History Of Chemistry Research Articles

New Ion-Exchange Membranes Derived from Polyketone

The centre piece at the heart of numerous energy storage and conversion devices, such as fuel cells and redox flow batteries, is the ion-exchange membrane (IEM). This typically polymeric material is responsible for the migration of ionic species, separation of fuel stocks and for providing additional support to the electrode assemblies. As a result, IEMs are required to possess excellent stability (both thermal and chemical), long lifetimes, electrical insulation, and high ionic conductivity and specificity. Current state-of-the-art polymer electrolytes possessing the more desirable properties tend to come with a price tag that can render their use in energy storage/conversion technologies somewhat cost prohibitive [1]. This has created a strong driving force aimed towards new, cheaper but still high performing materials, for use in energy storage/exchange systems. The copolymerization of carbon monoxide and ethylene (two readily available and cheap feedstocks) leads to the formation of polyketone, a high performance thermoplastic that has found many applications resulting in its global production of thousands of tonnes per annum. The alternating 1,4-dicarbonyl functionality of aliphatic polyketone enables access, via classic Paal-Knorr chemistry, to a variety of new functionalized polymers [2]. Here we present a new ion conducting polymeric material derived from polyketone, that possess N-functionalized pyrrole units in the backbone (FPK) [3]. Ion-conductivities on the order of 10.6 and 8.6 mScm-1 for the hydroxide and iodide forms of methylated FPKs have been achieved at 80 oC, with the hydroxide FPK demonstrating high resistance towards alkaline conditions for over 20 hours at 80 oC. The flexibility in the choice of the N-substituent renders these new materials higher tailorable and potentially useful in a range of energy storage/conversion technologies as either proton or anion exchange membranes. Acknowledgements The authors wish to thank the Strategic Project of the University of Padova “Materials for Membrane-Electrode Assemblies to Electric Energy Conversion and Storage Devices (MAESTRA)” for funding. V.D.N. thanks the University Carlo III of Madrid for granting him the “Catedra de Excelentia” (Chair of Excellence).

Exact and exclusive electron localization indices within QTAIM atomic basins

Novel measures of electron (de)localization within the Quantum Theory of Atoms in Molecules (QTAIM) atomic basins are presented which, unlike orthodox localization indices (LIs), are fully exclusive and can be easily visualized. This work shows that QTAIM-defined LIs describe a portion of interatomic delocalized electrons; hence, the chemical/physical interpretation of orthodox LIs is misleading. Using the recently introduced Fragment, Atomic, Localized, Delocalized, and Interatomic (FALDI) density decomposition technique we derive two novel sets of LIs and delocalization indices (DIs), by accounting for the overlap between localized and delocalized density functions. The FALDI-based LIs and DIs perfectly recover chemically expected core and bonded electron count. Usefulness of new (de)localization indices and their 3D representations were demonstrated on a number of examples, including formamide and benzene. We therefore expect that the scheme reported in this work will provide a valuable stepping stone between classical conceptual chemistry and quantum chemical topology. © 2018 Wiley Periodicals, Inc.

Discovery of a Short-Chain Dehydrogenase from Catharanthus roseus that Produces a New Monoterpene Indole Alkaloid.

Plant monoterpene indole alkaloids, a large class of natural products, derive from the biosynthetic intermediate strictosidine aglycone. Strictosidine aglycone, which can exist as a variety of isomers, can be reduced to form numerous different structures. We have discovered a short‐chain alcohol dehydrogenase (SDR) from plant producers of monoterpene indole alkaloids (Catharanthus roseus and Rauvolfia serpentina) that reduce strictosidine aglycone and produce an alkaloid that does not correspond to any previously reported compound. Here we report the structural characterization of this product, which we have named vitrosamine, as well as the crystal structure of the SDR. This discovery highlights the structural versatility of the strictosidine aglycone biosynthetic intermediate and expands the range of enzymatic reactions that SDRs can catalyse. This discovery further highlights how a sequence‐based gene mining discovery approach in plants can reveal cryptic chemistry that would not be uncovered by classical natural product chemistry approaches.

