Synthesis of oligo(lactose)-based thiols and their self-assembly onto gold surfaces

Abstract

Graphical abstract: HighlightsPlanar gold surfaces and gold nanoparticles are functionalized using oligosaccharide terminated alkanethiols. The properties of the SAMs are thoroughly characterized using infrared reflectionabsorption spectroscopy, contact angle goniometry and null-elllipsometry. The colloidal stability of the glyconanoparticles is monitored using UV-vis spectroscopy. AbstractThe ability to produce monomolecular coatings with well-defined structural and functional properties is of key importance in biosensing, drug delivery, and many recently developed applications of nanotechnology. Organic chemistry has proven to be a powerful tool to achieve this in many research areas. Herein, we present the synthesis of three oligo(lactosides) glycosylated in a (1→3) manner, and which are further functionalized with amide-linked short alkanethiol spacers. The oligosaccharides (di-, tetra-, and hexasaccharide) originate from the inexpensive and readily available lactose disaccharide. These thiolated derivatives were immobilized onto gold surfaces, and the thus formed self-assembled monolayers (SAMs) on planar gold were characterized by wettability, ellipsometry and infrared reflection-absorption spectroscopy. Further, the ability of these SAMs to stabilize gold nanoparticles in saline solutions was also demonstrated, indicating that the oligosaccharides may be used as stabilizing agents in gold nanoparticle-based assays.

Antifouling properties of oligo(lactose)-based self-assembled monolayers

“…The results overall were in good agreement with data presented in previous studies of Lac1-3 (Fyrner et al 2013), Mal-tri (Fyrner et al 2011) and of OEG-terminated SAMs (Valiokas et al 1999, Valiokas et al 2000. For the three SAMs Lac1-3, it is concluded from both the thicknesses and the IRAS data (showing that the amide carbonyl bonds are parallel to the surface), that the monolayers all formed with the hydrocarbon spacers in a near-upright conformation, and that the orientation of the sugar moieties were similar in all cases.…”

“…The latter peak overlaps with a smaller contribution from upright all-trans OEG at 1144 cm −1 , and integration of the deconvoluted band gives a ratio of 3:1 for the two peak areas. The results in Table 1 and the IRAS spectra are in good agreement with the results obtained in previous, detailed studies on these SAMs (Fyrner et al 2013, Fyrner et al 2011.…”

“…Figure 2b shows the fingerprint region of the SAM spectra. The saccharides have strongly suppressed Amide I bands (1650-1660 cm -1 ), indicating that the amide carbonyl is oriented parallel to the metal substrate (Fyrner et al 2013), and is thus invisible according to the surface selection rule. This is even more pronounced in mOEG, where complete removal of the Amide I band also is consistent with very weak N-H stretching (as discussed above), since both the amide carbonyl and the N-H stretch have similarly oriented transition dipole moments.…”

“…Three oligo(lactosides) glycosylated in a (1→3) manner and functionalized with amide-linked short alkanethiol spacers, forming di-, tetra-, and hexasaccharides with one (Lac1), two (Lac2), or three (Lac3) lactose units, were prepared and characterized as described in Fyrner et al (2013). The synthesis of the maltotrioside (Mal-tri) is described in Fyrner et al (2011).…”

“…Fibrinogen adsorption was low on the disordered SAMs, while settlement of zoospores of U. linza and barnacle cypris larvae was low overall. However, it was also demonstrated recently that large intermolecular interactions between relatively rigid saccharide moieties can instead improve the molecular order for longer oligosaccharides, as is the case in a series of oligo(lactose)-based thiol SAMs (Fyrner et al 2013). …”