bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Simple Procedure for Selective Hydroxylation of L‐Proline and L‐Pipecolic Acid with Recombinantly Expressed Proline Hydroxylases
Authors: Klein Christian , Hüttel Wolfgang 
Published: May 2011

AbstractDue to their diverse regio‐ and stereoselectivities, proline hydroxylases provide a straightforward access to hydroxprolines and other hydroxylated cylic amino acids, valuable chiral building blocks for chemical synthesis, which are often not available at reasonable expense by classical chemical synthesis. As yet, the application of proline hydroxylases is limited to a sophisticated industrial process for the production of two hydroxyproline isomers. This is mainly due to difficulties in their heterologues expression, their limited in vitro stability and complex product purification procedures. Here we describe a facile method for the production of cis‐3‐, cis‐4‐ and trans‐4‐proline hydroxylase, and their application for the regio‐ and stereoselective hydroxylation of L‐proline and its six‐membered ring homologue l‐pipecolic acid. Since in vitro catalysis with these enzymes is not very efficient and conversions are restricted to the milligram scale, an in vivo procedure was established, which allowed a quantitative conversion of 6 mM l‐proline in shake flask cultures. After facile product purification via ion exchange chromatography, hydroxyprolines were isolated in yields of 35–61% (175–305 mg per flask). L‐Pipecolic acid was converted with the isolated enzymes to prove the selectivities of the reactions. In transformations with optimized iron(II) concentration, conversions of 17–68% to hydroxylated products were achieved. The regio‐ and stereochemistry of the products was determined by NMR techniques. To demonstrate the applicability of the preparative in vivo approach for non‐physiological substrates, L‐pipecolic acid was converted with an E. coli strain producing trans‐4‐proline hydroxylase to trans‐5‐hydroxy‐L‐pipecolic acid in 61% yield. Thus, a synthetically valuable group of biocatalysts was made readily accessible for application in the laboratory without a need for special equipment or considerable development effort.
Direct Synthesis of 6‐Azabicyclo[3.2.1]oct‐6‐en‐2‐ones and Pyrrolizidines from Divinyl Ketones and Observation of Remarkable Substituent Effects
Authors: Xu Xianxiu , Li Yifei , Zhang Yu , Zhang Lingjuan , Pan Ling , Liu Qun 
Published: May 2011

AbstractSubstituents create access to molecular diversity. Under basic conditions, 6‐azabicyclo[3.2.1]oct‐6‐en‐2‐ones 3 and pyrrolizidines 4 are efficiently synthesized, respectively, in a single step from ethyl isocyanoacetate 2 and divinyl ketones 1 bearing an aryl or alkyl group at the 2‐position. For comparison, only the corresponding pyrrolizidines 4′ can be obtained from divinyl ketones 1′ bearing a methoxycarbonyl group at the 2‐position.
Highly Active and Diastereoselective N,O‐ and N,N‐Yttrium Complexes for Intramolecular Hydroamination
Authors: Lauterwasser Frank , Hayes Paul G. , Piers Warren E. , Schafer Laurel L. , Bräse Stefan 
Published: May 2011

AbstractThe intramolecular hydroamination of aminoalkynes and unactivated aminoalkenes catalyzed by yttrium N,O‐ and N,N‐complexes has been investigated. The N,N‐yttrium complexes are highly active, catalyzing the conversion of a wide range of terminal aminoalkenes at room temperature, and internal aminoalkenes at elevated temperature, to yield pyrrolidine and piperidine products in high yields. A high diastereoselectivity of up to 23:1 is observed at 0 °C with 1‐methyl‐4‐pentenylamine as substrate.
Gold‐Catalyzed Direct Intermolecular Coupling of Ketones, Secondary Amines, and Alkynes: A Facile and Versatile Access to Propargylic Amines Containing a Quaternary Carbon Center
Authors: Cheng Ming , Zhang Qiang , Hu Xiao‐Yu , Li Bo‐Gang , Ji Jian‐Xin , Chan Albert S. C. 
Published: May 2011

AbstractThe first gold‐catalyzed direct intermolecular coupling of ketones, secondary amines, and alkynes was achieved under mild and solvent‐free conditions. The present methodology provides a promising and versatile tool for the construction of propargylic amines with a newly‐formed quaternary carbon center.
Synthesis, Rhodium Complexes and Catalytic Applications of a New Water‐Soluble Triphenylphosphane‐Modified β‐Cyclodextrin
Authors: Legrand François‐Xavier , Six Natacha , Slomianny Christian , Bricout Hervé , Tilloy Sébastien , Monflier Eric 
Published: May 2011

