Category Archives: Literature
The word ‘umpolung‘ is not used often enough in my opinion, and that’s a shame since this phenomenon refers to one of the most classic tropes or deus ex machina used in sci-fi movies—prominently in the Dr. Who lore*—and that is ‘reversing the polarity‘. Now, reversing the polarity only means that for any given dipole the positively charged part now acquires a negative charge, while the originally negatively charged part becomes positively charged, and thus the direction of the dipole moment is, well, reversed.
In chemistry, reversing the polarity of a bond is an even cooler matter because it means that atoms that typically behave as positively charged become negatively charged and react with other molecules accordingly. Such is the case of this new research conducted experimentally by Prof. Rong Shang at Hiroshima University and theoretically elucidated by Leonardo “Leo” Lugo, who currently works jointly with me and my good friend the always amazing José Oscar Carlos Jimenez-Halla at the University of Guanajuato, Mexico.
Production of molecular hydrogen from water splitting at room temperature is a remarkable feat that forms the basis of fuel cells in the search for cleaner sources of energy; this process commonly requires a metallic catalyst, and it has been achieved via Frustrated Lewis Pairs from Si(II), but so far the use of an intramolecular electron relay process has not been reported.
Prof. Rong Shang and her team synthesized an ortho-phenylene linked bisborane functionalized phosphine (Figure 1), and proved their stoichiometric reaction with water yielding H2 and phosphine oxide quantitatively at room temperature. During the reaction mechanism the umpolung occurs when a proton from the captured water molecule forms a hydride centered on the borane moiety of BPB. The reaction mechanism is shown in Figure 2.
According to the calculated mechanism, a water molecule coordinates to one of the borane groups via the oxygen atom, and the phosphorus atom later forms a hydrogen bond via their lone pair separating the water molecule into OH– and H+, this latter migrates to the second borane and it is during this migration (marked TSH2 in Figure 2) where the umpolung process takes place; the natural charge of the hydrogen atom changes from positive to negative and stays so in the intermediate H3. This newly formed hydride reacts with the hydrogen atom on the OH group to form the reduction product H2, the final phosphine oxide shows a PO…B intramolecular forming a five membered ring which further stabilizes it.
This results are now available in Chemical Science, 2021, 12, 15603 DOI:10.1039/d1sc05135k. As always, I deeply thank Prof. Óscar Jiménez-Halla for inviting me to participate on this venture.
* Below there’s a cool compilation of the Reverse the Polarity trope found in Dr. Who:
Having a paper rejected is one of the certainties of academic life. While there are some strategies to decrease the probability of facing a rejection, today I want to focus on my tips to deal with them—particularly for the benefit of younger scientists.
There are two broad kinds of rejections: Desk Rejections and Rejections from reviewers. In any case, the best advice is never to take action after receiving the dreaded rejection letter. Take a day or two, then react accordingly with a cooler head. Remember, this isn’t about you it’s hard not to make it personal but trust me it isn’t.
The first kind, desk rejections, are provided directly from the chief or associated editors of the journal to which you submitted your work. They tend to be quick and rather uninformative except for maybe the incompatibility—to put it nicely—of your work with the scope of the journal. These are also sometimes the hardest to face since they make you feel your work is simply not good enough to be published; but they’re also the quickest and in the publish-or-perish scheme of things, time is key. After getting a desk rejection, if no other input is given, just try again; one tip—though not infallible—to chose a proper journal is to look at which journals are you citing in your own work and chose one with the highest frequency. Sometimes, editors might offer a transfer to another journal from the same publishing house; my advice is always say yes to transfers: the submission is made for you by the editorial staff, it sort of becomes recommended between the involved editors, and expedites the start-again process. Of course, a transfer does not mean you’re manuscript will get accepted but whenever offered there is a good chance the first editor thinks your work should be kept inside their editorial instead of risking you going to another publishing house. Appealing to a desk rejection is highly discouraged since it practically never works. Sure, you may think the editor will kick himself in the rear once you get the Nobel prize but telling them so, particularly in a colorful language, will not make them change their minds.
