Int J Pharm Pharm Sci, Vol 6, Issue 10, ??-??Original Article

DETERMINATION OF PARTIAL MOLAR PROPERTIES AND ACOUSTIC PARAMETERS OF AMINO ACIDS IN AQUEOUS METHANOL SOLUTIONS IN PRESENCE OF SODIUM BENZOATE

SMRUTI* PATTNAIK, UPENDRA NATH DASH

Institute of Technical Education & Research (SOA), BBSR, Odisha.
Email: smrutipattanaik1@gmail.com

Received: 14 Jul 2014 Revised and Accepted: 01 Sep 2014

ABSTRACT

Objective: To study the partial molar properties and acoustic parameters of amino acids in the solutions of 5, 10 and 15 wt %of aqueous methanol in presence of sodium benzoate.

Methods: Effect on solute –solvent interaction is studied by determining the densities of pure solvents and the ultrasonic velocity of pure solvent and solutions is measured by using an ultrasonic interoferometer.

Results: The results are discussed in the light of molecular interaction, ion-solvent interactions ion-solvent interactions dominate over ion-ion interactions, β-alanine has higher ion-solvent interaction than α-alanine & glycine.

Conclusion: Overall,β-alanine shows high ion-solvent interaction due to higher mass which represents structural effect of solute on solvent in solution.

Keywords: Amino-acids, Methanol, Ultrasonic velocity, Solvation number, Sodium benzoate.

INTRODUCTION

The study of alcohol– protein interactions is very important for immunology, pharmacology, and medicine. Due to complex molecular structure of proteins direct study is quite difficult. So the amino acids which are the building blocks of proteins are studied. In continuation of our previous work in aqueous medium [1], the present investigation aims at studying the molecular interactions of amino acids in aqueous solutions of (5,10,and15 wt.%) methanol in the presence of 0.1Mcompostion of sodium benzoate ranging from 298.15K to 313.15K at an interval of 5K. Various parameters such as apparent molar volume (VΦ), limiting apparent molar volume (V⁰Φ), apparent molar expansibility (EΦ), limiting apparent molar expansibility (E⁰Φ), isentropic compressibility (Ks)and apparent molar compressibility(Ks,Φ) have been calculated from the density (d) and ultrasonic velocity (U) data, which provide qualitative information regarding molecular interactions

MATERIALS AND METHODS

All the chemicals used were of AnalaR grades and used as such. The solutions of amino acids were prepared on the molal basis and conversion of molality to molarity was done by using the standard expression [3] using the density values of the solutions determined at 298.15K. Conductivity water (Specfic conductance ~10⁶ Scm-¹ ) was used to prepare solutions of methanol in presence of 0.1M compostion of sodium benzoate and the solutions were used on the same day. The densities of pure solvents and their solutions were determined by using a specific gravity bottle (25 ml capacity) as described else where [3]. At least 5 observations were taken and differences in any two readings did not exceed ± 0.02%.

The ultrasonic velocity was measured by using Ultrasonic interferometer (Mittal Enterprises, New Delhi, Model No F-81) using a frequency of 2MHz. The precision of the ultrasonic velocity measurement was within ± 0.5 m/s. The amino acids content in the solutions varied over a concentration range of 0.006 to 0.08 mol dm‾³ in various solvents. Measurement of density was done in the temperature range 298.15K to 313.15K and speed of sound at 298.15K only.

From the density data the apparent molar volume (VΦ) was calculated by using equation [4]

VΦ = 1000 (cd0)-¹(d0-d) + M₂d0-¹ (1)

Where d0 is the density of solvent

It was found that the VΦ varied linearly with concentration c1/2

The VΦ data were fitted by a method of least squares to Masson equation [4]

VΦ = V⁰Φ + Sv c1/2(2)

to obtain V⁰Φ (limiting apparent molar volume) and the slope SE

The apparent molar Expansibility, EΦ was determined from equation [4]

EΦ = α0VΦ + (α-α0) 1000c-¹ (3)

The EΦ data were fitted by a method of least squares to the Masson equation [4]

EΦ = E⁰Φ + SE c1/2(4)

The ultrasonic velocities ‘U’ of amino acids in aqueous methanol

Solutions at different concentrations were fitted to an equation of the form [5-7]

U = U₀ + Fc + Gc3/2 + Hc² (5)

U₀ is the sound velocity in pure solvent and F,G,H, are the empirical constants

U = (Ksd)-1/2 (6)

The values of Ks obtained were fitted to an equation of the form

Ks = Ks0 + A'c +B'c3/2 + C'c (7)

where A', B' and C' are the empirical constants.

