Chemical Education Today
Reports from Other Journals
Nanotechnology by Sabine Heinhorst and Gordon Cannon In recent issues of Nature, we found a plethora of articles that describe exciting developments in nanotechnology. We decided to focus the column on this topic and selected papers which demonstrate the enormous potential of this technology to be the springboard for the development of ever smaller and “smarter” separation, sensing, and mechanical devices. The work of two research groups to control the pattern of crystal growth on surfaces was undoubtedly inspired by the desire to mimic the remarkable accuracy displayed by biological mineralization events. S. M. D’Souza and colleagues from the Institute of Food Research in Reading, UK and from Unilever Research Laboratories in the UK and in the Netherlands (1999, 398, March 25 issue, 312–316) polymerized divinylbenzenecross-linked methacrylamidohexanoic acid onto a calcite template crystal. After dissolving the calcite in acid, nucleation of new calcite crystals was directed by the imprint of the original crystal on the polymer surface. The ability to efficiently control crystal growth appeared to depend on the monomeric species used, the molecular interactions between its functional groups and the growing crystal, and the identity of the imprinted crystal template. J. Aizenberg from Bell Laboratories and G.M. Whitesides’ group from Harvard University used self-assembling monolayers (SAM) of molecules with charged or polar functionalities to “ink” a surface with a raised pattern “stamp” (1999, 398, April 8 issue, 495–498; News and Views article by L. Addadi and S. Weiner, pp 461–462). The SAM pattern was transferred to a metal surface, with non-functionalized SAM deposited on the residual surface space as a filler. The imprinted metal, when suspended in a CaCO3 solution, supported crystal formation on its surface. The crucial physical parameter responsible for directing crystal growth to the areas of functionalized SAM appeared to be the result of ions migrating to the faster-nucleating sites. This would cause a selective ionic depletion in the solution surrounding the methyl-terminated SAM, thereby preventing crystal growth elsewhere on the surface. By varying the metal substrate and the functional groups on the SAM, one could not only control the surface distribution pattern but also influence the orientation of the growing crystals. Molecular recognition between surface imprints and proteins was explored by teams from the University of Washington and from the Universita Degli Studi Di Trento in Italy (H. Shi et al. 1999, 398, April 15, 593–597). A pattern of a template protein was “stamped” onto a mica surface; the entire surface was filled in with an unrelated protein (bovine serum albumin) and covered with a disaccharide and a fluorinated polymer coating. Removal of the mica, followed by alkaline hydrolysis of the protein, left disaccharide-imprinted surface cavities with chemical and spatial features that were
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Figure 1. A mechanical device that is based on the B to Z transition of a double crossover DNA structure. The domain depicted in yellow can change conformation from right- to left-handed double helix. The two circles denote the fluorescent dye pair.
complementary to the surface of the template protein. Although any protein can apparently bind nonspecifically to the entire surface of the imprint, competition experiments with solutions containing the template and the unrelated protein revealed imprint-pattern-dependent surface deposition of the target protein, probably due to the more numerous non-covalent interactions between the oriented disaccharide groups in the pits and the surface of the template protein. Finally, a biomechanical nanodevice that is based on the DNA secondary structural transition from the familiar righthanded B-form to the left-handed Z-form was reported by N. C. Seeman’s group at New York University (1999, 397, January 14 issue, 144–146). Synthetic oligonucleotides were used to construct a double-crossover DNA structure that was sufficiently rigid to allow detection of the conformational change as a mechanical translation. A donor–acceptor pair of fluorescent dyes was connected to two non-catenated ends of the structure that were close enough to support a fluorescence-resonance-energy transfer when the entire DNA was in the B-form. The central domain of the structure contained a sequence motif that was able to assume the left-handed Zhelical conformation at high ionic strength. This conformational change rotated the dyes relative to each other and increased their distance which, in turn, translated into a greatly reduced fluorescence-resonance-energy transfer signal. Sabine Heinhorst and Gordon Cannon are in the Department of Chemistry and Biochemistry, University of Southern Mississippi, Hattiesburg, MS 39406-5043; email:
[email protected] and
[email protected].
Journal of Chemical Education • Vol. 76 No. 11 November 1999 • JChemEd.chem.wisc.edu
