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DBL%20Hendrix%20small.png College chemistry, 1983

Derek Lowe The 2002 Model

Dbl%20new%20portrait%20B%26W.png After 10 years of blogging. . .

Derek Lowe, an Arkansan by birth, got his BA from Hendrix College and his PhD in organic chemistry from Duke before spending time in Germany on a Humboldt Fellowship on his post-doc. He's worked for several major pharmaceutical companies since 1989 on drug discovery projects against schizophrenia, Alzheimer's, diabetes, osteoporosis and other diseases. To contact Derek email him directly: derekb.lowe@gmail.com Twitter: Dereklowe

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May 20, 2011

Like Charges, Er, Attract?

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Posted by Derek

Now, this is a strange little paper in Chem. Comm. The authors are studying small reverse micelles (RMs, basically, for those of you not in the field, bits of water enclosed by a layer of soap-like organic molecules).

Nothing wrong with that - micelles and reverse micelles have been objects of study for many years now. But they're saying that when they look at positively charged molecules and the way that they associate with positively charged RMs - that once the size of the reverse micelles gets small enough, that like charges attract instead of repel:

Comparing the results in the RMs and in the conventional micelles, it is quite evident that the violation in the principle of electrostatic interaction is not a general phenomenon and is quite specific for the nano-confined environment, like in RMs. Thus, the charged surface formed under the nano-confinement shows quite extraordinary electrostatic behaviour as compared to other normal charged surfaces.

They have some possible explanations, such as the large number of counterions in the small micellar pool of water providing electrostatic screening. They go on to suggest that if this effect is robust, that it could have real implications for behavior in biological systems (and for various drug-carrier ideas). Any thoughts from the more physical-chemistry oriented members of the crowd?

Comments (18) + TrackBacks (0) | Category: Chemical News


COMMENTS

1. student on May 20, 2011 9:07 AM writes...

Electrostatic interactions between like charges repel.

Exceptions? There are none.

It's possible that other forces overcome electrostatic repulsion but to say that "violation in the principle of electrostatic interaction" is total bullshit.

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2. surface_tension on May 20, 2011 9:32 AM writes...

I remember from my p-chem class, that small bubbles have a very high free energy.
http://en.wikipedia.org/wiki/Surface_tension#Surface_curvature_and_pressure

Perhaps this the counter balancing energy to the electrostatic attraction.

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3. Michael Sullivan on May 20, 2011 9:54 AM writes...

I'm not a chemist, but when reading about any scientific field my reaction to a claim as extraordinary as this is to not even bother to think about it until someone duplicates it.

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4. ReneeL on May 20, 2011 10:04 AM writes...

It is possible to see the supplemental info for this article on the Chem. Comm. page.

They have the structure of the AOT surfactant wrong. First of all, it is a sodium salt, making it an anionic surfactant. They also have an extra carbon in the succinate part of the structure. There is no excuse for this - the online Sigma-Aldrich catalog clearly shows the correct structure. They state that they bought the chemical from Sigma.

It's not clear from the supplemental info what exactly they were making and then measuring. It is also not clear if they are trained surface/colloid chemists. They appear to be physical chemists doing their work at a photochemistry institute.

I suggest the authors send this manuscript to the Journal of Colloid and Interface Science and see how far they get. The journal has 45+ years of publishing articles in this field, and they'll be able to spot something unique or something bogus.

I beieve this shows the idiotic results of publishing an article in the field of surface/colloid chemistry in a journal of non-surface/colloid chemistry.

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5. Explanation on May 20, 2011 10:31 AM writes...

Peer reviewers asleep at the wheel is the Occam's razor for this one. I've worked on RM and electrostatics, and I can't tell what they've done here.

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6. Omar on May 20, 2011 10:55 AM writes...

I have not looked at the paper in question, but note that like-charge attraction in complex solutions is a known, and somewhat understood, physical phenomena. Typically, it requires the presence of multivalent counterions to bridge the macroscopic charged particles. Here, for example, is a slightly old review of the situation of attraction between (negatively-charged) DNA molecules, which happens in the presence of ions of valency 3+ or higher:
http://dx.doi.org/10.1016/S0959-440X(96)80052-2

Permalink to Comment

7. student on May 20, 2011 11:17 AM writes...

Omar, in that case the attraction of the negatively charged ions is to the positively charged cations, not to the other negatively charged ions (which is repulsive). If the authors are suggesting removing the coulombic portion of the schrodinger equation's Hamiltonian, or revising it, then they should write a science paper. Otherwise, they should stop bullshitting.

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8. Rick on May 20, 2011 11:36 AM writes...

