Screening molecular associations with lipid membranes using natural abundance 13C cross-polarization magic-angle spinning NMR and principal component analysis

We describe an NMR approach for detecting the interactions between phospholipid membranes and proteins, peptides, or small molecules. First, 1H-13C dipolar coupling profiles are obtained from hydrated lipid samples at natural isotope abundance using cross-polarization magic-angle spinning NMR methods. Principal component analysis of dipolar coupling profiles for synthetic lipid membranes in the presence of a range of biologically active additives reveals clusters that relate to different modes of interaction of the additives with the lipid bilayer. Finally, by representing profiles from multiple samples in the form of contour plots, it is possible to reveal statistically significant changes in dipolar couplings, which reflect perturbations in the lipid molecules at the membrane surface or within the hydrophobic interior.     

Caput mortuum: spectroscopic and structural studies of an ancient pigment

The use of a pigment variously described as caput mortuum, usta or ostrum to provide a deep purple colour in ancient wall-paintings was highly prized, despite the technical difficulties associated with its application. With the Raman spectroscopic characterization of pigments in ancient frescoes and wall-paintings becoming more widespread, it is timely to consider the identification of this material either as a generic haematite alone or in admixture with contemporary blue pigments. Here, Raman and infrared spectroscopic, X-ray diffractometric and scanning electron microscopic structural studies have been undertaken to characterize caput mortuum and to identify a specimen of Roman wall-painting dating from the 3rd century.     

Dimensional regularization and renormalization of QED

We give an -space definition of dimensional regularization suited to the tree expansion method of renormalization. We apply the dimensionally regularized tree expansion to QED, obtaining sharp bounds on the size of a renormalized graph. Subtractions are made with the Lagrangian counterterms of the tree expansion, not by minimal subtraction techniques, and so do not entail a knowledge of the meromorphic structure of a graph as a function of dimension. This renormalization procedure respects the Ward identities, and the counterterms required are gauge invariant.     

Chelates formed by a constrained bis(diphenylphosphino)xylene; the crystal structures of [FeCl2(anphos)] and [RhCl(CO)(anphos-monoxide)]

The indan derived diphosphine, cis-1,3-(diphenylphosphino)indan (anphos) is synthesised by the addition of Ph₂P(BH₃)Li to cis-1,3-dibromoindan followed by deprotection with diethylamine. Anphos readily forms the bicyclic chelates [RhCl(CO)(anphos)], [PtCl₂(anphos)], [PtCl(Me)(anphos)] and [FeCl₂(anphos)]. The crystal structures of [FeCl₂(anphos)] and the monoxide complex, [RhCl(CO)(anphosO)] have been determined. Reaction of the diphosphine with [Rh(acac)(CO)₂] under moderate hydroformylation conditions catalysed the formation of 1-heptanal and branched aldehydes from 1-hexene in a ratio of 1.5:1.     

Studies on the synthesis of bafilomycin A(1): stereochemical aspects of the fragment assembly aldol reaction for construction of the C(13)-C25) segment

Highly stereoselective syntheses of aldols 8a-c corresponding to the C(13)-C(25) segment of bafilomycin A(1) were developed by routes involving fragment assembly aldol reactions of chiral aldehyde 6a and the chiral methyl ketones 7. A remote chelation effect plays a critical role in determining the stereoselectivity of the key aldol coupling of 6a and the lithium enolate of 7b. The protecting group for C(23)-OH of the chiral aldehyde fragment also influences the selectivity of the lithium enolate aldol reaction. In contrast, the aldol reaction of 6a and the chlorotitanium enolates of 7a,c were much less sensitive to the nature of the C(15)-hydroxyl protecting group. Studies of the reactions of chiral aldehydes with Takai's (gamma-methoxyallyl)chromium reagent 40 are also described. The stereoselectivity of these reactions is also highly dependent on the protecting groups and stereochemistry of the chiral aldehyde substrates.     

Synthesis of novel alpha-substituted and alpha,alpha-disubstituted amino acids by rearrangement of ammonium ylides generated from metal carbenoids

[reaction: see text] A new and general four-step synthesis of protected alpha-substituted and alpha,alpha-disubstituted amino acids has been developed. The key step involves intramolecular ammonium ylide generation from a copper carbenoid with concomitant [2,3] rearrangement. The aromatic template serves as a tether, protecting group, and activating group for peptide coupling. The ylide rearrangement products can be converted into protected cyclic amino acids by ring-closing metathesis.