Simple Coupling Chemistry Linking Carboxyl-Containing Organic Molecules to Silicon Oxide Surfaces under Acidic Conditions

Abstract

The coupling chemistry of carboxymethylated amylose with organo-silanized silicon oxide surfaces at pH 7.4 and 2.0 was investigated using atomic force microscopy (AFM) based single-molecule force spectroscopy. At close to neutral pH, carbodiimide activation of a carboxylic acid affords formation of an amide bond with an amino surface linker. At pH 2.0, no activation with carbodiimide was required to anchor carboxymethylated amylose between an AFM tip and a glass substrate. At the same time, the mean bond rupture force f(r) dropped from 1.65 ± 0.37 nN at pH 7.4 to 1.39 ± 0.30 nN at pH 2.0 without carbodiimide, indicating that a different link to the surface can be formed at low pH. The coupling mechanism at pH 2.0 was elucidated by a series of experiments, in which the surface was functionalized with four different organosilanes, each containing characteristic functional groups. The results are rationalized with an acid-catalyzed ester condensation between a carboxyl group and a free, unreacted silanol group in the surface anchor or on the surface.

Mechanically induced silyl ester cleavage under acidic conditions investigated by AFM-based single-molecule force spectroscopy in the force-ramp mode

“…44 The conducted experiments revealed biexponential rupture kinetics, which have been rationalized with the silyl ester hydrolysis depending on the moieties at the silicon atom under acidic conditions.…”

Covalent incorporation of non-chemically modified gelatin into degradable PVA-tyramine hydrogels

“…This suggests complete conversion of carboxyl groups into phenol groups. Previous studies have shown that proteins can be immobilised onto silicon oxide or PEG surfaces using this chemistry [30,31]. Glycosaminoglycans have also been conjugated to PEG hydrogels using the same chemistry [26].…”

Pinpointing Mechanochemical Bond Rupture by Embedding the Mechanophore into a Macrocycle

“…In the vast majority of successful attachments, only a single rupture event was observed, which is associated with rupture of the silane surface anchor. [11][12][13][14]19] Table 1). The inset shows that the slope of the force-extension curve is the same before and after the rupture.…”