Efficient Preparation of Novel Phenolic Surfactants for Self-Assembled Monolayers

<div><p></p><p>Novel molecules have been synthesized that combine the phenolic nature of tannins and self-assembling properties of surfactants. These single-chain (C₁₂) surfactants with potential biocompatibility have been synthesized with an ω-thiol or disulfide functionality, both commonly used anchors in self-assembly onto gold surfaces, using a modular route. Protecting groups for the phenol and thiol moieties played a key role for overcoming the challenges often associated with the purification of surfactants. The tasks of unmasking the thiol moiety and simultaneously deprotecting the acetyl protecting groups of the phenols were accomplished using sodium thiomethoxide. This modular route can be extended to synthesize other surfactants with the potential ability to form robust layers with biocompatible properties.</p> <p>[Supplementary materials are available for this article. Go to the publisher's online edition of <i>Synthetic Communications</i>® for the following free supplemental resource(s): Full experimental and spectral details.]</p> </div

Surface Behavior of Boronic Acid-Terminated Silicones

Silicone polymers, with their high flexibility, lie in a monolayer at the air–water interface as they are compressed until a critical pressure is reached, at which point multilayers are formed. Surface pressure measurements demonstrate that, in contrast, silicones that are end-modified with polar groups take up lower surface areas under compression because the polar groups submerge into the water phase. Boronic acids have the ability to undergo coordination with Lewis bases. As part of a program to examine the surface properties of boronic acids, we have prepared boronic acid-modified silicones (SiBAs) and examined them at the air–water interface to better understand if they behave like other end-functional silicones. Monolayers of silicones, aminopropylsilicones, and SiBAs were characterized at the air–water interface as a function of end functionalization and silicone chain length. Brewster angle and atomic force microscopies confirm domain formation and similar film morphologies for both functionalized and non-functionalized silicone chains. There is a critical surface pressure (10 mN m^–1) independent of chain length that corresponds to a first-order phase transition. Below this transition, the film appears to be a homogeneous monolayer, whose thickness is independent of the chain length. Ellipsometry at the air–water interface indicates that the boronic acid functionality leads to a significant increase of film thickness at low molecular areas that is not seen for non-functionalized silicone chains. What differentiates the boronic acids from simple silicones or other end-functionalized silicones, in particular, is the larger area occupied by the headgroup when under compression compared to other or non-end-functionalized silicones, which suggests an in-plane rather than submerged orientation that may be driven by boronic acid self-complexation