Rejections after peer review are trickier. If your manuscript went up to peer review, it means the editors in charge of it thought your work is publishable but of course it needs to be looked at by experts to make sure it was done in the right way with all or most things covered (you know what they say, two heads are better than one, try three!). Now, this kind of rejection takes longer, usually two or three weeks—sometimes even longer—but all things being fair, polite, and objective, they are also the most informative. Reviewers will try to find holes in your logic, flaws in your research, and when they find them they will not hold back their thoughts; you’re in for the hard truth. So of course this kind of rejection is also hard to take, makes you feel again like your work is not worthy, that you’re not worthy as a scientist. But the big advantage here is you now have a blueprint of things to fix in your manuscript: a set of experiments are missing? run them, key literature wasn’t cited? read it and cite it appropriately. Take peer review objectively but never dismiss it by trying to just go and submit it again to a different journal as is, for chances are you’ll get some of the same reviewers, and even if you don’t, it’s unethical to dismiss the advice of peers, they are your peers in the end, not your bosses but your peers, don’t loose sight of it. Also, it’s very frustrating for reviewers to find that authors managed to get published without paying the slightest attention to their suggestions. Appealing a peer review rejection is hard but doable and then you have to put on a scale what is it that you value the most: your paper in its original condition being published in that specific journal or fixing it and start again. An appeal upon a flat rejection is hardly ever won but it may well establish a conversation with other scientists (the referees) about their point of view on your work, just don’t think you’ve made instant buddies who will now coach you through academic life.
The peer review system is far from perfect, but if done properly it is still the best thing we’ve got. Some other alternatives are being tested nowadays to reduce biases like open reviews signed and published by reviewers themselves; double and even triple blind peer review (in the latter not even the editor knows the identities of authors or reviewers) but until proven useful we have to largely cope and adapt to single blind peer review (just play nice, people). In some instances the dreaded third reviewer appears, and even a fourth and a fifth. Since there are no written laws and I’m not aware of any journal specifying the number of referees to be involved in the handling of a manuscript there may be varied opinions among reviewers, so different as from ranging from accept to reject. This may be due to the editor thinking one or more of the reviewers didn’t do their job properly (in either direction) and then brings another one to sort of break the tie or outweigh the opinion of a clearly biased reviewer. If you think there are bias, consult with the editor if a new set of reviewers may be included to complete the process, more often than not they will say no but if you raise a good point they might feel compelled to do so.
Science is a process that starts at the library and ends at the libraryDr. Jesús Gracia-Mora, School of Chemistry UNAM ca. the nineteen nineties
These are truths we must learn from a young age. Any science project does not end at the lab but at the library, therefore I let my students—even the undergrads—do the submission process of their manuscripts along with me, and involve them in the peer review process (sometimes and to some limited extent even when I’m the reviewer) just so they now that getting a rejection letter is part of the process and should never be equated with the relative quality or self-worth of a scientist since that is hardly what the publication process looks at.
So, in a nutshell, if you got a rejection letter, get back on the proverbial saddle and try again. And again. And once again.
The format of a research paper hasn’t changed much throughout history, despite the enormous changes in platforms available for their consumption and the near extinction of the library issue. Convenient electronic files such as PDFs still resemble printed-and-bound-in-issues papers in their layout instead of exploiting the seemingly endless capabilities of the electronic format.
For instance, why do we still need to have page numbers? a DOI is a full, traceable and unique identification for each work and there are so many nowadays that publishers have to pour them out as e-first, ASAPs, and just accepted before having them assigned page numbers, a process which is still a concern for some researchers (and even for some of the organizations funding them or evaluating their performance). Numbers for Issues, Volumes and Pages are library indexes needed to sort and retrieve information from physical journals but in the e-realm where one can browse all issues online, perform a search and download the results these indexes are hardly of any use, only the year is helpful in establishing a chronological order to the development of ideas. This brings me to the next issue (no pun intended): If bound-issues are no longer a thing then neither should be covers. Being selected for a cover is a huge honor, it means the editorial staff think your work stands out from the published works in the same period; but nowadays is an honor that comes to a price, sometimes a high price. With the existence of covers, back-covers, inner-covers and inner-back-covers and whatnot at USD$1,500 a piece, the honor gets a bit diluted. Advertisers know this and now they place their ads as banners, pop-ups and other online digital formats instead of -to some extent- paying for placing ads in the pages of the journals.
I recently posted a quick informal poll on Twitter about the scientific reading habits of chemists and I confirmed what I expected: only one in five still prefers to mostly read papers on actual paper*, the rest rely on an electronic version such as HTML full text or the most popular PDF on a suitable reader.
— Joaquin Barroso (@joaquinbarroso) June 3, 2019
What came as a surprise for me was that in the follow up poll, Reference Manager programs such as Mendeley, Zotero, EndNote or ReadCube are only preferred by 15% while 80% prefer the PDF reader (I’m guessing Acrobat Reader might be the most popular.) A minority seems to prefer the HTML full text version, which I think is the richest but hardly customizable for note taking, sharing, or, uhm hoarding.
