Poly nuclear Overhauser enhancement

Table II. Nuclear Overhauser Enhancement Factors for Poly (n-...

C Spin lattice relaxation times, Tj, spin-spin relaxation times, T2, and nuclear Overhauser enhancements, NOE, for the a-carbons of PBLG of various molecular weights have been used to study transitions from rigid to flexible forms of this polymer (Allerhand and Oldfield, 1973). Effective rotational correlation times, reff, calculated from 7 - and NOE-values, for the a-carbons were 24-32 nanoseconds for the helical form and approximately 0-8 nanoseconds for the random coil (Allerhand and Oldfield, 1973). The transition from the a-helix to the random-coil of PLM causes the resonances of the a- and carbonyl carbons to move upfield 2-3 and 3-4 ppm respectively (Tadokoro et al., 1973), which is consistent with results obtained for PBLG and PCBO. Further work is required before the reasons for the chemical shift differences between the corresponding carbons in the helical and random-coil forms in deuterochloroform-TFA systems can be elucidated. Plots of chemical shifts and relaxation times vs. pH have been used to study the helix-coil transition of poly-L-lysine hydrochloride in aqueous solution (Saito and Smith,... 

Two-dimensional nuclear Overhauser enhancement spectroscopy (2D-NOESY) provided qualitative information about spatial proximities of protons in a molecule. The unimer micelle of poly(A/l-Np(60)) (poly(A/l-Np(x)) where x = 60 mol%) in D2O gave cross-peaks between the aromatic and aliphatic protons owing to dipolar interactions, whereas the same polymer showed no such cross-peaks in DMF-rfv [29], This is indicative of a highly compact conformation of the unimer micelle in water. 

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