Abdullah Aydogan

Poly(methyl methacrylate)s with Pendant Calixpyrroles and Crown Ethers: Polymeric Extractants for Potassium Halides **

The selective separation of alkaline salts from aqueous media is of fundamental importance in chemistry. It is, for instance, critical to the production of commodity materials (e.g., bromine and potassium) from high-salt sources, such as the Dead Sea and the Great Salt Lake[1] and, on a very different scale, to the regulation of taste[2] and the maintenance of osmotic balance in cells.[3] Materials that could allow for such separations are thus of potential interest in a wide range of applications.[4] Polymeric systems are particularly attractive in this regard because they are generally easy to isolate from solutions or mixtures.

Decoration of Gold Nanoparticles by a Double‐Armed Calix[4]pyrrole: A Receptor‐Decorated Nanoensemble for Anion Sensing and Extraction

Gold nanoparticles decorated with a double-armed, deep-cavity calix[4]pyrrole were prepared and fully characterized. Transmission electron microscopy imaging revealed that the average diameter of the particles was approximately 4 nm both before and after attachment of the receptor to the surface. The calix[4]pyrrole-functionalized nanoparticles exhibited highly elevated sensing behavior (approximately 1000 times in dichloromethane) relative to its monomeric congener while maintaining its guest selectivity. The receptor-nanoparticle conjugate (nanoreceptor) showed significant aggregation upon addition of the biphenolate anion, an effect ascribed to anion-mediated interparticle linking. The receptor-nanoparticle conjugate is also capable of extracting the fluoride anion (as its tetrabutylammonium salt) from an aqueous layer to an organic medium. Control experiments revealed that this extraction is not possible when using the analogous monomeric receptor.

EDOT-Functionalized Calix(4)pyrrole for the Electrochemical Sensing of Fluoride in Water

A new calix[4]pyrrole compound bearing an electropolymerizable EDOT substituent (1) was synthesized, and its electrochemical behavior was investigated. The anion sensor ability of 1 was also studied in solution and in the solid state. Compound 1 interacts with halide ions selectively in solution, which illustrates its possible application as an anion sensor. To test possible practical applications, 1 and EDOT were electropolymerized on an ITO electrode, and this electrode was used as an effective fluoride anion sensor in the solid state.

Calix(4)pyrroles with Long Alkyl Chains: Synthesis, Characterization, and Anion Binding Studies

Calix[4]pyrrole derivatives bearing long n-alkyl ester chains have been synthesized from calix[4]pyrroles containing carboxylic acid functional groups. These systems, which contain ester groups on either the meso- carbon atoms of the calixpyrrole ring or the β-positions of individual pyrrole rings, were prepared from the corresponding carboxylic acids. Esterification was effected using dicyclohexylcarbodiimide/4-dimethylaminopyridine (DCC/DMAP) to obtain long alkyl chain substituted calix[4]pyrroles. In the context of this work, several brominated calixpyrrole derivatives were prepared using N-bromosuccinimide (NBS) as the brominating agent. Anion binding studies carried out by isothermal titration calorimetry (ITC) in 1,2-dichloroethane with Cl− and in the form of their respective tetrabutylammonium salts, revealed that the functionalized ester derivatives have anion binding affinities similar to those of the unsubstituted “parent” systems, octamethylcalix[4]pyrrole (1) and β-octabromocalix[4]pyrrole (2). The new alkylated systems proved soluble in nonpolar solvents, such as hexanes. Structure identification studies, carried out by single crystal X-ray diffraction analyses, revealed that the control ester system 4 contains two unique crystal structures per asymmetric unit. These asymmetric units interact via intermolecular hydrogen bonds in the solid state to produce a continuous intermolecular structure. Such interactions are not present in the case of the corresponding brominated ester 5.

Reversible Assembly and Disassembly of Receptor‐Decorated Gold Nanoparticles Controlled by Ion Recognition

The controlled assembly of randomly dispersed colloidal particles can provide access to materials with advanced optical and electronic properties while providing fundamental insights into self-assembly processes in nature and nanotechnology. Typically, self-assembled nanoparticles are prepared by exploiting electrostatic interactions, lithographic techniques, and covalently linked molecular scaffolds. This results in static morphologies that cannot be disassembled easily. On the other hand, having access to systems that can be assembled or disassembled in a controlled manner could allow for in-depth understanding of the nanoparticles as well as rational control over the morphology and fundamental properties of the resulting constructs. If the changes in aggregation are induced by a specific external chemical stimulus, it could also permit the development of new chemosensors. Here we demonstrate the reversible assembly and disassembly of gold nanoparticles achieved by modulating the noncovalent interactions between surface-bound calix[4]pyrroles and added bis-imidazolium cations. We also demonstrate the use of these nanoparticles in the selective sensing of anions.

5,10,10,15,20,20-Hexamethylcalix[4]pyrrole 5,15-diethyl diester

In the title compound, C32H40N4O4, the pyrrole rings and ester groups adopt a 1,3-alternate conformation in which the alternating pyrrole and ester units are in opposite directions. The structure displays N—H⋯O hydrogen bonding and exhibits disorder [site occupancies of 0.81(2) and 0.71(2)] in the peripheral ethyl groups.