bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of a New Generation of Gold Catalysts for Amine Oxidation
Authors: Aschwanden Linda , Mallat Tamas , Maciejewski Marek , Krumeich Frank , Baiker Alfons 
Published: April 2010

AbstractA new type of outstandingly active gold catalysts has been developed for the aerobic oxidation of amines to imines. The gold nanoparticles are generated in situ in an organic medium prior to the oxidation reaction. Various gold salts, preferably AuCl3 and HAuCl4⋅3 H2O, can be applied in the presence of nanoceria and the amine substrate acts as the reducing agent. The synergism between gold and ceria evacuated at 200 °C has a remarkable positive effect on the oxidation activity. The catalysts have been tested in the oxidation of dibenzylamine, N‐tert‐butylbenzylamine, and indoline. Apparently, the presence of organic and inorganic residue after the in situ catalyst preparation does not diminish the oxidation activity of gold. An alternative, less efficient route is the quantitative adsorption of [Au(PPh3)Cl] precursor onto ceria in an organic medium and the subsequent ex situ evolution of gold nanoparticles (ca. 5 nm) via calcination at 250–400 °C. This catalyst is still tenfold more active than conventional supported gold nanoparticles. In addition, it is free from impurities evolving during the in situ preparation and thus may find application in reactions other than amine oxidation.
Cyclic 1,2‐Diketones as Core Building Blocks: A Strategy for the Total Synthesis of (−)‐Terpestacin
Authors: Trost Barry M. , Dong Guangbin , Vance Jennifer A. 
Published: April 2010

AbstractWe report a full account of our work towards the total synthesis of (−)‐terpestacin (1), a sesterterpene originally isolated from fungal strain Arthrinium sp. FA1744. Its promising anti‐HIV and anti‐cancer activity, as well as its novel structure, make terpestacin an attractive synthetic target. A strategy based on the unique reactivity of cyclic 1,2‐diketones (diosphenols) was developed and total synthesis of 1 was achieved in 20 steps, in the longest linear sequence, from commercially available 2‐hydroxy‐3‐methyl‐2‐cyclopenten‐1‐one. The key feature of our synthesis is the double usage of a “Pd AAA‐Claisen” protocol (AAA=asymmetric allylic alkylation), first in the early stages to generate the C1 quaternary center and then in the late stages to install the side chain. In addition, a rather unusual ene‐1,2‐dione moiety was synthesized and utilized as an excellent Michael acceptor to attach the C15 substituent. Several possible routes towards the total synthesis have been examined and carefully evaluated. During our exploration many interesting chemoselectivity issues have been addressed, such as a highly selective ring‐closing metathesis and a challenging oxidation of a disubstituted olefin in the presence of three trisubstiuted ones.
Oligomerization of 1,2‐Ethanedithiol: An Expedient Approach to Oligothiaethylenethioglycols
Authors: Berkovich‐Berger Dvora , Lemcoff N. Gabriel , Abramson Sarah , Grabarnik Mikhail , Weinman Sarah , Fuchs Benzion 
Published: April 2010

AbstractReactions of ethylenedithioglycol (ETG) with Na2CO3, K2CO3, and Cs2CO3 provided the oligothiaethylenethioglycols (nETG): di‐ (DETG), tri‐ (TrETG), tetra‐ (TETG), and pentathiaethylenethioglycol (PETG), along with higher polymers. The most efficient carbonate was K2CO3 and reactions using DETG and TrETG as starting materials—or their mixtures—were also found to afford similar species. This largely unknown oligomerization process was thoroughly explored and potential pathways were put forward. A convenient conversion of ETG to laboratory quantities of the otherwise scarce and/or expensive DETG, TrETG, TETG, and PETG oligomers, in organic or aqueous media was achieved. Notably, this straightforward reaction takes place without the addition of expensive or toxic metal catalysts and with pure water as the solvent, thereby highlighting its potential as a green chemical reaction. Moreover, the process opens up new approaches to dynamic combinatorial libraries (DCLs) of oligomers and macrocycles with manifolded nETG [(SCH2CH2)nS] bridges.
Stereodivergent Quaternization of 2‐Alkyl‐2‐p‐tolylsulfinylacetonitriles: NMR Spectroscopic Evidence of Planar and Pyramidal Benzylic Carbanions
Authors: García Ruano José Luis , Martín‐Castro Ana M. , Tato Francisco , Torrente Esther , Poveda Ana M. 
Published: April 2010

