Hydrogen donors properties required

Compounds that are more polar, and which can better hydrogen-bond with water, require less drastic alterations to the solvent environment to cause dissolution to occur. On the right side of Figure 3, we associate solute polarity with each formulation concept. Drugs that are good hydrogen donors, in the extreme sense, have acidic properties. Likewise, those that are very good acceptors have basic properties. For these compounds, formation of a salt by protonation or deprotonation is a feasible route. 

As shown in Fig. 1, the enzyme catalyzes the reduction of ribonucleoside diphosphates (Fig. lA) by dithiothreitol (Fig. IB). K values for CDP and DTT are 70 x Af and 20 mAf, respectively. The requirement for a dithiol suggests that, as for other class II RNRs, such as the extensively studied enzyme from Lactobacillus leichmannii, the hydrogen donor is very likely to be a dithiol protein such as thioredoxin or glutaredoxin. However, there is still no experimental evidence that an archaeal thioredoxin operates as an electron source for RNRs. The enzyme also requires AdoCbl for which a value of 1 pAf has been obtained (Fig. 1C). Finally, the reaction has an optimal temperature of 80° (Fig. ID), with very little activity at 30°. How AdoCbl resists such a high temperature and how the enzyme controls Co-C bond homolysis required for catalysis in thermophilic AdoCbl-dependent enzymes is an intriguing question. These properties are shared by other isolated thermophilic class II RNRs (Table II). 

Antioxidant activity is de ned as a property of antioxidants to neutralize any free radicals. Generally speaking of antioxidants, their activity is required to act as a hydrogen donor. On the other hand, the aromatic ring plays a signi cant role and especially phenolic hydroxyl groups enhance the inhibition of oxidation (Giilcin, 2011). 

The thermal properties of the benzo-crown enediynes esters and their complexes were studied by DSC [397]. In the absence of a hydrogen donor, the radicals polymerized evolving heat, which gave an exothermic peak in the DSC curve. The onset temperature of the exothermic peak corresponds to the temperature required for Bergman cyclization confirming the generation of free radicals. For the crown ether derivative 3.495 and its complexes 3.496 and 3.876, this temperature was... 

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