Kurt E. Geckeler

Synthesis and metal complexation of poly(ethyleneimine) and derivatives

This article surveys the research work on the synthesis and modification reactions of poly(ethyleneimine) as well as its applications to metal complexation processes. Poly(ethyleneimine), one of the most simple heterochain polymers exists in the form of two different chemical structures: one of them is branched, which is a commercially available and the other one linear which is synthesized by cationic polymerization of oxazoline monomers and subsequent hydrolysis of poly[(N-acylimino)ethylene]. The most salient feature of poly(ethyleneimine) is the simultaneous presence of primary, secondary, and tertiary amino groups in the polymer chain which explains its basic properties and gives access to various modification reactions. A great number of synthetic routes to branched and linear poly(ethyleneimine)s and polymer-analogous reactions are described. In addition, the complexation of poly(ethyleneimine) and its derivatives with metal ions is investigated. Homogeneous and heterogeneous metal separation and enrichment processes are reviewed.

Liquid-phase polymer-based retention, a new method for separation and preconcentration of elements

Abstract A method based on the retention of inorganic ions by water-soluble polymeric reagents (liquid-phase polymer-based retention) in a membrane filtration cell is suggested for the separation and preconcentration of various elements. The preseparated elements remain in the aqueous solution, which is convenient for most instrumental methods of completing the analysis. The water-soluble poly(ethyleneimine) and its thiourea and methylated derivatives are shwon to be useful for retention of different inorganic ions and their separation from elements not bound to the polymer reagent.

Dispersion of Single‐Walled Carbon Nanotubes by Using Surfactants: Are the Type and Concentration Important?

Single-walled carbon nanotubes (SWNTs) are of a great interest due to their unique mechanical, electronic, and optical properties as well as their interesting applications. Unfortunately, their existence in the form of aggregated and parallel bundles (as a result of substantial van der Waals tube–tube attractions) make this material inadequately soluble or dispersible in most of the common solvents, which is crucial to their processing. In order to explore these unique properties and to understand the chemistry of SWNTs, so far, some developments have been made toward the dispersion or solubilization of SWNTs in both organic and aqueous media. The dispersion of SWNTs in organic media has been studied with both pristine and chemically modified SWNTs. It can be improved by chemical substitution, but this creates defects in SWNTs, which hamper the electronic properties. Hence, SWNTs are generally dispersed using surfactants, which can successfully suspend them through supramolecular interactions. Further, stable dispersions of SWNTs in aqueous media are essential owing to potential biomedical applications, which have been facilitated by surfactants and polymers. However, in most of the studies the well-known common surfactant, namely sodium dodecylsulfate (SDS), has been used with particular concentrations, and, astonishingly, very few works have been reported on the optimization of the surfactants or experimental parameters. A few polymers such as poly(vinylpyrrolidone) (PVP), poly(phenylene vinylene), and in the biomedical field, poly(ethylene oxide) (PEO) and DNA are the favored solubilizing polymers to effectively solubilize SWNTs for various applications. Recently, Wenseleers et al. demonstrated that bile salt detergents are extremely efficient in solubilizing pristine SWNTs. Despite the progress in the suspension of SWNTs with surfactants, there are only very few systematic studies on the dispersion of SWNTs by using different types of surfactants such as anionic, cationic, and neutral in view of the optimization of the surfactant concentration and mass percent conversion of SWNTs. Our research group has long been involved in the study of CNTs and we have lately reported a novel and simple route to obtain supramolecular adducts of DNA– CNT conjugates from both multi-walled carbon nanotubes (MWNTs) and SWNTs based on a novel solid-state mechanochemical reaction. In a previous report we have also shown rapid purification and individualization/dispersion techniques for SWNTs. Very recently, we introduced novel approaches to disperse SWNTs in aqueous solution by using polymers and to synthesize SWNTs-polymer nanocomposites. Motivated by these approaches developed in our laboratory in connection with novel polymeric materials and surfactants we thought of expanding this idea to the dispersion of SWNTs with different surfactants in water following a systematic scheme. In this study, we used three different surfactants namely Igepal CO-990 [polyoxyethylene ACHTUNGTRENNUNG(100) nonylphenyl ether] (neutral), cetyltrimethylammonium bromide (CTAB) (cationic), and sodium dodecylsulfate (SDS) (anionic), for dispersing a high concentration of individual SWNTs in an aqueous solution by a supramolecular approach. To the best of our knowledge, this study is the first example of a systematic study on the dispersion of SWNTs in aqueous solution by comparing three different types (neutral, cationic, and anionic) of surfactants, and also considering the effect of significant parameters such as the surfactant and SWNT concentrations. More importantly, we calculated the maximum concentrations of SWNT that can be suspended under different experimental conditions for practical applications. This systematic approach presented here is anticipated to be commonly useful for the dispersion of SWNTs with a high mass percent conversion. The primary move on the way to the dispersion of SWNTs was to define the appropriate concentration proportion of SWNTs to surfactant. To this point, 12 mg of SWNT [a] J.-Y. Shin, Dr. T. Premkumar, Prof. Dr. K. E. Geckeler Department of Materials Science and Engineering Gwangju Institute of Science and Technology (GIST) 1 Oryong-dong, Buk-gu, Gwangju 500-712 (South Korea) Fax: (+82)62-970-2338 E-mail : keg@gist.ac.kr Supporting information for this article is available on the WWW under http://www.chemistry.org or from the author.

