Environmentally friendly synthesis of-caprolactam

September 27, 2005 兩 vol. 102 兩 no. 39 兩 13711–14122

In This Issue

PNAS

Proceedings of the National Academy of Sciences of the United States of America

13732 13755 13783 14058 14116

www.pnas.org

Environmentally friendly synthesis of ␧-caprolactam Volatile fractionation in early solar system Crystal aggregates in bone contain well preserved DNA A natural protein battery Innate abstract number and arithmetic skills

CHEMISTRY

Environmentally friendly synthesis of ␧-caprolactam John Meurig Thomas and Robert Raja describe a viable singlestep, solvent-free, low-temperature synthesis of ␧-caprolactam, the precursor of nylon-6. Nylon-6 is currently manufactured from cyclohexanone by one of two methods, which entail organic solvents, aggressive oxidants, and the generation of ammonium sulfate waste. With industrial demand for nylon-6 increasing, Thomas and Raja sought to develop a more ecologically responsible method. Using microporous bifunctional aluminophosphate (AlPO) crystals as the reaction catalysts and air as the oxidizer, the authors conModel of a microporous AlPO crys- verted cyclohexanone to ␧tal, the catalyst for the single-step caprolactam with efficiencies conversion of cyclohexanone to of 65–78%; the reaction is carried out in ammonia ␧-caprolactam. at 80°C and produces no ammonium sulfate waste. The AlPO crystals act as single-site heterogeneous catalysts (SSHCs), wherein the active redox and acidic centers are spatially isolated from one another and uniformly distributed throughout the solid. The authors believe that their specially designed SSHCs can be used to create environmentally desirable alternatives to other hazardous or wasteproducing chemical conversions. — N.Z. ‘‘Design of a ‘green’ one-step catalytic production of ␧-caprolactam (precursor of nylon-6)’’ by John Meurig Thomas and Robert Raja (see pages 13732–13736) CHEMISTRY

Volatile fractionation in early solar system Philip Bland et al. suggest that carbonaceous chondrites (CCs), the most primitive rock available for study, formed from a mawww.pnas.org兾cgi兾doi兾10.1073兾iti3905102

terial reservoir that was already depleted in volatile and moderately volatile elements. This finding implies that volatile fractionation occurred in the earliest epoch of solar system history. Bland et al. determined the compositions of fine-grained matrices for 20 samples of a variety of CCs, with minor and trace element abundance data for Representative matrix composi47 elements for each meteortions of chondrites. ite. The authors found that trace element abundances in CC matrices were depleted relative to CI chondrites but enriched relative to the bulk compositions of their parent meteorites. This result provides evidence against volatile depletion models that posit a pristine matrix with uniform CI-like chemistry across chondrite groups. Also, chondrules and matrix were found to be formed in the same nebular region, providing a fundamental constraint on chondrule formation. — R.N. ‘‘Volatile fractionation in the early solar system and chondrule兾matrix complementarity’’ by Philip A. Bland, Olivier Alard, Gretchen K. Benedix, Anton T. Kearsley, Olwyn N. Menzies, Lauren E. Watt, and Nick W. Rogers (see pages 13755–13760) ANTHROPOLOGY

Crystal aggregates in bone contain well preserved DNA Michal Salamon et al. demonstrate that well preserved DNA is occluded within crystal aggregates in both modern and fossil bones. DNA preserved in bones could be valuable in studying the genetics and evolution of different animals, but postmortem DNA degradation and the potential of contamination with contemporary DNA make acquiring reliable samples difficult, especially from human bones. However, adjoining bone crystals often fuse together to form intergrown aggregates, and Salamon et al. speculated that these crystal clusters, which tend to be resistant to oxidizing agents, might preserve organic material more effectively than the bone as a whole. The authors extracted and amplified PNAS 兩 September 27, 2005 兩 vol. 102 兩 no. 39 兩 13711–13712

DNA samples from both isolated aggregates treated with sodium hypochlorite (NaOCl) and untreated whole bone powder prepared from eight different modern and fossil bones. Longer and more well preserved DNA molecules were obtained from the aggregate samples, although amplifiable DNA could not be extracted from all of the fossilized samples. Although treating a bone sample with the strong oxidizer NaOCl may seem counterintuitive, the authors note that the protective environment created within the aggregate allowed the oxidizer to safely remove modern contaminants and PCR inhibitors, eliminating two key elements that can hinder DNA acquisition. — N.Z. ‘‘Relatively well preserved DNA is present in the crystal aggregates of fossil bones’’ by Michal Salamon, Noreen Tuross, Baruch Arensburg, and Steve Weiner (see pages 13783–13788) NEUROSCIENCE

A natural protein battery Xinle Wu et al. report that aggregates of the mammalian protein Sprouty2 may act like a natural battery inside cells, capable of receiving, maintaining, and dissipating electrical charge. This finding suggests an unusual way for a cell to respond to changes in its state and affect intracellular signaling. Sprouty proteins are thought to be intracellular inhibitors of tyrosine kinase signaling and are essential for multiple developmental pathways. Wu et al. found that ⬇24 Sprouty2 proteins clumped into large, pure particles that could store electrical charge internally. The protein’s cysteine residues formed iron兾sulfur complexes in the aggregate’s core, and the electronic state of these complexes were protected from Sprouty2 in neuroblastoma cells. charges in the cell’s immediate

13712 兩 www.pnas.org兾cgi兾doi兾10.1073兾iti3905102

environment. The authors hypothesized that these charges are protected until the protein aggregate meets its proper receptacle and requires electron transport. — P.D. ‘‘Mammalian sprouty proteins assemble into large monodisperse particles having the properties of intracellular nanobatteries’’ by Xinle Wu, Peter B. Alexander, Ying He, Masahide Kikkawa, Pia D. Vogel, and Steven L. McKnight (see pages 14058–14062) PSYCHOLOGY

Innate abstract number and arithmetic skills Hilary Barth et al. report that preschool children can compare and add large sets of elements without counting, both within and across modalities. The authors sought to investigate whether 5-year-old children with no school experience or relevant symbolic knowledge could perform arithmetic operations by using different abstract number representations. In the first set of experiments, participating children viewed computer animations and either compared one visible array of dots to a second array, or added two successive dot arrays and compared the sum with a third array. In the cross-modal experiments, a dot array was replaced by a sequence of sounds, thus requiring the children to integrate aural and visual information. In all experiments, the children were able to perform tasks without resorting to guessing strategies or responding to continuous variables. Their accuracy declined as the ratio of the two quantities being compared approached 1, which is characteristic of large, approximate number representation in adult humans and animals. The children showed no relevant knowledge of arithmetic when tested with symbolic versions of the addition tasks. Therefore, abstract knowledge of number and addition precedes language-based instruction in mathematics, the authors say. — R.N. ‘‘Abstract number and arithmetic in preschool children’’ by Hilary Barth, Kristen La Mont, Jennifer Lipton, and Elizabeth S. Spelke (see pages 14116–14121)