The three-dimensional structure of humic substances and soil ...

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Table 2. Aromatic compounds characteristic for soil organic matter (see Table 1) [1]
CH=CH 2
H3C0 OCH 3
(78) v\CH3 0H
1118) 1134)
(154)
O%C--H ~J_C~N CH3
H 3 OH
(94) ~ CN2-CH3 (CH2)4-CH3
(104)
CH3 Y "0CH3
H3 OH CH=CH-CHa
OCH 3
1120) 0CH 3
(106) CH 3
CH3_C=CH 2
H 3 CH2-CH3 (CH3)2 OCH 3
1106) OH 1164)
(144) OC--CH 3
0CH3 1146) OCH3
(106) OH OH
~OH ~CH3 (124) ~--~CH2)3-CH 3 ~(164)
1108) (130) 1148) 1166)
CH3 CH 3 - CH=CH2 ~3
OH OH
(116) y "OCH 3
(134) OH
ed as a first draft 2D structure [3]. It had the elemental
composition of C308H328090N 5 with a molecular mass of
5 540.027 g tool -1 and an elemental analysis of 66.8% C,
6.0% H, 26.0°70 O, 1.3% N. Compared to isolated stan-
dard HAs with about 56.3070 C and 32.8% O, this pro-
posed HA structure is obviously too high in carbon and
too low in oxygen. However, carbohydrates have been re-
ported to account for about 10% of the HA weight and
a similar value has been suggested for proteinaceous ma-
terials in HA [3]. Thus, it has been assumed that one HA
molecule traps within its voids approximately 10% carbo-
hydrates and 10% proteinaceous materials. The resulting
HA complex has then an elemental composition of
C342H3880124N12 with a molecular mass of 6650.912g
mo1-1 and an elemental analysis of 61.8% C, 5.9% H,
_CH3 (CHe)s-CH3
(152) 1176)
29.8% O, 2.5% N. If more carbohydrates and/or pro-
teinaceous materials are added, the C content decreases
and the O content increases.
Thus, for a stereochemical understanding of the
structure of humic substances and their reactions with
biological and anthropogenic compounds three main,
urgent questions emerged:
1. What is a fast, reliable and versatile method to convert
the 2D structure into a 3D structure?
2. Is it possible to optimize the geometry of the chemical
3 D structure and to determine and minimize its en-
ergy?
3. How can chemical reactions of such complex biomac-