Supramolecular cruciforms

By self-assembling fluorescent pyridyl cruciforms with bis-Pd-pincer complexes, supramolecular assemblies with attractive optical properties were synthesized; these assemblies show potential as electro-optical materials.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

Cruciforms' polarized emission confirms disjoint molecular orbitals and excited states

Steady-state and time-resolved polarized spectroscopy studies reveal that electronic excitation to the third excited state of 1,4-distyryl-2,5-bis(arylethynyl)benzene cruciforms results in fluorescence emission that is shifted an angle of ca. 60°. This result is consistent with quantum chemical calculations of the lowest electronic excited states and their transition dipole moments. The shift originates from the disjointed nature of the occupied molecular orbitals being localized on the different branches of the cruciforms.     

General approach to low-molecular-weight metallogelators via the coordination-induced gelation of an L-glutamate-based lipid

A twin-tailed glutamate-based lipid with a pyridine headgroup was prepared in good yield using standard amide coupling and protection/deprotection chemistry. The resulting Lewis basic lipid gels a wide array of hydrocarbon solvents at a critical gelation concentration (C(g)) of 0.3 wt %. The gelation of more polar solvents, such as ethanol, THF, dichloromethane, and chloroform, occurs with a C(g) of between 2 and 5 wt %, demonstrating the importance of hydrogen bonding interactions in gel formation. The importance of hydrogen bonding in this system was also demonstrated by IR observation of the amide bands, which show a substantial shift upon gelation. Solutions of this new organogelator with concentrations below C(g) rapidly form gels upon the introduction of a wide variety of metal salts or complexes, providing a convenient general method for the preparation of metallogelators. Spectroscopic evidence suggests that the enhanced gelation seen in the metal-containing systems can be explained by a cross-linking of gel fibril aggregates similar to those formed by the unmetalated gelator.     

Water-soluble cruciforms: response to protons and selected metal ions

The syntheses of three water-soluble cruciform fluorophores (XF) carrying aniline- N, N-bisacetic acid, 2-hydroxyaniline- N, N, O-trisacetic acid, and 1,2-phenylenediamine- N, N, N', N'-tetrakisacetic acid are reported. The XF skeleton was synthesized by a Horner reaction to assemble the distyrylbenzene unit followed by a Sonogashira coupling to attach the phenyleneethynylene modules. The photophysics of both the sodium salts and the ethyl esters of the three carboxylated 1,4-bis(aminostyryl)-2,5-bis(phenylethynyl)benzenes were investigated in chloroform and in aqueous buffered solution at a pH of 7.0 and compared to that of 1,4-bis(dibutylaminostyryl)-2,5-bis(phenylethynyl)benzene (BDB). The attachment of the carboxylate units to the aniline nitrogens influenced the photophysics and the sensory responses of the XFs, as the combined effect of steric bulk and charge repulsion led to a blue-shifted absorption when compared to that of BDB. While the fluorescence of the water-soluble XFs is sensitive toward metal cations, the mode of sensing action is different from that of BDB, where direct complexation to the aniline nitrogen lowers the energy of the HOMO (but not of the LUMO), leading to a blue-shifted emission. In the case of the 2-hydroxyaniline- N, N, O-trisacetic acid and 1,2-phenylenediamine- N, N, N', N'-tetrakisacetic acid-functionalized XFs, interaction with metal cations in aqueous buffered solution is guided by a breakup of excimers that form in water at XF concentrations as low as 50 micromol x L (-1).