Inclusion compounds of a diol host with xylidines: controlled stoichiometries.
The diol host, 1,1'-bis-(4-hydroxyphenyl)cyclohexane (DHPC) and a number of xylidine isomers as guests formed a series of inclusion compounds that gave rise to various host:guest ratios controlled by crystallization temperatures. For the host DHPC with a particular xylidine isomer, the number of guests included generally decreases as the crystallization temperature increases. The crystal structures of these host-guest compounds were elucidated using single-crystal X-ray diffraction. Their thermal stabilities were characterized by TG and DSC analysis. The selectivity of enclathration by the host was measured by carrying out a series of competition experiments. The kinetics of guest decomposition were studied using isothermal and non-isothermal methods and reconciled with the crystal structures.
A Simple Correlation between the Structures of Different Crystal Modifications of a Given Host–Guest Complex and their Crystallization Temperatures
The formation of different crystal modifications of a given host-guest complex depending on the crystallization temperature (pseudopolymorphism) is studied. It is shown that such pseudopolymorphism is a characteristic feature of versatile host compounds. A very important rule for host-guest chemistry is derived from the results of the X-ray structural investigations of pseudopolymorphs: the higher the crystallization temperature of the modification the more closed is the space occupied by guest molecules. On the basis of the formulated rule a recommendation for the topological control and solution of some central problems of supramolecular chemistry is proposed.
Euthanasia — again: “Letting die” is not in the patient's best interests: a case for active euthanasia
Recent discussions in the Journal on the subject of euthanasia have relied on intuitive appeals to distinctions traditionally considered to be morally relevant, such as the distinction between acts and omissions (or killing and letting die), or ordinary and extraordinary means of treatment. These discussions remained inconclusive. However, the question of euthanasia no longer remains inconclusive if one adopts the perspective suggested by the United States President's Commission for the Study of Ethical Problems in Medicine and Biomedical and Behavioral Research and by the World Medical Assembly – that a doctor should act in his or her patient's best interests. From this vantage point, it is argued, there will be instances when active euthanasia is the proper cause of action.