Water-Soluble imide-amide copolymers. II. Preparation and characterization of poly (acrylamide-co-p-maleimidobenzoic acid)

The comonomer required, p-maleimidobenzoic acid (MBA) was first prepared in good yield by refinements of published methods. p-Carboxysuccinanilic acid (CSA), and p-succinimidobenzoic acid (SBA), were also prepared to provide models useful for IR and NMR for spectroscopic assignments of the new copolymers. Polymerization of MBA with acrylamide in glacial acetic acid at 60°C gave copolymers with estimated viscosity average molecular weights of 60,000 to 90,000. Yields and viscosity average molecular weights decreased as the MBA to acrylamide monomer feed ratio was increased. The rate of incorporation of MBA into the copolymer rose from 7 to 23% when the mole ratio in the feed was raised from 5 to 20%. Decreasing the initiator concentration increased molecular weights by less than predicted and reduced the yield of copolymer for any given feed ratio of MBA to acrylamide. In all cases about 30–40% of the MBA units in the purified copolymers were hydrolyzed. A change to dimethyl sulfoxide solvent gave good, and poor yields of copolymer at 5 and 10 mol % MBA, respectively, and no copolymer at 20 mol % MBA. Viscosity average molecular weights of the copolymer products prepared in DMSO were somewhat lower than obtained for the copolymers prepared in acetic acid. Polymerization in a DMSO-water mixture gave a negligible yield of polymeric product. Instead, only hydrolysates of MBA precipitated when the coloured polymerization solutions were added to methanol.     

Atomistic-continuum multiscale modelling of magnetisation dynamics at non-zero temperature

In this article, a few problems related to multiscale modelling of magnetic materials at finite temperatures and possible ways of solving these problems are discussed. The discussion is mainly centred around two established multiscale concepts: the partitioned domain and the upscaling-based methodologies. The major challenge for both multiscale methods is to capture the correct value of magnetisation length accurately, which is affected by a random temperature-dependent force. Moreover, general limitations of these multiscale techniques in application to spin systems are discussed.     

Determination of charge density of anionic polyacrylamide flocculants by NMR and DSC

New methods are suggested for the determination of the charge density of acrylamide/acrylate copolymers.¹³C nuclear magnetic resonance spectroscopy was used to determine the comonomer ratio by comparing the peak intensities of the methine carbon in acrylamide and acrylate monomers. Results were compared with those obtained by conductometric and potentiometric titration and were found to be in good agreement. Differential scanning calorimetry was employed to determine the glass transition temperatures (T _g) of the copolymers. A master curve was established by plottingT _g versus charge density of the copolymers previously determined by NMR and conductometric titration. Compositions of poly(acrylamide-co-acrylate) samples can thus be determined by measuring theT _g and reading the percent composition directly from the master curve.     

Synthesis of C 2 Symmetric Potential Inhibitors of HIV-1 Protease From D-Mannitol

ABSTRACT

D-Mannitol was used as precursor for the synthesis of acyclic C ₂ symmetric potential HIV-1 protease inhibitors. The 1- and 6-hydroxy groups of D-mannitol were substituted by -NHBoc, -NHValZ, -SAr, -SOAr and -SO₂Ar and the 2-and 5-hydroxy groups were benzylated. In some products one of the central hydroxyl groups was either inverted or deoxygenated. Despite a close structural similarity to previously published inhibitors none of the products showed significant inhibitory activity against HIV-1 protease.

     

Determination of diphenhydramine in biological fluids by capillary gas chromatography using nitrogen-phosphorus detection. Application to placental transfer studies in pregnant sheep

A nitrogen-phosphorus detection-gas chromatographic method, which provides improved sensitivity and selectivity for diphenhydramine, is reported. A 25 m X 0.31 mm cross-linked, 5% phenylmethyl silicone-coated fused-silica capillary column (film thickness 0.52 micron) was used for all analyses. The splitless capillary injection mode was employed with a 2-microliter sample being introduced by an automatic liquid sampler. Standard curves, using orphenadrine as an internal standard, were linear in the range 2-320 ng of diphenhydramine per 0.5 ml of sheep plasma. This represents an amount of diphenhydramine from ca. 40 pg to 6.4 ng at the detector. Chromatographic separation of diphenhydramine and orphenadrine was excellent, with no interference from endogenous plasma constituents. Applicability of the method was demonstrated by a placental transfer study in a chronically instrumented pregnant sheep following a 100 mg intravenous injection of diphenhydramine to the ewe.     

