Thiol silanization

Fig. 2 Diagram of the nanoprinting process. A master chip is produced with a DNA oligonucleotide silanized with a thiol silane. An acrylamide thin layer is allowed to form between an empty slide coated with acrylic silance and the master chip. After the acrylamide becomes polymerized, the complex is heated for 10-60 s. When the master chip is removed, the acrylamide thin layer will remain attached to the empty slide to form a copy chip. Such a copy process can be done repeatedly from a single master chip...

Silanization steps are performed in a N2-filled glove bag in a ventilated hood. This is to prevent air-oxidation of the thiol-silane, as well as to protect laboratory personnel from inhaling silane fumes. Triethoxy silanes are used in preference to trimethoxy silanes, due to decreased toxicity. 

Variation of the head group of the monolayer makes it possible to control wettability etc., and also allows the introduction of different chemical moieties with specific properties such as nonspecific binding of proteins to surfaces. For example the introduction of oligoethylene glycol functionality to the end of the alkyl chain results in protein-resistant properties (37). Thus instead of synthesizing different thiols/silanes with different head groups, it is more convenient to use a number of standard SAMs and subsequently perform reactions on SAMs to modify the surface chemistry. Performing reactions on... 

Fluoropolymers, such as poly(tetrafluoroethylene) (PTFE), and SAM-forming molecules, such as perfluorinated thiols, silanes, and n-alkanoic acids, are widely used for surface fluorina-tion in academia and industry (e.g., as easy-to-clean surfaces). The modification of surfaces with PTFE is chemically challenging because of its low reactivity and solubility. Thiols, on the other hand, generally form stable layers on (noble) metals only and are thus not applicable to the functionalization of most materials. Utilizing catechol derivatives to fluorinate a wide variety of surfaces in order to render them hydrophobic or nonadhesive is therefore a promising alternative. 

Rhodium(II) carbenoid intermediates are also useful. For example, carbene transfer reaction with allylic sulfides followed by [2,3]-sigmatropic rearrangement of the resulting sulfur ylides (Doyle-Kirmse reaction) gives furan-containing sulfides 133 in good yields (Scheme 19.32) [50]. In contrast, reaction with allylic compounds (R—H) or alcohols/amines/thiols/silanes (X—H) furnishes the 1,1-insertion products 134 or 135, respectively [51],... 

The formation of a single monolayer on the surface of an electrode relies on the chemisorption or the formation of a covalent bond between a molecule and surface atoms. Three molecule families are reported for the development of electrodes modified in the view of analytical applications thiols, silanes, and diazonium salts. These monolayers are called self-assembled when organization of the molecules constituting the monolayer present a degree of self-organization achieved during the modification process. 

Patterns of ordered molecular islands surrounded by disordered molecules are common in Langmuir layers, where even in zero surface pressure molecules self-organize at the air—water interface. The difference between the two systems is that in SAMs of trichlorosilanes the island is comprised of polymerized surfactants, and therefore the mobihty of individual molecules is restricted. This lack of mobihty is probably the principal reason why SAMs of alkyltrichlorosilanes are less ordered than, for example, fatty acids on AgO, or thiols on gold. The coupling of polymerization and surface anchoring is a primary source of the reproducibihty problems. Small differences in water content and in surface Si—OH group concentration may result in a significant difference in monolayer quahty. Alkyl silanes remain, however, ideal materials for surface modification and functionalization apphcations, eg, as adhesion promoters (166—168) and boundary lubricants (169—171). 

Instabihty in the wettabiUty behavior of OH surfaces was noticed when OH-terminated silane monolayers were exposed to hydrophobic solvents, such as CCI4 (175). Similarly, monolayers of 11-hydroxyundecane-thiol (HUT), HO—(CH2)2] SH, on Au(lll) surfaces have been found to undergo surface reorgani2ation by exposure to ambient atmosphere for a few hours (328). After that, the water contact angle reached a value of ca 60°, and only ca 25% of... 

One may envisage polymerizations analogous to the thiol-enc process using other bis- or multi transfer agents (e.g. radical-induced hydrosilylation between bis-silanes and dienes). However, none has been described or achieved significance. 

The low reactivity of alkyl and/or phenyl substituted organosilanes in reduction processes can be ameliorated in the presence of a catalytic amount of alkanethiols. The reaction mechanism is reported in Scheme 5 and shows that alkyl radicals abstract hydrogen from thiols and the resulting thiyl radical abstracts hydrogen from the silane. This procedure, which was coined polarity-reversal catalysis, has been applied to dehalogenation, deoxygenation, and desulfurization reactions.For example, 1-bromoadamantane is quantitatively reduced with 2 equiv of triethylsilane in the presence of a catalytic amount of ferf-dodecanethiol. 

Thiols, Phosphines, Amines, and Silanes. With these ligands, ethanol addition clearly gives a precipitate that can be isolated and readily redispersed in toluene or any other non-polar solvent again. 

Luderer F, Walschus U (2005) Immobilization of Oligonucleotides for Biochemical Sensing by Self-Assembled Monolayers Thiol-Organic Bonding on Gold and Silanization on Silica Surfaces. 260 37-56... 

As with the halogens, the thiols, phosphines, silanes, and germanes undergo photoaddition to olefins via homolytic cleavage. Representative examples follow a24 130) ... 

Figure 13.9 Epoxy-containing silane coupling agents form reactive surfaces that can be used to couple amine-, thiol-, or hydroxyl-containing ligands.

Reductive Thiolation. Ketones are reductively thiolated when treated first with a thiol under acidic conditions followed by addition of a silane (Eq. 252).365,426... 

Tris(trimethylsilyl)silane [20,21], thiols [22], germanes [23-25] and gallium hydride [26] can be added easily to terminal alkynes in the presence of Et3B/02. This process was extended to internal alkenes (Scheme 8, Eq. 8a) as well as silyl enol ethers (Eq. 8b) by using tri-2-furylgermane. In this last case, basic or acidic treatment of the main syn /J-siloxygcrmanc furnishes the corresponding E- or Z-alkene, respectively [24],... 

Roberts and co-workers have employed a number of chiral carbohydrate-derived thiols as polarity reversal catalysts in the radical hydrosilylation of electron-rich prochiral alkenes [68-70]. In these thiols, the SH group is attached to the anomeric carbon atom. Scheme 21 demonstrates the non-catalyzed reaction and in step b, the hydrogen atom transfer from the silane... 

---