Colorimetric sensing of iodide based on triazole-acetamide functionalized gold nanoparticles

We have modified gold nanoparticles (AuNPs) with triazole acetamide to obtain a material for the sensitive and selective colorimetric determination of iodide. The functionalized AuNPs were prepared by a reductive single chemical step using a Cu(I)-catalyzed click reaction. The presence of iodide ions induces the aggregation of these AuNPs and results in a color change from wine-red to purple. The iodide-induced aggregation can be detected visually with bare eyes, but also by photometry. The detection limit is as low as 15 nM. The method displays excellent selectivity for iodide over other anions due to the selective interaction with the amido groups of the triazole. The method was applied to the determination of iodide in spiked lake waters.

Synthesis, characterization, DNA interaction and potential applications of gold nanoparticles functionalized with Acridine Orange fluorophores

Two new water-soluble gold nanoparticles (AO-TEG-Au and AO-PEG-Au NPs) are prepared and characterized. They are stabilized by thioalkylated oligoethylene glycols and functionalized with fluorescent Acridine Orange (AO) derivatives. Despite the different core sizes (11.8 and 3.9 nm respectively) and shell composition, they are both well dispersed and are stable in water, even if some self-aggregation is observed in the case of AO-TEG-Au NPs. However, AO-PEG-Au NPs show much lower emission efficiency with respect to AO-TEG-Au NPs. Spectrophotometric and spectrofluorometric experiments indicate that both types of nanoparticle are able to bind to calf thymus DNA, either by external binding or partial intercalation. Preliminary FACS flow cytometry tests seem to indicate that the AO-TEG-Au nanoparticle is able to cross the cell membrane where it is absorbed by Chinese hamster ovary (CHO) cells at the picomolar concentration level.     

Facile one-pot synthesis of gold nanoparticles and their sensing protocol

This communication reports facile one pot synthesis of amoxicillin and sodium salt of amoxicillin stabilized gold nanoparticles (Au-NPs). Primarily the cyclic thioether linkage i.e. the thiozolidine ring of amoxicillin is utilized for sequestering Au(III). Fluorescence quenching of these clusters makes it an efficient protocol for sensing Cu(2+) at nano scale levels.     

Synthesis, characterization, and antifouling potential of functionalized copper nanoparticles

The synthesis, characterization, and antimicrobial properties of functionalized copper nanoparticle/polymer composites are reported. Copper nanoparticles (Cu NPs) are stabilized by surface attachment of the acrylic functionality that can be copolymerized with other acrylic monomers, thus, becoming an integral part of the polymer backbone. Biological experiments show that Cu NP/polymer composites exhibit antimicrobial activity similar to that of conventional copper-based biocides. Atomic absorption spectroscopy shows the smallest amount of copper ions leaching from chemically bound acrylated Cu NPs compared to the nonfunctionalized biocides. These composites have a strong potential for use in antibacterial or marine antifouling coatings.     

Mixed sugar-nylon 14-, 28- and 42-membered ring macrocyclic lactams

Hydrogenation of linear ω-azido-pentafluorophenyl esters from mixed oligomers of 6-amino-6-deoxy-d-galactonic acid (or 6-amino-6-deoxy-d-mannonic acid) and 6-aminohexanoic acid gives cyclic peptides containing 14-, 28- and 42-membered ring lactams. Hydrogenation of a tetrameric peptide derived from ε-amino acids gave a 28-membered ring lactam in 79% yield.     

Polymer-mediated chain-like self-assembly of functionalized gold nanoparticles

We report an easy solution phase template-based method to assemble mercaptoundecanoic acid-functionalized gold nanoparticles (MUA-GNPs) along poly(ethylene oxide) (PEO) chains. Transmission electron microscopy (TEM) images show one-dimensional and two-dimensional chain-like sequences of GNPs resembling PEO chains. The progress of the assembly was monitored by the evaluation of surface plasmon resonance band of MUA-GNPs with time by UV-vis spectroscopy. The assembly process is a result of hydrogen bonding interaction between the ethereal oxygen of PEO and carboxylic acid group of MUA attached to GNPs surface, which was confirmed through FTIR spectroscopy. The interaction between PEO and MUA-GNPs was further confirmed by thermal analysis using differential scanning calorimetry.     

Synthesis and transannular diels-alder reaction of a trans-cis-cis 13-membered macrocyclic trienono

Upon heating at 300°C, TCC trienone 14 gave tricyclic ketone 15.     

Synthesis and transannular diels-alder reaction of a cis-trans-trans 13-membered macrocyclic trienone

Upon heating at 300°C, CTT macrocyclic trienone 17 underwent 1,5-H shift and/or transannular Diels-Alder yielding three tricyclic isomers 18, 19, and 20.     

