Sarah K. McIntyre

Self-assembly and magnetic alignment in cetyltrimethylammonium bromide/sodium perfluorooctanoate surfactant mixtures investigated using 2H nuclear magnetic resonance spectroscopy.

Deuterium nuclear magnetic resonance (2H NMR) spectroscopy has been used to investigate the phase behavior for mixtures of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the anionic surfactant sodium perfluorooctanoate (FC7) for total surfactant concentrations ranging from 1 to 25 wt %. The deuterated methyl of the quaternary methyl-ammonia group in CTAB-y-d3 gives rise to a superposition of spectral components in the 2H NMR spectra allowing for the identification and quantification of the different phases present. The CTAB/FC7 mixture exhibits a coexisting two-phase region composed of an isotropic (Iso) micelle/vesicle phase along with a lamellar (Lalpha) phase for all of the composition ranges investigated. The variation of the phase composition as a function of sample temperature, total wt % surfactant, and surfactant molar ratio are presented. In addition, the 2H NMR reveals that the Lalpha phase spontaneously aligns in the magnetic field, with the extent and distribution of magnetic alignment being determined. The 2H NMR results are discussed in light of previously reported surfactant-templated material synthesis involving the CTAB/FC7 mixture.

Structural diversity in a series of alkyl-substituted cesium aryloxides.

A family of cesium aryloxides [Cs(OAr)](n) were synthesized and structurally characterized from the reaction of 1:1 or 1:excess stoichiometry of Cs(0) and the appropriate alkyl-substituted phenol: 2-alkylphenol [alkyl = methyl (H-oMP), isopropyl (H-oPP), and tert-butyl (H-oBP)] and 2,6-dialkylphenol [alkyl = methyl (H-DMP), isopropyl (H-DIP), tert-butyl (H-DBP), and phenyl (H-DPhP)]. The products were structurally identified as [Cs(oMP)(H-oMP)(2)](n) (1), [Cs(5)(oPP)(5)](n) (2), [Cs(4)(oBP)(4)(H-oBP)(6)](n) (3x, shown), [Cs(3)(DMP)(3)](n) (4), [Cs(2)(DIP)(2)](n) (5), [Cs(DIP)(H-DIP)](n) (5x), and [Cs(DPhP)](n) (7). Compounds 1-7 were found to adopt complex polymeric structures employing π interactions from the neighboring pendant phenoxide ligands. The solution behavior of these compounds was studied using solution (133)Cs NMR spectroscopy, and for each compound, a single (133)Cs NMR resonance was observed, with chemical shift values found to be strongly solvent-dependent. This implies that monomeric cesium salt species involving solvent interactions exist in solution.

Development of a Micro Flow-Through Cell for High Field NMR Spectroscopy

A highly transportable micro flow-through detection cell for nuclear magnetic resonance (NMR) spectroscopy has been designed, fabricated and tested. This flow-through cell allows for the direct coupling between liquid chromatography (LC) and gel permeation chromatography (GPC) resulting in the possibility of hyphenated LC-NMR and GPC-NMR. The advantage of the present flow cell design is that it is independent and unconnected to the detection probe electronics, is compatible with existing commercial high resolution NMR probes, and as such can be easily implemented at any NMR facility. Two different volumes were fabricated corresponding to between {approx}3.8 and 10 {micro}L detection volume. Examples of the performance of the cell on different NMR instruments, and using different NMR detection probes were demonstrated.

Tools for characterizing biomembranes : final LDRD report.

A suite of experimental nuclear magnetic resonance (NMR) spectroscopy tools were developed to investigate lipid structure and dynamics in model membrane systems. By utilizing both multinuclear and multidimensional NMR experiments a range of different intra- and inter-molecular contacts were probed within the membranes. Examples on pure single component lipid membranes and on the canonical raft forming mixture of DOPC/SM/Chol are presented. A unique gel phase pretransition in SM was also identified and characterized using these NMR techniques. In addition molecular dynamics into the hydrogen bonding network unique to sphingomyelin containing membranes were evaluated as a function of temperature, and are discussed.