bluuebunny/crossref_metadata_2025 huggingface dataset:
The Diastereoselective Formation of 1,2,4‐Trioxanes and 1,3‐Dioxolanes by the reaction of endoperoxides with chiral cyclohexanones
Authors: Jefford Charles W. , Jin Shu‐Juan , Bernardinelli Gérald
Published: December 2004

1,4‐Diphenyl‐2,3‐dioxabicyclo[2.2.1]hept‐5‐ene (2), on treatment with a catalytic amount of trimethylsilyl trifluoromethanesulfonate (Me3SiOTf) in CH2Cl2 at −78°, reacts with excess (−)‐menthone (10) to give (1S,2S,4′aS,5R,7′aS)‐4′a,7′a‐dihydro‐2‐isopropyl‐5‐methyl‐6′,7′‐diphenylspiro[cyclohexane‐1,3′‐[7′H]cyclopenta‐[1,2,4]trioxine] (11) and its (1R,2S,4′aR,5R,7′aR)‐diastereoisomer 12 in a 1:1 ratio and in 21% yield. Repeating the reaction with 1.1 equiv. of Me3SiOTf with respect to 2 affords 11, 12, and (1S,2S,3′a.R,5R,6′aS)‐3′a,6′a‐dihydro‐2‐isopropyl‐5‐methyl‐3′a‐phenoxy‐5′‐phenylspiro[cyclohexane‐l,2′‐[4′H]cyclopenta[1,3]dioxole] (13) together with its(1R,2S,3′aS,5R,6′aR)‐diastereoisomer 14 in a ratio of 3:3:3:1 and in 56% yield. (+)‐Nopinone(15) in excess reacts with 2 in the presence of 1.1 equiv. of Me3SiOTf to give a pair of 1,2,4‐trioxanes (16 and 17) analogous to 11 and 12, and a pair of 1,3‐dioxolanes (18 and 19) analogous to 13 and 14, in a ratio of 8:2:3:3 and in 85% yield. (−)‐Carvone and racemic 2‐(tert‐butyl)cyclohexanone under the same conditions behave like 15 and deliver pairs of diastereoisomeric trioxanes and dioxolanes. In general, catalytic amounts of Me3SiOTf give rise to trioxanes, whereas 1.5 equiv. overwhelmingly engender dioxolanes. Adamantan‐2‐one combines with 2 giving only (4′aRS,7′aRS)‐4′a,7′a‐dihydro‐6′.7′a‐diphenylspiro[adamantane‐2,3′‐[7′H]cyclopenta[1,2,4]trioxine] in 98% yield regardless of the amount of Me3SiOTf used. The reaction of 1,4‐dipheny 1‐2,3‐dioxabicyclo[2.2.2]oct‐5‐ene (32) with 10 and 1.1 equiv. of Me3SiOTf produces only the pair of trioxanes 33 and 34 homologous to 11 and 12. Treatment of the (S,S)‐diastereoisomer 33 with Zn and AcOH furnishes (1S,2S)‐1,4‐diphenylcyclohex‐3‐ene‐1,2‐diol. The crystal structures of 11–13 and 16 are obtained by X‐ray analysis. The reaction courses of 10 and the other chiral cyclohexanones with prochiral endoperoxides 2 and 32 to give trioxanes are rationalized in terms of the respective enantiomeric silylperoxy cations which are completely differentiated by the si and re faces of the ketone function. The origin of the 1,3‐dioxolanes is ascribed to 1,2 rearrangement of the corresponding trioxanes, which occurs with retention of configuration of the angular substituent.
Stereoselective Reactions of Phthalimido‐Substituted Radicals Derived from (±)‐Threonine: A comparison with reactions of N‐phthaloyliminium ions
Authors: Stojanovic Aleksandar , Renaud Philippe , Schenk Kurt
Published: December 2004

Stereoselective reactions of phthalimido‐substituted radicals derived from (±)‐threonine with different radical traps are reported (Scheme 3, Table 1). A strong influence of the nature of the radical trap on the stereoselectivity was noticed. Small nucleophilic radical traps gave preferentially the syn products. The observed selectivities are explained with the A1,3 strain model and depend on steric and electronic effects (Fig. 2). Reactions with electrophilic radical traps such as diphenyl diselenide gave the anti diastereoisomers with moderate stereocontrol, presumably due to stereoelectronic effects. The same stereochemical outcome, i.e., preferential formation of the anti products, was observed for the reactions of the related N‐phthaloyliminium ion (Scheme 5, Table 2). The stereochemistry of the ionic reaction is rationalized by a Felkin‐Anh model (Fig. 3).
An Unusual Acyliminium Cyclization and Other Drawbacks during an Attempted Synthesis of a Chiral Primary α‐Phosphinoalkanamine
Authors: Christoffers Jens
Published: December 2004

Studies towards the synthesis of a chiral primary α‐phosphinoalkanamine 1a are reported. O‐Activated. N‐carbamate‐protected phenylalaninol 3a did not undergo SN reaction with KPPh2: instead, after N‐deprotonation, intramolecular substitution led to formation of the aziridine derivative 5a (Scheme 2). N‐Phthalimido‐protected, O‐activated phenylalaninol 3b also underwent an intramolecular process on treatment with KPPh2, i.e., an unusual aryl‐acyliminium cyclization furnishing the (epoxymethano)isoindolo[1,2‐a]isoquinolinone 7 (Scheme 3). In a reaction with KPPh2, the N,N‐dibenzyl‐protected and activated phenylalaninol 3d finally yielded the intermolecular SN reaction product 2a (Scheme 4). However, debenzylation by catalytic hydrogenation turned out to be impossible.
Synthesis and Some Transformations of 2‐Acetamido‐5‐amino‐3,4,6‐tri‐O‐benzyl‐2,5‐dideoxy‐D‐glucono‐1,5‐lactam
Authors: Granier Thierry , Vasella Andrea
Published: December 2004