Synthesis of new chiral bis-imidazolidin-4-ones: comparison between the classic method and green chemistry conditions

Synthesis of new chiral bis-imidazolidin-4-ones: comparison between the classic method and green chemistry conditions

Investigation of curing rates of bio-based thiol-ene films from diallyl 2,5-furandicaboxylate

The bio-based monomer, 2,5-furandicarboxylic acid, has been adapted to classic thiol-ene chemistry by derivatization of the acid with allyl alcohol. This new monomer has allowed for the synthesis of new thermoset systems, capable of forming green, sustainable materials through UV-crosslinking. In this study, the synthesis of the new monomer along with thorough kinetic studies of the new thermoset systems are presented. In order to determine kinetic values for the systems, all reactions have been followed by real-time FT-IR. Initially, a study of three different photoinitiators is performed on a classic TEMPIC-TATATO system, in order to determine the superior initiator for the new systems. The new monomer is crosslinked with five different thiol compounds in both stoichiometric and off-stoichiometric ratios, yielding an array of bio-based thermosets. The properties of these systems are determined through DSC, TGA and tensile testing, allowing determination of the systems with superior properties. In general, most systems proved to cure fully, with the exception of issues encountered from thiols with long ethoxylated chains.

Reinventing Fenton Chemistry: Iron Oxychloride Nanosheet for pH-Insensitive H2O2 Activation

This study intends to reinvent classical Fenton chemistry by enabling the Fe(II)/Fe(III) redox cycle to occur on a newly developed FeOCl nanosheet catalyst for facile hydroxyl radical (•OH) generation from H2O2 activation. This approach overcomes challenges such as low operating pH and large sludge production that have prevented a wider use of otherwise attractive Fenton chemistry for practical water treatment, in particular, for the destruction of recalcitrant pollutants through nonselective oxidation by •OH. We demonstrate that FeOCl catalysts exhibit the highest performance reported in the literature for •OH production and organic pollutant destruction over a wide pH range. We further elucidate the mechanism of rapid conversion between Fe(III) and Fe(II) in FeOCl crystals based on extensive characterizations. Given the low-cost raw material and simple synthesis and regeneration, FeOCl catalysts represent a critical advance toward application of iron-based advanced oxidation in real practice.

Molecular modeling of immersion optical clearing of biological tissues.

The interaction of six low-molecular tissue-clearing agents (1,2 and 1,3-propanediol, ethylene glycol, glycerol, xylitol, sorbitol) with the collagen mimetic peptide (GPH)3 was studied by applying the methods of classical molecular dynamics (GROMACS), molecular docking (AutoDock Vina) and quantum chemistry (PM6 and B3LYP). The spatial configurations of intermolecular complexes were determined and interaction energies calculated. The dependence of the volume occupied by the collagen peptide on the clearing agent concentration in an aqueous solution was calculated. This dependence is not linear, and has a maximum for almost all the agents in the study. The correlations between the optical clearing potential and intermolecular interactions parameters, such as the time of an agent being in a hydrogen-bonded state, and the relative probability of formation of double hydrogen bonds and interaction energies, were determined. Using the correlations determined, we predicted the numeric value of the optical clearing potential of dextrose molecules in rat skin, which correlates with experimental data. A molecular mechanism of tissue optical clearing within the post-diffusion stage is suggested. Graphical abstract The molecular modeling of the interaction between clearing agents and collagen.

Computational Design, Synthesis, and Structure Property Evaluation of 1,3-Thiazole-Based Color-Tunable Multi-heterocyclic Small Organic Fluorophores as Multifunctional Molecular Materials.

Probing the chemical space of luminescent organic materials built on novel cores is highly imperative for its potential to expand the horizons of advanced functional materials. Small organic fluorophores possessing therapeutic traits can contribute to theranostics. We coupled computational and classical synthetic chemistry strategies for the rational design of 5-(hetero-2-yl)-1,3-thiazoles as color-tunable fluorophore core. With the aid of DFT and TD-DFT, we prove that the multi-heterocyclic system is built on a thiazole-het core with three inherent tunable sites on thiazole (C2, C4, and C5) capable of accommodating a panoply of substituents as a multifunctional molecular materials' platform. This de novo design offered unprecedented freedom to control strength and direction of charge transfer by varying donor-acceptor fragments. A 30-member fluorophore library built on thiazole-thiophene/furan core was accomplished using commercial reagents by a simple [4 + 1] synthesis. Structure-photophysical property studies revealed large Stokes shift, positive solvatochromism, acidochromism, and color tunability in different solvents and were rationalized using computational calculations. In vitro studies indicated 1a to be active against HL-60 cell lines, suggesting the possibility of expanding the core for theranostics. The lower values of computed hole reorganization energies indicated their potential as hole transporting materials in optoelectronics and widen the scope of these molecules as advanced functional materials.

