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The photoinduced polymerization of acrylic monomers using dyes in a protein-restricted medium is reported. We studied dyes of different families as potential polymerization catalysts, exploiting the observation that the photophysical properties of some dyes are altered when bound to biopolymers. The light induced polymerization of acrylic monomers in the presence of bovine serum albumin or gelatin using triphenylmethane and azo dyes proceeded smoothly. Using GE Miser 120 W spotlights as a convenient illumination source, we found polymerization could be achieved in some cases within 60 min of irradiation. The polymerization rates were found to be dependent on the concentrations of the dye and the protein. In the absence of protein or dye polymerization was virtually non-existent. When the reaction mixture was blanketed with nitrogen, polymerization was observed to be faster than that that in air equilibrated samples. We believe these photopolymerizations may proceed via a free-radical pathway. Our results suggest the possible role of some of these dyes as polymerization catalysts, though they had previously seemed inert in fluid solutions.

Nonlinear multiphoton photo-cross-linking and photopolymerization of proteins and polymers in solution have been used to direct the three-dimensional assembly of micron scale objects. Two aspects of fabricated proteinatious matrixes are examined in this paper: the efficiency of protein photopolymerization and the application of fabricated matrixes as sustained release devices. The efficiency of photoactivated cross-linking of the proteins bovine serum albumin and fibrinogen, using rose bengal, have been determined and found to vary with photosensitizer concentration. This concentration dependence suggests that the mechanism for protein cross-linking is a direct hydrogen transfer between an amino acid residue of the protein and the dye molecule itself. A comparison of the surface structure of single and multiple protein oligomers is undertaken and shown to vary significantly depending on fabrication materials. Alkaline phosphatase bioactivity, upon entrapment in a protein structure, is maintained. The pro...

Debromination of 8-bromo-2′-deoxyguanosine was accomplished in high yield under neutral conditions in aqueous methanol by irradiating with visible light in the presence of methylene blue as a sensitizer and triethylamine as an electron donor. The method can be extended for the debromination of other bromoaromatic compounds.

Irradiation of epoxides in the presence of amines and sodium borohydride leads cleanly to a regioselective opening of the epoxide, giving the lesser substituted alcohol as a product.

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.

Debromination of 8-bromo-2′-deoxyguanosine was accomplished in high yield under neutral conditions in aqueous methanol by irradiating with visible light in the presence of methylene blue as a sensitizer and triethylamine as an electron donor. The method can be extended for the debromination of other bromoaromatic compounds.

A new protecting group for the alcohol functionality was devised and shown to be removed photochemically under ultraviolet light in the presence of a radical scavenger in high yields.

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.

Quantitation of the conversion of nonradioactive supercoiled DNA to its open circular or linear forms on ethidium-stained electrophoretic gels has been difficult because of differential binding of ethidium to supercoiled DNA vs other forms under different conditions and the nonlinear response of photographic film. We have developed methods for adding a linear DNA as an internal fluorescence standard to “normalize” the quantity of DNA loaded into each lane of a gel. Inclusion of a linear normalizing DNA in samples before partitioning for individual supercoil cleavage reactions allows the quantitation of the resultant species, is technically easy, and does not require quantitative application of the sample to the gel. If the presence of a normalizing DNA during supercoil cleavage is undesirable, the addition of a normalizing plasmid to each sample after supercoil cleavage (but before electrophoresis) or the quantitative application of samples containing test DNA alone to the gel gives similar data, but with increased variability. We use the normalizing DNA method in cleavage by a physical agent (ionizing radiation) and in a more complex situation, by a protein-based, light-dependent synthetic endonuclease. We show how the fraction of intact supercoiled DNA can be calculated from measurement of the cleaved and normalizing species only. The method also can be used in reactions involving the depletion of one DNA species, whether supercoiled or not, such as protein-DNA interactions as detected by gel retardation assays.

The Rose Bengal-induced photofragmentation of β-amino alcohols has been previously reported to proceed through a mechanism involving singlet oxygen sensitization, followed by attack of singlet oxygen and superoxide on the β-amino alcohol. An alternative mechanism involving electron transfer from the amine to the excited state Rose Bengal is supported by new evidence.

Photocatalytic reduction of chloroaromatics to the corresponding aromatic compounds has been accomplished using visible dyes in the presence of amines. An electron transfer mechanism is implicated by the experimental results, with the formation of an aryl chloride radical anion being the key step leading to dechlorination.

The regioselective cleavage of epoxides using visible light and a catalytic dye is reported in this study as an alternative mild synthetic approach. The epoxide radical anion is generated via visible light in an electron transfer reaction, induced by non-toxic dyes, leading to ring opening and formation of the corresponding alcohol with the hydroxyl group on the less substituted carbon in excellent yields.

