires and their applications in the electrochemical detection of halide

A silver nanowires modified platinum (Ag NWs/Pt) electrode was developed for simultaneous and selective determination of chloride, bromide and iodide ions by cyclic voltammetry in aqueous solutions. Silver nanowires were synthesized by an l-cysteine-assisted poly (vinyl pyrrolidone) (PVP)-mediated polyol route. X-ray diffraction (XRD) and scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) were employed to investigate the prepared nanowires. The intrinsic high surface area and the fast electron transfer rate ascribed from the nanowire structure could further improve halide detection performance. The determination was based on measurement of the well-separated oxidation peak currents of respective silver halides formed on the surface of silver during an anodic potential sweep. The concentration range was linear from 50 μM to 20.2 mM for bromide and iodide and 200 μM to 20.2 mM for chloride, and the sensitivity was 0.059 μA/mM, 0.042 μA/mM and 0.032 μA/mM for chloride, bromide and iodide, respectively. The correlation coefficient was 0.999 in each case. The Ag NWs/Pt electrode offered a useful platform for the development of a highly sensitive halide sensor.     

Electrochemical oxidation of several oxocarbon salts in N,N-dimethylformamide

The oxocarbon salts of croconic acid and its dicyanomethylene derivatives have been shown to undergo two consecutive reversible one-electron transfers in N,N-dimethylformamide to produce stable radical anions and the neutral croconates. Disproportion equilibrium constants were found to be quite small for all the crononate radical anions investigated. Following chemical reactions accompanied the second oxidation process of dicyanomethylene-substituted crononates. Substituent effects were shown to be ring position-independent and are discussed with respect to the unique resonance structure of the crononates.     

Vinylogous N,N-dimethylaminomethylenation of 3-[(1-substituted)ethylidene]-oxindoles with N,N-dimethylformamide dimethylacetal

An efficient stereoselective synthesis of various 3-(3-dimethylaminoprop-2-enylidene)oxindoles has been disclosed. The compounds were synthesized via a vinylogous N,N-dimethylaminomethylenation at the γ-position of 3-[(1-substituted)ethylidene]oxindoles with DMF-DMA.     

Preparation and characterization of copper/silver bimetallic nanowires with core‐shell structure

Core‐shell copper/silver bimetallic nanowires were prepared by replacement reaction with citric acid and polyvinylpyrollidone at room temperature. A uniform silver coating was obtained by strictly controlling the molar ratio of Ag/Cu. The copper/silver composite was characterized by X‐ray diffraction, scanning electron microscopy, electron probe microanalysis and X‐ray photoelectron spectroscopy. Microscopic analysis shows that a well‐copper/silver core‐shell structure was formed. Thermo‐gravimetry and differential thermal analysis to the composite nanowires show that the silver coatings efficiently inhibit the oxidation of Cu. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis, characterization and optical properties of silver and gold nanowires embedded in mesoporous MCM-41

Uniform nanowires of silver and gold inside the channels of MCM-41 were prepared by controlled reduction of their respective metal salts with sodium borohydride (NaBH₄). Presence of nanowires of silver and gold in MCM-41 were confirmed by high angle X-ray diffraction (XRD) data (peaks between 2ϑ = 30 − 60°) and transmission electron microscopy (TEM) confirmed the diameter of the nanowires. Diameter of nanowires is found to be ∼ 2.8 nm which is coincident with channel diameter of MCM-41. Optical properties of these heterostructured materials Ag-MCM-41 and Au-MCM-41 reveals the presence of surface plasmon absorption peaks of silver and gold respectively, and the shift in the absorption bands are associated to agglomeration of clusters inside the channels. Room temperature photoluminescence spectra exhibits interesting optical properties as observed for direct band gap semiconductors. Non-linear optical properties (NLO) corresponding to second harmonic generation (SHG) values were also recorded for self supported films of these heterostructured materials. Enhanced optical non-linearity was found to be arising from a corresponding increase of local field near the surface plasmon resonance. Further enhancement in SHG was found with poling due to an induction of orientation order.     

