bluuebunny/crossref_metadata_2025 huggingface dataset:
Difference spectra for the reduction of the feasible bands of response profiles of multivariate curve resolution: comparison of the feasible bands of difference spectra and ordinary data
Authors: Bahram Morteza , Beth‐Moushoul Elsie
Published: October 2013

In multivariate curve resolution (MCR) methods, a bilinear decomposition of the experimental data matrix (D) is performed to estimate, for example, the concentration profiles (C) and the spectra (S) using the model equation, D = CST + E, where E is the error or noise matrix. The main limitation of all soft‐modeling methods is the fact that there is often no unique solution and sometimes a range of feasible solutions that fit the data equally well (while fulfilling the applied constraint) is obtained. This fact is known as rotational ambiguity. In the present work, the effect of differencing the spectra as a preprocessing method on the feasible bands of response profiles of the MCR results is investigated. The feasible band of several simulated ordinary and difference data sets of pH titration of a diprotic acid as a three‐component system was analyzed and compared. Also, a real experimental data were studied by the proposed method. The results showed that by using this pretreatment strategy, the feasible bands of MCR results are reduced.

Actually, the reason is the fact of reducing the number of compounds in one and, hence, reducing the compounds overlapping. For analyzing the data with high degree of overlapping, this effect is very obvious. Copyright © 2013 John Wiley & Sons, Ltd.
Multitarget fragment‐based design of novel inhibitors for AChE and SSAO/VAP‐1 enzymes
Authors: Gharaghani Sajjad , Khayamian Taghi , Ebrahimi Malihe
Published: October 2013

In Alzheimer's disease, increased human semicarbazide‐sensitive amine oxidase/vascular adhesion protein‐1 (SSAO/VAP‐1) expression has been found to colocalize with abnormal amyloid deposition. In addition, inhibition of acetylcholinesterase in Alzheimer's disease treatment should allow the lowered levels of acetylcholine in the synapses a chance to induce a signal in the downstream nerve. We designed inhibitors that interacted with both enzymes. The known inhibitors of acetylcholinesterase and SSAO/VAP‐1 were deconstructed into small fragments. Each fragment was docked to both enzymes, and the scoring function together with the ‘rule of three’ was used for fragment selection. The active fragments were combined with each other and resulted in 121 compounds. The docked pose of these compounds showed that seven compounds interacted in the binding site of both enzymes. Absorption, distribution, metabolism, elimination, and toxicity properties of these compounds were then calculated. The results showed that four of these inhibitors need to be synthesized for further experimental evaluation. Copyright © 2013 John Wiley & Sons, Ltd.
Supervised principal components: a new method for multivariate spectral analysis
Authors: Bin Jun , Ai Fang‐Fang , Liu Nian , Zhang Zhi‐Min , Liang Yi‐Zeng , Shu Ru‐Xin , Yang Kai
Published: October 2013

The supervised principal components (SPC) method was proposed by Bair and Tibshirani for statistics regression problems where the number of variables greatly exceeds the number of samples. This case is extremely common in multivariate spectral analysis. The objective of this research is to apply SPC to near‐infrared and Raman spectral calibration. SPC is similar to traditional principal components analysis except that it selects the most significant part of wavelength from the high‐dimensional spectral data, which can reduce the risk of overfitting and the effect of collinearity in modeling according to a semi‐supervised strategy. In this study, four conventional regression methods, including principal component regression, partial least squares regression, ridge regression, and support vector regression, were compared with SPC. Three evaluation criteria, coefficient of determination (R2), external correlation coefficient (Q2), and root mean square error of prediction, were calculated to evaluate the performance of each algorithm on both near‐infrared and Raman datasets. The comparison results illustrated that the SPC model had a desirable ability of regression and prediction. We believe that this method might be an alternative method for multivariate spectral analysis. Copyright © 2013 John Wiley & Sons, Ltd.
Theoretical Modelling of Photoswitching of Hyperpolarisabilities in Ruthenium Complexes
Authors: Coe Benjamin J. , Avramopoulos Aggelos , Papadopoulos Manthos G. , Pierloot Kristine , Vancoillie Steven , Reis Heribert
Published: October 2013

Static excited‐state polarisabilities and hyperpolarisabilities of three RuII ammine complexes are computed at the density functional theory (DFT) and several correlated ab initio levels. Most accurate modelling of the low energy electronic absorption spectrum is obtained with the hybrid functionals B3LYP, B3P86 or M06 for the complex [RuII(NH3)5(MeQ+)]3+ (MeQ+=N‐methyl‐4,4′‐bipyridinium, 3) in acetonitrile. The match with experimental data is less good for [RuII(NH3)5L]3+ (L=N‐methylpyrazinium, 2; N‐methyl‐4‐{E,E‐4‐(4‐pyridyl)buta‐1,3‐dienyl}pyridinium, 4). These calculations confirm that the first dipole‐ allowed excited state (FDAES) has metal‐to‐ligand charge‐transfer (MLCT) character. Both the solution and gas‐phase results obtained for 3 by using B3LYP, B3P86 or M06 are very similar to those from restricted active‐space SCF second‐order perturbation theory (RASPT2) with a very large basis set and large active space. However, the time‐dependent DFT λmax predictions from the long‐range corrected functionals CAM‐B3LYP, LC‐ωPBE and wB97XB and also the fully ab initio resolution of identity approximate coupled‐cluster method (gas‐phase only) are less accurate for all three complexes. The ground state (GS) two‐state approximation first hyperpolarisability β2SA for 3 from RASPT2 is very close to that derived experimentally via hyper‐Rayleigh scattering, whereas the corresponding DFT‐based values are considerably larger. The β responses calculated by using B3LYP, B3P86 or M06 increase markedly as the π‐conjugation extends on moving along the series 2→4, for both the GS and FDAES species. All three functionals predict substantial FDAES β enhancements for each complex, increasing with the π‐conjugation, up to about sevenfold for 4. Also, the computed second hyperpolarisabilities γ generally increase in the FDAES, but the results vary between the different functionals.
Group Additive Values for the Gas‐Phase Standard Enthalpy of Formation, Entropy and Heat Capacity of Oxygenates
Authors: Paraskevas Paschalis D. , Sabbe Maarten K. , Reyniers Marie‐Françoise , Papayannakos Nikos , Marin Guy B.
Published: October 2013

