Quantities of adult, fetal and embryonic globin chains in the blood of eighteen- to twenty-week-old human fetuses

The prenatal diagnostic program, established at Hacettepe University in Ankara for the purpose of detecting beta-thalassemia (beta-thal), sickle cell anemia (SS), and Hb S-beta-thal, offered the opportunity of evaluating the relative quantities of adult (beta A, beta S), fetal (G gamma, A gamma, A gamma T), and embryonic (epsilon, zeta) chains in 26 fetuses, aged 18-20 weeks. Methodology involved micro high-performance liquid chromatographic (HPLC) procedures and immunology using an mAb, specific for the embryonic epsilon chain. A good correlation was observed between the beta/gamma in vitro chain synthesis ratio and the level of beta A and/or beta S chains determined by reversed-phase HPLC; the combination of these two sets of data strengthens the prenatal diagnostic approach of detecting beta-thal major but not beta-thal trait. The levels of the different gamma chains were about as observed in newborn babies; the frequency of the A gamma T variant in the 26 fetuses was the same as observed for a larger group of Turkish newborn babies. The level of the embryonic zeta chain was higher than seen in full-term babies and varied between 0 and 1.3%; 5 of the 26 fetuses showed the complete absence of zeta. The embryonic epsilon chain was not detectable, not even in babies with beta-thal major. These data indicate that the synthesis of epsilon is completely turned off in fetuses at the age of 18-20 weeks, while that of zeta continues, albeit at a low level.     

A Titration Microcalorimetric Study of the Effects of Halide Counterions on Vesicle-Forming Aggregation in Aqueous Solution of Branched-Chain Alkylpyridinium Surfactants

Titration microcalorimetry is used to study the influences of iodide, bromide, and chloride counterions on the aggregation of vesicle-forming 1-methyl-4-(2-pentylheptyl)pyridinium halide surfactants. Formation of vesicles by these surfactants was characterised using transmission electron microscopy. When the counterion is changed at 303 K through the series iodide, bromide, to chloride, the critical vesicular concentration (cvc) increases and the enthalpy of vesicle formation changes from exo- to endothermic. With increase in temperature to 333 K, vesicle formation becomes strongly exothermic. Increasing the temperature leads to a decrease in enthalpy and entropy of vesicle formation for all three surfactants. However the standard Gibbs energy for vesicle formation is, perhaps surprisingly, largely unaffected by an increase in temperature, as a consequence of a compensating change in both standard entropy and standard enthalpy of vesicle formation. Interestingly, standard isobaric heat capacities of vesicle formation are negative, large in magnitude but not strikingly dependent on the counterion. We conclude that the driving force for vesicle formation can be understood in terms of overlap of the thermally labile hydrophobic hydration shells of the alkyl chains. Copyright 2000 Academic Press.