US 2019/0287691 Al  17  Sep. 19,2019  [0257]  The scaffold can include one or more amine  groups. An amine group can include a nitrogen atom bonded  to three substituents. In particular embodiments, an amine  [0256]  The chelators can include a number of functional  groups having metal-coordinating atoms with the functional  groups being bonded to a linear scaffold or a branched  scaffold.  The  functional  groups  and/or  substituents  described herein may be substituted or unsubstituted. Sub› stituted functional groups and/or substituents can be substi› tuted by one or more hydroxyl groups, one or more alkyl  groups having no greater than 10 carbon atoms, one or more  amine groups, one or more thiol groups, one or more ester  groups, or combinations thereof.  [0255]  The metal-coordinating atoms of the chelators can  be included in combinations of two or more of one or more  CAM groups, one or more HA groups, or one or more  HOPO groups. In illustrative examples, the metal-coordi› nating atoms of the chelators can be included in one or more  CAM groups and one or more HA groups. In other illustra› tive examples, the metal-coordinating atoms of the chelators  can be included in one or more CAM groups and one or  more HOPO groups. In additional illustrative examples, the  metal-coordinating atoms of the chelators can be included in  one or more HA groups and one or more HOPO groups. In  further illustrative examples, the metal-coordinating atoms  of the chelators can be included in one or more HA groups,  one or more CAM groups, and one or more HOPO groups.  [0252]  In particular embodiments, the metal-coordinating  atoms of the chelators described herein can be included in  one or more functional groups of the chelators. In some  examples, the metal-coordinating atoms of the chelators can  be included in one or more catecholate (CAM) groups. A  CAM group can include at least a phenyl ring substituted by  hydroxyl groups on adjacent carbon atoms. According to  some illustrative embodiments, a CAM group can include:  [0251]  In particular embodiments, chelators can include a  number of metal-coordinating atoms that bond with a metal.  The metal-coordinating atoms can bond with metals having  cations with a +1 charge. The metal-coordinating atoms can  also bond with metals having cations with a +2 charge.  Additionally, the metal-coordinating atoms can bond with  metals having cations with a +3 charge. Further, the metal› coordinating atoms can bond with metals having cations  with a +4 charge. The chelators described herein can, in  some cases, include siderophores.  [0254]  In some embodiments, the metal-coordinating  atoms of the chelators can be included in one or more  hydroxypyridinone (HOPO) groups. A HOPO group can  include a pyridinone ring substituted by a hydroxyl group on  the N atom. In some cases, a HOPO group can include a  1,2-HOPO group. According to some illustrative embodi› ments, a 1,2-HOPO group can include:  where  Ra  can include H or an alkyl group including no  greater than 5 carbon atoms. For example,  Ra  can include a  methyl group, an ethyl group, a propyl group, an isopropyl  group, a butyl group, a sec-butyl group, an iso-butyl group,  a tert-butyl group, a pentyl group, a tert-pentyl group, a  neopentyl group, or an iso-pentyl group.  [0250]  Although this disclosure is in the context of certain  embodiments and examples, those skilled in the art will  understand that the present disclosure extends beyond the  specifically disclosed embodiments to other alternative  embodiments and/or uses of the embodiments and obvious  modifications and equivalents thereof. In addition, while  several variations of the embodiments have been shown and  described in detail, other modifications, which are within the  scope of this disclosure, will be readily apparent to those of  skill in the art based upon this disclosure.  It  is also contem› plated that various combinations or sub-combinations of the  specific features and aspects of the embodiments may be  made and still fall within the scope of the disclosure.  It  should be understood that various features and aspects of the  disclosed embodiments can be combined with, or substituted  for, one another in order to form varying modes or embodi› ments of the disclosure. Thus, it is intended that the scope of  the present disclosure herein disclosed should not be limited  by the particular disclosed embodiments described above.  For example, chemical conditions (e.g., acidity, concentra› tions, etc.) could be carried to match those of interest for  various applications. In some embodiments, the ligand 3,4,  3-LI(l,2-HOPO) could also be immobilized on a solid  support if the chromatographic technique is preferred over  the liquid-liquid extraction methods. Thus, in some embodi› ments, any extraction process described herein can instead  be performed instead via a solid support and a chromato› graphic technique. Additionally, one or more embodiments  herein can be combined with any one or more of the other  embodiments herein.  phase) for various embodiments. Thus, each process dis› closed herein regarding a chelator separation, is envisioned  not only as an option for collecting the metal associated with  the chelator (in the aqueous phase) but also as an option for  collecting the metal that is separated therefrom (in the  organic phase). This applies for all embodiments provided  herein.  [0253]  In some embodiments, the metal-coordinating  atoms of the chelators can be included in one or more  hydroxamate (HA) groups. According to some embodi› ments, a HA group can include:  OH  OH. 