ULTRASONIC VELOCITY STUDIES OF AMINO ACIDS IN

www.wjpps.com Vol 5, Issue 1, 2016.

1423

Nagaraj et al. World Journal of Pharmacy and Pharmaceutical Sciences

ULTRASONIC VELOCITY STUDIES OF AMINO ACIDS IN AQUEOUS

TERTIARY BUTYL ALCOHOL AT 303.15K

S. Nagaraj1*

, M.C.S. Subha2, C. Nagamani

3 and K. Chowdoji Rao

4

*1

Department of Chemistry, IIBS, R T Nagar, Bangalore – 560 032 Karantaka, India.

2Department of Chemistry, S.K. University, Anantapur – 515003 A.P., India.

3Department of Chemistry, Vijaya College, Bangalore – 560 004 Karnataka, India.

4Department of Polymer Science and Technology, S.K. University, Anantapur – 515003 A.P.,

India.

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.

KEYWORDS: Apparent molar volume, Density, Viscosity, Amino acids, Tertiary butyl

alcohol.

1. INTRODUCTION

Proteins 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 solutions.[1-4]

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

WORLD JOURNAL OF PHARMACY AND PHARMACEUTICAL SCIENCES

SJIF Impact Factor 5.210

Volume 5, Issue 1, 1423-1441 Research Article ISSN 2278 – 4357

Article Received on

19 Oct 2015,

Revised on 10 Dec 2015,

Accepted on 30 Dec 2015

*Correspondence for

Author

S. Nagaraj

Department of Chemistry,

IIBS, R T Nagar,

Bangalore – 560 032

Karantaka, India.


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wide applications in characterizing the physico-chemical behaviour of liquid mixtures[9-11]

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 liquids[12]

,

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 process.[16-21]

The attempts made by Ernst and Glinski[22]

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 Kudriavtsev.[25]

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. From the Ultrasonic

velocity (µ); adiabatic compressibility (), apparent molar compressibility (φK),

intermolecular free length (Lf) and change in free energy (ΔG) were calculated. These

parameters were used to discuss the solute-solvent/co solvent and solute-solute interactions.

MATERIALS AND METHODS

All 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 (λ), the ultrasonic velocity (µ) can be calculated by the relation .

Velocity = Wavelength x Frequency

µ = λf (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/ dµ2

(2)

Where µ is ultrasonic velocity and d is density of the medium.


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Apparent molar compressibility (Φk) 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 (ΦK) is expressed as

Φk = 1000/Cd0 (d0β- dβ0) + β0M/ d0 (3)

Where d, β and d0, β0 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 Jacobson as

Lf = K(β)1/2

(4)

Where „K‟ is the temperature dependant constant and „β‟ is the adiabatic compressibility.

The change in free energy of activation is calculated by

ΔG = - KB T ln (h/τ KB T) kJmol-1

(5)

Where, KB is Boltzmann‟s constant (1.3806 x 10-23

JK-1

), T is temperature, h is Planck‟s

constant (6.626 x 10-34

Js) and τ 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

(β)

(x10-10

m2 N

-1)

Apparent molar

compressibility

(-Φk)

(x10-7

m2 N

-1)

Intermolecular

free-length (Lf)

(10-11

m)

Change in

Free Energy

(-ΔG)

(kJmol-1

)

Glycine + Water

0 0.9953 1501.95 4.45 - 5.13 -

0.001 0.9953 1502.52 4.45 3.08 5.13 5.05

0.005 0.9954 1504.73 4.43 2.96 5.12 5.05

0.01 0.9956 1507.37 4.42 2.86 5.12 5.05

0.05 0.9969 1527.01 4.3 2.84 5.08 5.05

0.07 0.9975 1536.33 4.24 2.76 5.06 5.06

0.1 0.9984 1549.57 4.17 2.64 5.04 5.06

DL-Alanine + Water

0 0.9953 1504.16 4.44 - 5.12 -

0.001 0.9953 1504.63 4.4 3.27 5.11 5.05

0.005 0.9954 1506.52 4.42 3.24 5.1 5.05

0.01 0.9956 1508.78 4.41 3.22 5.09 5.06


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0.05 0.9967 1527.56 4.29 3.16 5.08 5.06

