Donor Selection Criteria

In order to expand the number of potential donors, selection criteria have been modified over the years with the aim of recruiting older donors as well. Like recipient selection, the evaluation of potential donor hearts depends on universally accepted objective criteria that may be modified by the particular circumstances and program-based trends within each case. 

The April 2001 version of the CCSD database was searched using the Windows software Conquest 1.2. The database was searched for nonionic compounds containing Pb with an R-factor <0.05 and no disorder. Lead-to-donor distance criterion was set for 0-3.50 A. A subsearch was done to select for compounds with Pb(II). A total of 295 compounds were found. 

Base polyads are understood as base complexes linked by H-bonds. Even though many of these base motifs are approximately planar the notion of base polyads as used here does also cover strongly non-planar structures. The selection criterion is the base-base H-bond link and not the overall planarity of a certain base polyad. We adopt the following geometrical criteria to classify an interaction of the type D-H...A (D - H-bond donor, A - H-bond acceptor) as an H-bond distance H...A < 2.5 A, angle D-H...A > 90. Interactions with smaller angles or larger distances are not considered as H-bonds. 

The space arrangement of the important feature is also to be considered. Indeed, many SAR studies include length modifications in scaffold side-chains to estimate the influence of flexibility and steric tolerance of the binding site (see, for example, [29, 30]). Chirality of the model is another spatial criterion that is necessary if two enantiomers of different activity level are to be discriminated. At least four points are necessary, but not sufficient to assure enantio-selectivity. The use of directional features (H-bond acceptor/donor) or shape criteria can help in obtaining chiral models. 

A simulation study performed for an aqueous excess proton and IM HCl [40] has shown that the oudined criterion is simple, time-independent and selective. Simplicity implies that this H-transfer criterion depends only on the position of the transferring hydrogen and the involved donor- and acceptor-atoms, but not on properties of other atoms (such as angle and dihedral data with respect to other hydrogen atoms bound to the donor or the acceptor). Enforcing such a simplicity in the update criterion results in a general formalism that is not restricted to H-transfer reactions between water molecules but can be applied to other systems as well as for example the transfer of a proton between a hydrohalogenide and a halide ... 

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