Measurements of the Refractive Index Increment on Hydroxyethyl Starch as a Basis for Absolute Molecular Weight Determinations

Solutions of hydroxyethyl starch are used as a blood plasma substitute. If their physiological efficiency is to be optimized, they need to be accurately characterized in terms of their molecular weight and its distribution. The absolute determination of molecular weight and molecular weight distribution by means of light scattering require a knowledge of the refractive index increment. Although numerous investigations of the refractive index increment of hydroxyethyl starch have already been published, the results vary significantly due to the use of different samples and the choice of different measuring parameters. There was therefore an urgent need to examine the extent to which the refractive index increment depends on molecular parameters, the experimental method used and the type of processing. Here it was found that different sample preparations result in different contents of solid matter, so that an exact determination of the quantity is required. Hydroxyethyl starches in the molecular weight range of about Mw = 200.000 g/mol and varying degrees of substitution between DS 0.38 and 0.50 which are regarded as optimal for clinical use give a refractive index increment of dn/dc^633nm = 0.146 = 0.005 cm³/g (solvent: H₂O/0.02% NaN₃; T = 25°C).     

Liquid circulation in columns due to bubble drift

The profiles of liquid velocity and gas hold-up in convection cells of bubble columns were calculated numerically. Development of a circulation cell was calculated from momentum and mass balances. Breakdown of the circulation cell was calculated taking into account the drift motion of bubbles ascending in accordance with the velocity gradient of the liquid. A limit of stability for the development of circulation cells has been obtained.     

Measurement of radiation emitted from thin vaporizing liquid films for the calculation of surface temperature

Evaporation of liquid films, not subjected to motion, and with a starting thickness of 1 mm, was tested. Solvents dichloromethane and ethanol were used as liquids. Surface temperature during evaporation was measured in a non-intrusive way using pyrometry. The employed pyrometer was calibrated against a black body radiant. Measurement accuracy in the region of the ambient temperature is 0.2 K. Since any principal stray radiation is always measured along with the thermal radiation emitting from the liquid film, the measurement results are at first distorted. A correction calculation is described. With this, the various proportions of stray radiation can be subsequently calculated. In order to do this, the dimensions of the test equipment and the spectral data of the evaporating solvents must be taken into account. The quantity of stray radiation depends mainly on the properties of the surface onto which the liquid film is applied, as well as on the spectral transmissivity of the liquid. This was measured for every tested liquid according to wavelength and layer thickness. Where the spectral transmissivity of a liquid is low, a correction calculation of the measured surface temperature is not necessary, while a high level of accuracy is still retained.     

Acylierung von Heterocyclen mit Kohlensäurederivaten. I. Kinetik und Mechanismus der Reaktion von 2-Aminobenzimidazolen mit Arylcyanaten

Acylation of Heterocycles with Carbonic Acid Derivatives. I. Kinetics and Mechanism of the Reaction of 2-Aminobenzimidazoles with Aryl Cyanates The second order rate constants for the reaction of 2-amino-benzimidazoles (2-ABI) with aryl cyanates forming 2-amino-benzimidazole aryl ester imide 3 have been determined in dependence on substituent effects by u. v. measurements. The results are interpreted by a six-membered cyclic transition state in which the electrophilic attack of the cyanate on the endocyclic N atom is catalyzed by an H bridge interaction of the exocyclic amino group of 2-ABI with the OCN group.     

Spaltung von 1,2,4-Thiadiazol-3-onen mit Triphenylphosphan: Triphenylphosphonio-thioimidazolate und ihre Folgereaktionen

Fission of 1,2,4-Thiadiazol-3-ones by Triphenylphosphane: gewidinet Triphenylphosphonio Thioimidazolates and Their Consecutive Reactions Treatment of benzimidazo[1,2-d][1,2,4]thiadiazol-3(2H)-ones ( 1 ) and imidazo[1,2-d]-[1,2,4]thiadiazol-3(2H)-ones ( 17 ) with triphenylphosphan leads to the liberation of isocyanate and the formation of triphenylphosphonio-thiobenzimidazolat ( 4 ) and triphenylphosphonio-thioimidazolat ( 18 ), respectively. 2,4-Diphenyl-5-phenylimino-1,2,4-thiadiazol-3-one ( 23 ) is desulfurized with Ph₃P and decomposed into phenyl isocyanate and diphenylcarbodiimide whereas the N-unsubstituted imino-thiadiazol-3-one ( 25 ) is attacked at the exocyclic imino group by Ph₃P to give the N-phosphoranylidene thiourea ( 26 ). The structure of 4 can be rationalized as a dynamic system between polar and apolar valence isomeres. Reactions of 1 and 17 with cyanates, isocyanates, carbon disulfide, acetic anhydride, amines, benzyl chloride, grignard compounds, and CH acidic compounds are described.     

Zur Radikalischen Copolymerisation ungesättigter Isocyanate mit Vinylchlorid

On the Free Radical Copolymerization of Unsaturated Isocyanates with Vinylchloride The free radical copolymerization of vinyl-, isopropenyl- and p-vinyl-phenylisocyanate with vinylchloride in mass and tetrahydrofurane solution at 50°C is investigated. The incorporation of the isocyanate monomers in the copolymers is favoured. These monomers effect a great decrease of the rate of copolymerization and a crosslinking of the formed homo- and copolymers, whose extent depends on the kind and the quantity of the incorporated monomers. The crosslinking is caused by the forming of isocyanurate units.     

Über die Reaktionen von Benzimidazol-2-carbonsäurehydrazid mit Elektrophilen

About the Reactions of Benzimidazole-2-carbohydrazide with Electrophilic Compounds Benzimidazole-2-carbohydrazide ( 1 ) reacts with aldehydes and ketones to form N-alkylidene-benzimidazole-2-carbohydrazides( 2a–j ). With carbon disulfide, diphenyl carbonate and cyanates, ring closure takes place to afford 1,2,4-triazines and 1,3,4-oxadiazoles. Attempts to synthezise 2-isocyanato-benzimidazole failed. ¹H-n.m.r. and ¹³C-n.m.r. spectroscopic data of the compounds are given.     

Nuclear fuels for low-beta fusion reactors: Lithium resources revisited

In searching to attain optimum conditions for the controlled release of nuclear energy by fusion processes, the stationary confinement of low-pressure ring-shaped plasmas by strong magnetic fields is now regarded as the most promising approach. We consider a number of fuel combinations that could be operated in such low-beta reactor systems and look upon the relevant fuel reserves. The classical D-T-Li cycle will be used as a standard and is extensively discussed therefore. It could supply most of mankind's future long-term power needs—but only on condition that the required lithium fuel can be extracted from seawater at reasonable expenses. The estimated landbound lithium reserves are too small to that end, they will last for about 500 years at most, depending on forecasts of future energy consumption and on assumptions about exploitable resources. Recovery of lithium from seawater would extend the possible range by a factor of 300 or so, provided that extraction technologies which are at present available in the laboratory, could be extended to a very large and industrial scale. Deuterium is abundant on earth but D-D fusion is difficult, if not impossible, to be achieved in the low-beta systems presently investigated for D-T fusion. The same arguments apply to so-called advanced concepts, such as the D-³He and the D-⁶Li cycles.