Insoluble contradiction

Background (skip if you have been following this from the beginning): The stripy nanoparticle hypothesis was first proposed in Nature Materials in 2004 by the group of Professor Stellacci (then at MIT and now at the EPFL). This hypothesis now forms the basis of 23 articles by the same group, mostly published in high impact journals including Nature Materials, Nature Nanotechnology, Nature Communications, Science, Journal of the American Chemical Society, Small, etc: 1234567 , 8910111213141516171819202122 and 23. In November 2012, we published Stripy Nanoparticles Revisited which was followed by a response from Professor Stellacci.

Insoluble contradiction; In Stripy Nanoparticles Revisited (Fig S4, reproduced below), we pointed to a contradiction in the solubility  reported for  the same type of nanoparticles in two “stripy” articles: Jackson 2004 and Centrone 2008.

The response from Professor Stellacci was that the particles in both studies are different:

Stripy Nanoparticles Revisited claims that there are contradictions between our statements on particle solubility in Jackson 2004 and Centrone 2008 […] . Yet Jackson 2004 describes octanethiol, mercaptoproprionic acid-coated particles, Centrone 2008 describes octanethiol, mercaptoproprionate-coated particles, […]. Why would or should all of these particles behave the same way in terms of solubility […] given that the molecules that coat them are different? [emphasis mine]

Centrone 2008 focuses on the structure-solubility relationships of stripy nanoparticles in solvents of different polarities. The only measurement of structure in Centrone 2008 is in Fig 1. As shown below, Fig 1 in Centrone 2008  is data re-use (without attribution in the figure legend) from Jackson 2004.

There are only two possibilities:

1) The particles in Jackson 2004 are similar enough to those in Centrone 2008  to justify using the former STM images to discuss the latter structure and solubility. In this case, the data re-use is ‘ordinary’ self-plagiarism but the contradictions we noted in Stripy Nanoparticles Revisited remain to be explained.

2) The particles in Jackson 2004 are different from those in Centrone 2008 which may help explain the differences in solubility but the data re-use is a more misleading form of data re-use.

Update 1 (15/02): Dave Fernig has contacted journal Editors about various data reuse in the stripy articles. Here is the response from PNAS:

“Thank you for bringing this to our attention. We have taken a look at the figures, and while they are similar, they are not identical. Also, the authors have referenced the earlier Nature publication in their PNAS article.”

After pointing out to PNAS that the images are indeed identical and directing them to check out the images side by side, with contrast, colour balance and scale adjusted, on Raphael’s blog, they came back on a much more positive note:

“Thank you for providing a link to Raphael Levy’s blog posting. Based on this additional information and clear explanation of the issue, we will follow up with the authors to discuss the matter.”

Update 2 (25/03): The PNAS article has now been ‘corrected’: the re-used image has been substituted for another one. It would therefore appear that the second possibility is more accurate.

 

Adapted from Jackson 2004 and Centrone 2008; the figure legend of Centrone et al reads: "Fig. 1. STM image of gold nanoparticles coated with a 2:1 ratio of OT/MPAshowing ordered phase separation in their ligand shell. (Scale bar, 25 nm.)(Insets) Close up of nanoparticles showing the encircling, ribbon-like domains(Left) and a corresponding simplified schematic diagram in which the redpillars represent MPA, and the yellow represent OT (Right). (Scale bar, 5 nm.)"

Adapted from Jackson 2004 and Centrone 2008; the figure legend of Centrone et al reads: “Fig. 1. STM image of gold nanoparticles coated with a 2:1 ratio of OT/MPA
showing ordered phase separation in their ligand shell. (Scale bar, 25 nm.)
(Insets) Close up of nanoparticles showing the encircling, ribbon-like domains
(Left) and a corresponding simplified schematic diagram in which the red
pillars represent MPA, and the yellow represent OT (Right). (Scale bar, 5 nm.)”

FigS4

Figure S4: Comparison of the results reported by Centrone et al., 2008 (black curve, left Y axis) and by Jackson et al., 2004 (red curve, right Y axis) for solubility in ethanol; The solubility was measured as a saturation concentration expressed in molar in the 2008 study, while in the 2004 study, the solubility scale (right axis) was defined as follows: “4 = highly soluble, that is, no precipitation visually observed, 3 = mostly soluble, that is, little precipitation observed over time with consequent slight decolouration of the solution; 2 = slightly soluble, that is, most of sample precipitated but a small coloration of the solution remains, 1 = totally insoluble.” The data points are shown with symbols, black and red continuous lines (3-points splines) are shown to facilitate the visualization of the trends.

9 comments

  1. I’m not a scientist, just one Raphaël’s blog follower and not able to understand scientific argumentation. However a thing is certain: it’s impossible to represent the Earth in 2 D without distortions; same result for stripy nanoparticles, unavoidably!

    Paul Picard
    Mulhouse France

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    1. very wise, indeed!

      With this thought, let’s revert to stripy nanoparticles geometry “controversy”:

      “…When cartographers flatten a 3D Earth onto a 2D surface, they use a projection [modified mercator] that preserves some aspects of our roughly-spherical planet while distorting others…” Take a look for yourself: https://plus.google.com/app/basic/stream/z13ijfv4ezz0flpff22dvhrpvybkuxd2f
      Perhaps some bloggers could benefit from the puzzle in the previous link. So much about 2D projections of spherical objects.

      While I do understand that —for some people—this is a rather troublesome and non-intuitive concept, maybe a simpler starter exercise is to project 3D objects onto cylindrical surfaces, as shown in http://en.wikipedia.org/wiki/Mercator_projection . Now, what’s larger: Greenland or Australia?

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  2. Often simple arguments are the best ones. I am honored by this comment from my most conscientious follower… who happens to be my own grand dad! (I believe that this is his first comment on any blog so also welcome to the blogosphere)

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  3. I guess I need those two pdfs also. (yeah, I know…not having the nature04 one.)

    Also, what is the difference of the two molecules? Mercaptoproprionic acid and mercaptoproprionate sound like conjugate acid and base (basically same thing once in water). But I’m shooting from hip. Also when you try to google structure, seems like they want to say -propionic, not proprionic. I HAVE to assume that the chemistry is clear and I just need a little tutorial. 🙂

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