bluuebunny/crossref_metadata_2025_split huggingface dataset:
Orbital‐Symmetry Effects in Bimolecular Electron‐Transfer Reactions: Back Electron Transfer
Authors: Haselbach Edwin , Pilloud Denis , Suppan Paul 
Published: December 2004

AbstractPrevious work has indicated orbital‐symmetry effects upon forward electron transfer inbimolecular systems, with magnitude similar to that encountered in rigidmonomolecular systems. The present work, which employs back electron transfer, supports and extends these earlier findings.
New Axially Chiral Bis(dihydrooxazoles) as Ligands in Stereoselective Transition‐Metal Catalysis
Authors: Rippert Andreas Johannes 
Published: December 2004

AbstractThe new, axially chiral bis(4,5‐dihydrooxazoles) 4 have been synthesized in a straightforward manner, starting from the substituted, racemic 1,1′‐biphenyl‐2,2′‐dicarboxylic acids 1 and optically active amino alcohols 2. The adducts were resolved by medium‐performance liquid chromatography (MPLC; see Scheme 1). Formation of Cu1 complexes of 4 was followed by 1H‐NMR spectroscopy. The catalytic behavior of these complexes has been investigated by asymmetric cyclopropanation of styrene with ethyl diazoacetate. Beside the influence of steric factors, a significant electronic effect on asymmetric induction could also be observed (see Scheme 2 and Table).
Selective Derivatization of the Ionophore X‐206 at C(22) Maintaining Potassium Binding
Authors: O'Sullivan Anthony C. , Struber Fritz 
Published: December 2004

AbstractThe insecticidal polyether antibiotic X‐206 (1) complexes potassium ions using nearly all of its O‐atoms either for binding to the metal ion or for participation in a H‐bonding network which helps to hold X‐206 in the ionophoric tertiary structure. The group OHC(22) is not involved in these processes. It was supposed that derivatization of this group would not affect the ionophoric properties and would produce insecticidally active compounds. The chemistry leading to selective modification of OHC(22) via the intermediate 6 was developed. The potassium‐binding properties and insecticidal activities of the MeCOOC(22) and MeOC(22) compounds 3 and 11, respectively, confirmed that derivatization of the peripheral OHC(22) was a valid strategy for the synthesis of biologically active compounds.
Cooperative Interactions of the Catalytic Nucleophile and the Catalytic Acid in the Inhibition of β‐Glycosidases. Calculations and their validation by comparative kinetic and structural studies of the inhibition of glycogen phosphorylase b
Authors: Heightman Tom D. , Vasella Andrea , Tsitsanou Katerina E. , Zographos Spyros E. , Skamnaki Vicky T. , Oikonomakos Nikos G. 
Published: December 2004

AbstractThe difference between the strong inhibition of retaining β‐glucosidases by the tetrazole 1 and the weak inhibition by the triazole 3 has been explained by the protonation by the enzymic catalytic acid of N(3) of 1, replaced by CH in 3. One also expects a contribution to the inhibition from the charge‐dipole interaction between the enzymic catalytic nucleophile and the azole ring. The extent of this contribution was estimated from the calculated, distance‐dependent heats of formation of the acetate‐azole complexes. The calculations were validated by comparison of the charge‐dipole interaction between phosphate and the inhibitors 1 and 3 in the glycogen phosphorylase b (GPb)‐azole‐phosphate complexes, as derived from differences in the Ki values for 1 and 3, while the structural invariance of the complexes was demonstrated by X‐ray analysis. The difference between the charge‐dipole interactions of (dihydrogen) phosphate and 1 or 3 as derived from Δ Ki is 1.1 kcal mol−1, while the calculated difference is 1.3 kcal mol−1. The calculated difference for the interaction of 1 or 3 with acetate, representing the catalytic nucleophile in β‐glycosidases, is 2.0 kcal mol−1, while the differences of the binding energies as derived from the Ki values for the inhibition by 1 or 3 of different β‐glycosidases range from 2.4 to 5.3 5 kcal mol−1. The calculated difference for 1 and the imidazole 6 is 2.5 kcal mol−1 in favour of 1, whereas the Ki‐derived difference is 3.7 kcal mol−1 in favour of 6, equal to the calculated difference between 1 and the protonated imidazole 6. Thus, protonation by the catalytic acid and the charge‐dipole interaction with the catalytic nucleophile contribute cooperatively to the binding of inhibitors possessing a trigonal anomeric centre bonded to a heteroatom.
γ‐Peptides Forming More Stable Secondary Structures than α‐Peptides: Synthesis and helical NMR‐solution structure of the γ‐hexapeptide analog of H‐(Val‐Ala‐Leu)2‐OH
Authors: Hintermann Tobias , Gademann Karl , Jaun Bernhard , Seebach Dieter 
Published: December 2004

