Synthesis of a Series of Oligo(ethylene glycol)-Terminated Alkanethiol Amides Designed to Address Structure and Stability of Biosensing Interfaces

• Published in: Journal of organic chemistry Vol. 66; no. 13; pp. 4494 - 4503
• Main Authors: Svedhem, Sofia, Hollander, Carl-Åke, Shi, Jing, Konradsson, Peter, Liedberg, Bo, Svensson, Stefan C. T
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 29.06.2001; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Organic; Physical Sciences; Science & Technology; TECHNOLOGY; TEKNIKVETENSKAP; SUPPORTED MEMBRANES; GOLD; SELF-ASSEMBLED MONOLAYERS; MODEL SYSTEM; PROTEIN ADSORPTION; LIGANDS; CONFORMATION; DERIVATIVES; BINDING; SURFACES
• ISSN: 0022-3263; 1520-6904; 1520-6904
• DOI: 10.1021/jo0012290

A strategy for the synthesis of a series of closely related oligo(ethylene glycol)-terminated alkanethiol amides (principally HS(CH2) m CONH(CH2CH2O) n H; m = 2, 5, 11, 15, n = 1, 2, 4, 6, 8, 10, 12) and analogous esters has been developed. These compounds were made to study the structure and stability of self-assembled monolayers (SAMs) on gold in the prospect of designing new biosensing interfaces. For this purpose, monodisperse heterofunctional oligo(ethylene glycols) with up to 12 units were prepared. Selective monoacylation of the symmetrical tetra- and hexa(ethylene glycol) diols as their mesylates with the use of silver(I) oxide was performed. The synthetic approach was based on carbodiimide couplings of various oligo(ethylene glycol) derivatives to ω-(acetylthio) carboxylic acids via a terminal amino or hydroxyl function. SAM structures on gold were studied with respect to thickness, wettability (water contact angles ∼30°), and conformation. A good fit was obtained for the relation between monolayer thickness (d) and the number of units in the oligo(ethylene glycol) chain (n):  d = 2.8n + 21.8 (Å). Interestingly, the corresponding infrared spectroscopy analysis showed a dramatic change in conformation of the oligomeric chains from all-trans (n = 4) to helical (n ≥ 6) conformation. A crystalline helical structure was observed in the SAMs for n > 6.