NEWS OF THE WEEK
PICTURING DNA ON A SURFACE SPECTROSCOPY: Label-free method probes hybridization and chirality of bound nucleotides
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NEW TECHNIQUE allows researchers for the first time to determine the structure and chirality of surface-bound oligonucleotides. Based on vibrational spectroscopy, the technique provides the first direct method for observing DNA base pairing and other basic biochemical processes that occur on surfaces, and it may lead to advances in biodetection technologies and medical diagnostics. Years of investigations have led to in-depth understanding of the chemistry that drives complementary strands of oligonucleotides to hybridize (form duplexes) in solution. The surface analogs of those reactions, however, are not well-understood, yet they are critical to a variety of DNA detection methods. For example, DNA chips, which are widely used in genomics and in studies of diseases, rely on strands of DNA (probe molecules) that are tethered to a solid surface to form duplexes with complementary analyte strands in solution. The analyte molecules are often tagged with nanoparticles or fluorescent labels to facilitate detection. Then, after hybridization, the target labels are exploited in a subsequent step to signal the presence of the hybridized form of the analyte on the DNA chip. Now, that detection can be carried out directly— without labels—by using a variant of sum frequency generation (SFG), a nonlinear optical process based on the interaction of two beams of light having different frequencies. Probing the reaction between thymine and adenine chains (T15 and A15) as a test case, research-
ers at Northwestern University have demonstrated that the SFG technique can track the molecular ordering that occurs as surface-bound molecules react to form helical duplexes (J. Am. Chem. Soc, DOI: 10.1021/ jao7i848r). The research team, which includes Grace Y. Stokes, JulianneM. Gibbs-Davis, Faith G. Boman, and chemistry professors Franz M. Geiger and SonBinh T. Nguyen, also showed that the method reveals a difference in the chirality of surface-bound T15 strands hybridized with A1S and that of the duplexes formed when A15 strands tethered to a surface react with T15. The difference results from the orientation of a thymine methyl group, which varies depending on the order in which the reaction steps are carried out. Describing the work as "interesting and stimulating," SFG pioneer Yuen-Ron Shen, an emeritus physics professor at the University of California, Berkeley, notes that, to his knowledge, this study marks the first time that the effect of conformational changes on the chirality of the secondary structure of adsorbed molecules has been monitored. Zhan Chen, a University of Michigan, Ann Arbor, chemistry professor, says SFG is a powerful technique for elucidating the structures of biological molecules such as lipids, peptides, and proteins at interfaces. "By studying interfacial DNA, this innovative and excellent work further demonstrates that SFG has the ability to revolutionize research related to interfacial phenomena in life sciences."—MITCH JACOBY
Northwestern chemists (front row, from left) Boman, Stokes, Allyson G. Condie, (back row, from left) Brian R. Stepp, Gibbs-Davis, Nguyen, and Geiger spectroscopically studied the structure of the adenine-thymine complex they're displaying.
SURVEY Market challenges dim the confidence of the world's chemical CEOs Chief executive officers of the world's chemical companies are less confident about the next 12 months than are their counterparts in industry as a whole. According to a survey just released by the tax and advisory services firm PricewaterhouseCoopers (PwC), only 4 4 % of chemical CEOs are very confident about the next 12 months, compared with 5 2 % of CEOs in general. Moreover, only 3 6 % of chemical CEOs are more confident than they were a year ago, compared with 5 0 % of CEOs in general. PwC surveyed nearly 1,100 CEOs,
36 of whom lead chemical companies. The main drains on chemical CEOs' confidence, PwC reports, are low-cost competition, energy prices, energy security, and overregulation. "It is not surprising to see that regulation is concerning chemical CEOs," says Volker Fitzner, global chemicals advisory leader at PwC. He notes that REACH—Europe's new system for the registration, evaluation, and authorization of chemicals—will have a considerable impact on manufacturers in Europe and elsewhere. Concerns aside, chemical company
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chief executives are more global in their deal-making than are their colleagues in other industries. PwC found that 3 9 % of chemical CEOs completed a cross-border acquisition in the past year, compared with just 27% of CEOs in general. Of those chemical acquisitions, 4 1 % involved the Asian market. Chemists should be heartened that R&D seems to be important to chemical industry CEOs: 2 8 % of them identified new product development as the key means of future growth.—MICHAEL MCCOY
