bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microwave Plasma Systems in Optical and Mass Spectroscopy
Authors: Jankowski Krzysztof J. , Reszke Edward , Broekaert Jose A.C. 
Published: September 2016

AbstractThe art and science of microwave plasma (MWP) optical and mass spectroscopy is briefly presented including very recent advances in the field up to 2015. The use of MWPs as radiation sources for optical emission (OES) and atomic fluorescence (AFS) spectroscopy and as atom reservoirs for atomic absorption (AAS) and cavity ringdown (CRDS) spectroscopy as well as ion sources for both elemental and molecular mass spectrometry (MS) is treated.Devices for producing both E‐type capacitively coupled microwave plasma (CMP)‐electrode and microwave‐induced plasma (MIP)‐electrodeless MWPs, including ICP‐like H‐type plasmas, are classified and discussed, in addition to techniques of their diagnostics, and results for the analytically relevant plasma parameters are presented. The means of generation of voluminous symmetrical plasmas and uses of microplasma devices are also presented with an effort to comment on general classification of microwave cavities. Further, the use of microwaves for boosting of glow discharges (GDs) and laser‐induced plasmas (LIBS) is treated along with other tandem sources. Methods for introduction of gaseous, liquid, and solid samples into the MWP are discussed. They include direct vapor sampling (DVS), chemical vapor generation (CVG) and hydride generation (HG) techniques, dry aerosol generation techniques (electrothermal vaporization (ETV), spark (SA) and laser ablation (LA) and continuous powder introduction (CPI)), and wet aerosol generation techniques using both solution and slurry nebulization. Special reference is made to coupling with gas chromatography (GC) and also with various separation techniques for liquids including high‐performance liquid chromatography (HPLC), supercritical fluid chromatography (SFC), and size‐exclusion chromatography (SEC). The analytical figures of merit in the case of OES with MIPs, CMPs, microwave plasma torch (MPT), MWP‐electrode sources including rotating‐field‐sustained plasma, and H‐type MWP as well as microplasmas are given. There are also described cases of atomic absorption and fluorescence with these sources. The developments in both elemental and molecular MS in the case of both cold and hot MWPs and in the case of various types of sample introduction techniques are discussed.Applications of MWP analytical spectroscopy are in the fields of biological, clinical, environmental, and industrial samples with special reference to multielement analysis, element speciation, on‐line monitoring, particle sizing, and direct solids analysis. A critical comparison of the methodology with other spectroscopic methods for the determination of the elements and their species is given.
Multivariate and Hyperspectral Image Analysis
Authors: Grahn Hans F. , Geladi Paul , Esbensen Kim H. 
Published: September 2016

AbstractHyperspectral analysis is an imaging and an analytical technique. The simplest hyperspectral images are of the typex‐coordinate ×y‐coordinate × variable and these can become huge in size, requiring special considerations for storage and analysis. The article gives a general introduction to the importance of imaging in the sciences, followed by definitions and ways of creating hyperspectral images for both planar and volume images. A number of techniques for creating variables are summed up and a didactical example is given of how an analysis would take place in different systematic steps. The example gives special emphasis on the visual‐interactive interpretation. The article is supplemented by numerous general literature references.
Chemometrics in Bioanalytical Chemistry
Authors: Wu Hai‐Long , Yin Xiao‐Li , Gu Hui‐Wen , Xie Li‐Xia , Yu Ru‐Qin 
Published: September 2016

AbstractChemometrics, as a young science in chemical discipline, has been widely applied in many fields, such as environmental, clinical and forensic, food, industrial, biological, theoretical, and physical sciences. With the advent of postgenomic era, a powerful tool was urgently needed to extract useful chemical information from huge biological data, which results in the development and application of chemometrics in bioanalytical chemistry. At present, the application of chemometrics in bioanalytical chemistry mainly involves in quantitative bioanalysis and ‘‐omics’. This article focuses on multivariate and multiway calibration in quantitative bioanalysis, which covers fundamentals, current situations, innovative applications, and research trends of these chemometric methods.
Direct and Stereoselective Synthesis of Diversely Substituted 2,4‐trans‐(NH)‐Pyrrolidines by Copper(I)‐Catalyzed Radical Cyclization at Low Temperature
Authors: Ram Ram N. , Gupta Dharmendra Kumar 
Published: September 2016

