Aspects of the coordination chemistry of phosphorus(V) chloro-compounds

Acceptor properties of several phosphorus(v) chloro compounds have been studied by solution and solid state (^31)P n.m.r. techniques, using pyridine, 1,10-phenanthroline, 2,2'-dipyridyl and chloride ions as ligands. Six co-ordinate adduct formation has been detected in most systems. As reported previously(^1), phosphorus pentachloride forms a molecular 1:1 adduct with pyridine. Bidentate pyridines produce PC1(_4)(L-L)(^+) PC1(_6)(^-) (L-L = 2,2'-dipyridyl or 1,10-phenanthroline). Non-stoichiometric adducts PC1(_4)phen(+)(PC1(_6)(^-))(_1-x)C1(^-)(_x) (x<l) disproportionate on dissolution to the 2:1 complex. PC1(_4)(^+) SbC1(_6)(^-) reacts with pyridine in nitrobenzene to give the equilibrium PC1(_4) (pyridine)(_2)(^+) SbC1(_6)(^-) = PC1(_5).pyridine + SbC1(_5).pyridine Solid PC1(_4)(pyridine)(_2)(^+) SbC1(_6)(^-) has been successfully isolated, however. Solution-stable adducts PC1(_4)(L-L)(^+) SbC1(_6)(^-) are formed with bidentate pyridines. Phenyltetrachlorophosphorane PhPC1(_4), catechyl phosphorus trichloride (C(_6)H(_4)0(_2))PC1(_3) and bis-catechyl phosphorus monochloride (C(_6)H(_4)0(_2))(_2) PC1 yield chloride ion adducts which are partially dissociated in solution. Each has been isolated as a solid. These phosphoranes also form molecular 1:1 adducts with pyridine, of which only PhPC1(_4) pyridine dissociates in solution. In the presence of excess pyridine, (C(_6)H(_4)0(_2))PCl(_2) (pyridine)(_2)(^+)C1(^-) and (C(_6)H(_4)0(_2))(_2)P (pyridine)(_2)(^+)C1(^-) equilibrate with the 1:1 adducts. The acceptors slowly produce cationic adducts with bidentate pyridines viz. PhPC1(_3)(L_L)(^+) C1(^-), (C(_6)H(_4)0(_2))PC1(_2)(L-L)(^+) (C(_6)H(_4)0(_2))PC1(_4)(^-) and (C(_6)H(_4)0(_2))(_2)P(dipyridyl)(^+) C1(^-). Similar cationic adducts Z(_4)P(L-L)(^+) MC1(_6)(^-) are rapidly formed by addition of bidentate ligands to PhPC1(_3)(^+) SbC1(_6)(^-), PhPC1(_3)(^+) PC1(_6_(^-), (C(_6)H(_4)0(_2))PC1(_2) (^+) SbC1(_6)(^-) and (C(_6)H(_4)0(_2))(_2)P(^+) SbC1(_6)(^-). The solid hexachloroantimonate adducts possess unexpected stability to water and moist air. Pyridine adducts Z(_4)P(pyridine)(_2)(^+)SbC1(_6)(^-) are formed with (C(_6)H(_4)0(_2))PC1(_2)(^+) SbC1(_6)(^-) and (C(_6)H(_4)0(_2))(_2)P(^+) SbC1(_6)(^-) but not with PhPC1(_3)(^+) SbC1(_6)(^-). Preliminary experiments with methyltetrachlorophosphorane (MePC1(_4)) show the formation of MePC1(_5)(^-) on addition of chloride ions. The addition of substituted pyridines to PCl(_5) and PCl(_4)(^+) SbC1(_6)(^-) has been investigated. 3- and 4-substituted non- methylated pyridines yield complexes, but 2-substituted pyridines show a much lower tendency to co-ordinate. Methyl pyridines are attacked by the phosphorus species in solution. Reactions of the type R(_3)P + PC1(_5) → R(_3)PC1(-2) + PC1(_3) R(_3)PC1(_2) + PC1(_5) → R(_3)PC1(^+) PC1(_6)(^-) have also been studied. By variation of the reaction stoichiometry, either R(_3)PC1(_2) or R3PC1(^+) PC1(_6)(^-) may be prepared. With PhPC1(_2), however, only PhPC1(_3)(+)PC1(_6)(^-) has been isolated

On some non-conformal fractals

This paper presents a simple method of calculating the Hausdorff dimension for a class of non-conformal fractals

The effects of an experimental programme to support students’ autonomy on the overt behaviours of physical education teachers

