bluuebunny/crossref_metadata_2025_split huggingface dataset:
Substitution‐Inert Polynuclear Platinum Complexes as Metalloshielding Agents for Heparan Sulfate
Authors: Gorle Anil Kumar , Katner Samantha J. , Johnson Wyatt E. , Lee Daniel E. , Daniel A. Gerard , Ginsburg Eric P. , von Itzstein Mark , Berners‐Price Susan J. , Farrell Nicholas P. 
Published: April 2018

AbstractCleavage of heparan sulfate proteoglycans (HSPGs) by the enzyme heparanase modulates tumour‐related events including angiogenesis, cell invasion, and metastasis. Metalloshielding of heparan sulfate (HS) by positively charged polynuclear platinum complexes (PPCs) effectively inhibits physiologically critical HS functions. Studies using bacterial P. heparinus heparinase II showed that a library of Pt complexes varying in charge and nuclearity and the presence or absence of a dangling amine inhibits the cleavage activity of the enzyme on the synthetic pentasaccharide, Fondaparinux (FPX). Charge‐dependent affinity of PPC for FPX was seen in competition assays with methylene blue and ethidium bromide. The dissociation constant (Kd) of TriplatinNC for FPX was directly measured by isothermal titration calorimetry (ITC). The trend in DFT calculated interaction energies with heparin fragments is consistent with the spectroscopic studies. Competitive inhibition of TAMRA‐R9 internalization in human carcinoma (HCT116) cells along with studies in HCT116, wildtype CHO and mutant CHO‐pgsA745 (lacking HS/CS) cells confirm that HSPG‐mediated interactions play an important role in the cellular accumulation of PPCs.
A Computational Mechanistic Investigation into Reduction of Gold(III) Complexes by Amino Acid Glycine: A New Variant for Amine Oxidation
Authors: Chipman Antony , Gouranourimi Ali , Farshadfar Kaveh , Olding Angus , Yates Brian F. , Ariafard Alireza 
Published: April 2018

AbstractDensity functional theory (DFT) was utilized to explore the reduction of gold(III) complexes by the amino acid glycine (Gly). Interestingly, when the nitrogen atom of Gly coordinates to the gold(III) center, its Cα‐hydrogen atom becomes so acidic that it can be easily deprotonated by a mild base like water. The deprotonation converts the amino acid into a potent reductant by which gold(III) is reduced to gold(I) with a moderate activation energy. To our knowledge, this is the first contribution suggesting that primary amines are oxidized to imines via direct α‐carbon deprotonation. This finding may provide new insights into the mechanistic interpretation of amine oxidations catalyzed/mediated by a center with high cathodic reduction potential. This work also provides a rationalization behind why gold(III) complexes with amine‐based polydentate ligands are reluctant to undergo a redox process. Gold(III) reduction occurs most efficiently if the Cα proton leaves in the plane of the Cα, N and Au atoms. Chelation prevents this alignment, resulting in the gold(III) complex being unreactive toward reduction. It has been experimentally found that gold(III) is capable of oxidizing Gly to glyoxylic acid (GA) as the initial product. The latter, in the presence of another gold(III) complex, has been reported to undergo oxidative decarboxylation to afford CO2 and HCOOH. This process is found to be mediated by formation of a geminal diol intermediate produced by reaction of water with the aldehyde functional group of the coordinated GA.
Enantiopure versus Racemic Mixture in Reversible, Two‐Step, Single‐Crystal‐to‐Single‐Crystal Transformations of Copper(II) Complexes
Authors: Ene Cristian D. , Maxim Catalin , Rouzières Mathieu , Clérac Rodolphe , Avarvari Narcis , Andruh Marius 
Published: April 2018

