Arsenic (Again) and Drugs

Following up on last week's post concerning the relationship between elevated levels of arsenic in drinking water and a diminished immune response to certain types of influenza (swine flu?), I ran across the following article describing the use of nanorust (actually tiny particles of iron oxide coated on sand) to provide a possible low cost means of removing arsenic from water. You can’t get much more inorganic than this.


In a previous post, I discussed my general reluctance for taking drugs, somewhat skeptical that it might be possible to develop a drug which didn’t cause some problem somewhere else in the body. Now, Derek Lowe has written a column describing how much we don’t know about drugs and their mechanisms inside the body. He even says:” I try not to take any medication unless I feel it's absolutely needed, and I'm often not very happy about taking it even then.” A man after my own heart! I just might finally consider throwing out all that aspirin I’ve been suspicious of for a while now.

Donut Powered Solar Cells

I came across the following video this weekend. Apparently powdered donuts are an important constituent in the drive to harness the power of the sun. Yes, nano-chemists will do anything for attention. And yes, magnetic stirrers DO rule!



So the powdered sugar in donuts can contain up to 1% TiO₂? I guess organic chemistry always benefits from the addition of some inorganic chemicals.

This video is one of the entries in the ACS Nanotation Video contest. If you want to see more, click here.


EDIT: I now see that this video was already posted over at the Chemistry Blog earlier last week. Not sure how I missed it, but this demonstrates the importance of keeping up with the literature when writing about current events.

Chemical Symbolism

So, they are now making nano particles from volcanic lava.

Yes.

From lava.

Really.

When is this nano madness going to end?

Okay, so perhaps I'm exaggerating here a little bit. It would be more correct to say that Dang Sheng Su and his team are making nano particles using volcanic lava. Lava obtained from Mt. Etna in Sicily contains nanosized Fe2O3 particles, which can be reduced to iron nanoparticles at 700C in the presence of hydrogen. These iron particles are apparently good templates for the production of carbon nanotubes and nanofibers when exposed to ethylene and hydrogen at high temperatures.

I know I tend to rag on nano-technology a bit too much on this blog. My first post on nanoparticles wasn't too complimentary. But I've been coming around lately as I read more and more articles on the subject. Much of the research may eventually just turn out to be hype (which can probably be said about any emerging field), but it certainly seems as if there is a lot of potential in this area. Who knows? Maybe I'll be offered a job in nanotechnology sometime in the future. I wouldn't want my views on this blog to limit my opportunities. :)
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Back in 1803, John Dalton developed a series of atomic symbols for some of the known elements at that time. Here is his representation of the table of elements. It cannot be called a periodic table yet since it doesn't demonstrate the periodicity of the elements.

Picture obtained from Wired

Now it's not like there wasn't already a series of symbols for most of these elements already. Alchemists had been using a set of elemental symbols for centuries before Dalton came along, but a lack of standardization was a significant problem, especially since alchemists often used many different symbols for the same element. Certainly, part of the problem was due to the lack of a central authority (IUPAC hadn’t been invented yet). There are at least 20 different versions of the symbol for gold that I know of, and probably a lot more. But the biggest roadblock to standardization among the alchemists was their need for secrecy. Treatises by alchemists were often ambiguous and confusing, apparently to confuse the competition. For example, alchemists often used the term "mercury" for the element mercury, the element gold, the liquid fraction of certain reactions, and various metaphysical concepts such as spiritual goodness. You really need a course to understand what these alchemists were trying to say.

I'm guessing that Dalton was doing his part to disassociate chemistry from the art of alchemy by refusing to use any of the common alchemical symbols of the time. Ironically, his symbol for hydrogen is the same as (one of) the alchemical symbols for gold. Remove the circle from the symbol for phosphorus and you have the alchemical symbol for phosphorus. His symbol for sulfur is the same as the alchemical planetary symbol of earth. Nevertheless, it was a start. It wasn't until Berzelius started using letters based on the Latin version of the element names that everything became manageable. Can you imagine writing out chemical formulas for large organic molecules using Dalton's symbols? If that wouldn't drive you toward Inorganic chemistry, then nothing would. ;P

Nano-gold Catalysts

Reports of nano-gold and its use as a catalytic material are beginning to pile up. Last week I mentioned nanogold particles in stained glass windows and their ability to oxidize organic pollutants. This week, two more articles showed up, here and here. Hmmm…. seems like we’re beginning to reach a critical mass here. Pretty good for a metal that hasn’t been considered a particularly good catalyst over the years. Perhaps I'll start paying more attention to this area. I’ve read articles about nano-particle based catalysts in the past and have generally been underwhelmed, but nano-gold catalysts may be about to change that view. And that’s because of two words that are often found in these reports.

