H NMR chemical shifts are presented for virtually all the protons in 166 steroids. These comprise mainly the hormones testosterone, androst-4-ene-3,17-dione, progesterone, and a wide range of their hydroxylated derivatives, some corticosteroids including aldosterone and a series of its derivatives, together with miscellaneous steroids comprising a variety of androstane and pregnane derivatives, bile acids, and sterols, to provide the first extensive collection of data for use in correlating 'H chemical shifts with structure.Most of the spectra were assigned with the aid of two-dimensional 'H homonuclear correlated spectroscopy (COSY), or in a few cases by use of a,-decoupled COSY (COSYDEC) spectroscopy. Limited use was made of other techniques, especially selective nuclear Overhauser effect difference spectroscopy (NOEDS), to complete the more difficult assignments. Procedures for the rapid analysis of high-field 'H N M R spectra of steroids are suggested: they include the application of templates for the recognition of signals due to particular protons from their characteristic profiles, which generally vary only slightly between different steroids unless simplified by adjacent substitution. Substituent increments for all protons are reasonably additive, except where drastic conformational change occurs or adjacent substituents interact strongly. The conformational dependences of hydroxy-substitution increments are analysed empirically, and some regularities are identified.

Multicomponent high-resolution 1 H and 13 C NMR analysis has been employed for the purpose of detecting and quantifying a wide range of fatty acids (as triacylglycerols or otherwise) in encapsulated marine cod liver oil supplements. The 1 H NMR technique provided quantitative data regarding the docosahexaenoic acid content of these products, which serves as a valuable index of fish oil quality, and a combination of both 1 H and 13 C spectroscopies permitted the analysis of many further components therein, including sn -1 monoacylglycerols, sn -1,2 and -1,3 diacylglycerol adducts, together with a range of minor components, such as trans -fatty acids, free glycerol and cholesterol, and added vitamins A and E. The identities of each of the above agents were confirmed by the application of two-dimensional 1 H-1 H spectroscopies. The NMR techniques employed also uniquely permitted determinations of the content of nonacylglycerol forms of highly unsaturated (or other) fatty acids in these products (i.e., ethyl esters), and therefore served as a means of distinguishing "natural" sources of cod liver oils from those subjected to chemical modification to and/ or supplementation with synthetic derivatives such as ethyl docosahexaenoate or eicosopentaenoate. The analytical significance and putative health effects of the results acquired are discussed.

We report the addition of M–H bonds (M = Al, Zn, Mg) to a Rh(iii) intermediate generated from the reductive elimination of triethylsilane from [Cp*Rh(H)2(SiEt3)2].

Prion diseases are associated with the misfolding of the prion protein (PrP C ) from a largely a-helical isoform to a b-sheet rich oligomer (PrP Sc ). Flexibility of the polypeptide could contribute to the ability of PrP C to undergo the conformational rearrangement during PrP C -PrP Sc interactions, which then leads to the misfolded isoform. We have therefore examined the molecular motions of mouse PrP C , residues 113-231, in solution, using 15 N NMR relaxation measurements. A truncated fragment has been used to eliminate the effect of the 90-residue unstructured tail of PrP C so the dynamics of the structured domain can be studied in isolation. 15 N longitudinal (T 1 ) and transverse relaxation (T 2 ) times as well as the proton-nitrogen nuclear Overhauser effects have been used to calculate the spectral density at three frequencies, 0, x N, and 0.87x H . Spectral densities at each residue indicate various time-scale motions of the main-chain. Even within the structured domain of PrP C , a diverse range of motions are observed. We find that removal of the tail increases T 2 relaxation times significantly indicating that the tail is responsible for shortening of T 2 times in full-length PrP C . The truncated fragment of PrP has facilitated the determination of meaningful order parameters (S 2 ) from the relaxation data and shows for the first time that all three helices in PrP C have similar rigidity. Slow conformational fluctuations of mouse PrP C are localized to a distinct region that involves residues 171 and 172. Interestingly, residues 170-175 have been identified as a segment within PrP that will form a steric zipper, believed to be the fundamental amyloid unit. The flexibility within these residues could facilitate the PrP C -PrP Sc recognition process during fibril elongation.

Prion diseases are associated with the misfolding of the PrP (prion protein) from a largely α-helical isoform to a β-sheet-rich oligomer. CD has shown that lowering the pH to 4 under mildly denaturing conditions causes recombinant PrP to convert from an α-helical protein into one that contains a high proportion of β-sheet-like conformation. In the present study, we characterize this soluble pH 4 folding intermediate using NMR.15 N-HSQC (heteronuclear single-quantum correlation) studies with mPrP (mouse PrP)-(23-231) show that a total of 150 dispersed amide signals are resolved in the native form, whereas only 65 amide signals with little chemical shift dispersion are observable in the pH 4 form. Three-dimensional 15 N-HSQC-TOCSY and NOESY spectra indicate that the observable residues are all assigned to amino acids in the N-terminus: residues 23-118.15 N transverse relaxation measurements indicate that these N-terminal residues are highly flexible with additional fast motions. These observations are confirmed via the use of truncated mPrP-(112-231), which shows only 16 15 N-HSQC amide peaks at pH 4. The loss of signals from the C-terminus can be attributed to line broadening due to an increase in the molecular size of the oligomer or exchange broadening in a molten-globule state.