The lactam 21 was obtained in an overall yield of 72% from the hydroxy amide 16 by oxidation with the Dess‐Martin periodinane, acid‐catalysed isomerization of the oxidation products in toluene, whereupon 18/19 precipitated, and reductive dehydroxylation of 18/19 (Et3SiH/BF3 · OEt2; Scheme 1). The amide 16 was obtained by ammonolysis of the N‐acetylglucosamine‐derived lactone 15. Depending on the oxidation method, 16 yielded the keto amide 17, the hydroxy lactams 18/19, and the pyrrolidinecarboxamide 20 in widely different proportions. The pyrrolidinecarboxamide 20 was not reduced under the conditions of the reductive dehydroxylation. Hydrogenolysis of the benzyl‐protected lactam 21 gave the trihydroxy lactam 22, while reduction with NaBH4/BF3 · OEt2 led to the 2‐acetamidopiperidine derivative 24 (Scheme 2). Selective (tert‐butoxy)carbonylation of the lactam 21 (→ 25) followed by NaBH4 reduction and acid‐catalysed solvolysis in EtOH led to the α‐ethoxycarbamates 28/29. Similarly, (tert‐butoxy) carbonylation of 1 (→ 31) followed by reduction to 32/33 and glycosidation yielded the ethoxycarbamate 34. Treatment of the GlcNAc‐derived ethyl glycosides 28/29 with Me3SiCN/BF3 · OEt2 gave the equatorial amino nitrile 30. Under similar conditions, the Glc‐derived glycoside 34 led to the iminooxazolidinone 35. In the presence of a larger proportion of Me3SiCN at 5°, 34 was transformed into the axial, selectively monodebenzylated amino nitrile 36.
Heterosupramolecular Chemistry: Synthetic strategies for the covalent and noncovalent assembly and organization of nanocrystals and molecules
Authors: Rao S. Nagarajo , Fitzmaurice Donald
Published: December 2004

Described are the preparation of nanocrystals and the synthesis of molecules that may be covalently or noncovalently assembled in solution to yield heterosupermolecules possessing a well‐defined heterosupramolecular function. Also described are preparative and synthetic methods that yield organized assemblies of heterosupermolecules possessing an addressable heterosupramolecular function. Finally, the development of these synthetic strategies to permit the covalent and noncovalent assembly and organization of a wide range of condensed phase and molecular components is outlined.
Synthesis of Oligo(3‐hydroxybutanoate)(OHB)‐Containing Peptides with High Binding Affinity to a Class‐I‐MHC Protein
Authors: Seebach Dieter , Poenaru Sorana , Folkers Gerd , Rognan Didier
Published: December 2004

In the center of the immune system, there are major histocompatibility (MHC) protein/nonapeptide complexes which are recognized by T cell. The nonapeptides consist of three regions, an N‐terminal one containing three amino‐acid residues with a mandatory arginine in position 2, a C‐terminal one with a lysine or arginine in position 9, and a central, variable one of five residues (cf. Fig. 1). We have now synthesized the first conjugates (1–4) of oligopeptides with oligo[(R)‐3‐hydroxybutanoates] (OHB) as analogs of MHC‐binding peptides. Of the approaches chosen (Scheme 1), a fragment coupling of a hydroxy‐butanoyl‐amido ester (17 and 19) with an [(aminoalkanoyl)oxy]butanoyl chloride (27; Scheme 3), followed by two peptide‐coupling steps (Scheme 4), turned out to be most efficient. The conjugates H‐Gln‐Arg‐Leu‐(HB)3,4‐Lys‐OH (1 and 2) and H‐Ala‐Arg‐Leu‐(HB)3,4‐Lys‐OH (3 and 4) were thus obtained in pure form. The conjugates 1 and 2 with N‐terminal glutamine have a tendency to undergo cyclization with formation of a pyroglutamate residue (ef. Fig. 2). CD Measurements at different temperatures and so‐called epitope‐stabilization assays show that the complexes of the conjugates 2 and 4, containing four HB units, with the HLA‐B27 class‐I‐MHC protein are more stable than those of a model nonapeptide (C50 values of 2.25 and 1.60 μM vs. 10 μM), while the conjugates 1 and 3 with three HB units incorporated form less stable complexes (C50 values of 30 and 21 μM). The tetra(hydroxybutanoate)‐peptide conjugates 2 and 4 are the first nonapeptide analogs for which the modification of the central part leads to increased affinities for a class‐I‐MHC protein, as compared to a model nonapeptide.
A Novel and Efficient Synthesis of 14‐Alkoxy‐Substituted Indolo‐ and Benzofuromorphinans in the Series of Selective δ Opioid Receptor Antagonists
Authors: Schmidhammer Helmut , Schwarz Peter , Wei Zhong‐Yong
Published: December 2004

A novel and more efficient synthesis of 14‐alkoxy‐substituted indolo‐ and benzofuro‐morphinans in three steps starting from either naltrindole (1) or naltriben (2), using methoxymethyl or silyl protecting groups, is reported. The 14‐O‐alkyl group is introduced at the penultimate step of the procedure. This is an additional advantage of the described procedure since the late introduction of the 14‐O‐alkyl group makes it much easier to produce a greater diversity of 14‐alkoxy derivatives in this series of δ opioid receptor antagonists. Thus, compounds 14–19, 20–25, and 27–29 were synthesized.
Synthesis of Thiophene‐Substituted 3H‐Naphtho[2,1‐b]pyrans, Precursors of Photomodulated Materials
Authors: Moustrou Corinne , Rebière Nicole , Samat André , Guglielmetti Robert , Yassar Abd Errahim , Dubest Roger , Aubard Jean
Published: December 2004

The synthesis of 3H‐naphtho[2,1‐b]pyrans 9–21 linked to a thiophene moiety is described. Two different synthetic approaches were applied to prepare these novel functionalized compounds, and their spectrokinetic properties in solution are reported.
Theoretical Parameters to Characterize Antioxidants. Part 2. The cases of melatonin and carvedilol
Authors: Migliavacca Eugenia , Ancerewicz Jacek , Carrupt Pierre‐Alain , Testa Bernard
Published: December 2004

