bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recent Advances in Trifluoromethylation Reactions with Electrophilic Trifluoromethylating Reagents
Authors: Barata‐Vallejo Sebastián , Lantaño Beatriz , Postigo Al 
Published: October 2014

AbstractElectrophilic trifluoromethylation reactions have been the latest approach to achieve the fluoroalkylation of compounds with newly‐discovered reagents, such as the Togni’s (1‐trifluoromethyl‐1,2‐benziodoxol‐3‐(1 H)‐one), Umemoto’s (S‐(trifluoromethyl)dibenzothiophenium tetrafluoroborate), Yagupolskii’s (S‐(trifluoromethyldiarylsulfonium salts), Shreeve’s (S‐(trifluoromethyl)dibenzothiophenium triflate), and Shibata’s (trifluoromethylsulfoximine salts) reagents. All these reagents produce an electrophilic trifluoromethylating (CF3+) species that undergoes reaction with nucleophiles. In addition, these latter reactive species (i.e. CF3+) can undergo electron‐transfer (ET) processes affording CF3⋅ radicals that expand the scope to substrates other than conventional nucleophiles that can undergo reaction. In this Review, we shall discuss the trifluoromethylation reactions of diverse families of organic substrates of biological interest as a means to comparing the reagents scope and best reaction conditions. Some, though not all, of these reactions require the assistance of metal or organometallic catalysts. Some require additives and catalysts to promote the fluoroalkylation reaction, but invariably all are initiated and carried out by electrophilic trifluoromethylating species.
Rapid Characterization of Molecular Diffusion by NMR Spectroscopy
Authors: Pudakalakatti Shivanand M. , Chandra Kousik , Thirupathi Ravula , Atreya Hanudatta S. 
Published: October 2014

AbstractAn NMR‐based approach for rapid characterization of translational diffusion of molecules has been developed. Unlike the conventional method of acquiring a series of 2D 13C and 1H spectra, the proposed approach involves a single 2D NMR spectrum, which can be acquired in minutes. Using this method, it was possible to detect the presence of intermediate oligomeric species of diphenylalanine in solution during the process of its self‐assembly to form nanotubular structures.
Tunable Trimers: Using Temperature and Pressure to Control Luminescent Emission in Gold(I) Pyrazolate‐Based Trimers
Authors: Woodall Christopher H. , Fuertes Sara , Beavers Christine M. , Hatcher Lauren E. , Parlett Andrew , Shepherd Helena J. , Christensen Jeppe , Teat Simon J. , Intissar Mourad , Rodrigue‐Witchel Alexandre , Suffren Yan , Reber Christian , Hendon Christopher H. , Tiana Davide , Walsh Aron , Raithby Paul R. 
Published: October 2014

AbstractA systematic investigation into the relationship between the solid‐state luminescence and the intermolecular Au⋅⋅⋅Au interactions in a series of pyrazolate‐based gold(I) trimers; tris(μ2‐pyrazolato‐N,N′)‐tri‐gold(I) (1), tris(μ2‐3,4,5‐ trimethylpyrazolato‐N,N′)‐tri‐gold(I) (2), tris(μ2‐3‐methyl‐5‐phenylpyrazolato‐N,N′)‐tri‐gold(I) (3) and tris(μ2‐3,5‐diphenylpyrazolato‐N,N′)‐tri‐gold(I) (4) has been carried out using variable temperature and high pressure X‐ray crystallography, solid‐state emission spectroscopy, Raman spectroscopy and computational techniques. Single‐crystal X‐ray studies show that there is a significant reduction in the intertrimer Au⋅⋅⋅Au distances both with decreasing temperature and increasing pressure. In the four complexes, the reduction in temperature from 293 to 100 K is accompanied by a reduction in the shortest intermolecular Au⋅⋅⋅Au contacts of between 0.04 and 0.08 Å. The solid‐state luminescent emission spectra of 1 and 2 display a red shift with decreasing temperature or increasing pressure. Compound 3 does not emit under ambient conditions but displays increasingly red‐shifted luminescence upon cooling or compression. Compound 4 remains emissionless, consistent with the absence of intermolecular Au⋅⋅⋅Au interactions. The largest pressure induced shift in emission is observed in 2 with a red shift of approximately 630 cm−1 per GPa between ambient and 3.80 GPa. The shifts in all the complexes can be correlated with changes in Au⋅⋅⋅Au distance observed by diffraction.
BODIPY‐Based Oligo(ethylene glycol) Dendrons as Fluorescence Thermometers: When Thermoresponsiveness Meets Intramolecular Electron/Charge Transfer
Authors: Wang Hua , Wu Yongquan , Tao Pan , Fan Xing , Kuang Gui‐Chao 
Published: October 2014

