‘Biting effect’ stabilizing gallate-type catechin/quaternary ammonium ion complexes

Inhibition of the intracellular Ca(2+) transporter SERCA (Sarco-Endoplasmic Reticulum Ca(2+)-ATPase) by the natural polyphenol epigallocatechin-3-gallate

The use of a microsomal preparation from skeletal muscle revealed that both Ca(2+) transport and Ca(2+)-dependent ATP hydrolysis linked to Sarco-Endoplasmic Reticulum Ca(2+)-ATPase are inhibited by epigallocatechin-3-gallate (EGCG). A half-maximal effect was achieved at approx. 12 μM. The presence of the galloyl group was essential for the inhibitory effect of the catechin. The relative inhibition of the Ca(2+)-ATPase activity decreased when the Ca(2+) concentration was raised but not when the ATP concentration was elevated. Data on the catalytic cycle indicated inhibition of maximal Ca(2+) binding and a decrease in Ca(2+) binding affinity when measured in the absence of ATP. Moreover, the addition of ATP to samples in the presence of EGCG and Ca(2+) led to an early increase in phosphoenzyme followed by a time-dependent decay that was faster when the drug concentration was raised. However, phosphorylation following the addition of ATP plus Ca(2+) led to a slow rate of phosphoenzyme accumulation that was also dependent on EGCG concentration. The results are consistent with retention of the transporter conformation in the Ca(2+)-free state, thus impeding Ca(2+) binding and therefore the subsequent steps when ATP is added to trigger the Ca(2+) transport process. Furthermore, phosphorylation by inorganic phosphate in the absence of Ca(2+) was partially inhibited by EGCG, suggesting alteration of the native Ca(2+)-free conformation at the catalytic site.

Offset pi-pi interaction in crystal structure of (-)-gallocatechin-3-O-gallate

The single crystal of (-)-gallocatechin-3-O-gallate (GCg) was prepared using a solution containing an equimolecular amount of GCg and (-)-epigallocatechin-3-O-gallate (EGCg) in water. The crystal structure of GCg determined by X-ray crystallographic analysis was monoclinic with the space group P2(1) at 223 K. Offset pi-pi interactions formed between the A and A rings, B and B rings, and gallate and gallate rings of GCg, and five intermolecular hydrogen bonds formed between GCgs, GCg and water. The B ring of GCg bonded to C2 was in the axial position and the gallate ring of GCg bonded to C3 was in the pseudoaxial position with respect to the C ring of GCg.

Molecular recognition of organic ammonium ions in solution using synthetic receptors

Ammonium ions are ubiquitous in chemistry and molecular biology. Considerable efforts have been undertaken to develop synthetic receptors for their selective molecular recognition. The type of host compounds for organic ammonium ion binding span a wide range from crown ethers to calixarenes to metal complexes. Typical intermolecular interactions are hydrogen bonds, electrostatic and cation-π interactions, hydrophobic interactions or reversible covalent bond formation. In this review we discuss the different classes of synthetic receptors for organic ammonium ion recognition and illustrate the scope and limitations of each class with selected examples from the recent literature. The molecular recognition of ammonium ions in amino acids is included and the enantioselective binding of chiral ammonium ions by synthetic receptors is also covered. In our conclusion we compare the strengths and weaknesses of the different types of ammonium ion receptors which may help to select the best approach for specific applications.

Chemiluminescence enhancement of 1,2-di[3,4,5-tri(3,4,5-trihydroxybenzoyloxy)benzoyloxy] benzene in the presence of quaternary ammonium ions

The chemiluminescence intensity of 1,2-di[3,4,5-tri(3,4,5-trihydroxybenzoyloxy)benzoyloxy] benzene increased in the presence of quaternary ammonium ions, such as acetylcholine chloride, choline chloride or benzyltrimethylammonium chloride. The complex of 1,2-di[3,4,5-tri(3,4,5-trihydroxybenzoyloxy)benzoyloxy] benzene with acetylcholine chloride, choline chloride or benzyltrimethylammonium chloride was investigated by (1)H-NMR spectroscopy. The structure of the complex formed from 1,2-di[3,4,5-tri(3,4,5-trihydroxybenzoyloxy)benzoyloxy] benzene with choline chloride was described by an ab initio quantum chemical calculation.