0.07 0.9973 1536.93 4.24 3.14 5.06 5.07

0.1 0.9981 1551.21 4.16 3.11 5.05 5.07

L-Valine + Water

0 0.9953 1502.76 4.44 - 5.13 -

0.001 0.9953 1503.36 4.44 3.21 5.12 5.05

0.005 0.9954 1505.73 4.43 3.18 5.12 5.05

0.01 0.9955 1508.7 4.41 3.16 5.11 5.06

0.05 0.9966 1532.5 4.27 3.09 5.07 5.06

0.07 0.9971 1544.6 4.2 3.05 5.05 5.07

0.1 0.9979 1562.9 4.1 3.03 5.02 5.07

L-Arginine HCl + Water

0 0.9953 1501.95 4.47 - 5.13 -

0.001 0.9956 1502.19 4.45 2.64 5.13 5.05

0.005 0.9957 1504.84 4.43 2.64 5.12 5.05

0.01 0.9962 1507.48 4.41 2.58 5.11 5.05

0.05 0.999 1530.95 4.27 2.57 5.07 5.06

0.07 1.0003 1542.73 4.2 2.55 5.05 5.06

0.1 1.0024 1560.35 4.09 2.53 5.01 5.06



in 20% TBA at 303.15K.

Conc Density

(d)

Ultrasonic

Velocity

Adiabatic

Compressibility

(β)

Apparent molar

compressibility

(-Φk)

Intermolecular

free-length

(Lf)

Change in

Free Energy

(-ΔG)

(g mol l-1

) (g cm-3

) (ms-1

) (x10-10

m2 N

-1) (x10

-7 m

2 N

-1) (10

-11m) (kJmol

-1)

Glycine in 20% TBA + 80% Water

0 0.9717 1606.2 3.98 - 5.02

0.001 0.9717 1606.73 3.98 2.6 5.02 5.07

0.005 0.9718 1608.78 3.97 2.51 5.01 5.07

0.01 0.972 1611.22 3.96 2.42 5.01 5.08

0.05 0.9732 1627.1 3.88 2.06 4.98 5.09

0.07 0.9738 1633.75 3.84 1.94 4.97 5.09

0.1 0.9746 1645.34 3.79 1.8 4.95 5.09

DL-Alanine in 20% TBA + 80% Water

0 0.9717 1606.21 3.96 - 5 -

0.001 0.9726 1665.21 3.99 2.52 4.99 5.07

0.005 0.9737 1665.35 3.98 2.46 4.98 5.07

0.01 0.9745 1606.43 3.97 2.33 4.96 5.08

0.05 0.9779 1620.06 3.89 2.27 4.94 5.08

0.07 0.9791 1627.72 3.85 2.15 4.93 5.08

0.1 0.9803 1640.06 3.79 2.02 4.91 5.08

L-Valine in 20% TBA + 80% Water

0 0.9717 1608.35 3.97 - 5.01 -

0.001 0.9717 1608.95 3.97 2.5 5.01 5.07

0.005 0.9718 1611.35 3.96 2.49 5.01 5.07


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0.01 0.972 1614.31 3.94 2.48 5 5.08

0.05 0.9731 1637.9 3.83 2.4 4.96 5.09

0.07 0.9737 1649.95 3.77 2.39 4.95 5.09

0.1 0.9746 1667.66 3.68 2.34 4.94 5.09

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

0 0.9717 1606.21 3.98 - 5.02 -

0.001 0.9717 1606.72 3.98 2.35 5.02 5.08

0.005 0.972 1608.75 3.97 2.32 5.01 5.08

0.01 0.9724 1611.26 3.96 2.29 5.01 5.08

0.05 0.9751 1631.06 3.85 2.21 4.97 5.08

0.07 0.9765 1640.88 3.8 2.18 4.95 5.08

0.1 0.9785 1655.65 3.72 2.15 4.92 5.08



in 40% TBA at 303.15K.

