Examination of the Brønsted-Evans-Polanyi relationship for the hydrogen evolution reaction on transition metals based on constant electrode potential density functional theory.

In the search for efficient and inexpensive electrocatalysts for the hydrogen evolution reaction (HER), the hydrogen binding energy is often used as a descriptor to represent the catalytic activity. The success of this approach relies on the Brønsted-Evans-Polanyi (BEP) relationship. In this study, we used constant electrode potential density functional theory calculations to examine this relationship. Eight fcc metals with a low hydrogen adsorption concentration of 1/9 were used as the model systems. We found that the HER kinetic barriers are indeed correlated to the . Both the s of the hollow site and less favourable top site correlate to the kinetic barriers; however, the correlation is better for the latter. This behaviour leads to a set of equations for estimating the HER kinetic barriers with improved accuracy that can be used to predict the HER performance of the materials with a low hydrogen adsorption concentration. This work demonstrates the importance of calculating the of a suitable adsorption site to establish good BEP relationships.

Gold-Catalyzed [3+2]-Annulations of α-Aryl Diazoketones with the Tetrasubstituted Alkenes of Cyclopentadienes: High Stereoselectivity and Enantioselectivity.

This work reports gold-catalyzed [3+2]-annulations of α-diazo ketones with highly substituted cyclopentadienes, affording bicyclic 2,3-dihydrofurans with high regio- and stereoselectivity. The reactions highlights the first success of tetrasubstituted alkenes to undergo [3+2]-annulations with α-diazo carbonyls. The enantioselective annulations are also achieved with high enantioselectivity using chiral forms of gold and phosphoric acid. Our mechanistic analysis supports that cyclopentadienes serve as nucleophiles to attack gold carbenes at the more substituted alkenes, yielding gold enolates that complex with chiral phosphoric acid to enhance the enantioselectivity.

[2,2](5,8)Picenophanedienes: Syntheses, Structural Analyses, Molecular Dynamics, and Reversible Intramolecular Structure Conversion.

This study presents an important and efficient synthetic approach to 5,8-dibromo-2,11-di-tert-butylpicene (3), with multigram scale, which was then converted to a new series of picenophanes (6-10). The tub-shaped [2,2](5,8)picenophanediene 8 with two cis-ethylene linkers was explored using X-ray crystallography. The tub-to-tub inversion proceed through the successive bending of the linkers and the barrier for isopropyl-substituted derivative 10 was experimentally estimated to be 18.7 kcal/mol. Picenophanes with a large π-system and semi-rigid structure exhibited anomalous photophysical properties. The ethano-bridged picenophane shows the weak exciton delocalization while the cis-ethylene-bridged picenophane exhibits dual emission rendered by the weakly delocalized exciton and excimer. With the aid of the ultrafast time-resolved emission spectroscopy, the mechanism of the excimer formation is resolved, showing a unique behavior of two-state reversible reaction with fast structural deformation whose lifetime is around 20 ps at 298 K. This work demonstrates that the slight difference in the bridge of tub-shaped picenophanes renders distinct photophysical behavior, revealing the potential of harnessing inter-moiety reaction in the picenophane systems.

Gold-Catalyzed Oxidative Aminocyclizations of Propargyl Alcohols and Propargyl Amines to Form Two Distinct Azacyclic Products: Carbene Formation versus a 3,3-Sigmatropic Shift of an Initial Intermediate.

Gold-catalyzed oxidations of propargyl alcohols with nitrones by using a P(tBu)2 (o-biphenyl)Au+ catalyst, afforded bicyclic annulation products from the Mannich reactions of gold enolates. The same reactions of propargyl amines with nitrones by using the same gold catalyst gave distinct oxoarylation products. Our DFT calculations indicate that oxidation of propargyl alcohols with nitrones by using electron-rich gold catalysts lead only to gold carbenes, which can generate gold enolates or oxoarylation intermediates with enolate species having a barrier smaller than that of oxoarylation species.

