Multi-functional molecules

All wet strength agents are bi- or multi-functional molecules with the capability to cross-link with each other or with cellulose. The choice of chemistry depends to a large extent on pH. In acid systems, the main wet strength agents are urea-formaldehyde (U/F) and melamine-formaldehyde (M/F) resins, whereas in neutral and alkaline systems polyamine-polyamide-epichlorohydrin resins are more effective. However, these are not the only systems in use, and a summary of these and other available methods is provided in Figure 7.22. 

In all the examples of exodendrally functionalized enantioselective den-drimer catalysts, the active sites in the periphery of the support were well-defined immobilized molecular catalysts. An alternative is provided by the possibility of attaching chiral multi-functional molecules to the end groups of dendrimers which, due to their high local concentrations, may interact more or less strongly with an achiral reagent and thus induce enantioselectivity in a transformation of a prochiral substrate. Asymmetric induction thus occurs by way of a chiral functionalized microenvironment for a given reaction. 

Relevcuit improvements have been reported in selective organic redox reac tions on illuminated semiconductor particles [2-3 ]. However, most invest gations have been concerned with functional-group activation, and little at tenticai has been devoted ccaiceming the ability of an excited semiconductor to selectively initiate redox reactivity at one site in a multi-functional molecule. 

The diverse class of polypeptides allows for the realization of, on the one hand, high-performance construction materials, such as dragline spider silk, microtubules, or collagen fibers. On the other hand, (multi)functional molecules or molecular assemblies can be found, for example, necessary for biocatalysis (enzymes) or for the function of the immune system (immune globulins). Moreover, proteins participate in the storage and the directed transport of materials in biological systems and are essential components for the communication in complex biosystems in form of, for example, cell-surface markers, receptors, regulators, or hormones. 

Based on the working hypothesis described above, the author focuses on the chemistry of cyclic porphyrin oligomers (CPOs). As described in the next section, porphyrin is a multi-functional compound and the nano-sized closed space created by these molecules should therefore be of interest to chemists. 

Provided that the research needs are satisfied, the development of bioprocessing alternatives would be dependent on improved biocatalysts. The biocatalyst has to be active towards multiple molecules (broader substrate specificity), with multi-functional capability (BDS-BDN-BDM), and adaptability to function in an oil environment, with... 

The multi-functionality of metal oxides1,13 is one of the key aspects which allow realizing selectively on metal oxide catalysts complex multi-step transformations, such as w-butane or n-pentane selective oxidation.14,15 This multi-functionality of metal oxides is also the key aspect to implement a new sustainable industrial chemical production.16 The challenge to realize complex multi-step reactions over solid catalysts and ideally achieve 100% selectivity requires an understanding of the surface micro-kinetic and the relationship with the multi-functionality of the catalytic surface.17 However, the control of the catalyst multi-functionality requires the ability also to control their nano-architecture, e.g. the spatial arrangement of the active sites around the first centre of chemisorption of the incoming molecule.1... 

The concept presented in Fig. 6 could use also other type of ordered mesoporous membranes, based on silica for example. As discussed before, oxides such as Ti02 provide better multi-functionalities for the design of such a type of nanofactory catalysts. Worth to note is that in the cover picture of the recent US DoE report Catalysis for Energy a very similar concept was reported. This cover picture illustrates the concept, in part speculative, that to selectively convert biomass-derived molecules to fuels and chemicals, it is necessary to insert a tailored sequence of enzyme, metal complexes on metal nanoparticles in a channel of a mesoporous oxide. 

After numerous answers were brought to the synthetic challenge itself, there arose ever more insistently the quest for functions and properties of such special compounds. Already, even if still far from real applications, one can imagine, based on interlocked, threaded or knotted multi-component molecules, new organic materials, specific polymers, molecular devices or machines able to process and transfer energy, electrons or information. 

The formation of such multiply coordinated surface intermediates would be expected to be enhanced by adsorption of multi-functional reagents, e.g., oxygenates with hydrocarbon chains more reactive than saturated alkyl ligands. To test this hypothesis, we have also examined the adsorption and reaction of allyl alcohol (CH2=CH-CH20H) and acrolein (CH2=CH-CHO) on the Rh(lll) surface. While these molecules do exhibit evidence for interaction with the surface via both their oxygen and vinyl functions, and while they appear to preserve the divergence of decarbonylation pathways observed for their aliphatic counterparts, their reactivity patterns add yet another layer of complexity to the puzzle of oxygenate decarbonylation. 

Smirnoff N (2000) Ascorbic acid metabolism and functions of a multi-facetted molecule. Current Opinion Plant Biology 3,229-35. 

Previous chapters have discussed comprehensively protein and DNA-based function and bioelectrochemical systems. Single- and multi-functional monolayers of proteins, DNA-based molecules, and enzymes, and of monolayers of amino acids and DNA-bases as their building blocks testify towards bioelectrochemical control at the nanoscale and sometimes singlemolecule levels. In these respects interfacial bioelectrochemistiy is undergoing a process similar to what has been the case in physical... 

X-ray diffraction.) The protein molecules in the microcrystals are then covalently cross-linked by treatment with an appropriate multi-functional reagent, usually glutaraldehyde. This renders the crystals insoluble on transfer to different aqueous media. The cross-linked crystals are effectively another form of immobilized enzyme, and can be dried for transfer to low-water media by the same methods (again see further details in the discussion of water effects below). Cross-linked crystals are available commercially for a number of enzymes. Figure 8-1 shows a diagrammatic representation of the organization of the protein molecules in lyophilized powders, immobilized enzymes and cross-linked crystals. 

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