bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthèse par voie radicalaire de polymères à extrémités hydroxylées, 11. Etude de la copolymérisation du méthacrylate de méthyle avec divers acrylates et méthacrylates. Détermination des rapports de réactivité
Authors: Brosse Jean‐Claude , Gauthier Jean‐Marie , Lenain Jean‐Claude
Published: April 2003

Methylmethacrylate (MMA) was polymerized in an oxygen or argon atmosphere with butyl or isobutyl acrylates, and butyl, isobutyl, or 2,3‐epoxypropyl methacrylates, by hydrogen peroxyde in the presence of ethanol under UV irradiation (254 nm) at room temperature. The reactivity ratios were determined. MMA shows a higher reactivity than its comonomers, in good agreement with the results of the literature, except for isobutyl and 2,3‐epoxypropyl methacry‐lates.
Molmassenverteilung und lösungszustand von linearen polyethylenen, 1. Lichtstreuungs‐, viskositäts‐ und GPC‐messungen
Authors: Böhm L. L. , Lanver U. , Lechner M. D.
Published: April 2003

Light scattering, viscosity and GPC measurements were performed on a homologous series of linear polyethylenes with viscosity average molar masses in decahydronaphthalene at 135°C between 1,0 · 105 and 2,7 · 106 g · mol−1 and relatively broad molar mass distributions. 1,2,4‐Trichlorobenzene, α‐chloronaphthalene, decahydronaphthalene (decalin) and decane were used as solvents. In the case of linear polyethylene in decahydronaphthalene and decane relationships between intrinsic viscosity and weight average molar mass were established. The values of the weight average molar masses obtained by light scattering are considerably higher than those obtained by viscosity and GPC measurements. These discrepancies are explained by molecular aggregation of the polyethylene macromolecules.
Über polyarylenalkenylene und polyheteroarylenalkenylene, 14. Synthesen und charakterisierung von poly(thieno[2′,3′:1,2]benzo[4,5‐b]thiophen‐2,6‐diylvinylenarylenvinylen)en, poly(4,8‐dimethoxythieno[2′,3′:1,2]benzo[4,5‐b]thiophen‐2,6‐diylvinylenarylenvinylen)en und einigen modellverbindungen
Authors: Koßmehl Gerhard , Beimling Peter , Manecke Georg
Published: April 2003

Wittig‐reactions of thieno[2′,3′:1,2]benzo[4,5‐b]thiophene‐2,6‐dicarboxaldehyde (8a) with “mono‐ and bis‐Wittig‐salts” 12a–c and 9a–c poly(thieno[2′,3′:1,2]benzo[4,5‐b]thiophene‐2,6‐diylvinylenearylenevinylene)s 10a–c and some model compounds 13a–c were obtained. Analogous reactions of 4,8‐dimethoxythieno[2′,3′:1,2]benzo[4,5‐b]thiophene‐2,6‐dicarboxaldehyde (8b) gave the corresponding poly(4,8‐dimethoxythieno[2′,3′:1,2]benzol[4,5‐b]thiophene‐2,6‐diylvinylenearylenevinylene)s 11a–c and their model compounds 14a–c. Wittig‐reactions of benzo[b]thiophene‐2‐carboxaldehyde (15) with “mono‐ and bis‐Wittig‐salts” gave model compounds 16a–c and 17a, c. A new synthesis of thieno[2′,3′:1,2]benzo[4,5‐b]thio‐phene (4) was worked out. 4,8‐Dimethoxythieno[2′,3′:1,2]benzo[4,5‐b]thiophene (7) and dicarboxaldehydes 8a and 8b were synthesized for the first time. The structures of all compounds were confirmed by elemental analyses, IR and electronic spectra, those of the model compounds additionally by mass spectra, and in case of sufficient solubility by 1H NMR spectra. The electrical conductivities of all polymers and their model compounds were investigated.
Main features of hydrolysis of polymeric enaminones based on a water‐soluble copolymer from N‐vinyl‐2‐pyrrolidone and 5‐methyl‐5‐hexene‐2,4‐dione
Authors: Panarin Evgenii F. , Kopeikin Victor V.
Published: April 2003

Water‐soluble polymeric enaminones (2) were obtained by condensation of a copolymer (1) from N‐vinyl‐2‐pyrrolidone and 5‐methyl‐5‐hexene‐2,4‐dione with amines. It was found first that polymers 2 undergo hydrolysis by water much more slowly than low molecular weight enaminones of similar structure and, secondly, their hydrolysis does not obey the pseudo‐first‐order rate law. These differences in the kinetic behaviour of polymers and model compounds are due, respectively, first to a steric hindrance of the attack of water at the polymer chains and, secondly, to the association of low molecular reaction products with the monomeric units of N‐vinylpyrrolidone in the copolymers. A detailed study of the hydrolysis of polymeric enaminones of amino acids, characterized by extraordinary high hydrolysis rates confirmed the existence of the intramolecular base catalysis of the attack of water at the protonated enaminone by their own carboxylate groups.
Reactive microgels by the self‐emulsifying copolymerization of unsaturated polyester resins with acrylic and methacrylic esters
Authors: Miyata Mikiyi , Funke Werner
Published: April 2003

The self‐emulsifying copolymerization of unsaturated polyesters (UP) with various acrylic and methacrylic esters was studied. The structure of comonomers significantly influences the character of microgels obtained. Among these monomers the copolymerization of UP with methyl methacrylate (MMA) was investigated in detail in order to make clear the behavior of this polymerization as compared with that of styrene. The water/monomer and UP/MMA ratios were found to be the most important factors controlling the molecular weight and solution viscosity of the microgels. The relationship between M̄w and intrinsic viscosity of microgels suggests that the microgels from MMA have less compact structure than those from styrene.
The measurement of the tacticity of poly(vinyl chloride) by 13C nuclear magnetic resonance spectroscopy
Authors: King Janice , Bower David I. , Maddams William F. , Pyszora Henryk
Published: April 2003

