Interaction of Cu(II) with Cytosine in Britton-Robinson Buffer Solution - A Cyclic Voltammetric Study

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1 Dhk Univ. J. Si. 63(1): 31-36, 215 (Jnury) Intertion of Cu(II) with Cytosine in Britton-Roinson Buffer Solution - A Cyli Voltmmetri Stuy A. A. Shikh *, Jnntul Firws, S. Islm n P. K. Bkshi Deprtment of Chemistry, Dhk University, Dhk-1, Bnglesh (Reeive : 16 April 214; Aepte : 1 August 214) Astrt Eletrohemil reox ehvior of Cu(II) t ifferent ph in Britton-Roinson (BR) uffer solution hs een investigte using yli voltmmetry t glssy ron eletroe (GCE). Cu(II) shows thoi pek n hump-like pek, n n intense noi pek t ph,.59, 1.59, 3.1 n 4.8. Although t lower ph (.59 n 1.59) thoi pek, hump n n noi pek re oserve, t higher ph (3.1 n 4.8) the hump-like thoi pek isppere. Cyli voltmmetry hs lso een use to oserve the intertion of Cu(II) with ytosine in BR uffer solution t vrious ph. A resonly strong intertion etween Cu(II) n ytosine t ifferent Cu(II)/ytosine molr rtio is oserve t ll the stuie ph. However, mximum intertion ours t 1:4 molr rtio t ph 4.8, this is perhps the most suitle onition for Cu(II)-ytosine intertion. Keywors: Cytosine; Britton-Roinson uffer; Glssy ron eletroe; Pek potentil I. Introution Cytosine is one of the five min nitrogenous ses use in storing n trnsporting geneti informtion within ell 1. It is pyrimiine erivtive, with heteroyli romti ring n two sustituent tthe (n mine group t position 4 n keto group t position 2). The nuleosie of ytosine is ytiine 2. DNA methyltion involves the ition of methyl group to the 5 position of the ytosine pyrimiine ring or the numer 6 nitrogen of the enine purine ring (ytosine n enine re two of the four ses of DNA). DNA methyltion lso plys ruil role in the evelopment of nerly ll types of ner 3. DNA methyltion involves the ition of methyl group to DNA, for exmple, to the numer 5 ron of the ytosine pyrimiine ring, in this se with the speifi effet of reuing gene expression. DNA methyltion t the 5 position of ytosine hs een foun in every verterte exmine. Cytosine plys vitl role in piring, through hyrogen ons with the gunine se of gunosine n eoxygunosine. Cytosine is involve in the geneti oon of 17 mino is n ontrols the essentil fetures of life 4. Although ytosine is se it n t s lign euse of the presene of unpire eletrons on nitrogen n oxygen whih re ville to onte in omplextion retion. Cyli voltmmetri ehviour of ytosinto rige omplexes of ruthenium(ii) n pltinum(ii) with 1-lkyl-2- (rylzo)imizoles were investigte 5. Eletrohemil properties of the omplexes hve een exmine y yli voltmmetry in CH 3 CN in presene of [n-bu 4 N][ClO 4 ] s supporting eletrolyte using Pt-is working eletroe t the sn rte of 5 mv/s. Although severl groups 6-8 hve trie to investigte the eletrohemil intertion of metlytosine with ifferent eletroes, our im is to investigte the intertion of Cu(II) with ytosine in BR uffer meium mintining vrious ph t GCE using yli voltmmetry. II. Experimentl Mterils Anlr gre Cu(NO 3 ) 2.3H 2 O ws purhse from Merk, Germny n use without further purifition. Anlytil gre ytosine (BDH, UK) ws use in this stuy. Aeti i (BDH, UK), phosphori i (Merk, Germny), n ori i (Merk, Germny) were lso use for the preprtion of BR uffer. Soium hyroxie (Merk, Germny) n perhlori i (BDH, UK) were use s it is ville for mintining the ph of the solution. All queous solutions were prepre in ouly istille wter otine from Milli-Q wter purifition system. The experiments were rrie out t room temperture. Equipments Three eletroes system onsisting of GCE s the working eletroe, Ag/AgCl (st. KCl) s the referene eletroe n pltinum wire s the ounter eletroe ws use. Cyli voltmmetri mesurement ws performe using Computerize Eletrohemil System, Moel HQ-24 evelope y Avne Anlytis, USA. Solution ph ws mesure with ph meter (Miroproessor ph meter, moel ph 211, HANNA Instruments). Methos Preprtion of Britton-Roinson uffer solution For the preprtion of BR uffer solution,.4 M H 3 BO 3,.4 M H 3 PO 4 n.4 M CH 3 COOH solutions were prepre seprtely, n the three solutions were then mixe together with sme volume rtio. By ing.2 M NOH or HClO 4 solution the esire ph vlues (ph vlues re.59, 1.59, 3.1 n 4.8) were juste. Preprtion of metl ion n ytosine solution Metl ion solution of.5 mm Cu(II) ws prepre using BR uffer. For the omplextion stuy,.5, 1., 1.5 n 2. mm ytosine solutions were lso prepre using BR uffer solution. *Author for Corresponene. e-mil: ftshikh@univhk.eu

