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الكلية كلية الصيدلة
القسم فرع الصيدلانيات
المرحلة 2
أستاذ المادة ظافر قحطان سعيد الامين الماشطة
5/28/2011 1:12:18 PM
Chelates
Ions such as Cu and Ni, which form square planar complexes, and Fe and Co, which form octa¬hedral complexes, can exist in either of two geometric forms. As a consequence of this isomerism only cis-coordinated ligands-ligands adjacent on a molecule will be readily replaced by reaction with a chelating agent. Vitamin B12 and the hemoproteins are incapable of reacting with chelating agents because their metal is already coordinated in such a way that only the trans-coordination positions of the metal are available for complexation. In contrast, the metal ion in certain enzymes, such as alcohol dehydrogenase, which con¬tains zinc, can undergo chelation, suggesting that the metal is bound in such a way as to leave two cis positions available for chelation.
Chlorophyll and hemoglobin, two extremely important compounds, are naturally occurring chelates involved in the life processes of plants and animals. Albumin is the main car¬rier of various metal ions and small molecules in the blood serum. The amino-terminal portion of human serum albumin binds Cu and Ni with higher affinity than that of dog serum albumin. This fact partly explains why humans are less susceptible to copper poisoning than are dogs. Chelation can be applied to the assay of drugs.
Organic molecular complexes
An organic coordination compound or molecular complex consists of constituents held together by weak forces of the donor-acceptor type or by hydrogen bonds. The difference between complexation and the formation of organic compounds has been shown by the two com¬pounds: dimethylaniline and 2,4,6-trinitroanisole, which react in the cold to give a molecular complex. On the other hand, these two compounds react at an elevated temperature to yield a salt, the constituent molecules of which are held together by primary valence bonds. It is not to be considered as a clearly defined bond, but rather as an overall attraction between the two aro¬matic molecules.
Quinhydrone complexes
The quinhydrone molecular complex is formed by mixing alcoholic solutions of equimolar quantities of benzoquinone and hydroquinone. The complex settles as green crystals. When an aqueous so¬lution is saturated with quinhydrone, the complex dissociates into equivalent amounts of quinone and hydroquinone and is used as an electrode in pH determinations.
The 1:1 complex formed between benzoquinone and hy¬droquinone may be said to result from the overlap of the pi framework of the electron-deficient quinone molecule with the pi framework of the electron-rich hydroquinone molecule.
Drug complexes
The complexing of caffeine with a number of acidic drugs was investigated where the interaction between caffeine and a drug such as a sulfonamide or a barbiturate is attributed to a dipole-dipole force or hydrogen bonding between the polarized carbonyl groups of caffeine and the hydrogen atom of the acid. A secondary interaction probably occurs between the nonpolar parts of the molecules, and the resultant complex is "squeezed out" of the aqueous phase owing to the great internal pressure of water. These two effects lead to a high degree of interaction.
The complexation of esters is of particular concern to the pharmacist because many important drugs belong to this class. The complexes formed between esters and amines, phe¬nols, ethers, and ketones have been attributed to the hydrogen bonding between a nucleophilic carbonyl oxygen and an ac¬tive hydrogen. This, however, does not explain the complex¬ation of esters such as benzocaine, procaine, and tetracaine with caffeine. It might be suggested that, in the caffeine molecule, a relatively positive center exists that serves as a likely site of complexation.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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