The word antiprotons is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 16
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (34 words)
anoints, instant, intorts, introns, nations, nonarts, nonpros, nonriot, nonstop, notator, notions, options, oration, patriot, patrons, portion, potions, protist, protons, rations, rattons, rattoon, risotto, saponin, soprano, sporont, station, straint, taproot, tinpots, torsion, transit, triptan, tropist