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ULTRASONIC VELOCITY STUDIES OF AMINO ACIDS IN AQUEOUS TERTIARY BUTYL ALCOHOL AT 303.15K

ABSTRACT

Ultrasonic velocity and Adiabatic compressibility of Glycine, DL-Alanine, L-Valine and L-Arginine HCL have been measured in Water + Tertiary Butyl Alcohol(TBA) mixtures ranging from pure water to 80% TBA by mass at 303.15K. From the Ultrasonic Velocity, the adiabatic compressibility of the four amino acids in the mixtures has been calculated. From the Ultrasonic Velocity and adiabatic compressibility, apparent molar compressibility, intermolecular free length and change in free energy were calculated. These values were interpreted in terms of structure-breaking or structure making effects of these amino acids in the water + TBA mixtures.

Key words: Apparent molar volume, Density, Viscosity, Amino acids, Tertiary butyl alcohol

1. INTRODUCTIONProteins are the large, complex molecules composed of smaller structural subunits called amino acids. Since proteins are large molecules, the direct study of protein-water interactions is difficult. So it can be studied by the interaction of amino acids in aqueous and mixed aqueous solutions1-4. (REFERENCE FROM PREVIOUS PUBLICATION) The process of hydration plays an important role in the stability, dynamics, structural characteristics and functional activities of the amino acids. The physiochemical and thermodynamic properties in aqueous solution provides the information about solute-solute and solute-solvent interactions. The ultrasonic velocity measurements find wide applications in characterizing the physico-chemical behaviour of liquid mixtures9-11 and in the study of molecular interactions. Ultrasonic velocity of a liquid is related to the binding forces between the atoms or the molecules. Ultrasonic velocities have been adequately employed in understanding the nature of molecular interaction in pure liquids12, binary and ternary mixtures.13-15 The method of studying the molecular interaction from the knowledge of variation of thermodynamic parameter values with composition gives an insight into the molecular process16-18. (REFERENCE FROM THESIS)The attempts made by Ernst and Glinski22 and Kiyohara et al.23,24 indicate that ultrasonic velocities evaluated making use of thermodynamically valid expressions may be utilized to obtain excess Ultrasonic velocities which are useful in understanding the binary liquid mixtures interactions. It is worthwhile to note here that Kudriavtsev25 derived expressions for evaluating theoretically the velocity of sound in pure liquids and liquid mixtures based on thermodynamically valid equations for internal energy in liquids and liquid mixtures and found that the expressions yield velocity data in good agreement with the experimental data for binary mixtures. (REFERENCE FROM THESIS)From the Ultrasonic velocity (); adiabatic compressibility (), apparent molar compressibility (K), intermolecular free length (Lf) and change in free energy (G) were calculated. These parameters were used to discuss the solute-solvent/co solvent and solute-solute interactions.

2. EXPERIMENTALAll the chemicals used are of analytical grade. Commercially obtained chemicals were further purified wherever necessary. In the present investigation, a single crystal variable path interferometer was used to measure the ultrasonic velocities of the solutions. From the knowledge of wavelength (), the ultrasonic velocity () can be calculated by the relationVelocity = Wavelength x Frequency = f (1)Adiabatic compressibility () is an important parameter which throws light on the solute-solvent interactions in solutions. This parameter is widely used to study the behavior of amino acids in solutions. The adiabatic compressibility () is expressed as = 1/ d2 (2) Where is ultrasonic velocity and d is density of the medium

Apparent molar compressibility (k) can be defined as a measure of intermolecular association or dissociation or repulsion. This parameter describes about the interactions between the molecules. The apparent molar compressibility (K) is expressed ask = 1000/Cd0 (d0- d0) + 0M/ d0 (3)Where d, and d0, 0 are the densities and the adiabatic compressibilities of solvent and solution respectively, C is molar concentration of the solute and M is molar mass of the solute.The intermolecular free-length is the distance covered by a sound wave between the surfaces of the neighboring molecules and is given by Jacobson15 asLf = K()1/2 (4)Where K is the temperature dependant constant and is the adiabatic compressibility.

