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Accounts of Chemical Research

Michael J Walsh, Wenming Tong, Hadas Katz-Boon, Paul Mulvaney, Joanne Etheridge, Alison M Funston
The phenomenon of symmetry breaking-in which the order of symmetry of a system is reduced despite manifest higher-order symmetry in the underlying fundamental laws-is pervasive throughout science and nature, playing a critical role in fields ranging from particle physics and quantum theory to cosmology and general relativity. For the growth of crystals, symmetry breaking is the crucial step required to generate a macroscopic shape that has fewer symmetry elements than the unit cell and/or seed crystal from which it grew...
November 16, 2017: Accounts of Chemical Research
Roman Elfgen, Oldamur Hollóczki, Barbara Kirchner
The structure-directing or template effect has been invoked several times for ionic liquids to explain the different outcome in material synthesis, namely, different scaffolds or geometrical arrangements with varying ionic liquids. It is obvious to assume that such an effect can originate from the most likely complex microstructure, being present within the ionic liquid itself. In that regard, ionic liquids have already been shown to undergo a nanosegregation into polar and nonpolar phases, which is commonly known and denoted as microheterogeneity...
November 13, 2017: Accounts of Chemical Research
Pankaj Chauhan, Suruchi Mahajan, Dieter Enders
In the last two decades, organocatalysis has emerged as an intensively investigated and rapidly growing area of research facilitating many known and many new transformations to provide efficient novel entries to complex molecules of high stereochemical purity. The organocatalysts have not only shown their efficiency for catalyzing the reactions in which one bond is formed, but they have also been effectively exploited in various versions of one-pot reactions. Domino reactions are one of the most important classes of one-pot reactions, where the target structure can be obtained in one pot without changing any reaction conditions while each reaction occurs as a consequence of the intermediates generated in previous steps...
November 10, 2017: Accounts of Chemical Research
Stefan Kubik
Anion receptors often rely on coordinative or multiple ionic interactions to be active in water. In the absence of such strong interactions, anion binding in water can also be efficient, however, as demonstrated by a number of anion receptors developed in recent years. The cyclopeptide-derived receptors comprising an alternating sequence of l-proline and 6-aminopicolinic acid subunits are an example. These cyclopeptides are neutral and, at first sight, can only engage in hydrogen-bond formation with an anionic substrate...
November 10, 2017: Accounts of Chemical Research
Ryan J Trovitch
In recent years, interest in homogeneous manganese catalyst development has intensified because of the earth-abundant and nontoxic nature of this metal. Although compounds of Mn have largely been utilized for epoxidation reactions, recent efforts have revealed that Mn catalysts can mediate a broad range of reductive transformations. Low-valent Mn compounds have proven to be particularly effective for the hydrosilylation of carbonyl- and carboxylate-containing substrates, and this Account aims to highlight my research group's contributions to this field...
November 9, 2017: Accounts of Chemical Research
Constanze N Neumann, Tobias Ritter
Late-stage fluorination reactions aim to reduce the synthetic limitations of conventional organofluorine chemistry with respect to substrate scope and functional group tolerance. C-F bond formation is commonly thermodynamically favorable but almost universally associated with high kinetic barriers. Apart from PhenoFluor chemistry, most modern aromatic fluorination methods reported to date rely on the use of transition metal catalysts, with C-F bonds often formed through reductive elimination. Reductive elimination chemistry to make C-X bonds becomes increasingly challenging when moving to higher atomic numbers in the periodic table from C-C to C-F, in part because of higher metal-X bond dissociation energies...
November 9, 2017: Accounts of Chemical Research
Yun-Fang Yang, Xin Hong, Jin-Quan Yu, K N Houk
C-H activation and functionalization are on the forefront of modern synthetic chemistry. Imagine if any C-H bond of a molecule could be converted to a C-X bond, where X is the target functionality-this would alter the synthetic blueprints for complex target molecules since it would provide novel disconnections in retrosynthetic analysis. Collaborations between many experimental and computational groups have led to rapid developments of new C-H functionalization methods. Our groups represent an example of this; we were brought together as part of the NSF-supported Center for Selective C-H Functionalization...
