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Inflammatory bowel disease (IBD) is a common chronic intestinal disorder characterised by a loss of epithelial barrier function leading to the unregulated movement of luminal antigenic material into mucosal tissue with resultant inflammation. In IBD, multiple components of the inflammatory response lead to tissue hypoxia. Mucosal hypoxia leads to the inactivation of prolyl hydroxylase domain-containing (PHD) enzymes, which in turn leads to the stabilisation of the hypoxia-inducible factor (HIF), which induces the expression of barrier protective genes. Furthermore, pharmacological hydroxylase inhibition has been shown to be protective in colitis, at least in part through enhancing intestinal epithelial barrier function through HIF-1-dependent barrier-protective gene expression. Therefore, targeting hypoxia-sensitive pathways represents a new and promising therapeutic approach in IBD.

[Image: see text] We identified and explored the structure–activity-relationship (SAR) of an adamantane carboxamide chemical series of Ebola virus (EBOV) inhibitors. Selected analogs exhibited half-maximal inhibitory concentrations (EC(50) values) of ∼10–15 nM in vesicular stomatitis virus (VSV) pseudotyped EBOV (pEBOV) infectivity assays, low hundred nanomolar EC(50) activity against wild type EBOV, aqueous solubility >20 mg/mL, and attractive metabolic stability in human and nonhuman liver microsomes. X-ray cocrystallographic characterizations of a lead compound with the EBOV glycoprotein (GP) established the EBOV GP as a target for direct compound inhibitory activity and further provided relevant structural models that may assist in identifying optimized therapeutic candidates.

The response of simple polymers to shock loading is governed by a number of factors such as the complexity of the polymer chains and nature of the atoms attached to the main carbon-carbon backbone. In the case of polyethylene based materials such as polyethylene, polypropylene and polytetrafluoroethylene the competing effects of inter chain tangling (tacticity) and electrostatic repulsion between adjacent polymer chains have been shown to have a profound effect on shock velocity, release velocity and shear strength development. In this work, we apply these considerations to a commercially available fluoro-tripolymer, Viton-B, where all these molecular features are present.

The shock response of four common semicrystalline thermoplastic polymers—polyethylene (PE), polyvinylchloride (PVC), polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE)—have been studied in terms of their Hugoniots, release velocities and shear strengths. Through the variations in behaviour caused by changes to the attached atoms to the carbon backbone, it has been possible to suggest that there are two main factors in play. The first is an electrostatic repulsion between adjacent polymer chains. Where this force is large, for example in PTFE with highly electronegative fluorine atoms, this results in this force dominating the shock response, with low shock velocities, high release velocities and little if no hardening behind the shock front. In contrast, in materials such as PE, this force is now weaker, due to the lower electronegativity of hydrogen, and hence this force is easier to overcome by the applied shock stress. Now the main factor affecting shock behaviour is controlled by the shape of the polymer chain allowing inter chain tangling (tacticity). This results in higher shock velocities, lower release speeds and significant hardening behind the shock front as the chains are forced together. This is prevalent in materials with a relatively open structure such as PE and is enhanced with the presence of large side groups or atoms off the main polymer chain.

Dynamic-Tensile-Extrusion (Dyn-Ten-Ext) is a novel test method for the investigation of material response under extreme tensile conditions, comprising the combined conditions of large tensile strains (ɛ > 1) and high strain rates (dɛ/dt > 10,000 s−1), effectively serving as a tensile analog to the Taylor cylinder impact test. The ability to apply this mechanical state is particularly useful for elucidating the deformation and damage responses of polymers under extreme mechanical conditions since they are more ductile, rate-dependent and sensitive to hydrostatic tension than other engineering materials. The technique, in general, generates stable extruded polymer jets that are observed via high-speed photography undergoing large tensile strains at high rates. These jets may accumulate subcritical damage during deformation, revealing damage processes that may only activate in a principally tensile deformation. Ultimately, the jet ruptures, either progressively due to damage or catastrophically. Dyn-Ten-Ext produces spatially and temporally heterogeneous deformation fields, making it an integrated test, analogous to Taylor Impact. The range of strains and strain rates that evolve throughout the test, combined with the simple well defined boundary conditions, produce outstanding datasets for the validation of material models under conditions not accessible by classic testing techniques. This work presents an overview of Dyn-Ten-Ext as a technique for investigating extreme tensile deformation and damage in polymers with representative results for the elastomer polyurea and semicrystalline polymers high density polyethylene, polytetrafluoroethylene, and polychlorotrifluoroethylene.

