Thioflavin T (ThT) has been widely employed to detect amyloid fibrils in tissues and recently in presence of SDS micelles. However, the contribution of membranes or micelles to ThT fluorescence has never been investigated. In this paper, we show for the first time that the anionic micellar microenvironment of SDS has a profound impact on the absorption and fluorescence spectra of ThT in sharp contrast to cationic (CTAB) and neutral micelles (Triton X-100 & Tween 20). Unlike CTAB or Triton X-100 or Tween 20 micelles, formation of SDS micelles shifts the lambdamax for ThT absorption from 412 nm in buffer to 428 nm inside the micelle, with a 28% increase in the peak molar absorptivity and an approximately 13 fold increase in ThT fluorescence (lambdamax=489 nm). Extending these observations to cell plasma membranes, we show that ThT can quickly enter and appear selectively fluorescent inside mammalian cells like BHK21 and HT29, against a dark background owing to negligible fluorescence from free ThT in aqueous medium. The above results suggest that ThT can be a useful probe for live cell imaging and for selectively labeling micelles on the basis of the charge in the polar headgroup.

Logic gates with different radixes have been constructed using a biologically active molecule, 2-(4'-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine (DMAPIP-b). Taking advantage of the multiple binding sites of the fluorophore, a series of different molecular logic gates are developed using fluorescence intensities at different wavelengths. The high emission of the molecule is drastically quenched in the presence of Fe(3+). It is regained by the addition of an equivalent amount of F(-). The fluorescence On-Off nature has been used to construct molecular full subtractor and molecular keypad lock system with Boolean logic. A ternary system is generated by considering three defined fluorescence intensities at particular wavelengths. The smooth dependency of emission intensities with analyte concentration is utilized to construct an infinite-valued fuzzy logic system. The fuzzy logic system is further coupled with a neuro-adaptation method to predict more accurately the dependency of molecular intensity on external inputs.

The photophysical [1] and photochemical [2] behaviors of alltrans-1,6-diphenyl-1,3,5-hexatriene (ttt-DPH) have attracted a great deal of attention because, as the first member of the family of vinylogous a,w-diphenylpolyenes with a 2A g lowest excited state, ttt-DPH serves as a polyene model. Mediumimposed constraints enhance the torsional barriers of olefins in the lowest excited singlet state [3] and inhibit cis-trans photoisomerization.[4] Two mechanisms involving concerted rotation about two bonds in the S 1 state, which were initially postulated to explain retinyl photoisomerization within the protein environments in rhodopsin and bacteriorhodopsin, have been applied generally to account for photoisomerization in volume-confining media: The bicycle-pedal mechanism (BP) involves simultaneous rotation in the S 1 state about two polyene double bonds, [5] and the hula-twist mechanism (HT) involves simultaneous rotation about a double bond and an adjacent essential single bond (equivalent to a 1808 translocation of one CH unit).[6] Our recent work on the cis,cis-1,4-diphenyl-and cis,cis-1,4-di(o-tolyl)-1,3-butadienes (cc-DPB and cc-DTB) revealed the BP process as the only photoisomerization pathway in the solid state at room temperature [7] and as a significant pathway competing with the usual one-bond-twist pathway in the soft isopentane glass at 77 K. [8] Recognizing that the BP process accounts for the interconversion of ctt-DPH and tct-DPH isomers in solution [2] and for the one-way ctc-DPH!ttt-DPH photoisomerization of symmetrical p,p'-disubstituted cis,trans,cis-1,6-diphenyl-1,3,5-hexatriene derivatives in the solid state, [9] we reasoned that the analogous extended BP process in the hitherto unknown all-cis DPH might give tct-DPH in the solid state. Observations reported herein show that instead, irradiation of ccc-DPH in the solid state gives ttt-DPH directly in a crystalto-crystal reaction. To our knowledge this is the first observation of simultaneous three-bond cis-trans photoisomerization.cis-1,6-Diphenylhex-3-en-1,5-diyne was prepared from phenylethyne and cis-1,2-dichloroethene as previously described [10] and hydrogenated over the Lindlar palladium catalyst to afford ccc-DPH as an oil (Scheme 1). Purification by chromatography on alumina, followed by crystallization from hexane yielded white crystals of ccc-DPH (m.p. 71 8C). The compound was characterized mainly by 1 H NMR spectroscopy [11] and X-ray crystallography.[12] The synthesis, purification, and handling of ccc-DPH were carried out under red light to avoid photoisomerization. The other DPH isomers are present in the photostationary state and were previously described. [13] Powder X-ray diffraction patterns were measured before and after irradiation (l = 400 nm) of samples of ccc-DPH (%5 mg) that had been ground to a powder with a mortar and pestle. The X-ray diffraction data were collected with a Rigaku X-ray diffractometer Ultima III (scan angle 7-318, 176 KW, 0.018 resolution, 1.5418 , slits 0.5 nm, 600 s for data collection, and cali...

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