SAMs supramolecular

The advent of methods to create nanoscale structures such as SAMs, supramolecular assemblies, lithographic patterns, and the like, gave birth to a field called nanotechnology (see Section 4.3.2 for a brief introduction). 

A second class of monolayers based on van der Waal s interactions within the monolayer and chemisorption (in contrast with physisorption in the case of LB films) on a soHd substrate are self-assembled monolayers (SAMs). SAMs are well-ordered layers, one molecule thick, that form spontaneously by the reaction of molecules, typically substituted-alkyl chains, with the surface of soHd materials (193—195). A wide variety of SAM-based supramolecular stmctures have been generated and used as functional components of materials systems in a wide range of technological appHcations ranging from nanoHthography (196,197) to chemical sensing (198—201). 

Another well-represented category was that of self-assembled monolayers (SAMS) and other supramolecular systems. The experiments on the SAMS included studies of the surface pKa of one system (110), the kinetics and thermodynamics of the self-assembly process (111), and the characterization of the SAM surface by study of solution contact angles (112). The experiments on supramolecular systems included studies on chemical equilibria in such systems (113, 114, 115), the kinetics of inclusion phenomena (116), and the use of solvatochromic probes in studying inclusion phenomena (117). 

Finally, self-assembled monolayers (SAMs) on gold electrodes constitute electrochemical interfaces of supramolecular structures that efficiently connect catalytic reactions, substrate and product diffusion and heterogeneous electron transfer step when enzymes are immobilised on them. Resulting enzyme-SAM electrodes have demonstrated to exhibit good performance and long-term enzyme stability. 

Different cyclodextrin monolayers have been synthesized and their surface properties have been characterized. Kaifer et al. prepared per-6-thiol-cyclodextrins, and described the interfacial monovalent ferrocene complexation at the monolayer.55 Mittler-Neher et al. studied the kinetics of the adsorption of mono- and multithiolate-functionalized CD SAMs.56,57 Beulen et al.,58 Huskens et al.,59 Auletta et al.,60 and Nijhuis et al.61 reported on the concept of molecular printboards, that is, (3-cyclodextrin ((3-CD) SAMs on gold or silicon oxide substrates, onto which complementary multivalent guest-functionalized dendrimer molecules were adsorbed, resulting in the formation of kinetically stable supramolecular assemblies. With the... 

Figure 13.7 The adsorption and desorption of CD-functionalized nanoparticles onto and from a CD SAM with ferrocenyl dendrimers as a reversible supramolecular glue.

Figure 13.15 The preparation of a multilayered supramolecular nanostructure of Au nanoparticles and dendrimers on PDMS via supramolecular LbL assembly and transfer printing onto a CD SAM.

NIL patterns were also used for the assembly of nanoparticles via supramole-cular host-guest interactions.95 The NIL-patterned substrate was functionalized with CD SAMs via a three-step synthesis process. The fabrication of 3D nanostructures was achieved by the alternating assembly of multivalent guest-functionalized dendrimers and CD-fnnctionalized Au nanoparticles.88 This methodology can be applied to various nanoparticles, regardless of their size and core material. For instance, CD-functionalized silica and polystyrene nanoparticles were adsorbed onto NIL-patterned CD SAMs with preadsorbed guest-fnnctionalized dendrimers.60 92 Recently, Huskens et al. demonstrated the supramolecular LbL assembly of 3D multicomponent nanostructures of nanoparticles by alternating assembly steps of complementary ferrocenyl-functionalized silica nanoparticles and different kinds of host-fnnctionalized nanoparticles (see Fig. 13.8).66... 

The formal potential, E0/, contains useful information about the ease of oxidation of the redox centers within the supramolecular assembly. For example, a shift in E0/ towards more positive potentials upon surface confinement indicates that oxidation is thermodynamically more difficult, thus suggesting a lower electron density on the redox center. Typically, for redox centers located close to the film/solution interface, e.g. on the external surface of a monolayer, the E0 is within 100 mV of that found for the same molecule in solution. This observation is consistent with the local solvation and dielectric constant being similar to that found for the reactant freely diffusing in solution. The formal potential can shift markedly as the redox center is incorporated within a thicker layer. For example, E0/ shifts in a positive potential direction when buried within the hydrocarbon domain of a alkane thiol self-assembled monolayer (SAM). The direction of the shift is consistent with destabilization of the more highly charged oxidation state. 

Although the structure of the interfacial supramolecular assembly is often less well defined, carbon and metal oxides offer certain advantages over SAM-modified... 

Since an EG (or OEG, alike) SAM is the base layer of the supramolecular architectures of almost all the protein interaction studies presented here, the absence of NSB on such a matrix enables a good start for the observation of specific protein interactions. 

Fig. 69 a Formation of supramolecular polymers between an AFM-tip and a SAM via quadrupolar hydrogen bonds, b Force-extension curves of the aggregates. Reprinted with permission from [237]... 

This chapter is organized as follows. Section 4.2 addresses the study of photoisomerization and photoinduced orientation of azobenzene molecules at the molecular level in SAMs of azo-silane molecules. Section 4.3 discusses photoinduced effects in supramolecular assemblies, i.e., LBK multilayer structures containing azobenzene molecules, and compares the photoinduced movement of azobenzenes in these structures to that observed in spin-cast films. Section 4.4 focuses on the isomerization and sub-Tg photoinduced orientation in a series of very high Tg (up to 350°C) nonlinear optical polyimide and thermoplastic donor-embedded polyurethane polymers containing azo dye, especially focusing on polymer structure-Tg-photoinduced molecular movement relationships. Section 4.5 describes pressure effects on photoisomerization and photo-orientation in films of a PMMA polymer containing azo dye. Finally, we make some concluding remarks in Section 4.6. 

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