bluuebunny/crossref_metadata_2025_split huggingface dataset:
Universal Features of the Electron Density Distribution in Hydrogen‐Bonding Regions: A Comprehensive Study Involving H⋅⋅⋅X (X=H, C, N, O, F, S, Cl, π) Interactions
Authors: Mata Ignasi , Alkorta Ibon , Molins Elies , Espinosa Enrique 
Published: January 2010

AbstractTopological analyses of the theoretically calculated electron densities for a large set of 163 hydrogen‐bonded complexes show that H⋅⋅⋅X interactions can be classified in families according to X (X=atom or π orbital). Each family is characterised by a set of intrinsic dependencies between the topological and energetic properties of the electron density at the hydrogen‐bond critical point, as well as between each of them and the bonding distance. Comparing different atom‐acceptor families, these dependencies are classified as a function of the van der Waals radiusrXor the electronegativity χX, which can be explained in terms of the molecular orbitals involved in the interaction. According to this ordering, the increase of χXleads to a larger range of H⋅⋅⋅X distances for which the interaction is of pure closed‐shell type. Same dependencies observed for H⋅⋅⋅O interactions experimentally characterised by means of high‐resolution X‐ray diffraction data show a good agreement with those obtained from theoretical calculations, in spite of a larger dispersion of values around the expected fitting functions in the experimental case. Theoretical dependencies can thus be applied to the analysis of the experimental electron density for detecting either unconventional hydrogen bonds or problems in the modelling of the experimental electron density.
2,2‐Bis(ethoxycarbonyl)vinyl (BECV) as a Versatile Amine Protecting Group for Selective Functional‐Group Transformations
Authors: Ilangovan Andivelu , Kumar Rajendran Ganesh 
Published: January 2010

AbstractA 2,2‐Bis(ethoxycarbonyl) vinyl‐ (BECV) group was used for the selective protection of amines at room temperature in the presence of potentially interfering functional groups such as OH, SH, COOH as well as other NH2 groups. Several functional group transformations such as esterification, O‐alkylation, O‐acylation, N‐alkylation, N‐acylation, S‐alkylation can selectively be carried out in the presence of the BECV group. The selective deprotection of the BECV group was achieved in a short time using ethylenediamine at room temperature while several other functional groups such as benzoate, aliphatic esters, amides and ethers remain intact. The BECV group shows orthogonal stability against the common protecting groups such as Fmoc, Cbz and Boc.
Gold(I)‐ and Yb(OTf)3‐Cocatalyzed Rearrangements of Epoxy Alkynes: Transfer of a Carbonyl Group in a Five‐Membered Carbocycle
Authors: Dai Lun‐Zhi , Shi Min 
Published: January 2010

AbstractWe report here the intramolecular reactions between α,β‐epoxy ketones and alkynes cocatalyzed by gold(I) and Yb(OTf)3. This new catalytic system based on a combination of gold(I) and Yb(OTf)3 allows facile transformation of epoxy alkynes to give novel indene derivatives in moderate to good yields under mild conditions. Moreover, we describe here the first observation of a transfer of a carbonyl group in a five‐membered carbocycle during gold‐catalyzed reactions. This proposed mechanism is corroborated by isotope‐labeling experiments (D and 13C). Furthermore, the probable role of each catalyst in this interesting domino reaction has been examined by 31P NMR experiments. The utilization of gold catalysts combined with rare‐earth metal salts offers a new concept for the design of catalyst combinations for domino or cascade reactions.
First‐Principles Prediction of Nucleophilicity Parameters for π Nucleophiles: Implications for Mechanistic Origin of Mayr’s Equation
Authors: Wang Chen , Fu Yao , Guo Qing‐Xiang , Liu Lei 
Published: January 2010