A complete and consistent set of 60 Benson group additive values (GAVs) for oxygenate molecules and 97 GAVs for oxygenate radicals is provided, which allow to describe their standard enthalpies of formation, entropies and heat capacities. Approximately half of the GAVs for oxygenate molecules and the majority of the GAVs for oxygenate radicals have not been reported before. The values are derived from an extensive and accurate database of thermochemical data obtained by ab initio calculations at the CBS‐QB3 level of theory for 202 molecules and 248 radicals. These compounds include saturated and unsaturated, α‐ and β‐branched, mono‐ and bifunctional oxygenates. Internal rotations were accounted for by using one‐dimensional hindered rotor corrections. The accuracy of the database was further improved by adding bond additive corrections to the CBS‐QB3 standard enthalpies of formation. Furthermore, 14 corrections for non‐nearest‐neighbor interactions (NNI) were introduced for molecules and 12 for radicals. The validity of the constructed group additive model was established by comparing the predicted values with both ab initio calculated values and experimental data for oxygenates and oxygenate radicals. The group additive method predicts standard enthalpies of formation, entropies, and heat capacities with chemical accuracy, respectively, within 4 kJ mol−1 and 4 J mol−1 K−1 for both ab initio calculated and experimental values. As an alternative, the hydrogen bond increment (HBI) method developed by Lay et al. (T. H. Lay, J. W. Bozzelli, A. M. Dean, E. R. Ritter, J. Phys. Chem.­ 1995, 99, 14514) was used to introduce 77 new HBI structures and to calculate their thermodynamic parameters (ΔfH°, S°, Cp°). The GAVs reported in this work can be reliably used for the prediction of thermochemical data for large oxygenate compounds, combining rapid prediction with wide‐ranging application.
Porphyrins Fused to N‐Heterocyclic Carbenes (NHCs): Modulation of the Electronic and Catalytic Properties of NHCs by the Central Metal of the Porphyrin
Authors: Lefebvre Jean‐François , Lo Mamadou , Gisselbrecht Jean‐Paul , Coulembier Olivier , Clément Sébastien , Richeter Sébastien
Published: October 2013

We report herein a detailed study of the use of porphyrins fused to imidazolium salts as precursors of N‐heterocyclic carbene ligands 1 M. Rhodium(I) complexes 6 M–9 M were prepared by using 1 M ligands with different metal cations in the inner core of the porphyrin (M=NiII, ZnII, MnIII, AlIII, 2H). The electronic properties of the corresponding N‐heterocyclic carbene ligands were investigated by monitoring the spectroscopic changes occurring in the cod and CO ancillary ligands of [(1 M)Rh(cod)Cl] and [(1 M)Rh(CO)2Cl] complexes (cod=1,5‐cyclooctadiene). Porphyrin–NHC ligands 1 M with a trivalent metal cation such as MnIII and AlIII are overall poorer electron donors than porphyrin–NHC ligands with no metal cation or incorporating a divalent metal cation such as NiII and ZnII. Imidazolium salts 3 M (M=Ni, Zn, Mn, 2H) have also been used as NHC precursors to catalyze the ring‐opening polymerization of L‐lactide. The results clearly show that the inner metal of the porphyrin has an important effect on the reactivity of the outer carbene.
Visualizing Lithium‐Ion Migration Pathways in Battery Materials
Authors: Filsø Mette Ø. , Turner Michael J. , Gibbs Gerald V. , Adams Stefan , Spackman Mark A. , Iversen Bo B.
Published: October 2013

The understanding of lithium‐ion migration through the bulk crystal structure is crucial in the search for novel battery materials with improved properties for lithium‐ion conduction. In this paper, procrystal calculations are introduced as a fast, intuitive way of mapping possible migration pathways, and the method is applied to a broad range of lithium‐containing materials, including the well‐known battery cathode materials LiCoO2, LiMn2O4, and LiFePO4. The outcome is compared with both experimental and theoretical studies, as well as the bond valence site energy approach, and the results show that the method is not only a strong, qualitative visualization tool, but also provides a quantitative measure of electron‐density thresholds for migration, which are correlated with theoretically obtained activation energies. In the future, the method may be used to guide experimental and theoretical research towards materials with potentially high ionic conductivity, reducing the time spent investigating nonpromising materials with advanced theoretical methods.
Thermal Cyclization of Phenylallenes That Contain ortho‐1,3‐Dioxolan‐2‐yl Groups: New Cascade Reactions Initiated by 1,5‐Hydride Shifts of Acetalic H Atoms
Authors: Alajarin Mateo , Bonillo Baltasar , Marin‐Luna Marta , Sanchez‐Andrada Pilar , Vidal Angel
Published: October 2013

