bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthèse et caractérisation de copolymères séquencés poly(vinyl‐2 pyridine)/poly(oxyéthylène)
Authors: Marie Pascal , Lingelser Jean‐Paul , Gallot Yves
Published: April 2003

Hydrophobic‐hydrophilic poly(2‐vinlypyridine)/poly(ethylene oxide) block copolymers were synthesized by anionic polymerization in tetrahydrofuran in vacuum with diphenylmethylpotassium as initiator. The resulting polymers were fractionated from benzene solution by progressive precipitation with 2,2,4‐trimethylpentane at 35°C. Gel permeation chromatography, light scattering, osmometry, and 1H NMR were used to characterize the fractions. The copolymers, thus prepared, were found to have a well defined structure and a low polydispersity in both molecular weight and chemical composition.
Nature et conséquence des interactions se développant lors de la mise en contact de polyéthylène avec des produits mouillants et non mouillants, 2. Cas des produits non mouillants polaires (eau) et apolaires (iodure de méthylène)
Authors: Escoubes Marcelle , Berticat Philippe , Chabert Bernard , Chauchard Jacques , Sage Daniel
Published: April 2003

The nature of interactions between polyethylene and a non‐wetting solute was analyzed to know if the interface can be characterized by the expression of the energy of wetting or if phenomena other than adhesion and wetting must be taken into account. In this way, the isotherms of sorption, the molar heats of interaction, the kinetic behaviour of the sorption, the permeation, and the changes of length during liquid immersion gave informations on the existence of a limited diffusion into the polymer. Two types of systems were investigated: polyethylene/water and polyethylene/methylene iodide. The formation of aggregates is discussed.
Synthesis of AB and BAB poly(styrene‐b‐4‐vinylpyridine) and solution properties of their quaternized compounds
Authors: Ishizu Koji , Kashi Yasuo , Fukutomi Takashi , Kakurai Toshio
Published: April 2003

Well‐definded AB and BAB poly(styrene(S)‐b‐4‐vinylpyridine(4VP))s were prepared by anionic polymerization in tetrahydrofuran (THF) at −78°C. Quaternization of these block copolymers was carried out with methyl iodide and P4VP blocks were completely quaternized. The emulsifying effect, viscosity behavior, and binding of methyl orange to the quaternized compounds are discussed in detail from a view‐point of sequential arrangements.
Hochdruck‐hochtemperatur‐reaktionen in einem strömungsreaktor, 12. Thermische dimerisierung von acrylsäauremethylester, methylvinylketon und acrylnitril
Authors: Metzger Jürgen O. , Köll Peter
Published: April 2003

Thermal dimerization of methyl acrylate to dimethyl 2‐methyleneglutarate was performed in a high pressure‐high temperature flow apparatus at temperatures up to 420°C and pressures up to 200 bar. The head to head dimer dimethyl 2‐methyl‐3‐methylenesuccinate was observed, too. Methyl vinyl ketone and acrylonitrile are able to dimerize analogously.
Role of hydrophobic interaction in the enantioselective solvolyses of amino acid p‐nitrophenyl esters by optically active imidazole‐containing polymers
Authors: Cho Iwhan , Shin Jae‐Sup
Published: April 2003

Solvolytic reactions of N‐benzyloxycarbonyl‐D‐phenylalanine p‐nitrophenyl ester and N‐benzyloxycarbonyl‐L‐phenylalanine p‐nitrophenyl ester by optically active imidazole‐containing polymers were performed at different temperatures and in aq. ethanol of different water contents. The catalyst polymers employed were homopolymers of N‐methacryloyl‐L‐histidine (1a) and N‐methacryloyl‐L‐histidine methyl ester (1b), as well as copolymers of 1a with dodecyl methacrylate (DMA) and 1b with DMA. In 30 vol. ‐% aqueous ethanol at pH 7,02 the homopolymers did not show any enantioselective catalysis. However, the copolymers did exhibit enantioselective catalysis, viz., kcat(L)/kcat(D) = 1,25 for poly (1b‐co‐DMA) containing 5,7 mol‐% of DMA. As the reaction temperature was lowered, the reaction rate increased and the enantioselectivity was enhanced (kcat(L)/kcat(D) = 1,67 for poly (1b‐co‐DMA) at 10°C). When the ethanol content was decreased, enhanced reaction rates and enantioselectivity (kcat(L)/kcat(D) = 1,65 for poly (1 b‐co‐DMA) in 20 vol.‐% aqueous ethanol) were observed. From these results it is concluded that hydrophobic interaction plays an important role in the enantioselective catalysis of optically active imidazole‐containing polymers.
OH Radical‐induced chemical reactions of polynucleotide complexes
Authors: Denk Otmar , Washino Komei , Schnabel Wolfram
Published: April 2003

Poly(A + U), the 1:1 complex of poly(riboadenylic acid), poly A, and poly(ribouridylic acid), poly U, at pH 8 and self‐complexed poly A at pH 4 exist as double helices in dilute aqueous solution. These complexes exhibit a similar behavior as native calf thymus DNA upon irradiation with 16 MeV electron pulses. Thus time resolved Rayleight light scattering measurements showed that crosslinking and double strand breakage can be clearly separated, the former proceeding faster than the latter. The extent to which the two processes occur depends on the ionic strength of the solution. At ionic strenghts exceeding 10 −1 mol/l crosslinking is the dominant process indicating that hcrit, the critical length between two single strand breaks for the accomplishment of double strand breaks, is strongly reduced. The investigation of complexes of poly A and Mg2+ ions revealed that the destruction of salt bridges is the rate determining process for the decrease of the light scattering intensity due to mainchain scission. This implies that life‐times of salt bridges can be determined.
Synthesis and investigation of the properties of cardo‐copolyimides with different microstructure
Authors: Korshak V. V. , Vinogradova S. V. , Vygodskii Ya. S. , Nagiev Z. M. , Urman Ya. G. , Alekseeva S. G. , Slonium I. Ya.
Published: April 2003

