Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 3(8), 73-77, August (2013) Res. J. Chem. Sci. International Science Congress Association 73 Study of Interactions of Tryptophan through Acoustic and Thermodynamic PropertiesMalasane P.R. Department of Engineering, College of Engineering and Technology, Amravati, MS, INDIA Available online at: www.isca.in Received 9th November 2012, revised 5th January 2013, accepted 14th February 2013Abstract Molecular interactions of Tryptophan (an essential amino acid) in the presence of essential metal ions like Zn2+ and Co2+ at 303.15K have been studied by using ultrasonic interferometer supplied by M/s Mittal Enterprises, New Delhi, operating at a frequency of 2 MHz. and a bicapillary pyknometer to measure the density of solution. The data is processed to obtain the various acoustic and thermodynamic parameters to study the molecular interactions in aqueous solutions. The values of apparent molar volume, apparent molar compressibility, partial molar volume, partial molar compressibility, specific acoustic impedance, relative association, intermolecular free length have been calculated by using standard mathematical relations. The concentration dependences of the density and ultrasonic velocity were tried to fit into linear and polynomial equations. It is interesting to see the associative interaction among the molecules and ions as well as the increase in the stacking interactions between the metal ions and tryptophan. Keywords: Interactions, biomolecules, ultrasonic, molar volume, compressibility. Introduction The study of biomolecular interactions have been of intense activity in the recent past in all branches of chemistry and in other parallel disciplines as well, since these interactions are the driving force for the essential biochemical reactions. Amino acids, nucleosides and nucleotides are the important biochemicals in life processes, as these constitute a part of proteins, nucleic acids and other essential biomolecules. Also the metals like iron, zinc, cobalt, magnesium etc have been recognized as essential micronutrients, which provide structure and activity basis to several metallobiomolecular systems. Investigation of conformational properties of such biomolecules, interactions of their chemical groups with metal ions and their interaction in aqueous solution play an important role in understanding the biochemical processes occurring in the living systems. Material and MethodsTryptophans (AR grade, Qualigens fine chemicals Pvt. Ltd., Bombay, India) were used without further purification. The solutions were prepared by using triple distilled water. The purity of triple distilled water was further ascertained by measuring it’s ultrasonic velocity at 298.15K, which agreed with the corresponding literature values. The ultrasonic interferometer and bycapilliary pyknometer was calibrated before the measurements. The aqueous solutions of various concentrations of tryptophan with CaCl as well as with CoClwere prepared by using triple distilled water. Data Analysis: The experimentally calculated values of density, ultrasonic velocity, relative viscosity, apparent molar volume and apparent molar compressibility, for tryptophan in aqueous solution of Zn2+ and Co2+ at 303.15K, are recorded in table 1 and 2. The values of partial molar volume and partial molar compressibility are calculated by using following equations. v = + Sm (1) k = + Sm (2) Where, and are apparent molar volume and compressibility respectively at infinite dilution and S and S are experimental slopes. These limiting values of apparent molar volumes and compressibility along with the slopes are listed in the table 5. The concentration dependence of ultrasonic velocity of sound and density were tried to fit into following equations. Y = a + b m. (3) Y = a + b m + c (4) Where Y = u or and a = u or . 