# Scientists out there (Especially Chemists)!

Discussion in 'Community' started by themadchemist, Feb 16, 2005.

1. ### themadchemist macrumors 68030

Joined:
Jan 31, 2003
Location:
Chi Town
#1
I have a question for you. Let's say you have a solution and you want to find out the distribution of particles within it. Of course, the typical assumption is that particles are evenly distributed in a solution, but imagine that there are forces acting on a particle such that that might not be the case. Then, it is a non-trivial issue as to the distribution of the particles.

So, what I want to know is if there is a way to determine the THREE-DIMENSIONAL distribution of particles in solution.

Would 3D fluorescence spectroscopy work?

Thanks!

2. ### jared_kipe macrumors 68030

Joined:
Dec 8, 2003
Location:
Seattle
#2
Well what kind of forces are you talking about? For something like that one would most likely use Nuclear Magnetic Resonance Imaging.

In case you are wondering, a basic typical approach would be to put the said solution into a very large magnetic field (B>1 Tesla) then make a smaller osculating magnetic field in another direction (usually perpendicular) and have another pickup coil to essentially scan the resonance of the substance. This works best if you can make the B field have a touch of a gradient so that the same substance would resonate at a different frequency in different places.

The reason it works is quantum mechanical in nature, just search for something like "nuclear magnetic resonance Bohr magnetron" in google to learn more. Or ask, I should know a great deal.

3. ### Mr. Anderson Moderator emeritus

Joined:
Nov 1, 2001
Location:
VA
#3
Just out of curiosity, but if some of the particles in solution were iron, wouldn't the testing with a magnetic field of any sort cause the results to invalid?

So what are your particles made of?

D

4. ### Mechcozmo macrumors 603

Joined:
Jul 17, 2004
#4
I just learned about figuring out how many particles are in a substance... from moles you multiply by 6.02e23...

Sorry I can't help you on this one.

5. ### jared_kipe macrumors 68030

Joined:
Dec 8, 2003
Location:
Seattle
#5
You're thinking classically, if the solution contained iron, then it would detect iron. Thing you aren't thinking of is that iron isn't the only thing that has a magnetic moment, electrons protons have magnetic moments because they are charges that are spinning, however even neutrons have magnetic moments because of their inner working.

We commonly use Nuclear magnetic resonance to look at the inner workings of human beings, and while they are encouraged to take out the keys from their pockets, they still have iron in their bodies.

6. ### jim. macrumors 6502

Joined:
Dec 22, 2004
Location:
C-ville, VA
#6
To look at distributions and accumulation of proteins in cells we use dynamic light scattering. I'm not sure if it would offer the resolution that you want though.

Would X-ray diffraction help any with this? It's been a long time since I have done any anal chem, so I don't remember much about it. I remember it was used for protein structure modeling. Can it be scaled up? Now that I think of it, solutions are so dynamic that the diffraction probably wouldn't help too much.

Jim

7. ### Mr. Anderson Moderator emeritus

Joined:
Nov 1, 2001
Location:
VA
#7
True, and I really don't know the magnitude of the em fields you're talking about here. I just found it interesting.

D

8. ### jim. macrumors 6502

Joined:
Dec 22, 2004
Location:
C-ville, VA
#8
With an NMR apparatus we are talking some POWERFUL em fields. The one I used as an undergrad was 7T (140,000x) that of Earth's magnetic field. I think there was an even more powerful one on campus too. Decent resolution on those machines.

Jim

9. ### themadchemist thread starter macrumors 68030

Joined:
Jan 31, 2003
Location:
Chi Town
#9
Thanks for the quick responses guys! Let me provide more information. I am interested in the formation of polymers of self-aggregating peptides. I want to see if, during the early stages of the polymerization process, the aggregates are unevenly distributed in clumps throughout the solution. Therefore, I want an assay that will not interfere with the distribution of the peptide in solution. This is why I was thinking something like fluorescence. Please let me know what you think.

edit: I also want something that can scan on a picosecond or nanosecond time scale...