bluuebunny/crossref_metadata_2025 huggingface dataset:
Deciphering the Non‐Equivalence of Serine and Threonine O‐Glycosylation Points: Implications for Molecular Recognition of the Tn Antigen by an anti‐MUC1 Antibody
Authors: Martínez‐Sáez Nuria , Castro‐López Jorge , Valero‐González Jessika , Madariaga David , Compañón Ismael , Somovilla Víctor J. , Salvadó Míriam , Asensio Juan L. , Jiménez‐Barbero Jesús , Avenoza Alberto , Busto Jesús H. , Bernardes Gonçalo J. L. , Peregrina Jesús M. , Hurtado‐Guerrero Ramón , Corzana Francisco
Published: June 2015

The structural features of MUC1‐like glycopeptides bearing the Tn antigen (α‐O‐GalNAc‐Ser/Thr) in complex with an anti MUC‐1 antibody are reported at atomic resolution. For the α‐O‐GalNAc‐Ser derivative, the glycosidic linkage adopts a high‐energy conformation, barely populated in the free state. This unusual structure (also observed in an α‐S‐GalNAc‐Cys mimic) is stabilized by hydrogen bonds between the peptidic fragment and the sugar. The selection of a particular peptide structure by the antibody is thus propagated to the carbohydrate through carbohydrate/peptide contacts, which force a change in the orientation of the sugar moiety. This seems to be unfeasible in the α‐O‐GalNAc‐Thr glycopeptide owing to the more limited flexibility of the side chain imposed by the methyl group. Our data demonstrate the non‐equivalence of Ser and Thr O‐glycosylation points in molecular recognition processes. These features provide insight into the occurrence in nature of the APDTRP epitope for anti‐MUC1 antibodies.
Structure Elucidation and Activity of Kolossin A, the D‐/L‐Pentadecapeptide Product of a Giant Nonribosomal Peptide Synthetase
Authors: Bode Helge B. , Brachmann Alexander O. , Jadhav Kirtikumar B. , Seyfarth Lydia , Dauth Christina , Fuchs Sebastian W. , Kaiser Marcel , Waterfield Nick R. , Sack Holger , Heinemann Stefan H. , Arndt Hans‐Dieter
Published: June 2015

The largest continuous bacterial nonribosomal peptide synthetase discovered so far is described. It consists of 15 consecutive modules arising from an uninterrupted, fully functional gene in the entomopathogenic bacterium Photorhabdus luminescens. The identification of its cryptic biosynthesis product was achieved by using a combination of genome analysis, promoter exchange, isotopic labeling experiments, and total synthesis of a focused collection of peptide candidates. Although it belongs to the growing class of D‐/ L‐peptide natural products, the encoded metabolite kolossin A was found to be largely devoid of antibiotic activity and is likely involved in interspecies communication. A stereoisomer of this peculiar natural product displayed high activity against Trypanosoma brucei rhodesiense, a recalcitrant parasite that causes the deadly disease African sleeping sickness.
Three‐Component Azidation of Styrene‐Type Double Bonds: Light‐Switchable Behavior of a Copper Photoredox Catalyst
Authors: Fumagalli Gabriele , Rabet Pauline T. G. , Boyd Scott , Greaney Michael F.
Published: June 2015

[Cu(dap)2]Cl effectively catalyzes azide addition from the Zhdankin reagent to styrene‐type double bonds, and subsequent addition of a third component to the benzylic position. In the presence of light, a photoredox cycle is implicated with polar components such as methanol or bromide adding to a benzylic cation. In the absence of light, by contrast, double azidation takes place to give diazides. Therefore, regioselective double functionalization can be achieved in good to excellent yields, with a switch between light and dark controlling the degree of azidation.
Asymmetric Synthesis of Axially Chiral Isoquinolones: Nickel‐Catalyzed Denitrogenative Transannulation
Authors: Fang Zhi‐Jia , Zheng Sheng‐Cai , Guo Zhen , Guo Jing‐Yao , Tan Bin , Liu Xin‐Yuan
Published: June 2015

The first Ni0/bis(oxazoline)‐catalyzed asymmetric denitrogenative transannulation of 1,2,3‐benzotriazin‐4(3H)‐ones with bulky internal alkynes to form novel axially chiral isoquinolones in an atroposelective manner has been developed. This method provides direct asymmetric access to axially chiral isoquinolones with excellent functional‐group tolerance in excellent yields and stereoselectivities from readily available starting materials under mild reaction conditions. These axially chiral isoquinolones exhibit high cytotoxicity against a number of human cancer cell lines. DFT calculations reveal the nature of the transition state in the key annulation step.
Highly Efficient CSeCF3 Coupling of Aryl Iodides Enabled by an Air‐Stable Dinuclear PdI Catalyst
Authors: Aufiero Marialuisa , Sperger Theresa , Tsang Althea S.‐K. , Schoenebeck Franziska
Published: June 2015

Building on our recent disclosure of catalysis at dinuclear PdI sites, we herein report the application of this concept to the realization of the first catalytic method to convert aryl iodides into the corresponding ArSeCF3 compounds. Highly efficient CSeCF3 coupling of a range of aryl iodides was achieved, enabled by an air‐, moisture‐, and thermally stable dinuclear PdI catalyst. The novel SeCF3‐bridged dinuclear PdI complex 3 was isolated, studied for its catalytic competence and shown to be recoverable. Experimental and computational data are presented in support of dinuclear PdI catalysis.
Reductive Insertion of Elemental Chalcogens into Boron–Boron Multiple Bonds
Authors: Braunschweig Holger , Dellermann Theresa , Ewing William C. , Kramer Thomas , Schneider Christoph , Ullrich Stefan
Published: June 2015

