Aqueous solutions of the achiral, monomeric, nucleobase mimics (2,4,6-triaminopyrimidine,T AP,and acyanuric acid derivative,C yCo6) spontaneously assemble into macroscopic homochiral domains of supramolecular polymers.T hese assemblies exhibit ah igh degree of chiral amplification. Addition of asmall quantity of one handedness of ac hiral derivative of CyCo6 generates exclusively homochiral structures.T his system exhibits the highest reported degree of chiral amplification for dynamic helical polymers or supramolecular helices.S ignificantly,h omochiral polymers comprised of hexameric rosettes with structural features that resemble nucleic acids are formed from mixtures of cyanuric acid (Cy) and ribonucleotides (l-,d -pTARC) that arise spontaneously from the reaction of TAPw ith the sugars. These findings support the hypothesis that nucleic acid homochirality was ar esult of symmetry breaking at the supramolecular polymer level.
We synthesized a novel water-soluble porphyrin THPP and its metalated derivative Zn-THPP having excellent triplet excited state quantum yields and singlet oxygen generation efficiency. When compared to U.S. Food and Drug Administration approved and clinically used sensitizer Photofrin, THPP showed ca. 2-3-fold higher in vitro photodynamic activity in different cell lines under identical conditions. The mechanism of the biological activity of these porphyrin systems has been evaluated through a variety of techniques: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, comet assay, poly(ADP-ribose)polymerase (PARP) cleavage, CM-H(2)DCFDA assay, DNA fragmentation, flow cytometric analysis, fluorescence, and confocal microscopy, which confirm the apoptotic cell death through predominantly reactive oxygen species (ROS). Moreover, THPP showed rapid cellular uptake and are localized in the nucleus of the cells as compared to Hoechst dye and Photofrin, thereby demonstrating its use as an efficient sensitizer in photodynamic therapy and live cell NIR nucleus imaging applications.
The free nucleobases and mononucleotides of RNA do not form Watson-Crick base pairs in water, a fact that presents several challenges for the prebiotic synthesis of RNA. 2,6-Diaminopurine and adenosine-5'-monophosphate (AMP) are shown to form supramolecular assemblies with cyanuric acid in water. These assemblies and their propensity to form liquid crystals suggest a possible means by which non-covalent structures might have originally selected the shape of the Watson-Crick base pairs.
The Gram-negative Aggregatibacter actinomycetemcomitans and Fusobacterium nucleatum are major causative agents of aggressive periodontal disease. Due to increase in the number of antibiotic-resistant bacteria, antimicrobial Photodynamic therapy (aPDT) seems to be a plausible alternative. In this work, photosensitization was performed on Gram-positive and Gram-negative bacteria in pure culture using new-age cationic porphyrins, namely mesoimidazolium-substituted porphyrin derivative (ImP) and pyridinium-substituted porphyrin derivative (PyP). The photophysical properties of both the sensitizers including absorption, fluorescence emission, quantum yields of the triplet excited states and singlet oxygen generation efficiencies were evaluated in the context of aPDT application. The studied porphyrins exhibited high ability to accumulate into bacterial cells with complete penetration into early stage biofilms. As compared with ImP, PyP was found to be more effective for photoinactivation of bacterial strains associated with periodontitis, without any signs of dark toxicity, owing to its high photocytotoxicity.
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