Ionic Guests Research Articles

Linear aromatic amide foldamer-derived supramolecular architectures and materials

Intramolecular hydrogen bonding in oligomeric aromatic amides may induce the backbones to adopt folded, zigzag, or other extended conformations, depending on the positions of the amide units and the hydrogen-bonding sites on the aromatic rings. This article summarizes our efforts in exploring the applications of this family of preorganized oligomers in supramolecular and materials chemistry. Several series of preorganized frameworks or foldamers have been developed as efficient acyclic receptors for binding both neutral and ionic guests. The backbones have been modified with discrete functional groups from the ends or the side chains. The resulting molecules have been applied for designing new molecular tweezers, assembling ordered supramolecular architectures (organogels and vesicles), and directing the formation of complicated macrocyclic and capsular systems. When the hydrogen-bonded folded segments are connected to n-butyl methacrylate copolymers as cross-links, the resulting copolymers display unique reversible mechanical properties owing to the breaking and recovering of the intramolecular hydrogen bonds. When the folded segments are incorporated into the dumbbell components of the donor–acceptor interaction-based pseudo[2]rotaxanes and [2]rotaxanes, they are capable of tuning the slippage/deslippage and switching of the ring component between the discrete “stations” in their dumbbell component.

Metal ion directed self-assembly of sensors for ions, molecules and biomolecules

Recent years have seen a surge of interest in the metal-ion directed construction of discrete molecular assemblies. Once the versatility of this approach for the construction of hitherto inaccessible molecular architectures was demonstrated, work towards fully functional systems rapidly developed. Since these architectures have a wide range of possible applications, this perspective review will focus on one important aspect of this research: the construction of hosts with optical or electrochemical sensing outputs. As this overview will illustrate, research in this area is now producing working examples of sensors for variety of ionic, molecular, and biomolecular guests.

Intercalation synthesis of functional hybrid materials based on layered simple hydroxide hosts and ionic liquid guests – a pathway towards multifunctional ionogels without a silica matrix?

Functional hybrid materials on the basis of inorganic hosts and ionic liquids (ILs) as guests hold promise for a virtually unlimited number of applications. In particular, the interaction and the combination of properties of a defined inorganic matrix and a specific IL could lead to synergistic effects in property selection and tuning. Such hybrid materials, generally termed ionogels, are thus an emerging topic in hybrid materials research. The current article addresses some of the recent developments and focuses on the question why silica is currently the dominating matrix used for (inorganic) ionogel fabrication. In comparison to silica, matrix materials such as layered simple hydroxides, layered double hydroxides, clay-type substances, magnetic or catalytically active solids, and many other compounds could be much more interesting because they themselves may carry useful functionalities, which could also be exploited for multifunctional hybrid materials synthesis. The current article combines experimental results with some arguments as to how new, advanced functional hybrid materials can be generated and which obstacles will need to be overcome to successfully achieve the synthesis of a desired target material.

Tri- and Tetraurea Piperazine Cyclophanes: Synthesis and Complexation Studies of Preorganized and Folded Receptor Molecules

A series of symmetrical tri- and tetrameric N-ethyl- and N-phenylurea-functionalized cyclophanes have been prepared in nearly quantitative yields (86-99 %) from the corresponding tri- and tetraamino-functionalized piperazine cyclophanes and ethyl or phenyl isocyanates. Their conformational and complexation properties have been studied by single-crystal X-ray diffraction, variable-temperature NMR spectroscopy, and ESI-MS analysis. The rigid 27-membered trimeric cyclophane skeleton assisted by a seam of intramolecular hydrogen bonds results in a preorganized ditopic recognition site with an all-syn conformation of the urea moieties that, complemented by a lipophilic cavity of the cyclophane, binds molecular and ionic guests as well as ion pairs. The all-syn conformation persists in acidic conditions and the triprotonated triurea cyclophane binds an unprecedented anion pair, H(2)PO(4)(-)⋅⋅⋅HPO(4)(2-), in the solid state. The tetra-N-ethylurea cyclophane is less rigid and demonstrates an induced-fit recognition of diisopropyl ether in the solid state. The guest was encapsulated within the lipophilic interior of a quasicapsule, formed by intramolecular hydrogen-bond-driven folding of the 36-membered cyclophane skeleton. In the gas phase, the essential role of the urea moieties in the binding was demonstrated by the formation of monomeric 1:1 complexes with K(+), TMA(+), and TMP(+) as well as the ion-pair complexes [KI+K](+), [TMABr+TMA](+) and [TMPBr+TMP](+). In the positive-mode ESI-MS analysis, ion-pair binding was found to be more pronounced with the larger tetraurea cyclophanes. In the negative mode, owing to the large size of the binding site, a general binding preference towards larger anions, such as the iodide, over smaller anions, such as the fluoride, was observed.

