Visual detection of AMP and real-time monitoring of cyclic nucleotide phosphodiesterase (PDE) activity in neutral aqueous solution. Chemosensor-coupled assay of PDE and PDE inhibitors

Enzyme assays with supramolecular chemosensors - the label-free approach

Enzyme activity measurements are essential for many research areas, e.g., for the identification of inhibitors in drug discovery, in bioengineering of enzyme mutants for biotechnological applications, or in bioanalytical chemistry as parts of biosensors. In particular in high-throughput screening (HTS), sensitive optical detection is most preferred and numerous absorption and fluorescence spectroscopy-based enzyme assays have been developed, which most frequently require time-consuming fluorescent labelling that may interfere with biological recognition. The use of supramolecular chemosensors, which can specifically signal analytes with fluorescence-based read-out methods, affords an attractive and label-free alternative to more established enzyme assays. We provide herein a comprehensive review that summarizes the current state-of-the-art of supramolecular enzyme assays ranging from early examples with covalent chemosensors to the most recent applications of supramolecular tandem enzyme assays, which utilize common and often commercially available combinations of macrocyclic host molecules (e.g. cyclodextrins, calixarenes, and cucurbiturils) and fluorescent dyes as self-assembled reporter pairs for assaying enzyme activity.

Anion recognition and sensing with Zn(II)-dipicolylamine complexes

This critical review covers the developments in anion recognition and sensing using Zn(II)-dipicolylamine functionalized receptors over the past decade with emphasis on recent rapid advances in the last five years.

Design of dual-emission chemosensors for ratiometric detection of ATP derivatives

Nucleoside pyrophosphate (nucleoside PP) derivatives are widespread in living cells and play pivotal roles in various biological events. We report novel fluorescence chemosensors for nucleoside PPs that make use of coordination chemistry. The chemosensors, which contain two Zn(II)-dipicolylamine units, bind strongly to nucleoside PPs (K(app)>10(6) M(-1)) in aqueous solution and sense them by a dual-emission change. Detailed fluorescence and UV/Vis spectral studies revealed that the emission changes of the chemosensors upon binding to nucleoside PPs can be ascribed to the loss of coordination between Zn(II) and the acridine fluorophore. This is a unique sensing system based on the anion-induced rearrangement of the coordination. Furthermore, we demonstrated the utility of these chemosensors in real-time monitoring of two important biological processes involving nucleoside PP conversion: the apyrase-catalyzed hydrolysis of nucleoside PPs and the glycosyl transfer catalyzed by beta-1,4-galactosyltransferase.

Synthesis of a large amino-phenolic cage. Synthesis, crystal structures, and acid-base and coordination behavior toward cations and anions

The synthesis and characterization of the new polyaza-phenolic-macrobicycle 32-hydroxy-1,4,7,10,13,16,19,22-octaazatricyclo-[11.11.7.1(26,30)]-diatriconta-26,28,Delta(30,32)-triene (L) are reported. L incorporates a 2,6-dimethyl-phenolic unit bridging two opposite amine functions of the [24]aneN(8) polyazamacrocyclic base to obtain a large cage. The basicity and binding properties of L toward Cu(II), Zn(II), and Cl(-) were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I = 0.15 mol dm(-3)). L can add up to six acidic protons, yielding the H(5)L(5+) species or the H(6)L(6+) species, depending on the ionic medium used. The molecular topology of L permits the formation of a highly positive three-dimensional cavity in the polyprotonated species that is able to host the chloride anion. This was detected both using potentiometric data, log K = 41.33 for the reaction L + 6H(+) + Cl(-) = H(6)LCl(5+), and in (35)Cl NMR experiments that showed interactions also with the H(5)L(5+) and H(4)L(4+) species. The anion is probably hosted inside the three-dimensional cavity of L, and stabilized by H-bonding interactions with the ammonium groups, as depicted in the crystal structure of the H(6)L(6+) cation reported. L forms mono- and dinuclear complexes with all the metal ions investigated; the dinuclear species are the only existing species with an L:M(II) molar ratio of 1:2 at pH higher than 6. The phenolate oxygen atom coordinates the two metal ions in a bridged disposition, drawing them inside the macrobicyclic cavity. The two metals were found to be quite isolated by the medium, and were coordinated by all the amine groups of L, as shown by the crystal structure of the dinuclear [Zn(2)H(-1)L](3+) species. This species can bind guests such as hydroxide and phosphate anions. Studies of anion binding in aqueous solution using pyrochatecol violet as the sensing guest revealed that the [Zn(2)H(-1)L](3+) species is able to bind one phosphate at physiological pH.

Species-differentiable sensing of phosphate-containing anions in neutral aqueous solution based on coordinatively unsaturated lanthanide complex probes

A new chromogenic/fluorogenic molecular probe was developed for highly selective and species-differentiable detection of phosphate-containing anions in neutral aqueous solution. The coordinatively unsaturated lanthanide complex, made from Eu(III) ion and 2-[(8-hydroxy-5-sulfo-7-quinoline)azo]-1,8-dihydroxy-3,6-naphthalene disulfonic acid, changed its conformation when binding to the incoming target anions, which resulted in differential absorption or fluorescence responses. It was demonstrated that not only phosphate and pyrophosphate but also DNA and RNA could be clearly distinguished by visible absorption or fluorescence spectra. Also, differential responses in absorption spectra were observed when AMP, ADP, and ATP were added into the sensing system. Selective quantitation of these phosphate-containing anions in aqueous solutions, therefore, can be easily available. DNA and RNA were distinguished by different colors and independent fluorescence emissions due to their intrinsic differences in beta-D-ribose residues. Simultaneous or independent quantitation of DNA and RNA in a mixture sample, therefore, is possible without pretreatment with nuclease. Furthermore, the influence from the base selectivity can be eliminated by the use of the probe. The detection limits of phosphate and 5'-ATP in neutral water were 6.0 x 10(-7) and 9.0 x 10(-7)M, respectively, by the UV/Vis spectrophotometric method; the detection limits were 12.3 ng/mL for DNA by fluorimetry and 2.3mg/L for RNA by UV/Vis spectrophotometry.

A Lanthanide Hybrid Cluster as a Selective Optical Chemosensor for Phosphate-containing Anions in Aqueous Solution

An europium-chelating [2Fe-2S] cluster was used to assemble an optical molecular chemosensor highly selective for phosphate-containing anions. Phosphate, pyrophosphate, AMP, ADP, ATP, DNA and RNA were well distinguished by UV/V is absorption or fluorescence studies.