AbstractFor a comparison with the corresponding α‐ and β‐hexapeptides H‐(Val‐Ala‐Leu)2‐OH (A) and H‐(β‐HVal‐β‐HAla‐β‐HLeu)2‐OH (B), we have now prepared the corresponding γ‐hexapeptide 1 built from the homochirally similar (S)‐4‐aminobutanoic acid, (R)‐4‐amino‐5‐methylhexanoic acid, and (R)‐4‐amino‐6‐methylheptanoic acid. The precursors were prepared either by double Arndt‐Eistert homologation of the protected amino acids Boc‐Val‐OH, Boc‐Ala‐OH, and Boc‐Leu‐OH (Schemes 1 and 2), or by the superior route involving olefination/hydrogenation of the corresponding aldehydes (Boc‐valinal, Boc‐alaninal, and Boc‐leucinal; Scheme 3). Conventional peptide‐coupling methodology (EDC/HOBt) furnished the γ‐hexapeptide 1 (through the intermediate γ‐di‐ and γ‐tripeptide derivatives 9–11). Analysis of NMR measurements in (D5)pyridine and CD3OH solution (COSY, TOCSY, HSQC, HMBC, ROESY) reveals that the γ‐hexapeptide 1 adopts a right‐handed helical structure ((P)‐2.61 helix of ca. 5‐Å pitch, containing 14‐membered H‐bonded rings) which is to be compared with the left‐handed helix of the corresponding β‐peptide B ((M)‐31 helix of 5‐Å pitch, 14‐membered H‐bonded rings) and with the familiar right‐handed, so‐called α‐helix of α‐peptides ((P)‐3.61 helix of 5.4‐Å pitch, 13‐membered rings). Like the helix sense, the helix dipole reverses when going from α‐, (N + → C) to β‐(C + → N) to γ‐peptides (N + → C). The surprising difference between the natural α‐, and the analogous β‐ and γ‐peptides is that the helix stability increases upon homologation of the residues.
Sulfur‐Containing Heterocycles Derived by Reaction of ω‐Keto Amides with Lawesson's Reagent
Authors: Nishio Takehiko 
Published: December 2004

AbstractThe reaction of ω‐keto amides with Lawesson's reagent (LR: 2,4‐bis(4‐methoxyphenyl)‐1,3,2,4‐dithiadiphosphetane 2,4‐disulfide) is described. Treatment of 3‐keto amides (2‐acylacetamides) 1 with LR gave the corresponding 3‐keto thioamides 2, along with 1,2‐dithiole‐3‐thiones 3. Treatment of 4‐keto amides, 3‐acyl propionamides 5, with LR yielded five‐membered heterocycles, pyrroles 6 and/or 2‐aminothiophenes 7. 5‐Keto amides, 3‐benzoyl butyramides 8, reacted with LR to give dihydrothiopyran‐2‐thione 9 as the sole product, but in low yield. 2‐Acylbenzamides 10 also reacted with LR to afford 3‐mercaptoisoindolin‐2‐ones 11 or dihydroisobenzothiophene‐1‐thiones 12.
On the Origin of Asymmetric Induction of the Palladium‐Catalyzed Allylic Substitution Reaction with Chiral 4,4‐Disubstituted 4,5‐Dihydro‐2‐(phosphinoaryl)oxazole Ligands
Authors: Schaffner Silvia , Müller Jürgen F. K. , Neuburger Markus , Zehnder Margareta 
Published: December 2004

