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Journal of the American Chemical Society

Marlies V Hager, Lisa M Johnson, Denise Wootten, Patrick M Sexton, Samuel H Gellman
Activation of a G protein-coupled receptor (GPCR) causes recruitment of multiple intracellular proteins, each of which can activate distinct signaling pathways. This complexity has engendered interest in agonists that preferentially stimulate subsets among the natural signaling pathways ("biased agonists"). We have examined analogues of glucagon-like peptide-1 (GLP-1) containing β-amino acid residues in place of native α residues at selected sites and found that some analogues differ from GLP-1 in terms of their relative abilities to promote G protein activation (as monitored via cAMP production) versus β-arrestin recruitment (as monitored via BRET assays)...
November 4, 2016: Journal of the American Chemical Society
Luke A Baldwin, Jonathan W Crowe, David A Pyles, Psaras L McGrier
Constructing metalated three-dimensional (3D) covalent organic frameworks is a challenging synthetic task. Herein, we report the synthesis and characterization of a highly porous (SABET = 5083 m2 g-1) 3D COF with a record low density (0.13 g cm-3) containing π-electron conjugated dehy-drobenzoannulene (DBA) units. Metalation of DBA-3D-COF 1 with Ni to produce Ni-DBA-3D-COF results in a minimal reduction in the surface area (SABET = 4763 m2 g-1) of the material due to the incorporation of the metal within the cavity of the DBA units, and retention of crystallinity...
November 4, 2016: Journal of the American Chemical Society
Moustafa R K Ali, Yue Wu, Tiegang Han, Xiaoling Zang, Haopeng Xiao, Yan Tang, Ronghu Wu, Facundo M Fernandez, Mostafa A El-Sayed
In cancer plasmonic photothermal therapy (PPTT), plasmonic nanoparticles are used to convert light into localized heat leading to cancer cell death. Among plasmonic nanoparticles, gold nanorods (AuNRs) with specific dimensions so as to absorb the near-infrared (NIR) laser light have been widely used. The detailed mechanism of PPTT therapy, however, still remains poorly understood. Typically, surface enhanced Raman spectroscopy (SERS) has been used to detect time-dependent changes in the intensity of the vibration frequencies of molecules that appear or disappear during different cellular processes...
November 3, 2016: Journal of the American Chemical Society
Joshua P Barham, Matthew P John, John A Murphy
We report a simple one-pot protocol that affords functionalization of N-CH3 groups in N-methyl-N,N-dialkylamines with high selectivity over N-CH2R or N-CHR2 groups. The radical cation DABCO+., prepared in situ by oxidation of DABCO by a triarylaminium salt, effects highly selective and contra-thermodynamic C-H abstraction from N-CH3 groups. The intermediates that result react in situ with organometallic nucleophiles in a single pot, affording novel and highly selective homologation of N-CH3 groups. Chemoselectivity, scalability and recyclability of reagents are demonstrated and a mechanistic proposal is corroborated by computational and experimental results...
November 3, 2016: Journal of the American Chemical Society
Rahul S Kathayat, Lijun Yang, Tosaporn Sattasathuchana, Laura Zoppi, Kim K Baldridge, Anthony Linden, Nathaniel S Finney
We provide herein a mechanistic analysis of aryl sulfoxide excited state processes, inspired by our recent report of aryl sulfoxide-based fluorescent chemosensors. The use of aryl sulfoxides as reporting elements in chemosensor development is a significant deviation from previous approaches, and thus warrants closer examination. We demonstrate that metal ion binding suppresses non-radiative excited state decay by blocking formation of a previously unrecognized charge transfer excited state, leading to fluorescence enhancement...
November 3, 2016: Journal of the American Chemical Society
Chi P Ting, Gong Xu, Xianhuang Zeng, Thomas J Maimone
Synthetic pathways to complex meroterpenes derived from 3,5-dimethylorsellinic acid (DMOA) and farnesyl pyrophosphate have not been reported despite heavy biosynthetic and medicinal interest. Herein we report a concise, 13-step total synthesis of berkeleyone A, a potential gateway compound to a plethora of fungal-derived meroterpenes. In addition, we have developed a novel annulation reaction for the assembly of hydroxylated 1,3-cyclohexadiones in a single step.
November 3, 2016: Journal of the American Chemical Society
Jung Tae Han, Won Jun Jang, Namhyeon Kim, Jaesook Yun
An efficient synthetic method for preparing enantioenriched secondary borylalkanes has been achieved through a copper-catalyzed regio- and enantioselective hydroallylation of alkenyl boronates and boramides employing hydrosilanes and allylic phosphates. In the presence of a copper catalyst with chiral Walphos ligand, a range of alkenylboron compounds with an aryl, heteroaryl, or alkyl substituent produced secondary homoallylic alkylboron compounds in good yields and with high enantioselectivities up to 99% ee...
