Monolayer assemblies, reproducibility

Figure 15. (a) A schematic representation of organic amphiphilic molecules at air-water interface, (b) Schematic representation of the various deposition modes for monolayer films and the resulting L-B assemblies. (Reproduced with permission from H. Kuhn, D. Mobius, and H. Bucher, Physical Methods of Chemistry, Vol. I, Part IIIB, A. Weissberger and B. W. Rossiter, Eds., Wiley, New York, 1972, p. 577.)... 

Figure 4.7. These diagrams are designed to emphasize the reproducibility of various physical parameters in monolayer assemblies of different thicknesses a) reciprocal capacitance per unit area versus number of monolayers of cad-mium arachidate on an aluminum substrate (see r erence 38), (Jb) absorption intensity versus number of monolayers for the symmetric carboxylate stretching mode of cadmium arachidate at 1432 cm (see r erence 39), (c) count rate of rays versus number of layers of barium stearate labeled with (see reference 40), and d) X-ray photoelectron signal (XPS) intensity versus number of layers of cadmium dimethylarcwhidate on silver (see reference 28).

Figure 10. Scheme of (A) two-dimensional MPA monolayer assembled on planar gold surface and (B) three-dimensional MPA monolayer assembled on gold nanoparticle-modified ITO. Reproduced from [35], copyright 2007, with permission from Elsevier. 

FIGURE 4-14 Formation of a self-assembled monolayer at a gold sustrate. (Reproduced... 

We start with examples of the sequential approach. With this approach, you begin with more routine experiments, ones that are reasonably likely to succeed (e.g., calibration or optimization procedures). The initial set of experiments can also serve as a test case and/or show that you can reproduce literature values. For example, Aga (P6) proposes first to explore conditions that will optimize immunoassay sensitivity, and Spain (P7) proposes to begin with a study of topography, using published methods and a self-assembled monolayer with a known structure. 

Fig. 4 Water contact angle data (a) and surface energy data (b) from a surface energy library produced through the graded UV-ozonolysis of an ODS self-assembled monolayer on sihcon. (Reproduced with permission from [17])...

SnOi was deposited on hydrolyzed Si and on Si coated with sulphonate-terminated self-assembled monolayers from a solution of SnCU in dilute HCl at 80° [45]. The films, up to 65 nm thick and consisting of a dense-packed aggregate of SnOi nanocrystals (5-10 nm) together with some amorphous basic tin oxide, contained ca. 3 at.% Cl. They were adherent on all substrates, although the adherence and homogeneity on Si was less reproducible than on the monolayer-coated Si. Films were also deposited using a continuous flow system. The films were sim-... 

Cyclic voltammograms of the COx/Cyt.c electrode corresponding to the bioelectrocatalyzed reduction of 02 (i), and to the reference system, where 02 is excluded (ii). (c) Assembly of an integrated LDH electrode for the bioelectrocatalyzed oxidation of lactate by the surface cross-linking of an affinity complex formed between LDH and different structures of a boronate-linked PQQ-NAD monolayer. Parts (a) and (b) Reproduced from Ref. 27 by permission of the Royal Society of Chemistry (RSC). Part (c) Reproduced with permission from Ref. 25. Copyright 2002 American Chemical Society. 

FIG. 6.1 Control of wettability of surfaces through chemistry (a) schematic illustration of formation of hydrophobic lines on a hydrophilic surface with self-assembled monolayers (SAMs) and micromachining (b) top view of the shapes and confinement of water drops on an engineered surface. (Reproduced with permission of Abbott et al. 1992.)... 

All four types of polymerizable lipids shown in Fig. 4 have been realized synthetically. In this context, one need not attempt to reproduce mother nature slavishly (Fendler 8)). Kunitake 9) was able to show that simple molecules like dialkyldimethyl-ammonium salts also form bilayer assemblies. Fuhrhop 10) and Kunitake U) could accomplish the formation of monolayer liposomes with molecules containing only one alkyl chain and two hydrophilic head groups. Acryloylic and methacryloylic groups (type a and d, Table 1), as well as diacetylenic, butadienic, vinylic and maleic acid groups (type b and c), have been used as polymerizable moieties. A compilation of amphiphilic, photopolymerizable molecules is given in Table 1. 

Figure 6.12 The molecular capsule 6.33b-6.34 held by interactions to cyclodextrins as a self-assembled monolayer on gold. (Reproduced by permission of The Royal Society of Chemistry).

