Name this organic chemistry phenomenon of silicon replacing carbon

February 2, 2005 1:48 PM

Is there a branch of physical chemistry concerned with the synthesis and study of the material properties of originally organic compounds where carbon is replaced by silicon? [+]

I'm particularly interested in whether anyone is working on silicon-substituted chlorophyll for a photovoltaic cell. Just plain intellectual curiosity. Thanks.

posted by ZenMasterThis to Science & Nature (12 answers total)

How would this work? Chlorophyll (plus a host of other compounds involved in the process) uses light to convert carbon dioxide and water to sugars. Sugars are a great way for living things to store chemical energy, but not that great if you're looking to get electrical energy out of the process.

I can't say for sure that no one is working on this, but it seems unlikely, as I can't see any practical value. If you want to make sugar, just use plants (traditional chlorophyll) to start with. If you want electrical energy, you're not going to get any (at least not with any appreciable efficiency) using silicon chlorophyll--why not just use traditional photovoltaic cells?
posted by DevilsAdvocate at 2:49 PM on February 2, 2005

In the early 60's, I had a physics professor whose last name as I recall, was Varshni. He specialized in the theoretical exploration of a Silicon based universe. I know he published many papers, however, I have forgotten what journals he used. If you have access to a good University library, you might check out his name in some of the physics journals.
posted by RMALCOLM at 2:56 PM on February 2, 2005

Or Google Scholar might do as well.
posted by Gyan at 4:13 PM on February 2, 2005

DevilsAdvocate:

I think we're talking about a photo cell that would exploit the oxidation-reduction mechanism of chlorophyll and its accessory proteins, and skip the sugar-making process (which really doesn't have that much to do with the chlorophyll itself). In fact, these folks seem to be working on a chlorophyll-like photo cell. Whatever they're using seems to be proprietary -- maybe they've stumbled on the silicon idea themselves!

Why exactly would silicon be better than carbon, anyway?
posted by greatgefilte at 5:14 PM on February 2, 2005

Can silicon-based life forms exist? (scroll down a bit)
posted by gimonca at 7:07 PM on February 2, 2005

Silicon-based gunpowder may propel MEMS devices, EE Times, 1/24/2002
posted by gimonca at 7:12 PM on February 2, 2005

This page has a fairly good explanation as to why carbon dioxide is a gas, while silicon dioxide is a solid.

This diagram of a chlorophyll molecule shows at least one carbon-oxygen double bond. The previous article says that silicon can't do that double bond with oxygen. This suggests that you can't replace carbon with silicon in chlorophyll and retain the same structure (but I don't know 100% for sure).
posted by gimonca at 7:23 PM on February 2, 2005

Creating Artificial Life has a chapter that speculates on silicate-based life, and other chemistries that could support non-carbon life on other planets.
posted by AlexReynolds at 7:48 PM on February 2, 2005

OK, this question set off a series of horrible memories about my second and third year courses in mineralogy. So, thank you for that.

"...material properties of originally organic compounds where carbon is replaced by silicon?"

Basically, this wouldn't work. Silicon compounds tend to a completely different structure than carbon ones - there's no real analogue for the more complex and interesting structures you can put together with carbon in the silicon universe - it's all SiO3 tetrahedra in chains (pyroxenes), double chains (amphiboles), sheets (micas) and so on.
There's a lack of flexibility in the physics that makes the idea of a straight substitution not work.
posted by thatwhichfalls at 8:08 PM on February 2, 2005

crap - SiO4 tetrahdra.

Try and look like some kind of authority and I screw up the formula of the basic unit.
posted by thatwhichfalls at 8:10 PM on February 2, 2005

I've heard chlorophyll is horrendously inefficient. I believe present-day solar cell tech beats it out.
posted by five fresh fish at 8:41 PM on February 2, 2005

Response by poster: My thought was that silicon lies directly below carbon on the periodic table, thus has similar properties. Likewise, the silicon-based compounds might have similar, useful properties as their carbon-based counterparts, but being silicon-based would be more stable(?), work at higher temperatures(?), and not be attractive to microorganisms.
posted by ZenMasterThis at 4:49 AM on February 3, 2005