AbstractThe temperature‐dependent photophysical properties of a series of 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) derivatives with different oligo(ethylene glycol) (OEG) dendrons were investigated. Weak fluorescence emission was observed for these BODIPY derivatives in dilute solution with low viscosity. BDP‐G0 and BDP‐G1‐TEG exhibit a high quantum yield in viscous glycerol solutions, contrary to the moderate and little fluorescence enhancement for BDP‐G1 and BDP‐G2 under the same conditions. The photoinduced electron transfer (PET) may have quenched the fluorescence, as supported by calculation. Interestingly, the thermoresponsive BODIPY derivatives show heat‐induced luminescence enhancement with a high signal‐to‐noise ratio and their emission maxima are dependent on the structures of branched tri(ethylene glycol) moieties. Finally, preliminary studies on the BODIPY derivatives as intracellular fluorescence indicators in living HeLa cells were carried out.
Photochemically Engineering the Metal–Semiconductor Interface for Room‐Temperature Transfer Hydrogenation of Nitroarenes with Formic Acid
Authors: Li Xin‐Hao , Cai Yi‐Yu , Gong Ling‐Hong , Fu Wei , Wang Kai‐Xue , Bao Hong‐Liang , Wei Xiao , Chen Jie‐Sheng 
Published: October 2014

AbstractA mild photochemical approach was applied to construct highly coupled metal–semiconductor dyads, which were found to efficiently facilitate the hydrogenation of nitrobenzene. Aniline was produced in excellent yield (>99 %, TOF: 1183) using formic acid as hydrogen source and water as solvent at room temperature. This general and green catalytic process is applicable to a wide range of nitroarenes without the involvement of high‐pressure gases or sacrificial additives.
Surface Architectures Built around Perylenediimide Stacks
Authors: Charbonnaz Pierre , Zhao Yingjie , Turdean Raluca , Lascano Santiago , Sakai Naomi , Matile Stefan 
Published: October 2014

AbstractSimple stacks of perylenediimides (PDIs) grown directly on solid surfaces are an intriguing starting point for the construction of multicomponent architectures because their intrinsic activity is already very high. The ability of PDI stacks to efficiently generate photocurrent originates from the strong absorption of visible light and the efficient transport of both electrons and holes after generation with light. The objective of this study was to explore whether or not the excellent performance of these remarkably simple single‐channel photosystems could be further improved in more sophisticated multicomponent architectures. We report that the directional construction of strings of anions or cations along the PDI stacks does not significantly improve their activity; that is, the intrinsic activity of PDI stacks is too high to yield ion‐gated photosystems. The directional construction of electron‐ and hole‐transporting stacks of naphthalenediimides (NDIs) and oligothiophenes along the central PDI stack did not improve photocurrent generation under standard conditions either. However, the activity of double‐channel photosystems increased with increasing thickness, whereas increasing charge recombination with single‐channel PDI stacks resulted in decreasing activity with increasing length. Most efficient long‐distance charge transport was found with double‐channel photosystems composed of PDIs and NDIs. This finding suggests that over long distances, PDI stacks transport holes better than electrons, at least under the present conditions. Triple‐channel photosystems built around PDI stacks with oligothiophenes and triphenylamines were less active, presumably because hole mobility in the added channels was inferior to that in the original PDI stacks, thus promoting charge recombination.
Water‐Induced Formation, Characterization, and Photoluminescence of Carbon Nanotube‐Based Composites of Gadolinium(III) and Platinum(II) Dithiolenes
Authors: Begum Ameerunisha , Tripathi Kumud M. , Sarkar Sabyasachi 
Published: October 2014

