Nature and composition of organic acids

Hydrophobicity is repulsion between a nonpolar compoimd and a polar environment, such as water. The distribution and hydrophobicity of hydrophobic amino acids are characteristic of each protein, so a specific separation is possible with use of hydrophobic supports. Different models are used for the description of protein hydrophobicity and hydrophobic interactions, and different theories are proposed for the retention mechanism of proteins in HIC [31]. In addition to the important role of water in the strengthening—weakening of the hydrophobicity, these interactions can be induced by changing the ionic strength, presence of organic solvents, temperature, and the pH value of the chromatographic media. Based on these properties, the HIC separation occurs by the modulation of the frequency and distribution of surface-exposed hydrophobic amino-acid residues, the hydrophobicity of the medium, the nature and composition of the sample, as well as type and concentration of salt in the mobile phase (see Figure 7.6). 

Like other dissolved organic nutrients, the chemical composition of organic P is relatively unknown. Marine dissolved organic phosphorus (DOP) composition has been mostly identified as particular compound classes such as monophosphate esters, phosphonucleotides, nucleic acids, phospholipids, phosphonates and polyphosphates (Benitez-Nelson, 2000). Kolowith et al. (2001) found that monophosphate esters and phosphonates are major components in the Pacific Ocean, the Atlantic Ocean and the North Sea. ATP (adenosine triphosphate), ubiquitous in aU living cells, has been used as a model DOP compound in radiotracer experiments to obtain information on P sources and fluxes in natural environments (Bjorkman et al., 2000 Karl and Bossard, 1985) and cyanobacterial cultures (Fu et al., 2006). 

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