Interpnictogen Cations DOI: 10.1002/anie.201307658

Interpnictogen Cations: Exploring New Vistas in
Coordination Chemistry
Alasdair P. M. Robertson, Paul A. Gray, and Neil Burford*

Okay, pnictogens! Now, this is something I'll be able to understand actually. Still, I can remember a time, long long ago when I didn't really know what a pnictogen was. Yes, now to take us back to that time, when I got sent by my supervisor during my undergrad days, to the library, to look up some compound that I can't remember right now in chemical abstracts, and to figure out a way of making it. Now I may be dating myself here, but chemical abstracts still existed at the time. And after I did go to the library, I seriously thought about quitting chemistry. When you enter the rows with the abstracts there is an undescribable smell of old paper and boredom, and after half an hour of leafing through them your brain starts turning off and you begin to fall asleep, prevented from passing out by the rigid metal shelves and the stone floor of the library. Still, you find a chair and spend an hour sleeping. It was after that one hour of sleeping that I opened a random chemistry journal on another shelf, anything to get away from the sleep demon that is the chemical abstracts.

The article that I opened talked about pnictogens. It looked really crazy with phosphorous making some crazy structures when chlorophospines or alkylchlorophosphines were reacted together with something and water was present in small amounts. There was no way I could make any sense of the reactions, and now in retrospect, I'm guessing the authors couldn't either, but the products looked pretty cool. I couldn't really figure out what a pnictogen was, but I noticed that they talked about it with regards to nitrogens and phosphorous, so I guessed it was a group V element. It's not like we had Wikipedia back then. Later I asked somebody, and they said, 'yes, it is a group V element'. Then I probably forgot and learned that factoid again. Well that's it. Probably not that interesting of a story actually.

Now for something more interesting! A review about pnictogen-pnictogen bonds, where inevitably you end up with a cation when you go to the more heavy ones. The process of making them involves taking a halopnictogen RPnCl and reacting it with another pnictogen that has a free lone pair and can substitute the chloride. Because the chloride (or Br or I) is actually a pretty good Lewis Base itself, sometimes you need to activate it a bit with AlCl3, so you end up in the end with an AlCl4 counterion that leaves your resulting molecule stable. You can also do anion substitution in situ to get a PF6 in there and let the NaCl salt fall out of solution. That's it. Pretty simple, but it can get complicated as your products can dimerize to give you a cyclic product, a linear Pn-Pn-Pn-Pn compound (Figure 8) or something crazy like a sandwich in Figure 23.
The chemistry, after you look at a few mechanisms at the beginning, is easy to follow for the more simple examples, but complicated reactions that create a tetraphosphine cation that coordinates to As for example, are not so easy to predict.

I did get lost in the writing quite a bit, but I think it's because of my bad pnictogen experience back in undergrad. My eyes glaze over whenever I see that word, and all the proper name endings associated with various anions or cations of arsenic or antimony. But chemistry is a visual science and it has become much more visual with chemdraw. The authors do an excellent job with figures so that you can read almost the entire review by just looking at the pictures, which happen to be on the same page as the text about them, which is also very helpful. Of course since I was reading on a smartphone small-screen, this advantage proved to be moot. I did enjoy reading this review because I understood most of it right away and I think the figures played a very big part in that, but also when the product was predictable, the simple rules for making the products at the beginning helped me to figure out the mechanism after looking at a figure for a few seconds. If you're looking for a quick and fun review to read to make yourself smarter (but it probably won't actually, as I doubt more than 1% remains in my head a week after I slog through them), read this one.

Obviously a lot of it is basic science research. There is a big part of it where it's really unpredictable with bismuth (which has a much higher coordination number so you get 'surprised' a lot) and if you introduce water, oxygen, or even a bit too much AlCl3. It makes sense since as the authors say at the beginning the energy of a Pn-Pn bond is much less than that of many other bonds. And if one of them serves as a Lewis base for another, well water can serve as a pretty good Lewis base. Or oxygen...

All (okay, let's say 'most' since I don't know for sure) these compounds are very sensitive to moisture and air. Also halogen substituted amine starting materials are very hard to work with, plus a lot of the heavy pnictogens are toxic and especially their compounds, with a notable exception being bismuth for some reason. I did a few experiments with making air sensitive phosphines and inevitably, my lab would always have some few specialized pieces of equipment missing. You're supposed to have a Schlenk line, but also some specialty glassware to filter under nitrogen, distill under nitrogen, etc...  it's always a few more extra steps than common organic chemistry. But this is still some basic science that makes interesting stuff and needs to be done. Some of it can't be predicted so well. The review focuses on saying whether a bond is ionic or covalent by looking at bond lengths and comparing them to the sum of the covalent radii and making comments to the effect that the bond is short because such and such substitution makes one of the pnictogens a better Lewis base. I always found that as filler since you just get an interesting product, but you now need to describe it in detail. I don't really care much for the bond lengths and I won't remember them tomorrow, but I will remember the crazy bismuth compound with an antimony donor.

