Cytosine geometrical parameters

Figure 16-14. Computed energy levels for the ground state (S0) and the lowest triplet excited state (T) of the cytosine dimer in its triplet locally excited state 3(LE), step-wise intermediate 3(SWI), and ground-state cyclobutane cytosine (CBC) dimer. The main intermolecular geometric parameters (in A) for 3(SWI) are included. At the 3(SWI) optimized structure a singlet-triplet crossing, (T1/S0)x, takes place...

In Figures 1 and 2, the geometrical parameters of CH2SOH and 03H, obtained at PWP/TZVP, BP/TZVP and B3LYP/6-31G levels, are reported together with other theoretical results [79,80J. The data of protonated cytosine reported in figure 3 are obtained at BP/TZVP level and comptired to the experimental ones [81,82]. 

Table 1. Selected geometric parameters (distances in A, angles in degrees) for monohydrated cytosine tautomers and transition states optimized at the HF/3-2IG level.

The analyses of the structural parameters of the investigated monohydrated complexes reveal that the hydrogen bonds between the base and water molecule should be classified as rather weak. The geometrical parameters of the monohydrated amidic fragment of guanine and cytosine are very similar. 

Figure 8. Selected geometrical parameters of the monohydrated cytosine species.

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