Michael Kupfer

Physicochemical properties of 1,2-bis(F-alkyl)ethenes studied by CW-ESR

Abstract 1,2-Bis(F-alkyl) ethenes are very useful as model compounds for perfluorocarbons under several headings. The ability of these highly-fluorinated substances to dissolve remarkable quantities of gases such as O 2 , CO 2 etc. as well as the time dependent changes of the partial pressures of these gases was studied using spin probes (TEMPOL) by cw-ESR. In addition, primary and secondary radicals created by UV/VIS- and ionizing radiation, respectively were detected by cw-ESR, demonstrating the close relationship of 1,2-bis (F-alkyl)ethenes and perfluorocarbons. The presence of the CH=CH-unit in 1,2-bis(F-alkyl)ethenes is the reason that additional secondary reactions occur and aggregates could be observed.

Some further remarks about the dual fluorescence of photoexcited N,N-dialkylanilines

Abstract Different relaxation mechanisms is aprotic and protic solvents appear to account for the long-wavelength fluorescence of ϱ-N,N-dimethylaminobenzonitrile and related N,N-dialkylanilines. This is deduced from emission measurements in protic solvents by Cox, Hauptmann and Turro, using modified multiparameter models based on those of Kamlet, Abboud and Taft.

Multiparametermodelle für die Interpretation von Lösungsmitteleinflüssen auf spektroskopische und photophysikalische Parameter, 2. Mitt.

The anomalous photophysical desactivation behaviour ofp-dimethylaminobenzonitrile and relatedN,N-dialkylanilines depends on specific solvents-solute interactions. The application of multiparameter models based onKamlet andTaft to the solvatochromism of absorption and fluorescence and photophysical parameters demonstrates different relaxation mechanisms in aprotic and protic solvents, respectively. The main process is determined by solvent viscosity in protic solvents only.

Aspects of chemical and physical properties of perfluorochemicals and their emulsions

Abstract Perfluorochemicals (PFCs) dissolve ca. 40–50 vol % of oxygen and ca. 100–150 vol % of carbon dioxide. According to experiments and calculations, the physical solubility of oxygen cannot exceed 60 vol %. Emulsions of perfluorochemicals are used as oxygen carriers instead of blood. The surfactant most frequently used is Pluronic F-68, often with adjunction of yolk phospholipids, as in the case of Fluosol DA. These emulsions are difficult to formulate, it requires a high amount of energy, ultrasonic vibrations or pressure homogenization for instance, and a certain concentration of free surfactant. Even then stability is not assured, and the emulsions must be stored frozen. PFCs containing heteroatoms, especially in cyclic molecules form more stable emulsions. Therefore tailor-made PFCs are of interest. The possibilities for synthesis of these compounds are limited. By application of more effective surfactants emulsions can be prepared with contents of PFCs up to 50 vol %. These emulsions enable a better O 2 -delivery and have lower viscosities and smaller particle sizes.

ESR-Measurements on radicals generated in perfluorocarbons

Abstract Perfluorocarbons (PFC) are well-known as compounds useful as blood substitutes. Because of immiscibility in water PFC can only be used as O/W- emulsions. Therefore emulsions stable over a long period of time are necessary. For this reason attempts to determine structure-property relationships and the chemical behaviour are required. An interesting class of compounds which should be included are highly fluorinated olefines like 1 and 2 . According to Riess [1] these compounds are supposed to belong to the second generation of blood substitutes. CF3(CF2)nCF2CHCHCF2(CF2)nCF3 n = 2 and 4 1 and 2 The existence of the double bond, perhaps comparible to a heteroatom, appears to favour emulsion stability. The lack of chemical inertness of the double bond, however, could effect toxicity in medical application. Therefore chemical reactions of 1 and 2 were investigated, which had been started by -radiation and UV-irradiation, respectively. Different mechanisms have to be taken into account for variable conditions e.g. temperature from 77 to 300 K, presence of oxygen. The following radicals were detected by ESR: primary radicals of 1 and 2 , different types of peroxyradicals and of aggregates. Under UV-excitation at 300 K the concentration of paramagnetic species observed by cw-ESR depends strongly on experimental conditions: wavelength of excitation, exposure time and the presence of an sensitizing agent. Consequences of the above-mentioned questions are discussed.

Determination of particle size distribution in perfluorocarbon emulsions

Abstract The application of oil/water-emulsion of perfluorocarbons (PFC) as oxygen-carrying media for medical purpose requires the consideration of several prerequisities. For instance, the emulsion must not contain particles with a diameter larger than 400 nm. Otherwise, the reticuloendothelial system is blocked quickly by larger particles showing toxic effects. Therefore, a method is desirable which makes possible a fast determination of particle size and size distribution. Measurements of PFC-emulsions have shown that the desired informations can be obtained from dynamic light scattering. The experimental autocorrelation function yields a mean particle diameter and some information about the polydispersity of the emulsion. Moreover, performing the inverse Laplace transformation of the autocorrelation function by the method of Provencher (1), the size distribution of the scattering particles in the emulsion can be evaluated. In this connection, a model for light scattering of PFC-particles with surfactants like Pluronic F-68 was developed, which is based on PFC-spheres enveloped by a surfactant layer. The thickness of this layer can be assumed to be in the range from 5 to 1O nm. The above-mentioned technique has been used for the characterization of several PFC-emulsions. The influence of temperature, time of storage and additives have been investigated. First conclusions of conditions which influence floculation and coalescence, respectively, are drawn. The results are compared with others known from literature.