Radical polymer-wrapped SWNTs at a molecular level: high-rate redox mediation through a percolation network for a transparent charge-storage material.

The functionalization of carbon nanotubes (CNTs) has been widely investigated, [ 1–3 ] and, in particular, in conjunction with redox-active molecules this would lead to potential applications for electronic devices. [ 4 , 5 ] Attachment of redox molecules on CNTs is available due to relatively strong interactions, such as covalent bonding, π – π interactions, and π –cation interactions. [ 6–8 ] However, these interactions often require destructive and severe conditions that damage the CNTs and/or extra functional groups that interfere with the electrochemical and optical properties of the redox-active sites. An effi cient functionalization with a non-destructive interaction is required to maintain the inherent properties of both the CNTs and the redox-active molecules. Polymer wrapping, which interacts in 3D with CNTs by weak interactions, could be one of the best methods for functionalizing CNTs with redox-active molecules. Charge-storage materials or electrode-active materials for rechargeable batteries consisting of organics have been developed using redox-active molecules [ 9 ] and polymers. [ 10–14 ] We have been developing the organic radical battery, [ 10–20 ] utilizing a series of synthesized polymers containing redox-active organic radicals fenced by bulky alkyl groups. [ 15–18 ] Typically poly(2,2,6,6-tetramethylpiperidine-1-oxy-4-yl methacrylate) (PTMA) was employed as the organic cathode-active pendant group. [ 10 ] The PTMA ideally consists of the fl exible polymethacrylate backbone and the spherical pendant 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) group and could be expected to impart the TEMPO’s specifi c redox functionality to its CNT nanocomposite ( Figure 1 a). Here, we describe that PTMA-wrapped single-walled carbon nanotubes (SWNT) provide a high dispersibility of the SWNTs and successfully provide the nanocomposite electrode, which displays both a high electrical conductivity through the SWNT network and a quantitative and remarkably high-rate charge-storage capability while maintaining the high transparency of the nanocomposite. We focused on SWNTs with a diameter of 1–3 nm and a large surface area. To exfoliate the SWNT bundles without

Carbon Nanotube and Gold-Based Materials: A Symbiosis

Carbon nanotubes constitute a novel class of nanomaterials with potential applications in many areas. The attachment of metal nanoparticles to carbon nanotubes is new way to obtain novel hybrid materials with interesting properties for various applications such as catalysts and gas sensors as well as electronic and magnetic devices. Their unique properties such as excellent electronic properties, a good chemical stability, and a large surface area make carbon nanotubes very useful as a support for gold nanoparticles in many potential applications, ranging from advanced catalytic systems through very sensitive electrochemical sensors and biosensors to highly efficient fuel cells. Here we give an overview on the recent progress in this area by exploring the various synthesis approaches and types of assemblies, in which nanotubes can be decorated with gold nanoparticles and explore the diverse applications of the resulting composites.

Supramolecular Nanoencapsulation as a Tool: Solubilization of the Anticancer Drug trans -Dichloro(dipyridine)platinum(II) by Complexation with β-Cyclodextrin

A novel, water-soluble trans-platinum complex was synthesized by inclusion complexation with beta-cyclodextrin. The complexation was confirmed by (1)H NMR, FT-IR, TGA, and XRD as well as by SEM and EDX. As the precursor complex is not water-soluble, it is difficult to employ it for biological applications. Here, we report that the encapsulation with cyclodextrin allowed to solubilize the complex to a solubility value of 1.6 mg/mL. Moreover, the cytotoxicity in vitro of the novel inclusion complex indicated a much higher activity after encapsulation.