AbstractA new triphenylphosphane based on a β‐cyclodextrin skeleton (PM‐β‐CD‐OTPP) was synthesized. This ligand can be dispersed in water by using the nanoprecipitation method. Transmission electron microscopy and NMR spectroscopy showed that PM‐β‐CD‐OTPP is aggregated in water and forms a stable dispersion. Its aqueous solubility can be dramatically increased in the presence of selected water‐soluble guests by formation of inclusion complexes. Associated to a rhodium precursor, PM‐β‐CD‐OTPP is able to generate soluble rhodium species in water. In addition, NMR experiments showed that the cyclodextrin cavity remains accessible for a guest even when PM‐β‐CD‐OTPP is coordinated to rhodium. Finally, this ligand was efficient for rhodium‐catalyzed hydrogenation and hydroformylation performed in aqueous medium.
Ring Size‐Selective Ring‐Closing Olefin Metathesis: Taking Advantage of the Deleterious Effect of Ethylene Gas
Authors: Yoshida Kazuhiro , Kano Yuto , Takahashi Hidetoshi , Yanagisawa Akira 
Published: May 2011

AbstractThe deleterious effect of ethylene gas on the ring‐closing olefin metathesis (RCM) for the formation of 5‐ to 8‐membered rings was investigated. Significant rate differences caused by ethylene gas were observed among the different ring‐size formation reactions. Nevertheless, the rate differences can be advantageously utilized for chemoselective RCM.
Asymmetric Aerobic Oxidation of α‐Hydroxy Acid Derivatives Catalyzed by Reusable, Polystyrene‐Supported Chiral N‐Salicylidene Oxidovanadium tert‐Leucinates
Authors: Salunke Santosh B. , Babu N.Seshu , Chen Chien‐Tien 
Published: May 2011

AbstractThe direct immobilization of two different C‐5‐propargyl ether‐modified, chiral N‐salicylidene vanadyl(V) tert‐leucinates onto 4‐azidomethyl‐substituted polystyrene by click chemistry was examined. Among the eight different solvents investigated, the resulting polystyrene‐supported catalysts promote the asymmetric, aerobic oxidation of α‐hydroxy (thio)esters and amides with enantioselectivities of up to 99% ee (selectivity factor up to 41) in chloroform. These polystyrene‐supported catalysts can be readily recovered by filtration and reused for at least four consecutive runs without discernible loss of reactivity and enantioselectivity.
Efficient Recovery and Reuse of an Immobilized Peptidic Organocatalyst
Authors: Arakawa Yukihiro , Wiesner Markus , Wennemers Helma 
Published: May 2011

AbstractReadily reusable immobilized organocatalysts are important from a practical, economic, and environmental viewpoint. However, their successful development has proven challenging and only limited reaction and recovery cycles have been achieved. We report an extraordinarily robust resin‐bound tripeptidic organocatalyst that can be readily reused for at least 30 reaction and recovery cycles without loss in catalytic activity or stereoselectivity. The immobilized catalyst can be directly reused for conjugate addition reactions between aldehydes and nitroolefins after a simple filtration from the reaction products. The catalytic efficiency and chemoselectivity of the immobilized peptidic catalysts is so high that a broad range of γ‐nitroaldehydes were isolated easily after filtration and removal of all volatiles in quantitative yields, excellent diastereoselectivities and enantioselectivities and, most remarkably, perfect analytical purities. The ease of handling allows for a facile scale‐up of reactions catalyzed by the immobilized peptidic catalyst. In addition, the results provide a guide for the further development of immobilized organocatalysts.
Brief communication: The relation between standard error of the estimate and sample size of histomorphometric aging methods
Authors: Hennig Cheryl , Cooper David 
Published: May 2011