Poly-ether-ether-ketone (PEEK) is a high-performance semi-crystalline polymer with mechanical and thermal stability characteristics that are superior to most tough polymers. The mechanical characteristics of this polymer are modeled over a broad range of mechanical loading conditions using a thermodynamically consistent modeling process. This preliminary model, which ignores the thermal response and the possible recrystallization of this material during loading, shows an outstanding ability to capture the multidimensional nonlinear response of PEEK up to 60 % compression, with loading rates from 0.0001 to 3000 1/s at room temperature. The model includes the measured anisotropy in the wave response that develops with plastic flow, captures the evolution of the measured equilibrium stress, and correctly matches the evolution of the tangent modulus at equilibrium. This broad range of rates and experimental conditions are achieved by using a two-element nonlinear thermodynamically-consistent model.

Strain measurements by neutron diffraction are employed as an in situ technique to obtain insight into the deformation modes of crystalline domains in a deformed semi-crystalline polymer. The SMARTS (Spectrometer for MAterials Research at Temperature and Stress) diffractometer has been used to measure the crystalline lattice displacements in polytetrafluoroethylene (PTFE) for crystalline phase IV (at room temperature) in tension and compression and for crystalline phase I (at 60°C) in compression. The chemical structure of PTFE, -(C2F4)-n, makes it ideally suited for investigation by neutron methods as it is free of hydrogen that results in limited penetration depths and poor diffraction acquisition in most polymers. Deformation parallel to the prismatic plane normals is shown to occur by inter-polymer chain compression with a modulus ∼10× bulk, while deformation parallel to the basal plane normal occurs by intra-polymer chain compression with a modulus ∼1000× bulk, corresponding with theoretical values for a PTFE chain modulus. Deformation parallel to the pyramidal plane normals is accommodated by inter-polymer chain shear.

The current work presents the characterization and comparison of the mechanical response of three different industrial forms of polyethylene. Specifically, high-density polyethylene (HDPE), ultra high molecular weight polyethylene (UHMWPE), and cross-linked polyethylene (PEX) were tested in compression as a function of temperature (−75 to 100°C) and strain-rate (10−4 to 2,600 s−1). The responses of UHMWPE and PEX are very similar, whereas HDPE exhibits some differences. The HDPE samples display a significantly higher yield stress followed by a flat flow behavior. Conversely UHMWPE and PEX both exhibit significant strain hardening after yield. The temperature and strain-rate dependence are captured by simple linear and logarithmic fits over the full range of conditions investigated. The yield behavior is presented in terms of an empirical mapping function that is extended to analytically solve for the mapping constant. The power-law dependence on strain-rate observed in some polymers is explained using this mapping function.

Polytetrafluoroethylene (PTFE) is a semi-crystalline polymer, which has been employed in a range of engineering applications due to its extremely low coefficient of friction, resistance to corrosion, and excellent electrical insulation properties. Despite failure-sensitive applications such as surgical implants, aerospace components, motor seals, and barriers for hazardous chemicals, the mechanisms of crack propagation in PTFE have received limited coverage in the literature. Moreover, PTFE exhibits complex crystalline phase behavior that includes four well-characterized phases with both local and long range order. Three crystalline structures (phases II, IV, and I) are observed at atmospheric pressure with transitions between them occurring at 19 and 30 °C. This observation provides a unique opportunity for investigation of the effects of a polymers crystalline phase on fracture and microstructure evolution. Moreover, due to the presence of three unique ambient pressure phases near room temperature, it is essential to develop an understanding of the effects of temperature-induced phase transitions on fracture mechanisms of PTFE to prevent failure over the normal range of operating temperatures. In this work, we present values for the J-integral fracture toughness of PTFE for a range of temperatures and loading rates employing the single specimen normalization technique. Crack propagation in PTFE is found to be strongly phase dependent with a brittle-to-ductile transition in the crack propagation behavior associated with the two room temperature phase transitions. Increases in fracture toughness are shown to result from the onset of stable fibril formation bridging the crack plane and increased plastic deformation. The stability of drawing fibrils is primarily determined by temperature and crystalline phase with additional dependence on loading rate and microstructure anisotropy. [LAUR-05-0004]

The synthesis of chiral 1,2,3,5-substituted tetrahydropyrans has been realized via an asymmetric hetero Diels–Alder (HDA) reaction. The key step that involved a trisubstituted chiral enol ether derived from (R)-mandelic acid as the dienophile promoted the creation of three stereogenic centers with a remarkable and unprecedented endo and facial stereocontrol. The hydrogenation of the heteroadduct 2 was optimized by using Pd on charcoal and diisopropylethylamine, leading to a unique isomer. The chiral inductor was cleanly and stereoselectively removed via an acetal reduction, which demonstrated the potential of this methodology for the efficient construction of key intermediate of biologically active molecules.