This theoretical study focuses on two indole derivatives, melatonin (1) and carvedilol (8), with the objective of improving our understanding of the molecular mechanisms underlying their radical‐scavenging activity. Quantum‐mechanical calculations were carried out using the AM1 semi‐empirical method, some results being confirmed by ab initio (3‐21G) calculations. The quantum‐chemical descriptor Δ Hox (relative adiabatic oxidation potential) and the shape of the SOMO (singly occupied molecular orbital) indicate that the stabilization of its radical cation can partially explain the well‐documented antioxidant efficacy of melatonin. This stablization may result from electrostatic interactions and from a hyperconjugative effect existing in a family of conformers of the melatonin radical cation having the side chain almost perpendicular to the plane of the aromatic rings. Furthermore, 6‐hydroxymelatonin (7) appears to be a better free‐radical scavenger than melatonin (1) in agreement with experimental results. According to the theoretical parameters Δ Hox and Δ Habs (relative bond dissociation enthalpy), carvedilol (8) is not a good antioxidant, in contrast to its ring‐hydroxylated metabolites whose powerful antioxidant effects are explained by the formation of an oxyl radical stabilized by delocalization over the carbazole nucleus.
Lipase‐Catalyzed Acetylation of 3‐Substituted 2,3‐Dihydro‐1H‐1,4‐benzodiazepin‐2‐ones: Effect of temperature and conformation on enantioselectivity and configuration
Authors: Avdagić Amir , Lesac Andreja , Majer Zsuzsa , Hollòsi Miklòs , Šunjić Vitomir
Published: December 2004

Enantioselectivity of acetylation by vinyl acetate/AcOEt catalyzed by immobilized Candida antarctica lipase (Novozym 435) is studied for rac‐3‐(hydroxymethyl)‐1,4‐benzodiazepin‐2‐ones 7, 9, 14 (n = 1; number of CH2 groups in the chain at C(3)), 20 (n = 2), and for prochiral 3,3‐bis(hydroxymethyl) derivative 16. Enantiomeric excess (ee [%]) is correlated with conformational properties of substrates (relative conformation, energy difference between two boat‐like ground‐state conformations, ring‐inversion barrier) as determined by DNMR and MM2 calculations. (3S)‐Enantiomers of acetates (+)‐8, (+)‐10, (+)‐15, and (+)‐21 were preferentially formed. In the case of the acetate (−)‐17 (ee 90.2%), formation of the (3R)‐enantiomer was favored. C(3)OH Group with hemiaminal‐like character in rac‐3 (n = 0) cannot be acetylated by any of 23 tested lipases and four esterases. For racemic alcohols 7, 9, 14, and 20, preferred acetylationof the (3S)‐enantiomers, present in solution in absolute (M)‐conformation, was established; only in prochiral diol 16 (n = 1) the CH2OH group in the (pro‐R)‐position is prevalently acetylated, presumably due to the binding to the enzyme, in absolute (P)‐conformation. Temperature dependence of enantioselectivity revealed inverse correlation of the E value of rac‐9, and ee values for prochiral 16, with T[K], indicating prevalent contribution of the enthalpy term to enantioselection. Absolute conformation (M/P) and absolute configuration at C(3) of all products was determined by combining CD and 1H‐NMR data.
The effect of the cooling rate of dental alloys on their amalgamation properties
Authors: Johnson L. B. , Carwile A. C.
Published: December 2004

Silver–tin alloys of various compositions (60–80 atomic % Ag) have been prepared from the melt using cooling rates from about 50°C/hr to about 106°C/sec. Structural differences due to the different cooling rates were shown by metallographic and x‐ray diffraction techniques. From each composition and cooling rate, powders were then prepared and amalgamated. The amalgams were tested for Hg content, dimensional change during setting, and tensile strength. Changes in cooling rates had some effect on the relative amounts of phases present but primarily affected the grain sizes. In general, the faster the cooling rate, the smaller the grain size; the smaller the grain size, the faster and more uniform the amalgamation; the more uniform the amalgamation, the stronger the amalgam. Storage of the alloy powders at room temperature slowed their amalgamation rates, destroyed their uniformity, and resulted in weaker amalgams. However, no phase changes were observed by x‐ray diffraction in the freshly comminuted alloys after aging at room temperature for two months.
The effect of shear, specific surface, and air interface on the development of blood emboli and hemolysis
Authors: Solen Kenneth A. , Whiffen James D. , Lightfoot Edwin N.
Published: December 2004

Heparinized dog blood was exposed to shear and foreign surfaces in conicylindrical test cells. The cells were injection molded from polycarbonate and were filled using a technique that avoided contact of the blood with air. Particulate‐matter formation was measured and was found to be dominated by the surface‐to‐blood–volume ratio and to be independent of shear rate. Hemolysis was also measured and was found to vary linearly with shear rate and to increase with increasing surface‐to‐blood volume ratio. Thus, at low shear rates and high specific surface conditions, the degree of hemolysis was found to be minimal while particulate‐matter formation was high. The results suggest that the safety of extracorporeal perfusion procedures cannot be inferred from hemolysis measurements alone. In one series of tests, a gas–blood interface was generated at a rate equivalent to the rate of surface renewal in conventional disc oxygenators. The gas–blood interface failed to contribute significantly to the damage indices, which suggests that the apparent superiority of membrane oxygenators may be a result of factors other than the absence of a blood–gas interface.
Biocompatibility tests of components of an implantable cardiac assist device
Authors: von Recum Andreas F. , Imamura Hiroji , Freed Paul S. , Kantrowitz Adrian , Chen Shan‐Te , Ekstrom Merlin E. , Baechler Charles A. , Barnhart Marion I.
Published: December 2004

