The effect of polymorphism in dimethyl-3,6-dichloro-2,5-dihydroxyterephthalate on the principal shift values and quadrupolar coupling parameters is studied utilizing ab initio methods and solid state nuclear magnetic resonance (NMR). The effect of the quadrupolar nuclei 35,35Cl on the 13C solid state NMR spectra of 13C is investigated.; The experimental complication arising from dipolar coupling between a spin-½ and a spin-1 in the 5π replicated magic angle turning experiment is studied and a method to simulate the spectra is outlined. The treatment allows for extraction of the dipolar coupling constant, the chemical shift principal values and the orientation of the C-N bond vector in the chemical shift principal axis system. The accuracy of the method is verified on the isolated 13C-14N spin systems in several amino acids with natural isotope abundance.; Furthermore, this method is applied to the tripeptide Melanostatin ( L-Pro-L-Leu-Gly amide). The solid state backbone conformation is determined by comparison of the solid state NMR chemical shift principal values and the C-N bond vector orientation in the chemical shift principal axis system to theoretical shift tensor calculations; the obtained conformation is compared to the single crystal X-ray structure. The quality of the theoretical calculations is validated utilizing several techniques to account for intermolecular effects in the computations.; The applicability of this method to larger systems is explored on three C-terminal gastrin peptides. The 13C and 1H shift assignment are obtained in solution and the 13C principal shift values are reported. The solution and solid state shifts are discussed in terms of conformational differences between the three peptides.
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