Various chiral N,N-dialkylhydrazines were prepared in four to five steps from (R)-(–)-2-aminobutan-1-ol 6. They reacted with various prochiral ketones, thus giving the corresponding hydrazones. Reduction of the latter by means of LiAlH4 afforded N,N,N′-trisubstituted hydrazines whose d.e.s were in the range 43–100%. Interestingly, LiAlH4 reduction of the four N-trifluoroethylhydrazones 34 and 38–40 yielded the hydrazines 46 and 48–50, respectively, and with d.e.s=100% by 1H and 13C NMR.

The hydrazine (R)-(−)-28 was obtained in four steps from 2-aminobutan-1-ol (R)-(−)-11, and reacted with benzaldehyde to give the hydrazone (R)-(−)-29. Nucleophilic addition of various alkyl Grignard reagents to the latter yielded the corresponding trisubstituted hydrazines (R,R)-30a–g in 70–89% yields and having d.e.s=100% (1H and 13C NMR). Catalytic hydrogenolysis of these hydrazines afforded the corresponding (R)-(+)-α-phenylalkanamines (R)-(+)-31a–g having e.e.s=90–92% (chiral GPC).

Dynamic-tensile-extrusion (DTE) is an integrated test technique that allows the study of material deformation at high strain-rates (>10,000 s−1) and large strains (>1), under hydrostatic tension. This is an important compliment to the more traditional Taylor cylinder impact test, which achieves large strain and high strain-rate deformation, but under hydrostatic compression. Hydrostatic compression is known to suppress many forms of damage in materials. DTE has been previously employed on a number of metal and polymer systems that manifested tensile instabilities. More recently, this technique has explored stable tensile damage in high-density polyethylene (HDPE), which pointed to a pressure-mediated shear damage phenomenon. The current work extends the technique to the behavior of the glassy polymers poly-methylmethacrylate (PMMA) and polycarbonate (PC). PMMA was found to undergo unstable brittle fracture at nearly all conditions, and therefore did not yield interpretable experimental results. PC (discussed herein) necked and either failed in a brittle fashion or the neck was arrested prior to failure. In the arrested condition, the neck was seen to become opaque from an apparent accumulation of small-scale damage, and a void nucleated at the centerline. A corkscrew fracture process was observed in PC, though its mechanics are not yet understood. It is worth noting that simulations of pressure-hardening PC indicate that it will not extrude or even neck during DTE without the action of a damage process reducing the flow strength of the material.

Megacerotonic acid 1 has a highly exceptional structure, since it is probably the only γ-butyrolactone lignan in which the lactone ring is substituted by an aryl, an arylidene and a carboxy group. The structure of this lignan was confirmed by a racemic total synthesis which involved as key-steps a Stobbe condensation of the 3-arylglutaric ester 8 with p -anisaldehyde 9 , and the hydroxylation at C-4 of the intermediate 2,3-disubstituted glutaric ester 14 .

Transfer of oxygen atoms from epoxides to triphenylphosphine is efficiently catalyzed by Tp'ReO 3 [Tp' = hydrido-tris-(3,5-dimethylpyrazolyl)borate] in benzene at 75-105 °C. The reaction tolerates a wide variety of functional groups including ketones (conjugated or non-conjugated to the new double bond), esters, nitriles, ethers, silyl ethers and phthalimides. Relative rates vary with substitution pattern and electronics; in general, monosubstituted and 2,2-disubstituted epoxides react fastest, and cis-2,3-disubstituted systems react faster than trans. Electron-withdrawing substituents promote the reaction.

