International Journal of Scientific & Engineering Research, Volume 5, Issue 1, January-2014 73

ISSN 2229-5518

Viscometric and Compressibility behavior of Arginine in Aqueous-Glucose solutions Umadevi. Ma, Kesavasamy. Rb, Palani. Rc, Priya N.Sb, Rathina.Kd

Abstract— Densities , Ultrasonic Speeds and Viscosity of aqueous-glucose (5, 10, and 15% of glucose, in water) and of solutions of Arginine in three aqueous-glucose solvents were measured at 303, 308, and 313 K. From these experimental data Compressibility, Apparent Molar Compressibility , Limiting Apparent Molar Compressibility and the Slope , Transfer Compressibility , Falkenhagen coefficient, Jones Dole coefficient, Free energy of activation of Viscous flow per mole of solvent and Viscous flow per mole of solute were calculated. The results are interpreted in terms of solute_solvent and solute_ solute interactions in Arginine systems. It is observed that there exist strong solute_solvent interactions, which increases with increase in glucose concentration.

Index Terms— Arginine, Apparent Molar Compressibility, Transfer Compressibility, ultrasonic speeds, Viscosity.

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1 INTRODUCTION

NOWLEDGE of the interactions is responsible for stabi- lizing the native state of a globular protein in aqueous solution, which is essential to understand its structure
and function. The study of these interactions provides an im- portant insight into the conformational stability and unfolding behavior of globular proteins [1]. Hydration of proteins plays
Salt solutions are known to influence the stability and struc- ture of proteins [13],[14]. Remarkable experimental work has been reported on the thermodynamic and transport properties of amino acids in aqueous salt solutions [11],[12], but very few studies exist on the volumetric and compressibility properties

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a significant role in the stability, dynamics, structural charac-
teristics, and functional activity of these biopolymers. Since
proteins are large complex molecules, the direct study of pro-
tein–water interactions is difficult. Therefore, one useful ap- proach is to investigate interactions of the model compounds of proteins, i.e., amino acids in aqueous and mixed aqueous solutions [2],[3],[4],[5]. Since amino acids are the building
blocks of all living organisms and incorporate structural fea- tures of proteins, their physicochemical and thermodynamic properties in aqueous solutions are found to provide valuable information on solute–solute and solute–solvent interactions that are important in understanding the stability of proteins. Some of these interactions are found implicated in several bio- chemical and physiological processes in a living cell [6]. The choice of water for preparing mixed solvent is important and unique role in determining the structure and stability of pro- tein since its presence is known to give rise to hydrophobic forces [7], which are of prime importance in stabilizing the native globular structure of protein [8].
Due to complex structure of proteins, the study of conformational stability and unfolding behavior of globular proteins has proved quite challenging and still remains a sub- ject of extensive investigations [9,10]. Therefore, protein model compounds such as amino acids, which are basic components of proteins, have been investigated in detail with respect to their thermodynamic properties in aqueous and mixed aque- ous solutions [11], [12], [13], [14], [15], [16].
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aDepartment of Physics, SVS College of Engineering, Coimbatore,

India. PH - 9788150590. E-mail: devuma55@gmail.com

bDepartment of Physics, Sri Ramakrishan College of Engineering, Coimbatore, India.

c DDE Wing, Annamalai University, Chidambaram, India.

dDepartment of Physics, Kumaraguru College of Technology, India.

of amino acids in aqueous organic salt solutions [15], [16], [17],
[18], [19], [20], [21], [22] probably due to the complex nature of
their interactions. Moreover, no systematic studies are availa-
ble on the thermodynamic and transport properties of amino acids having polar side group (chain) in the presence of organ- ic salt solutions. To the best of our knowledge, no Viscometric and compressibility studies have been reported on Arginine in
aqueous-glucose solutions.
In the present paper, we report the Densities (ρ), Ultrasonic
speeds (u) and Viscosities (η) of aqueous-glucose (5, 10,
and15% of glucose, in water) and of solutions of Arginine in
three aqueous-glucose solvents were measured at 303, 308,
and 313 K. From these experimental data Compressibil- ity(β),Apparent Molar Compressibility (Ks, ϕ ), Limiting Ap- parent Molar Compressibility (K°s, ϕ ) and the Slope (Sk ), Transfer Compressibility (K°s, ϕ,tr ), free energy of activation of
Viscous flow per mole of solvent (Δμ1 °#) and Viscous flow per
mole of solute, (Δμ2°#) for Arginine in aqueous-glucose solu- tions were also calculated. The thermodynamics of viscous
flow has also been discussed.

