Methylene Blue Incorporation into Alkanethiol SAMs on Au(111): Effect of Hydrocarbon Chain Ordering

Abstract

A detailed polarization modulation infrared reflection absorption spectroscopy, scanning tunneling microscopy, and electrochemical study on methylene blue (MB) incorporation into alkanethiolate self-assembled monolayers (SAMs) on Au(111) is reported. Results show that the amount of MB incorporated in the SAMs reaches a maximum for intermediate hydrocarbon chain lengths (C10-C12). Well-ordered SAMs of long alkanethiols (C > C12) hinder the incorporation of the MB molecules into the SAM. On the other hand, less ordered SAMs of short alkanethiols (C < or = C6) are not efficient to retain the MB incorporated through the defects. For C12 the amount of incorporated MB increases as the SAM disorder is increased. This information is essential to the design of efficient thiol-based Au vectors for transport and delivery of molecules as well as thiol-based Au devices for molecular sensing.

Electrochemistry, AFM, and PM‐IRRA Spectroscopy of Immobilized Hydrogenase: Role of a Hydrophobic Helix in Enzyme Orientation for Efficient H2 Oxidation

“…The lipophilic methylene blue (MB) molecule can be incorporated into SAMs. [13] Thus, when the endcharged alkyl chain contains more than 11 methylene groups (see SI 3 in the Supporting Information), H 2 oxidation proceeds only through a MET process, in agreement with Marcus-theory long-range ET. [14] Adsorption of Aa Hase on a 1-butanethiol (C 3 CH 3 ) hydrophobic SAM mimicking the physiological environment unexpectedly results in a majority MET process (Figure 1 c).…”

Manifestation of intermolecular interactions in FTIR spectra of methylene blue molecules

“…It was concluded that FTIR spectra were registered from free MB molecules [50]. In the high-frequency region of the IR spectrum, the peak at 3015 cm -1 corresponds to vibrations of the CH groups of the heterocycle [22,[51][52][53][54][57][58][59][60].…”

“…The broad bands at 2979-2929 and 2858 cm -1 correspond to the CH 3 stretching vibrations of the terminal dimethylamino groups [1,7,18,21,22,28,[51][52][53][58][59][60][61][62]. The peaks at 2819 and 2775 cm -1 correspond to the C het -N-(CH 3 ) 2 vibrations [7,18,22,32].…”

“…In the lower-frequency region the FTIR spectrum becomes complicated due to noticeable rotational structure. The absorption in the region of 1520-1420 cm -1 and at 1397 cm -1 is attributed to the symmetrical and asymmetrical bending vibrations of the CH 3 functional groups of MB [1,7,22]. Peaks at 1320 cm -1 and 1338 cm -1 correspond to the stretching vibrations of the C-N terminal saturated dimethylamino groups [22,25,31] and the characteristic region of the C=S + vibrations [51,64].…”

A polyelectrolyte–surfactant complex as support layer for membrane functionalization

“…A more refined analysis of the position of the CH 2 symmetric and asymmetric stretching bands indicates a structure in which most of the aliphatic chains are elongated and maintain some order. [22,23] X-ray reflectometry (XRR) and grazing-incidence small-angle X-ray scattering (GISAXS) measurements for the same complex have previously shown a highly oriented lamellar structure [15].…”