SynopsisBased on equilibrium binding studies, as well as on kinetic investigations, two types of interactions of Cu2+ ions with native DNA a t low ionic strength could be characterized, namely, a nondenaturing and a denaturing complex formation. During a fast nondenaturing complex formation a t low relative ligand concentrations and a t low temperatures, different binding sites at the DNA bases become occupied by the metal ions. This type of interaction includes chelate formation of Cu2+ ions with atoms N(7) of purine bases and the oxygens of the corresponding phosphate groups, chelation between atoms N(7) and 0 of C(6) of the guanine bases, as well as the formation of specific interstrand crosslink complexes a t adjacent G.C pairs of the sequence dGpC. CD spectra of the resulting nondenatured complex (DNA-CU~+),,~ may be interpreted in terms of a conformational change of DNA from the B-form to a C-like form on ligand binding. A slow cooperative denaturing complex formation occurs a t increased copper concentrations and/or a t increased temperatures. The uv absorption and CD spectra of the resulting complex, (DNA-Cu2+)denat, indicate DNA denaturation during this type of interaction. Such a conclusion is confirmed by microcalorimetric measurements, which show that the reaction consumes nearly the same amount of heat as acid denaturation of DNA.From these and the kinetic results, the following mechanism for the denaturing action of the ligands is suggested: binding of Cu2+ ions to atoms N(3) of the cytosine bases takes place when the cytosines come to the outside of the double helix as a result of statistical fluctuations. After the completion of the binding process, the bases cannot return to their initial positions, and thus local denaturation at the G-C pairs is brought about. The probability of the necessary fluctuations occurring is increased by chelation of Cu2+ ions between atoms N(7) and 0 of C(6) of the guanine bases during nondenaturing complex formation, which loosens one of the hydrogen bonds within the G-C pairs, as well as by raising the temperature. The implications of the new binding model, which comprises both the sequence-specific interstand crosslinks and the described mechanism of denaturing complex formation, are discussed and some predictions are made. The model is also used to explain the different renaturation properties of the denatured complexes of Cu2+, Cd2+, and Zn2+ ions with DNA.In temperature-jump experiments with the nondenatured complex (DNA-CU~+),,~, a specific kinetic effect is observed, namely, the appearance of a lag in the response to the per-

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Furfuryl alcohol polymerizes in a suspension of dispersed inorganic solids such as silica in 1,2-dichloroethane using trifluoroacetic acid as initiator. Depending on the experimental conditions the reactions lead to 1) agglomeration of particles, 2) composite and soluble polymer formation, 3) composite formation. The chemical structure of the soluble polymers is not regular but the furfurylic sequence is predominant. The polymer grafted on the surface of the solid is a strongly reticulated poly(furfury1 alcohol), which also possesses conjugated double bonds that are involved in an acid-base equilibrium with trifluoroacetic acid.

Ni(COD)2 reagiert in TMED mit Bernsteinsäureanhydrid unter Decarbonylierung zum (TMED) (1b). Die IR‐, 1H‐ und 13C‐NMR‐Spektren belegen, daß TMED als starker n‐Donor eine Polarisierung der Nickel‐Kohlenstoff‐σ‐Bindung bewirkt. Bei der Umsetzung von 1b mit überschüssigem CO entsteht in Methanol Bernsteinsäuremonomethylester (3).

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