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POTENTIOMETRIC STUDY ON STABILITY OF BINARY AND TERNARYCOMPLEXES OF NICOTINAMIDE IN AQUEOUS SOLUTION WITH

COPPER (II) METAL ION1Kayande, D. D. Abdulbaset, 2Zaid, A., 2Vidya Pradhan, 2,3Mazahar Farooqui

1S BES Science College, Aurangabad.bPost Graduate and Research Center, Maulana Azad College, Aurangabad (MS).

3 Dr. Rafiq Zakaria college for women, Aurangabad (MS).

ABSTRACTFormation of binary and ternary complexes of Cu (II) metal ion with nicotinamide (NA) as a secondary ligand and somebiologically important aliphatic carboxylic acids (glycine, alanine, valine, cysteine and penicillamine) as primary ligands wasstudied by the potentiometric technique at 25±0.1°C and 0.1M (NaClO4) ionic strength. The ternary complex formation wasfound to take place in a stepwise manner. The stability constants of these binary and ternary systems were calculated. .

KEYWORDS: Nicotinamide (NA), glycine, alanine, valine, cysteine and penicillamine, Copper (II), stability constant, potentiometrictitration.

INTRODUCTIONThe widespread occurrence and use of copper in biologicalsystems is a result of its ability to chemically interact withorganic and inorganic substances. This has sponsoredwidespread examination and discussion of copperchemistry in medicine and biology. Copper-containingsuperoxide dismutase is an important anti-inflammatoryagent. The ability of copper to combine with organics hasmade it widely used in chemistry, to examine some of thefundamental chemical concepts, to determine the nature oforganometallic compounds (and the organisms thatproduce them), to synthesize potentially useful agents andto assist in purification of noxious chemicals/fuels.Because of its reactive nature, copper is also used in awide range of chemical purifications and reactions.Nicotinamide (3-pyridine carboxamide) is a pyridinederivative which is important bioligand for human health.

Nicotinamide (NA) is very prevalent in plants and humantissues. The NA is not free in body. It may exist in at least twonucleotide structures such as nicotinamide adeninedinucleotide (NAD) and nicotinamide adenine dinucleotidephosphate (NADP). In the recent decade, the synthesis andstructure of new series of bimetallic complexes with NA hasbeen studied by various methods because of biologicalimportance of NA [1-2]. In the present investigation theformation and stability of binary and ternary Cu(II)complexes[3] containing nicotinamide (N.O) donor ligands[4]and with glycine, alanine, valine, cysteine and penicillamine(N,O-) donor ligands (fig.1) are reported at 25±0.10C in 0.1M (NaClO4). The effect of the substituent[5], on thedissociation constants, and on the stability & formation of thebinary and ternary complexes have been evaluated bycomparing the relevant data for systems containingdetermined under identical experimental conditions.

Nicotinamide

NO

H2N

glycine

H2N

O

OH

alanineNH2

O

OH

Binary and ternary complexes of Nicotinamide in aqueous solution with copper (II) metal ion

417

v a l i n e

N H 2

O

H O

cystine

NH2

SS

NH2

O

HO

O OH

p e n ic il la m in e

H 2N

SH

O

O H

FIGURE 1. Structure of the compounds

EXPERIMENTALMaterials and solutionNicotinamide is 3-pyridine carboxamide was of analyticalgrade and NaOH, NaClO4, HClO4 and copper salt were ofAnalar grade. The solutions used in the potentiometrictitrations were prepared in double distilled water. The NaOH(0.041M) solution was standardized against oxalic acidsolution (0.1M) and the standard alkali solution was againused for standardization of HClO4. The copper salt solutionwas standardized using EDTA titrations [6]. The ligand(NA) is soluble in double distilled water. The pH meter wascalibrated before each titration with standard buffer solutionsof 4.00, 7.00, and 9.2. The pH-meter (ELICO, L1-120) wasused with a combined glass electrode assembly.Potentiometric Procedure:In the study of binary and ternary chelates by thepotentiometric titration technique. The following sets wereprepared in the standard:(1)Free HClO4(2)Free HClO4 +Ligand (LP)(3) Free HClO4 +Ligand (LP) +Metal ion(4)Free HClO4 +Ligand (LS)(5) Free HClO4 +Ligand (LS) +Metal ion (M)(6) Free HClO4 +Ligand (LP) +Ligand (LS) +Metal ion (M)Against standard sodium hydroxide, the ionic strength ofsolutions was maintained constant by adding appropriateamount of (0.1M) Sodium perchlorate solution. Thetitrations were carried out at room temperature in inertatmosphere by bubbling oxygen free nitrogen gas through anassembly containing the electrode to keep out CO2 .bynoting the pH of precipitation for MLP, MLS and MLPLStitration, the formation of mixed ligand complexes can beconcluded.CalculationsThe protonation constants of the ligand were calculated fromthe potentiometric pH titrations data of solutions accordingto Irving and Rossetti’s method [7]. For this purpose, theaverage proton-ligand formation number (n-

