Cell membranes are generally impermeable to charged or large, polar molecules because of the lipophilic fatty acyl chains comprising their interior.
sˈɛl mˈɛmbɹeɪnz ɑːɹ dʒˈɛnɚɹəli ɪmpˈɜːməbəl tə tʃˈɑːɹdʒd ɔːɹ lˈɑːɹdʒ, pˈoʊlɚ mˈɑːlɪkjˌuːlz bɪkˈʌz ʌvðə lˌɪpəfˈɪlɪk fˈæɾi ɐkˈɪl tʃˈeɪnz kəmpɹˈaɪzɪŋ ðɛɹ ɪntˈɪɹiɚ.