AbstractHistomorphometric aging methods report varying degrees of precision, measured through Standard Error of the Estimate (SEE). These techniques have been developed from variable samples sizes (n) and the impact ofnon reported aging precision has not been rigorously examined in the anthropological literature. This brief communication explores the relation betweennand SEE through a review of the literature (abstracts, articles, book chapters, theses, and dissertations), predictions based upon sampling theory and a simulation. Published SEE values for age prediction, derived from 40 studies, range from 1.51 to 16.48 years (mean 8.63; sd: 3.81 years). In general, these values are widely distributed for smaller samples and the distribution narrows asnincreases—a pattern expected from sampling theory. For the two studies that have samples in excess of 200 individuals, the SEE values are very similar (10.08 and 11.10 years) with a mean of 10.59 years. Assuming this mean value is a ‘true’ characterization of the error at the population level, the 95% confidence intervals for SEE values from samples of 10, 50, and 150 individuals are on the order of ±4.2, 1.7, and 1.0 years, respectively. While numerous sources of variation potentially affect the precision of different methods, the impact of sample size cannot be overlooked. The uncertainty associated with SEE values derived from smaller samples complicates the comparison of approaches based upon different methodology and/or skeletal elements. Meaningful comparisons require larger samples than have frequently been used and should ideally be based upon standardized samples. Am J Phys Anthropol, 2011. © 2011 Wiley‐Liss, Inc.
Light Microscopy with Doughnut Modes: A Concept to Detect, Characterize, and Manipulate Individual Nanoobjects
Authors: Züchner Tina , Failla Antonio Virgilio , Meixner Alfred J. 
Published: May 2011

AbstractHigher order laser modes, mainly called doughnut modes (DMs) have use in many different branches of research, such as, bio‐imaging, material science, single‐molecule microscopy, and spectroscopy. The main reason of their increasing importance is that recently, the techniques to generate well‐defined DMs have been refined or rediscovered. Although their potential is still not fully utilized, their specifically polarized field distribution gives rise to a wide field of applications. They are contributing to complete our fundamental knowledge of the optical properties of single emitting species, such as molecules, nanoparticles, or quantum dots, offering insight into the three‐dimensional dipole or particle orientation in space. The perfect zero intensity in the focus center qualifies some DMs for stimulated emission depletion (STED) microscopy. For the same reason, they have been suggested for trapping and tweezing applications.
Cyclometalated iridium(III) complex of 6‐hydroxydipyrido[3,2‐a:2′,3′‐c]phenazine: synthesis, and acid–base and avid DNA binding properties
Authors: Chen Yan‐Min , Zhang An‐Guo , Wang Ke‐Zhi 
Published: May 2011

AbstractA new cyclometalated Ir(III) complex [Ir(ppy)2(hdppz)]PF6 (Hppy = 2‐phenylpyridine and hdppz = 6‐hydroxydipyrido[3,2‐a:2′,3′‐c]phenazine) was synthesized and characterized. The pH effects on the UV–vis absorption spectra were studied and ground‐state acid ionization constant pKa values of the complex were derived. The calf thymus DNA (ct‐DNA) binding properties of the complex were investigated with UV‐vis absorption spectrophotometric titrations, DNA competitive binding with ethidium bromide, DNA melting experiments, viscosity measurements and density functional theory (DFT) calculations. The complex was demonstrated to act as a ct‐DNA intercalator with a large DNA binding constant value of (6.06 ± 0.32) × 106 M−1 in 50 mM NaCl. The avid DNA binding affinity observed was rationalized by the DFT calculations. Copyright © 2011 John Wiley & Sons, Ltd.
Burden and viability of Borrelia burgdorferi in skin and joints of patients with erythema migrans or lyme arthritis
Authors: Li Xin , McHugh Gail A. , Damle Nitin , Sikand Vijay K. , Glickstein Lisa , Steere Allen C. 
Published: May 2011

AbstractObjectiveTo determine the burden and viability of Borrelia burgdorferi in the skin and joints of patients with Lyme disease.MethodsStandard and quantitative polymerase chain reaction (PCR) techniques were used to detect B burgdorferi DNA in skin samples from 90 patients with erythema migrans (EM) and in synovial fluid (SF) from 63 patients with Lyme arthritis (LA) and in synovial tissue from 9 patients. Quantitative PCR determinations of B burgdorferi DNA, messenger RNA (mRNA), and ribosomal RNA (rRNA) were made in 10 skin samples from EM patients and 11 SF samples from LA patients.ResultsSkin lesions in most patients with EM had positive PCR results for B burgdorferi DNA. In the majority of patients with LA, a late disease manifestation, PCR results in pretreatment SF samples were positive. In patients with antibiotic‐refractory arthritis, positive PCR results persisted for as long as 11 months, but positive results in samples taken during the postantibiotic period did not correlate with relapse or with the subsequent duration of arthritis, and at synovectomy, all results of PCR of synovial tissue were negative. B burgdorferi mRNA, a marker of spirochetal viability, was detected in 8 of 10 skin samples from EM patients, but in none of 11 SF samples from LA patients, even when obtained prior to antibiotic administration. Moreover, the median ratio of spirochetal rRNA to DNA, a measure of ribosomal activity, was 160 in the 10 EM skin samples, but only 0.15 in the 3 LA SF samples with positive results.ConclusionB burgdorferi in the skin lesions of EM patients were active and viable, whereas those in the SF of LA patients were moribund or dead at any time point. Thus, detection of B burgdorferi DNA in SF is not a reliable test of active joint infection in Lyme disease.
Anatomical Sciences Education Vol. 4, Issue 3, 2011 Cover Image
Authors: Macchi Veronica , Porzionato Andrea , Stecco Carla , Tiengo Cesare , Parenti Anna , Cestrone Adriano , De Caro Raffaele 
Published: May 2011

