IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 Conductometric Studies of Aqueous Solution of Thymine and Adenosine At Different Temperatures S. S. Al-Ani Department of chemistry , College of Education , Ibn-Al- Haitam, University of Baghdad Abstract Molar conductivity of different concentrations of thymine and adenosine in water , sodium acetate and ammonium chloride solution at different temperatures , 283. 15-323.15 K has been determined from direct conductivity measurements , examination of aqueous mixture of thymine and adenosine with Onsager equation reveal deviation from linearity at high concentration .This deviation was explained in term of molecular interaction . Ostwald dilution law also examined with the above mixtures lead to calculation of limiting molar conductivities and dissociation constants of both nucleic acid in water , sodium acetate and ammonium chloride. The agreement between the values obtained for Onsager equation and Ostwald law was reasonable . Calculation of activation energies of flow using modified Arrhenius equation gives a result showed that the molecular interaction of both acids in all different mixtures were the same . Introduction Measuremens of the conductivity of solute in solution-provide us with important information concering the nature and dissolvation phenomenone of solute-solvent interaction [1]. Therefore , this work was chosen to study the behaviour of nucleic acids in aqueous solution . Information concerning such behaviour is considered to be of a fundamental importance in understanding the factors that determine the stability of bioacids [2,3]. In recent years , in biochemical studies , aqueous solvent or mixture of water and organic solvent have been used more and more frequently as media in which to carry out these studies , because the rate of the reaction is much effected in this solvent system [4]. Thymine (I) and Adenosine (II) are stable nucleic weak acids , PKa at 25 o C are 9.94 and 10.2 respectively. IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 Both of those acids are widely used in biochemical research [5].In sp ite of these interesting physical and biochemical properties., little work has been done on the properties of aqueous solution an acid-water interaction . Since those acids have many interaction sites with water , the solute-water interaction with this system might provide us with some interesting results The present investigation was undertaken to discover the molecular interaction between those acids and water in presence of acids and basic salts. Materials Thymine and adenosine (BHD) , were purified by tewic recrystallization from water , thymine decomposes at 335-337ОC lit. , 335ОC ,adenosine m.p. 234-2335О C lit. , 234O C. Sodium acetate and ammonium Choloride , Aldrich chemical were with purity not less than 99.99 % . Conductivity water had a conductivity of 0.3 X 10-6 S.Cm-1 at 25 О C. Conductivity measurements were performed with a Pye –Unicam conductivity bridge model E 7566/4 , and Mullard conductivity cell type /E 7597/A . The platinum electrodes of the conductivity cell were plated with platinum black by the electrolysis of 100 ml of solution contanies 3 gm of chloroplatinic acid and 0.02 gm of lead acetate, the current was adjusted so as to produce a moderate flow of hydrogen . The precicion of the conductivity measurements was withine ± 0.04 % .The cell constant was determined using KCl solution prior to each of conductivity measurements The temperature precision of the thermostate , Hewlettpaclacard quartz thermometer , used was ± 0.1 о C . The solution were prepared by weighting out (0.32070 gm) of adenosine and (0.15134 gm ) of thymine in volumetric flask (100 ml) to give stock solution of 0.012M . from these stock solutions different concentrations were prepared for 0.0001 to 0.00075 M. The concentration were prepared in Sodium acetate 0.05 M solution and ion ammonium chloride 0.05 M solutions. For in compiated electrolytes such as thymine and adenosine the following Onsager equation can be used [6,8] : =    -  (A+B   )(  C) 1/2……………..