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Title: Electrochemical Study of Metal Complexes of Active Ingredient of Nigella sativa (Black seed)
Authors: Kishwar, Farah
Keywords: Natural Sciences
Chemistry & allied sciences
Physical chemistry
Techniques, equipment & materials
Analytical chemistry
Inorganic chemistry
Organic chemistry
Issue Date: 2013
Publisher: Federal Urdu University of Arts, Science and Technology Gulshan-e-Iqbal Campus University Road, Karachi
Abstract: Nigella sativa (Kalongi) seeds are well-known for the improvement of human health and used as folk medicine in treatment of various ailments. This is because of the fact that the seeds are a good source of several essential macro and micro nutrients as well as of many biologically active compounds. In present work electrochemical study of thymoquinone, which is the main active constituent of the N. sativa seed, was done using cyclic voltammetric technique at glassy carbon electrode versus saturated calomel electrode. Through cyclic voltammetry different quantitative and qualitative characteristics of Fe(III)-Thymoquinone complex, Cr(VI)-Thymoquinone complex, Cu(II)-Thymoquinone complex and Co(II)-Thymoquinone complex were determined. In all cases NaCl was used as supporting electrolyte except Cu(II)-Thymoquinone complex where LiCl was also used. The results showed quasi-reversible electron transfer reaction for all above mentioned complexes; however, in case of Cu(II)-Thymoquinone complex a shift from quasi-reversible to reversible behavior was observed. Effect of various parameters, such as scan rate, concentration and metal ligand ratio on complexes was noted by varying any one of them at one time while keeping others constant. Effect of repeated scanning was also examined. Results revealed presence of pre equilibrium charge transfer process in cases of Cr(VI)-Thymoquinone complex, Co(II)-Thymoquinone complex and Cu(II)-Thymoquinone complex, whereas post equilibrium charge transfer process in Fe(III)-Thymoquinone complex. The quantitative study with cyclic voltammetry showed that the use of a glassy carbon electrode could be helpful to quantify these complexes (Fe(III)-Thymoquinone complex and Co(II)- Thymoquinone complex 2 x 10 -5 to 1.2 x 10 -3 M, Cr(VI)-Thymoquinone complex 2 x 10 -4 to 1.2 x 10 -3 M and Cu(II)-Thymoquinone complex 2 x 10 -4 to 1.6 x 10 -3 M ). Hence this method can be used in the pharmaceutical quality control assay of these complexes. Values of transfer coefficient α and β, diffusion coefficient and E ̊ were also calculated for each complex. In addition, electrochemical study of V(IV)-Thymoquinone complex and Fe(III)-Thymol complex, Cr(VI)-Thymol complex, Cu(II)-Thymol complex, V(IV)-Thymol complex and Co(II)-Thymol complex was also performed which was not done in detail due to lack of time and facilities. Thymol is another active constituent of the black seed. Results indicated that cyclic voltammetry could also be helpful for determination of various quantitative and qualitative parameters of this constituent and its complexes. VIBefore performing electrochemical study some physical properties of the black seed were determined including moisture content and dissolved (DS) and undissolved solid (UDS) contents of the seed. Comparison of the results obtained for DS and UDS in aqueous and acidic medium showed that fast absorption of the seeds may take place in the acidic environment of stomach. The seed was also examined for its elemental composition using scanning electron microscopy which showed presence of several essential macro as well as micro elements in the seed. In order to find out suitable pH for complex formation, complexation of thymoquinone and thymol with Fe(III), Cr(VI), Cu(II), V(IV) and Co(II) was also investigated by pH-metry. Results revealed that out of above mentioned metals Fe(III) and V(IV) forms relatively stable complexes with both ligands. Moreover, they formed complexes at low pH while rest of the metals at high pH. Comparison of thymol and thymoquinone complexes indicates that thymoquinone forms more stable complexes with all mentioned metals as compared to thymol. pK a of both ligands was also determined. Present research also reveals that in case of heavy metal toxicity (specially by Fe(III), Cr(VI), Cu(II), V(IV) and Co(II)) thymoquinone and thymol could be helpful to remove them from the body. As both of the compounds form complexes with all above mentioned metals, they can be used in chelation therapy to remove toxic metals. It is also possible that both thymoquinone and thymol being antioxidants could reduce these metals, for example Fe (III) to Fe (II), Cr (VI) to Cr (III) etc. and hence converting these metals into their reduced form which is beneficial for the human body.
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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