bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carbo‐biphenyls and Carbo‐terphenyls: Oligo(phenylene ethynylene) Ring Carbo‐mers
Authors: Zhu Chongwei , Poater Albert , Duhayon Carine , Kauffmann Brice , Saquet Alix , Maraval Valérie , Chauvin Remi 
Published: March 2018

AbstractRing carbo‐mers of oligo(phenylene ethynylene)s (OPEn, n=0–2), made of C2‐catenated C18 carbo‐benzene rings, have been synthesized and characterized by NMR and UV‐vis spectroscopy, crystallography and voltammetry. Analyses of crystal and DFT‐optimized structures show that the C18 rings preserve their individual aromatic character according to structural and magnetic criteria (NICS indices). Carbo‐terphenyls (n=2) are reversibly reduced at ca. −0.42 V/SCE, i.e. 0.41 V more readily than the corresponding carbo‐benzene (−0.83 V/SCE), thus revealing efficient inter‐ring π‐conjugation. An accurate linear fit of E1/2red1 vs. the DFT LUMO energy suggests a notably higher value (−0.30 V/SCE) for a carbo‐quaterphenyl congener (n=3). Increase with n of the effective π‐conjugation is also evidenced by a red shift of two of the three main visible light absorption bands, all being assigned to TDDFT‐calculated excited states, one of them restricting to a HOMO→LUMO main one‐electron transition.
Site‐Directed Dimerization of Bowl‐Shaped Radical Anions to Form a σ‐Bonded Dibenzocorannulene Dimer
Authors: Spisak Sarah N. , Zabula Alexander V. , Alkan Melisa , Filatov Alexander S. , Rogachev Andrey Yu. , Petrukhina Marina A. 
Published: March 2018

AbstractDesigned site‐directed dimerization of the monoanion radicals of a π‐bowl in the solid state is reported. Dibenzo[a,g]corannulene (C28H14) was selected based on the asymmetry of the charge/spin localization in the C28H14.− anion. Controlled one‐electron reduction of C28H14 with Cs metal in diglyme resulted in crystallization of a new dimer, [{Cs+(diglyme)}2(C28H14−C28H14)2−] (1), as revealed by single crystal X‐ray diffraction study performed in a broad range of temperatures. The C−C bond length between two C28H14.− bowls (1.560(8) Å) measured at −143 °C does not significantly change upon heating of the crystal to +67 °C. The single σ‐bond character of the C−C linker is confirmed by calculations. The trans‐disposition of two bowls in 1 is observed with the torsion angles around the central C−C bond of 172.3(5)° and 173.5(5)°. A systematic theoretical evaluation of dimerization pathways of C28H14.− radicals confirmed that the trans‐isomer found in 1 is energetically favored.
The Curious Case of a Parasitic Twin of the Corroles
Authors: Basumatary Biju , Ramana Reddy R. V. , Rahul  , Sankar Jeyaraman 
Published: March 2018

AbstractAn expanded porphyrinoid has been obtained by a simple ring expansion from a contracted porphyrinoid, namely corrole. Spectroscopic, structural, and computational investigations reveal peculiar π‐conjugation and geometry. The effect of extended π‐conjugation is evident from perturbed redox behavior and photophysical properties. Owing to the strong diatropic ring current of the corrole and cross‐conjugation, the molecule exhibits a non‐aromatic nature for the expanded π‐circuit, as evident from NMR studies.
Carbon Nanozymes: Enzymatic Properties, Catalytic Mechanism, and Applications
Authors: Sun Hanjun , Zhou Ya , Ren Jinsong , Qu Xiaogang 
Published: March 2018

