Preparative high performance size exclusion chromatography (HPSEC) was used to size-fractionate a humic acid (HA) solution with 0.05 M ionic strength before and after having made the humic solution 0.5 x 10(-3) M in acetic acid (AcOH). Size-fractions were characterized by pyrolysis-gas-chromatography/mass spectrometry (Pyr-GC-MS) and 1H NMR spectroscopy. Pyr-GC-MS showed that the AcOH treatment altered the distribution of humic molecular components in the size-fractions. The unsaturated alkyl chains were moved from size-fractions of larger molecular-size into those of lower molecular-sizes. Most of the aromatic moieties, which were found in larger molecular-size fractions for the untreated HA, were spread into fractions of lower molecular size after AcOH addition to HA. Carbohydrates, which were undetectable in anyfraction of the untreated HA, appeared instead in the pyrogram of the lowest molecular-size and most hydrophilic fraction after treatment with AcOH. Our results suggested that AcOH disrupted the weakly bound association of humic supramolecularstructures and HPSEC elution separated size-fractions of different composition without losing humic matter by adsorption on the HPSEC column. The fractions with the largest apparent molecular size were the richest in alkyl chains, thereby suggesting that humic molecules were stabilized into supramolecular associations by multiple weak interactions among apolar groups such as alkyl chains and aromatic moieties. 1H NMR spectra of size-fractions were greatly simplified and more resolved after AcOH treatment. This was attributed to a less complex molecular association in the size separates which provided a larger solubility in the NMR solvent and more favorable relaxation times. Combination of the procedure used here for size-fractionation with NMR and Pyr-GC-MS methods appears to be promising to advance knowledge on the molecular composition of humic substances.

The proton NMR characterization of bombesin has been carried out at 500 MHz in DMSO-d, using twodimensional homo-and 'H-'V hetero-correlated techniques. All resonances in the NMR spectra have been assigned and several coupling constants have been measured. The backbone JaCH+,,, coupling constants have constant values that vary between 7.8 and 8.2 Hz and indicate an unfolded structure in DMSO-4. Discrepancies with data recently obtained at 300 MHz [(1987[( ) Eur. J. B&hem. 168, 193-1991

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Triacylglycerols from cows and buffaloes' milk fat were investigated by 13C nuclear magnetic resonance (NMR) spectroscopy. By the addition of pure triacylglycerols standards, we identified the resonances of both milk fats, and the peaks were used for qualitative and quantitative analysis of acyl groups. Multivariate analysis treatment of triacylglycerols distribution and composition parameters enabled us to identify milk. This study shows that NMR can safely be used to quantitate milk fatty acid content, providing unique information for milk identification of different animal species.

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Petroformynes are unusual metabolites contained in the Mediterranean sponge Petrosia ficiformis. The structure and absolute stereochemistry of the most abundant of these compounds, which display long unbranched alkyl chains, have only recently been rigorously proven. The structures of twelve minor compounds are now reported, providing a better understanding of the chemistry of P. ficiformis. In addition, complete spectroscopic characterization of eleven partial structures (a^k) frequently contained in P. ficiformis metabolites is provided as an aid to future structure elucidation among compounds of this type.Polyacetylenes represent a unique class of natural products that possess a variety of biological activities ranging from antimicrobial to cytotoxic and antitumor (1,2). The Mediterranean sponge Petrosia ficiformis Poiret (family Petrosiidae, order Petrosida/ Haplosclerida) contains unusual polyacetylenes (3-7), the petroformynes, which are characterized by long unbranched alkyl chains, and which also show interesting bioactivity (3). Recently, we have reinvestigated the Petrosia polyacetylenes in order to establish their absolute stereochemistry (8). Application of high-field nmr to Mosher's method determined the stereochemistry (S) at all chiral centers of petroformynes-1-5, and petroformynes A and B. In addition, the mol wts of petroformynes-1-9 (3), previously deduced from the gc retention time of the parent hydrocarbons, were definitively determined (8) by recording positive fabms spectra with a matrix of mnitrobenzyl alcohol (9). In the course of this study, a series of minor metabolites was also isolated. The present paper deals with isolation and structural elucidation of the novel molecules 5-16, all closely related to the more abundant petroformynes-1-4 [1-4} but exhibiting either different oxidative patterns or isomerization of double bonds. The complete characterization, mainly by nmr spectroscopy, of a series of partial fragments 3 (CK2)16 'On leave at ICMIB from the Nanj ing Institute of Materia Medica, 210009 Nanj ing, People's Republic of China.