bluuebunny/crossref_metadata_2025_split huggingface dataset:
A new method to visualize and characterize the pore structure of TENCEL® (Lyocell) and other man‐made cellulosic fibres using a fluorescent dye molecular probe
Authors: Abu‐Rous Mohammad , Varga Ksenija , Bechtold Thomas , Schuster Kurt Christian 
Published: July 2007

AbstractThe internal porous structures of the man‐made cellulosic fibers Lyocell (TENCEL®), Modal, and Viscose fibers were visualized by applying fluorescence microscopy on fiber cross sections. The fiber pore structure was probed by the optical brightener Uvitex BHT, and the dye penetration depth was measured. The main differences in the pore structures of these three fiber types could be visualized. Only TENCEL shows a significant difference between dried and never‐dried fibers. A fiber structure model of TENCEL was obtained, which discriminates three different porous zones with respect to dye diffusion kinetics. The results are discussed in relationship with the fiber physical and chemical properties. The dye penetration depth and kinetics in TENCEL fibers was found to be sensitive to the production and treatment conditions, in particular to changes in the pore system by drying, and following alkali swelling processes. The performance of surface‐specific enzymatic peeling could also be observed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Preparation and characterization of novel poly(glycidyl methacrylate) beads carrying amidoxime groups
Authors: Çaykara Tuncer , Alaslan Şerife Ş. 
Published: July 2007

AbstractPoly(glycidyl methacrylate) (PGMA) beads with an average size of 350 μm were synthesized by suspension polymerization technique. The PGMA beads were first modified with iminodiacetonitrile (IDAN). Then, the IDAN‐modified beads were subsequently modified by hydroxylamine. The IDAN modification and the conversion of the nitrile groups to amidoxime were followed by FT‐IR spectroscopy. The surface morphology and thermal behavior of the PGMA and its modified forms were also characterized by scanning electron microscopy and thermogravimetric analysis techniques, further confirming modification and amidoximation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Data cleansing for Web information retrieval using query independent features
Authors: Liu Yiqun , Zhang Min , Cen Rongwei , Ru Liyun , Ma Shaoping 
Published: July 2007

AbstractUnderstanding what kinds of Web pages are the most useful for Web search engine users is a critical task in Web information retrieval (IR). Most previous works used hyperlink analysis algorithms to solve this problem. However, little research has been focused on query‐independent Web data cleansing for Web IR. In this paper, we first provide analysis of the differences between retrieval target pages and ordinary ones based on more than 30 million Web pages obtained from both the Text Retrieval Conference (TREC) and a widely used Chinese search engine, SOGOU (www.sogou.com). We further propose a learning‐based data cleansing algorithm for reducing Web pages that are unlikely to be useful for user requests. We found that there exists a large proportion of low‐quality Web pages in both the English and the Chinese Web page corpus, and retrieval target pages can be identified using query‐independent features and cleansing algorithms. The experimental results showed that our algorithm is effective in reducing a large portion of Web pages with a small loss in retrieval target pages. It makes it possible for Web IR tools to meet a large fraction of users' needs with only a small part of pages on the Web. These results may help Web search engines make better use of their limited storage and computation resources to improve search performance.
On optimal operating conditions for a data processing system: A stochastic approach
Authors: Cha Ji Hwan , Mi Jie 
Published: July 2007

AbstractIn this paper, we consider the problem of determining optimal operating conditions for a data processing system. The system is burned‐in for a fixed burn‐in time before it is put into field operation and, in field operation, it has a work size and follows an age‐replacement policy. Assuming that the underlying lifetime distribution of the system has a bathtub‐shaped failure rate function, the properties of optimal burn‐in time, optimal work size and optimal age‐replacement policy will be derived. It can be seen that this model is a generalization of those considered in the previous works, and it yields a better optimal operating conditions. This paper presents an analytical method for three‐dimensional optimization problem. An algorithm for determining optimal operating conditions is also given. Copyright © 2007 John Wiley & Sons, Ltd.
Recent advances in DNA catalysis
Authors: Höbartner Claudia , Silverman Scott K. 
Published: July 2007

