The present invention relates to a unit for partial coordination of Ca2+ ions (herein called 'CPCU'), which unit has at least one Ca2+ binding sites (CBS), each CBS meeting the following conditions: it provides at least three electronegative atoms, at the proper three-dimensional orientation for the coordination of a Ca2+ ion; after binding of Ca2+ to a binding site (CBS), the Ca2+ ion still has one or more coordination sites that are unoccupied; and the electronegative atoms of the CBS, coordinating the Ca2+ ion (hereinafter; 'coordinating atoms' or CA) are individually selected among oxygen, nitrogen, sulfur and fluorine. In said CPCU the coordination atoms CA are advantageously oxygen atoms, and the CA are part of coordinating atom-bearing groups (CABGs). The present invention relates also to a NST 400 compound consisting of a CPCU, being connected to groups A¿b?, Lc, and Bd in any desired order, in which b stands for an integer of 1-3, d stands for an integer of 0-6 and c stands for an integer, ranging from 0 to (b+d); A stands for hydrophobic moiety, L stands for a linker, linking CPCU, A and B and D moieties if present within the NST400 compound; D being a functional group selected among amine, carboxyl, hydroxyl, thiol, and aldehyde; and B stands for amine or an acid addition salt thereof. The NST400 compounds are optionally conjugated to another pharmaceutically active compound (T-NST400 conjugate). The present invention relates also to a pharmaceutical composition comprising a NST400 compound and/or a T-NST conjugate. The present invention relates also to various methods and uses utilizing a NST400 compound and/or a T-NST400 conjugate. It also relates to an affinity filter comprising NST400 compound and/or a T-NST400 conjugate.