Conc Density

(d)

Ultrasonic

Velocity

Adiabatic

Compressibility

(β)

Apparent molar

compressibility

(-Φk)

Intermolecular

free-length

(Lf)

Change in

Free Energy

(-ΔG)

(g mol l-1

) (g cm-3

) (ms-1

) (x10-10

m2

N-1

) (x10-7

m2 N

-1) (10

-11m) (kJmol

-1)


0 0.9382 1674.75 3.79 - 5 -

0.001 0.9383 1675.27 3.79 2.39 5 5.1

0.005 0.9384 1677.23 3.78 2.34 5 5.11

0.01 0.9385 1679.3 3.77 2.16 4.99 5.11

0.05 0.9396 1693.94 3.7 1.75 4.97 5.11

0.07 0.9403 1699.66 3.68 1.64 4.96 5.11

0.1 0.9412 1707.47 3.64 1.49 4.94 5.11


0 0.9382 1676.25 3.79 - 4.95 -

0.001 0.9717 1676.65 3.79 1.9 4.94 5.09

0.005 0.9384 1678.11 3.78 1.88 4.94 5.1

0.01 0.9385 1679.94 3.77 1.76 4.93 5.1

0.05 0.9397 1694.15 3.7 1.69 4.92 5.1

0.07 0.9403 1700.95 3.67 1.55 4.91 5.1

0.1 0.9411 1711.62 3.62 1.44 4.9 5.1


0 0.9382 1679.16 3.79 - 4.99 -

0.001 0.9383 1679.65 3.77 2.24 4.99 5.1

0.005 0.9384 1681.6 3.76 2.21 4.99 5.11

0.01 0.9385 1684 3.75 2.19 4.99 5.11

0.05 0.9396 1703.03 3.66 2.11 4.95 5.11

0.07 0.9402 1712.14 3.62 2.08 4.95 5.11

0.1 0.941 1725.7 3.56 2.05 4.93 5.11


0 0.9382 1674.75 3.79 - 5 -

0.001 0.9383 1675.16 3.79 2.77 5 5.1


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0.005 0.9386 1675.81 3.79 2.75 5 5.1

0.01 0.9389 1676.83 3.78 2.75 5 5.1

0.05 0.9417 1684.27 3.74 2.65 4.96 5.1

0.07 0.943 1688.18 3.72 2.62 4.95 5.1

0.1 0.9451 1692.45 3.69 2.55 4.91 5.1



in 60% TBA at 303.15K.

Conc Density

(d)

Ultrasonic

Velocity

Adiabatic

Compressibility

(β)

Apparent molar

compressibility

(-Φk)

Intermolecular

free-length

(Lf)

Change in

Free Energy

(-ΔG)

(g mol l-1

) (g cm-3

) (ms-1

) (x10-10

m2 N

-1) (x10

-7 m

2 N

-1) (10

-11m) (kJmol

-1)


