Reactivity in the Confinement of Self-Assembled Monolayers: Chain Length Effects on the Hydrolysis of N-Hydroxysuccinimide Ester Disulfides on Gold

B. Dordi, Holger Schönherr, Gyula J. Vancso

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Two N-hydroxysuccinimide (NHS) ester disulfides, 16,16'-dithiobis(N-hydroxysuccinimidylhexadecanoate) (NHS-C15) and 11,11'-dithiobis(N-hydroxysuccinimidylundecanoate) (NHS-C10), were synthesized and adsorbed as self-assembled monolayers (SAMs) on gold surfaces. These SAMs, together with SAMs of 3,3'-dithiobis(N-hydroxysuccinimidylpropionate) (NHS-C2), were used as model systems for an examination of the factors that affect the kinetics of interfacial reactions. The SAMs and the rate of the base-catalyzed hydrolysis of the incorporated NHS ester groups were characterized by grazing incidence reflection Fourier transform infrared (GIR-FTIR) spectroscopy and contact angle measurements. GIR-FTIR spectroscopy shows that SAMs of NHS-C2 and NHS-C10 undergo a pseudo-first-order hydrolysis with second-order rate constants of (61 ± 11) × 10-2 M-1 s-1 and (4.5 ± 0.4) × 10-2 M-1 s-1, respectively. SAMs of NHS-C15 show a sigmoid behavior with a half reaction time of 1700 ± 20 s in 10 mM aqueous NaOH. The rate constants determined based on the contact angle data and application of the Cassie equation are in excellent agreement with the GIR-FTIR spectroscopy results. The increase in conformational order with increasing chain length and the concomitant improvement of packing of the NHS ester end groups, as seen by GIR-FTIR spectroscopy, account for the observed differences in reactivity. Our results imply that surface reactions in SAMs can be controlled via careful design of the adsorbate structure.
Original languageUndefined
Pages (from-to)5780-5786
Issue number14
Publication statusPublished - 2003


  • IR-59381

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