article seaweed Seaweed priority journal carrageenan nonhuman Support, Non-U.S. Gov't Carrageenan Polysaccharides algae Carrageenans Magnetic Resonance Spectroscopy carbohydrate analysis galactose Galactans galactan polysaccharide unclassified drug Male human Antiviral Agents Carbohydrate Conformation Carbohydrate Sequence Human Molecular Sequence Data Rhodophyta antiviral activity carbon nuclear magnetic resonance chemical structure controlled study