AbstractNanozymes have advantages over natural enzymes, such as facile production on large scale, long storage time, low costs, and high stability in harsh environments. Carbon nanomaterials (CNMs), including fullerenes, carbon nanotubes, graphene, carbon quantum dots, and graphene quantum dots, have become a star family in materials science. As a new class of nanozymes, the catalytic activity of CNMs and their hybrids has been extensively reported. In this Minireview, recent progress of CNMs based artificial enzymes, focusing on those with peroxidase‐like activity, has been summarized. The enzymatic properties, catalytic mechanisms, and novel applications of CNM nanozymes in sensing, therapy, and environmental engineering are discussed in detail. Additionally, we also highlight the remaining challenges and unsolved problems. With the fast development of bionanotechnology, the unique enzymatic properties and advantages of CNM nanozymes have received much attention and will continue to be an active and challenging field for the years to come.
One‐Pot Sequence‐Controlled Synthesis of Oligosiloxanes
Authors: Matsumoto Kazuhiro , Oba Yuki , Nakajima Yumiko , Shimada Shigeru , Sato Kazuhiko 
Published: March 2018

AbstractSilicones (organopolysiloxanes) have found applications in a wide range of research areas, and their unique and valuable properties have rendered these materials virtually irreplaceable. Despite the fact that silicones have been employed industrially for more than 70 years, synthetic routes to generate silicones remain limited, and the sequence‐controlled synthesis of oligo‐ and polysiloxanes still represents a major challenge in silicone chemistry. Described here is a highly selective sequence‐controlled synthesis of linear, branched, and cyclic oligosiloxanes by simple iteration of two reactions, specifically, a B(C6F5)3‐catalyzed dehydrocarbonative cross‐coupling of alkoxysilanes with hydrosilanes and a B(C6F5)3‐catalyzed hydrosilylation of carbonyl compounds, in a single flask. The sequence of the resulting oligosiloxanes can be controlled precisely by the order of addition of the hydrosilane monomers.
An Argon–Oxygen Covalent Bond in the ArOH+ Molecular Ion
Authors: Wagner J. Philipp , McDonald David C. , Duncan Michael A. 
Published: March 2018

AbstractThe OH+ cation is a well‐known diatomic for which the triplet (3Σ−) ground state is 50.5 kcal mol−1 more stable than its corresponding singlet (1Δ) excited state. However, the singlet forms a strong donor–acceptor bond to argon with a bond energy of 66.4 kcal mol−1 at the CCSDT(Q)/CBS level, making the singlet ArOH+ cation 3.9 kcal mol−1 more stable than the lowest energy triplet complex. Both singlet and triplet isomers of this molecular ion were prepared in a cold molecular beam using different ion sources. Infrared photodissociation spectroscopy in combination with messenger atom tagging shows that the two spin isomers exhibit completely different spectral signatures. The ground state of ArOH+ is the predicted singlet with a covalent Ar−O bond.
A latent class analysis of self‐identified reasons for experiencing homelessness: Opportunities for prevention
Authors: Barile John P. , Pruitt Anna Smith , Parker Josie L. 
Published: March 2018

AbstractIndividuals experience homelessness due to a vast number of factors. Therefore, the methods used to prevent individuals from experiencing homelessness should match their diverse needs. This study utilized survey data obtained from 577 adults experiencing homelessness to identify self‐reported causes of homelessness. A latent class analysis was conducted in order to identify classes or subgroups of respondents with distinct patterns of reported causes of homelessness. A latent class analysis is a person‐centred statistical approach that is used to determine groups of individuals who share similar characteristics. Findings from this analysis identified 5 distinct classes based on individuals' responses to 19 potential vulnerabilities or events that contributed to experiencing homelessness. Individuals tended to cluster around issues associated with (a) disability or physical health issues (4%), (b) substance abuse or mental health issues (30%), (c) report major life changes (3%), (d) financial crises (7%), or (e) employment difficulties (55%). Significant group differences occurred across military veteran status, history of homelessness, depression, and health‐related quality of life. Results for these analyses suggest that individuals report notable differences in their reasons for becoming homeless and therefore require unique preventative solutions.
Sequence‐Dependent Diastereospecific and Diastereodivergent Crosslinking of DNA by Decarbamoylmitomycin C
Authors: Aguilar William , Paz Manuel M. , Vargas Anayatzinc , Clement Cristina C. , Cheng Shu‐Yuan , Champeil Elise 
Published: March 2018

