Carbohydrate spin systems

The common theme so far in our correlation experiments has been to allow spins to evolve during q under the influence of directly coupled nuclear spins. We have seen the power of COSY, HMQC, HMBC, and INADEQUATE to provide us with detailed structural information for ipsenol, caryophyllene oxide, and lactose. In this section, we will develop another method for showing correlations and apply it to molecules with distinct, isolated proton spin systems such as carbohydrates, peptides, and nucleic acids. 

There are various hybrid 2-D correlation experiments that combine features of two simpler 2-D experiments. A popular and useful example is the HMQC-TOCSY spectrum that correlates one-bond H—13C couplings (HMQC) but shows these correlations throughout an entire spin system (TOCSY). This experiment simplifies complex carbohydrate and peptide systems and allows ready assignments of systems of protons and carbons. 

A limited number of more complex spin-systems of carbohydrates have been analyzed by manual methods. For example, H-4, H-5, H-3, H-6, andH-6 of 3,4,5,6-tetra-O-acetyl-l,2-dideoxy-1-nitro-D-xi/Zo-hex-1-enitol (75) have been analyzed, respectively, as an ABMRX... 

FIGURE 18.1 Scavenging effects of 90% chitosan( ), 75% chitosan (o), and 50% chitosan (t) on hydroxyl radical obtained in Fenton reaction system (a) and on superoxide radical obtained in hypoxanthine-xanthine oxidase system (b) at various concentrations of hetero-chitosans. Inset shows ESR spectrum of the spin adduct of DMPO-OH (a) and superoxide radical (b). (From Park, P.J. et al., Carbohydr. Polym., 55, 17, 2004c. With permission.)... 

Furanics Avantium Technologies in Amsterdam, a spin-off of Royal Dutch Shell, developed furanics for bioplastics and biofuels from biomass. This technology uses proprietary catalytic systems for the conversion of biomass into carbohydrates that are then converted to furanics. 

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