Random packings of granular chains are presented as a model polymer system to investigate the contribution of entanglements to strain-stiffening in the absence of Brownian motion. The chain packings are sheared in triaxial compression experiments. For short chain lengths, these packings yield when the shear stress exceeds a the scale of the confining pressure, similar to packings of spherical particles. In contrast, packings of chains which are long enough to form loops exhibit strain-stiffening, in which the effective stiffness of the material increases with strain, similar to many polymer materials. The latter packings can sustain stresses orders-of-magnitude greater than the confining pressure, and do not yield until the chain links break. X-ray tomography measurements reveal that the strain-stiffening packings contain system-spanning clusters of entangled chains., Comment: 4 pages, 4 figures. submitted to Physical Review Letters

The secretory pathway of the yeast Pichia pastoris has been engineered to produce complex human-type N-glycans (Choi et al., Proc Natl Acad Sci USA 100:5022-5027, 2003; Hamilton et al., Science 301:1244-1246, 2003; Hamilton et al., Science 313:1441-1443, 2006). In contrast to the heterogeneous glycans produced on the therapeutic glycoproteins expressed in mammalian cell lines, glycoengineered P. pastoris can be designed to produce a specific, preselected glycoform. In order to achieve glycan uniformity on the target protein, No Open Reading Frame (NORF) yeast cell lines are screened extensively during various stages of glycoengineering. In the absence of the target protein of interest, screening the NORF yeast cell lines for glycoform uniformity becomes a challenge. The common approach so far has been to analyze the total cell glycan pool released from glycoproteins of the NORF yeast cells to predict the N-glycan uniformity. As this does not always accurately predict the N-glycan end product, we describe in this chapter a detailed protocol for a non-affinity-based high-throughput purification of an endogenous glycoprotein. This protein of interest has been introduced during the early stages of glycoengineering process and its N-glycan profile is utilized as a tool for glycoengineering screening.

Polyurea was investigated under Dynamic-Tensile-Extrusion (Dyn-Ten-Ext) loading where spherical projectiles were propelled at 440 to 509 ms-1 through a conical extrusion die with an area reduction of 87%. Momentum of the leading edge imposes a rapid tensile deformation on the extruded jet of material. Polyurea is an elastomer with outstanding high-rate tensile performance of interest in the shock regime. Previous Dyn-Ten-Ext work on semi-crystalline fluoropolymers (PTFE, PCTFE) elucidated irregular deformation and profuse stochastic-based damage and failure mechanisms, but with limited insight into damage inception or progression in those polymers. The polyurea behaved very differently; the polymer first extruded a jet of apparently intact material, which then broke down via void coalescence, followed by fibrillation and tearing of the material. Most of the material in the jet elastically retracted back into the die, and only a few unique fragments were formed. The surface texture of all failed surfaces was found to be tortuous and covered with drawn hair-like filaments, implying a considerable amount of energy was absorbed during damage progression.

15 Chiral acids were esterified with optically pure (R)-(+)-2-(trifluoromethyl)benzhydrol (R)-(+)- 1 , a readily available reagent. With respect to the carboxy group, the stereogenic centre is in the β position in the case of the acids 5a–10a and 12a–16a , and in the α position in the case of the acids 17a–20a . The diastereomeric excesses of the corresponding esters 5b–10b and 12b–20b , respectively, were easily determined by means of 19 F NMR. These d.e. values were in very good agreement with the e.e. values of the corresponding acids when the latter were known compounds.

Treatment of the readily available (R)-(-)enantiomer of 2-aminobutan-1-ol 1 with sodium hydride followed by benzyl chloride afforded the O-benzyl base (R)-(-)-2. The latter was successfully used for the resolution of racemic α-methylsuccinic and α-bromosuccinic acids, as well as of the racemic α-benzylhemisuccinic esters 8 and 9 resectively.

Prior research on surfactant solubilization has emphasized steady-state conditions in the presence of excess hydrocarbon for single-component systems. These conditions do not accurately emulate the natural subsurface environment. Evaluation of solubilization potential for unsaturated hydrocarbon concentrations revealed influences of micellar core and palisade layer effects on hydrocarbons of varying polarity. Naphthane, naphthalene, and 1-naphthol were utilized to probe for core and palisade effects. Surfactants evaluated were sodium dodecyl benzenesulfonate and C16-alkyl diphenyl oxide disulfonate. Use of semiequilibrium dialysis cells provided quantitative solubilization information for unsaturated hydrocarbon concentrations. Palisade and core solubilization effects were observed as follows : as the more fraction increased, K m increased for naphthane, decreased for naphthol, and remained relatively constant for naphthalene.