The syntheses of sulfur‐ and selenium‐bridged cyclic compounds containing boron stabilized by N‐heterocyclic carbenes (NHCs) have been achieved by the reductive insertion of elemental chalcogens into boron–boron multiple bonds. The three pairs of bonding electrons between the boron atoms in the triply bonded diboryne enabled six‐electron reduction reactions, resulting in the formation of [2.2.1]‐bicyclic systems wherein bridgehead boron atoms are spanned by three chalcogen bridges. A similar reaction using a diborene (boron–boron double bond) resulted in the reductive transfer of both pairs of bonding electrons to three sulfur atoms, yielding a NHC‐stabilized trisulfidodiborolane. The demonstration of these six‐ and four‐electron reductions lends support to the presence of three and two pairs of bonding electrons between the boron atoms of the diboryne and diborene, respectively, a fact that may be useful in future discussions on bond order.
Toward Naphthocyclinones: Doubly Connected Octaketide Dimers with a Bicyclo[3.2.1]octadienone Core by Thiolate‐Mediated Cyclization
Authors: Ando Yoshio , Hori Subaru , Fukazawa Takumi , Ohmori Ken , Suzuki Keisuke
Published: June 2015

A viable method is reported for the synthesis of the bicyclo[3.2.1]octadienone scaffold in naturally occurring octaketide dimers. The procedure employs a reductive cyclization reaction mediated by an unusual ethanedithiol monosodium salt.
Reversible α‐Hydrogen and α‐Alkyl Elimination in PC(sp3)P Pincer Complexes of Iridium
Authors: Jonasson Klara J. , Polukeev Alexey V. , Marcos Rocío , Ahlquist Mårten S. G. , Wendt Ola F.
Published: June 2015

Despite significant progress in recent years, the cleavage of unstrained C(sp3)C(sp3) bonds remains challenging. A CC coupling and cleavage reaction in a PC(sp3)P iridium pincer complex is mechanistically studied; the reaction proceeds via the formation of a carbene intermediate and can be described as a competition between α‐hydrogen and α‐alkyl elimination; the latter process was observed experimentally and is an unusual way of C(sp3)C(sp3) bond scission, which has previously not been studied in detail. Mechanistic details that are based upon kinetic studies, activation parameters, and DFT calculations are also discussed. A full characterization of a CC agostic intermediate is presented.
Multidimensional Design of Anticancer Peptides
Authors: Lin Yen‐Chu , Lim Yi Fan , Russo Erica , Schneider Petra , Bolliger Lea , Edenharter Adriana , Altmann Karl‐Heinz , Halin Cornelia , Hiss Jan A. , Schneider Gisbert
Published: June 2015

The computer‐assisted design and optimization of peptides with selective cancer cell killing activity was achieved through merging the features of anticancer peptides, cell‐penetrating peptides, and tumor‐homing peptides. Machine‐learning classifiers identified candidate peptides that possess the predicted properties. Starting from a template amino acid sequence, peptide cytotoxicity against a range of cancer cell lines was systematically optimized while minimizing the effects on primary human endothelial cells. The computer‐generated sequences featured improved cancer‐cell penetration, induced cancer‐cell apoptosis, and were enabled a decrease in the cytotoxic concentration of co‐administered chemotherapeutic agents in vitro. This study demonstrates the potential of multidimensional machine‐learning methods for rapidly obtaining peptides with the desired cellular activities.
Ring Expansion to 1‐Bromo‐1‐alumacyclonona‐2,4,6,8‐tetraene by Insertion of Two Alkyne Molecules into the AlC Bonds
Authors: Agou Tomohiro , Wasano Tatsuya , Sasamori Takahiro , Guo Jing‐Dong , Nagase Shigeru , Tokitoh Norihiro
Published: June 2015

Treatment of 1‐bromo‐2,3,4,5‐tetraethylalumole (1) with 3‐hexyne afforded the corresponding product 1‐bromo‐1‐alumacyclonona‐2,4,6,8‐tetraene (2), accompanied by the formation of hexaethylbenzene. In the crystalline state, 2 forms a Br‐bridged dimer with a pseudo C2‐symmetric and twisted AlC8 nine‐membered ring. Deuterium‐labeling experiments and DFT calculations on the reaction of 1 with 3‐hexyne suggested that 1‐bromo‐1‐alumacyclohepta‐2,4,6‐triene, which is formed by the insertion of one molecule of 1‐hexyne into the AlC bond of alumole 1, is the key intermediate for the generation of 2 as well as hexaethylbenzene.
A Multidimensional Research Strategy for the Evaluation of Settlement Pits: 3D Electrical Resistivity Tomography, Magnetic Prospection and Soil Chemistry
Authors: Nowaczinski Erich , Schukraft Gerd , Rassmann Knut , Reiter Samantha , Müller‐Scheeßel Nils , Hecht Stefan , Eitel Bernhard , Bubenzer Olaf , Bátora Jozef
Published: June 2015

Irrespective of the region and time period, settlement pits are common features at archaeological sites. Variations in shape, size and fill reflect great diversity in terms of primary and secondary functions. Careful analysis of these aspects and a pit's refilling history yield key information for the reconstruction of economic, social and chronological aspects of settlement history. At present, it is unusual for a settlement site to undergo complete excavation; in most cases, only small areas within a larger settlement are opened to archaeological inquiry and, accordingly, only a scarce few pits can be excavated. Therefore, the application of a combination of new prospection methods can help to classify and preselect representative pits for subsequent excavation in order to guarantee the highest information output. The interdisciplinary investigations at the Early Bronze Age of Fidvár in Slovakia enabled the development of just such a multidimensional research strategy for the evaluation of settlement pits. Used in concert, magnetic survey and electromagnetic prospection delivered 2D data which revealed the locations of pits at the site. This was the basis for the 3D electrical resistivity tomography measurements which followed, enabling the three‐dimensional reconstruction of prehistoric pits' geometries. Supplementary sedimentological and geochemical investigations of the pits' contents revealed important information about the pits' former functions as well as the mechanisms of the processes through which they were filled in. Thus, the integrated approach provides us with a new means of obtaining an overview of pit assemblages at archaeological sites in general and demonstrates its potential for the acquisition of valuable information about the food acquisition and storage processes at Fidvár in specific. Copyright © 2015 John Wiley & Sons, Ltd.
Tea consumption is not associated with reduced plasma folate concentration among chinese pregnant women
Authors: Liu Jufen , Jin Lei , Zhang Yali , Zhang Le , Li Zhiwen , Wang Linlin , Ye Rongwei , Ren Aiguo
Published: June 2015

Background

The aim of this study was to evaluate the relationship between tea consumption and plasma folate concentration in populations with high and low prevalence of neural tube defects (NTDs) in China.