The authors end the review with: "We anticipate that the fundamental development of coordination chemistry between the pnictogens, and the p-block elements in general, will lead to the discovery of new materials and catalysts to rival those developed from the chemistry of carbon and transition metals."

This is not true. There is not even a single planet in the universe that doesn't have lots of oxygen in some sort of pnictogen devouring form probably. It's fun basic chemistry that maybe someone will use in a practical process in a reactor some years from now. But rival the chemistry of carbon and transition metals? No...

One last not to someone who wants a quick JACS Angewandte article, is to take a look at Figure 1 in the beginning and more importantly (since many of those in Figure 1 will remain imaginary forever) at Table 2 at the end. If you can make any of those that have not been made yet, make sure to submit them to the aforementioned journal first. Don't worry... I won't be your competition, but the Burford lab at UVic might be. Good luck.

Insung S. Choi Date of birth: January 9, 1969 Professor of Chemistry and of Bio and Brain Engineering KAIST

DOI: 10.1002/anie.201310974

I thought about doing a post about that microfluidics minireview, but that would require me reading it in detail. And I'm already getting ready for next week's review. Eventually as I'll get better at this, maybe I'll have time to comment on the second review that comes out with each issue as well. And maybe even on some of the more inane two page 'comments' written by some famous professor. But until then, more of these fun posts that make me relax after reading an intense review.

Right, let's see here. Piece of equipment the person would like to be is 'stopwatch'. Okay, moving on we have a safe-bet pick of a famous French expressionist as favorite painter... Well, to tell the truth I actually like this one. You don't get any useful information really out of these profiles, and I thought the answer about following your curiosity in science as great. Not enough people do this these days. Especially with tight funding and universities wanting you to bring in money. Writing a sci-fi novel is also what I wanted to do if I ever became unemployed... but after looking into it seriously for a bit, I decided the competition was a bit too stiff and I'm better off reading Angewandte reviews.

The best answer of course, is as to what he sees himself doing in the future. Raising rabbits. That might seem like a whimsical answer, but it actually reveals that Insung Choi has thought deeply about the future and the coming apocalypse, where the few human survivors are forced to survive in a cruel, radioactive world. That, coupled with a story I saw on TV about a giant rabbit breed from Russia being grown for meat to be shipped to Asia, makes me think that being a giant rabbit farmer is a useful post-apocalyptic occupation. Another one is being an giant rabbit farm guard to stop the raiders, but you need some serious firearms training for that. I mean, have you seen some of these things!? They are freakin' huge. Lots of meat.

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

Saxitoxin: Arun P. Thottumkara, William H. Parsons, and J. Du Bois

DOI: 10.1002/anie.201308235

I have to admit, I really wanted to read the minireview instead on microfluidic chemistry... Okay, maybe I will read it anyways since it's ten pages, and I'm still alive after getting through that Saxitoxin review. Which is more than can be said for anyone ingesting 1 mg of the stuff.

Admittedly, the review starts off kind of easy with a good historical background on this toxin and some color pictures of poisonous living things and structures of some other related toxins. But, since I read the abstract and I'm somewhat familiar with what the group from which this review came from does (and it's not my field, once again), I was ready for slogging through total synthesis schemes which, while I might see how you got from point A to point B with this reagent, I have no idea of the mechanism really, since it's been a while since my Advanced Orgo grad course and the hardest things I had to make didn't have as many nitrogens in it as saxitoxin. Which reminds me, that thing has a lot of nitrogens. Together with the four oxygens, it has 11 heteroatoms, more than the 9 carbons. Still, it'll kill you dead with only 1 mg, and that is because of the two guanidinium residues, that makes it a dication actually. That quality makes it really good for blocking the ion transport channels, and mainly the sodium transport channels in mammalian, and especially primate, cells. That means the review will have lots of other things such as talking about the structure of the Na transport proteins and how exactly its function is blocked, plus the synthesis of saxitoxin analogues that will attack a specific Na transport protein, something that will only block the ones responsible for pain but not the ones that keep your heart muscles moving for example. Humans have a lot of these different type of membrane proteins and some of these analogues can be pretty selective for just one of them (a several hundred fold difference in activity, which ideally means 1 mg could stop pain, but you would need 200 mg to end it all).