N -Alkylation of (R)-(−)-2-aminobutan-1-ol 1 (a readily available reagent) with ortho -fluorobenzyl chloride, followed by reaction with cinnamoyl chloride, afforded the cinnamamide (R)-(+)-6. Michael addition of n -alkyl magnesium halides to the latter gave the corresponding adducts (R,R)-8a-e whose diastereomeric excesses were higher than 92% as evidenced by 19F NMR. Acidic hydrolysis of these adducts yielded the corresponding β-phenylalkanoic acids (R)-(−)-9a-e.

The hydrazine (R)-(−)-28 was obtained in four steps from 2-aminobutan-1-ol (R)-(−)-11, and reacted with benzaldehyde to give the hydrazone (R)-(−)-29. Nucleophilic addition of various alkyl Grignard reagents to the latter yielded the corresponding trisubstituted hydrazines (R,R)-30a–g in 70–89% yields and having d.e.s=100% (1H and 13C NMR). Catalytic hydrogenolysis of these hydrazines afforded the corresponding (R)-(+)-α-phenylalkanamines (R)-(+)-31a–g having e.e.s=90–92% (chiral GPC).

Various chiral N,N-dialkylhydrazines were prepared in four to five steps from (R)-(–)-2-aminobutan-1-ol 6. They reacted with various prochiral ketones, thus giving the corresponding hydrazones. Reduction of the latter by means of LiAlH4 afforded N,N,N′-trisubstituted hydrazines whose d.e.s were in the range 43–100%. Interestingly, LiAlH4 reduction of the four N-trifluoroethylhydrazones 34 and 38–40 yielded the hydrazines 46 and 48–50, respectively, and with d.e.s=100% by 1H and 13C NMR.

Resume Racemic and optically active α,β-dibenzyl-γ-butyrolactones (of synthetic origin) were hydroxylated in the α position with respect to the carbonyl group, using oxygen in the presence of LHDS. This led to (−)-trachelogenin 1 , (−)-nortrachelogenin 2 and (+)-wikstromol 3 , whose interesting pharmacological properties were recently described. These natural lignans were correlated to (±)-methyltrachelogenin 12 whose relative structure was definitely established by X-ray cristallography.

Condensation of vanillin with dimethyl succinate (using LiOMe) gave the ethylenic hemiester 3. Hydrogenation of 3 gave (R,S)-4. The latter was resolved into both its enantiomers by means of (+)-α-methylbenzylamine. Ca(BH 4 ) 2 reduction of (R)-(+)-4 and (S)-(−)-4 gave the corresponding β-vanillyl-γ-butyrolactones (R)-(+)-1 and (S)-(−)-1, respectively. The lactone (R)-(+)-1 was used for the total syntheses of five naturally occurring and optically active lignans such as (−)-anhydrosecoisolariciresinol and (+)-isolariciresinol

Resolution of methyl α-(3,4,5-trimethoxybenzyl) hemisuccinate, (R,S)-2, by means of (−)-ephedrine, followed by Ca(BH 4 ) 2 reduction, afforded (R)−(+)-β-(3,4,5-trimethoxybenzyl) butanolide. This lactone was used as a starting material for the asymmetric syntheses of eight recently discovered lignans belonging to, or deriving from, the α,β-dibenzylbutanolide series, such as cubebinone and dihydroclusin

LiAlH 4 previously treated with 2 equivalents of (R)-(−)-2-(2-iso-indolinyl) butan-1-ol (a readily available reagent) reduced 2-chloro and 2,4-dimethyl benzophenones into the corresponding benzhydrols with 100% enantiomeric excess. Other examples of ketone reductions are given.

Resume Alkyl isocyanates reacted with 1.5 equivalent of α-methyl-glucoside, ucose or galactose in pyridine at room temperature, and lectively gave the corresponding 6- N -alkylcarbamates in good yields. The readily available glucosylamine and lactosylamine (1.5–2 eq.) reacted with alkyl isocyanates and isothiocyanates in polar aprotic solvents (pyridine, NMP or DMF), thus affording good yields of the corresponding N -glycosyl N' -alkyl ureas and thioureas. These new sugar derivatives are non-ionic detergents.