1 Experimental

Analytical reagent grade Arginine, used after recrystalliza- tion twice from (ethanol + water) mixtures. Glucose (analytical reagent) was dried over P2 O5 in vacuum desiccators for 72 hrs at room temperature before use. Water used in the experi- ments was deionized and distilled, and was degassed prior to making solutions. Solutions of Glucose were prepared by mass and used on the day they were prepared. The mass per- centage of Glucose in these solutions ranged from 5% to 10% by 15% increments. Solutions of amino acids were prepared by mass on the molality scale with an accuracy of 0 to .1 g. The density of all compounds was measured by 10 ml specific gravity bottle calibrated with double distilled water and ace-

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International Journal of Scientific & Engineering Research, Volume 5, Issue 1, January-2014 74

ISSN 2229-5518

tone.
The ultrasonic velocity was measured by a single crystal
interferometer with a high degree of accuracy operating at a
frequency of 3 MHz (Model F-05, with digital micrometer) at
303, 308 and 313K. The viscosity was measured by Ostwald’s
viscometer. An electronically operated constant temperature
water bath is used to circulate water through the double
walled measuring cell made up of steel containing the experi-
mental solution at the desired temperature.

3 RESULTS AND DISCUSSIONS

The experimental values of Densities (ρ), ultrasonic speeds (u) and viscosities (η) of Arginine solutions in water and in aque- ous-glucose solvents as functions of Arginine concentration and temperature are listed in Table 1.
The apparent molar compressibility, K S, ϕ of the Arginine so-
lutions in aqueous glucose were calculated by using the rela-
tions
(1) where m is the molar concentration of the solute (Arginine), ρ and ρo are the densities of the solution and the solvent (aque-
ous-glucose), respectively; M is the molar mass of the solute
A perusal of Table (3) reveals that the values of K°s, ϕ , Sk are
negative for Arginine in aqueous-glucose solutions indicating
the presence strong solute–solvent interactions in these sys- tems. The trends observed in K°s, ϕ values can be due to their
hydration behavior [13],[14],[15],[16],[17] which comprises of
following interactions in these systems: (a) The terminal
groups of zwitterions of amino acids, NH3 + and COOare hydrated in an electrostatic manner whereas, hydration of R
group depends on its nature, which may be hydrophilic, hy- drophobic or amphiphilic; and (b) the overlap of hydration co- spheres of terminal NH3 + and COOgroups and of adjacent
groups results in volume change. The K°s, ϕ values increase
due to reduction in the electrostriction at terminals, whereas it
decreases due to disruption of side group hydration by that of
the charged end.
The increase in K°s, ϕ values with increase in temperature for
Arginine in aqueous-glucose solutions can be explained by
considering the size of primary and secondary solvation layers
around the zwitterions. At higher temperatures the solvent
from the secondary solvation layer of Arginine zwitter ions is
released into the bulk of the solvent, resulting in the expansion of the solution, as inferred from larger K°s, ϕ , Sk values at
higher temperatures [18], [19].Similar trends have also been
reported [12] for amino acids in aqueous-glucose solutions.
This further supports the conclusion that the hydrophilic–

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(Arginine), and κs and κs ° are the isentropic compressibilities
of the solution and the solvent (aqueous-glucose) respectively,
calculated using the relation

