the glass surface. Fluorescent dye release kinetics and fluorescence imaging studies
confirmed the immobilization and stability of the liposomes over the solid surface.
The bioavailability of the sugar head groups in liposomal microarrays has been
ascertained by specific interaction studies with fluorescently labeled lectins from
Cholera toxin B (CTB), Maackia amurensis agglutinin (MAA), and peanut lectin
from Arachis hypogea (PNA lectin). Control studies with PSA lectin (which does
not have any specificity for 105 and 106) confirmed the specificities of the
interactions at the liposomal surface.
9 Micelles
Micelles are monolayer aggregates of lipids with hydrophobic and hydrophilic
groups. For every lipid, there is a certain concentration known as critical micelle
concentration (CMC), above which lipids cannot be soluble as individual molecules
and are forced to form micelles in aqueous medium to decrease the aqueous contact
with hydrophobic groups. In aqueous medium, the hydrophobic groups are located
at the core of the micelles, whereas the hydrophilic groups will be in contact with
the water at the surface of the micelles. Due to their hydrophobic core, micelles can
solubilize hydrophobic molecules and can act as carriers for applications in drug
delivery. Self-aggregates of amphiphilic glycolipids have been used in a variety of
biomedical applications [106]. Mignet and coworkers designed perfluoroalkylated
glycolipids (108–110, Fig. 19) for imaging studies [107]. The perfluoroalkyl groups
were chosen as the lipid portion due to their low miscibility with natural
phospholipids as compared with “hydrocarbons”, which minimizes the toxicity of
the amphiphilic perfluoro-glycolipids [108]. Glycolipids have been functionalized
with chelating agents such as DTPA (diethylenetriaminepentaacetic acid), which
was used for complexation to fluorescent or radiolabel markers for biological
studies. In aqueous medium, glycolipids form self-aggregates with 10–50 nm
diameters. In agglutination studies with the galactoside-binding RCA lectin, the
glycolipid micelles formed large aggregates that could be quantified by absorbance
at 490 nm, thus confirming the formation of multivalent complexes. In competitive
inhibition studies, a decrease in the absorbance of the aggregates with the addition
of lactose was evidence for the specificity of the interactions. In vivo scintigraphy
imaging studies in mice showed that, at pH 6, glycolipid micelles complexed with
radiolabeled
99m Tc accumulated mostly in the liver. Further, fluorescence studies
showed that micelles complexed with europium interacted very poorly with blood
serum proteins. The poor reactivity with the complex blood serum proteins and
organ-specific accumulation of micelles dictated by the sugar head groups of the
perfluoro-glycolipids can be used for specific drug delivery applications.
Fort and coworkers studied the aggregation and protein binding properties of
amphiphilic rod–coil type of glycoconjugates (111 and 112, Fig. 19) synthesized
using click chemistry between suitably functionalized precursors [109]. The glycanfunctionalized amphiphiles were self-assembled in aqueous medium and their size
and morphologies were dictated by the amphiphilic balance (volume fraction of
Applications of Glyconanoparticles as “Sweet” Glycobiological. . .
327
confirmed the immobilization and stability of the liposomes over the solid surface.
The bioavailability of the sugar head groups in liposomal microarrays has been
ascertained by specific interaction studies with fluorescently labeled lectins from
Cholera toxin B (CTB), Maackia amurensis agglutinin (MAA), and peanut lectin
from Arachis hypogea (PNA lectin). Control studies with PSA lectin (which does
not have any specificity for 105 and 106) confirmed the specificities of the
interactions at the liposomal surface.
9 Micelles
Micelles are monolayer aggregates of lipids with hydrophobic and hydrophilic
groups. For every lipid, there is a certain concentration known as critical micelle
concentration (CMC), above which lipids cannot be soluble as individual molecules
and are forced to form micelles in aqueous medium to decrease the aqueous contact
with hydrophobic groups. In aqueous medium, the hydrophobic groups are located
at the core of the micelles, whereas the hydrophilic groups will be in contact with
the water at the surface of the micelles. Due to their hydrophobic core, micelles can
solubilize hydrophobic molecules and can act as carriers for applications in drug
delivery. Self-aggregates of amphiphilic glycolipids have been used in a variety of
biomedical applications [106]. Mignet and coworkers designed perfluoroalkylated
glycolipids (108–110, Fig. 19) for imaging studies [107]. The perfluoroalkyl groups
were chosen as the lipid portion due to their low miscibility with natural
phospholipids as compared with “hydrocarbons”, which minimizes the toxicity of
the amphiphilic perfluoro-glycolipids [108]. Glycolipids have been functionalized
with chelating agents such as DTPA (diethylenetriaminepentaacetic acid), which
was used for complexation to fluorescent or radiolabel markers for biological
studies. In aqueous medium, glycolipids form self-aggregates with 10–50 nm
diameters. In agglutination studies with the galactoside-binding RCA lectin, the
glycolipid micelles formed large aggregates that could be quantified by absorbance
at 490 nm, thus confirming the formation of multivalent complexes. In competitive
inhibition studies, a decrease in the absorbance of the aggregates with the addition
of lactose was evidence for the specificity of the interactions. In vivo scintigraphy
imaging studies in mice showed that, at pH 6, glycolipid micelles complexed with
radiolabeled
99m Tc accumulated mostly in the liver. Further, fluorescence studies
showed that micelles complexed with europium interacted very poorly with blood
serum proteins. The poor reactivity with the complex blood serum proteins and
organ-specific accumulation of micelles dictated by the sugar head groups of the
perfluoro-glycolipids can be used for specific drug delivery applications.
Fort and coworkers studied the aggregation and protein binding properties of
amphiphilic rod–coil type of glycoconjugates (111 and 112, Fig. 19) synthesized
using click chemistry between suitably functionalized precursors [109]. The glycanfunctionalized amphiphiles were self-assembled in aqueous medium and their size
and morphologies were dictated by the amphiphilic balance (volume fraction of
Applications of Glyconanoparticles as “Sweet” Glycobiological. . .
327