Cross-link long-range

Fig. 2. Schematic limiting binding modes for a di- or trinuclear bifunctional DNA-binding compound. The l,l/f,f geometry forms both types of adduct the 1,1 tc,c (n = 4, 6) forms only interstrand cross-links. Long-range intrastrand cross-links can, however, occur for a species such as BBR 3464.

Figure 4 Examples of long-range interactions in protein a disulfide cross-link and a polypeptide turn.

The polynuclear platinum compounds stand in vivid contrast to mononuclear platinum complexes because the predominant DNA lesions are long-range inter- and intrastrand cross-links where the sites of platination may be separated by up to four base pairs. The consequent structural and conformational changes in DNA are also distinct. 

Rubber elasticity, which is a unique characteristic of polymers, is due to the presence of long chains existing in a temperature range between the Tg and the Tm. The requirements for rubbery elasticity are (1) a network polymer with low cross-link density, (2) flexible segments which can rotate freely in the polymer chain, and (3) no volume or internal energy change during reversible deformation. 

UV curable powders is in the 175 to 250°F (80 to 121°C) range/ much less heat is required, and it is needed only long enough to melt the powder, not to cure it. Cross-linking by the UV light is nearly instantaneous thus, the process is finished in a fraction of the time required for convenfional powders. 

Psoralens must be photoactivated by long-wavelength ultraviolet light in the range of 320-400 nm (ultraviolet A [UVA]) to produce a beneficial effect. Psoralens intercalate with DNA and, with subsequent UVA irradiation, cyclobutane adducts are formed with pyrimidine bases. Both monofunctional and bifunctional adducts may be formed, the latter causing interstrand cross-links. These DNA photoproducts may inhibit DNA synthesis. The major long-term risks of psoralen photochemotherapy are cataracts and skin cancer. 

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