Chelation Study of Captopril with Cd 2+ and Pb 2+ Ions

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1 Amerin Journl of Biohemistry n Biotehnology 4 (3): , 28 ISSN Siene Pulitions Cheltion Stuy of Cptopril with C 2+ n P 2+ Ions ohmm Joshghni,.B. Gholivn n A.R. osvt Deprtment of Chemistry, Fulty of Siene, Rzi University, Kermnshh, Irn, Kermnshh Oil Refining Compny, Kermnshh, Irn Astrt: The protontion onstnts of Cptopril, (1-(3-merpto-2-(S)-methyl-1-oxopropyl)-S() proline, (CP) n stilities of its two ivlent metl ions C(II) n P(II) were etermine potentiometrilly in two ifferent metl to lign rtio 1:1 n 1:2 systems n in wter n methnol-wter inry mixtures using the omputer Best progrm. Two protontion onstnts were otine whih were ssigne to the roxyli n thiol groups. All protontion n stility onstnts inrese with eresing the ieletri onstnt on going from the pure wter to the inry mixtures. An exellent similrity in stilities of stuie metl ions strongly suggests tht oth metl ions re oorinte y CP in sme mnner through the thiol group. Key wors: Potentiometry, stility onstnt, ptopril, inry solvents mixture INTRODUCTION Cptopril (CP) is n effetive hypertensive gent whih ws me se on tive frgment of nno peptie, one of the most tive omponents of the South Amerin Snke s Venoms [1-4]. It is pplie suessfully for tretment of high loo pressure isese in mny ptients whose hypertension oul not e ontrolle y other ville rugs [5-9]. It inhiits the tive sites of zin glyoprotein, the ngiotension I onverting enzyme (ACE), loking the onversion of ngiotension I to ngiotension II, whose levels re elevte in ptients. The key funtionl group in the metolism of CP is the thiol group [4,7,1,11]. H S O H O C H 3 Sheme: Struture of Cptopril Over the lst ee, lose ttention hs een pi to the intertion of Cptopril with vrious metl ions CP hs three ifferent funtionl groups, whih n involve in oorintion to metl ions. These oorintion sites hve ifferent hr n soft nture, so hve ifferent ffinity towr ifferent metl ions n so my e oorinte from ifferent sites. In ition to moe of oorintion, ifferent metl- N O Cptopril mole rtio n e otine epening to the experimentl onitions. In ii, the omplex is more stle, wheres, in the rnge , the 2 omplex is the min speies [12]. For exmple, Zn hs polymeri struture where the zin is oorinte y the thiolte n ronyl oxygen of one lign n the ientte roxylte group of nother. In the Zn 2 omplex, two moleules of lign re oun vi sulfur n ronyl oxygen [13-14]. In opper se, however, EPR spetr inite tht ining to Cu (II) ours vi the lign oxygen s rther thn the thiol moiety [15] ATERIAS AND ETHODS Sujets n smples: The CP ws purhse from the erk n ws use without ny further purifition. etl ions were prepre from nlytil gre nitrte slt (erk) n their stok solutions were stnrize omplexometrilly y EDTA titrtion [22]. All KOH solutions were prepre with ouly istille wter n stnrize ginst potssium hyrogen phthlte (KHP) with phenol phthlein s n initor. The HNO 3 solution (.1 titrsol) ws stnrize with stnr KOH. Potentiometri titrtions were performe y mens of Hn- 3 series Benh -Top meter equippe with etrohm piston urette (715 Dosimt) with 5. m exhnge unit tht ws use for preise elivery of the stnr KOH. The meter ws lirte to re hyrogen ion onentrtion in queous uffer solutions se on Btes et l. [23]. The re on the meter re orrete y introution Corresponing Author: ohmm Joshghni, Deprtment of Chemistry, Rzi University, Kermnshh, Irn 245

