bluuebunny/crossref_metadata_2025_split huggingface dataset:
Biosynthesis and Cellular Localization of Functional Polyketides in the Gastropod Mollusc Scaphander lignarius
Authors: Cutignano Adele , Avila Conxita , Rosica Annamaria , Romano Giovanna , Laratta Bruna , Domenech‐Coll Anna , Cimino Guido , Mollo Ernesto , Fontana Angelo 
Published: July 2012

AbstractOpisthobranchs belong to a subclass of highly evolved and specialised marine gastropods that rely on the use of secondary metabolites for their survival. Here we report the full elucidation of the biosynthesis of aromatic metabolites, lignarenones, in one of these gastropods, the cephalaspidean Scaphander lignarius. Feeding experiments with 2H‐ and 13C‐labelled precursors revealed a mixed acetate/propionate polyketide pathway primed by benzoic acid. Phenylalanine ammonia lyase (PAL), unprecedented in animals, is central to the synthesis of this aromatic precursor by oxidative deamination of L‐phenylalanine to cinnamic acid. Lignarenones are synthesised in the cytoplasm of specialised eukaryotic cells named Blochmann's glands, which are distributed in biosynthetic tissue localised in the vulnerable mantle of the mollusc. This result supports the hypothesis that this lineage of gastropods has acquired the genetic information to produce the chemical substances that they use for their survival.
DFT Calculations Suggest a New Type of Self‐Protection and Self‐Inhibition Mechanism in the Mammalian Heme Enzyme Myeloperoxidase: Nucleophilic Addition of a Functional Water rather than One‐Electron Reduction
Authors: Sicking Wilhelm , Somnitz Holger , Schmuck Carsten 
Published: July 2012

AbstractThe mammalian heme enzyme myeloperoxidase (MPO) catalyzes the reaction of Cl− to the antimicrobial‐effective molecule HOCl. During the catalytic cycle, a reactive intermediate “Compound I” (Cpd I) is generated. Cpd I has the ability to destroy the enzyme. Indeed, in the absence of any substrate, Cpd I decays with a half‐life of 100 ms to an intermediate called Compound II (Cpd II), which is typically the one‐electron reduced Cpd I. However, the nature of Cpd II, its spectroscopic properties, and the source of the additional electron are only poorly understood. On the basis of DFT and time‐dependent (TD)‐DFT quantum chemical calculations at the PBE0/6‐31G* level, we propose an extended mechanism involving a new intermediate, which allows MPO to protect itself from self‐oxidation or self‐destruction during the catalytic cycle. Because of its similarity in electronic structure to Cpd II, we named this intermediate Cpd II′. However, the suggested mechanism and our proposed functional structure of Cpd II′ are based on the hypothesis that the heme is reduced by charge separation caused by reaction with a water molecule, and not, as is normally assumed, by the transfer of an electron. In the course of this investigation, we found a second intermediate, the reduced enzyme, towards which the new mechanism is equally transferable. In analogy to Cpd II′, we named it FeII′. The proposed new intermediates Cpd II′ and FeII′ allow the experimental findings, which have been well documented in the literature for decades but not so far understood, to be explained for the first time. These encompass a) the spontaneous decay of Cpd I, b) the unusual (chlorin‐like) UV/Vis, circular dichroism (CD), and resonance Raman spectra, c) the inability of reduced MPO to bind CO, d) the fact that MPO‐Cpd II reduces SCN− but not Cl−, and e) the experimentally observed auto‐oxidation/auto‐reduction features of the enzyme. Our new mechanism is also transferable to cytochromes, and could well be viable for heme enzymes in general.
Monomer–Dimer Control and Crystal Engineering in TASPs
Authors: Freeman Jon O. , Murphy Michael E. P. , Sherman John C. 
Published: July 2012

