Gold Steps Up

Update, 4/5/14: On Twitter, Yunus chimes in to recommend this Hashmi paper, showing a mononuclear Au(I) catalyst - with crazy adamantyl appendages - that gets down to 0.0001% loading!

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Catalyst: A substance that increases the rate of a reaction without modifying the overall standard Gibbs energy change in the reaction (IUPAC Gold Book).

Though most chemists agree on the above definition, there have always been two camps: "Academic" catalysis (1-20 mol%, 5-100 turnovers), and "Industrial" Catalysis (<0.01 mol%, >10,000 turnovers). As more researchers seek to translate early discoveries into efficient, "green" processes, the desire for robust organometallic species has skyrocketed.

Right now, a few such homogeneous catalysts have made the jump: the Grela Ru metathesis catalysts (0.001%), copper catalysts for boron addition (0.005%), and some iridium and palladium species.

Gerald Hammond and Bo Xu (Louisville) want to add one more to the list: a highly-stable gold catalyst. Their new catalyst, dubbed "BisPhePhosXD-AuCl" (Phew!), takes development lessons from Buchwald (electron-rich, C-to-metal bond) and Widenhoefer (steric bulk to discourage off-cycle species). 

Now here's the fun part: the authors run several typical gold-catalyzed reactions side-by-side with their improved catalyst. In most cases, they're able to shave off 99.9% of the catalyst loading, with comparable yields. Granted, certain reactions take more time with this approach, but a few finish ahead of their literature counterparts. Wow.

Aldrich sells the precatalyst, if you're itching to try it yourself. I'll be very interested to see the next generation of bulked-up ligands, and whether this reactivity transfers over to other precious metals, namely platinum, iridium, or rhodium.

Precious Serendipity

Serendipity often drives scientific inquiry.

Ask a famous scientist - Feynman, Archimedes, Fleming, to name a few beneficiaries - they'd tell you it's better to be lucky than good. But Pasteur's paraphrased "Fortune favors the prepared mind" spells things out more clearly; diving into the nitty-gritty of chemical transformations often brings up a chance pearl of wisdom.

Such is the case for a recent JACS ASAP, out of the Wang group at Xiamen University in China. Let's set the stage: the scientists attempt to create a stabilized bimetallic cluster compound from gold, silver, and hemilabile P-N ligands. When the starting Ag-Au complex meets acetonitrile and methanol, something interesting occurs: a dimeric crystalline compound forms, bridged by two fully deprotonated acetonitriles!

Those golden pyramids are pretty schnazzy.
Source: JACS | Wang group

So, why am I so excited?

1. That's a CCN (3-) anion stuck in there! What if you could, say, build a tetra-substituted carbon center just by adding electrophiles in sequence?

2. C-H activation of sp3 bonds = hard. Especially at room temp.
Well, there's (technically) 6 sp3 C-H bonds missing in that complex!

3. The authors note that water forms as the reaction progresses. Most nitriles, in the presence of Au/Ag catalysts and water, will hydrate to form amides. Not so here.

4. The authors point out that a gold oxo intermediate must be present for the cluster to form. They also point out that similar gold oxo catalysts (and silver oxide bases) pop up in the literature. Perhaps crazy intermediates like this commonly arise in gold-catalyzed reactions?

The best part? Studies like this always leave you with more questions than answers.
Perfect fodder for future projects.

Cutting-Edge, Nobel-Worthy Chemistry

After all the early fuss about the merits of the 2012 Chemistry Nobel Prize, I noticed this challenge, couched in an earlier Chemjobber comment thread:

"The organic chemists seem to get their hides chapped most easily when a Nobel gets awarded to a 'biologist'. It's worth asking 'what are the fundamental unanswered questions in organic chemistry?'" (Emphasis mine)

Here are three areas, broadly defined, that I believe could win the Chemistry prize next year.

Synthetic trachea
University College London, 2011

1. Whither Polymers?  Darlings of early 20th-century industry, yet they've taken a back burner lately, winning their most recent Nobel in 2000. But, what a decade! Self-healing polymers. Fluoroelastomers you can print into any shape. Synthetic organs, even, grown from biodegradable polymer scaffolds. Trouble with this prize? Picking only three winners...

2. Biochemical Assembly Lines. Yes, cue the "it's not chemistry!" complaints, but I really like work which elucidates the cellular mechanisms plants, animals, and microbes use to assemble huge, medicinally-relevant natural products. Researchers can prompt E. coli to make an antifungal compound, for instance, or yeast to make a cancer therapy. Directed evolution of these assembly proteins, or the DNA which encodes them, can lead to products with wild substitutions and unexpected properties.  Bonus: All the 'big wheels' tend to be card-carrying chemists, and work in chemistry departments. The overarching goal tends to be chemical - utilization of Nature's machinery to produce new compounds.

Usual suspects: Christopher Walsh, Chaitan Khosla, David Liu, Ben Shen.

Walsh Group, JACS 2012

3. Fundamental Catalysis. Technically, there have been a few Nobels for this fairly recently (2001, 2005, 2011). But, what a decade! Here's some currently-exploding fields:

Organocatalysis
Chiral Anion Catalysis
Gold Catalysis
New carbene ligands
Frustrated Lewis pairs
Catalytic C-H activation

Any discipline on this short list could take home a Nobel within 10 years. Admittedly, some of these are rather young, but, as Ash has pointed out, the committee has rewarded ever-shorter publication-to-prize gaps, so it's not without precedent.

Usual Suspects: Dean Toste, Melanie Sanford, Anthony Arduengo, Graham Hutchings, Douglas Stephan, David MacMillan, Benjamin List

Readers, who would you award a Chemistry Nobel?

