Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 1(8), 12-17, Nov. (2011) Res.J.Chem.Sci. International Science Congress Association 12 Acoustic and thermodynamic properties of cholesterol in ethanol and 1-propanol solution in different concentration at 303K Ravichandran S.Department of Physics, Sathyabama University, Chennai 600119 Tamilnadu, INDIAAvailable online at: www.isca.in (Received 01st August 2011, revised 25th August 2011, accepted 4th October 2011) Abstract Ultrasonic velocity and density are measured in the mixture of cholesterol in ethanol and 1-propanol solution at different concentration to study the thermodynamic properties. Acoustical parameters like adiabatic compressibility, intermolecular free length, acoustic impedance and surface tension are calculated using the ultrasonic velocity and density. These data are particularly discussed with respect to the concentration of cholesterol. The variation of ultrasonic velocity shows a dip at higher concentration of cholesterol. These properties are used to illustrate the nature of interactions between component molecules. Keywords: Cholesterol-acoustical properties-ethanol-1-propanol-molecular interactions. IntroductionCholesterol is a sterol. It is interacted with lipoproteins and with bile salts. Moreover, studies of cholesterol aggregation in aqueous medium are essential for an understanding of the physico-chemical properties of cholesterol. The physical state of the cholesterol/lipids in relation to the bio chemical environment can be understood on the basis of their interaction with an aqueous system. Knowledge of the physico-chemical properties of cholesterol aggregates in aqueous medium are thus essential for an understanding of structural properties. Aqueous solutions of cholesterol have been little investigated to understand the cholesterol –cholesterol and cholesterol-water interactions to form the complex systems. Ultrasonic parameters are used extensively to study molecular interactions in liquid mixtures. In the recent years, it has been found that, the acoustical properties of solution should be an important parameter in the study of several chemical reactions and in the investigation of molecular interactions. Thermodynamic properties of liquid mixtures have been extensively used to study the departure of a real liquid mixture from ideality. Recently, more number of researchers has studied the properties of cholesterol/lipids. Researchers had examined cholesterol aggregates in water employing a dialysis technique and studied the micelle equilibrium, critical micelle concentration and solubility of cholesterol1-4. The same author(s) have studied the ultrasonic study and allied properties of cholesterol in chloroform solution at 294K. In this work, the thermodynamic properties of cholesterol like adiabatic compressibility, intermolecular free length, acoustic impedance and surface tension are studied in ethanol and 1-propanol solution at 303K by ultrasonic velocity measurement and the non-linear variations have been calculated by (B/A) Hartmann and baluu and Empirical relation. Material and MethodsIn the present investigation, cholesterol (Merck) of molecular weight of 386.66 gm/mol was taken. Cholesterol was added in Ethanol (AR-Grade) at different concentration. Density and ultrasonic velocity was measured in different concentrations of mixed solution at 303K. Ultrasonic interferometer (Mittel Enterprises, New Delhi) of fixed frequency (2 MHz) was used for measuring ultrasonic velocity. Density of a binary mixture was measured using gravimetric method. These values were found to be accurate up to ± 0.1 kg/m. The same experiment was repeated in 1-propanol solution with different concentration of cholesterol. Acoustical parameters, acoustical impedance, intermolecular free length, compressibility, internal pressure, volumetric parameters, relaxation time and classical absorption coefficient are calculated using as usual formula. Results and DiscussionThe experimental values of ultrasonic velocity, adiabatic compressibility, density, intermolecular free length for the system of cholesterol in ethanol and in 1-propanol at 303K are presented in Table 1 and Table 2. The adiabatic compressibility, s, of donor-acceptor for solutions have been determined from the sound velocity, using an expression Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 1(8), 12-17, Nov. (2011) Res.J.Chem.SciInternational Science Congress Association 13 