CONCENTRATES
1
science/ technology Antibodies zero in on chiral carbons of α-amino acids Antibodies that distinguish between L- and EKX-amino acids without regard to the amino acid's side chains offer a simple way to isolate or assign configurations to such chiral compounds [/. Am. Chem. Soc, 120, 3251 (1998)]. Research profes- sor Bernard S. Green at Hebrew University of Jerusalem's department of pharmaceuti- cal chemistry and coworkers raised rabbit antibodies against a protein coupled to p- amino-L-phenylalanine and against a pro- tein coupled to the corresponding i>com- pound. In competitive binding assays, the antibodies specifically recognized amino acids with the same absolute configuration as the original compounds—even if the side chains were significantly different from phenylalanine. Hie "anti-D" antibody, for example, bound D-tryptophan and D- histidine tightly, whereas "anti-L" specifi- cally bound the opposite enantiomers. Amino acids such as proline that don't car- ry a primary amino group, a carboxylate, and a hydrogen on the chiral carbon were not bound by the antibodies. The discrim- inating antibodies could be used to isolate and purify amino acids in affinity chroma- tography and to assign configuration easily and rapidly to very small samples of unde- rivatized α-amino acids, the researchers suggest.^ Termites fumigate their nests with naphthalene Naphthalene—the stuff of moth balls—is an ingredient in termites' nests. Entomol- ogists Jian Chen and Gregg Henderson at Louisiana State University's Agricultural Center, Baton Rouge, along with col- leagues in both the university's depart- ment of biochemistry and chemistry and USDA's Agricultural Research Service, New Orleans, discovered the naphtha- lene component while analyzing extracts of the wood-and-soil-composite nests of Formosan subterranean termites. Con- centrations of the fumigant varied from 51 to 215 Mg per kg of extract [Nature, 392, 558 (1998)]. This is the first time naphthalene has been found naturally as- sociated with any insect species, the team notes. The researchers have shown it inhibits proliferation of fungi and para- lyzes ants at concentrations that have no visible effect on the termites. They sug- gest the compound plays two roles: It defends the termites from predators and acts as an attractant or guide for the "sol- dier" termites—those designated to guard the nests and forage for food. Team lead- er Henderson believes the naphthalene may be a metabolite of woody material ingested by the termites rather than a pheromone they produce. "But we don't know that yet," he says. The group is working to develop a naphthalene-based termite detector.^ Nine-atom silicon cluster joins the family "We have discovered and structurally char- acterized the first 'naked' silicon clusters larger than four atoms, Si/", in the [new] compound Rb 12 Si 17 ," reports a team led by Slavi C. Sevov, assistant professor of chemistry at the University of Notre Dame in Indiana \J. Am. Chem. Soc, 120, 3263 (1998)]. If the clusters can be extracted into solution, Rb 12 Si 17 might serve as a pre- cursor for solu- tion-phase sili- con nanoparti- cles, which are expected to have valuable optical properties. Previous attempts to extract Si 4 4 " tetrahedra from compounds containing these species have been unsuccessful. Sevov and coworkers Virginie Queneau and Evgeny Todorov made Rb 12 Si 17 by reacting elemental rubid- ium and silicon at 900 °C. X-ray data sug- gest that the extremely reactive product is best described as ionic, with isolated S^ 4 " and Si 4 4 " anions and Rb + counterions, the researchers note. At first glance, the Si/" clusters (shown) all look much the same, but they actually fall into four distinct groups with slightly different shapes, an- gles, and bond distances. Nine-atom clus- ters of germanium, tin, and lead already were known, so the Sic, 4 " cluster was the sole missing member in the family, exclud- ing carbon, the chemists say.^ Thermal screening of catalyst libraries debuts A technique that potentially will make it easier to screen for promising catalysts in large combinatorial libraries of catalysts has been developed by graduate student Steven J. Taylor and assistant professor of chemistry James P. Morken of the Uni- versity of North Carolina, Chapel Hill [Science, 280, 267 (1998)]. The research- ers used infrared thermography to detect the small amount of heat generated by reactions accelerated by active catalysts in encoded polymer-bound libraries. They demonstrated the technique by si- multaneously screening a library of 3,150 candidate compounds for their ability to catalyze a solution-phase acylation reac- tion. Three of four compounds identified in the screen were found to be responsi- ble for most of the library's catalytic power. The screen did not select anoth- er compound with appreciable (but less- er) activity. According to Taylor and Morken, methods for assessing the kinet- ics of reactions involving polymer-bound libraries previously were not available. They believe the infrared thermographic method could be used to evaluate organ- ometallic libraries or ligand libraries for ligand-accelerated metal catalysis.^ A way to whisk proteins through cell membranes Although scientists would like to be able to direct peptides and proteins into cells for functional studies and potential thera- pies, cell membranes generally are resis- tant to the passage of most peptides and proteins. In 1995, Yao-Zhong Iin, Jacek Hawiger, and coworkers in the depart- ment of microbiology and immunology at Vanderbilt University, Nashville, reported a way to get peptides into cells by linking them to a peptide sequence that interacts strongly with lipid bilayers. Lin and co- workers Mauricio Rojas, John P. Donahue, and Zhongjia Tan now have found that en- tire proteins can be similarly spirited through cell membranes by fusing their C- termini to a 12-amino-acid membrane-trans- locating sequence [Nat. Biotechnol, 16, 370 (1998)]. The researchers were able to get glutathione ^transferase (GST) fusion proteins as large as 45 kilodaltons into liv- ing cells this way. Furthermore, they dem- onstrated that a three-way fusion protein including GST, the membrane-translocat- ing sequence, and a protein fragment that controls signal transduction not only en- tered cells but exhibited biological activity there. According to Iin, the protein deliv- ery technique should be useful for intra- cellular functional studies and drug and vaccine development.^ 40 APRIL 13, 1998 C&EN concentrates
