Date of Award

Winter 1-19-2016

Document Type

Thesis

Degree Name

B.S. with honors

Honors Designation

yes

Program of Study

Chemistry

Language

English

First Advisor

Chandrika Kulatilleke

Second Advisor

Pablo Peixoto

Third Advisor

Joel Brind

Abstract

Toxic heavy metal poisoning with metals including lead, mercury, and cadmium, whether in the environment or through ingestion, remains a persistent problem. Remediation of metal contamination and poisoning has generally been treated with chelating agents that bind metals, rendering them inert, and allow for easier removal. Chelation involves the formation of two or more separate coordinate covalent bonds between a polydentate ligand and a single central atom. However, chelators are not without side effects. Due to the similar size of metal ions and lack of specificity of ligands, chelators can also remove beneficial metals like iron and zinc from the body. This thesis focuses on identifying macrocyclic chelators that will bind specifically to toxic heavy metals and not physiologically important transition metals such as iron and zinc. It is well known that toxic metals have an affinity for sulfurs and therefore macrocyclic thiaethers are potential chelating agents for these toxic metals. The macrocycle 1,4,7-Trithiacyclononane ([9]aneS3) is the ligand of interest for this study due to its small cavity size. Previous studies (unpublished) indicated that [9]aneS3 binds mercury very strongly. This study probes further into the strength of metal-ligand complexes of 1,4,7-Trithiacyclononane with first row transition metals by using absorbance values measured with UV-Visible spectroscopy. Stability constant calculations were performed based on the McConnell-Davidson equation. Molar extinction coefficients (€) of M([9]aneS3)2 2+ complexes were determined to be in the range of 10000 – 34000 M-1 cm-1 . The stability constants (log β) of M([9]aneS3)2 2+ were found to be in the range of 1.4– 4.9 (Table 7). These results show that the chelator, 1,4,7-Trithiacyclononane binds several first row transition metal ions weakly. This weak binding with transition metals yet strong binding with mercury suggests that 1,4,7-Trithiacyclononane may function as a potential selective chelator for mercury. The ratio of metal to ligand complexes was also determined using Job’s plot analysis. Results show that first row transition metals bind to the ligand in a ratio of 1:2. This suggests that the ligand 1,4,7-Trithiacyclononane, presumably binds metal ions in an octahedral geometry, where the metal ion is sandwiched between two molecules of ligands. In this preferential geometry the metal ion is bound to six sulfur atoms from two ligand molecules. Taken together, these results help us understand binding preferences and mechanisms of transition metals and toxic heavy metals towards macrocyclic thiaethers.

Included in

Chemistry Commons

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