Table-1 Experimental values of ultrasonic velocity, density, compressibility, acoustic impedance, intermolecular free length, surface tension and relative association of cholesterol in ethanol at different concentrations Concentration of cholesterol (mg) Velocity (U) (m/s) Density ) (kg/m) Adiabatic compressibility 10-10 (kg-1ms) Acoustic impedance (Z) X10(kg/ms) Free length (L10-10(m) Surface Tension ) (N/m) Relative association (R) 0 1159.21 784 9.492 9.088 1.319 19494 0.000 20 1156.87 790 9.455 9.142 1.316 19589 1.008 30 1163.70 794 9.301 9.239 1.305 19856 1.011 40 1158.40 791 9.418 9.166 1.314 19657 1.009 50 1163.94 795 9.285 9.254 1.304 19889 1.013 60 1166.55 793 9.264 9.253 1.303 19911 1.010 70 1180.40 802 8.949 9.467 1.280 20490 1.016 80 1169.67 803 9.107 9.388 1.292 20227 1.021 90 1182.33 804 8.893 9.510 1.277 20602 1.033 100 1184.87 808 8.813 9.578 1.271 20770 1.084 125 1177.64 802 8.993 9.443 1.284 20414 1.017 Table-2 Experimental values of ultrasonic velocity, density, compressibility, acoustic impedance, intermolecular free length and surface tension of cholesterol in 1-propanol in different concentrations Concentration of cholesterol (mg) Velocity (U) (m/s) Density ) (kg/m) Adiabatic compressibility 10-10 (kg-1ms) Acoustic impedance (Z) X10(kg/ms) Free length (L10-10(m) Surface Tension ) Relative association (R) 0 1206.25 803 8.555 9.691 1.252 21205 0.000 20 1203.60 771 8.952 9.281 1.281 20285 0.961 30 1196.68 801 8.717 9.587 1.264 20893 0.999 40 1194.94 805 8.705 9.613 1.263 20935 1.004 50 1206.12 805 8.535 9.714 1.250 21254 1.003 60 1206.74 808 8.502 9.747 1.248 21332 1.005 70 1208.38 808 8.478 9.761 1.246 21376 1.004 80 1208.82 809 8.460 9.778 1.245 21418 1.006 90 1206.11 808 8.507 9.747 1.248 21325 1.006 100 1209.31 809 8.450 9.786 1.244 21439 1.0064 125 1214.20 810 8.379 9.830 1.239 21577 1.005 Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 1(8), 12-17, Nov. (2011) Res.J.Chem.SciInternational Science Congress Association 14 s = 1/Ud Where, s, U, and d refer to the adiabatic compressibility, velocity and density of the solutions respectively. Similarly, o = 1/U d Where, Uo, and d refers to the adiabatic compressibility, velocity and density of the solvent respectively. The compressibility lowering is expressed as, = s o The variation of ultrasonic velocity with concentration of cholesterol for two different systems is shown in Figure-1. It is observed that the ultrasonic velocity varies non-linearly with increasing the concentration of cholesterol. It shows some dip at a concentration of 40mg and 80mg of cholesterol with ethanol. The sources of non-linear variations are observed with 1-propanol as reported earlier with chloroform. The deviation in adiabatic compressibility can be explained by taking into consideration of the following factor. Figure-1 Variation of ultrasonic velocity of cholesterol in ethanol and 1-propanol solution Loss of di-polar association and difference in size and shape of the component molecules Which lead to decrease in velocity and increase in compressibility. Dipole-dipole interaction or hydrogen bonded complex formation between unlike molecules Which lead to increase in sound velocity and decrease of compressibility. The actual deviation depends on the resultant effect. The observed decrease/increase in adiabatic compressibility, intermolecular free length and acoustic impedance with composition is an evidence of significant interaction between the component molecules in the binary mixtures. The variations of adiabatic compressibility of cholesterol in ethanol and 1-propanol are shown in figure-2. Increase in the compressibility value indicates the weakening of molecular interactions. The compressibility decrease with increase in the concentration of cholesterol and it increases at a concentration of 80mg. According to the Fort and Moore, compressibility studies of binary liquids mixture involve hydrogen bonding. According to them, hydrogen bonding between unlike components made a negative contribution to compressibility. The increase in velocity and decrease in compressibility forms a tight bond system. Hence, it is observed that the compressibility of a binary mixture non-linearly varies with concentration of cholesterol. Figure-2 Variation of adiabatic compressibility of cholesterol in ethanol and 1-propanol solution Figure-3 Variation of intermolecular free length of cholesterol in ethanol and 1-propanol solution The variation of ultrasonic velocity