AbstractEnantiomerically enriched α,α‐disubstituted phenylacetonitriles have been readily prepared by stereoselective quaternization of 2‐alkyl‐2‐[2‐(p‐tolylsulfinyl)phenyl]acetonitriles with different alkylating electrophiles in the presence of bases. The use of potassium hexamethyldisilazane (KHMDS)/[18]crown‐6 ether and NHMDS with alkyl halides afforded S,SS and R,SS diastereoisomers, respectively, in high enantiomeric purities, thus providing stereodivergent processes for synthesizing both isomers. The dependence of the stereochemical course of the reactions on the experimental conditions (mainly on the counterion) has been rationalized by assuming a planar or pyramidal structure for the benzylic carbanions. This hypothesis has been supported by NMR spectroscopic studies, which permit one to assign a chelated pyramidal structure to the sodium benzylic carbanions and an almost planar naked carbanionic structure to the potassium benzylic carbanions generated in the presence of [18]crown‐6 ether.
Response to the Comment on “The Interplay between Steric and Electronic Effects in SN2 Reactions”
Authors: Fernández Israel , Frenking Gernot , Uggerud Einar 
Published: April 2010

AbstractOnly by allowing full geometry optimization for all energy points along the reaction coordinates does it become possible to perform a meaningful analysis of the variation of the various energy terms during a chemical reaction. Great care should also be taken in the definitions of the energy terms, and only Pauli repulsion should be included in the steric interaction term.
Double CH Activation of Ethane by Metal‐Free SO2.+ Radical Cations
Authors: de Petris Giulia , Cartoni Antonella , Troiani Anna , Barone Vincenzo , Cimino Paola , Angelini Giancarlo , Ursini Ornella 
Published: April 2010

AbstractThe room‐temperature CH activation of ethane by metal‐free SO2.+ radical cations has been investigated under different pressure regimes by mass spectrometric techniques. The major reaction channel is the conversion of ethane to ethylene accompanied by the formation of H2SO2.+, the radical cation of sulfoxylic acid. The mechanism of the double CH activation, in the absence of the single activation product HSO2+, is elucidated by kinetic studies and quantum chemical calculations. Under near single‐collision conditions the reaction occurs with rate constant k=1.0×10−9 (±30 %) cm3 s−1 molecule−1, efficiency=90 %, kinetic isotope effect kH/kD=1.1, and partial H/D scrambling. The theoretical analysis shows that the interaction of SO2.+ with ethane through an oxygen atom directly leads to the CH activation intermediate. The interaction through sulfur leads to an encounter complex that rapidly converts to the same intermediate. The double CH activation occurs by a reaction path that lies below the reactants and involves intermediates separated by very low energy barriers, which include a complex of the ethyl cation suitable to undergo H/D scrambling. Key issues in the observed reactivity are electron‐transfer processes, in which a crucial role is played by geometrical constraints. The work shows how mechanistic details disclosed by the reactions of metal‐free electrophiles may contribute to the current understanding of the CH activation of ethane.
New Chiral N‐Heterocyclic Carbene Ligands in Palladium‐Catalyzed α‐Arylations of Amides: Conformational Locking through Allylic Strain as a Device for Stereocontrol
Authors: Jia Yi‐Xia , Katayev Dmitry , Bernardinelli Gérald , Seidel Thomas M. , Kündig E. Peter 
Published: April 2010

AbstractNew Enders/Herrmann‐type chiral N‐heterocyclic carbene (NHC) ligands have been developed and applied in asymmetric palladium‐catalyzed intramolecular α‐arylations of amides. The best ligands feature the bulky tert‐butyl group and ortho‐substituted aryl groups at the stereogenic centers. Aryl bromides readily react at room temperature and aryl chlorides at 50 °C. The highly enantiomerically enriched (up to 96 % ee) 3‐alkyl‐3‐aryloxindole products were obtained in generally high yields (>95 %) except in cases of steric congestion. The critical roles both of the bulky alkyl group and of the ortho‐aryl substituent at the stereogenic center of the ligand were revealed in the crystal structure of a [Pd(η3‐allyl)(NHC‐L*)(I)] complex. The ligand aryl location and orientation is fixed by conformational locking that minimizes A1,3‐strain and enables optimal transfer of chiral information.
Supramolecular Tetrad of Subphthalocyanine–Triphenylamine–Zinc Porphyrin Coordinated to Fullerene as an “Antenna‐Reaction‐Center” Mimic: Formation of a Long‐Lived Charge‐Separated State in Nonpolar Solvent
Authors: El‐Khouly Mohamed E. , Ju Dong Kyu , Kay Kwang‐Yol , D'Souza Francis , Fukuzumi Shunichi 
Published: April 2010