Methods

Cross‐sectional survey was conducted in three cities/counties in China, in which 1724 pregnant women during early second trimester were recruited and interviewed about tea consumption and folic acid use in 2011 to 2012. A total of 5‐ml nonfasting blood sample was collected and plasma folate concentration was determined by microbiological assay.

Results

Approximately 16.2% of the women reported that they had ever drank tea during and before the current pregnancy, women with higher educational level, and those who resided in urban were more likely to drink tea. Most of them prefer green tea (55.2%); 13.6% of women drank tea “>6 times/week,” and 29.0% of them drank “less than once a week.” The median of plasma folate concentration was 48.7 nmol/L in women who drank tea while it is 45.2 nmol/L in women who did not drink tea, with no statistical difference. The results showed there was no association between tea drinking and plasma folate concentration in Chinese pregnant women stratified by folic acid supplementation and other selected characteristics.

Conclusion

Low level of tea drinking is not associated with decreased plasma folate concentration in the Chinese populations with high and low prevalence of NTDs. Birth Defects Research (Part A) 103:747–753, 2015. © 2015 Wiley Periodicals, Inc.
Peptide Fragments of Odin‐Sam1: Conformational Analysis and Interaction Studies with EphA2‐Sam
Authors: Mercurio Flavia A. , Di Natale Concetta , Pirone Luciano , Scognamiglio Pasqualina L. , Marasco Daniela , Pedone Emilia M. , Saviano Michele , Leone Marilisa
Published: June 2015

Odin is a protein belonging to the ANKS family, and has two tandem Sam domains. The first, Odin‐Sam1, binds to the Sam domain of the EphA2 receptor (EphA2‐Sam); this interaction could be crucial for the regulation of receptor endocytosis and might have an impact on cancer. Odin‐Sam1 associates with EphA2‐Sam by adopting a “mid‐loop/end‐helix” model. In this study three peptide sequences, encompassing the mid‐loop interacting portion of Odin‐Sam1 and its C‐terminal α5 helix, were designed. Their conformational properties were analyzed by CD and NMR. In addition, their abilities to interact with EphA2‐Sam were investigated by SPR studies. The peptides adopt a predominantly disordered state in aqueous buffer, but a higher helical content is evident in the presence of the cosolvent trifluoroethanol. Dissociation constants towards EphA2‐Sam were in the high micromolar range. The structural findings suggest further routes for the design of potential anti‐cancer therapeutics as inhibitors of EphA2‐Sam heterotypic interactions.
Hydrothermal Preparation of a Robust Boehmite‐Supported N,N‐Dimethyldodecylamine N‐Oxide‐Capped Cobalt and Palladium Catalyst for the Facile Utilization of Formic Acid as a Hydrogen Source
Authors: Choudhary Hemant , Nishimura Shun , Ebitani Kohki
Published: June 2015

Bimetallic CoPd nanoparticles (NPs) on boehmite (AlOOH) were synthesized under hydrothermal conditions using three different capping agents for the facile utilization of formic acid (FA) as a hydrogen source. The CoPd NPs capped with N,N‐dimethyldodecylamine N‐oxide (DDAO) supported on AlOOH (CoPd‐DDAO/AlOOH) exhibited superior catalysis and recyclability in the hydrogenation of maleic anhydride (MAn) in water without metal leaching. The formation of monodispersed CoPd‐DDAO NPs on AlOOH that contained both cobalt oxides and CoPd alloy in each NP was indicated by TEM with energy‐dispersive spectroscopy, XRD, and X‐ray absorption spectroscopy (XAS) studies. X‐ray photoelectron spectroscopy and XAS supported the partial electron transfer phenomenon in CoPd‐DDAO NPs. The as‐prepared CoPd‐DDAO/AlOOH catalyst showed activity for the utilization of FA formed in situ from biomass for the hydrogenation of MAn. It suggested that the DDAO capping agent contributed strongly to the favorable electronic/geometric changes in CoPd alloy for the facile utilization of FA.
Oxidation‐Induced Structural Changes in Sub‐Nanometer Platinum Supported on Alumina
Authors: Moses‐DeBusk Melanie , Allard Lawrence F. , Blom Douglas A. , Narula Chaitanya K.
Published: June 2015

Pt supported on alumina is an essential component of emission treatment catalysts used in transportation. Theoretical, experimental, and mechanistic aspects of Pt particles supported on a variety of supports have been studied extensively; however, available experimental information on the behavior of single versus sub‐nanometer Pt is extremely limited. To bridge the knowledge gap between single supported Pt and well‐formed supported Pt nanoparticles, we have performed the synthesis, characterization, and CO and NO oxidation studies of sub‐nanometer Pt supported on α‐, θ‐, and γ‐Al2O3 and monitored the changes in structure upon exposure to CO and NO oxidation conditions. We find that sub‐nanometer Pt is highly effective for CO oxidation because of the high Pt dispersion, but it is not very efficient as a NO oxidation catalyst. Furthermore, sub‐nanometer Pt agglomerates rapidly under CO or NO oxidation conditions to form nanoparticles.
Preferential Oxidation of CO in H2 on Pure Co3O4−x and Pt/Co3O4−x
Authors: Nguyen Luan , Zhang Shiran , Yoon Seog Joon , Tao Franklin (Feng)
Published: June 2015