A permanently implantable in‐series left ventricular assist device, the dynamic aortic patch (DAP), has been tested in chronic animal experiments. The DAP replaces a section of the intrathoracic aortic wall. Hemothorax and hematocele at the implantation site have been complications in recent experiments. Primary postoperative hemorrhage was ruled out, and the biocompatibility of all components was therefore examined. Dacron velour, Teflon felt, conductive polyurethane, segmented polyether polyurethane, and Teflon‐coated polyester fiber sutures were implanted in the pleural cavities of dogs and tested in vitro by culturing canine saphenous vein explants on them. In vivo experiments demonstrated that all components elicited mild to moderate inflammatory reactions, but hematocele occurred only when the components were implanted in the aorta with direct blood contact and exposed to arterial blood pressures. In vitro, cells were cultured on all components with no signs of toxic reactions. These results indicated that the host tolerated all implant components without major inflammatory responses. However, histological data indicated that chronic slow bleeding into or through the Dacron velour in contact with the arterial blood serum could account for hemothorax or hematocele formation. Therefore, a configuration of the assist device using materials impermeable to blood may obviate these difficulties.
Histopathology and metallurgical analysis of a removed Lane plate at 53 years postimplantation: A case report
Authors: Tarr Richard R. , Jorge Rolando , Latta Loren L. , Ghandur‐Mnaymneh Latifa
Published: December 2004

A vanadium steel Lane plate with nickel coating and low grade steel screws were removed from a patient 53 years postimplantation. Corrosion of the parts was extreme, but the reaction in the surrounding tissues was surprisingly quiescent under the circumstances. By today's standards, the materials, their application, and their performance were totally unacceptable. However, the biological system tolerated this “insult” well.
Water sorption and mechanical properties of 2‐hydroxyethyl‐methacrylate and methylmethacrylate copolymers
Authors: Migliaresi C. , Nicodemo L. , Nicolais L. , Passerini P. , Stol M. , Hrouz J. , Cefelin P.
Published: December 2004

Randomly cross‐linked copolymers of 2‐hydroxyethyl‐methacrylate (HEMA) and methyl‐methacrylate (MMA) have been prepared and studied in the dry and swollen state. Tensile and indentation tests indicate that by changing the composition of copolymers, it is possible to obtain materials with a wide range of mechanical properties and corresponding glass transition temperatures. Water diffusion coefficients in sorption and desorption experiments have been calculated and compared.
Biodegradable PEO/PLA block copolymers
Authors: Cohn Daniel , Younes Hani
Published: December 2004

Poly(ether ester) block copolymers based on polyethylene oxide (PEO) and polylactic acid (PLA) segments were synthesized and characterized, with the aim of developing a new family of bioabsorbable polymers. The materials developed were tailored to meet various mechanical and degradation requirements, and overcome the limitations of the few existing biodegradable polymers. The copolymeric matrices were characterized by means of infrared spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance spectroscopy. The composition of the copolymers synthesized varied between 20 and 84 mol% lactic acid, with PEO chains in the 600–6000 molecular weight range. The solubility properties of the copolymers in a series of organic solvents are described. The equilibrium water content and the water contact angle of various matrices were determined and related to their composition and structure. The incorporation of PEO into the chain yielded highly hydrophilic materials, with equilibrium water contents higher than 60%. Stress/strain curves are presented.
Characterization of alkyl grafted polyurethane block copolymers by variable takeoff angle X‐ray photoelectron spectroscopy
Authors: Grasel Timothy G. , Castner David G. , Ratner Buddy D. , Cooper Stuart L.
Published: December 2004

Variable takeoff angle x‐ray photoelectron spectroscopy was used to determine the surface composition of five polyurethane block copolymers. The high‐resolution C1s spectra from all five polyurethane samples had peaks at binding energies of 285.0, 286.5, and 289.5 eV, which are consistent with the presence of hydrocarbon, ether, and urethane carbon species. Both the measured elemental compositions at the low takeoff angles (deepest sampling depths) and the calculated elemental compositions for depths > 15 Å generally showed good agreement with the expected bulk compositions. The outer 15 Å of the surface of all five samples was depleted in the nitrogen‐containing hard segment. For the base polyurethane sample in this series, an enrichment of the poly(tetramethylene oxide) soft segment and the presence of an organic silicone impurity were detected. Doubling the chain length of both the hard and soft segments resulted in a further decrease of the hard segment concentration in the outer surface of the sample. The grafting of C2 and C18 alkyl groups onto 10 or 20% of the ure‐thane linkages resulted in an increase in the percentage of aliphatic carbon species present on the surface. In the case of the C18‐alkylated material, the presence of alkyl chains at the surface was inferred using contact angle measurements.
Adherence of coagulase‐negative staphylococci to heparin and other glycosaminoglycans immobilized on polymer surfaces
Authors: Paulsson Marianne , Gouda Ibrahim , Larm Olle , Ljungh Åsa
Published: December 2004

The adherence of clinical isolates of staphylococci to surfaces immobilized with various glycosaminoglycans (GAGs) was studied. In general, cells of strains of coagulase‐negative (CNS) staphylococci showed a greater adherence to polyethylene surfaces than did cells of Staphylococcus aureus, as studied by bioluminescence. When the surface was heparinized, the adherence of staphylococcal cells decreased, but CNS cells still adhered in greater numbers than did cells of S. aureus. The adherence of CNS to serum‐coated heparinized surfaces was of the same magnitude, or increased compared with nonheparinized surfaces. When the surfaces were preasorbed with different proteins with known heparinbinding domains, i.e., vitronectin, fibronectin, laminin, or collagen, the S. epidermidis cells showed higher binding to heparinized surfaces than to nonheparinized ones, and also in greater numbers than did other staphylococcal cells. Different CNS strains showed a greater ability to agglutinate polystyrene beads immobilized with heparin than did S. aureus. The adherence of S. epidermidis strain 3380 to polyethylene coated with various GAGs such as heparin and chondroitin, dextran, dermatan, and heparan sulfate was shown to be pH‐dependent, with the highest adherence at pH 7.2. This may indicate that CNS have the ability to bind to other domains of host proteins when they are adsorbed to heparinized surfaces, versus to nonheparinized ones. © 1994 John Wiley & Sons, Inc.
Synthesis, surface, and cell‐adhesion properties of polyurethanes containing covalently grafted RGD‐peptides
Authors: Lin Horng‐Ban , Sun Wen , Mosher Deane F. , García‐Echeverría Carlos , Schaufelberger Kenneth , Lelkes Peter I. , Cooper Stuart L.
Published: December 2004

