diphosphate(4-) Pyrophosphate Pyrophosphat PPi CHEBI:13420 Diphosphat CHEBI:18361 KEGG:C00013 P2O7(4-) [O3POPO3](4-) DIPHOSPHATE CHEBI:42009 diphosphate mu-oxido-bis(trioxidophosphate)(4-) Diphosphate PDBeChem:DPO pyrophosphate ion mu-oxo-hexaoxodiphosphate diphosphate(3-) diphosphate ion