Driven by the development of a catalyst made of earth‐abundant elements for on‐board purification of H2 of this energy conversion technology, preferential oxidation (PROX) on pure Co3O4 nanorods and Co3O4 nanorods with supported Pt nanoparticles was explored with the aid of in situ studies. This catalyst remains its 100 % conversion of CO in H2 at a gas hourly space velocity of 42 857 mL h−1 g−1 at 120 °C for at least 96 h. In situ studies showed that the active surface phase during PROX is nonstoichiometric Co3O4−x. A correlation between density of surface oxygen vacancies and conversion of CO to CO2 suggest that oxygen vacancy is a necessary component of a catalytic site for PROX on Co3O4−x. Compared to pure Co3O4 nanorods, anchoring Pt nanoparticles on Co3O4 nanorods unfortunately increases selectivity for oxidation of H2 owing to the low dissociation barrier of molecular H2 on Pt. Co3O4−x exhibits much higher selectivity for CO oxidation in PROX than Pt/Co3O4−x at a temperature lower than 140 °C.
Functionalized Magnetic Mesoporous Silica Nanoparticle‐Supported Palladium Catalysts for Carbonylative Sonogashira Coupling Reactions of Aryl Iodides
Authors: Natour Suzana , Abu‐Reziq Raed
Published: June 2015

Magnetic mesoporous silica nanoparticles (MMSN) were prepared and used as a support for palladium catalysts. MMSN with a surface area of 1909 m2 g−1 were synthesized by a nanoemulsification process involving the dispersion of hydrophobic magnetite nanoparticles in chloroform in the presence of cetyltrimethylammonium bromide, followed by the addition of tetraethoxysilane and its polycondensation by a sol–gel route. The MMSN were modified with phosphine and N‐heterocyclic carbene‐based ligands, which provided coordination sites for conjugation with a palladium catalyst. These modified particles were fully characterized and employed as catalyst nanosupports. The palladium catalyst was immobilized on the surface and within the pores of MMSN and applied in copper‐free carbonylative Sonogashira coupling reactions of aryl iodides with terminal alkynes.
Diarylethene Self‐Assembled Monolayers: Cocrystallization and Mixing‐Induced Cooperativity Highlighted by Scanning Tunneling Microscopy at the Liquid/Solid Interface
Authors: Frath Denis , Sakano Takeshi , Imaizumi Yohei , Yokoyama Soichi , Hirose Takashi , Matsuda Kenji
Published: June 2015

Stimulus control over 2D multicomponent molecular ordering on surfaces is a key technique for realizing advanced materials with stimuli‐responsive surface properties. The formation of 2D molecular ordering along with photoisomerization was monitored by scanning tunneling microscopy at the octanoic acid/highly oriented pyrolytic graphite interface for a synthesized amide‐containing diarylethene, which underwent photoisomerization between the open‐ and closed‐ring isomers and also a side‐reaction to give the annulated isomer. The nucleation (Kn) and elongation (Ke) equilibrium constants were determined by analysis of the concentration dependence of the surface coverage by using a cooperative model at the liquid/solid interface. It was found that the annulated isomer has a very large equilibrium constant, which explains the predominantly observed ordering of the annulated isomer. It was also found that the presence of the closed‐ring isomer induces cooperativity into the formation of molecular ordering composed of the open‐ring isomer. A quantitative analysis of the formation of ordering by using the cooperative model has provided a new view of the formation of 2D multicomponent molecular ordering.
Anion‐, Solvent‐, Temperature‐, and Mechano‐Responsive Photoluminescence in Gold(I) Diphosphine‐Based Dimers
Authors: Deák Andrea , Jobbágy Csaba , Marsi Gábor , Molnár Miklós , Szakács Zoltán , Baranyai Péter
Published: June 2015

A series of [Au2(nixantphos)2](X)2 (nixantphos=4,6‐bis(diphenylphosphino)‐phenoxazine; X=NO3, 1; CF3COO, 2; CF3SO3, 3; [Au(CN)2], 4; and BF4, 5) complexes that exhibit intriguing anion‐switchable and stimuli‐responsive luminescent photophysical properties have been synthesized and characterized. Depending on their anions, these complexes display yellow (3), orange (4 and 5), and red (1 and 2) emission colors. They exhibit reversible thermo‐, mechano‐, and vapochromic luminescence changes readily perceivable by the naked eye. Single‐crystal X‐ray studies show that the [Au2(nixantphos)2]2+ cations with short intramolecular Au⋅⋅⋅Au interactions are involved as donors in an infinite NH⋅⋅⋅X (X=O and N) hydrogen‐bonded chain formation with CF3COO− (2 C) and aurophilically linked [Au(CN)2]− counterions (4 C). Both crystals show thermochromic luminescence; their room temperature red (2 C) and orange (4 C) emission turns into yellow upon cooling to 77 K. They also exhibit reversible mechanochromic luminescence by changing their emission color from red to dark (2 C), and orange to red (4 C). Compounds 1–5 also display reversible mechanochromic luminescence, altering their emission colors between orange (1) or red (2) to dark, as well as between yellow (3) or orange (4 and 5) to red. Detailed photophysical investigations and correlation with solid‐state structural data established the significant role of NH⋅⋅⋅X interactions in the stimuli‐responsive luminescent behavior.
Calcium Hydride Catalyzed Highly 1,2‐Selective Pyridine Hydrosilylation
Authors: Intemann Julia , Bauer Heiko , Pahl Jürgen , Maron Laurent , Harder Sjoerd
Published: June 2015

