Natural system analogues

The outcomes of applying these natural system analogues to construction would be a built environment ... 

The 2-azadiene system of the pyrazinone scaffold undergoes inter- and intramolecular cycloaddition reactions with a variety of (functionalized) alkenes forming bicyclic adducts, leading to the stereoselective generation of a variety of natural product analogues as well as peptidomimetics [58]. These bicyclic compounds could serve as key intermediates in the synthesis... 

The pyridinium salt NAD 19a and its reduced form NADH 20a are important co-factors for many enzymes, fhe reduced form is involved in enzyme mediated reductions where it is converted to NAD. In natural systems, NAD is converted back to NADH by another enzyme-controlled process. Attempts to effect the direct electrochemical conversion of NAD to NADH are not very successful. Reduction on a mercury cathode at -1.1 V see on the first one-electron reduction wave leads to the radical-zwitterion, which reacts further to give dimers. Three stereoisomers of the 4,4 -dimer account for 90 % of the mixture and three 4,6 -dimers form the remainder [78]. Reduction at -1.8 V on the second reduction wave produces only 50 % of enzymatically active 1,4-NADH. The NAD analogue 19b shows related behaviour and one-electron reduction affords two diastereoisomers... 

Once it was established that a number of enzymes contained non-peptidic structures, and that these features were present as binding sites for catalytic metals, researchers started to look for simple analogues that could be used as models for the more complex natural systems. The motivation behind these investigations was to gain a greater understanding into how the natural systems work by reducing the active... 

The speculations about bifurcation in autocatalytic systems lead us to conclude that the adaptive natural selection of biological systems analogue may have a primitive in analogue, and even in abiogenic autocatalytic, systems where chemical "mutations" of the autocatalyst may occur [2],... 

In order to attempt to address the issues of oral bioavailability and compound stability a number of synthetic analogues of the natural products were generated. It was found that long chain alkyl amides of the 5 5 bicycle system possessed comparable activity to their natural imide analogues. (Table 3, Activity of synthetic analogues). Whilst these compounds were more stable to pH extremes than the natural compounds, however, their solubility was lower, and they showed no oral bioavailability. 

Due to the specificities of the RBS technique, model systems representative of colloids, heavy elements and surfaces encountered in natural systems relevant to radwaste disposal have been selected. Hence, investigations have been devoted to the study of i) colloids representative of those met in granitic or sedimentary formations (11, 16) such as silica, iron oxide and humic acids which may be considered as carrier colloids, ii) heavy elements as chemical analogues of radionuclides of interest such as Nd(III) or U(V1) as ionic species... 

Nature shows how complicated it is to construct metal-containing macromolecules that are active but also selective with respect to a specific property. Natural systems do not need to exhibit a high stability towards storage and heat because the active materials are readily replaced. On the other hand, artificial systems must be more stable over time and towards heat. Therefore extreme demands are placed upon artificial metal-containing macromolecules. It IS important to point out that the fundamental behaviors of low molecular weight metal complexes will be shown also in macromolecular analogues. But these behaviors, and thus the properties, are strongly influenced by the kind of macromolecular environment or the kind of incorporation into a macromolecule. 

These mutually interacting molecules occur naturally in organisms (except analogues) and thus may be called bioaffinity systems. In contrast, similar artificial systems exist which mimic these natural systems and they may also be utilized. Such frequently used couples are ... 

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