November 3, 2016: Journal of the American Chemical Society
Erik W Martin, Alex S Holehouse, Christy R Grace, Alex Hughes, Rohit V Pappu, Tanja Mittag
Many cell signaling events are coordinated by intrinsically disordered protein regions (IDRs) that undergo multisite Serine / Threonine phosphorylation. The conformational properties of these IDRs prior to and following multisite phosphorylation are directly relevant to understanding their functions. Here, we present results from biophysical studies and molecular simulations that quantify the conformational properties of an 81-residue IDR from the S. cerevisiae transcription factor Ash1. We show that the unphosphorylated Ash1 IDR adopts coil-like conformations that are expand-ed and well-solvated...
November 3, 2016: Journal of the American Chemical Society
David M Novitski, Aslan Kosakian, Thomas Weissbach, Marc Secanell, Steven Holdcroft
Mass transport of oxygen through ionomer contained within the cathode catalyst layer in an anion exchange membrane fuel cell is critical for a functioning fuel cell, yet is relatively unexplored. Moreover, since water is a reactant in the oxygen reduction reaction (ORR) in alkaline media, an adequate supply of water is required. In this work, ORR mass transport behavior is reported for methylated hexamethyl-p-terphenyl polymethylbenzimidazoles (HMT-PMBI), charge balanced by hydroxide ions (IEC from 2.1 meq/g to 2...
November 2, 2016: Journal of the American Chemical Society
Rafael A Masitas, Stacy L Allen, Francis P Zamborini
Here we describe size-dependent electrophoretic deposition (EPD) of citrate-stabilized Au nanoparticles (NPs) onto indium-tin-oxide-coated glass (glass/ITO) electrodes as studied by linear sweep stripping voltammetry (LSSV) and scanning electron microscopy (SEM). LSSV allows both the determination of the Au NP coverage and NP size from the peak area and the peak potential, respectively. Two-electrode EPD in aqueous solutions of Au NPs plus H2O2 reveal that a minimum potential of 1.5 V is needed for significant deposition of 4 nm diameter Au NPs as opposed to 2...
November 2, 2016: Journal of the American Chemical Society
Yusheng Xie, Jingyan Ge, Haipeng Lei, Bo Peng, Huatang Zhang, Danyang Wang, Sijun Pan, Ganchao Chen, Lanfang Chen, Yi Wang, Quan Hao, Shao Q Yao, Hongyan Sun
HDACs play important roles in regulating various physiological and pathological processes. Developing fluorescent probes capable of detecting HDAC activity can help further elucidate the roles of HDACs in biology. In this study, we first developed a set of activity-based fluorescent probes by incorporating Kac residue and O-NBD group. Upon enzy-matic removal of the acetyl group in Kac residue, the released free amine reacted intramolecularly with the O-NBD moiety, resulting in turn-on of fluorescence. These designed probes are capable of detecting HDAC activity in a continuous fashion, thereby eliminating the extra step of fluorescence development...
November 2, 2016: Journal of the American Chemical Society
Kathrin C Knirsch, Ferdinand Hof, Vicent Lloret, Udo Mundloch, Frank Hauke, Andreas Hirsch
Herein, the combined application of characterization tools, such as Raman spectroscopy, thermal gravimetric analysis coupled with mass spectrometry as well as optical and atomic force microscopy, confirms the reductive silylation of synthetic carbon allotropes as a new covalent functional-ization strategy for the formation of heteroatom-carbon bonds. In particular, our study gives interesting insights into the topology driven retrofunctionalization of nanotubide and graphenide derivatives.
November 2, 2016: Journal of the American Chemical Society
Wei Liu, Dingchang Lin, Allen Pei, Yi Cui
The widespread implementation of high-energy-density lithium metal batteries has long been fettered by lithium dendrite-related failure. Here we report a new strategy to address the issue of dendrite growth by a polyimide-coating layer with vertical nanoscale channels of high aspect ratio. Smooth, granular lithium metal was deposited on the modified electrode instead of typical dendritic or filamentary growths. Compared with bare planar electrode, the modified electrode achieved greatly enhanced Coulombic efficiency and longer cycle life...
November 2, 2016: Journal of the American Chemical Society
Mercedes K Taylor, Tomče Runčevski, Julia Oktawiec, Miguel I Gonzalez, Rebecca L Siegelman, Jarad A Mason, Jinxing Ye, Craig M Brown, Jeffrey R Long
Metal-organic frameworks that flex to undergo structural phase changes upon gas adsorption are promising materials for gas storage and separations, and achieving synthetic control over the pressure at which these changes occur is crucial to the design of such materials for specific applications. To this end, a new family of materials based on the flexible metal-organic framework Co(bdp) (bdp(2-) = 1,4-benzenedipyrazolate) has been prepared via the introduction of fluorine, deuterium, and methyl functional groups on the bdp(2-) ligand, namely, Co(F-bdp), Co(p-F2-bdp), Co(o-F2-bdp), Co(D4-bdp), and Co(p-Me2-bdp)...