The apparent molar compressibility Ks, Φ has been computed from equation (8) [5-7]

Ks, Φ = 1000 Ksc-1 – Ks0d0-1(1000c-1d-M2)(8)

The Ks, Φ data were fitted to Eqn. 9

Ks,Φ = K⁰s,Φ + F'c1/2+ G'c (9)

to obtain K0s, Φ (the limiting apparent isentropic compressibility)

The solvation number Sn can be related to Ks by equation (10)

Sn = n1n2-1[1-VKs(n1V10Ks0)-1] (10)

Where V is the volume of the solution containing n₂ moles of solute

V₁⁰ is the molar volume of solvent and n₁ is the number of moles of solvent

The variation of solvation number with molar concentration of the solute leads to the limiting solvation number, Sn0 which was obtained from the relation (11)

Lim Ks,φ = -Sn0V10Ks0 (11)

c->0

From the density and sound velocity values,the magnitude of relative association, RA was calculated from the relation [5-7]

RA = (d/d0)(U0/U)1/3 (12)

RESULTS AND DISCUSSION

The values of partial molar volume (VΦ0), partial molar expansibility (EΦ0), the slope (Sv) of the plot of VΦvs c1/2and the slope SE of EΦ vs c1/2 are given in Table1 for amino acids in different wt.%(5,10, and 15) of methanol in water at temperatures ranging from 298.15K to 313.15K at an interval of 5K.

The density values of the solutions of amino acids vary linearly with concentrations in all wt.% of aqueous solutions of methanol in presence of 0.1 M sodium benzoate at different temperatures. It was found that the VΦ values vary linearly with c ½ for all the solutions at the experimental temperatures Since VΦ0 value indicates the ion-solvent interactions at infinite dilution (as the ion-ion interaction vanishes at infinite dilution), the positive values indicate the presence of ion-solvent interaction which decreases with rise of temperature. The presence of ion-solvent interactions between the molecules promotes structure making effect of amino acids in the solutions of methanol. As observed (Table-1) the VΦ0 values of β-alanine are higher in all wt.% of methanol solutions pointing to the fact that ion-solvent interactions take place strongly in β-alanine as compared to the other amino acids solutions. As the magnitude of Sv is a measure of ion-ion interaction, the positive value of Sv, in most of the solutions, are indicative of strong ion-ion interaction. However, they vary with change of temperature and the content of amino acids. As observed magnitudes of VΦ0 values are much greater than those of Sv for all the solutions which suggest that the ion-solvent interactions dominate over ion-ion interaction in all the solutions and at all experimental temperatures.

The values of limiting apparent molar expansibility EΦ0 (Table 1) are also positive and decrease with increase of temperature, and the values are higher in 15wt.% of methanol solutions than in other wt.%. This may be due to the gradual disappearance of caging or packing effect in the solutions with increase of temperature. But the higher EΦ0 values in 15wt.%solutions as compared to those in other wt.% suggest that the appearance of caging or packing effect occurs to a greater extent in the former solution than in the other wt.% of the solutions.

Table 1: Values of VΦ0 (m3 mol-1), Sv(m3/2 mol-3/2), EΦ0 (m3 mol-1 K-1), and SE(m3/2 mole-3/2 K-1) for amino acids in different wt.%(5,10,and15wt.%) of methanol solutions in presence of sodium benzoate at different temperatures)

Wt% Temperature (K) VΦ0 Sv EΦ0 SE
Glycine+methanol+0.1M sodium benzoate
5 298.15 72.6 8.6 18.7 19.2
303.15 69.8 8.2 17.8 19.6
308.15 59.6 84 17.2 19.7
313.15 56.2 7.8 16.8 196
10 298.15 55.8 6.7 23.8 24.4
303.15 54.7 5.2 23.6 24.6
308.15 54.3 4.9 22.8 24.6
313.15 53.8 9.8 21.6 24.8
298.15 46.2 9.6 30.9 31.6
15 303.15 45.6 8.8 30.4 31.5
308.15 45.2 7.9 29.4 31.6
313.15 44.8 7.2 27.2 31.7