2 32 A. A. Shikh, Jnntul Firws, S. Islm n P. K. Bkshi Preprtion of working eletroe GCE ws polishe with fine lumin power of.3 miron on wet polishing loth. For oing so prt of the loth ws me wet with eionize wter, n lumin power ws sprinkle over it. The GCE ws then polishe on this surfe y pressing softly the eletroe ginst the polishing surfe for out 1 minutes. A shiny lk mirror like eletroe surfe ws then thoroughly wshe with eionize wter. First of ll, the ell ws fille with esire volume of the experimentl solution n the Teflon p ws ple on the ell. The purging glss tue together with referene eletroe ws inserte through the holes. Uner omputer ontrolle stirring, experimentl solution ws eerte y purging for t lest 1 minutes with % pure nitrogen gs. Thus tres of issolve oxygen were remove from the solution. III. Results n Disussion Cyli voltmmetri investigtion of the reox ehvior of Cu(II) in BR uffer solution, n its intertion with ytosine in n ientil voltmmetri onition hs een performe. The effet of ph for this stuy ws lso exmine. The results re presente elow: Voltmmetri response of Cu(II) in BR uffer solution Cyli voltmmetri stuy of.5 mm Cu(II) in BR uffer t ifferent ph vlues (.59 to 4.8) hs een investigte t GCE within the potentil winow of 5 to -5 mv. At more positive or negtive potentil vlues only non-fri urrent is oserve. Figure 1() shows yli voltmmogrm of.5 mm Cu(II) in BR uffer solution with sn rte of 1 mvs -1 t ph In the forwr sn two thoi peks i p1 ( hump like pek) n i p2 t out 9.84 mv n mv respetively, n in the reverse sn n intense noi pek i p2 t out 67.6 mv re oserve. The thoi peks re ue to the reution of Cu(II) to Cu(I) n Cu(I) to Cu(), while the intense noi pek is for the oxition of Cu() to Cu(II). However, yli voltmmogrm of ytosine in n ientil experimentl onition shows no pek (Figure 1()). Pek urrent, i p 9 i p i p2 i p Fig. 1. Cyli voltmmogrms of ().5 mm Cu(II) n ().5 mm ytosine in Britton-Roinson uffer t ph 1.59 with sn rte of 1 mvs -1 t GCE. Pek urrent, i p mv/s 1 mv/s 75 mv/s 5 mv/s 25 mv/s Fig. 2. Cyli voltmmogrms of.5 mm Cu(II) in Britton- Roinson uffer solution with sn rte of 25, 5, 75, 1 n 125 mvs -1 t ph The effet of the sn rte on the eletrohemil response of Cu(II) t ph 1.59 is lso exmine y gining the yli voltmmogrms of Cu(II) with sn rte of 25, 5, 75, 1 n 125 mvs -1 uner ientil onition. The voltmmogrms re shown in Figure 2. Tle 1. Dt otine from the yli voltmmogrms of.5 mm Cu(II) in Britton-Roinson uffer with ifferent sn rte t ph Sn rte, v (mvs -1 ) Cthoi pek urrent, i p i p1 (-) i p2 (-) APC, i p Cthoi pek potentil, E p (mv) i p2 E p1 E p2 (-) APP, E p (mv) E p2 PCR i p2 /i p2 E p =E p2 E p2 (mv) APC= Anoi pek urrent, APP= Anoi pek potentil, PCR= Pek urrent rtio The reore voltmmogrms re nlyze n vrious prmeters suh s noi n thoi pek urrent, pek potentil seprtion n pek urrent rtio re gthere s shown in Tle 1. It is foun tht with the inrese of sn rte, oth the thoi n noi pek urrents re inrese (Figure 2). This oservtion suggests tht the eletroe proess is uner iffusion ontrolle in BR uffer meium. The noi (E p2 ) n thoi (E p2 ) pek potentil seprtion ( mv) n noi (i p2 ) n thoi (i p2 ) pek urrent rtio ( ) revel tht the reox proess of opper system is qusi-reversile, in greement with the oservtions on the shpe of the thoi n noi peks 9.

