Post Modifications

The Ugi reaction is the four-component condensation of an amine, aldehyde or ketone, carboxylic acid and isocyanide to give an o -acylamino amide [22-24], Although this process has the potential to introduce considerable diversity, the products themselves are not heterocycles but through appropriate choice of substrates, latent functionality in one of the precursors can intercept either an intermediate or further derivatize the acylamino amide Ugi product through post-modification. Thus variants of the Ugi reaction have been investigated under microwave-assisted conditions for the synthesis of diverse heterocyclic libraries [16,19-24],... 

This work demonstrates that functionalization of the internal cavities of various dendrimers can be done via a post modification of the skeleton. Various functional groups can be selectively introduced aminophosphite, aldehyde, hydrazone, dichlorophosphane sulfide. Therefore all the chemistry reported on the surface of dendrimers can be now envisaged to be done into the cavities and it is demonstrated for the first time that a macromolecular chemistry can be performed into the internal voids of a dendrimer. 

The second method of catalyst incorporation in mesoporous materials involves, generally, multi-step syntheses where organic moieties (i.e. amines, phosphines, thiols) are immobilized followed by post modification toward the final product. Alternatively, the catalyst may be synthesized as the corresponding alkoxysilane complex followed by immobilization into the mesostructured materials. For instance, Kiihn and co-workers demonstrated covalent... 

It was also reported by PruP et al. [31] that in situ formed cobalt(III) complexes of pyridine-4-ylmethyl-propyl-amine (PYPA) on preformed organomodified HMS are active as catalysts in the aerobic oxidation of styrene and also 1-decene (Figure 3). Incorporation of PYPA may be achieved by following several routes viz. sol-gel synthesis, post modification of sol-gel AMP-HMS, and grafting. The authors proposed that all materials are able to act as... 

A third step in diversity enhancement involves post-modification, mostly by oxidation or reduction, elimination, or side chain attachment. 

The natural antibiotic novobiocin (Fig. 3) is an example of diversity enhancement by the combination of building blocks from different pathways, such as aromatic rings, isoprenoid, amino acid, and sugar components, finished by post-modification [22]. 

Fig. 2 Typical biosynthesis of a complex natural product (I) iterative oligomerization, (II) cyclization, (III) combination/conjugation, and/or (IV) (post-)modification...

Another example of solid phase DOS involves post-modification of the natural product macrolide antibiotic erythromycin (34) [77]. Erythromycin was first converted to analogue 32 which resembles a third generation macrolide antibiotic with high activity against resistant strains (ABT-773, 35), but is attached to solid phase-bound amino acids by reductive amination. Two further reductive amination steps and cleavage from solid support form a library of compounds of type 33 (Fig. 10). 

In this chapter, we have presented a great deal of information on important physicochemical and functional characteristics of native potato starch in comparison with some cereal starches. In addition, we have also discussed various modification techniques being used to modify potato starch, with an emphasis on the post-modification changes (particularly after derivatization)... 

As pointed out already, free NH-sulfoximines were considered to be the most useful synthetically, because they allowed a variety of post-modifications at the sulfoximine nitrogen. Although at the outset of our studies the binding site of metals (in the sense of metal ions, metal complexes, and suchlike) was uncertain and it was difficult to predict which heteroatom of the sulfoximine (or even both) would coordinate [38, 39], we expected the sulfoximine nitrogen to play an important role in the activity and the stereoselectivity of a given catalytic system. 

Y. Feng, L. Billon, B. Grassl, A. Khoukh and J. Francois, Hydrophobically associating polyacrylamides and their partially hydrolyzed derivatives prepared by post-modification. 1. Synthesis and characterization, Polymer, 2002, 43, 2055-2064. 

The post-modification reactions of acrylamide polymers were run as follows.6 A solution of poly(acrylamide[75mol%]-acrylic acid) (150 g, 27.5% in water) and sodium formaldehyde bisulfite (15.5 g), pH 4.3, was heated to 150° C and maintained at that temperature for four hours in a 300 ml Parr reactor which was equipped with a mechanical stirrer and a thermocouple. The pH of the resulting polymer solution at room temperature was 5.9. 

