IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (2) 2011 Conductometric Studies of Aqueous Solution of Thymine and Adeno sine At Different Temperatures S. S. Al-Ani Department of chemistry , College of Education , Ibn-Al- Haitam, Unive rsity of Baghdad Abstract M olar conductivity of different concentrations of thy mine and adenosine in water , sodium acetate and ammonium chloride solution at different temp eratures , 283. 15-323.15 K has been determined from direct conductivity measurements , examination of aqueous mixture of thy mine and adenosine with Onsager equation reveal deviation from linearity at high concentration .This deviation was exp lained 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 M easuremens of the conductivity of solute in solution-provide us with imp ortant information concering the nature and dissolvation p henomenone of solute-solvent interaction [1]. Therefore , this work was chosen to st udy the behaviour of nucleic acids in aqueous solution . Information concerning such behaviour is considered to be of a fundamental imp ortance in understanding the factors that determine the stability of bioacids [2,3]. In recent y ears , in biochemical st udies , aqueous solvent or mixture of water and organic solvent have been used more and more frequently as media in which to carry out these st udies , because the rate of the reaction is much effected in this solvent sy st em [4]. Thy mine (I) and Adenosine (II) are st able nucleic weak acids , PKa at 25 o C are 9.94 and 10.2 resp ectively. IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (2) 2011 Both of those acids are widely used in biochemical research [5].In sp ite of these interesting p hy sical and biochemical p rop erties., little work has been done on the p rop erties of aqueous solution an acid-water interaction . Since those acids have many interaction sites with water , the solute-water interaction with this sy st em might p rovide us with some interesting results The present invest igation was undertaken to discover the molecular interaction between those acids and water in presence of acids and basic salts. Materials Thy mine and adenosine (BHD) , were p urified by tewic recry st allization from water , thy mine decomp oses at 335-337 О C lit. , 335 О C ,adenosine m.p . 234-2335 О C lit. , 234 O C. Sodium acetate and ammonium Choloride , Aldrich chemical were with p urity 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 p erformed with a Py e –Unicam conductivity bridge model E 7566/4 , and M ullard conductivity cell ty p e /E 7597/A . The platinum electrodes of the conductivity cell were p lated with p latinum black by the electrolysis of 100 ml of solution contanies 3 gm of chlorop latinic acid and 0.02 gm of lead acetate, the current was adjust ed so as to p roduce a moderate flow of hy drogen . The p recicion of the conductivity measurements was withine ± 0.04 % .The cell constant was determined using KCl solution prior to each of conductivity measurements The temp erature p recision of the thermost ate , Hewlett p aclacard quartz thermometer , used was ± 0.1 о C . The solution were p repared by weighting out (0.32070 gm) of adenosine and (0.15134 gm ) of thy mine in volumetric flask (100 ml) to give st ock solution of 0.012M . from these st ock solutions different concentrations were prepared for 0.0001 to 0.00075 M . The concentration were p repared in Sodium acetate 0.05 M solution and ion ammonium chloride 0.05 M solutions. For in comp iated electrolytes such as thy mine and adenosine the following Onsager equation can be used [6,8] :  =    -  (A+B   )(  C) 1/2 ……………..(1). IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (2) 2011 Where (  ),(   ) are the molar and limiting conductivities , resp ectivety ,( C ) is the molar concentration and (A,B) are const ants . 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 (C 1/2 ) 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 plott ed 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 temp eratures , 283.15 to 323.15 K are list ed in Table 1,2,3 and 4 resp ectively. Onsager equation was p lott ed in Figure (1) for thy mine and adenosine , resp ectively in water at 298.15 K ,t he , the limiting molar conductivity of thy mine 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 p resence of more then one active sites comp ared with that of thy mine molecule (see st ructural 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 Bronst ed 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 app roximate equation (1) to the following :      …………………….