Thermodynamic parameters for the binding of sulfate by open chain polyammonium cations

The interaction of sulfate with some open chain polyammonium cations was quantitatively studied by potentiometric (H(+)-glass electrode) measurements. Enthalpy changes, for some systems, were determined calorimetrically. Some literature data were also considered in the discussion of results. In all the systems, A(SO4)Hi(i-2) species are formed (i = 1, ...m; m = maximum protonation degree of amine), and, for i > or = 4, also A(SO4)2Hi(i-4) species were found. Both the stability and the formation enthalpies, for these complexes, are a direct function of the charges of reactants, and some empirical relationships are reported. A small, but significant, difference was found between the stability of unsubstituted and N-alkylsubstituted polyammonium cation-sulfate complexes.     

Assembly of ferrocenylhexanethiol functionalized gold nanoparticles for ascorbic acid determination

Gold nanoparticles functionalized with self-assembled films of ferrocenylhexanethiol and mercaptoundecanoic acid (MUA) were used for the determination of ascorbic acid (AA). The modified nanoparticles (mNPs) were prepared by a combination of the modified Schifrin’s and the place-exchange methods. Well-organized films were obtained due to electrostatic attraction between the carboxy groups of MUA and cationic surface of poly(diallyldimethylammonium chloride). The mNP films are highly stable and can be exploited to fabricate an enzyme-less sensor for AA whose function is based on the highly electrocatalytic activity of ferrocene in the mNPs towards AA. The sensor was characterized by cyclic voltammetry and chronoamperometry. Under optimal conditions, the response current towards AA is proportional to its concentration in the range from 8.0 μM to 6.0 mM, with a detection limit of 0.14 μM (at a signal-to-noise ratio of 3). This work represents a simple controlled test-bed for fundamental studies on the use of self-assembled mNPs for sensor applications.     

Electrochemical and optical characterization of triarylamine functionalized gold nanoparticles

This paper describes the synthesis, structural analysis, and investigations of the optical and electrochemical properties of some gold nanoparticles (AuNPs) which consist of a triarylamine ligand shell attached to small gold cores (Au-Tara). The triarylamine chromophores were attached to small 4-bromobenzenethiol covered gold nanoparticles (ca. 2 nm in diameter) by Sonogashira reaction. This procedure yields triarylamine redox centers attached via π-conjugated bridging units of different length to the gold core. The AuNPs were analyzed with (1)H NMR spectroscopy, diffusion ordered NMR spectroscopy (DOSY), thermogravimetric analysis (TGA), and scanning transmission electron microscopy (STEM). Cyclic voltammetry (CV) technique was used to determine the composition of the redox active particles via the Randles-Sevcik equation. The optical and electrochemical properties of the Au-Tara nanoparticles and of their corresponding unbound ligands (Ref) were investigated with UV/vis/NIR absorption spectroscopy, Osteryoung square wave voltammetry (OSWV), and spectroelectrochemistry (SEC). These data show that the assembling of triarylamines in the vicinity of a gold nanoparticle can change the optical and electrochemical properties of the triarylamine redox chromophores depending on the kind and length of the bridging unit. This is due to gold core-chromophore and chromophore-chromophore interactions.     

Photochemistry of ruthenium trisbipyridine functionalized on gold nanoparticles

Design of nanohybrid systems possessing several ruthenium trisbipyridine (Ru(bpy)(3)(2+)) chromophores on the surface of gold nanoparticles, by adopting a place exchange reaction, was reported and their photophysical properties were tuned by varying the density of chromophores. The charge shift between the excited and ground-state Ru(bpy)(3)(2+) chromophores was reported for the first time, leading to the formation of Ru(bpy)(3)(+) and Ru(bpy)(3)(3+). Electron-transfer products were not observed on decreasing the concentration of Ru(bpy)(3)(2+) functionalized on Au nanoparticles or in a saturated solution of unbound chromophores. The close proximity of the chromophores on periphery of the gold core may lead to an electron transfer reaction and the products sustained for several nanoseconds before undergoing recombination, probably due to the stabilizing effect of the polar ethylene glycol moieties embedded between the chromophore groups.     

Binding of fluoride and carbonate by open chain polyammonium cations

The formation of open chain polyammonium cation-fluoride and -carbonate complexes was studied by potentiometric and calorimetric techniques at t=25 °C. Several species of H_iAL (A=amine; L=F⁻, CO₃²⁻) are formed in both systems with a mean stability (ζ=|z_anion×z_cation|) and for fluoride and carbonate, respectively. The comparison with analogous systems (chloride and acetate for fluoride and hydrogenphosphate, sulfate and malonate for carbonate) showed that fluoride and carbonate form the most stable species with open chain polyammonium cations, among low molecular weight anions. The N-alkyl substitution does not play negligible role in the stability of these complexes, the species formed by substituted amines being more stable.     

