Structurally Compact, Blue-Green-Red Fluorescence Trackers for the Outer Cell Membrane: Zwitterionic (Naphthylvinyl)pyridinium Dyes.

The cell membrane regulates the flux of materials in and out of cell, cell adhesion, and signaling. Fluorophores that selectively localize on it are in demand for investigations of the molecular events occurring on the outer cell membrane. Commercial membrane trackers based on phospholipids are structurally complex and difficult to modify further. We disclose the zwitterionic (naphthylvinyl)pyridinium dyes that selectively localize on the outer cell membrane and emit blue, green, and red fluorescence, respectively. Notably, they are structurally compact and provide bright fluorescence images of the cell membrane. By comparing with control compounds, we identified minimal structural elements for the "robust" localization of dye on the outer cell membrane. Further, the dyes are two-photon active, enabling high-resolution, deep-tissue imaging. One of the dyes was used to image a spleen tissue, which provided high-resolution fluorescent images with a distinct morphology. In addition, the materials and results disclosed are valuable for the development of membrane-targeting probes and structurally compact fluorophores.

[2 + 2] Photodimerization of Naphthylvinylpyridines through Cation-π Interactions in Acidic Solution.

Irradiation of (E)-4-(2-(2-naphthyl)vinyl)pyridine (1a) and (E)-4-(2-(1-naphthyl)vinyl)pyridine (1b) with a 250 W high-pressure mercury lamp in acidic solution afforded synHT dimers in high stereoselectivities. Similar results were obtained by visible light irradiation. On the other hand, when the reactions were carried out under neutral conditions, the stereoselectivities were very low, and the yields were decreased by visible light irradiation. Comparison of the UV-vis spectra between the acidic and the neutral conditions elucidated that the red shift was observed in acidic solutions. These results show that HCl plays essential roles not only in the preorientation of substrates through cation-π interactions, but also in the changes in the absorption properties of substrates that enable visible light reactions.

Novel naphthylstyryl-pyridium potentiometric dyes offer advantages for neural network analysis.

The submucous plexus of the guinea pig intestine is a quasi-two-dimensional mammalian neural network that is particularly amenable to study using multiple site optical recording of transmembrane voltage (MSORTV) [Biol. Bull. 183 (1992) 344; J. Neurosci. 19 (1999) 3073]. For several years the potentiometric dye of choice for monitoring the electrical activity of its individual neurons has been di-8-ANEPPS [Neuron 9 (1992) 393], a naphthylstyryl-pyridinium dye with a propylsulfonate headgroup that provides relatively large fluorescence changes during action potentials and synaptic potentials. Limitations to the use of this dye, however, have been its phototoxicity and its low water solubility which requires the presence of DMSO and Pluronic F-127 in the staining solution. In searching for less toxic and more soluble dyes exhibiting larger fluorescence signals, we first tried the dienylstyryl-pyridinium dye RH795 [J. Neurosci. 14 (1994) 2545] which is highly soluble in water. This dye yielded relatively large signals, but it was internalized quickly by the submucosal neurons resulting in rapid degradation of the signal-to-noise ratio. We decided to synthesize a series of naphthylstyryl-pyridinium dyes (di-n-ANEPPDHQ) having the same chromophore as di-8-ANEPPS and the quaternary ammonium headgroup (DHQ) of RH795 (resulting in two positive charges versus the neutral propylsulfonate-ring nitrogen combination), and we tested the di-methyl (JPW3039), di-ethyl (JPW2081), di-propyl (JPW3031), di-butyl (JPW5029), and di-octyl (JPW5037) analogues, all of them soluble in ethanol. We found that the di-propyl (di-3-ANEPPDHQ) and the di-butyl (di-4-ANEPPDHQ) forms yielded the best combination of signal-to-noise ratio, moderate phototoxicity and absence of dye internalization.

Molecular modeling of (E)-1-alkyl-4(3)-[2-(1H-azolyl)vinyl]-pyridinium salts and evaluation of their behavior towards choline acetyltransferase.

A new type of extended pi-system aza-analogue of (E)-4-[2-(1-naphthylvinyl)]-1-substituted pyridinium salts (NVP+) has been designed and its inhibitory activity towards choline acetyltransferase (ChAT) has been evaluated in vitro. Among the several examples of the title quaternary salts synthesized 2 and 3, the indolylvinylpyridinium salt 2e is the only one to show a very low ChAT inhibition. The molecular modeling study is highly illustrative of their behavior towards ChAT and interaction with the recognition site. Thus, several selected cations together with the reference NVP+ compound 1a were studied at the PM3 and AM1 levels respectively. At the global minima, all the compounds are planar, which, from the electron charge distribution, shows a degree of polarization similar to the NVP+ model compound 1a. However, the fitting of all optimized structures indicated that only the indole derivative 2e showed the same aromatic fragment orientation as 1a, which allows us to define a volume that is not accessible to ligands in the enzyme and consequently to a refined model of the choline acetyltransferase recognition site.

Molecular modeling studies of some choline acetyltransferase inhibitors.

Choline acetyltransferase (ChAT) inhibitors related to trans-1-methyl-4- (1-naphthylvinyl)-pyridinium (NVP+) have been assumed to depend upon a nearly or completely planar conformation for their enzyme-inhibitor interaction. In an effort to investigate the geometries and preferred conformations for these compounds, geometry optimizations using the semiempirical molecular orbital method AM1 and a modified version of the molecular mechanics method MM2(92) have been carried out. The results indicate that the active inhibitors are either planar or nearly coplanar, lying in relatively flat potential wells in the vicinity of the corresponding planar structures. When nonplanarity is favored, one ring is twisted out of the plane by approximately 30 degrees. Where steric features significantly deter assumption of a nearly planar conformation, the analogs are inactive. The inactivity of analogs bearing tricyclic aryl groups appears to result from bulk-related hindrance to ChAT receptor binding rather than lack of coplanarity.