AbstractThe reaction of chiral sodium complexes, 1∞[Na(S‐valmetH)]⋅H2O (1‐S) and 1∞[Na(R‐valmetH)]⋅H2O (1‐R), with copper(II) acetate affords chiral one‐dimensional coordination polymers with the formulas 1∞[Cu(S‐valmet)(H2O)]⋅H2O (2‐S) and 1∞[Cu(R‐valmet)(H2O)]⋅H2O (2‐R) (R/S‐valmetH2 are Schiff base proligands resulting from the condensation reactions between o‐vanillin and R/S‐methionine). The copper ions are connected by the carboxylato groups belonging to the amino‐acid moieties, resulting in infinite chains showing syn‐anti out‐of‐plane bridging mode. The circular dichroism spectra of 1‐S, 1‐R, 2‐S, and 2‐R confirm their enantiomeric nature. Compounds 2‐S and 2‐R undergo a two‐step single‐crystal‐to‐single‐crystal transformation, with the elimination of the lattice and coordinated water molecules: 1∞[Cu(S‐valmet)(H2O)]⋅H2O (2‐S)→1∞[Cu(S‐valmet)]⋅H2O (3‐S⋅H2O)→1∞[Cu(S‐valmet)] (3‐S) and 1∞[Cu(R‐valmet)(H2O)]⋅H2O (2‐R)→1∞[Cu(R‐valmet)]⋅H2O (3‐R⋅H2O)→1∞[Cu(R‐valmet)] (3‐R), respectively. During these transformations, every pair of face‐to‐face chains present in 2‐S (or 2‐R) has been “zipped up” into a chiral double chain through the removal of the aqua ligands and their replacement by the carboxylato oxygen atoms from the neighboring chain. Consequently, each carboxylato group now bridges three copper ions. The conversion of the single chains, 2‐S and 2‐R, into the double chains, 3‐S and 3‐R, is accompanied by a change of the strength of the exchange interactions between the copper ions: weak antiferromagnetic couplings are observed in compound 2‐S (J/kB=−1.23(5) K, H=−2J ΣSiSi+1) and relatively strong in compound 3‐S (J/kB=−76.0(8) K). When the racemic mixture of the ligands, R,S‐valmetH2, is employed, in the same experimental conditions, a racemic mixture of mononuclear compounds, [Cu(R,S‐valmet)(H2O)2]⋅H2O (4‐RS), is obtained. Compound 4‐RS also undergoes a SCSC transformation with the elimination of the lattice and one of the coordinated water molecules, resulting in a racemic mixture of chiral chains, 1∞[Cu(R‐valmet)(H2O)]⋅1∞[Cu(S‐valmet)(H2O)] (5‐RS). In this compound, the coupling of the copper(II) ions within the chains is weak and ferromagnetic (J/kB=+0.10(2) K). These results prove that the chirality of the valmetH2 ligands (optically pure or racemic mixture) plays a key role in the self‐assembly process of the copper(II) complexes.
Porous Nanocomposite Comprising Ultralong Hydroxyapatite Nanowires Decorated with Zinc‐Containing Nanoparticles and Chitosan: Synthesis and Application in Bone Defect Repair
Authors: Sun Tuan‐Wei , Yu Wei‐Lin , Zhu Ying‐Jie , Chen Feng , Zhang Yong‐Gang , Jiang Ying‐Ying , He Yao‐Hua 
Published: April 2018

