Zwitterion-containing compounds for the modification of hydrophobic molecules to improve their solubility and/or to lower their non-specific binding as provided. The zwitterion-containing compounds may be suitable for modification of detectable labels such as biotin and fluorescein to improve their solubility. The zwitterion-containing compounds may also be useful for the preparation of conjugates of proteins, peptides and other macromolecules or for crosslinking molecules and/or macromolecules.