AbstractWe report here the formation of a long‐lived charge‐separated state of a self‐assembled donor–acceptor tetrad, formed by axial coordination of a fulleropyrrolidine appended with an imidazole coordinating ligand (C60Im) to the zinc center of a subphthalocyanine–triphenylamine–zinc porphyrin (SubPc–TPA–ZnP), as a charge‐stabilizing antenna reaction center mimic in toluene. The subphthalocyanine and triphenylamine entities, with their high‐energy singlet states, act as an energy‐transferring antenna unit to produce a singlet zinc porphyrin. The formation constant for the self‐assembled tetrad was determined to be 1.0×104 M−1, suggesting a moderately stable complex formation. The geometric and electronic structures of the covalently linked SubPc–TPA–ZnP triad and self‐assembled SubPc–TPA–ZnP:C60Im tetrad were examined by using an ab initio B3LYP/6‐31G method. The majority of the highest occupied frontier molecular orbital was found over the ZnP and TPA entities, whereas the lowest unoccupied molecular orbital was located over the fullerene entity, suggesting the formation of the radical‐ion pair (SubPc–TPA–ZnP.+:C60Im.−). The redox measurements revealed that the energy level of the radical‐ion pair in toluene is located lower than that of the singlet and triplet states of the zinc porphyrin and fullerene entities. The femtosecond transient absorption measurements revealed fast charge separation from the singlet porphyrin to the coordinated C60Im with a lifetime of 1.1 ns. Interestingly, slow charge recombination (1.6×105 s−1) and the long lifetime of the charge‐separated state (6.6 μs) were obtained in toluene by utilizing the nanosecond transient measurements.
Transition States and Origins of 1,4‐Asymmetric Induction in Alkylations of 2,2,6‐Trialkylpiperidine Enamines
Authors: Um Joann M. , Kaka Naeem S. , Hodgson David M. , Houk K. N. 
Published: April 2010

AbstractThe asymmetric C‐alkylation of chiral enamines derived from terminal epoxides and lithium 2,2,6‐trialkylpiperidides has previously been shown to provide α‐alkylated aldehydes by intermolecular nucleophilic substitution in good levels of asymmetric induction. We now report a computational study of the origins of asymmetric induction in these reactions. Computational modeling with density functional theory (B3LYP/6‐31G(d)) agrees closely with the experimental observations. This stereoselectivity is attributed to a preferential conformation of the enamine and the piperidine ring that places the C‐6 alkyl substituent in an axial position due to A1, 3 strain. Preferential attack occurs away from the axial group, for steric reasons. The effects of changing the C‐6 substituent from methyl to isopropyl were studied, and twist transition states were found to contribute significantly in the latter alkylations.
Counterion Effects on the Columnar Mesophases of Triphenylene‐Substituted [18]Crown‐6 Ethers: Is Flatter Better?
Authors: Kaller Martin , Deck Christopher , Meister Annette , Hause Gerd , Baro Angelika , Laschat Sabine 
Published: April 2010

AbstractThe twisted lateral tetraalkyloxy ortho‐terphenyl units in dibenzo[18]crown‐6 ethers 1 a–f were readily converted into the flat tetraalkyloxytriphenylene systems 2 a–f by oxidative cyclization with FeCl3 in nitromethane. Reactions of the latter with potassium salts gave complexes KX⋅2, which displayed mesomorphic properties. The aromatization increased both the clearing and melting points; the mesophase stabilities, however, were mainly influenced by the respective anions upon complexation with various potassium salts. In contrast, the alkyl chain lengths played only a secondary role. Among the potassium complexes of triphenylene‐substituted crown ethers KX⋅2, only those with the soft anions I− and SCN− displayed mesophases with expanded phase temperature ranges of 93 °C and 132 °C (for KX⋅2 e), respectively, as compared to the corresponding o‐terphenyl‐substituted crown ether complexes KI⋅1 e (ΔT=51 °C) and KSCN⋅1 e (plastic crystal phase). Anions such as Br−, Cl−, and F− decreased the mesophase stability, and PF6− led to complete loss of the mesomorphic properties of KPF6⋅2 although not for KPF6⋅1. For crown ether complexes KX⋅2 (X=F, Cl, Br, I, BF4, and SCN), columnar rectangular mesophases of different symmetries (c2 mm, p2 mg, and p2 gg) were detected. In contrast to findings for the twisted o‐terphenyl crown ether complexes KX⋅1, the complexation of the flat triphenylene crown ethers 2 with KX resulted in the formation of organogels. Characterization of the organogel of KI⋅2 e in CH2Cl2 revealed a network of fibers.
Immunosuppressive Resveratrol Aneuploids from Hopea chinensis
Authors: Ge Hui Ming , Yang Wen Hao , Shen Yan , Jiang Nan , Guo Zhi Kai , Luo Qiong , Xu Qiang , Ma Jing , Tan Ren Xiang 
Published: April 2010