Fourier transform 1H‐decoupled 13C NMR spectra were obtained on seven poly(vinyl chloride), (PVC), samples in solution in o‐dichlorobenzene. Four of the polymers were of the commercial type and the others were prepared by suspension polymerisation at +90°C, +5°C, and ‐30°C. Measurements of the spectra were used to assess the precision and accuracy with which information about the tacticity of PVC can be obtained from such spectra. The results show that the well‐resolved α‐carbon triad and β‐carbon tetrad spectra obtained may be reliably analysed to give values of the probability of syndiotactic placement with a precision of about 0,005 for measurements on a single run on a single sample. The simplest and probably the most reliable method of measuring the areas under the peaks which correspond to specific triads ot tetrads is to use the spectrometer integrator, although results of slightly lower precision may be obtained by the use of a curve resolver. Consideration of possible systematic errors due to different T1 relaxation times, unequal nuclear Overhauser enhancement (NOE) factors, and incomplete dissolution of the polymer has shown that the only one of these which is possibly significant is that due to NOE, which is almost certainly less than 0,008, so that the absolute accuracies of the Pr values should be better than that. A more detailed study of the data shows that the polymers made at 5°C and ‐30°C are almost certainly non‐Bernoullian and that firstoder Markov statistics can adequately describe the observed departures from Bernoullian statistics. These departures may have significant consequences for the physical properties of the polymers.
Low temperature elastomeric polyamides containing perfluorinated polyether building blocks
Authors: Caporiccio Gerardo , Strepparola Ezio , Bargigia Gianangelo , Novaira Giuseppe , Peveri Glauco
Published: April 2003

Reductive cleavage of derivatives from tetrafluoroethylene photooxidation resulted in perfluorinated polyethers with α,ω‐carboxylic ester groups B. Their condensation with suitable aliphatic and aromatic diamines gave a new class of elastomers, crosslinkable by organic peroxides. A good balance of low temperature elasticity, resistance to solvents, and thermostability was particularly found for aromatic polyamides.
Polyurethanes containing poly(oxyethylene) block units and their properties as polychelatogenes
Authors: Bayer Ernst , Grathwohl Paul‐Anton , Geckeler Kurt
Published: April 2003

Polyurethanes 6 and 7 based on poly(oxyethylene) (5) were synthesized and investigated for the application as macromolecular chelating agents. 4,4′‐Diaminobenzil (3c) and 4,4′‐diaminobenzil monoxime (4a) were prepared as monomer precursors in 70 and 80% yield. Copolymers were obtained in yields between 40 and 60% by polyaddition of the corresponding diisocyanates 3d and 4b to poly(oxyethylene) (5) of different chain length and characterized by IR and 13C NMR spectroscopy. The application of the resulting polyurethanes containing functional aromatic block units as polychelatogenes was studied in homogeneous phase by membrane filtration. The metal content was determined in both the filtrate and the retentate and in the case of Ni2+ at different pH values. At pH 2, for example, the molar binding capacity of a polyurethane sample of 6 was 3 times as high as that of 5.
Caractérisation physico‐chimique d'un polymère phosphore
Authors: Chakra Taher Abou , De Jaeger Roger , Baillet Christiane , Delfosse Lucien , Cavrot Jean‐Paul , Rietsch François
Published: April 2003

A mixture, probably composed of a poly(chlorotrimethylsilyloxy)phosphazene and a compound with the general formula H2Cl2NOP (inactive toward THF) was used to initiate the polymerization of tetrahydrofuran. The resulting polymer (PTHFP) contains phosphorus associated with nitrogen, as assessed by IR, 31P and 1H NMR spectroscopy. The thermal stability of PTHFP, observed by thermogravimetry, was found to be much higher than that of polytetrahydrofuran (PTHF). At the end of its decomposition a solid residue remains, which was identified as a poly(phosphazene oxide) (PNO)n. The combustion behaviour is also modified in that the cool flame combustion area is raised up in the pressure‐temperature coordinates. In addition, the disappearance of the so‐called secondary cool flame (SCF) phenomenon is in favour of the heterogeneous action of the phosphorus derivatives during the inhibition of combustion at higher temperatures. The thermochemical analysis (DSC‐Rheovibron) shows the existence of a semi‐cristalline structure proportional to the amount of phosphorus introduced into the PTHF chain. The glass transition temperature of PTHFP was found to be slightly higher than that of PTHF without any apparent relation to their structures. The same conclusion arises from the viscoelastic measurements.
Magic‐angle 13C NMR spectroscopy of chloral polymers
Authors: Harris William J. , Vogl Otto , Havens J. R. , Koenig Jack L.
Published: April 2003

The homopolymer of chloral and a copolymer of chloral and p‐chlorophenyl isocyanate were studied by magic‐angle 13C NMR spectroscopy. 13C NMR Measurements with magic‐angle spinning and cross polarization show for the acetal carbon a chemical shift of 101, 4 p.p.m. downfield from tetramethylsilane. The observation of a symmetrical, reasonably sharp (3 p.p.m.) resonance suggests that the polychloral is stereoregular. Spectra of chloral copolymers with 5 moles percent p‐chlorophenyl is steroregular. Spectrical of chloral copolymers with 5 moles percent p‐chlorophenyl isocynate have additional peaks between 130 and 150 p.p.m. from the aromatic carbons of the p‐chlorophenyl isocyanate moiety.
Singlet oxygen quenching by polyconjugated polymers derived from acenaphthene and acenaphthylene
Authors: Schopov Ivan , Kirowa Pluma
Published: April 2003

