Amino acids ionic properties

It is to note that, although ammonium and pyrrolidium based amino-acid ionic liquids, subsequently prepared by the same authors, do not show improved properties compared to die corresponding imidazolium based salts, positive results have been obtained introducing the tetrabutyl-phosphonium cation/ ... 

He, L., Tao, G.-H., Parrish, D.A. and Shreeve, J.M., Slightly viscous amino acid ionic liquids Synthesis, properties, and calculations, J. Phys. Chem. B113 (46), 15162-15169 (2009). 

The dielectric constants of amino acid solutions are very high. Thek ionic dipolar structures confer special vibrational spectra (Raman, k), as well as characteristic properties (specific volumes, specific heats, electrostriction) (34). 

Separation methods based on size include size exclusion chromatography, ultra-filtration, and ultracentrifugation (see Chapter Appendix). The ionic properties of peptides and proteins are determined principally by their complement of amino acid side chains. Furthermore, the ionization of these groups is pH-dependent. 

Table XIX contains stability constants for complexes of Ca2+ and of several other M2+ ions with a selection of phosphonate and nucleotide ligands (681,687-695). There is considerably more published information, especially on ATP (and, to a lesser extent, ADP and AMP) complexes at various pHs, ionic strengths, and temperatures (229,696,697), and on phosphonates (688) and bisphosphonates (688,698). The metal-ion binding properties of cytidine have been considered in detail in relation to stability constant determinations for its Ca2+ complex and complexes of seven other M2+ cations (232), and for ternary M21 -cytidine-amino acid and -oxalate complexes (699). Stability constant data for Ca2+ complexes of the nucleosides cytidine and uridine, the nucleoside bases adenine, cytosine, uracil, and thymine, and the 5 -monophosphates of adenosine, cytidine, thymidine, and uridine, have been listed along with values for analogous complexes of a wide range of other metal ions (700). Unfortunately comparisons are sometimes precluded by significant differences in experimental conditions.

This mode of binding of HI to the nucleosome is consistent with the findings that at low histone-to-DNA ratios and/or at low ionic strength histone HI binds preferentially to supercoiled DNA (Vogel and Singer, 1975, 1976). This preferential binding has been shown to be the property of the HI peptide fragment, amino acid residues (73-106). 

New brush-type phases (donor-acceptor interactions) are appearing all the time. " Examples are stationary phases comprising quinine derivatives and trichloro-dicyanophenyl-L-a-amino acids as chiral selectors. Quinine carbamates, which are suitable for the separation of acidic molecules through an ionic interaction with the basic quinine group, are also commonly used but in general they are classified with the anion-exchange type of chiral selectors (see further) because of their interaction mechanism, even though r-donor, r-acceptor properties occur. (Some separations on Pirkle-type CSPs are shown in Table 2.)... 

A. The ionic properties of proteins at pH 7.4 are determined by the mixture of their acidic and basic amino acids. 

Amino acids vary in their acid-base properties and have characteristic titration curves. Monoamino monocarboxylic amino acids (with nonionizable R groups) are diprotic acids (+H3NCH(R)COOH) at low pH and exist in several different ionic forms as the pH is increased. Amino acids with ionizable R groups have additional ionic species, depending on the pH of the medium and the pIQ of the R group. 

Each of these amino acids has a nonpolar side chain that does not bind or give off protons or participate in hydrogen or ionic bonds (see Figure 1.2). The side chains of these amino acids can be thought of as "oily" or lipid-like, a property that promotes hydrophobic interactions (see Figure 2.9, p. 18). 

The acid-base properties, and hence ionic character, of peptides and proteins also can be used to achieve separations. Ion-exchange chromatography, similar to that described for amino acids (Section 25-4C), is an important separation method. Another method based on acid-base character and molecular size depends on differential rates of migration of the ionized forms of a protein in an electric field (electrophoresis). Proteins, like amino acids, have isoelectric points, which are the pH values at which the molecules have no net charge. At all other pH values there will be some degree of net ionic charge. Because different proteins have different ionic properties, they frequently can be separated by electrophoresis in buffered solutions. Another method, which is used for the separation and purification of enzymes, is affinity chromatography, which was described briefly in Section 9-2B. 

Within the sequence of the first 40 amino acids of the N-terminus, which is generally regarded as the coenzyme-binding site, six amino acid differ from each other in the L. brevis and L. kefir ADHs. Three of them are responsible for differing ionic properties of this region, Asn-3 (L. brevis) changed into Asp (L. kefir), Asp-6 into Lys, and Thr-25 into Asp. The coenzyme-binding sequence G-G-T-L-G-I-G found at the positions 14—20 of L. brevis ADH is identical in both enzymes. 

While cyclic peptides have proven to be problematic, we beheve that amino acids are ideal candidates for derivatization of our macrocyclic scaffolds. Mary natural and unnatural amino acids with appropriately protected side chains are commercially available or can be readily prepared providing facile access.22 The a-amino- and a-carboxy- groups common to all of these will provide constant sites for attachment to a macrocyclic scaffold core. Side chains varying in aromatic, aliphatic, polar and ionic characters should provide sufficient chemical diversity. Finally, amino acids may be combined in many ways to form short acyclic peptides, allowing access to more diverse chemical properties not found in individual amino acids. 

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