Competitive Charge Separation Pathways in a Flexible Molecular Folda-Dimer

We report the photophysical properties of a molecular folda-dimer system PDI-AnEt2-PDI, where the electron-donating N,N-diethylaniline (AnEt2) moiety bridges two electron-accepting perylene diimide (PDI) chromophores. The conformationally flexible PDI-AnEt2-PDI adopts either an open (two PDIs far apart) or folded (two PDIs within π-stacking distance) conformation, depending on the solvent environment. We characterized the photoinduced charge separation dynamics of both open and folded forms in solvents of varying polarity. The open form undergoes charge separation to give PDI•–-AnEt2•+-PDI (Bridge electron transfer) independent of solvent polarity. The folded form exhibits two charge separation photoproducts, yielding both PDI•–-AnEt2•+-PDI and PDI•–-AnEt2-PDI•+, the latter of which is formed via symmetry-breaking charge separation (SBCS) between the two π-stacked PDI chromophores. Our results further indicate that the conformational flexibility of the folda-dimer leads to unexpected excimer formation in some open form conditions. In contrast, no excimer formation is observed in the folded form, indicating that this geometry preferentially yields the SBCS instead. Our results provide insight into how conformationally flexible folda-dimer systems can be designed and built to tune competitive photophysical pathways

“Simple Methods to Derive Primary Malignant Glioma Cell Lines and Assay of Cellular Damage for Preclinical Studies”

<p>Primary malignant glioma cell lines are being used for initial screening of anticancer agents. We utilized a simple mechanical disaggregation method for deriving cell lines from tumor tissues; and a Coverslip Culture-Acridine Orange Staining method to study cellular damage. Cell lines could be grown for up to three passages within three weeks after surgery. Cell proliferation, total cellular damage, and MTT assay were studied as parameters of cytotoxic response. Frequencies of damaged cells varied in different cell lines; and increased after cytotoxic treatments under clinically relevant conditions. These methods could contribute to preclinical evaluation of treatment response before commencement of radio-chemotherapy.</p

Human Behavior-Inspired Linchpin-Directed Catalysis for Traceless Precision Labeling of Lysine in Native Proteins

The complex social ecosystem regulates the spectrum of human behavior. However, it becomes relatively easier to understand if we disintegrate the contributing factors, such as locality and interacting partners. Interestingly, it draws remarkable similarity with the behavior of a residue placed in a social setup of functional groups in a protein. Can it inspire principles for creating a unique environment for the precision engineering of proteins? We demonstrate that localization-regulated interacting partner(s) could render precise and traceless single-site modification of structurally diverse native proteins. The method targets a combination of high-frequency Lys residues through an array of reversible and irreversible reactions. However, excellent simultaneous control over chemoselectivity, site selectivity, and modularity ensures that the user-friendly protocol renders acyl group installation, including post-translational modifications (PTMs), on a single Lys. Besides, it offers a chemically orthogonal handle for the installation of probes. Also, a purification protocol integration delivers analytically pure single-site tagged protein bioconjugates. The precise labeling of a surface Lys residue ensures that the structure and enzymatic activities remain conserved post-bioconjugation. For example, the precise modification of insulin does not affect its uptake and downstream signaling pathway. Further, the method enables the synthesis of homogeneous antibody–fluorophore and antibody–drug conjugates (AFC and ADC; K183 and K249 labeling). The trastuzumab–rhodamine B conjugate displays excellent serum stability along with antigen-specific cellular imaging. Further, the trastuzumab–emtansine conjugate offers highly specific antiproliferative activity toward HER-2 positive SKBR-3 breast cancer cells. This work validates that disintegrate theory can create a comprehensive platform to enrich the chemical toolbox to meet the technological demands at the chemistry, biology, and medicine interface