Reaction of the calcium hydride complex (DIPPnacnac‐CaH⋅THF)2 with pyridine is much faster and selective than that of the corresponding magnesium hydride complex (DIPPnacnac = [(2,6‐iPr2C6H3)NC(Me)]2CH). With a range of pyridine, picoline and quinoline substrates, exclusive transfer of the hydride ligand to the 2‐position is observed and also at higher temperatures no 1,2→1,4 isomerization is found. The heteroleptic product DIPPnacnac‐Ca(1,2‐dihydropyridide)⋅(pyridine) shows fast ligand exchange into homoleptic calcium complexes and therefore could not be isolated. Calcium hydride reduction of isoquinoline gave well‐defined homoleptic products which could be characterized by X‐ray diffraction: Ca(1,2‐dihydroisoquinolide)2⋅(isoquinoline)4 and Ca3(1,2‐dihydroisoquinolide)6⋅(isoquinoline)6. The striking selectivity difference in the dearomatization of pyridines by Mg or Ca complexes could be explained by DFT theory and was utilized in catalysis. Whereas hydroboration of pyridine with pinacol borane with a calcium hydride catalyst gave only minor conversion, the hydrosilylation of pyridine and quinolines with PhSiH3 yields exclusively 1,2‐dihydropyridine and 1,2‐dihydroquinoline silanes with 80–90 % conversion. Similar results can be achieved with the catalyst Ca[N(SiMe3)2]2⋅(THF)2. These calcium complexes represent the first catalysts for the 1,2‐selective hydrosilylation of pyridines.
Mechanistic Insights into the Post‐Cyclization Isomerization in Gold‐Catalyzed 7‐exo‐dig‐Hydroarylations
Authors: Pflästerer Daniel , Schumacher Sören , Rudolph Matthias , Hashmi A. Stephen K.
Published: June 2015

The subsequent double‐bond isomerization in the synthesis of dibenzocycloheptenes and their heteroaromatic analogues was investigated. In the case of biphenyls, a basic additive completely prevented an isomerization to the thermodynamic product. With electron‐rich intramolecular heteroaromatic nucleophiles, the isomerization was still observed, but the kinetic product can be obtained by careful control of the reaction times in most cases. Mechanistic studies demonstrated that a slow isomerization is also possible with the gold catalyst at elevated temperatures, but much faster isomerization rates were observed with acidic additives. An observed initiation period for the gold‐catalyzed isomerization indicates that not the homogenous catalyst, but a decomposition product of it may be the catalytically active species.
Hydroboration of Alkynes with Zwitterionic Ruthenium–Borate Complexes: Novel Vinylborane Complexes
Authors: Anju R. S. , Mondal Bijan , Saha Koushik , Panja Subir , Varghese Babu , Ghosh Sundargopal
Published: June 2015

Building upon previous studies on the synthesis of bis(sigma)borate and agostic complexes of ruthenium, the chemistry of nido‐[(Cp*Ru)2B3H9] (1) with other ligand systems was explored. In this regard, mild thermolysis of nido‐1 with 2‐mercaptobenzothiazole (2‐mbzt), 2‐mercaptobenzoxazole (2‐mbzo) and 2‐mercaptobenzimidazole (2‐mbzi) ligands were performed which led to the isolation of bis(sigma)borate complexes [Cp*RuBH3L] (2 a–c) and β‐agostic complexes [Cp*RuBH2L2] (3 a–c; 2 a, 3 a: L=C7H4NS2; 2 b, 3 b: L=C7H4NSO; 2 c, 3 c: L=C7H5N2S). Further, the chemistry of these novel complexes towards various diphosphine ligands was investigated. Room temperature treatment of 3 a with [PPh2(CH2)nPPh2] (n=1–3) yielded [Cp*Ru(PPh2(CH2)nPPh2)‐BH2(L2)] (4 a–c; 4 a: n=1; 4 b: n=2; 4 c: n=3; L=C7H4NS2). Mild thermolysis of 2 a with [PPh2(CH2)nPPh2] (n=1–3) led to the isolation of [Cp*Ru(PPh2(CH2)nPPh2)(L)] (L=C7H4NS2 5 a–c; 5 a: n=1; 5 b: n=2; 5 c: n=3). Treatment of 4 a with terminal alkynes causes a hydroboration reaction to generate vinylborane complexes [Cp*Ru(RCCH2)BH(L2)] (6 and 7; 6: R=Ph; 7: R=COOCH3; L=C7H4NS2). Complexes 6 and 7 can also be viewed as η‐alkene complexes of ruthenium that feature a dative bond to the ruthenium centre from the vinylinic double bond. In addition, DFT computations were performed to shed light on the bonding and electronic structures of the new compounds.
A Reversible Proton Relay Process Mediated by Hydrogen‐Bonding Interactions in [FeFe]Hydrogenase Modeling
Authors: Chu Kai‐Ti , Liu Yu‐Chiao , Huang Yi‐Lan , Hsu Cheng‐Huey , Lee Gene‐Hsiang , Chiang Ming‐Hsi
Published: June 2015

A reversible and temperature‐dependent proton‐relay process is demonstrated for a Fe2 complex possessing a terminal thiolate in the presence of nitrogen‐based acids. The terminal sulfur site (St) of the complex forms a hydrogen‐bond interaction with N,N‐dimethylanilinium acid at 183 K. The Fe2 core, instead, is protonated to generate a bridging hydride at 298 K. Reversibility is observed for the tautomerization between the hydrogen‐bonded pair and the Fe–hydride species. X‐ray structural analysis of the hydrogen‐bonded species at 193 K reveals a short N(H)⋅⋅⋅St contact. Employment of pyridinium acid also results in similar behavior, with reversible proton–hydride interconversion. DFT investigation of the proton‐transfer pathways indicates that the pKa value of the hydrogen‐bonded species is enhanced by 3.2 pKa units when the temperature is decreased from 298 K to 183 K.
Direct Evidence for a [4+2] Cycloaddition Mechanism of Alkynes to Tantallacyclopentadiene on Dinuclear Tantalum Complexes as a Model of Alkyne Cyclotrimerization
Authors: Yamamoto Keishi , Tsurugi Hayato , Mashima Kazushi
Published: June 2015