Coordination steric effect of N,N-dimethylformamide, N,N-dimethylacetamide and N-methyl-2-pyrrolidone on the assembly of coordination polymers

Three coordination polymers 1, 2 and 3 have been synthesized in DMF (N,N-dimethylformamide), DMA (N,N-dimethylacetamide) and NMP (N-methyl-2-pyrrolidone), respectively. In 1, DMF solvent molecule coordinates to zinc ion as an ancillary ligand, and 1D chain structure is obtained. 2 and 3 are isostructural, in which solvent molecules, DMA and NMP, do not coordinate to zinc ions, and 1D double stranded chain structures are formed. The coordination steric hindrance of the solvents is suggested as the decisive factor of the assemblies. Crystallography and thermoanalysis reveal that 2 and 3 are more stable and also include more guest solvent molecules than 1.     

The calorimetric investigation of phosphoric acid-N,N-dimethylformamide system

Solution and mixing enthalpies for the orthophosphoric acid (H₃PO₄)-N,N-dimethylformamide (DMF) system were measured over the whole concentration range at 25 °C. The standard value of solution enthalpy of phosphoric acid in DMF and the standard transference enthalpy of H₃PO₄ from water to DMF were calculated. The mixing enthalpy concentration dependence permitted making assumptions on complex formation in the system under investigation.     

Synthesis, manipulation and conductivity of supramolecular polymer nanowires

The synthesis of supramolecular conducting nanowires can be achieved by using DNA and pyrrole. Oxidation of pyrrole in DNA-containing solutions yields a material that contains both the cationic polypyrrole (PPy) and the anionic DNA polymers. Intimate interaction of the two polymer chains in the self-assembled nanowires is indicated by FTIR spectroscopy. AFM imaging shows individual nanowires to be continuous, approximately 5 nm high and conformationally flexible. This feature allows them to be aligned by molecular combing in a similar manner to bare DNA and provides a convenient method for fabricating a simple electrical device by stretching DNA/PPy strands across an electrode gap. Current-voltage measurements confirm that the nanowires are conducting, with values typical for a polypyrrole-based material. In contrast to polymerisation of pyrrole on a DNA template in bulk solution, attempts to form similar wires by polymerisation at surface-immobilised DNA do not give a continuous coverage; instead, a beads-on-a-string appearance is observed suggesting that immobilisation inhibits the assembly process.     

Remarks on the process of homogeneous carbonylation of rhodium compounds by N,N-dimethylformamide

Reductive carbonylation of rhodium(III) chloride complexes, commercial RhCl₃ · nH₂O neutralized with BaCO₃, (Me₂NH₂)₂[RhCl₅(DMF)], (PPh₄)[RhCl₄(H₂O)₂], RhCl₃(DMF)₃, RhCl₃(CH₃CN)₃, RhCl₃(CH₃CN)₂(DMF), [Rh(CO)₂Cl₃]₂, and rhodium(I) complex, Rh(PPh₃)₃Cl, by N,N-dimethylformamide (DMF) is studied. The data obtained support the conception of direct carbonyl group transfer from DMF molecule to the Rh metal center. The mechanistic scheme of carbonylation process is refined and discussed with regard of new experimental results.     

Synthesis and characterization of UV-irradiated silver/montmorillonite nanocomposites

We have successfully developed a simple method for preparing silver nanoparticles (Ag NPs) using UV irradiation of AgNO₃ in the interlamellar space of a montmorillonite (MMT) without any reducing agent or heat treatment. The properties of Ag/MMT nanocomposites were studied as a function of the UV irradiation period. UV irradiation disintegrated the Ag NPs into smaller size until a relatively stable size and size distribution were achieved. The results from UV–vis spectroscopy show that particles size of Ag NPs decrease with the increase of irradiation period. The crystalline structure of Ag NPs was determined by powder X-ray diffraction (PXRD).     

Solvation of monovalent anions in acetonitrile and N,N-dimethylformamide: Parameterization of the IEF-PCM model

The present work reports the parameterization of the polarizable continuum model for predicting the free energies of solvation for monovalent anions in acetonitrile and N,N-dimethylformamide. The parameterization of the model for acetonitrile employed the experimental free energies of solvation for a set of 12 charged solutes, containing H, C, N, O, S, F, Cl, Br, and I atoms. For the N,N-dimethylformamide solutions, experimental solvation free energies for 11 monovalent anions were used. A mean absolute error of 0.7 kcal/mol in the solvation free energies has been achieved for the 12 anions in acetonitrile, whereas the mean absolute error for the 11 anions corresponds to 0.5 kcal/mol in N,N-dimethylformamide. These results indicate that the polarizable continuum model is a suitable methodology for the study of thermodynamic effects in solutions of monovalent anions in both solvents.     