The change in free energy of activation is calculated by G = - KB T ln (h/ KB T) kJmol-1 (5)Where, KB is Boltzmanns constant (1.3806 x 10-23 JK-1), T is temperature, h is Plancks constant (6.626 x 10-34 Js) and is the relaxation time. Table 1: Change in Ultrasonic Velocity, Adiabatic compressibility, Apparent Molar Compressibility, Intermolecular Free length and Change in Free Energy of Amino acids in Water at 303.15K Conc (g mol l-1)Density (d)(g cm-3)Ultrasonic Velocity(ms-1)Adiabatic Compressibility ()(x10-10 m2 N-1)Apparent molar compressibility (-k)(x10-7 m2 N-1)Intermolecular free-length (Lf)(1011m)Change in Free Energy (-G) (kJmol-1)

Glycine + Water

00.99531501.954.45-5.13-

0.0010.99531502.524.453.085.135.05

0.0050.99541504.734.432.965.125.05

0.010.99561507.374.422.865.125.05

0.050.99691527.014.32.845.085.05

0.070.99751536.334.242.765.065.06

0.10.99841549.574.172.645.045.06

DL-Alanine + Water

00.99531504.164.44-5.12-

0.0010.99531504.634.43.275.115.05

0.0050.99541506.524.423.245.15.05

0.010.99561508.784.413.225.095.06

0.050.99671527.564.293.165.085.06

0.070.99731536.934.243.145.065.07

0.10.99811551.214.163.115.055.07

L-Valine + Water

00.99531502.764.44-5.13-

0.0010.99531503.364.443.215.125.05

0.0050.99541505.734.433.185.125.05

0.010.99551508.74.413.165.115.06

0.050.99661532.54.273.095.075.06

0.070.99711544.64.23.055.055.07

0.10.99791562.94.13.035.025.07

L-Arginine HCl + Water

00.99531501.954.47-5.13-

0.0010.99561502.194.452.645.135.05

0.0050.99571504.844.432.645.125.05

0.010.99621507.484.412.585.115.05

0.050.9991530.954.272.575.075.06

0.071.00031542.734.22.555.055.06

0.11.00241560.354.092.535.015.06

Table 2: Change in Ultrasonic Velocity, Adiabatic compressibility, Apparent Molar Compressibility, Intermolecular Free length and Change in Free Energy of Amino acids in 20% TBA at 303.15K Conc Density (d)Ultrasonic VelocityAdiabatic Compressibility ()Apparent molar compressibility (-k)Intermolecular free-length (Lf)Change in Free Energy (-G)

(g mol l-1)(g cm-3)(ms-1)(x10-10 m2 N-1)(x10-7 m2 N-1)(1011m)(kJmol-1)

