Chemical transformations, surface groups

An enzyme circumvents these problems by providing a specific environment within which a given reaction can occur more rapidly. The distinguishing feature of an enzyme-catalyzed reaction is that it takes place within the confines of a pocket on the enzyme called the active site (Fig. 6-1). The molecule that is bound in the active site and acted upon by the enzyme is called the substrate. The surface of the active site is lined with amino acid residues with substituent groups that bind the substrate and catalyze its chemical transformation. Often, the active site encloses a substrate, sequestering it completely from solution. The enzyme-... 

Surface functionalisation of PE with succinic anhydride followed by derivatisation via ring opening reaction yielded surfaces with different functional groups [128]. The PE films were photochemically grafted with maleic anhydride in vapour phase in a reaction involving benzophenone and acetone at 60 °C for 5 h under UV irradiation with a 400 W mercury vapour lamp. The chemical transformation of PE film bearing succinic anhydride group is schematically presented in Scheme 8. 

One approach to this problem is to start with the alkyl terminated surfaces and carry out chemical transformations of the methyl end group. Chidsey and co-workers employed this approach by forming sulfonyl chloride terminal groups via a photoinitiated free radical reaction of CI2 and SO2 with the original methyl-terminated monolayer [45]. These were then converted to sulfonamides by reaction with amines. Schematically this two-step reaction scheme can be written as ... 

The second route to postsynthetic modification of SAMs is the chemical transformation of functional groups present on their outermost surface this approach mostly relies on chemistries already established for the functionalization of solid supports (Fig. 4.3). Two important points to bear in mind are (1) it is essentially impossible to extensively characterize the structure of the reaction products or purify them without destroying the SAM and (2) many solution-phase reactions may be very difficult when carried out on a surface because of the steric hindrance due to the very closely packed end groups. 

In spite of their seeming variety, theoretical approaches of different authors to the consideration of solid-state heterogeneous kinetics can be divided into two distinct groups. The first group takes account of both the step of diffusional transport of reacting particles (atoms, ions or, in exceptional cases if at all, radicals) across the bulk of a growing layer to the reaction site (a phase interface) and the step of subsequent chemical transformations with the participation of these diffusing particles and the surface atoms (ions) of the other component (or molecules of the other chemical compound of a binary multiphase system). This is the physicochemical approach, the main concepts and consequences of which were presented in the most consistent form in the works by V.I. Arkharov.1,46,47... 

Other chemical transformations are suitable as well to discriminate between different types of tubes in a sample. The reaction with diazonium salts, for example, selectively functionalizes metallic nanotubes. Their solubility is enhanced by the surface modification so they may be separated from the unaltered, insoluble semiconducting tubes. Subsequent removal of the functional groups and annealing at elevated temperatures yield nanotubes with most of them being metallic conductors. As metallic nanotubes possess higher electron density close to the... 

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