Imaging Lipid Distributions in Model Monolayers by ToF-SIMS with Selectively Deuterated Components and Principal Components Analysis

Abstract Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) provides the capability to image the distribution of molecular ions and their associated fragments that are emitted from monolayer films. ToF-SIMS can be applied to the analysis of monolayers of complex lipid mixtures that act as a model to understand the organization of cell membranes into solid-like domains called lipid rafts. The ability to determine the molecular distribution of lipids using ToF-SIMS in monolayer films is also important in studies of the function of pulmonary surfactant. One of the limitations of the use of ToF-SIMS to studies of complex lipid mixtures found in biological systems, arises from the similarity of the mass fragments that are emitted from the components of the lipid mixture. The use of selectively deuterated components in a mixture overcomes this limitation and results in an unambiguous assignment of specific lipids to particular surface domains. The use of deuterium labeling to identify specific lipids in a multi-component mixture can be done by the deuteration of a single lipid or by the addition of more than one lipid with selectively deuterated components. The incorporation of deuterium into the lipid chains does not alter the miscibility or phase behavior of these systems. The use of deuterium labeling to identify lipids and determine their distribution in monolayer films will be demonstrated using two biological systems. Principal components analysis (PCA) is used to further analyze these deuterated systems checking for the origin of the various mass fragments present

Two-directional synthesis and biological evaluation of alkaloid 5-epi-cis-275B′

The first total synthesis of myrmicine ant alkaloid 5-epi-cis-275B0 (4) is presented. A tandem cyclisation stablished the entire core of the structure in a single transformation as well as the required 2,5-anti stereochemistry. Two-directional synthesis was used to furnish the cyclisation precursor 2, as in each of the subsequent steps towards the natural product. The first electrophysiology studies for 4 (against nicotinic acetylcholine receptors) were also conducted, finding modest inhibition of current

Role of Caustic Addition in Bitumen-Clay Interactions

Coating of bitumen by clays, known as slime coating, is detrimental to bitumen recovery from oil sands using the warm slurry extn. process. Sodium hydroxide (caustic) is added to the extn. process to balance many competing processing challenges, which include undesirable slime coating. The current research aims at understanding the role of caustic addn. in controlling interactions of bitumen with various types of model clays. The interaction potential was studied by quartz crystal microbalance with dissipation monitoring (QCM-D). After confirming the slime coating potential of montmorillonite clays on bitumen in the presence of calcium ions, the interaction of kaolinite and illite with bitumen was studied. To represent more closely the industrial applications, tailings water from bitumen extn. tests at different caustic dosage was used. At caustic dosage up to 0.5 wt % oil sands ore, a negligible coating of kaolinite on the bitumen was detd. However, at a lower level of caustic addn., illite was shown to attach to the bitumen, with the interaction potential decreasing with increasing caustic dosage. Increasing concn. of humic acids as a result of increasing caustic dosage was identified to limit the interaction potential of illite with bitumen. This fundamental study clearly shows that the crit. role of caustics in modulating interactions of clays with bitumen depends upon the type of clays. Thus, clay type was identified as a key operational variable

Segregation of saturated chain lipids in pulmonary surfactant films and bilayers.

The physical properties of organized system (bilayers and monolayers at the air water interface) composed of bovine lipid extract surfactant (BLES) were studied using correlated experimental techniques. 6-Dodecanoyl-2-dimethylamino-naphthalene (LAURDAN)-labeled giant unilamelar vesicles (mean diameter approximately 30 microm) composed of BLES were observed at different temperatures using two-photon fluorescence microscopy. As the temperature was decreased, dark domains (gel-like) appeared at physiological temperature (37 degrees C) on the surface of BLES giant unilamelar vesicles. The LAURDAN two-photon fluorescent images show that the gel-like domains span the lipid bilayer. Quantitative analysis of the LAURDAN generalized polarization function suggests the presence of a gel/fluid phase coexistence between 37 degrees C to 20 degrees C with low compositional and energetic differences between the coexisting phases. Interestingly, the microscopic scenario of the phase coexistence observed below 20 degrees C shows different domain's shape compared with that observed between 37 degrees C to 20 degrees C, suggesting the coexistence of two ordered but differently organized lipid phases on the bilayer. Epifluorescence microscopy studies of BLES monomolecular films doped with small amounts of fluorescent lipids showed the appearance and growth of dark domains (liquid condensed) dispersed in a fluorescent phase (liquid expanded) with shapes and sizes similar to those observed in BLES giant unilamelar vesicles. Our study suggests that bovine surfactant lipids can organize into discrete phases in monolayers or bilayers with equivalent temperature dependencies and may occur at physiological temperatures and surface pressures equivalent to those at the lung interface

Influence of the spermicidal compound nonoxynol-9 on the adhesion of E. coli to human epithelial cells

Urinary tract infections (UTI) associated with prostheses continue to cause significant morbidity despite the development and implementation of new biomaterials and device coatings. Ureteral stents, placed to improve drainage of the kidney can become a nidus for infection and potentially serious kidney damage, through attachment of pathogens and biofilm formation. The present study investigated two approaches to reducing the risk of ureteral stent infection. The first involved comparing the resistance to bacterial attachment of medical grade silicone rubber, the current gold standard biomaterial for urinary tract devices, to that of polyisobutylene-polystyrene block copolymer (PIB-PS), a polymer with proven biomaterial potential but as yet untested within the urinary tract. The second approach studied the capacity of a recombinant protein (p29) originally isolated from Lactobacillus fermentum RC-14 to inhibit bacterial attachment when used as a device coating. The protein coat was successfully identified by atomic force microscopy (AFM), gel electrophoresis and surface enhanced laser desorption/ionization (SELDI) protein chip analysis and shown to be present for at least 96 h. The coating and the PIB-PS surface alone were found to significantly reduce the attachment of two common uropathogenic species, Escherichia coli 67 and Enterococcus faecalis 1131 in vitro in the presence of phosphate buffered saline alone. However, the effect was negated following additional urine coating of the sections prior to challenge, likely due to p29 desorption and the development of a urinary conditioning film. These findings highlight the complexity of translating in vitro data to the in vivo setting and the critical role urinary constituents play in the development of urinary tract device-associated infections. © 2002 Elsevier Science B.V. All rights reserved

Atomic Force Microscopic and Encrustation Studies of Novel Prospective Polyisobutylene-based Thermoplastic Elastomeric Biomaterials

This paper investigates the surface morphology of polyisobutylene–polystyrene (PIB–PS) block-type thermoplastic elastomers, emerging new biomaterials, by atomic force microscopy (AFM). A novel aborescent PIB–PS block polymer (AR15) was synthesized through inimer-type living carbocationic polymerization and characterized in comparison with a semi-commercial PIB–PS thermoplastic elastomer (TPE) (TS30). Tapping-mode AFM revealed that PS spheres with a domain size of 45–60 nm were very irregularly distributed in the continuous PIB phase of the aborescent AR15 polymer, whereas ordered and mixed cylindrical/lamellar morphology with 25–31 nm hard phase appeared in a linear TS30 triblock polymer. Moreover, AFM revealed rough surface features of a 1 mm thick compression molded TS30 polymer disk coated with a probiotic protein. AR15 disks were used for in vivo urinary tract encrustation study. Encrustation of the PIB–PS disks was comparable or better than that of medical-grade silicone rubber. The preliminary results imply the prospect of PIB–PS thermoplastic elastomers as emerging soft biomaterials. Copyright © 2003 John Wiley & Sons, Ltd