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1. Optomagneto control of singlet fission charge multiplication dynamics in single organic semiconductor crystals

   https://doi.org/10.1364/CLEO_FS.2023.FF2G.4  

   Mayonado, Gina; Zhu, Fangyi; Goldthwaite, Winston; Zhu, Liangdong; Anthony, John E.; Ostroverkhova, Oksana; Graham, Matt W. (January 2023, Optica Publishing Group)

   Over a 0-7 T range, transient absorption microscopy on anthradithiophene organic crystals shows that singlet to triplet pair state conversion is anticorrelated with fluorescence yield. This shows how the dominant singlet fission charge multiplication pathway can be switched-off with increasing B-field or by changing the molecular packing motifs. 

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2. DNA capture by a CRISPR-Cas9–guided adenine base editor

   https://doi.org/10.1126/science.abb1390  

   Lapinaite, Audrone; Knott, Gavin J.; Palumbo, Cody M.; Lin-Shiao, Enrique; Richter, Michelle F.; Zhao, Kevin T.; Beal, Peter A.; Liu, David R.; Doudna, Jennifer A. (July 2020, Science)

   CRISPR-Cas–guided base editors convert A•T to G•C, or C•G to T•A, in cellular DNA for precision genome editing. To understand the molecular basis for DNA adenosine deamination by adenine base editors (ABEs), we determined a 3.2-angstrom resolution cryo–electron microscopy structure of ABE8e in a substrate-bound state in which the deaminase domain engages DNA exposed within the CRISPR-Cas9 R-loop complex. Kinetic and structural data suggest that ABE8e catalyzes DNA deamination up to ~1100-fold faster than earlier ABEs because of mutations that stabilize DNA substrates in a constrained, transfer RNA–like conformation. Furthermore, ABE8e’s accelerated DNA deamination suggests a previously unobserved transient DNA melting that may occur during double-stranded DNA surveillance by CRISPR-Cas9. These results explain ABE8e-mediated base-editing outcomes and inform the future design of base editors. 

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3. Isolation of a Novel Pythium Species, P. thermoculicivorax, and Trichoderma sp. from Natural Enzootic Mosquito Larval Infections

   https://doi.org/10.3390/jof10030199  

   Joseph, Ross; Darrisaw, Constance; Lloyd, Aaron; Hoel, David; Keyhani, Nemat O (March 2024, Journal of Fungi)

   Only a handful of microbial mosquito larval pathogens have been described to date. Sampling several natural enzootic infections of mosquito larvae in southwestern Florida indicated the presence of microbial pathogens capable of extensive larval mortality. A microscopic analysis of one sample site revealed extensive apparent growth of a Pythium-like microbe on mosquito larvae, with the highest degree of infection observed in the siphon and head regions. Structures consistent with sporangia were seen on infected insects after lactophenol blue staining, and higher-resolution scanning electron microscopy (SEM) micrographs showed sporangia and encysted zoospores targeting the head and siphon regions. The isolate was single-colony purified, and molecular identification targeting the ITS and COX1 loci coupled to phylogenetic reconstruction indicated that the isolate belonged to the Pythium genus but was distinct from its closest characterized species, P. inflatum. Morphological features were characterized, with the isolate showing rapid growth on all mycological media tested and relatively high thermotolerance, capable of robust growth at 37 °C; hence, it was designated P. thermoculicivorax. Sampling from a second series of natural infections of mosquito larvae resulted in the molecular identification of three Trichoderma isolates, one with high similarity to T. strigosum and the other two clustering closely with T. asperellum. These data highlight the occurrence of natural enzootic infections of mosquito larvae, potentially as a resource for the identification of new mosquito pathogens. 

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4. Colossal Strain Tuning of Ferroelectric Transitions in KNbO ₃ Thin Films

   https://doi.org/10.1002/adma.202408664  

   Hazra, Sankalpa; Schwaigert, Tobias; Ross, Aiden; Lu, Haidong; Saha, Utkarsh; Trinquet, Victor; Akkopru‐Akgun, Betul; Gregory, Benjamin_Z; Mangu, Anudeep; Sarker, Suchismita; et al (November 2024, Advanced Materials)

   Abstract Strong coupling between polarization (P) and strain (ɛ) in ferroelectric complex oxides offers unique opportunities to dramatically tune their properties. Here colossal strain tuning of ferroelectricity in epitaxial KNbO₃thin films grown by sub‐oxide molecular beam epitaxy is demonstrated. While bulk KNbO₃exhibits three ferroelectric transitions and a Curie temperature (T_c) of ≈676 K, phase‐field modeling predicts that a biaxial strain of as little as −0.6% pushes itsT_c> 975 K, its decomposition temperature in air, and for −1.4% strain, toT_c> 1325 K, its melting point. Furthermore, a strain of −1.5% can stabilize a single phase throughout the entire temperature range of its stability. A combination of temperature‐dependent second harmonic generation measurements, synchrotron‐based X‐ray reciprocal space mapping, ferroelectric measurements, and transmission electron microscopy reveal a single tetragonal phase from 10 K to 975 K, an enhancement of ≈46% in the tetragonal phase remanent polarization (P_r), and a ≈200% enhancement in its optical second harmonic generation coefficients over bulk values. These properties in a lead‐free system, but with properties comparable or superior to lead‐based systems, make it an attractive candidate for applications ranging from high‐temperature ferroelectric memory to cryogenic temperature quantum computing. 

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5. Work function and temperature dependence of electron tunneling through an N-type perylene diimide molecular junction with isocyanide surface linkers

   https://doi.org/10.1039/C7NR06461F  

   Smith, Christopher E.; Xie, Zuoti; Bâldea, Ioan; Frisbie, C. Daniel (January 2018, Nanoscale)

   Conducting probe atomic force microscopy (CP-AFM) was employed to examine electron tunneling in self-assembled monolayer (SAM) junctions. A 2.3 nm long perylene tetracarboxylic acid diimide (PDI) acceptor molecule equipped with isocyanide linker groups was synthesized, adsorbed onto Ag, Au and Pt substrates, and the current–voltage ( I – V ) properties were measured by CP-AFM. The dependence of the low-bias resistance ( R ) on contact work function indicates that transport is LUMO-assisted (‘n-type behavior’). A single-level tunneling model combined with transition voltage spectroscopy (TVS) was employed to analyze the experimental I – V curves and to extract the effective LUMO position ε l = E LUMO − E F and the effective electronic coupling ( Γ ) between the PDI redox core and the contacts. This analysis revealed a strong Fermi level ( E F ) pinning effect in all the junctions, likely due to interface dipoles that significantly increased with increasing contact work function, as revealed by scanning Kelvin probe microscopy (SKPM). Furthermore, the temperature ( T ) dependence of R was found to be substantial. For Pt/Pt junctions, R varied more than two orders of magnitude in the range 248 K < T < 338 K. Importantly, the R ( T ) data are consistent with a single step electron tunneling mechanism and allow independent determination of ε l , giving values compatible with estimates of ε l based on analysis of the full I – V data. Theoretical analysis revealed a general criterion to unambiguously rule out a two-step transport mechanism: namely, if measured resistance data exhibit a pronounced Arrhenius-type temperature dependence, a two-step electron transfer scenario should be excluded in cases where the activation energy depends on contact metallurgy. Overall, our results indicate (1) the generality of the Fermi level pinning phenomenon in molecular junctions, (2) the utility of employing the single level tunneling model for determining essential electronic structure parameters ( ε l and Γ ), and (3) the importance of changing the nature of the contacts to verify transport mechanisms. 

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