C&EN: COVER STORY - CHEMISTRY HIGHLIGHTS 2003

This was also a busy year for those who like to "get physical" and to focus on the surface of things.


	BEND OVER BACKWARD Langer's group created this controllably switchable self-assembled monolayer surface. © SCIENCE 2003

The speed of aqueous proton transfer from acid to base was measured and a detailed mechanism proposed by Ehud Pines of Ben-Gurion University of the Negev, Israel; Erik T. J. Nibbering of Max Born Institute for Nonlinear Optics & Short Pulse Spectroscopy, Berlin, Germany; and coworkers [Science, 301, 349 (2003)]. They found an extra stage of the mechanism that had never been observed previously.

Also awash with significance were findings by Anne Willem Omta of the FOM Institute for Atomic & Molecular Physics, Amsterdam, the Netherlands, and coworkers that ion solvation affects water's hydrogen-bonding network only in the single layer of water molecules surrounding the ion [Science, 301, 347 (2003)]. This contradicts existing views that ions cause nonlocalized water-structure effects throughout an entire solution.

A truly momentous development was the determination of the largest transient dipole moment ever measured--150 debyes (D), in a carotene-porphyrin-fullerene artificial photosynthetic system--by Sergei N. Smirnov of New Mexico State University; Devens Gust, Ana L. Moore, and Thomas A. Moore of Arizona State University; and coworkers [J. Phys. Chem. A, 107, 7567 (2003)]. The previous record was 100–120 D. The study is of fundamental interest and could have implications for ultrafast switching.


MOLECULAR RULERS Walker and Steel developed surfactants (green oval linked to red circle) capable of profiling polarity changes across water-oil interfaces (surrounding molecules). COURTESY OF R. A. WALKER

In surface science this year, a switchable surface created by MIT's Robert S. Langer and coworkers was hailed as "amazing" by one observer. The self-assembled alkanethiolate monolayer can be made to stand or collapse by applying an electrical potential to reversibly switch its conformational state [Science, 299, 371 (2003)]. Such surfaces might be useful for microfluidics, drug delivery, electro-optics, or offset printing.

Little has been known about the atomic-scale dynamics of defects on transition-metal oxide crystal surfaces. But using time-lapse scanning tunneling microscopy, Flemming Besenbacher of the University of Aarhus, in Denmark, and coworkers showed this year that oxygen vacancies diffuse across a surface along specific crystal directions; these findings could aid the ability to control the number and distribution of oxygen vacancies on such surfaces [Science, 299, 377 (2003)].

A method to profile polarity changes across water-oil interfaces was developed by Robert A. Walker and William H. Steel of the University of Maryland, College Park [Nature, 424, 296 (2003)]. It's based on "molecular rulers": surfactants that each contain a hydrophobic probe, a spacer, and an anionic head group. The technique has implications for phase-transfer catalysis, drug bioavailability, and other interfacial phenomena.