Transition metal catalysis is of utmost importance for the development of sustainable processes in academia and industry. The activity and selectivity of metal complexes are typically the result of ...the interplay between ligand and metal properties. As the ligand can be chemically altered, a large research focus has been on ligand development. More recently, it has been recognized that further control over activity and selectivity can be achieved by using the “second coordination sphere”, which can be seen as the region beyond the direct coordination sphere of the metal center. Hydrogen bonds appear to be very useful interactions in this context as they typically have sufficient strength and directionality to exert control of the second coordination sphere, yet hydrogen bonds are typically very dynamic, allowing fast turnover. In this review we have highlighted several key features of hydrogen bonding interactions and have summarized the use of hydrogen bonding to program the second coordination sphere. Such control can be achieved by bridging two ligands that are coordinated to a metal center to effectively lead to supramolecular bidentate ligands. In addition, hydrogen bonding can be used to preorganize a substrate that is coordinated to the metal center. Both strategies lead to catalysts with superior properties in a variety of metal catalyzed transformations, including (asymmetric) hydrogenation, hydroformylation, C–H activation, oxidation, radical-type transformations, and photochemical reactions.
The interaction between a co‐catalyst and photocatalyst usually induces spontaneous free‐electron transfer between them, but the effect and regulation of the transfer direction on the ...hydrogen‐adsorption energy of the active sites have not received attention. Herein, to steer the free‐electron transfer in a favorable direction for weakening S−Hads bonds of sulfur‐rich MoS2+x, an electron‐reversal strategy is proposed for the first time. The core–shell Au@MoS2+x cocatalyst was constructed on TiO2 to optimize the antibonding‐orbital occupancy. Research results reveal that the embedded Au can reverse the electron transfer to MoS2+x to generate electron‐rich S(2+δ)− active sites, thus increasing the antibonding‐orbital occupancy of S−Hads in the Au@MoS2+x cocatalyst. Consequently, the increase in the antibonding‐orbital occupancy effectively destabilizes the H 1s‐p antibonding orbital and weakens the S−Hads bond, realizing the expedited desorption of Hads to rapidly generate a lot of visible H2 bubbles. This work delves deep into the latent effect of the photocatalyst carrier on cocatalytic activity.
To create a beneficial transfer direction for cultivating moderate hydrogen‐atom adsorption/desorption on a co‐catalyst, an electron‐reversal strategy is proposed that optimizes the antibonding‐orbital occupancy. The embedded Au can reverse the free‐electron transfer to MoS2+x to form electron‐rich S(2+δ)−, which causes an increased antibonding‐orbital occupancy, thus weakening S−Hads bonds for photocatalytic H2 evolution.
Scalability, optimal reagent usage, high yields, easy isolation, and cost‐effectiveness, are key for the applicability of synthetic methodologies in the production of potential therapeutics. Hydrogen ...bond surrogate (HBS) constrained α‐helical peptides (α‐helicomimics) have shown promise as therapeutics based on their efficiency to interfere with protein‐biomolecular interactions. The propyl HBS‐constrained α‐helicomimics have shown the highest helicities in both single turn and extended, α‐helices (STαH, EαH). Here we present a solution‐phase synthetic (SPS) method, for the rapid, large‐scale, low‐cost synthesis of libraries of STαH and EαH in high yields. The key to efficiency is our trimodular (M1, M2, M3) synthetic protocol where M1 is a library of HBS‐linked peptidomimetic synthons of both STαH and EαH; M2 and M3 are desired oligopeptide libraries. Advantages of the trimodular method over conventional unimodular methods are demonstrated through the synthesis of large‐scale libraries of M1, STαH, and EαH.
A cost‐effective, high‐yielding, rapid trimodular solution‐phase method has been demonstrated to synthesize the hydrogen bond surrogate (HBS) constrained single α‐helical turn and C‐terminal extended helices. The HBS‐constrained α‐helicomimic is divided into three modules and each of them was synthesized in 100 mmol scale followed by connecting them to adopt the α‐helicomimic.
