IJCRR - Vol 04 ISSUE 16, August, 2012
Date of Publication: 28-Aug-2012
Download XML Download PDF
THERMODYNAMIC AND SPECTROSCOPIC INVESTIGATION OF POLAR PROTIC SOLUTIONS OF L. ARGININE MONO HYDROCHLORIDE
Author: K. Kannagi, E. Jasmine Vasantha Rani, R. Padmavathy, N. Radha
Category: General Sciences
Abstract:FTIR spectroscopic techniques are widely used as a tool with unique capability and sensitivity. The shift and splitting up of the frequencies of molecular ions are interpreted in terms of molecular interactions. In the present investigation an attempt is made to correlate the spectroscopic results with thermodynamic study of L. Arginine mono hydrochloride in non-aqueous solutions. FTIR spectra of L. Arginine mono hydrochloride solutions and pure solvent are recorded. The observed vibrational spectra are analysed. Thermodynamic parameters such as internal pressure, free volume, Rao's constant, Wada's constant and adiabatic compressibility are measured. The results obtained from FTIR ananlysis are found to be in good agreement with the thermodynamic studies.
Keywords: Internal pressure, Free volume, Vibrational spectra
The molecular behaviour of liquids can be investigated both by spectroscopic and nonspectroscopic methods. The ultrasonic velocity measurement is a unique technique for the characterization of structure and properties of liquid and solution. During the past decades, studies of ultrasonic velocity have been carried out to investigate the hydration of proteins using volume and ultrasonic measurements because these properties are sensitive to the degree and nature of hydration.[3,4] The amino acids and proteins are the basic components which have been investigated in detail with respect to their thermodynamical behavior in solutions. Salt solutions have large effects on the structure and properties of proteins, including such properties like solubility and dissociation[6,7]. In the present work L.Arginine monohydro chloride in non-acqueous solution is analyzed for the specific bonding interactions. The ultrasonic velocity along with other experimental data such as density and viscosity furnish wealth of information about the interaction between ions-dipoles, hydrogen bonding, multi-polar and dispersive forces. Internal pressure is the important thermo dynamic parameter to determine the various molecular interactions occurring in the solution. FTIR spectroscopic study finds wide spread application in qualitative and quantitative analysis of many components and it is well employed to understand the nature of interatomic bonding and for the identification of the various phases present in the sample and shifts in frequencies. L-Arginine mono hydrochloride is commonly used in cell culture media and drug development.
L-Arginine monohydrochloride solutions of different concentration is prepared with AR grade salt. It is used without further purification. The sample solution is studied at different concentrations (0.001, 0.01, 0.05,0.1, 0.2) mol. d.m-3 with an accuracy of 0.0001gm is maintained. The density of the solutions is determined using 25ml specific gravity bottle, using the thermostatic bath with a compressor unit. A Cannon Fenske viscometer (10ml) is used for the viscosity measurements. Variable bath interferometer having a frequency of 2MHz (Mittal Enterprises, New Delhi) with overall accuracy of 0.1% is used for velocity measurements. The fundamental parameters such as density, viscosity and ultrasonic velocity are measured for different molalities in the temperature range of 278.15K to 328.15K. The FTIR spectrum of this solution is recorded in the region of 4000-400 cm-1 using (PERKIN ELMER) model SPECTRUM RXI FTIR spectrometer. The following formulae are used for the computation of Internal Pressure (π i), Free Volume(Vf), Rao’s constant and Wada’s constant:
RESULTS AND DISCUSSIONS
Internal Pressure and Free Volume Internal pressure and free volume are easily measurable parameters which are fundamentally responsible for various interactions occurring in the solution. Internal pressure can be expressed as sum of an attractive and repulsive contribution. The attractive forces mainly comprise hydrogen bonding. Dipole-dipole, multipolar, and dispersion interactions. Repulsive forces, acting over very small intermolecular distances, play a minor role in the cohesion process under normal conditions. Generally, the significance of the internal pressure and its correlation with the solubility parameter (widely used for instance in paints, pharmaceutics, polymers, and petroleum industry) has been discussed among others in review articles by Dack  and Barton . Internal pressure varies due to all the internal interactions. The variations of internal pressure and free volume with temperatures and molalities are shown in figures 1 and the values are tabulated in Table 1. The increase in internal pressure of the solution at very low concentrations suggests that there is a structure promoting nature of the salt in non-aqueous. It is also confirmed from the free volume values of the solution. The temperature increases, there is a tendency for the ions to move away from each other. Hence, there is a