Editors' Choice

Science  21 Aug 2009:
Vol. 325, Issue 5943, pp. 921
  1. Plant Science

    Cereal Mutation

    1. Pamela J. Hines
    CREDIT: PALMER ET AL., PLOS ONE 4, E6301 (2009)

    More than 9000 years ago, the domestication of barley began. Today, wild barley carries spikelets with two rows of grains, whereas domesticated barley varieties are found with two or six rows. The latter has a higher protein content and greater fecundity, although the grains of the former are larger and hence yield roughly equal biomass. Six-row varieties are commonly preferred and have been available in northern Africa for thousands of years. A loss-of-function mutation in the gene Vrs1 produces a six-row morphology.

    Archaeological analysis at Qasr Ibrim, a settlement on the boundary of the Nubian and Roman Empires, has shown that two-row barley (shown above) predominates. By analysis of ancient barley samples found at Qasr Ibrim, Palmer et al. discovered the same loss-of-function mutation in Vrs1 and infer that a subsequent and as yet unidentified mutation derived the two-row morphology from the domesticated six-row variety. The agricultural preference for two-row barley hints at a competitive advantage, such as its greater tolerance to drought. That the several cultures that occupied Qasr Ibrim during the past 3000 years all adopted the local two-row barley suggests that this strain is particularly well suited for cultivation at this locale.

    PLoS ONE 4, e6301 (2009).

  2. Chemistry

    Gilded Coupling

    1. Phil Szuromi

    Contrary to gold's historical reputation as an inert element, increasingly versatile examples of catalysis by nanoparticulate morphologies of the precious metal are emerging. Zhou et al. now show that even larger particles of bulk gold (5 to 50 µm in diameter) can promote organic coupling reactions. Carbene precursors such as diazoalkanes (R2C=N=N, where R is an alkyl group) and 3,3-diphenylcyclopropene react in the presence of this gold powder to form olefins through apparent carbene coupling at the metal surface. Cyclopropanation reactions with added styrene were also observed. The surface morphology affected reactivity: Initially reduced powders (incorporating residual carbon) were less active than the smoother, shinier surfaces that formed after a round of diazo substrate couplings.

    J. Am. Chem. Soc. 131, 10.1021/ja900653s (2009).

  3. Education

    A Matter of Animation

    1. Melissa McCartney*

    Students of chemistry often have trouble making the connection between macroscopic phenomena they can see and the underlying molecular events operating on a scale too small to visualize directly. Chang et al. investigated whether seventh-grade students' understanding of the molecular structure of matter could improve with the help of computer animation software to portray molecular events in familiar processes such as boiling. Specifically, the authors sought to assess the relative efficacies of three approaches: design and interpretation by individual students of animations illustrating chemical phenomena; self-design of animations followed by interactive critiquing sessions with peers in the class; and examination by students of purely teacher-generated animations. Assessments were based on comparative test performance before and after the animation project. Data from 178 students supported significantly greater gains in understanding among students who participated in peer evaluation than among those who simply prepared animations alone. Thus, including an interactive evaluation component may take more time, but it appears to be time well spent. There was no significant difference in test outcome between the students in the peer-evaluation group and those in the teacher-generated animation group, though the former students did perform slightly better in an assessment of their ability to interpret molecular animations in class.

    Sci. Educ. 93, 10.1002/sce.20352 (2009).

    • * Melissa McCartney is a summer intern in Science's editorial department.

  4. Chemistry

    Zooming in on pH

    1. Julia Fahrenkamp-Uppenbrink
    CREDIT: HARBUZARU ET AL., ANGEW. CHEM. INT. ED. 48, 6476 (2009)

    Local acidity plays a central role in many chemical and physiological processes. Molecular-scale tools that can sense or alter the pH of their environment are therefore eagerly sought. Harbuzaru et al. present a miniaturized pH sensor operative in the physiologically relevant pH 5 to 7.5 range. The sensor is based on a metal-organic framework material (optical micrograph shown below) that contains strongly photoluminescent trivalent europium ions in two distinct coordination environments. The authors combined this material with a commercial optical fiber in their prototype design. Because only one of the two ion sites is sensitive to pH, the sensor is self-calibrating.

    In a similarly directed study, Alibrandi et al. show that [1,1,1]cryptand—a cagelike molecule that gradually captures protons from aqueous solution—can be used as a molecular-scale automatic titrator to smoothly vary the pH of a solution through nearly two units over time. Beyond pKa determinations (which the authors demonstrate), this system may find use in studying phenomena such as the pH-dependent unfolding of proteins.

    Angew. Chem. Int. Ed. 48, 6476; 6332 (2009).

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