0 is the velocity of sound in pure solvent and 0 is density of pure solvent. The equation (D) yields better fit than the equation (C). The table 1 and 2 indicates that the values of density, ultrasonic velocity and relative viscosity increase with increase in the concentration of tryptophan in aqueous solutions of Zn2+ and Co2+. These values are higher for 0.05 M Zn2+ solutions and decrease continuously with the decrease in concentration Zn2+. This may be attributed to the cohesion brought about by ionic Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(8), 73-77, August (2013) Res. J. Chem. Sci. International Science Congress Association 74 hydration. A similar trend of variation is also observed for tryptophan in 0.05M, 0.01M, and 0.005 M Co2+ solution. The values of density, ultrasonic velocity and relative viscosities are higher for tryptophan in Co2+solution than in Zn2+ solution. This may indicate stronger interaction of tryptophan in aqueous solution of Co2+. Table-1 Density, relative viscosity, ultrasonic velocity, apparent molar volume apparent molar compressibility of tryptophan in 0.05, 0.01 and 0.005M Zinc Chloride solution at 303.15K Molality Density Relative Viscosity Ultrasonic Velocity Apparent molar Volume Apparent Molar Compressiblity m x10 - 3  r U v x10 - 6  k x10 - 15 (moles.kg - 1 ) (Kg.cm - 3 ) (ms - 1 ) (m 3 mol - 1 ) (m 3 mol - 1 pa) 0.05M zinc chloride 0.005016 1.002062 1.0079 1502.98 162.304 -1.5117 0.010004 1.002262 1.0162 1503.39 163.052 -4.2982 0.015087 1.002461 1.0237 1503.89 163.603 -3.555 0.020212 1.002658 1.0298 1504.48 164.039 -5.5272 0.025024 1.002823 1.0341 1504.91 165.073 -3.0478 0.03011 1.002998 1.0399 1505.57 165.776 -5.3038 0.01M zinc chloride 0.005037 0.997262 1.0035 1499.78 139.692 -3.6486 0.01008 0.997586 1.0151 1500.38 139.885 -3.7035 0.015131 0.997899 1.0202 1500.78 140.687 -2.8592 0.020189 0.998212 1.0286 1501.17 141.085 -2.4048 0.025116 0.998498 1.0321 1501.77 142.06 -2.5936 0.030198 0.998809 1.0389 1502.17 142.184 -2.3389 0.005M zinc chloride 0.005073 0.996661 1.0024 1498.79 145.563 -3.1508 0.010154 0.996958 1.0103 1499.19 145.762 -1.9974 0.015083 0.997246 1.0138 1499.59 145.807 -1.6685 0.020178 0.997537 1.0206 1499.98 146.146 -1.398 0.025122 0.997821 1.0273 1500.58 146.259 -1.7755 0.030232 0.998114 1.0308 1501.18 146.343 -1.9936 Table-2 Density, relative viscosity, ultrasonic velocity, apparent molar volume apparent molar compressibility of tryptophan in 0.05, 0.01 and 0.005M CobaltousChloride solution at 303.15KMolality Density Relative Viscosity Ultrasonic Velocity Apparent molar Volume Apparent Molar Compressiblity m x10 - 3  r u v x10 - 6  k x10 - 15 (moles.kg - 1 ) (Kg.cm - 3 ) (ms - 1 ) (m 3 mol - 1 ) (m 3 mol - 1 pa) 0.05M cobaltous chloride 0.005126 1.00226 1.0081 1503.56 149.375 3.066 0.010094 1.002528 1.0169 1504.16 149.671 -1.5381 0.01507 1.002792 1.0248 1504.76 150.037 -1.9283 0.020054 1.003059 1.0302 1505.55 150.072 -2.6861 0.025043 1.003323 1.0356 1506.14 150.208 -2.6628 0.030209 1.003594 1.0412 1506.94 150.368 -3.0037 0.01M cobaltous chloride 0.005072 0.997341 1.0042 1501.38 147.471 -7.6596 0.010151 0.997626 1.0133 1501.77 147.868 -6.3262 0.015079 0.997899 1.0199 1502.17 148.204 -6.5467 0.020172 0.998182 1.0266 1502.76 148.317 -1.1913 0.025115 0.998453 1.0332 1503.36 148.511 -1.5559 0.030223 0.998769 1.0367 1503.77 147.433 -1.5002 0.005M cobaltous chloride 0.00505 0.9967883 1.0035 1500.38 150.609 -2.521 0.010121 0.997048 1.0101 1500.78 151.929 -2.2474 0.015091 0.997298 1.0167 1501.18 152.642 -2.2083 0.019867 0.997522 1.0201 1501.57 153.798 -1.6325 0.025111 0.997739 1.0267 1502.17 155.707 -4.3161 0.030744 0.997999 1.0334 1502.56 156.137 -2.0225 Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(8), 73-77, August (2013) Res. J. Chem. Sci. International Science Congress Association 75 Table-3 Specific acoustic impedence,relative association,isentropic compressibility, intermolecular free-length and conductance of tryptophan in 0.05, 0.01 and 0.005M Zinc Chloride solution at 303.15K Molality Specific acou. Impedence Relative Association Isentropic Compress. free