Characterization of CdS nanoparticles in solutions of P(TFE-co-PVDF-co-Prop)/N,N-dimethylformamide

We report in here the preparation of CdS nanoparticles (Q-CdS) in N,N-dimethylformamide (DMF) and poly(tetrafluoroethylene-co-vinylidenefluoride-co-propylene) (PTFE-co-PVDF-co-Prop) by reaction of cadmium acetate and thiourea at room temperature. The formation and size evolution of Q-CdS particles were followed by optical absorption spectroscopy as a function of the aging process of the solutions. The obtained results indicated that not only the Q-CdS particles were more stable in DMF than in aqueous solutions, probably due to the interaction with the CHNO group, but also they were formed in smaller sizes. The particle size obtained in DMF was estimated in 4-6 nm against 10-20 nm in aqueous solution. The results also showed that the velocity of Q-CdS formation is lower when the reaction was carried out in PTFE-co-PVDF-co-Prop dissolved in DMF. The Q-CdS particles formed in this system were also less stable than in pure DMF, probably due to the interaction of the CHNO fragment and CF₂ of polymer chain or phase segregation.     

A convenient microwave-assisted desulfitative dimethylamination of the 2(1H)-pyrazinone scaffold using N,N-dimethylformamide

A convenient microwave-assisted methodology is developed for the generation of 5-chloro-3-(dimethylamino)pyrazin-2(1H)-ones. The method entails a chemoselective desulfitative removal of a phenylthioether bond upon DMF/H₂O treatment in the presence of sodium carbonate, yielding the desired compounds in 73-96%.     

Selective synthesis and characterization of single-crystal silver molybdate/tungstate nanowires by a hydrothermal process

Selective synthesis of uniform single crystalline silver molybdate/tungstate nanorods/nanowires in large scale can be easily realized by a facile hydrothermal recrystallization technique. The synthesis is strongly dependent on the pH conditions, temperature, and reaction time. The phase transformation was examined in details. Pure Ag(2)MoO(4) and Ag(6)Mo(10)O(33) can be easily obtained under neutral condition and pH 2, respectively, whereas other mixed phases of Mo(17)O(47), Ag(2)Mo(2)O(7,) Ag(6)Mo(10)O(33) were observed under different pH conditions. Ag(6)Mo(10)O(33) nanowires with uniform diameter 50-60 nm and length up to several hundred micrometers were synthesized in large scale for the first time at 140 degrees C. The melting point of Ag(6)Mo(10)O(33) nanowires were found to be about 238 degrees C. Similarly, Ag(2)WO(4), and Ag(2)W(2)O(7) nanorods/nanowires can be selectively synthesized by controlling pH value. The results demonstrated that this route could be a potential mild way to selectively synthesize various molybdate nanowires with various phases in large scale.     

An iodide/anion exchange route to benzimidazolylidene silver complexes from benzimidazolium iodide: Crystal structures of N,N′-dibutylbenzimidazolylidene silver chloride, bromide, cyanide and nitrate

Syntheses of N,N′-dibutylbenzimidazolylidene silver complexes having chloride, nitrate or cyanide as an anion part through an iodide/anion exchange from N,N′-dibutylbenzimidazolium iodide are described, representing a practical route to benzimidazolylidene silver complexes from readily accessible benzimidazolium iodide. The crystal structures of N,N′-dibutylbenzimidazolylidene silver chloride, bromide, cyanide and nitrate have been determined, showing a close ligand-unsupported Ag-Ag interaction in [(NHC)₂]Ag⁺[AgX₂]⁻ and a “T” shape geometry about the silver(I) cation in complexes of chloride, bromide and cyanide, but a nearly linear shape in the bis(N,N′-dibutylbenzimidazolylidene) silver complex [ with non-coordinating nitrate anion.     

