Richard I. Willing

Oxindoles from Phalaris coerulescens

A phytochemical examination of various accessions of Phalaris coerulescens for the presence of toxic phenylethylamines, indoloamines and tetrahydro-β-carbolines revealed the presence of oxindoles previously not reported to occur in Phalaris species. One of the oxindoles, the structure of which was elucidated by spectroscopic methods, has not hitherto been reported to occur naturally and has been given the trivial name coerulescine.

Tacticity of Poly(Methyl Methacrylate). Evidence for a Penpenultimate Group Effect in Free-Radical Polymerization

The tacticity of poly(methyl methacrylate ) prepared by free-radical polymerization has been determined by analysing the carbonyl region of the 13C n.m.r . spectrum. This analysis demonstrates that the addition of poly(methyl methacrylyl ) radical to methyl methacrylate in benzene at 60°C is subject to a significant penpenultimate unit effect. The probability of forming a meso dyad is some 20% less if the preceding dyad in the chain is also meso . The polymerization (60°C, benzene) is described by the following parameters P(m) = 0.202, P(m|m) = 0.159, P(r | m) = 0.212.

(−)-Phalarine, a furanobisindole alkaloid from Phalariscoerulescens

Abstract Chemical examination of Phalaris coerulescens revealed a new alkaloid, phalarine.Extensive mass spectrometric and NMR spectroscopic examination of phalarine and itsmonoacetyl and monomethyl derivatives indicated a novel furano bis indole structure.

13C NMR studies on fluorescent probes: 13C chemical shifts and longitudinal relaxation times of n-hydroxy-fatty (n=2,6,9,12) acids and n-(9-anthroyloxy)-stearic (n=6,12) acids

Abstract 13C NMR has been used to confirm the structure of two fluorescent probes, n-(9-anthroyloxy)-stearic acids (n=6,12), and the series of n-hydroxy-fatty acids (n=2,6,9,12) from which the set of fluorescent fatty acids may be synthesised. 13C longitudinal relaxation times and correlation times of the individual carbon atoms in 12-hydroxy- and 6- and 12-(9-anthroyloxy)-stearic acids show differences in motional properties between these derivatives and the parent stearic acid in chloroform(d) solution. The correlation times of the substituted carbons in 6-, 9-, and 12-hydroxy-stearic acids are longer than the corresponding carbons in stearic acid. The change in correlation times at the substituted carbons reflects the increase in motion along the acyl chain. Attachment of the bulky anthracene ring causes greater restriction of motion at the substituted carbon atom but the gradient of motion along the chain is preserved. These results are discussed in terms of the types of motion which lead to fluorescence depolarization when the fluorescent fatty acids are used as fluidity probes in biomembranes.

13C Nuclear magnetic resonance studies of the composition and fluidity of several chloroplast monogalactosyldiacylglycerols

The motional properties of four monogalactosyldiacylglycerols isolated from photosynthetic membranes, and containing different fatty acid chain lengths and degrees of unsaturation, have been determined using 13C nuclear magnetic resonance. These properties have been compared with those of a lipid containing only saturated fatty acids. The 13C longitudinal relaxation times (T1) of the carbon atoms of the acyl chains in [2H4] methanol were measured as an index of the rates of motion of the lipid molecules and used to compare the relative fluidity of the acyl chains. The T1 values of the glyceryl and galactosyl carbon atoms in each monogalactosyldiacylglycerol are essentially constant, when allowance is made for concentration differences and the presence of two hydrogens on a methylene carbon versus one on a methine carbon. These results indicate similar rates of motion for the headgroup carbons in each lipid. However, for the acyl chains, the T1 values increase with the introduction of a double bond and increase further with additional unsaturation. This increase in the rate of motion only occurs at carbon atoms beyond the first double bond in an acyl chain. These results differ to those reported for monolayer experiments where changes in packing characteristics are predominantly dependent on the introduction of the first double bond and then vary little between species.

Monolayer and 13C nuclear magnetic resonance studies on the interaction between melittin and chloroplast lipids

Abstract The interaction of the polypeptide melittin with chloroplast membrane lipids has been studied by monolayer and 13 C-NMR techniques. Under conditions favouring the existence of a melittin monomer, the interaction of the polypeptide with monolayers of chloroplast lipids is largely confined to negatively charged lipids. Conditions favouring the formation of the melittin tetramer result in a marked interaction of the polypeptide with monolayers of uncharged lipids. 13 C-NMR measurements of the rate of motion of fatty acyl carbon atoms in multibilayers of chloroplast membrane lipids demonstrate that melittin penetrates deeply into the bilayer irrespective of the proportion of negatively charged lipids. It is concluded that interaction of melittin which chloroplast membrane lipids is the primary factor in its capacity to inhibit membrane-associated reactions in chloroplasts.

Pulse sequence for the generation of a13C subspectrum of both aromatic and aliphatic quaternary carbons

A simple heteronuclear spin-echo pulse sequence is described which provides an accurate 13C subspectrum of just aromatic and aliphatic quaternary carbons, especially when the method is applied in conjunction with the recent distortionless enhancement by polarisation transfer (DEPT) sequence.

Cyanoisopropyl radical induced cyclization and cyclopolymerization of N-methyl-N-(2-alkylallyl)amines and N-methyl-NN-bis-(2-alkylallyl)amines. A 13C nuclear magnetic resonance study

The structures of the cyclic products from the cyanoisopropyl radical induced cyclization and cyclo-polymerization of N-methyl-N-allyl-N-(2-alkylallyl)amines and N-methyl-NN-bis-(2-alkylallyl)amines are shown by 13C n.m.r. spectroscopy to be pyrrolidines and piperidines, the proportion of each depending upon the bulk of the 2-alkyl substituent.

Preparation and comparison of model bilayer systems from chloroplasts thylakoid membrane lipids for 13C-NMR studies

Model bilayer systems from individual purified chloroplast thylakoid membrane lipids, from reconstituted mixtures of these purified lipids, and from leaf total polar lipid extracts have been prepared in water, and the longitudinal relaxation times (T1s) of the individual carbon atoms of the fatty acyl chains measured by 13C-NMR spectroscopy. The T1s increase with increasing distance of the carbon atoms from the polar headgroups in all cases, and as the results from each of the preparations are similar, all can be used as models of chloroplast membrane bilayers. Relaxation time measurements on intact chloroplast thylakoid membranes indicate the presence of chlorophyll resonances in the 13C-NMR spectrum of the membrane.

A two-pulse sequence for the analysis of unresolved multiline resonances in 13C Fourier transform NMR spectra

Abstract A 13C Fourier transform NMR two-pulse sequence, (α−τ−δ−5 × T1)n, is used to induce phase and intensity changes in the spectra of multiline, tacticity-induced, resonance signals of polymers. By varying τ through times less than the spin-spin relaxation time ( T 2 ∗ ) a series of spectra can be obtained which vary greatly in peak shape. The steady-state response of spins subjected to this pulse sequence has been determined and the equations have been adapted to a Fortran program to produce theoretical spectra. Good agreement has been obtained between series of measured and theoretical spectra for the carbonyl carbon resonances of polymethylmethacrylate and for the fully substituted carbon of polystyrene.