AbstractWe have reported a template assembled synthetic protein (cavitein Q4) as an unexpected dimer in the solid state and as a monomer–dimer equilibrium in solution. We have since reported an ability to bias a cavitein’s monomer–dimer equilibrium in solution by sequence design involving histidine metal chelation or disulfide incorporation. However, little remains known about the forces contributing to dimeric cavitein crystal nucleation and lattice stabilization. We, therefore, designed glutamine variants to probe factors involved in dimeric cavitein crystallization. It was found that a key glutamate hydrogen‐bonding interaction between dimers is integral to crystal formation and stabilization. Additionally, we obtained a crystal structure of a cavitein (Q4‐E3H) designed to bias the dimeric structure via histidine metal coordination. The resolved structure indicates a histidine cluster interaction that likely accounts for the biased dimeric form observed in solution.
Chemical and Photochemical Functionality of the First Molecular Bismuth Vanadium Oxide
Authors: Tucher Johannes , Nye Leanne C. , Ivanovic‐Burmazovic Ivana , Notarnicola Antonio , Streb Carsten 
Published: July 2012

AbstractAnionic metal oxide clusters, so‐called polyoxometalates, can be developed as molecular model compounds to mimic the chemical and photochemical reactivity of solid‐state metal oxides on the molecular level. Inspired by the well‐known visible‐light photocatalyst BiVO4, the first molecular bismuth vanadium oxide has been synthesized to investigate the chemical and photochemical similarities between the solid‐state and molecular compounds. The cluster H3[(Bi(dmso)3)4V13O40]⋅ca. 4 DMSO was obtained from simple precursors in almost quantitative yield. Structural analysis showed that the cluster shell is based on the unusual all‐vanadium ε‐Keggin framework [ε‐V12O40]15−, which is stabilized by coordination of four BiIII centers. The acidic character of the three cluster protons was demonstrated by titration studies. The cluster shows promising photocatalytic properties in visible‐light photooxidation reactions and has high activity (turnover number >1200), high quantum yield (Φ=7.6 %), and good recyclability, which make it a promising first example of a new class of heterometallic polyoxometalates.
Effects of Phosphorus Substituents on Reactions of α‐Alkoxyphosphonium Salts with Nucleophiles
Authors: Goto Akihiro , Otake Kazuki , Kubo Ozora , Sawama Yoshinari , Maegawa Tomohiro , Fujioka Hiromichi 
Published: July 2012

AbstractThe effects of phosphorus substituents on the reactivity of α‐alkoxyphosphonium salts with nucleophiles has been explored. Reactions of α‐alkoxyphosphonium salts, prepared from various acetals and tris(o‐tolyl)phosphine, with a variety of nucleophiles proceeded efficiently. These processes represent the first examples of high‐yielding nucleophilic substitution reactions of α‐alkoxyphosphonium salts. The reactivity of these salts was determined by a balance between steric and electronic factors, respectively, represented by cone angles θ and CO stretching frequencies ν (steric and electronic parameters, respectively). In addition, a novel reaction of α‐alkoxyphosphonium salts derived from Ph3P with Grignard reagents was observed to take place in the presence of O2 to afford alcohols in good yields. A radical mechanism is proposed for this process that has gained support from isotope‐labeling and radical‐inhibition experiments.
Regioselective Hydration of Alkynes by Iron(III) Lewis/Brønsted Catalysis
Authors: Cabrero‐Antonino Jose R. , Leyva‐Pérez Antonio , Corma Avelino 
Published: July 2012