AbstractThe X‐ray analyses of (η3‐allyl){4‐benzyl‐2‐[2‐(diphenylphosphino‐κP)phenyl]‐4,5‐dihydro‐4‐4‐methyloxazole‐κN}palladium(II) hexafluorophosphate (5) and the analogous [Pd(η3‐1,3‐diphenylallyl)] complex 6 are presented. A comparison with the (η3‐allyl)‐ and (η‐1,3‐diphenylallyl)palladium complexes 2 and 3, respectively, containing the 4‐monosubstituted 4,5‐dihydro‐2‐(phosphinoaryl)oxazole ligand 1a reveals important structural differences (Fig. 3). 1H‐NMR Spectroscopic investigation confirm that the 4,4‐disubstituted 4,5‐dihydro‐2‐(phosphinoaryl)oxazole ligand 4 of 5 and 6 shows the same conformation in solution as in the solid state (Table 2). The application of ligand (S)‐4 in the Pd‐catalyzed allylic substitution demonstrates a configurational relationship between the orientation of the allyl ligand in the intermediate (cf. complex 6) and the absolute configuration of the allylic‐substitution product (Table 3).
Partial Synthesis and Characterization of Capsokarpoxanthins and 3,6‐Epoxcapsanthins
Authors: Deli József , Molnár Péter , Matus Zoltán , Tóth Gyula , Steck Andrea , Pfander Hanspeter 
Published: December 2004

AbstractThe acid‐catalyzed hydrolysis of (3S,5R,6S,3′S,5′R)‐5,6‐epoxycapsanthin (5) led to (3S,5R,6R,3′S,5′R)‐(7) and (3S,5R,6S,3′S,5′R)‐capsokarpoxanthin (8). In addition, (3S,5R,8R,3′S,5′R)‐ (9), (3S,5R,8S,3′S,5′R)‐capsochrome (10), and (3S,5R,6R,3′S,5′R)‐3,6‐epoxycapsanthin (6) afforded (3S,5S,6R,3′S,5′R)‐capsokarpoxanthin (12) (3S,5S,8S,3′S,5′R)‐ (13) and (3S,5S,8R,3′S,5′S)‐capsochrome (14) as well as (3S,5S,6R,3′S,5′R)‐3,6‐epoxyepicapsanthin (15). Compounds 5–15 were isolated in crystalline form and characterized by their UV/VIS, CD, 1H‐ and 13C‐NMR, and mass spectra.
Synthesis and Structure Elucidation of a New Potent Sandalwood‐Oil Substitute
Authors: Bajgrowicz Jerzy A. , Frank Iris , Fráter Georg , Hennig Michael 
Published: December 2004

AbstractNew derivatives of campholenaldehyde (= 2‐(2,2,3‐trimethylcyclopent‐3‐enyl)ethanal bearing two cyclopropane moieties were synthesized, and the structure of the stereoisomer responsible for its exceptionally strong, diffusive, and natural sandalwood‐oil scent, ((1S,2S)‐1‐methyl‐2‐{[1S,3R,5R)‐1,2,2‐trimethylbicyclo[3.1.0]hex‐3‐yl]methyl}cyclopropyl)methanol (13a), was elucidated.
A Synthetic Receptor for β,β‐Carotene: Towards an enzyme mimic for central cleavage
Authors: French Richard R. , Wirz Jakob , Woggon Wolf‐Dietrich 
Published: December 2004

AbstractWe report on the synthesis of a receptor 4 for β,β‐carotene (1), and on the binding interaction between the two which yields inclusion complex 5. The cyclodextrin ‘dimer’ 4 was obtained via condensation of the corresponding 4,4′‐(porphyrin‐5,15‐diyl)bis phenol 8 with 6A‐deoxy‐6A‐iodo‐β‐cyclodextrin (6) in the presence of Cs2CO3. Fluorescence studies of the binding interaction between ‘dimer’ 4 and β,β‐carotene (1) gave a binding constant Ka of (2.4 ± 0.1) · 106 M−1.
Blood compatibility of methyl, methyl vinyl, methyl phenyl, and trifluoropropylmethylvinyl silicone rubber without silica fillers in the spiral‐coiled membrane lung
Authors: Kolobow T. , Tomlinson T. A. , Pierce J. E. 
Published: December 2004

