Thomas S. Corbitt

Light-Induced Biocidal Action of Conjugated Polyelectrolytes Supported on Colloids

A series of water soluble, cationic conjugated polyelectrolytes (CPEs) with backbones based on a poly(phenylene ethynylene) repeat unit structure and tetraakylammonium side groups exhibit a profound light-induced biocidal effect. The present study examines the biocidal activity of the CPEs, correlating this activity with the photophysical properties of the polymers. The photophysical properties of the CPEs are studied in solution, and the results demonstrate that direct excitation produces a triplet excited-state in moderate yield, and the triplet is shown to be effective at sensitizing the production of singlet oxygen. Using the polymers in a format where they are physisorbed or covalently grafted to the surface of colloidal silica particles (5 and 30 microm diameter), we demonstrate that they exhibit light-activated biocidal activity, effectively killing Cobetia marina and Pseudomonas aeruginosa. The light-induced biocidal activity is also correlated with a requirement for oxygen suggesting that interfacial generation of singlet oxygen is the crucial step in the light-induced biocidal activity.

Light and Dark-Activated Biocidal Activity of Conjugated Polyelectrolytes

This Spotlight on Applications provides an overview of a research program that has focused on the development and mechanistic study of cationic conjugated polyelectrolytes (CPEs) that function as light- and dark-active biocidal agents. Investigation has centered on poly-(phenylene ethynylene) (PPE) type conjugated polymers that are functionalized with cationic quaternary ammonium solubilizing groups. These polymers are found to interact strongly with Gram-positive and Gram-negative bacteria, and upon illumination with near-UV and visible light act to rapidly kill the bacteria. Mechanistic studies suggest that the cationic PPE-type polymers efficiently sensitize singlet oxygen ((1)O(2)), and this cytotoxic agent is responsible for initiating the sequence of events that lead to light-activated bacterial killing. Specific CPEs also exhibit dark-active antimicrobial activity, and this is believed to arise due to interactions between the cationic/lipophilic polymers and the negatively charged outer membrane characteristic of Gram-negative bacteria. Specific results are shown where a cationic CPE with a degree of polymerization of 49 exhibits pronounced light-activated killing of E. coli when present in the cell suspension at a concentration of 1 μg mL(-1).

Light-Induced Antibacterial Activity of Symmetrical and Asymmetrical Oligophenylene Ethynylenes

The light-induced antibacterial activity of symmetric and asymmetric oligophenylene ethynylenes (OPEs) was investigated against Gram-positive (Staphylococcus aureus and Staphylococcus epidermidis) and Gram-negative (Escherichia coli) bacteria. To understand the light-induced biocidal effect better, the transient absorption and triplet lifetime of OPEs were studied in methanol and water. A higher triplet lifetime was observed for OPE samples in water than in methanol. The magnitudes of the changes in optical density (ΔOD) of the S-OPE-n(H) series of symmetric oligomers are much higher than that of the asymmetric OPE-n series in water and are generally correlated with the singlet oxygen yield. It was found that the antibacterial activity against both Gram-positive and Gram-negative bacteria is size-, concentration-, and time-dependent. The light-induced antibacterial activity may result from the coordinated interactions of membrane disruption and interfacial or intracellular singlet oxygen generation, and the dominant factor is most likely the latter. The results obtained in this study will aid in the design of more efficient biocides in the future.

Direct Visualization of Bactericidal Action of Cationic Conjugated Polyelectrolytes and Oligomers

The bactericidal mechanisms of poly(phenylene ethynylene) (PPE)-based cationic conjugated polyelectrolytes (CPE) and oligo-phenylene ethynylenes (OPE) were investigated using electron/optical microscopy and small-angle X-ray scattering (SAXS). The ultrastructural analysis shows that polymeric PPE-Th can significantly remodel the bacterial outer membrane and/or the peptidoglycan layer, followed by the possible collapse of the bacterial cytoplasm membrane. In contrast, oligomeric end-only OPE (EO-OPE) possesses potent bacteriolysis activity, which efficiently disintegrates the bacterial cytoplasm membrane and induces the release of bacterial cell content. Using single giant vesicles and SAXS, we demonstrated that the membrane perturbation mechanism of EO-OPE against model bacterial membranes results from a 3D membrane phase transition or perturbation.

Aerosol‐assisted chemical vapor deposition of copper: A liquid delivery approach to metal thin films

Aerosol‐assisted chemical vapor deposition has been used to attain high deposition rates (up to 800 A min−1 at 140 °C) of crystalline, low‐resistivity (1.7–3.5 μΩ cm) Cu films at low temperatures (120–200 °C) from toluene solutions of (hfac)Cu(1,5‐COD), where 1,5‐COD=1,5‐cyclooctadiene, in a warm‐wall reactor. Activation energies calculated from the deposition rate as a function of the preheating temperatures and the substrate temperature (varying also the nozzle‐substrate distance) were 6.8, 8.9 (0.7 cm), and 9.1 (1.7 cm) kcal mol−1, respectively. The activation energy of 6.8 kcal mol−1 is similar to the enthalpy of vaporization of (hfac)Cu(1,5‐COD).

