At ph 7 tryptophan crosses the lipid layer 1000 times slower than indole, why?

Question

At ph 7 tryptophan crosses the lipid layer 1000 times slower than indole, why?

Answer 1

Tryptophan at pH 7 is charged while indole is uncharged and acts like a typical hydrophobe. Hydrophobic materials are much more "soluble " in the lipid bi-layer than polar or charged compounds.

Answer 2

At pH 7 tryptophan has three ionized groups.