3 Intertion of Cu(Ii) with Cytosine in Britton-Roinson Buffer Solution - A Cyli Voltmmetri Stuy 33 The thoi pek is slightly shifte towrs negtive potentil while the noi pek is move little towrs positive potentil with the inese of sn rte. The shifting of the pek potentil t vrious sn rtes lso inites tht the reox proess is shifte from qusi-reversile to irreversile iretion. Figure 3 pprently shows tht the pek urrent for the reox ehvior of opper system in BR uffer ers liner reltionship with squre root of sn rte n it psses through the origin. The rtio of the oxition pek urrent to its orresponing reution ounterprt, i p2 /i p2 is out It is foun (Figure 4) tht the pek urrent rtio is erese with the inrese of sn rte. It is gin in fvor of the ft tht the eletroe proess is iffusion-ontrolle. It is lso in goo greement with the previous stuy 1. 1 Effet of ph on the reox ehvior of Cu(II) The effet of ph on reox ehvior of Cu(II) in BR uffer hs lso een investigte t GCE. Voltmmogrms for Cu(II) in BR uffer t ph.59, 1.59, 3.1 n 4.8 re reore. A series of voltmmogrms t ifferent ph of the solution re shown in Figure 6. Pek urrent, i p Pek urrent, i p Squre root of sn rtes 1/2 (mvs -1 ) 1/2 Fig. 3. Vrition of pek urrent with squre root of sn rte for Cu(II) in Britton-Roinson uffer t ph Pek urrent, i p i p2 /i p Sn rte, v (mvs -1 ) Fig. 4. Pek urrent rtio (i p2 /i p2 ) epenene on sn rte of.5 mm Cu(II) in Britton-Roinson uffer meium t ph The pek potentil seprtion, E p is in etween mv n it is inrese with the inrese of sn rte (Figure 5). It is evient tht the reox proess is qusi-reversile rther thn reversile. 15 Pek urrent, i p Pek potentil seprtion, E p (mv) Pek urrent, ip Sn rte, v (mvs -1 ) Fig. 5. Vrition of pek potentil seprtion with sn rte of.5 mm Cu(II) in Britton- Roinson uffer t ph E (mv) Vs. Ag/AgCl (st. KCl) Fig. 6. Cyli voltmmogrms of.5 mm Cu(II) in Britton- Roinson uffer t ifferent ph: ().59, () 1.59, () 3.1 n () 4.8 t GCE.

