Stefan Kubik

Bio: Stefan Kubik is an academic researcher from Kaiserslautern University of Technology. The author has contributed to research in topics: Anion binding & Amino acid. The author has an hindex of 32, co-authored 99 publications receiving 3328 citations. Previous affiliations of Stefan Kubik include Schrödinger & University of Düsseldorf.

Anion recognition in water

Abstract: Anion recognition by synthetic receptors in water is not a new field, indeed the first receptors that were shown to interact with anionic species exhibited high affinity in aqueous solutions. Anion recognition in aqueous solution was, however, for a long time the domain of receptors containing multiple positive charges and/or metal ions while interactions of neutral receptors with anions were believed to be too weak to be efficient in water. Independent work in several groups has recently shown that this assumption is not necessarily correct. As a consequence, a much wider range of receptors is now available with which anion recognition in competitive aqueous media can be achieved. This tutorial review presents selected examples of synthetic anion receptors active in aqueous solutions and guidelines to achieve anion recognition in water.

Amino acid containing anion receptors

Abstract: Nature has devised highly efficient and selective ways of recognizing anionic substrates by using surprisingly few building blocks the most important of which are the amino acids serine, tryptophane, and arginine in addition to NH groups along the protein backbone. Deliberate use of amino acids for the construction of abiotic anion receptors could lead to systems that mimic the anion coordinating properties of anion binding proteins. With this aim in mind several groups have focused their attention on the development of anion receptors containing amino acid building blocks and came up with remarkably efficient systems. This critical review summarizes the different approaches (174 references).

Recognition of Anions by Synthetic Receptors in Aqueous Solution

Abstract: Natural anion binding systems achieve high substrate affinity and selectivity most often by arranging converging binding sites inside a cavity or cleft that is well shielded from surrounding solvent molecules by the folded peptide chain. Types of interactions employed for anion recognition are electrostatic interactions, hydrogen-bonding, and coordination to a Lewis-acidic metal center. In this review, successful strategies aimed at the development of synthetic receptors active in water or aqueous solvent mixtures are described. It is shown that considerable progress has been made during recent years in the development of potent anion receptors and that for every type of interaction used in nature for anion binding, corresponding synthetic models exist today. Representative examples of these systems are presented with a special emphasis on synthetic receptors whose characterization involved a detailed thermodynamic analysis of complex formation to demonstrate the important interplay between enthalpy and entropy for anion recognition in water.

Dynamic Combinatorial Optimization of a Neutral Receptor That Binds Inorganic Anions in Aqueous Solution

Abstract: A dynamic combinatorial library of potential anion receptors was generated from a cyclic peptide disulfide dimer and a series of dithiol spacers. Exposing the library to KI or K2SO4 led to the amplification of two new neutral receptors that bind anions through hydrogen bonding with up to micromolar affinity in aqueous solution. Thermodynamic studies suggest that these second-generation receptors outclass the previously described first-generation receptor, largely as a result of a more favorable enthalpy of binding. These results demonstrate that dynamic combinatorial optimization of designed hosts can be a powerful strategy, bringing synthetic receptors that approach the efficiencies of proteins one step closer.

A molecular oyster: a neutral anion receptor containing two cyclopeptide subunits with a remarkable sulfate affinity in aqueous solution.

Abstract: An artificial anion receptor is presented, in which two cyclohexapeptide subunits containing l-proline and 6-aminopicolinic acid subunits in an alternating sequence are connected via an adipinic acid spacer. This compound was devised to stabilize the 2:1 sandwich-type anion complexes that are observed when the two cyclopeptide moieties are not covalently connected and to obtain a 1:1 stoichiometry for these aggregates. Electrospray ionization mass spectrometry and NMR spectroscopic investigations showed that the bridged bis(cyclopeptide) does indeed form defined 1:1 complexes with halides, sulfate, and nitrate. ROESY NMR spectroscopy and molecular modeling allowed a structural assignment of the sulfate complex in solution. The stabilities of various anion complexes were determined by means of NMR titrations and isothermal titration microcalorimetry in 50% water/methanol. Both methods gave essentially the same quantitative results, namely stability constants that varied in the range 105−102 M-1 and decreas...

Functional Molecular Flasks : New Properties and Reactions within Discrete, Self-Assembled Hosts

Abstract: The application of self-assembled hosts as "molecular flasks" has precipitated a surge of interest in the reactivity and properties of molecules within well-defined confined spaces. The facile and modular synthesis of self-assembled hosts has enabled a variety of hosts of differing sizes, shapes, and properties to be prepared. This Review briefly highlights the various molecular flasks synthesized before focusing on their use as functional molecular containers--specifically for the encapsulation of guest molecules to either engender unusual reactions or unique chemical phenomena. Such self-assembled cavities now constitute a new phase of chemistry, which cannot be achieved in the conventional solid, liquid, and gas phases.

Super-tough carbon-nanotube fibres

Abstract: These extraordinary composite fibres can be woven into electronic textiles. The energy needed to rupture a fibre (its toughness) is five times higher for spider silk than for the same mass of steel wire, which has inspired efforts to produce spider silk commercially1,2,3. Here we spin 100-metre-long carbon-nanotube composite fibres that are tougher than any natural or synthetic organic fibre described so far, and use these to make fibre supercapacitors that are suitable for weaving into textiles.

Molecular imprinting science and technology: a survey of the literature for the years up to and including 2003

Abstract: Molecular imprinting science and technology: a survey of the literature for the years up to and including 2003