November 8, 2017: Accounts of Chemical Research
Xiaotian Qi, Yingzi Li, Ruopeng Bai, Yu Lan
Transition-metal-catalyzed cross-coupling has emerged as an effective strategy for chemical synthesis. Within this area, direct C-H bond transformation is one of the most efficient and environmentally friendly processes for the construction of new C-C or C-heteroatom bonds. Over the past decades, rhodium-catalyzed C-H functionalization has attracted considerable attention because of the versatility and wide use of rhodium catalysts in chemistry. A series of C-X (X = C, N, or O) bond formation reactions could be realized from corresponding C-H bonds using rhodium catalysts...
November 7, 2017: Accounts of Chemical Research
Xingwen Yu, Arumugam Manthiram
Electrode-electrolyte interfacial properties play a vital role in the cycling performance of lithium-sulfur (Li-S) batteries. The issues at an electrode-electrolyte interface include electrochemical and chemical reactions occurring at the interface, formation mechanism of interfacial layers, compositional/structural characteristics of the interfacial layers, ionic transport across the interface, and thermodynamic and kinetic behaviors at the interface. Understanding the above critical issues is paramount for the development of strategies to enhance the overall performance of Li-S batteries...
November 7, 2017: Accounts of Chemical Research
Volodymyr Smetana, Melissa Rhodehouse, Gerd Meyer, Anja-Verena Mudring
The design of new materials with desired chemical and physical characteristics requires thorough understanding of the underlying composition-structure-property relationships and the experimental possibility of their modification through the controlled involvement of new components. From this point of view, intermetallic phases, a class of compounds formed by two or more metals, present an endless field of combinations that produce several chemical compound classes ranging from simple alloys to true ionic compounds...
November 7, 2017: Accounts of Chemical Research
Samuel J Hein, Dan Lehnherr, Hasan Arslan, Fernando J Uribe-Romo, William R Dichtel
Aromatic compounds and polymers are integrated into organic field effect transistors, light-emitting diodes, photovoltaic devices, and redox-flow batteries. These compounds and materials feature increasingly complex designs, and substituents influence energy levels, bandgaps, solution conformation, and crystal packing, all of which impact performance. However, many polycyclic aromatic hydrocarbons of interest are difficult to prepare because their substitution patterns lie outside the scope of current synthetic methods, as strategies for functionalizing benzene are often unselective when applied to naphthalene or larger systems...
November 7, 2017: Accounts of Chemical Research
Jian Li, Junliang Sun
All crystalline materials in nature, whether inorganic, organic, or biological, macroscopic or microscopic, have their own chemical and physical properties, which strongly depend on their atomic structures. Therefore, structure determination is extremely important in chemistry, physics, materials science, etc. In the past centuries, many techniques have been developed for structure determination. The most widely used one is X-ray crystallography (single-crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD)), and it remains the most important technique for structure determination of crystalline materials...
November 1, 2017: Accounts of Chemical Research
Kimberly M Osten, Parisa Mehrkhodavandi
Inexorably, the environmental persistence and damage caused by polyolefins have become major drawbacks to their continued long-term use. Global shifts in thinking from fossil-fuel to renewable biobased resources have urged researchers to focus their attention on substituting fossil-fuel based polymers with renewable and biodegradable alternatives on an industrial scale. The recent development of biodegradable polyesters from ring opening polymerization (ROP) of bioderived cyclic ester monomers has emerged as a promising new avenue toward this goal...
October 31, 2017: Accounts of Chemical Research
Brandon L Greene, Gregory E Vansuch, Bryant C Chica, Michael W W Adams, R Brian Dyer
Rapid and facile redox chemistry is exemplified in nature by the oxidoreductases, the class of enzymes that catalyze electron transfer (ET) from a donor to an acceptor. The key role of oxidoreductases in metabolism and biosynthesis has imposed evolutionary pressure to enhance enzyme efficiency, pushing some toward the diffusion limit. Understanding the detailed molecular mechanisms of these highly optimized enzymes would provide an important foundation for the rational design of catalysts for multielectron chemistry, including fuel production...
