Gary A. Epling

Investigation of retardation effects on the titanium dioxide photodegradation system

The photocatalytic bleaching of dyes using TiO2 has appeared promising in laboratory studies, but little attention has been focused on whether other species such as might be found in wastewater have a deleterious effect on the photobleaching. This study describes the effects that result from the presence of ionic species, organic solvents and humic substances on the photobleaching of several dyes. The manner in which the photobleaching was affected by the presence of adventitious materials was carefully examined with an eye toward elucidating the mechanistic origin of the loss of the photochemical efficiency in the reaction. The overall retardation effects can be attributed to the combination of light attenuation, inhibition and competition effects.

Mechanistic studies of the phototoxic potential of PD 117596, a quinolone antibacterial compound

PD 117596 is a novel quinolone compound that is being investigated for use as an antibacterial agent. Early investigations demonstrated a significant phototoxic liability associated with this compound. These studies were undertaken to investigate the mechanism of phototoxicity using an in vitro model. In the UVA region, PD 117596 was found to be a more efficient producer of singlet oxygen than rose bengal, ciprofloxacin, nalidixic acid, or PD 118879, another quinolone under investigation. The quantum yield of photoreaction for PD 117596 was relatively low (phi = 0.021); however, it was approximately 10-fold higher than other tested quinolones. In vitro studies using a mouse erythrocyte model were used to further investigate the mechanism of phototoxicity. PD 117596-induced photohemolysis was found to be oxygen dependent with a relatively rapid onset that progressed even after removal of light. Preirradiation of the compound prevented subsequent hemolytic or photohemolytic action. BHA, BHT, alpha-tocopherol, and the iron chelator DTPA were all found to be effective at ameliorating the photohemolytic response. The photohemolytic response was markedly enhanced when D2O was substituted for H2O in the incubation medium, indicating a singlet oxygen-mediated mechanism of action. A rise in thiobarbituric acid products was noted within 1 hr of irradiation and was maximal at the time of onset of overt photohemolysis. These data suggest that singlet oxygen production by irradiated PD 117596 is responsible for secondary changes in mouse red blood cells including lipid peroxidation and ultimately results in cellular lysis.

Borohydride, micellar, and exciplex-enhanced dechlorination of chlorobiphenyls.

The photodechlorination of polychlorinated biphenyls (PCBs) has been studied in the presence of sodium borohydride, detergents, and exciplex-forming additives. In a family of 13 representative PCBs these variations generally led to a dramatically increased rate of photodegradation. Further, the products of photoreaction in the presence of sodium borohydride are more cleanly the simple dechlorinated aromatics, with fewer side reactions than observed with ordinary photolysis.

Photosensitized cleavage of the dithio protecting group by visible light

Abstract Dithio derivatives of aldehydes and ketones have been deprotected under neutral conditions using visible light provided by a 120 Watt spotlight and methylene green as a sensitizer. The key step in the deprotection is apparently an electron transfer from the dithio derivative to the electronically excited visible dye. The resulting dithio radical cation undergoes fragmentation, and the corresponding aldehydes and ketones are isolated in excellent yields.

PHOTOADDITION OF CHLORPROMAZINE TO GUANOSINE-5′-MONOPHOSPHATE

Abstrart—The photochemistry of chlorpromazine (CPZ) with guanosine‐5′‐monophosphate (GMP) was studied as a model for the photoaddition of CPZ to DNA. Irradiation of CPZ with calf thymus DNA produced a product emitting at 520 nm, whereas with GMP emission was at 495 nm. HPLC separation of photolysis mixtures of [3H]CPZ with GMP and [14C]GMP with CPZ indicated that three photoadducts were formed. One of the adducts fluoresced at 500 nm and appeared to be the product detected but not separated by Fujita et al. (Photochem. Photobiol. 1981, 34, 101–105). A second adduct emitted at 460 nm, and the third was nonfluorescent. The photoadduct emitting at 500 nm was characterized by UV, fluorescence, and NMR to be an adduct from coupling of the C‐8 position of guanine to the C‐2 position of the phenothiazine ring of CPZ. The cation radical of CPZ (CPZ +) does not appear to be an intermediate since enzymatically generated CPZ + formed a product that eluted with a retention time close to that of the photoadducts, but did not emit at 520 nm.

Enhanced photodehalogenation of chlorobiphenyls

Summary The rate of photodechlorination of chlorobiphenyls in acetonitrile/water is dramatically enhanced when the compounds are irradiated in the presence of sodium borohydride. This rate enhancement is even larger in mi cellar solutions.

Borohydride-enhanced photodehalogenation of Aroclor 1232, 1242, 1254, and 1260

Abstract The photochemical dechlorination of Aroclor 1232, 1242, 1254, and 1260 was examined in the presence and absence of sodium borohydride. In both cases the photoreduction proceeded to give dechlorinated biphenyls by sequential loss of chlorines, but the photoreactions in the presence of borohydride were much faster. In the absence of the borohydride the total removal of chlorines was impractically slow, but its presence made it possible to proceed to essentially total destruction of the PCBs.

A new photochemically removable protecting group for amines

Abstract A new arylmethylsulfonyl chloride reacts with secondary or primary amines to give sulfonamides which can be photochemically cleaved, making it suitable for use as a photoremovable protecting group.

Photochemical transformations in salicylanilide photoallergy

Abstract— The photochemical transformations of 3,3′,4′,5‐tetrachlorosalicylanilide, have been characterized by isolation and spectroscopic determination of the primary and secondary photoproducts. The photoreactivity cleanly involves photochemical dechlorination; three chlorines are ultimately lost in an efficient stepwise fashion. A radical mechanism was implicated by formation of a dimer and hydrogen atom abstraction from cysteine when present during photolysis. In the presence of HSA or BSA, the initial dehalogenation leads to a photoadduct with the protein, but dehalogenation of the primary photoproduct, a trichloro compound, does not lead to an efficient photobinding to protein.

Photosensitized lysis of red blood cells by phototoxic antimalarial compounds

Abstract A family of 12 phototoxic quinolinemethanol antimalarials and three other non‐phototoxic clinically used compounds were irradiated in the presence of red blood cells to determine if the resulting hemolysis would be a reliable predictor of phototoxicity. The most phototoxic compounds from in vivo tests were also the most phototoxic in this study. Quinine caused little RBC lysis, paralleling its non‐phototoxicity in humans. The quinolinemethanol‐induced photohemolysis occurs both in the presence and absence of oxygen. Enriching the RBC with BHA and cholesterol was particularly effective at protecting the cells from photohemolysis. Other compounds offered some measure of protection, while superoxide dismutase and sodium azide, among others, afforded no protection.