reduction in internal pressure with increases in temperature. Internal pressure shows an increasing trend upto 0.01 molality at all the temperatures. A dip is observed at 0.05m at all the temperature in the solution. These results supports that there is a weak ion-solvent interaction within the solution. Free volume is one of the significant factors in explaining the variations in the physicochemical properties of liquids. The molecules of the liquids are not closely packed and there is some free space between the molecules for movements which is called as free volume . The concept of free volume is an extension of the idea that each molecule is enclosed by its neighbours in a cell, the free volume is however not the whole cell volume but rather than average volume in which the center of the molecule can move inside the hypothetical cell due to the repulsion of the surrounding molecules. Free Volume is the free space available for the ions to move. The variations of free volume with respect to molalities and temperatures figures 2 confirm that there is a weak interaction in L-Arginine Mono- hydrochloride solution. Rao's and Wada’s Constant Studying the molecular interactions is to evaluate certain parameters which are constant in non interacting systems. The variation of this constant indicates the measure of interaction in interacting systems. In liquid systems the sound velocity varies linearly with concentration. It is known that in two component liquid systems which are noninteracting, the sound velocity varies linearly with concentration. Rao  established an empirical relation linking molecular weight, density and ultrasonic velocity of a mixture. Rao's constant is found to be independent of concentration in non-interacting systems. The variation in the Rao’s constant was explained as arising from molecular association. The irregular behavior of Rao’s and Wada’s constants in Table 2, figures 3 and4 also supports that there is a molecular dissociation existing in the solution. Adiabatic Compressibility The orientation of solvent molecules around the solute is determined by adiabatic compressibility. Elastic deformation is propagated by acoustic waves. The longitudes waves are generated by isotropic pressure, causing a uniform compression and thus a deformation in the direction of propagation. The primary effect of dissolving a solute is to lower the compressibility of the solvent. The lowering is attributed to the influence of the electrostatic field of the ions on the surrounding solvent molecules. This variation represents the existence of weak hydrogen bonding arising as a result of hydrophobic interactions occurs between the solute and solvent molecules. This weak bond is responsible for the existence of weak interactions. In L-Arginine Monohydrochloride system, the rise and fall in compressibility shows in Table 2 and figure 4 supports the pre-dominance of dissociation of molecules occurring in the solution.
FTIR spectral analysis of L.Arginine Mono Hydrochloride: Solute-solvent interactions are conveniently studied by several spectroscopic techniques. Infrared spectroscopy is normally carried out in the mid infrared region 4000 – 200 cm-1 . The near infrared region at higher frequency 12500 – 4000cm-1 and the far infrared region at lower frequency 200 to 10cm-1 required special techniques. L.Arginine mono hydrochloride is dissolved in non-aqueous solution, the following spectral changes are observed. Table 3, figures 6 and 7. L-Arginine mono hydrochloride exists in ionic form and it is solvated both at NH3 + site of guanidino group and COOsites of solute in which the existence of zwitterionic form to a greater extent. These findings support that at lower molalities there is a strong solute-solvent interaction. There is a significant shift by 88cm-1 of the enolic form of solvent, towards the lower wave number region. this indicates the binding of the solute molecule to C=N of solvent resulting in bond lengthening, on the others hand there is a shift of NH2 stretching vibration by 21cm-1 and about 50 cm-1 for the bending vibration for the salt shown in Table 3. These shifts confirms that L-Arginine mono hydrochloride exists in Enolic and Amide forms figure 8 and 9 by the solvent. CONCLUSION In the present investigation, L-Arginine and LArginine Monohydrochloride in non-aqueous medium have been analyzed both by acoustic and spectroscopic methods. The results obtained from the above two methods are as follows. The results obtained from the acoustic study supports that there is a weak ion-solvent interaction with in the solution. A weak hydrogen bonding exists in the solution. It exhibits the hydrophobic interaction takes place within the solution. This weak bond is responsible for the existence of weak interactions in the solution of L-Arginine Monohydrochloride. From FTIR analysis L.Arginine mono hydrochloride is present in protonated ionic form and it is solvated both at NH3 + site of guanidino group and coosites and also the existence of zwitterionic form is found to be very high in the solution. The results obtained from FTIR analysis are found to be in good agreement with the acoustic studies.
