SUSTAINABILITY
▸ Nanocomposites cut leather tanning waste The cost of soft, supple leather shoes and handbags goes beyond the price tag. Chromium tanning agents transform roughly 90% of the world’s animal hides into leather, and a good deal of the chromium ends up in wastewater, where it becomes a hazard. To cut pollution levels, several groups have turned to nanocomposites, which improve chromium uptake into the network of polymerized collagen fibrils that makes up leather. Along those lines, Bin Lyu and Jianzhong Ma of China’s Key Laboratory of Leather Cleaner Production and colleagues now
This micrograph shows that leather fibers pretreated with nanocomposites (top) are more separated compared with controls (bottom), suggesting that the nanocomposites are adequately penetrating the fibers.
BIOCHEMISTRY
Improving an enzyme for better plastic recycling Stabilizing a bacterial enzyme by strategically decorating it with sugars could help it recycle polyethylene terephthalate (PET), the polymer widely used to make plastic water and shampoo bottles (Biochemistry 2018, DOI: 10.1021/ acs.biochem.7b01189). The enzyme, called cutinase, breaks down PET into ethylene glycol and terephthalic acid, which can be recovered to make new bottles. But at the optimal PET processing temperaGlycosylating three asparagine residues ture of 75 °C, cutinase begins to (purple) in a bacterial cutinase enzyme unfold and form clumps. To premakes it more difficult for the enzyme vent formation of these inactive to form inactive clumps. clumps, Richard A. Gross of Rensselaer Polytechnic Institute and colleagues genetically engineered yeast to produce a cutinase originally isolated from microbes found in leaf and branch compost. The yeast cells naturally glycosylated the enzyme at three sites, adding short strings of sugars. The glycosylated cutinase formed fewer clumps and degraded more PET than the nonglycosylated protein. The improved stability and activity marks a big step toward optimizing the enzyme for commercial recycling of PET, Gross says.—MELISSAE FELLET,
C R E D I T: B I OC H EM IST RY ( 3- D MO D E L) ; ACS S USTA IN A B L E C H EM . EN G. (MI CRO G RA P H )
special to C&EN report that pretreating cowhide with vinyl polymer-zinc oxide nanocomposites before tanning improves chromium uptake in the resulting leather. The process also reduces chromium content in wastewater by 50 to 80% (ACS Sustainable Chem. Eng. 2018, DOI:10.1021/ acssuschemeng.8b00233). Compared to conventionally tanned samples, the resulting shoe leather has similar durability and softness. Sujay Prabakar of New Zealand’s Leather and Shoe Research Association praised the work but would like to see techniques such as small-angle X-ray scattering employed in the future to learn more about the tanning mechanism and chromium uptake.—CARMEN DRAHL
SYNTHESIS
▸ Flipping from E- to Z-alkenes In their search for new medicines, chemists often choose the trusty
Suzuki-Miyaura reaction to construct essential carbon-carbon bonds. This reliable reaction connects alkyl halides with various classes of organoborane compounds, including alkenyl organoboranes, which can be further classified by alkene configuration, either cis (Z) or trans (E). E-alkenylboron compounds are faster and simpler to make than their thermodynamically unfavored twin, the Z-configured compounds, and thus have received more attention as precursors for the Suzuki-Miyaura reaction. Now, using
O B
Iridium photocatalyst, light
O
New method flips the compound’s trans configuration to the harder-to-access cis shape and lets scientists expand the exploration of C–C coupling reactions.
photoredox catalysis, researchers led by University of Münster’s Ryan Gilmour and University of St. Andrews’ Allan Watson are offering Z-alkenes a turn in the spotlight (Angew. Chem. Int. Ed. 2018, DOI: 10.1002/anie.201800286). Starting with the more accessible E-styrenyl organoboranes, the team employs an iridium catalyst and visible light to generate an excited state intermediate that may be swayed to collapse into either alkene conformation. An intentionally situated methyl substituent in the compound exerts the strain necessary to convince the molecule’s boron pinacol group to flip to the Z configuration. Though the reaction is currently B O O limited to styrenyl boranes, Gilmour says it’s a good first step to providing access to Z-alkenyl organoboranes, which represent an underexplored area of chemical space for Suzuki-Miyaura crosscouplings.—TIEN NGUYEN MARCH 5, 2018 | CEN.ACS.ORG | C&EN
7
