In a gallon-sized, re-sealable plastic bag, dissolve 1/4 cup of salt in the warm water. Add the vinegar, red pepper flakes, brown sugar, ice cubes and the pork. Brine for exactly 20 minutes -- the pork becomes mealy if its brined longer. Meanwhile, prepare the Blackberry Jalapeno Glaze.
Add the butter to a saucepan over medium-high heat. Once melted, add the jalapeos and garlic, and saut for 3-4 minutes. Stir in the blackberry preserves and 1 cup wine, and combine well. Simmer until reduced by half. Add the cornstarch to the remaining 1/4 cup red wine in a small bowl and mix well. Pour the cornstarch mixture into the pan and cook for 5-6 minutes more. Keep the glaze warm until serving.
Remove the pork from the brine and pat dry. Rub the pork with the olive oil and season with 1 teaspoon salt and freshly cracked black pepper. Preheat a grill or grill pan to medium heat.
Add the pork tenderloin and cook for 6 minutes on each side, browning evenly and the internal temperature registers 135 degrees F on an instant-read thermometer. At this point, evenly spread 1/4 cup of the glaze over the pork. Cook for an additional 4-5 minutes. Remove the pork from heat to a cutting board and keep it warm tented with aluminum foil.