Copolyimides, their microstructure being determined by the method of synthesis, were prepared by copolycondensation of 4,4′‐oxydiphthalic anhydride (1a), 4,4′‐carbonyldipthalic anhydride (1b), or 1,8:4,5‐naphthalenetetracarboxylic anhydride with a mixture of two diamines, hexa‐, octa‐, or dodecamethylene diamine (5a, 6a, 7a) and cardo‐diamines 9,9‐bis(4′‐aminophenyl)fluorene (3a) and 3,3‐bis(4′‐aminophenyl)phthalide (4) or two aromatic diamines, 4,4′‐oxydianiline (9) and 2,2‐bis(4‐aminophenyl)hexafluoropropane (8), at various mole ratios of the comonomers. Blockcopolyimides with five‐membered imide cycles were formed by catalytic imidization of the intermediate polymers prepared by addition of the solid dianhydride to a solution of the mixture of the two diamines, whereas the thermal cyclization of such polymers and the one‐step high‐temperature synthesis led to random copolyimides. The thermal and mechanical properties of the copolyimides with various microstructure and their solubility in organic solvents were compared.
Preparation of poly[(3S)‐1,2,3,4‐tetrahydroisoquinoline‐2,3‐diylmethylene] and its use as chiral catalyst in the addition of arenethiols to 2‐cyclohexen‐1‐one
Authors: Yamashita Tetsushi , Kagigaki Eizo , Takahashi Nozomu , Nakamura Nobuo
Published: April 2003

Poly[(3S)‐1,2,3,4‐tetrahydroisoquinoline‐2,3‐diylmethylene] (4) and (3S)‐3‐(1,2,3,4‐tetrahydroisoquinolin‐2‐ylmethyl)‐2‐methyl‐1,2,3,4‐tetrahydroisoquinoline (7) were prepared using (3S)‐1,2,3,4‐tetrahydro‐3‐isoquinolinecarboxylic acid (1) as starting material. The optically active amines 4 and 7 were used as asymmetric catalysts for the addition of thiophenol (8a), 4‐tert‐butylthiophenol (8b), or 4‐chlorothiophenol (8c) to 2‐cyclohexen‐1‐one (9). 4 yielded 3‐phenylthiocyclohexanone (10a) with the highest optical yield of 24% at −25°C, showing a marked polymer effect with respect to enantiomeric excess.
Functional metal‐porphyrazine derivatives and their polymers, 7. Synthesis and properties of metal‐2,9,16,23‐tetracarboxyphthalocyanine covalently bound to poly(2‐ or 4‐vinylpyridine‐co‐styrene)
Authors: Higaki Seigo , Hanabusa Kenji , Shirai Hirofusa , Hojo Nobumasa
Published: April 2003

Metal‐2,9,16,23‐tetracarboxyphthalocyanines(Mt‐taPc's) [Mt = Fe(III), Co(II), Ni(II), Cu(II)] covalently bound to poly(2‐ or 4‐vinylpyridine‐co‐styrene) were synthesized by Friedel‐Crafts reaction of the styrene units of the copolymers with Mt‐taPc tetraacid chloride. The copolymers contain about 0,3 to 14,6 mol‐% Mt‐Pc rings and are soluble in methanol, ethanol, and N,N‐dimethylformamide. The coordination spheres around the Mt‐Pc rings were characterized by electronic as well as ESR spectra and by viscosity measurements. The dimerization of Mt‐taPc in the copolymers is sterically hindered by the polymer chain. The copolymer supported Fe(III)‐ or Co(II)‐taPc's are of the five coordinate high spin type in DMF solution. One coordination site at axial position of the Mt‐Pc ring may be occupied by an N atom of a pyridine group. The electronic structures of the metal atoms may be useful in catalytic reactions.
Kinetic determination of stereoselectivity in the anionic polymerization of α‐ethyl‐α‐phenyl‐β‐propiolactone
Authors: Biela Tadeusz , Penczek Stanislaw , Slomkowski Stanislaw , Vogl Otto
Published: April 2003

The kinetics of the anionic polymerization of optically active α‐ethyl‐α‐phenyl‐β‐propiolactone (optical purity 16,8%) initiated with bis(triphenylphosphine)iminium acetate was investigated and the rate constants for the homo‐(kph) and crosspropagation (kpc) (considering R and S enantiomers as comonomers) were determined. The knowledge of the values of kph and kpc, equal to 1,53·10−4 and 9,0·10−51· mol−1·s−1, respectively (25°C, CH2Cl2 solvent), allowed us to calculate the distribution of homosequences in the polymer prepared from racemic monomer. The concentration of homosequences was slightly higher than calculated for the process with random enchainment of enantiomers. Thus, the content of homodyads, homotriads, and homotetrads equals 63, 40, and 25%, whereas for the random process it was 50, 25, and 13%, respectively. This difference is, however, too small to create homoblocks which could be responsible for the observed crystallinity of these polymers.
Polymer conformation and NMR chemical shifts, 8. Monomer‐ and stereo‐sequence dependences of 13C NMR spectrum of poly(methyl acrylate‐co‐styrene)
Authors: Sato Kota , Koinuma Hideomi , Hirai Hidefumi
Published: April 2003