Chemistry Bumper Cars - Bertrand Edition

A little birdie has written to tell me of another fairly high-profile move - Prof. Guy Bertrand, formerly of UC-Riverside, seems to have moved to UC-San Diego* as early as June 2012.

Not familiar? His research covers main group complexes of phosphorus and boron, metathesis, gold catalysis, and some really neat takes on the N-heterocyclic carbene ligand framework (P.S. It certainly doesn't hurt when you're averaging a Science paper every other year!)

No word on whether the move was precipitated in order to fill a "Nicolaou-sized" hole in the UCSD faculty...

Congrats, Prof. Bertrand! We'll add you to the new map next year.

*I may be the only one entertained by this, but Prof. Bertrand is listed in the UC-San Diego "new faculty" page as "Professor, Above Scale (Distinguished)." Which begs the question, UCSD - show me that scale!

Elemental Beer

It's October, which means falling leaves, football, cider, und Oktoberfest. Cracking open my copy of the latest WIRED Magazine last night, I came face-to-face with a full-page ad for Bud Light Platinum:

Source: Anheuser-Busch

Now, I understand the idea: an expensive noble metal speaks to the supposed quality of this latest beer offering. But it got me thinking - How often do you see element-themed noms de booze?

Let’s examine the obvious first. For the last few NFL seasons, Coors Light has run a promo with a speeding train called “The Silver Bullet.” Care for something else? Maybe some Molsen Golden, or anything from the Coors brewery in Golden, CO. With the help of Google and Beer Advocate, we’ll stray a little farther afield for a few more periodic pints…

Dieu du Ciel Helium, Montreal, Canada

Lithia Beer, West Bend, WI

Mount Carbon Beer, Pottsville, PA

(I know it’s cheating a bit, but how about the nitrogen Guinness rocket / widget?)

Gordon Finest Titanium, Scotland

Barney Gumble holds a
'Hassium Hefeweizen'

Fuji No Kina Vanadium Beer, Nigata Brewery, Japan

Carling Chrome, Molson Coors UK

Iron City Beer, Pittsburgh, PA

OMB Copper, Mecklenberg, NC

Arsenic, Belgium

Tsingtao Selenium-Riched 8, China

Krypton Rye PA, Victoria, BC, Canada

Tungsten Strong Lager, England

Tin Roof Beer, New Orleans, LA

There’s a brewery in Richland, WA called Atomic Ale, located just down the street from an historical plutonium reactor*. The ambience has apparently rubbed off; their beer roster includes Plutonium Porter, Seaborgium 106 Scottish Ale, Dysprosium DunkelWeisen, and Proton Pale Ale.

Surprisingly, several apt elements seem to have no brew to call their own. Quaff a Rubidium Red? A Lanthanum lambic, or maybe a Germanium Doppelböck? Americium Amber, Indium Pale Ale, Barium Brown…these things just write themselves!

Readers, have I missed any other elemental beers? Have any suggestions for ones you’d like to see?

Update (10/6/12) - How about elemental breweries? Telluride Brewing Co., Element Brewing Co.

*Several folks have commented that I might be grossly oversimplifying the importance of the Hanford site, akin to calling dinosaurs "those prehistoric dragons," or the Super Bowl "the last football game of the season." My apologies; I'll look deeper into it, and plan a follow-up post.

Golden Bacteria?

An amazing breakthrough (!) recently made the rounds on Wired and Gizmodo: a synthetic chemistry / art-house installation in which microbes "...turn liquid gold into 24-karat gold." Two professors from Michigan State University - a microbiologist and a science artist - teamed up to produce the exhibit, entitled "The Great Work of the Metal Lover," which is currently on display at an Austrian art competition.

Credit: G.L. Kohuth | MSU

Hold your applause - the science doesn't travel well across multiple media outlets. The bacterium in question, Cupriavidus metallidurans, reduces gold(III) chloride solution (likely HAuCl4) and precipitates out pure metallic gold. C. metallidurans actually does have some 'super powers' - the last decade (PubMed) shows similar successes with copper, mercury, and lead. Heck, it's even been shot into space! 

But the MSU press release may win the hyperbole 'gold medal.' Here's a few choice lines:

"Cupriavidus metallidurans can grow on massive concentrations of gold chloride – or liquid gold, a toxic chemical compound found in nature"

Gold chloride, liquid gold? Oh, you mean the solid gold salt? With almost no tox data on the MSDS?  

"[the installation] uses a combination of biotechnology, art and alchemy to turn liquid gold into 24-karat gold"

Ye Gods. No alchemy here! I'm not a biochemist - just a #KnuckleDraggingOrganiker - but I'd guess there's a perfectly reasonable, well-studied reduction mechanism operating. Can I get a reductase over here? (P.S. the only "liquid gold" I know of is molten gold)

“This is neo-alchemy. Every part, every detail of the project is a cross between modern microbiology and alchemy"

No comment (see above). 

"...the researchers’ success in creating gold raises questions about greed, economy and environmental impact, focusing on the ethics related to science and the engineering of nature"

Unless we're talking phlogiston and aether here, there's no "creation" of gold: it's a reduction. And utilizing a bacterium to do what it likes to do anyway hardly sets up an ethical or social inquiry.

"[this work]...speaks directly to the scientific preoccupation while trying to shape and bend biology to our will within the postbiological age"  

I really don't understand what they're trying to say here. (Perhaps I need to read Art for Dummies...)

OK, scientific criticism aside, the work looks pretty neat. How often do you get to see electrochemistry in an art exhibit? In the end, I guess the ends justify the means - if just a few people look at it, and think "I wonder how that works?" it will have served its purpose.