Singlet oxygen quenching by polymers derived from acenaphthene and acenaphthylene is investigated by the oxidation of cis‐1,4‐polybutadiene with photochemically generated singlet oxygen. It is found that only the polymers with conjugated double bonds in the main chain, poly (1,2‐acenaphthenediylidene) (1) and poly (1,2‐acenaphthylenylene) (2), are singlet oxygen quenchers. Poly(1,2‐acenaphthenylene) (3), with a saturated main chain, is no singlet oxygen quencher. Polymer 2 does not react with singlet oxygen. This is an indication that the quenching mechanism is a physical process.
Secondary structure of peptides, 10. FT‐IR and 13C NMR CP/MAS study on tacticity and secondary structure of poly(D,L‐leucine)s
Authors: Stulz Josef , Müller Detlef , Hull William E. , Kricheldorf Hans R.
Published: April 2003

A series of poly (L‐leucine)s with average degrees of polymerization in the range between 10 and 100 and various poly (D,L‐leucine)s were prepared by polymerization of L‐leucine‐N‐carb‐oxyanhydride (NCA) or D,L‐Leu‐NCA. The FT‐IR spectra measured in KBr show that the amide I and II bands are exclusively sensitive to the secondary structure of the poly (leucine)s and not to their tacticity. The tacticities of the poly(D,L‐leucines) were determined in solution of trifluoroacetic acid by means of 13C NMR spectra, while 13C NMR CP/MAS spectra of the solid polymers revealed that the poly(D,L‐leucine)s contain 40 – 60 wt.‐ % α‐helix structure. For this reason the broad amide I and II bands do not enable one to distinguish isotactic and more or less atactic poly(leucine)s. However, the IR‐bands between 500 and 900 cm−1 allow a differentiation between poly(L‐leucine) and poly(D,L‐leucine)s and also between poly(D,L‐leucine)s of different tacticity. The IR‐spectra confirm that primary amine‐initiated polymerizations of D,L‐Leu‐NCA do not lead to long stereo blocks.
Metalloester, 10. Untersuchung des anfangsstadiums der anionischen polymerisation von methylmethacrylat. einfluß von reaktionsbedingungen auf die umsetzung von methyl‐2‐sodioisobutyrat mit methylmethacrylat
Authors: Lochmann Lubomir , Pokorný Svatopluk , Trekoval Jiři , Adler Hans‐Jürgen , Berger Werner
Published: April 2003

In continuation of a preceding study, the course of the reaction between methyl methacrylate (2) and methyl 2‐sodioisobutyrate (1) was investigated, applying reaction times between 0,02 and 1,4 s, as a function of the following conditions: character of the solvent, effect of the addition of sodium tert‐butoxide, mole ratio 2/1, concentration of the reactants, and temperature. Under all conditions used, the reaction between 2 and 1 was very fast and gave rise, along with other compounds, to a mixture of oligomers of 2 with the average molecular weight obeying the ratio [2]:[1]eff.. The balance of products showed that in some cases only a part of 1 has reacted with 2, giving rise to the expected oligomers. The efficiency of 1 varied in the range from 24 to 100%, being mainly dependent on the character of the solvent (efficiency in THF > in toluene). Moreover, it was higher in the presence of sodium tert‐butoxide and with a higher 2/1 mole ratio. In experiments with a low efficiency of 1 a certain part of it remained unreacted, in spite of the presence of 2, for reasons not yet clear. The resulting oligomers undergo consecutive reactions. Starting with the trimer 3b, cyclizing selfcondensation was the most important of the consecutive reactions and could be easily investigated in the case of the trimer. The rate of this cyclization was much higher in THF than in other solvents used, and it was, therefore, difficult to obtain the linear trimer at room temperature. On the contrary, the addition of sodium tert‐butoxide or lowering the temperature suppressed the cyclization, which was especially easy to perceive in THF. Using the experience described in the study, it is possible to choose such conditions of the reaction between 1 and 2, under which the required oligomers are formed in good yield.
Excess gibbs function and structure for the systems CCl4(1)/chloroalkane(2), at 298 K. study by laser light scattering
Authors: Katime Issa Antonio , Ochoa José Ramón
Published: April 2003

Laser light scattering (LLS) at 632 nm was used in measurements of both activity coefficients, γi, and excess Gibbs functions, GE, in the systems CCl4(1)/chloroalkane(2) (butyl chloride, sec‐butyl chloride, isobutyl chloride, and tert‐butyl chloride). The GE values for these systems are positive. From both activity coefficients and anisotropic Rayleigh ratios, the ordered structure of these binary mixtures were studies.
Hyperfeinstruktur in den ESR‐spektren von thermisch behandeltem polyphenylacetylen
Authors: Bartl Anton , Freudenberg Getraud , Fröhner Jürgen , Pietraß Bernhard , Wuckel Lothar
Published: April 2003

A highly resolved ESR spectrum of dissolved polyphenylacetylene has been measured at 120°C. It was found by simulation that the protons of three phenyl groups and two protons of the carbon chain contribute to the spectrum. The structure of the corresponding paramagnetic centre is given.
Action de différentes especes d'amorçage dans la polymérisation hydrolytique du dodécanelactame‐12
Authors: Froyer Gerard , Sekiguchi Hikaru
Published: April 2003

The study of the initiation step in the hydrolytic polymerization of 12‐dodecanelactam showed the prominent role of chain‐ends in the monomer consumption and especially that of amino end groups. Different initiators, dodecylamine hydrochloride, 12‐aminododecanoic acid, or lauric acid, where employed and in some experiments water was added. This led to the formation of new end groups and thus to an enhancement of the monomer consumption rate. It could be shown that during this process large changes in the polymer chain length distribution occur.
Photostability of trityl salts with different anions under argon
Authors: Toncheva Veska D. , Velichkova Rumyana S.
Published: April 2003

