Applications of Langmuir-Blodgett films and Langmuir monolayers: Supported catalysis and membrane models for urinary stone formation

This dissertation looks at the precipitation of calcium oxalate monohydrate (COM) at phospholipid Langmuir monolayers with the aid of Brewster angle microscopy (BAM). COM crystals are monitored in situ with BAM as they appear as bright objects that are easily identified and quantified. Crystal precipitation was monitored at monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in liquid condensed (LC) and liquid expanded (LE) phases as well as biphasic LC/LE and LE/gas (G). COM appears preferentially at phase boundaries of the single-component monolayers. However, when an LC/LE phase boundary is created by two different phase segregated phospholipids, crystal formation occurs away from the interface within the LC phase. COM growth at phase boundaries is preferred only when there is molecular exchange between phases. Biologically relevant monolayers were prepared by mixing 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC)/Sphingomyelin (SM)/dihydrocholesterol in a 2:1:1 ratio where the SM/sterol components form domains equivalent to lipid rafts in membranes. COM precipitation at these monolayers occurs exclusively at phase boundaries.; An investigation of organized monolayer films of a manganese tetraphenylporphyrin used as supported oxidation catalysts is also discussed. Manganese 5,10,15,20-tetrakis(tetrafluorophenyl-4 '-octadecyloxyphosphonic acid) porphyrin (1) has been immobilized as a monolayer film by a combination of Langmuir-Blodgett (LB) and self-assembled monolayer techniques. Film analysis shows that the films consist of non-interacting molecules anchored and oriented nearly parallel to the surface. The monolayers are stable to the solvent and temperature conditions needed to explore organic oxidations. The activity of films of 1 towards the epoxidation of cyclooctene using iodosylbenzene as the oxidant was compared to that of Manganese 5,10,15,20-tetrakis(pentafluorophenyl) porphyrin (2) and 1 under equivalent homogeneous conditions. The immobilized porphyrin 1 shows an enhanced activity relative to either homogeneous reaction. The main difference between 1 and 2 is the four alkyl phosphonate arms in 1 designed to incorporate the porphyrin within the films. The increased activity of immobilized 1 is a combination of the porphyrin structure, which prohibits the formation of mu-oxo dimers even in solution, and a change in conformation when anchored to the surface. The study demonstrates that careful monolayer studies can provide useful models for the design and study of supported molecular catalyst systems.