Although the benefits of autonomy supportive behaviours are now well established in the literature, very few studies have attempted to train teachers to offer a greater autonomy support to their students. In fact, none of these studies has been carried out in physical education (PE). The purpose of this study is to test the effects of an autonomy-supportive training on overt behaviours of teaching among PE teachers. The experimental group included two PE teachers who were first educated on the benefits of an autonomy supportive style and then followed an individualised guidance programme during the 8 lessons of a teaching cycle. Their behaviours were observed and rated along 3 categories (i.e., autonomy supportive, neutral and controlling) and were subsequently compared to those of three teachers who formed the control condition. The results showed that teachers in the experimental group used more autonomy supportive and neutral behaviours than those in the control group, but no difference emerged in relation to controlling behaviours. We discuss the implications for schools of our findings

The Impacts of a Subglacial Discharge Plume on Calving, Submarine Melting, and Mélange Mass Loss at Helheim Glacier, South East Greenland

Almost half of the Greenland ice sheet’s mass loss occurs through iceberg calving at marine terminating glaciers. The presence of buoyant subglacial discharge plumes at these marine termini are thought to increase mass loss both through submarine melting and by undercutting that consequently increases calving rates. Plume models are used to predict submarine melting and undercutting. However, there are few observations that allow these relationships to be tested. Here we use airborne lidar from the terminus of Helheim Glacier, SE Greenland to measure the bulge induced at the surface by the upwelling plume. We use these measurements to estimate plume discharge rates using a high‐resolution, three‐dimensional plume model. Multi‐year observations of the plume are compared to a record of calving from camera and icequake data. We find no evidence to suggest that the presence of a plume, determined by its visibility at the surface, increases the frequency of major calving events and also show that mass loss at the terminus driven directly by plume discharge is significantly less than mass loss from major calving events. The results suggest that the contribution of direct plume‐driven mass loss at deep marine‐terminating glaciers may be less than at shallower termini

Expression of Insulinlike Growth Factor (IGF) and IGF-Binding Protein Genes in Human Lung Tumor Cell Lines

Background: The presence of multiple, low-molecular-weight, insulinlike growth factor (IGF)-binding proteins in lung tumor cell-conditioned medium and lung cancer patient serum has been recently reported. Purpose: To begin to elucidate the genetic basis for these observations, the present study examines the expression by lung tumor cell lines of three IGF-binding protein genes, namely, IGFBP-1, IGFBP-2, and IGFBP-3. Since IGF-binding proteins are thought to modulate the biologic action of the IGFs, the relationship between the expression of IGF-binding protein genes and the genes encoding IGF-I and IGF-II also has been investigated. Methods: Gene expression was studied in four small-cell lung cancer (SCLC) and three non—small-cell lung cancer (NSCLC) cell lines using Northern blot analysis and reverse transcriptase polymerase chain reaction (RT-PCR) for IGFBP-1. Results: IGFBP-1 gene expression was detected by Northern blot analysis in one NSCLC cell line only. However, RT-PCR revealed that the IGFBP-1 gene was expressed in all four SCLC cell lines and in two of the three NSCLC lines. Northern blot analysis of IGFBP-2 gene expression demonstrated that all lung tumor cell lines expressed this gene. A low level of IGFBP-3 gene expression was detected in one SCLC cell line and in all three NSCLC cell lines. All lung tumor cell lines expressed the IGF-II gene as determined by Northern blot analysis. In marked contrast, none of the lines showed evidence of IGF-I gene expression using this method. However, RT-PCR revealed a low level of IGF-I gene expression in one SCLC and one NSCLC cell line only. Conclusions: These observations indicate 1) that IGF-binding proteins secreted by lung tumors are encoded by at least three different genes; 2) that there may be a close association between IGF-II and IGFBP-2 gene expression, such that, where there is production of IGF-II, IGFBP-2 is the principal BP; and 3) that the IGF-II gene is more widely expressed than the IGF-I gene in human lung tumor cell lines. [J Natl Cancer Institute 84: 628-634, 1992

Variable prey development time suppresses predator-prey cycles and enhances stability

© 2016 John Wiley & Sons Ltd/CNRS. Although theoretical models have demonstrated that predator-prey population dynamics can depend critically on age (stage) structure and the duration and variability in development times of different life stages, experimental support for this theory is non-existent. We conducted an experiment with a host-parasitoid system to test the prediction that increased variability in the development time of the vulnerable host stage can promote interaction stability. Host-parasitoid microcosms were subjected to two treatments: Normal and High variance in the duration of the vulnerable host stage. In control and Normal-variance microcosms, hosts and parasitoids exhibited distinct population cycles. In contrast, insect abundances were 18-24% less variable in High- than Normal-variance microcosms. More significantly, periodicity in host-parasitoid population dynamics disappeared in the High-variance microcosms. Simulation models confirmed that stability in High-variance microcosms was sufficient to prevent extinction. We conclude that developmental variability is critical to predator-prey population dynamics and could be exploited in pest-management programs