The visible light‐induced photolysis of trityl salts with anions such as PF⊖6, FeCl⊖4, BF⊖4 or AsF⊖6 was investigated in an inert atmosphere. The rates of decoloration of the dichloroethane solutions of the trityl cation (10−5 mol · 1−1) in the presence of different anions are compared. The results indicate that the order of photostability is (C6H5)3 C⊕PF⊖6. > (C6H5)3 C⊕FeCl⊖4 ≥ (C6H5)3 C⊕ BF⊖4 > (C6H5)3 C⊕ AsF⊖6 ≥ (C6H5)3 C⊕SbCl⊖6. A comparison of the overall rate of photolysis of (C6H5)3 C⊕SbCl⊖6 in argon and oxygen suggests that the photo‐induced reactions are both of radical and ionic type. The composition of the reaction mixtures after photolysis was determined.
Radical efficiency and ionic reactions of some unsymmetrical azo compounds
Authors: Nuyken Oskar , Dyckerhoff Lutz , Schuster Herbert , Kerber Robert
Published: April 2003

Compounds with the structure R1NNR2 decompose either thermally or photochemically to yield nitrogen and the radicals \documentclass{article}\pagestyle{empty}\begin{document}${\rm R}^{1 \atop {^\bullet}}\hbox{and}\ {\rm R}^{2\atop ^\bullet}$\end{document}. These radicals, under appropriate conditions, can either act as polymerization initiators or can be trapped by radical scavengers such as iodine. In the presence of suitable reagents the title compounds behave like diazonium salts and thus, since they are relatively stable, may provide a safe and readily available diazonium ion source.
Novel monomeric and polymeric azo initiators
Authors: Nuyken Oskar , Schuster Herbert , Kerber Robert
Published: April 2003

1‐Methyl‐1‐(3‐vinylphenylazo)ethyl acetate (1a), diphenyl‐(3‐vinylphenylazo)methyl acetate (1b), and α‐phenylazo‐α‐(4‐vinylphenyl)benzyl acetate (2) were prepared and copolymerized with styrene using AIBN as initiator at 50°C. The azo functions of the monomers remain unaltered during the polymerization process at this temperature. The resulting copolymers 3a, 3b, and 4 were used as initiators for the polymerization of methacrylonitrile (MAN). The grafted copolymers of styrene and MAN were separated from polystyrene and poly(methacrylonitrile). The different rates of polymerization of MAN, initiated by the azo group containing polymer 3b or 4 or by diphenylphenylazomethyl acetate, a low molecular model initiator, and the different molar masses obtained allow a discussion of the mechanism involved.
Optically active vinyl polymers, 24. Copolymers of 4‐methyl‐1‐penten‐3‐one and (S)‐4‐methyl‐1‐hexen‐3‐one
Authors: Nguyêñ‐t́ât‐Thiên  , Suter Ulrich W. , Pino Piero
Published: April 2003

Copolymers of 4‐methyl‐1‐penten‐3‐one and (S)‐4‐methyl‐1‐hexen‐3‐one have been synthesized by radical‐ and anionic initiation and their composition has been determined by 13C NMR and 1H NMR spectroscopy. A comparison between the composition of the initial monomer mixture, F, and the composition of the monomeric units in the copolymers, f, indicates Bernoullian copolymerization statistics with both types of initiators. The intrinsic viscosity, the number‐average molecular weight, and the second virial coefficient of the osmotic pressure were measured and an unusually high increase of the intrinsic viscosity with f was noticed. The results can be interpreted by assuming a strong increase in the unperturbed chain dimensions with increasing content of optically active monomeric units in the copolymer.
Optically active vinyl polymers, 25. Chiroptical Properties and Conformation of Copolymers from 4‐Methyl‐1‐penten‐3‐one and (S)‐4‐Methyl‐1‐hexen‐3‐one
Authors: Nguyêñ‐t́ât‐Thiên  , Suter Ulrich W. , Pino Piero
Published: April 2003

The molar optical rotation at 589 nm, the UV‐, CD‐and ORD‐spectra of atactic and highly isotactic random copolymers of 4‐methyl‐1‐penten‐3‐one (4MP3O) and (S)‐methyl‐1‐hexen‐3‐one ((S)‐4MH3O) were measured in different solvents at different temperatures. The ellipticity observed in the isotactic copolymers between 240 and 320 nm is much larger than that calculated for a mixture of the two homopolymers, showing that in the isotactic (but not in the atactic) copolymers chiral conformations, giving contributions of negative sign to the CD, prevail also in the monomeric units arising from the non‐chiral monomer. The decrease of the ellipticity with increasing temperature for the copolymers is not linear; the average value between 20°C and 60°C is larger for the copolymers than for the homopolymers. The results indicate that in the isotactic copolymers main‐chain helical conformations of one handedness are favoured over those of the opposite screw sense, and that achiral units incorporated in helical sections are forced to assume chiral conformations similar to the conformations that chiral units assume in the same helical section.
Polyméres porteurs de dérivés du glycérol, 3. Modification chimique du méthacrylate d′époxy‐2,3 propyle et de son polymére par i′acide phényl‐2 butyrique
Authors: Soutif Jean‐Claude , Mouity‐Mousounda Francçois , Brosse Jean‐Claude
Published: April 2003

