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https://www.readbyqxmd.com/read/29149501/the-weakly-coordinating-tris-trichlorosilyl-silyl-anion
#1
Marian Olaru, Maxie F Hesse, Elena Rychagova, Sergey Ketkov, Stefan Mebs, Jens Beckmann
Closely following the procedure for the preparation of the base-stabilized dichlorosilylene complex NHCDipp∙SiCl2 by Roesky and Stalke et al. (Angew. Chem. Int. Ed. 2009, 48, 5683-5686), besides the reported by-product [NHCDipp-H+∙∙∙Cl-], few crystals of the salt [NHCDipp-H∙∙∙Cl∙∙∙H-NHCDipp]Si(SiCl3)3 were isolated and characterized by X-ray crystallography (NHCDipp = N,N-di(2,6-isopropylphenyl)-imidazo-2-ylidene). They feature the weakly-coordinating anion Si(SiCl3)3-, which was more rationally obtained in high yields upon deprotonation of conjugate Brønsted acid HSi(SiCl3)3 with NHCDipp or PMP (PMP = 1,2,2,6,6-pentamethylpiperidine)...
November 17, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/29147561/synthesis-and-reactivity-of-a-4his-enzyme-model-complex
#2
Jia Li, Atanu Banerjee, Timothy A Hasse, Reza Loloee, Shannon M Biros, Richard J Staples, Ferman A Chavez
A new iron(II) complex has been prepared and characterized. [Fe(TrIm)4(OTf)2] (1, TrIm = 1-Tritylimidazole). The solid state structure of 1 has been determined by X-ray crystallography. Compound 1 crystallizes in triclinic space group P1̄, with a = 13.342(7) Å, b = 13.5131(7) Å and c = 13.7025(7) Å. The iron center resides in distorted octahedral geometry coordinated to four equatorial imidazole groups and two axial triflate oxygens groups. The complex is high spin between 20 K and 300 K as indicated by variable field variable temperature magnetic measurements...
2017: RSC Advances
https://www.readbyqxmd.com/read/29147002/capturing-an-initial-intermediate-during-the-p450nor-enzymatic-reaction-using-time-resolved-xfel-crystallography-and-caged-substrate
#3
Takehiko Tosha, Takashi Nomura, Takuma Nishida, Naoya Saeki, Kouta Okubayashi, Raika Yamagiwa, Michihiro Sugahara, Takanori Nakane, Keitaro Yamashita, Kunio Hirata, Go Ueno, Tetsunari Kimura, Tamao Hisano, Kazumasa Muramoto, Hitomi Sawai, Hanae Takeda, Eiichi Mizohata, Ayumi Yamashita, Yusuke Kanematsu, Yu Takano, Eriko Nango, Rie Tanaka, Osamu Nureki, Osami Shoji, Yuka Ikemoto, Hironori Murakami, Shigeki Owada, Kensuke Tono, Makina Yabashi, Masaki Yamamoto, Hideo Ago, So Iwata, Hiroshi Sugimoto, Yoshitsugu Shiro, Minoru Kubo
Time-resolved serial femtosecond crystallography using an X-ray free electron laser (XFEL) in conjunction with a photosensitive caged-compound offers a crystallographic method to track enzymatic reactions. Here we demonstrate the application of this method using fungal NO reductase, a heme-containing enzyme, at room temperature. Twenty milliseconds after caged-NO photolysis, we identify a NO-bound form of the enzyme, which is an initial intermediate with a slightly bent Fe-N-O coordination geometry at a resolution of 2...