The 13C NMR spectra of poly(methyl acrylate‐co‐styrene) are interpreted by a theoretical procedure which consists of conformational analysis of the random copolymer chain and shielding calculation. The conformational probabilities of the diad sequences constituting poly(methyl acrylate‐co‐styrene) are calculated by a matrix method which is conducted by the statistical mechanics of polymer chains. All the elements of the matrices are determined by the force field method. As significant shielding factors for 13C nuclei, paramagnetic, diamagnetic, and anisotropic terms are taken into account. The calculation is used to assign the observed split peaks for the carbonyl carbon and methoxyl carbon in the copolymer. A good agreement between calculation and observation of the peak splittings due to the distribution of the monomer sequence as well as that of the stereo sequence was obtained by considering the feasibility of rotational isomerization at the side chain ester group in two successive MA units.
Solution properties of ultrahigh molecular weight polymers, 1. Methyl methacrylate‐styrene 50:50 random copolymers
Authors: Simionescu Cristofor I. , Simionescu Bogdan C. , Ioan Silvia
Published: April 2003

The paper is concerned with light scattering studies on solutions of ultrahigh molecular weight random copolymers of methyl methacrylate and styrene (50:50 mol/mol). The dependence of the radius of gyration and of the second virial coefficient on the weight‐average molecular weight of the copolymers was established. The value of the steric factor of the copolymer compared to those of the corresponding homopolymers confirms the random character of the copolymer chain. The interpenetration function Ψ(Z), calculated on the basis of different theoretical approximations, is discussed for the expansion factor αs3 > 7.
Degradation and depolymerization of poly(propylene carbonate) by diethylzinc
Authors: Kuran Witold , Górecki Piotr
Published: April 2003

Poly(propylene carbonate) (PPC) was treated with diethylzinc in 1,4‐dioxane solution at 30°C, Zn(C2H5)2 being used in excess or defficiency with regard to carbonate units. PPC was found to undergo degradation and depolymerization reactions, which were followed via the polymer intrinsic viscosity and the propylene carbonate yield. A model reaction between diethyl carbonate and diethylzinc was carried out too. From the results, a mechanistic view for both pathways, degradation and depolymerization, is proposed.
Synthesis, polymerization, and copolymerization of lactams containing vinyl groups
Authors: Samyn Celest , Smets Georges
Published: April 2003

Two new lactam monomers containing vinyl groups were synthesized, namely 1‐benzyl‐3‐methylene‐5‐methyl‐2‐pyrrolidone (1) and 5‐oxo‐2‐pyrrolidinylmethyl methacrylate (2). Their homopolymerization and copolymerizations with methyl methacrylate (MMA), styrene, or methylacrylate were studied. The copolymerization parameters r1 and r2 were also evaluated. Poly(1) is a stable polymer which decomposes at ≈ 300°C under nitrogen and at 250°C in air. Its pyrrolidone ring is resistant towards acids and bases.
Characterization of polyesters resulting from 1,2‐propanediol and phthalic anhydride and their model compounds by 1H and 13C NMR spectroscopy
Authors: Judas Didier , Fradet Alain , Maréchal Ernest
Published: April 2003

In order to study the side reactions taking place during the synthesis of polyesters, the structures of several model compounds were determined. Diesters or polyesters from 1,2‐propanediol and phthalic acid were used as models. Their synthesis and characterization are described. The interpretation of their 1H and 13C NMR spectra is reported; resonances due to the various end groups could be fully assigned.
Chemical modification of polydienes, 1. Grafting of chlorohydrinated polybutadiene and nitrile rubbers with poly(tetrahydrofuran)
Authors: Cameron G. Gordon , Duncan Alexander W. S.
Published: April 2003

cis‐1,4‐Polybutadiene and nitrile rubbers were functionalised with chlorohydrin groups up to levels of 10 mol‐% in a two‐stage process. In the first stage epoxide groups were introduced by reaction of the rubber with m‐chloroperbenzoic acid and in the second stage the epoxide ring was opened by reaction with hydrochloric acid to yield chlorohydrin groups. Both steps in the process are clean and virtually quantitative. Graft chains of poly(tetrahydrofuran) were introduced by coupling the hydroxyl groups with living poly(tetrahydrofuran) cations. The lengths of the graft chains were determined by the time between initiation (by the action of silver perchlorate on ethyl bromide in tetrahydrofuran solution) and the coupling step with the functionalised rubber.
Kinetik der radikalischen polymerisation und copolymerisation von N‐vinyl‐N‐methylacetamid
Authors: Fischer Johannes Paul , Rösinger Sigurd
Published: April 2003

In order to get information on the kinetics of free radical polymerization of N‐vinyl‐N‐methylacetamide (VIMA) polymerizations of the purified monomer were performed in dilatometers using the temperature range from 25 to 70°C, monomer concentrations of 10 to 100% in methanol, and initiation either by γY‐irradiation or by radical initiators. Molecular weight meassurements of the polymer were calibrated by light scattering determinations of Mw according to the following equation at 30 °C in methanol: [η]/(ml/g) = 5,02 · 10−3 · Mw0,7946. Normal kinetics of free radical polymerization were found to be valid and Arrhenius parameters were calculated for the ratio kp2/kt of the propagation rate constant kp and the termination rate constant kt as well as for the monomer transfer constant CM and for the efficiency of initiation f. For copolymerizations of N‐vinyl‐N‐methylacetamide with different comonomers the mean Q‐e‐values were calculated as follows: QVIMA ≅ 0,06; eVIMA ≅ − 1,8.
Differential scanning calorimetric studies on bound water in 1,4‐dioxane acidolysis lignin
Authors: Hatakeyama Tatsuko , Hirose Shigeo , Hatakeyama Hyoe
Published: April 2003