0 0.9081 1739.5 3.63 - 4.99 -

0.001 0.9081 1739.9 3.63 1.82 4.99 5.11

0.005 0.9082 1741.47 3.63 1.77 4.98 5.11

0.01 0.9085 1743.13 3.62 1.81 4.98 5.12

0.05 0.9096 1745.43 3.6 0.69 4.97 5.12

0.07 0.9101 1747.23 3.59 0.57 4.97 5.12

0.1 0.911 1749.33 3.58 0.37 4.96 5.13


0 0.9081 1739.52 3.63 - 4.88 -

0.001 0.9081 1739.63 3.63 1.36 4.88 5.11

0.005 0.9082 1740.07 3.63 1.08 4.88 5.11

0.01 0.9084 1740.47 3.63 0.84 4.87 5.11

0.05 0.9095 1744.15 3.61 0.71 4.87 5.11

0.07 0.9101 1745.21 3.6 0.62 4.86 5.11

0.1 0.9109 1746.93 3.59 0.56 4.86 5.11


0 0.9081 1750.25 3.59 - 4.97 -

0.001 0.9081 1750.44 3.59 1.96 4.97 5.11

0.005 0.9082 1751.14 3.59 1.86 4.96 5.11

0.01 0.9084 1751.98 3.58 1.84 4.95 5.12

0.05 0.9095 1757.98 3.55 1.7 4.94 5.12

0.07 0.91 1760.6 3.54 1.6 4.93 5.12

0.1 0.9109 1763.97 3.52 1.59 4.91 5.13


0 0.9081 1750.25 3.59 - 4.97 -

0.001 0.9082 1750.87 3.59 1.63 4.97 5.1

0.005 0.9084 1751.87 3.58 1.58 4.97 5.11

0.01 0.9088 1756.83 3.56 1.31 4.96 5.11

0.05 0.9116 1760.22 3.54 1.24 4.94 5.11

0.07 0.913 1764.38 3.51 1.15 4.93 5.11

0.1 0.915 1766.25 3.5 1.05 4.91 5.11


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in 80% TBA at 303.15K.

Conc Density

(d)

Ultrasonic

Velocity

Adiabatic

Compressibility

(β)

Apparent molar

compressibility

(-Φk)

Intermolecular

free-length

(Lf)

Change in

Free Energy

(-ΔG)

(g mol l-1

) (g cm-3

) (ms-1

) (x10-10

m2 N

-1) (x10

-7 m

2 N

-1) (10

-11m) (kJmol

-1)


0 0.8929 1815.24 3.4 - 4.93 -

0.001 0.8929 1815.23 3.4 1.29 4.93 5.12

0.005 0.893 1815.22 3.39 1.09 4.92 5.12

0.01 0.8931 1815.25 3.39 0.93 4.92 5.13

0.05 0.8942 1816.51 3.38 0.33 4.92 5.12

0.07 0.8947 1817.6 3.38 0.13 4.92 5.12

0.1 0.8955 1820.25 3.4 0.11 4.92 5.13


0 0.8929 1799.51 3.45 - 4.91 -

0.001 0.8929 1799.48 3.45 0.23 4.91 5.11

0.005 0.893 1799.4 3.45 0.19 4.9 5.11

0.01 0.8931 1799.39 3.45 0.12 4.9 5.12

0.05 0.8943 1799.95 3.45 0.09 4.9 5.12

0.07 0.8948 1800.61 3.44 0.06 4.9 5.12

0.1 0.8957 1801.73 3.43 0.05 4.9 5.12


0 0.8929 1815.24 3.39 - 4.96 -

0.001 0.8929 1815.23 3.39 1.64 4.95 5.11

0.005 0.893 1815.22 3.39 1.53 4.94 5.11

0.01 0.8931 1815.25 3.39 1.48 4.93 5.12

0.05 0.8942 1816.51 3.38 1.47 4.93 5.12

0.07 0.8947 1817.6 3.38 1.46 4.91 5.12

0.1 0.8955 1820.25 3.37 1.45 4.91 5.13


0 0.8929 1815.24 3.39 - 4.95 -

0.001 0.8929 1815.96 3.39 0.89 4.94 5.11

0.005 0.8932 1817.08 3.39 0.72 4.93 5.11

0.01 0.8936 1819.66 3.37 0.52 4.92 5.11

0.05 0.8963 1820.93 3.36 0.35 4.91 5.11

0.07 0.8998 1821.46 3.34 0.23 4.9 5.12

0.1 0.8997 1822.74 3.34 0.18 4.89 5.12

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 (β), Apparent

Molar Compressibility (ΦK), Intermolecular Free length (Lf) and Change in Free Energy


1430


(ΔG) have been calculated from the measured ultrasonic velocities, densities and

viscosities.[26]

Ultrasonic Velocity

In Water

The 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 makers.[27]

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 water.[28]

In Aqueous TBA mixtures

The 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


1431


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

order.