2 the prmeter δ using the eqution (C) = (R)-δ where (C) is the orrete n (R) is the meter reing. The is the ifferenes in tivity oeffiients n liqui juntion potentil. Smples were titrte in oule-wlle glss ell mintine t 25±.1 C y irulting wter n stirre mgnetilly uner ontinuous flow of purifie nitrogen. The rnge for urte mesurements ws onsiere CP protontion onstnts n CP-C (II) n CP- P (II) metl omplexes in wter n inry methnolwter mixtures were lulte using the progrm BEST esrie y rtell n otekitis [24]. RESUTS AND DISCUSSION Am. J. Biohem. & Bioteh., 4 (3): , 28 The protontion onstnts of Cptopril hs een etermine using potentiometri tehniques n lulte using the omputer Best progrm. The results re shown in Tle 1. The orresponing ieletri onstnts of these solutions re lso evlute y interpoltion of the t of Akerlof [25-26] n liste for omprison. Two protontion onstnts were otine whih were ssigne to the roxyli n thiol group, respetively. The otine vlues in pure wter re in goo greement with the previous vlues [12,27] whih re shown in Tle 1 for omprison. It is interesting to note tht the omposition nture of the inry mixture hs istint effet on the protontion onstnts. Both protontion onstnts inrese with inresing the mole frtion of methnol n/or with eresing the ieletri onstnt of the inry mixture. Tle 1 shows liner reltionship etween the og KH n reiprol of ieletri onstnt s typil. This orer n e interprete y solvent effets on proton trnsfer retions s Grunwl n Coworker hve stuie previously [28-29]. It hs een shown tht the solvting ility [3] (s expresse y the Gutmnn oniity sle) n ieletri onstnt of the solvent ply funmentl role in protontion retions. It hs een Tle 1: Protontion onstnts of CP in wter n inry mixtures of ethnol-wter t 25 C n ioni strength.1 (KNO 3) Wter og ß 1 og ß 2 (D = 8) (-SH) (-COOH) (fit =.18) , 13.15, (D = 69) (fit =.13) (D = 61) (fit =.15) 5 (D = 54) (fit =.1) D: Dieletri onstnt, Ref. 12, Ref resonly ssume tht preferentil slvtion of the hrge prtiles y wter is minly responsile for suh monotoni epenene of the iity onstnts of CP on the solvent omposition. It is ler tht the issoition of n unhrge i in solvent requires the seprtion of two ions of opposite hrges. The work require to seprte these hrges in inversely proportionl to the ieletri onstnt of the solvent. The energy require for issoition is supplie y slvtion of the ions n lso the proton trnsfer from the i to the solvent moleule supplies n itionl energy. If the ieletri onstnt n the solvting ility of the solvent re erese, more energy will e require to seprte the tion n nion n onsequently the extent of issoition of the i will e lowere. Wter is solvent of high solvting ility, (i.e. onor numer DN = 33 [31] n ieletri onstnts = 78) whih n issoite the i n stilize the proue nion n hyrogen ion. Thus, it is expete tht ition of methnol with lower onor numer n ieletri onstnt (DN = 19 n ε = 32.6) respet to wter, ereses the extent of intertion of the solvent n lign issoition prouts n so ereses the iity onstnt of i. The sme tren hs lrey een reporte for vrious orgni moleules in ifferent solvent mixtures [32-33]. The istriution urves of speies in inry mixtures re shown in Fig. 1. The most importnt fetures of istriution igrms re the limit of evolving n ispperne of ompouns. So oring to istriution igrms t smller thn 4, the H 2 form is ominte. The H - n 2- forms ppere t intervls 6-1 n >1, respetively Fig. 1: Speies istriution igrm for CP() in () wter, () 2, () in 35 n () 5 (ethnol-wter) t 25 C n ioni strength.1 (KNO 3 )