α-Alanine+methanol+0.1M sodium benzoate

5

298.15

78.4

10.8

30.6

31.4

303.15

70.6

11.2

30.2

31.5

308.15

69.2

10.6

29.6

31.6

313.15

67.4

10.2

29.4

31.6

10

298.15

64.6

9.6

23.4

28.6

303.15

63.7

8.5

33.6

28.5

308.15

62.8

6.2

31.2

28.4

313.15

63.6

6.6

30.6

28.2

15

298.15

58.6

8.6

34.2

26.4

303.15

57.2

7.7

34.5

26.3

308.15

53.4

6.4

34.2

26.2

313.15

52.1

5.6

34.1

26.2

β –alanine+methanol+0.1M sodium benzoate

5

298.15

90.2

23.6

45.3

46.2

303.15

89.4

25.2

45.2

46.2

308.15

87.2

14.6

44.8

46.4

10

313.15

82.4

14.2

44.7

46.4

298.15

81.9

11.6

46.7

43.1

303.15

80.2

23.2

46.4

43.6

308.15

79.4

12.1

46.4

43.1

15

313.15

78.6

12.4

46.3

43.2

298.15

76.8

23.8

48.8

40.1

303.15

74.6

24.6

48.4

40.1

308.15

72.4

24.2

48.3

40.2

313.15

70.4

24.1

48.1

40.3

A study of ultrasonic behaviour of solutions of in different wt% of aqueous methanol solutions at 298.15K reveals that the sound velocity increases and the isentropic compressibility (Ks) decreases as the contents of methanol in water+.0.1M sodium benzoate increases. The values of U0 and the empirical constants F, G and H are given in Table 2.

Table 2: Values of U0 (ms-1) and the constants F, G, H at 298.15K

Glycine+methanol+0.1Msodium benzoate

Wt%

U0(ms-1)

F

G

H

5

1524.0

1022.4

627.4

-2022.2

10

1536.8

812.2

-1413.2

-1914.6

15

1544.0

413.4

-1028.4

-1128.2

α –alanine+methanol+0.1Msodium benzoate

5

1552.0

938.2

-1931.0

712.8

10

1564.0

526.2

-1365.2

623.4

15

1572.0

465.4

-1024.6

1816.7

β –alanine+methanol+0.1Msodium benzoate

5

1524.0

1022.4

627.4

-2022.2

10

1536.8

812.2

-1413.2

-1914.6

15

1544.0

413.4

-1028.4

-1128.2

Such changes are also reported by other workers in other aqueous solvent mixtures like water + methanol [10], and water + PG [11]. As observed, the sound velocity increases with an increase in concentrations of the solutions The values of sound velocities of β-alanine are higher in methanol+.1M sodium benzoate solutions in all wt% than in the solutions of other amino acids. A typical plot of U-U0/C vs. C1/2 in 10wt% of methanol at 298.15K is given in fig1. The value of isentropic compressibility (Ks) decreases with increase in concentration of the solutions in all the amino acids. As observed the values of Ks of β-alanine are less in different wt% of methanol solutions than for other amino acids and are in the reverse order to the sound velocities

Fig. 1: plot of u-u0//c vs c1/2 in 10wt% of methonal solution in presence sodium benzoate


Fig. 2: Plot of ksφ vs c1/2in 15wt% of methanol solution in the presence of sodium benzoate. The apparent isentropic molar compressibility Ks,Φ increases with concentration of the solutions. The values of Ks,Φ are negative and so also the values of K0s,Φ. The negative values may be explained by two different phenomena, i. e., electrostriction and hydrophobic solvation. A typical plot of Ks,φ vs c1\2 in 15wt% of methanol +.1sodium benzoate is given in fig2.

The loss of compressibility of the surrounding solvent molecules due to strong electrostrictive forces leads to the electrostrictive solvation. In other words, a tight solvation layer is formed around the ion for which the medium is little compressed by application of pressure.

