Route to Smooth Silica-Based Surfaces Decorated with Novel Self-Assembled Monolayers (SAMs) Containing Glycidyl-Terminated Very Long Hydrocarbon Chains

Abstract

Novel glycidyl-terminated organosilicon coupling agents possessing a trialkoxysilyl head group and a very long hydrocarbon chain (C22) were synthesized. Their ability to afford densely packed self-assembled monolayers (SAMs) grafted on silica-based surfaces was investigated. Transmission FT-IR spectra showed that the most regular films were obtained by using trichloracetic acid as the catalyst (10 M%). Atomic force microscopy (AFM) and optical ellipsometry were consistent with well ordered monolayers exhibiting a marked decrease of the surface roughness. Epifluorescence microscopy revealed that these SAMs possessed a better surface reactivity than monolayers obtained with the commercially available (3-glycidoxypropyl) trimethoxysilane (GPTS) upon grafting of a fluorescent probe (dansylcadaverin). Moreover, direct attachment of fluorescent antibodies (RAG-TRITC) through covalent binding led to higher mean fluorescence intensities, showing that these new SAMs possess high potential for the immobilization of biological molecules.

Epoxy-Terminated Self-Assembled Monolayers Containing Internal Urea or Amide Groups

“…Contact angle values of 72°±1° and 70°±2° (with water) were measured for SAM-8 and SAM-15. These values are similar to those found in the literature for an organosilicon coupling agent containing a long hydrocarbon chain (C 22 ) and a glycidyl endgroup (72°±1°) 22. They are much higher than that reported in the literature (55°±10°) for a GPTS monolayer 45.…”

“…The 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 10 intermediate alcohol 6 was reacted with epichlorhydrine and NaH under anhydrous conditions in one step procedure, yielding 7 (28%). 22 To obtain the amido silylated coupling agent 8, the addition of the Si(OMe) 3 group was achieved by hydrosilylation reaction of the unsaturated precursor 7 with a large excess of HSi(OMe) 3 in the presence of Karstedt's catalyst. 29 The synthesis of novel epoxy alkoxyorganosilane with an urea group in the alkyl chain required 7 steps (Scheme 2).…”

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 possessing long alkyl chains. 22 This feature is certainly due to the fact that using hidden polar functionalities increased the solubility in organic solvent and also the affinity with hydrophilic surfaces.…”

“…The long-chain SAM affords a higher density of accessible epoxide groups to immobilize antibodies receptors. 22 However, it must be noticed that the synthetic routes leading to long-chain alkyl groups are time consuming and give relatively weak yields with poorly soluble silylated coupling agents. The urea group is widely recognized as an important building block in supramolecular architectures, 23 and the assemblies of organic/inorganic hybrid materials.…”

“…In contrast, for amido silylated coupling agent, the C=O groups seem to be randomly oriented.Evidence of the presence of reactive epoxide groups on the surface was provided in epifluorescence microscopy using a fluorescent probe. The dansylcadaverin (λ ex = 335 nm, λ em = 508 nm in methanol) was grafted onto the surface via a nucleophilic attack of the epoxide groups by the amino group and ring-opening condensation 22. For both surfaces, the fluorescence intensity is homogenously distributed on the whole surfaces, showing that the fluorophore was homogeneously distributed on the surfaces.…”