in a solution depends on the intermolecular free length of mixing. Ultrasonic velocity increases on decrease of free length and vice-versa. The computed values are given in table-1. The intermolecular free length decreases with concentration of cholesterol and it is shown in figure-3. This is an indication that the structural readjustment in the liquid binary mixture proceeds in the direction of less compressible phase or closer packing of molecules. A sudden increase in molecular free length shows a looser packing molecules or weak interaction10. Acoustic 1150.001160.001170.001180.001190.001200.001210.001220.00050100150concentration of Cholesterol(mg)Ultrasonic Velocity(m/s) Ethanol 1-propanol 8.28.48.68.89.29.49.6050100150 Concentration of cholesterol(mg)adiabatic compressibility Ethanol 1-propanol 1.231.241.251.261.271.281.291.31.311.321.33020406080100120140concentration of cholesterol(mg) Ethanol 1-propanol Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 1(8), 12-17, Nov. (2011) Res.J.Chem.SciInternational Science Congress Association 15 impedance is almost reciprocal of compressibility. The increase in velocity, impedance and decrease in compressibility and free length with the addition of ethanol and 1-propanol indicates that, intermolecular forces increase with addition of solvents11. The calculated values of acoustic impedance are shown in table-1 and table-2. Compressibility decreases with increase in the concentration, whereas, impedance increases for a given concentration. A sudden decrease of impedance at a particular concentration may be due to the complex formation in the solution, and this may be on the basis of the interaction between solute and solvent molecules12. The non linear variation of surface tension also supports this interaction113. Relative association was found as non linear variations with ethanol and 1-propanol and it shows the weak and strong interactions and this conclusion is fortified by the values of relative association and it is shown in Figure-4 14. Table-3 shows the variations of the B/A values calculated from Hartmann and Ballou relation and the variations are shown in Figure-5. The values of lowering compressibility were computed using the above formula and the variations are shown in figure 6. The lowering compressibility values are positive at lower concentration. It is almost linear decreasing in ethanol solution while it randomly varies in 1-propanol solution. It confirms the interaction between the solvent and solute molecules15. Nonlinearity parameter of salts-polyvinyl alcohol mixed solution calculated by Harymann and Ballou relation: In the last few years a number of theoretical methods have been proposed for estimating the nonlinearity parameter (B/A) for pure liquids and liquid mixtures16. This parameter has been further correlated with other thermo acoustical parameters which are used to deduce the available volume and intermolecular free length of liquid mixtures. General formulation for non-linearity in terms of acoustical parameters of liquids has been made using the experiment for sound velocity (U) and introducing the contribution due to isobaric acoustic parameters (k) and the isothermal acoustic parameter (k”). The expression for B/A is given by. B/A = 2k + 2k” Computations of k and k” require only the knowledge of thermal expansion co-efficient. Detailed method of calculation is given by Hartmann and Balizer obtained the following relation for B/A17-18 B/A = 2+ ((0.98 × 10)/U) (1) Empirical relation proposed by Ballou is given by B/A = – 0.5 + ((1.2 × 10 )/U) (2) Where U is the velocity in m/s. Table-3 shows the variations of the B/A values calculated from Hartmann and Ballou relation and it shows decreased trend with increase in concentration. The B/A values for the liquids have been interpreted as the quantity representing the magnitude of the hardness of liquids. The B/A values are concenerned with interactions between the components of the binary systems19. The interaction between the components of the binary mixtures is weaker at a particular concentration of cholesterol. From the graphs of ultrasonic velocity, density, compressibility, molecular free length, impedance and surface tension with concentration of cholesterol, it is clear that, ultrasonic velocity increases with concentration of cholesterol in binary mixture of ethanol up to 70mg. Here, ethanol promotes acyl-chain order. At a concentration of 80mg, a sudden decrease of velocity occurs due to weak interaction between solute and solvent molecules. It may be due to H---O---H bonding interactions. 