AbstractMedical Gross Anatomy lecture at the University of Padova, Italy. Gross Anatomy at the University of Padova is taught utilizing both traditional and technological resources, which are integrated with practical laboratory exercises (mainly on plastic models and plastinated specimens) as well as radiological anatomy. In this issue of ASE, Dr. Veronica Macchi and her colleagues from the Department of Human Anatomy and Physiology at the University of Padova discuss an innovative pilot project with their University Hospital in which they obtain body parts removed from patients during surgical procedures and utilize them for gross anatomy education. The cover photograph shows one of the co‐authors of this paper, Professor Raffaele De Caro and his students, performing dissection of the distal forearm and hand in the anatomy lecture theater at the University of Padova.
Coverage‐Dependent Variation of Adsorption Configurations of Methionine on Ge(100)
Authors: Yang Sena , Kim Yaewon , Park Sunmin , Kim Ki‐jeong , Lee Hangil 
Published: May 2011

AbstractThe adsorption configurations of methionine molecules on the Ge(100) surface have been studied by using DFT calculations, core‐level photoemission spectroscopy (CLPES), and low‐energy electron diffraction (LEED) to scrutinize the adsorption structure as a function of coverage. At first, we obtained two important and stable structures. One is the most stable structure between these structures described as an “OH dissociated‐N dative‐S dative‐bonded structure” and the other is a less stable adsorption structure of these indicating an “OH dissociated‐S dative‐bonded structure” by using DFT calculations. We also performed CLPES to clarify our DFT calculation results. Through the spectral analysis of the S 2p, C 1s, N 1s, and O 1s core‐level spectra, we acquired the reasonable results that also revealed quite different bonding configurations depending on the methionine coverage. At low coverage (ca. 0.30 ML), a single type of sulfur and charged nitrogen peaks, which indicate an “OH dissociated‐N dative‐S dative‐bonded structure”, were observed. On the other hand, two types of sulfur peaks with thiol formation and two nitrogen peaks with neutralized and charged characteristics were monitored at a higher coverage (0.60 ML and above), which can be described as an “OH dissociated‐S dative‐bonded structure”. Hence, we can clearly demonstrate that our results obtained from CLPES spectra and DFT calculations are matched well with each other. Moreover, we additionally confirmed that the relative population of the two types of thiols and amines being included in methionine in between half monolayer induces a surface reorientation in the ordering from 2×1 to 1×1 employing LEED. This interesting variation of the methionine adsorbed on the Ge(100) surface by coverage dependence will be precisely discussed by using DFT calculations, CLPES, and LEED.
Why is it crucial to reintegrate pathology into cancer research?
Authors: Rodriguez‐Canales Jaime , Eberle Franziska C. , Jaffe Elaine S. , Emmert‐Buck Michael R. 
Published: May 2011

AbstractThe integration of pathology with molecular biology is vital if we are to enhance the translational value of cancer research. Pathology represents a bridge between medicine and basic biology, it remains the gold standard for cancer diagnosis, and it plays an important role in discovery studies. In the past, pathology and cancer research were closely associated; however, the molecular biology revolution has shifted the focus of investigators toward the molecular alterations of tumors. The reductionist approach taken in molecular studies is producing great insight into the inner workings of neoplasia, but it can also minimize the importance of histopathology and of understanding the disease as a whole. In turn, pathologists can underestimate the role of molecular studies in developing new ancillary techniques for clinical diagnosis. A multidisciplinary approach that integrates pathology and molecular biology within a translational research system is needed. This process will require overcoming cultural barriers and can be achieved through education, a more effective incorporation of pathology into biological research, and conversely an integration of biological research into the pathology laboratory.
Metal ion‐assembled micro‐collagen heterotrimers
Authors: LeBruin Lyndelle Toni , Banerjee Sunandan , O'Rourke Bruce Delany , Case Martin Ashley 
Published: May 2011

