(a) The donor of a power of appointment:
(1) Must be a person capable of transferring the appointive property.
(2) Must have created or reserved the power by a written instrument executed by him in the manner required by law.
(3) Must manifest his intention to confer the power on a person capable of holding the appointive property.
(4) Cannot nullify or alter the rights of creditors of the donee, as defined in this article, by any language in the instrument creating or reserving the power purporting to give the interest of such donee a spendthrift character.