AbstractMitomycin C (MC), a potent antitumor drug, and decarbamoylmitomycin C (DMC), a derivative lacking the carbamoyl group, form highly cytotoxic DNA interstrand crosslinks. The major interstrand crosslink formed by DMC is the C1′′ epimer of the major crosslink formed by MC. The molecular basis for the stereochemical configuration exhibited by DMC was investigated using biomimetic synthesis. The formation of DNA‐DNA crosslinks by DMC is diastereospecific and diastereodivergent: Only the 1′′S‐diastereomer of the initially formed monoadduct can form crosslinks at GpC sequences, and only the 1′′R‐diastereomer of the monoadduct can form crosslinks at CpG sequences. We also show that CpG and GpC sequences react with divergent diastereoselectivity in the first alkylation step: 1“S stereochemistry is favored at GpC sequences and 1′′R stereochemistry is favored at CpG sequences. Therefore, the first alkylation step results, at each sequence, in the selective formation of the diastereomer able to generate an interstrand DNA‐DNA crosslink after the ”second arm“ alkylation. Examination of the known DNA adduct pattern obtained after treatment of cancer cell cultures with DMC indicates that the GpC sequence is the major target for the formation of DNA–DNA crosslinks in vivo by this drug.
Can Remote N‐Heterocyclic Carbenes Coordinate with Main Group Elements? Synthesis, Structure, and Quantum Chemical Analysis of N+‐Centered Complexes
Authors: Patel Neha , Arfeen Minhajul , Sood Radhika , Khullar Sadhika , Chakraborti Asit K. , Mandal Sanjay K. , Bharatam Prasad V. 
Published: March 2018

AbstractRemote N‐heterocyclic carbenes (rNHCs), such as N‐methyl‐4‐pyridylidene, are known to form coordination complexes with TMs. Herein, it is established that rNHCs can also coordinate to the N+ centre. Synthesis of some novel divalent NI complexes with the general formula (rNHC)→N+←(NHC) and (rNHC)→N+←(rNHC) was achieved, and X‐ray diffraction studies supported the coordination bond character between the rNHCs and the N+ centre. Quantum chemical analysis established the presence of divalent NI character at the central nitrogen in these systems.
Tuning the Mesomorphism and Redox Response of Anionic‐Ligand‐Based Mixed‐Valent Nickel(II) Complexes by Alkyl‐Substituted Quaternary Ammonium Cations
Authors: Nakamura Yuichi , Matsumoto Takeshi , Sakazume Yasutaka , Murata Junnosuke , Chang Ho‐Chol 
Published: March 2018

AbstractThe combination of the redox‐active mesogenic anion [NiII(Bdt)(BdtSQ)]− (Bdt=1,2‐benzenedithiolato; BdtSQ=1,2‐dithia‐semi‐benzoquinonato) with alkyl‐substituted ammonium cations afforded a series of redox‐active ionic complexes of the type [NR4][NiII(Bdt)(BdtSQ)] [R=nC16H33 (NC164Ni) and C8,10 (NC8,104Ni); C8,10=6‐octylhexadecyl] or [NMe2R2][NiII(Bdt)(BdtSQ)] [R=nC16H33 (NMe2C162Ni) and C8,10 (NMe2C8,102Ni)]. X‐ray crystallographic analyses of NMe2C162Ni and NC164Ni revealed the formation of cation‐dependent integrated ionic layers separated by interdigittated alkyl chains. Complexes NMe2C162Ni and NC164Ni commonly form crystalline phases at room temperature, whereas complexes NMe2C8,102Ni and NC8,104Ni, which contain branched alkyl chains, form a metastable mesophase and an amorphous phase at the same temperature, respectively. Furthermore, complexes NMe2C162Ni, NMe2C8,102Ni, and NC164Ni commonly form a smectic A phase (SmA) at 375, 317, and 342 K, respectively. For the four complexes, well‐defined cyclic voltammetry responses, derived from ligand‐based oxidation and reduction, were observed in solution and the condensed phases, that is, upon casting these complexes on an indium‐doped tin oxide working electrode. The present study demonstrates the tunability of the mesomorphism of ionic molecular assemblies composed of alkyl‐substituted quaternary ammonium cations, while maintaining the well‐defined redox responses of the anions even in the condensed phases.
Amyloid‐Like Fibrillary Morphology Originated by Tyrosine‐Containing Aromatic Hexapeptides
Authors: Diaferia Carlo , Balasco Nicole , Sibillano Teresa , Ghosh Moumita , Adler‐Abramovich Lihi , Giannini Cinzia , Vitagliano Luigi , Morelli Giancarlo , Accardo Antonella 
Published: March 2018