Glycine in 20% TBA + 80% Water

00.97171606.23.98-5.02

0.0010.97171606.733.982.65.025.07

0.0050.97181608.783.972.515.015.07

0.010.9721611.223.962.425.015.08

0.050.97321627.13.882.064.985.09

0.070.97381633.753.841.944.975.09

0.10.97461645.343.791.84.955.09

DL-Alanine in 20% TBA + 80% Water

00.97171606.213.96-5-

0.0010.97261665.213.992.524.995.07

0.0050.97371665.353.982.464.985.07

0.010.97451606.433.972.334.965.08

0.050.97791620.063.892.274.945.08

0.070.97911627.723.852.154.935.08

0.10.98031640.063.792.024.915.08

L-Valine in 20% TBA + 80% Water

00.97171608.353.97-5.01-

0.0010.97171608.953.972.55.015.07

0.0050.97181611.353.962.495.015.07

0.010.9721614.313.942.4855.08

0.050.97311637.93.832.44.965.09

0.070.97371649.953.772.394.955.09

0.10.97461667.663.682.344.945.09

L-Arginine HCl in 20% TBA + 80% Water

00.97171606.213.98-5.02-

0.0010.97171606.723.982.355.025.08

0.0050.9721608.753.972.325.015.08

0.010.97241611.263.962.295.015.08

0.050.97511631.063.852.214.975.08

0.070.97651640.883.82.184.955.08

0.10.97851655.653.722.154.925.08




00.93821674.753.79-5-

0.0010.93831675.273.792.3955.1

0.0050.93841677.233.782.3455.11

0.010.93851679.33.772.164.995.11

0.050.93961693.943.71.754.975.11

0.070.94031699.663.681.644.965.11

0.10.94121707.473.641.494.945.11


00.93821676.253.79-4.95-

0.0010.97171676.653.791.94.945.09

0.0050.93841678.113.781.884.945.1

0.010.93851679.943.771.764.935.1

0.050.93971694.153.71.694.925.1

0.070.94031700.953.671.554.915.1

0.10.94111711.623.621.444.95.1


00.93821679.163.79-4.99-

0.0010.93831679.653.772.244.995.1

0.0050.93841681.63.762.214.995.11

0.010.938516843.752.194.995.11

0.050.93961703.033.662.114.955.11

0.070.94021712.143.622.084.955.11

0.10.9411725.73.562.054.935.11


00.93821674.753.79-5-

0.0010.93831675.163.792.7755.1

0.0050.93861675.813.792.7555.1

0.010.93891676.833.782.7555.1

0.050.94171684.273.742.654.965.1

0.070.9431688.183.722.624.955.1

0.10.94511692.453.692.554.915.1

Table 4: Change in Ultrasonic Velocity, Adiabatic compressibility, Apparent Molar Compressibility, Intermolecular Free length and Change in Free Energy of Amino acids in 60% TBA at 303.15K

Conc Density (d)Ultrasonic VelocityAdiabatic Compressibility ()Apparent molar compressibility (-k)Intermolecular free-length (Lf)Change in Free Energy (-G)



00.90811739.53.63-4.99-

0.0010.90811739.93.631.824.995.11

0.0050.90821741.473.631.774.985.11

0.010.90851743.133.621.814.985.12

0.050.90961745.433.60.694.975.12

0.070.91011747.233.590.574.975.12

0.10.9111749.333.580.374.965.13


00.90811739.523.63-4.88-

0.0010.90811739.633.631.364.885.11

0.0050.90821740.073.631.084.885.11

0.010.90841740.473.630.844.875.11

0.050.90951744.153.610.714.875.11

0.070.91011745.213.60.624.865.11

0.10.91091746.933.590.564.865.11


00.90811750.253.59-4.97-

0.0010.90811750.443.591.964.975.11

0.0050.90821751.143.591.864.965.11

0.010.90841751.983.581.844.955.12

0.050.90951757.983.551.74.945.12

0.070.911760.63.541.64.935.12

0.10.91091763.973.521.594.915.13


00.90811750.253.59-4.97-

0.0010.90821750.873.591.634.975.1

0.0050.90841751.873.581.584.975.11

0.010.90881756.833.561.314.965.11

0.050.91161760.223.541.244.945.11

0.070.9131764.383.511.154.935.11

0.10.9151766.253.51.054.915.11




00.89291815.243.4-4.93-

0.0010.89291815.233.41.294.935.12

0.0050.8931815.223.391.094.925.12

0.010.89311815.253.390.934.925.13

0.050.89421816.513.380.334.925.12

0.070.89471817.63.380.134.925.12

0.10.89551820.253.40.114.925.13


00.89291799.513.45-4.91-

0.0010.89291799.483.450.234.915.11

0.0050.8931799.43.450.194.95.11

0.010.89311799.393.450.124.95.12

0.050.89431799.953.450.094.95.12

0.070.89481800.613.440.064.95.12

0.10.89571801.733.430.054.95.12


00.89291815.243.39-4.96-

0.0010.89291815.233.391.644.955.11

0.0050.8931815.223.391.534.945.11

0.010.89311815.253.391.484.935.12

0.050.89421816.513.381.474.935.12

0.070.89471817.63.381.464.915.12

0.10.89551820.253.371.454.915.13


00.89291815.243.39-4.95-

0.0010.89291815.963.390.894.945.11

0.0050.89321817.083.390.724.935.11

0.010.89361819.663.370.524.925.11

0.050.89631820.933.360.354.915.11

0.070.89981821.463.340.234.95.12

0.10.89971822.743.340.184.895.12

3. RESULTS AND DISCUSSION

Ultrasonic Velocity has been measured for four amino acids in water over the concentration range from 0.001 to 0.1m solution. Parameters like Adiabatic Compressibility (), Apparent Molar Compressibility (K), Intermolecular Free length (Lf) and Change in Free Energy (G) have been calculated from the measured ultrasonic velocities, densities and viscosities (reference Nagaraj Sir previous paper).