November 17, 2017: Nature Communications
https://www.readbyqxmd.com/read/29142195/structural-basis-for-trna-dependent-cysteine-biosynthesis
#4
Meirong Chen, Koji Kato, Yume Kubo, Yoshikazu Tanaka, Yuchen Liu, Feng Long, William B Whitman, Pascal Lill, Christos Gatsogiannis, Stefan Raunser, Nobutaka Shimizu, Akira Shinoda, Akiyoshi Nakamura, Isao Tanaka, Min Yao
Cysteine can be synthesized by tRNA-dependent mechanism using a two-step indirect pathway, where O-phosphoseryl-tRNA synthetase (SepRS) catalyzes the ligation of a mismatching O-phosphoserine (Sep) to tRNA(Cys) followed by the conversion of tRNA-bounded Sep into cysteine by Sep-tRNA:Cys-tRNA synthase (SepCysS). In ancestral methanogens, a third protein SepCysE forms a bridge between the two enzymes to create a ternary complex named the transsulfursome. By combination of X-ray crystallography, SAXS and EM, together with biochemical evidences, here we show that the three domains of SepCysE each bind SepRS, SepCysS, and tRNA(Cys), respectively, which mediates the dynamic architecture of the transsulfursome and thus enables a global long-range channeling of tRNA(Cys) between SepRS and SepCysS distant active sites...
November 15, 2017: Nature Communications
https://www.readbyqxmd.com/read/29142015/aqueous-ball-milling-of-nacre-constituents-facilitates-directional-self-assembly-of-aragonite-nanoparticles-of-the-gastropod-haliotis-glabra
#5
Marie-Louise Lemloh, Andreas Verch, Ingrid M Weiss
A ball-milling approach was developed to investigate the constituents of isolated nacre tablets of the gastropod Haliotis glabra in aqueous suspension without additional chemical additives. The obtained particle mixtures were characterized using X-ray crystallography as well as scanning and transmission electron microscopy. Aragonite nanoparticles retained their crystal structure even after 14 h of ball milling. The long-term stability of the particle mixtures varied as a function of the ball-milling duration...
November 2017: Journal of the Royal Society, Interface
https://www.readbyqxmd.com/read/29140680/helicity-inversion-of-supramolecular-hydrogels-induced-by-achiral-substituents
#6
Guofeng Liu, Xin Li, Jianhui Sheng, Pei-Zhou Li, Wee Kong Ong, Soo Zeng Fiona Phua, Hans Ågren, Liangliang Zhu, Yanli Zhao
Probing the supramolecular chirality of assemblies and controlling their handedness are closely related to the origin of chirality at supramolecular level and the development of smart materials with desired handedness. However, it remains unclear how achiral residues covalently bonded to chiral amino acids can function in the chirality inversion of supramolecular assemblies. Herein, we report macroscopic chirality and dynamic manipulation of chiroptical activity of hydrogels self-assembled from phenylalanine derivatives, together with the inversion of their handedness achieved solely by exchanging achiral substituents between oligo(ethylene glycol) and carboxylic acid groups...
November 15, 2017: ACS Nano
https://www.readbyqxmd.com/read/29139153/a-four-step-synthesis-of-substituted-5-11-dicyano-6-12-diaryltetracenes-with-enhanced-stability-and-high-fluorescence-emission
#7
Nicolas Kerisit, Przemyslaw Gawel, Brian Levandowski, Yun-Fang Yang, Víctor García-López, Nils Trapp, Laurent Ruhlmann, Corinne Boudon, Kendall N Houk, François Diederich
A four-step synthesis of substituted 5,11-dicyano-6,12-diaryltetracenes was developed, starting from readily available para-substituted benzophenones. The key step of this straightforward route is the complex cascade reaction between tetraaryl[3]cumulenes and tetracyanoethene (TCNE) resulting in 5,5,11,11-tetracyano-5,11-dihydrotetracenes. The mechanism of this transformation was reinvestigated by means of theoretical calculations. The target tetracenes were obtained by a newly developed decyanation/aromatization reaction catalyzed by Cu(I) or Cu(II) complexes in solution, conditions compatible with a broad range of functional groups...