0.20.40.60.81.2020406080100120140concentration of cholesterol(mg)relative association Ethanol 1-propanol 9.29.49.69.81010.210.410.6050100150 concentration of cholesterol (mg)values of non-linearity Ethanol-eqn (1) 1-propanol-eqn (1) ethanol-eqn (2) 1-propanoleqn (2) Figure-4 Variation of relative association of cholesterol in ethanol and 1-propanol solution Figure-5Variation of non-linearity (B/A) of cholesterol in ethanol and 1-propanol solution using equation (1) and equation (2) solution Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 1(8), 12-17, Nov. (2011) Res.J.Chem.SciInternational Science Congress Association 16 Figure-6 Variation of lowering compressibility values of cholesterol in ethanol and 1-propanol Table-3 Non-linearity (B/A) values of a binary mixtures of cholesterol in ethanol and in 1-propanol solution at different concentrations using different equations Concentration of cholesterol (mg) Cholesterol in ethanol Cholesterol in 1-propanol Equation (1) Equation (2) Equation (1) Equation (2) 0 10.454 9.852 10.124 9.448 20 10.471 9.873 10.142 9.470 30 10.421 9.812 10.189 9.527 40 10.460 9.859 10.201 9.542 50 10.419 9.809 10.125 9.449 60 10.400 9.787 10.121 9.444 70 10.302 9.666 10.110 9.430 80 10.378 9.759 10.107 9.427 90 10.288 9.649 10.125 9.449 100 10.271 9.627 10.104 9.423 125 10.321 9.689 10.071 9.383 Cholesterol molecules may act as a structure breaker, at higher concentration and ethanol disorders the hydrocarbon interior by tilting the cholesterol chain. An increase in ethanol concentration allows the liquid-ordered phase to exist at higher concentrations. Recall that at low concentration, ethanol disorders the hydrocarbon interior by tilting the lipid chain20. Similarly, ultrasonic velocity increases up to a concentration of 80mg and there is a closer interaction between cholesterol and 1-propanol mixture. While, at a concentration of 90mg, there is a weaker interaction. Further increase in the concentration, indicates the strong interaction with 1-propanol. The weak interaction might be due to the two lone pairs of electrons of cholesterol. It shows some immiscibility of solute and solvent molecules and this behavior is the result of structural changes occurring due to the formation of hydrogen bond complexes in the solution. But, in the case of cholesterol with 1-propanol solution, it shows the closer interaction between the solute and solvent molecules. The present study points out clearly that the emergence of a new complex structure is temporarily formed in this system at a particular concentration. Hence, it is concluded that, some disordered structure is formed in the solution and it may be due the formation of micelle. Further study may give more details about complex ion formation. Conclusion The ultrasonic velocity and other acoustical parameters of cholesterol in ethanol and in 1-propanol solution were studied. The variations in the acoustical parameters might be due to the formation of complex structures. The present study points out clearly that the emergence of a new complex structure is temporarily formed in this system at a particular -0.8-0.6-0.4-0.20.20.40.6050100150 concentration of cholesterol(mg)lowering compressibility value Ethanol 1-propanol Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 1(8), 12-17, Nov. (2011) Res.J.Chem.SciInternational Science Congress Association 17 concentration. Hence it is concluded that, some disordered structure is formed in the solution and it may be due the formation of micelle. Further study may give more details about complex ion formation.AcknowledgementThe authors thanks to Ramanathan K., Head, Department of Physics, Thiagarajar College of Engineering, Madurai, Tamilnadu, for his valuable guidance. The authors are also thanks to Dr. Palanisami, Professor, Department of Chemistry, Anna University, Chennai, Tamilnadu, Prof. A.N. Kanappan, Department of Physics, Annamalai University, and Dr. Chandramouleeswaran, Professor and Head (Rtd), Government of College of Engineering, Salem, Tamilnadu, India for their support in this work. References1.Small D.M. and Shipley G.G., Physical-chemical basis of lipids deposition in atherosclerosis, Sci.,185, 222-229 (1974) 2.Haberland M.E. and Roynolds J.A., Self association of cholesterol in aqueous solution, Proc. 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