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Creators/Authors contains: "Jabeen, Shakeela"

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  2. Abstract

    A density functional theoretical (DFT) study is presented, implicating a1O2oxidation process to reach a dihydrobenzofuran from the reaction of the natural homoallylic alcohol, glycocitrine. Our results predict an interconversion between glycocitrine and aniso‐hydroperoxide intermediate [R(H)O+O] that provides a key path in the chemistry which then follows. Formations of allylic hydroperoxides are unlikely from a1O2‘ene’ reaction. Instead, the dihydrobenzofuran arises by1O2oxidation facilitated by a 16° curvature of the glycocitrine ring imposed by a pyramidalN‐methyl group. This curvature facilitates the formation of theiso‐hydroperoxide, which is analogous to theisospecies CH2I+Iand CHI2+Iformed by UV photolysis of CH2I2and CHI3. Theiso‐hydroperoxide is also structurally reminiscent of carbonyl oxides (R2C=O+O) formed in the reaction of carbenes and oxygen. Our DFT results point to intermolecular process, in which theiso‐hydroperoxide's fate relates to O‐transfer and H2O dehydration reactions for new insight into the biosynthesis of dihydrobenzofuran natural products.

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  3. Abstract

    Compounds have been devised whose supportive actions make them important adjuvants in the priming of photosensitization to selectively target cancer cells. Here, we highlight the paper by Maytin and Hasan in this issue ofPhotochemistry & Photobiology, which describes adjuvants methotrexate, 5‐fluorouracil, vitamin D and its analogs leading to improved photodynamic therapy outcome. These small molecule adjuvants act by different mechanisms to enhance the cytotoxicity in tumor cells and the therapeutic effect in cancers. These findings add to the list of strategies for enhancement of photodynamic therapy.

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  4. Abstract

    The sensitized photooxidation ofortho‐prenyl phenol is described with evidence that solvent aproticity favors the formation of a dihydrobenzofuran [2‐(prop‐1‐en‐2‐yl)‐2,3‐dihydrobenzofuran], a moiety commonly found in natural products. Benzene solvent increased the total quenching rate constant (kT) of singlet oxygen with prenyl phenol by ~10‐fold compared to methanol. A mechanism is proposed with preferential addition of singlet oxygen to prenyl site due to hydrogen bonding with the phenol OH group, which causes a divergence away from the singlet oxygen ‘ene’ reaction toward the dihydrobenzofuran as the major product. The reaction is a mixed photooxidized system since an epoxide arises by a type I sensitized photooxidation.

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  5. Abstract

    A unique approach is used to relate the HOMO‐LUMO energy difference to the difference between the ionization potential (IP) and electron affinity (EA) to assist in deducing not only the colors, but also chromophores in elemental nonmetals. Our analysis focuses on compounds with lone pair electrons and σ electrons, namely X2(X = F, Cl, Br, I), S8and P4. For the dihalogens, the [IP – EA] energies are found to be: F2(12.58 eV), Cl2(8.98 eV), Br2(7.90 eV), I2(6.78 eV). We suggest that theinterahalogen X–X bond itself is the chromophore for these dihalogens, in which the light absorbed by the F2, Cl2, Br2, I2leads to longer wavelengths in the visible by a π → σ* transition. Trace impurities are a likely case of cyclic S8which contains amounts of selenium leading to a yellow color, where the [IP – EA] energy of S8is found to be 7.02 eV. Elemental P4with an [IP – EA] energy of 9.09 eV contains a tetrahedral and σ aromatic structure. In future work, refinement of the analysis will be required for compounds with π electrons and σ electrons, such as polycyclic aromatic hydrocarbons (PAHs).

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