Artificial enzymatic system

To prepare artificial enzymatic systems possessing molecular recognition ability for particular molecules, molecular imprinting methods that create template-shaped cavities with the memory of the template molecules in polymer matrices, have been developed [22, 30-35] and established in receptor, chromatographical separations, fine-chemical sensing, etc. in the past decade. The molecular... 

A second approach created a fusion protein from a PSI subunit (PsaE) and a nickel-iron [NiFe] hydrogenase [12], This new protein was then assembled into a PSI mutant lacking the PsaE subunit. The fused enzymatic system was attached to a gold surface in the same way as the PSn electrode described above using a His-tag on PSI, Ni(n) and NTA functionalities on the surface (Fig. 4a, right side). A soluble electron shuttle was used to transfer electrons from the electrode to PSI. From these two approaches the fusion protein is to date the most effective artificial enzymatic system for photo-driven hydrogen production and the activity is comparable to the electrocatalytic activity of the hydrogenase alone immobilized directly on an electrode. 

Such an inter-type difference will not be utilized in this book, mainly because it complicates the classification and is not necessary as tbe focus is placed on the substrates and the products. The argument is also valid for enzymatic transformations [12d, 14], where one enzymatic system with one enzyme or different independent enzymatic systems with one or more enzymes may be used. In Nature, as well as in several artificial enzymatic domino reactions, a mixture of different enzymes catalyzing independent cycles is employed. 

Growing membrane systems have been used to obtain artificial infrabiological systems. Walde et al. [47] have carried out the synthesis of polyadenylic acid in self-reproducing vesicles [48], in which the enzyme polynucleotide phosphorylase carried out the synthesis of poly-A, and membrane vesicle multiplication was due to the hydrolysis of externally provided oleic anhydride to oleic acid. The snag is that the enzyme component is not auto-catalytic. Enzymatic RNA replication in vesicles [49] suffers from the same problem. It is also not known whether redistribution of the entrapped enzymes into newly formed vesicles occurs or not. An affirmative answer would be evidence for vesicle reproduction by fission. 

In Chap. 6, biological supermolecules are explained and classified by function. Artificial supramolecular systems that mimic biological ones are also described. Biomimetic chemistry, which mimics the essence of a biosystem and then develops an artificial system that is better than the biological one, is widely used in this field. Fimctional developments, such as molecular transport, information transmission and conversion, energy conversion and molecular conversion (enzymatic functionaUty) based on biomimetic chemistry are described. New methodologies such as combinatorial chemistry and in vitro selection mimic evolutionary processes in nature. We leave this topic until the end of the book because we want to show that there is still lots to do in supramolecular chemistry, and that supramolecular chemistry has huge future potential. 

Diffusion is an efficient means of materials transport in natural and artificial nanoscale systems and can be readily employed in the study of enzymatic reactions in fluid membrane reactors of static or of changing geometries and morphologies. Other means of transport, e.g. electrophoretic or tension-driven modes are also available. 

Native enzymes, which can spatially and chemically recognize substrate molecules, are powerful catalytic systems in many biochemical processes under mild reaction conditions. The preparation of artificial enzymatic catalysts with the capability of molecular recognition capability, by a molecular-imprinting method, which creates cavities with a similar shape and size to the template molecule in polymer matrices has been developed [1-14]. The technique has been mainly established in the field of analytical chemistry - molecular receptors [15-23], chromatographic separations [24-28], fine chemical sensing [29-33]. All of the methods rely on the selective adsorption of target molecules on imprinted adsorption sites. The number of papers reported per year on molecular imprinting is summarized in Fig. 22.1. 

DNA polymerase - two polymerases that are not suitable for PCR. Here, it is shown that the simultaneous engineering of two different enzymatic activities within an enzyme can improve its application in artificial biochemical systems such as the PCR. 

Vigneswaran, C., Ananthasubramanian, M., and Anbumani, N. (2012b). Prediction and process optimization of bioscouring of organic cotton fabrics through specific mixed enzymatic system using artificial neural network lANNl. 1. Nat Fibres. 9(1), 1-22. 

Regarding the iron coordination geometry, the most active catalysts exhibit two available cis-coordination sites that facilitate the activation of the oxidant. Conversely, relatively inactive complexes usually show only one available coordination site or have two available sites in a trans position. As stated before, iron-based enzymatic systems in nature involve the formation of high-valent metal intermediates within the catalytic cycle. Similarly, oxo-iron complexes have been proposed as the main intermediate for artificial oxidation processes. Depending on the iron complex, the type of oxidant and substrate and the mechanism involved in the oxidation process, this intermediate could be a Fe =0 or H0-Fe =0 species. Wieghard et al. 

As an industrial and commercial product, PVA is valued for its solubility and biodegradability, which contributes to its very low environmental impact. Several microorganisms ubiquitous in artificial and natural environments — such as septic systems, landfills, compost and soil — have been identified and they are able to degrade PVA through enzymatic processes. 

The wide variety of enzymes available gives for promise enzymatic derivatization to become a potent analytical tool in the future. Better understanding and theoretical formulations will lead to commercial availability of immobilized enzymes and consequently to more ready use of them. Since in such systems a low content of organic cosolvent in the mobile phase can only be tolerated (whereas a compromise has to be made as far as the optimum mobile phase pH is concerned), artificial enzymes, which are synthetic polymer chains having functional groups that mimic the biocatalytic activity of natural enzymes, are currently being synthesized and investigated as a means to overcome such limitations (276). 

This process was extended to the phosphorylation of various substrates, in particular to the synthesis of ATP from ADP in mixed solvent [5.62a] and in aqueous solution in the presence of Mg2, probably via formation of a ternary catalytic species 83 [5.62b]. The latter abiotic ATP generating system has been coupled to sets of ATP consuming enzymes resulting in the production of NADH by a combined artificial/natural enzymatic process (Fig. 9) [5.63]. 

In natural processes, metal ions are often in high oxidation states (2 or 3), whereas in chemical systems the metals are in low oxidation states (0 or 1). This fact inverts the role of the metal center, such that it acts as a one-electron sink in a natural system, but as a nucleophile in an artificial ones (see other chapters of this book and the review by Aresta et al. [109]). Nevertheless, important biochemical processes such as the reversible enzymatic hydration of C02, or the formation of metal carbamates, may serve as natural models for many synthetic purposes. Starting from the properties of carbonic anhydrase (a zinc metalloenzyme that performs the activation of C02), Schenk et al. proposed a review [110] of perspectives to build biomimetic chemical catalysts by means of high-level DFT or ah initio calculations for both the gas phase and in the condensed state. The fixation of C02 by Zn(II) complexes to undergo the hydration of C02 (Figure 4.17) the use of Cr, Co, or Zn complexes as catalysts for the coordination-insertion reaction of C02 with epoxides and the theoretical aspects of carbamate synthesis, especially for the formation of Mg2+ and Li+ carbamates, are discussed in the review of Schenk... 

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