Subject that's of potential interest, chemistry first of all (5)
I believe the answer is:
topic
'subject' is the definition.
(as in a topic for discussion)
'that's of potential interest chemistry first of all' is the wordplay.
'first of all' says to take the initial letters.
The first letters of 'that of potential interest chemistry' is 'TOPIC'.
(Other definitions for topic that I've seen before include "Issue (for discussion)" , "Theme of discourse" , "Subject (of a talk, etc)" , "Subject (of speech, etc)" , "might this be hot?" .)