[NTG-context] u-diaeresis

I use a font for \chapter that does print u-diearesis with \"u. Then I decided to write a small definition \udotdot that uses \char200 to print the diaeresis on top of the letter u. The problem now is that in my table of contents, the font is different, and the \char200 has a different meaning. How do I resolve this problem? thank you Ciro