TOF-SIMS imaging of chlorhexidine-digluconate transport in frozen hydrated biofilms of the fungus Candida albicans

The diffusion of the anti-microbial chlorhexidine digluconate (CHG) has been studied in C. albicans biofilms by time-of-flight secondary-ion mass spectrometry (TOF-SIMS). C. albicans has been shown to become resistant to common anti-microbial agents, including CHG, when growing as a biofilm. Mass transport resistance within biofilms has commonly been suggested as a resistance mechanism, but measurement of transport for most anti-microbial agents in biofilms has proven extremely difficult because of the heterogeneity of the biofilms and the difficulty in detecting these agents within an intact biofilm. In this study, TOF-SIMS has been used to study the transport of CHG and glucose in a frozen hydrated biofilm. The TOF-SIMS images reveal a progression of CHG from the top of the biofilm to its base with time. Images suggest that there are channels within the biofilm and show preferential binding of CHG to cellular components of the biofilm. Additionally, both living and dead cells can be identified in the TOF-SIMS images by the sequestration of K⁺ and the presence of cell markers. This study demonstrates that TOF-SIMS has the unique potential to simultaneously observe the presence of an antimicrobial agent, concentration of nutrients, and the viability of the cell population.     

A hexacyclic ent-trachylobane diterpenoid possessing an oxetane ring from Mitrephora glabra

[chemical reaction: see text]. Three new ent-trachylobane diterpenoids (1-3) were isolated and structures elucidated from Mitrephora glabra Scheff. (Annonaceae). Mitrephorone A (1) possesses a hexacyclic ring system with adjacent ketone moieties and an oxetane ring, both of which are unprecedented among trachylobanes. All compounds were evaluated for cytotoxicity against a panel of cancer cells, where 1 displayed the most potent and broadest activity, and against a battery of antimicrobial assays, where all compounds were approximately equipotent.     

π-Olefin—iridium -komplexe : III. Über (η4-cyclodien)(η5-cyclodienyl)iridium-verbindungen,einen neuartigen hydridoiridium-komplex und das (η4-cyclooctadien)(η6-cyclooctatrien)iridium-kation

The complexes [Ir(COD)(η⁵-C₇H₉)] and [Ir(COD)(η⁵-C₈H₁₁)] are obtained by the isoprophyl Grignard synthesis of [Ir(COD)Cl]₂ (COD = η⁴-1,5-cyclooctadiene) in the presence of cycloheptatriene, and cyclooctatriene, respectively. The later reaction yields [IrH(COD)(δ⁴-1,3,6-C₈H₁₀)] as a by-product which, in contrast to other [IrH(η⁴-cyclodiene)₂] complexes, does not show H-addition-elimination equilibria. Reduction of [Ir(1,3-C₇H₁₀)₂Cl] with C₂H₅OH/Na₂CO₃ yields [Ir(η⁴-1,3-C₇H₁₀)](η⁵-C₇H₉)] which was characterized by X-ray analysis. [Ir(COD)Cl]₂ reacts with Na₂C₈H₈, and after hydrolysis unstable [Ir(COD)(η⁵-C₈H₉)] is formed which by protonation with HPF₆ is converted into the [Ir(COD)(η⁶-1,3,5-C₈H₁₀)]⁺ cation. All these compounds are fluxional in solution.     

Baylis-Hillman mechanism: a new interpretation in aprotic solvents

Using reaction rate data collected in aprotic solvents, we have determined that the Baylis-Hillman rate-determining step is second order in aldehyde and first order in DABCO and acrylate. On the basis of these data, we have proposed a new mechanism involving a hemiacetal intermediate. The proposed mechanism was then supported using two different kinetic isotope experiments.     

Structural control in thin layers of poly(p-phenyleneethynylene)s: photophysical studies of Langmuir and Langmuir-Blodgett films

We present the relationship between the spatial arrangement and the photophysical properties of fluorescent polymers in thin films with controlled structures. Eight surfactant poly(p-phenyleneethynylene)s were designed and studied. These detailed studies of the behavior of the polymers at the air-water interface, and of the photophysical properties of their transferred LB films, revealed key structure-property relationships. Some of the polymers displayed pi-aggregates that are characteristic of an edge-on structure at the air-water interface. Monolayer LB films of these polymers showed greatly reduced quantum yields relative to solution values. Other polymers exhibited a highly emissive face-on structure at the air-water interface, and did not form pi-aggregates. The combination of pressure-area isotherms and the surface pressure dependent in situ UV-vis spectra of the polymers at the air-water interface revealed different behavioral details. In addition, the UV-vis spectra, fluorescence spectra, and quantum yields of the LB films provide design principles for making highly emissive films.     

Self-assembly, optical behavior, and permeability of a novel capsule based on an azo dye and polyelectrolytes

A novel capsule composed of an azo dye, Congo red (CR), and different polymers, including poly(styrenesulfonate, sodium salt) (PSS), poly(allylamine hydrochloride) (PAH), and poly(diallyldimethylammonium chloride) (PDDA), have been successfully fabricated by the layer-by-layer self-assembly technique. The stepwise linear deposition process was monitored by means of UV-visible absorption measurements. The formation of hollow capsules was verified by confocal laser scanning microscopy (CLSM) and scanning force microscopy (SFM). The resulting hollow PSS/PAH/CR/PDDA capsules displayed a sensitive response to visible light. Optical changes of the hollow capsules prior to and after the photoreaction were investigated in detail by means of UV-visible spectroscopy, CLSM, and SFM. It was found that the photochemical reaction of the assembled hollow capsules depends strongly on the matrix. Qualitative results on the permeability of the hollow capsule walls with CR as one component indicate that the permeability of the walls can be easily photo-controlled at varying irradiation time intervals without addition of external chemicals.