AbstractThis work describes a successful copper(I)‐catalyzed radical cyclization of β‐haloethylallylamines bearing an unprotected NH‐group while retaining catalyst‐redox activity. The cyclization occurs regio‐ and diastereoselectively at 0 °C and furnishes diversely substituted 1,3‐trans‐(NH)‐pyrrolidines directly in high isolated yields. An involvement of the bulky copper complex in the cyclization step as the possible reason for the diastereoselectivity was proposed. Synthetic applications of the products in the preparation of useful 4‐chloro‐NH‐pyrrole in a single step, has also been demonstrated. A quick, mild and general method involving simple addition of trichloroacetic acid/dimethyl sulfoxide (CCl3CO2H‐DMSO) solution to readily accessible N‐allylaldimines and ketimines tolerating acid‐sensitive and highly deactivating substituents was developed to access the amine precursors.magnified image
Wear and its effects on dental topography measures in howling monkeys (Alouatta palliata)
Authors: Pampush James D. , Spradley Jackson P. , Morse Paul E. , Harrington Arianna R. , Allen Kari L. , Boyer Doug M. , Kay Richard F. 
Published: September 2016

AbstractObjectivesThree dental topography measurements: Dirichlet Normal Energy (DNE), Relief Index (RFI), and Orientation Patch Count Rotated (OPCR) are examined for their interaction with measures of wear, within and between upper and lower molars inAlouatta palliata. Potential inferences of the “dental sculpting” phenomenon are explored.Materials and methodsFifteen occluding pairs of howling monkey first molars (15 upper, 15 lower) opportunistically collected from La Pacifica, Costa Rica, were selected to sample wear stages ranging from unworn to heavily worn as measured by the Dentine Exposure Ratio (DER). DNE, RFI, and OPCR were measured from three‐dimensional surface reconstructions (PLY files) derived from high‐resolution CT scans. Relationships among the variables were tested with regression analyses.ResultsUpper molars have more cutting edges, exhibiting significantly higher DNE, but have significantly lower RFI values. However, the relationships among the measures are concordant across both sets of molars. DER and EDJL are curvilinearly related. DER is positively correlated with DNE, negatively correlated with RFI, and uncorrelated with OPCR. EDJL is not correlated with DNE, or RFI, but is positively correlated with OPCR among lower molars only.DiscussionThe relationships among these metrics suggest that howling monkey teeth adaptively engage macrowear. DNE increases with wear in this sample presumably improving food breakdown. RFI is initially high but declines with wear, suggesting that the initially high RFI safeguards against dental senescence. OPCR values in howling monkey teeth do not show a clear relationship with wear changes.
Rapid Photoactivated Generation of Nitroxyl (HNO) under Neutral pH Conditions
Authors: Zhou Yang , Cink Ruth B. , Dassanayake Rohan S. , Seed Alexander J. , Brasch Nicola E. , Sampson Paul 
Published: September 2016

AbstractDirectly obtaining kinetic and mechanistic data for the reactions of nitroxyl (HNO) with biomolecules (k≈103–107 m−1 s−1) is not feasible for many systems because of slow HNO release from HNO donor molecules (t1/2 is typically minutes to hours). To address this limitation, we have developed a photoactivatable HNO donor incorporating the (3‐hydroxy‐2‐naphthalenyl)methyl phototrigger, which rapidly releases HNO on demand. A “proof of concept” study is reported, which demonstrates that, upon continuous xenon light excitation, rapid decomposition of the HNO donor occurs within seconds. The amount of HNO generated is strongly dependent on solvent and the rate of the reaction is dependent on the light intensity.
Covalent Assembly and Characterization of Nonsymmetrical Single‐Molecule Nodes
Authors: Nacci Christophe , Viertel Andreas , Hecht Stefan , Grill Leonhard 
Published: September 2016

AbstractThe covalent linking of molecular building blocks on surfaces enables the construction of specific molecular nanostructures of well‐defined shape. Molecular nodes linked to various entities play a key role in such networks, but represent a particular challenge because they require a well‐defined arrangement of different building blocks. Herein, we describe the construction of a chemically and geometrically well defined covalent architecture made of one central node and three molecular wires arranged in a nonsymmetrical way and thus encoding different conjugation pathways. Very different architectures of either very limited or rather extended size were obtained depending on the building blocks used for the covalent linking process on the Au(111) surface. Electrical measurements were carried out by pulling individual molecular nodes with the tip of a scanning tunneling microscope. The results of this challenging procedure indicate subtle differences if the nodes are contacted at inequivalent termini.
Use of an Octapeptide–Guanidiniocarbonylpyrrole Conjugate for the Formation of a Supramolecular β‐Helix that Self‐Assembles into pH‐Responsive Fibers
Authors: Li Mao , Radić Stojković Marijana , Ehlers Martin , Zellermann Elio , Piantanida Ivo , Schmuck Carsten 
Published: September 2016

