Cytosine Diffusion

Fig. 8 Long range charge transport between dppz complexes of Ru(III) and an artificial base, methyl indole, in DNA. The methyl indole is paired opposite cytosine and separated from the intercalating oxidant by distances up to 37 A. In all assemblies, the rate constant for methyl indole formation was found to be coincident with the diffusion-controlled generation of Ru(III) (> 107 s )> indicating that charge transport is not rate limiting over this distance regime...

L.D. Stegman, A. Rehemtulla, D.A. Hamstra, D.J. Rice, S.J. Jonas, K.L. Stout, T.L. Chenevert, B.D. Ross, Diffusion MRI detects early events In the response of a glioma model to the yeast cytosine deaminase gene therapy strategy. Gene Then 7 (2000) 1005-1010. 

Solvated Electron Reaction Rates. Purines and Pyrimidines. The reaction rates of e aq with purines and pyrimidines at neutral pH are shown in Table II. All are very reactive, the reaction rates being close to diffusion controlled. However, the pyrimidine cytosine, which has an amino group at the C-4 position, is somewhat less reactive than thymine and uracil which have carbonyl groups at this position. Adenine, which also has an amino group in this position, has a very high reactivity, but this is probably because of the presence of the positively charged imidazole ring. 

The pyrimidines react with the solvated electron at practically diffusion-controlled rates. The ensuing reactions are well understood in uracil and thymine, while in the case of cytosine more questions remain unresolved. 

The double stranded structure of DNA may also influence the site of interaction of diffusible water radicals through reduced accessibility to certain sites [19-21]. For instance, C-5 and C-6 of thymine and cytosine and C-5 and C-8 of adenine and guanine face into the major groove of DNA and are therefore solvent accessible. The distribution of radical attack at the different carbon atoms of the nucleobases may be different to that determined with the mononucleotides. In section 4.3, the influence of the accessibility of the minor groove to the hydroxyl (OH) radical on H-atom abstraction from the various carbon sites of sugar moiety is discussed. 

Transretinoic acid has dramatically changed the management of acute promye-locytic leukemia. It allows the maturation of leukemic cells and induces remission. It is typically used in association with daunombicin and cytosine arabinoside. The retinoic acid syndrome occurs in 25% of patients and consists of a capillary leak syndrome with noncardiogenic pulmonary edema (14). Diffuse alveolar hemorrhage is also a well-documented complication. 

A second example is a 220 GHz EPR study of an oligonucleotide with a newly synthesized cytosine spin-label. The spectrum from a monomer in an aqueous solution exhibited a three-line pattern characteristic of a nitroxide in a fast motion regime. The anisotropic diffusion tensor estimated from this fast motion spectrum was consistent with the expected rapid motion of the probe molecule around its tether. 

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