Cationic amino acids

The formation of intramolecular hydrogen bonds can also anchor specific conformations of the amino acid cation-radicals. Using a combination of resonant two-photon laser ionization and... 

Sader HS, Fedler KA, Rennie RP, Stevens S, Jones RN. (2004) Omiganan pentahydrochloride (MBI 226), a topical 12-amino-acid cationic peptide Spectrum of antimicrobial activity and measurements of bactericidal activity. Antimicrob Agents Chemother 48 3112-3118. 

B. Thermodynamic Functions for the Interaction of Strong-Acid Cation-Exchange Resin in the H -Ion Form with Amino Acid Cations... 

The exchange of an amino acid cation, R—CH(NHj)COOH, for hydrogen ion in the strong-acid cation-exchange resin at a pH < pK j o H can be described with the equation... 

Table 3 Thermodynamic Functions of Ion Exchange of Amino Acid Cations on Strong-Acid Cation-Exchange Resin in Hydrogen Form...

Figure 5.10 Selectivity coefficient behaviour for amino acid cation exchange against sodium on styrenesulfonate resins of various percent crosslinking (Reprinted from J. Feitelson, in Ion Exchange (A Series of Advances) , ed. J. A. Marinsky, Marcel Dekker, New York, Vol. 2, p. 135, by courtesy of Marcel Dekker Inc.)...

There are a number of organic acids used as ionic carriers for metal ions and amines or amino acids pertraction. The mostly used anionic carrier for metal ions and amino acids is di-2-ethylhexyl phosphoric acid. The carrier is dissolved in the membrane phase as a dimmer, which reacts at the donor phase-membrane interface with amino acid cation, forming an ion pair and releasing a proton. For example, selective speciation of different chromium species (chromate and chromium ions) was achieved by the combination of... 

P amino acids cation stepwise or gradient elution, with citrate buffers... 

Amino acids Cation exchangers DC-4A, DC-6A and Aminex A-9 Buffers Post-column derivation with o-phthalaldehyde or ninhydrin fluorescence 96... 

The desired stereochemistry for the amino acid cation synthon is achieved by inversion of the stereocenter of 795 with thiolacetic acid under Mitsunobu conditions to give 796. Functional group manipulation then gives the target iodide 799. The optical purity of alcohol 797 is >95%... 

HOD IMS methods (5.2.1). The magnitude of necessary for HOD IMS analyses of order n depends on the a values for ions of interest (rigorously, on the spreads between for the species to be resolved, 3.1.7). The most extensive compilations of 02 values are the measurements for 17 amino acid cations and anions that we looked at in the context of FAIMS waveform optimization (3.1). In that set, the means (medians) are 6.8x10 (6.0x10 ) Td for a-[ and 1.5x10 ° for fl2 the similarity of means and medians for either suggests that the selection of a and 02 values is representative. ... 

FIGURE 5.9 Pairwise correlations between ion mass (or m/z), absolute mobility, and coefficients Oi and 02 for amino acid cations ( ) and anions (o). (From Shvartsburg, A.A., Mashkevich, S.V., Smith, R.D., J. Phys. Chem. A, 110, 2663, 2006.) The transport properties (in N2 gas) are from IMS and FAIMS experiments. No values of K for anions have been... 

By the above general argument, HOD IMS methods should also be more orthogonal to DT IMS than FAIMS. Indeed, the K and a values for amino acid cations are nearly proportional with Xc = 0-93 (Figure 5.9d), whereas K and 02 are independent with x — Xc2 — 0.15 (Figure 5.9e). Further, there is virtually... 

Anion exchangers are mainly employed in the extraction of carbohydrates, peptides, nucleosides, and amino acids. Cation exchangers are useful for extracting amino acids and nucleosides [217]. 

In a similar manner we may assume that the amino acid cation IX accepts a proton in very acid solution to form the dibasic ion XI. It may at first seem rather surprising to consider a carboxyl group basic, but the work of Hammett (for review see Hammett, 1940) has demonstrated that carboxylic acids behave as proton acceptors in sulfuric acid. The positive charges on the ion will promote ionization on the a-carbon atom and the resulting polar form (XII) will be a resonance hybrid of the nonpolar form (XIII) and thus be stabilized ... 

Steps X to XIV would therefore transform the asymmetric cation X into a symmetrical ion which on reversal of the prototropie changes would revert to the racemized amino acid cation (X). 

Table 1 Hydration numbers of amino acid cations loaded in strong cation exchangers. Two inorganie eations are presented for comparison. The table contains data obtained with different experimental methods. Reprinted from Vestnik Voronezhskogo Gosudarstvennogo Universiteta[ll V. F. Selemenev...

Crystals of L-tryptophan hydrochloride and hydrobromide are iso-morphous with each other and the conformation of the amino acid cations is essentially the same in both crystals (405). The plane of the... 

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