AbstractCollagen mimetic peptides (CMPs) provide critical insight into the assembly, stability, and structure of the triple helical collagen protein. The majority of natural fibrous collagens are aab or abc heterotrimers, yet few examples of heterotrimeric CMPs have been reported. Previously, CMP heterotrimers have only been accessible by total syntheses or by introducing complementary interstrand electrostatic or steric interactions. Here, we describe an abc CMP heterotrimer in which each contributing CMP consists of only three amino acids: glycine, proline and 4‐hydroxyproline. Assembly of the heterotrimeric triple helix is directed by a combination of metal‐ion coordination to set the relative register of the CMPs, and minimization of valence frustration to direct heterotrimerization. Assembly of the four‐component mixture is facile and extremely rapid, and equilibration to the abc heterotrimer occurs within a few hours at modestly elevated temperatures. The melting temperatures of the metal‐assembled collagen trimers are higher by some 30°C than the apopeptide assemblies. Two iterations of the design are described, and the outcomes suggest possibilities for designing self‐assembling abc and abb heterotrimers. © 2011 Wiley Periodicals, Inc. Biopolymers 95: 792‐800, 2011.
The Sintering of Supported Pd Automotive Catalysts
Authors: Xu Qing , Kharas Karl C. , Croley Brandon J. , Datye Abhaya K. 
Published: May 2011

AbstractThis work is directed at investigating the contribution of metal particle sintering to catalyst deactivation in close‐coupled automotive catalysts that are aged at elevated temperatures. We focus on the evolution of metal particle sizes in Pd/Al2O3 under conditions typically used for accelerated aging of automotive exhaust catalysts (10 mol % H2O at 900 °C). By using multiple analytical techniques (transmission electron microscopy, X‐ray diffraction, chemisorption, and CO oxidation) we can determine the role of support surface area collapse (encapsulation) versus metal particle sintering. The final dispersion (% metal atoms exposed) after sintering for 96 h ranged from 1.94 to 0.86 % for metal loadings ranging from 0.1 to 7.0 wt % (a 70‐fold variation). Thus, it appears that metal loading (over the range studied) has only a limited effect on the final dispersion in the sintered catalyst. The sintering kinetics were found to obey a relationship dn−${d{{n\hfill \atop 0\hfill}}}$=kt for which the exponent n is approximately 2.0 and d is the number average particle diameter at time t. This relationship and the fact that metal particle size continues to grow with time are both consistent with Ostwald ripening as the dominant mechanism. Furthermore, no limiting (equilibrium) particle size was achieved within the sintering times studied here (up to 200 h). These results have important implications for the design of thermally stable automotive catalysts.
NMR Spectroscopy of Intermetallic Compounds: An Experimental and Theoretical Approach to Local Atomic Arrangements in Binary Gallides
Authors: Haarmann Frank , Koch Katrin , Jeglič Peter , Pecher Oliver , Rosner Helge , Grin Yuri 
Published: May 2011

AbstractThe results of the investigation of MGa2 with M=Ca, Sr, Ba and of MGa4 with M=Na, Ca, Sr, Ba by a combined application of NMR spectroscopy and quantum mechanical calculations are comprehensively evaluated. The electric‐field gradient (EFG) was identified as the most reliable measure to study intermetallic compounds, since it is accessible with high precision by quantum mechanical calculations and, for nuclear spin I>1/2, by NMR spectroscopy. The EFG values obtained by NMR spectroscopy and quantum mechanical calculations agree very well for both series of investigated compounds. A deconvolution of the calculated EFGs into their contributions reveals its sensitivity to the local environment of the atoms. The EFGs of the investigated di‐ and tetragallides are dominated by the population of the px‐, py‐, and pz‐like states of the Ga atoms. A general combined approach for the investigation of disordered intermetallic compounds by application of diffraction methods, NMR spectroscopy, and quantum mechanical calculations is suggested. This scheme can also be applied to other classes of crystalline disordered inorganic materials.