Transition-metal-catalysed direct C-H bond functionalization of aliphatic amines is of great importance in organic and medicinal chemistry research. Several methods have been developed for the direct ...sp3 C-H functionalization of secondary and tertiary aliphatic amines, but site-selective functionalization of primary aliphatic amines in remote positions remains a challenge. Here, we report the direct, highly site-selective γ-arylation of primary alkylamines via a palladium-catalysed C-H bond functionalization process on unactivated sp3 carbons. Using glyoxylic acid as an inexpensive, catalytic and transient directing group, a wide array of γ-arylated primary alkylamines were prepared without any protection or deprotection steps. This approach provides straightforward access to important structural motifs in organic and medicinal chemistry without the need for pre-functionalized substrates or stoichiometric directing groups and is demonstrated here in the synthesis of analogues of the immunomodulatory drug fingolimod directly from commercially available 2-amino-2-propylpropane-1,3-diol.
High-level double-hybrid DFT simulations reveal that strong hydrogen-bond-donor catalysts (
e.g.
, ethylene glycol, guanidine, and thiourea) significantly accelerate the migration of epoxy oxygen on ...the surface of graphene oxide, enhancing the reaction rate by 6-12 orders of magnitude. These results shed light on previously puzzling experimental observations.
Double-hybrid DFT simulations predict that strong hydrogen-bond donor catalysts can significantly accelerate epoxy group migration on graphene oxide.
Тhe adequacy of chemical property predictions strongly depends on the structure representation, including the proper treatment of the tautomeric and isomeric forms. A combination of an in-house ...developed open-source tool for automatic generation of tautomers, Ambit-Tautomer, based on H-atom shift rules and standard quantum chemical (DFT) calculations is used for a detailed investigation of the possible geometric isomers, conformers and tautomers of unsubstituted and para-substituted phenylhydrazones, systems with experimentally observed unusual para-substituent effects on the intramolecular hydrogen bond (IMHB) for E-isomers of the compounds. The computational results show that the energetically preferred E-isomers are characterized by stronger IMHBs than the corresponding Z-isomers. The HN–N=C–C=N molecular fragment in the E-configurations is less sensitive to the substitution effect than the HN–N=C–C=O fragment in the isomers with Z-configuration. A probable reason for this decreased sensitivity of E-isomers to phenyl ring substitution is the more efficient conjugation and charge distribution in the HN–N=C–C=N fragment.
Designing robust bifunctional catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction in all‐pH conditions for overall water splitting (OWS) is an effective way to achieve ...sustainable development. Herein, a composite Ru‐VO2 containing Ru‐doped VO2 and Ru nanoparticles (NPs) is synthesized, and it shows a high OWS performance in full‐pH range due to their synergist effect. In particular, the OER mass activities of Ru‐VO2 at 1.53 V (vs RHE) in acidic, alkaline, and PBS solutions are ≈65, 36, and 235 times of commercial RuO2 in the same conditions. The “Ru‐VO2 || Ru‐VO2” two‐electrode electrolyzer only needs a voltage of 1.515 V (at 10 mA cm−2) in acidic water splitting, which can operate stably for 125 h at 10 mA cm−2 without significant voltage decay. In situ Raman spectra and in situ differential electrochemical mass spectrometry prove that the OER of Ru‐VO2 in acid follows the adsorption evolution mechanism. Density functional theory calculations further reveal the synergistic effect between Ru NP and Ru‐doped VO2, which breaks the hydrogen bond network formed by *OH adsorbed on the Ru single‐atom site, and thereby significantly enhances the OER activity. This work provides new insights into the design of novel bifunctional pH‐universal catalysts for OWS.
Ru‐VO2 catalysts containing Ru‐doped VO2 and Ru nanoparticles are synthesized, and it shows excellent water splitting performance in all‐pH range. The in‐situ characterizations and Theoretical calculations reveal that synergy of Ru Nanoparticles and Ru‐doped VO2 breaks the hydrogen bond network formed by *OH adsorbed on the Ru single‐atom site, and thereby significantly boosts the acidic oxygen evolution.
Photocatalytic oxygen reductive H2O2 production is a promising approach to alternative industrial anthraquinone processes while suffering from the requirement of pure O2 feedstock for practical ...application. Herein, we report a spaced double hydrogen bond (IC−H‐bond) through multi‐component Radziszewski reaction in an imidazole poly‐ionic‐liquid composite (SI‐PIL‐TiO2) and levofloxacin hydrochloride (LEV) electron donor for highly efficient and selective photocatalytic air reductive H2O2 production. It is found that the IC−H‐bond formed by spaced imino (−NH−) group of SI‐PIL‐TiO2 and carbonyl (−C=O) group of LEV can switch the imidazole active sites characteristic from a covered state to a fully exposed one to shield the strong adsorption of electron donor and N2 in the air, and propel an intenser positive potential and more efficient orbitals binding patterns of SI‐PIL‐TiO2 surface to establish competitive active sites for selectivity O2 chemisorption. Moreover, the high electron enrichment of imidazole as an active site for the 2e− oxygen reduction ensures the rapid reduction of O2. Therefore, the IC−H‐bond enables a total O2 utilization and conversion efficiency of 94.8 % from direct photocatalytic air reduction, achieving a H2O2 production rate of 1518 μmol/g/h that is 16 and 23 times compared to poly‐ionic‐liquid composite without spaced imino groups (PIL‐TiO2) and TiO2, respectively.