AbstractHydroxyapatite nanowires exhibit a great potential in biomedical applications owing to their high specific surface area, high flexibility, excellent mechanical properties, and similarity to mineralized collagen fibrils of natural bone. In this work, zinc‐containing nanoparticle‐decorated ultralong hydroxyapatite nanowires (Zn‐UHANWs) with a hierarchical nanostructure have been synthesized by a one‐step solvothermal method. The highly flexible Zn‐UHANWs exhibit a hierarchical rough surface and enhanced specific surface area as compared with ultralong hydroxyapatite nanowires (UHANWs). To evaluate the potential application of Zn‐UHANWs in bone regeneration, the biomimetic Zn‐UHANWs/chitosan (CS) (Zn‐UHANWs/CS) composite porous scaffold with 80 wt % Zn‐UHANWs was prepared by incorporating Zn‐UHANWs into the chitosan matrix by the freeze‐drying process. The as‐prepared Zn‐UHANWs/CS composite porous scaffold exhibits enhanced mechanical properties, highly porous structure, and excellent water retention capacity. In addition, the Zn‐UHANWs/CS porous scaffold has a good biodegradability with the sustainable release of Zn, Ca, and P elements in aqueous solution. More importantly, the Zn‐UHANWs/CS porous scaffold can promote the osteogenic differentiation of rat bone marrow derived mesenchymal stem cells and facilitate in vivo bone regeneration as compared with the pure CS porous scaffold or UHANWs/CS porous scaffold. Thus, both the Zn‐UHANWs and Zn‐UHANWs/CS porous scaffold developed in this work are promising for application in bone defect repair.
Facile Synthesis of Highly Efficient Amorphous Mn‐MIL‐100 Catalysts: Formation Mechanism and Structure Changes during Application in CO Oxidation
Authors: Zhang Xiaodong , Li Hongxin , Lv Xutian , Xu Jingcheng , Wang Yuxin , He Chi , Liu Ning , Yang Yiqiong , Wang Yin 
Published: April 2018

AbstractA comprehensive study was carried out on amorphous metal‐organic frameworks Mn‐MIL‐100 as efficient catalysts for CO oxidation. This study focused on explaining the crystalline–amorphous–crystalline transformations during thermolysis of Mn‐MIL‐100 and studying the structure changes during the CO oxidation reaction. A possible formation mechanism of amorphous Mn‐MIL‐100 was proposed. Amorphous Mn‐MIL‐100 obtained by calcination at 250 °C (a‐Mn‐250) showed a smaller specific surface area (4 m2 g−1) but high catalytic activity. Furthermore, the structure of amorphous Mn‐MIL‐100 was labile during the reaction. When a‐Mn‐250 was treated with reaction atmosphere at high temperature (giving used‐a‐Mn‐250‐S), the amorphous catalysts transformed into Mn2O3. Meanwhile, the BET surface area (164 m2 g−1) and catalytic performance both sharply increased. In addition, used‐a‐Mn‐250‐S catalyst transformed from Mn2O3 into Mn3O4, and this resulted in a slight decrease of catalytic activity in the presence of 1 vol % water vapor in the feed stream. A schematic mechanism of the structure changes during the reaction process was proposed. The success of the synthesis relies on the increase in BET surface area by using CO as retreatment atmosphere, and the enhanced catalytic activity was attributed to the unique structure, a large quantity of surface active oxygen species, oxygen vacancies, and good low‐temperature reduction behavior.
Acquiring High‐Performance Deep‐Blue OLED Emitters through an Unexpected Blueshift Color‐Tuning Effect Induced by Electron‐Donating ‐OMe Substituents
Authors: Peng Song , Zhao Yihuan , Fu Caixia , Pu Xuemei , Zhou Liang , Huang Yan , Lu Zhiyun 
Published: April 2018

AbstractA series of blue‐emissive 7‐(diphenylamino)‐4‐phenoxycoumarin derivatives bearing ‐CF3, ‐OMe, or ‐N(Me)2 substituents on the phenoxy subunit were synthesized. Although both the ‐CF3 and ‐N(Me)2 modifications were found to trigger redshifted fluorescence, the ‐OMe substitution was demonstrated to exert an unexpected blueshift color‐tuning effect toward the deep‐blue region. The reason is that the moderate electron‐donating ‐OMe group can endow coumarins with unaltered HOMO but elevated LUMO energy levels. Moreover, the ‐OMe substitution was found to be beneficial to the thermal stability of these coumarins. Therefore, the trimethoxy‐substituted objective compound can act as a high‐performance deep‐blue organic light‐emitting diode (OLED) emitter, and OLED based on it emits deep‐blue light with CIE coordinates of (0.148, 0.084), maximum luminance of 7800 cd m−2, and maximum external quantum efficiency of 5.1 %. These results not only shed light on the molecular design strategy for high‐performance deep‐blue OLED emitters through color‐tuning, but also show the perspective of coumarin derivatives as deep‐blue OLED emitters.
Real‐Space In Situ Bond Energies: Toward A Consistent Energetic Definition of Bond Strength
Authors: Menéndez‐Crespo Daniel , Costales Aurora , Francisco Evelio , Martín Pendás Ángel 
Published: April 2018