AbstractThe triflimide iron(III) salt [Fe(NTf2)3] promotes the direct hydration of terminal and internal alkynes with very good Markovnikov regioselectivities and high yields. The enhanced carbophilic Lewis acidity of the FeIII cation mediated by the weakly‐coordinating triflimide anion is crucial for the catalytic activity. The iron(III) metal salt can be recycled in the form of the OPPh3/[Fe(NTf2)3] system with similar activity and selectivity. However, spectroscopic and kinetic studies show that [Fe(NTf2)3] hydrolyzes under the reaction conditions and that catalytically less active Brønsted species are formed, which points to a Lewis/Brønsted co‐catalysis. This triflimide‐based catalytic system is regioselective for the hydration of internal aryl‐alkynes and opens the door to a new synthetic route to alkyl ketophenones. As a proof of concept, the synthesis of two antipsychotics Haloperidol and Melperone, with general butyrophenone‐like structure, is shown.
Stereoselective Synthesis of D‐ and L‐Carbocyclic Nucleosides by Enzymatically Catalyzed Kinetic Resolution
Authors: Mahler Miriam , Reichardt Bastian , Hartjen Philip , van Lunzen Jan , Meier Chris 
Published: July 2012

AbstractAn efficient synthesis of (S)‐ or (R)‐3‐(benzyloxy‐methyl)‐cyclopent‐3‐enol was developed by appling an enzyme‐catalyzed kinetic‐resolution approach. This procedure allowed the syntheses of the enantiomeric building blocks (S)‐ and (R)‐cyclopentenol with high optical purity (>98 % ee). In contrast to previous approaches, the key advantage of this procedure is that the resolution is done on the level of enantiomers that only contain one stereogenic center. Owing to this feature, it was possible to chemically convert the enantiomers into each other. By using this route, the starting materials for the syntheses of carbocyclic D‐ and L‐nucleoside analogues were readily accessible. 3′,4′‐Unsaturated D‐ or L‐carbocyclic nucleosides were obtained from the condensation of various nucleobases with (S)‐ or (R)‐cyclopentenol. Functionalization of the double bond in 3′‐deoxy‐3′,4′‐didehydro‐carba‐D‐thymidine led to a variety of new nucleoside analogues. By using the cycloSal approach, their corresponding phosphorylated metabolites were readily accessable. Moreover, a new synthetic route to carbocyclic 2′‐deoxy‐nucleosides was developed, thereby leading to D‐ and L‐carba‐dT. D‐Carba‐dT was tested for antiviral activity against multidrug‐resistance HIV‐1 strain E2‐2 and compared to the known antiviral agent d4T, as well as L‐carba‐dT. Whilst L‐carba‐dT was found to be inactive, its D‐analogue showed remarkably high activity against the resistant virus and significantly better than that of d4T. However, against the wild‐type virus strain NL4/3, d4T was found to be more‐active than D‐carba‐dT.
The Coordination of NiII and CuII Ions to the Polyhistidyl Motif of Hpn Protein: Is It as Strong as We Think?
Authors: Witkowska Danuta , Politano Rossella , Rowinska‐Zyrek Magdalena , Guerrini Remo , Remelli Maurizio , Kozlowski Henryk 
Published: July 2012

AbstractHpn, one of Helicobacter pylori′s nickel‐accessory proteins, is an amazingly peculiar protein: Almost half of its sequence consists of polyhistidyl (poly‐His) residues. Herein, we try to understand the origin of this naturally occurring sequence, thereby shedding some light on the bioinorganic chemistry of Hpn′s numerous poly‐His repeats. By using potentiometric, mass spectrometric, and various spectroscopic techniques, we studied the NiII‐ and CuII complexes of the wild‐type Ac‐THHHHYHGG‐NH2 fragment of Hpn and of its six analogues, in which consecutive residues (His or Tyr) were replaced by Ala (Ala‐substitution or Ala‐scan approaches), thereby resulting in Ac‐TAHHHYHGG‐NH2, Ac‐THAHHYHGG‐NH2, Ac‐THHAHYHGG‐NH2, Ac‐THHHAYHGG‐NH2, Ac‐THHHHAHGG‐NH2, and Ac‐THHHHYAGG‐NH2 peptides. We found that the His4 residue is critical for both NiII‐ and CuII‐ion binding and the effectiveness of binding varies even if the substituted amino acid does not take part in the direct binding interactions.
Ca3Sm3[Si9N17] and Ca3Yb3[Si9N17] Nitridosilicates with Interpenetrating Nets that Consist of Star‐Shaped [N[4](SiN3)4] Units and [Si5N16] Supertetrahedra
Authors: Huppertz Hubert , Oeckler Oliver , Lieb Alexandra , Glaum Robert , Johrendt Dirk , Tegel Marcus , Kaindl Reinhard , Schnick Wolfgang 
Published: July 2012