AbstractUnderstanding the nature of interactions of targeted drug‐delivery vehicles, such as functionalized carbon nanotubes (f‐CNTs) and their composites, with a cell or its organelles or DNA, where water is a major constituent, requires molecular‐level understanding of f‐CNTs with analogous chemical systems. The nature of interaction has not yet been explored within the scope of formation of giant aggregates by self‐assembly processes. Crystals of platinum(II) dithiolene [Pt(mnt)2][PPh4]2 (1) and gadolinium(III) dithiolene [Gd(mnt)3][PPh4]3 (2) (mnt=maleonitrile dithiolate) form nanospheres (diameter 88 nm) and nanoflowers (400–600 nm) in acetonitrile/water and DMF/water solvent mixtures, respectively. The formation of nanospheres or nanoflowers is proposed to be a water‐induced phenomenon. These nanospheres and nanoflowers interact with f‐CNTs by forming either spherical supramolecular assemblies (3, diameter up to 45. 5 μm) in the case of platinum(II) dithiolene or composite flowers (4) with CNT buckling for gadolinium(III) dithiolene. Both nanostructures, (3) and (4), show emission upon excitation at a range of wavelengths (λex=385–560 nm). The fluorescence emissions of the composite materials 3 and 4 are proposed to be due to separation of energy states of the nanospheres of 1 or the nanoflowers of 2 by the energy states of the f‐CNTs, leading to the possibility of new electronic transitions.
Microwave‐Assisted Tandem Organocatalytic Peptide‐Coupling Intramolecular aza‐Michael Reaction: α,β‐Unsaturated N‐Acyl Pyrazoles as Michael Acceptors
Authors: Sánchez‐Roselló María , Mulet Cristina , Guerola Marta , del Pozo Carlos , Fustero Santos 
Published: October 2014

AbstractConjugated N‐acyl pyrazoles have been successfully employed in the organocatalytic enantioselective intramolecular aza‐Michael reaction as ester surrogates. Bifunctional squaramides under microwave irradiation provided the best results in this transformation. Furthermore, this protocol has been combined with a peptide‐coupling reaction in a tandem sequence. The final products were easily converted into the corresponding ethyl esters.
Enantiopure Narrow Bite‐Angle POP Ligands: Synthesis and Catalytic Performance in Asymmetric Hydroformylations and Hydrogenations
Authors: Fernández‐Pérez Héctor , Benet‐Buchholz Jordi , Vidal‐Ferran Anton 
Published: October 2014

AbstractHerein is reported the preparation of a set of narrow bite‐angle P–OP ligands the backbone of which contains a stereogenic carbon atom. The synthesis was based on a Corey–Bakshi–Shibata (CBS)‐catalyzed asymmetric reduction of phosphomides. The structure of the resulting 1,1‐P–OP ligands, which was selectively tuned through adequate combination of the configuration of the stereogenic carbon atom, its substituent, and the phosphite fragment, proved crucial for providing a rigid environment around the metal center, as evidenced by X‐ray crystallography. These new ligands enabled very good catalytic properties in the Rh‐mediated enantioselective hydrogenation and hydroformylation of challenging and model substrates (up to 99 % ee). Whereas for asymmetric hydrogenation the optimal P–OP ligand depended on the substrate, for hydroformylation, a single ligand was the highest‐performing one for almost all studied substrates: it contains an R‐configured stereogenic carbon atom between the two phosphorus ligating groups, and an S‐configured 3,3′‐diphenyl‐substituted biaryl unit.
Carbonic Anhydrase‐Mimetic Bolaamphiphile Self‐Assembly for CO2 Hydration and Sequestration
Authors: Kim Min‐Chul , Lee Sang‐Yup 
Published: October 2014

AbstractA biomimetic catalyst was prepared through the self‐assembly of a bolaamphiphilic molecule with histidine moieties for the sequestration of carbon dioxide. The histidyl bolaamphiphilic molecule bis(N‐α‐amidohistidine)‐1,7‐heptane dicarboxylate has been synthesized and self‐assembled to produce analogues of the active sites of carbonic anhydrase (CA) after association with Zn2+ ions. Spectroscopic analysis demonstrated the coordination of the Zn2+ ions with histidine imidazole moieties, which is the core conformation of CA active sites. The Zn‐associated self‐assembly worked as a CA‐mimetic catalyst that shows catalytic activity for CO2 hydration. Evaluation of the kinetics of using para‐nitrophenylacetate revealed that the kinetic parameters of the CA‐mimetic catalyst were maximized at the optimal Zn concentration and that excess Zn ions resulted in deteriorated catalytic activity. The performance of the CA‐mimetic catalyst was enhanced by changing the pH value and temperature of the reaction, which implies that the hydrolysis of the substrate is the rate‐determining step. The catalyst‐assisted sequestration of CO2 was demonstrated by CaCO3 precipitation upon the addition of Ca2+ ions. This study offers an easy way to prepare enzyme analogues for CO2 sequestration through the self‐assembly of bolaamphiphile molecules with designer biochemical moieties.
Expanded‐Ring N‐Heterocyclic Carbenes for the Stabilization of Highly Electrophilic Gold(I) Cations
Authors: Phillips Nicholas , Dodson Tristan , Tirfoin Rémi , Bates Joshua I. , Aldridge Simon 
Published: October 2014