In an attempt to improve endothelial cell adhesion and growth on a polyurethane copolymer, cell adhesive RGD‐containing peptides were grafted to the polymer backbone. Two peptide grafting reaction schemes, including one‐step and two‐step approaches, were developed. FTIR and amino acid analysis confirmed that coupling of the peptide to the polyurethane backbone was achieved by both the one‐step and two‐step methods. However, the two‐step approach showed a higher peptide coupling efficiency and resulted in better control of the orientation of the grafted peptide. The two‐step reaction scheme was used to prepare Gly‐Arg‐Gly‐Asp‐Ser‐Tyr (GRGDSY), Gly‐Arg‐Gly‐Asp‐Val‐Tyr (GRGDVY), and Gly‐Arg‐Gly‐Glu‐Ser‐Tyr (GRGESY) peptide‐grafted polyurethanes with two different peptide densities (100 and 250 μmol/g polymer). Dynamic contact angle measurements indicated that the surfaces of the peptide‐grafted polyurethanes were more hydrophilic than the starting and carboxylated versions of the precursor polyurethane. In addition, the surface hydrophilicity of the peptide‐grafted polymers increased with increasing bulk peptide density. Electron spectroscopy for chemical analysis suggested that the grafted peptide was present at the polymer—air interface, in vacuo, for the peptide‐grafted polyurethanes. The surface peptide density appeared to correlate with the incorporated peptide density in the bulk. In vitro endothelial cell adhesion experiments showed that, without the presence of serum in culture medium, the GRGDVSY‐ and GRGDVY‐grafted polyurethanes dramatically enhanced cell attachment and spreading compared with the starting, carboxylated, and GRGESY‐grafted polymers. Increasing the peptide density from 100 to 250 μmol/g polymer for the GRGDSY‐ grafted polyurethanes resulted in an increase in cell attachment. With approximately the same peptide density (100 or 250 μmol/g polymer), the GRGDVY‐grafted polymers supported more adherent cells than did the GRGDSY‐grafted polymers. Similar trends were observed in the in vitro endothelial cell growth studies using culture medium containing serum and endothelial cell growth supplement. The GRGDSY‐ and GRGDVY‐grafted polyurethanes promoted more cell growth than did the starting polyurethane. However, the presence of adhesive serum proteins and growth factor diminished the differences between the cell‐adhesive peptide grafted polymers and the GRGESY‐grafted polymers. © 1994 John Wiley & Sons, Inc.
Degradation of polyetherurethane by subcutaneous implantation into rats. I. Molecular weight change and surface morphology
Authors: Xi Tingfei , Sato Michio , Nakamura Akitada , Kawasaki Yasushi , Umemura Takashi , Tsuda Mitsuhiro , Kurokawa Yuji
Published: December 2004

Two kinds of polyetherurethane (PEU), U‐3 and U‐8, were coated in thin layers on an ethylene‐vinylalcohol copolymer (EVAL) film 0.1 mm thick. U‐3 is a nonsegmented PEU prepared from 4,4′‐diisocyanatodiphenylmethane (MDI) and poly(tetramethylene oxide) of Mn = 1,000 (PTMO 1000), and U‐8 is a segmented PEU prepared from MDI, PTMO 1000, and 1,4‐butanediol. The coating thicknesses were 0.0068 and 0.022 mm for U‐3 and U‐8, respectively. These coated films were implanted subcutaneously into rats and retrieved after various weeks. The coatings on the retrieved samples were dissolved in tetrahydrofuran (THF), and the average molecular weight (MW) was determined by injecting the THF solution into a gel permeation chromatograph. In the case of U‐3, MW increased after 2 weeks, then decreased over the implantation period. After 10 weeks, U‐3 almost disappeared from the base film. In the case of U‐8, MW reached the maximum at 4 weeks postimplantation then decreased gradually over the implantation period. The rate and degree of MW change were greater in U‐3 than in U‐8. Here, we argue that, in the early stage, low molecular weight PTMO/MDI oligomers leached out from the PEUs to the inflammatory exudate to increase MW, and in the later stage macrophage attachment/activation had a role in the degradation of PEUs. The surface morphologic changes observed by scanning electron microscopy are also discussed. © 1994 John Wiley & Sons, Inc.
Biocompatibility of a biodegradable matrix used as a skin substitute: An in vivo evaluation
Authors: Beumer G. J. , van Blitterswijk C. A. , Ponec M.
Published: December 2004

Synthetic biodegradable polymeric matrices, with a dense top layer and porous under‐layer, made of a (poly)ether/(poly)ester (PEO:PBT) copolymer called PolyactiveTM, and also of poly‐L‐lactide (PLLA), are under investigation as part of a cell‐seeded skin substitute for third‐degree, large‐scale skin defects. The biocompatibility of subcutaneously implanted matrices representing large body surface areas, were studied at 2, 4, 13, 26, and 52 weeks in rats. To investigate local or systemic effects, the weight development of the complete animal and of their hearts, kidneys, lungs, livers, and spleens, as well as the macroscopic and histologic appearance of the implants and organs, were monitored. Early inflammatory response was associated with surgical implantation trauma. All matrices showed neovascular and fibrous tissue ingrowth into the porous underlayer within 2–4 weeks after implantation. Copolymeric and PLLA matrices increasingly fragmented and liquified. After 1 year, small polymeric fragments embedded in fibrous, vascularized tissue could be retrieved at the implantation site. No systemic effects of the implants on the organs or on the animal as a whole were observed. These results and earlier studies on (skin) cell substrate properties and physicochemical characteristics of the matrices indicate the suitability of the matrices as part of a cell‐seeded skin substitute. © 1994 John Wiley & Sons, Inc.
Ab initio studies of RO− … HOR′ complexes. Solvent effects on the relative acidities of water and methanol
Authors: Jorgensen William L. , Ibrahim Mustafa
Published: December 2004