Synthesis, molecular structures and solution NMR studies of N-heterocyclic carbene-amine silver complexes

The synthesis of the Boc-protected 1-(2-aminoethyl)-3-methylimidazolium salts [BocNHCH₂CH₂ImMe]X [2]X (X = I, PF₆) and their straightforward transformation into [NH₂CH₂CH₂ImMe]X [3]X is reported. The reaction between [2]X and Ag₂O leads to the formation in the solid state of three different bonding motifs: a biscarbene salt [(NHC-NHBoc)₂Ag]PF₆ ([4]PF₆, NHC-NHBoc = 1-(2-BocNH-ethyl)-3-methyl-imidazolin-2-ylidene), a tetranuclear complex [Ag(NHC-NHBoc)₂]₂[Ag₂I₄], (5), and a polymeric silver “staircase” [(NHC-NHBoc)₂-Ag₄-I₄]_n, (6) composed of Ag₄I₄ clusters. The same reaction carried out with [3]I showed that a primary silver mono-NHC-NH₂ carbene complex of the type [(NHC-NH₂)AgI] (7) is likely to form but it is unstable in solution. The solid state molecular structures of [4]PF₆, 5 and 6 were determined by X-ray diffraction analysis, whereas PGSE NMR experiments were employed to investigate the hydrodynamic dimension of the imidazolium salts and silver complexes and, consequently, to gain information on the level of aggregation in solution. PGSE NMR studies were complemented by NOE NMR investigations in order to obtain information on anion-cation relative orientation within aggregates.     

Synthesis, characterization, and X-ray analysis of new N,N′-disubstituted-1,4-diazepanes

The synthesis and structural characterization of six 1,4-diazepanes prepared by condensation of 2,2′-(1,3-propanediyldiimino)diphenols with glyoxal or 2,3-butanedione to give bisbenzoxazolidines and subsequent reduction with BH₃-DMS is reported. The new 1,4-diazepanes were obtained in yields between 75% and 83% and characterized by NMR, IR, and HRMS. In addition, the crystal structure analysis showed that the seven-membered ring in 1,4-diazepanes (12a, 12e, and 12d) and bisbenzoxazolidines (11a, 11c, 11f) adopt in all cases twisted chair conformation. Compounds 12a and 12e show disorder in the seven member ring, as a result of the conformational flexibility of the seven-membered ring.     

Synthesis and aromatic nucleophilic N-N, N-S and N-O exchange reactions of N,N-dimethyl-2-trifluoroacetyl-1-naphthylamine

We succeeded in the synthesis of N,N-dimethyl-2-trifluoroacetyl-1-naphthylamine (10) by the regioselective deacylation of N,N-dimethyl-2,4-bis(trifluoroacetyl)-1-naphthylamine with trifluoroacetic acid and water. The aromatic nucleophilic substitutions of 10 with various amines, thiols and alcohols proceeded cleanly to give the corresponding N-N, N-S and N-O exchanged products in moderate to excellent yields.     

Synthesis and characterization of silver nanoparticle/kaolinite composites

Ag nanoparticles were synthetized in the interlamellar space of a layered kaolinite clay mineral. Disaggregation of the lamellae of non-swelling kaolinite was achieved by intercalation of dimethyl sulfoxide. The kaolinite was suspended in aqueous AgNO₃ solution and, after adsorption of Ag⁺, the ions were reduced with NaBH₄. The interlamellar space limits particle growth (d_ave=3.8–4.2 nm); however, larger silver particles may be formed on the exterior surface of kaolinite with d_ave=5.6–10.5 nm diameter. The diameter of the particles prepared in this way is depending on the initial AgNO₃ concentration. The silver nanoparticles prepared were characterized by UV–vis spectroscopy, X-ray diffraction (XRD), Small angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS) and Transmission electron microscopy (TEM).     

N-Functionalised heterocyclic dicarbene complexes of silver: Synthesis and structural studies

A range of new diimidazolium salts, held together by an alkyl unit and bearing alcohol pendant arms on their nitrogen, was synthesized. A short modular reaction pathway leads to the N-heterocyclic carbene (NHC) precursors, differing by the flexibility of the bridge, the steric bulk of substituents in α-position of the OH groups and the anions. Treatment of diimidazolium salts with Ag₂O yields Ag^I(carbene)₂ complexes. The related trimethylene-bridged bis-NHC silver complexes 6 and 7 were crystallised with di-tosylate and di-hexafluorophosphate anions, respectively. Their X-ray structures revealed dimeric species, involving two ligands with different arrangements around the Ag cations, leading to crossed and parallel conformations.