Pentafluorinated probes for the X-ray photoelectron spectroscopic study of immobilized bifunctional silanes

Bifunctional silanes constitute valuable linking agents for attachment of biomolecules at high levels of surface population density through the formation of thioether or disulfide bonds. Three such compounds, 1-((trifluoroacetyl)-thio)-11-(trichlorosilyl)undecane, 1-bromo-11-(trichlorosilyl)undecane, and 1-((bromoacetyl)oxy)-11-(trichlorosilyl)undecane, are discussed in terms of their surface chemistry on silicon wafers. To examine the electrophilic and nucleophilic generation of sulfur-containing linkages, three new probes, N'-(pentafluorophenyl)iodoacetohydrazide, N'-(pentafluorophenyl)-3-(2-pyridylthio)propriono-hydrazide, and N'-(pentafluorophenyl)mercaptoacetohydrazide, are introduced with respect to their reactions with silanized surfaces (studied by X-ray photoelectron spectroscopy). Thiol-functionalized surfaces obtained by silanization act as nucleophiles toward the probes. In air, low yields of conjugation are exhibited which are attributed to the unavailability of thiol groups because of intramolecular disulfide group formation instigated by oxygen or by disulfide exchange with the proprionyl probe. The behavior of electrophilic silanized surfaces toward the mercaptoacetyl-containing probe is governed by the nature of the leaving group and by steric factors.