Synthesis of four novel pendant armed macrocyclic ligands and their interaction with lanthanide(III) cations

The ability of La³⁺ ions to form stable complexes with four novel pendant-armed N_xO_y-macrocycles derived from 2,6-bis(2-formylphenoxymethyl)pyridine, L¹, L², L³, and L⁴, has been studied. The corresponding (unsubstituted) parent ligands were prepared by the reaction between 2,6-bis(2-formylphenoxymethyl)pyridine and three different amines: 1,2-bis(2-aminophenoxy)propane (L¹), diethylenetriamine (L²), and 3,6-dioxa-1,8-octanediamine (L³ and L⁴). This was followed for the parent ligands of L¹, L³, and L⁴ by in situ reduction with sodium borohydride. The pendant-armed ligands were then synthesized by the alkylation of the free-NH groups with p-(L¹ and L³) and o-nitrobenzyl bromide (L⁴), and 2-chloromethylpyridine chlorohydrate (L²). A series of Ln(III) complexes were prepared for the four ligands by the direct synthesis between the corresponding macrocycle and Ln(III) hydrated nitrates and perchlorates. The number of complexes obtained from the pendant-armed macrocycles is lower than that of the (unsubstituted) parent ones, suggesting that the introduction of pendant arms in the macrocyclic skeletons increases the selectivity of the ligands. More complexes were synthesized when using nitrate as the counterion, showing the important role of the counterion in the complexation reaction. The text was submitted by the authors in English.     

Synthesis of chiral threefold and sixfold functionalized macrocyclic imidazole peptides

Starting from 4-oxa- or 4-azasubstituted 2-amino-3-oxoesters and (S)-valine, chiral imidazole diamino monocarboxylic acids as well as diamino dicarboxylic acids were prepared in a few synthetic steps. Macrolactamization of the side chain protected imidazole amino acids yields the corresponding 18- and 24-membered ring analogues of the naturally occurring cyclic peptide Westiellamide with various anchoring sites. The threefold functionalized scaffolds 2b-4b and the sixfold functionalized scaffold 5 are versatile central modules for artificial receptors and ligands. Structural investigations of threefold functionalized scaffolds based on oxazole and N-methylimidazole units by DFT modeling are provided.     

Site-selective immobilization of gold nanoparticles functionalized with DNA oligomers

The organization of metal and semiconductor nanoparticles to form micro- and nanostructured assemblies is currently of tremendous interest. This communication reports on the utilization of DNA molecules as positioning elements for generating microstructured surface architecture from gold nanoparticles. Citrate-passivated 40 nm gold colloids were modified by chemisorptive coupling with a 5′-thiol-derivatized DNA oligomer. The nucleic acid was used as a molecular handle for the specific immobilization on solid supports, previously functionalized with capture DNA oligomers, complementary to the nanoparticle-bound DNA. As a consequence of the enormous specificity of nucleic acid hybridization, the DNA-directed immobilization (DDI) allows, to site-specifically target the hybrid nanoparticles to microlocations which contain the complementary oligomers. The site-selectivity of the surface adsorption is demonstrated by immobilizing the gold colloids on a DNA microarray on a glass cover slide. Moreover, scanning force microscopy (SFM) analysis, used to characterize the intermediate steps of the DDI on a gold substrate, provided initial insights into the specificity and efficiency of this technique. The application of the DDI to fabricate complex colloidal micro- and nanostructures is anticipated. Received: 26 July 2000/Accepted: 5 October 2000     

Foam films in the presence of functionalized gold nanoparticles

Dry aqueous foams made of anionic surfactant (SDS) and spherical gold nanoparticles are studied by small angle X-ray scattering and by optical techniques. To obtain stable foams, the surfactant concentration is well above the critical micelle concentration. The specular reflectivity signal obtained on a very thin film (thickness 20 nm) shows that functionalized nanoparticles (17 nm typical size) are trapped within the film in the form of a single monolayer. In order to isolate the film behavior, investigations are made on a single film confined in a tube. The film thinning according to the ratio of functionalized nanoparticle and SDS micelles (1:1, 1:10, 1:100) is mainly governed by the structural arrangement of SDS micelles. In thick films, nanoparticles tend to form aggregates that disappear during drainage. In particular self-organization of nanoparticles (with different surface charge) inside the film is not detected.     

Planar monolithic porous polymer layers functionalized with gold nanoparticles as large-area substrates for sensitive surface-enhanced Raman scattering sensing of bacteria

For the first time, large-area surface-enhanced Raman scattering sensing active substrates using porous polymer monolithic layers have been successfully prepared. Our approach includes a simple photoinitiated polymerization process using glycidyl methacrylate and ethylene dimethacrylate in a glass mold, followed by a chemical reaction of the epoxy functionalities leading to thiols, and the attachment of preformed gold nanoparticles. We demonstrated that this very simple process produced uniform and reproducible large area surfaces that significantly enhance sensitivity of Raman spectroscopy. Experiments were also carried out that confirmed preferential adsorption of living bacteria Escherichia coli from a very dilute solution on the surface of the monolithic layer, and immediate detection of the captured microorganisms using the SERS spectrum.