Ecotoxicity and analysis of nanomaterials in the aquatic environment

Nanotechnology is a major innovative scientific and economic growth area. However nanomaterial residues may have a detrimental effect on human health and the environment. To date there is a lack of quantitative ecotoxicity data, and recently there has been great scientific concern about the possible adverse effects that may be associated with manufactured nanomaterials. Nanomaterials are in the 1- to 100-nm size range and can be composed of many different base materials (carbon, silicon and metals, such as gold, cadmium and selenium) and they have different shapes. Particles in the nanometer size range do occur both in nature and as a result of existing industrial processes. Nevertheless, new engineered nanomaterials and nanostructures are different because they are being fabricated from the “bottom up”. Nanomaterial properties differ compared with those of the parent compounds because about 40–50% of the atoms in nanoparticles (NPs) are on the surface, resulting in greater reactivity than bulk materials. Therefore, it is expected that NPs will have different biological effects than parent compounds. In addition, release of manufactured NPs into the aquatic environment is largely an unknown. The surface properties and the very small size of NPs and nanotubes provide surfaces that may bind and transport toxic chemical pollutants, as well as possibly being toxic in their own right by generating reactive radicals. This review addresses hazards associated and ecotoxicological data on nanomaterials in the aquatic environment. Main weaknesses in ecotoxicological approaches, controversies and future needs are discussed. A brief discussion on the scarce number of analytical methods available to determinate nanomaterials in environmental samples is included.     

The Orthogonal (e,e,e)‐Tris‐Adduct of 9,10‐Dimethylanthracene with C60‐Fullerene: A Hidden Cornerstone of Fullerene Chemistry. Preliminary Communication

Tris(9′,10′‐dimethyl[9,10]ethanoanthracene[11′,12′: 1,9;11″,12″: 16,17;11′′′,12′′′: 30,31])[5,6]fullerene C₆₀, the orthogonal (e,e,e)‐tris‐adduct of C₆₀ and 9,10‐dimethylanthracene, was obtained from [4+2]‐cycloaddition (Diels–Alder reaction) at room temperature. The thermally unstable orange red (e,e,e)‐tris‐adduct was purified by chromatography and was isolated in the form of red monoclinic crystals. Its C₃‐symmetric addition pattern was established spectroscopically. Its structure could be further investigated by single crystal X‐ray diffraction. The (e,e,e)‐tris‐adduct of C₆₀ and 9,10‐dimethylanthracene has earlier been suggested as intermediate and reversibly formed critical component in ‘template directed’ addition reactions of C₆₀. This previously elusive compound has now been isolated and structurally characterized.     

The Effect of Thermal Treatment on the Morphology and Charge Carrier Dynamics in a Polythiophene–Fullerene Bulk Heterojunction

The influence of various thermal treatment steps on the morphology and the photoconductive properties of a non‐contacted, 50 nm thick blend (50:50 wt.‐%) of [6,6]‐phenyl C₆₁‐butyric acid methyl ester (PCBM) and poly(3‐hexyl thiophene) (P3HT) spin‐coated from chloroform has been studied using transmission electron microscopy (TEM) and the electrodeless time‐resolved microwave conductivity technique. After annealing the film for 5 min at 80 °C, TEM images show the formation of crystalline fibrils of P3HT due to a more ordered packing of the polymer chains. The thermal treatment results in a large increase of the photoconductivity, due to an enhancement of the hole mobility in these crystalline P3HT domains from 0.0056 cm² V^–1 s ^–1 for the non‐annealed sample to 0.044 cm² V^–1 s ^–1 for the sample annealed at 80 °C. In contrast, the temporal shape of the photoconductivity, with typical decay half‐times, τ_1/2, of 1 μs for the lowest excitation intensities, is unaffected by the temperature treatment. Further annealing of the sample at 130 °C results in the formation of three different substructures within the heterojunction: a PCBM:P3HT blend with PCBM‐rich clusters, a region depleted of PCBM, and large PCBM single crystals. Only a minor increase in the amplitude, but a tenfold rise of the decay time of the photoconductivity, is observed. This is explained by the formation of PCBM‐rich clusters and large PCBM single crystals, resulting in an increased diffusional escape probability for mobile charge carriers and hence reduced recombination.     

Synthesis and solvent dependence of the photophysical properties of [60]fullerene-sugar conjugates

A method for the synthesis of optically pure C₆₀ derivatives containing one or two d-galactose or d-glucose units is described. It involves the synthesis of sugar-malonate derivatives followed by a cyclopropanation reaction with C₆₀. The solvent dependence of the photophysical properties of the methano[60]fullerene-sugar derivatives was studied using nanosecond laser flash photolysis coupled with kinetic UV-vis absorption spectroscopy and time-resolved singlet oxygen luminescence measurements. The triplet properties of these fullerenes, including transient absorption spectra, molar absorption coefficients and quantum yield for the photosensitised production of ¹O₂ were determined in toluene, benzonitrile and acetonitrile solutions. The transient absorption spectral profiles are solvent independent although small differences are observed in the transient absorption maximum: 720±5 nm for toluene, 710±5 nm for benzonitrile and 700±5 nm for acetonitrile. Triplet state molar absorption coefficients (ε_T) of C₆₀ derivatives vary from 9456±2090 M⁻¹ cm⁻¹, for compound 10 in toluene, and 15,272±4462 M⁻¹ cm⁻¹, for compound 6 in acetonitrile. Triplet state lifetimes (τ_T) for methano[60]fullerene-sugar derivatives, under our experimental conditions, are similar in toluene or benzonitrile solutions (47.5±1.1 μs≤τ_T≤51.4±2.0 μs) but are lower in acetonitrile solutions (31.8±0.6 μs≤τ_T≤43.0±1.1 μs). Toluene and benzonitrile solutions of C₆₀ derivatives have Φ_Δ close to unity.     

