bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magic‐angle 13C NMR spectroscopy of chloral polymers
Authors: Harris William J. , Vogl Otto , Havens J. R. , Koenig Jack L. 
Published: April 2003

AbstractThe 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

AbstractSinglet 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

AbstractA 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

AbstractIn 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

AbstractLaser 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractCompounds 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

Abstract1‐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

AbstractCopolymers 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractAimsTo examine the prevalence of chromosomal defects and outcome of fetuses with megacystis at 10–14 weeks of gestation.MethodsAt 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.ResultsChromosomal 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.ConclusionsIn 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.
Haemoglobin Marseille-Long Island and interpretation of HbA1c: which HbA1c result is the “right answer”?
Authors: Florkowski C M , Walmsley T A , Brennan S O , George P M 
Published: April 2003

Abstract
A woman was screened for diabetes using glycated haemoglobin (HbA1c). Vastly different results were obtained by high performance liquid chromatography (45%), immunoassay (2.9%), and affinity chromatography (4.2%) compared with the non-diabetic range of less than 6.4%. Mass spectral studies confirmed the presence a haemoglobin variant, haemoglobin Marseille-Long Island which had confounded interpretation by all methods.
Use of Fish Oils Appears to Reduce Infarct Size as Estimated from Peak Creatine Kinase and Lactate Dehydrogenase Activities
Authors: Landmark Knud , Abdelnoor Michael , Urdal Petter , Kilhovd Bente , Dørum Hans-Petter , Borge Nina , Refvem Hilde 
Published: April 2003

In 753 patients with acute myocardial infarction, use of fish oils (FO, n = 242) before onset of infarction seemed to reduce infarct size as estimated from peak creatine kinase (CK<sub>max</sub>) and lactate dehydrogenase (LD<sub>max</sub>) activities. The study had an observational exposed/nonexposed design, and both crude and adjusted effects were looked for. <b>Crude Effects:</b> In the restricted cohort of patients not receiving thrombolytic treatment (n = 411), FO reduced CK<sub>max</sub> from 879 to 759 U/l (2 p = 0.030) and LD<sub>max</sub> from 870 to 768 U/l (2 p = 0.011), respectively. More of these patients in the lowest enzyme quartiles used FO, p for linear trend was for CK<sub>max</sub> 0.008 and for LD<sub>max</sub> 0.06, respectively. <b>Adjusted Effects:</b> In patients not receiving thrombolytic treatment, FO reduced CK<sub>max</sub> (2 p = 0.007) and LD<sub>max</sub> (2 p = 0.005), but in patients receiving such treatment, CK<sub>max</sub> and LD<sub>max</sub> values increased, 2 p being 0.036 and 0.097, respectively. In patients not receiving thrombolysis, FO increased the incidence of small infarcts (the 25% quartile), odds ratio for CK<sub>max</sub> was 1.82 (2 p = 0.018) and for LD<sub>max</sub> 1.66 (2 p = 0.048), respectively. The results indicate that FO may reduce infarct size and the incidence of large infarcts. In addition, FO seems to enhance the effect of thrombolysis.
Lipid Peroxidation and Cardiac Troponin T Release during Routine Cardiac Surgery
Authors: Inselmann Gerhard , Köhler Katrin , Lange Volkmar , Silber Rolf , Nellessen Ulrich 
Published: April 2003

Myocardial injury after cardiac surgery with cardiopulmonary bypass may be related to free oxygen radical-induced lipid peroxidation. The purpose of this study was to monitor perioperative changes of cardiac troponin t and malondialdehyde as an indicator of lipid peroxidation in patients who underwent routine cardiac operation and had no signs of perioperative myocardial infarction. Patients with thoracic surgery alone served as controls. We studied 20 patients with cardiopulmonary bypass (CPB) and 9 patients with other thoracic operations. Serum troponin t, malondialdehyde, myoglobin, creatine kinase (CK) including CK-MB isoenzyme levels were monitored before CPB, immediately after cessation of CPB, 20 and 44 h after CPB. Patients with signs of myocardial infarction before or up to 44 h after surgery were excluded. Of 20 patients with CBP, 18 patients showed a significant increase of troponin t and 16 patients had elevated malondialdehyde serum levels following CPB. Troponin t serum values were raised immediately after CPB to 0.60 ± 0.12 µg/l and increased further to 0.90 ± 0.17 µg/l after 44 h (p < 0.005, in comparison to preoperative: 0.08 ± 0.02 µg/l). Patients undergoing the other thoracic operations showed neither any detectable troponin t serum values nor significant changes of serum malondialdehyde during the observed period. In the CPB group serum malondialdehyde peaked immediately after CPB to 98 ± 9 nmol/g albumin (p < 0.005) and returned to preoperative levels (63 ± 3 nmol/g albumin) within 20 h (60 ± 3 nmol/g albumin). Individual maximal troponin t serum levels did not correlate with individual maximal serum malondialdehyde levels. The observed increase of troponin t levels had no influence on patients’ outcome followed up for 18 months. The results demonstrate that troponin t and lipid peroxidation increase during uncomplicated cardiac surgery in patients without signs of myocardial infarction. Following uncomplicated cardiac surgery, a moderate increase of cardiac troponin t may not reflect severe cardiac injury.