3.1 Ultrasonic Velocitya. In WaterThe measured ultrasonic velocities of the four amino acids(Glycine, DL-Alanine, L_Valine and L-Arginine HCl) in water are included in table 1. The measured ultrasonic velocity values in the present study increase with the increase in the concentration of all the four amino acids under study. The increase or decrease in ultrasonic velocity depends on the structural properties of solute. The rising trend in the ultrasonic velocity with concentration is due to the cohesion brought about by ionic hydration. The electrostriction effect which brings about the shrinkage in the volume of solvent caused by zwitterion portion of amino acid is increased in the solvent. This implies that all the amino acids in water behave like structure makers30. reference thesis) It is observed that as the chain length of the four amino acids under study increases, cohesion between them becomes stronger. This means the structure making ability of these four amino acids in water show the following trend L-Arginine HCl > L-Valine > DL- Alanine > Glycine A similar report was reported by Thirumaran et al in their ultrasonic velocity studies on four amino acids i.e. L-alanine, L-Leucine, L-Valine and L-Proline in water58(reference thesis). b. In Aqueous TBA mixturesThe measured Ultrasonic Velocities along with densities of Glycine, DL-Alanine, L-Valine, and L-Arginine HCl in different TBA + Water Mixtures (20% TBA + 80% Water, 40% TBA + 60% Water, 60% TBA + 40% Water, 80% TBA + 20% Water) at 303.15K are presented in Tables 2 to 5 respectively.In the present study the values of ultrasonic velocity increases with the increase in the concentration of TBA. These trends clearly suggest the presence of ionic, dipolar and hydrophilic interactions occurring in the systems under study. Since more number of water molecules is surrounding the TBA and amino acid molecules, the chances for the penetration of solute into the solvent are highly favored. Further, the increasing values of ultrasonic velocity with the increase in the TBA concentration in the concerned systems reveal about the more strengthening in solute-solvent interactions existing in these mixtures. These values also suggest that TBA has an induced effect on the weakening of solute-solute interactions between amino acids.The increasing trend of ultrasonic velocity values is due to disruption of side group hydration by that of the charged end. The increase in ultrasonic velocity values from Glycine, DL-Alanine, L-Valine and L-Arginine HCl may be attributed to the increase in hydrophobic-hydrophobic interactions between R-Group of amino acids and R-group of TBA. It is evident from the Table 6.5 to 6.8 and figures 6.46 to 6.49 that the positive values of ultrasonic velocity in all the four amino acid systems clearly indicate the presence of strong solute-solvent interactions. Further it can be concluded that the amino acid systems under study possess structure making tendency of the solute molecules in the solvent in the following orderL-Arg. HCl >L-Val >DL-Ala>GlyA similar observations are reported by Rajinder K Bamezai et al from their studies on L-Threonine in aqueous THF at 313.15 K30. 3.2 Adiabatic compressibilitya. In WaterBy using the Eq. (2) the values of adiabatic compressibility () of Glycine, DL-Alanine, L-Valine and L-Arginine HCl in water at 303.15K were calculated from measured density and Ultrasonic velocity values. These values are included in table 1.Adiabatic compressibility () is found to be decreased with increasing concentration of amino acids. This kind of trends implies that there is an enhanced molecular association in the systems under study on increase in the solute content. The decrease in adiabatic compressibility is attributed to the influence of electrostatic fields of ions on the surrounding molecules so called electrostriction. The increasing electrostrictive compression of water around the molecules results in a large decrease in the compressibility of the solution. A similar observation was made Anjana et al from the compressibility function study threonine in mixed aqueous THF solutions30. As the chain length increases among amino acids under study the adiabatic compressibility of these in water are in the following orderGlycine >DL-Alanine>L-Valine>L-ArginineThis trend is expected one because these values are reciprocal of ultrasonic velocity values . b. In Aqueous TBA mixturesBy using the Eq. (2) the values of adiabatic compressibility () of Glycine, DL-Alanine, L-Valine and L-Arginine HCl in different TBA + Water Mixtures (20% TBA + 80% Water, 40% TBA + 60% Water, 60% TBA + 40% Water, 80% TBA + 20% Water) at 303.15K were calculated from measured density and Ultrasonic velocity values. These values are presented in Tables 2 to 5 respectively.The values of