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Investigating the New Interaction Model between Cu(II) and PVA by the Proton Relaxation Method
Author(s) -
Chen JyhHorung,
Hwang LianPin
Publication year - 1988
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.198800041
Subject(s) - chemistry , aqueous solution , copper , ion , relaxation (psychology) , dipole , proton , crystallography , inorganic chemistry , organic chemistry , psychology , social psychology , physics , quantum mechanics
An aqueous PVA‐Cu 2+ solution at pH = 3 is in the hydrated form and becomes green at pH ⩾ 6 with a decrease in viscosity. The structure of the copper ion is suggested to be that of a polynuclear complex at pH > 6. For the green solution the polynuclear chains of the copper complex are believed to be surrounded by the PVA chains with the hydrophobic backbones facing toward the inside and the hydrophilic OH groups oriented toward the outside facing the bulk water. The proton spin‐lattice relaxation rate 1/T 1p and the spin‐spin relaxation rate 1/T 2 of CH and CH 2 in PVA and H 2 O for aqueous PVA‐Cu 2+ solutions at pH = 3, can be explained by the two site exchange model in the region of the fast exchange limit. The dipolar correlation time τ c is dominated by the reorientational process with a dipolar correlation time of 2.11 × 10 −11 s. When the pH rises from pH=3 to pH=12.5, the variation of 1/T 1 p and 1/T 2 p of CH and CH 2 in PVA with Cu 2+ ion concentration in aqueous PVA‐Cu 2+ solution at pH=12.5 can be explained in terms of the relaxation by an inclusive model of the polynuclear copper complex and PVA. Furthermore, the frequency (or field) dependence of 1/T 1 p, 1/T 2 p of CH in PVA for aqueous PVA‐Cu 2+ solution at pH = 12.5 suggests that the dipolar relaxation is dominated by the electron‐spin relaxation with the electron spin relaxation time T 1e = 1 ˜ 2 × 10 −10 s. The invariance of 1/T 1 p and 1/T 2 p of H 2 O with the variation of the Cu 2+ ion concentration in aqueous PVA‐Cu 2+ solution at pH = 12.5 supports the hypothesis that the water is not directly bound to the Cu 2+ ion.