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.

Titanium dioxide was shown to be generally effective as a catalyst for photobleaching many structural classes of organic dyes in aqueous solution, using visible light. However, results from study of 15 dyes indicate that photobleaching rates differ significantly from families of dyes with different functionalities, and are dependent on the light source and crystalline form of TiO2 used. Sorption characteristic on the TiO2 surface and the aqueous solubility of the dyes also play an important role in the photobleaching rate. Kinetic analysis indicates that the dye photobleaching rates can usually be approximated as pseudo-first-order kinetics. In addition to the generally proposed photocatalytic oxidation mechanism for TiO2 reactions, we observed evidence for two kinds of electron transfer mechanisms that are “photosensitized reduction” and “photosensitized oxidation”. Natural sunlight was effectively used to photobleach some of the dyes.

A new protecting group for the alcohol functionality was devised and shown to be removed photochemically under ultraviolet light in the presence of a radical scavenger in high yields.

We have constructed a synthetic photoendonuclease composed of T7 RNA polymerase linked to rose bengal. The promoter-specific polymerase confers site-specific binding, and the photosensitizer rose bengal allows light-induced DNA cleavage. Using a gentle labeling procedure, we find that the polymerase can be labeled with 1-30 rose bengals. Polymerase labeled to about 8 rose bengals per molecule retains the same efficiency and specificity of binding to promoter-containing DNA as unlabeled polymerase. At this level of rose bengal substitution, the synthetic endonuclease, in the presence of visible light, specifically cleaves linear or supercoiled DNA containing a T7 promoter. It induces frank single-strand breaks, rather than labile sites convertible to breaks upon additional treatments. Neither the free rose bengal moiety not bonded to polymerase nor the free (not bound to DNA) rose bengal-substituted polymerase cleaves DNA. Although rose bengal is an efficient generator of singlet oxygen, depletion of oxygen from reaction mixtures increases the cleavage rate. This indicates that singlet oxygen cleavage is not a major mechanism of DNA nicking by the synthetic endonuclease. At higher levels of rose bengal substitution, the labeled polymerase shows decreased binding efficiency and increased nonspecific binding to DNA without a T7 promoter; the specificity of DNA cleavage also decreases. These results indicate that the site specificity of rose bengal photocleavage by the synthetic endonuclease results from specific binding of the polymerase, and thus rose bengal photonicking reflects polymerase binding.

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.

Irradiation of epoxides in the presence of amines and sodium borohydride leads cleanly to a regioselective opening of the epoxide, giving the lesser substituted alcohol as a product.

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.

The photoreduction of a family of quinolinemethanols has been examined both in the presence and absence of exciplex-forming additives. Photoreduction of the alcohol group and cleavage of the side chain occurs on direct photolysis. However, irradiation with triethylamine led to predominant cleavage of the side chain while irradiation with 1,3-dicyanobenzene predominantly led to photoreduction of the alcohol functionality. A variety of other experiments supported the involvement of exciplexes in these transformations.

The photochemistry of mefloquine, an experimental antimalarial drug, has been examined with an eye towards understanding its comparatively low phototoxicity.

The photodechlorination of polychlorinated biphenyls (PCB's) has been studied in the presence of sodium borohydride, detergents, and exciplex-forming additives. In a family of 13 representative PCB's 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.

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.

The photochemical debromination of a series of bromobiphenyls was examined in the presence and absence of sodium borohydride. In both cases the photoreduction proceeded cleanly to give the corresponding debrominated biphenyls, but the photolyses in the presence of borohydride were accelerated up to a 100-fold. A free radical chain mechanism is involved.

The efficient fluorescence of 2-phenylquinoline compounds is readily quenched by heteroatom-containing compounds such as amines and sulfides. The mechanism of quenching involves the formation of an exciplex between the quencher and the quinoline; in a few cases a new, red-shifted emission from the exciplex was observed. The efficiency of quenching depends on the ionization potential of the quencher - the compounds having low ionization potentials quench the fluorescence at a diffusion-controlled rate.

The “Photo-Birch” reduction of o-, m-, and p-xylene, using NaBH 4 , 1,3-dicyanobenzene, and photolysis, gives 1,4-dienes as products. The regioselectivity of these reactions is greatly different from the normal Birch reduction.

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 PCB's.

The synthesis and antimalarial activity of six new 2-arylquinoline-4-methanols is described. The compounds bearing a sulfur were prepared to determine if antimalarial activity can be retained while photo-reactivity and phototoxicity is diminished by such substituents. The observed antimalarial activity of some of the new compounds show this to be possible.

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.

lrradiation of quadricyclene in solution leads to isomeric products in addition to bicyclo [2.2.1]hepta-2,5-diene, which reduces its usefulness in solar energy storage.

— 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.