Made ineffective portal in wrong end (7)
I believe the answer is:
negated
'made ineffective' is the definition.
(I've seen this in another clue)
'portal in wrong end' is the wordplay.
'portal' becomes 'gate' (I've seen this before).
'in' means one lot of letters goes inside another.
'wrong' indicates anagramming the letters.
'end' with letters rearranged gives 'ned'.
'gate' placed within 'ned' is 'NEGATED'.
(Other definitions for negated that I've seen before include "Abrogated" , "Denied" , "Nullified" , "Cancelled or destroyed the effect of something" , "Discredited" .)