AbstractNew nitridosilicates Ca3Sm3[Si9N17] and Ca3Yb3[Si9N17] were synthesized from the reactions of the pure metals (calcium and samarium/ytterbium) with silicon diimide “Si(NH)2” in a radio‐frequency (rf) furnace at temperatures of up to 1650 °C. These isotypic compounds crystallize in the cubic space group P$\bar 4$3m (no. 215) with lattice parameters a=739.50(3) pm; V=0.4044(1) nm3; Z=1; wR2=0.029 (240 diffraction data, 26 parameters) for Ca3Sm3[Si9N17] and a=730.20(2) pm; V=0.3893(1) nm3; wR2=0.039 (387 diffraction data, 27 parameters) for Ca3Yb3[Si9N17]. The new structure type of Ca3RE3[Si9N17] (RE=Sm, Yb) consists of two independent infinite networks, each of which have an expanded sphalerite (ZnS) topology in which the positions of the Zn and S atoms are replaced by voluminous [N[4](SiN3)4] units and [Si5N16] supertetrahedra, respectively, thereby displaying twofold interpenetration. As well, a structural description of Ca3Yb3[Si9N17], its thermal stability, and magnetic properties, as well as UV/Vis, IR, and Raman spectra, are presented.
A Stand‐Alone Mesoporous Crystal Structure Model from in situ X‐ray Diffraction: Nitrogen Adsorption on 3 D Cagelike Mesoporous Silica SBA‐16
Authors: Miyasaka Keiichi , Hano Hiroko , Kubota Yoshiki , Lin Yangzheng , Ryoo Ryong , Takata Masaki , Kitagawa Susumu , Neimark Alexander V. , Terasaki Osamu 
Published: July 2012

AbstractWe present a modeling scheme to analyze cagelike silica mesoporous crystals based on in situ X‐ray diffraction (XRD) data collected during gas adsorption–desorption (physisorption) processes. Nitrogen physisorption on a silica mesoporous crystal of SBA‐16 was directly monitored by using synchrotron in situ powder XRD measurements conducted at SPring‐8. SBA‐16 is a well‐ordered mesoporous silica in which three‐dimensional interconnected cagelike primary mesopores are located at the body‐centered cubic lattice points. In addition, the surrounding silica matrix contains random microporous and mesoporous intrawall porosities that are significantly influential to the diffusion properties, and thus important to be quantified for this media. The in situ XRD data exhibits seven Bragg reflections throughout the measurements, and the present method allows one to obtain the maximal and stand‐alone information about the pore structure (for example, the mesopore size, the matrix density, the intrawall porosity, and pore surface roughness) together with the nitrogen film evolution in the primary mesopores and the intrawall pore‐filling in the silica matrix. We furthermore observe a macroscopic amount of nitrogen adsorbed assuming the density of the fluid, and confirm that the XRD “isotherm” recalculated from the analysis result is consistent with the conventional nitrogen isotherm on a semi‐quantitative level; however, these results suggest that the intrawall pores would have a greater contribution to the adsorption than considered based on the conventional isotherm analyses. The present method is readily extendable to any ordered mesopores wrapped by the wall matrix containing a certain intrawall porosity.
The Excess Electron in a Boron Nitride Nanotube: Pyramidal NBO Charge Distribution and Remarkable First Hyperpolarizability
Authors: Zhong Rong‐Lin , Xu Hong‐Liang , Sun Shi‐Ling , Qiu Yong‐Qing , Su Zhong‐Min 
Published: July 2012