ChemInform Abstract: Rigidified Macrocyclic Phosphoramides - A New Family of Preorganized Ligands.

Abstract Macrocyclic molecules capable of selective recognition of ionic or neutral guests are of considerable current interest. The design and synthesis of host molecules that contain phosphorus have been developed recently. Typically, the model compound A is modified to the more rigid molecule B which can exist as two exo/endo isomers. B represents a new family of preorganized ligands that can involve the phosphorus group during complexation of various guests. The exo/endo isomerisni was investigated by NMR studies. The complexing properties of B were studied by NMR and extraction method with alkaline and ammonium cations. The complexation constants mainly depend on the molecular geometry and the size of the cavity. The highest Ka constants are obtained with the endo isomer where the P=O bond is directed toward the center of the macrocycle. Complex formation and detailed stereochemical data for A and B will be presented.

Optical properties of matrix confined species

A majority of optically functional materials can be perceived as a liaison between ionic or molecular guests and a more or less rigid host. The guests exhibit an optical function, whereas the host provides suitable space, both of them synergistically complementing each other. The embracement of guests and hosts is often very intimate, as e.g. in typical phosphors, where luminescent ions even become part of the host. While the host–guest terminology usually is not applied to such marriages, the term becomes appropriate, if the host grants some degrees of spatial freedom, yet giving order and structure to its guests. Zeolites, clays and inverse opals are porous materials naturally providing hospitable cavities, channels or other compartments, and at the same time the guests are often demanded to occupy preassigned positions within these, or to structurally adapt to the interior host topology. Whereas zeolites and clays are merely patient providers of guest space, inverse opals, can actively turn the light on and off. The present article summarises and highlights recent experimental evidence, ongoing research and some envisaged merits resulting from the interaction of matrix confined luminescent ions, complexes and molecules with a focus on the optical properties of rare earth based materials.

ChemInform Abstract: Synthesis and Hg(II)-Selective Ionophoric Properties of Kemp′s Triacid-Based Amidine Derivative.

This hydrolytic instability mightbe a crucial drawback of thus designed derivatives in theextreme pH conditions which are often required for theapplications as transport carriers for ionic guests. In thispaper, we would like to report the synthesis and Hg(II)-selective ionophoric properties of the amidine derivative 3,which is designed to enhance the hydrolytic stability and thepreorganization of the ionophore, by means of the competi-tive transport experiments.The amidine derivative was prepared by the condensationof vicinal diaminocatechol derivative with Kemp’s triacid.The 4,5-dinitrocatechol was reacted with 1-bromooctane(Cs

Superoxide Ions Entrapped in Water Cages of Ionic Clathrate Hydrates

In the present work, we first described the stable entrapment of the superoxide ions in gamma-irradiated (Me(4)NOH + O(2)) clathrate hydrate. Owing to peculiar direct guest-guest ionic interaction, the lattice structure of gamma-irradiated (Me(4)NOH + O(2)) clathrate hydrate shows significant change of lattice contraction behavior even at relatively high temperature (120 K). Such findings are expected to provide useful information for a better understanding of unrevealed nature (such as icy nanoreactor concept, ice-based functional material synthesis and lattice tuning by specific ionic guests) of clathrate hydrate fields.