The influence of time, temperature, and concentration on the addition rate of 2‐phenylbutyric acid (1) to 2,3‐epoxypropanol (4), 2,3‐epoxypropyl methacrylate (2), and its polymer 3 was studied in chloroform and 1, 4‐dioxane. The variation of the yeld with time and concentration of catalyst (tetramethyl ammonium salt of 1) can be fairly well represented by the equation v = k [Acid] · [Epoxide] · [Catalyst], with k ∼ 0,6 to 0,8 12 · mol ‐2 ·h‐1 at T = 60°C and [Acid] ≈ 1 mol · 1‐1. The Arrhenius activation energy was found to be 70 to 80 kJ · mol‐1. With variation of the epoxide and acid concentrations, deviations were observed.
Non‐newtonian flow behaviour of poly(decyl methacrylate) solutions
Authors: Herold F. K. , Wolf B. A.
Published: April 2003

The viscosity of solutions of poly(decyl methacrylate)s, PDMA, in 1‐pentanol (thermodynamically poor solvent) and in toluence or isooctane (good solvents) was measured up to shear rates of 3 · 104s−1 by means of rotational viscosimeters. The observed pronounced shear thinning is for all solutions well described by the theory of Graessley, with the extension, introduced by Ito. Two parameters, resulting from the evaluation of the flow curves on the basis of the above theory, are discussed: τ0, a characteristic relaxation time of the polymer chain, is found to be in the range of ms. ηfric, a frictional parameter, independent of shear rate, amounts upto 50% of the zero‐shear viscosity for the measured solutions. Both, τ0 and ηfric, increase with decreasing solvent quality, increasing molecular weight, and increasing concentration, in accord with theory. A comparatively sharp downward bend, separating two power‐law regimes, shows up with moderately concentrated solutions, as the shear rate exceeds about 103 to 104 s−1. This transition is tentatively interpreted as an orientation of the long side chains of PDMA.
Crystallization and stereo assocation of stereoregular PMMA, 2. Crystallization behavious of the stereocomplex in comparison with that of pure stereoregular PMMA
Authors: Könnecke Klaus , Rehage Günther
Published: April 2003

The crystallization behaviour of stereoregular PMMA was studied by means of DSC and X‐ray measurements. Both nucleation and crystallization rates of i‐PMMA. are slower by orders of magnitude compared with s‐PMMA and with the 1:1‐i/s‐stereocomplex of PMMA. The investigation of the nucleation and crystallization of i‐PMMA by means of the DSC method leads to the results that both nucleation and crystallization rates show a maximum in the region between melting and glass transition temperature. As a result of the fast crystallization rates of s‐PMMA and the stereocomplex, however, these polymers do crystallize without annealing showing a very broad distribution of crystallite sizes. From the shape of the melting curves as a function of annealing time it can be concluded that the crystallization of i‐PMMA gels leads to the formation of a physical network, which contains small and big crystallites. The results of the measurements allow the determination of the heat of stereocomplex formation. The value found of 24 J · g−1 agrees with values obtained directly on mixing dilute solutions of i‐ and s‐PMMA. As a result of calorimetric measurements the liquidus curves of the quasi‐binary systems of solvent (o‐xylene) and stereoregular PMMA are obtained. Taking into account data of former work for the quasi‐binary system of i‐PMMA and s‐PMMA, the shape of the liquidus surface in the quasi‐ternary system of i‐PMMA, s‐PMMA, and solvent (o‐xylene) can be constructed.
IR‐bandenstrukturanalyse der amidstreckschwingungen von N‐methylacetamid als modellsubstanz für makromoleküle mit peptidbindungen
Authors: Hummel Helmut , Bonart Richard
Published: April 2003

The C0 and NH stretching vibrations of N‐methylacetamide in solution were studied at different concentrations and temperatures. By means of bandfitting and using the second derivative, the CO stretching band (Amide I) was resolved into four component bands. An assignment of these frequencies is discussed. The band splitting of amide I indicates the presence of cis‐trans isomerism about the peptide (CONH) link and a frequency shift of the free CO end groups of associated molecules. The H‐bond enthalpy seems to be influenced by the chain length of the associates.
Megacystis at 10–14 weeks of gestation: chromosomal defects and outcome according to bladder length
Authors: Liao A. W. , Sebire N. J. , Geerts L. , Cicero S. , Nicolaides K. H.
Published: April 2003

Aims

To examine the prevalence of chromosomal defects and outcome of fetuses with megacystis at 10–14 weeks of gestation.

Methods

At the 10–14‐week scan fetal megacystis was defined by a longitudinal bladder diameter of 7 mm or more. In 145 such fetuses the fetal karyotype and pregnancy outcome were examined in relation to the longitudinal diameter of the fetal bladder.

Results

Chromosomal defects, mainly trisomies 13 and 18, were present in 30 cases. In the group with longitudinal bladder diameter of 7–15 mm the incidence of chromosomal defects was 23.6% (26/110), whereas in those with bladder diameter > 15 mm the incidence was 11.4% (4/35). The fetal nuchal translucency (NT) was above the 95th centile of the normal range for crown–rump length in a higher proportion of cases with abnormal rather than normal karyotype (76.7% compared to 31.3%; Chi‐square P < 0.0001). The expected number of cases of trisomy 21, estimated on the basis of maternal age, gestational age and fetal NT, was 6.2 rather than the observed 2 and the corresponding numbers for trisomies 13 or 18 were 4.2 for expected and 24 for observed. In the chromosomally normal group with longitudinal bladder diameter of 7–15 mm follow‐up scans demonstrated spontaneous resolution of the megacystis in 90% of the cases and enlargement of the megacystis and/or the development of echogenic kidneys in 10%. In contrast, none of the cases with bladder diameter > 15 mm demonstrated spontaneous resolution of the megacystis.