(1). IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 Where ( ),(   ) are the molar and limiting conductivities , respectivety ,( C ) is the molar concentration and (A,B) are constants . Equation (1) can be written As: =   =  [   -(A+B   )] ( C) 1/2 =  [   -(A+B   )](  /  C) 1/2   =  [   -K(C/  )1/2]  =   -K(C/  ) 1/2 Where(  ) is the molar condctivity of one mole of ions at any concentration and K=A+B   . Poltting ( ) against (C1/2) gives (   ) by extraplating to zero concentration . In order to obtain a batter value of(  ) it was introduced in term (C  /  )1/2 as (  -   ) by using the values of ( ) and (C) . Then ,the corrected values of (  ) were plotted against ( C) 1/2 to obtain the correct value of (   ) [9,10]. The coductivities of solution of thmine and adenosine with different concentrations in water , sodium acetate and ammonium chloride at different temperatures , 283.15 to 323.15 K are listed in Table 1,2,3 and 4 respectively. Onsager equation was plotted in Figure (1) for thymine and adenosine , respectively in water at 298.15 K ,the , the limiting molar conductivity of thymine is 900 S. Cm 2 mole-1 and adenosine 1110 S. Cm 2 mole-1 .The hihg value of   of adenosine could be due to presence of more then one active sites compared with that of thymine molecule (see structural formula above) . The deviation from linearity with both nucleic acid at high concentration reflects that solvent effect become weaker and weaker when concentration increases until no solvent effect is shown in a concentration above 0.006 mole L -1. The conductivity of weak electrolyte like weak Bronsted acids such as thmine and adenosine depends on the number of ions in the solution , and therefore on the degree of dissociation ( ) of those electrolyte . The degree of dissociation ( ) for the acid (HA) at molar concentration ( C ) at equilibrium : HA  H+ + A- [ ][ ] ( )( ) [ ] H A C C Ka HA C C         2 1 C Ka     ………………….(2) When concentration of ions in solution is low , we can approximate equation (1) to the following :      …………………….(3) By substitute the value of equation (3) in eqution(2) , we obtain Ostwald dilution law [11]. 2 1 1 Ka C         …………………….(4) IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 The estimation of (   ) and (Ka) values is done by plotting of Ostwald dilution law for both nucleic acids in water . The agreement between the values of calculated using Onsager and Ostwald equation can not take the number of active sites in consideration and it is applied only to mono-mono valent acids The value of (Ka) for thymine and adenosine obtained from the plot of Ostwald equation gives values 1.1x10-13 and 1x10-14 respectively , which is reasonable comparing with that given in literature[12] Conductivities of thymine and adenosine were also measured in solutions of 0.05 mole sodium acetate and 0.05 mole ammonium chloride as well as in water. Figures (2,3) show the plotting of (C) against (1/ ) of those solutions . The values of (   ) ,(Ka) are presented in Table (4) . As expected the values are high in ammonium chloride and low in sodium acetate . The acid and basic character of those solvent p lay an important rule in dissolution of thymine and adenosine nucleic acids . Conductivity of electrolyte solution can be related to the activation energy of flow through Arrhenius equation /aE RTA e   ……………………………………….