length Conductance m Z x10 - 3 R A Ks L f x10 - 3 (moles.kg - 1 ) (Kg.m - 2 s - 1 ) 0 mhos.cm - 2 0.05M zinc chloride 0.005016 1506.079 1.000078 4.4177 0.40003 7.14 0.010004 1506.791 1.000186 4.4144 0.39988 7.08 0.015087 1507.591 1.000274 4.4106 0.39971 6.98 0.020212 1508.479 1.00034 4.4063 0.39951 6.87 0.025024 1509.158 1.000409 4.4031 0.39937 6.76 0.03011 1510.084 1.000438 4.3984 0.39916 6.63 0.01M zinc chloride 0.005037 1495.674 1.000196 4.458 0.40185 1.81 0.01008 1496.758 1.000387 4.4529 0.40162 1.8 0.015131 1497.627 1.000612 4.4492 0.40145 1.79 0.020189 1498.486 1.00084 4.4455 0.40129 1.78 0.025116 1499.514 1.000993 4.4406 0.40107 1.77 0.030198 1500.381 1.001216 4.4369 0.4009 1.75 0.005M zinc chloride 0.005073 1493.786 1.000169 4.4665 0.40224 0.949 0.010154 1494.629 1.000378 4.4628 0.40207 0.947 0.015083 1495.46 1.000578 4.4592 0.4019 0.944 0.020178 1496.286 1.000783 4.4555 0.40174 0.942 0.025122 1497.31 1.000935 4.4507 0.40152 0.94 0.030232 1498.349 1.001095 4.4458 0.4013 0.935 Table-4 Specific acoustic impedence,relative association, isentropic compressibility, intermolecular free-length and conductance of tryptophan in 0.05, 0.01 and 0.005M Zinc Chloride solution at 303.15K Molality Specific acou. Impedence Relative Association Isentropic Compress. Intermolecular free length Conductance m Z x10 - 3 R A Ks L f x10 - 3 (moles.kg - 1 ) (Kg.m - 2 s - 1 ) 0 mhos.cm - 2 0.05M Cobaltous chloride 0.005126 1506.958 1.000191 4.4134 0.39984 7.15 0.010094 1507.963 1.000325 4.4087 0.39963 7.08 0.01507 1508.961 1.000456 4.4041 0.39941 6.99 0.020054 1510.155 1.000547 4.3983 0.39915 6.95 0.025043 1511.145 1.00068 4.3937 0.39894 6.89 0.030209 1512.356 1.000773 4.3878 0.39868 6.76 0.01M Cobaltous chloride 0.005072 1497.388 1.000201 4.4481 0.40141 1.898 0.010151 1498.205 1.0004 4.4445 0.40124 1.896 0.015079 1499.014 1.000585 4.4409 0.40108 1.89 0.020172 1500.028 1.000738 4.4362 0.40087 1.882 0.025115 1501.034 1.000876 4.4315 0.40065 1.867 0.030223 1501.919 1.001102 4.4276 0.40048 1.856 0.005M Cobaltous chloride 0.00505 1495.561 1.000187 4.4565 0.40178 1.039 0.010121 1496.35 1.000358 4.453 0.40162 1.031 0.015091 1497.124 1.00052 4.4495 0.40147 1.027 0.019867 1497.849 1.000658 4.4462 0.40132 1.023 0.025111 1498.774 1.000743 4.4417 0.40111 1.017 0.030744 1499.553 1.000917 4.4382 0.40096 1.004 Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(8), 73-77, August (2013) Res. J. Chem. Sci. International Science Congress Association 76 Table-5 Limiting values of apparent molar volume and apparent molar compressibility for tryptophan along with slops at 303.15 KConc. of 0 v x 10 – 6  0 k x 10 – 15 S v x 10 – 6 S k x 10 - 15 Zinc (m 3 mol - 1 ) (m 3 mol - 1 pa - 1 ) (m 3 mol - 2 kg) (m 3 mol - 2 pa - 1 kg) Chloride 0.05 M 161.59 -9.02 135.71 0.0002 0.01 M 138.99 -4.12 110.11 0.0005 0.005 M 145.41 -3.42 32.597 0.0011 Results and Discussion Volumetric data: From the table 1 and 2, it is evident that the values of apparent molar volume () are positive and increase gradually with increase in concentration of tryptophan in 0.05M, 0.01M and 0.005 M aqueous solution of Zn2+ and Co2+. This clearly indicates that there are strong solute-solvent, solvent-solvent and ion-solvent interactions. The values decrease with decrease in the concentration of metal ions, which may be attributed to the ionic concentration and electrostriction effect. This may be accounted to the associative interaction among the molecules and ions also increase the stacking interactions between the metal ions and tryptophan. Several workers4-7 have also reported the volumetric studies of different amino acids in aqueous solution of electrolytes. The plots of versus m show that the for tryptophan is linear function of its molal concentration (m). The slopes of plots of versus m are positive for all concentration of Zn2+ and Co2+. The graphically calculated values of along with slopes are listed in the table 5. The data of table 5 shows that the values are positive and higher