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Acta Chim. Slov. 2010, 57, 651–659 651 Acta Chim. Slov. 2010, 57, 651–659 651 Sinha et al.: Apparent Molar Volumes and Viscosity B-Coefficients ... Sinha et al.: Apparent Molar Volumes and Viscosity B-Coefficients ... V V V
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   Acta Chim. Slov. 2010, 57, 651  –  659 651  Acta Chim. Slov. 2010, 57, 651  –  659 651 Sinha et al.:  Apparent Molar Volumes and Viscosity B-Coefficients ...  Sinha et al.:  Apparent Molar Volumes and Viscosity B-Coefficients ...   V   Scientific paper    Apparent Molar Volumes and Viscosity B-Coefficients of Glycine in Aqueous Silver Sulphate Solutions at   T = (298.15, 308.15, 318.15) K    Biswajit Sinha,* Pran Kumar Roy and Mahendra Nath Roy*    Department of Chemistry, University of North Bengal, Darjeeling- 734013, India   * Cor responding author: E-mail: biswachem @  gmail.com mahendraroy2002 @  yahoo.co.in    Received: 08-09-2009   Abstract    –  3 Apparent molar volumes (ϕ V ) and viscosity  B -coefficients for glycine in 0.005, 0.010, 0.015, and 0.020 mol.dm aque-ous silver sulphate (Ag 2 SO 4 ) solutions have been determined from solution density and viscosity measurements at (298.15, 308.15, and 318.15) K as a function of glycine concentration. The standard partial molar volume (ϕ   0 ) and ex-  perimental slopes ( S * ) obtained from the Masson equation have been interpreted in terms of solute-solvent and solute- solute interactions, respectively. The viscosity data were analyzed using the Jones-Dole equation, and the derived pa- rameters  A and  B were interpreted in terms of solute-solute and solute-solvent interactions, respectively. The standard volumes of transfer (Δϕ   0 ) and viscosity  B -coefficients of transfer (Δ  B ) of glycine from water to aqueous Ag SO solu- tions were derived to study various interactions in the ternary solutions. The structure making or breaking ability of glycine has been discussed in terms of the sign of (δ 2 ϕ   0 /δ T  2  ) . The activation parameters of viscous flow for the terna- V  P    ry solutions were also calculated and explained in terms of transition state theory. Keywords: Density, Viscosity, Partial molar volume, Viscosity  B -coefficient, Glycine, Aqueous silver sulphate solu- tions. 1. Introduction   Amino acids and peptides are the fundamental structural units of proteins and thermodynamic proper- ties of these model compounds in aqueous medium pro- vide information about solute-solvent and solute-solute interactions that help us to understand several biochemi- cal processes such as protein hydration, denaturation, aggregation etc. 1  –  4 It has been found that salt solutions have large effects on the structure and the properties of  proteins including their solubility, denaturation, dissoci- ation into subunits, and the activity of enzymes. 5,6  Proteins are complex molecules, and their behavior in solution is governed by a combination of many specific interactions. One approach that reduces the degree of complexity and requires less complex measurement techniques is to study the interaction in systems contain- ing smaller bio-molecules, such as amino acids and pep-   Acta Chim. Slov. 2010, 57, 651  –  659 652  Acta Chim. Slov. 2010, 57, 651  –  659 652 Sinha et al.:  Apparent Molar Volumes and Viscosity B-Coefficients ...  Sinha et al.:  Apparent Molar Volumes and Viscosity B-Coefficients ...  tides. Many cations and anions of neutral salts affect the properties of proteins such as their solubility, stability and biological activity in widely different manner. 5,6 It is well established that various co-solutes, co-solvents such as guanidine hydrochloride, 7,8  potassium thio- cyanate, 9  potassium chloride, 10 tetraalkylammonium salts, 11,12 can act as effective probes of their conforma- tion in solutions. 13  –  16  Thermodynamic properties of amino acids in aque- ous electrolyte solution thus provide valuable information about solute-solvent and solute-solute interactions. Hence there has been a number of works 7  –  12,21,32 revealing the ef- fect of electrolytic solutions on amino acids. But to the best of our knowledge such studies in aqueous Ag 2 SO 4 so- lutions are rare in the literature. Hence in this paper, an at- tempt has been made to unravel the various interactions in the ternary systems of glycine + Ag 2 SO 4 + water at 298.15, 308.15 and 318.15 K.   Acta Chim. Slov. 2010, 57, 651  –  659 653  Acta Chim. Slov. 2010, 57, 651  –  659 653 Sinha et al.:  Apparent Molar Volumes and Viscosity B-Coefficients ...  Sinha et al.:  Apparent Molar Volumes and Viscosity B-Coefficients ...  