I'm not quite interested enough to pay the 32 GBP to look at an article that claims to say that identical charges attract unless it's accompanied by the hoopla one sees when a longstanding theory is demonstrated to be inadequate (e.g. Newtonian physics vs. relativity), but here's an idea that might explain the bottom line conclusion of the abstract, which was free, without violating basic electrostatics: What if confining the positive ions onto a sufficiently tiny surfaces caused an induced dipole in ions embedded in the micelle surface that resulted in their electrons spending a bit more time on one side of the micelle surface than on the other. Any (very weak) attraction would be due to London Dispersion forces.

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9. opsomath on May 20, 2011 11:50 AM writes...

Okay, I can't breach the paywall either, but chill, folks. It's most likely a physical argument for other forces overcoming Coulombic repulsions in this work, much like the work of Jack Roberts who explained why, for instance, the dianion of 1,4-butanedioic acid assumes a gauche rather than trans configuration. It is a counterintuitive result that is worth a note.

Now, it's these guys' fault a bit for making it sound like they were revising the form of the quantum Hamiltonian. But if we got chased off every time we make our results sound cooler than they actually are, we'd be running a lot.

Permalink to Comment

10. sgcox on May 20, 2011 12:27 PM writes...

Authors of that strange paper should first learn some basic physics:

http://en.wikipedia.org/wiki/Shell_theorem

Even though this example is for gravitational attraction, same hold for electrostatic repulsion

Permalink to Comment

11. Saintmichael on May 20, 2011 2:35 PM writes...

Dang, sgcox beat me to it. It may have been a few years since I took university physics, but at least I recall that E=0 inside a conducting sphere. Yeah these micelles are not perfect spheres, nor are they really conducting, but I'd still expect the charges to be spread relatively evenly. Am I missing something here?

Another note: In the paper they also refer to "overruling" the electrostatic interactions, which is a much better word to use than "violating". But these guys are from India, so I'll forgive them for their terrible word choice.

Permalink to Comment

12. Andy on May 20, 2011 5:03 PM writes...

Can cold fusion be far behind? I don't think so!

Permalink to Comment

13. Rikard on May 22, 2011 2:06 PM writes...

Charges on a small sphere can be tighter packed than charges on a larger sphere. This can result in a localised charge concentration around a small sphere that will polarise the surrounding matrix in a way that will effectively push similar charges towards the sphere, thus making it look like similar charges attract. The same effect can be seen in electron pairing in semiconductors etc.

Now, I dont know if this applies to this paper, but there certainly are cases where similar charges appear to attract and nanoscale spheres are full of surprises.

Permalink to Comment

14. Stephe Moratti on May 22, 2011 7:15 PM writes...

SaintMichael, insulating spheres act different to conducting spheres - there is a field in the former.

No the real problem as Derek alluded to is they totally fail to address where the counterions are - e,g, if they are tightly bound in a Debye layer then they will screen the middle of the sphere and even invert the field. This paper is awful and needs to be thumped by a proper physical chemist (just a humble organic chemist here)

Permalink to Comment

15. Jonadab on May 23, 2011 7:00 AM writes...

> It's possible that other forces overcome
> electrostatic repulsion

That was my first thought too, for about half a second, but then I mentally went through the list of other known forces... these things don't have enough mass, relative to their charge, for gravitation to do much (heck, the imbalance in charge between the O side and the H side of the embedded water molecules is enough to overwhelm gravity on a significantly larger scale, as you know if you've ever done one of the surface-tension experiments popular in gradeschool science curricula), and the other two known forces fall off way too sharply with distance to overcome inertia, to say nothing of electromagnetic interaction, at the molecular scale. And if you propose some new previously-unknown force, I'm definitely going to want to see some rather serious peer review going on.

No, I don't think there are other forces at work here. It's vaguely conceivable, but only just barely, and the experiment hasn't been run nearly enough times to jump at conclusions like that. If the results can't be explained by electromagnetic force, my money's on experimental error. Start over and run the experiment again, with a fresh batch of materials, and see what happens.

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16. Vader on May 23, 2011 12:58 PM writes...

Superconductivity is a manifestation of Cooper pairs. Two electrons pair up in spite of their electrostatic repulsion due to interactions with phonons in the crystal lattice. I can, with difficulty, imagine something like this occurring in a very small micelle.

But, like the other commenter, I'll wait for the result to be reproduced before I give it much thought.


Permalink to Comment

17. Andrew Glasgow on May 25, 2011 5:46 AM writes...

I'm not a scientist, I just have one thing to say...


LISA! In this house we obey the laws of electrodynamics!!

Permalink to Comment

18. Carbocat on May 25, 2011 7:55 AM writes...

ALL charges attract at sufficiently short distances. In fact everything does.

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