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Accounts of Chemical Research

Mingming Wang, Wei Zhan
The grand scale, ultimate efficiency, and sustainability of natural photosynthesis have inspired generations of researchers in biomimetic light energy utilization. As an essential and ubiquitous component in all photosynthetic machinery, lipids and their assemblies have long been recognized as powerful molecular scaffolds in building artificial photosynthetic systems. Model lipid bilayers, such as black lipid membranes and liposomes (vesicles), have been extensively used to host natural as well as synthetic photo- and redox-active species, thereby enabling key photosynthetic processes, such as energy transfer and photoinduced electron transfer, to be examined in well-defined, natural-like membrane settings...
October 19, 2016: Accounts of Chemical Research
Gregory J O Beran, Joshua D Hartman, Yonaton N Heit
Molecular crystals occur widely in pharmaceuticals, foods, explosives, organic semiconductors, and many other applications. Thanks to substantial progress in electronic structure modeling of molecular crystals, attention is now shifting from basic crystal structure prediction and lattice energy modeling toward the accurate prediction of experimentally observable properties at finite temperatures and pressures. This Account discusses how fragment-based electronic structure methods can be used to model a variety of experimentally relevant molecular crystal properties...
October 18, 2016: Accounts of Chemical Research
Dennis G Hall, Taras Rybak, Tristan Verdelet
Multicomponent reactions (MCR), transformations employing three or more simple substrates in a single and highly atom-economical operation, are very attractive in both natural product synthesis and diversity-oriented synthesis of druglike molecules. Several popular multicomponent reactions were designed by combining two well-established individual reactions that utilize mutually compatible substrates. In this regard, it is not surprising that the merging of two reactions deemed as workhorses of stereoselective synthesis, the Diels-Alder cycloaddition and carbonyl allylboration, would produce a powerful and highly versatile tandem MCR process...
October 18, 2016: Accounts of Chemical Research
Hyunbum Kang, Wonho Lee, Jiho Oh, Taesu Kim, Changyeon Lee, Bumjoon J Kim
All-polymer solar cells (all-PSCs), consisting of conjugated polymers as both electron donor (PD) and acceptor (PA), have recently attracted great attention. Remarkable progress has been achieved during the past few years, with power conversion efficiencies (PCEs) now approaching 8%. In this Account, we first discuss the major advantages of all-PSCs over fullerene-polymer solar cells (fullerene-PSCs): (i) high light absorption and chemical tunability of PA, which affords simultaneous enhancement of both the short-circuit current density (JSC) and the open-circuit voltage (VOC), and (ii) superior long-term stability (in particular, thermal and mechanical stability) of all-PSCs due to entangled long PA chains...
October 18, 2016: Accounts of Chemical Research
Qin Wang, Katherine J Franz
Metal ions are essential for a wide range of physiological processes, but they can also be toxic if not appropriately regulated by a complex network of metal trafficking proteins. Intervention in cellular metal distribution with small-molecule or peptide chelating agents has promising therapeutic potential to harness metals to fight disease. Molecular outcomes associated with forming metal-chelate interactions in situ include altering the concentration and subcellular metal distribution, inhibiting metalloenzymes, enhancing the reactivity of a metal species to elicit a favorable biological response, or passivating the reactivity of a metal species to prevent deleterious reactivity...
October 17, 2016: Accounts of Chemical Research
Alexander von Weber, Scott L Anderson
Mass-selected Ptn(+) ion deposition in ultrahigh vacuum (UHV) was used to prepare a series of size-selected electrodes with Ptn (n ≤ 14) clusters supported on either glassy carbon (GC) or indium tin oxide (ITO). After characterization of the physical properties of the electrodes in UHV, an in situ method was used to study electrocatalytic activity for the oxygen reduction and ethanol oxidation reactions, without significant air exposure. For each reaction studied, there are similarities between the catalytic properties of Ptn-containing electrodes and those of nanoparticulate or bulk Pt electrodes, but there are also important differences that provide mechanistic insights...
October 17, 2016: Accounts of Chemical Research
Guoyin Yin, Xin Mu, Guosheng Liu
Difunctionalization of alkenes to incorporate two functional groups across a double bond has emerged as a powerful transformation to greatly increase molecular complexity in organic synthesis with improved efficiency. Historically, palladium-catalyzed difunctionalization of alkenes has suffered from difficulties with introducing a second functional group through reductive elimination of a Pd(II) intermediate and competing β-hydride elimination reactions. To overcome these challenges, one strategy involves utilizing a steric bulky ligand to promote the reductive elimination steps from the Pd(II) center and impeding the β-hydride elimination reactions, which are beyond the scope of this Account...
