| Natural polymers play an important role in the nature. Studies on molecular structures of natural polymers can help to understand their biological functions. This work seeks to understand the molecular structures of three natural polymers: lime fruit cutin, potato suberin, and C. neoformans fungal melanin. Due to the intractability of these materials, strategies of solid state NMR, isotopic labeling were employed in these studies. Partial degradation strategy was also employed in the study of lime fruit cutin and poato suberin.; Lime cutin was degraded with KOH and HF. Six monomers, 4 dimers, 5 trimers, and a tetramer were isolated from the degradation products by TLC, HPTLC, and HPLC. Structures of these isolated compounds were elucidated from NMR and MS data. Dimers of the two most abundant monomers in lime cutin, 10,16-dihydroxyhexadecanoic acid and 10-oxo-16-hydroxyhexadecanoic acid, with different combinations were separated and identified. Trimers separated and identified in our studies mainly consist of these two most abundant monomers. Other monomers and their oligomers were also separated and identified. A modified KOH degradation method was developed in order to enhance oligomeric compositions and sizes in the products. A separation protocol was also developed to improve isolation efficiency of target compounds. KOH degradation method was also applied to potato suberin, trends of retention time in liquid chromatography were linked to structural features of the compounds.; Cross-Polarization (CP) magic-angle spinning (MAS) 13C NMR reveals function groups of esters, aliphatic chain, and polysaccharide in lime cutin and potato suberin with different relative amounts. High-Resolution (HR) MAS NMR reveals more structural details of lime cutin, which are consistent with the degradation results. Polysaccharide moieties of potato suberin were evidenced in HRMAS NMR spectra.; The incorporation of labeled precursors into the melanin products is demonstrated by the NMR data. Melanins derived from different precursors have generally similar aliphatic and aromatic spectroscopic features, but structural differences are also suggested by their NMR spectra. A polysaccharide moiety found in [1-13C] D-mannose melanin suggests close association or covalent binding of melanin to the fungal cell wall. |