Polymers are becoming increasingly used in aerospace structural applications, where they experience complex, non-static loads. Correspondingly, the mechanical properties at high strain rates are of increasing importance in these applications. This paper presents an investigation of the properties of Dupont 9B polytetrafluoroethylene (PTFE) across strain rates from 10−3 to 105 s−1. The samples were tested using an Instron mechanical testing machine for static loading, traditional split Hopkinson pressure bars (SHPBs) for high strain rates, and a miniaturized SHPB for ultra-high strain rates. Additionally, the material was tested using dynamic mechanical analysis to determine the effects of time–temperature superposition on the strain rate behavior of the samples. The results of the experiments are analyzed using the Zerilli–Armstrong model for polymers, which shows good agreement with other PTFE studies.

Polytetrafluoroethylene (PTFE) is a semi‐crystalline polymer exhibiting complicated pressure and temperature dependent phases. High strain rate applications in aerospace, defense, and automotive industries have lead to interest in the shock response of PTFE and resulting changes in the polymer structure. Experimental studies on pressure‐induced phase transitions using shock‐loading techniques and the resulting changes in crystalline structure are presented. Gas launcher experiments were performed on pedigreed PTFE 7C momentum trapped assemblies with impact pressures from 0.4 to 0.85 GPa to investigate the material response above and below the phase II to phase III crystalline transition. [LAUR‐05‐5945]

Taylor impacts experiments were conducted on PEEK at velocities between 150 & 360 m s−1. The material was found to respond in a ductile manner and exhibit a color change later found to be associated with large compressive strains in PEEK, irrespective of strain‐rate. No changes in molecular weight were detected as a result of high‐strain rate or large strain deformation. Melting has been shown not to be responsible for the ductile deformation and limited tearing response of PEEK subject to Taylor impact.

A dithioacetalisation procedure at low temperature using TMSOTf as the promoter is described. This method proved highly efficient for unprecedented transprotection of ketone enol ethers and was successfully applied to polyfunctional sensitive substrates.

International audience; The [4+2] heterocycloaddition reaction between (E)‐γ‐substituted β‐unsaturated α‐oxo esters 1a−d and cyclic and acyclic ketone enol ethers 2a−l afforded heteroadducts 3−5 in high yields when either [Eu(fod)3] or SnCl4 were used as the catalyst. With methyl (E)‐benzylidenepyruvate (1a), the two catalytic modes displayed divergent stereoselectivities. In the case of the heterocycloaddition of silyl enol ether 2h, X‐ray investigations established the relative configurations of the bicyclic adducts 3h and 5h, each obtained as the major isomer with [Eu(fod)3] and with SnCl4, respectively. These assignments provided valuable information concerning the concerted vs. nonconcerted mechanism of these acid‐catalysed reactions. With methyl (E)‐tert‐butoxymethylenepyruvate (1d), the scope of the reaction proved to be restricted to alkyl enol ethers as the dienophiles. In this case, the stereochemical process followed a different pathway, exemplified by the X‐ray structure of the adduct 4q, obtained with total stereoselectivity from 1d and 1‐methoxycyclohexene (2f) when SnCl4 was the catalyst.

Structural polymers are susceptible to damage in the form of cracks, which form deep within the structure where detection is difficult and repair is almost impossible. Cracking leads to mechanical degradation of fibre-reinforced polymer composites; in microelectronic polymeric components it can also lead to electrical failure. Microcracking induced by thermal and mechanical fatigue is also a long-standing problem in polymer adhesives. Regardless of the application, once cracks have formed within polymeric materials, the integrity of the structure is significantly compromised. Experiments exploring the concept of self-repair have been previously reported, but the only successful crack-healing methods that have been reported so far require some form of manual intervention. Here we report a structural polymeric material with the ability to autonomically heal cracks. The material incorporates a microencapsulated healing agent that is released upon crack intrusion. Polymerization of the healing agent is then triggered by contact with an embedded catalyst, bonding the crack faces. Our fracture experiments yield as much as 75% recovery in toughness, and we expect that our approach will be applicable to other brittle materials systems (including ceramics and glasses).

The high strain-rate response of polymers is a subject that has gathered interest over recent years due to their increasing engineering importance, particularly in load bearing applications subject to extremes of pressure and strain rate. The current work presents two specific sets of experiments interrogating the effect of dynamic, high-pressure loading in the regime of the phase II to phase III pressure-induced crystalline phase transition in polytetrafluoroethylene (PTFE). These are gas-gun driven plate- and Taylor impact. Together these experiments highlight several effects associated with the dynamic, pressure-induced phase transitions in PTFE. An elevated release wave speed shows evidence of a pressure-induced phase change at a stress commensurate with that observed statically. It is shown that convergence between analytic derivations of release wave speed and the data requires the phase II to III transition to occur. Taylor impact is an integrated test that highlights continuum behavior that has origin in mesoscale response. There is a rapid transition from ductile to brittle behavior observed that occurs at a pressure consistent with this phase transition.