AbstractPeptides that adopt β‐helix structures are predominantly found in transmembrane protein domains or in the lipid bilayer of vesicles. Constructing a β‐helix structure in pure water has been considered difficult without the addition of membrane mimics. Herein, we report such an example; peptide 1 self‐assembles into a supramolecular β‐helix in pure water based on charge interactions between the individual peptides. Peptide 1 further showed intriguing transitions from small particles to helical fibers in a time‐dependent process. The fibers can be switched to vesicles by changing the pH value.
Self‐Healing Molecular Crystals
Authors: Commins Patrick , Hara Hideyuki , Naumov Panče 
Published: September 2016

AbstractOne of the most inevitable limitations of any material that is exposed to mechanical impact is that they are inexorably prone to mechanical damage, such as cracking, denting, gouging, or wearing. To confront this challenge, the field of polymers has developed materials that are capable of autonomous self‐healing and recover their macroscopic integrity similar to biological organisms. However, the study of this phenomenon has mostly remained within the soft materials community and has not been explored by solid‐state organic chemists. The first evidence of self‐healing in a molecular crystal is now presented using crystals of dipyrazolethiuram disulfide. The crystals were mildly compressed and the degree of healing was found to be 6.7 %. These findings show that the self‐healing properties can be extended beyond mesophasic materials and applied towards the realm of ordered solid‐state compounds.
A Three‐Dimensional Origami Paper‐Based Device for Potentiometric Biosensing
Authors: Ding Jiawang , Li Bowei , Chen Lingxin , Qin Wei 
Published: September 2016

AbstractCurrent paper‐based potentiometric ion‐sensing platforms are planar devices used for clinically relevant ions. These devices, however, have not been designed for the potentiometric biosensing of proteins or small molecule analytes. A three‐dimensional origami paper‐based device, in which a solid‐contact ion‐selective electrode is integrated with an all‐solid‐state reference electrode, is described for the first time. The device is made by impregnation of paper with appropriate bioreceptors and reporting reagents on different zones. By folding and unfolding the paper structures, versatile potentiometric bioassays can be performed. A USB‐controlled miniaturized electrochemical detector can be used for simple and in situ measurements. Using butyrylcholinesterase as a model enzyme, the device has been successfully applied to the detection of enzyme activities and organophosphate pesticides involved in the enzymatic system as inhibitors. The proposed 3D origami paper device allows the potentiometric biosensing of proteins and small molecules in a simple, portable, and cost‐effective way.
Pictet–Spengler Synthesis of Quinoline‐Fused Porphyrins and Phenanthroline‐Fused Diporphyrins
Authors: Gao Ke , Fukui Norihito , Jung Seok II , Yorimitsu Hideki , Kim Dongho , Osuka Atsuhiro 
Published: September 2016

AbstractDoubly and quadruply quinoline‐fused porphyrins were effectively synthesized through a reaction sequence consisting of Suzuki–Miyaura coupling of β‐borylated porphyrins with 2‐iodoaniline and subsequent Pictet–Spengler cyclization. These quinoline‐fused porphyrins display red‐shifted absorption bands and higher electron‐accepting abilities. This synthetic protocol also allowed the synthesis of phenanthroline‐fused porphyrin dimers, which bound either a NiII or ZnII cation. The resultant metal complexes displayed further red shifted absorption spectra and molecular twists to effect an almost perpendicular arrangement of the two porphyrins.
Switching on Supramolecular Catalysis via Cavity Mediation and Electrostatic Regulation
Authors: Qiao Yupu , Zhang Long , Li Jia , Lin Wei , Wang Zhenqiang 
Published: September 2016

