SAMs structure

Fig. 2.4 Self-assembled monolayer (SAM) structures from organosilane compounds.

Among the factors crucial for a SAM structure, the thiol-substrate bond has been a subject of particular controversy over more than 15 years. It is worth discussing the SAM/substrate interface in some detail since it is important not only for understanding SAM structures in general but also for electrochemical metal deposition when metal is intercalated at the SAM/Au interface (Section 5.4.3). As indicated above we limit the discussion to SAMs on Au(l 11) as this is the interface where theoretical and experimental work is sufficiently detailed to allow for a discussion at the atomic level. 

Figure 5.17 Illustration of different pathways for growth of a U PD layer on a SAM-modified electrode, (a) Uniform penetration across the whole SAM area, (b) deposition starting at a major defect with subsequent penetration at edge ofUPD island (1), penetration through SAM across the whole U PD area due to the distortion of SAM structure by UPD (2) and growth of UPD island through initial defect only (3).

ChiUcoti et al. took advantage of the pCP method to prepare patterned SAM of mercaptoundecanoic acid (MUA) for the binding of 2,2 -azobisisobutyramidine. Thermal SIP resulted in the topographical enhancement of the originally printed SAM structure with feature size of about 40 pm [219]. Also, the selective binding of thiols onto gold can be used for spatio-selective SIP. Dryer et al. [215] used gold... 

The Gibbs adsorption theory (Birdi, 1989,1999, 2002, 2008 Defay et al., 1966 Chattoraj and Birdi, 1984) considers the surface of liquids to be monolayer. The surface tension of water decreases appreciably on the addition of very small quantities of soaps and detergents. The Gibbs adsorption theory relates the change in surface tension to the change in soap concentration. The experiments that analyze the spread monolayers are also based on one molecular layer. The latter data indeed conclusively verifies the Gibbs assumption (as described later). Detergents (soaps, etc.) and other similar kind of molecules are found to exhibit self-assembly characteristics. The subject related to self-assembly monolayer (SAM) structures will be treated extensively (Birdi, 1999). However, no procedure exists that can provide information by direct measurement. The composition of the surface of a solution with two components or more would require additional comments. 

Micelle formation is one of the most common SAM structures. In fact, the whole basis of biological cell structure and function is dependent on the lipid-bilayer... 

Birdi, K. S., Self-Assembly Monolayer (SAM) Structures, Plenum Press, New York, 1999. 

While the capture on DNA chips of fluorophore-labelled targets, and the extension of arrayed primers with fluorophore-labelled nucleotides has been widely used for some time, it is only more recently that assay formats have developed that utilize immobilized nucleic acids already modified with fluorophores. Fundamental analyses of surface monolayer structures and chemistries can be readily performed by immobilizing such modified oligonucleotides into SAM structures [105,106], but it is those interactions that can be monitored using fluorescence quenching or fluorescence resonance energy transfer (FRET) that have gained the most attention. 

F. 3.6 This is a stereo view of the SAM structure determined by NMR. The characteristic five helices are shown. (The nbbon structure is reproduced from ref. 61, with permission of the authors and Protein SiSence.)... 

Figure 5.6 Factors determining a SAM structure solid circles, (a) Cooperative case. Molecular illustrated by the mutual influence of cove rage 9, structure allows all contributions to adopt an C-S-substrate bond angle < j and intermolecular energy minimum, (b) Competitive effect, interactions represented by distance r and their Molecular structure is such that not all dependencies on the molecular structure. For contributions can be optimized atthe same time, the different contributions the actual position of SAM structure is a result of balance of partially the system on the potential curves is indicated by opposing forces. For details see text.

The dependence of the molecular SAM organization on the interaction with substrate is strikingly illustrated by the organization of the same or similar alkanethiol-based molecules on different low-index Au electrode surfaces. Cys SAMs on Au(lll) and Au(llO) in both aqueous solution and ultrahigh vacuum (UHV) have been studied in particular detail and illustrate the strong effects of the atomic Au substrate structures on the SAM structures. 

Birdi, K.S., Lipid and Biopolymer Monolayers at Liquid Interfaces, Plenum Press, New York, 1989 Birdi, K.S., Self-Assembly Monolayer (SAM) Structures, Plenum Press, New York, 1999 Sparr, E. et al., Langmuir, 17, 164, 2001. 

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