AbstractStrategies for the synthesis of highly electrophilic AuI complexes from either hydride‐ or chloride‐containing precursors have been investigated by employing sterically encumbered Dipp‐substituted expanded‐ring NHCs (Dipp=2,6‐iPr2C6H3). Thus, complexes of the type (NHC)AuH have been synthesised (for NHC=6‐Dipp or 7‐Dipp) and shown to feature significantly more electron‐rich hydrides than those based on ancillary imidazolylidene donors. This finding is consistent with the stronger σ‐donor character of these NHCs, and allows for protonation of the hydride ligand. Such chemistry leads to the loss of dihydrogen and to the trapping of the [(NHC)Au]+ fragment within a dinuclear gold cation containing a bridging hydride. Activation of the hydride ligand in (NHC)AuH by B(C6F5)3, by contrast, generates a species (at low temperatures) featuring a [HB(C6F5)3]− fragment with spectroscopic signatures similar to the “free” borate anion. Subsequent rearrangement involves BC bond cleavage and aryl transfer to the carbophilic metal centre. Under halide abstraction conditions utilizing Na[BArf4] (Arf=C6H3(CF3)2‐3,5), systems of the type [(NHC)AuCl] (NHC=6‐Dipp or 7‐Dipp) generate dinuclear complexes [{(NHC)Au}2(μ‐Cl)]+ that are still electrophilic enough at gold to induce aryl abstraction from the [BArf4]− counterion.
Energetic N,N′‐Ethylene‐Bridged Bis(nitropyrazoles): Diversified Functionalities and Properties
Authors: Yin Ping , Zhang Jiaheng , Parrish Damon A. , Shreeve Jean'ne M. 
Published: October 2014

AbstractA new class of N,N′‐ethylene‐bridged bis(nitropyrazoles) was synthesized and fully characterized. The highly efficient formation of the N,N′‐ethylene bridge was accomplished using dibromoethane and ammonium or potassium pyrazolate. Further functional‐group transformations of diaminobis(pyrazole) and dichlorobis(pyrazole) gave rise to diversified derivatives, including dinitramino‐, diazido‐ and hexanitrobis(pyrazole). Single‐crystal X‐ray diffractions were obtained for hexanitro and diazido derivatives to illustrate the structural characteristics. Heats of formation and detonation performance were calculated by using Gaussian 03 and EXPLO5 v6.01 programs, respectively. Because of the different functionalized groups, the impact and friction sensitivities of these new compounds range from insensitive to sensitive. Among them, the hexanitro derivative displays the most promising overall energetic properties (density (ρ)=1.84 g cm−3; decomposition temperature (Td)=250 °C; detonation pressure (P)=34.1 GPa; detonation velocity (vD)=8759 m s−1; impact sensitivity (IS)=25 J; friction sensitivity (FS)=160 N), which is competitive with those of 1,3,5‐trinitrotriazacyclohexane (ρ=1.80 g cm−3; Td=205 °C; P=35.0 GPa; vD=8762 m s−1; IS=7 J; FS=120 N).
N‐Oxide 1,2,4,5‐Tetrazine‐Based High‐Performance Energetic Materials
Authors: Wei Hao , Gao Haixiang , Shreeve Jean'ne M. 
Published: October 2014

AbstractOne route to high density and high performance energetic materials based on 1,2,4,5‐tetrazine is the introduction of 2,4‐di‐N‐oxide functionalities. Based on several examples and through theoretical analysis, the strategy of regioselective introduction of these moieties into 1,2,4,5‐tetrazines has been developed. Using this methodology, various new tetrazine structures containing the N‐oxide functionality were synthesized and fully characterized using IR, NMR, and mass spectroscopy, elemental analysis, and single‐crystal X‐ray analysis. Hydrogen peroxide (50 %) was used very effectively in lieu of the usual 90 % peroxide in this system to generate N‐oxide tetrazine compounds successfully. Comparison of the experimental densities of N‐oxide 1,2,4,5‐tetrazine compounds with their 1,2,4,5‐tetrazine precursors shows that introducing the N‐oxide functionality is a highly effective and feasible method to enhance the density of these materials. The heats of formation for all compounds were calculated with Gaussian 03 (revision D.01) and these values were combined with measured densities to calculate detonation pressures (P) and velocities (νD) of these energetic materials (Explo 5.0 v. 6.01). The new oxygen‐containing tetrazines exhibit high density, good thermal stability, acceptable oxygen balance, positive heat of formation, and excellent detonation properties, which, in some cases, are superior to those of 1,3,5‐tritnitrotoluene (TNT), 1,3,5‐trinitrotriazacyclohexane (RDX), and octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX).
Doubly robust imputation procedures for finite population means in the presence of a large number of zeros
Authors: Haziza David , Nambeu Christian‐Olivier , Chauvet Guillaume 
Published: October 2014