Regioselective introduction of a benzoxy group, in the benzylic position of the β-benzyl-γ-butyrolactone (R)-(+)-8, was achieved by tretment with NBS followed with benzyl alcohol. α-Alkylation of the lithium enolate of the resulting intermediate 11, with O -benzylvanillyl bromide 5, gave the trans disubstituted lactone 13. Catalytic hydrogenolysis (PdC) of 13 selectively split the aryl benzyl ether linkage, thus giving the compound 14. Intramolecular Friedel-Crafts cyclisation of the latter, using the benzoxy group as the leaving group, was induced with BF3. Et2O and afforded high yields of (−)-α-conidendrin 2.

The high-strain rate response of polymers is a subject that has gathered interest over recent years due to their increasing engineering importance, particularly in the transport industries. This work explores the effect of fluorination upon semicrystalline thermoplastics. Polyethylene, with its simple hydrocarbon chain, is considered; with increasing fluorination of the carbon backbone polyvinylidene difluoride, and then polytetrafluorethylene (PTFE) is also compared. All three show a nonlinear equation of state behavior, which may be related to partial crystallinity. PTFE is shown to have anomalous release speed, which reflects its transformation from phase II to phase III transition at 0.7 GPa. Strength effects show a different ordering of behavior between the three materials. The first results are accountable purely using van der Waals forces between the chains. However, strength effects show the effect of further attractive forces that indicate some tacticity in the material associated with the state behind the shock.

Polymers are increasingly being utilized as monolithic materials and composite matrices for structural applications historically reserved for metals. High strain-rate applications in aerospace, defense, and the automotive industries have lead to interest in the shock response of polytetrafluoroethylene (PTFE) and the ensuing changes in polymer structure due to shock prestraining. We present an experimental study of crystalline structure evolution due to pressure-induced phase transitions in a semicrystalline polymer using soft-recovery, shock loading techniques coupled with mechanical and chemical postshock analyses. Gas-launched, plate impact experiments have been performed on pedigreed PTFE 7C, mounted in momentum trapped, shock assemblies, with impact pressures above and below the phase II to phase III crystalline transition. Below the phase transition only subtle changes were observed in the crystallinity, microstructure, and mechanical response of PTFE. Shock loading of PTFE 7C above the phase II-III...

Although poly(tetrafluoroethylene) (PTFE) is an unusually ductile polymer, it undergoes an abrupt ductile-brittle transition at modest impact velocities. No previous explanation for this behavior has been found after an extensive literature search. In this paper, we examine the role of a pressure-induced phase transition in PTFE in the dynamic failure of Taylor cylinder samples. There is a known phase transition in PTFE with a marked decrease in volume and compressibility that occurs at 0.5–0.65GPa at 21°C, with the transition pressure inversely related to temperature. Varying the temperature of the samples in the experiment revealed that the phase transition is probably involved in sample failure because the ductile/brittle transition velocity increased for decreasing temperature, despite the material fracture toughness decreasing. Additionally, Taylor tests were carried out on samples of poly(chlorotrifluoroethylene) PCTFE to investigate the behavior of a similar material to PTFE but without a pressure-...

An efficient and stereoselective total synthesis of C-nor D-homosteroid compounds is described, following a general pathway of the A→B→C→D type. The A-B ring system was provided by the Wieland-Miescher ketone 3 . the ring C was formed by intramolecular cyclisation of an appropiate γ-diketone such as 18 . Construction of the ring D was achieved by means of a Birch reductive alkylattion, followed by intramolecular cyclisation of the intermediate δ-diketone thus formed. C-nor D-homosteroids 1 and 2 having six asymmetric carbons as well as the required “natural” trans-anti-trans configuration were thus obtained in eleven steps from the Wieland-Miescher ketone 3 .

