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WOOD CELL WALLS AND
NANOSTRUCTURES: CHALLANGE FOR
WOOD SCIENCE AND INDUSTRY
Janis Gravitis
Latvian State Insitute of Wood Chemistry
Riga, Latvia, e-mail: [email protected]
Friday 30th May 2008
From genes to cells. The case of lignin?
In lignin biosynthesis interpretation recently we can
recognize two contradictory and sometimes aggressive to
each other viewpoints:
•The first one is based on idea that lignin biosynthesis is the
same as proteins, polysaccharides, DNA/RNA formed by
condensations, thermodynamically driven by coupled
dephosphorylations of nucleotide triphosphates and catalyzed
by proteins giving strictly gene controlled chemical structure.
That interpretation emphasize role in regio- and
stereoselective monolignol radical-radical coupling is
catalyzed by the dirigent proteins (DiP) discovered some years
ago. (Norman G. Levis, Laurence B. Davin. 59th Appita
Annual Conference and Exhibition incorporating the 13th
ISWFPC, Vol.2, 2005).
•The second one interprets that at least lignin and suberin are formed
by oxidative coupling, where the monomers are oxidized into
resonance stabilized radicals, which couple by uncatalized radicalradical reactions. Such coupling are followed by nucleophilic
reactions on quinone methide intermediates. The DiPs are probably
not involved in the lignin biosynthesis, since they only produce
optically active products. Lignins are completely racemic polymers.
In a -ether 110-mer, there are actually only 218 optical centers, and
therefore 2117 physically distinct isomers – an astronomically large
number. This is lignin random assembly combinatorial biochemistry
approach. Natural lignin to be produced by slow end-wise type
polymerization. (John Ralf. 59th Appita Annual Conference and
Exhibition incorporating the 13th ISWFPC, Vol.2, 2005. Anders
Holmgren et al. 59th Appita Annual Conference and Exhibition
incorporating the 13th ISWFPC, Vol.3, 2005. ).
OH
HO
OH
Lignin
OCH3
Lignin-O
OCH3
O
OCH3
H3CO
O
O
HO
OH
HO
HO
OH
OH
O
A
O
O
OH
HO
HO
H3CO
H3CO
H3CO
OH
HO
OCH3
HO
OCH3
O
HO
OH
OCH3
OH
O
O
OCH3
HO
H3CO
OH
HO
OH
O
HO
OH
O
HO
OCH3
HO
O
O
HO
OCH3
OCH3
O
HO
HO
O
B
OCH3
CHO
OCH3
O
HO
OH
O
OH
OH
H3CO
O
B
OH
HO
OCH3
O
HO
O
O
OCH3
O
OCH3
O
OH
HO
HO
HO
OH
O
HO
OCH3
OCH3
A
HO
OCH3
H3CO
O
O
HO
O
OCH3
CH2OH (or CHO)
OCH3
OH
A structural scheme for softwood lignin showing branch points and
chain breakage and the -1 structure according to G. Brunov
Our task is to use new general concepts (De Gennes, Mandelbrot) in
lignin science (scaling, fractal geometry, universal classes, etc.) to
characterize global macromolecular lignin structure independently from
from biological or physical control. Comparing experimental scaling
indexes of lignins, humic substances, coals and high molecular weight
fossil oil compounds we could elucidate carbon materials genesis in
nature. Unique, real lignin structure in situ is biologically, spin-,
electron-density and stereo-chemically regulated and in this meaning
deterministic. However, impossible replication of identical copies of
existing structures in vivo or in vitro gives us a strong evidence of
statistically averaged lignins. In principle, future genetically based
manipulations can create structurally homogeneous and linear “lignin”
chains. Although such manipulation is attractive from, for instance,
paramount interest of industry, this artificial bifurcation consequences
and threats for living systems are not clear. No doubt that lignin is a selforganizing, ordered chaos structure in self-adopting plant cell wall
evolution.
S team E xplosion U nit
W ater
S am ple
R eactor
B oiler
0.5 L in volum e
B allV alve
R eceiver
10 L in volum e
Free and associated CEF (~4-10 nm) after SE treatment. TEM. Urve Kallavus,
Freeze fracture replicas of rosettes terminal complexes associated with cellulose
microfibril biogenesis. C. Haigler, unpublished data, adopted from D. Delmer
Hypothetical structure of the terminal proteins nano-machine for
cellulose synthesis according to D. Delmer
Fractal Dimension ( Df ) calculation from Scaling
Indexes of Hydrodynamic Properties
Intrinsic Viscosity:
[] ~ Ma  Df = 3 / ( a + 1 ) ,
Diffusion Coefficient:
D ~ M-b  Df = 1 / b ,
Sedimentation Constant:
S ~ Mc  Df = 1 / ( 1 - c ) ,
g’ factor:
g’ ~ Md  Df = 3 / ( d + 3/2 ) ,
where: M - mass parameter or parameter proportional to mass (degree
of polymerization), V. Ozols-Kalnins et al.
