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OH
O
O
H
HO
N
N
O
N
N
O
OH
O
N
O
N
N
N
O
O
OH
O
Fig. 15 Structure of a GNL glycolipid.
OH
OH
OH
O
OH
H
2
N
O
HO
HO
OH
OH
OH
TriCat
O
O
P
HO
OH
OH
OH
O
OH
H
2
N
O
HO
HO
OH
OH
FluoCat
O
N
NO
2
O
N
N
O
Fig. 16 Chemical structures of TriCat and FluoCat used in catanionic vesicles.
diameter. A study using confocal laser scanning microscopy and flow
cytometry showed the high ability of these glycosylated catanionic ves-
icles to be internalized into phagocytic and non-phagocytic cells, human
cell lines or primary cells, through endocytosis and/or fusion processes.
42
Encapsulation of both hydrophilic and hydrophobic substances into the
cationic vesicles was eciently achieved, thus demonstrating their po-
tential use as simple and cheap drug nanocarriers.
41
The membrane core lipids of some extremophilic Archaea, that rep-
resent one of the three main domains of life, are composed of saturated
isoprenoid chains attached to glycerol by ether linkages with a sn-2
stereochemistry opposite to that of conventional mesophilic lipids. Of
particular interest are the unusual bipolar lipids present in thermo-
acidophilic, methanogenic and some psychrophilic species. These lipids
consist of tetraether 72-membered macrocycles formed by two biphytanyl
chains ether linked at both ends to a glycerol unit or a polyhydroxylated
cyclopentanic calditol group.
5,6
Tetraether bipolar lipids are thought to
span the membrane to form monolayers and allow the microorganisms
to maintain membrane integrity in harsh environments. These bipolar
membrane-spanning lipids can give rise to highly stable liposomes with
advantageous properties such as: (i) mechanical stability due to the
monolayer organization; (ii) chemical and enzymatic stability resulting
from the complete saturation of the chains and the presence of ether
bonds; (iii) thermal stability which allows heat sterilization of liposomes
without dramatic loss of the encapsulated substance; (iv) stability in air
and light (absence of yellowing); (v) low permeability to molecules and
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