Activity coefficient, of amino-acids

C. Molal Activity Coefficients of Amino Acids in Water... 

Khoskbarchi M, Vera JH (1996) Measurements of activity coefficients of amino acids in aqueous electrolyte solutions experimental data for the system HjO-iNaCl-iglycine and HjO-i-NaCl-hDL-sdanine at 25 °C. Ind Eng Chem Res 35 2735 - 2742... 

Activity Coefficients of Ampholytes.—The theoretical treatment of the electrical forces in a solution of an ampholyte containing free single ions, e.g., of added electrolytes, is very difficult it has, however, been carried out on the assumption that the amino-acid consists essentially of a spherical dipolar ion immersed in a continuous solvent medium. If R is the distance between the charges in the dipolar ion and a is the mean distance of closest approach of the other ions to this ion, the limiting value of the activity coefficient y of the dipolar ion in dilute solution is given by... 

It is possible to test equation (16) by means of solubility measurements of amino-acids in the presence of salts if /So is the solubility in a medium of ionic strength zero and dielectric constant Do, i.e., that in the pure solvent, and S is the solubility in a neutral salt solution of ionic strength p and dielectric constant D, then since /So/S is equal to the activity coefficient (cf. p. 177) it follows from equation (16) that... 

In Chapter 8, Zuyi Tao, in order to provide a better understanding of the ion-exchange behavior of amino acids, has compiled their particular acid-base properties, their solubility in water, their partial molal volumes, and their molal activity coefficients in water at 25 C. This information has been used in Gibbs-Donnan-based equations to facilitate a better understanding of the mechanism of amino acid uptake by ion exchangers at low and high solution concentration levels. Measurement of distribution coefficients and separation factors are also described. The eventual resolution of thermodynamic ion-exchange functions (AG, AH, and AS) is provided for the reader. 

The electronic properties of amino acid side chains are summarized in Table 3, and they represent a wide spectrum of measures. The NMR data are derived experimentally (37). The dipole (38), C mull, inductive, field, and resonance effects were derived from QM calculations (15). The VHSE5 (39) and Z3 (25) scales were developed for use in quantitative structure-activity relationship analysis of the biologic activity of natural and synthetic peptides. Both were derived from principal components analysis of assorted physico-chemical properties, which included NMR chemical shift data, electron-ion interaction potentials, charges, and isoelectric points. Therefore, these scales are composites rather than primary measures of electronic effects. The validity of these measures is indicated by their lack of overlap with hydrophobicity and steric parameters and by their ability to predict biologic activity of synthetic peptide analogs (25, 39). Finally, coefficients of electrostatic screening by amino acid side chains (ylocal and Ynon-local) were derived from an empirical data set (40), and they represent a composite of electronic effects. 

At 25°C a saturated aqueous solution of L-asparagine contains 0.186 M of the amino acid, while a saturated solution in ethanol is 2.3 x 10 M. What is the ratio of the activity coefficients of L-asparagine in these two soludons, and what is the Gibbs energy of transfer of a very small amount of L-asparagine from water to ethanol ... 

We used our PLSR-based sequence activity relationship to assign a regression coefficient to each varied amino acid. We then calculated the predicted activity for a proteinase K variant by summing the regression coefficients for amino acid variations that are present in that variant. In this case we did not include terms to account for interactions between the varied amino acids, though this can also be done 13). Figure 3 shows a good correlation between the predictions of our calculated sequence-activity relationship and the measured ability of heat-treated proteinase K variants to hydrolyze AAPL-p-NA. 

The prevalent receptor model for the excitatory amino acid is a tetrameric complex. As mentioned in the text, there is evidence that the channel conductance depends on the number of subunits that bind a ligand. Estimate the EC50 value and Hill coefficient for a dose-response curve assuming that the occupation at each subunit has a Kd value of 1 pi I, an % of 1, and that activation induces a transition to an active state independent of the state of the other subunits ... 

The peptide (melittin) was foimd associated to RMs in a single state as opposed to involvement of at least two forms of melittin with Upid in phospholipid vesicles. Folding and dynamics of this peptide in RMs were also investigated In RMs, activity of a-chymotrypsin was imaffected by pressurization while lipase lost its activity at low pressures and regained on depressurization. The use of pressure as a switch for lipase catalysis is discussed Partition coefficients for 11 amino acids, 17 dipeptides and 5 longer peptides in RMs were determined. 

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