AbstractStudies of catalytically active DNA sequences have expanded considerably since the first artificial deoxyribozyme was identified in 1994. Nevertheless, the field is still quite young, and advances in both fundamental understanding and practical applications of deoxyribozymes are still developing. Deoxyribozymes that either cleave or ligate two RNA substrates have been most widely investigated, and this review describes recent advances in the fundamental studies and applications of these DNA enzymes. Deoxyribozymes with catalytic activities other than RNA ligation and cleavage are also increasingly pursued, and this review covers several key examples. © 2007 Wiley Periodicals, Inc. Biopolymers 87: 279–292, 2007.This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Polymerase Recognition and Stability of Fluoro‐Substituted Pyridone Nucleobase Analogues
Authors: Hwang Gil Tae , Leconte Aaron M. , Romesberg Floyd E. 
Published: July 2007

AbstractRecently much effort has been focused on designing unnatural base pairs that are stable and replicated by DNA polymerases with high efficiency and fidelity. This work has helped to identify a variety of nucleobase properties that are capable of mediating the required interbase interactions in the absence of Watson–Crick hydrogen‐bonding complementarity. These properties include shape complementarity, the presence of a suitably positioned hydrogen‐bond donor in the developing minor groove, and fluorine substitution. In order to help characterize how each factor contributes to base pairing stability and replication, we synthesized and characterized three fluoro‐substituted pyridone nucleoside analogues, 3 FP, 4 FP, and 5 FP. Generally, we found that the specific fluorine substitution pattern of the analogues had little impact on unnatural pair or mispair stability, with the exception of mispairs with dG, which were also the most stable. The mispair between dG and 3 FP was less stable than that with 4 FP or 5 FP, which likely resulted from specific interbase interactions. While fluorine substitution had little impact on the synthesis of the unnatural base pairs, it significantly enhanced mispairing with dG. Remarkably, the mispair between dG and 3 FP was the most efficiently synthesized, due to a favorable entropy of activation, which possibly resulted from the displacement of water molecules from dG in the phosphoryl transfer transition state. The more efficient synthesis of the 3 FP–dG mispair, despite its being the least stable of the three, suggests that the determinants of synthesis and stability are distinct. Finally, we found that fluorine substitution significantly increased the rate at which the pyridone‐based unnatural base pairs were extended; this suggests that both minor groove hydrogen‐bond acceptors and fluorine substituents could be used to simultaneously optimize unnatural base pairs.
Homoscedastic controlled calibration model
Authors: Achic Betsabé G. Blas , Sandoval Mônica C. , Yoshida Olga Satomi 
Published: July 2007

AbstractIn the context of the usual calibration model, we consider the case in which the independent variable is unobservable, but a pre‐fixed value on its surrogate is available. Thus, considering controlled variables and assuming that the measurement errors have equal variances we propose a new calibration model. Likelihood‐based methodology is used to estimate the model parameters and the Fisher information matrix is used to construct a confidence interval for the unknown value of the regressor variable. A simulation study is carried out to asses the effect of the measurement error on the estimation of the parameter of interest. This new approach is illustrated with an example. Copyright © 2007 John Wiley & Sons, Ltd.
Trapping of Radicals in the Coordination Spheres of Metals
Authors: Hou Zhaomin , Wakatsuki Yasuo 
Published: July 2007

AbstractThe use of hexamethylphosphoramide (HMPA) or other sterically demanding groups as stabilizing ligands allows the successful isolation of a series of structurally characterizable complexes of ketyl radicals with alkali, alkaline earth, and lanthanide metal. It has been demonstrated that the stability and reactivity of the ketyl radicals strongly depend on both the nature of the metals to which they are bound and the steric and electronic properties of the ancillary ligands, as well as the structure of their parent ketones.
Design and Synthesis of Sugar‐Responsive Semiartificial Myoglobin Triggered by Modulation of Apoprotein–Cofactor Interactions
Authors: Hamachi Itaru , Tajiri Yusuke , Nagase Tsuyoshi , Shinkai Seiji 
Published: July 2007

