Search

Core-shell type dual fluorescent nanoparticles (NPs) in the 16 nm diameter range with a selective ligand (cyclam) attached to the surface and two fluorophores--9,10-diphenyl-anthracene (donor, D) and pyrromethene PM 567 (acceptor, A)--embedded within the polymer core were synthesized and their fluorescent and copper-sensing properties were studied and compared to single D-doped and A-doped NPs. The acceptor (A) and donor (D) dyes were chosen to allow two sequential Förster resonance energy transfer (FRET) processes from D to A and from the encapsulated dyes to copper complexes that form at the surface and act as quenchers. NPs with different D/A loads were readily obtained by two consecutive entrapments of the dyes. Dual NPs present tunable fluorescence emission that is dependent on the doping ratio. FRET from D to A results in sensitized emission from A upon excitation of D, with FRET efficiencies reaching 80 % at high acceptor loads. A 9-fold amplification of the signal of A is observed at high D-to-A ratios. Single- and dual-dye-doped NPs were used to detect the presence of cupric ions in water by using the quenching of fluorescence as a transduction signal. In accordance with the spectral overlaps and the values of the critical distance (R0) of D- and A-copper complex pairs, the acceptor is much more sensitive than the donor. In dual fluorescent NPs, the sensitized emission of A is efficiently attenuated whereas the remaining emission of D is much less affected, allowing the detection of copper in a ratiometric manner upon excitation at a single (D) wavelength. Dual-dye-doped NPs with the highest acceptor loads (23 A-per-NP) were found to be the most sensitive for the detection of copper over a wide range of concentrations (20 nM to 8.5 microM). Owing to its great convenience and modularity, the cascade FRET strategy based on dual fluorescent NPs holds great promise for the design of various sensing nanodevices.

The synthesis and properties of well-defined core–shell type fluorescent metal-chelating polymer nanoparticles NP, in the 15 nm diameter range, with a fluorophore (9,10-diphenylanthracene: DPA) entrapped in the particle core and a selective ligand (1,4,8,11-tetraazacyclotetradecane: Cyclam), grafted onto the surface are presented. NPs with different number of dye-per-particle are readily obtained by entrapment of the fluorophore within the polymer core. The ligand-coated NPs exhibit a high affinity for Cu2+ ions in aqueous solution and quenching of the DPA fluorescence is observed upon binding of copper. The quenching of fluorescence arises through energy transfer (FRET) from the dye to the copper-cyclam complexes that form at the NP surface with an operating distance (d) in the 2 nm range. A simple core–shell model accounts for the steady-state and time-resolved fluorescence titration experiments: dye molecules located in the outer sphere (thickness d) of the NPs are quenched while the fluorescence of dyes embedded more deeply is not affected by the binding of copper ions. The observed high quenching efficiency (60–65 %), which is tightly correlated to the volumic and microstructural features of the NPs, shed light on the enhanced accessibility inherent in nano-sized templates. The response towards different metal ions was investigated and this confirmed the selectivity of the nanoparticle template-assembled sensor for cupric ions.

Azamacrocycles bearing four arylsulfonyl or arylsulfinyl pendant arms have been synthesised with good yields through nucleophilic addition of 1,4,8,11-tetraazacyclotetradecane (cyclam) to phenylvinylsulfone, phenylvinylsulfoxide or (R)-tolylvinylsulfoxide in isopropanol/water media. The crystal structure of the tetraethylsulfonylphenyl substituted macrocycle has been determined by X-ray crystallography. Preliminary studies of the coordination properties of these functionalised macrocyles towards Cu(II) and Eu(III) indicate that pendant sulfoxide groups act as oxygen donor coordinating groups.

