Study of macroaggregate composition using FT-IR and 1H-NMR spectroscopy

Mucous macroaggregates, recently observed in the northern Adriatic in summer of 1997 and late spring of 2000, are primarily the product of phytoplanklon (diatom) exudates during favourable environmental conditions in late spring, and can be viewed as macrogels. The FT-IR and H-1-NMR spectra of macroaggregate samples from the northern Adriatic, collected in different formation stages in July 1997, August 1997, September 1997 and June 2000, as well as of cultured diatom Skeletonema costatum, showed that they are similar and composed of aliphatic components and polysaccharides bonded through carboxylic and amide groups, and organosilicon compounds, The stability of macrogels of macroaggregates is, according to FT-IR and X-ray analyses, most probably enhanced by interactions with entrapped particles of calcite, quartz and clay minerals, These organic-mineral associations seem to be important for mucous phenomena. According to H-1-NMR spectra, the temporal differences in macroaggregate composition show a relative increasing percentage of organosilicon compounds and aliphatic components bonded to carbohydrates through ester and amide groups, and an increasing ratio between aliphatic structures and carbohydrates. This indicates that aliphatic chains bonded to Si and carbohydrates may contribute to the persistence and stability of macroaggregates in the summer stratified waters in the northern Adriatic, while the temporal decrease of carbohydrate content is most probably due to microbial and photochemical degradation of algal reserve polysaccharides. (C) 2002 Elsevier Science B.V. All rights reserved.