Thiocarbohydrates on Gold Nanoparticles: Strong Influence of Stereocenters on Binding Affinity and Interparticle Forces

Abstract

Carbohydrates carrying thiol groups at the C-2 position have been attached to gold nanoparticles (AuNPs) with stereocenters in close proximity to the surface for the first time. Their configurations can be clearly distinguished by the tendency of particle aggregation. AuNP surface plasmon resonance (SPR), X-ray photoelectron spectroscopy (XPS), and IR spectroscopy indicate that the thiocarbohydrates replace citrate molecules at different rates, causing aggregation and eventually precipitation. A quantitative formulation of this aggregation process shows that reactivities can vary by several magnitudes. Adsorption isotherms and kinetics also demonstrate that the number of thiocarbohydrates varies by a factor of two. Molecular mechanics force field (MMFF) calculations reveal their relative orientations. Based on these models, the different binding behavior can be ascribed to attractive van der Waals forces and hydrogen bonds. Such interactions occur either between the carbohydrate and AuNPs, by lateral intermolecular forces at the surface, or by interparticle attraction, in analogy to cell-surface carbohydrates of biological recognition systems. Aggregation of NPs therefore act as an indicator to differentiate between various carbohydrates with defined configurations.

Nanoscale image of the drug/metal mono-layer interaction: Tapping AFM-IR investigations

“…Here, the significantly pronounced bands at 1,515 and at 1,436, 1,427, 1,410 cm −1 due to the ρw(OCH3) and ρw(CH2)CH 3 modes, respectively, together with the recorded changes in the band features (ΔFWHM = ~ 6 cm −1 and Δν = ~ 6 cm −1 ), suggest that in the erlotinib/AuNP mono-layer interaction, -OCH3 groups are strongly involved. There is some evidence indicating that the close proximity of the methoxy moiety to the AuNPs may result in charge transfer from the electropositive -OCH3 group to the metal [58]. It is known that molecules chemisorbed on metal surfaces exhibit large enhancements and changes in the band intensities [11].…”

Addition of Heteroatom Radicals to endo-Glycals †

“…The yields of the 2-deoxy-2-sulfur analogues 36 are moderate to good, but stereoisomers have to be separated. The thiocyanate groups can be cleaved to the corresponding thiols, which can bind to concanavalin A [66] or gold nanoparticles [67].…”

“…The yields of the 2-deoxy-2-sulfur analogues 36 are moderate to good, but stereoisomers have to be separated. The thiocyanate groups can be cleaved to the corresponding thiols, which can bind to concanavalin A [66] or gold nanoparticles [67]. In all reactions described above (Schemes 13-16), the C-S bond is formed selectively at the 2-position of the carbohydrates, due to the enol structure of the glycals.…”

Ligand‐Controlled Stereoselective Synthesis and Biological Activity of 2‐Exomethylene Pseudo‐glycoconjugates: Discovery of Mincle‐Selective Ligands

“…Thus, changing the functionality at C2 position is a promising strategy for altering the function of native glycans, as exemplified by the fact that pseudo-glycans including 2-fluorosugars, act as mechanism-based inhibitors, [9,10] or exhibit superior biological activities, [11] or are useful for structural analysis. [12] Isolation or synthesis of other analogues with different functionality at C2 [13][14][15][16] has also been reported. However, these examples all retain the sp 3 -hybrized center at C2, and so can adopt a similar conformation to native glycans.…”