Hydrogen bonds network, polarized water

Hydrophilic molecules are composed of ions (such as sulphonate, sulphate, carboxylate, phosphate and quaternary ammonium), polar groups (such as primary amines, amine oxides, sulphoxides and phosphine oxide) and non-polar groups with electronegative atoms (such as oxygen atom in ethers, aldehydes, amides, esters and ketones and nitrogen atoms in amides, nitroalkanes and amines). These molecules associate with the hydrogen bonding network in water. 

Variations of R with A suggest a two-step hydration process solvation and formation of disconnected water clusters centered on polar head groups, followed by the formation of a continuous hydrogen-bond network. At low A, Ri depends logarithmically on co, suggesting bidimensional diffusion of protons in the interfacial region between polymer and water. 

Whereas the polarity effect is ascribed to the dielectric constant, the hydrophobic effect is a consequence of the high cohesive energy density (c.e.d.) of water, resulting from a unique hydrogen-bonding network (Lubineau et al., 1994). Given table 6.5, which compares the cohesive energy density and the dielectric constant of selection of common solvents at 25°C, there is no correlation between the structuralization and the polarity of the solvents. 

Based on chemical considerations alone, ribozymes should be able to catalyze many different types of reactions. Ribozymes can maintain defined secondary and tertiary structures, just as protein enzymes do. Ribozymes can interact with substrates specifically via hydrogen bond networks, just as protein enzymes do. Finally, ribozymes have available to them a chemistry that, while more limited than of proteins, is substantial. RNA contains proton donors and acceptors with pK, values that cluster at 4 and 9.71 The critical lack of a good donor/acceptor with a pKt near 7 can be rectified by any of several simple expedients, such as modification of guanosine to 7-methylguanosine, protonation of triple base-paired cysto-sine,72 or inclusion of a proton donor/acceptor in an environment with a different polarity than water (in this respect, it is interesting to note that Dahm and Uhlenbeck have found that the cleavage reaction catalyzed by the hammerhead ribozyme is dependent on some dissociable proton with a pKa of 8.0).73... 

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