adiabatic compressibility decrease with the increase in the concentration of TBA. This kind of trends generally confirms the strong solute-solvent interactions in the present amino acid-aqueous TBA systems. It is also noticed that there exists an intermolecular interaction of electrostriction, hydrophilic-hydrophobic, hydrophobic-hydrophobic, ionic-dipolar and ion-solvent nature between the amino acids and aqueous TBA molecules which brings these molecules closer. The existence of ion-solvent/solute-solvent interactions resulting in attractive forces promotes the structure making tendency of amino acids. The existence of molecular interactions in the present study is in the order, L-Arginine HCl >L-Valine >DL-Alanine >GlycineThe values of adiabatic compressibility shows an inverse behavior compared to the ultrasonic velocity in the mixtures with increase in concentration. It is primarily the compressibility that changes with the structure and this lead to the change in ultrasonic velocity. This may be due to the increase in side chain of the amino acid molecules under study. The increase in the side chain of the interacting molecules leads to the breaking up of the molecular clustering of the other, thereby releasing several dipoles for the interactions. In view of greater force of interaction between the molecules there will be an increase in cohesive energy and the occurrence of structural changes, take place due to the existence of electrostatic field. Thus structural arrangement of molecules results in increasing adiabatic compressibility there by showing progressively intermolecular interactions. A similar report was reported by Thirumaran et al in their adiabatic compressibility studies on four amino acids i.e. L-alanine, L-Leucine, L-Valine and L-Proline in water58.3.3 Apparent Molar Compressibility (K)a. In WaterBy using the Eq. (3) the values of apparent molar compressibility (K) of Glycine, DL-Alanine, L-Valine and L-Arginine HCl in water at 303.15K were calculated from their measured density and Ultrasonic velocity values. These values are reported in table 1 and the variations of apparent molar compressibility (K) with concentration of all the four amino acids are shown in the Graph 1.1.In the present investigation the values of the apparent molar compressibility increases with the increase in the concentration of amino acids. The values are found to be negative which may be due to strong electrostrictive forces in the vicinity of ions, causing electrostrictive solvation of ions31. This may also be due to the approach of water molecules around the complex and formation of weak bonding between oxygen atom of water molecule and H-atom of the amino acid.with increase in chain length of amino acids the values of K are in the following order from the point of view of ve KL-Arginine>L-Valine>DL-Alanine>GlycineA similar observations was reported by R Palani et al in their apparent molar compressibility studies of L-Serine, L-Proline and L-Histidine in aqueous 1,4-dioxane solutions at 298.15 K33.b. In Aqueous TBA mixturesBy using equation (3), the apparent molar compressibility of Glycine, DL-Alanine, L-Valine and L-Arginine HCl in aqueous TBA at 303.15K has been calculated using the measured ultrasonic velocity and density values. These values are presented in tables 2 to 5 and the variations of apparent molar volume with concentration among the studied amino acids have been graphically represented in figures 1.2 to 1.5 respectively.From tables 2 to 5 and figures 1.2 to 1.5 it is evident that Apparent Molar Compressibility values increase with the increase in the concentration of all amino acids under study. The values thus obtained are in a negative range.In the present investigation the following results were obtainedi. The values of k are all negative over the entire range of molarity of amino acids.ii. The k values are increasing with increasing molarity of the solute in Glycine, DL-Alanine, L-Valine, and L-Arginine HCl amino acid systems.iii. Also k increase with increase in TBA concentration in all the four amino acid systems.iv. A linear relation between k and solute has been observed throughout the concentration range.The observations clearly suggest that the negative values of k indicate ionic, dipolar and hydrophilic interactions occurring in these systems. Further, the increasing values of k in the concerned systems reveal the strong strengthening in solute-solvent interactions existing in these mixtures. There is an increase in the k values with the increase in the % of TBA. The increasing trend is also observed from Glycine to L-Arginine HCl with the increase in the carbon chain length in side chains. These trends can be understood based on the various interactions occurring between the amino acid-solvent and co-solvent molecules.

