Site selectivity defined

A unique feature of such DNA-directed self-assemblies is their site-selective immobilization, which makes it possible to construct well-defined nanostructures. On the other hand, the possibility of the introduction of a vast number of substitutes (like peptidic sequences, nucleoproteins, of hydrophobic hydrocarbon chains) to an adamantane core (adamantyl) makes such a process capable of designing steric colloidal and supramolecular conformations by setting hydrophobic/hydrophilic and other interactions. In addition, the rigidity of the adamantane structure can provide strength and rigidity to such self-assemblies [150]. 

Altogether, the identification of the coordinating residues in the endogenous hDAT Zn2+ binding site followed by the engineering artificial sites have defined an important series of structural constraints in this transporter. This includes not only a series of proximity relationships in the tertiary structure, but also secondary structure relationships. The data also provided information about the orientation of TM7 relative to TM8. A model of the TM7/8 microdomain that incorporates all these structural constraints is shown in Fig. 4 (36). The model is an important example of how structural inferences derived from a series of Zn2+ binding sites can provide sufficient information for at least an initial structural mapping of a selected protein domain. 

In an alternative approach the site-selective functionalization reaction has been used to incorporate a galactose derivative into a folded foux-hehx bundle protein and the effect of glycosylation on the structure of the folded protein has been identified [65]. The unfunctionalized designed four-helix bundle did not have a well-defined tertiary structure but the introduction of the sugar improved the helical content and reduced the rate of conformational exchange. Glycosylation may therefore play a role in the maturation of poorly folded proteins. 

The network design phase already determined the countries where plants should be located or closed. Thus, site selection takes place within an individual country. As the location factors pertinent to the site selection phase are different from those used in the network design phase, the first step again is to establish the relevant location factors. These are mostly of qualitative nature but also include quantitative factors such as local factor cost differences, property and construction costs. Findings from industrial location science (cf. Chap. 2.2.2) can be used as a starting point to define the location factors, but industry-, company- and project-specific factors... 

The majority of the location factors shown in Figure 29 are self-explanatory. While no uniform scale is required when using the pairwise comparison approach in a site selection situation, it has proven helpful to create a joint definition of each attribute that also contains an indication of minimum requirements and ideal state together with all stakeholders involved in the site selection process. To this end, verbal scale descriptions were defined for all sub-objectives. The global scale to use the model for site controlling (see below) was then created based on these definitions. 

The second is a convergent approach that relies on the formation of the link late in the synthesis, once the protein scaffold for its presentation is in place. In this case, site-selective glycosylation must be in order to have chemically defined structures.17... 

The multiple potential pharmacophores for targets, such as protein active sites, are defined using complementary site points to exposed features accessible in the site. These site points (see section 2.3) create a hypothetical molecule that interacts with all pharmacophoric regions of the site. Figure 2 illustrates site points that were used for the thrombin site in selectivity studies for three serine protease inhibitors (see section 4.3). The potential pharmacophores are calculated for this molecule just as for any... 

An initial network configuration was set up by randomly choosing sizes for all sites and bonds, while observing the imposed twofold size distribution. Sites were placed at the nodes of the cubic lattice and bonds in between the nodes. Node to node distance was constant (i.e. equal to the diameter of the largest site) the length of each bond was adjusted to a value enough to connect its two neighbouring sites. This particular selection of bond-site distance defined the porosity of the network. 

Zeidan et al. [16] incorporated arylsulfonic acid and alkylthiol groups into mes-oporous silica by a cocondensation method, where 2-(4-chlorosulfonylphenyl)-ethyl-trimethoxysilane and 3-mercaptotrimethoxysilane were added to tetraethyl orthosilicate, forming a mesoporous silica (SBA-15) material via a sol-gel process (Fig. 23.4a). The resulting catalysts exhibited far greater activity and selectivity than materials containing only the acid. These randomly distributed catalysts achieved in the best case a per site yield (defined as moles of product per mole of sulfonic acid) of 82 and a 95% selectivity for bisphenol A, compared to a per site yield of 18 and 58% selectivity for bisphenol A when using homogeneous sulfonic acid alone. 

As opposed to the global reactivity descriptors described above, the analysis of site selectivity in a molecule demands the local descriptors like the Fukui function defined as [35,36],... 

Microporous and, more recently, mesoporous solids comprise a class of materials with great relevance to catalysis (cf. Chapters 2 and 4). Because of the well-defined porous systems active sites can now be built in with molecular precision. The most important catalysts derived from these materials are the acid zeolites. The acid site is defined by the crystalline structure and exhibits great chemical and steric selectivities for catalytic conversions, such as fluid catalytic cracking and alkane isomerization (cf. Chapter 2). In Section 9.5 we discuss the synthesis of zeolites and, briefly, of mesoporous solids. 

A unique strength of solid-state NMR is its ability to probe molecular dynamics with site selectivity.9132 In this section, we present some specific examples that illustrate the considerable insight into dynamic processes provided by advanced solid-state NMR experiments applicable to as-synthesized samples, i.e., without the requirement for isotopic labeling. These examples focus on well-defined processes that are fast as compared to the time scale of the H DQ MAS experiment, this being on the order of 10-6 to 10 4 s. In addition, it should be noted that the extraction of dipolar couplings by following the buildup of DQC in a H DQ MAS experiment has been shown to provide insight into the complex dynamic processes in polymer melts,172 block copolymers,173 and elastomers.174... 

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