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A best-fitting procedure for the quantitative determination of the molar fractions of the stereosequences that define the microstructure of an ethylene−norbornene (E−N) copolymer from 13C NMR spectra has been set up. The quantitative determination of copolymer microstructure will allow one to clarify the E−N copolymerization mechanism. This method utilizes the observed peak areas of the 13C signals and takes into account the consistency between peak areas and the stoichiometry of the copolymer chain. Thus, a further extension of signal assignments is made possible by guessing assignments of unknown signals and by discarding inconsistent hypotheses. This procedure has been applied to the analysis of the 13C NMR spectra of a large number of E−N copolymers, prepared with catalyst precursors rac-Et(indenyl)2ZrCl2 (1), rac-Me2Si(2-Me-benz[e]indenyl)2ZrCl2 (2), Me2Si(Me4Cp)(N t Bu)TiCl2 (3), and Me2C(Flu)(Cp)ZrCl2 (4). An estimate of the molar fractions of the various stereosequences with a standard deviation on the order of 1−2% has been obtained. The comparison between controversial assignments existing in the literature for a number of ethylene signals has confirmed our previous assignments. New signals such as those of the C2/C3 carbons of EENNEE meso sequences (M) and of the external carbons C5 of MM and MR triads in ENNNE sequences have been assigned.

Bovine [3-LG ([3-1actoglobulin) has been studied under a variety of solution conditions by one-and two-dimensional NMR spectroscopy. At highly acidic pH (pH = 2) and low ionic strength the protein is present in a monomeric form, exhibiting a highly structured [~-sheet core and less ordered regions as evidenced by both CD data and the NOESY spectra. Marginal protection was observed for most of the amide protons as a result of high conformational mobility. This structural state of [3-LG may be considered as an attractive model for a partially folded structure occurring late in the folding process of the protein.

Bovine b-lactoglobulin~BLG! in vivo has been found complexed with fatty acids, especially palmitic and oleic acid. To elucidate the still unknown structure-function relationship in this protein, the interactions between 13 C enriched palmitic acid~PA! and BLG were investigated by means of one-, two-, and three-dimensional NMR spectroscopy in the pH range 8.4-2.1. The NMR spectra revealed that at neutral pH the ligand is bound within the central cavity of BLG, with the methyl end deeply buried within the protein. The analysis of 13 C spectra of the holo protein revealed the presence of conformational variability of bound PA carboxyl end in the pH range 8.4-5.9, related to the Tanford transition. The release of PA starts at pH lower than 6.0, and it is nearly complete at acidic pH. This finding is relevant in relation to the widely reported hypothesis that this protein can act as a transporter through the acidic gastric tract. Ligand binding and release is shown to be completely reversible over the entire pH range examined, differently from other fatty acid binding proteins whose behavior is analyzed throughout the paper. The mode of interaction of BLG is compatible with the proposed function of facilitating the digestion of milk fat during the neonatal period of calves.Keywords: bovine b-lactoglobulin; lipocalin binding sites; nuclear magnetic resonance; palmitic acid; T 1 measurements; Tanford transition Bovine b-lactoglobulin~BLG! is a 18 kDa protein belonging to the lipocalin superfamily, a big family of proteins with a variety of biological functions related to the binding and transport of metabolites. Although lipocalins show low sequence similarity, they share a common b-barrel topology, as the major structural motif. Structure determination of bovine BLG has been performed by X-ray and NMR at neutral and low pH, respectively~Brownlow et al