Hydrogen bonded aryl amide and hydrazide oligomers: a new generation of preorganized soft frameworks

Hydrogen bonded aryl amide and hydrazide foldamers may adopt folded, zigzag or other extended conformations, depending on the positions of the amides and hydrogen bonding sites on the aromatic rings. In recent years, several series of such preorganized frameworks have been developed as efficient acyclic receptors for binding both neutral and ionic guests. The backbones can also be readily modified and appended with discrete functional units. Therefore, they have also been widely utilized in designing new molecular tweezers, for assembling ordered supramolecular architectures, and for directing the formation of complicated macrocyclic systems. This feature article highlights the recent advances, with a primary focus on our own work.

Design and Synthesis of Transition Metal and Inner Transition Metal Binding Calixarenes

Calixarenes, macrocycles containing a preorganized central cavity, are often used to bind molecular and ionic guests. Though these guests are mostly limited to alkali metal or organic cations, and solvents, it is possible to assemble transition metal coordination complexes from calixarene derivatives. This review will illustrate how careful design strategies can be employed to devise target compounds and focus on synthetic approaches to prepare the desired calixarene derivatives.

Maximized Proton Conductivity of the HPF6 Clathrate Hydrate by Structural Transformation

The unique and specific interaction of ionic guests with the surrounding cage framework might play a key role in promoting the electrochemical properties of ionic clathrate hydrates. In this work we focus on addressing (1) structural transformation simply due to an increase of water content, (2) structure-dependent ionic conductivity, (3) the existence of maximum ionic conductivity at a specific hydration number, and (4) proton migration through channels in the crystalline hydrate matrix. The melting temperature and ionic conductivity of hexafluorophosphoric acid hexahydrate (HPF6·6.0H2O) are found to be approximately 29.5 °C and 10−1 S·cm−1, respectively, showing that HPF6·6.0H2O possesses desirable features as a solid proton conductor.

Recognition of Ionic Guests by Ionic β‐Cyclodextrin Derivatives

Inclusion compounds of cationic, anionic, and neutral p-substituted derivatives of tert-butylbenzene complexed in beta-cyclodextrin and its ionic 6-mono and 6-hepta derivatives were systematically investigated by isothermal titration calorimetry (ITC). All inclusion compounds showed 1:1 stoichiometry with binding constants ranging from 10 to 3 x 10(6) M(-1). The binding free energies could be subdivided into apolar and electrostatic contributions. The electrostatic interactions could be quantitatively described by Coulomb's law by taking into account the degree of protonation of hosts and guests, the orientations of the guests within the hosts, and ion shielding as described by the Debye-Hückel-Onsager theory. The orientations of the guests within the cyclodextrin cavities were determined by ROESY NMR spectroscopy.

Conformational Characteristics of Free and Cesium Complexed p-H-Calix[6]arene Alkyl Ester Derivatives

Calixarenes have received much interest because of their versatile recognition properties toward a variety of ionic and organic guests including biomolecules, which result from the ease of functionalization at the lower rim or upper rim. The conformational characteristics of calixarenes are also known to have strong effects on their complex formation behaviors. Among the calixarene series, the appropriately functionalized calix[6]arenes are known to have a preference for cesium ion, which is one of the major components of nuclear wastes. Nevertheless, there are only a few reports on the complexation of cesium ion by calix[6]arenes and on the conformational behaviors of the complex and/or the free host itself. In this paper, we report the unusual conformational characteristics of p-H-calix[6]arene derivatives and their cesium ion complexes revealed by using H, C and Cs NMR spectroscopy at various temperatures.

Modern Potentiometry

For most chemists, potentiometry with ion-selective electrodes (ISEs) primarily means pH measurements with a glass electrode. Those interested in clinical analysis might know that ISEs, routinely used for the determination of blood electrolytes, have a market size comparable to that of glass electrodes. It is even less well known that potentiometry went through a silent revolution during the past decade. The lower detection limit and the discrimination of interfering ions (the selectivity coefficients) have been improved in many cases by factors up to 10(6) and 10(10), respectively, thus allowing their application in fields such as environmental trace analysis and potentiometric biosensing. The determination of complex formation constants for lipophilic hosts and ionic guests is also covered in this Minireview.