A series of 2‐(1,3‐dioxolan‐2‐yl)phenylallenes that contained a range of substituents (alkyl, aryl, phosphinyl, alkoxycarbonyl, sulfonyl) at the cumulenic C3 position were prepared by using a diverse range of synthetic strategies and converted into their respective 1‐(2‐hydroxy)‐ethoxy‐2‐substituted naphthalenes by smooth thermal activation in toluene solution. Electron‐withdrawing groups at the C3 position accelerated these tandem processes, which consisted of 1) an initial hydride‐like [1,5]‐H shift of the acetalic H atom onto the central cumulene carbon atom; 2) a subsequent 6π‐electrocyclic ring‐closure of the resulting reactive ortho‐xylylenes; and 3) a final aromatization step with concomitant ring‐opening of the 1,3‐dioxolane fragment. If the 1,3‐dioxolane ring of the starting allenes was replaced by a dimethoxymethyl group, the reactions led to mixtures of two disubstituted naphthalenes, which were formed by the migration of either the acetalic H atom or the methoxy group, with the latter migration occurring to a lesser extent. Two of the final 1,2‐disubstituted naphthalenes were converted into their corresponding naphtho‐fused dioxaphosphepine or dioxepinone through an intramolecular transesterification reaction. A DFT computational study accounted for the beneficial influence of the 1,3‐dioxolane fragment on the carbon atom from which the H‐shift took place and also of the electron‐withdrawing substituents on the allene terminus. Remarkably, in the processes that contained a sulfonyl substituent, the conrotatory 6π‐electrocyclization step was of lower activation energy than the alternative disrotatory mode.
Antifreeze Protein‐Induced Selective Crystallization of a New Thermodynamically and Kinetically Less Preferred Molecular Crystal
Authors: Wang Sen , Wen Xin , Golen James A. , Arifin Josh F. , Rheingold Arnold L.
Published: October 2013

The formation of a new, dihydrate crystalline form of 5‐methyluridine (m5U) was selectively induced by a protein additive, antifreeze protein (AFP) in a highly efficient manner (in 10−6 molar scale, whereas known kinetic additives need 0.1 molar scale). The hemihydrate form (form I, the only previously known crystalline form of m5U) and the dihydrate form of m5U (form II) obtained herein were characterized using X‐ray crystallography and differential scanning calorimetry (DSC). Compared to form I, remarkably, form II is thermodynamically and kinetically less preferred. The presence of AFP can selectively inhibit the appearance of form I and hence allows the growth of form II, the pure form of which cannot grow directly from m5U supersaturated solutions under the same conditions. An explanation supported by both experimental and theoretical results is provided for the AFP‐induced selection process. Implications on AFP‐induced ice shape changes are also discussed. Control of crystallization from supersaturated solutions is of great interest in both fundamental research and practical applications in fields like chemistry, pharmacology and materials science. These findings suggest that crystallization processes with AFPs could be valuable for selective growth of hydrates and polymorphs of important pharmaceutical compounds.
Grignard Reagent/CuI/LiCl‐Mediated Stereoselective Cascade Addition/Cyclization of Diynes: A Novel Pathway for the Construction of 1‐Methyleneindene Derivatives
Authors: Li De‐Yao , Wei Yin , Shi Min
Published: October 2013

Diynes containing a cyclopropane group smoothly undergo a novel intramolecular and stereoselective cascade addition/cyclization reaction to produce the corresponding 1‐methyleneindene derivatives in moderate to good yields. This interesting transformation is mediated by Grignard reagent/CuI with LiCl as an additive under mild conditions. The obtained product can easily be further functionalized through cyclopropyl ring opening. A plausible reaction mechanism has also been presented on the basis of deuterium labeling and control experiments.
Modular Total Synthesis of Rhizopodin: A Highly Potent G‐Actin Dimerizing Macrolide
Authors: Kretschmer Manuel , Dieckmann Michael , Li Pengfei , Rudolph Sven , Herkommer Daniel , Troendlin Johannes , Menche Dirk
Published: October 2013

A highly convergent total synthesis of the potent polyketide macrolide rhizopodin has been achieved in 29 steps by employing a concise strategy that exploits the molecule′s C2 symmetry. Notable features of this convergent approach include a rapid assembly of the macrocycle through a site‐directed sequential cross‐coupling strategy and the bidirectional attachment of the side chains by means of Horner–Wadsworth–Emmons (HWE) coupling reactions. During the course of this endeavor, scalable routes for synthesis of three main building blocks of similar complexity were developed that allowed for their stereocontrolled construction. This modular route will be amenable to the development of syntheses of other analogues of rhizopodin.
Organogelation‐Controlled Topochemical [2+2] Cycloaddition and Morphological Changes: From Nanofiber to Peculiar Coaxial Hollow Toruloid‐Like Nanostructures
Authors: Wang Xiufeng , Duan Pengfei , Liu Minghua
Published: October 2013

Novel amphiphilic molecules composed of naphthylacryl and L‐glutamide moieties (1‐NA and 2‐NA) have been designed and their organogel formation in various organic solvents as well as their self‐assembled nanostructures have been investigated. Both compounds formed organogels in many organic solvents, ranging from nonpolar to polar, and self‐assembled into essentially nanofiber structures, although some twist or belt structures could be observed in certain solvents. A gel of compound 2‐NA in ethanol initially self‐assembled into nanofibers and then these were transformed into a family of coaxial hollow toruloid‐like (CHTL) nanostructures under irradiation, in which various toroids and disks of different sizes were stacked coaxially. We have established that a topochemical [2+2] cycloaddition in the organogel triggers this transformation. When the gel was fabricated into xerogels in which no ethanol remained, such morphological changes could not happen. This might be the first report of an organogel, in which both organized nanofibers and solvent coexist, controlling a topochemical reaction as well as the self‐assembled nanostructures formed. Due to the formation of the toruloid‐like nanostructures, the gel collapsed to a precipitate. However, upon heating this precipitate with ethanol, it redissolved and then formed a gel and self‐assembled into nanofibers once more. Thus, a reversible morphological transformation between nanofibers and an unprecedented series of toruloid‐like nanostructures can be induced by alternately heating and irradiating the gel.
Pestalotiopens A and B: Stereochemically Challenging Flexible Sesquiterpene‐Cyclopaldic Acid Hybrids from Pestalotiopsis sp.
Authors: Hemberger Yasmin , Xu Jing , Wray Victor , Proksch Peter , Wu Jun , Bringmann Gerhard
Published: October 2013

