Equilibrium studies on Imipramine Hydrochloride-metal ion in 20% ethanol-water mixture

 

Shailendrasingh V. Thakur¹, R.L. Ware¹, Mazahar Farooqui² and S.D. Naikwade³

¹Department of Chemistry, Milliya Art’s Science and  Management Science College, Beed (MS) India

²Post Graduate and  Research Center, Maulana Azad College, Aurangabad (MS) India

³Mrs. K.S.K College ,Beed (MS) India

 

ABSTRACT:

The interaction of transition metal Ions and  rare earth metal ions with Imipramine Hydrochloride drug has been investigated in 20% ethanol-water mixture at 0.1 M ionic strength at temperature 25⁰C by Potentiometric titration. It is observed that transition metal ions and rare earth metal ions forms 1:1 and 1:2 complexes. The values of stability constants were reported.

 

 

 

INTRODUCTION:

Most of the d-block and  f block elements form complexes. There are different kinds of ligand used for complexation. For the present investigation, the ligand selected was Impramine Hydrochloride (IPA. HCl). It is antidepressant, tricyclic antidepressive analgesics agents, adrenergic uptake inhibitors, norepirephrine reuptake inhibitors. IPA.HCl is mainly used in the treatment of major depression and  enuresis (inability to control urination).It has also evaluated for use in panic disorder. IPA.HCl is a tertiary amine affects numerous neurotransmitter systems known to be involved in the etiology of depression, anxiety ADHD, enuresis and  numerous other mental and physical conditions. IPA.HCl is similar in structure to some muscle relaxations, having molecular formula C₁₉H₂₅N₂Cl    and IUPAC name 3-(5,6-dihydrobenzo[b] [1] benzazepin-11-yl)-N,N-dimethylpropan-1-amine. The other physical properties are- Molecular weight=316.9g/mol; M.P. =174ºC; B.P. =161ºC; Refractivity= 90.61; Polarizability = 33.39 and Solubility = Soluble in water 18.2mg/ lit or 6.64e-02gm/lit                                                                                                                                                                                                                                                                              

 

Fig1: Imipramine Hydrochloride

 

 Literature survey reveals that a very few researchers  have done such type of work using medicinal drug as a     ligand.^[1-12] There for we decide to study stabilitry constant of binary complexes of IPA-HCl with transition metal ions Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) and rare earth metal ions La(III), Ce(III) Nd(III), Sm(III),  Gd(III), Tb(III) and  Dy(III) using pH metry.

 

MATERIAL AND METHODS:

The ligand IPA.HCl is soluble in double distilled water. NaOH,NaClO_{4 ,}HClO₄ and  metal salts were of AR grade. The solutions used in the potentiometric titration were prepared in double distilled water. The NaOH solution was standardized against oxalic acid solution (0.1M)and standard alkali  solution was further used for standardization of HClO₄. The metal salt solutions were also standardized using EDTA titration.  All the measurements were made at 25⁰C in 20% ethanol-water mixture at 0.1 M NaClO₄ strength The Thermostat model SL-131 (Adar Dutt and Co (India) Pvt. Ltd. Mumbai) was used to maintain the temperature constant. The pH measurement were made using a digital pH meter model Elico L1- 120 in Conjunction with a glass and reference Calomel electrode (reading accuracy ±0.01 pH units) the instrument was calibrated at pH 4.00, 7.00 and 9.18 using the standard buffer solutions. For evaluating the protonation constant of the ligand and the formation constant of the complexes in 20% ethanol-water mixture with different metal ions we prepare the following sets of solutions.

 

(A)          HClO₄ (A)

(B)          HClO₄+ IPA.HCl (A+ L)

(C)          HClO₄+ IPA.HCl + Metal (A+ L+ M)             

 

Each of the above solutions was thermostated at 25⁰C with an accuracy of ±0.1⁰C where the solution was left to stand for 15 minutes before titration. The concentration of perchloric acid and  sodium perchlorate (0.1M) were kept constant for all sets. The volume of every mixture was made upto 50ml with double distilled water and the reaction solution were potentiometerically titrated against the standard carbonate free standard NaOH solution. Multiple titrations have been performed for each system.

                                                             

Table-1: Metal-ligand stability constant of transition metal ions with IPA.HCl drug at 0.1M ionic strength in 20% ethanol-water mixture.

 

Table-2: Metal-ligand stability constant of rare earth metal ions with IPA.HCl drug at 0.1M ionic strength in 20% ethanol-water mixture.

                                                                                     

RESULT AND DISCUSSION:

Proton ligand stability constant (pK) of IPA.HCl  was determined   by point wise calculation method. The protonation constant for IPA.HCl obtained under the experimental condition is 9.062.This is due to two ternary amine nitrogen present in the  IPA.HCl. Out of these two, the terminal of 3⁰ amino group might have been involved in the complexation. The dimethyl ammonium group is considered to be the most basic functional group of any ligand.^[13]The result reveals that the complexation curve bifurcate at lower pH, which indicate the formation of complexes. Further since there was no precipitation of hydrides at higher pH indicating strong tendency of ligand towards metal ions for complexation.^[14]

 

The interaction of metal with ligand in presence of acid can be represented as

 

M + A  MA

K₁ = K^M   = [MA] / [M] [A]          

          ^MA

MA + L  MAL

K₂ =  K^MA   = [MAL] / [MA] [L]      

            ^MAL                                                                                                    

The overall stability constant can be given as       

M + A + L  MAL

β = K^M   = [MAL] / [M] [A] [L]        

         ^MAL                                                           

 

Metal ligand stability constant (logK) of transition metal ions and rare earth metal ions with IPA.HCl ligand were calculated by point wise and half integral method as suggested by Irving and Rossotti. For the present investigation we have studied the stability constants of divalent transition metal ions except Fe which is in trivalent state. The probable structure of metal complex with IPA.HCl   is difficult to predict only on the basis of solution study .But, Since we got`n_A between 0.2 to 0.8 and 1.2 to 1.8 indicating 1:1 and 1:2 Complex formation .It will be interesting to study the solid state formation of such complex and to study its biological activity, which is included in our future plan. Till now very less or almost no work is observed on the complexation behavior of lanthanide with medicinal drug such as IPA.HCl. As Lanthanides are having less capacity to form complexes still there stability constant values (logβ) are comparable with that of transition metal ions. This might be due to the pressure of diffused f-orbitals, the trivalent charge present and effective nuclear charge etc.   Observed trend in the order of stability constant of transition metal ions was

 

Fe³⁺>Cu²⁺>Zn²⁺>Ni²⁺>Cd²⁺>Co²⁺                                                                                                                                           which are accordance with the William-Irring series and the order of stability constant of rare earth metal ions was      

 

La³⁺< Ce³⁺< Nd³⁺< Sm³⁺ > Gd³⁺< Tb³⁺ < Dy                                                                                                               The ratio of  log k₁/ log k₂ is positive and greater than one in all cases .This implies that there is little or no steric hindrance to ligand molecule.                                                                                                                                                      

 

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Received on 04.12.2012        Modified on 15.12.2012

Accepted on 20.12.2012        © AJRC All right reserved