November 15, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29138423/the-photocycle-of-orange-carotenoid-protein-conceals-distinct-intermediates-and-asynchronous-changes-in-the-carotenoid-and-protein-components
#8
E G Maksimov, N N Sluchanko, Y B Slonimskiy, E A Slutskaya, A V Stepanov, A M Argentova-Stevens, E A Shirshin, G V Tsoraev, K E Klementiev, O V Slatinskaya, E P Lukashev, T Friedrich, V Z Paschenko, A B Rubin
The 35-kDa Orange Carotenoid Protein (OCP) is responsible for photoprotection in cyanobacteria. It acts as a light intensity sensor and efficient quencher of phycobilisome excitation. Photoactivation triggers large-scale conformational rearrangements to convert OCP from the orange OCP(O) state to the red active signaling state, OCP(R), as demonstrated by various structural methods. Such rearrangements imply a complete, yet reversible separation of structural domains and translocation of the carotenoid. Recently, dynamic crystallography of OCP(O) suggested the existence of photocycle intermediates with small-scale rearrangements that may trigger further transitions...
November 14, 2017: Scientific Reports
https://www.readbyqxmd.com/read/29135057/oxime-ether-radical-cations-stabilized-by-n-heterocyclic-carbene
#9
Youngsuk Kim, Kimoon Kim, Eunsung Lee
N-heterocyclic carbene nitric oxide (NHCNO) radicals, which can be regarded as iminoxyl radicals stabilized by NHCs, were found to react with a series of silyl and alkyl triflates to generate the corresponding oxime ether radical cations. The structures of the resulting oxime ether radical cations were determined by X-ray crystallography, along with EPR and computational analysis. In contrast, lutidinium triflate produced a 1:1 mixture of [NHCNO+][OTf-] and [NHCNHOH+][OTf-] upon the reaction with NHCNO. This study adds an important example of stable singlet carbenes stabilizing main group radicals due to their π-conjugating effect, the synthesis and structures of which have never been elucidated previously...
November 14, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/29135029/quantum-crystallography-a-perspective
#10
Lou Massa, Chérif F Matta
Extraction of the complete quantum mechanics from X-ray scattering data is the ultimate goal of quantum crystallography. This article delivers a perspective for that possibility. It is desirable to have a method for the conversion of X-ray diffraction data into an electron density that reflects the antisymmetry of an N-electron wave function. A formalism for this was developed early on for the determination of a constrained idempotent one-body density matrix. The formalism ensures pure-state N-representability in the single determinant sense...
November 14, 2017: Journal of Computational Chemistry
https://www.readbyqxmd.com/read/29134431/impact-of-domain-knowledge-on-blinded-predictions-of-binding-energies-by-alchemical-free-energy-calculations
#11
Antonia S J S Mey, Jordi Juárez Jiménez, Julien Michel
The Drug Design Data Resource (D3R) consortium organises blinded challenges to address the latest advances in computational methods for ligand pose prediction, affinity ranking, and free energy calculations. Within the context of the second D3R Grand Challenge several blinded binding free energies predictions were made for two congeneric series of Farsenoid X Receptor (FXR) inhibitors with a semi-automated alchemical free energy calculation workflow featuring FESetup and SOMD software tools. Reasonable performance was observed in retrospective analyses of literature datasets...
November 13, 2017: Journal of Computer-aided Molecular Design
https://www.readbyqxmd.com/read/29134076/1-2-aminophenyl-1h-1-2-3-triazole-4-carboxylic-acid-activity-against-gram-positive-and-gram-negative-pathogens-including-vibrio-cholerae
#12
Krishnendu Maji, Debasish Haldar
We report a new synthetic aromatic ε-amino acid containing a triazole moiety with antimicrobial potential against Gram-positive, Gram-negative and pathogenic bacteria including Vibrio cholerae. Structure-property relationship studies revealed that all the functional groups are essential to enhance the antimicrobial activity. The 1-(2-aminophenyl)-1H-1,2,3-triazole-4-carboxylic acid was synthesized by click chemistry. From X-ray crystallography, the amino acid adopts a kink-like structure where the phenyl and triazole rings are perpendicular to each other and the amine and acid groups maintain an angle of 60°...