From the endophytic fungus Pestalotiopsis sp. isolated from the leaves of the Chinese mangrove, Rhizophora mucronata, two novel hybrid sesquiterpene‐cyclopaldic acid metabolites with an unusual carbon skeleton, named pestalotiopens A and B, were obtained, together with the already known phytotoxin altiloxin B. Pestalotiopen B even contains a third, triketide‐derived module. The constitutions and the absolute configurations of the new metabolites and of altiloxin B were unambiguously determined by a combination of spectroscopic methods and quantum‐chemical optical‐rotatory dispersion (ORD) and circular dichroism (CD) calculations. A biosynthetic pathway to pestalotiopens A and B is proposed with altiloxin B as one of the suggested precursors. Pestalotiopen A shows moderate antimicrobial activity against Enterococcus faecalis.
Probing Helical Hydrophobic Binding Sites in Branched Starch Polysaccharides Using NMR Spectroscopy
Authors: Beeren Sophie R. , Meier Sebastian , Hindsgaul Ole
Published: October 2013

Branched starch polysaccharides are capable of binding multiple hydrophobic guests, but their exploitation as multivalent hosts and in functional materials is limited by their structural complexity and diversity. Linear α(1–4)‐linked glucose oligosaccharides are known to bind hydrophobic guests inside left‐handed single helices in solution and the solid state. Here, we describe the development of an amphiphilic probe that binds to linear α(1–4)‐linked glucose oligosaccharides and undergoes a conformational switch upon complexation, which gives rise to dramatic changes in the 1H NMR spectrum of the probe. We use this probe to explore hydrophobic binding sites in the branched starch polysaccharides amylopectin and β‐limit dextrin. Diffusion‐ordered (DOSY), nuclear Overhauser effect (NOESY) and chemical shift perturbation (HSQC) NMR experiments are utilised to provide evidence that, in aqueous solution, branched polysaccharides bind hydrophobic guests in well‐defined helical binding sites, similar to those reported for complexation by linear oligosaccharides. By examining the binding affinity of the probe to systematically enzymatically degraded polysaccharides, we deduce that the binding sites for hydrophobic guests can be located on internal as well as external branches and that proximal α(1–6)‐linked branch points weaken but do not prevent complexation.
Ionic Liquid Crystals Derived from Amino Acids
Authors: Mansueto Markus , Frey Wolfgang , Laschat Sabine
Published: October 2013

Novel chiral amino acid derived ionic liquid crystals with amine and amide moieties as spacers between the imidazolium head group and the alkyl chain were synthesised. The key step in the synthesis utilised the relatively uncommon SO3 leaving group in a microwave‐assisted reaction. The mesomorphic properties of the mesogens were determined by differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X‐ray diffraction. All liquid crystalline salts exhibit a smectic A mesophase geometry with strongly interdigitated bilayer structures. An increase of the steric bulk of the stereogenic centre hindered the formation of mesophases. In case of phenylalanine‐derived derivatives a mesomorphic behaviour was observed for shorter alkyl chains as compared to other amino acid derivatives indicating an additional stabilising effect by the phenyl moiety.
Facile Tuning of Luminescent Platinum(II) Schiff Base Complexes from Yellow to Near‐Infrared: Photophysics, Electrochemistry, Electrochemiluminescence and Theoretical Calculations
Authors: Reid Ellen F. , Cook Vernon C. , Wilson David J. D. , Hogan Conor F.
Published: October 2013

The photophysical and related properties of platinum(II) Schiff base complexes can be finely and predictably tuned over a wide range of wavelengths by small and easily implemented changes to ligand structure. A series of such complexes, differing only in the number and positioning of methoxy substituents on the phenoxy ring, were synthesised and their photophysical, electrochemical and electrochemiluminescent (ECL) properties investigated. Theoretical calculations were performed in order to gain further insight into the relationship between structure and properties in these materials. By positioning methoxy groups para and/or ortho to either the imine or the oxygen group on the ligand, electron density could be directed selectively toward the LUMO or HOMO as required. This allowed the emission colour (both photoluminescent and electrochemiluminescent) to be tuned over a wide range between 587 and 739 nm. The variation in orbital energies was also manifested in the positions of the absorption bands and the redox properties of the complexes, as well as in the NMR shifts for the uncoordinated ligands. All reported complexes displayed intense electrochemiluminescence (ECL), which could be initiated either by annihilation or co‐reactant pathways. The relationship between the electrochemical and photophysical properties and the efficiency of the ECL is discussed. For two of the complexes solid‐state ECL could be generated from electrodeposited layers of the complex.
High‐Efficiency Encapsulation of Pt Nanoparticles into the Channel of Carbon Nanotubes as an Enhanced Electrocatalyst for Methanol Oxidation
Authors: Zhang Jianan , Guo Shaojun , Wei Junyi , Xu Qun , Yan Wenfu , Fu Jianwei , Wang Shoupei , Cao Mingjing , Chen Zhimin
Published: October 2013