Metal-chelating capacities attached to fullerenes

This review describes the synthesis, properties and application of fullerenes covalently attached to metal-chelating groups. The application of these structures in artificial photosynthetic systems and their reaction on external stimuli, such as light or electrons is described. Furthermore, the use of fullerene organometallic building blocks in macromolecular synthesis and catalysis has been highlighted.     

Liquid‐Crystalline Mixed [5 : 1]Hexa‐adducts of [60]Fullerene. Preliminary Communication

A liquid‐crystalline mixed [5 : 1]hexa‐adduct of [60]fullerene was synthesized by addition of two different malonate derivatives onto C₆₀. The hexa‐adduct derivative 2 was prepared by a stepwise synthetic procedure (fullerene→mono‐adduct of C₆₀→hexa‐adduct of C₆₀). Cyanobiphenyl and octyloxybiphenyl derivatives were selected as mesogens. The malonate derivatives showed either a monotropic nematic phase or a monotropic smectic A phase, and the hexa‐adduct derivative gave rise to an enantiotropic smectic A phase.     

High performance liquid chromatography on the chiral stationary phase (R,R)-DACH-DNB using carbon dioxide-based eluents

Fast and efficient separations of chiral stereolabile compounds were obtained at very low temperature on a π-acid chiral stationary phase (R,R-DACH-DNB) using carbon dioxide-based mobile phases containing alcoholic polar modifiers. Furthermore, efficient separations of the newly discovered spherical carbon cluster buckminsterfullerene (C₆₀) and the related higher fullerenes (C₇₀, etc.) have been performed on the same stationary phase using eluents based on either n-hexane or carbon dioxide.     

Ultrafast Spectroscopic Study of Photoinduced Electron Transfer in an Oligo(thienylenevinylene):Fullerene Composite

Photoinduced electron transfer and competing processes have been studied in composites of an oligo(thienylenevinylene) (OTV), comprised of ten dibuthoxyl‐thiophene units separated by vinylene units, and a C₆₀ derivative, [6,6]‐phenyl‐C₆₁ butyric acid methyl ester (PCBM), by using femtosecond transient absorption spectroscopy and sub‐nanosecond transient photoconductivity. We find that in OTV:PCBM the photoexcitations decay primarily via intrachain relaxation rather than photoinduced electron transfer from OTV to PCBM. The electron‐transfer process requires ca. 14 ps; larger by more than two orders of magnitude than the required time observed in conjugated‐polymer:C₆₀ composites, and also larger than the 0.6 ps singlet‐state lifetime in OTV. These observations indicate that the quantum efficiency for photoinduced electron transfer in OTV:PCBM is less than 5 %.     

Supramolecular Nanostructuring of Silver Surfaces via Self‐Assembly of [60]Fullerene and Porphyrin Modules

Recent achievements in our laboratory toward the “bottom‐up” fabrication of addressable multicomponent molecular entities obtained by self‐assembly of C₆₀ and porphyrins on Ag(100) and Ag(111) surfaces are described. Scanning tunneling microscopy (STM) studies on ad‐layers constituting monomeric and triply linked porphyrin modules showed that the molecules self‐organize into ordered supramolecular assemblies, the ordering of which is controlled by the porphyrin chemical structure, the metal substrate, and the surface coverage. Specifically, the successful preparation of unprecedented two‐dimensional porphyrin‐based assemblies featuring regular pores on Ag(111) surfaces has been achieved. Subsequent co‐deposition of C₆₀ molecules on top of the porphyrin monolayers results in selective self‐organization into ordered molecular hybrid bilayers, the organization of which is driven by both fullerene coverage and porphyrin structure. In all‐ordered fullerene–porphyrin assemblies, the C₆₀ guests organize, unusually, into long chains and/or two‐dimensional arrays. Furthermore, sublimation of C₆₀ on top of the porous porphyrin network reveals the selective long‐range inclusion of the fullerene guests within the hosting cavities. The observed mode of the C₆₀ self‐assembly originates from a delicate equilibrium between substrate–molecule and molecule–molecule interactions involving charge‐transfer processes and conformational reorganizations as a consequence of the structural adaptation of the fullerene–porphyrin bilayer.     

Dielectric response of cylindrical nanostructures in a magnetic field

We study the magnetic field dependence of the dielectric response of large cylindrical molecules such as nanotubes. When a field-induced level crossing takes place, an applied electric field has two effects: it may cause a linear instead of the usual quadratic Stark effect or the difference in the quadratic Stark coefficient of the two levels leads to a discontinuity in the polarization. Explicit calculations are performed for doped nanotubes and a rich structure in the real part of the low-frequency dielectric function is found when a magnetic field is applied along the cylinder axis. It is suggested that studies of can serve as a spectroscopic tool for the investigation of large ring-shaped or cylindrical molecules. Received 11 January 2000 and Received in final form 19 May 2000