for tryptophan at experimental temperature, indicating strong solute-solvent and ion-solvent interactions, at infinite dilution. Since tryptophan is an amino acid with non-polar R-group, it is less interactive towards the water molecules. But the presence of metal cations enhances the possibility of strong interaction through complexation. This fact is further supported by positive values of S for tryptophan in Zn2+ and Co2+ solutions. Compressibility data: Table 1, 2 and 7 shows the variation in compressibility in terms of k and values for tryptophan in Zn2+ and Co+ solutions. The negative values indicate the loss of structural compressibility of solvent molecules and these solutions are incompressible due to complex formation between tryptophan and Zn2+ or Co2+. These complex molecules may occupy interstitial space in a network structure associated with tetrahedrally bonded water molecules. The k values are found to increase with concentration of tryptophan in aqueous solutions of Zn2+ whereas in Co2+ solutions the reverse trend is observed except for 0.005M solutions where the variation gives nearly flat line. According to hypothesis of substitutional dissolution,the complex molecule and the free tryptophan molecule can be thought of as occupying the cavities exists in open water structure. Such suitable cavities are created according to the shape and size of solutes leading to strengthening of water structure in the vicinity of solute molecule giving negative value of k. The difference in the variation of k with concentration of tryptophan in Zn2+ and Co2+ solution may be due to difference in the size of respective metal ion as well as the suitability of the cavities in water structure for their fitting. The concentration dependence of apparent molar compressibility () has been used to obtain the limiting molar compressibility () values. The partial molar compressibility values for tryptophan in Zn2+ and Co2+ solutions are listed in the table 5. The values are more negative than those reported for amino acid in water8,9. The decrease in isentropic compressibility (K) with increase in concentration of tryptophan in aqueous solution of Zn2+ and Co2+ (table 3 and 4) may be due to approach of solvent molecules10 around the metal ions supporting the strong ion-solvent interaction. This may also support the formation of week H-boding between oxygen atom of water molecule and H-atom of COOH group of tryptophan molecule. Since tryptophan is an amino acid with non-polar R-group, it is less interactive towards the water molecules. But the presence of metal cations enhances the possibility of strong interactions through complexation. The parameter Z (acoustic impedance) shows linear variation with concentration of tryptophan (table 3, 4). The Z values decrease with decrease in concentration of metal ion. This may also be correlated with size of metal ions. In the present study relative association (R) increases with concentration suggesting that the solute-solvent interaction dominates. Viscosity Data: The values of relative viscosity of tryptophan in 0.05 M, 0.01M and 0.005 M aqueous solution of Zn2+ and Co2+ at 303.15K are given in the table 1 and 2 It can be observed from the table that the relative viscosity of tryptophan increases with increase in concentration of tryptophan as well as the concentration of aqueous solution of Zn2+ and Co2+. ConclusionThe overall data analysis for tryptophan in aqueous solution of Zn2+ and Co2+ suggest that in these solutions, complex formation occurs and fitting of such complexes at interstitial site of water Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(8), 73-77, August (2013) Res. J. Chem. Sci. International Science Congress Association 77 network is more probable. It also indicates the loss of compressibility of solvent due to strong electrostrictive forces in the vicinity of ions, causing electrostictive solvation of ions. 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