Chemical Education Today
Reports from Other Journals
Emerging Technologies: Something Borrowed, Something New by Sabine Heinhorst and Gordon Cannon The cover of the July 16, 1998 issue of Nature features a remarkable new “smart material” that can be used to print electronically on a variety of surfaces, including paper, plastic, and metal. The electrophoretic ink developed in J. Jacobson’s lab at the Massachusetts Institute of Technology consists of liquid with dispersed, oppositely charged black and white microparticles that are contained in microcapsules. Application of a potential results in migration of the microparticles to opposite sides of the microcapsule, thereby generating either a white or black image that depends on the direction of the potential. Unlike liquid crystal displays, the image generated with electrophoretic ink is stable even after the power has been turned off. Cost and resolution of this new technology compare favorably with most other electronic image display systems currently in use or under development. Promising applications for electrophoretic ink in the future may range from street signs to electronic books (Comiskey et al., Vol. 394, pp 253–255; “News and Views” commentary by R. Wisnieff on pp 225–227). In addition to their unquestioned importance as ultimate carbon sources for all life on earth, plants recently hit the spotlight as potential gold miners. According to a correspondence in the October 8 issue by researchers from New Zealand (C. W. N. Anderson et al., Vol. 396, pp 553–554), gold from natural and synthetic ores can be hyperaccumulated by various plant species if the ore substrate is amended by the addition of EDTA or other compounds that facilitate solubilization of the precious metal. At the current market price for gold, the levels of plant-sequestered gold reached in this study suggest that “phytomining” might be economically feasible in the future. The tensile strength of such cellular structures as the cell walls of plants and bacteria is determined by their carbohydrate components. Using ab initio calculations and singlemolecule atomic force microscopy, Marszalek and colleagues
from the Mayo Clinic (December 8 issue, Vol. 396, pp 661– 664) found that application of increasing force to polysaccharide chains leads to their elongation and finally to a switch of the pyranose rings to the more extended boat conformation. This study of the molecular rearrangements that are responsible for the elasticity of polysaccharides—such as amylose, pectin, dextran, and pullulan—dispels the common notion that the linked pyranose rings are locked into the energetically favorable chair conformation. The authors speculate that similar conformational changes could play a role in mediating polysaccharide–ligand interactions and in fine-tuning the properties of polysaccharide-containing structures in vivo. D. Needham’s group at Duke University has developed a strategy for controlled drug release from delivery vehicles that borrows ideas from secretory vesicles used in nature to store and release biologically active molecules in a controlled fashion (July 30 issue, Vol. 394, pp 459–462; “News and Views” commentary by R. Siegel on pp 427–428). The researchers prepared microspheres of cross-linked polymethacrylate hydrogel that reversibly shrinks and swells below and above its pKa, respectively. Coating the shrunken acidic microspheres with an ion-impermeable lipid bilayer prevents their swelling at neutral pH and an exchange of the doxorubicin guest molecules in the hydrogel with ions from the solution outside. Electroporation of the bilayer provides the trigger for doxorubicin release and hydrogel swelling as pH and ion concentrations equilibrate. The authors suggest that incorporation of transmembrane channels that open in response to a specific external signal might be a modification of the current model system that could bring about rapid and specific release of drugs in vivo. Sabine Heinhorst and Gordon Cannon are in the Department of Chemistry and Biochemistry, University of Southern Mississippi, Hattiesburg, MS 39406-5043; email:
[email protected].
Figure 1. The letter E (black) is produced with micro-encapsulated electrophoretic ink particles via appropriate electronic address circuits. The size of the microcapsules ranges from 30 to 300 micrometers. Photo by Felice Frankel, copyright ©1998.
Figure 2. Schematic drawing of electrophoretic ink particles oriented in an electric field. The negatively charged white ink particles produce a white image for the viewer, whereas the positively charged black particles have moved towards the opposite side of the microcapsule. Reprinted with permission from Nature (1998, 394 , 253), copyright ©1998 Macmillian Magazines Limited.
JChemEd.chem.wisc.edu • Vol. 76 No. 4 April 1999 • Journal of Chemical Education
457