AbstractPhenylalanine‐based nanostructures have attracted the attention of the material science community for their functional properties. These properties strongly depend on the hierarchic organization of the nanostructure that in turn can be finely tuned by punctual chemical modifications of the building blocks. Herein, we investigate how the partial or the complete replacement of the Phe residues in PEG8‐(Phe)6 (PEG8‐F6) with tyrosines to generate PEG8‐(Phe‐Tyr)3 (PEG8‐(FY)3) or PEG8‐(Tyr)6 (PEG8‐Y6) affects the structural/functional properties of the nanomaterial formed by the parental compound. Moreover, the effect of the PEG derivatization was evaluated through the characterization of the peptides without the PEG moiety (Tyr)6 (Y6) and (Phe‐Tyr)3 ((FY)3). Both PEG8‐Y6 and PEG8‐(FY)3 can self‐assemble in water at micromolar concentrations in β‐sheet‐rich nanostructures. However, WAXS diffraction patterns of these compounds present significant differences. PEG8‐(FY)3 shows a 2D WAXS oriented fiber diffraction profile characterized by the concomitant presence of a 4.7 Å meridional and a 12.5 Å equatorial reflection that are generally associated with cross‐β structure. On the other hand, the pattern of PEG8‐Y6 is characterized by the presence of circles typically observed in the presence of PEG crystallization. Molecular modeling and dynamics provide an atomic structural model of the peptide spine of these compounds that is in good agreement with WAXS experimental data. Gelation phenomenon was only detected for PEG8‐(FY)3 above a concentration of 1.0 wt % as confirmed by storage (G′≈100 Pa) and loss (G′′≈28 Pa) moduli in rheological studies. The cell viability on CHO cells of this soft hydrogel was certified to be 90 % after 24 hours of incubation.
Axial vs. Equatorial Ligand Rivalry in Controlling the Reactivity of Iron(IV)‐Oxo Species: Single‐State vs. Two‐State Reactivity
Authors: Kumar Ravi , Ansari Azaj , Rajaraman Gopalan 
Published: March 2018

AbstractHigh‐valent iron‐oxo species are known for their very high reactivity, and this aspect has been studied in detail over the years. The role of axial ligands in fine‐tuning the reactivity of the iron(IV)‐oxo species has been particularly well studied. The corresponding role of equatorial ligands, however, has rarely been explored, and is of prime importance in the development of non‐heme chemistry. Here, we have undertaken detailed DFT calculations on [(LNHC)FeIV(O)(CH3CN)]2+ (1; LNHC=3,9,14,20‐tetraaza1,6,12,17‐tetraazoniapenta‐cyclohexacosane‐1(23),4,6(26),10,12(25),15,17(24),21‐octaene) in comparison to compound II of cytochrome P450 [(porphyrin)FeIV(O)(SH)]− (2) to probe this aspect. The electronic structures of 1 and 2 are found to vary significantly, implying a large variation in their reactivities. In particular, the strong equatorial ligand present in 1 significantly destabilizes the quintet states as compared to species 2. To fully understand the reactivity pattern of these species, we have modelled the hydroxylation of methane by both 1 and 2. Our calculations reveal that 1 reacts via a low‐lying S=1 π pathway, and that the generally available S=2 σ pathway is not energetically accessible. In addition to having a significant barrier for C−H bond activation, the ‐OH rebound step is also computed to have a large barrier height, leading to a marked difference in reactivity between these two species. Of particular relevance here is the observation of pure triplet‐state reactivity for 1. We have also attempted to test the role of axial ligands in fine‐tuning the reactivity of 1, and our results demonstrate that, in contrast to heme systems, the axial ligands in 1 do not significantly influence the reactivity. This highlights the importance of designing equatorial ligands to fine‐tune reactivity of high‐valent iron(IV)‐oxo species.
A Rapid Colorimetric Method to Visualize Protein Interactions
Authors: Liu Bing , Wang Zhihao , Lan Ling , Yang Qianfan , Zhang Peipei , Shi Lei , Lang Yunhe , Tabib‐Salazar Aline , Wigneshweraraj Sivaramesh , Zhang Jiye , Wang Yawen , Tang Yalin , Matthews Steve , Zhang Xiufeng 
Published: March 2018

