The most common and most likely answer to this crossword clue is the 11 letter word ANTIPROTONS
I've seen this crossword clue in The Guardian
A
N
T
I
P
R
O
T
O
N
S
Buddy explains!

The straight part
We know that "being negative, they are charged" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case being negative, they are charged = antiprotons.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ANTIPROTONS mean?
ANTIPROTONS noun- The antiparticle of the proton, having a negative electric charge.