Conclusions

In fetal megacystis with longitudinal bladder diameter of 7–15 mm there is a risk of about 25% that the fetus will have a chromosomal defect but in the chromosomally normal group there is spontaneous resolution of the megacystis in about 90% of cases. If the bladder diameter is > 15 mm the risk of chromosomal defects is about 10% and in the chromosomally normal group the condition is invariably associated with progressive obstructive uropathy. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
The Impact of Work Hours and Schedules on the Physical and Psychological Well-Being in Medical Practices
Authors: Kirkcaldy Bruce , Trimpop Rüdiger , Levine Robert
Published: April 2003

In a random sample of just over 300 medical doctors and consultants throughout Germany, various job-related variables were assessed together with sociodemographic data including time-related parameters of work, and specific categories of accidents (moving vehicle and work-related). Occupational stress was related to number of weekly working hours, duration of the lunch-break, as well as age. Moving vehicle accidents (MVAs) were significantly correlated with the incidence of work-related accidents during the last year. There was no evidence that medical doctors working longer weekly hours were more likely to be involved in a driving or work-related accident per se, but they did tend to report more accidents during house visits. Moving vehicle accidents were best predicted by the onset of working day as well as the number of dependent children (more children associated with less accidents). Furthermore, work-related accidents were significantly more frequent in larger communities and when surgeries were later in finishing. The implication of these findings are discussed.
Report from Euroland: Assisting Individuals, Couples, and Families on the Move
Authors: Vercruysse Nathalie
Published: April 2003

Residential change over both short and long distances has become an increasingly common occurrence in modern society as the rise of multinational corporations and international nongovernmental institutions has drawn hundred of thousands overseas. This increase in international mobility around the globe has been accompanied by a growing interest in the sociocultural, educational, and psychological problems usually experienced by persons adjusting to new cultures. It has also encouraged the development of specialized services for assisting sojourners before, during, and after their move. Brussels—the capital of political Europe—is an increasingly diverse city with a great number of expatriates and a real demand for English-speaking mental health services specifically designed to promote the well-being of its international community. This report serves to inform readers about Community Help Service (CHS), the oldest and probably largest organization of its kind currently available in Europe.
The Role of the Immune System in Psychology and Neuroscience
Authors: Lekander Mats
Published: April 2003

The immune system and the nervous system are connected in a dynamic network that has important implications for psychology. First, if analyzed in functional terms, the immune system and the nervous system are not distinctly separated: The immune system can take part in neuronal signaling through the production of an array of transmitters and hormones, and brain cells can process and present antigen and produce immune proteins. Moreover, synapses seem to be formed between immune and neural cells in lymphoid tissue. The basis of this phenomenon may be a common evolutionary background of physiological systems that by tradition have been viewed as discrete rather than overlapping. Second, the immune system is actively involved in homeostatic regulation. Signals from immune cells can profoundly change the physiological state of the organism, with changes observed in metabolism, stress axes activity, behavior, motivation and cognition. Many of these changes have probably evolved to ease recuperation. Third, the activity in the immune system is dependent of homeostatic regulation by the neuroendocrine system in a biologically important network that is also capable of mediating psychological impact on immunity. In this review, it is argued that immunology should be ecological in nature and thereby related to psychological and neural science. Hypothetically, an ecological immunology will show cross-fertilizing properties, increasing the explanatory power of the seemingly disparate scientific disciplines involved.
Isolation and identification of short nucleotide sequences that affect translation initiation in
Saccharomyces
cerevisiae
Authors: Zhou Wei , Edelman Gerald M. , Mauro Vincent P.
Published: April 2003

In previous studies, we demonstrated the sufficiency of short nucleotide sequences to facilitate internal initiation of translation in mammalian cells. By using a selection methodology, we have now identified comparable sequences in
Saccharomyces cerevisiae
. For these studies, a library of constructs expressing dicistronic mRNAs with the
HIS3
gene as the second cistron and 18 random nucleotides in the intercistronic region was introduced into a yeast strain in which the endogenous
HIS3
gene was deleted. Untransformed cells or those containing the parent construct failed to grow on medium lacking histidine. Intercistronic sequences recovered from cells that did grow were evaluated by using various criteria. Fifty-six of the 18-nt sequences (≈1/400,000) functioned as synthetic internal ribosome entry sites (IRESes). The 14 most active sequences allowed growth in the presence of 0.1–0.6 mM 3-amino-1,2,4-triazole, a competitive inhibitor of the
HIS3
gene product. In addition, eight sequences were identified that were not IRESes, but that enhanced
HIS3
expression by an alternative mechanism that depended on the 5′ end of the mRNA and appeared to involve either shunting or reinitiation. Comparisons among the 56 selected IRESes identified eight significant sequence matches containing up to 10 nucleotides. Many of the selected sequences also contained extensive complementary matches to yeast 18S rRNA, some at overlapping sites. The identification of
cis
sequences that facilitate translation initiation in yeast enables detailed biochemical and genetic analyses of underlying mechanisms and may have practical applications for bioengineering.
Erythrocyte-binding antigen 175 mediates invasion in
Plasmodium falciparum
utilizing sialic acid-dependent and -independent pathways
Authors: Duraisingh Manoj T. , Maier Alexander G. , Triglia Tony , Cowman Alan F.
Published: April 2003

