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1. Chiral Brønsted acid-controlled intermolecular asymmetric [2 + 2] photocycloadditions

   https://doi.org/10.1038/s41467-021-25878-9  

   Sherbrook, Evan M.; Genzink, Matthew J.; Park, Bohyun; Guzei, Ilia A.; Baik, Mu-Hyun; Yoon, Tehshik P. (September 2021, Nature Communications)

   Abstract Control over the stereochemistry of excited-state photoreactions remains a significant challenge in organic synthesis. Recently, it has become recognized that the photophysical properties of simple organic substrates can be altered upon coordination to Lewis acid catalysts, and that these changes can be exploited in the design of highly enantioselective catalytic photoreactions. Chromophore activation strategies, wherein simple organic substrates are activated towards photoexcitation upon binding to a Lewis acid catalyst, rank among the most successful asymmetric photoreactions. Herein, we show that chiral Brønsted acids can also catalyze asymmetric excited-state photoreactions by chromophore activation. This principle is demonstrated in the context of a highly enantio- and diastereoselective [2+2] photocycloaddition catalyzed by a chiral phosphoramide organocatalyst. Notably, the cyclobutane products arising from this method feature atrans-cisstereochemistry that is complementary to other enantioselective catalytic [2+2] photocycloadditions reported to date. 

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2. Direct and indirect targets of the arabidopsis seed transcription factor ABSCISIC ACID INSENSITIVE3

   https://doi.org/10.1111/tpj.14854  

   Tian, Ran; Wang, Fangfang; Zheng, Qiaolin; Niza, Venus M. A. G. E.; Downie, A. Bruce; Perry, Sharyn E. (June 2020, The Plant Journal)

   SUMMARY Arabidopsis thalianaABSCISIC ACID INSENSITIVE3 (ABI3) is a transcription factor in the B3 domain family. ABI3, along with B3 domain transcription factors LEAFY COTYLEDON2 (LEC2) and FUSCA3 (FUS3), and LEC1, a subunit of the CCAAT box‐binding complex, form the so‐called LAFL network to control various aspects of seed development and maturation. ABI3 also contributes to the abscisic acid (ABA) response. We report on chromatin immunoprecipitation‐tiling array experiments to map binding sites for ABI3 globally. We also assessed transcriptomes in response to ABI3 by comparing developingabi3‐5and wild‐type seeds and combined this information to ascertain direct and indirect responsive ABI3 target genes. ABI3 can induce and repress its transcription of target genes directly and some intriguing differences exist incismotifs between these groups of genes. Directly regulated targets reflect the role of ABI3 in seed maturation, desiccation tolerance, entry into a quiescent state and longevity. Interestingly, ABI3 directly represses a gene encoding a microRNA (MIR160B) that targetsAUXIN RESPONSE FACTOR(ARF)10andARF16that are involved in establishment of dormancy. In addition, ABI3, like FUS3, regulates genes encodingMIR156but while FUS3 only induces genes encoding this product, ABI3 induces these genes during the early stages of seed development, but represses these genes during late development. The interplay between ABI3, the otherLAFLgenes, and theVP1/ABI3‐LIKE(VAL) genes, which are involved in the transition to seedling development are examined and reveal complex interactions controlling development. 

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3. Efficient scavenging of Criegee intermediates on water by surface-active cis-pinonic acid

   https://doi.org/10.1039/c7cp03869k  

   Enami, Shinichi; Colussi, A. J. (January 2017, Physical Chemistry Chemical Physics)

   null (Ed.)

   cis -Pinonic acid (CPA), the main product of the atmospheric oxidation of biogenic α-pinene emissions and a major component of secondary organic aerosol (SOA), is a potentially key species en route to extremely low volatility compounds. Here, we report that CPA is an exceptionally efficient scavenger of Criegee intermediates (CIs) on aqueous surfaces. Against expectations, millimolar CPA (a surface-active C 10 keto-carboxylic acid possessing a rigid skeleton) is able to compete with 23 M bulk water for the CIs produced in the ozonolysis of sesquiterpene solutes by O 3 (g) on the surface of a water:acetonitrile solvent. The significance of this finding is that CPA reactions with sesquiterpene CIs on the surface of aqueous organic aerosols would directly generate C 25 species. The finding that competitive reactions at the air–liquid interface depend on interfacial rather than bulk reactant concentrations should be incorporated in current chemical models dealing with SOA formation, growth and aging. 

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4. Formation and detection of metastable formic acid in a supersonic expansion: High resolution infrared spectroscopy of the jet-cooled cis -HCOOH conformer

   https://doi.org/10.1063/5.0093401  

   Doney, Kirstin D.; Kortyna, Andrew; Chan, Ya-Chu; Nesbitt, David J. (May 2022, The Journal of Chemical Physics)

   High-resolution direct absorption infrared spectra of metastable cis-formic acid (HCOOH) trapped in a cis-well resonance behind a 15 kcal/mol barrier are reported for the first time, with the energetically unstable conformer produced in a supersonic slit plasma expansion of trans-formic acid/H 2 mixtures. We present a detailed high-resolution rovibrational analysis for cis-formic acid species in the OH stretch ( ν 1 ) fundamental, providing first precision vibrational band origin, rotational constants, and term values, which in conjunction with ab initio calculations at the couple-cluster with single, double, and perturbative triple [CCSD(T)]/ANOn (n = 0, 1, 2) level support the experimental assignments and establish critical points on the potential energy surface for internal rotor trans-to-cis isomerization. Relative intensities for a- and b-type transitions observed in the spectra permit the transition dipole moment components to be determined in the body fixed frame and prove to be in good agreement with ab initio CCSD(T) theoretical estimates but in poor agreement with simple bond-dipole predictions. The observed signal dependence on H 2 in the discharge suggests the presence of a novel H atom radical chemical mechanism for strongly endothermic “up-hill” internal rotor isomerization between trans- and cis-formic acid conformers. 

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5. Molecular switching in transcription through splicing and proline-isomerization regulates stress responses in plants

   https://doi.org/10.1038/s41467-024-44859-2  

   Theisen, Frederik Friis; Prestel, Andreas; Elkjær, Steffie; Leurs, Yannick_H A; Morffy, Nicholas; Strader, Lucia C; O’Shea, Charlotte; Teilum, Kaare; Kragelund, Birthe B; Skriver, Karen (December 2024, Nature Communications)

   Abstract TheArabidopsis thalianaDREB2A transcription factor interacts with the negative regulator RCD1 and the ACID domain of subunit 25 of the transcriptional co-regulator mediator (Med25) to integrate stress signals for gene expression, with elusive molecular interplay. Using biophysical and structural analyses together with high-throughput screening, we reveal a bivalent binding switch in DREB2A containing an ACID-binding motif (ABS) and the known RCD1-binding motif (RIM). The RIM is lacking in a stress-induced DREB2A splice variant with retained transcriptional activity. ABS and RIM bind to separate sites on Med25-ACID, and NMR analyses show a structurally heterogeneous complex deriving from a DREB2A-ABS proline residue populatingcis- andtrans-isomers with remote impact on the RIM. Thecis-isomer stabilizes an α-helix, while thetrans-isomer may introduce energetic frustration facilitating rapid exchange between activators and repressors. Thus, DREB2A uses a post-transcriptionally and post-translationally modulated switch for transcriptional regulation. 

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