1. C. Kapota; J. Lemaire,; P. Maiitre, G.Ohanissian, J.Am.Chem.Soc. 2004, 126, 1836
2. R.A. Jocksuch, A.S. Lemof, E.R.Willuiams, J Am.Chem. Soc. 2001 123,12255.
3. A.S Lemoff, M.F. Bush, J.T. O’Brien, E.R. Williams, J. Phys. Chem.A 2006, 110, 8433.
4. S.K. Chauthan, and V.R. Singh, Ind. J. pure and Applied Physics, 635:(1993)
5. H.Eyring, and M.S. John, , Significance of liquid structures, Wiley (1969)
6. M Schafer, N.C. Polfer, J. Oomens, D. Blunk, M. Forbes, R.A. Jockusch, In Proceedings of the 54th ASMS conference on Mass Spetrometry and allied Topics, Seattle, WA, 2006
7. Journal of Chemical and Pharmaceutical Research J.Chem. Pharm. Res., 2011, 3(3): 587- 596.
8. Lennard – J.E.Jones, Proc. Roy. Soc., A., 106 (1924) 463.
9. J.A. Barker, Lattice theories of liquids(New York)Oxford., Pergaman
10. State (1963).
11. D.R. Bhadja, Y.V. Patel and P.H. Parasonia, Ind. J. Pure and Appl. Phys., 24 (2004) 47.
12. David R. Lide., Handbook of chemistry and physics, 86th edition, CRC press.
13. Peter Atkins and Julio de Paula, Physical Chemistry, 8th edition, 60–61.
14. Dack M.R.J., J. Chem. Soc. Rev., 4 (1975) 211-229.
15. A.F.M.Barton, J. Chem. Educ., 75(6), (1975) 731-753.
16. Edward Zor?bski, Molecular and Quantum Acoustics vol. 27 (2006) 327.
17. S.Glasstone, K.J. Laidler and H. Eyring, The theory of Rate Processes, Mc Graw Hills, NewYork, (1950).
18. R. Palani, S. Balakrishnan and G.Arumugam, J. Phy. Sci., 22(1), (2011) 131-141.
19. B.S.Patial, S.Chauhan and V.K.Syal, Ind. J. Chem., 41A (2002) 2039-2047.
20. E. Jasmine Vasantha Rani, R. Padmavathy, N. Radha, K. Kannagi, Proceedings on National Conference on Exploring the Frontiers of Vibrational Spectroscopy (EXFOVIS2011).
21. R. Badarayani, A.Kumar, J. Chem. Eng. Data, 48 (2003) 664-668.
22. R.Watson, Phil. Trans. Roy .Soc. London, 60 (1770) 325.
23. S.Holker, Phil. Magazine, 27 (1844) 207.
24. P.A. Favre and C.A.Valson, C.R. Acad sciences, 75 (1872) 1000.
25. F.Kohlraush and W.Hallwacks, Phys. Chem, 5 (1894) 14. 26. P.Drude and W.Nernst, Z. Phys. Chem., 15 (1894) 79.
27. D.V. Jahagiridar and A.G.Shankarwar, Ind. J. Pure and Appl. Phys, 38 (2000) 645-650.
28. R.Palani, S.Saravanan, J. Phy., 2 (2008)13- 21.
29. J.T.Eller, Hist. Acad. Roy. Berlin, 6 (1750) 82.