Quadrol, N,N,N',N'-tetrakis(2 -hydroxypropyl)ethylenediamine: Metal binding properties and separation of diastereomer

N,N,N$spprime$,N$sp prime$-Tetrakis(2-hydroxypropyl)ethylenediamine (Quadrol) is a metal chelator and an immunostimulant which exists as a mixture of four unique diastereomers. Reversed-phase ion-pair high performance liquid chromatography procedures (analytical and preparative) were developed with electrochemical detection for separation and isolation of the Quadrol diastereomers. A C$sb{18}$ column with mobile phase containing 20% methanol and 80% buffer at pH 5.5 and 3 mM octyl sodium sulfate provided optimum resolution. Analyzing synthesized mixtures of diastereomers allowed identification of the separated peaks, and the results were corroborated with GLC and NMR. The peaks were eluted in the order of SSRR, SSSR, SSSS, and SRSR with peak ratios of about 1:4:1:2.;The effects of structure on basicity and copper complexation were studied by analyzing derivatives of Quadrol with a pH potentiometric titration procedure. When carbon atoms were added between the nitrogen atoms in a series of ethylenediamines, diaminopropanes, and diaminobutanes, pKa values increased and stability constants decreased. Hydroxybutyl substitution on the nitrogen atoms resulted in more basic compounds and more stable complexes, while dihydroxypropyl substitution gave more acidic compounds and less stable complexes than hydroxypropyl substitution.;When Quadrol is incorporated into the polymer hydrogel (poly(Quadrol methacrylate)), it retains its metal binding and immunostimulatory properties. Dissociation constants, stability constants, chelating capacities, and metal ion release constants were determined for polymer samples by potentiometric titration and equilibrium dialysis. The pKa values were calculated from titration data with modified Henderson-Hasselbalch equations, and stability constants were obtained with the modified Bjerrum method applied to equations derived specifically for poly(Quadrol methacrylate). The polymer was found to be a weaker base and to bind metal ions more strongly than its monomer analogue, Quadrol. Chelating capacities followed a decreasing order of Cu $>$ Cd $>$ Co $>$ Zn $>$ Mn, and metal ion release constants increased in the same order. Calcium and magnesium did not bind. At pH 5.5, copper binds 2.4 mmol/g of polymer and is not released into solution, while zinc binds 0.9 mmol/g and is slowly released at a rate which decreases with time. The results of this study suggest that incorporation of Quadrol into hydrogel wound dressings may provide a means of releasing therapeutic metal ions into a healing wound.