Df from g’ factor data of Dioxane Lignin (close
to Ξ conditions)
ln (degree of polymerization)
2,8
3
3,2
3,4
3,6
3,8
4
4,2
-0,3
ln (g')
-0,4
-0,5
d = -0.270+-0.002
-0,6
D f = 2.440+-0.007
-0,7
Based on data:Pla F., Yan J.F. J.Wood Chem., 1984, 4(3), 285.
Computer simulation of DL Agreagation of P-Cl (Vitten-Sander model)
•It was concluded: the Witten-Sander diffusion-limited particle-cluster
aggregation (DLA P-Cl) model approximated growing lignin fragments.
•DLA P-Cl is the universal model for the systems formed under the following
limiting conditions: the lignin C9 (~ 0.7 nm) monomer makes the Brownian motion
to approach a growing lignin fragment. The growing cluster is much larger than
the unit, and the probability of joining after the particle C9 and the growing
cluster contact is sufficiently high to add the particle to the exterior part of the
cluster without entering its interior part. Existing carbohydrates environment
creates diffusion barrier for monomer movement.
•The phenylpropane free radical generated from C9 random recombination in vivo
and in vitro satisfies such DLA P-CL limiting conditions. The model allows the
cycles inside the branches, and growing proceeds in non-equilibrium conditions.
•The DLA P-Cl model describes adequately the lignin structure in wall layer S2 for
the degree of a polymerization range of  20 – 100 (~14-70 nm) with the scaling
indexes: fractal dimension  2.5, spectral dimension, which characterizes the
relaxation process in the system, is  1.2 - 1.4 and minimal dimension which
characterizes the connection of the C9 monomers is one.
Lignin in wood S2 layer is a
network of weakly connected
polydisperse DLA fractals. For a
lignin clusters with a scale less as
20, a compact structure with Df =
3 seems to be more possible. This
model concerns the inter-cell wall
layer ML.
Recently (Ulla Vainio et al.), lignin
fractal dimension is measured using
small- (SAXS) and ultra small(USAXS) X-ray scattering. SAXS is
performed at the X-ray laboratory of
the University of Helsinki and USAX
by using synchrotron facilities in
Hamburg and Grenoble. The length
scale for SAXS is 0.4 – 20nm.
Measurements show that the SAXS intensities obey a power law at small
values of q, where q is the length of the scattering vector, at room
temperature. The SAXS intensities were corrected for absorption and air
scattering, and the wide-angle x-ray scattering (WAXS) background was
subtracted. A mass fractal with mass fractal dimension Dm can be shown
to give a scattering law of the form I  q-, where  is Dm (mass) and a
surface fractal of surface fractal dimension Ds obeys also a power law
with  = 6 - Ds. For a mass fractal Ds = Dm and for a surface fractal Dm
is always 3. For compact particle with a sharp phase boundary Dm = 3,
Ds = 2 and  = 4. Porous solids with continuous charge density transition
have  > 4. However, measurements concern solid sedimented lignins.
So, there is second aggregation of primary nano-particles. For instance,
usually we can recognize secondary lignin aggregation spherical particles
on the cell wall after steam explosion autohydrolysis (SEA) treatment.
Model of wood cell wall composite
Network of Lignin Clusters Diffusion Limited Aggregates with
Df=2.5
(J. Gravitis, A. Kokorevics & V. Ozols-Kalnins)
Terachima honey-comb arrangement model with beads-like lignin
modules, 2005
Secondary aggregates of the primary lignin nano-clusters on wood cell
wall after SE treatment. TEM. Urve Kallavus & Janis Gravitis
Conclusions
•The hierarchical cell wall polymers bio-composite structure recently is studied
from the viewpoint of nano-materials and nano-technologies.
•In current study the steam explosion autohydrolysis (SEA) have been used as a
method for exposing main polymer components biodegradable nano-particles.
•TEM, SEM, solid-state 13C CP/MAS NMR proton spin-lattice relaxation time T1H
measurements, SAXS, USAXS gave strong evidence that the cell walls during SEA
treatment segregates in the nano-domains, where primary nano-particles are
cellulose nano-fibrils and lignin fractal type nano-clusters. The latter studies are
disturbed by secondary aggregation of primary structures.
•Studies of natural nano-cell walls structure and dynamics open diverse
opportunities for learning natural nano-composites and natural nano-technologies.
The nano-machine – cellulose rosettes type enzyme complex role in cellulose nanofibrils synthesis is futuristic challange for development.
Applied aspects of wood industry nanotechnology
•The multidisciplinary nature of nanotechnology makes the exploitation of new
technologies and ideas from other clusters escpecially important.
•The nanotechnologies reduced consumption of materials, emissions and facilitate
decrease of impact to environment. Nano-approach increase the quality of life.
•Opportunities for nanotechnologies in celluse industry and composite materials
containing cellulose and/or lignin.
•Opportunities for nanotechnologies in paper industry and other industries closely
related to papermaking – such as printing and packaging.
•Opportunities for nanotechnologies in wood protection.
•Commercial development is still hindered by a “chicken-and-egg”scenarious where are
no applications of the new nano-materials and as a consequance is lack of production
capacity to allow applications development.
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