AbstractThe unusual properties of species with excess electrons have attracted a lot of interest in recent years due to their wide applications in many promising fields. In this work, we find that the excess electron could be effectively bound by the B atoms of boron nitride nanotube (BNNT), which is inverted pyramidally distributed from B‐rich edge to N‐rich edge. Further, Li@B‐BNNT and Li@N‐BNNT are designed by doping the Li atom to the two edges of BNNT, respectively. Because of the interaction between the Li atom and BNNT, the 2s valence electron of Li becomes a loosely bound excess electron. Interestingly, the distribution of the excess electron in Li@N‐BNNT is more diffuse and pyramidal from B‐rich edge to N‐rich edge, which is fascinating compared with Li@B‐BNNT. Correspondingly, the transition energy of Li@N‐BNNT is 0.99 eV, which is obviously smaller than 2.65 eV of Li@B‐BNNT. As a result, the first hyperpolarizability (3.40×104 a.u.) of Li@N‐BNNT is dramatically larger (25 times) than 1.35×103 a.u. of Li@B‐BNNT. Significantly, we find that the pyramidal distribution of the excess electron is the key factor to determine the first hyperpolarizability, which reveals useful information for scientists to develop new electro‐optic applications of BNNTs.
Multiscale Charge Injection and Transport Properties in Self‐Assembled Monolayers of Biphenyl Thiols with Varying Torsion Angles
Authors: Masillamani Appan Merari , Crivillers Núria , Orgiu Emanuele , Rotzler Jürgen , Bossert David , Thippeswamy Ramakrishnappa , Zharnikov Michael , Mayor Marcel , Samorì Paolo 
Published: July 2012

AbstractThis article describes the molecular structure–function relationship for a series of biphenylthiol derivatives with varying torsional degree of freedom in their molecular backbone when self‐assembled on gold electrodes. These biphenylthiol molecules chemisorbed on Au exhibit different tilt angles with respect to the surface normal and different packing densities. The charge transport through the biphenylthiol self‐assembled monolayers (SAMs) showed a characteristic decay trend with the effective monolayer thickness. Based on parallel pathways model the tunneling decay factor β was estimated to be 0.27 Å−1. The hole mobility of poly(3‐hexylthiophene)‐based thin‐film transistors incorporating a biphenylthiol SAM coating the Au source and drain electrodes revealed a dependence on the injection barrier with the highest occupied molecular orbital (HOMO) level of the semiconductor. The possible role of the resistivity of the SAMs on transistor electrodes on the threshold voltage shift is discussed. The control over the chemical structure, electronic properties, and packing order of the SAMs provides a versatile platform to regulate the charge injection in organic electronic devices.
Comparison of Trace Elements in Bottled and Desalinated Household Drinking Water in Kuwait
Authors: Al‐Mudhaf Humood F. , Abu‐Shady Abdel‐Sattar I. 
Published: July 2012

AbstractThe levels of the trace elements aluminum (Al), arsenic (As), boron (B), barium (Ba), beryllium (Be), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), mercury (Hg), molybdenum (Mo), nickel (Ni), antimony (Sb), selenium (Se), strontium (Sr), titanium (Ti), vanadium (V), and zinc (Zn) were determined in 93 brands of non‐carbonated (BW) and carbonated (CBW) bottled water available in Kuwaiti markets and in 321 samples of desalinated household water (HW) collected from 99 sampling locations, which covered 95% of Kuwait's residential areas. The study yielded a large range of results for most of these elements, and the difference between the lowest and highest measured values exceeded three orders of magnitude for some elements in a number of the BW and CBW brands. With a few exceptions, the results for the HW and BW were found to comply with the United States‐Environmental Protection Agency and World Health Organization guideline values. The elements Fe, Pb, Hg, and Ni exceeded these GVs in 8.5, 0.3, 1.2, and 1% of the HW samples, respectively. One brand of BW exceeded the GV for B, while the levels of B, Ba, Be, Fe, and Mn exceeded the GVs in 35, 15, 5, 75, and 25% of the CBW brands, respectively. Correlations were found between the levels of some elements and either the desalination plant that produced the HW or the country of origin of the BW or CBW. The levels of the elements Al, Cu, Fe, and Zn in HW were higher in the summer than in the winter, with 14, 14, 42, and 18% increases, respectively. Nutritional evaluation revealed that significant percentages of the DRIs of Cr, Cu, Fe, and Se can be provided by drinking 2 L of HW, and significant percentages of the DRIs of B, Cr, Cu, and Mo can be provided by drinking 2 L of BW.
Revealing the Bonding Pattern from the Molecular Electron Density Using Single Exponential Decay Detector: An Orbital‐Free Alternative to the Electron Localization Function
Authors: de Silva Piotr , Korchowiec Jacek , Wesolowski Tomasz A. 
Published: July 2012