The
Plasmodium falciparum
erythrocyte-binding antigen 175 (EBA-175) is a ligand for merozoite invasion into human erythrocytes that binds to glycophorin A in a sialic acid-dependent manner.
P. falciparum
strain W2mef depends on sialic acid for invasion of erythrocytes, whereas 3D7 is sialic acid-independent. We generated parasites that lack expression or express truncated forms of EBA-175 in W2mef and 3D7. Lack of EBA-175 expression in W2mef parasites was associated with a switch to sialic acid-independent invasion. 3D7 parasites lacking expression of EBA-175 showed no alteration in their ability to utilize sialic acid-independent pathways. Strikingly, both W2mef and 3D7 parasites lacking EBA-175 expression invaded chymotrypsin-treated erythrocytes inefficiently compared with the parental lines. This loss of function suggests that the EBA-175/glycophorin A ligand–receptor interaction is the major chymotrypsin-resistant invasion pathway. Parasite lines with truncated EBA-175 had invasion phenotypes equivalent to parasites lacking expression of EBA-175. The EBA-175 ligand is functional in erythrocyte invasion by merozoites that utilize either sialic acid-dependent or -independent invasion pathways. This finding suggests a model where a minimal affinity supplied by multiple ligand–receptor interactions is required for successful invasion and has implications for EBA-175 as a malaria vaccine candidate.
Evidence that the retroviral DNA integration process triggers an ATR-dependent DNA damage response
Authors: Daniel René , Kao Gary , Taganov Konstantin , Greger James G. , Favorova Olga , Merkel George , Yen Tim J. , Katz Richard A. , Skalka Anna Marie
Published: April 2003

Caffeine is an efficient inhibitor of cellular DNA repair, likely through its effects on ATM (ataxia telangiectasia mutated) and ATR (ATM and Rad3-related) kinases. Here, we show that caffeine treatment causes a dose-dependent reduction in the total amount of HIV-1 and avian sarcoma virus retroviral vector DNA that is joined to host DNA in the population of infected cells and also in the number of transduced cells. These changes were observed at caffeine concentrations that had little or no effect on overall cell growth, synthesis, and nuclear import of the viral DNA, or the activities of the viral integrasein vitro. Substantial reductions in the amount of host-viral-joined DNA in the infected population, and in the number of transductants, were also observed in the presence of a dominant-negative form of the ATR protein, ATRkd. After infection, a significant fraction of these cells undergoes cell death. In contrast, retroviral transduction is not impeded in ATM-deficient cells, and addition of caffeine leads to the same reduction that was observed in ATM-proficient cells. These results suggest that activity of the ATR kinase, but not the ATM kinase, is required for successful completion of the viral DNA integration process and/or survival of transduced cells. Components of the cellular DNA damage repair response may represent potential targets for antiretroviral drug development.
Phosphorylation of p47

phox

directs phox homology domain from SH3 domain toward phosphoinositides, leading to phagocyte NADPH oxidase activation
Authors: Ago Tetsuro , Kuribayashi Futoshi , Hiroaki Hidekazu , Takeya Ryu , Ito Takashi , Kohda Daisuke , Sumimoto Hideki
Published: April 2003

Protein–phosphoinositide interaction participates in targeting proteins to membranes where they function correctly and is often modulated by phosphorylation of lipids. Here we show that protein phosphorylation of p47

phox

, a cytoplasmic activator of the microbicidal phagocyte oxidase (phox), elicits interaction of p47

phox

with phosphoinositides. Although the isolated phox homology (PX) domain of p47

phox

can interact directly with phosphoinositides, the lipid-binding activity of this protein is normally suppressed by intramolecular interaction of the PX domain with the C-terminal Src homology 3 (SH3) domain, and hence the wild-type full-length p47

phox

is incapable of binding to the lipids. The W263R substitution in this SH3 domain, abrogating the interaction with the PX domain, leads to a binding of p47

phox

to phosphoinositides. The findings indicate that disruption of the intramolecular interaction renders the PX domain accessible to the lipids. This conformational change is likely induced by phosphorylation of p47

phox

, because protein kinase C treatment of the wild-type p47

phox

but not of a mutant protein with the S303/304/328A substitution culminates in an interaction with phosphoinositides. Furthermore, although the wild-type p47

phox

translocates upon cell stimulation to membranes to activate the oxidase, neither the kinase-insensitive p47

phox

nor lipid-binding-defective proteins, one lacking the PX domain and the other carrying the R90K substitution in this domain, migrates. Thus the protein phosphorylation-driven conformational change of p47

phox

enables its PX domain to bind to phosphoinositides, the interaction of which plays a crucial role in recruitment of p47

phox

from the cytoplasm to membranes and subsequent activation of the phagocyte oxidase.
Assessing experimentally derived interactions in a small world
Authors: Goldberg Debra S. , Roth Frederick P.
Published: April 2003

Experimentally determined networks are susceptible to errors, yet important inferences can still be drawn from them. Many real networks have also been shown to have the small-world network properties of cohesive neighborhoods and short average distances between vertices. Although much analysis has been done on small-world networks, small-world properties have not previously been used to improve our understanding of individual edges in experimentally derived graphs. Here we focus on a small-world network derived from high-throughput (and error-prone) protein–protein interaction experiments. We exploit the neighborhood cohesiveness property of small-world networks to assess confidence for individual protein–protein interactions. By ascertaining how well each protein–protein interaction (edge) fits the pattern of a small-world network, we stratify even those edges with identical experimental evidence. This result promises to improve the quality of inference from protein–protein interaction networks in particular and small-world networks in general.
Frequency domain analysis of noise in autoregulated gene circuits
Authors: Simpson Michael L. , Cox Chris D. , Sayler Gary S.
Published: April 2003

We describe a frequency domain technique for the analysis of intrinsic noise within negatively autoregulated gene circuits. This approach is based on the transfer function around the feedback loop (loop transmission) and the equivalent noise bandwidth of the system. The loop transmission,
T
, is shown to be a determining factor of the dynamics and the noise behavior of autoregulated gene circuits, and this
T
-based technique provides a simple and flexible method for the analysis of noise arising from any source within the gene circuit. We show that negative feedback not only reduces the variance of the noise in the protein concentration, but also shifts this noise to higher frequencies where it may have a negligible effect on the noise behavior of following gene circuits within a cascade. This predicted effect is demonstrated through the exact stochastic simulation of a two-gene cascade. The analysis elucidates important aspects of gene circuit structure that control functionality, and may provide some insights into selective pressures leading to this structure. The resulting analytical relationships have a simple form, making them especially useful as synthetic gene circuit design equations. With the exception of the linearization of Hill kinetics, this technique is general and may be applied to the analysis or design of networks of higher complexity. This utility is demonstrated through the exact stochastic simulation of an autoregulated two-gene cascade operating near instability.
A secreted high-affinity inhibitor of human TNF from Tanapox virus
Authors: Brunetti Craig R. , Paulose-Murphy Mini , Singh Rajkumari , Qin Jing , Barrett John W. , Tardivel Aubry , Schneider Pascal , Essani Karim , McFadden Grant
Published: April 2003

