D. C. Neckers

COMPARISON OF PHOTODYNAMIC ACTION BY ROSE BENGAL IN GRAM-POSITIVE AND GRAM-NEGATIVE BACTERIA

Abstract— The photodynamic inactivation by illuminated Rose Bengal of a number of bacterial species was compared. The gram‐positive species, Bacillus subtilis, Staphylococcus aureus, Streptococcus faecalis and Streptococcus salivarius, were inactivated about 200x more quickly (99% inactivation) than a Salmonella typhimurium wildtype strain. The Salmonella inactivation curve exhibited an initial lag time during which bacteria were not significantly inactivated. The lag time for inactivation of a derivative of the wildtype Salmonella strain that is deficient in a large portion of its cell wall lipopolysaccharide coat was approximately half of the lag time for the wildtype strain but the subsequent rate of inactivation was approximately the same for the two strains. Dark preincubation of both Salmonella strains with Rose Bengal before illumination shortened the lag time, but did not increase the final rate of inactivation. Dark preincubation prior to illumination did not measurably change the inactivation curve of the gram‐positive species. The lag time observed in the inactivation curves for Salmonella bacteria may reflect the time required for penetration of the Rose Bengal anion through the outer portion of the gram‐negative cell wall to a critical location within the cell for effective photosensitization.

TYPE I AND TYPE II SENSITIZERS BASED ON ROSE BENGAL ONIUM SALTS

Abstract— New Rose Bengal oniurn salts containing one or two iodonium, sulfonium, phosphonium, and pyrylium ions have been prepared as part of a program to develop sensitizers which can function as Type I radical photoinitiators and Type II energy transfer donors depending on experimental conditions. The absorption spectra of the onium salts in different solvents indicate an equilibrium between tight and loose ion pairs which depends on the solvent polarity, the cation and concentration. Typical Rose Bengal photochemistry requires the structure be that of the loose ion pair in the solvent of choice. Similar factors also influence bleaching behavior, and bleaching is the result of electron transfer processes. The quantum yields of singlet oxygen production from the onium salts in polar solvents are similar to that of the parent, Rose Bengal disodium salt.

Applicability of decahydroacridine-1,8-dione derivatives as fluorescent probes for monitoring of polymerization processes

Abstract The behavior in polymerizable media of 3,3,6,6-tetramethyldecahydroacridine-1,8-diones substituted with aromatic rings at the 9- or 10-position has been studied. It has been found that the fluorescence of acridinediones shifts to shorter wavelengths upon polymerization of the medium, and this qualifies them as fluorescent molecular probes for monitoring the progress of polymerization processes. The shift in fluorescence is accompanied by a slow decomposition of the acridinediones to a fluorescent product under photopolymerization conditions. Acridinedione decay was slower than the polymerization of a typical photocurable formulation, thus allowing one to follow the progress of polymerization by fluorescence. The influence of the photoproduct on the monitoring of polymerization has been avoided by optimization of the monitoring parameters. Application of the acridinediones as fluorescent molecular probes for large scale applications in the coating industry is proposed.

Factors influencing the quantum yields for rose bengal formation of singlet oxygen

Abstract The φ for 1O2 formation obtained via the relative actinometric method is dependent on the quencher concentration when photo-oxidations in different solvents are compared; a method to determine the appropriate quencher concentration is described.

Photochemical reaction of halogenated xanthene dye with diaryliodonium salts

Abstract The photochemical reactions of ethyl erythrosin and ethyl eosin with diaryliodonium salts in acetonitrile were studied. All the photoproducts were isolated and identified, and the quantum yields measured. We demonstrate that the photochemical reactions are pure electron transfer processes; that the electron transfer is mainly from the triplet excited state of the xanthene dye to the diaryliodonium salt; and that this is immediately followed by the decomposition of the electron acceptor to aryl radicals and iodoaromatics. We demonstrate that there is no back electron transfer. The aryl radical formed either couples with a dye radical or displaces a halogen atom from the dye. The quantum yield of the reaction is dependent on the iodonium salt concentration. The maximum quantum yield for dye disappearance is 0.53 for ethyl erythrosin and 0.30 for ethyl eosin, respectively, at the dye concentration used.

ROSE BENGAL AGGREGATION IN RATIONALLY SYNTHESIZED DIMERIC SYSTEMS

Abstract— Rose Bengal derivatives (I‐VI) have been synthesized as part of a program to study the spectroscopy of model systems for Hpd dimer. The absorption and emission spectra as a function of solvent are diagnostic for the formation of aggregated conformers. Based on our spectroscopic results we conclude that these compounds exist in open conformation in ethanol and other organic solvents, and that they form intramolecular dimers in aqueous solution.

Visible light photopolymerization employing 2,4-diiodo-6-butoxy-3-fluorone and tetraorganylborate salts as photoinitiators

Several new tetraorganylborate salts have been synthesized and tested as coinitiators with 2,4-diiodo-6-butoxy-3-fluorone (DIBF) for the photopolymerization of acrylic monomer mixtures. The rate of photopolymerization has been found to be a function of chemical structure of the borates. Stability, solubility, and reactivity of these borates as coinitiators for photopolymerization have been investigated. Diphenyldialkylborates have been found to be the best among the tested coinitiators.

A low temperature luminiscence study of the colored merocyanine form of substituted 6-nitrobenzo-spiropyrans☆

Abstract The emission spectra of colored merocyanine forms of substituted 6-nitrobenzospiropyrans (1-4)were studied at 77 K. The merocyanine form obtained by UV irradiation of a solution of spiropyrans at room temperature is a dynamic equilibrium mixture of stable trans forms. The merocyanine form obtained by UV irradiation of the same solution at 77 K is a short- lived intermediate. The assignment of this short-lived intermediate to the trans-cis-cis (TCC) form is based on MM2 calculations. This TCC intermediate was also observed during the visible light irradiation of the hydrochloric acid salt form of 1 (5) prepared at 197 K.

Aggregation of rose bengal ethyl ester induced by alkali metal cations in aqueous solution

Abstract The spectrum of Rose Bengal C-2′ ethyl ester, C-6 sodium salt dimer in 2% ethanol has been observed in the presence of alkali metal cations. It is proposed that aggregation occurs in two steps: (a) formation of a neutral complex between the anion of the dye and the alkali metal cation and (b) reaction between the neutral complex and a second dye anion to produce the dimeric species. Both equilibrium constants, as well as the geometry of the dimer, are sensitive to the identity of the cation. The equilibrium constant for the first step ranges from 3.37 M −1 for Li + to 257 M −1 for Rb + and that for the second step ranges from 2.81 × 10 5 M −1 for Li + to 1.05 × 10 6 M −1 for Cs + . The driving force of the first reaction is purely electrostatic whereas the dimerization step is controlled mainly by the hydrophobicity of the dye anion.

Photochemistry and photophysics of hydroxyfluorones and xanthenes

Abstract Laser-initiated photopolymerization has opened the doors to the rapid prototyping revolution. Driven by computer control, the polymerization process can create plastic models which conform accurately to a programmed design in three dimensions. The control programs may be derived from various sources including CAD files, CT scans or other tomographic medical imaging sources such as MRI in a process called “stereolithography”. Models formed by stereolithography conform concisely to a design pattern in all dimensions, and the process has shortened the time required for implementation from months to days in industries ranging from automotive and glass to medical devices.