The amounts of three different types of water adsorbed on hydrolyzed lignin, which was obtained by acid hydrolysis of softwood meal in 1,4‐dioxane containing trace amounts of hydrochloric acid (in the following called DL), and on its derivatives, i.e., methylated and acetylated lignins, were determined by differential scanning calorimetry (DSC). The first type of water is non‐freezing water, the glass transition of which was detected by DSC. The second type of water corresponds to a kind of bound water which was detected from a crystallization peak in the vicinity of 225 K (peak II). This peak appeared when the water content exceeded a critical amount of non‐freezing water. The third type of water is free water, the crystallization peak (peak I) of which was found at the same temperature as that of pure water. From the enthalpies of crystallization of the above two types of water and the known weight of sorbed water, the amount of bound water in DL was determined to be 0,10 (weight of bound water/weight of dry sample). Furthermore, it was found that bound water breaks hydrogen bonds in DL and decreases its glass transition temperature (Tg) from 425 K to 330 K. The amount of hydroxyl groups, which varies with the degree of methylation or acetylation, was also found to affect the bound water content and inevitaby to decrease T g.
Copolymerization of unsaturated carboxylic acids with styrene and an unsaturated tertiary amine in dimethyl sulfoxide
Authors: Bezděk Milan , Hynková Vlasta , Hrabák František
Published: April 2003

The copolymerization parameters of N‐methyl‐N‐phenyl‐2‐aminoethyl methacrylate (MPAM) and 2‐acryloyloxybenzoic (AOB), 2‐methacryloyloxybenzoic (MOB), and methacrylic acid (MAA) with styrene in DMSO solution at 50°C were determined and used in the calculation of the Alfrey‐Price copolymerization constants e and Q for MPAM, AOB, MOB, and MAA. From the e and Q constants of the monomers thus determined, the copolymerization parameters of the pairs MPAM‐AOB, MPAM‐MOB, MPAM‐MAA were calculated and compared with those determined by the copolymerization of the corresponding pairs in DMSO.
Comparison of methods for determination of the number of active centers in Ziegler‐Natta polymerizations
Authors: Mejzlík Jiří , Lesná Marie , Majer Josef
Published: April 2003

Four intrinsically different methods for the determination of the number of active centers were employed in propylene polymerization catalyzed by the typical heterogeneous system TiCl3/AlEt2Cl: (i) determination of M̄n (GPC method) and calculation of number of macromolecules therefrom; (ii) quenching with BuOT and determination of tritium in the polymer; (iii) quenching with CO or CO2 and determination of carbonyl groups in the polymer (IR spectroscopy); (iv) quenching with SO2 and determination of sulfur in the polymer. The first two methods exhibited a reasonable agreement for the number of active centers. Method (iii) gave much lower values, whereas method (iv) was found to be virtually unsuitable due to a high extent of side reactions of SO2 with the polymer. A similar comparison of the methods was made in ethylene polymerization catalyzed by the typical homogeneous systems Cp2TiEtCl/AlEtCl2 and Cp2TiEtCl/alumoxane. Method (ii) gave a much lower number of active centers than method (i), due perhaps to a low extent of alcoholysis of the TiC bond or to a high kinetic isotope effect. CO2 appeared to be entirely inert as a quenching agent and CO had been reported to show side reactions. It follows that none of the above quenching methods have universal application and thus literature data should be considered with caution.
Correlation of data on intrinsic viscosities in mixed solvents by means of the modified flory‐huggins equation
Authors: Pouchlý Julius , Živný Antonín
Published: April 2003

An equation for the total sorption potential Y derived from the modified Flory‐Huggins equation and containing concentration‐dependent interaction parameters, including the ternary parameter χT, was used to correlate reported data on intrinsic viscosities in mixed solvents. Similarly to the evaluation of data on preferential sorption, the assumption of proportionality between the ternary parameter and the interaction parameter of components of the mixed solvent, g12, was successfully applied to the case of total sorption. The assumption proved to be useful in the treatment of 12 ternary systems, if the single‐liquid approximation was employed. The calculated proportionality constant between the ternary parameter and g12 has properties similar to that evaluated from the data on preferential sorption. The conditions of occurrence of a maximum or minimum in the dependence of total sorption on composition are discussed.
Study of conformational transitions of graft copolymers by UV spectrophotometry, 2. The behaviour of poly(vinyl acetate) grafted hydroxyethyl‐cellulose in selective solvents
Authors: Goşa Kristiana , Carp Nicoleta , Donescu Dan
Published: April 2003

The behaviour of poly(vinyl acetate) grafted hydroxyethylcellulose (PVAc/HEC) in the binary solvent mixture ethanol‐water (90:10 by vol.) was studied by absorption spectrophotometry. The macromolecules of PVAc/HEC graft copolymer exhibit a conformational transition at ca. 55°C where they pass from a monomicelle conformation to a segregated conformation. This intramolecular transition occurs both below and above the critical micellar concentration (c.m.c). In dilute solutions a critical concentration was evidenced, which is one order of magnitude higher than the c.m.c.
Hydrodynamic crossover in two‐polymer mixtures from viscosity measurements
Authors: Dondos Anastasios , Skondras Panayotis , Pierri Evgenia , Benoît Henri
Published: April 2003

A very sharp crossover is observed in the variation of the reduced viscosity ηsp/c as a function of the concentration c for mixtures of 1:1 by weight mixtures of polystyrene and poly(methylmethacrylate) in benzene at 20°C and a 1:1 by weight mixture of poly(ethylene glycol) and polystyrene in benzene at 20°C. The crossover is attributed to the critical to the concentration of the two respective polymers in the solution and its sharpness is due to the incompatibility between the two different polymers.
Study on the molecular weight dependence of dilute solution properties of narrowly distributed polystyrene in toluene and in the unperturbed state
Authors: Kniewske Reinhard , Kulicke Werner‐Michael
Published: April 2003