Delayed Reaction: The Tardy Embrace of Physical Organic Chemistry by the German Chemical Community

The emergence of physical organic chemistry, which focuses on the mechanisms and structures of organic reactions and molecules using the tools of physical chemistry, was a major development in twentieth-century chemistry. It first flourished in the interwar period, in the UK and then in the US. Germany, by contrast, did not embrace the field until almost a half century later. The great success of classical organic chemistry, especially in synthesis, encouraged indifference to the new field among German chemists, as did their inductivist research philosophy, as enunciated by Walter Hückel’s ground-breaking textbook (1931). This author also resisted new concepts and representations, especially those of the American theoretician, Linus Pauling. The arrival of the Nazi regime reinforced such resistance. Postwar conditions initiated a reaction against this conservative, nationalistic attitude, especially in the American Occupation Zone. Exposure to American textbooks and visiting lecturers influenced attitudes of younger chemists. The accompanying shift towards a more explanatory, less hierarchical mode of pedagogy was consonant with larger social and political developments.

Lipophilicity prediction of peptides and peptide derivatives by consensus machine learning.

Lipophilicity prediction is routinely applied to small molecules and presents a working alternative to experimental log P or log D determination. For compounds outside the domain of classical medicinal chemistry these predictions lack accuracy, advocating the development of bespoke in silico approaches. Peptides and their derivatives and mimetics fill the structural gap between small synthetic drugs and genetically engineered macromolecules. Here, we present a data-driven machine learning method for peptide log D 7.4 prediction. A model for estimating the lipophilicity of short linear peptides consisting of natural amino acids was developed. In a prospective test, we obtained accurate predictions for a set of newly synthesized linear tri- to hexapeptides. Further model development focused on more complex peptide mimetics from the AstraZeneca compound collection. The results obtained demonstrate the applicability of the new prediction model to peptides and peptide derivatives in a log D 7.4 range of approximately -3 to 5, with superior accuracy to established lipophilicity models for small molecules.

Short Oxoproline-Containing Peptides as Potential Pharmacological Means of Hypolipidemic and Antithrombotic Actions

The search and research of pharmacological agents that could combine lipid-lowering and antithrombotic effects on the human organism are one of the most urgent and important tasks of modern biological and medical research. The unique effects of the regulatory peptides of the oxoproline series (5-охо-Pro- His-Pro-NH2, 5-oxo-Pro-Trp-Pro, and 5-oxo-Pro-Arg-Pro or Pyr-His-Pro-NH2, Pyr-Trp-Pro, and Pyr- Arg-Pro) synthesized by the methods of classical peptide chemistry have been found in animals with experimental hypercholesterolemia. Repeated intranasal administration of these peptides to animals with developed hypercholesterolemia increased their anticoagulant, fibrinolytic and antiplatelet potential of the blood and simultaneously lowered increased concentrations of total cholesterol, low-density lipoprotein cholesterol, and triglycerides. In addition, they promoted normalization of blood glucose. A week after the last administration of these peptides, the hypocholesterolemic, normoglycemic and anticoagulant effects persisted. The relationship between the structure of the oxoproline-containing peptides and their functional properties is discussed. It is concluded that further studies of oxoproline-containing peptides are promising in the context of development of pharmacological agents, combining the antithrombotic activity with the improvement of lipid metabolism in the body.

Evidence for single metal two electron oxidative addition and reductive elimination at uranium

Reversible single-metal two-electron oxidative addition and reductive elimination are common fundamental reactions for transition metals that underpin major catalytic transformations. However, these reactions have never been observed together in the f-block because these metals exhibit irreversible one- or multi-electron oxidation or reduction reactions. Here we report that azobenzene oxidises sterically and electronically unsaturated uranium(III) complexes to afford a uranium(V)-imido complex in a reaction that satisfies all criteria of a single-metal two-electron oxidative addition. Thermolysis of this complex promotes extrusion of azobenzene, where H-/D-isotopic labelling finds no isotopomer cross-over and the non-reactivity of a nitrene-trap suggests that nitrenes are not generated and thus a reductive elimination has occurred. Though not optimally balanced in this case, this work presents evidence that classical d-block redox chemistry can be performed reversibly by f-block metals, and that uranium can thus mimic elementary transition metal reactivity, which may lead to the discovery of new f-block catalysis.

