Styrylpyridinium

Fast-response probes (response times less than milliseconds) styrylpyridinium and annellated hemicyanine dyes, merocyanine dyes, and 3-hydroxychromone dyes... 

Fig. 2 Examples of the structures of a few fast-response electric filed sensitive dyes N-(4-sulpho-butyl)-4-(4-(4-(dipentylamino)phenyl)butadienyl)pyridinium inner salt (RH421, a styrylpyridinium dye), ANNINE 5 (an annellated hemicyanine dye), merocyanine 540, and N-[(4 -dimethylamino)-3-hydroxy-6-flavonyl mcthyl-N,N-trimcthyl ammonium (F4N1, a 3-hydroxychromone dye)...

Fig. 3 Excited state charge transfer in styrylpyridinium dyes...

Slow dyes that respond via a redistribution across the entire membrane (sometimes called Nemstain dyes) do so because of a change in the transmembrane electrical potential. As such, they can only be used as probes of the transmembrane potential and not as probes of the surface potential or the dipole potential. Dyes whose electric field sensing mechanism involves a movement between the aqueous medium and its adjacent membrane interface on one side of the membrane can, in principle, respond to changes in both the transmembrane electrical potential and the surface potential. Fast dyes that remain totally in the membrane phase (e.g., styrylpyridinium, annellated hemicyanine, and 3-hydroxyflavone dyes) respond to their local electric field strength, whatever its origin. Therefore, these dyes can, in principle, be used as probes of the transmembrane electrical potential, the surface potential, or the dipole potential. 

Amoroso S, Agon VV, Starke-Peterkovic T et al (2006) Photochemical behaviour and Na+, K+-ATPase sensitivity of voltage-sensitive styrylpyridinium fluorescent membrane probes. Photochem Photobiol 82 495-502... 

Pham THN, Clarke RJ (2008) Solvent dependence of the photochemistry of the styrylpyridinium dye RH421. J Phys Chem B 112 6513-6520... 

In AChE-based biosensors acetylthiocholine is commonly used as a substrate. The thiocholine produced during the catalytic reaction can be monitored using spectromet-ric, amperometric [44] (Fig. 2.2) or potentiometric methods. The enzyme activity is indirectly proportional to the pesticide concentration. La Rosa et al. [45] used 4-ami-nophenyl acetate as the enzyme substrate for a cholinesterase sensor for pesticide determination. This system allowed the determination of esterase activities via oxidation of the enzymatic product 4-aminophenol rather than the typical thiocholine. Sulfonylureas are reversible inhibitors of acetolactate synthase (ALS). By taking advantage of this inhibition mechanism ALS has been entrapped in photo cured polymer of polyvinyl alcohol bearing styrylpyridinium groups (PVA-SbQ) to prepare an amperometric biosensor for... 

Constantinos G. Tsiafoulis et al. report the electrochemical behaviour of a composite film based on ferrocene intercalated V205.nH20 xerogel (FeCp2-VXG) with photocrosslinkable polyvinyl alcohol with styrylpyridinium residues (PVA-SbQ), in order to be used as an electrocatalyst and host protein platform to develop an amperometric biosensor. 

Similar reactions have also been observed for 1-azadiene 154145 (equation 85), 4-aryloxy-2-azabuta-l,3-dienes146 (equation 86), 1-styrylpyridinium salts147 (equation 87) and diaza-1,3-dienes148 (equation 88). 

The benzo[a Jquinolizinium ion and some of its derivatives (162) can be prepared by UV irradiation of styrylpyridinium salts (160 Scheme 91) (66JOC2616) in the presence of iodine (Table 6). It is believed that the styryl salt (160) is first isomerized to the cis configuration (161), then bond formation takes place, followed by loss of hydrogen. In view of the publication of an improved method for making styrylpyridinium salts (160) (69JMC1079) the photochemical method appears to offer an advantageous route to the parent compound (2). 

Table 6 Benzo[a]quinolizinium Salts by Irradiation of Styrylpyridinium Salts (Scheme...

Polymers with other pendant photosensitive moieties such as 0-furylacrylic ester (2) or / -styrylacrylic ester (5) are highly photosensitive and have even higher photosensitivity after the addition of photosensitizers. However, the thermal stability of these polymers is inferior to that of the polymer with pendant cinnamic esters (4). Polymers with pendant benzalacetophenone (5), styrylpyridinium (6), a-cyanocinnamic ester (7) or a-phenylmaleimide (8) have high photosensitivity but they can not be sensitized. In addition, the photosensitive moieties that are used in the syntheses of these polymers are not commercially available, in contrast to cinnamic acid. 

C-Styrylpyridines undergo photocyclization to give azaphenanthrenes, and Y-styrylpyridinium cation forms an azoniaophenanthrene (523 — 524). 

Compounds with a ring junction N atom result from the photochemical cyclization of cis-1-styrylimidazoles. Irradiation of the imidazole (141 R1 = H) in methanol in the presence of I2 gave imidazo[2,1 -ajisoquinoline (142) (76JCS(Pl)75). trans-1 -Styrylbenzimidazole similarly formed successively the cis isomer and the benzimidazo[2,l-a]isoquinoline (143). For similar reaction of 1-styrylpyridinium, see Section 3.2.2.3.9. 

An analogous cation radical chain process has been proposed for cis to trans isomerization of N-methyl-4-(6-stryl)-pyridinium ions via electron-transfer sensitization by Ru(bpy)-j2+ and metalloporphyrins (145). Quantum yields for isomerization are substantially higher in aqueous anionic micelles versus homogeneous solution due to the higher concentration of cis-styrylpyridinium ions. A radical cation chain mechanism may also account for previous reports of selective cis to trans sensitized photoisomerization of stilbene (25,26). 

D. Charge Resonance Band in the Near-Infrared Region and Ultrafast Dynamics for Styrylpyridinium Tetraphenylborate Salts... 

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