AbstractWe introduce a new tool (single exponential decay detector: SEDD) to extract information about bonding and localization in atoms, molecules, or molecular assemblies. The practical evaluation of SEDD does not require any explicit information about the orbitals. The only quantity needed is the electron density (calculated or experimental) and its derivatives up to the second order.
A mobicast routing protocol with carry‐and‐forward in vehicular ad hoc networks
Authors: Chen Yuh‐Shyan , Lin Yun‐Wei 
Published: July 2012

SUMMARYIn vehicular networks, safety and comfort applications are two quite different kinds of applications to avoid the emergency traffic accident and enjoy the non‐emergency entertainment. The comfort application drives the challenges of new non‐emergency entertainments for vehicular ad hoc networks (VANETs). The comfort application usually keeps the delay‐tolerant capability; that is, messages initiated from a specific vehicle at time t can be delivered through VANETs to some vehicles within a given constrained delay time λ. In this paper, we investigate a new mobicast protocol to support comfort applications for a highway scenario in VANETs. All vehicles are located in a geographic zone (denoted as zone of relevance (ZOR)) at time t; the mobicast routing must disseminate the data message initiated from a specific vehicle to all vehicles that have ever appeared in ZOR at time t. This data dissemination must be performed before time t + λ through the carry‐and‐forward technique. In addition, the temporary network fragmentation problem is considered in our protocol design. Also, the low degree of channel utilization is kept to reserve the resource for safety applications. To illustrate the performance achievement, simulation results are examined in terms of message overhead, dissemination success rate, and accumulative packet delivery delay. Copyright © 2012 John Wiley & Sons, Ltd.
Genetic diversity is positively associated with fine‐scale momentary abundance of an invasive ant
Authors: Gruber Monica A. M. , Hoffmann Benjamin D. , Ritchie Peter A. , Lester Philip J. 
Published: July 2012

AbstractMany introduced species become invasive despite genetic bottlenecks that should, in theory, decrease the chances of invasion success. By contrast, population genetic bottlenecks have been hypothesized to increase the invasion success of unicolonial ants by increasing the genetic similarity between descendent populations, thus promoting co‐operation. We investigated these alternate hypotheses in the unicolonial yellow crazy ant, Anoplolepis gracilipes, which has invaded Arnhem Land in Australia's Northern Territory. We used momentary abundance as a surrogate measure of invasion success, and investigated the relationship between A. gracilipes genetic diversity and its abundance, and the effect of its abundance on species diversity and community structure. We also investigated whether selected habitat characteristics contributed to differences in A. gracilipes abundance, for which we found no evidence. Our results revealed a significant positive association between A. gracilipes genetic diversity and abundance. Invaded communities were less diverse and differed in structure from uninvaded communities, and these effects were stronger as A. gracilipes abundance increased. These results contradict the hypothesis that genetic bottlenecks may promote unicoloniality. However, our A. gracilipes study population has diverged since its introduction, which may have obscured evidence of the bottleneck that would likely have occurred on arrival. The relative importance of genetic diversity to invasion success may be context dependent, and the role of genetic diversity may be more obvious in the absence of highly favorable novel ecological conditions.