Environmental Chemistry

Capturing Chromium(VI): Abby Knight is using a new class of molecules to remove metals from groundwater and blood

“Selective Chromium(VI) Ligands Identified Using Combinatorial Peptoid Libraries.” Knight, A. S., Zhou, E. Y., Pelton, J. G., Francis, M.B. J. Am. Chem. Soc. 2013. 135, 17488–93.

Abby Knight, fifth year chemistry PhD student in the Francis group at UC Berkeley
Abby Knight, a graduate student in the Francis group at UC Berkeley

Abby Knight is a fifth-year PhD student in the Francis Group at UC Berkeley, and she and Julia Roberts share a mutual acquaintance: hexavalent chromium.

Roberts may or may not remember the chemical’s name, but it was her nemesis in the 2000 film Erin Brokovich, when she played a single mother agitating for PG&E to pay for contaminating her town’s water. Brokovich successfully forced the industry giant to stop polluting, and that was the end of the movie. But that wasn’t the end of the story, because although the chromium was stopped at the source, no method exists to remove what was already in the water. That’s where Knight comes in.

“There’s no good way to clean up chromium contamination in groundwater,” Knight says. “Right now, the EPA strategy is to just say ‘don’t drink this water’ and wait for it to diffuse. “

That’s not an ideal solution, especially when drinking water is in short supply. But it’s very hard to remove a problematic metal, like chromium, from natural waters because they have lots of other ions that get in the way. But Knight was up for the challenge: She set out to come up with a method to selectively remove chromium and other heavy metals from complex solutions—like groundwater, or human blood—while leaving the natural and necessary elements.

Drawing inspiration from within

Knight and her adviser, Matthew Francis, looked to nature for a chemical solution to this problem. They knew humans and animals have naturally occurring proteins that are able to remove small doses of heavy metals from the blood.

“Proteins are kind of your body’s natural therapeutic response to low doses of heavy metal poisoning,” Knight says. Proteins grab on to (chelate), the metal ions and get them out of your bloodstream, but they’re easily degraded by enzymes and so don’t work well for environmental applications. But Knight thought maybe she could use a compound with a similar structure to perform the same function.

She narrowed in on a specific class of molecules called peptoids, a recently invented class of synthetic peptidomimetic (peptide-like) molecules. They are similar to naturally occurring peptides—a backbone of carbon, nitrogen and oxygen with side branches of varying structure attached along the spine—but in peptoids the side branches are attached to nitrogen atoms in the backbone, while in peptide they attach to the carbon.

Peptoids

Knight chose peptoids as her binders of choice for their stability and customizability.

“The scientist who invented peptoids is right here at Lawrence Berkeley National Lab,” Knight says, “So I was able to get a lot of help.” This was important because peptoids are so new that no one else in her lab had ever worked with them before.

Dyeing beads and building a library

Thousands of different peptoids have been synthesized, and there are infinite ways in which they could be modified. To find the best chromium binder, Knight created a library of peptoids with varying side chains. After she built her library, the only way to find out which molecules best grabbed on to chromium was through trial and error.

Knight with a vial of her peptide-coated polyresin beads.
Knight with a vial of her peptoid-coated polyresin beads.

Knight coated small polystyrene resin beads with each peptoid she synthesized. She then added the coated beads to a chromium solution, and painted them with a dye that turns pink when it reacts with chromium. Then Knight and her undergrad research assistant, Effie Zhou, painstakingly removed the pinkest beads—those that had most successfully chelated chromium—and made more of the peptoid on that bead. Then they would test that peptoid again.

Through this iterative process Knight identified a few winners. Then it was time for a real world test. Knight and Zhou collected natural water from Ocean Beach in San Francisco and Strawberry Canyon on the UC Berkeley campus.

Moment of truth

Water collected at Strawberry Creek on the UC Berkeley campus was used to test the efficacy of the peptoids
Water collected at Strawberry Creek on the UC Berkeley campus was used to test the efficacy of the peptoids

Fortunately, the ocean and creek water in the Bay Area don’t have high levels of chromium contamination, so Knight and Zhou had to pollute the samples of the? water before trying to clean it. They added chromium, in amounts 10 and 100 times higher than the EPA safety limit. After the water was sufficiently contaminated, the beads, armed with carefully selected peptoids, were sent in to do their job. They let the solutions incubate, and then measured the chromium concentrations to see if the peptoids had successfully removed the metal.

The results: 80-90% reduction in chromium concentrations. “We drastically out-performed the commercially available [non-selective] resin,” Knight says proudly.

There is still room for improvement—they started to lose efficiency and selectivity at lower chromium levels. But overall, she says this looks like a very promising method to clean up contaminated water.

A new toolbox

The peptoids were so good at removing chromium from groundwater, Knight decided to apply the same technique to new applications, and new metals. Her next project was getting cadmium out of human blood, and based on her preliminary results with human serum, this application seems succesful as well.

