Science Concentrates

Sulfanyl alcohols are culprits in smelly armpits

The typical smell associated with the human armpit is caused by a witches' brew of molecules, including steroids, fatty acids, and sulfur-containing compounds. The sulfur compounds are the most malodorous, but little has been known about them, until now. Research groups at two Swiss fragrance and flavor companies have identified these compounds as sulfanyl alcohols [Chem. Biodiversity, 1, 1022 and 1058 (2004)]. A team led by Anthony J. Clark at Firmenich found eight sulfanyl alcohols in sweat from exercising volunteers, including the major component (S)-3-methyl-3-sulfanylhexan-1-ol (shown), which has an onionlike smell that is likely the "most important contributor to the typical and repulsive sweat malodor." A second team led by Andreas Natsch at Givaudan Schweiz also identified 3-methyl-3-sulfanylhexan-1-ol, as well as three additional sulfanyl alcohols with equally pungent odors. Both teams identified Corynebacterium, Staphylococcus, and other bacteria that dwell in the armpits and produce enzymes that convert precursor compounds in the initially odorless sweat to the stinky compounds. The Givaudan team also showed that the sulfanyl compounds are derived from compounds that contain the sulfur-based amino acid cysteine.

  DNA lesion poses a triple threat

A common type of DNA damage may give rise to proteins lacking a single amino acid, examples of which have been implicated in cancer and other diseases. A variety of DNA-damaging agents, including -radiation and antitumor agents such as the enediynes and bleomycin, create abasic sites (shown) that are oxidized at the 4´-position of the deoxyribose ring (red). Marc M. Greenberg and coworkers at Johns Hopkins University show that when DNA containing such an abasic site undergoes replication in bacteria, the lesion causes the deletion of three consecutive nucleotides in the DNA [Biochemistry, 43, 13621 (2004)]. Three-nucleotide deletions may be unusually detrimental to cells because they can lead to the production of proteins that lack a single amino acid, Greenberg points out. One- or even two-nucleotide deletions--which are far more common--give rise to grossly altered proteins that the cell quickly destroys. But the deletion of a single amino acid, he adds, "is a far more subtle alteration" that isn't readily recognized and fixed by the cell.

Nanoparticles tag bacteria

Rapid and sensitive methods for detecting bacteria are needed to protect food and water supplies and for early disease diagnosis. Most assays for bacteria detection require DNA amplification or enrichment of the bacteria, making the methods laborious and time-consuming. Now, Weihong Tan and his coworkers at the University of Florida, Gainesville, have developed an assay that can detect a single bacterial cell within 20 minutes using fluorescent nanoparticles conjugated to antibodies for the bacteria [Proc. Natl. Acad. Sci. USA, published online Oct. 11, http://www.pnas.org/cgi/doi/10.1073/pnas/0404806101]. Each nanoparticle encapsulates thousands of fluorescent dye molecules in a silica matrix, and thousands of antibody-conjugated nanoparticles can bind to a single bacterial cell. The resulting signal is highly amplified, allowing the detection of a single cell. Tan and his colleagues have used the nanoparticles to detect Escherichia coli O157:H7 spiked in ground beef samples.

Nanocomposite membranes are highly sensitive

Nanocomposite organic-inorganic films are unique candidates for a new generation of membrane-based pressure, chemical, and temperature microsensor arrays, according to researchers at Iowa State University [Nat. Mater., 3, 721 (2004)]. Vladimir V. Tsukruk and Chaoyan Jiang used spin-assisted layer-by-layer assembly to fabricate 25–70-nm-thick films consisting of a central gold nanoparticle layer sandwiched between alternating monolayers of two polyelectrolytes: poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate). The membranes are lightweight, flexible, mechanically robust, and can be freely suspended over openings with diameters of several hundred micrometers. Their sensitivity to external forces is three to four orders of magnitude higher than that of an ultrathin silicon membrane with the same diameter. The extreme elasticity and recovery capabilities of nanocomposite membranes that have been pushed to the limits of their mechanical stability are outstanding and unexpected, the authors note. They hypothesize that these unparalleled abilities are caused by the unique multilayered structure of the membranes combined with a high level of spreading of the macromolecular chains in the plane of the films and over the metal nanoparticles.

SCIENCE & TECHNOLOGY ROUNDUP

The 1.2 million-base-pair genome of the largest known virus, called Mimivirus, contains many genes not seen before in other viruses, including those required for protein translation [Science, published online Oct. 14, http://dx.doi.org/10.1126/ science.1101485]. Given the number of enzymes and pathways encoded by its genome, Mimivirus is in some ways more complex than the simplest of cellular organisms. The genomic information could help shed light on the role of viruses in the origin of life and the evolution of cells.

"Strong yet gentle" is how Christopher A. Reed of the University of California, Riverside, and coworkers describe the strongest isolable Brønsted acid, the chlorinated carborane H⁺(CHB₁₁Cl₁₁)^- [Angew. Chem. Int. Ed., 43, 5352 (2004)]. The carborane acid stabilizes carbocations such as protonated benzene and tert-butyl cation without decomposing them the way traditional superacids do. The team assessed the relative strength of the acid using ¹³C NMR and a new method based on infrared N-H stretching of the ammonium salt.