3 Complextion of C(II) n P(II) with CP: CP hs three funtionl groups with ifferent hr-soft nture n so, n e oorinte to soft metl ions through soft thiol onting group. The stilities of P(II) n C(II) omplexes of CP were etermine y potentiometri tehnique n re summrize in Tle 2. The istriution igrms of -CP re shown in Fig The resulte stility onstnts shown in Tle 2 show tht the stility of ll omplexes inreses grully with inresing the mount of orgni solvent. This tren is the sme s protontion onstnts of the lign n n e interprete y the sme explntion. Figure 2 shows the speies istriution igrms for P-CP (1:1) systems in the pure wter n methnol-wter inry mixtures. The min metl speies in ll systems re n 2 3. In the queous system (Fig 2), in ition to these speies, is oserve s min speies in ii region whih is grully onverte to y inresing the solution. This speies my e proue y metlltion of speies n/or metlltion n susequently eprotontion of 2 speies. The onentrtion of inreses while inresing the n eresing the 2 onentrtion. In ition, erese in metl ion onentrtion is ourre t lower respet to inry mixtures. So, the is proly otine from 2 vi metlltion-eprotontion pth. If the ws proue vi iretly metlltion of, the might e expete to e present in oservle mount in 2 n 35 inry mixtures with reltive signifint onentrtion of. The sene of speies in inry mixtures my e ue to reltive higher stility of 2 in inry mixtures respet to pure wter, whih prevents the metlltion followe y eprotontion of 2. The CP is proly oorinte to P(II) s monoentte lign in speies n my eome ientte while seon eprotontion step in speies. Proton issoition le some potentilly linkle position on the lign, whih initilly were oupie y the protons. This feture enfores the system to form multinuler speies suh s 2 3, whih hs not signifint onentrtion in elow 4. In 2:1 system (Fig. 3), the min speies in inry mixture solvents re, 2 3 n 2 4. Agin, itionl speies seems to e importnt in pure wter (Fig 3). The formtion of even efore formtion of strongly supports its formtion from 2 vi metlltion-eprotontion pth, whih tkes ple t more ii ompre to 1:1 system. Contrst to 1:1 system, the 2 4 speies is oserve Am. J. Biohem. & Bioteh., 4 (3): , Tle 2: Stility onstnts of CP omplexes (2:1) in wter n 2, 35, n 5 (ethnol-wter) t 25 C n ioni strength.1 (KNO 3 ) C P Vlues in prentheses re from 1:1 metl to lign onentrtion rtio Fig. 2: Speies istriution igrm for CP-P (1:1) in (): wter, (): 2, (): 35 n (): 5 (ethnol-wter) t 25 C n ioni strength.1 (KNO 3 ) Fig. 3: Speies istriution igrm for CP-P (2:1) in (): wter, (): 2, (): 35 n (): 5 (ethnol-wter) t 25 C n ioni strength.1 (KNO 3 )

4 Am. J. Biohem. & Bioteh., 4 (3): , Fig. 4: Speies istriution igrm for CP-C (1:1) in : wter, : 2, : 35, n : 5 (ethnol-wter) t 25 C n ioni strength.1 (KNO 3 ) H Fig. 5: Speies istriution igrm for CP-C (2:1) in (): wter, (): 2, (): 35 n (): 5 (thnol-wter) t 25 C n ioni strength.1 (KNO 3 ) whih eomes more signifint on going into inry mixtures. A series of omplex equiliri my e responsile for prouing the 2 3 n 2 4 omplexes. Simultneous ollision of, n t out 5 my e responsile for formtion of 2 3 wheres, the 2 4 is proly proue y omintion of 2 3 n followe y fst eprotontion t ove 8. This suggeste formtion pttern oul e supporte from the shrp esening of onentrtion in this region. In C-CP (1:1) system (Fig. 4), the min speies in inry mixtures re n 2 3. Interestingly, speies istriution igrms hve istint ifferene with tht of pure wter. Agin, itionl n lso -1 speies were oserve in pure wter igrm. The lter speies ws not oserve in the P(II) se ue to limittion in the stuie rnge. The sene of in the inry mixtures my e interprete similr to the P(II) se. The metlltion n susequently eprotontion of proues the, whih onverts to -1 on going to higher Fig 4. Similrly, multinuler speies suh s 2 3 is proue y linking the n 2 monomers vi vnt positions on the lign, whih initilly were oupie y the protons. In pure wter, the onentrtion of 2 3 erese with inresing ove 6, wheres in inry mixtures, 2 3 long with, re ominnt speies in mentione rnge. In ition, their onentrtions seem to e inepenent. Sine 2 3 otine y ggregtion of n 2 speies, the following equiliri n explin the istriution urves t ove 6 + K K K 3 The sene of 2 n reltively signifint presene of 2 3 strongly suggeste tht the onsumption pth of 2 (K 3 ) is muh greter thn its formtion (K 2 ). In the other hn, the 2 speies is onsume very fster thn its proution. A ifferent pttern is oserve in 1:2 system wherein, the 2 4 (or 2 ) speies eomes the min speies in si region (Fig. 5). The formtions of multinuler speies re prevente ue to the presene of reltively lower mount of the metl ion. The high stility onstnt of 2 le reution n/or removing of uffere region. Hughes n Coworker hve reporte the formtion of C-CP omplexes suh, 2, 3, 2 3, 4 4 in the presene of NCl s supporting eletrolyte in queous solution with reltively lrge stility onstnts. The sene of some speies in our stuy my e ue to the ifferent supporting eletrolyte use in this stuy n/or the higher onentrtion of the lign neessity for the formtion of suh speies. ACKNOWEDGENTS The uthors re grteful to the Rzi University Reserh Counil n Kermnshh Oil Refining Compny for the support of this work. REFERENCES 1. Ferreir, S.H., D.C. Brtelt n.j. Greene, 197. Biohemistry, 9:

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