Pt‐based nanostructures serving as anode catalysts for the methanol oxidation reaction (MOR) have been widely studied for many years. Nevertheless, challenging issues such as poor reaction kinetics and the short‐term stability of the MOR are the main drawbacks of such catalysts and limit their applications. Herein, we have developed a facile approach to encapsulate Pt nanoparticles (NPs) inside the nanochannels of porous carbon nanotubes (CNTs; Pt‐in‐CNTs) as a new enhanced electrocatalytic material. The as‐prepared CNTs offer simultaneously ordered diffusion channels for ions and a confinement effect for the NPs, which both facilitate the promotion of catalytic kinetics and avoid the Ostwald ripening of Pt NPs, thus leading to high activity and durable cycle life as an anode catalyst for MOR. This work provides a new approach for enhancing the stability and activity by optimizing the structure of the catalyst, and the Pt‐in‐CNTs represent the most durable catalysts ever reported for MOR.
Dysprosium Complexes and Their Micelles as Potential Bimodal Agents for Magnetic Resonance and Optical Imaging
Authors: Debroye Elke , Laurent Sophie , Vander Elst Luce , Muller Robert N. , Parac‐Vogt Tatjana N.
Published: October 2013

Six diethylene triamine pentaacetic acid (DTPA) bisamide derivatives functionalized with p‐toluidine (DTPA‐BTolA), 6‐aminocoumarin (DTPA‐BCoumA), 1‐naphthalene methylamine (DTPA‐BNaphA), 4‐ethynylaniline (DTPA‐BEthA), p‐dodecylaniline (DTPA‐BC12PheA) and p‐tetradecyl‐aniline (DTPA‐BC14PheA) were coordinated to dysprosium(III) and the magnetic and optical properties of the complexes were examined in detail. The complexes consisting of amphiphilic ligands (DTPA‐BC12PheA and DTPA‐BC14PheA) were further assembled into mixed micelles. Upon excitation into the ligand levels, the complexes display characteristic DyIII emission with quantum yields of 0.3–0.5 % despite the presence of one water molecule in the first coordination sphere. A deeper insight into the energy‐transfer processes has been obtained by studying the photophysical properties of the corresponding GdIII complexes. Since the luminescence quenching effect is decreased by the intervention of non‐ionic surfactant, quantum yields up to 1 % are obtained for the micelles. The transverse relaxivity r2 per DyIII ion at 500 MHz and 310 K reaches a maximum value of 27.4 s−1 mM−1 for Dy‐DTPA‐BEthA and 36.0 s−1 mM−1 for the Dy‐DTPA‐BC12PheA assemblies compared with a value of 0.8 s−1 mM−1 for Dy‐DTPA. The efficient T2 relaxation, especially at high magnetic field strengths, is sustained by the high magnetic moment of the dysprosium ion, the coordination of water molecules with slow water exchange kinetics and long rotational correlation times. These findings open the way to the further development of bimodal optical and magnetic resonance imaging probes starting from single lanthanide compounds.
Vaulted Biaryls in Catalysis: A Structure–Activity Relationship Guided Tour of the Immanent Domain of the VANOL Ligand
Authors: Guan Yong , Ding Zhensheng , Wulff William D.
Published: October 2013

The active site in the BOROX catalyst is a chiral polyborate anion (boroxinate) that is assembled in situ from three equivalents of B(OPh)3 and one of the VANOL ligand by a molecule of substrate. The substrates are bound to the boroxinate by H bonds to oxygen atoms O1–O3. The effects of introducing substituents at each position of the naphthalene core of the VANOL ligand are systematically investigated in an aziridination reaction. Substituents in the 4,4′‐ and 8,8′‐positions have a negative effect on catalyst performance, whereas, substituents in the 7‐ and 7′‐positions have the biggest impact in a positive direction.
Distinct Stepwise Reduction of a NickelNickel‐Bonded Compound Containing an α‐Diimine Ligand: From Perpendicular to Coaxial Structures
Authors: Dong Qingsong , Yang Xiao‐Juan , Gong Shida , Luo Qiong , Li Qian‐Shu , Su Ji‐Hu , Zhao Yanxia , Wu Biao
Published: October 2013

A nickelnickel‐bonded complex, [{Ni(μ‐L.−)}2] (1; L=[(2,6‐iPr2C6H3)NC(Me)]2), was synthesized from reduction of the LNiBr2 precursor by sodium metal. Further controllable reduction of 1 with 1.0, 2.0 and 3.0 equiv of Na, respectively, afforded the singly, doubly, and triply reduced compounds [Na(DME)3]⋅[{Ni(μ‐L.−)}2] (2; DME=1,2‐dimethoxyethane), [Na(Et2O)]Na[(L.−)NiNiL2−] (3), and [Na(Et2O)]2Na[L2−NiNiL2−] (4). Here L represents the neutral ligand, L.− denotes its radical monoanion, and L2− is the dianion. All of the four compounds feature a short NiNi bond from 2.2957(6) to 2.4649(8) Å. Interestingly, they display two different structures: the perpendicular (1 and 2) and the coaxial (3 and 4) structure, in which the metalmetal bond axis is perpendicular to or collinear with the axes of the α‐diimine ligands, respectively. The electronic structures, NiNi bonding nature, and energetic comparisons of the two structure types were investigated by DFT computations.
Heterogeneous CuII‐Catalysed Solvent‐Controlled Selective N‐Arylation of Cyclic Amides and Amines with Bromo‐iodoarenes
Authors: Kundu Debasish , Bhadra Sukalyan , Mukherjee Nirmalya , Sreedhar Bojja , Ranu Brindaban C.
Published: October 2013

A selective N‐arylation of cyclic amides and amines in DMF and water, respectively, catalysed by CuII/Al2O3 has been achieved. This protocol has been employed for the synthesis of a library of arenes bearing a cyclic amide and an amine moiety at two ends, including a few scaffolds of therapeutic importance. The mechanism has been established based on detailed electron paramagnetic resonance (EPR) spectroscopy, X‐ray photoelectron spectroscopy (XPS), UV diffuse reflectance spectroscopy (DRS) and inductively coupled plasma‐mass spectrometry (ICP‐MS) studies of the catalyst at different stages of the reaction. The CuII/Al2O3 catalyst was recovered and recycled for subsequent reactions.
A New Chiral Binaphthalene‐Based Fluorescence Polymer Sensor for the Highly Enantioselective Recognition of Phenylalaninol
Authors: Wei Guo , Zhang Shuwei , Dai Chunhui , Quan Yiwu , Cheng Yixiang , Zhu Chengjian
Published: October 2013

