Effect of solvent on the conformational equilibrium of 2-substituted 5,6-benz-1,3-dithiepins

Conclusions From an analysis of the variation of¹ H NMR spectra with temperature it has been shown that 2-substituted 5,6-benz-1,3-dithiepins exist in solution in the chair-e and boat-e conformations, the equilibrium between which depends considerably on the nature of the solvent.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 545–548, March, 1987.The authors wish to thank E. N. Klimovitskii and D. Yu. Strel'nik for submitting compound (III).     

75As NQR in cyclic arsenic compounds

Theoretical and Experimental Chemistry -     

Inhibition of Na+, K+-ATPase in the presence of crown ethers: modulation of ionic composition or pharmacological effects

It is believed that the biological effects of chelating agents such as crown ethers are largely related to their ability to form complexes with ions and/or to facilitate ion transport across membranes. Specific influences are rarely related. Here we present the evidence that even one of the simplest representatives of the crown ether super-family, 1,4,7,10,13,16-hexaoxacyclooctane (18-crown-6), is able to affect the activity of Na⁺, K⁺-ATPase directly. Using nonlinear regression fitting to kinetic data we have found that the crown ether diminishes the apparent Michaelis constant, K _m , and the maximal rate of ATP hydrolysis, V _m , acting as noncompetitive inhibitors. The apparent dissociation constants, K _i , for the crown interaction with the free ATPase and with the enzyme-substrate complex were established to be of 77 ± 3 mM and 21 ± 2 mM, respectively. So 18-crown-6 possesses weak but “direct” pharmacological activity on Na⁺, K⁺-ATPase hinders the formation of enzyme–substrate complex and detains the enzyme in this state.     

Polysaccharides of Eremurus. XXIII. Carbohydrates from leaves of some species of Eremurus

Institute of the Chemistry of Plant Substances, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 588–589, July–August, 1988.