Title

I. Water-driven chemoselective reactions of squarate derivatives with amino acids and peptides: Mechanism and applications. II. Biocompatible hydrogels: Transferring bioinert chemistry from surfaces to 3-dimensional materials

Date of Award

2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

Yan-Yeung Luk

Keywords

Surface immobilization, Water-driven, N-terminal cysteine, Chemoselective, Squarate derivatives, Bioinert

Subject Categories

Chemistry | Organic Chemistry | Physical Sciences and Mathematics

Abstract

Chemoselective organic reactions in entirely aqueous environment are useful for interfacing chemistry with life sciences, including immobilization of peptides and mammalian cells on surfaces, and running designed reaction in living systems. This dissertation describes a fundamentally new class of highly chemoselective reaction employing rationally designed squarate derivatives - molecules with abiotic structures - and N-terminal cysteine residue of peptides (or proteins) in an entirely aqueous solution at neutral pH. The mechanistic study of this chemoselective ligation revealed that the reaction not only proceeds in water, but also promoted by the hydrogen bonding of water. By fine tuning the reactivity of squarate derivative and controlling the pH of the solution, a methodology had been established for immobilizing peptides and mammalian cells using only the N-terminus cysteine for conjugation to surface bound squarates. This highly resolved control of selectivity enables the immobilization and biological studies of peptides and protein containing internal cysteines. Few other potential application of this reaction were also presented including a new class of labeling reagent for peptides, proteins and mammalian cells that have long-term stability in water and has potential for the development of a biotin probe that can survive the complex biological environment. Mimics of the ligand for mediating mammalian cell adhesion, Agr-Gly-Asp (RGD) tripeptide, were also constructed based on a squarate core structure. The synthesis of this new class of non-peptidic molecules is highly efficient - consisting of 1-5 steps. Inhibition assays suggest that this class of molecules block the specific binding site on integrin membrane protein for the natural ligand RGD. Cell adhesion assays were conducted on bioinert self-assembled monolayers (SAMs) of alkanethiols on gold film to reduce the high signal-to-noise ratio usually associated with traditional fibronectin based assay. Exploring the transfer of the bioinert anti-biofouling surface chemistry of the mannitol-terminated self-assembled monolayer into three-dimensional materials, a novel hydrogel composed of mannitol-derivatized acrylamide monomers was synthesized. This polymeric material prevents mammalian cell adhesion more effectively than other hydrogel materials based on monomers such as glycerol and acrylamide. This result validates the hypothesis that assembly of molecules known as Kosmotropes, which render the folding structure of proteins, also exhibit bioinertness.

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