Cavities, catalytic

The catalysis takes place in a specific region of the enzyme named the active site or catalytic cavity. This active site involves those amino acid residues (i.e., side chains) directly implicated in the mode of binding and the specificity of the substrate, as well as in the catalytic process itself. 

Both imprinted polymers showed an enhancement in the catalytic activity that was about 50-fold higher than the control polymer (P0) and turnover of the catalytic cavities was also demonstrated. However, when comparison was made with a polymer containing Co(II) but which was not imprinted with the template (PI), the rate acceleration dropped to about fourfold. In addition, the control of the enantioselectivity of the reaction was very low. In fact, the polymer, imprinted with the diketone derived from the / -camphor, was able to catalyse the reaction, between the 5-camphor and benzaldehyde, with an acceleration rate almost identical to that obtained with the polymer imprinted with the opposite enantiomer. The rate enhancement between the two polymers was in fact equal to 1.04. 

Polymer with free imprinted catalytic cavity... 

In the lipase assay system, when the (E, THLc, E-THLoj and E-THL02) mixture was added to a TAG emulsion, the weakef complex (E-THLoj) was hydrolyzed, explaining the reactivation process as revealed by the existence of lag times. The hydrolysis of this weak complex was enhanced when bile salts were present in the assay medium, probably due to the formation of a mixed orlistat/lipase/bile salt complex. The fact that the reactivation of HPL did not reach 100% of its initial value (before incubation with THL) at the end of the kinetic experiments (Fig. 9.13) might be attributable to the existence of a second fraction of lipase molecules, which is covalently and irreversibly inhibited by orlistat (E-THL02). The coexistence of two different forms of orlistat covalently bound to HPL may be due to the inhibitor molecule being differently oriented in the catalytic cavity of the lipase molecule. The existence in the catalytic cleft of lipases of two different orientations in the case of molecules of substrate analogues was previously reported [113, 114]. 

The disordered water molecules are not seen in x-ray structure, yet they are critical for proton transport in the enzyme. In MD simulations, we have discovered [21] that water molecules in the catalytic cavity in CcO form two branching chains (Figures 4.5 and 4.6) that connect an experimentally known proton donor Glu242, the Fe-Cu binuclear center, and the putative PLS His291, from which protons can be pumped using our mechanism of proton-proton repulsion. The possibility of such connectivity has been discussed however, they were never observed through computer simulations before. 

Earlier in our simulations, we found two bifurcated water chains in the catalytic cavity of CcO that connect Glu242, an experimentally known donor of both chemical and pumped protons, to the binuclear Fea3-Cue catalytic center, and to PropD/ Arg438/His291 groups [21] (Figure 4.13). 

Matsuishi T., Shimada T. and Morihara K. (1992) Definite evidence for enantioselective catalysis over "Molecular Footprint" catalytic cavities chirally imprinted on a Sibca (alumina), Chem. Lett., 1921-1924. 

As enzymes encapsulate multiple functionalities within their catalytic cavity, they have also served as a major source of inspiration for the fields of biomimetic chemistry and supramolecular catalysis. Early mechanistic theories about how enzymes work have prompted scientists from various fields to explore similar approaches for synthetic systems. One of these approaches is host-guest catalysis, where one or more substrates are bound in a cavity next to the catalytically active site. 

When a polymer is prepared in the presence of "print molecules" as the transition state or intermediate analogues, which are extracted after polymerization, the remaining polymer may contain catalytic cavities capable of recognizing the print molecules. By analogy to the catalytic antibodies, where a function complementary to that of the hapten can be induced in a specific place, polymers can be imprinted with print molecules containing suitable catalytic functionalities. Because dendrimers are stmcturally regulated polymers with an inner core like an enzyme active site, their characteristics as enzyme mimics also attract attention. 

The imprinted polymer was produced by oil in water emulsion polymerization and, after washing and drying, the imprinted material displayed considerably greater activity than the nonimprinted polymer, as well as the functional host monomer assayed as a catalyst in solution. The preparation of catalytic cavities at the surface of silica particles and other inorganic oxides has also been demonstrated by Markowitz et al. [68,69]. Silica particles were grown in a microemulsion, where the... 

In the middle of the last century, synthesis techniques were develop>ed that enabled the fabrication of well-defined and highly regular micropwrous silica materials, such as zeolites, with pore sizes comparable to the size of the molecules one would like to catalyze . The appropriate matching of size and shape of these micropores with shape and size of reactant, intermediate or product molecules has been demonstrated to be an important factor in the control of catalytic p>erformance. This is analogous to the lock and key reactivity principle which was developed in the early part of the last century as a way to describe the activity of enzymes, the biochemical proteins in living systems. This process involves matching the shape and size of the catalytic cavity with that of the reactant molecules. 

Figure 30 Catalysis with molecular baskets, (a) Formation of Cu(I)/02 adducts with basket-based dicopper(I) complexes and their absorption maxirna. (b) Threading of a polymer inside a catalytic cavity associating a Mn porphyrin catalyst and a diphenylglycoluryl molecular basket (oxidizing species generate by PhIO). ° ...

Matsuishi T, Shimada T, Morihara K. Definitive evidence for enantioselective catalysis over molecular footprint catalytic cavities chirally imprinted on a silicat(alumina) gel surface. Chem Lett 1992 1921-1924. 

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