AbstractSpiral‐coiled membrane lungs of 0.6 m2 surface area were fabricated from silicone rubber membranes coated with four types of commercially available pure‐gum polysiloxane rubber: 1) polytrifluoropropylmethylvinylsiloxane, 2) polymethylphenylsioxane, 3) polymethylvinylsiloxane, and 4) polydimethylsiloxane.Membrane lungs were tested in an arteriovenous shunt without added heparin after bypass was begun. All groups except group 4 had major rise in resistance to blood flow or clotting in over 33% of the membrane lungs studied, after 6 hr of bypass. Membrane lungs with polydimethylsiloxane (group 4) had no rise in resistance to blood flow during 24 hr of bypass and had the least amount of changes in blood platelet count.
Influence of cold plastic deformation on critical pitting potential of AISI 316 L and 304 L steels in an artificial physiological solution simulating the aggressiveness of the human body
Authors: Cigada A. , Mazza B. , Pedeferri P. , Sinigaglia D. 
Published: December 2004

AbstractThe effect of cold working on critical pitting potential of AISI 316 L and 304 L steels in a buffered physiological solution has been studied. In particular, the importance of deformation degree, orientation of the specimen surface to the deformation direction, and cold working temperature in lowering the critical pitting potential is shown.
Wear of dental amalgam
Authors: Roberts J. C. , Powers J. M. , Craig R. G. 
Published: December 2004

AbstractThe wear of dental amalgam was studied by single‐ and double‐pass sliding and by a silicon carbide abrasion test. A dispersed amalgam showed significantly better resistance to two‐body abrasion than the spherical amalgams tested. The wear of amalgam was determined by resistance to penetration and by a ductile mode of surface failure over the load range studied. Differences in the wear of amalgam and restorative resins and composites are discussed.
An in vitro and in vivo analysis of anodized tantalum capacitive electrodes: Corrosion response, physiology, and histology
Authors: Johnson P. F. , Bernstein J. J. , Hunter G. , Dawson W. W. , Hench L. L. 
Published: December 2004

AbstractOxidation–reduction reactions which can destroy high current‐density metalstimulating electrodes are avoided when using capacitive electrodes. The results of in vitro and in vivo testing of anodized, high surface area, sintered tantalum electrodes are presented. The corrosion response of the electrodes is excellent; there is no evidence of dissolution of the electrode. A deposit forms on the surface of the electrodes, but has little effect on the voltage response to constant current stimulation. The physiological and histopathological results indicate the capacitive tantalum electrode to be the safest yet tested.
Evaluation of hip arthroprostheses by means of body environment simulators
Authors: Cappozzo Aurelio , Cini Leopoldo , Pizzoferrato Arturo , Trentani Claudio , Cortesi Sergio Sandrolini 
Published: December 2004

AbstractLaboratory tests carried out by means of body environment simulators have proved to be very important for the evaluation of endoprostheses potentially useful for implantation. The present paper examines the problems connected with the design of such a simulator. The results obtained with an initial, very primitive simulator concerning the outlines of the phenomena of wear, corrosion, and friction and some wear properties of commercially available hip endoprostheses are presented. From these results, the motivation that led to the design of a more advanced simulator is presented. This latter simulator is also described.
Temperature control of a bone cement by addition of a crystalline monomer
Authors: Lee H. B. , Turner D. T. 
Published: December 2004

AbstractThe peak temperature reached during the polymerization of a bone cement was reduced by addition of solid N‐vinylcarbazole to the powder component. It was also necessary to saturate the liquid component with N‐vinylcarbazole to prevent dissolution from the modified powder component on mixing. It is believed that this technique is generally applicable and opens up the possibility of achieving temperature control of bone cements with choice from a range of crystalline monomers.
Immobilization of urea cycle enzymes. I. Characterization of immobilized carbamoylphosphate synthetase and ornithine carbamoyltransferase
Authors: Miura Yoshiharu , Miyamoto Kazuhisa , Raze J. M. , Urabe Hideaki 
Published: December 2004