AbstractQuantitative nucleophilicity scales are fundamental to organic chemistry and are usually constructed on the basis of Mayr’s equation [log k=s(N+E)] by using benzhydrylium ions as reference electrophiles. Here an ab initio protocol was developed for the first time to predict the nucleophilicity parameters N of various π nucleophiles in CH2Cl2 through transition‐state calculations. The optimized theoretical model (BH&HLYP/6‐311++G(3df,2p)//B3LYP/6‐311+G(d,p)/PCM/UAHF) could predict the N values of structurally unrelated π nucleophiles within a precision of ca. 1.14 units and therefore may find applications for the prediction of nucleophilicity of compounds that are not readily amenable to experimental characterization. The success in predicting N parameters from first principles also allowed us to analyze in depth the electrostatic, steric, and solvation energies involved in electrophile–nucleophile reactions. We found that solvation does not play an important role in the validity of Mayr’s equation. On the other hand, the correlations of the E, N, and log k values with the energies of the frontier molecular orbitals indicated that electrostatic/charge‐transfer interactions play vital roles in Mayr’s equation. Surprising correlations observed between the electrophile–nucleophile CC distances in the transition state, the activation energy barriers, and the E and N parameters indicate the importance of steric interactions in Mayr’s equation. A method is then proposed to separate the attraction and repulsion energies in the nucleophile–electrophile interaction. It was found that the attraction energy correlated with N+E, whereas the repulsion energy correlated to the s parameter.
Transition‐State Stabilization by a Secondary Substrate–Ligand Interaction: A New Design Principle for Highly Efficient Transition‐Metal Catalysis
Authors: Šmejkal Tomáš , Gribkov Denis , Geier Jens , Keller Manfred , Breit Bernhard 
Published: January 2010

AbstractA library of monodentate phosphane ligands, each bearing a guanidine receptor unit for carboxylates, was designed. Screening of the library gave some excellent catalysts for regioselective hydroformylation of β,γ‐unsaturated carboxylic acids. A terminal alkene, but‐3‐enoic acid, was hydroformylated with a linear/branched (l/b) regioselectivity up to 41. An internal alkene, pent‐3‐enoic acid was hydroformylated with regioselectivity up to 18:1. Further substrate selectivity (e.g., acid vs. methyl ester) and reaction site selectivity (monofunctionalization of 2‐vinylhept‐2‐enoic acid) were also achieved. Exploration of the structure–activity relationship and a practical and theoretical mechanistic study gave us an insight into the nature of the supramolecular guanidinium–carboxylate interaction within the catalytic system. This allowed us to identify a selective transition‐state stabilization by a secondary substrate–ligand interaction as the basis for catalyst activity and selectivity.
Structures and Properties of Spherical 90‐Vertex Fullerene‐Like Nanoballs
Authors: Scheer Manfred , Schindler Andrea , Bai Junfeng , Johnson Brian P. , Merkle Roger , Winter Rainer , Virovets Alexander V. , Peresypkina Eugenia V. , Blatov Vladislav A. , Sierka Marek , Eckert Hellmut 
Published: January 2010

