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51.
52.
Matthias Müller Dr. Silke Koser Olena Tverskoy Dr. Frank Rominger Dr. Jan Freudenberg Prof. Dr. Uwe H. F. Bunz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(24):6082-6086
This work reports the synthesis and characterization of bis- and tetrakis(thiadiazolo)-appended di- and tetraazaacenes, displaying up to seven catenated benzene/pyrazine rings. The targets are obtained by condensation of benzo-bis(thiadiazole)-4,5-dione with aromatic di- and tetraamines. The condensation products—up to a heptacene-like species—are stable but can be insoluble. Soluble derivatives are readily processible, but do not show enhanced electron affinities, as the two or four attached benzothiadiazole units are effectively resonance-separated from the acene body, maximizing the number of Clar-sextets. 相似文献
53.
Hui‐Min Lin Jian‐Rong Li Chao Mu Ao Li Xu‐Feng Liu Pei‐Hua Zhao Yu‐Long Li Zhong‐Qing Jiang Hong‐Ke Wu 《应用有机金属化学》2019,33(11)
Five monophosphine‐substituted diiron propane‐1,2‐dithiolate complexes as the active site models of [FeFe]‐hydrogenases have been synthesized and characterized. Reactions of complex [Fe2(CO)6{μ‐SCH2CH(CH3)S}] ( 1 ) with a monophosphine ligand tris(4‐methylphenyl)phosphine, diphenyl‐2‐pyridylphosphine, tris(4‐chlorophenyl)phosphine, triphenylphosphine, or tris(4‐fluorophenyl)phosphine in the presence of the oxidative agent Me3NO·2H2O gave the monophosphine‐substituted diiron complexes [Fe2(CO)5(L){μ‐SCH2CH(CH3)S}] [L = P(4‐C6H4CH3)3, 2 ; Ph2P(2‐C5H4N), 3 ; P(4‐C6H4Cl)3, 4 ; PPh3, 5 ; P(4‐C6H4F)3, 6 ] in 81%–94% yields. Complexes 2 – 6 have been characterized by elemental analysis, spectroscopy, and X‐ray crystallography. In addition, electrochemical studies revealed that these complexes can catalyze the reduction of protons to H2 in the presence of HOAc. 相似文献
54.
Pierre Thureau Simone Sturniolo Miri Zilka Fabio Ziarelli Stéphane Viel Jonathan R. Yates Giulia Mollica 《Magnetic resonance in chemistry : MRC》2019,57(5):256-264
Structure determination of functional organic compounds remains a formidable challenge when the sample exists as a powder. Nuclear magnetic resonance crystallography approaches based on the comparison of experimental and Density Functional Theory (DFT)-computed 1H chemical shifts have already demonstrated great potential for structure determination of organic powders, but limitations still persist. In this study, we discuss the possibility of using 13C-13C dipolar couplings quantified on powdered theophylline at natural isotopic abundance with the help of dynamic nuclear polarization, to realize a DFT-free, rapid screening of a pool of structures predicted by ab initio random structure search. We show that although 13C-13C dipolar couplings can identify structures possessing long range structural motifs and unit cell parameters close to those of the true structure, it must be complemented with other data to recover information about the presence and the chemical nature of the supramolecular interactions. 相似文献
55.
Luca Mazzei Michele Cianci Stefano Benini Stefano Ciurli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(52):12145-12158
Urease uses a cluster of two NiII ions to activate a water molecule for urea hydrolysis. The key to this unsurpassed enzyme is a change in the conformation of a flexible structural motif, the mobile flap, which must be able to move from an open to a closed conformation to stabilize the chelating interaction of urea with the NiII cluster. This conformational change brings the imidazole side chain functionality of a critical histidine residue, αHis323, in close proximity to the site that holds the transition state structure of the reaction, facilitating its evolution to the products. Herein, we describe the influence of the solution pH in modulating the conformation of the mobile flap. High-resolution crystal structures of urease inhibited in the presence of N-(n-butyl)phosphoric triamide (NBPTO) at pH 6.5 and pH 7.5 are described and compared to the analogous structure obtained at pH 7.0. The kinetics of urease in the absence and presence of NBPTO are investigated by a calorimetric assay in the pH 6.0–8.0 range. The results indicate that pH modulates the protonation state of αHis323, which was revealed to have pKa=6.6, and consequently the conformation of the mobile flap. Two additional residues (αAsp224 and αArg339) are shown to be key factors for the conformational change. The role of pH in modulating the catalysis of urea hydrolysis is clarified through the molecular and structural details of the interplay between protein conformation and solution acidity in the paradigmatic case of a metalloenzyme. 相似文献
56.
