A cascade of reactions involving anchimeric assistance leads to a highly 'crowded' hexa(alkylcarboxy)benzene.

The substitution of hexabromomethylbenzene with 1-adamantyl carboxylate quantitatively leads to the corresponding hexacyl derivative via anchimeric assistance by the alkylcarboxy substituents.

A colorimetric sensing ensemble for heparin.

A receptor possessing ammoniums and a novel amino acid with a boronic acid side chain was designed and synthesized. The receptor shows good affinity and selectivity for heparin over similar polysaccharides possessing lower anionic charge density. The affinity for heparin is similar to that for a heparin disaccharide, indicating that disaccharidic units are the likely sites for binding to the receptor.

Stochastic sensing of IP(3) has far-reaching consequences.

Hagan Bayley's group at Texas A&M University has devised a stochastic sensing methodology for the quantitation of the second messenger inositol 1,4,5-trisphosphate. The unique sensing scheme is very selective and has the potential to measure cytosolic concentrations of IP(3).

Novel C3-symmetric molecular scaffolds with potential facial differentiation.

The conversion of 1,3,5-substituted benzene and mesitylene by electrophilic aromatic substitution and Sonogashira cross-coupling, respectively, furnished the C3-symmetric, hexasubstituted benzene derivatives 1 and 2 with an alternating substitution pattern. Based on the molecular scaffolds obtained, the two systems serve as model compounds for novel receptor molecules with distinct geometric features. X-ray structures have been obtained for 1 and 2, which are discussed in regard to their aptitude as receptor platforms or supramolecular building blocks.

1,3,5-2,4,6-functionalized, facially segregated benzenes-exploitation of sterically predisposed systems in supramolecular chemistry.

In the present article, we introduce the unique steric features of 1,3,5-substituted triethylbenzenes as a design principle for host molecules and supramolecular systems. Due to steric gearing, all three functional substituents are disposed on the same side of the phenyl plane. The use of this benzene scaffold has lead to the synthesis of various receptor molecules for a wide range of different guest species.

Toward a stable hydroxyphosphorane.

[reaction: see text] Hydroxy-pentaoxy-phosphoranes are transient intermediates formed during the hydrolysis of various phosphoesters. Kinetic analyses support the existence of such compounds, although they are not isolated. In an attempt to create a stable example, 2 equiv of a ligand possessing a very high effective molarity were attached to a central phosphorus.

Teaching old indicators new tricks.

Most synthetic sensors are designed with covalent attachment between a receptor and a reporter moiety. In this report, we describe the current progress of our use of noncovalently attached indicators to signal binding of analytes. With these systems, analyte binding leads to indicator displacement from the binding cavity, which in turn yields an optical signal modulation.

Artificial receptors involved in enolization and pK(a) shifts.

Abiotic receptors used to enolize carbonyl compounds or to shift substrate pK(a) values are reviewed. These systems exhibit disparate frameworks and several approaches to binding and anion stabilization. Detailed emphasis is placed on a bicyclic cyclophane that induces pK(a) shifts in active methylene compounds through NH-pi hydrogen bonding with the resultant enolates.

Sensing A Paradigm Shift in the Field of Molecular Recognition: From Selective to Differential Receptors.

Molecular recognition has evolved from a science designed to understand biological systems into a much more diverse area of research. While work continues to elucidate "nature's tricks" with respect to intermolecular interactions, much attention has turned to the perspective that molecular recognition, by design, can lead to new technologies. Applications ranging from molecular sensing to information storage and even working molecular machines have been envisioned.

Development of multianalyte sensor arrays composed of chemically derivatized polymeric microspheres localized in micromachined cavities.

The development of a chip-based sensor array composed of individually addressable polystyrene-poly(ethylene glycol) and agarose microspheres has been demonstrated. The microspheres are selectively arranged in micromachined cavities localized on silicon wafers. These cavities are created with an anisotropic etch and serve as miniaturized reaction vessels and analysis chambers.

