Simple coupling chemistry linking carboxyl-containing organic molecules to silicon oxide surfaces under acidic conditions.
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.
Schmidt
Sebastian W
SW
Department of Precision- and Micro-Engineering, Engineering Physics, Munich University of Applied Sciences, Lothstr. 34, 80335 Munich, Germany.
Christ
Timo
T
Glockner
Christian
C
Beyer
Martin K
MK
Clausen-Schaumann
Hauke
H
D000143:Acids / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D018625:Microscopy, Atomic Force; D010087:Oxides / Q000737:chemistry; D012825:Silicon / Q000737:chemistry*; D013499:Surface Properties
D000143:Acids; D010087:Oxides; D012825:Silicon