Synthesis and uses of macrobicyclic cryptands: from complexation of transition metal ions to molecular devices
01 Jun 1996-Vol. 108, Iss: 3, pp 229-233
TL;DR: In this article, a number of cryptands having heteroditopic as well as heterotritopic receptor sites have been achieved using alkali metal ions as templates, and these cryptands exhibit interesting properties and can further accomodate small anions inside the cavity.
Abstract: Syntheses of a number of cryptands having heteroditopic as well as heterotritopic receptor sites have been achieved using alkali metal ions as templates. Some of the cryptands can be synthesized on a multi-gram scale without using any templating metal ions at low temperature (278 K). Each of these cryptands readily forms inclusion complexes with transition metal ions. These cryptands exhibit interesting properties and can further accomodate small anions inside the cavity. Further, upon suitable derivatization, some of the cryptands can behave as amphiphiles and form Langmuir-Blodgett films very readily. When derivatized with 9-methylanthracene, some of the cryptands show interesting fluorescence properties and can be of use as molecular photonic devices.
TL;DR: Laterally non-symmetric aza cryptands incorporating N atoms in the three bridges, readily make inclusion complexes with a number of transition as well as maingroup metal ions.
Abstract: Laterally non-symmetric aza cryptands incorporating N atoms in the three bridges, readily make inclusion complexes with a number of transition as well as maingroup metal ions. The donor ability of the N a toms in the bridges can be modulated through attachment of electron-withdrawing groups. In this modified cryptand, a metal ion can be translocated from inside the cavity to the outside depending on the nature of the counter anion. Translocation of a metal ion between inside and outside a cryptand cavity is highly desi rable as it can lead to the development of par adigms for a new class of molecular systems, adding a new dimension to the kinetic, thermodynamic and a multitude of other properties in these systems. This process of transloc ation of a metal ion can be studied in sol ution when a suitable group is attached and in some cases, the co mplexes can be characterized by X-ray crystallography.
TL;DR: In this article, the authors proposed a self-assembly approach for the generation of a well-defined supramolecular architecture by self-assembling from their components under a given set of conditions.
Abstract: The selective binding of a substrate by a molecular receptor to form a supramolecular species involves molecular recognition which rests on the molecular information stored in the interacting species. The functions of supermolecules cover recognition, as well as catalysis and transport. In combination with polymolecular organization, they open ways towards molecular and supramolecular devices for information processing and signal generation. The development of such devices requires the design of molecular components performing a given function (e.g., photoactive, electroactive, ionoactive, thermoactive, or chemoactive) and suitable for assembly into an organized array. Light-conversion devices and charge-separation centers have been realized with photoactive cryptates formed by receptors containing photosensitive groups. Eleclroactive and ionoactive devices are required for carrying information via electronic and ionic signals. Redox-active polyolefinic chains, like the “caroviologens”, represent molecular wires for electron transfer through membranes. Push-pull polyolefins possess marked nonlinear optical properties. Tubular mesophases, formed by organized stacking of suitable macro-cyclic components, as well as “chundle”-type structures, based on bundles of chains grafted onto a macrocyclic support, represent approaches to ion channels. Lipophilic macrocyclic units form Langmuir-Blodgett films that may display molecular recognition at the air-water interface. Supramolecular chemistry has relied on more or less preorganized molecular receptors for effecting molecular recognition, catalysis, and transport processes. A step beyond preorganization consists in the design of systems undergoing self-organization, that is, systems capable of spontaneously generating a well-defined supramolecular architecture by self-assembling from their components under a given set of conditions. Several approaches to self-assembling systems have been pursued: the formation of helical metal complexes, the double-stranded helicates, which result from the spontaneous organization of two linear polybipyridine ligands into a double helix by binding of specific metal ions; the generation of mesophases and liquid crystalline polymers of supramolecular nature from complementary components, amounting to macroscopic expression of molecular recognition; the molecular-recognition-directed formation of ordered solid-state structures. Endowing photo-, electro-, and ionoactive components with recognition elements opens perspectives towards the design of programmed molecular and supramolecular systems capable of self-assembly into organized and functional supramolecular devices. Such systems may be able to perform highly selective operations of recognition, reaction, transfer, and structure generation for signal and information processing at the molecular and supramolecular levels.
TL;DR: A receptor is described that operates as a logic device with two input channels: the fluorescence signal depends on whether the molecule binds hydrogen ions, sodium ions or both and the input/output characteristics of this molecular device correspond to those of an AND gate.
Abstract: MOLECULES that perform logic operations are prerequisites for molecular information processing and computation1–11. We12,13 and others14–16 have previously reported receptor molecules that can be considered to perform simple logic operations by coupling ionic bonding or more complex molecular-recognition processes with photonic (fluorescence) signals: in these systems, chemical binding (the 'input') results in a change in fluorescence intensity (the 'output') from the receptor. Here we describe a receptor (molecule (1) in Fig. 1) that operates as a logic device with two input channels: the fluorescence signal depends on whether the molecule binds hydrogen ions, sodium ions or both. The input/output characteristics of this molecular device correspond to those of an AND gate.
TL;DR: Supramolecular chemistry is the study of the structures and functions of the supermolecules that result from binding substrates to molecular receptors.
Abstract: Supramolecular chemistry is the study of the structures and functions of the supermolecules that result from binding substrates to molecular receptors. Macropolycyclic receptors and coreceptors have been designed that form cryptate inclusion complexes and display molecular recognition towards spherical, tetrahedral, and linear substrates of various kinds (metal cations, inorganic anions, and organic or biological cations or anions). Anion binding has led to the development of anion coordination chemistry. Metalloreceptors simultaneously bind organic molecules and metal ions; speleands combine polar and nonpolar binding subunits. Receptors bearing reactive functional groups may act as molecular reagents or catalysts, performing a chemical transformation on the bound substrates (by such reactions as hydrogen transfer, ester cleavage, and protoadenosinetriphosphatase and protokinase activities). Receptors fitted with lipophilic groups can operate as molecular carriers, translocating bound species through a membrane; this transport can be coupled to chemical potentials (proton and redox gradients).