The effects of post-synthesis alumination on purely siliceous MCM-41 material with A1(NC>3)3 on acidity have been studied by FTIR, NH3-TPD, and IPA decomposition reaction. The FTIR results of pyridine absorption show that both Lewis and Bronsted acid sites are increased by the post-modification. The amount of NH3 adsorbed on the alumina-modified MCM-41 samples increases with the loading of Al onto the surface of MCM-41. Due to the improved acidity, the alumina-modified MCM-41 materials show considerably higher catalytic activity for dehydration of isopropanol than purely siliceous MCM-41. In addition, XRD and N2 adsorption results show that all MCM-41 samples maintained their uniform hexagonal mesoporous structure well after they have been subjected to post-synthesis alumination with the loading of Al species on Si-MCM-41 varied from 0.1 wt. % up to 10 wt. % (calculated based on AI2O3). 

Mesoporous solids including silicas and acid-treated clays can be functionalised at their surfaces so as to provide high local concentrations of active sites. These sites can be introduced by post-modification or via sol-gel preparations. In this way a range of novel materials with useful catalytic and other properties can be prepared. One of the most valuable applications for these materials is as replacements for environmentally hazardous reagents including corrosive mineral and Lewis acids, caustic bases and toxic metallic compounds. 

The materials can be made by post-modification of preformed or commercial mesoporous solids or in some cases via sol-gel preparation of organically modified solids. The former method has been successfully used to prepare immobilised Lewis... 

Several amine functionalized hyperbranched PGs have been reported as potential gene delivery systems after a proper surface group functionalization. In comparison to other dendritic structures, these scaffolds have the added advantage of being open, flexible, and possessing a polyether backbone which keeps the toxicity profile low. Different systems have been studied by post-modification of the hydroxyl groups... 

Self-assembly can be divided into a number of classes 1. strict self-assembly, 2. irreversible self-assembly, 3. precursor modification followed by self-assembly, 4. self-assembly with post-modification, 5. assisted self-assembly, 6. directed self-assembly, 7. self-assembly with intermittent processing. 

Fig. 21. Self-assembly of (HHH)-[f Con(L5)3]5+ followed by oxidation (post-modification) to give (HHH)-[RCom(L5)3]6+. The representation of [i Co(L5)3]6+ corresponds to the crystal structure of [LaCo(L5)3 ](C104)5 5 (OH)0.5(CH3CN)4 (H20)2 (adapted from Rigault et al. (1998)).

Moreover, the nanosized fibers of the swollen nanocelluloses can be coated with different components and the pore system can be loaded with agents (post-modification). Further methods in this field use well-known procedures... 

Pei Y, Moos WEI, Post-modification of peptoid side chains (3 + 2) cycloaddition of nitrile oxides with alkenes and alkynes on the solid-phase, Tetrahedron Lett., 35 5825-5828, 1994. 

In another part of this study we wished to see the effects of post-modification treatments on the properties of the modified LDPE surface. Polyethylene samples were photosulfonated for different periods of time. Afterwards they were subjected to an after-treatment by conditioning in an electrolyte solution (aqueous KC1, 10-3 M) for 48 hours and then characterized by zeta potential measurements. This conditioning process resulted in a shift of f to even less negative values (see Fig. 8). This finding may be explained by the swelling of the polymer samples (water adsorption) in water that causes a shift of the shear plane of the electrochemical double layer into the liquid phase. This effect demonstrates that storage conditions and pre-conditioning may exert a pronounced influence on the zeta potential recorded for surface-modified polymers. Phenomena of this kind have already been described in previous literature [26,27],... 

Post-modification treatments like storage conditions (air/water) and preconditioning may exert a pronounced influence on the zeta potential obtained for surface modified polymers. Sulfonated LDPE samples, which were subjected to an after-treatment by conditioning in an electrolyte solution, showed a shift of the zeta potential to even less negative values. This may be explained by the swelling of the polymer samples, which occur during storage in aqueous media. 

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