complexation

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A) Classification Metal complexes Organic molecular complexes Inclusion compounds (B) Methods of analysis‑ solubility method Distribution method method of continuous variations. (C) Application of complexes

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Application of complexation Physical state : liquid to solid-nitroglycerine inclusion complex with beta Cyclodextrin----15% nitroglycerine containing complex- Explosion proof Volatility : Reduce volatility and odor . Ex.PVP iodine complex. Solid stability : stability of drug enhanced . Ex. β cyclodextrin with vit . A and D Chemical stability : Alter the chemical reaction by (inhibitory or catalytic) Benzocaine- caffine complex Solubility : solubility enhanced . Ex.low conc of Caffine enhance the solubility of PABA

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Dissolution : Increase solubility….dissolution also increased. Ex. phenobarbital inclusion complex with β cyclodextrin Absorption and bioavailability : Tetracycline complex with cal.,mag., Alu .----- in soluble complex β cyclodextrin complex with indomethacin ,barbiturates---- more soluble complex. Reduced toxicity : cyclodextrin reduce ulcerogenic effect of indomethacin and local tissue toxicity of chlorpromazine.

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Antidote for metal poisoning: toxic metal ions- arsenic,mercury,antioney …etc Compound dimercaprol ---form a water soluble complex-eliminate rabidly from body Beryllium poisoning-salicylic acid Lead poisoning-EDTA Drug action through metal poisoning:8-hydroxyquinoline complex with iron-penetrate through the malarial parasite membrane(excess acco.iron ) … better antimalarial action PVP iodine complex : water soluble , low toxicity and prolong action

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Metal complexes Inorganic complexes

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chelates The term chelation (derived from the Greek chele meaning lobster’s claw) relates to the interaction between a metal atom or ion and another species, known as the ligand , by which a hetero atomic ring is formed. Chelation changes the physical and chemical characteristics of the metal ion and of the ligand . For example Ethylenediamine tetraacetic acid (EDTA) has two donor nitrogens and acts as a bidentate (two-toothed) Ligand . When a drug forms a metal chelate , the solubility and absorption of both drug and metal ion may be affected, and drug chelation can lead to either increased or decreased absorption. Ex.citric acid,tartrates and EDTA metal ion coordinate group of ligand ( hexadentate ) EDTA

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Application of chelating agents Increase in stability-oxidative degradation of ascorbic acid fruit juices and in drug preparation is prevented by ? Purification of hard water ( complexing calcium ions) Citrate,oxalates,EDTA -anticoagulant There is evidence for complex formation of a coumarin derivative with magnesium ions present in antacid formulations. In this case the formation of a more absorbable species is indicated since plasma levels of bishydroxy coumarin are elevated in the presence of magnesium hydroxide but are unaffected by aluminium hydroxide. Bishydroxy coumarin –Mg chelate It is simplest to consider the ligand as the electron pair donor and the metal as the electron pair acceptor, with the donation establishing a coordinate bond (see, for example, the copper– glycine chelate ). 1:1 copper– glycine chelate

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Therapeutic chelators are used in syndromes where there is metal ion overload. For example, ethylenediaminetetraacetic acid (EDTA) as the monocalcium disodium salt is used in the treatment of lead poisoning. The antibacterial action of the tetracyclines depends on their metal-binding activity, as their main site of action is on the ribosomes , which are rich in magnesium. Therapeutically active tetracyclines form 2:1 complexes with cupric, nickel and zinc ions while inactive analogues form only 1:1 complexes.

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binding of tetracycline to teeth. (calcium) Ferrous sulfate has the greatest inhibitory effect on tetracycline absorption Tetracyclines with calcium poses a problem in paediatric medicine. Chelation of ciprofloxacin by aluminium hydroxide and calcium carbonate reduces bioavailability. Tetracycline ciprofloxacin

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Chelation of Nalidixic acid and Norfloxacin by aluminium hydroxide and calcium carbonate reduces bioavailability. Norfloxacin Nalidixic acid

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Desferrioxamine (as the mesylate ) is used as a drug to sequester iron in iron poisoning or chronic iron overload penicillamine is similarly used to aid the elimination of copper in Wilson disease. Chelation is also used for the safe delivery of toxic ions such as gadolinium (Gd 3++) , which is used as a magnetic resonance imaging enhancing agent. gadolinium-BOPTA octodentate chelate .

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Olefin types These type of complexes are used as catalysts in the manufacture of bulk drugs, intermediates and in the analysis of drug. Organic molecular complexes Molecular complexes of many types may be observed in systems containing two or more drug molecules. In this type of coordination complexes, components are organic molecule and these are held together by weaker forces or hydrogen bonding. molecular complexes identification Form at elevated temperature Strong electrostatic interaction is involved They can be separated from soln .

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The interaction therefore takes place between electron-rich donors and electron poor acceptors. Interactions between aromatic rings in which there is a parallel overlap of π-systems fall into this category, as in the following example involving nicotinamide (acceptor) and the indole moiety of tryptophan (donor) Donor-acceptor type

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benzocaine caffeine Imidazole Caffeine not only increases the solubility of ergotamine but also that of benzoic acid. The marked difference in the solubilizing properties of caffeine and dimethyl uracil Theophylline Dimethyl uracil

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Methods of analysis Continuous variation method

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Solubility method

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