Nonexchangeable proton spectra

Nonexchangeable Proton Spectra Proton spectra of the daunomycin poly(dA-dT) complex in 1 M NaCl, solution have... 

Consistent with the dithiolene structure proposed for the oxidized derivative of molybdopterin (3), no nonexchangeable H resonances are observed in the region expected for the CH protons of a dithiolate structure (5b). The mass spectrum of 3 is also consistent with the proposed dithiolene structure (19, 34). Resonance Raman spectra of DMSO reductase show bands at 1575 cm (oxidized form) and 1568 cm (reduced form) that are assigned to the C=C stretch of the dithiolene unit of 2 (40). However, the delocalized electronic structure of dithiolene ligands makes it difficult to assign the C=C stretch with certainty. As Rajagopalan notes (19), ultimate proof of the structure [of molybdopterin] will have to await either X-ray studies on a molyb-doenzyme or unequivocal chemical synthesis of the molecule. ... 

---