Structural Effects on Encapsulation as Probed in Solution - Based and Surface - Confined Redox - Active Core Dendrimers

Constitutional Isomer;Electrochemistry;Iron-Sulfur Cluster;Structure-Property Relationships;Encapsulation;Dendrimer

Chasse, Tyson Lee ; Dr. Christopher B. Gorman, Committee Chair,Dr. Edmond F. Bowden, Committee Member,Dr. David A. Shultz, Committee Member,Dr. Daniel L. Feldheim, Committee Member,Dr. Jack R. Edwards, Committee Member,Chasse, Tyson Lee ; Dr. Christopher B. Gorman ; Committee Chair ; Dr. Edmond F. Bowden ; Committee Member ; Dr. David A. Shultz ; Committee Member ; Dr. Daniel L. Feldheim ; Committee Member ; Dr. Jack R. Edwards ; Committee Member

University:North Carolina State University

关键词: Constitutional Isomer;    Electrochemistry;    Iron-Sulfur Cluster;    Structure-Property Relationships;    Encapsulation;    Dendrimer;   

Others  :  https://repository.lib.ncsu.edu/bitstream/handle/1840.16/4854/etd.pdf?sequence=1&isAllowed=y

美国|英语

来源: null

【 摘 要 】

The purpose of this research was to study structure — property relationships of iron sulfur core [Fe4S4(S-Dend)4]2- dendrimers.Previous studies have demonstrated that biasing dendrimer architecture increases the effective encapsulation of redox-active, paramagnetic, Fe4S4 clusters.To further examine structure-property relationships of iron-sulfur core dendrimers, studies were carried out to 1) probe the relationship between dendritic architecture and encapsulation via the study of solution-based and surface-confined constitutional isomers differing only in their benzyl substitution patterns, and 2) studying the effects of counterion concentration and permeability on the electronic properties of iron-sulfur core dendrimer thin films.Three pairs of isomeric, iron-sulfur core dendrimers were synthesized.Each isomer pair was distinguished by a 3,5-aromatic substitution pattern (extended) versus 2,6-aromatic substitution pattern (backfolded).Several observations were made supporting the hypothesis that the iron-sulfur cluster cores were encapsulated more effectively in the backfolded isomers as compared to their extended counterparts.The backfolded isomers were more difficult to reduce electrochemically, consistent with encapsulation in a less polar microenvironment.Furthermore, heterogeneous electron-transfer rates for the backfolded molecules were attenuated compared to the extended molecules.From diffusion measurements obtained by pulsed field gradient spin-echo NMR and chronoamperometry, the backfolded dendrimers were found to be smaller than the extended dendrimers.Comparison of longitudinal proton relaxation (T1) values also indicated a smaller, more compact dendrimer conformation for the backfolded architectures.These findings indicated that dendrimer size was not the major factor in determining electron-transfer rate.Instead, the effective electron-transfer distance, determined by the relative core position and mobility, is most relevant for encapsulation.In addition to solution studies, the electrochemical behavior of thin films composed of redox-active, iron-sulfur core dendrimers were studied as a function of the type of counterion available during reduction and re-oxidation.The rate of permeation/migration of counterions into the film appeared to be the bottleneck to electron transfer through the film.As the dendrimer is essentially non-polar, decreasing the relative polarity of the counterion increased the rate and extent of electron hopping within the films.