A new (S)‐binaphthalene‐based polymer (P‐1) was synthesized by the polymerization of 5,5′‐((2,5‐dibutoxy‐1,4‐phenylene)bis(ethyne‐2,1‐diyl))bis(2‐hydroxy‐3‐(piperidin‐1‐ylmethyl) benzaldehyde (M‐1) with (S)‐2,2′‐dimethoxy‐(1,1′‐binaphthalene)‐3,3′‐diamine (M‐2) through the formation of a Schiff base; the corresponding chiral polymer (P‐2) could be obtained by the reduction of polymer P‐1 with NaBH4. Chiral polymer P‐1 exhibited a remarkable “turn‐on” fluorescence‐enhancement response towards (D)‐phenylalaninol and excellent enantioselective recognition behavior with enantiomeric fluorescence difference ratios (ef) as high as 8.99. More importantly, chiral polymer P‐1 displays a bright blue fluorescence color change upon the addition of (D)‐phenylalaninol under a commercially available UV lamp, which can be clearly observed by the naked eye. On the contrary, chiral polymer P‐2 showed weaker enantioselective fluorescence ability towards the enantiomers of phenylalaninol.
Integrated Hollow Mesoporous Silica Nanoparticles for Target Drug/siRNA Co‐Delivery
Authors: Ma Xing , Zhao Yun , Ng Kee Woei , Zhao Yanli
Published: October 2013

A hollow mesoporous silica nanoparticle (HMSNP) based drug/siRNA co‐delivery system was designed and fabricated, aiming at overcoming multidrug resistance (MDR) in cancer cells for targeted cancer therapy. The as‐prepared HMSNPs have perpendicular nanochannels connecting to the internal hollow cores, thereby facilitating drug loading and release. The extra volume of the hollow core enhances the drug loading capacity by two folds as compared with conventional mesoporous silica nanoparticles (MSNPs). Folic acid conjugated polyethyleneimine (PEI‐FA) was coated on the HMSNP surfaces under neutral conditions through electrostatic interactions between the partially charged amino groups of PEI‐FA and the phosphate groups on the HMSNP surfaces, blocking the mesopores and preventing the loaded drugs from leakage. Folic acid acts as the targeting ligand that enables the co‐delivery system to selectively bind with and enter into the target cancer cells. PEI‐FA‐coated HMSNPs show enhanced siRNA binding capability on account of electrostatic interactions between the amino groups of PEI‐FA and siRNA, as compared with that of MSNPs. The electrostatic interactions provide the feasibility of pH‐controlled release. In vitro pH‐responsive drug/siRNA co‐delivery experiments were conducted on HeLa cell lines with high folic acid receptor expression and MCF‐7 cell lines with low folic acid receptor expression for comparison, showing effective target delivery to the HeLa cells through folic acid receptor meditated cellular endocytosis. The pH‐responsive intracellular drug/siRNA release greatly minimizes the prerelease and possible side effects of the delivery system. By simultaneously delivering both doxorubicin (Dox) and siRNA against the Bcl‐2 protein into the HeLa cells, the expression of the anti‐apoptotic protein Bcl‐2 was successfully suppressed, leading to an enhanced therapeutic efficacy. Thus, the present multifunctional nanoparticles show promising potentials for controlled and targeted drug and gene co‐delivery in cancer treatment.
Formation of Quaternary Stereogenic Centers by Copper‐Catalyzed Asymmetric Conjugate Addition Reactions of Alkenylaluminums to Trisubstituted Enones
Authors: Müller Daniel , Alexakis Alexandre
Published: October 2013

Alkenylaluminums undergo asymmetric copper‐catalyzed conjugate addition (ACA) to β‐substituted enones allowing the formation of stereogenic all‐carbon quaternary centers. Phosphinamine–copper complexes proved to be particularly active and selective compared with phosphoramidite ligands. After extensive optimization, high enantioselectivities (up to 96 % ee) were obtained for the addition of alkenylalanes to β‐substituted enones. Two strategies for the generation of the requisite alkenylaluminums were explored allowing for the introduction of aryl‐ and alkyl‐substituted alkenyl nucleophiles. Moreover, alkyl‐substituted phosphinamine (SimplePhos) ligands were identified for the first time as highly efficient ligands for the Cu‐catalyzed ACA.
Regio‐ and Stereochemical Studies on the Nitroso‐Diels–Alder Reaction with 1,2‐Disubstituted Dienes
Authors: Galvani Gilles , Lett Robert , Kouklovsky Cyrille
Published: October 2013

The regioselectivity of the nitroso‐Diels–Alder reaction between unsymmetrical acyclic dienes and Boc‐nitroso (Boc=tert‐butoxycarbonyl) reagent or the Wightman chiral chloronitroso reagents has been studied. With the Boc‐nitroso reagent, the selectivity is a consequence of steric effects at the C1‐position in the diene and electronic effects at the C2‐position in the diene. The combination of an unprotected hydroxyethyl side chain at C1 and an electron‐withdrawing group at C2 allows complete regioselectivity in favour of the proximal isomer. The same isomer was obtained exclusively with the chiral nitroso reagent with high enantioselectivities. A model based on steric effects is proposed.
Highly Hydrogenated Graphene through Microwave Exfoliation of Graphite Oxide in Hydrogen Plasma: Towards Electrochemical Applications
Authors: Eng Alex Yong Sheng , Sofer Zdenek , Šimek Petr , Kosina Jiri , Pumera Martin
Published: October 2013

