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A free-base tetraarylporphyrin was synthesized by the [2 + 2] macrocyclization of a dipyrromethane derivative with 3,4,5-tris(dodecyloxy)benzaldehyde in 61% yield. The free-base porphyrin was metallated with zinc acetate in 94% conversion. The free-base and metallated porphyrins show typical intense Soret bands at 426 and 425 nm, respectively, along with the expected number and intensity of Q-bands. Both porphyrins are also fluorescent and display small Stokes shifts between 13 and 18 nm. Cyclic voltammetry established that each porphyrin underwent two reversible one-electron oxidations at 492 and 725 mV (vs Fc/[Fc.sup.+] (ferrocene reference)) for the free-base porphyrin and at 329 and 589 mV (vs Fc/[Fc.sup.+]) for the Zn-metalloporphyrin. Electron-transfer rates were also determined to fall between 1.2 x [10.sup.-3] and 2.4 x [10.sup.-3] cm [s.sup.-1]. In addition, spectroelectrochemistry and density functional theory calculations of the oxidized products were carried out to confirm the macrocyclic ring oxidations. Key words: porphyrinoids, electrochemistry, redox chemistry, photochemistry, density functional calculations. On a realise la synthase d'une tetraaraylporphyrine sous la forme de base libre avec un rendement de 61 % par macrocyclisation [2 + 2] d'un derive; de dipyrromethane avec du 3,4,5-tris(docecyloxo)benzaldehyde. On a effectue la metallation de la porphyrine a l'etat de base libre, avec un rendement de 94 %, par traitement avec de l'acetate de zinc. La base libre et la porphyrine metallee presentent respectivement les bandes typiques intenses de Soret a 426 et a 425 nm ainsi que le nombre et l'intensite attendu des bandes Q. Les deux porphyrines sont aussi fluorescentes et elles presentent de faibles deplacements de Stokes, entre 13 et 18 nm. La voltamperometrie cyclique a permis d'etablir que chaque porphyrine subit deux oxydations reversibles a un electron, a 492 et 725 mV (vs Fc/[Fc.sup.+]) pour la base libre et a 329 et 589 mV (vs Fc/[Fc.sup.+]) pour la Zn-metalloporphyrine. On a aussi determine que les vitesses de transfert d'electron se situent entre 1,2 x [10.sup.-3] et 2,4 x [10.sup.-3] cm [s.sup.-1]. De plus, de la spectroelectrochimie et des calculs d'apres la theorie de la fonctionnelle de la densite effectues sur les produits oxydes pour confirmer les oxydations des noyaux macrocycliques. Mots-cles: porphyrinoldes, electrochimie, chimie d'oxydoreduction, photochimie, calculs de la fonctionnelle de la densite. [Traduit par la Redaction], Introduction Porphyrinoids are commonly found compounds in both the animal and plant kingdoms, as they play important roles in the key steps of photosynthesis that ultimately convert sunlight into chemical [...]

Microelectrode arrays having eight 10-[micro]m-diameter gold microelectrodes arranged on a gold-covered Si chip were designed and characterized. The chips prove useful for the detection of single-nucleotide mismatches in unlabeled and prehybridized DNA by electrochemical impedance spectroscopy.

The detection of a single-nucleotide mismatch in unlabeled duplex DNA by electrochemical methods is presented. Impedance spectroscopy is used to characterize a perfect duplex monolayer and three DNA monolayers differing in the position of the mismatch. The monolayers were studied as B-DNA (normal duplex DNA) and after conversion to M-DNA (a metalated duplex). Modeling of the impedance data to an equivalent circuit provides parameters that are useful in discriminating the four monolayer configurations. The resistance to charge transfer, [R.sub.CT], was lower for all duplexes after conversion to M-DNA. Contrary to expectations, [R.sub.CT] was also found to decrease for duplexes containing a mismatch. However, [R.sub.CT] was found to be diagnostic for mismatch detection. In particular, the difference in [R.sub.CT] between B- and M-DNA ([DELTA][R.sub.CT]) decreased from 190(22) [OMEGA]x[cm.sup.2] for a perfectly matched duplex to 95(20), 30(20), and 85(20) [OMEGA]x[cm.sup.2] for a mismatch at the top (distal), middle, and bottom (proximal) positions of the monolayer with respect to the gold surface. Further, a method to form loosely packed single-stranded (ss)-DNA monolayers by duplex dehybridization that is able to rehybridize to target strands is presented. Rehybridization efficiencies were in the range of 40-70%. Under incomplete hybridization conditions, the [R.sub.CT] was the same for matched and mismatched duplexes under B-DNA conditions. However, [DELTA][R.sub.CT] between B- and M-DNA, under incomplete hybridization, still provided a distinction. The [DELTA][R.sub.CT] for a perfect duplex was 76(12) [OMEGA]x[cm.sup.2], whereas a mismatch in the middle of the sequence yielded a [DELTA][R.sub.CT] value of 30(15) [OMEGA]x[cm.sup.2]. The detection limit was measured and the impedance methodology reliably detected single DNA base pair mismatches at concentrations as low as 100 pM.

A study is conducted to characterizes that (ferrocenoyl) Fc-labeled (double stranded)ds-DNA can form reproducible monolayers on Au (gold) surfaces. In this a comparison of two configurations is made which differ only in the Fc attachment point.