A class of secreted poxvirus tumor necrosis factor (TNF)-binding proteins has been isolated from Tanapox-infected cell supernatants. The inhibitor bound to a TNF-affinity column and was identified as the product of the 2L gene. Sequence analysis of 2L family members from other yatapoxviruses and swinepox virus yielded no sequence homology to any known cellular gene. The expressed Tanapox virus 2L protein bound to human TNF with high affinity (
K
d
= 43 pM) and exhibits an unusually slow off-rate. However, 2L is unable to bind to a wide range of human TNF family members. The 2L protein can inhibit human TNF from binding to TNF receptors I and II as well as block TNF-induced cytolysis. Thus, Tanapox virus 2L represents an inhibitor of human TNF and offers a unique strategy with which to modulate TNF activity.
Assembly of high-affinity insulin receptor agonists and antagonists from peptide building blocks
Authors: Schäffer Lauge , Brissette Renee E. , Spetzler Jane C. , Pillutla Renuka C. , Østergaard Søren , Lennick Michael , Brandt Jakob , Fletcher Paul W. , Danielsen Gillian M. , Hsiao Ku-Chuan , Andersen Asser S. , Dedova Olga , Ribel Ulla , Hoeg-Jensen Thomas , Hansen Per Hertz , Blume Arthur J. , Markussen Jan , Goldstein Neil I.
Published: April 2003

Insulin is thought to elicit its effects by crosslinking the two extracellular α-subunits of its receptor, thereby inducing a conformational change in the receptor, which activates the intracellular tyrosine kinase signaling cascade. Previously we identified a series of peptides binding to two discrete hotspots on the insulin receptor. Here we show that covalent linkage of such peptides into homodimers or heterodimers results in insulin agonists or antagonists, depending on how the peptides are linked. An optimized agonist has been shown, both
in vitro
and
in vivo
, to have a potency close to that of insulin itself. The ability to construct such peptide derivatives may offer a path for developing agonists or antagonists for treatment of a wide variety of diseases.
Stability of magnesiowüstite in Earth's lower mantle
Authors: Lin Jung-Fu , Heinz Dion L. , Mao Ho-kwang , Hemley Russell J. , Devine James M. , Li Jie , Shen Guoyin
Published: April 2003

Magnesiowüstite [(Mg,Fe)O] is the second most abundant mineral of Earth's lower mantle. Understanding its stability under lower mantle conditions is crucial for interpreting the physical and chemical properties of the whole Earth. Previous studies in an externally heated diamond anvil cell suggested that magnesiowüstites decompose into two components, Fe-rich and Mg-rich magnesiowüstites at 86 GPa and 1,000 K. Here we report an
in situ
study of two magnesiowüstites [(Mg
0.39
,Fe
0.61
)O and (Mg
0.25
,Fe
0.75
)O] at pressures and temperatures that overlap with mantle conditions, using a laser-heated diamond anvil cell combined with synchrotron x-ray diffraction. Our results show that addition of Mg in wüstite (FeO) can stabilize the rock-salt structure to much higher pressures and temperatures. In contrast to the previous studies, our results indicate that Mg-rich magnesiowüstite is stable in the rock-salt structure in the lower mantle. The physical and chemical properties of magnesiowüstite should change gradually and continuously in the lower mantle, suggesting that it does not make a significant contribution to seismic-wave heterogeneity of the lower mantle. Stable Mg-rich magnesiowüstite in lowermost mantle can destabilize FeO in the core–mantle boundary region and remove FeO from the outer core.
Epstein–Barr virus-infected B cells expanding in germinal centers of infectious mononucleosis patients do not participate in the germinal center reaction
Authors: Kurth Julia , Hansmann Martin-Leo , Rajewsky Klaus , Küppers Ralf
Published: April 2003

To assess the impact of the germinal center (GC) reaction on viral spread in Epstein–Barr virus (EBV) infection, we isolated EBV
+
GC B cells from the tonsils of two infectious mononucleosis patients, sequenced their rearranged V genes, and determined expression of the EBV latency genes EBV nuclear antigen 2 and latent membrane protein 1. Most EBV
+
GC B cells belonged to clones of cells harboring somatically mutated V gene rearrangements. Ongoing somatic hypermutation, the hallmark of the GC reaction, was seen only in uninfected GC B cell clones, not in EBV
+
B cell clones. Thus, in infectious mononucleosis, GC and/or memory B cells are directly infected by EBV and expand without somatic hypermutation, whereas the GC passage of EBV-infected naive B cells does not contribute detectably to the generation of infected memory B cells, the main reservoir of EBV during persistence. Most, if not all, EBV-infected cells in GCs exhibited an unusual EBV gene expression pattern in that they were positive for EBV nuclear antigen 2 but negative for latent membrane protein 1. Although the three main types of EBV-associated B cell lymphomas (Burkitt's, Hodgkin's, and posttransplant lymphomas) presumably are derived from GC B cells, EBV
+
GC B cells resembling these EBV
+
GC B cell lymphomas in terms of EBV gene expression and somatic hypermutation pattern could not be identified.