Crosslinking coordination

While the critical role of intrastrand 1,2-crosslinks in the mechanism of action of the anti-tumor drug cis- [PtCl2(NH3)2] is well established, much less is known about the few frans-analogs that exhibit similar efficacy. A series of 1,3-adducts has been characterized with 3-mers generally involving purine N7 coordination (32-34), and either monofunctional or interstrand adducts are formed with duplex DNA (35). However, one of the most active compounds, frans-[PtCl2 ( )-HN = C(OMe)Me 2], (2), has been shown to form a 1,2-adduct with 2-mer ribonucleotide sequence r(AG) (36). Though the formation of the... 

The choice of metal ion in this work is interesting since it has been known for a considerable time that Ag+ is a rare example of a d-block metal ion that does not disrupt the duplex DNA structure (172,173). Rationalization of this effect has tended to focus on the possible base-pair crosslinking due to the preferred linear coordination geometry of Ag1 ions (174). The importance of Ag+ DNA coordination chemistry to the procedure described is not clear. However, reports that other metal ions, e.g., Pdri (175), can be plated to DNA to fabricate metallic wires (Fig. 51) suggests that this may not be essential. 

The connection between polymer chemistry and ceramic science is found in the ways in which linear macromolecules can be converted into giant ultrastructure systems, in which the whole solid material comprises one giant molecule. This transformation can be accomplished in two ways—first by the formation of covalent, ionic, or coordinate crosslinks between polymer chains, and second, by the introduction of crystalline order. In the second approach, strong van der Waals forces within the crystalline domains confer rigidity and strength not unlike that found when covalent crosslinks are present. 

Species such as XXV, XXVI, or XXVII readily form coordination complexes when treated with AuCl, H20So(C0)j q, Idn(CO)3(r -C5Hj), Fe(C0)3(PhCH=CHC(0)CH3>, or [RhCl(CO)2]2 ( ) Tw results are of special interest. First, the skeletal nitrogen atoms in XXV-XXVII do not participate in the coordination process. Presumably, they are effectively shielded by the aryloxy units and are of low basicity. Second, coordinatlve crosslinking can occur when two phosphine residues bind to one metal atom. Ligand-exchange reactions were detected for the rhodium-bound species. The tri-osmium cluster adducts of XXV, XXVI, and XXVII are catalysts for the isomerization of 1-hexane to 2-hexene. 

The exact mechanism by which HIER works is unknown. It is thought to reverse the masking effects of formaldehyde fixation and routine tissue processing. Hydrolytic-proteolytic cleavage of formaldehyde-related crosslinks, unfolding of inner epitopes, as well as the extraction of calcium ions from coordination complexes with proteins are among the hypothesized mechanisms (13-15). 

Other results reported concern the reactivity of Fe(II)porphyrin attached to the surface of a solid. Collman et al.99) prepared Fe(II)(TPP) 39 coordinated to an imidazole group bonded to crosslinked poly(styrene), as represented in 40. Treatment of 40 with oxygen in benzene caused oxidation and formed the n-oxo dimer... 

Edwards (300) was able to make some progress on the problem by showing that topological classification can serve only to raise the modulus. As a simple example, consider all strand pairs in a network which have, within some small tolerance, a specified set of internal junction coordinates. Suppose there are B such pairs, and that the strands of each pair, labeled 1 and 2, have co1 and co2 distinguishable configurations each as free strands, and fractions (gt)0 and (g2)o respectively which have the end-to-end distances specified by the equilibrium junction coordinates. If the crosslinks were formed in the system at equilibrium, then the total number of configurations for each strand of the pair is cj1(g1)0 and o)2(02h> and the number available to the pair is (o1(o2(gl)0(g2)0. 

Fig. 22. Schematic diagram of coordinate system related to one inter-crosslink chain (adapted from Ref.3I)...

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