Conjugated-polyelectrolyte-grafted cotton fibers act as "micro flypaper" for the removal and destruction of bacteria.

We demonstrate herein a method for chemically modifying cotton fibers and cotton-containing fabric with a light-activated, cationic phenylene-ethynylene (PPE-DABCO) conjugated polyelectrolyte biocide. When challenged with Pseudomonas aeruginosa and Bacillus atropheaus vegetative cells from liquid suspension, light-activated PPE-DABCO effects 1.2 and 8 log, respectively, losses in viability of the exposed bacteria. These results suggest that conjugated polyelectrolytes retain their activity when grafted to fabrics, showing promise for use in settings where antimicrobial textiles are needed.

Photophysics and light-activated biocidal activity of visible-light-absorbing conjugated oligomers.

The photophysical properties of three cationic π-conjugated oligomers were correlated with their visible light activated biocidal activity vs S. aureus. The oligomers contain three arylene units (terthiophene, 4a; thiophene-benzotriazole-thiophene, 4b; thiophene-benzothiadiazole-thiophene, 4c) capped on each end by cationic -(CH2)3NMe3(+) groups. The oligomers absorb in the visible region due to their donor-acceptor-donor electronic structure. Oligomers 4a and 4b have high intersystem crossing and singlet oxygen sensitization efficiency, but 4c has a very low intersystem crossing efficiency and it does not sensitize singlet oxygen. The biocidal activity of the oligomers under visible light varies in the order 4a > 4b ≈ 4c.

Chemistry of copper(I) β-diketonate complexes: VI. Synthesis, characterization and chemical vapor deposition of 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione (fod), copper(I)L complexes and the solid state structure of (fod)Cu(PMe3)

Abstract A series of copper(I) compounds of the general formula (fod)CuL, where fod = 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione, and L  PMe 3 , PEt 3 , 1,5-cyclooctadiene (1,5-COD), vinyltrimethylsilane (VTMS), 2-butyne, bis(trimethylsilyl)acetylene (BTMSA), have been prepared by the reaction of Na[fod] with CuCl in the presence of the appropriate amount of the Lewis base, L. All the compounds were characterized by elemental analysis, 1 H, 13 C, 19 F, 31 P and IR spectroscopies. The spectroscopic data are consistent with the chelation of the β- diketonate ligand through its oxygen atoms to the copper(I) center. The analytical data are consistent with the empirical formula (fod)CuL. One compound, (fod)CuPMe 3 , was characterized in the solid-state by single-crystal X-ray diffraction which confirmed the empirical formula and revealed the monomeric nature of this species in the solid state. The distorted trigonal planar coordination environment observed for this species is common to these species. The CuO distances are significantly different within the limits of error on the data possibly as a result of inductive effects of the different β-diketonate substituents. Crystal data: Triclinic space group P 1, a = 10.052(2) A, b = 11.871 (2) A, c = 16287(3) A, α = 109.84(1)°, β = 92.18(2)°, γ = 90.34(2)°, V = 1826.5(6) A 3 , Z = 4, R F , = 7.09% and R wF = 7.28%. Hot- and cold-wall chemical vapor deposition experiments revealed that these species are generally not suitable as precursors for the deposition of copper due to their low thermal stability. While pure copper films could be deposited, as determined by Auger electron spectroscopy, from the compounds (fod)CuL, where L = PMe 3 , 2-butyne and BTMSA, heating the precursors to increase their vapor pressures resulted in significant thermal decomposition in the source reservoir. As a result, deposition rates of only 100 A/min were achieved. No selectivity was observed on W versus SiO 2 substrates under the conditions employed. The other compounds, (fod)CuL, where L = 1,5-COD, VTMS, were too thermally unstable for CVD experiments.

Principles of molecular precursor selection for aerosol synthesis of materials

The influence of precursor design on gas-phase and liquid/solid-phase (spray pyrolysis) aerosol materials synthesis is described. The necessity for the incorporation of reaction mechanisms that lead to complete removal of organic by-products is emphasized by the examples of aerosol-assisted CVD of Cu and Ag films and the formation of ZnS films and powders. The role of “single-source” precursors in the formation of complex materials including ZnS, perovskite phase PbTiO3 and yttrium aluminum garnet, Y3Al5O12 is described.

Rapid Evaluation of the Antibacterial Activity of Arylene–Ethynylene Compounds

A series of oligo(arylene-ethynylene) (1-3 repeat units) compounds functionalized with quaternary ammonium groups was screened for their antibacterial activity in the dark and with activation by long-wavelength (365 nm) UV irradiation. Several of these compounds have effective bactericidal activity (>99.9% killing) at concentrations between 0.01 and 10 μg/mL. Our approach uses flow cytometry to rapidly screen and evaluate the susceptibility of bacterial populations. The rapidity, high information content, and accuracy of this approach make it an extremely valuable method for the study of antibacterial compounds.