Spectral Properties of Fluorogenic Thiophene-derived Triarylmethane Dyes.

Spectral properties and fluorogenic behaviors of five novel thiophene variants of malachite green (MG), termed MGTs, were determined. Appreciable changes as a function of homologation and substitution pattern, including absorption band positions and intensities and fluorescence quantum yields were observed. In particular, the shorter wavelength y-band absorption was found to shift over a nearly 200 nm range based on aryl group variation, allowing fine-tuning of the excitation wavelength for these dyes.

Stereochemically probing the photo-Favorskii rearrangement: a mechanistic investigation.

Using model (R)-2-acetyl-2-phenyl acetate esters of (S)- or (R)-α-substituted-p-hydroxybutyrophenones (S,R)-12a and (R,R)-12b, we have shown that a highly efficient photo-Favorskii rearrangement proceeds through a series of intermediates to form racemic rearrangement products. The stereogenic methine on the photoproduct, rac-2-(p-hydroxyphenyl)propanoic acid (rac-9), is formed by closure of a phenoxy-allyloxy intermediate 17 collapsing to a cyclopropanone, the "Favorskii" intermediate 18. These results quantify the intermediacy of a racemized triplet biradical (3)16 on the major rearrangement pathway elusively to the intermediate 18.

Fluorinated photoremovable protecting groups: the influence of fluoro substituents on the photo-Favorskii rearrangement.

To further explore the nature of the photo-Favorskii rearrangement and its commitment to substrate photorelease from p-hydroxyphenacyl (pHP), an array of ten new fluorinated pHP gamma-aminobutyric acid (GABA) derivatives was synthesized and photolyzed. The effects of fluorine substitution on the chromophore and the photophysical and photochemical properties of these new chromophores were shown to be derived primarily from the changes in the ground state pK(a) of the phenolic groups. The quantum yields and rate constants for release are clustered around Phi(dis) = 0.

Deoxycholate interacts with IpaD of Shigella flexneri in inducing the recruitment of IpaB to the type III secretion apparatus needle tip.

Type III secretion (TTS) is an essential virulence function for Shigella flexneri that delivers effector proteins that are responsible for bacterial invasion of intestinal epithelial cells. The Shigella TTS apparatus (TTSA) consists of a basal body that spans the bacterial inner and outer membranes and a needle exposed at the pathogen surface. At the distal end of the needle is a "tip complex" composed of invasion plasmid antigen D (IpaD).