Conjugate additions of cyclam to perfluorohexyl vinyl sulfone and sulfoxide, which act as efficient fluorous Michael acceptors, readily give access to new fluoro-ponytail tetraazamacrocycles in good yields. The solubility of the N-tetrasubstituted macrocycles depends dramatically on the nature of the polar function (SO or SO2): the sulfoxide cyclam derivative is soluble in perfluorodecaline (pfd) and perfluoromethylcyclohexane (pfmc) while the sulfonyl derivative is almost insoluble in organic or fluorous solvents. In agreement with the well known affinity of cyclam for copper(II) ions, stable copper complexes of the fluorous macrocyclic ligands have been isolated and characterized. In chloroform/methanol, complexes with four perfluorinated tails have been obtained from reaction of the tetra-N-perfluorohexylsulfinyl-substituted macrocycle with copper nitrate and copper perfluorocarboxylate. In trifluoroethanol, a selective retro-Michael reaction has been observed and the same reaction specifically gives copper complexes of the tri-N-substituted macrocycle. Complexes with three and four fluorous tails associated with perfluorocarboxylate counteranions are soluble in fluorous solvents (pfd and pfmc). These copper complexes were tested as catalysts for the oxidation of cyclohexene by molecular oxygen in the presence of tert-butyl hydroperoxide (tbhp). The oxidation reactions proceed under fluorous biphasic conditions and the catalyst can be recovered and reused. Quenching experiments indicate that cyclohexenyl hydroperoxide is the main oxidation product of the reaction performed with or without tbhp. Interestingly, these perfluorinated copper complexes are good, recyclable catalysts for the oxidation of cyclohexene by molecular oxygen without tbhp at room temperature and 65 °C.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Metal-complexing nanoparticles, with average diameters ranging from 15 to 25 nm, are prepared using a two-step procedure: synthesis of reactive nanoparticles followed by post-functionalisation with a selective macrocyclic ligand, cyclam (tetraazacyclotetradecane). The starting nanoparticles, containing benzylhalide reactive groups are readily prepared by copolymerisation of vinylbenzylchloride in ternary oil-in-water microemulsions stabilized by a cationic surfactant (dodecyltrimethyl ammonium bromide). Elemental analyses of the polymer reveals that exchange of chlorine for bromine as well as hydrolysis of chloromethyl residues occur within the reaction medium, the rate of both side reactions being dependent upon the experimental conditions. The overall content of reactive chloro- and bromobenzyl moieties range from 0.7 to 1.1 mmol g–1. Reaction of cyclam, performed directly in the aqueous suspensions, gives rise to stable suspensions of functionalised nanoparticles containing 0.2 to 0.3 mmol ligand g–1. Spectrophotometric measurements show that these cyclam post-functionalized nanoparticles exhibit a ‘solution-like’ complexation behaviour thus demonstrating remarkable ligand accessibility. To cite this article: C. Larpent et al., C. R. Chimie 6 (2003).

N,N′-disubstitution of cyclam without the use of protecting groups was investigated. This macrocycle reacted with two equivalents of a Michael acceptor in chloroform to yield as a major isolated compound the 1,8 di-N,N′-substituted macrocycle. Running the same reaction in the presence of one equivalent of para-toluenesulfonic acid led to the 1,11-di-N,N′-substituted macrocycle as the major product. Each regioisomer has been isolated and fully characterized. The observed regioselectivity is discussed with respect to the reactivity of the unprotonated or protonated monoalkylated intermediate. A site of protonation for the latter intermediate is deduced from an NMR study. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Stable translucent aqueous suspensions of ligand-functionalized nanoparticles, with average diameters ranging from 12 to 20 nm and containing from 0.25 to up to 0.75 mmol of ligand/g, are readily obtained by copolymerization in oil-in-water microemulsions of a polymerizable tetraaza macrocycle, vinylbenzylcyclam (cyclam: 1,4,8,11-tetraazacyclotetradecane). These nanoparticles exhibit a very high selectivity for cupric ions with binding capacities of up to 0.65 mmol of Cu/g as well as a remarkable ligand accessibility, deduced from spectrophotometric titration, with about 75% of the cyclam residues located near the surface for nanoparticles in the 12-13 nm range. Core-shell bimetallic nanoparticles are obtained by cation exchange. The cyclam-functionalized nanoparticles are comparable to high-generation PAMAM dendrimers in their ability to complex metals.