A dinuclear tantalum complex, [Ta2Cl6(μ‐C4Et4)] (2), bearing a tantallacyclopentadiene moiety, was synthesized by treating [(η2‐EtCCEt)TaCl3(DME)] (1) with AlCl3. Complex 2 and its Lewis base adducts, [Ta2Cl6(μ‐C4Et4)L] (L=THF (3 a), pyridine (3 b), THT (3 c)), served as more active catalysts for cyclotrimerization of internal alkynes than 1. During the reaction of 3 a with 3‐hexyne, we isolated [Ta2Cl4(μ‐η4:η4‐C6Et6)(μ‐η2:η2‐EtCCEt)] (4), sandwiched by a two‐electron reduced μ‐η4:η4‐hexaethylbenzene and a μ‐η2:η2‐3‐hexyne ligand, as a product of an intermolecular cyclization between the metallacyclopentadiene moiety and 3‐hexyne. The formation of arene complexes [Ta2Cl4(μ‐η4:η4‐C6Et4Me2)(μ‐η2:η2‐Me3SiCCSiMe3)] (7 b) and [Ta2Cl4(μ‐η4:η4‐C6Et4RH)(μ‐η2:η2‐Me3SiCCSiMe3)] (R=nBu (8 a), p‐tolyl (8 b)) by treating [Ta2Cl4(μ‐C4Et4)(μ‐η2:η2‐Me3SiCCSiMe3)] (6) with 2‐butyne, 1‐hexyne, and p‐tolylacetylene without any isomers, at room temperature or low temperature were key for clarifying the [4+2] cycloaddition mechanism because of the restricted rotation behavior of the two‐electron reduced arene ligands without dissociation from the dinuclear tantalum center.
Indachlorins: Nonplanar Indanone‐Annulated Chlorin Analogues with Panchromatic Absorption Spectra between 300 and 900 nm
Authors: Samankumara Lalith P. , Dorazio Sarina J. , Akhigbe Joshua , Li Ruoshi , Nimthong‐Roldán Arunpatcha , Zeller Matthias , Brückner Christian
Published: June 2015

Indaphyrins, pyrrole‐modified porphyrins containing a cleaved pyrrole β,β′‐bond and two annulated indanone moieties, possess unusually broadened and redshifted UV/Vis spectra because of their π‐expanded chromophores. The parent free base indaphyrin has been crystallographically characterized, highlighting its strongly ruffled conformation incorporating a helimeric twist. It was shown to be susceptible to regiospecific derivatizations at the opposite side of the ring‐cleaved pyrrole (dihydroxylation, followed by functional group transformations of the resulting diol functionality), generating indaphyrin‐based chlorin analogues, indachlorins, that incorporate a dihydroxypyrroline, pyrrolindione, oxazolone, or a morpholine moiety. Structural modifications resulted in further broadening and hyper‐ and bathochromic shifts of the optical spectra, some of which possess a nearly panchromatic absorption between 300 to well above 900 nm. The extents to which these modifications affect their solid‐state conformations were analyzed.
Synthesis of Polysubstituted γ‐Butenolides via a Radical Pathway: Cyclization of α‐Bromo Aluminium Acetals and Comparison with the Cyclization of α‐Bromoesters at High Temperature
Authors: Bénéteau Romain , Despiau Carole F. , Rouaud Jean‐Christophe , Boussonnière Anne , Silvestre Virginie , Lebreton Jacques , Dénès Fabrice
Published: June 2015

Polysubstituted butenolides were obtained in good to high yields from α‐bromoesters derived from propargyl alcohols by a one‐pot reaction involving the radical cyclization of α‐bromo aluminium acetals, followed by the oxidation of the resulting cyclic aluminium acetals in an Oppenauer‐type process and migration of the exocyclic CC bond into the α,β‐position. Comparison with the direct cyclization of α‐bromoesters at high temperature and under high dilution conditions is described. Deuterium‐labelling experiments allowed us to uncover “invisible” 1,5‐hydrogen atom transfers (1,5‐HATs) that occur during these cyclization processes, together with the consequences of the latter in the epimerization of stereogenic centres. Compared to the classical approach, the cyclization of aluminium acetals proved to be highly chemoselective and its efficiency was illustrated by the short total syntheses of optically enriched γ‐butenolides isolated from Plagiomnium undulatum and from Kyrtuhrix maculans.
Supramolecularly Regulated Ligands for Asymmetric Hydroformylations and Hydrogenations
Authors: Vidal‐Ferran Anton , Mon Ignasi , Bauzá Antonio , Frontera Antonio , Rovira Laura
Published: June 2015

Herein we report the use of polyether binders as regulation agents (RAs) to enhance the enantioselectivity of rhodium‐catalyzed transformations. For reactions of diverse substrates mediated by rhodium complexes of the α,ω‐bisphosphite‐polyether ligands 1–5,a–d, the enantiomeric excess (ee) of hydroformylations was increased by up to 82 % (substrate: vinyl benzoate, 96 % ee), and the ee value of hydrogenations was increased by up to 5 % (substrate: N‐(1‐(naphthalene‐1‐yl)vinyl)acetamide, 78 % ee). The ligand design enabled the regulation of enantioselectivity by generation of an array of catalysts that simultaneously preserve the advantages of a privileged structure in asymmetric catalysis and offer geometrically close catalytic sites. The highest enantioselectivities in the hydroformylation of vinyl acetate with ligand 4 b were achieved by using the Rb[B(3,5‐(CF3)2C6H3)4] (RbBArF) as the RA. The enantioselective hydrogenation of the substrates 10 required the rhodium catalysts derived from bisphosphites 3 a or 4 a, either alone or in combination with different RAs (sodium, cesium, or (R,R)‐bis(1‐phenylethyl)ammonium salts). This design approach was supported by results from computational studies.
Crystal Engineering of Energetic Materials: Co‐crystals of Ethylenedinitramine (EDNA) with Modified Performance and Improved Chemical Stability
Authors: Aakeröy Christer B. , Wijethunga Tharanga K. , Desper John
Published: June 2015