AbstractPhenylboronic acid groups as sugar recognition sites were successfully introduced into native myoglobin by a cofactor‐reconstitution method. Spectrophotometric pH titration demonstrated the sugar‐induced pKa shift of the H2O coordinated to the heme center of the semisynthetic myoglobin bearing phenyl‐boronic acids (met‐Mb(PhBOH)2). By means of circular dichroism (CD) and paramagnetic 1H NMR spectroscopies, it was proven that sugars that were bound to phenylboronic acid sites induced the rearrangement of the heme crevice to reinforce the heme cofactor‐apoprotein interactions. The structural changes that were induced by the binding of sugars subsequently enhanced the dioxygen storage activity of Mb(PhBOH)2. Such sugar‐induced structural and functional changes did not occur for other modified Mbs that had no sugar‐recognition units. Interestingly, a randomly modified Mb with phenylboronic acid units did not show any sugar response. In Mb(PhBOH)2, the information from the sugar‐binding event was efficiently transmitted to the active center, so that the activity was efficiently altered upon sugar binding. In conclusion, the active site specific incorporation of molecular recognition units as nonnatural functional molecules can provide a novel strategy for the design of stimuli‐responsive semisynthetic proteins.
Iceman's Mummification—Implications from Infrared Spectroscopical and Histological Studies
Authors: Bereuter Thomas L. , Mikenda Werner , Reiter Christian 
Published: July 2007

AbstractA skin sample from the Iceman (Ötzi, Similaun Man, Man from Hauslabjoch) was studied by means of IR spectroscopy and histology, and the results were compared to those obtained from nine other more recent human tissue samples with known case reports. Attenuated total reflection IR spectroscopy was used for studying the fate of proteins and lipids in these rare skin tissues. This technique provided a simple yet powerful means for semiquantitative determination of the main compound classes found in skin samples, namely, triacylglycerols, their main breakdown products (fatty acids), and proteins. When combined with histology, IR spectroscopy provided reliable information about the main conditions under which mummification of the samples had taken place. In the case of the 5300‐year‐old Iceman, preserved collagen contributed to the conservation of morphological structures of the skin, although no cellular structures such as nuclei survived. In addition, post‐mortal alterations such as hydrolysis of triacylglycerols and phospholipids into fatty acids were unequivocally demonstrated. The solidified fatty acids provided a certain degree of preservation to the tissue characteristic of adipocere. Based on this observation, taken together with the concomitant loss of epidermis, we suggest that Iceman's body was submerged in water for a period of at least several months prior to desiccation. Results from other research disciplines support our conclusions.
Triprotonated Hydrogen Sulfide: Pentacoordinate Sulfonium Trication SH3+5 and the Search for its Parent Pentacoordinate Oxonium Trication OH3+5
Authors: Olah George A. , Rasul Golam , Surya Prakash G. K. 
Published: July 2007

AbstractThe pentahydridosulfonium trication SH3+5 was found by ab initio MP2/ 6‐31G** and QCISD(T)/6‐311G** levels of calculation to be a stable minimum with Cs symmetric structure 1. It is isostructural with the parent pentacoordinate carbonium ion CH+5. Structure 1 resembles a complex between SH3+3 and molecular hydrogen forming a 2e–3c bond. This structure involving a pentaco‐ordinate sulfur atom is unprecedented. Rotation of the H2 unit around the pseudo‐C3 axis of SH3 is facile. The structure of SF3+5 was also calculated and compared with that of 1. In addition, our studies at the ab initio MP2/6‐31G** level showed that the parent pentacoordinate oxonium trication OH3+5 is not a minimum on its potential energy surface, and dissociation into OH2+4 and H+ occurs upon optimization.
Reactive Pseudorotaxanes: Inclusion Complexation of Reduced Viologens by the Hosts β‐Cyclodextrin and Heptakis(2,6‐di‐o‐Methyl)‐β‐Cyclodextrin
Authors: Mirzoian Armen , Kaifer Angel E. 
Published: July 2007

AbstractThe complexation of three guests containing 4,4′‐bipyridinium redoxactive residues by β‐cyclodextrin (β‐CD) and its heptakis‐(2,6‐O‐dimethyl) analogue (DM‐β‐CD) was investigated by means of voltammetric techniques. The three 4,4′‐bipyridinium (viologen) derivatives used as guests were designed to be water‐soluble in all three accessible oxidation states. The N‐substituents chosen to enhance aqueous solubility were: 2‐(2‐(2‐ethoxy)ethoxy)ethanol (guest 12+), 6‐hexanoate (guest 2), and 3‐propanesulfonate (guest 3). Detailed analysis of the voltammetric results by digital simulation techniques revealed that the oxidized forms of the guests did not interact appreciably with either CD host; the two‐electron reduced guests formed extremely stable inclusion complexes, with association constants in the range 103–104M−1, while the cation radical forms exhibited intermediate binding affinities (≈︁102M−1). In all cases, DM‐β‐CD was found to form more stable complexes than unmodified β‐CD.
Indium‐Mediated Reactions of Enamines in the Presence of Acid
Authors: Tussa Laurent , Lebreton Chrystèle , Mosset Paul 
Published: July 2007