November 2, 2016: Journal of the American Chemical Society
Hang Shi, Peng Wang, Shin Suzuki, Marcus E Farmer, Jin-Quan Yu
Pd-catalyzed meta-C-H chlorination of anilines and phenols is developed using norbornene as the mediator. The presence of heterocycles, including indole, thiophene and indazole, are tolerated. The identification of a new pyridone-based ligand is crucial for the success of this meta-C-H chlorination reaction. Subsequent diverse transformations of the chlorinated products demonstrate the versatility of meta-C-H chlorination.
November 2, 2016: Journal of the American Chemical Society
Domenick F Leto, Allyssa A Massie, Derek B Rice, Timothy A Jackson
The mononuclear Mn(IV)-oxo complex [MnIV(O)(N4py)]2+, where N4py is the pentadentate ligand N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine, has been proposed to attack C-H bonds by an excited-state reactivity pattern [Cho, K.-B.; Shaik, S.; Nam, W., J. Phys. Chem. Lett. 2012, 3, 2851-2856]. In this model, a 4E excited state is utilized to provide a lower-energy barrier for hydrogen-atom transfer. This proposal is intriguing, as it offers both a rationale for the relatively high hydrogen-atom transfer reactivity of [MnIV(O)(N4py)]2+ and a guideline for creating more reactive complexes through ligand modification...
November 1, 2016: Journal of the American Chemical Society
Senmiao Xu, Yuanzhe Zhang, Bo Li, Shih-Yuan Liu
A concise synthesis of monobenzofused 1,4-azaborine phosphine ligands (Senphos) is described. These Senphos ligands uniquely support Pd-catalyzed trans-selective hydroboration of terminal and internal 1,3-enynes to furnish corresponding dienylboronates in high efficiency and diastereoselectivity. X-ray structural analysis of the Senphos-Pd(0) complex reveals a κ(2)-P-η(2)-BC coordination mode, and this isolated complex has been shown to serve as a competent catalyst for the trans-hydroboration reaction. This work demonstrates that the expanded chemical space provided by the BN/CC isosterism approach translates into the functional space in the context of stereoselective catalytic transformations...
November 1, 2016: Journal of the American Chemical Society
Zhou Li, Chong Xiao, Hao Zhu, Yi Xie
Defect engineering, at the core of the field of thermoelectric studies, serves as a scaffold for engineering the intrinsic electrons' and phonons' behaviors to tailor thermoelectric parameters through the direct impacts of band engineering and phonon engineering, which can modify electronic band structure and phonon transport behavior to enhance the power factor (PF = σS(2)) and reduce the lattice thermal conductivity (κl). By virtue of the implementation of defect engineering, the past decades have witnessed great progress in thermoelectric research through synergistic optimization of the inter-correlated transport parameters, and substantial enhancement has been achieved in the performance of various thermoelectric materials...
November 1, 2016: Journal of the American Chemical Society
Dooshaye Moonshiram, Yuliana Pineda-Galvan, Darren Erdman, Mark C Palenik, Ruifa Zong, Randolph P Thummel, Yulia N Pushkar
The realization of artificial photosynthesis carries the promise of cheap and abundant energy, however, significant advances in the rational design of water oxidation catalysts are required. Detailed information on the structure of the catalyst under reaction conditions and mechanisms of O-O bond formation should be obtained. Here, we used a combination of Electron Paramagnetic Resonance (EPR), stopped flow freeze quench on a millisecond-second time scale, X-ray absorption (XAS), Resonance Raman (RR) spectroscopy and Density Functional Theory (DFT) to follow the dynamics of the Ru-based single site catalyst, [Ru(II)(NPM)(4-pic)2(H2O)](2+) (NPM = 4-t-butyl-2,6-di(1',8'-naphthyrid-2'-yl)pyridine, pic = 4-picoline), under the water oxidation conditions...
November 1, 2016: Journal of the American Chemical Society
Douglas W Agnew, Milan Gembicky, Curtis E Moore, Arnold L Rheingold, Joshua S Figueroa
The preparation of 3D and 2D Cu(I) coordination networks using ditopic m-terphenyl isocyanides is described. The incorporation of sterically encumbering substituents enables the controlled, solid-state preparation of Cu(I) tris-isocyanide nodes with a labile solvent ligand in a manner mirroring solution-phase chemistry of monomeric complexes. The protection afforded by the m-terphenyl groups is also shown to engender significant stability towards heat as well as acidic or basic conditions, resulting in robust single-metal-node networks that can transition from 3D to 2D extended structures...
November 1, 2016: Journal of the American Chemical Society
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