In the area of energetic materials, co‐crystallization is emerging as a new technology for modifying or enhancing the properties of existing energetic substances. Ethylenedinitramine (EDNA) is a known energetic material which requires attention partly due to its chemical instability originating with its two highly acidic protons. In order to stabilize EDNA, a co‐crystallization approach targeting the acidic protons using a series of co‐crystallizing agents with suitable hydrogen‐bond acceptors was employed. Fifteen attempted co‐crystallizations resulted in eight successful outcomes and six of these were crystallographically characterized and all showed evidence of hydrogen bonds to the intended protons. Calculated detonation properties and experimental thermal and impact data for the co‐crystals were obtained and compared with those of pure EDNA. The co‐crystal of EDNA and 1,2‐bis(4‐pyridyl)ethylene was recognized as a more thermally stable alternative to EDNA while the co‐crystal of EDNA and pyrazine N,N′‐dioxide showed comparable detonation strengths (and much improved chemical stability) compared with that of EDNA. The co‐crystals EDNA:4,4′‐bipyridine and EDNA:pyrazine N,N′‐dioxide were found to be about 50 % less impact sensitive than EDNA, all of which illustrate how co‐crystallizations can be utilized for successfully modifying specific aspects of energetic materials.
Active Site Mapping of Human Cathepsin F with Dipeptide Nitrile Inhibitors
Authors: Schmitz Janina , Furtmann Norbert , Ponert Moritz , Frizler Maxim , Löser Reik , Bartz Ulrike , Bajorath Jürgen , Gütschow Michael
Published: June 2015

Cleavage of the invariant chain is the key event in the trafficking pathway of major histocompatibility complex class II. Cathepsin S is the major processing enzyme of the invariant chain, but cathepsin F acts in macrophages as its functional synergist which is as potent as cathepsin S in invariant chain cleavage. Dedicated low‐molecular‐weight inhibitors for cathepsin F have not yet been developed. An active site mapping with 52 dipeptide nitriles, reacting as covalent–reversible inhibitors, was performed to draw structure–activity relationships for the non‐primed binding region of human cathepsin F. In a stepwise process, new compounds with optimized fragment combinations were designed and synthesized. These dipeptide nitriles were evaluated on human cysteine cathepsins F, B, L, K and S. Compounds 10 (N‐(4‐phenylbenzoyl)‐leucylglycine nitrile) and 12 (N‐(4‐phenylbenzoyl)leucylmethionine nitrile) were found to be potent inhibitors of human cathepsin F, with Ki values <10 nM. With all dipeptide nitriles from our study, a 3D activity landscape was generated to visualize structure–activity relationships for this series of cathepsin F inhibitors.
Topographic organization and possible function of the posterior optic tubercles in the brain of the desert locust Schistocerca gregaria
Authors: Beetz M. Jerome , el Jundi Basil , Heinze Stanley , Homberg Uwe
Published: June 2015

Migrating desert locusts, Schistocerca gregaria, are able to use the skylight polarization pattern for navigation. They detect polarized light with a specialized dorsal rim area in their compound eye. After multistage processing, polarization signals are transferred to the central complex, a midline‐spanning brain area involved in locomotor control. Polarization‐sensitive tangential neurons (TB‐neurons) of the protocerebral bridge, a part of the central complex, give rise to a topographic arrangement of preferred polarization angles in the bridge, suggesting that the central complex acts as an internal sky compass. TB‐neurons connect the protocerebral bridge with two adjacent brain areas, the posterior optic tubercles. To analyze the polarotopic organization of the central complex further, we investigated the number and morphologies of TB‐neurons and the presence and colocalization of three neuroactive substances in these neurons. Triple immunostaining with antisera against Diploptera punctata allatostatin (Dip‐AST), Manduca sexta allatotropin (Mas‐AT), and serotonin (5HT) raised in the same host species revealed three spatially distinct TB‐neuron clusters, each consisting of 10 neurons per hemisphere: cluster 1 and 3 showed Dip‐AST/5HT immunostaining, whereas cluster 2 showed Dip‐AST/Mas‐AT immunostaining. Five subtypes of TB‐neuron could be distinguished based on ramification patterns. Corresponding to ramification domains in the protocerebral bridge, the neurons invaded distinct but overlapping layers within the posterior optic tubercle. Similarly, neurons interconnecting the tubercles of the two hemispheres also targeted distinct layers of these neuropils. From these data we propose a neuronal circuit that may be suited to stabilize the internal sky compass in the central complex of the locust. J. Comp. Neurol. 523:1589–1607, 2015. © 2015 Wiley Periodicals, Inc.
Anatomical evidence that the uninjured adjacent L4 nerve plays a significant role in the development of peripheral neuropathic pain after L5 spinal nerve ligation in rats
Authors: Shehab Safa , Anwer Mehwish , Galani Divya , Abdulkarim Afaf , Al‐Nuaimi Khuloud , Al‐Baloushi Abdullah , Tariq Saeed , Nagelkerke Nico , Ljubisavljevic Milos
Published: June 2015

Rats develop hyperalgesia and allodynia in the hind paw after L5 spinal nerve ligation. Phosphorylated extracellular regulated kinase (pERK) was used as a pain marker to investigate the potential role of adjacent uninjured L4 nerve in the development of heat hyperalgesia after L5 nerve injury. Left L5 nerve was ligated and sectioned in rats. Three days later, rats were randomly assigned to five groups; each had both hind paws immersed in water at different temperatures (no heat, 37, 42, 47, and 52°C) under sevoflurane anesthesia for 2 minutes. Five minutes after stimulation the rats were sacrificed and sections of L3–L6 spinal segments were stained immunocytochemically with pERK antibody. pERK immunoreactivity, which is not detectable in the normal spinal cord, was discernible in neurons (not glia) of the superficial dorsal horn after noxious heat stimuli. pERK‐positive neurons clearly overlapped in laminae I–II with normal unmyelinated and thin myelinated afferents labeled with calcitonin gene‐related peptide and isolectin B4, and injured unmyelinated afferents labeled with vasoactive intestinal polypeptide. There was a linear increase in pERK immunoreactivity on both sides with an increase in temperature. Importantly, the number of positive pERK neurons was significantly higher in the ipsilateral side of L4 spinal segment, which receives innervation from uninjured L4 nerve, compared with the contralateral control side, which receives both uninjured L4 and L5 spinal nerves. The data demonstrate that the uninjured L4 nerve plays an important role in the development of heat hyperalgesia at the spinal cord level after L5 nerve injury. J. Comp. Neurol. 523:1731–1747, 2015. © 2015 Wiley Periodicals, Inc.
Influence of the Metal Work Function on the Photocatalytic Properties of TiO2 Layers on Metals
Authors: Freitag Janna , Bahnemann Detlef W.
Published: June 2015