AbstractTwo novel resveratrol aneuploids, hopeachinols A (1) and B (2), as well as a potent immunosuppressive polyphenol diptoindonesin G (3) were characterized from the ethanol extract of Hopea chinensis stem barks. The structure of the polyphenols was accommodated by comprehensive spectroscopic analysis with the absolute stereochemistry determined by the CD approach coupled with theoretical ECD spectra computer‐generated through the Gaussian 03 program. The distinct structure and biological profile of 3 recommended it as a starting molecule for the relevant drug discovery.
Open system approaches in deterministic models of the emergence of homochirality
Authors: Lente Gábor 
Published: April 2010

AbstractThree different general strategies are proposed for kinetic models of the emergence of homochirality in open systems: flow‐through reactors, photochemical energy input, and chemical energy input from a sacrificial reagent. Using a simple, second‐order chiral autocatalytic core model, it is shown that all these scenarios lead to similar mathematical description despite the fundamentally different chemical background and practically complete homochirality is reached in all of these cases. It is also argued that the photochemical energy input scenario might not be compatible with a sunlight‐driven natural process. Chirality, 2010. © 2010 Wiley‐Liss, Inc.
ESI‐MS investigation of solvent effects on the chiral recognition capacity of tartar emetic towards neutral side‐chain amino acids
Authors: Wijeratne Aruna B. , Yang Samuel H. , Gracia Jose , Armstrong Daniel W. , Schug Kevin A. 
Published: April 2010

AbstractThe effect of solvent systems on previously‐reported ESI‐MS based proton‐assisted enantioselective molecular recognition phenomena of tartar emetic, L‐antimony(III)‐tartrate, was evaluated. This was achieved by carrying out a series of competitive binding experiments using chiral selectors, bis(sodium) D‐ and ‐L‐antimony(III)‐tartrates with chiral selectands, neutral side‐chain amino acid enantiomeric isotopomers of alanine (Ala), valine (Val), leucine (Leu) and phenylalanine (Phe), in three different solvent systems, ACN/H2O (75/25 v/v), H2O (100%) and H2O/MeOH (25/75 v/v). Observations from these experiments suggest that the effect of solvent systems on previously reported proton‐assisted chiral recognition capacity of D,L‐antimony(III)‐tartrates is small, but not negligible. It was observed that an ACN/H2O (75/25 v/v) solvent system facilitates and enhances the chiral discrimination capacity of protonated {[D,L‐Sb2‐tar2][H]}− ionic species. Further, amino acid enantiomers showed a general trend of increasing selectivity order, Val ≤ Ala < Leu ≈ Phe towards the protonated {[D,L‐Sb2‐tar2][H]}− ionic species which was independent of the solvent system employed. The lack of enantioselective binding for {[D,L‐Sb2‐tar2]}2− ionic species was consistently recorded in respective mass spectra from all performed experiments, which suggests that ESI‐friendly solvent systems have no effect and do not influence this phenomenon. Chirality, 2011. © 2010 Wiley‐Liss, Inc.
The product operator formalism: A physical and graphical interpretation
Authors: Goldenberg David P. 
Published: April 2010