Intrinsic viscosities [η], second and third virial coefficients A2 and A3, respectively, and mean square radius of gyration 〈RG2〉 of a polymer homologous series of narrow‐molecular‐weight‐distribution polystyrene samples in a molecular weight range of 2000 up to 24 · 106 were determined in toluene at 25°C by light scattering and viscometry measurements. The results are (3 · 104 < Mw < 24 · 106, Mw/Mn ≤ 1,3):

These results were obtained by consideration of the limit of the dilute solution regime, the determination of zero‐shear rate intrinsic viscosities, and the molecular weight dependence of the refractive index increment dn/dc. It was found that dn/dc increases slightly up to Mw = 1,8 · 106. A comparison of the [η]−Mw‐relationship with literature data is given. In addition the unperturbed (theta) dimension parameters K0, 〈h2〉0/M, the characteristic ratio C∞, the steric factor σ, and the thermodynamic interaction parameter B were calculated from the modified Burchard‐Stockmayer‐Fixman procedure using polymolecularity correction and the results compared with experimental data from the literature.
Small angle neutron scattering studies of poly(ethylene oxide) in the melt
Authors: Kugler Joachim , Fischer Erhard W. , Peuscher Manfred , Eisenbach Claus D.
Published: April 2003

The neutron scattering from mixtures of deuterated and undeuterated poly(ethylene oxide), (D‐PEO, H‐PEO), in the small angle and intermediate angle region has been measured in the melt. We found no indications of a molecular segregation. The value of molecular weight evaluated agreed with that obtained by other methods. For a sample with a molar mass of 120000 g/mol the radius of gyration 〈rw2〉1/2 was found to be 13,6 nm, which corresponds to a characteristic ratio of C = 6,9. The form factor of a single chain can be described by the Debye equation for a random coil with the same unperturbed dimensions. Our results are compared with rotational isomeric state calculations and measurements in solvents.
A chain of intramolecular hydrogen bonds, an important factor for the acidity of oligo[(2‐hydroxy‐1,3‐phenylene)methylene]s
Authors: Böhmer Volker , Schade Eckart , Antes Claus , Pachta Jiri , Vogt Walter , Kämmerer Hermann
Published: April 2003

The first dissociation constant of oligonuclear phenolic compounds consisting of one nitrophenol unit besides further alkyl phenol units (10 dinuclear, 15 trinuclear, 6 tetranuclear compounds, and 4 nitrophenols as model) was determined spectroscopically in water/methanol (50/50 by vol.) at 25°C. For the ortho‐linked title compounds with the nitrophenol unit at the end of the molecule a decrease of pK1 is observed which becomes stronger with increasing chain length. The introduction of bulky groups in ortho‐position of the dissociating phenolic unit, as well as at the opposite end of the molecule causes a further decrease of pK1. The lowest value is found for a p‐nitrophenol unit in the middle of the molecule. The results do not only prove the stabilization of the monoanion by intramolecular hydrogen bonds, but they give also strong evidence for a chain of intramolecular hydrogen bonds in the undissociated molecule. The UV‐spectra of the monoanions directly show the existence of intramolecular hydrogen bonds. Especially the p‐nitrophenol system makes it possible, to differentiate according to their strength.
Decay of the spin echo in a pulsed magnetic field gradient NMR
Authors: Peterlin A.
Published: April 2003

The additional attenuation of the spin echo of a pulsed magnetic field gradient NMR caused by the diffusion of the spins carrying molecules is calculated for a time dependent diffusion coefficient. The cases of a Constant D0, of an exponential decay with time, and an abrupt drop from D0 to zero at time t0 are considered. In all cases the time dependence of the experimentally observed attenuation is less steep than that of D. The time scale, however, Changes very little. The calculation was based on the consideration that the diffusion transports the precessing spins to a location with a different Larmor frequency so that a complete reversal after the 180° pulse is not possible any more. Hence, any deviation from a straight line in a plot of the excess attenuation versus δ2(1 − δ/3Δ) may by interpreted in terms of a time dependence of the diffusion coefficient.
Free‐radical polymerization kinetics of methyl methacrylate at very high conversions
Authors: Stickler Manfred
Published: April 2003

The free‐radical polymerization of methyl methacrylate (MMA) at very high conversions (x > 0,8) was studied in the temperature range 60C° to 160C°. 2,2′‐Azodiisobutyronitrile (AIBN) and benzoyl peroxide (BPO) were used as initiators. In the case of the latter, decomposition kinetics at very high monomer conversions was investigated, too. For temperatures T ⩽ 120C° where depropagation can be neglected a simple kinetic model based on “reaction diffusion” and free volume theory was developed. The model contains only a single adjustable parameter, the critical free volume fraction V*. Good agreement between model predictions and experiments was obtained. V* is independent of initial initiator concentration and reaction temperature, and there is some evidence that V* is also independent of the chemical nature of the initiator.
Properties of liquid crystalline polymers in solution, 2. Viscosimetric investigations of polymethacrylates with mesogenic sidegroups
Authors: Springer J. , Weigelt F. W.
Published: April 2003

Dilute solutions of poly(methacrylic acid) derivatives with mesogenic side groups of the benzoic acid phenyl ester type are structurally viscous. This property due to aggregation appears during storage and is attributed to the geometric shape of the dissolved particles. While solutions of freshly polymerized samples show no, or only a slight temperature dependence of the intrinsic viscosity between 298 and 368 K, the intrinsic viscosity of the stored samples decreases suddenly at temperatures above 348 K.
Relation between structure and thermal transitions in comb‐like polymers, 1. Poly(N‐n‐alkylmaleimide)s
Authors: Barrales‐Rienda José M. , Fernandez‐Martín Fernando , Galicia Carmen Romero , Chaves Manuel Sánchez
Published: April 2003

