Organic Preservation of Biopolymers in Fossil Leaves - Biopolymers: A Molecular Paleontology Approach - page 63

of the matrix may interfere with the signal from the sample (Landais et al. 1993 ).
EM shows that all leaves are covered with diatoms and the FTIR spectrum of fossil
Populus specimen 1 exhibits a strong silicate signal (Fig. 3.12b ). Hence, spectra for
amorphous silica (diatom) were obtained as a control (Fig. 3.12a ). Figure 3.12c
shows the micro-FTIR spectrum for fossil Castaneavesca specimen 1 which provides
much greater information and better resolution than for Populus , as analysis under
the microscope allows areas with mineral concentrations to be avoided. Table 3.2
provides a list of the absorption bands, their vibration modes and associated func-
tional groups identifi ed in the spectra. The aliphatic nature of the biopolymers is
expressed by strong absorption peaks between 2,800 and 3,000 cm −1 (those related
to both symmetric and asymmetric stretching vibrations: see Table 3.2 ) and peaks at
1,450 and 1,375 cm −1 (related to deformation vibrations). Absorption peaks maxi-
mising at 1,600 cm −1 indicate the presence of double bonds, and the shoulder around
1,700 cm −1 indicates the possible presence of C

O bonds hinting at the presence of
carbonyl and carboxyl functionalities. Hydroxyl groups are represented by a broad
band related to OH stretching vibrations at 3,100-3,700 cm −1 maximising at 3,400.
Micro-FTIR also allowed detection of ether bonds (those associated with aromatic,
saturated and vinyl linkages, in peaks between 1,020 and 1,280 cm −1 , Table 3.2 ) and
aromatic components (750-900 cm −1 , Table 3.2 ), signals that are that are swamped
in global analysis by silicate contamination.

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Saponifi cation

Extracted residues of leaves of Quercushispanica specimen 1 and Pinus were
hydrolysed under basic conditions in an attempt to remove ester-bound compo-
nents, in the same way that the modern counterparts were treated. However, after
saponifi cation, the released lipid extracts contained no aliphatic components
(Fig. 3.9c ), demonstrating that the aliphatic material is recalcitrant and that the acyl
moieties in the geomacromolecule are resistant to base hydrolysis. Consistent
with this, residues (residue 5, Fig. 3.1 ) after saponifi cation generated pyrolysates
containing fatty acids and pristenes, as also observed in the non-saponifi ed fossil
leaf pyrolysates (Fig. 3.9b ). In fact, the only difference between the pyrolysate of
the pre- (Fig. 3.9a ) and post saponifi ed (Fig. 3.9b ) leaf is the enhanced abundance of
fatty acids in the latter. This could be due to more effi cient pyrolysis in the absence
of diatom fossils that could have been dissolved during base hydrolysis.

Aliphatic Composition of Modern Plants

Previous work (Eglinton et al. 1962 ; Nip et al. 1986 ; Tegelaar et al. 1989a , b ) indicates
that the aliphatic component of leaves is represented by a range of free and macromo-
lecular moieties, characterized by a variety of functionalities. Long-chain n -alkyl