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UNIT IV COMPLEXATION & PROTEIN BINDING

UNIT IV COMPLEXATION & PROTEIN BINDING. By: Ms. Santoshi Naik Assistant Professor Yenepoya Pharmacy College and Research Centre. Introduction. Complexation is a process where complexes or coordination compounds are formed which involves association or interaction of 2 chemical species.

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UNIT IV COMPLEXATION & PROTEIN BINDING

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  1. UNIT IVCOMPLEXATION & PROTEIN BINDING By: Ms. Santoshi Naik Assistant Professor Yenepoya Pharmacy College and Research Centre

  2. Introduction • Complexation is a process where complexes or coordination compounds are formed which involves association or interaction of 2 chemical species. • Substrate – Central atom • Ligands – molecules or ions attached to central atom.

  3. Types of ligands 1. Monodentate/ Unidentate ligand Eg: Water, ammonia 2. Bidentate ligand Eg: Ethylenediamine 3. Tridentate ligand Eg: N’-(2-aminoethyl)ethane-1,2-diamine 4. Polydentate ligand Eg: EDTA

  4. Applications of Complexation • Physical state • Volatility • Stability of drugs • Solubility • Dissolution • Absorption and Bioavailability • Antidote for metal poisoning • Antibacterial activity

  5. CLASSIFICATION OF COMPLEXES

  6. METAL COMPLEXES • In this type metal ion constitutes central atom and interacts with ligands.

  7. a) Inorganic Complexes According to Werner’s Postulates: • There are 2 types of valencies Primary valency – ionic bond Secondary valency – coordinate bond 2. Same type of anions, radicals or molecules held by primary or secondary bonds 3. For each central atom there is fix number of non- ionic valencies referred as coordination number which is the maximum number of atoms binding to the central atom. 4. The non-ionic valencies are directed towards definite position by process of stereoisomerisation

  8. EXAMPLE: chloropentamminecobalt chloride complex CENTRAL ATOM LIGANDS [CoCl(NH3)5] Cl2 COORDINATION SPHERE IONISATION SPHERE CENTRAL ION- Incomplete electron shell LIGAND – donates electron pairs

  9. b) Chelates • Chelates are group of metal ion complexes in which a substance (ligand) provides 2 or more donor groups to combine with metal ion or central atom. • Example is EDTA –hexadentate ligand

  10. Applications of Chelates in Pharmacy 1. Purification of water EDTA combines with Calcium and Magnesium ions present in hard water and settles as precipitate. 2. Improves stability of drug 3. Analysis for drug molecule 4. Anticoagulants for blood.

  11. c) Olefin and Aromatic type • These types of Complexes are used as catalyst in the manufacturing of bulk drugs, intermediates and in the analysis of drugs. i) Olefin complex They are formed by interaction of aqueous solutions of metal ions (platinum, mercury, silver) with olefin such as ethylene. Eg: Ag-olefin complex.

  12. ii) Aromatic complex They are formed by interaction of metal ions as acceptors with aromatic molecules such as benzene, toluene and xylene. Eg: Complex of toluene with HCl.

  13. ORGANIC MOLECULAR COMPLEXES • Organic molecules are involved in complexation • Weak forces - dipole-dipole forces and hydrogen bonding involved. • Experimental conditions should be constant as any alteration in it molecular compounds are formed instead of molecular complexes. • Eg: Iodine with Tolnaftate enhances antifungal activity

  14. Difference between Molecular complex and Molecular compound

  15. a) Quinhydrone complex • The molecular complex formed by mixing alcoholic solutions of Benzoquinone and Hydroquinone in the ratio 1:1. • Green crystals of Hydroquinone are obtained. • Applications: used in manufacturing Quinhydrone electrode for pH determination.

  16. b) Picric acid Complex • Picric acid is strong acid. • If reacted with strong base molecular compounds are formed • If reacted with weak base, molecular complex is formed. • Eg: Butesin picrate as 1 % ointment for burns and paingul skin abrasions.

  17. c) Drug Caffeine complex • Many acidic drugs forms complexes with Caffeine by dipole dipole interactions. • Eg: Caffeine and Benzocaine • Eg 2: Caffeine and Gentisic acid complex in chewable tablets.

  18. d) Polymer Complex • Polymers are pharmaceutical additives which have nucleophilic oxygen. Eg: PEG, CMC. • This polymers form complexes with drug molecules like phenol, tannic acid and salicylic acid. • Disadvantages: Loss of preservative action, delay in absorption and undesirable physical, chemical and pharmacological effects. • Loss of therapeutic activity of the drug when stored in polymer containers.

  19. INCLUSION COMPLEXES • Also known as Occlusion compounds. • Inclusion complexes do not have specific chemical reactivity but are based on the architecture of the molecule, that means one molecule gets entraped within the second molecule.

  20. a) Channel lattice type • Molecule crystallises in the form of long chains forming hollow chain like structure and other molecules get entraped into the channel like structure. • Eg: Urea crystallises to hollow structure and methyl-α-lipoate fits in urea molecule. • Applications: separation of optical isomers and analysis of dermatological creams. A HOST GUEST

  21. b) Layer type complexes • In layer type of complexes one layer gets sandwiched between 2 parallel layers of host molecule. • Eg: Clays, montomorillorite entraps hydrocarbons, alcohols and glycols. • Applications: used in the process of catalysis. GUEST HOST

  22. c) Clathrates • Complexes formed are cage like structure wherein one molecule undergoes crystallisation and other molecule is involved in entrapment. • Eg: Hydroquinone molecule forms a small hole within it and the guest molecule undergoes rearrangement and entraps within it. • Applications: Storage of gases, toxic compounds or volatile substances. GUEST HOST

  23. d) Monomolecular Complexes • Also known as Monomolecular Inclusion compounds. • It involves entrapment of single guest molecule in the cavity of host molecule. • Eg:Cyclodextrinsα, βand 𝛾. • Applications: Enhancing solubility, dissolution rate and stability of drugs.

  24. ANALYSIS OF COMPLEXES

  25. PROTEIN BINDING • Protein binding is a type of complexation which occurs in the body. • Main proteins involved are Albumin and Globulin. • Albumin binds to acidic & basic drugs. • Globulin binds to basic drugs.

  26. Kinetics of Protein binding • Derivation of Klotz Reciprocal plot and Scatchard plot.

  27. Methods to determine Drug Protein binding

  28. Applications of Protein binding • Drug distribution • Metabolism • Excretion • Drug action • Sustained release • Carrier systems

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