4 34 A. A. Shikh, Jnntul Firws, S. Islm n P. K. Bkshi At low ph rnging from.59 to 3.8, thoi pek n hump-like pek, n n intense noi pek re ppere. With the inrese of ph, the first thoi pek urrent grully ereses n finlly isppers t ph 4.8. In generl, oth thoi n noi pek urrents re erese with the inrese of ph, s given in Tle 2. However, oth the noi n thoi peks re ientil in shpe n the pek potentil seprtion is omprle. At low ph limit [Cu(H 2 O) 6 ] 2+ n [Cu(H 2 O) 6-x ] + ions n e Tle 2. Dt otine from the voltmmogrm of Cu(II) t ifferent ph. Solution ph ssume to e present in signifint mount while t high ph (~ 4.8), [Cu(OH)(H 2 O) 5 ] + ion is unerstoo to e the only eletrotive speies 11,12. It hs een mentione efore tht Cu(I) s the solvte ion is stle in numer of nonqueous solvents suh s etonitrile 13, nitromethne 12. In suh solvents, the stility of Cu(I) is ue to the ft tht these solvents solvte Cu(II) less strongly thn oes wter n they solvte Cu(I) more strongly thn oes wter. Pek urrent, i p Pek potentil, E p (mv) Pek potentil seprtion, E p i p2 (-) i p2 (+) E p2 (-) E p2 (+) D Grph 1 Voltmmetri response of Cu(II) in presene of ytosine in BR uffer solution The voltmmogrms of Cu(II) in presene of ytosine in BR uffer t vrious Cu(II)/ytosine molr rtio, 1:1, 1:2, 1:3 n 1:4 hve een reore t ph.59, 1.59, 3.1 n 4.8 t GCE within the sme potentil winow. The reore voltmmogrms of Cu(II), n t vrious Cu(II)/ytosine molr rtio, 1:1, 1:2, 1:3 n 1:4 t ph.59 is shown in Figure 7. At this ph the thoi pek is signifintly reue n lrge reution of the noi pek height is oserve in the voltmmogrms n the pek urrents re reltively lower thn tht of Cu(II) lone. Moreover, the heights of the peks re pprently errti with respet to ytosine onentrtion. The lowest pek urrent is foun t 1:4 molr rtio of Cu(II) to ytosine onentrtion suggesting the mximum intertion ours t this molr rtio. It is note tht the voltmmogrm of ytosine in ientil onition exhiits no noi or thoi pek (Figure 1()) within the stuie potentil winow. Pek urrent, i p ( ) Fig. 7. Cyli voltmmogrms of () Cu(II) (soli), n Cu(II) n ytosine with ifferent molr rtio () 1:1 (otte), () 1:2 (short sh), () 1:3 (sh-ot-ot) n (e) 1:4 (long sh) in Britton-Roinson uffer t ph.59. e Pek urrent, i p ( ) Fig. 8. Cyli voltmmogrms of () Cu(II) (soli), n Cu(II) n ytosine with ifferent molr rtio () 1:1 (otte), () 1:2 (short sh), () 1:3 (sh-ot-ot) n (e) 1:4 (long sh) in Britton-Roinson uffer t ph Figure 8 shows the voltmmogrms of Cu(II), n Cu(II) in presene of ytosine with ifferent molr onentrtion t ph A signifint hnge of the shpe of voltmmogrms is oserve. The thoi pek ompletely isppere (t 1:3 n 1:4 molr rtio) while the noi pek urrent onsierly erese ompre to only Cu(II). The noi pek potentils lso shifte towrs negtive iretion. Furthermore, the heights of the peks re pprently inonsistent with respet to ytosine onentrtion. Sine the lowest pek urrent (Tle 3) is foun for 1:4 molr rtio of Cu(II) to ytosine, the mximum intertion, is inee, ourre t this molr rtio t ph In presene of ytosine, Cu(II) isplys lmost ientil eletrohemil ehvior t ph 3.1 n 4.8. In most of the ses the thoi pek isppers ompletely. The ehviors tht re ommon in oth ses, (i) signifint erese of the pek urrents of Cu(II), (ii) slight shifting of pek potentils, (iii) inonsistent respon of pek urrent with respet to Cu(II)/ytosine molr rtios, n (iii) mximum intertion of Cu(II) with ytosine t their 1:4 molr rtio. The voltmmogrms reore t ph 3.1 n t 4.8 re shown in Figures 9 n 1 respetively. e