formula formula 0.020 mol dm  –  3   298.15 1.0035 0.821 318.15) K are listed in Table 2. 308.15 1.0000 0.693 318.15 0.9965 0.609 2. Experimental   2. 1. Materials   Glycine (Analar, BDH, purity >99%), and silver sul-  phate (Ag 2 SO 4 ) were used for the present study. Glycine was purified by re-crystallizing from methanol-water mixture and dried at 373.15 K for 12 h in an infrared drier and then in vacuo over P 2 O 5 at room temperature. Ag 2 SO 4 (Loba Chemie, India, purity > 98.5%) was recrystallized from concentrated sulfuric acid, cooled, then diluted with de-ionized water and the precipitate was filtered, washed and dried at 120 o C. De-ionized, doubly distilled, degassed water with a specific conductance < 10  –  6 S cm  –  1 was used for the  preparation of different aqueous Ag 2 SO 4 solutions. The  physical properties of different aqueous Ag 2 SO 4 solutions are listed in Table 1. Tabele 1: Densities and viscosities of dilferent aqueous Ag 2 SO 4 so- lutions at different temperatures. Molarity of Ag SO T ρ   × 10  –  3 η   2 4   in Aqueous solution (K) (kg m  –  3 ) (mPa s)  0.005 mol dm  –  3 298.15 0.9990 0.751 308.15 0.9956 0.614 318.15 0.9907 0.502 0.010 mol dm  –  3 298.15 1.0005 0.817 308.15 0.9973 0.725 318.15 0.9930 0.567 0.015 mol dm  –  3 298.15 1.0021 0.842 308.15 0.9988 0.715 318.15 0.9940 0.577 K of the desired temperature. The pycnometer was then removed from the thermostat bath, properly dried and weighed. The mass measurements were done on a digital electronic analytical balance (Mettler, AG 285, Switzer- land) with a precision of ± 0.01 mg. Adequate precautions were taken to avoid evaporation loses during the actual measurements. An average of triplicate measurement was taken into account. The precision of density measure- ments was evaluated to be within ± 3 × 10  –  4 g cm  –  3 . 2. 3. Viscosity Measurements   The viscosity (η)  was measured by means of sus-  pended Ubbelohde type viscometer, calibrated at the ex-  perimental temperatures with doubly distilled water and  purified methanol. A thoroughly cleaned and perfectly dried viscometer filled with experimental solution was  placed vertically in a glass-walled thermostat maintained to ± 0.01 K. After attainment of thermal equilibrium, ef- flux times of flow were recorded with a stop watch correct to ± 0.1 s. At least three repetition of each data repro- ducible to ± 0.1 s were taken to average the flow time. The uncertainty in viscosity measurements is within ± 0.003 mPa s. Details of the methods and techniques of the density and viscosity measurements have been described elsewhere. 17  –  19  3. Results and Discussion   Experimental values of molarity ( c ), densities ( ρ ), viscosities (η),  and derived parameters at (298.15, 308.15,   2. 2. Preparation of solutions   Stock solutions of glycine in different aqueous Ag 2 SO 4 solutions were prepared by mass and the working solutions were prepared by mass dilution. The conversion of molality into molarity was accomplished using the ex-  perimental density values. The uncertainty of molarity of the glycine solutions is evaluated to be ± 0.0001 mol dm  –  3 . 3. 1. Apparent Molar Volumes   The apparent molar volumes (φ V  ) were determined from the solution densities using the following equation: 12  (1) where  M is the molar mass of the solute, c is the molarity of the glycine in Ag 2 SO 4 + water mixtures, ρ 0 and ρ  are the densities of the solvent and the solution respectively. As the plots of ϕ V  values against square root of molar con- centrations (√ c ) were linear, ϕ V  values were fitted to the   2. 3. Density Measurements   The densities (ρ)  were measured with an Ostwald- Massion equation: 20  0   (2)Sprengel type pycnometer having a bulb volume of about 25 cm 3 and an internal diameter of about 0.1 cm. The pyc- where ϕ V is the partial molar volume at infinite dilution and S * is the experimental slope. The ϕ   0 values have been V V  nometer was calibrated at the experimental temperatures determined by fitting the dilute data ( c < 0.1) to Eq. (2) us- 0 * with doubly distilled water and purified methanol. The   Acta Chim. Slov. 2010, 57, 651  –  659 654  Acta Chim. Slov. 2010, 57, 651  –  659 654 Sinha et al.:  Apparent Molar Volumes and Viscosity B-Coefficients ...  Sinha et al.:  Apparent Molar Volumes and Viscosity B-Coefficients ...   V     pycnometer with experimental liquid was equilibrated in a glass-walled thermostated water bath maintained at ± 0.01 ing a weighted least square fit. Values of ϕ V and S  V along with the corresponding standard deviation (σ)  are listed in Table 3. The estimated uncertainties in ϕ   0 are equal to
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