AbstractCarbamoylphosphate synthetase (EC 2.7.2.5) and ornithine carbamoyl‐transferase (EC 2.1.3.3) extracted from frog liver were successfully immobilized on CNBr‐activated Sepharose 4B. The immobilized preparation had a better stability towards heat. The apparent Michaelis constant values for N‐acetyl‐glutamate, ammonia, and ATP were not significantly changed by immobilization.
Immobilization of urea cycle enzymes. II. Characterization of immobilized argininosuccinate synthetase
Authors: Miura Yoshiharu , Miyamoto Kazuhisa , Urabe Hideaki , Nagata Chikako , Hane Yumiko 
Published: December 2004

AbstractArgininosuccinate synthetase (EC 6.3.4.5) was immobilized on CNBr‐activated Sepharose 4B. Properties of the immobilized enzyme are described and compared with those of the native enzyme. The immobilized enzyme was much more stable than the native enzyme at 37°C. It was further stabilized in the presence of the assay reagents. The optimum pH of the immobilized enzyme shifted towards alkalinity (approximately 0.5 unit). The apparent Michaelis constants measured for the immobilized enzyme were not greatly different from those measured for the native enzyme.Urea formation from citrulline was confirmed in a continuous column reactor by the coimmobilized argininosuccinate synthetase, argininosuccinate lyase (EC 4.3.2.1), and arginase (EC 3.5.3.1).
Force production and decay rate in Alastik modules
Authors: Varner Robert E. , Buck Douglas L. 
Published: December 2004

AbstractThe production and decay of forces produced by Alastik modules was studied under conditions simulating clinical usage over a time period of 2 hr to 4 weeks. Force decay was moderate and all Kx modules tested produced approximately 1 lb of force at the end of the 4‐week test period. Therefore, from a clinical standpoint, modules need not be changed more frequently than once every 4 weeks.
The effect of antibiotic additions on the mechanical properties of acrylic cement
Authors: Nelson Russell C. , Hoffman Richard O. , Burton Thomas A. 
Published: December 2004

AbstractEarly work on hip prosthesis showed that the metal component would loosen in bone even when screws were used. This practice resulted in the death and resorption of the bone; thus cement was used in orthopedic surgery for firm implantation of prostheses. In recent years antibiotics have been added to the cement as a prophylaxis against infection.This research investigates the effects of antibiotics on the diametral tensile and compression strength of the cement. Samples made with 2 g of antibiotic per surgical packet of bone cement containing the antibiotics gentamicin, keflin, and a combination of the two were tested. These samples were aged at ambient temperature for periods of 1 day and 1, 2, 8, 13, and over 30 weeks.A statistical analysis using a two‐way analysis of variance with interaction was conducted. It was concluded that the compression strength was affected by the antibiotic, and not by the aging period, but that there is an antibiotic‐aging period interaction. The tensile strength is not affected by either the antibiotic or the aging period, and there is an antibiotic‐aging period interaction. Current work being conducted will analyze additional factors and interactions.
Adhesive bonding of various materials to hard tooth tissues. X. Initial rates of adsorption of nickel or copper ions on hydroxyapatite surface
Authors: Misra D. N. , Bowen R. L. 
Published: December 2004

AbstractInitial rates of ion‐exchange adsorption of nickelous or cupric ions with calcium ions on the surface of synthetic hydroxyapatite were studied in aqueous nitrate solutions. A kinetic interpretation has been proposed. The determination of the initial rates is important for a systematic investigation of adhesion of certain properly designe substances that may mediate a chemical bonding between dental resins and “moralanted” calcified tissues.
Interactions of bovine thrombin and plasma albumin with low‐energy surfaces
Authors: Waugh David F. , Lippe Jo Ann , Freund Yvonne R. 
Published: December 2004

