Plant delta(15)N associated with arbuscular mycorrhization, drought and nitrogen deficiency

It has long been evident that plant (15)N chiefly reflects the processes which fractionate (15)N/(14)N rather than the (15)N of plant N source(s). It has emerged recently that one of the most important fractionating processes contributing to the whole plant (15)N is the presence/absence, type or species of mycorrhiza, especially when interacting with nutrient deficiency. Ecto- and ericoid mycorrhizas are frequently associated with (15)N-depleted foliar (15)N, commonly as low as -12 per thousand. As shown by the present study, plants having no mycorrhiza, or those infected with various species of arbuscular mycorrhiza (AM)-forming fungi, interact with varying concentrations of soil nitrogen [N] and moisture to enrich plant (15)N by as much as 3.5 per thousand. Hence the lack of a mycorrhiza, or variation in the species of AM-forming fungal associations, can account for about 25% of the usually reported variations of foliar (15)N found in field situations and do so by (15)N enrichment rather than depletion. Copyright 1999 John Wiley & Sons, Ltd.     

Asymmetric catalysis using self-assembled chiral bidentate P,P-ligands

A strategy is described for modular catalyst development based upon metal-directed self-assembly of bifunctional subunits around a structural metal to form a heteroleptic complex in which a second set of ligating groups are now suitably disposed to bind a second metal to form a catalytic site. A library of chiral diphosphites was prepared via metal-directed self-assembly and used in a simple asymmetric allylic amination, giving enantiomeric excesses as high as 97%.     

More Randomness of Environment Does Not Always Slow Down a Random Walk

We consider a random walk on in a stationary and ergodic random environment, whose states are called types of the vertices of . We find conditions for which the speed of the random walk is positive. In the case of a Markov chain environment with finitely many states, we give an explicit formula for the speed and for the asymptotic proportion of time spent at vertices of a certain type. Using these results, we compare the speed of random walks on in environments of varying randomness.     

Novel motifs for magnetic exchange interactions as exemplified in one dimensional magnets based on the FeCl3-α-di-imine system: Nuclear gamma resonance evidence of slow paramagnetic relaxation and 3D-ordering

The extremes of single ion slow paramagnetic relaxation and cooperative 3D-antiferromagnetic order are exemplified in a series of structurally characterized complexes based on the anhydrous FeCl₃-α-di-imine system. “Soft” Cl−Cl contacts, C−C (π-π) and hydrogen bonding interactions are found to lead to surprisingly strong magnetic exchange among five and six coordinate high-spin iron III monomers. The latter form the building blocks of novel “double chain” polymer magnets held together via the preceding “weak” interactions.