Inhibiting Reductive Elimination as an Intramolecular Disulfide Dramatically Enhances the Thermal Stability of SAMs on Gold Derived from Bidentate Adsorbents

Abstract

The bidentate aromatic adsorbate, 5-(octadecyloxy)-1,3-benzenedimethanethiol (R1ArmDT), with a specific design of extended S-S distance and a geometric constraint to resist cyclic disulfide formation was synthesized. The film formation and thermal stability of self-assembled monolayers (SAMs) derived from R1ArmDT were investigated and compared to those of SAMs derived from an analogous bidentate dithiol 2-(4-(octadecyloxy)-phenyl)propane-1,3-dithiol (R1ArDT), in which the two sulfur atoms can readily form a cyclic disulfide upon reductive elimination from the surface. Although the SAMs derived from R1ArmDT were less densely packed than those derived from R1ArDT, as judged by the data obtained by X-ray photoelectron spectroscopy and polarization modulation infrared reflection absorption spectroscopy, the SAMs derived from R1ArmDT were markedly more thermally stable than those derived from R1ArDT. The greater thermal stability of the R1ArmDT SAMs can be rationalized on the basis of the structure of the bidentate R1ArmDT headgroup, in which the two pendant sulfur atoms cannot access each other intramolecularly to form a cyclic disulfide upon reductive elimination from the surface.

Quaternary Ammonium-Terminated Films Formed from Mixed Bidentate Adsorbates Provide a High-Capacity Platform for Oligonucleotide Delivery

“…In this report, we describe the synthesis of two series of quaternary ammonium-terminated adsorbates, one having the customary monodentate headgroup and the other having a unique bidentate headgroup (Figure ), for generating films with enhanced stability . The three monodentate adsorbates contain either trimethylammonium termini (15-mercapto- N , N , N -trimethylpentadecan-1-ammonium; TMA-C15-MT ) or triethylammonium termini ( N , N , N -triethyl-15-mercaptopentadecan-1-ammonium; TEA-C15-MT ) and octadecanethiol ( ODT ) as a standard.…”

“…28 In this report, we describe the synthesis of two series of quaternary ammonium-terminated adsorbates, one having the customary monodentate headgroup and the other having a unique bidentate headgroup (Figure 1), for generating films with enhanced stability. 29 The three monodentate adsorbates contain either trimethylammonium termini (15- Herein, we investigate (1) the effects of increasing the lateral spacing of the terminal groups, (2) the effects of enhanced film stability, and (3) the effect of these phenomena on the nucleotide loading capacity on the surfaces. These studies provide the foundation for therapeutic oligonucleotide delivery using gold-based nanoparticles 17,30−32 and nanoshells, 33−35 where the latter nanostructures can be activated by tissuetransparent near-infrared light.…”

Janus Gold Nanostars–Mesoporous Silica Nanoparticles for NIR‐Light‐Triggered Drug Delivery

“…The “chemical messenger” succinic acid (p K a1 =4.21, p K a2 =5.64) induced protonation of benzimidazole (p K a =5.55) which produced dethreading of the benzimidazole‐β‐CD inclusion complex and Dox delivery. Although previous studies have shown the desorption of ligands from gold surfaces induced by heat, the temperature of N 1 suspensions upon NIR irradiation (Figure S19, Supporting Information) remained relatively low (ca. 36 and 45 °C at 1 and 3 W cm −2 , respectively) to be expected to produce direct desorption of derivative 5 .…”

“…This causes the reduction of nitrog roup and oxidation of the benzylic carbon,c onsequently inducing CÀOb ond cleavage and succinic acid formation, [42] as confirmed by control experiments( Figures S14-S18,S upporting Information). The "chemical messenger" succinic acid (pK a1 = 4.21, pK a2 = 5.64) induced protonation of benzimidazole (pK a = 5.55) which produced dethreading of the benzimidazole-b-CD inclusion complex and Dox delivery.A lthough previouss tudies have shown the desorptiono fl igandsf rom gold surfaces induced by heat, [43] the temperature of N1 suspensionsu pon NIR irradiation (Figure S19, Supporting Information) remained relativelyl ow (ca. 36 and 45 8Ca t1and 3Wcm À2 ,r espectively) to be expected to produce direct desorption of derivative 5.T ov erify the proposed mechanism, we performed control releasee xperiments with Janus AuNSt-MSNP nanoparticles in whicht he AuNSts had not been functionalized with 5.T he obtained results are shown also in Figure 4a.A sc ould be seen, Dox delivery was negligible both in the absence of irradiation (blue curve) and upon irradiation (cyan curve).…”

Molecular Level Structural Characterization of Self-Assembled Monolayers of Functionalized Bidentate Aromatic Thiols

“…Self-assembled monolayers (SAMs) generated from dithiol-based adsorbates, such as 5-(octyloxy)-1,3-phenylenedimethanethiol (OPDT) shown in Figure , have attracted much attention due to their greater thermal stability than their monothiol counterparts. , The differences in the molecular structure of dithiol versus thiol adsorbates, shown in Figure , provide possible rationales for the enhanced stability: namely, the presence of the aromatic ring and the two meta −CH 2 –SH groups linked to the ring in the aromatic dithiols. The benzene ring can plausibly give rise to stabilizing π–π interactions among adsorbates in the SAMs, while the two meta thiols provide a chelate effect to the Au(111) surface.…”