AbstractA rigorous definition of intrinsic bond strength based on the partitioning of a molecule into real‐space fragments is presented. Using the domains provided by the quantum theory of atoms‐in‐molecules (QTAIM) together with the interacting quantum atoms (IQA) energetic decomposition, we show how an in situ bond strength, matching all the requirements of an intrinsic bond energy, can be defined between each pair of fragments. Total atomization or fragmentation energies are shown to be equal to the sum of these in situ bond energies (ISBEs) if the energies of the fragments are measured with respect to their in‐the‐molecule state. These energies usually lie above the ground state of the isolated fragments by quantities identified with the standard fragment relaxation or deformation energies, which are also provided by the protocol. Deformation energies bridge dissociation energies with ISBEs, and can be dissected by using well‐known tools of real‐space theories of chemical bonding. Similarly, ISBEs can be partitioned into ionic and covalent contributions, and this feature adds to the chemical appeal of the procedure. All the energetic quantities examined are observable and amenable, in principle, to experimental determination. Several systems, exemplifying the role of each energetic term presented herein, are used to show the power of the approach.
A Pseudo‐Octahedral Cobalt(II) Complex with Bispyrazolylpyridine Ligands Acting as a Zero‐Field Single‐Molecule Magnet with Easy Axis Anisotropy
Authors: Rigamonti Luca , Bridonneau Nathalie , Poneti Giordano , Tesi Lorenzo , Sorace Lorenzo , Pinkowicz Dawid , Jover Jesus , Ruiz Eliseo , Sessoli Roberta , Cornia Andrea 
Published: April 2018

AbstractThe homoleptic mononuclear compound [Co(bpp‐COOMe)2](ClO4)2 (1) (bpp‐COOMe=methyl 2,6‐di(pyrazol‐1‐yl)pyridine‐4‐carboxylate) crystallizes in the monoclinic C2/c space group, and the cobalt(II) ion possesses a pseudo‐octahedral environment given by the two mer‐coordinated tridentate ligands. Direct‐current magnetic data, single‐crystal torque magnetometry, and EPR measurements disclosed the easy‐axis nature of this cobalt(II) complex, which shows single‐molecule magnet behavior when a static field is applied in alternating‐current susceptibility measurements. Diamagnetic dilution in the zinc(II) analogue [Zn(bpp‐COOMe)2](ClO4)2 (2) afforded the derivative [Zn0.95Co0.05(bpp‐COOMe)2](ClO4)2 (3), which exhibits slow relaxation of magnetization even in zero field thanks to the reduction of dipolar interactions. Theoretical calculations confirmed the overall electronic structure and the magnetic scenario of the compound as drawn by experimental data, thus confirming the spin‐phonon Raman relaxation mechanism, and a direct quantum tunneling in the ground state as the most plausible relaxation pathway in zero field.
Hypervalent Iodine Reagents by Anodic Oxidation: A Powerful Green Synthesis
Authors: Elsherbini Mohamed , Wirth Thomas 
Published: April 2018

AbstractThe anodic oxidation of aryl iodides is a powerful method for the synthesis of hypervalent iodine reagents, which eliminates the necessity to use expensive or hazardous chemical oxidizing reagents. The hypervalent iodine reagents generated at the anode are successfully used as either in‐cell or ex‐cell mediators for different valuable chemical transformations such as fluorinations and oxidative cyclizations. More recently, recyclable mediators and catalytic protocols have been developed.
Transformation of Perovskite BaBiO3 into Layered BaBiO2.5 Crystals Featuring Unusual Chemical Bonding and Luminescence
Authors: Li Hong , Zhao Qing , Liu Bo‐Mei , Zhang Jun‐Ying , Li Zhi‐Yong , Guo Shao‐Qiang , Ma Ju‐Ping , Kuroiwa Yoshihiro , Moriyoshi Chikako , Zheng Li‐Rong , Sun Hong‐Tao 
Published: April 2018