The optically active lignan (-)-steganol was prepared from natural (-)-steganacin by selective deacetylation and was transformed, via a three-step sequence, into the corresponding 4', 6'-O-ethylidene- and thenylidene-beta-D-glucopyranosides, 3b and 3c, respectively, which are the analogues, in the steganol series, of the podophyllotoxin derived, and clinically useful, anticancer drugs, VP16-213 and VM26. Formation of the dimeric compound distegyl ether as a minor by-product was established. Complete elucidation of all the asymmetric centres was performed with the help of high resolution 1H-nmr studies at 400 MHz, COSY experiment at 500 MHz and X-ray analysis. Contrary to the podophyllotoxin series, the glycosylation of (-)-steganol occurred with retention of configuration, and all the synthesized compounds, including distegyl ether, exhibited the starting natural R configuration at C-5.

Michael addition of the carbanion of the dithian 7 (derived from O-benzyl vanillin) on butenolide, afforded the saturated lactone 8. Alkylation of the latter with the benzylic bromide 6, followed by regeneration of the carbonyl group gave the α,β-disubstituted lactone 10. Reduction of the ketonic carbonyl group of compound 10 using NaBH4, followed by treatment with CF3CO2H and catalytic hydrogenolysis afforded (d,l)α-conidendrin 1.

The cross-polarization, magic-angle 13C-NMR spectra of solid samples of poly(p-phenylene), its nitro derivative, polymerized biphenyl, poly(p-phenylene sulfide), poly(1-methyl-2,5-pyrrolylene), poly(1-phenyl-2,5-pyrrolylene), poly(2,5-thienylene), and poly(2,5-selenienylene) and the high-resolution 13C-NMR spectrum of poly(m-phenylene) in solution are presented and assigned. In all cases the chemical shifts are similar to those of model compounds in solution. In most instances the resonances of the nonprotonated carbon atoms in the solid polymers are more intense than those of the protonated carbons and appear to depend on the charge distribution in the molecular orbitals.

The reaction of red phosphorus with poly(methyl methacrylate) under pyrolysis conditions was investigated with a number of physical techniques. A random methyl methacrylate/cyclic anhydride copolymer is formed from atatic PMMA, whereas a random methyl methacrylate/methacrylic acid copolymer is obtained with isotactic PMMA. The backbones of both these copolymers are more stable toward depolymerization than that of PMMA. The flame-retardant activity of red phosphorus with PMMA may arise in part from stabilization of the polymer toward depolymerization via modification of the sidechains.

The biphenyl 16 (obtained from α-bromopiperonal and the aromatic iodide 14 by a modified Ullmann reaction) was cyclized by intramolecular hydroxyalkylation to the isomeric alcohols 17a and 17b . These were oxidized using Jones' reagent, to afford the enol 18a , together with the tautomeric β-ketolactone Decarboxylation of this mixture using barium hydroxide, followed by Jones' oxidation gave the isomeric γ-ketoacids 11a and 11b . These were converted to (±)-steganone 1 using Raphael's method, in an overall yield of ca 10% starting from 3, 4, 5-trimethoxybenzaldehyde, and in 20,7% yield, starting from the biphenyl 16 .

Laser desorption/Fourier transform mass spectra of poly(phenylene sulfide), polyaniline, poly(vinyl phenol), polypyrene, poly(p-phenylene), poly(1-methyl-2,5-pyrrolylene), poly(1-phenyl-2,5-pyrrolylene), and poly(2,5-thienylene) are compared. Poly(phenylene sulfide) fragments at CS bonds during analysis, but rearrangement is minor. Evidence is found for dibenzothiophene moieties within the polymer chains. Unambiguous determination of the structure of polyaniline is not possible. Rearrangement appears to accompany chain scission. Completely aromatic polymers do not undergo similar reactions during analysis. Species with more carbons than can be accounted for by an integer multiple of six-membered rings arise from side reactions during dehydrocoupling of aromatic monomers. Carbon clusters, which are observed in the spectra of some aromatic polymers, appear to arise from laser volatilization and multiphoton ionization of large polynuclear components that are formed during synthesis. Negative ions of about 40–120 carbons and positive ions with about 120–400 atoms are detected. The results also suggest that the physical dimensions of some polymer molecules might be measured by Fourier transform mass spectrometry.

Laser desorption/Fourier transform mass spectrometry provides very detailed characterization of conjugated aromatic ‘conducting’ polymers that cannot be obtained by other currently available techniques. The technique shows that many of the synthetic routes to these materials yield complex mixtures of dissimilar oligomers. Thus, it is not appropriate at present to attribute electrical conductivities to distinct, individual polymers. The intent of this paper is to present an introductory description of this analytical technique and to give examples of the experimental results that can be expected with intractable aromatic polymers which become electrically conductive upon doping.