October 2017: Royal Society Open Science
https://www.readbyqxmd.com/read/29133784/gyri-like-proteins-catalyze-cyclopropanoid-hydrolysis-to-confer-cellular-protection
#13
Hua Yuan, Jinru Zhang, Yujuan Cai, Sheng Wu, Kui Yang, H C Stephen Chan, Wei Huang, Wen-Bing Jin, Yan Li, Yue Yin, Yasuhiro Igarashi, Shuguang Yuan, Jiahai Zhou, Gong-Li Tang
GyrI-like proteins are widely distributed in prokaryotes and eukaryotes, and recognized as small-molecule binding proteins. Here, we identify a subfamily of these proteins as cyclopropanoid cyclopropyl hydrolases (CCHs) that can catalyze the hydrolysis of the potent DNA-alkylating agents yatakemycin (YTM) and CC-1065. Co-crystallography and molecular dynamics simulation analyses reveal that these CCHs share a conserved aromatic cage for the hydrolytic activity. Subsequent cytotoxic assays confirm that CCHs are able to protect cells against YTM...
November 14, 2017: Nature Communications
https://www.readbyqxmd.com/read/29133410/unprecedented-pathway-of-reducing-equivalents-in-a-diflavin-linked-disulfide-oxidoreductase
#14
Rubén M Buey, Juan B Arellano, Luis López-Maury, Sergio Galindo-Trigo, Adrián Velázquez-Campoy, José L Revuelta, José M de Pereda, Francisco J Florencio, Peter Schürmann, Bob B Buchanan, Monica Balsera
Flavoproteins participate in a wide variety of physiologically relevant processes that typically involve redox reactions. Within this protein superfamily, there exists a group that is able to transfer reducing equivalents from FAD to a redox-active disulfide bridge, which further reduces disulfide bridges in target proteins to regulate their structure and function. We have identified a previously undescribed type of flavin enzyme that is exclusive to oxygenic photosynthetic prokaryotes and that is based on the primary sequence that had been assigned as an NADPH-dependent thioredoxin reductase (NTR)...
November 13, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/29133038/new-metalo-therapeutics-of-nsaids-against-human-breast-cancer-cells
#15
Christina N Banti, Constantina Papatriantafyllopoulou, Anastasios J Tasiopoulos, Sotiris K Hadjikakou
The non steroidal anti-inflammatory drugs (NSAID's)-silver(I) metallodrugs of aspirin (aspH), salicylic acid (salH2), naproxen (napH) acid or p-hydrobenzoic acid (pHbzaH) and the mitochondriotropic triphenylarsine (tpAs) with the formulae [Ag(asp)(tpAs)3] (1), [Ag(salH)(tpAs)3] (2), [Ag(nap)(tpAs)3] (3) and {[Ag(pHbza)(tpAs)3]∙(dmf)} (4) and [Ag(tpAs)3(NO3)] (5) have been synthesized and characterized by m.p., FT-IR, UV-vis and (1)H NMR, spectroscopic techniques and X-ray crystallography. The in vitro cytotoxic activity of 1-5 against human breast adenocarcinoma cancer cells: MCF-7 (positive to estrogen receptors (ERs)) and MDA-MB-231 (negative to estrogen receptors (ERs)) was evaluated...
November 10, 2017: European Journal of Medicinal Chemistry
https://www.readbyqxmd.com/read/29131938/a-crash-course-in-calcium-channels
#16
Gerald W Zamponi
Much progress has been made in understanding the molecular physiology and pharmacology of calcium channels. Recently, there have been tremendous advances in learning about calcium channel structure and function through crystallography and cryo-electron microscopy studies. Here, I will give an overview of our knowledge about calcium channels, and highlight two recent studies that give important insights into calcium channel structure.
