Spectroscopic studies of 7,8-diacetoxy-4-methylcoumarin and 7,8-dipentynoyl-4-methylcoumarin binding with calreticulin.

Calreticulin (CRT) is a protein found mainly in the endoplasmic reticulum (ER) that maintains calcium levels and controls protein folding, but has recently been found at the cell surface, cytoplasm, and in the extracellular matrix. CRT participates in multiple physiological processes such as gene expression, the immune response, and cancer. Calreticulin has been shown to autoacetylate with the binding of preferred ligand 7,8-diacetoxy-4-methylcoumarin (DAMC). This project aims to develop a chemical biology approach to investigate importance of CRT acylating abilities on its nonendoplasmic reticulum functions by targeting the downstream substrates of CRT acetylation. Our goal was to use CRT to transfer a pentynoyl tag (using a novel ligand, DPeMC) to its substrates, which can then be used as a handle for protein identification. Molecular modelling using available data in the literature was used to approximate the binding interface between CRT and the acylation ligands. Molecular Operating Environment (MOE) software was used to perform sequence alignment, simulated annealing, positional refinement, and blind docking of acylated coumarins with the CRT model. Docking studies pointed to the P domain as the most thermodynamically and sterically favourable region for acylated coumarin binding with tryptophan residue 200 within the active site on CRT. Absorption and fluorescence spectra of all coumarin compounds in ethanol:PBS (1:9 v/v) solution were investigated. Stern-Volmer quenching constant (KSV ), binding constant (K), and number of binding sites (n) of each coumarin compound with CRT was determined. Our studies demonstrated that acyl coumarin compounds bind to CRT using a dynamic quenching mechanism, bind to a single binding site on the P domain, and that the protein-ligand interaction is spontaneous and exothermic.

Aqua-(µ-cone-26,28-dibut-oxy-25,27-bis-{N-[5-(dimethyl-amino)-naphthalene-1-sulfon-yl]carbamoylmeth-oxy}-5,11,17,23-tetra-kis-(1,1-dimethyl-eth-yl)calix[4]arene(2-))disodium acetonitrile tetra-solvate.

The structure of the title complex, [Na(2)(C(80)H(98)N(4)O(10)S(2))(H(2)O)]·4CH(3)CN, obtained after crystallization from aceto-nitrile, contains two formula units in the asymmetric unit (Z' = 2) and an estimated four mol-ecules of acetonitrile per calixarene moiety. It is unusual for two Na(+) ions to occupy the lower rims of the cone calix[4]arene, as in this case, with one Na(+) ion forming two O→ Na(+) coordinate bonds with the two but-oxy groups and four such bonds with the two N-dansyl carboxamide groups, forming six dative bonds between Na(+) and O. On the other hand, the other Na(+) ion forms only five O→Na(+) coordinate bonds on the far end of the calix[4]arene lower rim, bringing the two dansyl groups in close proximity with each other. There also appears to be an O→Na(+) coordination coming from a dangling water mol-ecule. The structure contained both resolved and poorly resolved solvent mol-ecules. The latter were treated using the SQUEEZE routine in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148-155].

New fluorogenic dansyl-containing calix[4]arene in the partial cone conformation for highly sensitive and selective recognition of lead(II).

A new efficient and highly selective fluorescent chemosensor for determination of Pb (2+) has been obtained by covalent attachment of two pendent proton-ionizable dansylcarboxamide groups to the calix[4]arene preorganized in the partial cone conformation. This geometry of the calixarene moiety was chosen on the basis of the prior (1)H NMR study of conformations adopted by the flexible dansyl-containing prototype upon complexation with lead ion. In acidic MeCN-H2O (1:1 v/v) solutions, the partial cone fluoroionophore allowed for detection of Pb (2+) at the levels as low as 2.5 ppb, which is totally compatible with the regulations of the U.S. Environmental Protection Agency and the World Health Organization on the limiting content of this hazardous pollutant in drinking water.

Optical determination of thallium(I) and cesium(I) with a fluorogenic calix[4]arenebis(crown-6 ether) containing one pendent dansyl group.

A fluorogenic derivative of 1,3-alternate calix[4]arenebis(crown-6) (1) containing a dansyl group in the proton-ionizable side arm has been employed in selective sensing of Tl+ and Cs+ at low concentration levels in MeCN-H2O (1:1) mixed solvent. Optical recognition of these two metal cations by 1 occurs in contrasting modes. On the basis of the results of fluorescence, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), and 1H NMR studies, Tl+ and Cs+ react with 1 via formation of 1:1 complexes that differ in coordination arrangement around the metal ion.

Novel fluorogenic calix[4]arene-bis(crown-6-ether) for selective recognition of thallium(I).

A new fluorogenic, dansyl group-containing derivative of 1,3-alternate calix[4]arene-bis(crown-6-ether) provides optical recognition of Tl+ with selectivity over many other metal cations, including Na+, K+, Ca2+, Ag+, Hg2+ and Pb2+, and embodies the first example of a calixarene-based fluorescent Tl+-chemosensor.

Rigid versus flexible: how important is ligand "preorganization" for metal ion recognition by lower rim-functionalized calix[4]arenes?

For an assessment of the outcomes from use of an appropriately "preorganized" calixarene-based ionophore versus its conformationally mobile prototype, solvent extraction propensities of flexible calix[4]arene di-[N-(X-sulfonyl)carboxamides] for alkali, alkaline earth metal cations, Pb2+, Ag+ and Hg2+ are compared with those for seven new rigid analogs fixed in the cone, partial cone and 1,3-alternate conformations. For each of the metal ions, the preferred calix[4]arene conformation was determined from the NMR spectra for the metal salt of the flexible ligand. Except for Ag+, flexible calix[4]arene di-[N-(X-sulfonyl)carboxamides] were found to provide greater metal ion extraction efficiency and better selectivity than the corresponding "preorganized" ionophores.

New Proton-Ionizable Lariat Ethers with Picrylamino-Type Side Arms and Their Alkali Metal Salts. Synthesis and Structural Studies(1).

Twelve novel proton-ionizable dibenzo lariat ethers with picrylamino-type sidearms attached to the central carbon of a three-carbon bridge have been prepared in high yields by a three-step synthesis from the lariat ether alcohols via the corresponding lariat ether mesylates and amines. Structural studies conducted in solution by (1)H NMR spectroscopy and in the solid state by X-ray diffraction show that the picrylamino-type lariat ethers are preorganized for metal ion complexation with the sidearms oriented toward the macrocyclic polyether cavities due to intramolecular NH.O bonding. Structural investigations of the alkali metal salts of representative ionized picrylamino-lariat ethers in solution demonstrate cooperative coordination of the metal cation by the macrocyclic polyether unit and the ionized sidearm that serves as the counterion with the negative charge localized on the one of o-nitro groups. In the Li(+) salt of ionized sym-(picrylamino)dibenzo-14-crown-4, this places the aromatic ring of the sidearm perpendicular to the plane of the four ring oxygens.