AbstractBy applying the proper stoichiometry of 1:2 to [CpRFe(η5‐P5)] and CuX (X=Cl, Br) and dilution conditions in mixtures of CH3CN and solvents like CH2Cl2, 1,2‐Cl2C6H4, toluene, and THF, nine spherical giant molecules having the simplified general formula [CpRFe(η5‐P5)]@[{CpRFe(η5‐P5)}12{CuX}25(CH3CN)10] (CpR=η5‐C5Me5 (Cp*); η5‐C5Me4Et (CpEt); X=Cl, Br) have been synthesized and structurally characterized. The products consist of 90‐vertex frameworks consisting of non‐carbon atoms and forming fullerene‐like structural motifs. Besides the mostly neutral products, some charged derivatives have been isolated. These spherical giant molecules show an outer diameter of 2.24 (X=Cl) to 2.26 nm (X=Br) and have inner cavities of 1.28 (X=Cl) and 1.20 nm (X=Br) in size. In most instances the inner voids of these nanoballs encapsulate one molecule of [Cp*Fe(η5‐P5)], which reveals preferred orientations of π–π stacking between the cyclo‐P5 rings of the guest and those of the host molecules. Moreover, π–π and σ–π interactions are also found in the packing motifs of the balls in the crystal lattice. Electrochemical investigations of these soluble molecules reveal one irreversible multi‐electron oxidation at Ep=0.615 V and two reduction steps (−1.10 and −2.0 V), the first of which corresponds to about 12 electrons. Density functional calculations reveal that during oxidation and reduction the electrons are withdrawn or added to the surface of the spherical nanomolecules, and no Cu2+ species are involved.
Diastereo‐ and Enantioselective Intramolecular [2+2] Photocycloaddition Reactions of 3‐(ω′‐Alkenyl)‐ and 3‐(ω′‐Alkenyloxy)‐Substituted 5,6‐Dihydro‐1H‐pyridin‐2‐ones
Authors: Albrecht Dominik , Vogt Florian , Bach Thorsten 
Published: January 2010

Abstract3‐(ω′‐Alkenyl)‐substituted 5,6‐dihydro‐1H‐pyridin‐2‐ones 2–4 were prepared as photocycloaddition precursors either by cross‐coupling from 3‐iodo‐5,6‐dihydro‐1H‐pyridin‐2‐one (8) or—more favorably—from the corresponding α‐(ω′‐alkenyl)‐substituted δ‐valerolactams 9–11 by a selenylation/elimination sequence (56–62 % overall yield). 3‐(ω′‐Alkenyloxy)‐substituted 5,6‐dihydro‐1H‐pyridin‐2‐ones 5 and 6 were accessible in 43 and 37 % overall yield from 3‐diazopiperidin‐2‐one (15) by an α,α‐chloroselenylation reaction at the 3‐position followed by nucleophilic displacement of a chloride ion with an ω‐alkenolate and oxidative elimination of selenoxide. Upon irradiation at λ=254 nm, the precursor compounds underwent a clean intramolecular [2+2] photocycloaddition reaction. Substrates 2 and 5, tethered by a two‐atom chain, exclusively delivered the respective crossed products 19 and 20, and substrates 3, 5, and 6, tethered by longer chains, gave the straight products 21–23. The completely regio‐ and diastereoselective photocycloaddition reactions proceeded in 63–83 % yield. Irradiation in the presence of the chiral templates (−)‐1 and (+)‐31 at −75 °C in toluene rendered the reactions enantioselective with selectivities varying between 40 and 85 % ee. Truncated template rac‐31 was prepared as a noranalogue of the well‐established template 1 in eight steps and 56 % yield from the Kemp triacid (24). Subsequent resolution delivered the enantiomerically pure templates (−)‐31 and (+)‐31. The outcome of the reactions is compared to the results achieved with 4‐substituted 5,6‐dihydro‐1H‐pyridin‐2‐ones and quinolones.
(+)‐(R,Z)‐5‐Muscenone and (−)‐(R)‐Muscone by Enantioselective Aldol Reaction and Grob Fragmentation
Authors: Fehr Charles , Buzas Andrea K. , Knopff Oliver , de Saint Laumer Jean‐Yves 
Published: January 2010

Abstract(+)‐(R,Z)‐5‐Muscenone ((R)‐1) was synthesized by an enantioselective aldol reaction, catalyzed by new ephedrine‐type Ti reagents (up to 70 % enantiomeric excess). Substrate‐directed diastereoselective reduction of the aldol product and Grob fragmentation of the tosylate of the resultant 1,3‐diol afforded (+)‐1. This approach also gave access to (−)‐(R,E)‐5‐muscenone and (−)‐(R)‐muscone.
Mapping the Transformation [{RuII(CO)3Cl2}2]→[RuI2(CO)4]2+: Implications in Binuclear Water–Gas Shift Chemistry
Authors: Majumdar Moumita , Sinha Arup , Ghatak Tapas , Patra Sanjib K. , Sadhukhan Nabanita , Rahaman S. M. Wahidur , Bera Jitendra K. 
Published: January 2010