By their very nature, heterogeneous assemblies are difficult to characterize. Problems include the exact nature of the substrate surface and the structure of the modifying layer. In this chapter, typical examples are given of how surface assemblies can be prepared in a well-defined manner. This discussion includes the descriptions of various substrate treatment methods which lead to clean, reproducible surfaces. Typical methods for the preparation of thin films of self-assembled monolayers and of polymer films are considered. Methods available for the investigation of the three-dimensional structures of polymer films are also discussed. Finally, it will be shown that by a careful control of the synthetic procedures, polymer film structures can be obtained which have a significant amount of order. It will be illustrated that these structural parameters strongly influence the electrochemical and conducting behavior of such interfacial assemblies and that this behavior can be manipulated by control of the measurement conditions. 

Figure 5.42 Cyclic amperometric responses of a ft-CD functionalized monolayer on photoswitching of the bipyridinium-azobenzene diad currents are measured at a constant potential of —0.6 V. From M. Lahav, K. T. Ranjit, E. Katz and I. Willner, Photosimulated interactions of bipyridinium-azobenzene with a /3-aminocyclodextrin monolayer-functionalized electrode An optoelectronic assembly for the amperometric transduction of recorded optical signals, Isr.. Chem., 37, 185-195 (1997). Reproduced by permission of Laser Pages...

Fig. 14.37. Speculative cartoon of cytochrome adsorbed c on a COOH-termi-nated self-assembled monolayer on gold. A crys-talline region for HS(CH2)15COOH SAM is depicted. Alkanethiol molecules are represented as end-capped cylinders with a COOH terminus (black) and a thiolate (gray) attachment to the gold electrode. Polypeptide line diagrams of cytochrome c molecule are shown in an electrostatically favored orientation. For clarity, the heme group has been blackened. (Reprinted from Bowden, "Wiring Mother Nature, Interface 6(4) 40-45, Fig. 2, 1997. Reproduced by permission of the Electrochemical Society, Inc.)...

Figure 6.67. Schematic of a self-assembled monolayer (SAM), illustrating the organization of the alkyl chains via van der Waal interactions, and the close-packed array of sulfur atoms on the gold surface. Reproduced with permission from Xia, Y. Whitesides, G. M.Angew. Chem. Int. Ed. 1996, i7,550. Copyright 1996 Wiley-VCH.

Figure 4 The modified stalk mechanism of membrane fusion and inverted phase formation, (a) planar lamellar (La) phase bilayers (b) the stalk intermediate the stalk is cylindrically-symmetrical about the dashed vertical axis (c) the TMC (trans monolayer contact) or hemifusion structure the TMC can rupture to form a fusion pore, referred to as interlamellar attachment, ILA (d) (e) If ILAs accumulate in large numbers, they can rearrange to form Qn phases, (f) For systems close to the La/H phase boundary, TMCs can also aggregate to form H precursors and assemble Into H domains. The balance between Qn and H phase formation Is dictated by the value of the Gaussian curvature elastic modulus of the bIlayer (reproduced from (25) with permission of the Biophysical Society) The stalk in (b) is structural unit of the rhombohedral phase (b ) electron density distribution for the stalk fragment of the rhombohedral phase, along with a cartoon of a stalk with two lipid monolayers merged to form a hourglass structure (reproduced from (26) with permission of the Biophysical Society).

The LB techniques are a powerful tool used to assemble large-scale monolayers of hydrophobic metallic nanoparticles on a water surface [42]. The advantages of the LB techniques are the good reproducibility of the metallic nanoparticles substrates and the ability to disperse the particles on the surface of water [43]. Recently, the LB methods have received interest as a process for the fabrication of thin films SERS substrates. 

FK5.6.I9 Schematic representation of the structural formation and order-disorder transition for photoactive LBK showing (A) the compressed monolayer on the water surface with densely packed chromophore side chains oriented into the gas phase and the polymer backbone facing the water surface, and (B) LBK transfer from the water to a solid support, resulting in well-ordered smetic-tike (bilayered) multilayer assemblies. (C) After phcnoinduced trars to cts isomerization, a largely disordered struaure is obtained and the layered structure is completely lost (reproduced from reference 72 with permission from Wifey-VCH). 

Fig. 15. One version of the two-step model for lipoprotein biosynthesis. This model (Alexander et al., 1976) proposes that VLDL-sized emulsion particles lacking apoB were synthesized in the smooth ER (SER) and that these particles subsequently migrated to the junction between the smooth and the rough ER (RER), where the apoB was incorporated into the surface monolayer of the nascent VLDL. In this review it is suggested that the primary lipoprotein, shown in Fig. 14, is the vehicle that transports the apoB to the emulsion particle and merges with it to complete the assembly of the VLDL. Reproduced from the Journal of Cell Biology (Alexander et al., 1976), by copyright permission of the Rockefeller University Press.

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