Ian D. Rae

Seed dispersal by ants: behaviour-releasing compounds in elaiosomes

SummaryIn a study of the biochemical basis of seed dispersal by ants, elaiosomes of Acacia myrtifolia and Tetratheca stenocarpa induced seed collection: intact diaspores and elaiosomes were taken rapidly by ants while most seeds remained on the forest floor. Extracts of elaiosomes (non-polar lipids, polar lipids, and aqueous fractions) were differentially collected by ants. Small pieces of pith impregnated with the polar lipid fraction from elaiosomes of either species elicited a removal rate by ants equivalent to that of intact elaiosomes and significantly higher than that of untreated pith. The non-polar lipid fraction, highest in concentration in elaiosomes of both species, elicited removal that did not differ from that of untreated pith. In T. stenocarpa, however, the aqueous fraction also induced removal equivalent to the polar lipid fraction. 1,2-Diglycerides with unsaturated groups are present in the active polar fractions of both species and unsaturated oleate is the major acid group of the glycerides in elaiosomes. Most oleate-containing compounds tested were taken more rapidly by ants than saturated compounds, and oleic acid, associated with corpse-carrying in ants, induced rapid removal. 1,2-Diolein, but not 1,3-diolein, was taken suggesting that the specific configuration of fatty acid moieties influences collection by ants. We hypothesize that a small suite of oleyl-containing compounds in elaiosomes elicit a stereotyped carrying response by a variety of ants. While the nutrient composition of elaiosomes may provide the underlying selective advantage for ants in seed dispersal, specific compounds may manipulate their behaviour and maximize seed dispersal.

Detection and measurement of fluoroacetate in plant extracts by 19FNMR

Abstract Examination of extracts from seeds and foliage of several species known to contain fluoroacetate, using13F NMR spectroscopy, has shown the presence of the characteristic FCH2-signal in most of them and enabled quantitative determination of their fluoroacetate content. No other fluorine-containing plant metabolites were detected; fluoroacetate was not detected in the extracts of several non-toxic species. The limit of detection is estimated to beca 4 μg/g.

Synthesis of a new protected lactam-bridged dipeptide

Abstract A method has been developed for the synthesis of a new protected γ-lactam-bridged dipeptide. This R,S lactam has been prepared in good yield and incorporated into a peptide which is analogous to hGH (7–13) using standard solid phase peptide synthesis methodolgy. The peptide showed insulin-potentiating activity of the same order as those containing an imide in place of the lactam.

ISOLATION OF OPIATE RECEPTOR LIGANDS IN COFFEE

1. We have reported previously that instant coffee contains ligands for opiate receptors with characteristics similar to those of opiate antagonists.

Nuclear overhauser effects and the conformation of gramicidin S

Summary Nuclear Overhauser effects have been observed between NH and C α H protons in gramicidin S in dimethyl sulfoxide-d 6 . By use of the correlation time (τ c ) and a published relationship between τ c and maximal nuclear Overhauser effect, the observed changes in intensity have been used to derive internuclear distances, which are compared with those predicted from a calculated low energy structure.

Oxazolidines: prodrugs for the delivery of β-aminoalcohols through human skin from aqueous solution

Ephedrine (I) is delivered through human skin, in vitro, significantly faster from aqueous solutions of 3,4-dimethyl-5-phenyl-oxazolidine (II) with pH values between 7.0 and 10.88 than from corresponding solutions of I. The difference in penetration rates was most marked at pH 7.0 where 917 μg and < 10 μg of I was delivered through 1.3 cm2 of skin in 24 h from 1% w/v solutions of II and I, respectively. No detectable amounts of I were delivered through 1.3 cm2 of skin in 24 h from 1% w/v solutions of I or II in propylene glycol and delivery of I was faster from 1% w/v solutions of I in liquid paraffin than from corresponding solutions of II. Compound II has a lower pKa value than compound I (ca. 5.5 vs 9.63) and a higher partition coefficient between water and liquid paraffin (5.6 vs 1.0). Although II rapidly hydrolyzed to I plus formaldehyde (t50% < 1 min at pH values between 6 and 8), the system rapidly came to an equilibrium which increasingly favoured compound II as the initial concentration of II or the pH value was increased. Hence, it can be concluded that compound II and possibly other oxazolidines are potentially useful prodrugs for promoting the delivery through skin of I and other β-aminoalcohols from aqueous solutions with pH values close to 7.

Chemical design of peripherally acting compounds.

1. Some guanidines, related in structure to mianserin and to 2‐methyl‐1,2,9,13b‐tetrahydro‐3H‐dibenz[c,f]irnadazo[l,5a]azepin‐3‐imine hydrobromide (WAL 801), have been synthesized and shown to be peripherally acting 5‐HT2 antagonists. Structurally related compounds but not bearing a charged ionic group have been shown to have central activity.

Something in the air: connections between global warming, ozone depletion, POPs and particulates

Environmental context. The release of chemical substances to the environment was long seen simply as a way to get rid of them from the immediate vicinity of their generation. Until recently there was little consideration that regional or global problems might result. Further, the various releases were studied by specialists who lacked the breadth of knowledge to understand that many of their specialties were linked and that chemical identity, toxicity, bio-accumulation, regional and global weather patterns and some arcane physical chemistry would need to be involved in a comprehensive analysis of the impact of chemicals on the environment.

Shielding effects of the D-Phe aromatic ring in the 1H NMR spectrum of gramicidin S

Abstract Analysis of the side-chain coupling constants for the D-Phe residue of gramicidin S shows that the rotamer predicted for the minimum-energy structure is the predominant one. The aromatic ring of D-Phe shields the Pro C δ hydrogens, and the calculated shielding closely matches that found in the 1 H NMR spectrum. As the temperature is raised, the rotamer population changes and the shielding is reduced accordingly. The shielding is absent in the saturated analogue of gramicidin S in which the aromatic rings were hydrogenated without changing the conformation of the rest of the molecule.

False Start for the PhD in Australia

When the PhD was introduced in England, consideration was also being given to its introduction in Australia. The University of Melbourne first discussed the idea in 1918, and again in 1924, but other Australian universities were opposed. Arguments ran along lines familiar in England — some foresaw the PhD competing with other doctoral degrees, and others saw difficulties in providing resources. Others wished to continue the system whereby Australian graduates went to Britain for research training. Faced with a unanimous verdict by its sister institutions, Melbourne withdrew its proposal, and the idea of the PhD went underground, not to surface again until 1944 when Melbourne again led the way, this time successfully, in its introduction.