AbstractThe complete sequence of reactions in the base‐promoted reduction of [{RuII(CO)3Cl2}2] to [RuI2(CO)4]2+ has been unraveled. Several μ‐OH, μ:κ2‐CO2H‐bridged diruthenium(II) complexes have been synthesized; they are the direct results of the nucleophilic activation of metal‐coordinated carbonyls by hydroxides. The isolated compounds are [Ru2(CO)4(μ:κ2‐C,O‐CO2H)2(μ‐OH)(NPF‐Am)2][PF6] (1; NPF‐Am=2‐amino‐5,7‐trifluoromethyl‐1,8‐naphthyridine) and [Ru2(CO)4(μ:κ2‐C,O‐CO2H)(μ‐OH)(NP‐Me2)2][BF4]2 (2), secured by the applications of naphthyridine derivatives. In the absence of any capping ligand, a tetranuclear complex [Ru4(CO)8(H2O)2(μ3‐OH)2(μ:κ2‐C,O‐CO2H)4][CF3SO3]2 (3) is isolated. The bridging hydroxido ligand in 1 is readily replaced by a π‐donor chlorido ligand, which results in [Ru2(CO)4(μ:κ2‐C,O‐CO2H)2(μ‐Cl)(NP‐PhOMe)2][BF4] (4). The production of [Ru2(CO)4]2+ has been attributed to the thermally induced decarboxylation of a bis(hydroxycarbonyl)–diruthenium(II) complex to a dihydrido–diruthenium(II) species, followed by dinuclear reductive elimination of molecular hydrogen with the concomitant formation of the RuIRuI single bond. This work was originally instituted to find a reliable synthetic protocol for the [Ru2(CO)4(CH3CN)6]2+ precursor. It is herein prescribed that at least four equivalents of base, complete removal of chlorido ligands by TlI salts, and heating at reflux in acetonitrile for a period of four hours are the conditions for the optimal conversion. Premature quenching of the reaction resulted in the isolation of a trinuclear RuI2RuII complex [{Ru(NP‐Am)2(CO)}{Ru2(NP‐Am)2(CO)2(μ‐CO)2}(μ3:κ3‐C,O,O′‐CO2)][BF4]2 (6). These unprecedented diruthenium compounds are the dinuclear congeners of the water–gas shift (WGS) intermediates. The possibility of a dinuclear pathway eliminates the inherent contradiction of pH demands in the WGS catalytic cycle in an alkaline medium. A cooperative binuclear elimination could be a viable route for hydrogen production in WGS chemistry.
Self‐Discriminating Self‐Assembly of Dinuclear Heterochiral Rhombs from Tröger’s Base Derived Bis(pyridyl) Ligands
Authors: Weilandt Torsten , Kiehne Ulf , Bunzen Jens , Schnakenburg Gregor , Lützen Arne 
Published: January 2010

AbstractFive racemic dissymmetric bis(pyridyl) ligands based on 2,8‐ or 3,9‐difunctionalised Tröger’s base derivatives have been synthesised. Only those derived from a 2,8‐difunctionalised scaffold were found to undergo selective self‐assembly to discrete self‐assembled dinuclear metallosupramolecular aggregates of rhomboid shape upon coordination to cis‐protected Pd2+ or Pt2+ ions, as evidenced by ESI mass spectrometry, NMR spectroscopy and single‐crystal X‐ray diffraction. Interestingly, these processes were found to be highly diastereoselective leading to the formation of C2v‐symmetric heterochiral assemblies in a self‐discriminating manner.
Stable N‐Heterocyclic Carbene Adducts of Arylchlorosilylenes and Their Germanium Homologues
Authors: Filippou Alexander C. , Chernov Oleg , Blom Burgert , Stumpf Kai W. , Schnakenburg Gregor 
Published: January 2010