L-Arg. HCl >L-Val >DL-Ala>Gly.

Similar observations are reported by Rajinder K Bamezai et al from their studies on L-

Threonine in aqueous THF at 313.15 K.[27]

Adiabatic compressibility

In Water

By using the Eq. (2) the values of adiabatic compressibility (β) 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 (β) 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 solutions.[27]

As the chain length increases among amino acids under study the adiabatic compressibility of

these in water are in the following order.


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Glycine >DL-Alanine>L-Valine>L-Arginine.

This trend is expected one because these values are reciprocal of ultrasonic velocity values.


By using the Eq. (2) the values of adiabatic compressibility (β) 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 >Glycine.

The 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 water.[28]


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Apparent Molar Compressibility (φK)

In Water

By using the Eq. (3) the values of apparent molar compressibility (ΦK) 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 (ΦK) 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 ions[29]

. 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 ΦK are in

the following order from the point of view of –ve ΦK

L-Arginine>L-Valine>DL-Alanine>Glycine.

A 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

K.[30]


By 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 obtained

1. The values of φk are all negative over the entire range of molarity of amino acids.


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2. The φk values are increasing with increasing molarity of the solute in Glycine, DL-

Alanine, L-Valine and L-Arginine HCl amino acid systems.

3. Also φk increase with increase in TBA concentration in all the four amino acid systems.

4. A linear relation between φk and solute has been observed throughout the concentration

range.

The observations clearly suggest that the negative values of φk indicate ionic, dipolar and

hydrophilic interactions occurring in these systems. Further, the increasing values of φk in the

concerned systems reveal the strong strengthening in solute-solvent interactions existing in

these mixtures. There is an increase in the φk 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.

FIG 1.1 - ΦK Values in Pure Water.

FIG 1.2 - ΦK Values in 20% TBA.


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FIG 1.5- ΦK Values in 80% TBA.

X Axis – Concentrations of Amino acids in gmol-1

Y Axis - ΦK Values of Amino Acids in x10-10

m2 N

-1


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Intermolecular free length (Lf)

In water

By using the Eq. (4) the values of Intermolecular free length (Lf) of Glycine, DL-Alanine, L-


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-Arginine.

This 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 temperatures.[31]


The 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.


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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

solutions.[32]

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 bellow.

Glycine > DL-Alanine > L-Valine > L-Arginine HCl.

FIG 2.1 - Lf Values in Pure Water.

FIG 2.2- Lf Values in 20% TBA.


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FIG 2.3 - Lf Values in 40% TBA.

FIG 2.4 - Lf Values in 60% TBA.

FIG 2.5- Lf Values in 80% TBA.

X Axis – Concentrations of Amino acids in gmol-1

Y Axis - Lf Values of Amino Acids in 10-11

m


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Change in free energy of activation

In Water

By using the Eq. (5) the values of change in free energy (ΔG) of Glycine, DL-Alanine, L-


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 indicates 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 temperatures.[31]

In Aqueous TBA Solutions

The 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 Gibbs‟s 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 Gibb‟s Free Energy of activation flow in the

mixtures can be obtained on the basis of Eyring rate process theory.[33]

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

Gibb‟s 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 dissociation.[34,35]

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 temperatures.[31]


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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.

CONCLUSION

From the variations of ultrasonic Velocity, adiabatic compressibility, apparent molar

compressibility, intermolecular free length and change in free energy parameters suggest the

structure making property of amino acids under study, vary in the following order in aqueous

TBA mixtures at 303.15K.

Glycine<DL-Alanine<L-Valine<L-Argenine HCl.

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ULTRASONIC VELOCITY STUDIES OF AMINO ACIDS IN