Made ineffective portal in wrong end (7)
I believe the answer is:
negated
'made ineffective' is the definition.
(I've seen this before)
'portal in wrong end' is the wordplay.
'portal' becomes 'gate' (I've seen this before).
'in' is an insertion indicator.
'wrong' indicates anagramming the letters.
'end' is an anagram of 'ned'.
'gate' inserted into 'ned' is 'NEGATED'.
(Other definitions for negated that I've seen before include "Abrogated" , "Denied" , "Nullified" , "Cancelled or destroyed the effect of something" , "Discredited" .)