Date of Award

1-1-1986

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Abstract

Part I. The bioavailability of calcium, magnesium, and zinc is greater from human milk than bovine milk, even though individual concentration magnitudes are reversed. Reasons for this are investigated by studying the complexation and precipitation reactions of these minerals and the low molecular weight ligands present in both milks at pHs ranging from two to eight. These reactions control the solubility of these minerals and we assume that for a mineral to be bioavailable it must be in solution and arrive at the appropriate intestinal segment for absorption. Techniques used to study mineral solubilities are: computer modelling, synthetic models, and an ultrafiltration technique.In these studies, it was found that zinc precipitated in both milks and magnesium precipitated in the bovine milk. The precipitation of zinc occurred at about pH 4.5 in the bovine milk but not until pH 6 in the human milk. This precipitation of zinc from both milks is due to a coprecipitation reaction of zinc with calcium phosphate, and it occurs at more acidic pHs in bovine milk. Therefore, this coprecipitation reaction reduces the solubility and the bioavailability of zinc from bovine milk.Part II. There is little known about the interactions of low molecular weight ligand complexed (LMWLC) metal ions binding to biopolymers. In this research the interactions of a model biopolymer--poly(acrylic acid) (PAA)--with hydrated zinc ion and zinc-ammine complexes are studied. The technique used to measure the amount of zinc bound to the PAA was modified gel chromatography (MGC) where the zinc ion and, LMWLC forms of zinc are contained in the column eluant.The binding constant for free zinc was determined to be 3300 mole-1 by a direct Scatchard interpretation. A computer model was used to define the K(,o)'s for the zinc-ammonia PAA system using a multiple Scatchard's equation. The binding constants for the mono-, di-, and triamminezinc(2+) were determined to be 4000, 290,000 and 1700 mole-1 respectively. The large increase for the diamminezinc(II) K(,o) was attributed to some kind of steric or electronic cooperative effect.

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