Proton magnetic relaxation times have been measured in solutions of polyethylene oxide. Molecular weight, temperature, and solution concentration have been systematically varied. Several low-molecularweight oligomers have been studied as well as polymers which vary in molecular weight from 4X1Q3 to 4XIQ6. The results show that in dilute solution both TI and T. are independent of mdecular weight. TI decreases with increasing concentration for concentrations greater than 0.2 g per ml of polymer, but is independent of concentration for more dilute solutions. T. is independent of concentration in the limit of low concentration, but decreases rapidly with increasing concentration. The concentration dependence of T. is a sensitive function of molecular weight. The relaxation mechanism has been analyzed using a model of rotameric transitions and the molecular geometry calculated from the known crystal structure of tbe polymer. The most important term is that arising from a conformational change about the C-C bond, in which the oxygen atoms move from a gauche to a gauche' position. The relaxation times (TIl of water in aqueous polyethylene oxide solutions decrease with increasing polymer concentration, and are independent of the molecular weight of the polymer.
The binding of zinc by poly-N-vinylimidazole (PVI) in 1 M sodium nitrate a t 0.1 and 0.01 M polymer concentrations was studied potentiometrically and by dialysis equilibrium. Formation constants computed from the data of each technique were in excellent agreement with a maximum coordination number of 4 being found. The enhancement of the successive intrinsic stepwise association constants due to the polymeric effect was observed ; the four intrinsic formation constants log K~ could be read directly from the &-plotting method of Scatchard, and were 1.72, 2.65, 3.35, and 3.76 as contrasted with 1.98, 2.19, 2.41, and 2.62 for the binding of imidazole by Zn(I1). Analysis of the precipitated PVIZn(I1) complex showed that the ratio of nonprotonated PVI to Zn(I1) in the complex approached 1 with an excess of metal present and 4 with an excess of polymer. A turbidimetric study showed cross linking of polymer chains by Zn(I1) at high polymer-metal ratios, with an approximately 400-fold increase in molecular weight. Nitrilotriacetic acid formed a 1 : 1 : 1 molar complex with Cu(I1) and PVI; the tridentate ligand complex with the metal appeared to be attached to the chain by a single bond, with a formation constant of 1 0 4 . 0 as contrasted with the first and last stepwise constants of 103.50 and 103.76 for the binding of the polymer directly to Cu(I1).
IntroductionThe role of the imidazole group in proteins and other natural products has been of broad interest; extensive work on its complexes with metallic ions has been reported.2-5 The binding of Cu(I1) and Ag(1) ions by poly-N-vinylimidazole (PVI) has been described previously.6 I n the present paper, the formation of complexes of PVI with Zn(I1) was studied by both poten-
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