November 13, 2017: ACS Chemical Neuroscience
https://www.readbyqxmd.com/read/29131932/redox-dependent-metal-metal-bonding-in-trinuclear-metal-chains-probing-the-transition-from-covalent-bonding-to-exchange-coupling
#17
John Ewart McGrady, Nicholas Perkins, Mohammed Obies, Graham Heath, Alison Edwards, Vaida Arcisauskaite
We report here the synthesis and physical properties of two new cationic tri-metallic chains, [(PEt3)3RuCl3M'Cl3Ru(PEt3)3]1+, M' = Rh and Ir. These are isostructural with a previously reported 17-electron all-ruthenium analogue, but the switch from an open-shell d5 Ru3+ ion to d6 Rh3+/Ir3+ in the central position has profound impact on the nature of the metal-metal bonding. X-ray crystallography and spectro-electrochemistry, complemented by electronic structure analysis at the DFT and CASSCF levels, indicate that whilst the presence of a Ru3+ ion in the center of the chain allows multi-center covalent bonding to develop, a closed-shell Rh3+/Ir3+ ion pushes the system towards the exchange-coupled limit, where the terminal Ru centers are only weakly interacting...
November 13, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29131142/a-consensus-model-of-human-apolipoprotein-a-i-in-its-monomeric-and-lipid-free-state
#18
John T Melchior, Ryan G Walker, Allison L Cooke, Jamie Morris, Mark Castleberry, Thomas B Thompson, Martin K Jones, Hyun D Song, Kerry-Anne Rye, Michael N Oda, Mary G Sorci-Thomas, Michael J Thomas, Jay W Heinecke, Xiaohu Mei, David Atkinson, Jere P Segrest, Sissel Lund-Katz, Michael C Phillips, W Sean Davidson
Apolipoprotein (apo)A-I is an organizing scaffold protein that is critical to high-density lipoprotein (HDL) structure and metabolism, probably mediating many of its cardioprotective properties. However, HDL biogenesis is poorly understood, as lipid-free apoA-I has been notoriously resistant to high-resolution structural study. Published models from low-resolution techniques share certain features but vary considerably in shape and secondary structure. To tackle this central issue in lipoprotein biology, we assembled a team of structural biologists specializing in apolipoproteins and set out to build a consensus model of monomeric lipid-free human apoA-I...
November 13, 2017: Nature Structural & Molecular Biology
https://www.readbyqxmd.com/read/29129933/atomically-precise-colloidal-nanoparticles-of-cerium-dioxide
#19
Kylie J Mitchell, Khalil A Abboud, George Christou
Synthesis of truly monodisperse nanoparticles and their structural characterization to atomic precision are important challenges in nanoscience. Success has recently been achieved for metal nanoparticles, particularly Au, with diameters up to 3 nm, the size regime referred to as nanoclusters. In contrast, families of atomically precise metal oxide nanoparticles are currently lacking, but would have a major impact since metal oxides are of widespread importance for their magnetic, catalytic and other properties...
November 13, 2017: Nature Communications
https://www.readbyqxmd.com/read/29128496/nickel-ii-pyrrocorphin-enhanced-binding-ability-in-a-highly-reduced-porphyrin-complex
#20
Yuki Ide, Takamitsu Kuwahara, Syo Takeshita, Rei Fujishiro, Masaaki Suzuki, Shigeki Mori, Hiroshi Shinokubo, Mikio Nakamura, Katsumi Yoshino, Takahisa Ikeue
Pyrrocorphin is an air-sensitive porphyrinoid with a highly reduced hexahydroporphyrin core. In contrast, pyrrolidine-fused pyrrocorphin (Pyr) obtained by successive 1,3-dipolar cycloaddition reactions of azomethine ylide to 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin is less air-sensitive. In order to reveal the effect of highly reduced porphyrin rings on the physicochemical properties of their metal complexes, we have prepared diamagnetic (S=0) Ni(II) complex Ni(II)(Pyr). The addition of excess pyridine (Py) to the toluene solution of Ni(II)(Pyr) yielded five-coordinate Ni(II)(Pyr)(Py), which was then completely converted to six-coordinate paramagnetic (S=1) Ni(II)(Pyr)(Py)2...
November 4, 2017: Journal of Inorganic Biochemistry
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