A series of nine poly(N‐n‐alkylmaleimide)s (PMIs) with the n‐alkyl side chain ranging in length from ethyl to octadecyl and including only the even members of the series was studied by differential scanning calorimetry (DSC) from 100 K to above the glass transition temperature. The nine members of the PMI series generally were found to exhibit a glass transition temperature (Tg), a sub‐glass transition temperature (sub‐Tg = Tγ), and, but only the four higher homologs a melting point (Tm) with the respective melting enthalpy (ΔHf). The glass transition of the amorphous members is directly related to the number of methylene groups (including terminal methyl) of the n‐alkyl side chain of the repeating unit. The values of Tg estimated according to a semi‐empirical equation are in good agreement with the experimental data. The melting points of the members of the series presenting crystallinity in the n‐alkyl side chain were analyzed. A good fit of a Garner plot by a least‐mean‐squares procedure is obtained with T = 408,0K, a = −6,26 and b = −2,03. The contribution to the heat of melting per methylene unit clearly demonstrates that the hexagonal paraffin crystal structure is present in the crystalline members, in agreement with X‐ray data. The data when analyzed by Jordan′s procedure show that only part of the n‐alkyl side chain is forming a crystal lattice.
Sliding mode control design for uncertain time‐delay systems subjected to a class of nonlinear inputs
Authors: Yan Jun‐Juh
Published: April 2003

A sliding mode controller is developed for uncertain time‐delay systems with a class of nonlinear inputs. Two main results are derived in this paper. The first result is the presentation of a new delay‐dependent stability condition of uncertain time‐delay systems. In a comparison example, this stability condition is shown to be less conservative than the ones reported recently. The second result is to present a new sliding mode control for uncertain time‐delay systems subjected to a class of nonlinear inputs. The stability of time‐delay systems with unmatching condition in the sliding mode is also discussed. Two illustrative examples are included to demonstrate the superiority of the obtained results. Copyright © 2003 John Wiley & Sons, Ltd.
Venous pulsation in the fetal left portal branch: the effect of pulse and flow direction
Authors: Kiserud T. , Kilavuz Ö. , Hellevik L. R.
Published: April 2003

Objective

To determine whether the waveform in the left portal branch is reciprocal to the waveform found in the ductus venosus and umbilical vein due to difference in pulse direction compared to flow.

Methods

Ten fetuses (gestational age, 18–33 weeks), six with intrauterine growth restriction, three with non‐immune hydrops and one with sacrococcygeal teratoma, were examined using ultrasound imaging and pulsed Doppler. Techniques were adjusted to record simultaneously the waveform from neighboring sections of the veins, relate wave components to each other and determine degree of pulsatility. The corresponding vessel diameters were determined. ANOVA with t‐test or Wilcoxon signed rank test was used to compare paired measurements.

Results

Pulsation in the left portal branch was noted in all fetuses. The pulsatility index was higher than in the umbilical vein (P = 0.005) and the diameter smaller (P = 0.001). In the left portal branch the atrial contraction wave appeared as a velocity peak while there was a nadir during ventricular systole. Simultaneous recordings showed that the waveform was reciprocal to that found in the ductus venosus and umbilical vein. In three cases an augmented pulsatility represented a pendulation of blood in the left portal branch with time‐averaged velocity near zero.

Conclusions

The velocity waveform recorded in the left portal vein is an inverse image of that in the ductus venosus, proving that pulse wave and blood flow run in the same direction in the left portal vein. Low compliance (i.e. small diameter) is probably a main reason for the high incidence of pulsation in this vein. Time‐averaged velocity near zero recorded in three fetuses indicates that this area acts also as a watershed. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Intraobserver and interobserver agreement in the diagnosis of anal sphincter tears by postpartum endosonography
Authors: Faltin D. L. , Boulvain M. , Stan C. , Epiney M. , Weil A. , Irion O.
Published: April 2003

Objective

To evaluate intraobserver and interobserver agreement in the diagnosis of anal sphincter tears by endosonography when performed immediately postpartum by resident obstetricians.

Methods

Fifty‐four primiparous women who delivered vaginally and had no anal sphincter tears (third‐ or fourth‐degree perineal tears) diagnosed clinically were recruited. Four observers assessed photographic prints and video recordings of anal endosonography performed before the suture of the perineum. We calculated the intra‐ and interobserver agreement and the kappa coefficient to quantify the reliability of the diagnosis of clinically occult sphincter tears.

Results

The observers described sphincter tears in 13–28% of the prints, and in 7–32% of the video recordings. Intraobserver agreement was rated as substantial for prints (kappa, 0.63), and moderate for video recordings (kappa, 0.48). The interobserver agreement was fair for prints (kappa, 0.34) and moderate for video recordings (kappa, 0.42).

Conclusion

Endosonography performed immediately postpartum to diagnose anal sphincter tears is of moderate reliability. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Relationship of isolated fetal intracardiac echogenic focus to trisomy 21 at the mid‐trimester sonogram in women younger than 35 years
Authors: Anderson N. , Jyoti R.
Published: April 2003

Objective

To determine whether an isolated echogenic intracardiac focus in the fetal heart in the mid‐trimester (16–24 weeks) in women aged 18–34 years of age is associated with trisomy 21.

