News
Understanding chemisorbed CO The chemisorption and subsequent reaction of CO on transition metal surfaces is a topic of fundamental interest in heterogeneous catalysis. NMR spectroscopy of 13 CO has proven to be a powerful technique for probing the diatomic's structure, dynamics, and electronic structure on a metal surface. However, the relationship between the observed NMR values and the electronic properties of the metal surface are still being unraveled (Anal. Chem. 1998, 70, 518 A527 A). This type of information can lead to new ways of probing catalyst and electrocatalyst surface structures. Andrzej Wieckowski, Eric Oldfield, and their research groups at the University of Illinois at Urbana-Champaign
Lions, tigers, and bears Chemists are usually not the first people who come to mind for determining species of birds, reptiles, and mammals; however, recent work by Edgard 0. Espinoza and co-workers at the National Fish and Wildlife Forensics Laboratory and Southern Oregon University could make that a thing of the past. The researchers analyzed unpurified whole blood and dried blood samples from 980 animals, representing 62 species, looking for a- and B-protein pairs in hemoglobin whose molecular weights could serve as markers for species identification. Using electrospray ionization (ESI) MS, they were able to differentiate one species from another based on distinctive oc/B-pairs in 86% of the cases despite hemoglobin variability observed in many species. The authors believe that the 14% of cases with overlapping a/S-pair molecular weight values could be differentiated by implementing a separation such as HPLC before MS analysis. In some cases, more than one signal appeared in the mass spectrum around the regions associated with the molecular weights of the a- and B-protein chains in hemoglobin. The secondary signals might provide some information useful for species determination. However, the authors chose to use only the most abundant signals. Although the technique is unable to dif372 A
demonstrate a quantitative relationship between ligand NMR shut and the surface electronic state. To achieve that goal, they used 3 C and ' 'Pt NMR to collect Knight shift, relaxation, and/-coupling data for CO, which was chemisorbed on a platinum electrocatalyst in an electrochemical environment. This was combined with quantum chemical calculations based on density functional theory. They report a linear correlation between the 13C Knight shift of chemisorbed 13CO and the clean surface Fermi level local density of states of platinum catalysts, which amounts to —11 ppm/Ry^-atom"\ In addition, they investigated the li,5Pt NMR line shape, the 195Pt nuclear spin-lattice and the spin-spin relaxation behavior for a platinum electrocatalyst. (/. Am. Chem. Soc. 1999, 121, 2996-3003)
ferentiate all species, it offers some advantages over other techniques currently used for species identification, such as electrophoresis. The high resolving power of ESI-MS makes the technique more discriminating, allowing for the identification of polymorphic forms of hemoglobin, which go undetected by electrophoresis. The technique is also useful for corroborating hemoglobin-sequencing data. Although some of the authors' data agreed with the reported sequences, in many cases it did not, suggesting errors in the reported sequences. (Anal. Biochem. 1999 268 252-61)
MIP for estrogenic compounds Stilbene estrogenic compounds, such as hexestrol, 17B-estradiol, and fra«s-diethylstilbestrol, have been in the news as potential endocrine-disrupting compounds, which are thought to be linked to reproductive abnormalities in wildlife and increasing cases of breast cancer. Although they have been banned from use in the European Union, they continue to be used elsewhere as growth promoters by the meat industry. Jonathan A Tarbin and Matthew Sharman of CSL Food Science Laboratory (Norwich, U.K) have developed a selective method, which uses a molecularly imprinted polymer (MIP), prepared with a hexestrol template, to determine phenolic estrogenic compounds in animal tissues. The MIP was prepared using a noncovalent imprinting technique, in which 2-(diethylamino)ethyl methacrylate served as the functional monomer and trimethylolpropane trimethacrylate served as the cross-linking monomer. A blank polymer was also prepared without the hexestrol template using an analogous protocol Both polymers were packed in 150 x 4 6-mm i d stainless steel HPLC columns for evaluation The polymer synthesized with the hexestrol template showed selectivity towards hexestrol, as well as compounds containing the same carbon backbone as hexestrol (fraHS-diethylstilbestrol and dienestrol). Some recognition was shown for zeranol and the estradiols, but much less than that for hexestrol. (Anal. Commun. 1999,36, 105-07)
SCIENCE
Just say NO Dubbed by Science magazine as the 1992 "Molecule of the Year," nitric oxide (NO) continues to be one of the most versatile and important chemicals known. NO is a common air pollutant that forms when nitrogen is burned; however, in the body, it takes on various roles—from regulating blood pressure to triggering memories to killing off pathogens. Because of its biological importance, several attempts have been made to create fast, selective methods for detecting NO. In this issue (p 2071-75), Raoul Kopelman and co-workers at the University of Michigan describe a new type of NO biosensor based on a fluorescent dye-
Analytical Chemistry News & Features, June 1, 1999
labeled heme domain of soluble guanylate cyclase (sGC). The sGC-based sensor offers improved sensitivity (as much as an order of magnitude) over previously developed NO biosensors based on the hemoprotein cytochrome c' (Anal. Chem. 1999, 71,1767-72). "We believe the improved sensitivity is because of a difference in the binding constants of the proteins," says Susan Barker, a graduate student in Kopelman's lab. "They are both proteins that are well known to selectively bind nitric oxide. We expected the guanylate cyclase to bind more tightiy to nitric oxide because it is found in the human body; whereas the cytochrome c' was extracted from exotic bacteria" adds Kopelman.