(2) It is observed that, for Arginine in all the three aqueous-

glucose solvents, Ks, ϕ is linear in the studied concentration
range and at each investigated temperature (Table 2).
The values of Ks, ϕ are negative for Arginine aqueous-glucose
solutions, indicating that the water molecules around ionic
charged groups of amino acids are less compressible than the water molecules in the bulk solution [22]. The values K°s, ϕ
were obtained using the relations [12]
(3) where the intercepts, K°s, ϕ , by definition are free from solute– solute interactions and therefore provide a measure of solute–
solvent interactions, whereas the experimental slope Sk pro- vides information regarding solute–solute interaction. The
values of K°s, ϕ , and Sk for Arginine in aqueous-glucose solu-
tions at different temperatures are given in Table 3.
Limiting apparent molar properties provide qualitative as well
as quantitative information regarding solute–solvent interac-
tions without taking into account the effects of solute–solute
interactions [20]. In general, the types of interactions occurring
between Arginine and glucose can be classified as follows [15],
[16], [21]:
(a) The hydrophilic–ionic interaction between OH groups of
glucose and zwitterions of Arginine.
(b) Hydrophilic–hydrophobic interaction between the OH
groups of glucose molecule and non-polar (–CH2 ) in side chain of Arginine molecule.
ionic group interactions between OH groups of glucose with zwitter ions dominate in these systems. The values of K° s, ϕ
show a minimum for lower glucose concentrations (between 0 and 5%) at higher temperatures (313K). This increase in K°s, ϕ
may be due to higher expansion of solutions for lower glucose
concentrations, as the interactions are less pronounced at low-
er glucose concentration range as mentioned above. The val- ues of K°s, ϕ increase with increase in temperature, indicating
release of more water molecules from the secondary solvation
layer of Arginine zwitterions into the bulk, thereby, are mak-
ing the solutions more compressible.
The compressibility of transfer of Arginine from water to aqueous-glucose solutions, K° s, ϕ,tr were calculated by using
the relation

(4)

where K°s, ϕ,water is the limiting apparent molar volume of Ar- ginine in water. The K°s, ϕ, tr values for Arginine from water to
aqueous glucose solutions are included in Table 3. Table 3 in- dicates that K°s, ϕ, tr values are positive. The observed positive K°s, ϕ, tr values suggest that the hydrophilic–ionic groups inter- actions dominate in these systems. The K°s, ϕ, tr values increase
with increase in glucose concentration in the solutions (Table
3). This may be due to greater hydrophilic–ionic group inter-
actions with increased concentrations of glucose. The observed trends in K° s,Φ and K°s, ϕ, tr further support the conclusions.
The viscosity data were analyzed by using Jones–Dole equa-
tion of the form

(5)

where ηr is the relative viscosity of the solution, η and ηo

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International Journal of Scientific & Engineering Research, Volume 5, Issue 1, January-2014 75

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are the viscosities of solution and the solvent (aqueous– glucose), respectively, A and B are the Falkenhagen and Jones–Dole coefficients, respectively. Coefficient A accounts for the solute–solute interactions and B is a measure of struc- tural modifications induced by the solute– solvent interactions [20], [21]. The values of A and B are listed in Table 4. The val- ues of A- and B-coefficients are positive, however, the A- coefficients are much larger in magnitude as compared to B- coefficients, suggesting weak solute–solute and strong solute– solvent interactions in these solutions. The B-coefficients val- ues increase with increasing concentration of glucose also in- dicate a structure to allow the co-solute (glucose) to act on sol- vent [11].
B-coefficients increase when the water is replaced by glucose, i.e., glucose modifies water structure through H-bonding [11]. The B-coefficients increase with rise in temperature indicating increased solute–solvent interactions at higher temperatures in these systems. Thus, the values of coefficients A and B support
the behaviors of K°s,Φ , and K°s, ϕ, tr , which suggest strong so-
lute–solvent interactions as compared to solute–solute interac-
tions in these solutions.
The viscosity data have also been examined in the light of
transition state theory of the relative viscosity proposed by
[20], [22]. According to this theory, the B-coefficient is given by
the following relation

4 CONCLUSION

The results are interpreted in terms of solute–solvent and so- lute– solute interactions in Arginine systems. It is observed that there exist strong solute–solvent interactions, which in- creases with increase in glucose concentration. It is observed that Arginine act as structure-breaker in aqueous-glucose sol- vents. The thermodynamics of viscous flow has also been dis- cussed. This suggests that the interactions between Arginine and solvent (aqueous-glucose) molecules in the ground state are stronger than in the transition state.

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Table 3

Limiting Apparant Molar Compressibility, Slope, Transfer Compressibility

Table 4

Falkenhagen and Jones – Dole Coefficient

Table 5.

Free Energies of Activation of Viscous Flow per Mole of Solvent and Solute

Table 1

Densities, Ultrasonic Speeds and Viscosities

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Table 2

Adiabatic Compressibility, Apparent Molar Compressibility & Relative Viscosity

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