But Knight and peptoids are parting ways. She is graduating in May, and starts a post-doc at UC Santa Barbara in the fall. She’ll be working in the Hawker lab to create new, self-assembling materials. It’s a new problem, with new chemistries to explore, but Knight looks forward to the challenge.

“What I love about the day to day activities of ‘being a scientist’ is the opportunity to find new and creative solutions to problems,” Knight says.

Catalysis, Synthesis

Iron-catalyzed C-H Borylation

“Iron-Catalyzed C-H Borylation of Arenes” Dombray, T.; Werncke, C. G.; Jiang, S.; Grellier, M.; Vendier, L.; Bontemps, S.; Sortais, J-B.; Sabo-Etienne, S.; Darcel, C. J. Am. Chem. Soc. 2015, ASAP. DOI: 10.1021/jacs.5b00895

C-H borylation, itself a green reaction for generating useful borylated compounds, is traditionally catalyzed by Ir and Rh. Much of the work has been conducted by John Hartwig’s group at Berkeley and Mitch Smith’s group at Michigan St. French scientists have now reported an iron-catalyzed version, which complements recent reports with Co complexes and dinuclear transition metal complexes. I especially like that the reported reaction is free of H2 acceptors and utilizes light to activate the catalyst.

The authors first tested the borylation of ethylbenzene with pinacolborane. The substrate is in excess and serves as the solvent. The optimized catalyst was Fe(Me)2(dmpe)2, where dmpe is bis(dimethylphosphino)ethane, providing the borylated product in 73 % yield after 72 hours at room temperature under 350 nm light as a 68:32 mixture of the meta and para isomers. Interestingly, the dimethyl iron complex provided higher yields of the C-H borylated product than the dihydride (73 % vs 52 %, respectively).

scheme 1

Continue reading

Environmental Chemistry, Policy

Endocrine disruptors cost at least $175 billion annually in the E.U.

a children's room
Hormone-disrupting flame retardants often found in children’s toys and furniture were some of the chemicals investigated (jingdianjiaju/Flickr)

An international panel of scientists has found that endocrine disrupting chemicals likely cost the European Union over 100 billion dollars annually — and American officials say this expense could be even higher in the U.S.

The scientific panel, convened by the Endocrine Society, adopted strategies created by the Intergovernmental Panel on Climate Change  to evaluate how much causation of a particular disorder could be attributed to a particular chemical. For example, they found 70-100% probability that polybrominated diphenyl ether (PBDE) and organophosphates contribute to IQ loss, based on previously published epidemiological studies. They then estimated the costs incurred to the European Union from health issues caused by exposure to endocrine disrupting chemicals. The health effects investigated included neurobehavioral disorders, male reproductive health issues, and diabetes, and the total cost was found to be at least 100 billion dollars.

Linda Birnbaum, the top U.S. environmental health official, told National Geographic news that the panel’s findings on endocrine disruptors are a “wake-up call,” and added that, “If you applied these [health care] numbers to the U.S., they would be applicable, and in some cases higher.” Levels of exposure to endocrine disruptors are generally much higher among Americans than they are for citizens of the European Union.

The biggest contributors to cost were the effects of the chemicals on children’s brain development, potentially resulting in attention-deficit disorders and lost I.Q. points.

The scientists released their work in a series of studies  published in the Journal of Clinical Endocrinology and Metabolism (and summarized in this National Geographic news article). The studies were conducted at the behest of the European Commission for an impact assessment on the social cost of endocrine disrupting chemicals. The results will be used to inform future E.U. regulations as part of the REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) program and other legislation.

Mallory Pickett is a former chemist and a science journalism student at the UC Berkeley Graduate School of Journalism

Synthesis

Update: Improving atom economy of dehydrogenative decarbonylation

“Selective Metal-Catalyzed Transfer of H2 and CO from Polyols to Alkenes” Verendel, J. J.; Nordlund, M.; Andersson, P. G. ChemSusChem, 2013, 6, 426-429. DOI: 10.1002/cssc.201200843

In a recent post I commented on the byproducts of dehydrogenative decarbonylation, namely H2 and CO.

1st reaction scheme

I wondered whether this gas mixture, syngas, could be used in a subsequent reaction. This would improve the atom efficiency of the reaction and potentially also improve the safety (of both the syngas-producing and syngas-using reactions). Both are goals of green chemistry and I especially appreciate avoiding rolling cylinders of toxic and/or flammable gases around the lab.

After some digging I found some cool stuff, the most recent being the work from the Andersson group at Upsalla wherein the syngas produced from polyol deoxygenation is used in a subsequent hydroformylation of styrene. In addition, I found Madsen’s excellent paper, which includes lots of interesting references (such as this, where the CO liberated from decarbonylation of cinnamyl alcohol is used in the Pauson-Khand reaction. Note that cinnamyl alcohol can trap the evolved H2! Neat!).