October 14, 2016: Accounts of Chemical Research
Tian Sheng, Yue-Feng Xu, Yan-Xia Jiang, Ling Huang, Na Tian, Zhi-You Zhou, Ian Broadwell, Shi-Gang Sun
The performance of nanomaterials in electrochemical energy conversion (fuel cells) and storage (secondary batteries) strongly depends on the nature of their surfaces. Designing the structure of electrode materials is the key approach to achieving better performance. Metal or metal oxide nanocrystals (NCs) with high-energy surfaces and open surface structures have attained significant attention in the past decade since such features possess intrinsically exceptional properties. However, they are thermodynamically metastable, resulting in a huge challenge in their shape-controlled synthesis...
October 14, 2016: Accounts of Chemical Research
Michael T Marty, Kin Kuan Hoi, Carol V Robinson
Membrane proteins play critical physiological roles and make up the majority of drug targets. Due to their generally low expression levels and amphipathic nature, membrane proteins represent challenging molecular entities for biophysical study. Mass spectrometry offers several sensitive approaches to study the biophysics of membrane proteins. By preserving noncovalent interactions in the gas phase and using collisional activation to remove solubilization agents inside the mass spectrometer, native mass spectrometry (MS) is capable of studying isolated assemblies that would be insoluble in aqueous solution, such as membrane protein oligomers and protein-lipid complexes...
October 13, 2016: Accounts of Chemical Research
Manik Lal Saha, Xuzhou Yan, Peter J Stang
Over the past couple of decades, coordination-driven self-assembly has evolved as a broad multidisciplinary domain that not only covers the syntheses of aesthetically pleasing supramolecular architectures but also emerges as a method to form new optical materials, chemical sensors, theranostic agents, and compounds with light-harvesting and emissive properties. The majority of these applications depend upon investigations that reveal the photophysical nature and electronic structure of supramolecular coordination complexes (SCCs), including two-dimensional (2D) metallacycles and three-dimensional (3D) metallacages...
October 13, 2016: Accounts of Chemical Research
Todd J Anderson, Bo Zhang
Metal nanoparticles are key electrode materials in a variety of electrochemical applications including basic electron-transfer study, electrochemical sensing, and electrochemical surface enhanced Raman spectroscopy (SERS). Metal nanoparticles have also been extensively applied to electrocatalytic processes in recent years due to their high catalytic activity and large surface areas. Because the catalytic activity of metal nanoparticle is often highly dependent on their size, shape, surface ligands, and so forth, methods for examining and better understanding the correlation between particle structure and function are of great utility in the development of more efficient catalytic systems...
October 12, 2016: Accounts of Chemical Research
Richard J Nichols, Simon J Higgins
It is now possible to reliably measure single molecule conductance in a wide variety of environments including organic liquids, ultrahigh vacuum, water, ionic liquids, and electrolytes. The most commonly used methods deploy scanning probe microscopes, mechanically formed break junctions, or lithographically formed nanogap contacts. Molecules are generally captured between a pair of facing electrodes, and the junction current response is measured as a function of bias voltage. Gating electrodes can also be added so that the electrostatic potential at the molecular bridge can be independently controlled by this third noncontacting electrode...
October 7, 2016: Accounts of Chemical Research
Erik Stempel, Tanja Gaich
Seven-membered rings fused with an indole are termed cyclohepta[b]indoles. Compounds exhibiting this structure motif display a broad spectrum of biological activities, ranging from inhibition of adipocyte fatty-acid-binding protein (A-FABP), deacetylation of histones, inhibition of leukotriene production p53, antituberculosis activities, and anti-HIV activities. These biological profiles are found in natural products containing the cyclohepta[b]indole motif, as well as in pharmaceuticals that contain this structure motif...