Method

This was a prospective population‐based observational study. A search of all obstetric sonograms performed in our region from January 1997 to December 1999 was carried out. From 12 373 pregnancies we identified 267 cases of echogenic foci in the fetal heart. Trisomy 21 was detected in 38 deliveries (0.31%). An echogenic focus was seen in 193 of the 9167 women < 35 years of age who had an obstetric sonogram at 16–24 weeks' gestation, and an echogenic focus was seen in 67 of the 1968 women > 35 years. The study group comprised the 149 women aged 18–34 years who had an echogenic focus in the fetal heart as the only abnormality at an obstetric sonogram performed at 16–24 weeks' gestation.

Results

There were no abnormal outcomes or cases of trisomy 21 among the 149 pregnancies with an echogenic focus as an isolated finding in women aged 18–34 years (0% (95% confidence interval, 0.00–2.43)). The prevalence of isolated echogenic focus was 1.6% for women < 35 and 1.8% for women ≥ 35 years old. Of the 25 fetuses with trisomy 21 undergoing an obstetric sonogram at any gestational age, five (20%) had an echogenic focus. An isolated echogenic focus was present in one fetus with trisomy 21 seen at 26 weeks' gestation in a 17‐year‐old mother. Echogenic foci were single and in the left ventricle in 84.7% of cases.

Conclusion

An isolated echogenic focus in the fetal heart at mid‐trimester ultrasound in women aged 18–34 years is not associated with increased risk for trisomy 21. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Abdominal wall defects and congenital heart disease
Authors: Gibbin C. , Touch S. , Broth R. E. , Berghella V.
Published: April 2003

Objectives

To determine the incidence of cardiac disease associated with abdominal wall defects of fetuses and associated parameters including maternal age, sex, gestational age at delivery, outcome, karyotypes, Apgar scores and associated congenital anomalies.

Methods

This was a retrospective study of fetuses with a prenatal diagnosis of gastroschisis or omphalocele. The Maternal–Fetal Medicine Fetal Therapy (MFM) database was reviewed for all fetuses with abdominal wall defects identified prenatally. All available MFM records, fetal echocardiograms, neonatal echocardiograms and neonatal charts were reviewed for the types of abdominal wall defects and associated cardiac disease identified by ultrasound. Other parameters reviewed included: maternal age, sex, gestational age at delivery, outcome, karyotypes (when available), Apgar scores and associated congenital abnormalities.

Results

Forty‐eight fetuses with an abdominal wall defect and cardiac disease findings were identified. Of these fetuses 26 had gastroschisis and 22 had omphalocele. The mean maternal age was 24.0 ± 5.40 years in the gastroschisis and 29.2 ± 7.23 years in the omphalocele group (P < 0.01). Differences in mean gestational age at delivery, mean birth weight and median Apgar scores at 1 and 5 min were not statistically significant. Abnormal cardiac findings were seen in 4/26 (15%) cases of gastroschisis and included one case of peripheral pulmonary stenosis, two cases of supraventricular tachycardia and one case of persistent pulmonary hypertension (PPHN) of the newborn. Abnormal cardiac findings were seen in 10/22 (45%) cases of omphalocele and included one muscular ventricular septal defect, two atrial septal defects of the secundum variety, one ectopia cordis, one coarctation of the aorta, one dysplasia of the tricuspid valve, one large pericardial effusion and four cases of PPHN.

Conclusions

Fetuses with omphalocele appear to have an increased risk not only of congenital heart disease (CHD) but also of perinatal cardiac abnormalities, especially PPHN. A prenatal maternal hyperoxia test may be of predictive value in determining which patients may develop PPHN. The fact that both CHD and PPHN are increased in fetuses with abdominal wall defects may be of value in counseling parents prenatally, and stresses the importance of performing echocardiography both prenatally and postnatally in these cases. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Buffed energy landscapes: Another solution to the kinetic paradoxes of protein folding
Authors: Plotkin Steven S. , Wolynes Peter G.
Published: April 2003

The energy landscapes of proteins have evolved to be different from most random heteropolymers. Many studies have concluded that evolutionary selection for rapid and reliable folding to a given structure that is stable at biological temperatures leads to energy landscapes having a single dominant basin and an overall funnel topography. We show here that, although such a landscape topography is indeed a sufficient condition for folding, another possibility also exists, giving a previously undescribed class of foldable sequences. These sequences have landscapes that are only weakly funneled in the conventional thermodynamic sense but have unusually low kinetic barriers for reconfigurational motion. Traps have been specifically removed by selection. Here we examine the possibility of folding on these “buffed” landscapes by mapping the determination of statistics of pathways for the heterogeneous nucleation processes involved in escaping from traps to the solution of an imaginary time Schroedinger equation. This equation is solved analytically in adiabatic and “soft-wall” approximations, and numerical results are shown for the general case. The fraction of funneled vs. buffed proteins in sequence space is estimated, suggesting the statistical dominance of the funneling mechanism for achieving foldability.
Bioinformatic design of A-kinase anchoring protein-
in silico
: A potent and selective peptide antagonist of type II protein kinase A anchoring
Authors: Alto Neal M. , Soderling Scott H. , Hoshi Naoto , Langeberg Lorene K. , Fayos Rosa , Jennings Patricia A. , Scott John D.
Published: April 2003

