Ring closure rates

Rate constants for reaction of cis-[Pt(NH3)2(H20)Cl]+ with phosphate and with S - and 5/ -nucleotide bases are 4.6xl0-3, 0.48, and 0.16 M-1s-1, respectively, with ring closure rate constants of 0.17 x 10 5 and 2.55x10-5s-1 for subsequent reaction in the latter two cases 220). Kinetic aspects of interactions between DNA and platinum(II) complexes such as [Pt(NH3)3(H20)]2+, ds-[Pt(NH3)2(H20)2]2+, and cis-[Pt(NH3)2(H20)Cl]+, of loss of chloride from Pt-DNA-Cl adducts, and of chelate ring formation of cis-[Pt(NH3)2(H20)(oligonucleotide)]"+ intermediates implicate cis-[Pt(NH3)2(H20)2]2+ rather than cis-[Pt(NH3)2 (H20)C1]+, as usually proposed, as the most important Pt-binder 222). The role of aquation in the overall scheme of platinum(II)/DNA interactions has been reviewed 223), and platinum(II)-nucleotide-DNA interactions have been the subject of molecular modeling investigations 178). 

The use of less electron-releasing acetoxy substituent reduced the direct ring closure rate sufficiently to allow a complete C=N isomerization, thus affording pure trans products. 

The range of possible neighboring group participations mentioned above reflects the usual ring closure rates of five-membered > three-membered > six-membered other ring sizes. 

These compounds were extracted by refluxing the aged photochromic PU films. A kinetic analysis of the thermal bleaching of merocyanine in PU showed that, at variance with that was observed in toluene solution, no acceleration of the ring closure rate took place. The decoloration was described by a biexponential function ... 

A series of studies were also undertaken for substituted phenanthroline complexes of the type Mo(CO)5N—N. The ring-closure rate constant k2 in general decreases with increasing steric hindrance on the ligand, and the... 

Table 1. Ring Closure Rates of co-Bromoalkylamines in Water at...

In the aminoethanol complexes the rates of closure of the first and second chelate rings are similar for the c/j-complex, but for the trans-complex there is a large difference between the two ring-closure rates and it is possible to isolate the intermediate tra s-[Pt(aminoethanol)(aminoeth-oxide)Cl]. 

Table 2 The experimental values of absorption, M(III) SP formation rate constant (kj), thermal ring closure rate constant (k p, equilibrium (K ) constant of the reversible reaction, relaxation time and colorability in...

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