Defining the Field of Sequence‐Controlled Polymers

Over the last ten years, the development of synthetic polymers containing controlled monomer sequences has become a prominent topic in fundamental and applied polymer science. This emerging area is particularly broad and combines classical polymer chemistry tools with techniques imported from other domains such as biology, biochemistry, organic synthesis, engineering, and bioanalytics. Consequently, it also generates new structures, terminologies, and applications that are not within the traditional scope of polymer science. The term "sequence-controlled polymers" (SCPs) was recently proposed as a generic name to describe all these recent trends. However, since the field of SCPs has been growing very rapidly in recent literature, it is urgent to accurately define its scientific frontiers. In this important context, this review is an attempt to define, rationalize, and classify the field of SCPs. In particular, all synthetic approaches that have been reported for the synthesis of SCPs are discussed and categorized. In addition, the characterization tools, properties, and potential applications of these new polymers are described herein. Overall, this review serves as a reference guide for understanding the burgeoning field of SCPs.

Toward Green Acylation of (Hetero)arenes: Palladium-Catalyzed Carbonylation of Olefins to Ketones.

Green Friedel–Crafts acylation reactions belong to the most desired transformations in organic chemistry. The resulting ketones constitute important intermediates, building blocks, and functional molecules in organic synthesis as well as for the chemical industry. Over the past 60 years, advances in this topic have focused on how to make this reaction more economically and environmentally friendly by using green acylating conditions, such as stoichiometric acylations and catalytic homogeneous and heterogeneous acylations. However, currently well-established methodologies for their synthesis either produce significant amounts of waste or proceed under harsh conditions, limiting applications. Here, we present a new protocol for the straightforward and selective introduction of acyl groups into (hetero)arenes without directing groups by using available olefins with inexpensive CO. In the presence of commercial palladium catalysts, inter- and intramolecular carbonylative C–H functionalizations take place with good regio- and chemoselectivity. Compared to classical Friedel–Crafts chemistry, this novel methodology proceeds under mild reaction conditions. The general applicability of this methodology is demonstrated by the direct carbonylation of industrial feedstocks (ethylene and diisobutene) as well as of natural products (eugenol and safrole). Furthermore, synthetic applications to drug molecules are showcased.

Antiaromaticity flips single-molecule switch

Ultrasmall electronic devices require ultrasmall components. That’s why scientists have been working for the past few decades on electronic circuitry in which function is controlled by just a single molecule. Those molecules nearly always sport conjugated aromatic backbones because aromaticity in those molecules usually goes hand-in-hand with enhanced conductivity. But a team led by Latha Venkataraman and Luis M. Campos of Columbia University and Jeffrey B. Neaton of Lawrence Berkeley National Laboratory has shown that aromatic isn’t the only way to go: The team has demonstrated a highly conducting, reversible, single-molecule switch based on antiaromaticity (Sci. Adv. 2017, DOI: 10.1126/sciadv.aao2615). In classical organic chemistry, Hückel’s rule states that conjugated cyclic molecules with 4n+2 π electrons exhibit enhanced stability because they are aromatic. Related molecules with 4n π electrons are comparatively unstable and described as antiaromatic, a concept pioneered by Columbia’s Ronald Breslow, who died Oct. 25. Intrigued by the possibility

Discovery of new GPCR ligands to illuminate new biology.

Although a plurality of drugs target G-protein-coupled receptors (GPCRs), most have emerged from classical medicinal chemistry and pharmacology programs and resemble one another structurally and functionally. Though effective, these drugs are often promiscuous. With the realization that GPCRs signal via multiple pathways, and with the emergence of crystal structures for this family of proteins, there is an opportunity to target GPCRs with new chemotypes and confer new signaling modalities. We consider structure-based and physical screening methods that have led to the discovery of new reagents, focusing particularly on the former. We illustrate their use against previously untargeted or orphan GPCRs, against allosteric sites, and against classical orthosteric sites that selectively activate one downstream pathway over others. The ligands that emerge are often chemically novel, which can lead to new biological effects.