《Journal of computational chemistry》2018,39(17):1038-1043
The Kernel energy method (KEM) is a quantum chemical calculation method that has been shown to provide accurate energies for large molecules. KEM performs calculations on subsets of a molecule (called kernels) and so the computational difficulty of KEM calculations scales more softly than full molecule methods. Although KEM provides accurate energies those energies are not required to satisfy the variational theorem. In this article, KEM is extended to provide a full molecule single‐determinant N‐representable one‐body density matrix. A kernel expansion for the one‐body density matrix analogous to the kernel expansion for energy is defined. This matrix is converted to a normalized projector by an algorithm due to Clinton. The resulting single‐determinant N‐representable density matrix maps to a quantum mechanically valid wavefunction which satisfies the variational theorem. The process is demonstrated on clusters of three to twenty water molecules. The resulting energies are more accurate than the straightforward KEM energy results and all violations of the variational theorem are resolved. The N‐representability studied in this article is applicable to the study of quantum crystallography. © 2017 Wiley Periodicals, Inc. 相似文献
57.
Neda Choodari Milani Yazdan Maghsoud Mahdieh Hosseini Abouzar Babaei Hamidreza Rahmani Stephen Mark Roe Khodayar Gholivand 《应用有机金属化学》2020,34(4):e5526
Seven novel complexes (C1–C7) were synthesized by the interaction between Cu(I) metal cation, L1, L2, L3, X and PPh3, where L1–L3 are derivatives of ((pyridine-2-ylmethylene)amino)phenol imine ligands and X = Cl−, Br−, I−, NCS−. All the complexes were characterized using infrared, 1H NMR and 31P NMR spectroscopies. The crystal structures of C1–C7 were also determined using single-crystal X-ray diffraction. The organization of the crystal structures and the intermolecular interactions are discussed. The supramolecular assemblies are driven by cooperative π…π interactions and hydrogen bonds, followed by CH…π linkages. The potential anticancer effect of C1–C7 was assessed for human glioblastoma cells using several anticancer experiments, which showed that these complexes have marked anticancer property against U87 cells. It was also found that the minimum and maximum anticancer effects are shown by C3- and C4-treated samples, respectively. Furthermore, theoretical approaches were used to investigate the nature of metal–ligand interactions which suggest a closed-shell and electrostatic character for Cu…N, Cu…P and Cu…X bonds. 相似文献
58.
Four symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril-based compounds have been prepared and characterised by X-ray crystallography. Their crystal structures displayed the acetate anion-selective encapsulating capability of symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril. The host–guest interaction between the symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril and the acetate anion in aqueous solution has also been observed by variable temperature 1H NMR spectroscopy. 相似文献
59.
Charles Brenner 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):745-748
Fhit is a tumor suppressor protein encoded at the most fragile site in the human genome that is inactivated by genetic deletions early in the development of many cancers. A member of the Histidine Triad (HIT) superfamily of nucleotide-binding proteins, Fhit binds diadenosine triphosphate (ApppA) and cleaves it to produce AMP + ADP. The His96Asn mutation of Fhit, which reduces kcat by more than a million-fold, does not reduce tumor suppressor activity in a nude mouse assay. Thus, genetic and biochemical evidence suggest that ApppA binding but not cleavage is required for tumor suppression. Crystal structures of Fhit bound to a nonhydrolyzable ApppA analog revealed that Fhit binds two substrates per dimer, presenting all of the phosphates and two of the adenosines on the surface of the protein in place of a deep, positively charged groove in the empty Fhit protein dimer. It is proposed that signaling by Fhit is mediated by presentation of nucleotide substrates to cytosolic effectors. 相似文献
60.
Jorge Castellanos-Soriano Allen T. Ekubo Mark R. J. Elsegood Nuria Lastra-Calvo Aman Mantry Arturo Martinez-Insua-Rodriguez 《Phosphorus, sulfur, and silicon and the related elements》2017,192(5):570-575
New tetraalkylaminophosphonium chlorides were readily prepared by four-fold condensation of commercially available [P(CH2OH)4]Cl with a range of fifteen aryl based primary amines, in EtOH, at ambient temperature. All compounds have been characterized by FT–IR spectroscopy and elemental analysis. Solution 31P{1H} NMR studies of these chloride salts reveal their instability with respect to various PIII/PV species. The structures of three examples have been determined by single crystal X-ray diffraction and confirm the pseudotetrahedral arrangement around the PV center. Extensive N–H···Cl hydrogen bonding is observed. 相似文献