Intravesicular solids in chemical and biological systems

• Main Author: Mann, Stephen
• Other Authors: Williams, Robert Joseph Paton
• Published: University of Oxford 1982
• Subjects: 572; Solids : Silver oxide : Biological systems : Chemical systems
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233791

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 (pH_OUT) 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_OUT 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_OUT of 12.0. Solubility equilibria for intra-and extravesicular Ag₂O formation are the same. Further <u>in situ</u> 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 <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, 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.