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The hydrogen bond enthalpies of urea and methyl-substituted ureas with water and DMF have been determined by the pure-base calorimetric method. Transfer enthalpies between water and DMF have been calculated for dilute solutions of the ureas according to a previously developed model. The first solvation sphere of urea in water consists of five water molecules. Solvation spheres are given for other methyl-substituted ureas in water and DMF.

Methylation–fragmentation and periodate oxidation studies show that the mannan of Trichosporonaculeatumis branched with 2-Oand 6-O-monosubstituted units and 2,6-di-O-substituted D-mannopyranosyl units. It contains up to five consecutive α-D-(1 → 2)-linkages. The proton magnetic resonance spectrum of the mannan (recorded in D2O at 70° using a VananHA-100 spectrometer) indicates structural differences from other yeast mannans. It contains four distinct H-1 signals, but more than four H-1 environments are present since addition of sodium tetraborate shifts two signals downfleld so that six signals are observed (Fig. 1). Two of the four signals in the mannan spectrum at τ 4.40, and τ 4.20 can be assigned to chemical structures. The former signal arises from nonreducing end units attached to the 2-positions of adjacent mannopyranose units and from 2,6-di-O-substituted units and the latter from 2-O-substituted mannopyranose units. These assignments are based on the above chemical evidence, comparison with H-1 chemical shifts of known compounds, and the magnitudes of the H-1 shifts on borate addition. Downfleld shifts of H-1 proton signals on borate addition to known mannopyranosides vary from a maximum with compounds that can form 2,3-borate complexes to virtually none with 2-O-substituted derivatives. The magnitude of the downfleld shifts observed with α-D-linked mannopyranose derivatives is greater than that of their β-linked counterparts.

A survey of the alkali soluble polysaccharides of yeast cells shows that galactomannans are formed by certain species of the genera Trichosporon, Schizosaccharomyces, and Nadsonia. Different species of Trichosporonform galactomannans, pentosylmannans, and a mannan. The galactomannans are distinguishable from those of Schizosaccharomycesby the H-1 region of their proton magnetic resonance spectra (recorded at 70° in D2O using an HA-100 Varian spectrometer), but the spectra of Trichosporonhellenicumand Nadsoniafulvescensgalactomannans are virtually indistinguishable.The proton magnetic resonance spectrum of the Trichosporonfermentansgalactomannan contains fewer signals than those of other Trichosporongalactomannans. The polymer consists predominantly of a main-chain containing a high proportion of (1 → 6)-mannopyranosyl units substituted in their 2-positions by O-α-D-galactopyranosyl-(1 → 2)-O-α-D-mannopyranosyl side-chains (1).

Evidence for a ‘block-type’ structure involving α-(l→3)- and -(1→6)-D-mannopyranosyl units from the mannan in Candidaspecies PRL 1S20 is presented.