Strategies for Using Host—Guest Chemistry in the Extractive Separations of Ionic Guests

AbstractFor Abstract see ChemInform Abstract in Full Text.

Chromoionophoric Recognition of Alkylamines by Nitro Derivative of Calix[4]arene-crown-5 Ether

Department of Chemistry, Chung-Ang University, Seoul 156-756, KoreaReceived December 4, 2003Key Words : Calix-crown ether, Alkylamine, Chromoionophore, OR logic gate The molecular design of efficient and selective chromo-genic and fluorogenic ionophore systems for the sensing ofchemically and biologically important ionic guests hasattracted much attention in the past decade.

Ionic interactions and multilayer structures on self-assembled surfaces of calix[4]resorcinarene

The ionization of a self-assembled monolayer of tetrathiol calix[4]resorcinarene, which is a synthetic host in guest–host recognition phenomena, was investigated. Using surface plasmon resonance measurements, it was found that ionization of the self-assembled surface occurred in water at a pH of approximately 11.5. These ionized surfaces of calix[4]resorcinarene were used to bind ionic guests such as metallic copper ions that were further exploited in the formation of supramolecular ionic assemblies of calix[4]resorcinarene. The structure of the molecular assemblies was characterized using polarization modulation infrared reflection absorption spectroscopy. The use of ionic interactions to attach molecules such as 11-mercapotundecanoic acid to the upper rim of the calix[4]resorcinarene host was also investigated as a method for simple and non-covalent modification of the host cavity.

Ionic interactions and multilayer structures on self-assembled surfaces of calix[4]resorcinarene

The ionization of a self-assembled monolayer of tetrathiol calix[4]resorcinarene, which is a synthetic host in guest–host recognition phenomena, was investigated. Using surface plasmon resonance measurements, it was found that ionization of the self-assembled surface occurred in water at a pH of approximately 11.5. These ionized surfaces of calix[4]resorcinarene were used to bind ionic guests such as metallic copper ions that were further exploited in the formation of supramolecular ionic assemblies of calix[4]resorcinarene. The structure of the molecular assemblies was characterized using polarization modulation infrared reflection absorption spectroscopy. The use of ionic interactions to attach molecules such as 11-mercapotundecanoic acid to the upper rim of the calix[4]resorcinarene host was also investigated as a method for simple and non-covalent modification of the host cavity.

Calix[8]arene-based glycoconjugates as multivalent carbohydrate-presenting systems

An efficient approach for the introduction of eight mono- or disaccharide sugar moieties (d-glucose, N-acetyl-d-glucosamine, d-galactose, l-fucose, d-maltose and d-cellobiose) at the upper rim of calix[8]arene 1, using thioureido linkers, is reported. The obtained water-soluble, nanosized glycocalix[8]arenes 5b–10b may act as biomimetic carbohydrate systems and as hosts for highly polar organic molecules. Preliminary 1H NMR complexation experiments of octaglycosyl derivative 7b and 10b with ionic guests are also reported.

Characterization of Self-Assembling Encapsulation Complexes in the Gas Phase and Solution

The interaction of quaternary ammonium ion guests with self-assembling hosts was examined by 1H NMR and ESI-MS experiments. The hosts consist of four identical, self-complementary subunits, reversibly joined in a capsular assembly through hydrogen bonding. Both approaches show the ammonium ions to be encapsulated, held within the hollow shell of the capsule. Competition experiments with a series of different guest ions reveal a characteristic size selectivity. The NMR and MS methods are complementary: MS easily reveals the formation of heterotetramers from different subunits that could not be determined by NMR, while NMR allowed competitive encapsulations of neutral and ionic guests that were not possible to detect with MS. These competition experiments gave a lower limit of ca. 3.6 kcal/mol for the contribution of cation−π interactions involved in the encapsulation of the ionic guests.