Compartmentalization of the cAMP-dependent protein kinase (PKA) is coordinated through association with A-kinase anchoring proteins (AKAPs). A defining characteristic of most AKAPs is a 14- to 18-aa sequence that binds to the regulatory subunits (RI or RII) of the kinase. Cellular delivery of peptides to these regions disrupts PKA anchoring and has been used to delineate a physiological role for AKAPs in the facilitation of certain cAMP-responsive events. Here, we describe a bioinformatic approach that yields an RII-selective peptide, called AKAP-
in silico
(AKAP-
IS
),
that binds RII with a
K
d
of 0.4 nM and binds RI with a
K
d
of 277 nM. AKAP-
IS
associates with the type II PKA holoenzyme inside cells and displaces the kinase from natural anchoring sites. Electrophysiological recordings indicate that perfusion of AKAP-
IS
evokes a more rapid and complete attenuation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor currents than previously described anchoring inhibitor peptides. Thus, computer-based and peptide array screening approaches have generated a reagent that binds PKA with higher affinity than previously described AKAPs.
Regulation of myotubularin-related (MTMR)2 phosphatidylinositol phosphatase by MTMR5, a catalytically inactive phosphatase
Authors: Kim Soo-A , Vacratsis Panayiotis O. , Firestein Ron , Cleary Michael L. , Dixon Jack E.
Published: April 2003

The myotubularin (MTM) family constitutes one of the most highly conserved protein-tyrosine phosphatase subfamilies in eukaryotes. MTM1, the archetypal member of this family, is mutated in X-linked myotubular myopathy, whereas mutations in the MTM-related (MTMR)2 gene cause the type 4B1 Charcot–Marie-Tooth disease, a severe hereditary motor and sensory neuropathy. In this study, we identified a protein that specifically interacts with MTMR2 but not MTM1. The interacting protein was shown by mass spectrometry to be MTMR5, a catalytically inactive member of the MTM family. We also demonstrate that MTMR2 interacts with MTMR5 via its coiled-coil domain and that mutations in the coiled-coil domain of either MTMR2 or MTMR5 abrogate this interaction. Through this interaction, MTMR5 increases the enzymatic activity of MTMR2 and dictates its subcellular localization. This article demonstrates an active MTM member being regulated by an inactive family member.
New consumers: The influence of affluence on the environment
Authors: Myers Norman , Kent Jennifer
Published: April 2003

Growing consumption can cause major environmental damage. This is becoming specially significant through the emergence of over 1 billion new consumers, people in 17 developing and three transition countries with an aggregate spending capacity, in purchasing power parity terms, to match that of the U.S. Two of their consumption activities have sizeable environmental impacts. First is a diet based strongly on meat, which, because it is increasingly raised in part on grain, puts pressure on limited irrigation water and international grain supplies. Second, these new consumers possess over one-fifth of the world's cars, a proportion that is rising rapidly. Global CO
2
emissions from motor vehicles, of which cars make up 74%, increased during 1990–1997 by 26% and at a rate four times greater than the growth of CO
2
emissions overall. It is in the self-interest of new consumer countries, and of the global community, to restrict the environmental impacts of consumption; this restriction is achievable through a number of policy initiatives.
Prenatal exposure to a cannabinoid agonist produces memory deficits linked to dysfunction in hippocampal long-term potentiation and glutamate release
Authors: Mereu Giampaolo , Fà Mauro , Ferraro Luca , Cagiano Raffaele , Antonelli Tiziana , Tattoli Maria , Ghiglieri Veronica , Tanganelli Sergio , Gessa Gian Luigi , Cuomo Vincenzo
Published: April 2003

To investigate the possible long-term consequences of gestational exposure to cannabinoids on cognitive functions, pregnant rats were administered with the CB1 receptor agonist WIN 55,212-2 (WIN), at a dose (0.5 mg/kg) that causes neither malformations nor overt signs of toxicity. Prenatal WIN exposure induced a disruption of memory retention in 40- and 80-day-old offspring subjected to a passive avoidance task. A hyperactive behavior at the ages of 12 and 40 days was also found. The memory impairment caused by the gestational exposure to WIN was correlated with alterations of hippocampal long-term potentiation (LTP) and glutamate release. LTP induced in CA3–CA1 synapses decayed faster in brain slices of rats born from WIN-treated dams, whereas posttetanic and short-term potentiation were similar to the control group. In line with LTP shortening,
in vivo
microdialysis showed a significant decrease in basal and K
+
-evoked extracellular glutamate levels in the hippocampus of juvenile and adult rats born from WIN-treated dams. A similar reduction in glutamate outflow was also observed in primary cell cultures of hippocampus obtained from pups born from mothers exposed to WIN. The decrease in hippocampal glutamate outflow appears to be the cause of LTP disruption, which in turn might underlie, at least in part, the long-lasting impairment of cognitive functions caused by the gestational exposure to this cannabinoid agonist. These findings could provide an explanation of cognitive alterations observed in children born from women who use marijuana during pregnancy.
mRNA of placental origin is readily detectable in maternal plasma
Authors: Ng Enders K. O. , Tsui Nancy B. Y. , Lau Tze K. , Leung Tse N. , Chiu Rossa W. K. , Panesar Nirmal S. , Lit Lydia C. W. , Chan Kam-Wing , Lo Y. M. Dennis
Published: April 2003

The discovery of circulating fetal nucleic acid in maternal plasma has opened up new possibilities for noninvasive prenatal diagnosis. Thus far, a gender- and polymorphism-independent fetal-specific target that can be used for prenatal screening and monitoring in all pregnant women has not been reported. In addition, the origin of such circulating nucleic acid has remained unclear. Here we provide direct evidence that the placenta is an important source of fetal nucleic acid release into maternal plasma by demonstrating that mRNA transcripts from placenta-expressed genes are readily detectable in maternal plasma. The surprising stability of such placental mRNA species in maternal plasma and their rapid clearance after delivery demonstrate that such circulating mRNA molecules are practical markers for clinical use. The measurement of such plasma mRNA markers has provided a gender-independent approach for noninvasive prenatal gene expression profiling and has opened up numerous research and diagnostic possibilities.