A follow up on the previous poll. Dear #ChemTweeps, if you mostly read papers in electronic format what is your preferred platform?
— Joaquin Barroso (@joaquinbarroso) June 10, 2019
I’m a Mendeley user because I like the integration between users, its portability between platforms and the synchronization features but if I were to move to another reference manager software it would be ReadCube. I like taking notes, highlighting text, and adding summaries and ideas onto the file but above all I like the fact that I can conduct searches in the myriad of PDF files I’ve acumulated over the years. During my PhD studies I had piles of (physical) paper and folders with PDF files that sometimes were easier to print than to sort and organize (I even had a spreadsheet with the literature read-a nightmarish project in itself!)
So, here is my wish list for what I want e-papers in the 21st century to do. Some features are somewhat available in some journals and some can be achieved within the PDF itself others would require a new format or a new platform to be carried out. Please comment what other features would you like to have in papers.
- Say goodbye to the two columns format. I’m zooming to a single column anyway.
- Pop-up charts/plots/schemes/figures. Let me take a look at any graphical object by hovering (or 3D touching in iOS, whatever) on the “see Figure X” legend instead of having to move back and forth to check it, specially when the legend is “see figure SX” and I have to go to the Supporting Information file/section.
- Pop-up References. Currently some PDFs let you jump to the References section when you click on one but you can’t jump back but scroll and find the point where you left.
- Interactive objects. Structures, whether from X-ray diffraction experiments or calculations could be deposited as raw coordinates files for people to play with and most importantly to download** and work with. This would increase the hosting journals need to devote to each work so I’m not holding my breath.
- Audio output. This one should be trickier, but far most helpful. I commute long hours so having papers being read out loud would be a huge time-saver, but it has to be smart. Currently I make Siri read papers by opening them in the Mendeley app, then “select all“, “voice“, but when it hits a formula, or a set of equations the flow is lost (instead of reading water as ‘H-Two-O‘, it reads ‘H-subscript Two-O‘; try having the formula of a perovskite be read)
- A compiler that outputs the ‘traditional version‘ for printing. Sure, why not.
I realize this post may come out as shallow in view of the Plan-S or FAIR initiatives, sorry for that but comfort is not incompatible with accessibility.
What other features do you think research papers should have by now?
* It is true that our attention -and more importantly- our retention of information is not the same when we read on paper than on a screen. Recently there was an interview on this matter on Science Friday.
** I absolutely hate having a Supporting Information section with long PDF lists of coordinates to copy-paste and fix into a new input file. OpenBabel, people!
Today’s science is published mostly in English, which means that non-English speakers must first tackle the language barrier before sharing their scientific ideas and results with the community; this blog is a proof that non-native-English speakers such as myself cannot outreach a large audience in another language.
For young scientists learning English is a must nowadays but it shouldn’t shy students away from learning science in their own native tongues. To that end, the noble effort by Dr. José Cerón-Carrasco from Universidad Católica San Antonio de Murcia, in Spain, of writing a DFT textbook in Spanish constitutes a remarkable resource for Spanish-speaking computational chemistry students because it is not only a clear and concise introduction to ab initio and DFT methods but because it was also self published and written directly in Spanish. His book “Introducción a los métodos DFT: Descifrando B3LYP sin morir en el intento” is now available in Amazon. Dr. Cerón-Carrasco was very kind to invite me to write a prologue for his book, I’m very thankful to him for this opportunity.
Así que para los estudiantes hispanoparlantes hay ahora un muy valioso recurso para aprender DFT sin morir en el intento gracias al esfuerzo y la mente del Dr. José Pedro Cerón Carrasco a quien le agradezco haberme compartido la primicia de su libro
¡Salud y olé!
The concept of electronic orbital has become such a useful and engraved tool in understanding chemical structure and reactivity that it has almost become one of those things whose original meaning has been lost and replaced for a utilitarian concept, one which is not bad in itself but that may lead to some wrong conclusions when certain fundamental facts are overlooked.
Last week a wrote -what I thought was- a humorous post on this topic because a couple of weeks ago a viewpoint in JPC-A was published by Pham and Gordon on the possibility of observing molecular orbitals through microscopy methods, which elicited a ‘seriously? again?‘ reaction from me, since I distinctly remember the Nature article by Zuo from the year 2000 when I just had entered graduate school. The article is titled “direct observation of d-orbital holes.” We discussed this paper in class and the discussion it prompted was very interesting at various levels: for starters, the allegedly observed d-orbital was strikingly similar to a dz2, which we had learned in class (thanks, prof. Carlos Amador!) that is actually a linear combination of d(z2-x2) and d(z2-y2) orbitals, a mathematical -lets say- trick to conform to spectroscopic observations.