a) at various pHfor the ligand was determined according to the literature [8].The value of pKa was read directly from n-

a = f (pH) graph atn-

a =0.5. For the calculation of stability constants of binarycomplexes (using the

potentiometric titration data of the solutions and accordingto Irving and Rossotti’s method [7], the metal-ligand (M-NAand M-2NA) formation number(n-) at various pH for theligand was determined according to the literature [8]. ThenpL values were calculated with using the equation from theliterature [8].Having thus obtained corresponding values ofn- and pL, the formation curve of the metal-ligand system isdrawn and the stability constant is read directly at n-= 0.5 ,1.5. The calculation of the stability constant of ternarycomplex by the stepwise equilibria in solution would beconfirmed when the mixed ligand curve could besuperimposed over the binary or titration curve.The method of Thomson and Loraas [9] for calculation ofstepwise stability constants is widely used. The stabilities ofthe mixed –ligand complexes can be calculated by thereplacement of M= = by or in thefollowing expression.i) For monobasic acid as secondary ligand

(1)

Where

And + 1

ii) For dibasic acids as secondary ligand

(2)

Where

And

RESULTS AND DISCUSSIONThe dissociation constant of NA, glycine, alanine, valine,cysteine and penicillamine of the associated proton pKa[10]. The first proton association constant of neutral, HL,was determined potentiomtrically in aqueous solutions,under the experimental conditions (t=25±0.1°C, µ=0.1 MNaClO4). Proton ionization was assigned to the O at theposition assuming the negative charge. The protonationconstant of NA agree well with that given previously by

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Tuba Sismanoglu [11]. The second dissociation of the protonfrom the N group of glycine, alanine, valine, cysteine andpenicillamine takes place at higher buffer region (pH) andhence the corresponding dissociation constant could not becalculated by this method. The equilibria involved in theformation of 1:3 metal – ligand binary complexesmay be represented as follows:M + L ML ,

ML + L ML2 ,The stability constants of 1:3 binary complexes of inosinewith Cu (II) metal ion have been determined. The constantdetermined by us for Cu (NA) in 1:3 complexes agrees wellwith that given previously by Valentin A. Sharnin et al [12].The formation of a ternary complex is ascertained bycomparison of the mixed-ligand titration curve with thecomposite curve obtained by graphical addition of the NAtitration data to that of the (1:3) MII -carboxylic acidtitration curve. The Cu (II) – carboxylic and amino group–NA system is taken as representative. The mixed-ligandsystem was found to deviate considerably from the resultantcomposite curve indicating the formation of a ternarycomplex. Therefore, it is assumed that in the presence ofboth ligands, the carboxylic and amino groups are ligated tothe metal ion, and then followed by ligation of NA, i.e. theternary complex formation could be considered in stepwiseequilibria (Eqs. (3) and (4)):

M + Lp MLp (3)MLp + Ls MLpLs (4)

= (5)

Where Lp= carboxylic and amino groups and Ls= neutralligand nicotinamide.In the ternary systems studied in table2, the values of

were found to lie in the sequence: glycine \

penicillamine \alanine \ valine \ cysteine. The higher stabilityof glycine complex than another one may be due to theformation of neutral complexes (MLpLs). In which theelectrostatic repulsions are very minimal. The behavior ofmetals towards N, O donor ligands reflected in the stabilityconstant values of ternary complexes. The stereochemistryof metal chelates ring differs from that of carbon ring systemin the sense that all the atoms in the chelates ring are not ofthe same size and some of the bond angles normally varyfrom 1090 or 1200 C as a result of the directed valencesof metal ion. Clashing groups of two coordinated ligandsresult in the distortion of bond angles and a decrease instability. A steric effect [13], affects the mode of packing ofligands round a central metal ion, and imposes a particulargeometric arrangement like planar, tetrahedral o

r octahedral to the complex.

TABLE1. Protonation constants of ligands

TABLE2. Parameter based on some relationship between formations of mixed ligand complexes of Cu (II) withnicotinamide (drugs) and some (N, O-) compounds

CONCLUSIONThe present work describes the complex formation equilibriawas investigated to ascertain the composition and stabilityconstants of the complexes. The effect of ligand propertieson the stability of the complexes was investigated. Theligand and complexes may have interesting biologicalactivity. This would require specially designed researchconducted by specialized biologists.

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Ligandsnicotinamide 3.48glycine 2.34 9.60alanine 2.34 9.69valine 2.32 9.62cysteine 1.96 8.18penicillamine 1.8 10.7

Ligand LogKMALNicotinamide- glycine 10.54Nicotinamide- alanine 10.45Nicotinamide- valine 10.34Nicotinamide- cysteine 10.05Nicotinamide- penicillamine 10.46

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