What obstacles currently prevent chemists from making ‘any molecule they want’? This is assuming, of course, that the desired molecule can exist in three-dimensional space. But given that the desired molecule can exist, what prevents us from assembling it if we so desire? I read an article in the newspaper several years ago which stated that there are chemists working on the problem, but I didn’t get far enough into the article to find out what issues are involved in achieving this. My armchair guess is that it involves a scenario analogous to the traveling salesman problem, and that even our largest and fastest supercomputers are incapable of modeling every possible arrangement of atoms in a large molecule and discarding configurations that are undesirable or can’t exist. I’m also guessing that even if this obstacle is overcome, the issue of how to go about producing the chemical reactions necessary to produce the desired molecule may present an equal or even more daunting logistical problem. Are these guesses anywhere near close? Or are they completely off base and there are other reasons why we haven’t achieved this yet?
Also, if and when this ability is finally realized, what will it mean for us as a species? What will it enable us to do?
It would take an extremely large amount of energy to move a proton. Even then, no one knows how to do that, while many believe it is impossible. That would be alchemy, which has been discredited as far as I know.
Thank you for clarifying that. Please don’t frighten me like that ever again. You’re talking to somebody who can be reduced to a puddle of quivering Silly Putty by a quadratic equation. I thought you were saying something so esoteric that I was going to spend the rest of the weekend Googling it only to come away muttering to myself like a village idiot. I might have had to go to work on Monday morning and tell my boss that I wanted to give up the cashier job and move back to the fry station.
This is essentially what the field of nanotechnology is based on. Its a relatively new field though. You might want to look up nanoconstruction for more info.
The only tools we have to make chemicals are chemical reactions, and in many cases even if the chemical we would like to make would be stable, it could only be done through creating intermediaries that are not and couldn’t exist in circumstances we know. In many cases, we simply don’t know how to make a chemical. We can’t just arrange atoms into molecules - or to whatever extent we can, it would be an extremely slow, time-consuming process to make even tiny yields.
As Excalibre said, Chemists pretty much * can * make any molecule they desire, provided it (as well as any intermediates) are stable. They just can’t often do it quickly, easily, cheaply, or efficiently.
Sorry, Wes, but as I read the OP, this has nothing to do with nanotechnology, which seeks to build small-scale strucures from existing molecular substrates. Stuff like carbon nanotubes and buckeyballs are made by traditional chemical processes.
Yeah, easy, cheap, and efficient are key considerations. A lot of complex molecules can be made, in theory, using complex stepwise syntheses. For example, if I remember my organic chem correctly, it’s not all that complex to assemble arbitrary amino acids, starting from non-organic feedstock. And it’s actually fairly simple to assemble those into proteins. But a protein may have hundreds of amino acids, and each step must be done separately. Which means that you end up having to do hundreds and hundreds of steps to assemble an arbitrary protein, which makes it impractical to do for any mass use of it. Plus, you always lose some with each step, which means your eventual yields might be miniscule.
Another problem is chirality. Most complex molecules have several chiral centers. (Chirality refers to “handedness” - if you’re looking at complex three-dimensional molecules, they often have two different configurations that are mirror images of each other. This can be compounded if a molecule has multiple chiral centers - three such centers would mean eight different configurations (stereoisomers) based upon whether parts of the molecule are left-handed or right-handed.)
When dealing with chirality, a non-chiral molecule will react equally with either left- or right-handed molecules, so if your end result has even one chiral center (and it matters), half the yield will be the wrong rotation. Add a few more chiral centers, and you can end up with many different stereoisomers, with very different chemistry, so your yield would be a tiny fraction of the feedstock. It’s also generally chemically difficult to separate left- and right-handed molecules. (Sorry if any of the details are off - orgo was a long time ago.)
They are now, but my layman’s understanding was that nanotech was supposed to eventually provide ways to assemble arbitrary chemicals. Is that not true?
AIUI, this is a major problem with potential pharmaceuticals. Many potentially useful drugs are rejected because of serious side-effects. For many, the side effects are produced by the stereoisomers, rather than the drug itself. If the left- and right-handed molecules could be easily separated, we’d have lots more useful drugs.
I’ve also read that thalidomide (the drug used in the 50s (or so) in Canada and Europe that caused babies in utero to be born with severely malformed or missing limbs) actually has a therapeutic enantiomer and the other one, which causes the major birth defects. Problem is it gets converted from one form into another by the body, so even the correct enantiomer will get converted into the wrong one and cause those problems.
Many configurations are innately unstable and volatile - they have a very strong tendency to react with their environment or themselves, forming a different molecule or separating into many.
Efforts have been made to isolate these sorts of molecules, but I’ve heard that keeping them together for even one second is quite an achievement.
Another obstacle is practicality. Why make a chemical if there’s no use for it? This kind of stuff costs money, you know.