October 6, 2016: Accounts of Chemical Research
Dennis C Liotta, George R Painter
The HIV/AIDS epidemic, which was first reported on in 1981, progressed in just 10 years to a disease afflicting 10 million people worldwide including 1 million in the US. In 1987, AZT was approved for treating HIV/AIDS. Unfortunately, its clinical usefullness was severly limited by associated toxicities and the emergence of resistance. Three other drugs that were approved in the early 1990s suffered from similar liabilities. In 1990, the Liotta group at Emory University developed a highly diastereoselective synthesis of racemic 3'-thia-2',3'-dideoxycytidine and 3'-thia-2',3'-5-fluorodideoxycytidine and demonstrated that these compounds exhibited excellent anti-HIV activity with no apparent cytotoxicity...
October 5, 2016: Accounts of Chemical Research
Timothy P Lodge, Takeshi Ueki
Room temperature ionic liquids are of great interest for many advanced applications, due to the combination of attractive physical properties with essentially unlimited tunability of chemical structure. High chemical and thermal stability, favorable ionic conductivity, and complete nonvolatility are just some of the most important physical characteristics that make ionic liquids promising candidates for emerging technologies. Examples include separation membranes, actuators, polymer gel electrolytes, supercapacitors, ion batteries, fuel cell membranes, sensors, printable plastic electronics, and flexible displays...
October 5, 2016: Accounts of Chemical Research
Dinesh Kumar, Sandeep R Vemula, Narayanaganesh Balasubramanian, Gregory R Cook
Stereoselective indium-mediated organic reactions have enjoyed tremendous growth in the last 25 years. This is in part due to the insensitivity of allylindium to moisture, affording facile and practical reaction conditions coupled with outstanding functional group tolerance and minimal side reactions. Despite the plethora of articles about allylindium, there is much yet to be discovered and exploited for efficient and sustainable synthesis. In this Account, we describe indium-mediated synthetic methods for the preparation of chiral amines with the aim to present a balance of practical method development, novel asymmetric chemistry, and mechanistic understanding that impact multiple chemical and materials science disciplines...
October 4, 2016: Accounts of Chemical Research
Peiguang Hu, Limei Chen, Xiongwu Kang, Shaowei Chen
Noble metal nanoparticles represent a unique class of functional nanomaterials with physical and chemical properties that deviate markedly from those of their atomic and bulk forms. In order to stabilize the nanoparticles and further manipulate the materials properties, surface functionalization with organic molecules has been utilized as a powerful tool. Among those, mercapto derivatives have been used extensively as the ligands of choice for nanoparticle surface functionalization by taking advantage of the strong affinity of thiol moieties to transition metal surfaces forming (polar) metal-thiolate linkages...
October 3, 2016: Accounts of Chemical Research
Wen-Jie Lan, Martin A Edwards, Long Luo, Rukshan T Perera, Xiaojian Wu, Charles R Martin, Henry S White
Ion current rectification (ICR) refers to the asymmetric potential-dependent rate of the passage of solution ions through a nanopore, giving rise to electrical current-voltage characteristics that mimic those of a solid-state electrical diode. Since the discovery of ICR in quartz nanopipettes two decades ago, synthetic nanopores and nanochannels of various geometries, fabricated in membranes and on wafers, have been extensively investigated to understand fundamental aspects of ion transport in highly confined geometries...
September 30, 2016: Accounts of Chemical Research
Takuji Adachi, Michael D Ward
Low-density molecular host frameworks, whether equipped with persistent molecular-scale pores or virtual pores that are sustainable only when occupied by guest molecules, have emerged as a promising class of materials owing to the ability to tailor the size, geometry, and chemical character of their free space through the versatility of organic synthesis. As such, molecular frameworks are promising candidates for storage, separations of commodity and fine chemicals, heterogeneous catalysis, and optical and electronic materials...
September 30, 2016: Accounts of Chemical Research
Mark Burgess, Jeffrey S Moore, Joaquín Rodríguez-López
It is an exciting time for exploring the synergism between the chemical and dimensional properties of redox nanomaterials for addressing the manifold performance demands faced by energy storage technologies. The call for widespread adoption of alternative energy sources requires the combination of emerging chemical concepts with redesigned battery formats. Our groups are interested in the development and implementation of a new strategy for nonaqueous flow batteries (NRFBs) for grid energy storage. Our motivation is to solve major challenges in NRFBs, such as the lack of membranes that simultaneously allow fast ion transport while minimizing redox active species crossover between anolyte (negative electrolyte) and catholyte (positive electrolyte) compartments...
September 27, 2016: Accounts of Chemical Research
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