Pham and Gordon are pretty clear in their first paragraph: “The wave function amplitude Ψ*Ψ is interpreted as the probability density. All observable atomic or molecular properties are determined by the probability and a corresponding quantum mechanical operator, not by the wave function itself. Wave functions, even exact wave functions, are not observables.” There is even another problem, about which I wrote a post long time ago: orbitals are non-unique, this means that I could get a set of orbitals by solving the Schrödinger equation for any given molecule and then perform a unit transformation on them (such as renormalizing them, re-orthonormalizing them to get a localized version, or even hybridizing them) and the electronic density derived from them would be the same! In quantum mechanical terms this means that the probability density associated with the wave function internal product, Ψ*Ψ, is not changed upon unit transformations; why then would a specific version be “observed” under a microscope? As Pham and Gordon state more eloquently it has to do with the Density of States (DOS) rather than with the orbitals. Furthermore, an orbital, or more precisely a spinorbital, is conveniently (in math terms) separated into a radial, an angular and a spin component R(r)Ylm(θ,φ)σ(α,β) with the angular part given by the spherical harmonic functions Ylm(θ,φ), which in turn -when plotted in spherical coordinates- create the famous lobes we all chemists know and love. Zuo’s observation claim was based on the resemblance of the observed density to the angular part of an atomic orbital. Another thing, orbitals have phases, no experimental observation claims to have resolved those.
Now, I may be entering a dangerous comparison but, can you observe a 2? If you say you just did, well, that “2” is just a symbol used to represent a quantity: two, the cardinality of a set containing two elements. You might as well depict such quantity as “II” or “⋅⋅” but still cannot observe “a two”. (If any mathematician is reading this, please, be gentle.) I know a number and a function are different, sorry if I’m just rambling here and overextending a metaphor.
Pretending to having observed an orbital through direct experimental methods is to neglect the Born interpretation of the wave function, Heisenberg’s uncertainty principle and even Schrödinger’s cat! (I know, I know, Schrödinger came up with this gedankenexperiment in order to refute the Copenhagen interpretation of quantum mechanics, but it seems like after all the cat is still not out of the box!)
So, the take home message from the viewpoint in JPC is that molecular properties are defined by the expected values of a given wave function for a specific quantum mechanical operator of the property under investigation and not from the wave function itself. Wave functions are not observables and although some imaging techniques seem to accomplish a formidable task the physical impossibility hints to a misinterpretation of facts.
I think I’ll write more about this in a future post but for now, my take home message is to keep in mind that orbitals are wave functions and therefore are not more observable (as in imaging) than a partition function is in statistical mechanics.
As if I didn’t have enough things to do I’m launching a new blog inspired by the #365papers hashtag on Twitter and the naturalproductman.wordpress.com blog. In it I’ll hopefully list, write a femto-review of all the papers I read. This new effort is even more daunting than the actual reading of the huge digital pile of papers I have in my Mendeley To-Be-Read folder, the fattest of them all. The papers therein wont be a comprehensive review of Comp.Chem. must-read papers but rather papers relevant to our lab’s research or curiosity.
Maybe I’ll include some papers brought to my attention by the group and they could do the review. The whole endeavor might flop in a few weeks but I want to give it a shot; we’ll see how it mutates and if it survives or not. So far I haven’t managed to review all papers read but maybe this post will prompt to do so if only to save some face. The domain of the new blog is compchemdigest.wordpress.com but I think it should have included the word MY at the beginning so as to convey the idea that it is only my own biased reading list. Anyway, if you’re interested share it and subscribe, those post will not be publicized.
This post was inspired by this other one, featured in WordPress’ Freshly Pressed section, on how should non-scientist read a scientific paper. While the approach presented therein is both valid and valuable, I’d like to address the way I think a scientist should read a paper, given the fact that we need to read a lot of them at all times. Each scientist has their own reading style, not to mention their own writing style, and while my CV could indicate I don’t know how to do neither one, here I present to you my scientific-paper-reading style which I consider to be the most suitable for me.
