Tag Archives: Youssry Y. Botros

When mining for gold nanoparticles use substitute cornstarch for cyanide

A May 14, 2013 news release from Northwestern University (US) on EurekAlert notes that researchers have found cornstarch can be used in the place of cyanide to extract gold,

Northwestern University scientists have struck gold in the laboratory. They have discovered an inexpensive and environmentally benign method that uses simple cornstarch — instead of cyanide — to isolate gold from raw materials in a selective manner.

This green method extracts gold from crude sources and leaves behind other metals that are often found mixed together with the crude gold. The new process also can be used to extract gold from consumer electronic waste.

Commonly used techniques, according to the news release, are problematic,

Current methods for gold recovery involve the use of highly poisonous cyanides, often leading to contamination of the environment. Nearly all gold-mining companies use this toxic gold leaching process to sequester the precious metal.

“The elimination of cyanide from the gold industry is of the utmost importance environmentally,” said Sir Fraser Stoddart, the Board of Trustees Professor of Chemistry in the Weinberg College of Arts and Sciences. “We have replaced nasty reagents with a cheap, biologically friendly material derived from starch.”

Here’s how the researchers made their accidental discovery (from the news release),

Zhichang Liu, a postdoctoral fellow in Stoddart’s lab and first author of the paper, took two test tubes containing aqueous solutions — one of the starch-derived alpha-cyclodextrin, the other of a dissolved gold (Au) salt (called aurate) — and mixed them together in a beaker at room temperature.

Liu was trying to make an extended, three-dimensional cubic structure, which could be used to store gases and small molecules. Unexpectedly, he obtained needles, which formed rapidly upon mixing the two solutions.

“Initially, I was disappointed when my experiment didn’t produce cubes, but when I saw the needles, I got excited,” Liu said. “I wanted to learn more about the composition of these needles.”

…  said Stoddart, a senior author of the paper[,] “The needles, composed of straw-like bundles of supramolecular wires, emerged from the mixed solutions in less than a minute.”

After discovering the needles, Liu screened six different complexes — cyclodextrins composed of rings of six (alpha), seven (beta) and eight (gamma) glucose units, each combined with aqueous solutions of potassium tetrabromoaurate (KAuBr4) or potassium tetrachloroaurate (KAuCl4).

He found that it was alpha-cyclodextrin, a cyclic starch fragment composed of six glucose units, that isolates gold best of all.

“Alpha-cyclodextrin is the gold medal winner,” Stoddart said. “Zhichang stumbled on a piece of magic for isolating gold from anything in a green way.”

Alkali metal salt waste from this new method is relatively environmentally benign, Stoddart said, while waste from conventional methods includes toxic cyanide salts and gases. The Northwestern procedure is also more efficient than current commercial processes.

The supramolecular nanowires, each 1.3 nanometers in diameter, assemble spontaneously in a straw-like manner. In each wire, the gold ion is held together in the middle of four bromine atoms, while the potassium ion is surrounded by six water molecules; these ions are sandwiched in an alternating fashion by alpha-cyclodextrin rings. Around 4,000 wires are bundled parallel to each other and form individual needles that are visible under an electron microscope.

“There is a lot of chemistry packed into these nanowires,” Stoddart said. “The elegance of the composition of single nanowires was revealed by atomic force microscopy, which throws light on the stacking of the individual donut-shaped alpha-cyclodextrin rings.”

The atomic detail of the single supramolecular wires and their relative disposition within the needles was uncovered by single crystal X-ray crystallography.

As I’ve noted before, the perennial science story is a ‘mistake’ leading to an exciting discovery and this is one more example. I think it’s one of the things that scientists don’t get enough credit for, their ability to reshape a disappointing result into a new discovery or, in the vernacular, ‘make lemonade out of lemons’.

Here’s a link to and a citation for the research paper,

Selective isolation of gold facilitated by second-sphere coordination with α-cyclodextrin by Zhichang Liu, Marco Frasconi, Juying Lei, Zachary J. Brown, Zhixue Zhu, Dennis Cao, Julien Iehl, Guoliang Liu, Albert C. Fahrenbach, Youssry Y. Botros, Omar K. Farha, Joseph T. Hupp,  Chad A. Mirkin & J. Fraser Stoddart. Nature Communications 4, Article number: 1855  doi:10.1038/ncomms2891 Published 14 May 2013

This article is open access.

