Structural Variations of Lignin Macromolecules from Early Growth Stages of Poplar Cell Walls.
The paper I'll discuss in this post is this one: Structural Variations of Lignin Macromolecules from Early Growth Stages of Poplar Cell Walls (Sun et al, ACS Sustainable Chem. Eng. 2020, 8, 4, 1813-1822)
When I moved into my house about 24 years ago, there was a small tree in the front yard that was growing out of a hedge, a little taller than I am - I'm a short fat white bald guy. Despite being a member of a problematic demographic, I rather like trees, and didn't cut the thing down, even though it was growing in the middle of a hedge. I'd estimate that it is now about 10 or 15 meters tall, at the base more than half a meter in diameter. It's survived several major droughts, a few hurricanes, the sucker just grows and grows and grows.
It's tulip poplar, a very fast growing tree, quite remarkable.
In recent years, I've become very interested in the chemistry of wood, which is composed of three biopolymers, one quite regular, cellulose, one somewhat irregular, hemicellulose, and the other a remarkably irregular polymer, or co-polymer, lignin.
(Disclaimer: About 20 years ago, I briefly worked for a company that manufactured, albeit not in the department in which I worked, lignosulfonates, which are used as binders in concrete. They are a side product of the wood pulp industry - the paper industry - and when used in concrete, they represent sequestered carbon - carbon sequestered from the air. I actually didn't like that job, and didn't stay at it very long, but at the time, I was less interested in climate change than I am now. At the time I had no interest in lignin, which is sad, because the chemistry of lignin turns out to be quite fascinating. I wish I'd paid more attention.)
The structure of lignins is evoked by the cartoon introducing the paper:
I enjoyed the paper because of the wonderful analytical and biochemistry in it, and whether or not anyone cares, I thought I'd write about it to fix it in my mind. A fast growing tree, albeit one which is rather water hungry, might well prove to be an important tool for future generations to clean up the planetary atmosphere that we've been so enthusiastically wrecking for them in our sybaritic exercise in self indulgent ecstasy.
From the paper's introduction:
...With regard to the structural features of lignin, the relative abundance of interunit linkages and chemical composition differs among plant cell types, tissues, species, and growth stages. Besides the common units (H, G, and S), hydroxycinnamic acids (p-coumarate and ferulate) and tricin were found to be attached to wheat lignin.(11) Furthermore, the visualization of the plant cell wall is capable of providing important insights into the lignin distribution and accumulation in the plant cell wall.(12) Raman microscopy is an ideal technique for in situ visualizing the lignin distribution in plant cell walls...
...Poplar is a deciduous tree that has been naturalized in different areas of the China especially in northern China, which is a desirable lignocellulosic feedstock for pulping and papermaking as well as biorefinery industries due to several attractive features, including short growth period, high production yield, and wide adaptability. Poplar biomass constituents vary in abundances among the different species,(23) and characteristics the of these chemical constituents are closely associated with the biofuel conversion of poplar.(24) Although structural characteristics of lignin from poplar during different pretreatments have been studied, structural variations and evolution of the lignin macromolecule during different growth stages were rarely investigated. In the present study, the poplar (Populus tomentosa) woods with three different growth stages (3, 6, and 18 months) were selected to reveal structural variations of lignin macromolecules, and elucidate microscopic distribution and dynamic accumulation of lignin in different poplar cell walls. Herein, DEL samples were isolated from different poplar woods; 2D-HSQC NMR, 31P NMR, gel permeation chromatography (GPC), and pyrolysis GC/MS techniques were applied to delineate its structural characteristics during the early growth stages. In addition, confocal Raman microscopy (CRM) was adopted to monitor the dynamic and microcosmic distributions of lignin macromolecules in plant cell walls. Furthermore, CP/MAS 13C NMR spectroscopy was also performed to characterize the structural features of different poplar woods.
There is a nice description in this introduction, of separations of lignin from cellulose, both industrially and for analytical purposes. There's this nice little intriguing note:
I'm curious about that; after I'm done here I'll check out reference 19, which is surely in my files, and hopefully remember to pick up references 18 and 20.
Anyway, the authors did some cool analytical chemistry to get at the structures of lignins in different growth stages of poplar, as described in the final excerpt of the introduction above.
Some generalized composition of the wood at different points of the growth is shown in this table:
The following figure shows the Raman image of the lignins at different growth stages.
The caption:
The next figure shows spectra (with structural cartoons) that utilizes a type of two dimensional NMR known as HSQC (Heteronuclear Single Quantum Coherence) spectroscopy, which utilizes magnetic coupling between protons (which have a strong magnetic moment) to rare isotopes of either nitrogen (15N) or carbon (13C) which are also magnetically active. In the present case, 13C, was the coupled nuclei.
The figure:
The caption:
A DEL is a "double enzyme lignin" which results from separation of the wood by repeating an enzymatic isolation step twice.
The make up of the lignins was elucidated by derivatizing the free phenol hydroxyl functional groups with a standard phosphorylating agent, 2-Chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane, and running 31P NMR.
Other figures show other HSQC experiments.
The most interesting figure is that showing structures of the lignins at various growth points.
The caption:
A technique known as pyrolytic GC was utilized to thermally decompose, in the absence of oxygen, the lignin into monomeric species.
The following table shows some of the compounds obtained from this process:
Of particular interest are the "G" type phenolics.
4-vinylguiacol is commonly found in many flavored foods and is partially responsible for the taste of some wines, beers, cloves and other foods. It is a precursor to synthetic vanillin, as is the 4-methylguiacol. Interestingly, vanillin can be converted in a few chemical steps, demethylation, acetalization with formaldehyde and a few other steps to the illegal street drug MDA, known as "ecstasy."
Of the S type, one, syringaldehyde can be converted in three chemical steps to the illegal street drug mescaline.
I don't know how or why I know these things, but somehow I do. (There was a time in my life, too long ago, when I couldn't look at the structure of simple molecules without thinking how they might be synthesized. Life is very beautiful, and then you die.)
Trivia in a trivializing time, the self destruction of the United States by the installation of a criminal in its leadership.
Anyway. In a time in which we regret the wooden heads of our pResident and his minions of cowardly co-conspiratorial Senators, there is, great wonder it turns out, in wood, despite this.
Have a nice day tomorrow.
= new reply since forum marked as read
NNadir
Nice to see you around.
I liked your contribution to the post, the actual article ... WAY over my head.
Also ... since there's one topic in here I know about ... MDA is not ecstasy. That's MDMA. MDA is different (albeit only slightly). I've had both