AbstractSynthetic supercontainers constructed from divalent metal ions, carboxylate linkers, and sulfonylcalix[4]arene‐based container precursors exhibit great promise as enzyme mimics that function in organic solvents. The capacity of these artificial hosts to catalyze Knoevenagel condensation can be switched on when the aldehyde substrate possesses a molecular size and shape matching the nanocavity of the supercontainers. In contrast, little reactivity is observed for other aldehydes that do not match the binding pocket. This substrate‐dependent catalytic selectivity is attributed to the Brønsted acidity of the metal‐bound water molecules located inside the nanocavity, which is amplified when the size/shape of the aldehyde substrate fits the binding cavity. The electrostatic environment of the binding cavity and the Brønsted acidity of the supercontainer can be further modulated using tetraalkylammonium‐based regulators, leading to higher reactivity for the otherwise unreactive aldehydes.
Frequency‐Driven Self‐Organized Helical Superstructures Loaded with Mesogen‐Grafted Silica Nanoparticles
Authors: Gutierrez‐Cuevas Karla G. , Wang Ling , Zheng Zhi‐gang , Bisoyi Hari K. , Li Guoqiang , Tan Loon‐Seng , Vaia Richard A. , Li Quan 
Published: September 2016

AbstractAdding colloidal nanoparticles into liquid‐crystal media has become a promising pathway either to enhance or to introduce novel properties for improved device performance. Here we designed and synthesized new colloidal hybrid silica nanoparticles passivated with a mesogenic monolayer on the surface to facilitate their organo‐solubility and compatibility in a liquid‐crystal host. The resulting nanoparticles were identified by 1H NMR spectroscopy, TEM, TGA, and UV/Vis techniques, and the hybrid nanoparticles were doped into a dual‐frequency cholesteric liquid‐crystal host to appraise both their compatibility with the host and the effect of the doping concentration on their electro‐optical properties. Interestingly, the silica‐nanoparticle‐doped liquid‐crystalline nanocomposites were found to be able to dynamically self‐organize into a helical configuration and exhibit multi‐stability, that is, homeotropic (transparent), focal conic (opaque), and planar states (partially transparent), depending on the frequency applied at sustained low voltage. Significantly, a higher contrast ratio between the transparent state and scattering state was accomplished in the nanoparticle‐embedded liquid‐crystal systems.
Giant Hysteretic Sorption of CO2: In Situ Crystallographic Visualization of Guest Binding within a Breathing Framework at 298 K
Authors: Lama Prem , Aggarwal Himanshu , Bezuidenhout Charl X. , Barbour Leonard J. 
Published: September 2016

AbstractA dynamic ZnII‐MOF has been shown to exhibit extreme breathing behavior under gas pressure. The very narrow pore form of the activated framework opens up in the presence of carbon dioxide, thus making it a suitable material for CO2 capture. Sorption of CO2 at 298 K and relatively high pressure clearly shows a two‐step isotherm with giant hysteresis for the second step. In‐situ single‐crystal diffraction analysis was carried out under CO2 gas pressure at 298 K using an environmental gas cell in order to visualize the interaction between CO2 and the host framework. The results are well supported by pressure‐gradient differential scanning calorimetry (P‐DSC) and variable‐pressure powder X‐ray analysis. Theoretical calculations have been carried out in order to further back up the crystallographic data.
Stereoselective Organocatalyzed Synthesis of α‐Fluorinated β‐Amino Thioesters and Their Application in Peptide Synthesis
Authors: Cosimi Elena , Engl Oliver D. , Saadi Jakub , Ebert Marc‐Olivier , Wennemers Helma 
Published: September 2016

Abstractα‐Fluorinated β‐amino thioesters were obtained in high yields and stereoselectivities by organocatalyzed addition reactions of α‐fluorinated monothiomalonates (F‐MTMs) to N‐Cbz‐ and N‐Boc‐protected imines. The transformation requires catalyst loadings of only 1 mol % and proceeds under mild reaction conditions. The obtained addition products were readily used for coupling‐reagent‐free peptide synthesis in solution and on solid phase. The α‐fluoro‐β‐(carb)amido moiety showed distinct conformational preferences, as determined by crystal structure and NMR spectroscopic analysis.
One‐Pot Three‐Component Synthesis of Vicinal Diamines via In Situ Aminal Formation and Carboamination
Authors: Orcel Ugo , Waser Jerome 
Published: September 2016