AbstractThe reaction of enamines with allyl bromide and metallic indium in THF to afford homoallylamines was greatly accelerated by the addition of one equivalent of a suitable carboxylic acid, such as acetic acid. It was established that the likely mechanism consists of a nucleophilic addition of an indium sesquihalide to the iminium salt formed by protonation of the enamine. Substituted allyl bromides also reacted with complete allylic transposition (γ‐addition). In contrast to indium‐mediated allylation of carbonyl compounds in which only two of the three allyl groups of the sesquihalide are involved, all three allyl groups are involved in the reaction with enamines. As a result only 2/3 equiv of indium are required. This allylation was also performed with zinc, tin, bismuth, and aluminum in the presence of a catalytic amount of InCl3 instead of indium. However, these reactions invariably gave lower yields. The analogous reaction of methyl bromoacetate instead of allyl bromide was also studied. This “Reformatsky‐type” process was also greatly accelerated by the addition of one equivalent of acetic acid. In this case, the yields remained moderate for both indium and zinc.
π‐Electron Ring‐Current Effects in Multiple Adducts of 3He@C60 and 3He@C70: A 3He NMR Study
Authors: Rüttimann Markus , Haldimann Richard F. , Isaacs Lyle , Diederich François , Khong Anthony , Jiménez‐Vázquez Hugo , Cross R. J. , Saunders Martin 
Published: July 2007

AbstractBis‐ to hexakisadducts of C60 (1–6) and mono‐ to tetrakisadducts of C70 (7–13) containing 3He atoms (endo‐hedral helium complexes) were prepared and studied by 3He NMR spectroscopy to determine the influence of degree of functionalization and addition pattern on the chemical shift of the 3He atom. In the series of C60 derivatives, which included the previously measured 6–6 monoadduct 3He@C61H2, the 3He resonance was shifted considerably upfield relative to that of 3He@C60 (δ = −6.36) up to the bisadduct 1 (δ = −11.45). The resonances of the higher adducts 3–6, however, were shifted only slightly further up‐field and all appeared in a rather narrow spectral range between δ = −11.84 and −12.26. The absence of further substantial upfield shifts was rationalized in terms of the compensation of deshielding due to the functionalization‐induced decrease in the diamagnetic π‐electron ring currents that extend around the fullerene sphere by the shielding that results from the weaker pentagonal‐ring paramagnetic currents and the increased number of localized benzenoid substructures in 3–6. In contrast, all 3He resonances of the C70 adducts are shifted downfield relative to the signal of 3He@C70 (δ = −28.81). A monotonic relationship exists between the chemical shift and the degree of functionalization, whereby the 3He chemical shifts steadily decrease from monoadduct 7 (δ = −27.53) to the isomeric tetrakisadducts 12 (δ = −21.09) and 13 (δ = −20.68). This deshielding was explained by the reduction of the strong diamagnetic ring currents extending along the polar corannulene perimeters as a result of the functionalization at α‐ and β‐type polar bonds in 7–13. In both series, the addition pattern was also found to have a distinct influence on the 3He chemical shift.
Effect of Melamine‐Amphiphile Structure on the Extent of Two‐Dimensional Hydrogen‐Bonded Networks Incorporating Barbituric Acid
Authors: Koyano Hiroshi , Bissel Philippe , Yoshihara Kanami , Ariga Katsuhiko , Kunitake Toyoki 
Published: July 2007