A uniformly well-conditioned, unfitted Nitsche method for interface problems

A finite element method for elliptic partial differential equations that allows for discontinuities along an interface not aligned with the mesh is presented. The solution on each side of the interface is separately expanded in standard continuous, piecewise-linear functions, and jump conditions at the interface are weakly enforced using a variant of Nitsche’s method. In our method, the solutions on each side of the interface are extended to the entire domain which results in a fixed number of unknowns independent of the location of the interface. A stabilization procedure is included to ensure well-defined extensions. We prove that the method provides optimal convergence order in the energy and the L ² norms and a condition number of the system matrix that is independent of the position of the interface relative to the mesh. Numerical experiments confirm the theoretical results and demonstrate optimal convergence order also for the pointwise errors.     

Acoustic characteristics of a heavy duty vehicle cooling module

Studies dedicated to the determination of acoustic characteristics of an automotive cooling package are presented. A shrouded subsonic axial fan is mounted in a wall separating an anechoic- and a reverberation room. This enables a unique separation of the up- and downstream sound fields. Microphone measurements were acquired of the radiated sound as a function of rotational speed, fan type and components included in the cooling module. The aim of the present work is to investigate the effect of a closely mounted radiator upstream of the impeller on the SPL spectral distribution. Upon examination of the SPL spectral shape, features linked specifically to the source and system are revealed. The properties of a reverberant sound field combined with the method of spectral decomposition permit an estimation of the source spectral distribution and the acoustic transfer response, respectively. Additionally, purely intrinsic acoustic properties of the radiator are scrutinized by standardized ISO methods. A new methodology comprising a dipole sound source is adopted to circumvent limitation of transmission loss measurement in the low frequency range. The sound attenuation caused by the radiator alone was found to be negligible.     

Isolation of chlorinated fatty acid methyl esters derived from cell-culture medium and from fish lipids by using an aminopropyl solid-phase extraction column

An aminopropyl-based solid-phase extraction technique was used for isolation of chlorinated fatty acids in lipids. A range of different chlorinated fatty acids was eluted in a small volume of solvent (4 ml) and the recoveries of the different species and isomers were quantitative. Only 1% of the vastly dominating unchlorinated fatty acid methyl esters were recovered in the fractions containing the chlorinated fatty acid methyl esters. This method makes it possible to isolate and detect > or = 1 microg of a chlorinated fatty acid methyl ester in 1 g of lipid.     

Carbon-13 NMR linewidths of polyethylenes and related polymers

The carbon-13 NMR linewidth (proton decoupled) of linear and branched polyethylenes crystallized so as to yield different supermolecular structures, as well as a polyethylene oxide sample, have been studied in detail. The purpose has been to assess the different molecular contributions to the linewidth in the completely amorphous polymer as well as in the amorphous regions of the semicrystalline state. These studies on a number of different structures were complemented by both proton-decoupled and dipolar-decoupled magic-angle spinning experiments on a particular sample, as well as frequency dependence studies. It is found that the abnormally broad resonance lines previously reported for the molten polymer can be significantly reduced by adopting appropriate methods of sample preparation and magnetic-field homogenization at each temperature. Relatively narrow lines result which can be interpreted in a conventional manner. In the semicrystalline state, the resonance lines are relatively broad and are shown to be morphology dependent. Specific contributions and their temperature dependence are discussed.     

Multinuclear (13C, 15N) NMR study of polyethyleneimine-based polymers

Representative polyethyleneimine-based polymers have been studied by ¹³C- and ¹⁵N-nuclear magnetic resonance spectroscopy and an extensive set of chemical shift assignments has been proposed for the complex spectra obtained. The samples in question represent a complex mixture of both protonated and nonprotonated primary, secondary, and tertiary as well as quaternary monomeric units.