Characterization of supramolecular (H2O)18 water morphology and water-methanol (H2O)15(CH3OH)3 clusters in a novel phosphorus functionalized trimeric amino acid host

Phosphorus functionalized trimeric alanine compounds (L)- and (D)-P(CH2NHCH(CH3)COOH)(3) 2 are prepared in 90% yields by the Mannich reaction of Tris(hydroxyme'thyl)phosphine 1 with (L)- or (D)Alanine in aqueous media. The hydration properties of (L)-2 and (D)-2 in water and water-methanol mixtures are described. The crystal structure analysis Of (L)-2.4H(2)O, reveals that the alanine molecules pack to form two-dimensional bilayers running parallel to (001). The layered structural motif depicts two closely packed monolayers of 2 each oriented with its phosphorus atoms projected at the center of the bilayer and adjacent monolayers; are held together by hydrogen bonds between amine and carboxylate groups. The water bilayers are juxtaposed with the H-bonded alanine trimers leading to 18-membered (H2O)(18) water rings. Exposure of aqueous solution Of (L)-2 and (D)-2 to methanol vapors resulted in closely packed (L)-2 and (D)-2 solvated with mixed water-methanol (H2O)(15)(CH3OH)(3) clusters. The O-O distances in the mixed methanol-water clusters Of (L)-2.3H(2)O.CH3OH and (D)-2.3H(2)O.CH3OH (O-O(average) = 2.857 Angstrom) are nearly identical to the O-O distance observed in the supramolecular (H2O)(18) water structure (O-O(average) = 2.859 Angstrom) implying the retention of the hydrogen bonded structure in water despite the accommodation of hydrophobic methanol groups within the supramolecular (H2O)(15)(CH3OH)(3) framework. The O-O distances in (L)-2.3H(2)O.CH3OH and (D)-2.3H(2)O.CH3OH and in (H2O)(18) are very close to the O-O distance reported for liquid water (2.85 Angstrom).