N-Monoalkylated azamacrocycles are selectively obtained by reacting cyclam (1,4,8,11-tetraazacyclotetradecane) with equimolar amounts of Michael acceptors in chloroform in the presence of one equivalent of acid (TsOH). This chemoselective addition provides a general route to new mono-substituted azamacrocycles with various pendant groups such as sulfonic acid, ester, amide, nitrile, sugar or crown ether. The selectivity for monoaddition results from protonation of the azamacrocycles in the presence of one equivalent of acid.

Time-resolved laser-induced fluorescence (TRLIF) has been used for interaction studies between europium(III) used as a fluorescent probe and a new micellar system (TAC8) of a “diblock” surfactant–cage molecule containing a cage (cyclam) as a complexation part linked to a sugar-based surfactant part. The effect of each constituent (cage and surfactant unit) as well the complete molecule on the europium fluorescence have been studied. By using the hypersensitive transition of europium, it was shown that the separate constituents, e.g. cyclam and surfactant, had little effect. On the other hand, the complexation constant between europium and TAC8 was close to 102 demonstrating that a synergetic effect is achieved with such a diblock surfactant–cage molecule.

Bis-tetraazacyclotetradecanes (bis-cyclam) are readily prepared with fairly good yields in a one step procedure from non-protected cyclam. The synthesis involves a selective addition of cyclam on bis-acrylamides in chloroform in the presence of one equivalent of p-toluenesulfonic acid.

8 pages; International audience; We present a simple and rapid procedure for producing polymer-coated substrates that can be easily functionalized by ion-chelating proteins. The procedure consists of depositing 18 nm metal-chelating cyclam-modified polymer nanoparticles (cyclam-nps) onto a conductive substrate (an Indium Tin Oxide (ITO) electrode) from an aqueous dispersion of Cu2+-loaded cyclam-nps while being subjected to a direct current (DC) field. The density of deposited nps as measured by AFM is shown to be in direct correlation to the concentration of nps in the dispersion with deposition of the particles taking less than 5 s. Because of the functionalization of the nps with cyclam groups, they can be used as anchoring sites for 6-Histidine (6-His) tagged proteins through complexation with divalent metal ions. In this work 6-His Green Fluorescent Protein (6-His GFP) is used as a model protein. The characterization by fluorescence microscopy clearly shows that the protein affinity was ion dependent and that the 6-His GFP density can be controlled by np density, which is itself easily tunable. AFM observations confirmed the immobilization of 6-His GFP onto cyclam-nps and its subsequent removal by treatment with ethylenediaminetetraacetic acid (EDTA).

Bis-tetraazacyclotetradecanes (bis-cyclam) are readily prepared with fairly good yields in a one step procedure from non-protected cyclam. The synthesis involves a selective addition of cyclam on bis-acrylamides in chloroform in the presence of one equivalent of p-toluenesulfonic acid.

Latex nanoparticles functionalized with cyclam (1,4,8,11-tetraazacyclotetradecane), a copper chelator, have been doped with a fluorescent dye (BODIPY derivative: 4,4-difluoro-8-(2',4',6'-trimethyl)phenyl-2,6-diethyl-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene). The bulky, hydrophobic fluorophore dissolves within the nanoparticles' polymer core up to a concentration of about 88.4 micromol g(-1). At this concentration the fluorescence yield is about 0.80. Adding Cu2+ ions to the solution decreases the fluorescence because of the energy transfer between the dye and the violet copper cyclam complexes. The response is fast: 90% of the quenching occurs within 1 s. The Cu2+ detection threshold is of 1 nanomolar. No interferences were observed with zinc and nickel ions.

A fluorescent sensor for Cu(2+) at the nanomolar level in water has been designed by associating a BODIPY fluorophore and a selective ligand (cyclam) in ultrafine polymer nanoparticles.