Chemistry
Rhamnolipid Chemical Formulae
Rhamnolipids are class of glycolipid. They are constructed of rhamnose sugar combined with beta-hydroxy fatty acids. Rhamnose is a sugar. Fatty acids are ubiquitous in animals and plants. The carboxyl end of the fatty acid end is connected to the rhamnose. Rhamnolipids are compounds of only 3 common elements; carbon, hydrogen, and oxygen.
Chemical Composition
There are two major groups of rhamnolipids; mono-rhamnolipids and di-rhamnolipids.
Mono-rhamnolipids have a single rhamnose sugar ring.
The basic formula (which is most often produced by P. aeruginosa) is:
L-rhamnosyl-beta-hydroxydecanoyl-beta-hydroxydecanoate
(often referred to as Rha-C10-C10) with a formula of C26H48O9
The IUPAC Name is
3-[3-[(2R,3R,4R,5R,6S)-3,4,5-trihydroxy-6-methyloxan-2-yl]oxydecanoyloxy]decanoic
acid
Di-rhamnolipids have two rhamnose sugar rings.
The basic formula is:
L-rhamnosyl-L-rhamnosyl-beta-hydroxydecanoyl-beta-hydroxydecanoate
(often referred to as Rha-Rha-C10-C10) with a formula of
C32H58O13
The IUPAC Name is: 3-[3-[4,5-dihydroxy-6-methyl-3-(3,4,5-trihydroxy-6-methyloxan-2-yl)oxyoxan-2-yl]oxydecanoyloxy]decanoic
acid
Some other forms or names for the more common
di-rhamnolipids include:
L-rhamnopyranosyl-L-rhamnopyranosyl-beta-hydroxydecanoyl-beta-hydroxydecanoate
(often referred to as Rha-Rha-C10-C10)
L-rhamnopyranosyl-L-rhamnopyranosyl-beta-hydroxydecanoyl-beta-hydroxydodecanoate
(often referred to as Rha-Rha-C10-C12)
L-rhamnopyranosyl-L-rhamnopyranosyl-beta-hydroxytetradecanoyl-beta-hydroxytetradecanoate
(often referred to as Rha-Rha-C14-C14)
Other more specific naming conventions for rhamnolipids
include:
Decanoic acid,
3-[[6-deoxy-2-O-(6-deoxy-alpha-L-mannopyranosyl)-alpha-L-mannopyranosyl]oxy]-,
1-(carboxymethyl)octyl ester,
1-(carboxymethyl)octyl 3-[(6-deoxy-alpha-L-mannopyranosyl)oxy]decanoate,
3-[3′-(
-rhamnopyranosyloxy)decanoyloxy]decanoic acid
3-[3′-(2″-O-α- -rhamnopyranosyl-α- -rhamnopyranosyloxy)decanoyloxy]decanoic acid
To simplify these pages and avoid browser character set issues we will not use those naming conventions.
Rhamnolipids have been found with combinations of the
following fatty acids:
Hydroxyoctanoyl = C8
Hydroxydecanoyl = C10 Hydroxydecanate = C10
Hydroxydodecanoyl = C12 Hydroxydodecanate = C12
Hydroxytetradecanoyl = C14 Hydroxytetradecanate = C14
A compound where the total carbon count is the same, but the C10-C12 is switched to C12-C10 is called a structural isomer, meaning that the formula is the same for both molecules, but the bonds or links are connected differently.
In various papers instead of mono-rhamnolipid as Rha-, it may be abbreviated as Rh or RL2. Similarly, instead of Rha-Rha- designating a di-rhamnolipid, Rh-Rh- or RL1 is used. For historical reasons “rhamnolipid 2” is a mono-rhamnolipid and “rhamnolipid 1” is a di-rhamnolipid. This actually leads to some ambiguity in the usage or “RL1” and “RL2” in the literature.
In various studies the following rhamnolipids have been detected as produced by the following bacteria: (C12:1, C14:1 indicate fatty acyl chains with double bonds.)
Rhamnolipids produced by P. aeruginosa (mono-rhamnolipids):
Rha-C8-C10, Rha-C10-C8,
Rha-C10-C10, Rha-C10-C12, Rha-C10-C12:1,
Rha-C12-C10, Rha-C12:1-C10
Rhamnolipids produced by P. aeruginosa (di-rhamnolipids):
Rha-Rha-C8-C10, Rha-Rha-C8-C12:1,
Rha-Rha-C10-C8, Rha-Rha-C10-C10,
Rha-Rha-C10-C12:1, Rha-Rha-C10-C12,
Rha-Rha-C12-C10, Rha-Rha-C12:1-C12,
Rha-Rha-C10-C14:1
Rhamnolipids produced by P. aeruginosa (unidentified as either mono- or di-rhamnolipids):
C8-C8, C8-C10, C10-C8,
C8-C12:1, C12:1-C8, C10-C10,
C12-C10, C12:1-C10, C12-C12,
C12:1-C12, C14-C10, C14:1-C10,
C14-C14.
Rhamnolipids produced by P. chlororaphis (mono-rhamnolipids only):
Rha-C10-C8, Rha-C10-C10,
Rha-C12-C10, Rha-C12:1-C10, Rha-C12-C12,
Rha-C12:1-C12, Rha-C14-C10, Rha-C14:1-C10
Rhamnolipids produced by Burkholdera pseudomallei (di-rhamnolipids only):
Rha-Rha-C14-C14
Rhamnolipids produced by Burkholdera (Pseudomonas) plantarii (di-rhamnolipids only):
Rha-Rha-C14-C14