Influence of chain end groups on the matrix-assisted laser desorption/ionization spectra of polymer blends

The positive ion matrix-assisted laser desorption/ionization (MALDI) spectrum of an equimolar blend of Nylon 6 (Ny6) and hydroxyl-terminated polybutyleneterephthalate (PBT) shows a surprisingly strong imbalance between the two components. Since the average molar masses and the polydispersions of the two polymers are comparable, it follows that the efficiency of MALDI is quite different for the two components of the blend. This finding prompted us to a more detailed study, and to synthesize Ny6 and PBT samples terminated with different end groups, in order to analyze their blends by MALDI. The negative ion MALDI spectra of the mixtures investigated show that PBT samples do not yield signals, so that only Ny6 peaks appear in these spectra. By comparing positive and negative ion MALDI spectra of mixtures of Ny6 terminated with various end groups, it was found that the peak intensity depends on the nature of the end groups. The results reported in the present study may help to clarify some fundamental aspects of the mechanisms of ion formation, when MALDI mass spectrometry is applied to macromolecules. End group ionization efficiency appears to be the most important parameter in determining the relative intensity of peaks in the MALDI spectra of the polymer blends investigated. End-group-dependent ionization is the key to the rationalization of the relative peak intensities in MALDI spectra of polymer mixtures.     

Determination of retinoic acid (13-cis- and all-trans-) and aromatic retinoic acid analogs possessing anti-tumor activity, in biological fluids by high-performance liquid chromatography

A sensitive and specific high-performance liquid chromatographic assay was developed for the determination of 13-cis- and all-trans-retinoic acid in blood or urine with an overall recovery of 90 +/- 5.0% and a limit of detection of 10-20 ng/ml of sample. The method provides for rapid and simple quantitation of the compounds using 1 ml of blood. The assay was applied in the determination of blood levels of 13-cis-retinoic acid in the dog following intravenous and oral administration of 9.5 mg/kg and 2.0 mg/kg doses, and in man following a single 100-mg oral dose and following divided daily doses totalling 2 mg per kg of body weight. The assay is also applicable with minor modifications to the determination of a series of aromatic retinoic acid analogs of clinical interest as anti-tumor agents.     

Rapid determination of diazepam and nordiazepam in plasma by electron capture gas--liquid chromatography. Application in clinical pharmacokinetic studies.

A rapid method was developed for the determination of diazepam and nordiazepam (N-desmethyldiazepam) in human plasma using electron capture gas--liquid chromatography (GLC--ECE). The concentration of diazepam and nordiazepam is determined using 0.5 ml of plasma extracted with 1.0 ml of benzene containing 25 ng/ml of methylnitrazepam as the internal standard. The benzene extract is removed and an aliquot is subjected to automated GLC-ECD analysis. The method has a sensitivity limit of 5 ng diazepam and 10ng nordiazepam per milliliter of plasma. The method was used to determine the plasma levels in man following the first 5-mg diazepam dose, as well as during chronic oral administration of 5 mg diazepam three times daily and 15 mg diazepam once a day.     

Inelastic hard rods in a periodic potential

A simple model of inelastic hard rods subject to a one-dimensional array of identical wells is introduced. The energy loss due to inelastic collisions is balanced by the work supplied by an external stochastic heat bath. We explore the effect of the spatial nonuniformity on the steady states of the system. The spatial variations of the density, granular temperature, and pressure induced by the gradient of the external potential are investigated and compared with the analogous variations in an elastic system. Finally, we study the clustering process by considering the relaxation of the system starting from a uniform homogeneous state.     

Reliability of the volatilization method for determination of the activation energy in the thermal decomposition of polymers

The LPTD-MS method, used to determine kinetic parameters in the thermal degradation of polymers by means of volatilization curves, was applied to TG data and the results were compared with those obtained by the methods of Flynn & Wall, Friedman, Freeman & Carroll, and Coast & Redfern.

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Zusammenfassung Die LPTD-MS-Methode, benutzt zur Bestimmung der kinetischen Parameter des thermischen Abbaus von Polymeren aus Verflüchtigungskurven, wurde auf TG-Daten angewandt und die Ergebnisse wurden mit denen verglichen, die nach den Methoden von Flynn und Wall, Friedman, Freeman und Carroll sowie Coats und Redfern erhalten wurden.

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Резюме Совмещенньй метод ЛПТД-МС, используемый для определения кинетических параметров реакции термического распада полимеров с помощыью кривых испарения, бып применен к данным. ТГ. Результатю были сопоставлены с теми, которые были получены методами Флинна и Уолла, фриидмена, фримена и Карролла, а также Коуста и Радферна.

     

Matrix-assisted laser desorption/ionisation time-of-flight characterisation of biodegradable aliphatic copolyesters

Matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) and the off-line size exclusion chromatography matrix-assisted laser desorption/ionisation (SEC/MALDI) method has been applied to the structural characterisation and the molar mass (MM) determination of a series of biodegradable copolyesters synthesised by high temperature melt polycondensation reaction, and of two commercial copolyesters with the trade name Bionolle. The MALDI-TOF spectra of these copolymers showed the presence of cyclic oligomers in the lower mass region, in accord with expectations from polycondensation kinetics, and the presence of all linear species expected from their method of synthesis. The presence of unexpected linear species with olefin and carboxyl as end groups suggested the occurrence of undesirable thermal degradation processes during the melt polycondensation reaction. The absolute average molar masses obtained by the SEC-MALDI method turned out to be lower, by a factor of about two for succinate/adipate copolymers, and by a factor of three for succinate/sebacate copolymers, with respect to those computed by using polystyrene standards in SEC. Furthermore, the MALDI-TOF spectra of SEC fractions allowed not only the detection of linear and cyclic oligomers contained in these samples, but also the simultaneous determination of the average molar mass of both cyclic and linear oligomers. Due to the smaller hydrodynamic volume of cyclic chains with respect to linear ones, the ratio (M( cycle)/M( linear))( Ve) at a fixed elution volume was found to be 1.25, in good agreement with the theoretical value of 1.24. Copyright 2000 John Wiley & Sons, Ltd.     

Efficient synthesis of an enantiopure beta-lactam as an advanced precursor of thrombin and tryptase inhibitors

A new and efficient synthesis of a beta-lactam that is an advanced precursor of inhibitors of thrombin and tryptase is reported. The reaction sequence is based on the use of an inexpensive enantiomerically pure starting material and is designed to allow access to both enantiomers of the target molecules by epimerization of a side-product obtained along the synthesis. An improved procedure for the epimerization step that takes advantage of the use of a polymer-supported and recyclable phase-transfer catalyst is described.     

Irreducible Finitary Lie Algebras over Fields of Characteristic Zero

A Lie subalgebraLof (V) is said to befinitaryif it consists of elements of finite rank. We show that if Char = 0, if dim Vis infinite, and ifLacts irreducibly onV, then the derived algebra ofLis simple.     

Signal spatial filtering for co-phasing in seeing-limited conditions

We present the results of the co-phasing closed loop performed with a pyramid wavefront sensor for what we believe to be the first time in the presence of emulated atmospheric disturbance. The performance of the co-phasing loop is significantly improved by applying two spatial filters in the sensor signal space. The first is a zonal filter applied to the interaction matrix before the computation of the reconstructor; the second is a modal filter applied to the sensor signals before the correction command computation. The presented laboratory results demonstrate that, applying both filters, the time requested to average out the atmospheric disturbance in each loop step is reduced by 2 orders of magnitude, improving the loop stability and accuracy.