AbstractSingle imputation is often used in surveys to compensate for item nonresponse. In some cases, the variable requiring imputation contains a large amount of zeros. This is especially frequent in business surveys that collect economic variables. Motivated by a mixture regression model, we propose three imputation procedures and study their properties in terms of bias and variance. We show that these procedures are doubly robust, leading to consistent estimators of the finite population mean if either the imputation model or the nonresponse model is well specified. For the proposed procedures, we consider a jackknife variance estimator, which is consistent for the true variance, provided the overall sampling fraction is negligible. Finally, the results of a simulation study comparing the performance of point and variance estimators in terms of relative bias and mean square error are presented. The Canadian Journal of Statistics 42: 650–669; 2014 © 2014 Statistical Society of Canada
Statins in the Elderly: A Patient‐Focused Approach
Authors: Wilmot Kobina A. , Khan Abdullah , Krishnan Sandeep , Eapen Danny J. , Sperling Laurence 
Published: October 2014

ABSTRACTIndividuals age >65 years represent the fastest‐growing subpopulation in the United States. Although these individuals with the highest cardiovascular risk profile would be anticipated to be the most aggressively treated, paradoxically, treatment and baseline risk are inversely related. Presumably, the elderly population would benefit from high‐intensity statin therapy; however, as per the 2013 American College of Cardiology/American Heart Association guidelines, given the scarcity of evidence in patients age >75, there are only sufficient data from randomized controlled trials to support use of moderate‐intensity statin therapy for secondary prevention. Despite evidence demonstrating statins are beneficial in the elderly, the decision to initiate and sustain treatment should be a well‐informed and collaborative decision. One must balance the benefits (secondary atherosclerotic cardiovascular prevention, stroke reduction, decreased morbidity and mortality) with the potential risks to the elderly (altered metabolism, comorbidities, polypharmacy and drug‐drug interactions, side effects, cognitive limitations, and cost).
Application of Appropriate Use Criteria to Cardiac Stress Testing in the Hospital Setting: Limitations of the Criteria and Areas for Improved Practice
Authors: Gertz Zachary M. , O'Donnell William , Raina Amresh , Litwack Andrew J. , Balderston Jessica R. , Goldberg Lee R. 
Published: October 2014

ABSTRACTBackgroundImaging cardiac stress test use has risen significantly, leading to the development of appropriate use criteria. Prior studies have suggested the rate of inappropriate testing is 13% to 14%, but inappropriate testing in hospitalized patients has not been well studied.HypothesisAppropriate use of stress testing in hospitalized patients is not comparable to the ambulatory setting.MethodsWe studied 459 consecutive patients referred for imaging stress tests (nuclear imaging or stress echocardiography) at a single institution over a 6‐month period. Appropriate use was determined by research cardiologists blinded to patient outcomes.ResultsMost tests (68%) were in patients with chest pain or possible acute coronary syndrome (ACS). Another 20% were for preoperative evaluation. The rate of inappropriate testing was 13%. Imaging modality did not correlate with appropriate use. Only 2% of the chest pain or possible ACS were inappropriate, compared to 49% of the preoperative exams (P < 0.001). The most common reason a test was considered inappropriate was for a low‐risk patient for preoperative exam (77% of inappropriate tests). Using Thrombolysis in Myocardial Infarction score 0 to define inappropriate testing in the possible ACS cohort might make an additional 27% inappropriate.ConclusionsThe rate of inappropriate use of cardiac stress testing with imaging in the inpatient setting is similar to that in the ambulatory setting. However, there is wide variation in inappropriate testing based on the indication for the test. Taking risk into consideration in possible ACS patients could result in a larger number of tests being considered inappropriate.
Air Electrode for the Lithium–Air Batteries: Materials and Structure Designs
Authors: Wen Zhaoyin , Shen Chen , Lu Yan 
Published: October 2014

AbstractThe lithium–air battery, considered to be a promising candidate for future applications such as electric vehicles and energy storage, has captured worldwide attention recently because of its superhigh specific energy density even rivaling that of gasoline. This Review covers the most recent and significant scientific progress made in the fields relevant to Li–air batteries, with emphasis on the structure design of air electrodes. After a brief introduction to the operation principles and cathode electrochemical reactions, a discussion of the design and optimization of the cathode structure is presented sequentially, and the final conclusion remarks on future challenges and perspectives. The aim is to provide a better understanding of the effect of the cathode structure on the performance of the promising metal–air battery technologies, and to consider their challenges and perspectives in the future.