Effects of ultraviolet radiation on 3,4-benzpyrene and other polycyclic aromatic hydrocarbons; carcinogenic activity of aqueous extracts from irradiated 3,4-benzpyrene.
It was shown in preceding papers (2, 3) that when 3,4-benzpyrene dissolved in benzene was irradiated with monochromatic radiation of wave length 2,537 A. in the presence of oxygen, at least two water-soluble substances were included in the products and that these could be recognized, and some of their properties deduced, by spectrophotometric methods. The first, substance A, was characterized at pH 8 by an absorption band whose maximum intensity was at 3,600 A. It was labile, readily taking up atmospheric oxygen irreversibly when its aqueous solutions were allowed to stand at room temperature; but it could be stabilized by cooling them to 0 ~ C. and storing them in an atmosphere of nitrogen. The second substance, B, absorbed at 2,760 A. and was more stable to oxygen, but it was destroyed by strong alkali. It reacted readily with glutathione and with other compounds containing sulfhydryl groups. Water-soluble oxidation products of 3,4-benzpyrene are of course well known. A monohydroxy derivative is excreted as a metabolite when the hydrocarbon is fed to rats (8, 13); and a photoderivative has been described that has the power to inhibit respiratory enzymes (6, 7). None of them, however, has been reported to have any carcinogenic activity. Rideal and Schulman have shown (12) that materials very similar to, if not identical with, substances ,4 and B are readily adsorbed onto protein monolayers, and so might be expected to pass more readily than the unadsorbed hydrocarbon through cell membranes. By analogy with hemolytic substances, which they showed to possess this property to a high degree, substances ,4 and B might thus be expected to be biologically active. Other observations recorded in the literature, which were summarized in the introduction to Part I, seem to support this view. Since the absorption bands of ,4 and B do not accord with those of any derivative
Retardation of the Rate of Tumor Induction by Hydrolyzing Chlor-Compounds
The effect on the rate of tumor induction of a group of chlor-compounds which reversibly inhibit the glycolyric process of cells has already been described (5, 6). The compounds used were soluble in water and fats, and were nonhydrolyzable under physiological conditions of pH and temperature. The chemical reactivity of their chlorine atoms was the factor which determined the potency of their biological action. But their influence on tumor induction was not simple. Inhibitory or stimulatory effects could be obtained by a single chlor-compound, the final result being determined by the concentration used and also by the time of its application relative to the treatment with carcinogen. The most active nonhydrolyzing chlor-compound used was mono-chloracetone. It would have been possible to study the effects of still more active halogen compounds of this type; e.g., the bromine and iodine analogues of mono-chloracetone, had not the irritating properties of such compounds precluded their use. Chlor-compounds, considered from the point of view of increasing chemical reactivity, can be ranged from the nonhydrolyzing types used in the earlier work to types which are so reactive that contact with aqueous media causes hydrolysis. The acid chlorides are familiar examples of this type, and they can be graded according to their rate of hydrolysis. Berenblum (>3) has focused attention on mustard gas and related compounds which come under the heading of hydrolyzing halogen compounds. In the work reported here, a series of aliphatic, and one aromatic, acid chlorides has been used. The experiments demonstrate that all these acid chlorides exert an inhibiting influence on the process of tumor induction in the skin of mice by 3,4-benzpyrene. The degree of inhibition by the different members of this class of compounds varies with their physical and chemical characteristics, molecular size and rate of hydrolysis being the variable factors which probably determine their relative effectiveness.
Mining Words in the Minds of Second Language Learners: Learner-Specific Word Difficulty
While there have been many studies on measuring the size of learners’ vocabulary or the vocabulary they should learn, there have been few studies on what kind of words learners actually know. Therefore, we investigated theoretically and practically important models for predicting second language learners’ vocabulary and propose another model for this vocabulary prediction task. With the current models, the same word difficulty measure is shared by all learners. This is unrealistic because some learners have special interests. A learner interested in music may know special music-related terms regardless of their difficulty. To solve this problem, our model can define a learner-specific word difficulty measure. Our model is also an extension of these current models in the sense that these models are special cases of our model. In a qualitative evaluation, we defined a measure for how learner-specific a word is. Interestingly, the word with the highest learner-specificity was “twitter”. Although “twitter” is a difficult English word, some low-ability learners presumably knew this word through the famous micro-blogging service. Our qualitative evaluation successfully extracted such interesting and suggestive examples. Our model achieved an accuracy competitive with the current models.