EVIDENCE OF ANISOTROPIC REORIENTATIONS OF WATER-MOLECULES IN THE CORTEX OF THE RABBIT LENS DETECTED BY H-1-NMR SPECTROSCOPY

We studied the order of water molecules in different fragments of nucleus and cortex of lenses of 3 month old rabbits by investigating the H-1-NMR spin-spin relaxtion behaviour of the water protons at room temperature. The experiments were carried out using the Carr Purcell Meiboom Gill (CPMG) technique. The apparent relaxation rate was found to be dependent on the pulse spacing in the CPMG sequence in a different way for nucleus and cortex. While for the nucleus the pulse spacing dependence can be explained by chemical exchange of water protons, the pulse spacing dependence of the cortex protons suggests the existence of not fully averaged residual magnetic dipolar couplings among the protons of a water molecule. To support this interpretation, measurements of the ratio of the solid echo (90(x)-90(y)) to the Hahn echo (90(x)-180(x)) amplitude were carried out for the same samples. These experiments give the expected ratio of K = 0.5, characteristic of no residual couplings for the nucleus, but a ratio of K = 0.7 for the cortex, which is characteristic of residual dipolar couplings, caused by anisotropic reorientations of the water molecules. Thus, evidence for an ordered state of the water molecules in the cortex has been found.