In Andersson’s work the syngas-producing step is catalyzed by [Ir(cod)Cl]2 with (S)-BINAP in Reactor A (similar to Madsen’s work). The hydroformylation is simultaneously catalyzed by a different molecule, Rh(H)(CO)(PPh3)3, in Reactor B.

2nd reaction scheme

Continue reading

Uncategorized

Green Chemistry on your Smart Phone!

“Incorporating Green Chemistry Concepts into Mobile Chemistry Applications and Their Potential Uses.” Ekins, S.; Clark, A. M.; Williams, A. J. ACS Sustainable Chem. Eng. 2013, 1, 8-13. DOI: 10.1021/sc3000509

We here at GreenChemBlog have not posted in a while, but still hope to post and are still looking for contributors to the blog. Posts might be a bit shorter going forward, though, in order for us to post more frequently.

I’ve expanded my reading recently to include a new ACS journal, ACS Sustainable Chemistry & Engineering. In the first issue is the above article, which highlights a few recent additions to the smart phone/tablet world that utilize green chemistry!

The focus of the above paper is mostly on “Green Solvents”, which the authors developed based on the ACS GCI Pharmaceutical Roundtable Solvent Selection Guide. It is freely available for iPhone, iPod touch and iPad. (I personally use the Android platform for which the very similar app “Lab Solvents” is available) The authors also cover a few other green chemistry apps, so read the paper for more info! I especially like the Process Mass Intensity feature of the Yield101 app, though this app is $5.

For Green Solvents, the app entry page features a list of common solvents displayed as their chemical structures. More desirable solvents are color coded with a green background; less desirable solvents are color coded with a brown background. Selecting a solvent molecule brings up a box that lists the chemical’s name, CAS number, as well as scores on a scale of 1 – 10 for each of the five following categories: safety, health, environment (air), environment (water), and environment (waste). The lower the number, the greener the solvent. In addition, the numbers are color coded with 1-3 displayed as green, 4-7 displayed as yellow and 8-10 displayed as red. Furthermore, the selection box includes easily chosen links to the ChemSpider Web site, the Mobile Reagents app, and the Mobile Molecular DataSheet for more information on the selected solvent.

figure1

The power of the app is how quickly one can obtain info that should impact solvent choices in lab or in the field (without having to retreat to your desk or a nearby computer). And it’s free!

In the future I hope to see these apps provide suggestions for alternative solvent choices (for example, this editorial provides an example of a table Pfizer uses for solvent selection). For instance, I already know dichloromethane is a poor choice of solvent from a green chemistry perspective. How about an alternative choice, Green Solvents app? Trifluorotoluene?

Synthesis

Rh-catalyzed Alcohol Deoxygenation

“Acceptorless Photocatalytic Dehydrogenation for Alcohol Decarbonylation and Imine Synthesis.” Ho, H-A.; Manna, K.; Sadow, A. D. Angew. Chem. Int. Ed. 2012, 51, 8607-8610. DOI: 10.1002/anie.201203556

The use of biorenewables as feedstock chemicals for commodity chemicals as well as fuels requires mild, selective removal of oxygen-containing functional groups. This is in direct contrast to the production of these chemicals from petroleum products, which, at least for highly functionalized target molecules, necessarily involves oxygenation of hydrocarbons.

There are a large amount of methods development currently underway and I highlight the recent report from the Sadow group on the decarbonylation of alcohols under Rh catalysis. I think the described reaction is a good example of green chemistry, as the reaction is high-yielding, selective, and performed at room temperature under photocatalytic conditions. One serious drawback is the use of benzene as the solvent, although toluene works as a solvent in at least some cases.

Reasoning that photolysis would prevent catalyst inhibition by CO binding, the researchers first screened Rh(I) catalysts under photocatalytic conditions with the test substrate cyclohexanemethanol. Unfortunately, no cyclohexane was observed under these reaction conditions. The group then tested Rh and Ir compounds known for C-H activation, such as Cp*Ir(CO)2 and Tp*Rh(CO)2, and did observe cyclohexane for one of the tested catalysts, albeit in low yield (36 % NMR yield with Tp*Rh(CO)2). CO and H2 were also observed, consistent with the targeted alcohol decarbonylation reaction. Interestingly, using their previously reported rhodium tris(oxazolinyl)borate complex ToMRh(CO)2 (1) improved the yield to > 95%. Furthermore, the related dihydride, ToMRh(H)2CO (2) was roughly three times slower and the Ir complex ToMIr(CO)2 was inactive for this reaction.

Continue reading

Uncategorized

Want to Contribute to GreenChemBlog?

Hey chemistry fan!

Do you want to share any recent papers you think are cool examples of green chemistry, whether they are “marketed” as such or not?

Do you want to help promote and shape the national discourse around green chemistry?

Do you want to help make sure the awesome science behind green chemistry doesn’t get lost in all the hype?

If you said “Yes” “Yes” or “Yes,” you have come to the right place! GreenChemBlog is opening its doors to new contributors!

If you are interested, shoot us an e-mail at greenchemblog@gmail.com and we’ll help get you started.