XAS and XPS Characterization of Monolayers Derived from a Dithiol and Structurally Related Disulfide-Containing Polyamides

Abstract

X-ray absorption spectroscopy and X-ray photoemission spectroscopy have been used to examine sulfur−gold bond formation in monolayers derived from a dithiol monomer and related disulfide-containing polyamides. These compounds were designed to allow the molecules to adsorb to gold through two terminal sulfurs, forming surface-attached loops. Element and site-specific density of unoccupied electronic states were probed by X-ray absorption spectroscopy at the C 1s, N 1s, O 1s (K-edge), and S 2p (L2,3-edge) absorption edges. Photoemission measurements of the C 1s, N 1s, O 1s, and S 2p core lines were also used to estimate relative coverage, to confirm layer formation, and to evaluate chemical bonding of the monomer and polyamide to the gold-coated substrates. In the case of the dithiol monomer, the spectroscopic evidence clearly shows that most of the molecules adsorb through a single thiol end. The disulfide-containing precursors, in contrast to the monomer, attach to the surface through both sulfurs to form the anticipated surface-attached loop.

Design of Gold Nanoparticles for Magnetic Resonance Imaging

“…While the number of DTDTPA molecules per particle is in agreement with the values reported by Murray and co-workers [30] for gold particles coated by a monolayer of dodecanethiol molecules (monothiols), it appears to be too high to envisage the immobilization of these dithiolated ligands on gold nanoparticles by both sulfur atoms. The grafting of DTDTPA on the gold surface by only one thiol group is consistent with observations by Vance et al [31] They demonstrated that a,x-dithiol monomers are adsorbed onto gold preferentially by only one sulfur atom, whereas for the corresponding disulfide-containing polymer, after cleavage of the disulfide bonds, the monomer is grafted through both sulfur atoms, adopting a loop conformation.…”

Thiolate Chemistry: A Powerful and Versatile Synthetic Tool for Immobilization/Functionalization of Oligothiophenes on a Gold Surface

“…Each doublet results from spin-orbit splitting of the S 2p level and consists of a high-intensity S 2p3 = 2 peak at lower energy and a low-intensity S 2p1 = 2 peak at higher energy separated by 1.2 eV with an intensity ratio of 2:1. [58] The value of the S 2p3 = 2 peak at around 161.9 eV for monolayers of 14 and 15 is in excellent agreement with the binding energy for bound alkanethiolate on gold (161.9-162.0 eV). [53,59] Thus, peaks at 161.9 and 163.1 eV of the lower-energy doublet S 2p3 = 2 , 1 = 2 of [a] The corrected areas were calculated using empirically derived sensibility factors (C 1s: 0.3; S 2s: 0.4; S 2p: 0.57; Fe 2p: 2.7).…”

“…[58] www.chemeurj.org monolayers of 14 (161.9 and 163.0 eV for 15) may be assigned to the thiol chemisorbed on the Au surface. [58][59][60] The other doublet S 2p3 = 2 , 1 = 2 at 163.4 and 164.6 eV for 14 (163.6 and 164.8 eV for 15) corresponds to the other sulfur atoms of compound 14 (or 15).…”

“…[58] www.chemeurj.org monolayers of 14 (161.9 and 163.0 eV for 15) may be assigned to the thiol chemisorbed on the Au surface. [58][59][60] The other doublet S 2p3 = 2 , 1 = 2 at 163.4 and 164.6 eV for 14 (163.6 and 164.8 eV for 15) corresponds to the other sulfur atoms of compound 14 (or 15). Comparison of the areas of these two doublet signals leads to an estimated S À C/S À Au ratio of g = 3.6 AE 1, which is in agreement with the expected value (S À C/S À Au = 4) for a double fixation of molecule 14 on gold by formation of two SÀAu bonds.…”

Synthesis, stereochemistry and adsorption studies of new spiranes and polyspiranes containing 1,2‐dithiolane units

“…alkylmercaptanes [1b]) and cyclic disulfides showed to be efficient in the anchorage on gold of our spiro derivatives (other complex molecules as porphyrins [38] or catenanes [39] were successfully deposited on gold via cyclic disulfides). The degree of organization of the monolayers for our compounds is lower than in the case of the monolayers formed by the adsorbtion of more simple compounds (alkylmercaptanes [1b] or linear amides [40]). The relative flexible behavior of the absorbed spiro compounds determines a higher organization of the monolayers for our compounds than it was observed for the monoloyers obtained by the adsorbtion of the disulfides of rigid substrates (e.g.…”