(3) By subst itute 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. S CI. VOL. 24 (2) 2011 The est imation of (   ) and (Ka) values is done by p lott ing 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 app lied only to mono-mono valent acids The value of (Ka) for thy mine and adenosine obtained from the plot of Ostwald equation gives values 1.1x10 -13 and 1x10 -14 resp ectively , which is reasonable comp aring with that given in literature[12] Conductivities of thy mine 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 p lott ing of (  C) against (1/  ) of those solutions . The values of (   ) ,(Ka) are p resented in Table (4) . As exp ected 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 thy mine and adenosine nucleic acids . Conductivity of electrolyte solution can be related to the activation energy of flow through Arrhenius equation /aE RTAe  ……………………………………….(5). Where Ap re-exp onential factor , Ea activation energy of flow , R gas constant and T the absolute temp erature . Arrhenius equation can be writt en in the following form [13] ln ln /aA E RT   …………………….(6) Table 3 listed the data for the molar conductivies at different temp eratures 283.15-323.15 K for thy mine and adenosine in water , sodium acetate and ammonium chloride solution . By p lott ing logarithmic conductivity (ln  ) vereus (1/T) , Figures (4,5) show a st raight line obtained for thy mine and adenosine in each solvent , the slop e equals Ea/R , form which Ea. was calculated (see Table4). It was founed that values are the some ap p roximately with both sy st em and increase from water to ammonium chloride through sodium acetate solution . This result indicates that both thy mine and adenosine molecular interactions in theses solution are weak. Re ferences 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. Furt er ,F. W. .(1979) (Edition) Thermody namic Behaviour of Electroly tes in mixed solvents Amer . Chem .Soc. series , Washington D.G. 5. Rahway, J. N. (1986)''M erck Index'' , (8 th Edition) , M erch and Co., Washington D.C 6. At kins ,W. P. ,(1978) ''Phy sical Chemist ry '' , Oxford Univ . Press 7. Castellan,W. G (1971) .''Phy sical Chemist ry '' , 2 nd Ed . Addisonwesley Pub.Co ., U.S.A 8. Robinson, A. R. and Stokes ,H . R (1970) 'Electroly tic Solutions'' , Butterworths, London IBN AL- HAITHAM J. FOR PURE & APPL. S CI. 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. At kins , W.P. (1990). ''Phy sical Chemist ry '' (4 th Edition) , Ox ford p ress , Oxford 12. ''HandBook of chemical and phy sical const ants " 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 thymi ne in water , sodium acetate and ammoni um chloride at 298.15 K. Water Sodium acetate Ammonium chloride C mole/ L ^ S.Cm 2 /m ole C 1/2 ^ C 1/^ ^ S. Cm 2 /m ole ^ C 1/^ ^ S. Cm 2 /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. S CI. VOL. 24 (2) 2011 Table (2) The conducticity datya for adenosine in water , sodium acetate and ammoni um chl oride at 298.15 K. Table (3) molar conductivity of 0.0015 M aque ous sol uti on of thymine and adenosine at different temperature. Thy mine 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.Cm 2 /m ole C 1/2 ^ C 1/^ ^ S. Cm 2 / mole ^ C 1/^ ^ S. Cm 2 / 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. S CI. VOL. 24 (2) 2011 Table (4): Limitting mol ar conductivties , dissocation constants and activation e ne ries of viscous flow of thymi ne and adenosine in water , sodium acetate and ammoni um chloride at 298.15 K. Thy mine Water Sodium acetate Ammonium chloride 1215 o 139.95 10 aK X  / 18.48 aE KJ 1341 o 1 01.49 10 aK X  / 20.32 aE KJ 3472 o 1 25.76 10 aK X  / 23.92 aE KJ Adenosine Water Sodium acetate Ammonium chloride 335 o 1 211.35 10 aK X  / 17.30 aE KJ 1205 o 148.3 10 aK X  / 20.47 aE KJ 1651 o 1 10.636 10 aK X  / 25.98 aE KJ IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (2) 2011 Fig. (1): Molar conductivity as function of C 1/2 for (a) thymi ne and (b) adenosine in water at 298.15 k ○ IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (2) 2011 Fig.(2): Plotting betwee n  C agi nst 1/  for thymine in (a) water , (b) sodium acetate sol uti on , (C) ammoni um chl oride soluti on at 298.15 K o IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (2) 2011 Fig. (3): Plotting betwee n  C agi nst 1/  for adenosine in (a) water , (b) sodium acetate sol uti on , (C) ammoni um chl oride soluti on at 298.15 K o IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (2) 2011 Fig. (4) :Plotting betwee n l n  aginst 1/T for thymi ne in(a) water , (b) sodium acetate sol uti on , (c) ammoni um chl oride soluti on i n 0.0015 M. IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (2) 2011 Fig. (5): Plotti ng between ln  aginst 1/T for adenosine in(a) water , (b) sodium acetate sol uti on , (c) ammoni um chl oride soluti on i n 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 الریة لمخالیط الثایمین واالدنوسین في الماء ،خالت الصـودیوم ،وكلوریـد االمونـی تم قیاس التوصیلة المو .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