Modification of the biocompatible and haemocompatible properties of polymer substrates by plasma-deposited fluorocarbon coatings

The polymerization of gases present in a low temperature plasma is a technique particularly well suited for biomedical material processing. Therefore, the possibilities this technique offers to increase the biocompatibility and haemocompatibility of polysulphone and poly(hydroxybutyrate) membranes to be used in a new bioartificial pancreas device were studied. The deposition of thin fluorocarbon coatings from an argon plasma containing perfluorohexane gave very smooth and hydrophobic surfaces without affecting the filtering properties of the treated membranes. Adding hydrogen increased the reaction yield, but gave rougher and less hydrophobic coatings. We characterized the biological properties of the treated surfaces and discussed the influence of the modified surface properties on the biological behaviour of the treated polymers. The good biocompatibility of the deposited coatings was established by following in vitro the insulin secretion of Langerhans islets cultured on the treated membranes and by examining the fibrous capsule that developed on plasma-treated polymer disks after three months of in vivo incubation in the peritoneum of Wistar rats. Rough and haemocompatible films of poly(hydroxybutyrate) and smoother, but more thrombogenic, polysulphone films were treated by perfluorohexane and perfluorohexane + H2 plasmas to study the relative influence of surface roughness and surface energy on polymer thrombogenicity. In vitro protein adsorption and total blood clotting tests proved that the surface roughness influences the thrombogenicity more than the other surface properties. This study seems to show that the plasma deposition of smooth and hydrophobic fluorocarbon coatings can increase the biocompatibility and reduce the surface thrombogenicity of the treated membranes without affecting their filtering properties.

Carbon Nanotubes in the Biological Interphase: The Relevance of Noncovalence

With the increasing interest in the biological applications of carbon nanotubes, their interactions in the biological interphase and their general cytotoxicity have become major issues. In spite of their salient properties, major hurdles still exist for their use in biological applications, due to their main characteristics, including their hydrophobic surfaces and tendency to aggregate, as well as their unknown interactions in the cellular interphase. In this Research News, these characteristics of carbon nanotubes, a model nanomaterial, are investigated. Thus, the cytotoxicity of carbon nanotubes, the influence of functionalization, as well as their interactions with different mammalian cell lines are studied. Moreover, suggestions for the improvement of their biocompatibility and the design of biocompatible carbon nanotube-based systems are provided.

Surfactant-directed multiple anisotropic gold nanostructures: synthesis and surface-enhanced Raman scattering.

A facile and effective method for the synthesis of gold nanostructures using beta-cyclodextrin in aqueous alkaline medium is reported. The results demonstrate that leaf-like, rugged, dendritic, and tadpole-shaped gold nanostructures are obtained with high yield for the first time under the same experimental conditions by using four different surfactants. To study the effect of surfactant on the shape of the nanoparticles, the experiments were also carried out in the absence of surfactant and in the presence of poly(1-vinyl-2-pyrrolidone). The growth process of the dendritic gold nanostructures formed was investigated by withdrawing samples from the heated solution and examining the intermediate products formed by transmission electron microscopic analysis. The formation mechanism of the anisotropic gold nanostructures is discussed, and it is demonstrated that the cooperative effect of cyclodextrin and the surfactant molecules determines the ultimate morphology of the gold nanostructures obtained. In addition, the effect of the as-prepared nanostructures as an active material in surface-enhanced Raman scattering has been investigated by employing 4-aminothiophenol as a probe molecule. Thus, different enhancement signals are obtained for the different nanostructures; the dendritic nanostructures showed the strongest intensity of the SERS signals and smallest for the leaf-like nanostructures.

Liquid-Phase Polymer-Based Retention (Lpr)-A New Method for Selective Ion Separation

Abstract A new method based on the retention of ions by hydrophilic polymer reagents in a membrane filtration system, called Liquid-Phase Polymer-Based Retention, is described for selective ion separation. The principle and fundamentals of the method including the use of polychelatogens are explained and discussed. The effect of several polychelatogens on ion separation is documented and described by numerous retention profiles. It is shown that LPR is a convenient and effective method for selective ion separation of metal ions and anions.