Abiogenically Relevant Self-Assembly Processes Within Silica Hydrogels

In this thesis are presented studies which are aimed at elucidating the effects, if any, that the hydrogel phase has in influence chemical processes of relevance to abiogenesis over the aqueous phase. The significance of this is set in the light of the hydrogel hypothesis which suggests that the most primitive organisms would have emerged within a hydrogel environment rather than purely an aqueous one. Chapter 1 provides an introduction to the fundamental principles of interest to this work, discusses hydrogels, their synthesis, properties, applications and especially their potential role in abiogenesis. Also discussed are the concepts of amphiphilic self-assembly and molecular diffusions which are two molecular behaviours that have been looked at in most detail here. This chapter then concludes with some discussion of the analytical techniques used within the project. Chapter 2 describes the preparation of silica hydrogels (the main hydrogel used in this work) along with methods for isolating the silica matrix and surface analyses using electron microscopy and associated techniques (BET, EDX). This section also includes the results of dynamic light scattering and thermogravimetric studies on silica hydrogels. Chapter 3 outlines how amphiphilic self-assembly of a probe molecule, sodium dodecylsulphate (SDS), behaviour differs between the aqueous and silica hydrogel phases. This is achieved through measurements of critical micelle concentrations in both phases using UV-VIS spectrophotometry and colorimetric reporter dyes (merocyanine 540 and pinacyanol chloride). The key outcome being that CMC’s are definitively reduced in the salt-containing silica hydrogel over the pure aqueous phase. Chapter 4 describes investigations into a decolourisation phenomenon observed with the merocyanine 540 dye which says it complete colour bleach at high silicate concentrations of the hydrogel. Whilst the investigations did not produce a definitive answer to this issue it did highlight a protective role for amphiphiles in the decolourisation and also led, indirectly, to observations allowing us to probe gelation times using simple light scattering. Chapter 5 discusses the use of diffusion order spectroscopy (DOSY) as a technique for measuring and comparing molecular diffusion coefficients in both aqueous and silica hydrogel phases. Molecules of prebiotic significance such as the adenosine phosphates and condensed phosphates, AMP, ADP, ATP as well as the sugar d-ribose. Results suggest that direct measurements of diffusion coefficients in the silica hydrogel phase is effective and offers a potentially useful tool for probing more complex diffusional behaviours. Chapter 6 contains the experimental details from Chapters 2-5 and Chapter 7 offers a summary, conclusions and future work perspective.