Brassicasterol
Encyclopedia
Brassicasterol is a 28-carbon
sterol
synthesised by several unicellular algae
(phytoplankton
) and some terrestrial plants, e.g., oilseed rape. This compound has frequently been used as a biomarker for the presence of (marine) algal matter in the environment
.
and, as a consequence, a high octanol – water partition coefficient
(Kow = ??). This means that, in most environmental systems, brassicasterol will be associated with the solid phase.
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).
has a hydroxyl
(-OH) group, it is frequently bound to other lipids including glycerol
s; 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.
through campesterol
as an intermediate. A list of the algae in which brassicasterol has been identified is shown below together with approximate composition.
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 in a similar manner, 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.
biomarkers (e.g., other sterols, fatty acid
s, 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.
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
sterol
Sterol
Sterols, also known as steroid alcohols, are a subgroup of the steroids and an important class of organic molecules. They occur naturally in plants, animals, and fungi, with the most familiar type of animal sterol being cholesterol...
synthesised by several unicellular algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
(phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
) and some terrestrial plants, e.g., oilseed rape. This compound has frequently been used as a biomarker for the presence of (marine) algal matter in the environment
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
.
Solubility
Brassicasterol has a low water solubilitySolubility
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...
and, as a consequence, a high octanol – water partition coefficient
Partition coefficient
In chemistry and the pharmaceutical sciences, a partition- or distribution coefficient is the ratio of concentrations of a compound in the two phases of a mixture of two immiscible solvents at equilibrium. The terms "gas/liquid partition coefficient" and "air/water partition coefficient" are...
(Kow = ??). This means that, in most environmental systems, brassicasterol will be associated with the solid phase.
Degradation
In anaerobicHypoxia (environmental)
Hypoxia, or oxygen depletion, is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system...
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 moleculeMolecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
has a hydroxyl
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
(-OH) group, it is frequently bound to other lipids including glycerol
Glycerol
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...
s; most analytical methods, therefore, utilise a strong alkali
Alkali
In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...
(KOH or NaOH) to saponify the ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
linkages. Typical extraction solvents include 6% KOH in methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
. The free sterols are then separated from the polar lipids by partitioning into a less polar solvent (e.g, hexane
Hexane
Hexane is a hydrocarbon with the chemical formula C6H14; that is, an alkane with six carbon atoms.The term may refer to any of four other structural isomers with that formula, or to a mixture of them. In the IUPAC nomenclature, however, hexane is the unbranched isomer ; the other four structures...
). Prior to analysis, the hydroxyl group is frequently derivatised with BSTFA
BSTFA
N,O-Bistrifluoroacetamide is a chemical compound which is used to derivitise labile groups such as hydroxyl on other chemicals, with the more stable trimethylsilyl group, which protects the labile group and allows the compound to be used for analytical purposes or as a chemical reagent for...
(bis-trimethyl silyl trifluoroacetamide) to replace the hydrogen with the less exchangeable trimethylsilyl
Trimethylsilyl
A trimethylsilyl group is a functional group in organic chemistry. This group consists of three methyl groups bonded to a silicon atom [−Si3], which is in turn bonded to the rest of a molecule...
(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
Mass spectrum
A mass spectrum is an intensity vs. m/z plot representing a chemical analysis. Hence, the mass spectrum of a sample is a pattern representing the distribution of ions by mass in a sample. It is a histogram usually acquired using an instrument called a mass spectrometer...
for the TMS ether of brassicasterol can be seen in the Figure.
Algal sources
Brassicasterol is formed in plants from the isoprenoid squaleneSqualene
Squalene is a natural organic compound originally obtained for commercial purposes primarily from shark liver oil, though plant sources are used as well, including amaranth seed, rice bran, wheat germ, and olives. All plants and animals produce squalene, including humans...
through campesterol
Campesterol
Campesterol is a phytosterol whose chemical structure similar to that of cholesterol. Many vegetables, fruits, nuts and seeds contain campesterol, but in low concentrations. Banana, pomegranate, pepper, coffee, grapefruit, cucumber, onion, oat, potato and lemon grass are few examples of common...
as an intermediate. A list of the algae in which brassicasterol has been identified is shown below together with approximate composition.
| 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 Gymnodinium Gymnodinium is a genus of dinoflagellates. It is one of the few naked dinoflagellates, or species lacking armor . Since 2000, the species which had been considered to be part of Gymnodinium have been divided into several genera, based on the nature of the apical groove and the biochemistry... 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 = cholesterolCholesterolCholesterol is a complex isoprenoid. Specifically, it is a waxy steroid of fat that is produced in the liver or intestines. It is used to produce hormones and cell membranes and is transported in the blood plasma of all mammals. It is an essential structural component of mammalian cell membranes...
- B = campesterolCampesterolCampesterol is a phytosterol whose chemical structure similar to that of cholesterol. Many vegetables, fruits, nuts and seeds contain campesterol, but in low concentrations. Banana, pomegranate, pepper, coffee, grapefruit, cucumber, onion, oat, potato and lemon grass are few examples of common...
- C = sitosterol
- D = 22-dehydrocholesterol ((22E)-cholesta-5,22-dien-3β-ol)
- E = BRASSICASTEROL
- F = stigmasterolStigmasterolStigmasterol is one of a group of plant sterols, or phytosterols, that include beta-sitosterol, campesterol, ergosterol , brassicasterol, delta-7-stigmasterol and delta-7-avenasterol, that are chemically similar to animal cholesterol...
- G = 24-methylene cholesterol
- H = fucosterol
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
Loch Striven
Loch Striven is a sea loch adjoining the west side of the Firth of Clyde just north of the Isle of Bute, where it forms a narrow inlet about 8 miles long extending north into the Cowal peninsula. During times of recession in shipping the loch has been used as a sheltered anchorage for laid...
, Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
. Highest values may be seen in the top sections of the sediment, which decrease with depth. However, the cholesterol behaves in a similar manner, 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 lipidLipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
biomarkers (e.g., other sterols, fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s, 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
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
.
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.