Metallocyclodextrins as building blocks in noncovalent assemblies of photoactive units for the study of photoinduced intercomponent processes.

Cyclodextrin cups have been employed to build supramolecular systems consisting of metal and organic photoactive/redox-active components; the photoinduced communication between redox-active units assembled in water via noncovalent interactions is established. The functionalization of a beta-cyclodextrin with a terpyridine unit, ttp-beta-CD, is achieved by protection of all but one of the hydroxyl groups by methylation and attachment of the ttp unit on the free primary hydroxyl group. The metalloreceptors [(beta-CD-ttp)Ru(ttp)][PF(6)](2), [(beta-CD-ttp)Ru(tpy)][PF(6)](2), and [Ru(beta-CD-ttp)(2)][PF(6)](2) are synthesized and fully characterized. The [(beta-CD-ttp)Ru(ttp)][PF(6)](2) metalloreceptor exhibits luminescence in water, centered at 640 nm, from the (3)MLCT state with a lifetime of 1.9 ns and a quantum yield of Phi = 4.1 x 10(-)(5). Addition of redox-active quinone guests AQS, AQC, and BQ to an aqueous solution of [(beta-CD-ttp)Ru(ttp)](2+) results in quenching of the luminescence up to 40%, 20%, and 25%, respectively. Measurement of the binding strength indicates that, in saturation conditions, 85% for AQS and 77% for AQC are bound. The luminescence quenching is attributed to an intercomponent electron transfer from the appended ruthenium center to the quinone guest inside the cavity. Control experiments demonstrate no bimolecular quenching at these conditions. A photoactive osmium metalloguest, [Os(biptpy)(tpy)][PF(6)], is designed with a biphenyl hydrophobic tail for insertion in the cyclodextrin cavity. The complex is luminescent at room temperature with an emission band maximum at 730 nm and a lifetime of 116 ns. The osmium(III) species are formed for the study of photoinduced electron transfer upon their assembly with the ruthenium cyclodextrin, [(beta-CD-ttp)Ru(ttp)](2+). Time-resolved spectroscopy studies show a short component of 10 ps, attributed to electron transfer from Ru(II) to Os(III) giving an electron transfer rate 9.5 x 10(9) s(-)(1).

An Escherichia coli CS31A fibrillum chimera capable of inducing memory antibodies in outbred mice following booster immunization with the entero-pathogenic coronavirus transmissible gastroenteritis virus.

CS31A fibrillae are thin, flexible, heteropolymeric proteinaceous appendages exposed as a capsule-like material around the cell surface of certain Escherichia coli strains. Two antigenic peptides of the S spike glycoprotein (TGEV-S) amino acids (aa) 363-371 and 521-531 of the transmissible gastroenteritis virus (TGEV) were tandemly introduced in the loop-structured, variable region aa 202-218 of the major ClpG subunit protein composing the bulk of CS31A. The resulting hybrid fibrillae with a 25 aa heterologous peptide were produced at the cell surface. Using a monoclonal antibody (Mab) specific for the TGEV epitopes, purified hybrid fibrillae were analysed in Western blotting under native conditions, which showed that the two viral epitopes were recognized immunologically as an integral part of the hybrid fibrillae, and therefore that they were antigenically active. The immunogenicity of the fusion construct was evaluated with live recombinant bacteria, purified hybrid ClpG monomers, and purified chimeric CS31A polymers. Whatever the form of hybrid used as antigen, intraperitoneally immunized outbred mice elicited serum anti-TGEV peptides antibodies (Abs) with significant titres and capable of recognizing native TGEV particles, indicating that the epitopes are exposed in an immunogenic conformation in all cases. However, virus neutralization titres were only obtained after immunization with either purified polymers or monomers. Furthermore, 4 months after an ultimate immunization with 20 micrograms of hybrid fibrillae mice developed a strong anamnestic Ab response against the two TGEV peptides following booster inoculation with virions. We conclude that CS31A fibrillae carrying a combination of TGEV epitopes as insert can induce an immunological memory in outbred animals infected with TGEV, and therefore that hybrid CS31A fibrillae may prove efficient as components of a subunit vaccine.

Role of aerobactin in systemic spread of an opportunistic strain of Escherichia coli from the intestinal tract of gnotobiotic lambs.

To assess the role of the aerobactin-related system in the virulence of bovine opportunistic Escherichia coli, and to determine the stage(s) of the overall infectious process at which it is acting, germfree lambs were mixedly infected orally with two derivative strains of this bacterium differing in their ability (Iut+) or inability (Iut-) to express a functional aerobactin-mediated iron transport system. The Iut- strain was compared with the Iut+ strain for colonization of the gut, translocation to the mesenteric lymph nodes (MLN), and spread to other organs and to the body fluids of diassociated lambs. The Iut- mutant was found in smaller numbers in the duodenum, suggesting that aerobactin conferred a significant selective advantage for colonization of this intestinal segment. Although the two challenge strains translocated to MLN, the population level in the MLN was always higher for the Iut+ strain. Moreover, experimental infections resulted in recovery of only the Iut+ strain in the organs other than the MLN and in the body fluids. These results indicate a role for aerobactin in promoting systemic spread of the bacteria from the intestine. Direct evidence was obtained that aerobactin secretion occurred in vivo at both intestinal and extraintestinal sites of infection. In contrast to enterobactin, aerobactin was detected in the duodenum, jejunum, ileum, cecum, liver, spleen, kidney, urine, cerebrospinal fluid, and bile. The highest concentration of aerobactin was found in the urine, even when the samples were devoid of infecting bacteria. All of these findings suggest that aerobactin is released in vivo in a diffusible form and that it may be an important step in the production of disease by intestinal opportunistic E. coli.

Development of the rumen digestive functions in lambs placed in a sterile isolator a few days after birth.

The development of the rumen digestive functions was studied in lambs placed in sterile isolators at 1, 4, 8 or 9 days of age to define the role of the bacterial species that colonize the rumen just after birth. The values of the main rumen digestive parameters (pH, concentrations of volatile fatty acid, ammonia, lactic acid) in these lambs were close to those observed in conventional controls. Likewise, the digestive utilisation of the dry matter and starch was comparable in isolated and control animals but the digestibility of crude cellulose was higher in isolated lambs, which harboured only Fibrobacter succinogenes as the sole cellulolytic bacterial species. These results suggest that the rumen flora of the very young lamb play an essential role in the establishment of the rumen ecosystem and in the setting up of the digestive functions.