Ab initio molecular orbital calculations are reported for complexes of hydroxide and methoxide anions with water and methanol. The basis set dependence of the results is carefully considered for HO− ⃛ H2O. 4‐31G and 6‐31G* calculations yield similar geometrical predictions; however, the 6‐31G* basis set is superior for computing dissociation energies. Further extension to the 6‐31G** level provides little change. The dissociation energies for the complexes range from 25 to 37 kcal/mole with hydroxide ion and methanol acting as the strongest base and acid. The difference in gas phase acidities of water and methanol is halved by the introduction of one solvent molecule.
On the OCS2 Singlet potential energy surface
Authors: Carlsen Lars
Published: December 2004

The reaction between atomic oxygen and carbon disulfide is predicted to lead to at least two primary products, which are the dithiiranone (1) and the oxathiirane‐thione (2) and/or the carbon disulfide S‐oxide (4). The possible intramolecular equilibria 1 ⇄ 2, 1 ⇄ 3, 2 ⇄ 4, and 2 ⇄ 5 as well as the fragmentations of the possible intermediates 1–5 have been studied theoretically within the semiempirical CNDO/B framework as conceivable ground‐state reactions. On the basis of MO correlations and potential energy changes along the reaction paths, supplementary with previously reported experimental data, the single molecular transformations and the eventual product formations are discussed.
Approaches to charge calculations in molecular mechanics
Authors: Abraham Raymond J. , Griffiths Lee , Loftus Philip
Published: December 2004

Alternative methods of estimating atomic charges in haloalkanes are presented, derived from quantum mechanical and classical treatments. A scheme based on a breakdown of the transmission of charge by polar atoms into one‐bond, two‐bond, and three‐bond additive contributions is given, in which the one‐bond effect is proportional to the difference in the electronegativities of the bonded atoms, and the two‐ and three‐bond effects functions of the atomic electronegativity and polarizability. Suitable developments of the basic scheme, including an iterative self‐consistent process, give calculated dipole moments for a variety of haloalkanes in good agreement with the observed values. The atomic charges obtained by this scheme are compared with other estimates of these charges. They are similar to those derived from a simple LCAO–MO scheme but differ from those obtained by population analysis of more refined quantum mechanical calculations.
Electronic structure of UH, UF, and their ions
Authors: Krauss M. , Stevens W. J.
Published: December 2004

A relativistic effective core potential (REP) has been generated for the uranium atom and used in self‐consistent‐field calculations of the A states of UH, UF, and their ions. Energy curves were calculated at the base configuration level which ensures the dissociating atoms are described by Hartree–Fock wavefunctions. The electronic bonding of these molecules is found to be similar to that of comparable alkaline–earth hydrides and fluorides. The uranium 6p, 6d, and 5f orbitals retain their atomic character but the orbitals extend into the bonding region and are distorted by overlap repulsion and electrostatic effects. Nonetheless, the atomic energetic coupling determines that low energy states will have the maximum spin multiplicity and maximum orbital angular momentum projection consonant with the charge‐transfer bonding.
The use of CNDO/force and compliance constant methods in evaluating quadratic potential functions of carbonyl and formyl fluorides
Authors: Murthy A. S. N. , Ranganathan Shoba
Published: December 2004

CNDO/Force and compliance constant methods were applied to define general quadratic potential functions for F2CO and HCOF. A satisfactory set of compliants was obtained by suitably scaling down the stretching and stretch–stretch elements of the initial force constant matrix, evaluated by the CNDO/force approach, followed by fitting the compliants to available experimental data.
A theoretical study of the interaction of monomethylammonium with double‐stranded oligonucleotides
Authors: Gresh Nohad
Published: December 2004

Theoretical computations are performed of the interaction specificities of the monomethylammoniumion with double‐stranded oligonucleotides (dPu)n·(dPy)n in the B‐DNA conformation. The effects of base sequence and chain length are examined. In short oligomers (n = 2, 3), the interaction energies of the cation are larger in the major groove of (dG)n·(dC)n than in the minor groove of (dA)n·(dT)n. As a consequence of further shaping of the grooves and building up of the phosphates, a marked reversal in the affinities of the cation for the grooves occurs at the (dPu)5·(dPy)5 and the p(dPu)5p·p(dPy)5p levels: it is the binding in the minor groove of the adenine‐thymine oligomers that provides then the most favorable interaction energies.

It is also shown, at the level of the double helices built from dinucleoside monophosphates, that the interaction of monomethylammonium in the minor groove occurs in specific configurations involving the three NH bonds of the cation, and two successive bases on one strand; this binding is sequence‐specific, the order of inherent preferences being (TpA) > (TpT) > (ApA) > (ApT).
Implementation of an electronic structure program system on the CYBER 205
Authors: Ahlrichs Reinhart , Böhm Hans‐Joachim , Ehrhardt Claus , Scharf Peter , Schiffer Heinz , Lischka Hans , Schindler Michael
Published: December 2004

The CGTO integral evaluation, SCF, SCF‐gradient, integral transformation, and MR‐CI (SD) steps of the COLUMBUS system of programs have been adapted for the CYBER 205. A description is given of our efforts and the partly heavy modifications necessary to exploit the potential of this supercomputer and to avoid its shortcomings. Typical timings are reported, vector and scalar performance are compared.
Cluster analysis of periodic distributions; application to conformational analysis
Authors: Nørskov‐Lauritsen L. , Bürgi H. B.
Published: December 2004

A method is described to analyze observed conformations for molecular fragments with more than three torsional degrees of freedom. The method is an adaption of statistical cluster analysis to multidimensional, symmetric, periodic distributions of data points. Application to the molecular fragment M(PPh3)2 with eight torsional degrees of freedom reveals a model of conformational interconversion. The model implies gearing motion of the two PC3 fragments alternating with stepwise inversions of the helicities of the PPh3‐propellers.
Microscopic effect of an applied voltage on the solvated gramicidin a transmembrane channel in the presence of Na+and K+cations
Authors: Kim Kwang S.
Published: December 2004