Hydrogenated graphenes exhibit a variety of properties with potential applications in devices, ranging from a tunable band gap to fluorescence, ferromagnetism, and the storage of hydrogen. We utilize a one‐step microwave‐irradiation process in hydrogen plasma to create highly hydrogenated graphene from graphite oxides. The procedure serves the dual purposes of deoxygenation and concurrent hydrogenation of the carbon backbone. The effectiveness of the hydrogenation process is investigated on three different graphite oxides (GOs), which are synthesized by using the Staudenmaier, Hofmann, and Hummers methods. A systematic characterization of our hydrogenated graphenes is performed using UV/Vis spectroscopy, SEM, AFM, Raman spectroscopy, FTIR spectroscopy, X‐ray photoelectron spectroscopy (XPS), combustible elemental analysis, and electrical conductivity measurements. The highest hydrogenation extent is observed in hydrogenated graphene produced from the Hummers‐method GO, with a hydrogen content of 19 atomic % in the final product. In terms of the removal of oxygen groups, microwave exfoliation yields graphenes with very similar oxygen contents despite differences in their parent GOs. In addition, we examine the prospective application of hydrogenated graphenes as electrochemical transducers through a cyclic voltammetry (CV) study. The highly hydrogenated graphenes exhibit fast heterogeneous electron‐transfer rates, suggestive of their suitability for electrochemical applications in electrodes, supercapacitors, batteries, and sensors.
Enantiopurity Determination of the Enantiomers of the Triple Reuptake Inhibitor Indatraline
Authors: Grimm Stefanie H. , Allmendinger Lars , Höfner Georg , Wanner Klaus T.
Published: October 2013

The present study describes the development of two approaches for the determination of the enantiopurity of both enantiomers of indatraline. Initially, a method was developed using different chiral solvating agents (CSAs) for diastereomeric discrimination regarding signal separation in 1H nuclear magnetic resonance (NMR) spectroscopy, revealing MTPA as a promising choice for the differentiation of the indatraline enantiomers. This CSA was also tested for its ideal molar ratio, temperature, and solvent. Optimized conditions could be achieved that made determination of enantiopurity for (1R,3S)‐indatraline up to 98.9% enantiomeric excess (ee) possible. To quantify even higher enantiopurities, a high‐performance liquid chromatography (HPLC) method based on a modified β‐cyclodextrine phase was established. The influence of buffer type, concentration, pH value, percentage and kind of organic modifier, temperature, injection volume as well as sample solvent on chromatographic parameters was investigated. Afterwards, the reliability of the established HPLC method was demonstrated by validation according to the ICH guideline Q2(R1) regarding specificity, accuracy, precision, linearity, and quantitation limit. The developed method proved to be strictly linear within a concentration range of 1.25–1000 μM for the (1R,3S)‐enantiomer and 1.25‐750 μM for its mirror image that enables a reliable determination of enantiopurities up to 99.75% ee for the (1R,3S)‐enantiomer and up to 99.67% ee for the (1S,3R)‐enantiomer. Chirality 25:923–933, 2013. © 2013 Wiley Periodicals, Inc.
Bidirectional Chiral Inversion of Trantinterol Enantiomers After Separate Doses to Rats
Authors: Qin Feng , Wang Xintao , Jing Lijuan , Pan Li , Cheng Maosheng , Sun Guoxiang , Li Famei
Published: October 2013

The chiral inversion and pharmacokinetics of two enantiomers of trantinterol, a new β2 agonist, were studied in rats dosed (+)‐ or (−)‐trantinterol separately. Plasma concentrations of (+)‐ and (−)‐trantinterol were measured by chiral stationary phase liquid chromatography tandem mass spectroscopy (LC‐MS/MS). The apparent inversion ratio was calculated as the ratio of AUC0‐t of (−)‐trantinterol or (+)‐trantinterol inverted from their antipodes to the sum of the AUC0‐t of (−)‐ and (+)‐trantinterol. Following single intravenous administration, both given enantiomers declined in similar plasma concentrations, suggesting that the two enantiomers have approximately the same disposition kinetics by the route of intravenous administration. However, after single oral administration, plasma concentrations of uninverted (−)‐trantinterol at many timepoints were significantly higher than those of uninverted (+)‐trantinterol, suggesting that the two enantiomers undergo apparently different absorption or metabolism after oral administration. Significant bidirectional chiral inversion occurred after intravenous and oral administration of (+)‐ or (−)‐trantinterol. After dosing with optically pure enantiomer, the concentration of the administered enantiomer predominated in vivo. The AUC0‐36 of (+)‐trantinterol after intravenous and oral dosing of (−)‐trantinterol were 16.6 ± 5.2 and 33.3 ± 16%, respectively of those of total [(+) + (−)] trantinterol. The AUC0‐36 of (−)‐trantinterol after intravenous and oral dosing of (+)‐trantinterol were 19.6 ± 8.8 and 37.9 ± 4.5%, respectively, of those of total [(−) + (+)] trantinterol. After intravenous administration of (+)‐ and (−)‐trantinterol the chiral inversion ratios of the two enantiomers were not significantly different and similar results were found for oral administration. The extent of chiral inversion after intravenous administration was apparently lower, indicating that the bidirectional chiral inversion was not only systemic but also presystemic. Chirality 25:934–938, 2013.© 2013 Wiley Periodicals, Inc.
Significance of the Natural Occurrence of L‐ Versus D‐Pipecolic Acid: A Review
Authors: Vranova Valerie , Lojkova Lea , Rejsek Klement , Formanek Pavel
Published: October 2013

