| Summary: | This thesis is concerned with the formation and nature of intravesicular solids in chemical and biological systems. The precipitation of Ag<sub>2</sub>O within unilamellar vesicle microvolumes is described in detail. Formation of small (<10nm) single-domain cubic Ag<sub>2</sub>O crystallites occurs on membrane diffusion of hydroxide ions. Nucleation initiates at a single site on the inner membrane surface followed by slow crystal growth. No precipitation is observed below an extravesicular pH (pH<sub>OUT</sub>) of <u>ca</u>. 11.0. Permeable intravesicular nitrate ions permit hydroxide influx only when a critical membrane potential gradient is surpassed. Above a pH<sub>OUT</sub> of 11.0 rate of precipitation is dependent on the rate of crystal growth. Kinetics are firstorder with respect to intravesicular Ag(I) concentration and approximately first-order with respect to hydroxide concentration below a pH<sub>OUT</sub> of 12.0. Solubility equilibria for intra-and extravesicular Ag<sub>2</sub>O formation are the same. Further <u>in situ</u> intravesicular precipitation reactions are described for FeO(OH) (crystalline), FeO(OH) (amorphous), Ag<sub>2</sub>SiO<sub>3</sub> (crystalline), CoSiO<sub>3</sub> (amorphous), Co(OH)<sub>2</sub> (amorphous), Ag<sub>2</sub>S (crystalline), CoS (amorphous), and Agl (crystalline). Precipitation of single oxidation state compounds is the same in vesicle space as for normal aqueous solution. For a mixed valency state solid, Fe<sub>3</sub>0<sub>4</sub>, intravesicular precipitation results in an amorphous material compared with a crystalline material prepared in aqueous solution. Inclusion of pre-formed Fe<sub>3</sub>0<sub>4</sub>, into vesicles is of potential use as a magnetic drug carrier system and n.m.r. relaxation probe. Intravesicular silica deposition in <u>Stephenaoeca diplocostata</u> Ellis is investigated. Siliceous costal strips are found to be extremely amorphous in structure, have surfaces active to Co(II) and Fe(III) ions, and demineralise from their centre of axis. T-joins of costal strips in intact loricae are found to be joined by a connective material containing amorphous silica centred around a filamentous material of unknown composition. Sectioned material indicates that silicification possibly initiates on an organic preformer laid down within an elongated intracellular vesicle. Potential EM stains, K<sub>5</sub>SiPhGeW<sub>11</sub>0<sub>39</sub>, Gd(fod)<sub>3</sub>, and t-BuNH<sub>3</sub>[(nC<sub>22</sub>H<sub>45</sub>PO<sub>3</sub>)<sub>2</sub>Mo<sub>5</sub>O<sub>15</sub>] interact with vesicle bilayers resulting in observable images in the EM. Binding of K<sub>5</sub>SiPhGeW<sub>11</sub>0<sub>39</sub> can be followed by <sup>1</sup>H n.m.r. spectroscopy . Gd(fod)<sub>3</sub> loaded vesicles are potential n.m.r. probes for protein - membrane binding studies.
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