Stir together first 7 ingredients and 2 qt. water in a large stockpot. Heat over medium-high heat, stirring occasionally, until salt and sugar dissolve. Remove from heat, and cool 1 hour. Place chicken breasts in brine; cover and chill 1 to 3 hours.
Preheat grill to 350° to 400° (medium-high) heat. Drain chicken, discarding brine. Pat chicken dry with paper towels, and sprinkle with desired amount of black pepper. Grill chicken, covered with grill lid, 5 to 7 minutes on each side or until done. Remove from grill. Let stand 5 minutes before serving.
Note: This brine will season up to 12 chicken breasts.