Still, to get to all of that, you do have to get through the total synthesis part, which if you're not a total synthesis person, or a pharma researcher working on saxitoxin analogues, will be probably painful. Still, this blog is part of my self-challenge to make it through one review a week, reading the whole thing faithfully (up to a point), so, here's hoping there will only a bit of total synthesis since I actually enjoy reading through one or two of them once in a while.

First comes the biosynthesis, but beyond looking at one change and another, and seeing arginine turn into ornithine, I didn't really get much from it. The authors weren't probably too inspired by that 1 page section either. Maybe drawing out the structure of ornithine would have been better. I'm not going to look it up when I have a ton of total synthesis to still go through. Speaking of that total synthesis, I have to say that I did enjoy reading through the first two. I was wondering how easy it was to separate all the intermediate products on the column, since they are highly polar and have a ton of nitrogens probably. The first one by Kishi in 1977 answered that question by introducing the guanidium units as late as possible. I guess after you have preparative HPLC, it gets a bit easier, but back in 1977 there was a shortage of that instrument in academic labs. The second synthesis by Jacobi in 1984 has a very inspired transformation which you can see in Figure 10, where a ring expansion occurs through an NN cleavage of a hydrozide. Technically the word 'inspired' came from the review authors, but I thought that was a very neat transformation as well. Plus this transformation of compound 12 to 11 occurs with Na in NH3... always a reaction I wanted to try someday.

After this, the total synthesis got more modern and more involved, with all them fancy reagents. I couldn't really follow it so well beyond where the authors guided me through some mechanism that resulted in particular distereoselectivity. Especially the DuBois total synthesis started cheating on me, by talking about analogues, and I was getting stuck for so long on each scheme, my eyes started to glaze over at some point and I just power-read through it. Which means I probably didn't retain much.

Anyways, no reason to make my review of a review longer than necessary. On page 13 we once again come to the biochemistry part. Saxitoxin and friends are apparently used to figure out binding sites to these proteins. Since these are membrane proteins, they are very difficult to crystallize and there is not structure of them as of yet. Probably the structure highly depends on the membrane environment anyways. Everyone is really certain that these toxins target the channel through which the cations pass, and not some other part of the protein (that is responsible for sensing Na+ levels or receiving some other substrate that opens the channel), but they are probably right since I don't know anything. Plus the guanidiniums are cations like Na+ and people made models of them sticking in the channels (where they presume that that is the structure of the channel), so let's just go with it. Maybe the positive charge of saxitoxin sticking in there repels Na+ electrostatically, since from the picture it doesn't seem that they are blocking the entire thing so well.

What's really interesting, is that just one amino acid mutation, but often a couple, can have a dramatic effect on mortality, and it explains that while all living things and especially multicellular organisms (nerve communication) need to transport sodium in order to live, the from and the mollusk seem to be fine while humans die from a very small amount. It effects them too of course, as at a big enough concentrations even other forms of the Na transport proteins get blocked up, but they can deal up to a point.

The review then talks about computational attempts to guess the structure of the sodium channel part of the protein by sticking residues that they think make up that channel around the toxin structure that binds the best, but who knows if that is going to be even close to the real thing, once a crystal structure is available. While I was reading this of course, I thought of using saxitoxin for probing how many channels a cell has by attaching some sort of fluorescent probe. Well, the people working in the field thought of that long before I did at the end of reading the review. All these total synthesis introduced a route where you can modify a part right at the end and attach a fluorescent probe, then send it to the cell and gunk up all its channels and watch them move for a bit until the cell dies I guess. This is how they found that these channels move around a bit and are swallowed up by endocytosis once in a while. Still, maybe they were swallowed up because a cell decided it was gummed up by a toxin and needed replacing...

Interesting. I have to admit that I actually enjoyed reading through the last part, even if I don't understand much about the particulars of biochemistry and don't really know my amino acids by heart.

Okay, that's long enough. If you read this far, you should probably read the review of Saxitoxin by the DuBois group. Maybe I will read that microfluidics micro-review.

Rene Peters Date of birth: August 26, 1971 Position: Professor, Institut fuer Organische Chemie, Universitae t Stuttgart

Well, it was either do a post on one of these foolish author profiles, or read the other review in this issue, which was an Janus structures, but I decided I needed some desperate brushing up on organic chem instead.

