Dimaleimide fluorogens are being developed for application to fluorescent protein labeling. In this method, fluorophores bearing two maleimide quenching groups do not fluoresce until both maleimide groups have undergone thiol addition reactions with the Cys residues of the target protein sequence [J. Am. Chem. Soc. 2005, 127, 559-566]. In this work, a new convergent synthetic route was developed that would allow any fluorophore to be attached via a linker to a dimaleimide moiety in a modular fashion. Series of dimaleimide and dansyl derivatives were thus prepared conveniently and used to elucidate the mechanism of maleimide quenching. Intersystem crossing was ruled out as a potential quenching pathway, based on the absence of a detectable triplet intermediate by laser flash photolysis. Stern-Volmer rate constants were measured with exogenous dimaleimide quenchers and found to be close to the diffusion-controlled limits, consistent with electron transfer being thermodynamically favorable. The thermodynamic feasibility of the photoinduced electron transfer (PET) quenching mechanism was verified by cyclic voltammetry. The redox potentials measured for dansyl and maleimide confirm that electron transfer from the dansyl excited state to a pendant maleimide group is exergonic and is responsible for fluorescence quenching of the fluorogens studied herein. Taking this PET quenching mechanism into account, future fluorogenic protein labeling agents will be designed with spacers of variable length and rigidity to probe the structure-property PET efficiency relationship.

Novel azomethines consisting uniquely of thiophene units were examined. The highly conjugated compounds were prepared by condensing air stable aminothiophenes with 2-thiophene aldehydes, which were substituted with various electronic groups. The resulting azomethines are highly conjugated and are both reductively and hydrolytically resistant. Various electron donating and accepting groups placed in the 2-position of 5-thiophene carboxaldehyde lead to electronically delocalized push-push, pull-pull, and push-pull azomethines. These electronic groups affect both the HOMO and the LUMO levels, which influence the absorption and emission spectra. Colors spanning the entire visible spectrum ranging from yellow to blue are possible with these nitrogen containing conjugated compounds. Excited state deactivation of the singlet excited state occurs predominately by internal conversion while only a small amount of energy is dissipated by intersystem crossing to the triplet state and by fluorescence. The ensuing fluorescence and phosphorescence of the thiopheno azomethines are similar to those of their thiophene analogues currently used in functional devices, but with the advantage of a low triplet state and tunable HOMO-LUMO energy levels extending from 3.0 to 1.9 eV. Quasi-reversible electrochemical radical cation formation is possible while the oxidation potential is dependent on the nature of the electronic group appended to the thiophene. The crystallographic data of the electronic push-push system show the azomethine bonds are planar and linear and they adopt the E isomer.

The improved synthesis of thieno[3,4-c]pyrrole-4,6-dione (TPD) monomers, including Gewald thiophene ring formation, a Sandmeyer-type reaction, and neat condensation with an amine, is presented. This protocol enables faster, cheaper, and more efficient preparation of TPD units in comparison to traditional methods. Furthermore, a series of TPD homo- and pseudohomopolymers bearing various alkyl chains was synthesized via a direct heteroarylation polymerization (DHAP) procedure. UV-visible absorption and powder X-ray diffraction measurements revealed the relationship between the ratio of branched to linear alkyl chains and the optoelectronic properties of the polymers as well as their packing in the solid state.

An acidophilic, disulfide-oxidizing, mesophilic, aerobic bacterium was isolated from wastewater sludge. The new organism is a gram-positive sporulated rod. It can use elemental sulfur and pyrite as sole energy sources and grows on organic substrates such as glutamate and glucose. It also grows on the following organic sulfur substrates: oxidized and reduced glutathione, cysteine, cystine, and dithio(bis) benzothiazole and clearly shows a preference for disulfide bond-containing substrates. The optimal pH of growth is between 1.5 and 2.5, depending on the substrate used, and the growth temperature range varies from 4 to 40°C, with an optimal value at 35°C. The G+C chromosomal DNA content was measured at 53 A 1 mol%. Phylogenetic analysis of 16s genes coding for rRNA sequences places the new isolate in the genus Sulfobacillus. In addition, unique phenotypic and physiologic characteristics and DNA homology values assign the isolate to a new species in the genus. Therefore, this new isolate has been named Sulfobacillus disulJidooxidans and has been assigned ATCC number 51911.Many facultatively heterotrophic bacteria are known for their ability to grow under highly acidic conditions. Some of these within the genera Sulfolobus (5) and Acidianus (31) are extremely thermophilic archaebacteria. They obtain their energy by the oxidation or reduction of elemental sulfur or from organic substrates. Others are mesophilic gram-negative bacteria belonging to the genus Acidiphilium (2, 18) and are able to use organic substrates at pH 3.0 or belong to the genus Thiobacillus, such as Thiobacillus acidophilus (17), which is also known for its ability to grow with elemental sulfur or glucose at pH 2.5.However, the only acidophilic, facultatively autotrophic, gram-positive, spore-forming bacillus so far characterized is Sulfobacillus thermosu&dooxidans (16), together with two subspecies ("themzotolerans" and "asporogenes") that do not produce spores (19). Golovacheva and Karavaiko (16) first described the genus Sulfobacillus in 1978 as gram-positive, sporeforming bacteria growing on elemental sulfur, ferrous iron, and other metal sulfides. The rod-shaped cells were described as fairly pleomorphic. The spores were spherical or slightly oval, terminal, subterminal, or paracentral. S. therrnosulfdooxidans is a typical acidophilic, thermotolerant, and facultatively autotrophic bacterium. Since then, four isolates which are gramvariable, thermotolerant acidophiles have been recovered from mines: ALV (27), BC (27), C-MT1(15), and TH3 (4), and have been described as belonging presumably to this genus. Some other gram-positive bacteria from the genus Alicyclobacillus (7-9) can also grow under acidic conditions, but they are heterotrophic bacteria.This work reports on the isolation and characterization of a new facultatively autotrophic, mesophilic, acidophilic, grampositive, spore-forming bacterium (SD-11) that could belong to the genus Sulfobacillus. MATERIALS AND METHODSBacterial strains and culture conditions. The acidophilic strain SD-1...