PHOTOREACTIVITY OF HYDROXYPSORALENS AND THEIR PHOTOBIOLOGICAL EFFECTS IN BACILLUS SUBTILIS*

Abstract— Although psoralen and many substituted psoralens are potent skin-photosensitizing agents, hydroxypsoralens are not. A satisfactory molecular interpretation of this structural specificity has been given in terms of dissociation of the hydroxyl group of 5- and 8-hydroxypsoralens in their excited states. The dissociation process in the S₁ state effectively competes with S₁→T₁ intersystem crossing, thus reducing the photoreactive T₁ population. The T₁ states of the anions are more delocalized than those of neutral psoralens so that they are less reactive toward photocycloaddition with pyrimidine bases of DNA. The lack of significant phosphorescence of hydroxypsoralens in ionizing solvent or in the presence of base at low temperatures (14–77 K.) indicates ineffective S₁→T₁ and/or effective T₁→S₀ intersystem crossing. These factors make hydroxypsoralens unreactive, electronically and kinetically, as skin photosensitizers, which are known to react with DNA. In correlation with the hydroxypsoralens' spectroscopic characterization, they are also found to be ineffective or less effective photosensitizers in Bacillus subtilis.     

EXCITED STATES AND PHOTOBIOLOGICAL PROPERTIES OF POTENTIAL DNA CROSS-LINKING AGENTS, THE BENZODIPYRONES

Abstract —Potential DNA cross-linking agents, benzo{1,2-b:4,5-b'}dipyran-2,8-dione ( cis -benzodipyrone) and benzo{1,2-b:4,5-b'}dipyran-2,7-dione ( trans -benzodipyrone), have been synthesized. The excited triplet states of these reagents resemble those of other coumaryl derivatives in their spectroscopic assignments and characteristics and thus their reactivites. In particular, trans -benzodipyrone is significantly more reactive toward pyrimidine bases in solution than the other coumaryl derivatives examined, by virtue of its possessing two reactive pyrone C=C bonds within the molecular framework. The unique reactivity of trans -benzodipyrone, with its two reactive pyrone bonds across the long molecular axis, appears to be reflected in its ability to photoinduce mutation in certain Bacillus subtilis strains. This preliminary study provides data that will be useful in designing experiments to elucidate the molecular mechanisms for the biological activities of these compounds.     

Microbiological detection and quantitation of bioactive compounds in vegetation matrix by laser light scattering

Summary New approaches have been developed for the assessment of low levels of bioactive substances such as pesticides, organic and inorganic toxicants, as well as growth stimulating substances present in vegetation matrices. The new technology uses a laser /bacterial biossay which is capable off differentiating between various bioactive substances based on their mechanism of action, i.e., toxicity or nutritional fortification at the molecular/cellular level. The system uses a battery of isogeneic Bacillus subtilis mutant strains that were genetically constructed to respond differentially to specific toxicants. The response in terms of growth inhibition/stimulation is monitored by differential light scattering of a laser which is integrated with a computerized system that collects and analyzes the data. Making 1200 measurements on each sample set within 2 to 4 seconds, complete bioresponse data including concentration-related response is obtained on most samples within 60 min. By utilizing a non-toxic cocktail that was developed to solubilize and disperse water insoluble materials into an aqueous matrix, a number of pesticides including carbaryl, malation, chlorsulfuron, glyphosate, tributyltin, and beta-exotoxin could be assayed, specifically characterized, and their concentration directly correlated with the bioresponse of the bacterial strains. Since there was a differential response between mutant bacteria to each compound, a profile unique to each pesticide could be developed and stored in a software recognition library. Finally, the various pesticides could be detected in a vegetation matrix, e.g., citrus leaf, without using a chemical/physical extraction procedure. In addition, the effect of the leaf matrix on the bacterial response could be assessed. Thus, the laser-bacterial assay promises to be a rapid and inexpensive analytical tool for chemical assay in a complex matrix.