import re
rx = r'=[^\d-]*(?P<mean>-?\d*\.?\d+)\s*\+/-\s*(?P<sd>\d*\.?\d+)\W+(?P<units>.+)'
text = r"ΔG'° = (-19.9 +/- 0.4) kilojoule / mole"
m = re.search(rx, text)
if m:
print(m.groupdict())
aW1wb3J0IHJlCnJ4ID0gcic9W15cZC1dKig/UDxtZWFuPi0/XGQqXC4/XGQrKVxzKlwrLy1ccyooP1A8c2Q+XGQqXC4/XGQrKVxXKyg/UDx1bml0cz4uKyknCnRleHQgPSByIs6URyfCsCA9ICgtMTkuOSArLy0gMC40KSBraWxvam91bGUgLyBtb2xlIgptID0gcmUuc2VhcmNoKHJ4LCB0ZXh0KQppZiBtOgoJcHJpbnQobS5ncm91cGRpY3QoKSk=