October 30, 2017: Accounts of Chemical Research
Derek B Rice, Allyssa A Massie, Timothy A Jackson
Biological systems capitalize on the redox versatility of manganese to perform reactions involving dioxygen and its derivatives superoxide, hydrogen peroxide, and water. The reactions of manganese enzymes influence both human health and the global energy cycle. Important examples include the detoxification of reactive oxygen species by manganese superoxide dismutase, biosynthesis by manganese ribonucleotide reductase and manganese lipoxygenase, and water splitting by the oxygen-evolving complex of photosystem II...
October 24, 2017: Accounts of Chemical Research
Nathaniel S Sickerman, Markus W Ribbe, Yilin Hu
Nitrogenase is known for its remarkable ability to catalyze the reduction of N2 to NH3, and C1 substrates to short-chain hydrocarbon products, under ambient conditions. The best-studied Mo-nitrogenase utilizes a complex metallocofactor as the site of substrate binding and reduction. Designated the M-cluster, this [MoFe7S9C(R-homocitrate)] cluster can be viewed as [MoFe3S3] and [Fe4S3] subclusters bridged by three μ2-sulfides and one μ6-interstitial carbide, with its Mo end further coordinated by an R-homocitrate moiety...
October 24, 2017: Accounts of Chemical Research
Franz Heinemann, Johannes Karges, Gilles Gasser
Photodynamic Therapy (PDT) is an emerging technique to treat certain types of cancer, bacterial, fungal, and viral infections, and skin diseases. In past years, different research groups developed new ruthenium-containing photosensitizers (PSs) with tuned photophysical and biological properties to better fit the requirements of PDT. In this Account, we report and discuss the latest results in this research area, emphasizing particularly our own research. For example, inspired by the DNA intercalating complex [Ru(bpy)2(dppz)](2+) (bpy = 2,2'-bipyridine; dppz = (dipyrido[3,2-a:2',3'-c]phenazine), a series of ruthenium complexes bearing differently functionalized dppz ligands were synthesized to target DNA...
October 23, 2017: Accounts of Chemical Research
Jie Shi Chua, Balagurunathan Kuberan
Glycosaminoglycans (GAGs) are polysaccharides ubiquitously found on cell surfaces and in the extracellular matrix (ECM). They regulate numerous cellular signaling events involved in many developmental and pathophysiological processes. GAGs are composed of complex sequences of repeating disaccharide units, each of which can carry many different modifications. The tremendous structural variations account for their ability to bind many proteins and thus, for their numerous functions. Although the sequence of GAG biosynthetic events and the enzymes involved mostly were deduced a decade ago, the emergence of tissue or cell specific GAGs from a nontemplate driven process remains an enigma...
October 23, 2017: Accounts of Chemical Research
Jacob C Dean, Gregory D Scholes
The role of coherences, or coherently excited superposition states, in complex condensed-phase systems has been the topic of intense interest and debate for a number of years. In many cases, coherences have been utilized as spectators of ultrafast dynamics or for identifying couplings between electronic states. In rare cases, they have been found to drive excited state dynamics directly. Interestingly though, the utilization of coherences as a tool for high-detail vibronic spectroscopy has largely been overlooked until recently, despite their encoding of key information regarding molecular structure, electronically sensitive vibrational modes, and intermolecular interactions...
October 18, 2017: Accounts of Chemical Research
Tatsuki Morimoto, Osamu Ishitani
The photophysical and photochemical properties of transition metal complexes have attracted considerable attention because of their recent applications as photocatalysts in artificial photosynthesis and organic synthesis, as light emitters in electroluminescent (EL) devices, and as dyes in solar cells. The general control methods cannot be always used to obtain transition metal complexes with photochemical properties that are suitable for the above-mentioned applications. In the fields of solar energy conversion, strong metal-to-ligand charge-transfer (MLCT) absorption of redox photosensitizers and/or photocatalysts in the visible region with long wavelength is essential...
October 10, 2017: Accounts of Chemical Research
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