Let's see here... well, this author is Western since in his picture he is not wearing a tie and looking official and determined like the Angewandte profiles of the Chinese scientists. Also, obsessed with wolves and dogs that are similar enough to wolves (his husky). I can't really share anything there since a wolf is just some pack mammal that spends most of its life cold and hungry and being beat up by the Alpha, unless it is the Alpha and then it has to suffer constant psychological stress of keeping the others who want its job at bay. Nothing against pack animals. Humans are also pack animals, but at least we figured out a way to have a constant food supply and to hear our homes reliably. At least this time around they didn't ask him what piece of equipment he would be, although I suppose what car would you like to be is also not much of an inspiring question.

Still, this profile is a bit better than the Kim one from last week since you do get some very small insights into the person. I find the music and literature questions to be the most useful. However, since I don't know how music is tied to anything, I leave that stuff for others, especially when answers are Ozzy Osbourne and Concert Pianist, though I did have an image of a scene from 'This is Spinal Tap' after that one. The books are a great one since 'War and Peace' and 'Perfume' are highly philosophical works, where the first one describes people trying to find personal meaning in events that are greater than them and that sweep them along, and the second one is basically a parable from the early 20th century history and the relationship of society to a genius personality, despite it taking place in 17th century France. After all, Grenouille was a genius in creating perfumes and despite his personal inadequacies and repulsion felt towards him, all his mistakes and crimes are forgiven when people smell one of his inventions. So, Haber is forgiven for creating poison gas for use during wartime because he invented the ammonia synthesis process and was a chemistry genius, and this could explain how Germans were so enamored with a certain personality in the 1930s who was a political genius and turned the country's economy and pride in itself around, with many reasonable people ignoring the less palatable parts of his policy.

Well, I still don't know anything about Rene Peters really, except that he likes to read good literature and reading. And by the way, you should Read 'War and Peace' and 'Perfume' as well. Certainly beats setting up another experiment after a 10 hour workday. You're probably tired anyways and you will forget to add something and it will fail anyways. Might as well read 30 pages of 'War and Peace'.

Donor-Acceptor Cyclopropanes

Now this one is not my area of expertise... but it's closer than carbon-fibers, though due to my last job that could be a little debatable. The background for the review is laid out very nicely in simple terms in the introduction, namely that a cyclopropane has a lot of ring strain, and reactions that open up the ring or expand it are thermodynamically favored. Nonetheless, it's quite a stable motif and in general it's hard to to get a simple cyclopropane to react. However, when one carbon is substituted by an electron accepting group, and another one by an electron donating one, then you can draw convincing zwitterionic resonance structures with the ring being open, and now, it's a lot easier to get things to insert inside like a double bond, a keteone, a nucleophile, or an electophile. The possibilities are many and after a very nice introduction, the review quickly delves into the details one well organized topic after another, based on the substrate. It's the donor-acceptor motif that makes cyclopropanes such a powerful precursor for making large ring structures. The use of chiral ligands for a catalyst that can further activate the acceptor gives access to enantioselective transformations and you can obtain something that looks like a complicated natural product from something that looks like a deceptively simple cyclopropane.

It did remind me of my undergraduate organic classes, about how you could certainly memorize the reactions, or you could try and push the electrons around since all of organic chemistry is basically about adding an acid to a base. For the latter two substrates mentioned above, the nucleophile will attack the more positive site on the resonance structure of the donor-acceptor cyclopropane, and hydride transfer will occur to the more negative site to complete the reaction. Even though the products can get pretty complicated, and you often need a pen and some paper to scetch out the right product, it's pretty easy to figure out the mechanism and what is happening. It can get pretty complicated to follow in your head once you get one catalyst activated cyclopropane opening up and inserting into another one, and even though the review does give some intermediates (and in the case of that reaction it is essential to draw one intermediate), you really have to draw it out yourself on paper to see how to get from the starting materials to the product based on which partially negatively charged carbon attacks the partially positive charged carbon on the other cyclopropane.

