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<jats:p> Telomeres, usually consisting of repetitive sequences and proteins bound to them, form the ends of all chromosomes, where they protect against unwanted shortening during DNA replication and cell division. The Perspective by Hawley discusses two reports, one by Kirk <jats:italic>et al</jats:italic> . ( <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1478" related-article-type="in-this-issue" vol="275" xlink:href="10.1126/science.275.5305.1478" xlink:type="simple">p. 1478</jats:related-article> ) of this week's issue and the other in press at <jats:italic>Genes and Development</jats:italic> , that point to a surprising new function for telomeres in the separation of the ends of the chromosomes during cell division. </jats:p>

<jats:p> In biological systems such as plants, enzymes called nitrogenases “fix” nitrogen from the air for use by the organism. In his Perspective Update, Leigh discusses new work that examines how nitrogen is processed by simpler molecular complexes. Such studies may reveal how nitrogenases work, which would increase our fundamental understanding of plant biochemistry and could potentially lead to more efficient industrial processing of nitrogen. See also the two reports related to this Perspective by Shan <jats:italic>et al</jats:italic> . ( <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1460" related-article-type="in-this-issue" vol="275" xlink:href="10.1126/science.275.5305.1460" xlink:type="simple">p. 1460</jats:related-article> ) and Fryzuk <jats:italic>et al</jats:italic> . ( <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1445" related-article-type="in-this-issue" vol="275" xlink:href="10.1126/science.275.5305.1445" xlink:type="simple">p. 1445</jats:related-article> ). </jats:p>

<jats:p>The reaction of dihydrogen with a side-on bound dinitrogen complex of zirconium was investigated. Instead of a displacement of the dinitrogen moiety, which is the common mode of reactivity, a complex containing both a bridging hydride and a bridging hydrazido unit with a nitrogen-hydrogen bond was observed. This reaction was extended to primary silanes to produce a species that contained a nitrogen-silicon bond. In addition, an intermediate in the dihydrogen addition has been structurally characterized as having a bridging dihydrogen unit.</jats:p>

<jats:p>A method of preparing modified surfaces, referred to as soft-landing, is described in which intact polyatomic ions are deposited from the gas phase into a monolayer fluorocarbon surface at room temperature. The ions are trapped in the fluorocarbon matrix for many hours. They are released, intact, upon sputtering at low or high energy or by thermal desorption, and their molecular compositions are confirmed by isotopic labeling and high-resolution mass measurements. The method is demonstrated for various silyl and pyridinium cations. Capture at the surface is favored when the ions bear bulky substituents that facilitate steric trapping in the matrix.</jats:p>

<jats:p> A complete skeleton of the oldest known flying reptile, <jats:italic>Coelurosauravus jaekeli,</jats:italic> from the Upper Permian of Germany, and reexamination of other specimens demonstrate that this animal had a gliding apparatus unlike that of any other tetrapod. The lateral gliding membrane was supported by radially disposed, greatly elongated bony rods of dermal origin in the thoracolumbar region, rather than by internal skeletal elements such as ribs and limb bones. The rods are independent of the ribcage and arranged in distinct bundles to form a cambered wing. </jats:p>

<jats:p> An x-ray spectroscopic study of scleractinian coral skeletons indicated that, although some strontium substitutes for calcium in the aragonite structure, at concentrations of about 7500 parts per million, as much as 40 percent of the strontium resides in strontianite (SrCO <jats:sub>3</jats:sub> ). A doublet peak in the Fourier transform of the extended x-ray absorption fine structure of the coral corresponded to six metal and 13 oxygen neighbors surrounding strontium at about 4.05 angstroms in strontium-substituted aragonite and at about 4.21 angstroms in strontianite. Thus, the mechanism of the temperature-sensitive partitioning of strontium between seawater and coral skeleton used for paleothermometry is unexpectedly complex. </jats:p>

<jats:p> The Suess Effect is a gradual decrease of the <jats:sup>14</jats:sup> C/ <jats:sup>12</jats:sup> C ratio in tree rings from 1870 to 1950 that is attributed mostly to the burning of <jats:sup>14</jats:sup> C-free fossil fuels for energy. In contrast, pre-nuclear bomb high-precision measurements of <jats:sup>14</jats:sup> C/ <jats:sup>12</jats:sup> C ratios in banded corals from the North Atlantic Ocean do not exhibit the expected Suess Effect. Instead, large biennial-to-decadal shifts in the <jats:sup>14</jats:sup> C/ <jats:sup>12</jats:sup> C ratios appear throughout the coral records. This pattern indicates that rapid pulses of increased mixing between surface and subsurface waters occurred in the North Atlantic Ocean during the past century. </jats:p>

<jats:p> A simple technique for precisely controlling the interfacial energies and wetting behavior of polymers in contact with solid surfaces is described. End-functionalized statistical random copolymers of styrene and methylmethacrylate were synthesized, with the styrene fraction <jats:italic>f</jats:italic> varying from 0 to 1, and were end-grafted onto silicon substrates to create random copolymer brushes about 5 nanometers thick. For <jats:italic>f</jats:italic> &lt; 0.7, polystyrene (PS) films (20 nanometers thick) rapidly dewet from the brushes when heated well above the glass transition temperature. The contact angle of the resulting polymer droplets increased monotonically with decreasing <jats:italic>f</jats:italic> . Similar behavior was observed for poly(methylmethacrylate) (PMMA) films but with an opposite dependence on <jats:italic>f</jats:italic> . The interfacial energies of the random copolymer brushes with PS and PMMA were equal when <jats:italic>f</jats:italic> was about 0.6. Thus, precise control of the relative surface affinities of PS and PMMA was possible, demonstrating a way to manipulate polymer-surface interactions. </jats:p>

<jats:p> A family of dinitrogen complexes, [(LAu) <jats:sub>6</jats:sub> (N <jats:sub>2</jats:sub> )] <jats:sup>2+</jats:sup> (L = a phosphine), with the dinitrogen unit bridging two clusters of three gold atoms have been prepared from hydrazine and [(LAu) <jats:sub>3</jats:sub> (O)] <jats:sup>+</jats:sup> . Structural characterization of the PPh <jats:sub>2</jats:sub> <jats:sup>i</jats:sup> Pr (Ph, phenyl; <jats:sup>i</jats:sup> Pr, isopropyl) derivative shows a nitrogen-nitrogen single-bond distance indicative of hydrazido (N <jats:sub>2</jats:sub> <jats:sup>4−</jats:sup> ) character for the dinitrogen unit. The complexes can be reduced and protonated to give low [13% when L = PPh <jats:sub>2</jats:sub> Me (Me, methyl)] to quantitative [100% when L = P( <jats:italic>p</jats:italic> -MeOC <jats:sub>6</jats:sub> H <jats:sub>5</jats:sub> ) <jats:sub>3</jats:sub> ] yields of ammonia, establishing that bonding of dinitrogen to six metal atoms can lead to facile cleavage of the nitrogen-nitrogen bond. </jats:p>