Transcript of CONCENTRATES
science/ technology
Antibodies zero in on chiral carbons of α-amino acids Antibodies that distinguish between L- and EKX-amino acids without regard to the amino acid's side chains offer a simple way to isolate or assign configurations to such chiral compounds [/. Am. Chem. Soc, 120, 3251 (1998)]. Research professor Bernard S. Green at Hebrew University of Jerusalem's department of pharmaceutical chemistry and coworkers raised rabbit antibodies against a protein coupled to p-amino-L-phenylalanine and against a protein coupled to the corresponding i>com-pound. In competitive binding assays, the antibodies specifically recognized amino acids with the same absolute configuration as the original compounds—even if the side chains were significantly different from phenylalanine. Hie "anti-D" antibody, for example, bound D-tryptophan and D-histidine tightly, whereas "anti-L" specifically bound the opposite enantiomers. Amino acids such as proline that don't carry a primary amino group, a carboxylate, and a hydrogen on the chiral carbon were not bound by the antibodies. The discriminating antibodies could be used to isolate and purify amino acids in affinity chromatography and to assign configuration easily and rapidly to very small samples of unde-rivatized α-amino acids, the researchers suggest.^
Termites fumigate their nests with naphthalene Naphthalene—the stuff of moth balls—is an ingredient in termites' nests. Entomologists Jian Chen and Gregg Henderson at Louisiana State University's Agricultural Center, Baton Rouge, along with colleagues in both the university's department of biochemistry and chemistry and USDA's Agricultural Research Service, New Orleans, discovered the naphthalene component while analyzing extracts of the wood-and-soil-composite nests of Formosan subterranean termites. Concentrations of the fumigant varied from 51 to 215 Mg per kg of extract [Nature, 392, 558 (1998)]. This is the first time naphthalene has been found naturally associated with any insect species, the team notes. The researchers have shown it inhibits proliferation of fungi and para
lyzes ants at concentrations that have no visible effect on the termites. They suggest the compound plays two roles: It defends the termites from predators and acts as an attractant or guide for the "soldier" termites—those designated to guard the nests and forage for food. Team leader Henderson believes the naphthalene may be a metabolite of woody material ingested by the termites rather than a pheromone they produce. "But we don't know that yet," he says. The group is working to develop a naphthalene-based termite detector.^
Nine-atom silicon cluster joins the family "We have discovered and structurally characterized the first 'naked' silicon clusters larger than four atoms, Si/", in the [new] compound Rb12Si17," reports a team led by Slavi C. Sevov, assistant professor of chemistry at the University of Notre Dame in Indiana \J. Am. Chem. Soc, 120, 3263 (1998)]. If the clusters can be extracted
into solution, Rb12Si17 might serve as a precursor for solution-phase silicon nanoparti-cles, which are expected to
have valuable optical properties. Previous attempts to extract Si44" tetrahedra from compounds containing these species have been unsuccessful. Sevov and coworkers Virginie Queneau and Evgeny Todorov made Rb12Si17 by reacting elemental rubidium and silicon at 900 °C. X-ray data suggest that the extremely reactive product is best described as ionic, with isolated S^4" and Si44" anions and Rb+ counterions, the researchers note. At first glance, the Si/" clusters (shown) all look much the same, but they actually fall into four distinct groups with slightly different shapes, angles, and bond distances. Nine-atom clusters of germanium, tin, and lead already were known, so the Sic,4" cluster was the sole missing member in the family, excluding carbon, the chemists say.^
Thermal screening of catalyst libraries debuts A technique that potentially will make it easier to screen for promising catalysts in large combinatorial libraries of catalysts has been developed by graduate student
Steven J. Taylor and assistant professor of chemistry James P. Morken of the University of North Carolina, Chapel Hill [Science, 280, 267 (1998)]. The researchers used infrared thermography to detect the small amount of heat generated by reactions accelerated by active catalysts in encoded polymer-bound libraries. They demonstrated the technique by simultaneously screening a library of 3,150 candidate compounds for their ability to catalyze a solution-phase acylation reaction. Three of four compounds identified in the screen were found to be responsible for most of the library's catalytic power. The screen did not select another compound with appreciable (but lesser) activity. According to Taylor and Morken, methods for assessing the kinetics of reactions involving polymer-bound libraries previously were not available. They believe the infrared thermographic method could be used to evaluate organ-ometallic libraries or ligand libraries for ligand-accelerated metal catalysis.^
A way to whisk proteins through cell membranes Although scientists would like to be able to direct peptides and proteins into cells for functional studies and potential therapies, cell membranes generally are resistant to the passage of most peptides and proteins. In 1995, Yao-Zhong Iin, Jacek Hawiger, and coworkers in the department of microbiology and immunology at Vanderbilt University, Nashville, reported a way to get peptides into cells by linking them to a peptide sequence that interacts strongly with lipid bilayers. Lin and coworkers Mauricio Rojas, John P. Donahue, and Zhongjia Tan now have found that entire proteins can be similarly spirited through cell membranes by fusing their C-termini to a 12-amino-acid membrane-translocating sequence [Nat. Biotechnol, 16, 370 (1998)]. The researchers were able to get glutathione ^transferase (GST) fusion proteins as large as 45 kilodaltons into living cells this way. Furthermore, they demonstrated that a three-way fusion protein including GST, the membrane-translocating sequence, and a protein fragment that controls signal transduction not only entered cells but exhibited biological activity there. According to Iin, the protein delivery technique should be useful for intracellular functional studies and drug and vaccine development.^
40 APRIL 13, 1998 C&EN
concentrates
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