NEWS OF THE W EEK
AMPLIFYING SMALL MOLECULES ENZYME MIMIC: Supramolecular complex generates target compounds in PCR-like cascade reaction
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OLECULAR AMPLIFICATION may now be just as feasible for small organic molecules as it has been for nucleic acids, according to a new study (J. Am. Chem. Soc., DOI: 10.1021/ja804076q). Such amplification, which improves analytical sensitivity, has until now been restricted to use of the polymerase OH O O chain reaction (PCR) on nucleic acids. + “Name another type of system that can recogO nize a molecule, cause some sort of structurN al change, and then turn over a catalytic S S reaction that generates more of the molecule it recognized,” says study Ph2P PPh2 CO CO leader Chad A. Mirkin, a chemistry Rh Rh AcO AcO professor at Northwestern UniverPh2P PPh2 sity. “The bottom line is that when S S you move away from PCR, there are no Ph = phenyl other systems.” Ac = acetyl = Zn(II)-salen ligand Mirkin and graduate student Hyo Jae Yoon achieved their PCR-inspired O small-molecule detection system by using O a supramolecular complex that recognizes O O– acetate and catalyzes a reaction that gener+ OH ates more acetate. Mirkin previously used the O
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Dye
The supramolecular complex binds acetate (AcO), and its Zn(II)-salen ligands catalyze an acyl transfer reaction between acetic anhydride and pyridyl carbinol, generating acetate that can activate even more catalyst.
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same complex and reaction under acidic conditions to amplify the signal for small-molecule detection in a method analogous to enzyme-linked immunosorbent assays (C&EN, Jan. 24, 2005, page 9). In that technique, the complex recognized chloride and generated acetic acid. The macrocyclic complex consists of two Zn(II)salen groups connected on either side by rhodium(I)thioether linkers that pin the complex down and keep the catalyst inactive. Under basic conditions, acetate displaces the thioethers, opening the complex and forming a cavity capable of catalyzing an acyl transfer reaction between pyridyl carbinol and acetic anhydride. The reaction is coupled to a fluorescent readout with a pH-sensitive dye. The catalyzed reaction generates more acetate, which in turn activates more catalyst in a cascade of reactions. The method’s applicability is limited only by “the creativity of a chemist trying to design a structure to recognize a molecule of interest,” Mirkin says. Such molecules of interest could range from chemical weapons and biological toxins to neurotransmitters and small-molecule disease markers. A key challenge in moving forward is extending the methodology from bimetallic to monometallic catalytic systems to expand the potential repertoire of catalytic reactions. Mirkin’s group is building structures with pockets to protect the catalytic site. “We can toggle back and forth between open and closed states, or inactive and catalytically active states, with a single metal as opposed to two metals,” he says. Such structures could also be used to introduce cocatalysts, he adds. “The strategy outlined in this paper can potentially be implemented for the production and detection of chemically or biologically important species,” says Wenbin Lin, a chemistry professor at the University of North Carolina, Chapel Hill, who also studies enzymemimicking supramolecular complexes. “This work elegantly illustrates the great potential of metal-organic supramolecular systems in mimicking important biological processes.”—CELIA ARNAUD
WEB TOOLS ACS launches social networking site for chemical professionals Networking and staying connected with colleagues just got easier with the launch of the ACS Member Network at www. acs.org/membernetwork. The free social networking site is available to ACS members and student affiliates. Its goal is to facilitate scientific collaboration among chemical science professionals around the world. “Our hope is that scientists will use it to connect with members they may already know and seek out skills and talents of other scientists to evolve new
opportunities for knowledge exchange,” says Madeleine Jacobs, ACS executive director and CEO. More than 11,000 ACS members have pre-enrolled in the network since the society began promoting the site in early April. Once registered, ACS members can post their photos, create a profile, and search the entire network of members by name, keyword, area of expertise, technical division, local section, and location. They can then invite others to join their
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personal network and view each other’s private profiles. Members can also highlight their publications, and other members can download the citations. As an example of the site’s functionality, Robert M. Hammond, a chemistry professor at East Carolina University, plans to use the network to identify speakers for his ACS local section’s activities. Jacobs says ACS is continuing to improve the site and intends to add new functionality and features over the next year.—LINDA WANG