5 Intertion of Cu(Ii) with Cytosine in Britton-Roinson Buffer Solution - A Cyli Voltmmetri Stuy 35 9 Pek urrent, i p e Pek urrent, i p e Fig. 9. Cyli voltmmogrms of () Cu(II) (soli), n Cu(II) n ytosine with ifferent molr rtio () 1:1 (otte), () 1:2 (short sh), () 1:3 (sh-ot-ot) n (e) 1:4 (long sh) in Britton-Roinson uffer t ph 3.1. Fig. 1. Cyli voltmmogrms of () Cu(II) (soli), n Cu(II) n ytosine with ifferent molr rtio () 1:1 (otte), () 1:2 (short sh), () 1:3 (sh-ot-ot) n (e) 1:4 (long sh) in Britton-Roinson uffer t ph 4.8. From the ove oservtion it n e onlue tht Cu(II) interts strongly with ytosine t molr rtio of 1:4 t ll stuie ph in BR uffer meium. However, the mximum intertion ours t ph 4.8. The t for the ifferent voltmmogrms reore for Cu(II)/ytosine molr rtio of 1:4 t vrious ph is gthere in Tle 3. Tle 3. The t for the voltmmogrms reore for 1:4 molr rtio of Cu(II)/ytosine t ifferent ph t GCE with sn rte of 1 mvs -1. Solution ph Pek urrent, A Pek potentil, mv Pek urrent Pek potentil rtio (i p /i p ) seprtion, E p i p (-) i p (+) E p (-) E p (+) inites no signifint vlue IV. Conlusion Cyli voltmmogrm of Cu(II) in BR uffer exhiits n intense thoi pek n hump-like pek, n strong noi pek t ll stuie ph. However, t high ph, only thoi n n noi pek re foun. In presene of ytosine the thoi pek urrent of Cu(II) isppere signifintly or ompletely while the noi pek height is reue ppreily with the negtive shifting of pek potentil. This oservtion inites tht the intertion etween Cu(II) n ytosine ours in BR uffer meium t ii ph. Among the stuie ph region mximum intertion is foun t ph 4.8 when the molr rtio of Cu(II)/ytosine is 1:4. Aknowlegement Authors re grteful to the Ministry of Siene n Tehnology, Bnglesh for finnil support. Referenes 1. Berg, J., J. Tymozko n L. Stryer, 27. Biohemistry, 6 th e. W.H. Freemn n Compny. 2. Kossel, A. n H. Steuel, 193. Weitere Untersuhungen üer s Cytosin, Z Physiol Chem., 38, Jenish, R. n A. Bir, 23. Epigeneti regultion of gene expression: how the genome integrtes intrinsi n environmentl signls, Nt.Genet., 33, Kwski, T., K. Suzuki, Y. Hko n K. Soi, 28. Ahirl Nuleose Cytosine Ats s n Origin of Homohirlity of Biomoleules in Conjuntion with Asymmetri Autotlysis, Angew. Chem. Int. E., 47, S. Jsimuin, 26. Synthesis, spetrl n eletrohemil ehviour of ytosinto rige omplexes of ruthenium(ii) n pltinum(ii) with 1-lkyl-2-(rylzo)imizoles, Trns. Met. Chem., 31, Roriguez, M. n A. J. Br, 199. Eletrohemil stuies of the intertion of metl heltes with DNA. 4. Voltmmetri n eletrogenerte hemiluminesent stuies of the intertion of tris(2,2'-ipyriine)osmium(ii) with DNA, Anl. Chem., 62, Hu, L. Z. Bin, H. Li, S. Hn, Y. Yun, L. Go n G. Xu, 29. Ru(py) 2 ppz] 2+ Eletrohemiluminesene Swith n Its Applitions for DNA Intertion Stuy n Lel-free ATP Aptsensor, Anl. Chem., 81, Kurit, R., K. Ari, K. Nkmoto, D. Kto, n O. Niw, 212. Determintion of DNA Methyltion Using

6 36 A. A. Shikh, Jnntul Firws, S. Islm n P. K. Bkshi Eletrohemiluminesene with Surfe Aumulle Coretnt, Anl. Chem., 84, Quentel F. n C. Me, 199. Voltmmetri stuy of the opper-1, 1-phennthroline omplex, Anlyt. Chimi At. 83, Akhtr, H.M.N., M. M. Jml, A. A. Shikh n M. Q. Ehsn, 28. Cyli Voltmmetri Stuy of The Intertion of Copper with Glutmi Ai in Solution, J. Sui Chem. So., 12, Polyn, D. S. n I. Shin, Multistep Chrge Trnsfers in Sttionry Eletroe Polrogrphy, Anl. Chem., 38, J. L. Anerson, J. L. n I. Shin, Cyli voltmmetri stuies of the ph epenene of opper(ii) reution in ii queous nitrte n perhlorte solutions, Anl. Chem., 48, Miller, R. W. Ph. D. Thesis, The University of Illinois, Urn III, 1961.

7 Intertion of Cu(Ii) with Cytosine in Britton-Roinson Buffer Solution - A Cyli Voltmmetri Stuy 37

8 38 A. A. Shikh, Jnntul Firws, S. Islm n P. K. Bkshi

9 Intertion of Cu(Ii) with Cytosine in Britton-Roinson Buffer Solution - A Cyli Voltmmetri Stuy 39