So, going through the review was a bit hard at first, but eventually it all started to click in my head and I was following electron movement and even the most complicated transformation became easy to follow. That why, despite the awesomeness of the review, Section 3.3. and Scheme 14 is the part that stands out where I got stumped. This is on cycloadditons of alkenes to a cyclopropane to make a five membered ring. There a tin catalyst is used and if the aryl substituting one of the cyclopropyl carbons is electron donating, you get one regioselectivity, but if it's not you get another. I really got stuck on this for a while, because the scheme was suggesting that electronics are a factor, but the aryl is always the electron donating group no matter what the substituent, compared to the acceptor that has two CO2Me groups... surely it is sterics which should be the driving force for the product here? And the scheme doesn't mention the subustituents on the alkene and I was too lazy to look up the original papers... Anyways, I decided that since you get the other product at -30 degrees, then that's where sterics predominate, but it doesn't help that in that case the aryl can't be too donating as well, since you lower reactivity of the cyclopropane. The moment you increase it a bit, you only get the other isomer (even at -30 I assume?). Well eventually, I decided to move on, since thinking about it too much would lead me to look up the original paper and I did mention that I was lazy above. I suppose that my reading through of giant reviews on topics that are not related to mine is not laziness then. Maybe masochism of some sort? Doesn't feel exactly like that though...

Anyways, cycloaddition of nitrones and allenes got me back in the mood, and I found Scheme 15 to be particularly elegant (right below that Scheme 14 that stumped me for a bit). You get a really cool and complicated bicyclic structure of just a plain old cyclopropane with an intermolecular allene addition based on the conditions. The ring enlargement section 4, and especially 4.3, shows how you can get something that really looks like a natural product from a cyclopropane in Scheme 24. It's all really impressive actually, and as the authors mention, a lot of the results are really recent as the field is undergoing a Renaissance. Plus, there are still not many results about making six and seven membered rings (even though there was a section about 3+3 cycloaddition). However, one minor quibble which is very much evident in that last Scheme 24 that I spoke just so glowing about at the start of this paragraph, is that cyclopropanes like compound 115, which lead to complicated products such as 120, are themselves sort of complicated. I'm not disputing that the reactions are very elegant and you can get complex products with lots of stereocenters under mild conditions through the judicial use of catalysts, but, you know. 115 looks really hard to make on its own. Plus a lot of these really complex transformations need an acceptor, which in most of the cases is two CO2Me groups. How are you going to get rid of these methyl ester groups if you don't want them in your final product?

Maybe new ways of making cyclopropanes from metal carbines will become a really hot field in the future and my point will be moot. Or maybe I don't know enough about organic chemistry and it really is not a problem to have all these strange acceptors hanging off of your final product. Whatever the case, I have really enjoyed reading this review and it definitely revived some atrophied part of my organic electron pushing brain mass. Kudos to the authors, a recently tenured German professor and two of his students. I will definitely not be dissuaded to look at paper after I see an abstract with some cyclopropane, a few lines, and some crazy looking complex product, in the future. After all, it's only a simple Donor-Acceptor cyclopropane reaction.

"A New Golden Age for Donor–Acceptor Cyclopropanes
Tobias F. Schneider, Johannes Kaschel, and Daniel B. Werz"

DOI: 10.1002/anie.201309886

Dongho Kim
Date of birth: November 1, 1957
Position: Professor, Department of Chemistry, Yonsei University

After that really long review on carbon fibers, that still invades my dreams (well, I hope not, but my waking thoughts from time to time anyways), I need a break post and that's provided by the 'biography' of Dongho Kim from the same issue. Now, Angewandte biographies are all professional and you don't really learn anything about the person, like what it was like to study chemistry during the time of dictatorship in South Korea and the threat from the north that was credible at the time. Sometimes you get something interesting in regards to how the person chose to go into chemistry and later become a professor, but most of the time not really, and that's the case here as well. I'm pretty aware of the dissonance between useless anecdotes in a general Angewandte biography and a person's real-life experiences from the coverage of my post-doc advisor.

Nothing too interesting here, and the answer to 'what you would like to be if you were a piece of equipment' really nails the lack of useful anecdotal information here. If someone ever asks me that, I will tell them "I would like to be a $*^#ing futuristic android. So that I can do everything I do now but better and I will never die, and you would be afraid of me."

Anyways, Monet and Beethoven might be the staple of any Western oriented education for the upwardly mobile... but what's really interesting is the 'going hiking in a spare hour'. Really? I hike a lot and a one hour hike is not a real hike. And there is no way you're going to be drinking a beer after a long desert or mountain hike that took most of the day. It will destroy you.

It doesn't sound like a hike... but like a pleasant stroll. Still, this made me look up Yonsei University in Seoul on Google Earth, and it does have a pretty large forest park next to it and the pictures from it are pretty nice. So, I'm willing to believe that professor Kim goes there in a spare hour, but it's still a stroll. Not a hike.

