Everything about Brassicasterol totally explained
| Section2 =
2846
| MolarMass = 398.67 g/mol
| Appearance = white solid
| Density = ? g/ml, solid at room temperature
| Solubility = ? mg/l
| MeltingPt = 150-151°C
| BoilingPt =
}}
| Section7 =
| Section8 =
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Brassicasterol (24-methyl cholest-5,22-dien-3β-ol) is a 28
carbon sterol synthesised by several
unicellular algae (
phytoplankton) and some terrestrial plants
for example oilseed rape. This compound has frequently been used as a
biomarker for the presence of (marine) algal matter in the
environment.
Chemical Properties
Solubility
Brassicasterol has a low water
solubility and consequently a high
octanol – water partition coefficient (Kow = ??). This means that in most environmental systems, brassicasterol will be associated with the solid phase.
Degradation
In
anaerobic sediments and soils, brassicasterol is stable for many hundreds of years enabling it to be used as an indicator of past algal production (see below).
Chemical Analysis
Since the
molecule has a
hydroxyl (-OH) group, it's frequently bound to other
lipids including
glycerols; most analytical methods, therefore, utilise a strong
alkali (KOH or NaOH) to
saponify the
ester linkages. Typical extraction
solvents include 6% KOH in
methanol. The free
sterols are then separated from the
polar lipids by partitioning into a less polar solvent (
e.g.
hexane). Prior to analysis, the hydroxyl group is frequently derivatised with
BSTFA (bis-trimethyl silyl trifluoroacetamide) to replace the hydrogen with the less exchangeable trimethylsilyl (TMS) group. Instrumental analysis is frequently conducted on
Gas Chromatograph (GC) with either a
Flame Ionisation Detector (FID) or
Mass Spectrometer (MS). The
mass spectrum for the TMS ether of brassicasterol can be seen in the Figure.
Formation and Occurrence
Algal Sources
Brassicasterol is formed in plants from the
isoprenoid squalene through
campesterol as an intermediate. A list of the algae in which brassicasterol has been identified is shown below together with approximate composition (Data from an excellent review by Volkman, 1986).
dinoflagellates (as percentage). Data from Volkman, 1986>
| Species |
A |
B |
C |
D |
E |
F |
G |
H |
others |
| Gonyaulax spp |
100 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
| Peridinium foliaceum |
100 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
| Peridinium foliaceum |
80 |
20 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
| Gonyaulax diegensis |
39 |
0 |
0 |
0 |
0 |
0 |
0 |
29 |
32 |
| Pyrocystis lunula |
76 |
6 |
0 |
2 |
1 |
0 |
0 |
0 |
15 |
| Gonyaulax polygramma |
36 |
1 |
0 |
9 |
7 |
0 |
0 |
0 |
47 |
| Gymnodinium wilczeki |
26 |
39 |
0 |
35 |
1 |
0 |
0 |
0 |
0 |
| Glenodinium hallii |
8 |
50 |
0 |
0 |
0 |
42 |
0 |
0 |
0 |
| Noctiluca milaris |
0 |
1 |
1 |
5 |
73 |
0 |
6 |
0 |
14 |
| Gymnodinium simplex |
0 |
0 |
0 |
0 |
53 |
0 |
0 |
0 |
47 |
| Prorocentrum cordatum |
7 |
0 |
0 |
0 |
5 |
0 |
63 |
0 |
25 |
» A =
cholesterol
B =
campesterol » C =
sitosterol
D = 22-dehydrocholesterol ((22
E)-cholesta-5,22-dien-3β-ol)
» E = BRASSICASTEROL
F =
stigmasterol » G = 24-methylene cholesterol
H =
fucosterol
Other Sources
?
Use as a Tracer for Marine Algae
The principal source of brassicasterol in the environment is from marine algae. Its relatively high concentration and stability allows it to be used in the assessment of the origin of organic matter in samples, especially sediments.
Brassicasterol / Cholesterol Ratio
The concentration of brassicasterol in a core sample from
Loch Striven,
Scotland. Highest values may be seen in the top sections of the sediment which decrease with depth. However, the cholesterol behaves similarly and the ratio brassicasterol / cholesterol is fairly uniform at all depths indicating either a comparable degradation rate with no change in source or different degradation rates and a change in source.
Multivariate Analysis
Multivariate Statistical Analyses such as
Principal Component Analysis of a range of
lipid biomarkers (
for example other sterols,
fatty acids and
fatty alcohols) enable identification of compounds that have similar origins or behaviour. An example can be seen in the loadings plot for sediment samples from the
Mawddach Estuary,
Wales.
The location of brassicasterol in this figure (shown in red) indicates that the distribution of this compound is similar to that of the short chain fatty acids and alcohols which are known to be of marine origin. The terrestrially derived biomarkers such as β-sitosterol are on the opposite side of the figure and are mutually exclusive.
Further Information
Get more info on 'Brassicasterol'.
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