Review (127 Pages, Full Version). Benzene on the Basis of the Three-Electron Bond. (The Pauli Exclusion Principle, Heisenberg's Uncertainty Principle and Chemical Bond)

The present work shows the inapplicability of the Pauli principle to chemical bond, and a new theoretical model of the chemical bond is proposed based on the Heisenberg uncertainty principle. See pp. 88 - 104. Using the concept of three-electron bond we can represent the actual electron structure of benzene and other molecules, explain specificity of the aromatic bond and calculate the delocalization energy. Gives theoretical justification and experimental confirmation of existence of the three-electron bond. It was shown, that functional relation y = a + b/x + c/x^2 fully describes dependence of energy and multiplicity of chemical bond from bond distance.

Gas‐Phase Synthesis of the Elusive Cyclooctatetraenyl Radical (C8H7) via Triplet Aromatic Cyclooctatetraene (C8H8) and Non‐Aromatic Cyclooctatriene (C8H8) Intermediates

AbstractThe 1,2,4,7‐cyclooctatetraenyl radical (C8H7) has been synthesized for the very first time via the bimolecular gas‐phase reaction of ground‐state carbon atoms with 1,3,5‐cycloheptatriene (C7H8) on the triplet surface under single‐collision conditions. The barrier‐less route to the cyclic 1,2,4,7‐cyclooctatetraenyl radical accesses exotic reaction intermediates on the triplet surface, which cannot be synthesized via classical organic chemistry methods: the triplet non‐aromatic 2,4,6‐cyclooctatriene (C8H8) and the triplet aromatic 1,3,5,7‐cyclooctatetraene (C8H8). Our approach provides a clean gas‐phase synthesis of this hitherto elusive cyclic radical species 1,2,4,7‐cyclooctatetraenyl via a single‐collision event and opens up a versatile, unconventional path to access this previously largely obscure class of cyclooctatetraenyl radicals, which have been impossible to access through classical synthetic methods.

Gas-Phase Synthesis of the Elusive Cyclooctatetraenyl Radical (C8 H7 ) via Triplet Aromatic Cyclooctatetraene (C8 H8 ) and Non-Aromatic Cyclooctatriene (C8 H8 ) Intermediates.

The 1,2,4,7-cyclooctatetraenyl radical (C8 H7 ) has been synthesized for the very first time via the bimolecular gas-phase reaction of ground-state carbon atoms with 1,3,5-cycloheptatriene (C7 H8 ) on the triplet surface under single-collision conditions. The barrier-less route to the cyclic 1,2,4,7-cyclooctatetraenyl radical accesses exotic reaction intermediates on the triplet surface, which cannot be synthesized via classical organic chemistry methods: the triplet non-aromatic 2,4,6-cyclooctatriene (C8 H8 ) and the triplet aromatic 1,3,5,7-cyclooctatetraene (C8 H8 ). Our approach provides a clean gas-phase synthesis of this hitherto elusive cyclic radical species 1,2,4,7-cyclooctatetraenyl via a single-collision event and opens up a versatile, unconventional path to access this previously largely obscure class of cyclooctatetraenyl radicals, which have been impossible to access through classical synthetic methods.

(Invited) Molecular Electrochemical Catalysis of CO2 Reduction with Fe and Co Complexes. from Mechanistic Studies to Highly Selective CO Production and to More Reduced Products

Recent attention aroused by the reduction of carbon dioxide has as main objective the production of useful products - the “solar fuels” - in which solar energy would be stored. One route to this goal consists in first converting sunlight energy into electricity, then used to reduce CO2 electrochemically. Conversion of carbon dioxide into carbon monoxide is thus a key-step through the classical dihydrogen-reductive Fischer-Tropsch chemistry. We will describe our work in this field using variously substituted iron tetraphenylporphyrin derivatives, that prove to be the most efficient molecular catalysts of the reduction of CO2 to CO when generated electrochemical at the Fe(0) oxidation state, both in terms of selectivity, durability, overpotential and turnover frequency. These catalysts are remarkably active not only in organic solvent (e.g. DMF) but also in pure water at pH 7. Benchmarking of the catalytic performances, through catalytic Tafel plots, leads to a fair comparison between various reported catalysts and detailed mechanisms were obtained from electrochemical studies. Going further, a complete CO2 conversion electrochemical cell functioning in pure water was also designed. Finally, our recent work and strategy to reduce CO2 beyond CO (for generating hydrocarbons) will be briefly presented.