Room temperature.

Or at least, low temperature.

The obvious reason for using nano-particles is their much larger surface area to mass ratio. Higher surface areas generally mean better catalysts, so the drive to make smaller and smaller catalyst particles has been going on for decades. Back before “nano” became a marketing term, I recall at least one set of researchers making platinum nano-particle catalysts to improve the efficiencies of automotive exhaust catalysts. They succeeded, but unfortunately, at the high operating temperatures (generally above 400^oC) to which these catalysts were subjected, the platinum nano-particles tended to move around and coalesce into much larger particles, losing much of their surface area and eventually not looking all that different from more crudely prepared catalysts. In fact, with these types of catalysts, research is focused less on the catalyst itself and more on the substrate which supports the catalyst -- changing its properties so as to limit the movement of the catalyst particles. This is always a bit of a balancing act since too much interaction between the catalyst and substrate can change the properties of the catalyst in undesirable ways. But if the reactions to be catalyzed take place near room temperature, or at least at lower temperatures, you stand a much better chance of maintaining the catalyst nanoparticles and hence their benefits.

Gold has traditionally been the forgotten metal, with all catalyst discussion centering on its neighbors on the periodic table (Pt, Pd, Rh, Re, Ru, and Ag). That looks like it's about to change. The big question to be answered: Why are nanogold particles so much better than bulk gold? Here are some possibilities to consider.

1. Larger surface areas. Well yes, you would expect some benefit here, but gold has been so unremarkable as a catalyst, I don’t believe a simple increase of surface area would account for this big of an effect. If it were that easy, everyone would just have dumped more gold into their catalyst formulations in order to increase the available surface area.

2. More defect sites. In many cases, catalysis only occurs at specific sites on the catalyst surface, such as the so-called "steps" as shown in the figure below. Perhaps nano-gold particles naturally have more of these locations.

3. More of the appropriate crystal faces. Different lattice faces such as (111) or (100) often have significantly different catalytic rate constants. See figure above. Perhaps nano-gold particles have more of the correct lattice orientations at the defect sites than bulk gold.

4. Different surface oxide properties. One of the reasons metals like Pt and Rh make such good catalysts is their ability to maintain surfaces which are relatively clean of oxygen atoms. Whereas the early transition metals tend to form oxides, the late transition metals favor the metallic state. Heat vanadium or molybdenum in air and you form the oxides. Heat platinum or its salts in air and you wind up with platinum metal. Keeping the surface free of oxygen atoms makes the metal more available for catalyzing the desired reactions. Perhaps smaller gold particles tend to have less oxygen on their surface.

Figure obtained from http://www.pnas.org/content/103/28/10577.full.pdf

Golden Health

Gold has been used for medicinal purposes since the time of the Romans. Rightly or wrongly, gold was often used as a medical treatment for a variety of conditions. It does appear to have anti-bacterial properties, much like silver. In medieval Europe, pills were often coated with gold to "enhance" the benefits of the medicine. Paracelsus, the alchemist, developed a solution of colloidal gold which he named "Aurum Potable". He considered it a powerful elixer capable of curing all sorts of ills.

In recent years, gold has experienced a bit of a renaissance in the form of nano-particles. Gold nano-particles are being used for drug delivery systems, biosensors, optical devices, and catalysts, among other things. It's hard to get through a chemistry journal without seeing at least on paper on nano-gold. In retrospect, gold nano-particles aren't really all that new. First of all, they apparently already existed in nature. They were also used by the Romans to create red stained glass. In bulk form, gold is yellowish since it reflects light at the blue end of the spectrum less efficiently than other colors. However, if the size of the gold particles is significantly smaller than the wavelength of visible light, new interactions occur between the light and the gold surface, resulting in a red color. In aqueous suspensions, purple and yellow colors can also be obtained if the particles are allowed to aggregate. In fact, Paracelsus's purple "Aurum Potable" was a simple suspension of gold nano-particles.

As you can imagine, colloidal gold is now available all over the net (for example, here and here) for boosting your physical and mental health. Don't feel like drinking gold? No worries. They also sell nano-silver, nano-copper, nano-platinum, nano-palladium, nano-iridium, nano-titanium, and nano-zinc too.

Why am I mentioning gold's supposed health benefits? Apparently the Romans were on to something back in the day since it turns out their gold nano-particle based stained glass windows are good at removing volatile organic compounds from the air. Will we be seeing gold-based air purifiers in the stores soon? I can only imagine what the web marketeers are going to do with this information.