Using the previously reportedab initiointeraction energies among K+, Na+, water, and Gramicidin A (GA), this report presents Monte Carlo simulations for the microscopic effect of an applied voltage (0.5 V/32 Å) on a solvated gramicidin. The reorientation of water molecules due to the applied voltage is found to be marginal for both cations. The energy contribution due to water dipoles was within 10% of the total energy contribution due to the applied voltage. Inside the channel the total energy contribution varied almost linearly along the channel axis; outside the channel the slope of the total energy contribution with respect to the channel axis decreased.
An MNDO treatment of sigma values
Authors: Gilliom Richard D. , Beck Jean‐Paul , Purcell William P.
Published: December 2004

The Hammett σ and Taft σ0 constants have been examined using the MNDO computational procedure. They are both best explained by using computed properties based upon the benzoate ion, especially the reciprocal of the energy of the highest occupied molecular orbital.
Ishtar: An interactive system for quantitative investigation on dipolar and quadrupolar spin‐lattice relaxation
Authors: Allouche A. , Pouzard G.
Published: December 2004

Within the model of anisotropic rotational diffusion, the quantitative treatment of dipolar and quadrupolar spin‐lattice relaxation provides valuable information about molecular structures and molecular associations. When quadrupolar relaxation is involved, the title program calculates: (1) the electric field gradient tensor (EFGT) which is diagonalized; (2) the assymetry parameter, the components of the principal axes of the EFGT in the molecular frame of reference and the quadrupole coupling constant; and (3) the rotational diffusion constants which are iteratively determined from the experimental quadrupolar relaxation times. Analogously, for dipolar relaxation ISHTAR calculates the tensor of inertia, the diagonalization of which leads to diffusion constants and free rotor correlation times and the rotational diffusion constants from the experimental spectral densities.
Characteristic polynomials of organic polymers and periodic structures
Authors: Balasubramanian K.
Published: December 2004

It is shown that the Frame's method (also, Le Verrier‐Faddeev's method) for characteristic polynomials of chemical graphs can be extended to periodic graphs and structures. The finite periodic structures are represented by cyclic structures in the Born‐von Kárman boundary condition which leads to complex matrices. In this article we demonstrate that our earlier computer program (based on Frame's method) can be extended to these periodic networks. The characteristic polynomials of several lattices such as polydiacetylenes, one‐dimensional triangular, square, and hexagonal lattices are obtained. These polynomials can be obtained with very little computer time using this method.
A fast algorithm for the interactive docking maneuver with flexible macromolecules and probes
Authors: Karfunkel H. R.
Published: December 2004

A new algorithm for the interactive docking maneuver is presented. Full attention is given to the flexibility of both substrate and macromolecule, i.e., all the fragments are allowed to move. It is assumed that any numerical quantity which depends only on the isolated macromolecule at energy minimum is disposable when approximate expressions are derived. The central idea is the concept of relevant docking coordinates which reflect the essential features of the macromolecular deformations during the docking maneuver and which substantially diminish the number of considered degrees of freedom (DF). The conformational energy is divided into two parts. The first part, represented by condensed potential functions, needs no approximations. For the second part, termed Erest, a quadratic approximation in the subspace spanned by the relevant docking coordinates is used. All the pairwise interactions between the atoms of the macromolecule are eliminated. A simple computational example using the ECEPP force field is given. Atomic coordinate computations are simplified by the introduction of virtual rotation axes for the backbone. In connection with drug design the concept of pressure pattern is defined and related to quantities appearing in the energy gradient. Extensions to substrate induced allosteric transitions are discussed.
Sensitivity and uncertainty of reaction mechanisms for photochemical air pollution
Authors: Falls Andrew H. , McRae Gregory J. , Seinfeld John H.
Published: December 2004

A sensitivity/uncertainty analysis is performed on a mechanism describing the chemistry of the polluted troposphere. General features of the photochemical reaction system are outlined together with an assessment of the uncertainties associated with the formulations of mechanistic details and rate data. The combined effects of sensitivity and uncertainty are determined using the Fourier amplitude sensitivity test (FAST) method. The results of this analysis identify the key parameters influencing the chemistry of NO2, O3, and PAN. Based on these findings, a series of recommendations are made for future experimental kinetic studies.
The kinetics of the addition of alkyl radicals to carbonyl groups. Part I. The addition of methyl radicals to hexafluoroacetone in the gas phase. The formation of the hexafluoro‐t‐butoxy radical
Authors: Drew Roger M. , Kerr J. Alistair
Published: December 2004

By pyrolyzing di‐t‐butyl peroxide over the temperature range of 405–450 K in the presence of hexafluoroacetone the kinetics of the addition reaction (1), CH3 + (CF3)2CO→; (CF3)2C(Ȯ)CH3, have been studied. Detailed analyses have shown that the principal product of the adduct radical, (CF3)2C(Ȯ)CH3, is CF3COCH3 from reaction (2), (CF3)2C(Ȯ)CH3 → CF3COCH3 + CF3. The rate constant of the addition reaction was determined to be k1(dm3/mol·s) = (1.1 ± 4.0) + 109 exp(‐(3680 ± 480)/T) over the temperature range 405–450 K, based on the value k3 = 2.2 × 1010 dm3/mol·s for reaction (3), 2CH3 → C2H6. The results are discussed in relation to existing data for radical additions to carbonyl groups.
Über den Angriff von heißem Imprägnieröl auf Stahlblech und seine Verhütung
Authors: Schikorr G.
Published: December 2004

Die durchgeführte Untersuchung zeigte folgende Ergebnisse: Imprägnieröl kann Eisen in sehr erheblichem Ausmaß angreifen. Der Angriff nimmt mit steigender Temperatur zu und beträgt bei 240° etwa 200 g/m2.Tg. Er ist auf die sauren Bestandteile des Imprägnieröls zurückzuführen und kann durch Zugabe von etwa I % Calciumoxyd praktisch vollständig verhindert werden.
Wash‐Primer als Metall‐Vorbehandlung und universeller Haftgrund
Authors: Sarx H. F.
Published: December 2004

Aufgabe, Anwendungsmöglichkeit und Grenzen dieses Anstrichmittels, dem immer stärkere Bedeutung zukommt, sind in DIN E 55945 festgelegt.