The spaced double hydrogen bonds in an imidazole poly ionic liquid surface can change the active site from being a covered state to a fully exposed one. This results in a more positive potential and more efficient orbital binding patterns giving better active sites for the selective photocatalytic air reductive H2O2 production.
Conjugated polymers have been investigated widely as encouraging photocatalysts for hydrogen production. However, it is still arduous for polymer photocatalysts to achieve high photocatalytic ...activity under visible light. Herein, we demonstrate an efficient design to enhance the hydrogen evolution rate (HER) of conjugated polymers through the modification of surface chemistry by introducing the hydrophilic adenine group onto the side chain. The adenine group with plentiful nitrogen atoms can form multiple hydrogen bonds with water molecules, which improve the interactions between the resulting polymer surface and water molecules, leading to improved hydrophilicity and dispersity of the polymer photocatalyst in photocatalytic reaction solution. Density functional theory calculation indicated that the introduction of adenine groups also leads to the enhanced separation of the electrostatic potential on the surface of polymer photocatalyst, which is favorable for the photocatalytic hydrogen evolution reaction. Therefore, a high HER of 36.43 mmol h−1 g−1 was achieved by the adenine-functionalized polymer PF6A-SF without using Pt cocatalyst, which is almost 42 times higher than that of the alkyl-functionalized polymer PF6-SF (0.87 mmol h−1 g−1), demonstrating that rational design of side-chain engineering is an effective design for organic photocatalysts with high photocatalytic activity.
We designed and constructed an adenine-functionalized conjugated polymer PF6A-SF as an efficient photocatalyst for hydrogen evolution from water. Without using Pt cocatalyst, a 42-fold improvement in hydrogen evolution rate has been achieved than that of alkyl-functionalized conjugated polymer PF6-SF, which represents the state-of-the-art organic polymer photocatalysts. Display omitted
•An adenine-functionalized conjugated porous polymer was developed for highly efficient photocatalytic hydrogen evolution.•The intimate contact between adenine groups and water molecules enables more efficient charge transfer and separation.•The bare adenine-functionalized conjugated polymer achieved a high HER of 36.43 mmol g−1 h−1.
Nicotine addiction begins with high-affinity binding of nicotine to acetylcholine (ACh) receptors in the brain. The end result is over 4,000,000 smoking-related deaths annually worldwide and the ...largest source of preventable mortality in developed countries. Stress reduction, pleasure, improved cognition and other central nervous system effects are strongly associated with smoking. However, if nicotine activated ACh receptors found in muscle as potently as it does brain ACh receptors, smoking would cause intolerable and perhaps fatal muscle contractions. Despite extensive pharmacological, functional and structural studies of ACh receptors, the basis for the differential action of nicotine on brain compared with muscle ACh receptors has not been determined. Here we show that at the α4β2 brain receptors thought to underlie nicotine addiction, the high affinity for nicotine is the result of a strong cation-π interaction to a specific aromatic amino acid of the receptor, TrpB. In contrast, the low affinity for nicotine at the muscle-type ACh receptor is largely due to the fact that this key interaction is absent, even though the immediate binding site residues, including the key amino acid TrpB, are identical in the brain and muscle receptors. At the same time a hydrogen bond from nicotine to the backbone carbonyl of TrpB is enhanced in the neuronal receptor relative to the muscle type. A point mutation near TrpB that differentiates α4β2 and muscle-type receptors seems to influence the shape of the binding site, allowing nicotine to interact more strongly with TrpB in the neuronal receptor. ACh receptors are established therapeutic targets for Alzheimer's disease, schizophrenia, Parkinson's disease, smoking cessation, pain, attention-deficit hyperactivity disorder, epilepsy, autism and depression. Along with solving a chemical mystery in nicotine addiction, our results provide guidance for efforts to develop drugs that target specific types of nicotinic receptors. PUBLICATION ABSTRACT
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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