AbstractEngineering oxygen coordination environments of cations in oxides has received intense interest thanks to the opportunities for the discovery of novel oxides with unusual properties. Herein, the synthesis of stoichiometric layered BaBiO2.5 by a nontopotactic phase transformation of perovskite BaBiO3 is presented. By analyzing the synchrotron X‐ray diffraction data by the maximum‐entropy method/Rietveld technique, it was found that Bi is involved in an unusual chemical bonding situation with four oxygen atoms featuring one ionic bond and three covalent bonds, which results in an asymmetric coordination geometry. Photophysical characterization revealed that this peculiar structure shows near‐infrared luminescence differing from that of conventional Bi‐containing compounds. Experimental and theoretical results led to the proposal of an excitonic nature of the luminescence. This work highlights that synthesizing materials with uncommon Bi−O bonding and Bi coordination geometry provides a pathway to the discovery of systems with new functionalities. This could inspire interest in the exploration of a range of materials containing heavier p‐block elements with prospects for finding systems with unusual properties.
Reductive Elimination Leading to C−C Bond Formation in Gold(III) Complexes: A Mechanistic and Computational Study
Authors: Rocchigiani Luca , Fernandez‐Cestau Julio , Budzelaar Peter H. M. , Bochmann Manfred 
Published: April 2018

AbstractThe factors affecting the rates of reductive C−C cross‐coupling reactions in gold(III) aryls were studied by using complexes that allow easy access to a series of electronically modified aryl ligands, as well as to gold methyl and vinyl complexes, by using the pincer compounds [(C^N^C)AuR] (R=C6F5, CH=CMe2, Me and p‐C6H4X, where X=OMe, F, H, tBu, Cl, CF3, or NO2) as starting materials (C^N^C=2,6‐(4′‐tBuC6H3)2pyridine dianion). Protodeauration followed by addition of one equivalent SMe2 leads to the quantitative generation of the thioether complexes [(C^N‐CH)AuR(SMe2)]+. Upon addition of a second SMe2 pyridine is displaced, which triggers the reductive aryl−R elimination. The rates for these cross‐couplings increase in the sequence k(vinyl)>k(aryl)≫k(C6F5)>k(Me). Vinyl−aryl coupling is particularly fast, 1.15×10−3 L mol−1 s−1 at 221 K, whereas both C6F5 and Me couplings encountered higher barriers for the C−C bond forming step. The use of P(p‐tol)3 in place of SMe2 greatly accelerates the C−C couplings. Computational modelling shows that in the C^N‐bonded compounds displacement of N by a donor L is required before the aryl ligands can adopt a conformation suitable for C−C bond formation, so that elimination takes place from a four‐coordinate intermediate. The C−C bond formation is the rate‐limiting step. In the non‐chelating case, reductive C(sp2)−C(sp2) elimination from three‐coordinate ions [(Ar1)(Ar2)AuL]+ is almost barrier‐free, particularly if L=phosphine.
13C Kinetic Isotope Effects as a Quantitative Probe To Distinguish between Enol and Enamine Mechanisms in Aminocatalysis
Authors: Roytman Vladislav A. , Karugu Rachael W. , Hong Yun , Hirschi Jennifer S. , Vetticatt Mathew J. 
Published: April 2018

AbstractA combination of experimental 13C kinetic isotope effects (KIEs) and high‐level density functional theory (DFT) calculations is used to distinguish between “enamine” and “enol” mechanisms in the Michael addition of acetone to trans‐β‐nitrostyrene catalyzed by Jacobsen's primary amine thiourea catalyst. In light of the recent findings that the widely used 18O‐incorporation probe for these mechanisms is flawed, the results described in this communication demonstrate an alternative probe to distinguish between these pathways. A key advantage of this probe is that quantitative mechanistic information is obtained without modifying experimental conditions. This approach is expected to find application in resolving mechanistic debates, while providing valuable information about the key transition state of organocatalyzed reactions involving the α‐functionalization of carbonyls.
Turning Off Transcription with Bacterial RNA Polymerase through CuAAC Click Reactions of DNA Containing 5‐Ethynyluracil
Authors: Slavíčková Michaela , Janoušková Martina , Šimonová Anna , Cahová Hana , Kambová Milada , Šanderová Hana , Krásný Libor , Hocek Michal 
Published: April 2018

