The preparation, characterization, and application of thin film devices.

This thesis deals with the preparation of two thin film devices, in particular a nitrogen dioxide (NO\sb2) gas sensor and a rechargeable lithium battery. A number of different thin film preparation techniques were used for a variety of applications and the resultant films were characterized by spectroscopic and electrochemical methods. The NO\sb2 gas sensor was based on Langmuir-Blodgett (LB) monolayer films of the sandwich molecule europium bisphthalocyanine (EuPc\sb2). The intense UV-visible absorption spectrum of a monolayer of the EuPc\sb2 dye molecules was recorded before and after exposure to NO\sb2 gas. It was noted that with time the film spectrum returned to its original colour, thus indicating the process to be reversible. The powerful spectroscopic technique of surface enhanced Raman scattering (SERS) was also utilized for film characterization. As with the absorption spectroscopy, the SERS experiments also indicated a reversible NO\sb2 adsorption-desorption process. An interdigitated gold electrode was used to measure the electrical conductivity of LB monolayers of EuPc\sb2. The activation energy for conduction for this molecular semiconductor was determined to be 0.27 eV from thermal conductivity experiments. Upon exposure to NO\sb2 gas, the conductivity of the film increases considerably until it reaches saturation. Kinetics studies indicated that the conductivity changes resulted from two sources: the adsorption of NO\sb2 molecules on the surface, and the absorption of the molecules into the film. While the spectroscopic experiments suggested this process to be completely reversible, the electrical measurements indicated that heating was required to remove the residual absorbed NO\sb2. Thin film cathodes for a rechargeable lithium battery were fabricated by the magnetron sputtering technique. The cathodes were deposited from a sample of the LiMn\sb2O\sb4 pure spinel material. The Li-Mn-O film was characterized by grazing angle x-ray diffraction, Raman and infrared spectroscopies. Electrochemical analyses of the films deposited on aluminum gave charge/discharge capacities of around 78.9 mA h g\sp{-1}. Tests showed that these cells suffered from very high impedance most likely due to a high degree of polarization at the cathode:substrate interface. Deposition of a gold film onto the aluminum substrate proved to greatly reduce the impedance losses, resulting in an improvement in the total charge capacity of the cathode film to 211 mA h g\sp{-1}.Dept. of Chemistry and Biochemistry. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1996 .B47. Source: Dissertation Abstracts International, Volume: 59-08, Section: B, page: 4068. Adviser: Ricardo Aroca. Thesis (Ph.D.)--University of Windsor (Canada), 1997

High resolution spectroscopy of the Vanadium oxide B⁴ [pi] -X⁴ [sigma] ⁻ (0,0) Band

The B⁴Π—X⁴Σ⁻ (0,0) band of VO has been recorded at sub-Doppler resolution by intermodulated fluorescence spectroscopy. Spectral linewidths of 60 MHz were typical; which enabled the hyperfine structure due to the ⁵¹V nucleus (I = 7/2) to be resolved for most of the observed branches. The hyperfine structure of the B⁴Π state is narrow except where it is heavily perturbed by the v = 2 level of the a²Σ⁺ state. The electron configuration of the a²Σ⁺ state was determined to be (4sσ)¹(3dδ)² because of the large Fermi contact interaction which arose from an unpaired electron having primarily metal 4s atomic orbital character. The transition frequencies were fit to a model which included the rotational, fine and hyperfine structure of the B⁴Π, X⁴Σ⁻, and a²Σ⁺ states. The B⁴Π / a²Σ⁺ interaction required the inclusion of an effective higher order spin-orbit parameter as well as a new hyperfine parameter, denoted by parameter e. The new hyperfine parameter is required to describe the hyperfine interactions between ⁴Π and ²Σ⁺ states. The fit included 3211 data points and gave an r.m.s. error of 0.00038 cm⁻¹.Science, Faculty ofChemistry, Department ofGraduat

Lipid Segregation Explains Selective Toxicity of a Series of Fragments Derived from the Human Cathelicidin LL-37▿

The only human cathelicidin, the 37-residue peptide LL-37, exhibits antimicrobial activity against both gram-positive and gram-negative bacteria. We studied the ability of several fragments of LL-37, exhibiting different antimicrobial activities, to interact with membranes whose compositions mimic the cytoplasmic membranes of gram-positive or of gram-negative bacteria. These fragments are as follows: KR-12, the smallest active segment of LL-37, with the sequence KRIVQRIKDFLR, which exhibits antimicrobial activity only against gram-negative bacteria; a slightly smaller peptide, RI-10, missing the two cationic residues at the N and C termini of KR-12, which has been shown not to have any antimicrobial activity; a longer peptide, GF-17, which shows antimicrobial activity against gram-positive as well as gram-negative bacteria; and GF-17D3, with 3 d-amino-acid residues, which is also selective only for gram-negative bacteria. Those fragments with the capacity to cluster anionic lipids away from zwitterionic lipids in a membrane exhibit selective toxicity toward bacteria containing zwitterionic as well as anionic lipids in their cytoplasmic membranes but not toward bacteria with only anionic lipids. This finding allows for the prediction of the bacterial-species selectivity of certain agents and paves the way for designing new antimicrobials targeted specifically toward gram-negative bacteria

Substantial Decrease in Plasmalogen in the Heart Associated with Tafazzin Deficiency

Tafazzin is the mitochondrial enzyme that catalyzes transacylation between a phospholipid and a lysophospholipid in remodeling. Mutations in tafazzin cause Barth syndrome, a potentially life-threatening disease with the major symptom being cardiomyopathy. In the tafazzin-deficient heart, cardiolipin (CL) acyl chains become abnormally heterogeneous unlike those in the normal heart with a single dominant linoleoyl species, tetralinoleoyl CL. In addition, the amount of CL decreases and monolysocardiolipin (MLCL) accumulates. Here we determine using high-resolution ³¹P nuclear magnetic resonance with cryoprobe technology the fundamental phospholipid composition, including the major but oxidation-labile plasmalogens, in the tafazzin-knockdown (TAZ-KD) mouse heart as a model of Barth syndrome. In addition to confirming a lower level of CL (6.4 ± 0.1 → 2.0 ± 0.4 mol % of the total phospholipid) and accumulation of MLCL (not detected → 3.3 ± 0.5 mol %) in the TAZ-KD, we found a substantial reduction in the level of plasmenylcholine (30.8 ± 2.8 → 18.1 ± 3.1 mol %), the most abundant phospholipid in the control wild type. A quantitative Western blot revealed that while the level of peroxisomes, where early steps of plasmalogen synthesis take place, was normal in the TAZ-KD model, expression of Far1 as a rate-determining enzyme in plasmalogen synthesis was dramatically upregulated by 8.3 (±1.6)-fold to accelerate the synthesis in response to the reduced level of plasmalogen. We confirmed lyso-plasmenylcholine or plasmenylcholine is a substrate of purified tafazzin for transacylation with CL or MLCL, respectively. Our results suggest that plasmenylcholine, abundant in linoleoyl species, is important in remodeling CL in the heart. Tafazzin deficiency thus has a major impact on the cardiac plasmenylcholine level and thereby its functions