Love, hate, and the whole damn thing affect batteries, semiconductors, and electronic memory

A Jan. 24, 2013 news item on ScienceDaily features love triumphing over hate where tetracationic rings are concerned,

Northwestern University graduate student Jonathan Barnes had a hunch for creating an exotic new chemical compound, and his idea that the force of love is stronger than hate proved correct. He and his colleagues are the first to permanently interlock two identical tetracationic rings that normally are repelled by each other. Many experts had said it couldn’t be done.

On the surface, the rings hate each other because each carries four positive charges (making them tetracationic). But Barnes discovered by introducing radicals (unpaired electrons) onto the scene, the researchers could create a love-hate relationship in which love triumphs.

The Jan. 24, 2013 Northwestern University news release by Megan Fellman, which originated the news item, probes into the nature of the problem and its solution (Note: A link has been removed),

Unpaired electrons want to pair up and be stable, and it turns out the attraction of one ring’s single electrons to the other ring’s single electrons is stronger than the repelling forces.

The process links the rings not by a chemical bond but by a mechanical bond, which, once in place, cannot easily be torn asunder.

The study detailing this new class of stable organic radicals will be published Jan. 25 [2013] by the journal Science.

“It’s not that people have tried and failed to put these two rings together — they just didn’t think it was possible,” said Sir Fraser Stoddart, a senior author of the paper. “Now this molecule has been made. I cannot overemphasize Jonathan’s achievement — it is really outside the box. Now we are excited to see where this new chemistry leads us.”

The rings repel each other like the positive poles of two magnets. Barnes saw an opportunity where he thought he could tweak the chemistry by using radicals to overcome the hate between the two rings.

“We made these rings communicate and love each other under certain conditions, and once they were mechanically interlocked, the bond could not be broken,” Barnes said.

Barnes’ first strategy — adding electrons to temporarily reduce the charge and bring the two rings together — worked the first time he tried it. He, Stoddart and their colleagues started with a full ring and a half ring that they then closed up around the first ring (using some simple chemistry), creating the mechanical bond.

When the compound is oxidized and electrons lost, the strong positive forces come roaring back — “It’s hate on all the time,” Barnes said — but then it is too late for the rings to be parted. “That’s the beauty of this system,” he added.

Most organic radicals possess short lifetimes, but this unusual radical compound is stable in air and water. The compound tucks the electrons away inside the structure so they can’t react with anything in the environment. The tight mechanical bond endures despite the unfavorable electrostatic interactions.

The two interlocked rings house an immense amount of charge in a mere cubic nanometer of space. The compound, a homo[2]catenane, can adopt one of six oxidation states and can accept up to eight electrons in total.

“Anything that accepts this many electrons has possibilities for batteries,” Barnes said.

“Applications beckon,” Stoddart agreed. “Now we need to spend more time with materials scientists and people who make devices to see how this amazing compound can be used.”

For anyone interested in the details of the work, here’s a citation and link to the paper published in Science,

A Radically Configurable Six-State Compound by Jonathan C. Barnes, Albert C. Fahrenbach, Dennis Cao, Scott M. Dyar, Marco Frasconi, Marc A. Giesener, Diego Benítez, Ekaterina Tkatchouk, Oleksandr Chernyashevskyy, Weon Ho Shin, Hao Li, Srinivasan Sampath, Charlotte L. Stern, Amy A. Sarjeant, Karel J. Hartlieb, Zhichang Liu, Raanan Carmieli, Youssry Y. Botros, Jang Wook Choi, Alexandra M. Z. Slawin, John B. Ketterson, Michael R. Wasielewski, William A. Goddard III, J. Fraser Stoddart. Science 25 January 2013: Vol. 339 no. 6118 pp. 429-433 DOI: 10.1126/science.1228429

This is paper is behind a paywall.