I’d like to start by emphasizing that I dive into scientific literature in a bona fide fashion. That is not to say I’m totally naive or even gullible, but even when science is all about questioning and casting doubt onto all sorts of claims, we can’t re-develop every bit of science we need. At a certain point we must start
*gasp* believing trusting other scientists’ claims. Reading in what I call bona fide is not mutually exclusive with critical reading. This sort of scientific trust is earned, to a degree, mostly by two indicators: Author’s preceding reputation at the time of publication of any given paper as well as the journal’s. Both indicators aren’t without controversy and flaw.
The way I read a paper is the following: I start with the Abstract, then follow with the Conclusions, then the Results section, sometimes I read the details of the methodology and seldom read the Introduction. Let me explain.
I read the abstract first because I read in bona fide as I hope the authors wrote the paper in bona fide. If properly written, the abstract should include all the relevant information as to what was done, why, and how but also point to the knowledge derived from it all: Their conclusions! and that is why I follow with that section. I’m interested in knowing what the authors learned and ultimately want me to learn about their study. Once again I’m reading in bona fide, so I hope they weren’t tempering their results to fit their preconceptions, that all experiments were thoroughly self-judged, validated, correlated, referenced and controlled. Recently, my sister Janet, who is a physicist working on her PhD in neuroscience, told me about some friends of hers who never (shall I say, never have I ever?) read the conclusions as to not becoming biased by the authors. To me it seems like too much work having to scrutinize every piece of data again in order to come up with my own conclusions when authors, collaborators, people on the hallway down the lab (optional), referees and editors (vide infra) have already (hopefully) done it (properly). Still I put on my scientist badge and question everything I critically read in the results section trying thus to understand how did the authors reached their conclusions and asking myself if I could come up with something entirely different. No? OK, how about something slightly different? Still no? Well, do I agree with the authors on their findings and their observed results? And so on. I like thinking that my critical reading process resembles the Self Consistent Field method which iteratively reaches the best wavefunction for a set of certain given conditions, but it never reaches the exact one.
The methodology section is a bit tricky, specially when it comes to computational chemistry. Back when I was a grad student, working in an inorganic chemistry lab, I’d only read the methodology if I had any plans of reproducing the experiment, other than that I didn’t care too much if reagents were purchased from Aldrich or Fluka or if the spectrophotometer was a Perkin Elmer one, I just expected authors to have purified their reagents prior to usage and calibrated all spectrophotometers. Now in computational chemistry I read about the methods employed, which functional and what basis set were used and why were they selected are my most frequent questions, but the level of theory is usually stated in the abstract. I also take a look at what methods were used to calculate which properties; these questions are important when we have to validate our trust in the results in front of us.
Finally, I seldom read the introduction because, if the paper is relevant to my own research, I don’t need to read why is important or interesting, I’m already sold on that premise! that is why I’m reading the paper in the first place! If both me and the author act in bona fide, we both already know what the state of the art is, so lets move on because I have a ton of other papers to read. Hence, I read the introduction only when I’m trying to immerse myself in a new field or when reading something that seems interesting but which has little to do with my area of expertise. There is another reason why I almost never read introductions and that is that, even when I try to work in bona fide, there are a lot of people out there who don’t. Twice have I received the reviews from a mysterious referee who believes it would serve the work a great deal to cite two, maybe three, other papers which he or she lists for your convenience, only to find out that they all belong to the same author in each case and that they are not quite entirely related to the manuscript.
In the title of this post I also try to address the writing of a scientific paper, although I’m not an authority on it, I think today’s key phrase is bona fide. So to young and not so young scientists out there I’d ask you to write in bona fide, please. Be concise. Be convincing. Be thorough and be critical. This is science we are doing, not stamp collecting. It shouldn’t be about getting all sorts of things out there, it is about expanding the knowledge of the human race one paper at a time. But we are humans; therefore we are flawed. More and more cases of scientific misconduct are found throughout the literature and nowadays, with the speed of blogging and tweeting, we can point at too many of them. The role of bloggers in pointing this frauds, of which I’ve written before here, is the subject of recent controversy and possibly the topic of a future post. We are all being scrutinized in our work but that shouldn’t be an excuse to make up data, tinker or temper with it, to push our own personal agendas or to gain prestige in an otherwise wild academic environment.
I for one may never publish in Science or Nature; I may never be selected for any important prize, but even the promise of achieving any of those is not worth the guilt trip of lying to an entire academic society. I try then, to always remember that science is not about getting the best answers, but about posing the right questions.
What is your own style for reading papers? Any criticism to my style? How different is the style of a grad student from that of a researcher?
As usual thanks for reading, rating and commenting!