AbstractAs key molecules in most biological pathways, proteins physically contact one or more biomolecules in a highly specific manner. Several driving forces (i.e., electrostatic and hydrophobic) facilitate such interactions and a variety of methods have been developed to monitor these processes both in vivo and in vitro. In this work, a new method is reported for the detection of protein interactions by visualizing a color change of a cyanine compound, a supramolecule complex of 3,3‐di‐(3‐sulfopropyl)‐4,5,4′,5′‐dibenzo‐9‐methyl‐thiacarbocyanine triethylammonium salt (MTC). Nuclear magnetic resonance (NMR) studies suggest that the hydrophobic nature of the protein surfaces drives MTC into different types of aggregates with distinct colors. When proteins interact with other biomolecules, the hydrophobic surface of the complex differs, resulting in a shift in the form of MTC aggregation, which results in a color change. As a result, this in vitro method has the potential to become a rapid tool for the confirmation of protein–biomolecule interactions, without the requirements for sophisticated instrumentation or approaches.
Manipulating Clusters by Use of Competing N,O‐Chelating Ligands: A Combined Crystallographic, Mass Spectrometric, and DFT Study
Authors: Zheng Hui‐Li , Chen Xue‐Li , Li Tian , Yin Zheng , Zhang Yuexing , Kurmoo Mohamedally , Zeng Ming‐Hua 
Published: March 2018

AbstractTwo heptanuclear discs, [Co7(L1)6(CH3O)6]2+ (Co7‐L1) and [Co7(L2)12](ClO4)2 (Co7‐L2), have been prepared by the reaction of [Co(H2O)6](ClO4)2 with Schiff base HL1 (HL1=2‐methoxy‐6‐[(methylimino)methyl]phenolate) or benzimidazole derivative HL2 (HL2=(1H‐benzo[d]imidazol‐2‐yl)methanolate), respectively, at room temperature. In contrast, the reaction of [Co(H2O)6](ClO4)2 with a mixture of the two ligands, having similar coordination ability but different shapes, resulted in the butterfly‐structured tetranuclear cobalt cluster [Co4(L1)2(L2)4](ClO4)2⋅2H2O (Co4). Electrospray ionization mass spectrometry (ESI‐MS) analysis in real time revealed the {Co1}→{Co2}→{Co4}→{Co7} stepwise assembly when a single ligand was employed, but when both ligands were used only {Co4} was obtained, an intermediate of the former reactions. Interestingly, ligand competition was evidenced in the assembly process of the reaction with two ligands; for example, [Co4(L1)4(L2)2]2+ and [Co4(L1)3(L2)3]2+ were the primary clusters observed at the beginning of the reaction, but [Co4(L1)2(L2)4]2+ was the final product. This observation suggests ligand exchange is taking place, and DFT calculations confirmed that these transformations were possible. By varying the ratio of ligands, the abundance of a certain species in the competitive reaction could be controlled.
Efficient Detection of Structure and Dynamics in Unlabeled RNAs: The SELOPE Approach
Authors: Schlagnitweit Judith , Steiner Emilie , Karlsson Hampus , Petzold Katja 
Published: March 2018