AbstractFour alkyl melamine amphiphiles each containing identical triads of hydrogen‐bonding sites (hydrogen donor, acceptor, and donor) but different numbers of alkyl chains were examined in order to determine their monolayer properties and binding behavior towards barbituric acid (BA). Their structural organization in supramolecular assemblies at the air–water interface was affected by the bulkiness of the hydrophobic part of the amphiphile. Aqueous BA and amphiphiles with two or three alkyl chains formed a 1:1 alternate network structure. In contrast, a melamine amphiphile with four alkyl chains formed a 2:1 (BA:amphiphile) complex rather than a 1:1 alternate network structure. The 2:1 complex appears to behave like an independent molecular entity without further networking. The results point to the importance of size matching between the hydrophobic part of the monolayer and the underlying hydrogen‐bonded network in order to maintain the overall supramolecular structure.
A Comparative Study of Oxo‐Ligand Effects in the Gas‐Phase Chemistry of Atomic Lanthanide and Actinide Cations
Authors: Cornehl Hans H. , Wesendrup Ralf , Diefenbach Martin , Schwarz Helmut 
Published: July 2007

AbstractThe effects of oxo ligands on lanthanide and actinide cations have been examined for the mono‐ and dioxocations MO+ and MO+2 of cerium, neodymium, thorium, and uranium by probing C‐H and C‐C bond activation of hydrocarbons in an FT‐ICR mass spectrometer. The metal monoxide cations are readily available by reaction of the “bare” metal cations with O2, CO2, N2O, or H2O. In the ensuing oxidation of MO+, UO+2 is obtained by each of these oxidants, while CeO+ could only be oxidized by N2O. NO2 was necessary for the generation of ThO+2, and NdO+2 could not be prepared at all. The monoxides are rather unreactive and only dehydrogenate reactive substrates such as 1‐butene and 1,4‐cyclohexadiene to generate the corresponding butadiene or benzene complexes. In contrast, CeO+2 and ThO+2 react efficiently with different substrates by abstraction of a hydrogen atom and formation of the closed‐shell species OMOH+, or by oxygen atom transfer to unsaturated hydrocarbons. In marked contrast, UO+2 only undergoes very slow adduct formation with unsaturated hydrocarbons. The results are compared with the reactions of the “bare” metals with respect to the influence of the oxo ligand as well as to the underlying electronic features of the investigated complexes.
Large Quadratic Hyperpolarizabilities with Donor–Acceptor Polyenes Exhibiting Optimum Bond Length Alternation: Correlation Between Structure and Hyperpolarizability
Authors: Blanchard‐Desce M. , Alain V. , Bedworth P. V. , Marder S. R. , Fort A. , Runser C. , Barzoukas M. , Lebus S. , Wortmann R. 
Published: July 2007

AbstractDonor–acceptor polyenes of various lengths, and that combine aromatic electron‐donating moieties with powerful heterocyclic electron‐withdrawing terminal groups, have been synthesized and characterized as efficient nonlinear optical (NLO) chromophores. Their linear and nonlinear optical properties have been investigated, and variations in these properties have been related to ground‐state polarization (dipole μ) and structure. In particular, unprecedented quadratic hyperpolarizabilities (β) have been achieved (up to β(0) = 1500 × 10−30 esu) by reduction of the bond‐length alternation (BLA) in the polyenic chain. In each series of homologous compounds, increasing the number n of conjugated double bonds in the polyenic chain results in a marked bathochromic shift, more pronounced BLA, and exponential increases in μβ(0) values. As a result, polyenic chromophores displaying excellent optical quadratic nonlinearities (μβ values as large as 100 times that of the quadratic NLO benchmark 4‐dimethyl‐amino‐4′‐nitrostilbene (DANS)), as well as satisfactory solubility, have been obtained.
Dicyanopolyynes: A Homologuous Series of End‐Capped Linear sp Carbon
Authors: Schermann Günther , Grösser Thomas , Hampel Frank , Hirsch Andreas 
Published: July 2007

AbstractThe synthesis, isolation, spectroscopic characterization, and computational investigations of the rod‐shaped dicyanopolyynes 1–6 (C2nN2, n = 4–9), which are model substances for the hypothetical one‐dimensional carbon allotrope carbyne sp‐C∞, are described. Based on the trends in the spectroscopic behavior of 1–6 with increasing chain length, the electronic as well as the NMR properties of carbyne are predicted. For the investigation of the synthetic potential of this compound class, a first selected series of regioselective derivatizations is presented with the synthesis of the [4+2] and [3+2] cycloadducts 7–12.