Pipecolic acid naturally occurs in microorganisms, plants, and animals, where it plays many roles, including the interactions between these organisms, and is a key constituent of many natural and synthetic bioactive molecules. This article provides a review of current knowledge on the natural occurrence of pipecolic acid and the known and potential significance of its L‐ and D‐enantiomers in different scientific disciplines. Knowledge gaps with perspectives for future research identified within this article include the roles of the L‐ versus the D‐enantiomer of pipecolic acid in plant resistance, nutrient acquisition, and decontamination of polluted soils, as well as rhizosphere ecology and medical issues. Chirality 25:823–831, 2013. © 2013 Wiley Periodicals, Inc.
Enantioselective Liquid–Liquid Extraction of Zopiclone With Mandelic Acid Ester Derivatives
Authors: Peng Yangfeng , He Quan , Zuo Bin , Niu Haibo , Tong Tianzhong , Zhao Hongliang
Published: October 2013

Enantioselective liquid–liquid extraction of zopiclone was conducted by employing a series of (R)‐mandelic acid esters as chiral extractants. The effects of concentration of extractant, concentration of zopiclone, type of organic solvent, pH value, and temperature on the extraction efficiency were investigated. (R)‐o‐chloromandelic acid propyl ester was demonstrated to be an efficient chiral extractant for zopiclone resolution with a maximum enantioselectivity of 1.6. Chirality 25:952–956, 2013. © 2013 Wiley Periodicals, Inc.
Preparation and Characterization of Compact Binderless Zeolite Shapes with Faujasit and Linde Type A Structure
Authors: Schumann Kristin , Unger Baldur , Brandt Alfons , Fischer Gundula , Richter Hannes , Jänchen Jochen
Published: October 2013

Obwohl eine Vielzahl an industriellen Anwendungen für Zeolithe besteht, haben Bindemittel, die zu Herstellung von konventionellen Zeolithformkörpern benutzt werden, einen negativen Einfluss. Die Herstellung und Charakterisierung von mechanisch stabilen kompakten bindemittelfreien Zeolithformkörpern mit Faujasit‐ und Linde Typ A‐Struktur wird am Beispiel von Wabenkörper und Mehrkanalrohren beschrieben. Diese erhöhen aufgrund ihres hohen Zeolithanteils sowie ihrer großen Raumausfüllung beispielsweise die Effektivität von bekannten dynamischen Adsorptions‐, Katalyse‐ oder Filtrationsprozessen.
Hydrogenation of p‐Nitrophenol to p‐Aminophenol as a Test Reaction for the Catalytic Activity of Supported Pt Catalysts
Authors: Goepel Michael , Al‐Naji Majd , With Patrick , Wagner Gerald , Oeckler Oliver , Enke Dirk , Gläser Roger
Published: October 2013

Die Hydrierung von p‐Nitrophenol (PNP) zu p‐Aminophenol (PAP) mit NaBH4 als Reduktionsmittel wurde als Testreaktion für die Bestimmung der katalytischen Aktivität von Platin‐Trägerkatalysatoren untersucht. Als Maß für die Aktivität dient die Anfangsreaktionsgeschwindigkeit, die in weniger als 10 Minuten mittels Online‐UV‐vis‐Spektroskopie bei Raumtemperatur und Umgebungsdruck in Wasser als Lösungsmittel zugänglich ist. Für drei Pt‐Katalysatoren mit porösem SiO2, porösem Glas bzw. Al2O3 als Träger wurden deutliche Aktivitätsunterschiede beobachtet. Allerdings müssen vor allem bei sehr aktiven Katalysatoren mögliche Limitierungen der Umsetzung durch externe und interne Stofftransportvorgänge berücksichtigt werden.
Analysis and Interpretation of Zero Length Column Response Curves
Authors: Mangano Enzo , Brandani Stefano , Ruthven Douglas M.
Published: October 2013

To obtain reliable diffusivity data it is essential that the zero length columns (ZLC) response curve is measured under conditions of kinetic control. For systems with a mildly favorable isotherm, the form of the ZLC response curve under equilibrium control is very similar to that for a linear system under kinetic control. For an equilibrium controlled system, however, the response curve plotted as c/c0 vs Ft (total volume of purge gas passed through the sample at time t) should be invariant with the purge flow rate. Therefore, these two situations are easily distinguishable. Unfortunately this check has often been omitted in reported ZLC studies, leading to erroneous apparent diffusivity values.
Petroleum coke gasification: A review
Authors: Murthy Bontu N. , Sawarkar Ashish N. , Deshmukh Niteen A. , Mathew Thomas , Joshi Jyeshtharaj B.
Published: October 2013

The production of petroleum coke (petcoke) in the refineries is progressively peaking up because of the trend of processing heavy crudes and in turn, a renewed interest in delayed coking process. Therefore, an efficient, economical, and environmentally safe utilisation of petcoke has become imperative in the current petroleum refining scenario. Gasification of petcoke has emerged as one of the attractive options and is gaining increasing attention to convert the petcoke to value‐added products. The process offers the refiners a variety of product slates mainly via synthesis gas route. The products include steam, hydrogen, electricity, chemicals (viz. methanol, ammonia, etc.), liquid fuels via Fischer–Tropsch (F‐T) synthesis and so on. Petcoke has been identified as a potential feedstock for about 15% of the total planned gasification capacity worldwide. In the present communication, the published literature pertaining to petcoke gasification has been extensively analysed and a state‐of‐the‐art review has been written that includes: (1) the importance of petcoke gasification in the present petroleum refining scenario; (2) petcoke gasification reaction mechanism, kinetics, and typical product profile; (3) parametric sensitivity of the operating variables such as temperature and pressure; (4) various gasifiers for petcoke gasification; (5) modelling efforts on different types of gasifiers and (6) future prospects of petcoke gasification. An attempt has been made to get the afore‐mentioned aspects together in a thematic framework so that the information is available at a glance and is expected to be useful as a single point source to the researchers and practicing refiners.