AbstractThe knowledge of structure and dynamics is crucial to explain the function of RNAs. While nuclear magnetic resonance (NMR) is well suited to probe these for complex biomolecules, it requires expensive, isotopically labeled samples, and long measurement times. Here we present SELOPE, a new robust, proton‐only NMR method that allows us to obtain site‐specific overview of structure and dynamics in an entire RNA molecule using an unlabeled sample. SELOPE simplifies assignment and allows for cost‐effective screening of the response of nucleic acids to physiological changes (e.g. ion concentration) or screening of drugs in a high throughput fashion. This single technique allows us to probe an unprecedented range of exchange time scales (the whole μs to ms motion range) with increased sensitivity, surpassing all current experiments to detect chemical exchange. For the first time we could describe an RNA excited state using an unlabeled RNA.
Spiro Bicyclic Guanidino Compounds from Pufferfish: Possible Biosynthetic Intermediates of Tetrodotoxin in Marine Environments
Authors: Ueyama Nozomi , Sugimoto Keita , Kudo Yuta , Onodera Ken‐ichi , Cho Yuko , Konoki Keiichi , Nishikawa Toshio , Yotsu‐Yamashita Mari 
Published: March 2018

AbstractTetrodotoxin (TTX, 1) is a potent neurotoxin that is widely found in both terrestrial and marine animals; however, the biosynthetic pathway and genes for TTX have not yet been elucidated. Previously, we proposed that TTX originated from a monoterpene; this hypothesis was based on the structures of cyclic guanidino compounds that are commonly found in toxic newts. However, these compounds have not been detected in marine organisms. Instead, a series of deoxy analogues of TTX were found in toxic marine animals; thus, we further screened for TTX‐related compounds in marine animals. Herein, we report seven novel spiro bicyclic guanidino compounds 2–8 that were isolated from the pufferfish Tetraodon biocellatus. In compounds 2–5 and 7–8, a six‐membered cyclic guanidino amide is spiro‐fused with 2,4‐dimethyl cyclohexane, whereas in compound 6, the same cyclic guanidino amide is spiro‐fused with 2,3,5‐trimethylcyclopentane. Compounds 2–5 and 7–8 have the same carbon skeleton and relative configuration as TTX. Thus, we proposed that compounds 2–8 are biosynthetic intermediates of TTX in marine environments. TTX could be biosynthetically derived from compound 7 via intermediates 2–5 through several oxidations, amide hydrolysis, and formation of the hemiaminal and lactone found in 5,6,11‐trideoxyTTX, the major TTX analogue, whereas compounds 6 and 8 might be shunt products. LC‐MS analysis confirmed the wide distribution of compounds 2, 3, or both in TTX‐containing marine animals, namely pufferfish, crab, octopus, and flatworm, but compounds 2–8 were not detected in newts.
Synthesis of l‐[4‐11C]Asparagine by Ring‐Opening Nucleophilic 11C‐Cyanation Reaction of a Chiral Cyclic Sulfamidate Precursor
Authors: Xu Youwen , Cankaya Aylin Sibel , Hoque Ruma , Lee So Jeong , Shea Colleen , Kersting Lena , Schueller Michael , Fowler Joanna S. , Szalda David , Alexoff David , Riehl Barbara , Gleede Tassilo , Ferrieri Richard A. , Qu Wenchao 
Published: March 2018

AbstractThe development of a convenient and rapid method to synthesize radiolabeled, enantiomerically pure amino acids (AAs) as potential positron emission tomography (PET) imaging agents for mapping various biochemical transformations in living organisms remains a challenge. This is especially true for the synthesis of carbon‐11‐labeled AAs given the short half‐life of carbon‐11 (11C, t1/2=20.4 min). A facile synthetic pathway to prepare enantiomerically pure 11C‐labeled l‐asparagine was developed using a partially protected serine as a starting material with a four‐step transformation providing a chiral five‐membered cyclic sulfamidate as the radiolabeling precursor. Its structure and absolute configuration were confirmed by X‐ray crystallography. Utilizing a [11C]cyanide nucleophilic ring opening reaction followed by selective acidic hydrolysis and deprotection, enantiomerically pure l‐[4‐11C]asparagine was synthesized. Further optimization of reaction parameters, including base, metal ion source, solvent, acid component, reaction temperature and reaction time, a reliable two‐step method for synthesizing l‐[4‐11C]asparagine was presented: within a 45±3 min (n=5, from end‐of‐bombardment), the desired enantiomerically pure product was synthesized with the initial nucleophilic cyanation yield of 69±4 % (n=5) and overall two‐step radiochemical yield of 53±2 % (n=5) based on starting [11C]HCN, and with radiochemical purity of 96±2 % (n=5).