A t h reed i men s i o n a I Xray a n a I y s i s of a q u o -NN 'e t h y I e n e b i s (ace t y I a c e t o n e i m i n a t 0 ) copper ( I I ) h as con f i r m e d an eclipsed conformation for the carbon atoms of the ethylene bridge which are displaced, by 0.1 1 and 0.1 4 8, to the same side of the plane through the four donor-atoms of the chelating group. It is suggested that this is a result of the bending of the molecule consequent upon the adoption of a tetragonal pyramidal co-ordination geometry. Hydrogen atoms were located and the hydrogen-bonding scheme is revealed in some detail. Bifurcation occurs in the accepted sense, but in addition it is suggested that double interaction by a negative dipole, rather than a positive one, also takes place.COLOUR differences between anhydrous and hydrated crystals of NN'-ethylenebis (ace t ylacetoneiminato)copper(I1) have been found to reflect changes in the coordination stereochemistry about the copper atom.lS2The two-dimensional X-ray analysis of the hydrate also revealed an incidental but unusual detail concerning the geometry of the ethylene bridge, vix. that it is in the cis-conformation, with both carbon atoms displaced to the one side of the plane defined by the copper and two nitrogen atoms. Table 1 contains TABLE 1 Displacements of ethylene carbon atoms from the co-ordination plane Co-ordin-Distances (A) ation 1st 2nd Compound number carbon carbon a@) 4 NN'-en(acac),Cu ......... 4 -0.44 0.12 0.02 NN'-en(acac) ,Cu,&H,O ...
The results of the two independent X-ray analyses of the complex formed between cupric ions and the nucleotide guanosine 5'-monophosphate are presented and compared. The crystals are polymeric, with a spiralling sequence, (-Cu-phosphate-sugar-base-)oo, the turns of which are cross-linked by additional bonds between copper and phosphate O atoms and by hydrogen bonding between coordinated water molecules and phosphate O atoms. The purine bases project outwards from the spiral and intercalate between bases of neighbouring chains. This 'base stacking' is associated with significant differences in the sugar ring conformations where two are puckered C(Y)-endo and one is C(2')-endo. The square-pyramidal coordination pattern is not the same for the three independent Cu atoms. Each binds to N(7) of the purine, but two bind to three O(H20) and one O(phosphate) whereas the other binds to two O(H20) and two O(phosphate).
CRYSTALLOGRAPHY OF BIOLOGICAL MACROMOLECULES the orphaned 3U-tem1inal end in the minor groove of the adjacent duplex where it synm1etrically pairs with the 5'-terminal guanine to form a d[G*(G.C)] base-tliplet. Our findings extend to the minor groove a DNA hydrogen bonding pattem which permits basepair recognition dming homologous recombination.
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