Intravesicular solids in chemical and biological systems
This thesis is concerned with the formation and nature of intravesicular solids in chemical and biological systems. The precipitation of Ag2O within unilamellar vesicle microvolumes is described in detail. Formation of small (<10nm) single-domain cubic Ag2O 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 (pHOUT) of ca. 11.0. Permeable intravesicular nitrate ions permit hydroxide influx only when a critical membrane potential gradient is surpassed. Above a pHOUT 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 pHOUT of 12.0. Solubility equilibria for intra-and extravesicular Ag2O formation are the same. Further in situ intravesicular precipitation reactions are described for FeO(OH) (crystalline), FeO(OH) (amorphous), Ag2SiO3 (crystalline), CoSiO3 (amorphous), Co(OH)2 (amorphous), Ag2S (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, Fe304, intravesicular precipitation results in an amorphous material compared with a crystalline material prepared in aqueous solution. Inclusion of pre-formed Fe304, into vesicles is of potential use as a magnetic drug carrier system and n.m.r. relaxation probe. Intravesicular silica deposition in Stephenaoeca diplocostata 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, K5SiPhGeW11039, Gd(fod)3, and t-BuNH3[(nC22H45PO3)2Mo5O15] interact with vesicle bilayers resulting in observable images in the EM. Binding of K5SiPhGeW11039 can be followed by 1H n.m.r. spectroscopy . Gd(fod)3 loaded vesicles are potential n.m.r. probes for protein - membrane binding studies.