(5). Where Apre-exponential factor , Ea activation energy of flow , R gas constant and T the absolute temperature . Arrhenius equation can be written in the following form [13] ln ln /aA E RT   …………………….(6) Table 3 listed the data for the molar conductivies at different temperatures 283.15-323.15 K for thymine and adenosine in water , sodium acetate and ammonium chloride solution . By plotting logarithmic conductivity (ln  ) vereus (1/T) , Figures (4,5) show a straight line obtained for thymine and adenosine in each solvent , the slope equals Ea/R , form which Ea. was calculated (see Table4). It was founed that values are the some approximately with both system and increase from water to ammonium chloride through sodium acetate solution . This result indicates that both thymine and adenosine molecular interactions in theses solution are weak. References 1. Bates ,G. R; Roy, N. R. and Robenson ,A. R.(1974), J. Solution Chem ., 3:905 2. Petrella, G.; Castagenio, M.; Saccor, A. and DeGiglio ,A. (1979) .J. Solution Chem., 5: 621 3. Roy ,N. R.; E.Swensson, E. and Krueger ,W. G. (1975)Anal . Chem ., 47: 1407 4. Furter ,F. W. .(1979) (Edition) Thermodynamic Behaviour of Electrolytes in mixed solvents Amer . Chem .Soc. series , Washington D.G. 5. Rahway, J. N. (1986)''Merck Index'' , (8 th Edition) , Merch and Co., Washington D.C 6. Atkins ,W. P. ,(1978) ''Physical Chemistry '' , Oxford Univ . Press 7. Castellan,W. G (1971) .''Physical Chemistry '' , 2nd Ed . Addisonwesley Pub.Co ., U.S.A 8. Robinson, A. R. and Stokes ,H . R (1970) 'Electrolytic Solutions'' , Butterworths, London IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 9. Saleh , M.J . (1979) . Iraqi J. Sci., 20:387 10. Saleh , M.J. , (1980) Iraqi J. Sci ., 21:507. 11. Atkins , W.P. (1990). ''Physical Chemistry '' (4 th Edition) , Ox ford press , Oxford 12. ''HandBook of chemical and physical constants " CRC , (1984). vol.69, New York 13. Halifa, A.K.; Salman, E. A.and Al-Tair,H. A .(1990). Iraqi J.Chem., 15(2):225 Table (1) The conductivity data for thymine in water , sodium acetate and ammonium chloride at 298.15 K. Water Sodium acetate Ammonium chloride C mole/ L ^ S.Cm2/m ole C1/2 ^ C 1/^ ^ S.Cm2/m ole ^ C 1/^ ^ S.Cm2/m ole ^ C 1/^ 0.012 00 22.92 0.10 9 0.27 5 4.36 3 7.50 0.900 1.33 3 14.58 0.17 5 6.85 9 0.006 00 43.33 0.07 7 0.25 9 2.30 7 13.67 0.820 073 2 27.50 0.16 5 3.63 8 0.003 00 76.67 0.05 5 0.23 0 1.30 4 25.00 0.790 0.40 0 53.33 0.16 0 1.87 5 0.001 50 144.00 0.03 8 0.21 6 0.69 4 48.08 0.750 0.20 8 103.41 0.15 5 0.96 7 0.000 75 266.67 0.02 7 0.20 0 0.31 3 90.09 0.675 0.11 1 244.49 0.15 3 0.40 9 0.000 38 489.47 0.01 9 0.18 6 0.20 4 144.90 0.550 0.06 9 359.71 0.13 7 0.27 8 0.000 19 857.87 0.01 4 0.16 3 0.16 5 212.76 0.399 0.04 7 552.79 0.10 5 0.18 1 0.000 10 950.00 0.01 0 0.09 5 0.10 5 303.03 0.300 0.03 3 650.19 0.06 0 0.15 4 IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 Table (2) The conducticity datya for adenosine in water , sodium acetate and ammonium chloride at 298.15 K. Table (3) molar conductivity of 0.0015 M aqueous solution of thymine and adenosine at different temperature. Thymine Adenosine Water Sodium acetate Ammonium chloride Water Sodium acetate Ammonium chloride 1/T x10 -3 ln  ln  ln  ln  ln  ln  3.531 3.200 1.902 2.293 2.905 1.386 2.303 3.470 3.243 2.079 2.425 3.078 