Partial molar volume, amino acids

Equation (24) renders intelligible the behavior of the dielectric constant of dipolar ions in polar solutions. It explains the linear increase of D with concentration, since changes in partial molar volumes, only slightly dependent on concentration, can only affect the DyVi term. It also explains the nearly identical values of D of the amino acids of the same moment, and the fact that D of a given amino acid is insensitive to changes in the dielectric constant of the solvent, for the change of solvent can directly affect 8 only through the term D V2. 

B. Partial Molar Volumes of Amino Acids in Water... 

The composition dependence of the total volume of a solution at constant temperature and pressure is expressed in terms of the partial molar volumes of the solute and the solvent. Since we are concerned with solvation properties, the quantities which we need to discuss are the partial molar volumes in infinite dilution of the solute so that solute-solute interactions make no contribution. In practice, partial molar volumes are obtained indirectly from precise density measurements. The partial molar volumes at infinite dilution of the amino acids are compiled in Table 2 [7]. It is apparent from these data that an approximately linear correlation exists between the partial molar volume and the number of carbon atoms in the backbone. The data indicate volume contributions from the polar head group (NH, COj) and from the CH2 group and to be about... 

Partial molar volume of amino acids and pressure effects... 

In this section, we combine the K-B theory with the RISM theory and derive an equation that allows us to calculate the partial molar volume of a polyatomic solute immersed in molecular solvent. The equation is then applied to calculations for the series of 20 amino acids occurring naturally in living systems. These amino acids are chosen because they are of great biological interests as ingredients of proteins and they have... 

Calculation of partial molar volume of 20 amino acids [64]... 

Table 3.15. Partial Molar Volumes (cm /mol) of the Twenty Amino Acids in Aqueous Solutions (The values in parentheses represent the difference between the values in the previous and following columns. The values in square brackets represent the partial molar volumes of amino acids with non-dissociated residues.)...

We plot AFm = M.exp — kM(14i,exp) IS the experimentally measured value and Vm the theoretically calculated value) against the number of atoms in the amino acids in Fig.3-14. It is obvious that the discrepancy AVm increases as the number of atoms N becomes larger. There can be two major reasons for this. The first one is the ideal fluctuation volume discussed in 4.2. The partial molar volume can be decomposed into two terms, the ideal contribution VJJj and the excess quantity The former can further be decomposed into the ideal-gas contribution and the fluctuation volume... 

Figure 3.15. Partial molar volumes of the 20 amino acids calculated by the three different versions of the RISM theory. and denote the values theoretically...

By combining the K-B theory with the RISM theory, we have derived the equation for calculating the partial molar volume of a polyatomic solute in solvent. We have calculated the VM-values of the 20 amino acids, constituents of natural proteins. The calculated values are always smaller than the corresponding experimental values. Moreover, the discrepancy becomes larger as the number of the atoms in the amino-... 

Perkins (2001) discussed x-ray and neutron diffraction from the hydration shell of proteins, but did not refer to the experimental results of Svergun et al. (1998). Instead he used the estimate of 0.0245 nm for a water molecule in the hydration shell by Gerstein and Chothia (1996) to explain the apparent different partial molar volume measured densitomefrically for proteins in solution with the values calculated from their amino acid contents. 

TABLE 8.2. Temperature dependence of the partial molar volumes (cm mor ) of the peptide unit and of the side chains of amino acid residues for the temperature range 5-125 °C [11],... 

QSPR Modeling of Partial Molar Volumes of 20 Amino Acids... 

Up to now, the characterization of amino acids by theoretical structural descriptors has not received wide attention. The study reported in [35] employs for predicting the partial molar volumes (pMV) of 17 amino acids (AA) that include some heterocycHc molecules, and appear Usted in Table 3 together with the numerical values for x and Three of the compounds have unknown values for the experimental property (isoleucine, threonine, lysine). This particular molecular set involves four optimizable parameters for each type of atom x (carbon),y (oxygen), z (nitrogen), and w (sulfur). As a starting point in the search for the optimal values of the four parameters, it is assumed that all the variables have zero as the initial value. The simple... 

Table 9. Further experimental specific volumes of some selected small molecules and polymers under different environmental conditions. Some values presented in this table were taken from [86D1] for detergents and lipids primarily the compilation in [78S1] was used most values for electrolytes were derived from the partial molar volumes cited in [72M1]. Only in a few cases, calculated volumes (Vg) were mentioned instead of experimental ones. Note that a great number of values (e.g., for amino acids, betaines, small peptides, carbohydrates, lipids, nucleobases, denaturants, detergents, substrates, products and analogs of enzymic reactions) are given in Table 8.

In all measurements, the heating rate was 1 °C min-1. The partial molar heat capacity of a fully extended peptide is calculated from its amino acid composition according to the method of Privalov and Makhatadze.1 37 Partial specific volume of the peptides was calculated from amino acid composition according to Makhatadze et al.,[138l with a value of 0.751 mL-mg-1. 

To evaluate molar masses from equilibrium runs it is necessary to know (very accurately) the value of the partial specific volume of the species. The partial spedfic volumes of proteins and nucleic acids are not dependent on conformation so they can be evaluated from the amino acid or nucleotide composition (Laue et al. 1992). A satisfactory working value for proteins is v = 0.735 10-3 m3 kg-1. Partial specific volumes can also be measured by comparison of equilibrium runs carried out in H20, D20 and H280, using the different densities of the three isotopic forms of water. 

The D-xylanase system of Stereum sanguinolentum,199 the only D-xylanase for which an amino acid composition has as yet been published, was found to contain a high proportion of acidic and aromatic amino acid residues. The M.W., as determined from the amino acid composition, is 23,900, compared with 21,600 as calculated from ultracentrifugation data. Other physical parameters that have been determined199 for this D-xylanase include the sedimentation coefficient [2.8S, which is similar to that reported for a D-xylanase isolated from Trichoderma viride,203 namely, 2.IS], the partial specific volume (0.71 cm3.g 1), and the molar extinction coefficient (6.25 X 104). Activation energies have been reported for D-xylanases from Schizophyllum commune233 (EA 28.6 kj.mol-1) and from a commercial cellulase preparation229 (EA 34.0 kj.mol-1). 

The adsorption of proteins at interfaces is a key step in the stabilization of numerous food and non-food foams and emulsions. Our goal is to improve our understanding of the relationships between the sequence of proteins and their surface properties. A theoretical approach has been developed to model the structure and properties of protein adsorption layers using the analogy between proteins and multiblock copolymers. This model seems to be particularly well suited to /5-casein. However, the exponent relating surface pressure to surface concentration is indicative of a polymer structure intermediate between that of a two-dimensional excluded volume chain and a partially collapsed chain. For the protein structure, this would correspond to attractive interactions between some amino acids (hydrogen bonds, for instance). To test this possibility, guanidine hydrochloride was added to the buffer. A transition in the structure and properties of the layer is noticed for a 1.5 molar concentration of the denaturant. Beyond the transition, the properties of the layer are those of a two-dimensional excluded volume chain, a situation expected when there are no attractive interac-... 

Absolute Heat Capacity. The absolute partial molar heat capacity of the protein can be calculated using the temperature dependence of the heat capacity of the protein solution (i.e., a protein DSC scan), the heat capacity of the buffer (i.e., a buffer scan), the sample cell volume, the protein concentration, and the partial specific volume of the protein (calculated from the amino acid composition). ... 

PARTIAL MOLAR QUANTITIES 83 TABLE 4.4 Partial Specific Volume of Amino Acid Residne, v,-... 

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