Characterization of multicomponent monosaccharide solutions using an enzyme-based sensor array.

We report the development of a sensor for rapidly and simultaneously measuring multiple sugars in aqueous samples. In this strategy, enzyme-based assays are localized within an array of individually addressable sites on a micromachined silicon chip. Microspheres derivatized with monosaccharide-specific dehydrogenases are distributed to pyramidal cavities anisotropically etched in a wafer of silicon (100) and are exposed to sample solution that is forced through the cavities by a liquid chromatography pumping system.

pK(a) values and geometries of secondary and tertiary amines complexed to boronic acids-implications for sensor design.

[structure in text] The pK(a) values and the geometries of secondary and tertiary amines adjacent to boronic acids were determined using potentiometric and (11)B NMR titrations. The studies showed that the secondary ammonium ion has a pK(a) similar to that of the tertiary ammonium species, which leads to the formation of tetrahedral boron centers at pH values above approximately 5.5.

Anion recognition: synthetic receptors for anions and their application in sensors.

Important contributions to the field of anion sensing include electrochemical lipophilic uranyl salophene receptors incorporated into membranes that act as fluoride-selective potentiometric microsensors. A promising optical-based sensor, selective for cyclic AMP, involves a preorganized, molecularly imprinted polymer employing an intrinsic fluorophore. Competition methods using ensembles of recognition units and external indicators have been used to sense citrate in highly competitive media and micromolar concentrations of inositol(tris)phosphate in water.

Teaching Old Indicators New Tricks: A Colorimetric Chemosensing Ensemble for Tartrate/Malate in Beverages.

The competition between tartrate and a common indicator (1) for a synthetic host (2) has been used to quantitate tartrate in beverages derived from grapes. The approach demonstrates a general method for the development of colorimetric assays in highly competitive media.

A Chemosensor for Citrate in Beverages.

Competitive binding like that in immunoassays is the principle behind the chemosensor based on receptor 1, which was used to measure the concentration of citrate (2) in a series of common beverages. Citrate displaces the fluorescent colorimetric probe 5-carboxylfluorescein (3) from 1, and the process can be monitored by UV or fluorescence spectroscopy.

Using guanidinium groups for the recognition of RNA and as catalysts for the hydrolysis of RNA.

The guanidinium functional group is commonly used in nature to recognize and bind anions through ion pairing and hydrogen bonding. Specific hydrogen-bonding patterns can be found in crystal structures of simple guanidinium salts. Analysis of these simple salts reveals a variety of features which are found in natural systems.

Solid and Solution Phase Organic Syntheses of Oligomeric Thioureas.

In order to study supramolecular architectures built from unnatural oligomeric and polymeric structures, one must first have an efficient synthetic strategy to produce them. Oligomers built from thiourea groups should form complex secondary and tertiary structures due to the hydrogen-bonding capabilities of the thioureas. Herein, both solution and solid phase synthetic procedures that yield oligomeric thioureas are described.

Radioactive end labeling to determine hydrolytic rates of nuclease mimics.

Radioactive end labeling can be used to determine the hydrolytic rates of nuclease mimics on moderate to long lengths of RNA or DNA. However, the reliability of end labeling as an assay can vary depending on how well the unincorporated label is removed from the labeled RNA or DNA products. Therefore, gel filtration, acid precipitation, membrane diafiltration, and paper chromatography were tested to determine which technique was the most effective at such separation.

On the mechanism of action of ribonucleases: dinucleotide cleavage catalyzed by imidazole and Zn2+.

Cyclization/cleavage of the 2-(p-nitrophenyl) phosphate ester of propylene glycol is catalyzed by imidazole and, much more effectively, by Zn2+ with imidazole. In the latter case, the mechanism involves simultaneous Lewis acid/base catalysis. Similar Zn2+ and imidazole catalysis of cyclization/cleavage is seen with the dinucleotide 3',5'-UpU (uridylyluridine).