1.541 2.539 3.411 3.356 2.325 2.610 3.178 1.673 2.773 3.354 3.551 2.485 2.928 3.284 2.080 3.016 3.298 3.696 2.588 3.030 3.379 2.485 3.205 3.245 3.738 2.688 3.058 3.515 2.773 3.283 3.193 3.952 2.815 3.227 3.576 2.960 3.401 3.143 4.001 2.929 3.330 3.695 3.114 3.507 3.095 4.072 3.122 3.619 3.829 3.258 3.753 Water Sodium acetate Ammonium chloride C mole/ L ^ S.Cm2/m ole C1/2 ^ C 1/^ ^ S.Cm2/ mole ^ C 1/^ ^ S.Cm2/ mole ^ C 1/^ 0.012 00 29.67 0.10 9 0.35 6 3.37 0 10.42 2.1 49 1.04 4 19.58 0.23 4 5.107 0.006 00 54.33 0.07 7 0.32 6 1.84 1 20.00 2.0 99 0.54 6 36.67 0.22 0 2.727 0.003 00 103.67 0.05 5 0.31 1 0.96 5 38.33 2.0 55 0.27 3 70.00 0.21 0 1.428 0.001 50 200.67 0.03 8 0.30 1 0.50 0 73.33 1.2 00 0.14 9 116.6 7 0.20 9 0.857 0.000 75 381.33 0.27 0.28 6 0.26 2 133.3 3 1.1 43 0.05 3 186.6 7 0.20 0 0.375 0.000 38 542.11 0.01 9 0.20 6 0.18 5 250.0 0 0.8 43 0.04 3 342.1 0 0.14 4 0.209 0.000 19 652.63 0.01 4 0.12 4 0.15 3 388.9 5 0.6 99 0.02 7 578.9 5 0.11 0 0.173 0.000 10 700.00 0.01 0 0.07 0 0.14 3 465.5 5 0.4 00 0.02 5 680.0 0 0.06 8 0.147 IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 Table (4): Limitting molar conductivties , dissocation constants and activation eneries of viscous flow of thymine and adenosine in water , sodium acetate and ammonium chloride at 298.15 K. Thymine Water Sodium acetate Ammonium chloride 1215 o 139.95 10 aK X  / 18.48 aE KJ 1341 o 101.49 10 aK X  / 20.32 aE KJ 3472 o 125.76 10 aK X  / 23.92 aE KJ Adenosine Water Sodium acetate Ammonium chloride 335 o 1211.35 10 aK X  / 17.30 aE KJ 1205 o 148.3 10 aK X  / 20.47 aE KJ 1651 o 110.636 10 aK X  / 25.98 aE KJ IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 Fig. (1): Molar conductivity as function of C 1/2 for (a) thymine and (b) adenosine in water at 298.15 k○ IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 Fig.(2): Plotting between C aginst 1/ for thymine in (a) water , (b) sodium acetate solution , (C) ammonium chloride solution at 298.15 Ko IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 Fig. (3): Plotting between C aginst 1/ for adenosine in (a) water , (b) sodium acetate solution , (C) ammonium chloride solution at 298.15 Ko IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 Fig. (4) :Plotting between ln aginst 1/T for thymine in(a) water , (b) sodium acetate solution , (c) ammonium chloride solution in 0.0015 M. IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 Fig. (5): Plotting between ln aginst 1/T for adenosine in(a) water , (b) sodium acetate solution , (c) ammonium chloride solution in 0.0015 M. 2011) 2( 24المجلد مجلة ابن الھیثم للعلوم الصرفة والتطبیقیة دراسة توصیلیة للمحالیل المائیة للثایمین واالدنوسین في درجات حرارة مختلفة ساھرة صادق العاني ابن الھیثم ، جامعة بغداد –قسم الكیمیاء ،كلیة التربیة 1996كانون األول 22: استلم البحث في 1997حزیران 30: قبل البحث في الخالصة وم بتراكیـز تم قیاس التوصیلة الموالریة لمخالیط الثایمین واالدنوسین في الماء ،خالت الصـودیوم ،وكلوریـد االمونـی .كلفن 323و15، 283و15مختلفة وبدرجات حرارة تتراوح بین عـن ذللمحالیل االلكترونیـة المخففـة ووجـد ان ھـذه المخـالیط فـي محالیلھـا المائیـة تشـ قد تم استخدام معادلة اونساكرلو .ات والمذیبات لیتالخطیة بالتراكیز العالیة ولقد اعزي ھذا التصرف الى التاثیرات المتبادلة بین االلكترو ت التفكـك لھـا لھذه المحالیـالمحددة استخدمت معادلة اوستولد لحساب التوصیلة الموالریة تطابقـت .ل مـع حسـاب ثواـب اس التوصـیل. معادلة اوستولد مع معادلـة اونسـاكر النتائج المستحصلة من م قـی درجاتیكمـا ـت حـرارة ة الموالریـة للمخـالیط ـب د ان عملیـة مختلفة واستخدمت معادلة أرھینوس لحساب طاقـة التنشـیط لھـذه المخـالیط ووجـد انھـا متسـاویة تقریبـا ممـا یؤـی . ستذواب متشابھة من حیث استھالك الطاقة اال