Über die boronierung von polystyrol

Boronic acid groups can be introduced in crosslinked and linear polystyrene by metalation with the complex butyllithium/N,N,N′,N′-tetramethylethylenediamine and subsequent treatment with boric acid esters. Investigations of the photochemical boronation of polystyrene by boron tribromid show that the reaction is accompanied by strong chain degradation, whereas the former method leads to an increase in molecular weight.     

Experimental models for the biological detection of N-nitroso compounds formed from amines and nitrite

The secondary and tertiary amines morpholine, aminopyrine and cimetidine as well as their nitroso products were examined for mutagenicity with the Ames Salmonella typhimurium microsome test (strains TA1535 and TA100) and the host-mediated assay. The formation of mutagenic nitroso compounds from morpholine and aminopyrine in the presence of nitrite could be demonstrated in artificial gastric juice and was confirmed in the stomach of mice in vivo. In contrast, the positive response of the chemical nitrosation in vitro with cimetidine did not match with the mammalian host-mediated assay results. To enhance sensitivity the role of modifiers of nitrosation, such as ascorbic acid and thiocyanate as well as the influence of biotransformation were studied.     

Untersuchungen zu den orientierungs- und dichtefluktuationen in amorphen polymeren mit hilfe der lichtstreuung

Using a light scattering photometer we investigated the orientation- and density fluctuations in the amorphous polymers “polycarbonate” (poly(oxycarbonyloxy-1,4-phenylene-isopropylidene-1,4-phenylene)) and polystyrene as a function of temperature. In addition to this, we performed supplementary measurements on oligomers of polystyrene and on the liquid-crystal compound 4-butyl-N-(p-methoxybenzyliden)aniline (MBBA) in the isotropic phase. From the amount of depolarized light scattering it is evident that an orientation correlation, as suggested for some bundle models, does not exist. As far as polystyrene is concerned, we were able to draw particularly detailed conclusions. The depolarized light scattering was constant in the whole angular range and independent of temperature. The anisotropy per monomeric unit of the oligomers already has a similar value to that of the polymer, consequently no additional orientation fluctuations are present in the polymer. The orientation correlation of the monomeric units in the polymer could be totally attributed to that in a random coil. The amount and temperature dependence of the light scattering of polystyrene caused by density fluctuations agreed with the results of the fluctuation theory. Consequently, light scattering due to density fluctuations of a specific macromolecular species did not occur.     

Improved quality and information in thyroid scintigraphy

We compared rectilinear scanning, analogous gamma-camera imaging and imaging using a gamma camera interfaced to a computer in order to determine which of these techniques is superior for thyroid scintigraphy. Forty patients with and without goitre and irregular activity distribution were imaged using each of the three techniques. The sets of three scintigrams per patient were rated by seven physicians. These ratings were statistically analysed using a new distribution-free test. Thyroid scintigraphy using a gamma camera interfaced to a computer turned out to be the best method, especially for detecting circumscribed areas of increased uptake. We conclude that this was due to a combination of the following factors: a computer matrix of 128x128 pixels in combination with an acquisition zoom of 1.5, the high count density of the scintigrams, computer-controlled documentation after data acquisition and the use of a continuous grey scale for documentation. The improved quality and information content of the scintigrams obtained using a gamma-camera/computer system could improve the diagnostic value of thyroid scintigraphy, especially when the scintigrams are also evaluated quantitatively.     

The Endothelium: A Key to the Future

The vascular endothelium is a complex modulator of a variety of biological systems and may well be the key to definitive success in the treatment of cardiovascular disorders. Surgically-induced endothelial injury may occur preoperatively during cardiac catheterization and intraoperatively from mechanical manipulation, ischemia, hypothermia, and exposure to cardio-plegic solutions. The normal endothelium is antithrombogenic and yet promotes platelet aggregation and coagulation if injured. Vasospasm, occlusive intimal hyperplasia, and accelerated arteriosclerosis can also all occur as a result of endothelial injury. Furthermore, endothelial injury is harmful even in the absence of disruption of its monolayer integrity. Thus, preservation of the endothelium should be an additional objective for all cardiovascular surgeons. Synthetic vascular grafts, cardiac valves, and artificial ventricles do not spontaneously endothelialize and thus usually require some form of anticoagulation to maintain patency. Hence, endothelialization of prosthetic implants became an attractive concept. A number of different methods of obtaining an endothelial lining of prosthetic material has since been developed; these include facilitated endothelial cell migration, and endothelial cell seeding by using either venous or microvascular endothelial cells. Manipulating the endothelium might well provide the next major advancement for therapeutic and preventative measures for cardiovascular disease.     

Graft copolymers of poly(methyl methacrylate) and polythiophene

2-(2-Thienyl)ethyl methacrylate (2TEMA, 1 ), 2-(3-thienyl)ethyl methacrylate (3TEMA,2) and 2-(N-pyrrolyl)ethyl methacrylate (PEMA, 3 ) were synthesized and copolymerized with methyl methacrylate (MMA) by radical initiation with AIBN. The reactivity ratios for the system MMA/2TEMA were determined to be r_MMA = 0,57 ± 0,09 and r_2TEMA = 0,90 ± 0,03. Thiophen was grafted into the copolymers from 1 – 3 via oxidative polymerization in nitromethane. The graft copolymers were soluble as aggregates, and films cast from these solutions reached conductivities in the range of 0,2 to 0,4 S/cm.