The photocatalytic properties of titanium dioxide (TiO2) layers on different metal plates are investigated. The metal–semiconductor interface can be described as a Schottky contact, and is part of a depletion layer for the majority carriers in the semiconductor. Many researchers have demonstrated an increase in the photocatalytic activity, due to the formation of a metal–semiconductor contact that are obtained by deposition of small metal islands on the semiconductor. Nevertheless, the influence of a Schottky contact remains uncertain, sparking much interest in this field. The immobilization of nanoparticulate TiO2 layers by dip‐coating on different metal substrates results in the formation of a Schottky contact. The recombination rate of photoinduced electron–hole pairs decreases at this interface provided that the thickness of the thin TiO2 layer has a similar magnitude to the depletion layer. The degradation of dichloroacetic acid in aqueous solution and of acetaldehyde in a gas mixture is investigated to obtain information concerning the influence of the metal work function of the back contact on the efficiency of the photocatalytic process.
Nanocomposite Semi‐Solid Redox Ionic Liquid Electrolytes with Enhanced Charge‐Transport Capabilities for Dye‐Sensitized Solar Cells
Authors: Rutkowska Iwona A. , Marszalek Magdalena , Orlowska Justyna , Ozimek Weronika , Zakeeruddin Shaik M. , Kulesza Pawel J. , Grätzel Michael
Published: June 2015

The ability of Pt nanostructures to induce the splitting of the II bond in iodine (triiodide) molecules is explored here to enhance electron transfer in the iodine/iodide redox couple. Following the dispersal of Pt nanoparticles at 2 % (weight) level, charge transport was accelerated in triiodide/iodide‐containing 1,3‐dialkylimidazolium room‐temperature ionic liquid. If both Pt nanoparticles and multi‐walled carbon nanotubes were introduced into the ionic‐liquid‐based system, a solid‐type (nonfluid) electrolyte was obtained. By using solid‐state voltammetric (both sandwich‐type and microelectrode‐based) methodology, the apparent diffusion coefficients for charge transport increased to approximately 1×10−6 cm2 s−1 upon the incorporation of the carbon‐nanotube‐supported iodine‐modified Pt nanostructures. A dye‐sensitized solar cell comprising TiO2 covered with a heteroleptic RuII‐type sensitizer (dye) and the semisolid triiodide/iodide ionic liquid electrolyte admixed with carbon‐nanotube‐supported Pt nanostructures yielded somewhat higher power conversion efficiencies (up to 7.9 % under standard reporting conditions) than those of the analogous Pt‐free system.
Thiazolylidene‐Catalyzed Cleavage of Methyl Oleate‐Derived α‐Hydroxy Ketone to the Corresponding Free Aldehydes
Authors: Deruer Elsa , Duguet Nicolas , Lemaire Marc
Published: June 2015

The thiazolylidene‐catalyzed cleavage of the α‐hydroxy ketone derived from methyl oleate gave the corresponding aldehydes under nonoxidative conditions through a retro‐benzoin process. The aldehydes produced are in equilibrium with their corresponding acyloins. To illustrate the synthetic utility of this protocol, the aldehydes were recovered by distillation.
Effects of prenatal factors and temperament on infant cortisol regulation in low‐income Mexican American families
Authors: Luecken Linda J. , MacKinnon David P. , Jewell Shannon L. , Crnic Keith A. , Gonzales Nancy A.
Published: June 2015

Prenatal psychosocial exposures can significantly affect infant health and development. Infants with higher temperamental negativity are theorized to be more susceptible to environmental exposures. We evaluated the interaction of prenatal maternal exposures and infant temperamental negativity to predict infant cortisol response to mildly challenging mother‐infant interaction tasks. Participants included 322 Mexican American mother‐infant dyads (mother age 18–42; 82% Spanish‐speaking; modal family income $10,000–$15,000). Mothers reported depressive symptoms and social support prenatally and infant temperamental negativity at 6 weeks postpartum. Salivary cortisol was collected from infants before and after mother‐infant interaction tasks at 12 weeks. Higher prenatal maternal depressive symptoms and lower social support predicted higher cortisol among infants with higher temperamental negativity. Higher infant temperamental negativity predicted an increase in maternal distress and a decrease in social support from prenatal to 12 weeks postpartum. Interactive influences of maternal social‐contextual factors and infant temperament may influence the development of infant neurobiological regulation and promote or strain maternal and infant adaptation over time. © 2015 Wiley Periodicals, Inc. Dev Psychobiol 57: 961–973, 2015.
Context influences the interplay of endocrine axes across the day
Authors: Dismukes Andrew R. , Shirtcliff Elizabeth A. , Hanson Jamie L. , Pollak Seth D.
Published: June 2015

The current investigation examined stressors upon the coupling of the hypothalamic–pituitary–adrenal (HPA) and hypothalamic–pituitary–gonadal (HPG) axes. Emphasis is placed on the moderating role of context and time. One hundred and eighteen adolescent males and females provided up to 32 diurnal saliva samples across a visit to a research lab. This visit constituted a day‐long stress through which the impact on HPA–HPG axis coupling could be assessed. We tested four models of HPA–HPG axis coupling across the lab day. Sex and stress hormones operated synchronously (β = .404, p < .001), and the coupling of sex and stress hormones was moderated by the stress of the lab day (β = .010, p = .05). This pattern of co‐elevation did not appear to be moderated by the distal experience of early life adversity. Findings suggest that the notion of “stress” must disentangle proximal and distal challenges, each of which appears to impact neurobiological processes. © 2015 Wiley Periodicals, Inc. Dev Psychobiol 57: 731–741, 2015.