AbstractThe first N‐heterocyclic carbene adducts of arylchlorosilylenes are reported and compared with the homologous germanium compounds. The arylsilicon(II) chlorides SiArCl(Im‐Me4) [Ar=C6H3‐2,6‐Mes2 (Mes=C6H2‐2,4,6‐Me3), C6H3‐2,6‐Trip2 (Trip=C6H2‐2,4,6‐iPr3)] were obtained selectively on dehydrochlorination of the arylchlorosilanes SiArHCl2 with 1,3,4,5‐tetramethylimidazol‐2‐ylidene (Im‐Me4). The analogous arylgermanium(II) chlorides GeArCl(Im‐Me4) were prepared by metathetical exchange of GeCl2(Im‐Me4) with LiC6H3‐2,6‐Mes2 or addition of Im‐Me4 to GeCl(C6H3‐2,6‐Trip2). All compounds were fully characterized. Density functional calculations on ECl(C6H3‐2,6‐Trip2)(Im‐Me4), where E=Si, Ge, at different levels of theory show very good agreement between calculated and experimental bonding parameters, and NBO analyses reveal similar electronic structures of the two aryltetrel(II) chlorides. The low gas‐phase Gibbs free energy of bond dissociation of SiCl(C6H3‐2,6‐Trip2)(Im‐Me4) (Δ${G{{{\circ}\hfill \atop {\rm calcd}\hfill}}}$=28.1 kJ mol−1) suggests that the carbene adducts SiArCl(Im‐Me4) may be valuable transfer reagents of the arylsilicon(II) chlorides SiArCl.
Changes in colour appearance of a large display in various surround ambient conditions
Authors: Choi Seo Young , Luo Ming Ronnier , Pointer Michael R. , Li Changjun , Rhodes Peter A. 
Published: January 2010

AbstractThis article focuses on the change in colour appearance of a large display arising from various illumination conditions. Nine experimental phases were conducted according to different surround conditions including dark, indoor, and outdoor conditions. Each of the presented test colours was assessed by 10 observers using a magnitude estimation method. The surrounds used in all phases were divided into two groups: excluding and including veiling glare. Additionally, the effect due to different sizes of both stimuli and surround was investigated. Diverse visual effects were examined and reported. Finally, the visual colour appearance data were used to test the CIECAM02 colour appearance model. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010
Influences of psychological factors on image color preferences evaluation
Authors: Shing‐Sheng Guan , Po‐Sung Hung 
Published: January 2010

AbstractTo bring substantial benefits of image designing for image designers and image processing professionals, this study focused on the image samples taken by digital cameras and tried to explore the influence of psychological factors on image color preference. First, we collected 310 questionnaires to investigate the types of image that interest the people in Taiwan. The images that Taiwanese prefer were categorized into seven types: People, Scenery, Artificial Environment, Plants, Animals, Still Life, and Food. Then, based on the results of this survey, total 81 images were collected. Next, six psychological factors (Color Memory, Color Comfort, Colorfulness, Color Harmony, Color Image, Concerned Area) on image color preference were identified by the Delphi method and literature review and then developed into another survey. A total of 150 people, as subjects, took this survey and gave their evaluation according to their image color preferences. Finally, using multiple regression statistics, this study discussed the relationship between psychological factors and image color preferences. This study discovered that each psychological factor plays a different role in different image categories. For instance, Color Comfort plays the most influential role in the Scenery image. Color Harmony is influential in the Food and Plants image. Concerned Area, likewise, is important in the image categories of People, Artificial Environment, and Still Life. Based on the results of this research, it is suggested to take psychological factors into consideration when dealing with different image categories in obtaining the best color performance of images. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010
A novel method for determination of compatibility of dyes by means of principal component analysis
Authors: Khalili Haleh , Amirshahi Seyed Hossein 
Published: January 2010