Graph 1.2 - K Values in 20%TBAGraph 1.1 - K Values in Pure Water

Graph 1.3 - K Values in 40%TBAGraph 1.4 - K Values in 60%TBA

Graph 1.5 - K Values in 80%TBA

X Axis Concentrations of Amino acids in gmol-1Y Axis - K Values of Amino Acids in x10-10m2 N-1

3.4 Intermolecular free length (Lf)a. In water By using the Eq. (4) the values of Intermolecular free length (Lf) of Glycine, DL-Alanine, L-Valine and L-Arginine HCl in water at 303.15K were calculated from measured density and ultrasonic velocity values. These values are included in table 1 and the variations of Intermolecular free length (Lf) with concentration of these amino acids are shown in the figure 2.1.In the present investigation the values of intermolecular free length decreases with the increase in the concentration of amino acids. The decrease in free length with increase in concentration indicates that there are significant interactions between solute and the solvent molecules, suggesting a structure promoting behavior on addition of solute to solvent. These results are also supported by the ultrasonic velocity data as explained above. The values of the free length (Lf) for the four amino acids in water in the current studies follow the order given below Glycine > DL-Alanine > L-Valine > L-ArginineThis trend indicates the presence of more interactions with the increase in carbon chain length. A similar observation was reported by Rita Mehra et al from their intermolecular free length studies of DL-Alanine in aqueous galactose solutions in the presence of NaCl at different temperatures56. b. In Aqueous TBA mixturesThe free length of Glycine, DL-Alanine, L-Valine and L-Arginine HCl in aqueous TBA at 303.15K has been calculated using the equation (4) from the measured ultrasonic velocity and density values. These values are presented in tables 2 to 5 and the variation of Lf Vs concentration of the studied amino acids have been graphically represented in figures 2.2 to 2.5 respectively.The value of free length decreases with chain length of amino acids. This suggests that the increase of chain length offers more sterric hindrance on mutual correlation between different molecules in the solution. It may there be concluded that the resultant interactions in the amino acid systems of the present study, is not solely dependent on the molecular structure of the components, but also, influenced by other factors like dispersion forces, dipole-dipole interaction, hydrogen bonding, charge transfer interaction and/or complex formation. However it was observed that the polarity and size of the components plays a significant role in determining the strength of molecular interaction in a mixture. A similar abservation was reported by Katsutaka sasaki et al from their ultrasonic studies of amino acids in aqueous solutions59. The values of the free length for the four amino acids under study in aqueous TBA mixtures in the current studies follow the order as given bellowGlycine > DL-Alanine > L-Valine > L-Arginine HCl.

Graph 2.2 - Lf Values in 20% TBAGraph 2.1 - Lf Values in Pure Water

Graph 2.3 - Lf Values in 40% TBAGraph 2.4 - Lf Values in 60% TBA

Graph 2.5 - Lf Values in 80% TBA

X Axis Concentrations of Amino acids in gmol-1Y Axis - Lf Values of Amino Acids in 1011m

3.5 Change in free energy of activation a. In WaterBy using the Eq. (5) the values of change in free energy (G) of Glycine, DL-Alanine, L-Valine and L-Arginine HCl in water at 303.15K were calculated from measured density and Ultrasonic velocity values. These values are included in table 1.In the present investigation the values of change in free energy decreases with the increase in the concentration of the amino acids. The decrease in the values indicate that there is a significant interactions between solute and the solvent molecules, thereby suggests the presence of structure promoting behavior. Since the values are negative it may be ascribed to dispersion forces with systems. A similar observation was reported by Rita Mehra et al from their change in free energy studies of DL-Alanine in aqueous galactose solutions in the presence of NaCl at different temperatures56. b. In Aqueous TBA SolutionsThe Change in free energy of Glycine, DL-Alanine, L-Valine and L-Arginine HCl in aqueous TBA at 303.15K has been calculated by using the equation (5) through the measured ultrasonic velocity, density and viscosity values. These values are presented in tables 2 to 5. The observed values show that the Gibbss free energy (G) decreases with increase in concentration indicating the need for longer time for the co-operative process or the rearrangement of molecules in the mixtures. The Gibbs Free Energy of activation flow in the mixtures can be obtained on the basis of Eyring rate process theory44. So the change in free Gibbs energy (which is only of the system and does not mention the surroundings) is as valid a criterion of spontaneity as the total entropy (of the universe).The Gibbs free energy values confirm the availability of intermolecular interactions. The reduction of G indicates the need for smaller time for the cooperation process of the rearrangement of the molecules in the mixtures, decreases in the energy with increase in temperature leads to dissociation45,46. These studies provide a comprehensive investigation of molecular association between amino acids and TBA arising from the dipole-dipole and H-bonding between the solute and solvent molecules. A similar observation was reported by Rita Mehra et al from their change in free energy studies of DL-Alanine in aqueous galactose solutions in the presence of NaCl at different temperatures56.The values of change in free energy for the four amino acids in aqueous TBA mixtures in the current studies follow the order L-Arginine HCl > L_Valine > DL-Alanine > Glycine