Wash‐Primer ist ein haftungsvermittelndes und passivierendes Mittel zur Metallvorbehandlung. Er wird in 2 Komponenten geliefert, deren wesentliche Bestandteile bei der einen aus Polyvinylbutyral und einem speziell entwickelten Zinkchromat, bei der anderen aus Phosphorsäure bestehen. Bei der Anwendung auf Metall wird neben einer ausgezeichneten Haftung eine Passivierung der Metalloberfläche, z. B. auf Eisen und Leichtmetall, erzielt.

Auch auf nichtmetallischen Stoffen wie Glas, Hartfaserplatten, Bakelit‐Preßmassen und Beton ist das Problem der Anstrichhaftung durch Wash‐Primer in überzeugender Weise zu lösen.

Mit dem sog. Eintopf‐Wash‐Primer wurde die universelle Wirkung des 2‐Komponenten‐Primers nicht erreicht.

Da nach etwa 8 h die Umsetzung der Mischung soweit fortgeschritten ist, daß beim Auftragen die Haftung nicht mehr voll entwickelt werden kann, soll erst kurz vor der Verarbeitung gemischt werden. Die Konsistenz ist so zu wählen, daß ein Eindringen in tiefe Poren unter Ausbildung eines sehr dünnen Filmes gewährleistet ist.

Eim Wash‐Primer‐Film gewährleistet keinen Korrosionsschutz über eine längere Zeit und erübrigt auch die eigentliche Grundierung nicht. Der Auftrag eines weiteren dem Untergrund angepaßten Anstriches sollte deshalb bei Anwendung im Freien nach einigen Tagen, bei Anwendung in hallen in einigen Wochen, vorgenommen werden.
Zum Zusammenhang zwischen Eigenschaften und Gefügestruktur mehrphasiger Werkstoffe Teil I: Zielsetzung, Kenntnisstand und stereologische Beschreibung der Gefügestruktur
Authors: Ondracek G.
Published: December 2004

Die Eigenschaften mehrphasiger Werkstoffe hangen von den Eigenschaften ihrer Phasen und deren Geometrie und geometrischer Anordnung (Gefügestruktur) ab. Mikroskopische Gefügebilder mehrphasiger Werkstoffe sind vielfach auch dann verfügbar, wenn der Werkstoff extremen Zustandsbedingungen ausgesetzt ist (z. B. hohe Temperaturen, radioaktive Strahlung), unter denen Eigenschaftsmessungen unmöglich oder schwierig und daher aufwendig und/oder ungenau sind. Durch stereologische Gefügeanalyse kann aus solchen Gefügebildern die Gefügestruktur ermittelt werden. – Die Kenntnis des quantitativen Zusammenhangs zwischen Gefügestruktur und Eigenschaften würde dann die direkte Messung von Eigenschaftskenngrößen ersetzbar machen durch eine stereologische Gefügeanalyse. Da dies nicht nur für extreme Zustandsbedingungen gilt, würde die stereologische Gefügeanalyse in der konventionellen Qualitätskontrolle, ebenfalls ohne Eigenschaftsmessungen, Aussagen über Eigenschaftskenngrößen erlauben. Außerdem vertiefen solche Gefüge‐Eigenschafts‐Beziehungen das physikalische Verständnis des Verhaltens von Werkstoffen mit bestimmter Gefügestruktur und ermöglichen die Vorausberechnung von Eigenschaftsverbesserungen durch Gefügeoptimierung.

Diese Arbeit handelt in 4 Teilen die Ableitung und experimentelle Prüfung quantitativer Beziehungen zwischen der Gefügestruktur und der Leitfähigkeit, dem Elastizitätsmodul sowie dem thermischen Ausdehnungskoeffizienten zweiphasiger Werkstoffe. Im vorliegenden 1. Teil wird die quantitative Beschreibung des räumlichen Aufbaus zweiphasiger Werkstoffe mit Einlagerungsgefüge durch drei Stereologiefaktoren erörtert: – den Konzentrationsfaktor – den Formfaktor – den Orientierungsfaktor Die Definition dieser Stereologiefaktoren und ihre Ermittlung aus stereologischen Gefügeanalysen erfolgt so, daß sie den Etnfluß der Gefügestruktur durch Konzentration, Form und Orientierung der Phasen in Gefüge‐Eigenschafts‐Gleichungen richtig wiedergeben.
Der Kunststoff im Apparate‐ und Anlagenbau
Authors: Gaube E.
Published: December 2004

Die Arbeit soll in die Thematik „Konstruieren mit Kunststoffen im Apparate‐ und Anlagenbau”︁ einführen. Es wird ein Überblick über den Stand der Technik gegeben, wobei auch auf die Probleme hingewiesen wird, die nach Ansicht des Verfassers noch nicht oder noch nicht zufriedenstellend gelöst sind.
Qualitätskontrolle von Rohren aus HDPE
Authors: Diedrich G. , Müller W. , Gaube E.
Published: December 2004

Es wird über Versuche berichtet, eine Korrelation zwischen Ergebnissen aus Zeitstand‐Innendruckversuchen an HDPE‐Rohren und Zeitstandversuchen an Längszugstäben aus diesen Rohren zu finden.
Fiber‐matrix interactions
Authors: Piggott M. R.
Published: December 2004

The mechanical properties of short, fiber‐reinforced polymers are governed as much by the interface as by the properties of fiber or polymer. Interface properties of importance include adhesion and radial and longitudinal (frictional) stresses. These directly govern strength, modulus, and toughness of the composite and indirectly affect the resistance of the composite to environmental influences, such as water. These interface properties and the resulting interactions under applied stresses are examined and their influence on mechanical properties is discussed.