DOI: 10.1002/anie.201311143

Carbon Fibers: Precursor Systems, Processing, Structure, and Properties

1. Dr.  Erik Frank, 
2. Dipl.-Chem. Lisa M. Steudle, 
3. Dr. Denis Ingildeev, 
4. Dipl.-Chem. Johanna M. Spörl and
5. Prof. Michael R. Buchmeiser^*  

Angewandte Chemie International Edition
Volume 53, Issue 21, pages 5262–5298, May 19, 2014

This topic is completely outside of my area of expertise. I bet I'm going to be starting many a post with this sentence on this blog, so it seems like something appropriate to start this blog with. But yes, carbon fibers. The picture that first popped into my head was a string of something made out of stretchy carbon, like a polyethylene bag, but spun into some sort of fibers to make a sweater. The first sentence of the review mentions that these are things that are 92% at least made of carbon and later it's mentioned that they can be incorporated into textiles, so I was on the right track, if not completely wrong in the end anyways.

1. 
   
2. I made a point of not checking the Wikipedia entry on 'carbon fibers' until after finishing the review. But maybe I should have since it complements the article very well, especially in terms of polyacrylonitrile (PAN) that is used for making most of carbon fibers today.

So carbon fibers. Basically you take an ordered material, such as PAN, or some sort of tar pitch that is sort of polymeric, or even cellulose, and as I learned at the end even polyethylene. Now you have to spin this material into fibers with a big spooling machine, and the way this is done, with solvents, with additives, or without all that, and depending on the shape of the vessel and the speed of the spinning, will give you fibers that hopefully won't fuze together at the end. Afterwards this material is heated until heteroatoms are lost and you're mostly left with carbon. Then the temperature is increased to as much as a couple thousand degrees Celsius in order to turn the stuff into a material that is mostly graphite, but is sort of bent and has some hole features. That turns out to be key in fibers having these high tensile strengths. They end up being used in composite materials with plastics and make them much, much stronger.  

The review is very detailed and goes into the steps that are needed to turn PAN into a cyclyzed and dehydrogenated polymer that is ready for carbonizing… but then you have to oxidize it or the carbonization process won't take place properly. The oxygen leaves with some hydrogens and also helps HCN to leave (getting rid of that pesky nitrogen part and getting the carbon content high). Sounds like an enormous industrial undertaking, and it was, as you start realizing as you go through this 30 page review.
PAN precursors very were successful, but people are always interested in using renewable sources (such as pitch from coal… okay maybe not that section) such as cellulose. It turns out that cellulose needs to be spun very orderly before carbonizing to have a chance and it still doesn't compete so well with PAN (has anyone tried chitosan?). Lignin sounded like a better plan to me by the time I got to that section, since lignin has less heteroatoms to start with and seems to me to be better set up for carbonization than cellulose which really loses a lot of weight as CO due to the high oxygen content. However, lignin gave really bad results and was a big disappointment in terms of the section as well. It sounded like reminiscing by the primary PI with no pictures and anecdotes with paragraphs that took up half a page or more. This section almost killed me with its writing style and practical failures. That is, until I made it past it and got to the PE section where the results seem to be a bit better. Plus PE allows to make carbon fibers with weird shapes…

One thing I forgot to mention is that obviously carbonizing this stuff in an oxygen atmosphere is not done too often since your carbon will burn and fly away as carbon monoxide or dioxide, and the atmosphere affects the graphitization of the fibers. The last section is actually pretty fun and it talks about the structure of the final stuff with some pretty hypothetical schematics of what they look like. Plus, I realized that Raman spectroscopy is a good way to determine the level of carbonization and that it's possible to take an X-Ray of a carbon fiber… but solid state NMR with magic angle spinning still sounds (and looks from the date in the review) more reasonable.
I don't have any wish to make my summary of this 30 page review to get to record proportions, especially since this is my very first post. So… in the end, if you don't know much about carbon fibers, you're probably better off with reading Wikipedia. You will definitely learn more from reading the review and it will definitely be more memorable. But, you know… 32 pages. They really went overboard in some places, and especially in that lignin section. Still, I bet it's a useful summary for the many excellent scientists in industry, and some in academia I guess, who are working in this very important area that I am ashamed to say I was ignorant of before.

I do not check the biographies of the authors before finishing the review. That way lies madness, and by madness I mean time-wastage. Afterwards, I checked and it's a PI with two students, and two people who work at a specialty institute for carbon fibers. They are Germans, which sounds about right as this is one of those countries (along with the States and Japan like I learned from the review) that are capable of funding these huge research efforts into these products that have very clear industrial applications but require a lot of development.