AbstractA synthesis of vicinal diamines via in situ aminal formation and carboamination of allyl amines is reported. Employing highly electron‐poor trifluoromethyl aldimines in their stable hemiaminal form was key to enable both a fast and complete aminal formation as well as the palladium‐catalyzed carboamination step. The conditions developed allow the introduction of a wide variety of alkynyl, vinyl, aryl, and hetereoaryl groups with complete regioselectivity and high diastereoselectivity. The reaction exhibits a high functional‐group tolerance. Importantly, either nitrogen atom of the imidazolidine products can be selectively deprotected, while removal of the aminal tether can be achieved in a single step under mild conditions to reveal the free diamine. We expect that this work will promote the further use of mixed aminal tethers in organic synthesis.
Enzymatic Synthesis of Sequence‐Defined Synthetic Nucleic Acid Polymers with Diverse Functional Groups
Authors: Kong Dehui , Lei Yi , Yeung Wayland , Hili Ryan 
Published: September 2016

AbstractThe development and in‐depth analysis of T4 DNA ligase‐catalyzed DNA templated oligonucleotide polymerization toward the generation of diversely functionalized nucleic acid polymers is described. The NNNNT codon set enables low codon bias, high fidelity, and high efficiency for the polymerization of ANNNN libraries comprising various functional groups. The robustness of the method was highlighted in the copolymerization of a 256‐membered ANNNN library comprising 16 sub‐libraries modified with different functional groups. This enabled the generation of diversely functionalized synthetic nucleic acid polymer libraries with 93.8 % fidelity. This process should find ready application in DNA nanotechnology, DNA computing, and in vitro evolution of functional nucleic acid polymers.
Oxygen‐Tolerant Electrodes with Platinum‐Loaded Covalent Triazine Frameworks for the Hydrogen Oxidation Reaction
Authors: Kamai Ryo , Kamiya Kazuhide , Hashimoto Kazuhito , Nakanishi Shuji 
Published: September 2016

AbstractReducing the use of platinum (Pt) on polymer electrolyte fuel cell anodes is critical for the widespread dissemination of these energy conversion systems. Although Pt usage can be minimized by the even dispersion of isolated Pt atoms, no atomically dispersed Pt catalysts that promote hydrogen oxidation at a rate required for practical fuel cells have been reported to date. Covalent triazine frameworks with atomically dispersed Pt atoms (0.29 wt %) are described and it is demonstrated that the material has a high electrocatalytic hydrogen oxidation activity without an overpotential. Importantly, when the loading amount was increased to 2.8 wt %, the electrocatalytic hydrogen oxidation activity of the resulting electrode was comparable to that of commercial carbon supported 20 wt % Pt catalysts, and the catalytic activity for oxygen reduction was markedly reduced. Thus, Pt‐modified covalent triazine frameworks selectively catalyze hydrogen oxidation, even in the presence of dissolved oxygen, which is critical for limiting cathode degradation during the start–stop cycles of fuel cells.
Phosphine‐Catalyzed Asymmetric Umpolung Addition of Trifluoromethyl Ketimines to Morita–Baylis–Hillman Carbonates
Authors: Chen Peng , Yue Zhenting , Zhang Junyou , Lv Xi , Wang Lei , Zhang Junliang 
Published: September 2016

AbstractA novel phosphine‐catalyzed, highly enantioselective umpolung addition of trifluoromethyl ketimines to Morita–Baylis–Hillman carbonates was developed and it provides facile access to optically active trifluoromethyl amines with a chiral tertiary stereocenter under mild reaction conditions. The salient features of this reaction include general substrate scope, mild reaction conditions, good yields, high enantioselectivity, ease of scale‐up to gram scale, and further transformations of the products.
Synthesis of Linear (Z)‐α,β‐Unsaturated Esters by Catalytic Cross‐Metathesis. The Influence of Acetonitrile
Authors: Yu Elsie C. , Johnson Brett M. , Townsend Erik M. , Schrock Richard R. , Hoveyda Amir H. 
Published: September 2016

AbstractKinetically controlled catalytic cross‐metathesis reactions that generate (Z)‐α,β‐unsaturated esters selectively are disclosed. A key finding is that the presence of acetonitrile obviates the need for using excess amounts of a more valuable terminal alkene substrates. On the basis of X‐ray structure and spectroscopic investigations a rationale for the positive impact of acetonitrile is provided. Transformations leading to various E,Z‐dienoates are highly Z‐selective as well. Utility is highlighted by application to stereoselective synthesis of the C1–C12 fragment of biologically active natural product (−)‐laulimalide.