Table 3: Values of K0s, Φ (m3 mol-1 Pa-1) and the S0n

Wt% K0s, Φ S0n
Glycine+methanol+0.1Msodium benzoate
5 -8.00 -8.00
10 -0.2 -0.2
15 -7.00 -7.00
α- Alanine+methanol+0.1Msodium benzoate -7.00
5 -4.00 5.46
10 -0.8 5.48
15 -6.00 5.84
β +Alanine+methanol+0.1Msodium benzoate
5 -8.00 6.42
10 -6.00 6.48
15 -6.00 6.72

Fig. 3: Plot of RA vs c1/2 acids in 15 wt% of methanol solution in presence of sodium benzoate

The Sn values also increase with increasing methanol content in water higher Sn0for β- alanine in all wt% indicate strong electrostriction as compared to other amino acid solutions.

CONCLUSION

The results of the present investigations on amino acids in aqueous methanol solutions reveal that β-alanine shows high ion solvent interaction in solutions of methanol. The higher sound velocity values of β-alanine in aqueous methanol solutions in presence of sodium benzoate than in other amino acids solutions are due to higher mass. The decrease in value of Ks with increase in wt% of solutions may be due to occupation of the interstitial spaces of water by the solute molecules thereby making the medium less compressible. The increase in RA values The increase in RA values with increase in concentration of the solution indicates that ion-solvent interaction dominates over ion-ion interaction in all the solutions. The variation of Sn0 values predicts the degree of hard electrostrictive solvation, i. e., it represents the structural effect of amino acids on aqueous solutions of methanol in the presence of sodium benzoate.

CONFLICT OF INTERESTS

Declared None

REFERENCES

  1. Pattnaik S, Dash UN. influence of hydrotropic agents on the solute_solvent interactions in aqueous solutions, J Chem Pharm Res 2012;4(9):4364-9.
  2. Pattnaik S, Dash UN. Acoustic parameters of glycine in aqueous solutions of surfactants at 298.15K. Asian J Chem 2013;6(1):63-6.
  3. Robinson RA, Stokes RH. Electrolyte Solutions, Butterworths Scientific Publication: London; 1955. p. 30.
  4. Dash UN, Supkar S. Acoustic behavior of glycine and its salts in aqueous organic systems. J Chem Pharam Res 2012;4(1):754-62.
  5. Nikam PS, Nikam Neena, Hasan Mehdi Suryawanshi BS. Acoustical properties of monochloro acetic acid-Acetone-Water system at different temperatures. Asian J Chem 1994;6(2):237-45.
  6. Rath DC, Mishra SC, Samal K. ultrasonic study of excess thermodynamic parameter in binary mixtures of carbon disulphide. J Acoust Soc India 1987;15:198.
  7. Jacobson B. Intermolecular fee lengths in the liquid state I, Adiabatic and isothermal compressibilities of liquids. Actachem Scandinavica 1952;6:1485-98.
  8. Suryanarayan CV. internal pressure and free volume –the key parameters in characterizing liquids and electrolytic solutions. J Acoust Soc India 1979;7:131.
  9. Das S, Dash UN. Viscometric study of glycine, α-alanine, and β-alanine in aqueous and aqueous d-glucose solutions at different temperatures. J Chemical Pharm Res 2012;4(8):3869.
  10. a) Dash UN, Roy GS, Mohanty S. Ultrasonic studies on sodium thiosulphate and ammonium thiosulphate in water and water+acetone mixtures. Indian J Chemical Technol Ogy 2004;11(2):178-84.
  11. b) Das S, Dash UN. Studies on solute-solvent interactions of Amino acids inwater+D-glucose mixtures at different temperatures. J Chemical Pharm Res 2012;4(1):754-62.
  12. Ali A, Nain AK. Intermolecular interactions in ternary liquid mixtures by ultrasonic velocity measurements. Indian J Letters 1992;16(6):135.
  13. Thirumaran S, Sabu KJ. Ultrasonic investigation of Amino acids in aqueous sodium acetate medium. Indian J Pure Appl Physics 2009;87-96.
  14. Syal VK, Thakur SK, Chauhan S, Sharma P. Ultrasonic velocity studies of drug in mixed alcohol-water solvent system. Int J Thermodyn 26;3:807-26.
  15. Singh S, Singh R, Prasad N, Prakash S. Compressibility, free length and molar volume in ternary liquid systems. Indian J Pure Appl Physics 1977;629.