SCIENCE & TECHNOLOGY

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Chemical ligation reaction creates permanent thiol links A chemical ligation process has been devised for permanently adding organic functional groups and compounds to cysteine and other thiols (J. Am. Chem. Soc. 2006,128, 2544). The selenosul-fide-based ligation and subsequent rearrangement with loss of the selenium (shown) was developed R \^v/ ^ e ""̂ S 0 ~ by David Crich and coworkers at the Univer- ', sity of Illinois, Chicago. Benjamin G.Davis of the . rat University of Oxford, who helped develop a similar but I impermanent disulfîde-based chemical ligation method, comments that separate selenosulfide-based ligations ^ and rearrangements were known before but that Crich's <^η^ technique "nicely combines them. As it stands, it will 5 be a useful conjugation method for free thiols." If the reac- ^ R" tion can be demonstrated to extend to protein-based thiols, as the paper suggests should be possible, it could be broadly useful for chemical protein ligation, Davis says. Crich and coworkers note that "applications in combinatorial chemistry and for the attachment of a wide variety of groups, including polyethylene glycol) and fluorous chains and oligosaccharide units to thiols of biological interest, are currently under development."

Nanocrystal-silica composite lasers are stable in solvents

Tiny lasers made of s emi ­conductor nanocrystals incor­porated in a film would be ideal for use in microfluidic chemo-sensors. Such films made with titania matrices have already been shown to lase. Unfortu­nately, these nanocrystal-titania composites degrade in water and alcohols, so they are un­suitable for microfluidics. M I T chemistry professors Moungi G. Bawendi and Daniel G. Nocera and their coworkers have now made a solvent-stable laser with CdSe nanocrystals embedded in a silica matrix (J. Am. Chem. Soc, published online Feb. 15, dx.doi.org/10.1021/ja057980d). Earlier attempts to use silica matrices resulted in compos­ites lacking enough nanocrys­tals. The researchers overcame this problem by modifying the nanocrystal surfaces with 5-

amino-1-pentanol and using 3-aminopropyltrimethoxysilane as the silica precursor. Compos­ites made with the silane had a rough surface, but replacing a small amount of the silane with (triethoxysilyOpropyl isocyanate provided smooth films. The nanocrystal-silica composites lase at room temperature even while submerged in water or alcohol solutions.

Male gene may be linked to Parkinson's The S/y gene responsible for causing embryos to develop as male may also have a role in Par­kinson's disease, a finding that could explain why the disease strikes more men than women (Curr. Biol. 2006,16, 415). In Parkinson's, dopamine-produc-ing cells in the brain's substantia nigra are killed. University of California, Los Angeles, geneti­cist Eric Vilain and colleagues found that Sry is expressed in this same region of the brain

in male rodents. In fact, Sry is expressed in the same neurons that release tyrosine hydroxy­lase, a protein that is necessary for the production of dopamine. When the researchers used an-tisense technology to reduce Sry expression in rats, tyrosine hy-

S Q - droxylase output dropped, but only in males. The male

rats then developed Parkinson's symptoms. The researchers think that Sry serves as a pro­tective agent against the dis­ease: Men who get Parkinson's disease may have lower levels of the gene in their brains. Vilain's team is now testing whether es­trogen offers similar protection to women.

Detecting DNA-binding agents visually

A convenient colorimetric assay that could be used to screen drug candidates on the basis of how strongly they bind DNA has been developed by Chad A. Mirkin's group at Northwestern University (Angew. Chem. Int. Ed., pub­lished online Feb. 15, dx.doi. org/10.1002/anie.200504277). "This could dra- „ , matically speed f ij up the identifica- \ f 7 ^ ' / * tion of new an­ticancer agents," Mirkin says. The assay uses gold n a n o p a r t i c l e s that have been functionalized with one of two complementary oligonucleotides. When the parti­cles are mixed, the complemen­tary strands hybridize, thereby forming particle aggregates that appear blue. Heating the mix­ture above a critical tempera­ture reverses the process, and the particles dissociate with a concomitant blue-to-red color

change (shown). If the two vari­eties of nanoparticles are mixed in the presence of a drug candi­date that binds to duplex DNA, the duplexes formed between the particles will be more stable than ordinary duplexes, and it will require a higher temperature to dehybridize them and disso­ciate the aggregates. By visually monitoring the blue-to-red tran­sition temperature, the research­ers can determine how strongly or weakly a drug candidate binds to DNA to get an indication of its biological activity.

Functionalized 'nanocages' Adding an entry to the grow­ing collection of custom-made nanoparticles, Northwestern University chemical engineers report a procedure for prepar­ing "nanocages," a material characterized by 2-nm cages that have a porous cross-linked siloxane shell with amine groups anchored to the inside (J. Am. Chem. Soc. 2006,128, 2776). The material may be useful in drug delivery applications or for selective catalytic reactions in which the shell windows re­strict access to the nanocage

interior on the basis of | 1 a reactant molecule's ' # 5 size. The synthesis

| strategy, developed by o Young-Woong Suh, £ Yingmin Wang, May-

fair C. Kung, and Har­old H. Kung, is based on forming nanosized micelles that contain head groups that can be polymerized into the cross-linked shell and hydrophobic tails

containing carbamate units that can be converted to the amine groups. According to the team, the method provides flexibility in selecting the nature of the tethered functional group and the size of the cavity and shell opening.

4 0 C & E N / F E B R U A R Y 2 7 , 2 0 0 6 W W W . C E N - 0 N L I N E . O R G