Cyclodextrins (CDs), which are cyclic oligosaccharides consisting of six, seven or
eight glucopyranose units (a-, b- and g-CDs respectively), are versatile host molecules for ‘guests’ such as alkanethiols, forming what are known as ‘inclusion complexes’. Inclusion complexes of CD and alkanethiols in water have been selfassembled on gold thin films [68] as well as on gold nanoparticles [69]. We have
shown recently that gold nanoparticles may be capped with octadecanethiol (ODT)
molecules threaded with cyclodextrin and, furthermore, that during vigorous
shaking of a biphasic mixture of this hydrosol with chloroform, the gold nanoparticles were rapidly transferred to the organic phase [70]. The inset of Figure 3.6
shows the test tubes before (test tube to the left) and after (test tube to the right)
phase transfer of gold nanoparticles capped with inclusion complexes of ODT and
CD into chloroform. The process of phase transfer proceeds via detachment of the
CD molecules from the alkanethiol molecules capping the gold nanoparticles during stirring of the biphasic mixture. The gold nanoparticles become sufficiently
hydrophobic at this stage and are phase transferred into chloroform. The schematics accompanying the picture illustrate the changes occurring in the monolayer
of ODT on the surface of the gold nanoparticles during the shaking process leading
to hydrophobization of the gold nanoparticles [70].
Just as in the case of gold nanoparticles, appropriate choice of the capping agent
for modification of the surface of nanoparticles may be used to accomplish the
phase transfer of aqueous silver nanoparticles. Wang, Efrima and Regev have
shown that silver nanoparticles can be phase transferred from water to organic
solvents by binding the nanoparticles to sodium oleate present in cyclohexane/
Fig. 3.5. TEM micrograph of gold nanoparticles phase
transferred into toluene by complexation with ODA molecules
and self-assembled by solvent evaporation.
3 Moving Nanoparticles Around: Phase-Transfer Processes in Nanomaterials Synthesis
40
eight glucopyranose units (a-, b- and g-CDs respectively), are versatile host molecules for ‘guests’ such as alkanethiols, forming what are known as ‘inclusion complexes’. Inclusion complexes of CD and alkanethiols in water have been selfassembled on gold thin films [68] as well as on gold nanoparticles [69]. We have
shown recently that gold nanoparticles may be capped with octadecanethiol (ODT)
molecules threaded with cyclodextrin and, furthermore, that during vigorous
shaking of a biphasic mixture of this hydrosol with chloroform, the gold nanoparticles were rapidly transferred to the organic phase [70]. The inset of Figure 3.6
shows the test tubes before (test tube to the left) and after (test tube to the right)
phase transfer of gold nanoparticles capped with inclusion complexes of ODT and
CD into chloroform. The process of phase transfer proceeds via detachment of the
CD molecules from the alkanethiol molecules capping the gold nanoparticles during stirring of the biphasic mixture. The gold nanoparticles become sufficiently
hydrophobic at this stage and are phase transferred into chloroform. The schematics accompanying the picture illustrate the changes occurring in the monolayer
of ODT on the surface of the gold nanoparticles during the shaking process leading
to hydrophobization of the gold nanoparticles [70].
Just as in the case of gold nanoparticles, appropriate choice of the capping agent
for modification of the surface of nanoparticles may be used to accomplish the
phase transfer of aqueous silver nanoparticles. Wang, Efrima and Regev have
shown that silver nanoparticles can be phase transferred from water to organic
solvents by binding the nanoparticles to sodium oleate present in cyclohexane/
Fig. 3.5. TEM micrograph of gold nanoparticles phase
transferred into toluene by complexation with ODA molecules
and self-assembled by solvent evaporation.
3 Moving Nanoparticles Around: Phase-Transfer Processes in Nanomaterials Synthesis
40