AbstractThe product‐operator formalism is the most commonly used tool for describing and designing multidimensional NMR experiments. Despite its relative simplicity and sound theoretical underpinnings, however, students and practitioners often find it difficult to relate the mathematical manipulations to a physical picture. In an effort to address this pedagogical challenge, the present article begins with a quantum‐mechanical treatment of pure populations of scalar‐coupled spin pairs, rather than the equilibrium population of spin pairs in different quantum states, which is the usual starting point for treatments based on the density matrix and product operators. In the context of pure populations, the product operators are shown to represent quantum correlations between the nuclei in individual molecules, and a new variation on the classical vector diagram is introduced to represent these correlations. The treatment is extended to mixed populations that begin at thermal equilibrium, and the density matrix is introduced as an efficient means of carrying out quantum calculations for a mixed population. Finally, it is shown that the operators for observable magnetization and correlations can be used as a basis set for the density matrix, providing the formal justification for the widely used rules of the product‐operator treatment. Throughout the discussion, the vector diagrams are used to help maintain a connection between the mathematics and the sometimes subtle physical principles. An electronic supplement created with the Mathematica computer program is used to provide additional mathematical details and the means to carry out further calculations. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part A 36A: 1–23, 2010.
Compliance with quality assurance measures in patients treated for early oral tongue cancer
Authors: Hessel Amy C. , Moreno Mauricio A. , Hanna Ehab Y. , Roberts Dianna B. , Lewin Jan S. , El‐Naggar Adel K. , Rosenthal David I. , Weber Randal S. 
Published: April 2010

AbstractBACKGROUND:The objective of this study was to identify measurable parameters that provide quality data for assessing how well cancer care adheres to accepted treatment guidelines and is delivered to any given patient with oral tongue cancer.METHODS:A retrospective chart review included 116 patients treated for T1‐T2/N0‐N1 squamous cell carcinoma (SCC) of the oral tongue between 1998 and 2003. A set of quality measures considered critical for outcome included: 1) accurate TNM staging at presentation, 2) documentation of margin status, 3) appropriate referral for adjuvant radiation therapy, and 4) neck dissection for depth of invasion >4 mm. In addition, 26 clinical endpoints involving pretreatment assessment, staging, treatment, surveillance, and symptom control were analyzed.RESULTS:Patients comprised 73 men and 43 women (median age, 57 years). Forty‐one (35.3%) patients presented with stage I disease, 61 (52.6%) with stage II, and 14 (12.1%) with stage III. The overall 5‐year survival rate for all patients was 68.6%. There was a 90.5% compliance with TNM staging at presentation, 99.1% for documentation of margin status, 98.2% for adequate referral to radiation therapy, and 88.7% for appropriate neck dissection based on depth of invasion. Compliance with clinical endpoints was variable and ranged from 100% for endpoints related to radiation therapy to <40% for endpoints related to speech pathology and rehabilitation.CONCLUSIONS:Overall compliance with documenting the 4 parameters designated as quality measures for treatment of oral tongue SCC was acceptable, thus demonstrating that it is possible to use these data for measuring effective cancer care. Cancer 2010. © 2010 American Cancer Society.
A population‐based study of follow‐up care for Hodgkin lymphoma survivors
Authors: Hodgson David C. , Grunfeld Eva , Gunraj Nadia , Del Giudice Lisa 
Published: April 2010

AbstractBACKGROUND:The majority of Hodgkin lymphoma (HL) patients are cured, and post‐treatment visits are a major component of their management. Little is known about the quality of follow‐up care received by these survivors.METHODS:All patients who were diagnosed with HL in Ontario from 1992 through 2000 were identified from a population‐based cancer registry. Individual‐level linkage with physician claims was used to examine the follow‐up care received by 2071 1‐year survivors for up to 15 years after their HL diagnosis. Physician visits, imaging studies, and the use of routine and HL‐specific cancer screening tests were evaluated.RESULTS:Most patients had visits with both a primary care provider and an oncologist in Years 2 through 5 after their HL diagnosis. In Year 5 after HL diagnosis, 31.8% of patients had at least 1 computed tomography (CT) scan, and 62.9% had a chest x‐ray. There were 5352 CT scans performed in Years 2 through 5, and 125 patients subsequently received chemotherapy within 6 months of a CT. Among the survivors who met age criteria for routine screening, 62.5% had no evidence of colorectal cancer screening during Years 2 through 15, 32.3% had no evidence of breast cancer screening, and 19.9% had no evidence of cervical cancer screening. Among young women potentially at high risk of breast cancer because of radiation therapy, 87.1% had not received the recommended breast cancer screening.CONCLUSIONS:Radiologic surveillance of HL survivors rarely led to salvage therapy. Despite frequent physician contact, many survivors did not receive established cancer screening interventions, and the recommended early initiation of breast cancer screening among young women at high risk was not widely used. Cancer 2010. © 2010 American Cancer Society.