AbstractCopper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) click reaction in the major groove of DNA containing 5‐ethynyluracil (UE) with azides was used for turning off sequence‐specific protein–DNA interactions. The concept was first demonstrated on switching off cleavage of short modified DNA by restriction endonuclease BamHI‐HF. Finally, DNA template containing UE was used for in vitro transcription with E. coli RNA polymerase and the transcription was turned off by CuAAC with 3‐azidopropane‐1,2‐diol or 3‐azido‐7‐hydroxycoumarin.
Potent Inhibitors of Plasmodial Serine Hydroxymethyltransferase (SHMT) Featuring a Spirocyclic Scaffold
Authors: Schwertz Geoffrey , Witschel Matthias C. , Rottmann Matthias , Leartsakulpanich Ubolsree , Chitnumsub Penchit , Jaruwat Aritsara , Amornwatcharapong Watcharee , Ittarat Wanwipa , Schäfer Anja , Aponte Raphael A. , Trapp Nils , Chaiyen Pimchai , Diederich François 
Published: April 2018

AbstractWith the discovery that serine hydroxymethyltransferase (SHMT) is a druggable target for antimalarials, the aim of this study was to design novel inhibitors of this key enzyme in the folate biosynthesis cycle. Herein, 19 novel spirocyclic ligands based on either 2‐indolinone or dihydroindene scaffolds and featuring a pyrazolopyran core are reported. Strong target affinities for Plasmodium falciparum (Pf) SHMT (14–76 nm) and cellular potencies in the low nanomolar range (165–334 nm) were measured together with interesting selectivity against human cytosolic SHMT1 (hSHMT1). Four co‐crystal structures with Plasmodium vivax (Pv) SHMT solved at 2.2–2.4 Å resolution revealed the key role of the vinylogous cyanamide for anchoring ligands within the active site. The spirocyclic motif in the molecules enforces the pyrazolopyran core to adopt a substantially more curved conformation than that of previous non‐spirocyclic analogues. Finally, solvation of the spirocyclic lactam ring of the receptor‐bound ligands is discussed.
Stepwise Hierarchical Self‐Assembly of Supramolecular Amphiphiles into Higher‐Order Three‐Dimensional Nanostructures
Authors: della Sala Flavio , Verbeet Wessel , Silvestrini Simone , Fortunati Ilaria , Ferrante Camilla , Prins Leonard J. 
Published: April 2018

AbstractHierarchical self‐assembly describes the spontaneous formation of large well‐defined molecular structures through a sequence of spontaneous processes driven by noncovalent interactions between molecules and intermediate structures. The chemical information embedded in the initial molecules determines the structural outcome of the overall assembly process. This is clearly advantageous in terms of product accessibility, but poses limits to the extent of control that can be exerted over the process. Here we report the stepwise hierarchical self‐assembly of well‐defined three‐dimensional organic nanostructures with dimensions of over 100 nm in each single xyz‐direction and a total volume of up to 1.5×10−2 μm3. These structures are formed through three consecutive processes that rely exclusively on the establishment of noncovalent interactions between the components: (1) complex formation between Zn2+ and a macrocyclic ligand, (2) association of the amphiphiles in disk‐like micellar structures and, finally, (3) ATP‐induced stacking of the disks into large hexagonal prisms. The top and bottom surface of these structures are flat multivalent cationic surfaces covered with ATP with dimensions in the order of 2×105 nm2 onto which nanometer‐sized gold nanoparticles can be deposited through a final self‐assembly process. The stepwise hierarchical process bears a close analogy with a multistep covalent synthetic pathway with the difference that all steps rely exclusively on noncovalent interactions.