Gold(I)-Catalyzed Highly Diastereo- and Enantioselective Cyclization-[4+3] Annulation Cascades between 2-(1-Alkynyl)-2-alken-1-ones and Anthranils.

This work reports gold-catalyzed [4+3]-annulations of 2-(1-alkynyl)-2-alken-1-ones with anthranils to yield epoxybenzoazepine products with excellent exo-diastereoselectivity (dr>25:1). The utility of this new gold catalysis is manifested by applicable substrates over a broad scope. More importantly, the enantioselective versions of these [4+3]-cycloadditions have been developed satisfactorily with chiral gold catalysts under ambient conditions (DCM, 0 °C); the ee levels range from 88.0-99.9 %. With DFT calculations, we postulate a stepwise pathway to rationalize the preferable exo-stereoselection.

Copper-Catalyzed Decarboxylative Difluoromethylation.

We report herein a highly efficient Cu-catalyzed protocol for the conversion of aliphatic carboxylic acids to the corresponding difluoromethylated analogues. This robust, operationally simple and scalable protocol tolerates a variety of functional groups and can convert a diverse array of acid-containing complex molecules to the alkyl-CF2H products. Mechanistic studies support the involvement of alkyl radicals.

Data-Driven Models for Predicting Intrinsically Disordered Protein Polymer Physics Directly from Composition or Sequence.

The molecular-level understanding of intrinsically disordered proteins is challenging due to experimental characterization difficulties. Computational understanding of IDPs also requires fundamental advances, as the leading tools for predicting protein folding (e.g., AlphaFold), typically fail to describe the structural ensembles of IDPs. The focus of this paper is to 1) develop new representations for intrinsically disordered proteins and 2) pair these representations with classical machine learning and deep learning models to predict the radius of gyration and derived scaling exponent of IDPs. Here, we build a new physically-motivated feature called the bag of amino acid interactions representation, which encodes pairwise interactions explicitly into the representation. This feature essentially counts and weights all possible non-bonded interactions in a sequence and thus is, in principle, compatible with arbitrary sequence lengths. To see how well this new feature performs, both categorical and physically-motivated featurization techniques are tested on a computational dataset containing 10,000 sequences simulated at the coarse-grained level. The results indicate that this new feature outperforms the other purely categorical and physically-motivated features and possesses solid extrapolation capabilities. For future use, this feature can potentially provide physical insights into amino acid interactions, including their temperature dependence, and be applied to other protein spaces.

First-Principles Evaluation of One-Dimensional Metal-Organic Frameworks for Electrocatalytic C-H Activation of Natural Gas.

To replace the oxygen evolution reaction with thermodynamically more favorable and economically more profitable methane and ethane (the major components of natural gas) electrochemical partial oxidation, we employed constant electrode potential density functional theory calculations to screen 20 one-dimensional metal-organic frameworks containing heteroatom-substituted benzene as electrocatalysts. By computing the Pourbaix diagrams, O-H binding energies, and C-H activation barriers, we determined that although none of these catalysts were able to activate methane, one was able to hydroxylate ethane to ethanol with facile kinetics, making it a promising electrocatalyst for natural gas oxidation.

Copper-catalyzed carbo-difluoromethylation of alkenes via radical relay.

Organic molecules that contain alkyl-difluoromethyl moieties have received increased attention in medicinal chemistry, but their synthesis in a modular and late-stage fashion remains challenging. We report herein an efficient copper-catalyzed radical relay approach for the carbo-difluoromethylation of alkenes. This approach simultaneously introduces CF2H groups along with complex alkyl or aryl groups into alkenes with regioselectivity opposite to traditional CF2H radical addition. We demonstrate a broad substrate scope and a wide functional group compatibility. This scalable protocol is applied to the late-stage functionalization of complex molecules and the synthesis of CF2H analogues of bioactive molecules. Mechanistic studies and density functional theory calculations suggest a unique ligand effect on the reactivity of the Cu-CF2H species.