AbstractSurface configurations are vessels fabricated from tubing and plate, films deposited on the surface of vessels, and beads confined in vessels. The average association constant between thrombin and sites on commercial poly(methyl methacrylate) surface (Lucite) is near 4 × 108 liters/mole at 22°C, pH 7.0, and ionic strength 0.15. Depending on Lucite composition, average adsorption U, in molecules/cm2 of apparent solution‐surface interface, ranges from 0.7 to 8.8 × 1011. Analysis based on the assumptions that solution dimensions are preserved, adsorption is random, and surface rearrangement is negligible indicates a paucity of surface sites. Plasma albumin competes with thrombin for surface sites. Attempts to detect, by thrombin adsorption, the presence of free sites at 4.5 × 10−9 M albumin or the displacement of bound albumin indicate an albumin‐site association contrast greater than 1.6 × 109. Cross‐linked poly(methyl acrylate) bead surface has U less than 5 × 1010. In contrast to acrylic resins are silicone gum, polypropylene, and polyisobutylene, for which U ranges from 15 to 20 × 1011. Analysis as above indicates that sites are of frequent occurrence. Material composition suggests that thrombin can interact with nonpolar groups. Further characteristics of low‐energy surfaces are that progressive surface denaturation is small and there is a large variance between nominally equivalent configurations.
Defects in failed stems of hip prostheses
Authors: Rostoker W. , Chao E. Y. S. , Galante J. O. 
Published: December 2004

AbstractA study has been made of the fractures and associated material from 34 prostheses broken in service. All the fractures appear to be of the fatigue type. Search by me‐tallographic analysis for cracklike generating defects in material near the fracture reveals such conditions as abnormally coarse crystals, large nonmetallic inclusions, large inclusion population, undissolved master alloy particles, abnormal carbide segregation, interdendritic segregation, shrinkage, and gas porosity. Recommendations are made for the choice of metallic alloys for femoral stem application.
Adsorption of plasma proteins on hydrophobic surfaces. III. Serum, plasma, and blood
Authors: Bagnall R. D. 
Published: December 2004

AbstractLiquid–air and liquid–liquid interfaces were used as models for the liquid‐solid system of plasma proteins and hydrophobic surfaces in the study of adsorption of serum, plasma, and blood onto these surfaces. The interfacial tension is determined for three phases: air, methylene iodide, and isooctane. Curves of interfacial tension versus time for the various systems are given from which a triple‐intersection point, where the protein solution is in equilibrium with each surface, is found. It is shown that albumin, γ‐globulin, and a mixed solution of these at in vivo concentrations behave in characteristic and constant manners at the three interfaces of air, methylene iodide, and isooctane. A range of synthetic surfaces which have constant behavior at equilibrium is deduced and it is concluded that any soft tissue response differences between such surfaces could not be the result of albumin or γ‐globulin.
Interaction of fibroblasts and polymer surfaces: relationship between surface free energy and fibroblast spreading
Authors: van der Valk P. , van Pelt A. W. J. , Busscher H. J. , de Jong H. P. , Wildevuur Ch. R. H. , Arends J. 
Published: December 2004

AbstractCell spreading and cell division rates of a transformed line of mouse lung fibroblasts were studied on various polymer surfaces in the presence of serum proteins. The bare polymer surfaces, as well as the protein‐coated surfaces, were characterized by their polar (γ) and dispersion (γ) surface free energies. Cell spreading appeared to be dependent on the polar surface free energy. Cell spreading is low when the γ of the bare surface is lower than 5 erg cm−2; marked spreading occurs when γ is higher than 15 erg cm−2. A similar relationship was found between cell spreading and polarity of the protein‐coated surfaces, although less pronounced than for the bare surfaces. Cell spreading appeared independent of the dispersion surface free energy. Cell division rate was the same on all surfaces tested.
The development of modified denture base materials
Authors: Abou‐Tabl Z. M. , Tidy D. C. , Combe E. C. , Grant A. A. 
Published: December 2004

AbstractThis work has been undertaken in an attempt to develop improved materials for the construction of dentures. In particular, a material was sought that would combine radiopacity with high impact resistance. Eight particulate radiopaque glasses were prepared and incorporated into poly(methyl methacrylate) denture base material, and the properties of the resultant composites were measured. Experiments were also carried out with glass fiber fillers, which were found to increase impact strength. It was shown that the incorporation of both a particulate radiopaque glass and glass fiber, 20% of each, yielded composites with improved properties.