AbstractA novel method for determination of the compatibility of dyes in mixtures based on the application of principal component analysis is presented. The well known dip‐test method is used to dye samples in different binary combinations of cationic dyestuffs. The spectral reflectance of different samples of each mixture that dyed with a given set of dyestuffs by dip‐test method has been measured and the corresponding K/S values are calculated. The actual dimensional properties of each mixture are evaluated by using principal component analysis technique and determination of cumulative percentage variance of the eigenvalues of proposed datasets. Ideally, the K/S spectral data of fully compatible pairs scatter around one dimension, while proportional to the degree of incompatibility of dyes in the mixture, other dimensions should be taken into account and cannot be ignored. Strong correlations are found between the calculated percentage variance and the traditional compatibility values of dyes shown by K value for cationic dyestuffs. The validity of suggested technique is also reconfirmed by normalization of spectral K/S data obtained from different dye sets. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010
Exclusively Heteronuclear NMR Experiments to Obtain Structural and Dynamic Information on Proteins
Authors: Bermel Wolfgang , Bertini Ivano , Felli Isabella C. , Peruzzini Riccardo , Pierattelli Roberta 
Published: January 2010

AbstractProvided that 13C‐detected NMR experiments are either preferable or complementary to 1H detection, we report here tools to determine CαC′, C′N, and CαHα residual dipolar couplings on the basis of the CON experiment. The coupling constants determined on ubiquitin are consistent with the subset measured with the 1H‐detected HNCO sequences. Since the utilization of residual dipolar couplings may depend on the mobility of the involved nuclei, we also provide tools to measure longitudinal and transverse relaxation rates of N and C′. This new set of experiments is a further development of a whole strategy based on 13C direct‐detection NMR spectroscopy for the study of biological macromolecules.
Increased Left Ventricular Mass in Chronic Kidney Disease and End‐Stage Renal Disease: What Are the Implications?
Authors: Glassock Richard J. , Pecoits‐Filho Roberto , Barbareto Silvio 
Published: January 2010

AbstractRecently, new attention has been focused on an increase in left ventricular mass and the attendant cardiac fibrosis as possible substrates for the excess cardiovascular morbidity and mortality seen so frequently in patients with chronic kidney disease and end‐stage renal disease. We provide a summary of the strength of the connection between left ventricular hypertrophy and morbidity and mortality in these patients, examine possible biological mechanisms, and suggest new approaches to its management.
Progression of Coronary Artery Calcification Using a Multidetector CT on Hemodialysis Patients in One Year
Authors: Caro Pilar , Hernandez Raul , Delgado Ramon 
Published: January 2010

AbstractBACKGROUNDVascular calcification is increasingly appreciated as an important risk factor for cardiovascular morbidity and mortality.AIMSTo assess (1) the evolution of coronary calcification and (2) the relationship of the progression of coronary calcification with risk factors and adverse cardiovascular events.METHODSWe performed repeated 16 row multidetector computed tomography (CT) with an interval of 1 year on 33 patients on chronic hemodialysis.RESULTSProgression of coronary artery calcification was found in 70% of patients with a mean significant difference of calcium score. Patients older than 65 years demonstrated a higher progression of coronary calcification and patients who received non‐calcium phosphate binder treatments demonstrated less progression. During the year, 6 adverse cardiovascular events occurred. A total of 22% of patients with progression of coronary calcification had a cardiovascular event (p = .003). Factors associated with adverse cardiovascular events included diabetes, male gender, history of cerebrovascular and coronary disease, secondary hyperparathyroidism, hyperphosphatemia, and calcification of circumflex and right coronary arteries.CONCLUSIONSCoronary artery calcification progression is common, represents a risk factor to adverse cardiovascular events, and is associated with modifiable risk factors in chronic hemodialysis. Multidetector CT seems to be an effective and readily applicable method to assess and quantify the progression of coronary artery calcification.