Organic Preservation of Biopolymers in Fossil Leaves - Biopolymers: A Molecular Paleontology Approach - page 65

Table 3.2 Absorption bands, their vibration modes and associated functional groups identifi ed in
the FTIR spectra of fossil leaves and associated diatomite (Fig. 3.12 ) from the Ardèche locality
Position (cm −1 ) Group Type of vibration

3,700-3,100 O — H

−3,400 OH Stretching ν

3,000-2,800 C — H Aliphatic

−2,925 as + sCH 2 + CH 3 Stretching ν

−2,850 sCH 2 + CH 3 Stretching ν

1,710-1,705 C ═ O (carboxyls and carbonyl)

1,600 and 1,495 C ═ C (double bond)

1,450 CH 2 + CH 3 (aliphatic) Deformation δ

1,375 CH 3 (aliphatic) Deformation δ

900-750 C — H aromatic

−875 1 H adjacents γ

−830 2 H adjacents γ

−750 4 H adjacents γ

1,200-1,040 C — O — C (saturated ethers) Stretching ν

1,280-1,200 as ═ C — O — C (Vinyl ethers) Stretching ν

1,075-1,020 s ═ C — O — C (aromatic ethers) Stretching ν

1,095, 798 Mineral band, SiO 2

s-symmetric
as-asymmetric

compounds are major components of epicuticular waxes (Eglinton et al. 1962 ; Eglinton
and Hamilton 1967 ) and include n -alkanes, n -alkanols, n -alkanoic acids and wax
esters. The n -alkanols and n -alkanoic acids typically occur in higher plants as C 16 -C 36
homologues with a strong predominance of even-carbon-number homologues over
odd-numbered ones, refl ecting their biosynthesis from acetyl moieties (Kolattukudy
1981 ). n -Alkanes occur with carbon chain-lengths ranging from C 25 to C 35
(Kolattukudy 1981 ; Eglinton et al. 1962 ; Eglinton and Hamilton 1967 ) and with an
odd-over-even predominance (the most common being C 27 , C 29, C 31 and C 33 ), refl ecting
formation via decarboxylation of carboxylic acids.
In addition to free n- alkyl components, a variety of macromolecular components
including cutin, suberin and cutan has been described. Of these, cutin appears to be
almost ubiquitous and comprises C 16 and C 18 n -alkanoic acids and mono, di and
trihydroxy derivatives of these, cross-linked via ester bonds (Kolattukudy 1980 ).
Nip et al. ( 1986 ) fi rst described cutan, a highly aliphatic biopolymer comprised
of relatively high-molecular-weight n -alkyl components immune to hydrolysis,
in Agave americana . Subsequently, Tegelaar et al. ( 1991 ) reported the presence
of cutan co-occurring with cutin in the leaves of 14 plant species and, in the case of
Beta vulgaris (ssp. maritima ), occurring alone. As comparable fossil leaves showed
an aliphatic composition, it was concluded that selective preservation of cutan is
responsible for the aliphatic composition of the fossils and has a biasing infl uence
on the fossil record. However, the modern leaves investigated in this study were not
subjected to hydrolysis to check rigorously for the presence of cutan.