Mo. Rev. Stat. § 456.1015: Requisites for exercise of power of appointment.

A power of appointment is exercised only if:

(1) The instrument exercising the power is valid under applicable law;

(2) The terms of the instrument exercising the power:

(a) Manifest the powerholder's intent to exercise the power; and

(b) Subject to section 456.1030, satisfy the requirements of exercise, if any, imposed by the donor; and

(3) To the extent the appointment is a permissible exercise of the power.