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Keynote paper presented at the International Leucaena Conference, 1‒3 November 2018, Brisbane, Queensland, Australia.Leucaena (Leucaena leucocephala) is widely recognized in many countries as a commercially valuable plant, particularly when used as a nutritious fodder in subtropical and tropical regions. However, it is also considered an environmental weed in some countries due to its ability to form dense infestations in disturbed areas, where it is not proactively managed or grazed. These different perspectives have made leucaena a contentious species. Ideally, landholders and relevant jurisdictions in charge of invasive species need to work together to minimize its spread as a weed and manage existing infestations. To date, the response has been varied, ranging from no action through to some jurisdictions formally recognizing leucaena as an environmental weed within relevant legislation and applying requirements to minimize its impact. Between these extremes, there are initiatives such as an industry Code of Practice (i.e. The Leucaena Network in Australia), recommending that those growing leucaena adhere to certain principles and practices to minimize the risk of spread from their operations. The biology of weed leucaena (e.g. large seed production, relatively long-lived seed banks) and the situations in which it spreads (e.g. roadsides and riparian systems) pose management challenges to landholders and relevant jurisdictions. Adaptive management and experimental research are necessary to identify effective control strategies for a range of situations.

A structural health monitoring device has been developed capable of measuring the absolute distance between parallel surfaces using Fabry-Perot interferometry with micron resolution. This is achieved by fabricating turning mirrors on two opposite cores of a multi-core fibre.

We report on the novel utilisation of a circular multi-reflection (CMR) cell applied to materials ageing experiments. This enabled trace gas detection within a narrow interfacial region located between two sample materials and remotely interrogated with near-infrared sources combined with fibre-optic coupling. Tunable diode laser absorption spectroscopy was used to detect water vapour and carbon dioxide at wavelengths near 1,358 and 2,004 nm, respectively, with corresponding detection limits of 7 and 1,139 ppm m Hz−0.5. The minimum detectable absorption was estimated to be 2.82 × 10−3 over a 1-s average. In addition, broadband absorption spectroscopy was carried out for the detection of acetic acid, using a super-luminescent light emitting diode centred around 1,430 nm. The 69 cm measurement pathlength was limited by poor manufacturing tolerances of the spherical CMR mirrors and the consequent difficulty of collecting all the cell output light.

1. Weed eradication efforts often must be sustained for long periods owing to the existence of persistent seed banks, among other factors. Decision makers need to consider both the amount of investment required and the period over which investment must be maintained when determining whether to commit to (or continue) an eradication programme. However, a basis for estimating eradication programme duration based on simple data has been lacking. Here, we present a stochastic dynamic model that can provide such estimates. 2. The model is based upon the rates of progression of infestations from the active to the monitoring state (i.e. no plants detected for at least 12 months), rates of reversion of infestations from monitoring to the active state and the frequency distribution of time since last detection for all infestations. Isoquants that illustrate the combinations of progression and reversion parameters corresponding to eradication within different time frames are generated. 3. The model is applied to ongoing eradication programmes targeting branched broomrape Orobanche ramosa and chromolaena Chromolaena odorata. The minimum periods in which eradication could potentially be achieved were 22 and 23 years, respectively. On the basis of programme performance until 2008, however, eradication is predicted to take considerably longer for both species (on average, 62 and 248 years, respectively). Performance of the branched broomrape programme could be best improved through reducing rates of reversion to the active state; for chromolaena, boosting rates of progression to the monitoring state is more important. 4. Synthesis and applications. Our model for estimating weed eradication programme duration, which captures critical transitions between a limited number of states, is readily applicable to any weed.Aparticular strength of the method lies in its minimal data requirements. These comprise estimates of maximum seed persistence and infested area, plus consistent annual records of the detection (or otherwise) of the weed in each infestation. This work provides a framework for identifying where improvements in management are needed and a basis for testing the effectiveness of alternative tactics. If adopted, our approach should help improve decision making with regard to eradication as a management strategy.

A simulation model that combines biological, search and economic components is applied to the eradication of a Miconia calvescens infestation at El Arish in tropical Queensland, Australia. Information on the year M. calvescens was introduced to the site, the number of plants controlled and the timing of control, is used to show that currently there could be M. calvescens plants remaining undetected at the site, including some mature plants. Modelling results indicate that the eradication programme has had a significant impact on the population of M. calvescens, as shown by simulated results for uncontrolled and controlled populations. The model was also used to investigate the effect of changing search effort on the cost of and time to eradication. Control costs were found to be negligible over all levels of search effort tested. Importantly, results suggest eradication may be achieved within several decades, if resources are increased slightly from their current levels and if there is a long-term commitment to funding the eradication programme.

To eradicate a weed invasion, its extent must be delimited and each infestation must be extirpated. Measures for both of these criteria are utilized to assess the progress of current eradication programs targeting mikania vine and limnocharis in northern Australia. The known infested area for each species is less than 5 ha and has remained largely static for the last 3 or more years against a backdrop of refined and enhanced detection methods. This suggests that delimitation has been approached, if not achieved. Different methods of detection have their places, relative to the stage of the program and the spatial distribution of infestations. Although all known infestations of both species are effectively monitored and controlled, ongoing emergence from persistent seed banks limits progress towards the extirpation of infestations to a slow, but measurable, rate. Nomenclature: Glyphosate. N-(phosphonomethyl)glycine; fluroxypyr, [(4-amino-3,5-dichloro-6-fluoro-2-pyridinyl)oxy]acetic acid; limnochar...

International audience; A variety of amide-subsituted anthracene derivates have been synthesised and their anion complexation properties studied using 1H-NMR titration techniques. Additionally, bis-urea functionalised anthracene derivatives have been shown to serve as excellent receptors for oxo-anions and to function as sensors via fluorescence quenching in DMSO-d6/0.5% water and MeCN/DMSO (96.5:3.5 v/v).

Weed management is complicated by the presence of soil seed banks. The complexity of soil–seed interactions means that seed persistence in the field is often difficult to measure, let alone predict. Field trials, although accurate in their context, are time-consuming and expensive to conduct for individual species. Some ex situ techniques for estimating seed life expectancy have been proposed, but these fail to simulate the environmental complexity of the field. Also, it has been questioned whether techniques such as the controlled aging test (CAT) are useful indicators of field persistence. This study aimed to test the validity of the standard CAT (seed aging at 45 C and 60% relative humidity) in use at the Royal Botanic Gardens, Kew, U.K., for predicting field seed-persistence. Comparison of seed persistence and CAT data for 27 northwest European species suggested a significant positive correlation of 0.31. Subsequently, 13 species of emerging and common weeds of Queensland were assessed for their seed longevity using the CAT. The seed longevity data of these species in the CAT were linked with field seed-persistence data according to three broad seed-persistence categories: < 1 yr, 1 to 3 yr, and > 3 yr. We discuss the scope for using the CAT as a tool for rapid assignment of species to these categories. There is a need for further studies that compare predictions of seed persistence based on the CAT with seed persistence in the field for a larger range of species and environments.

A self-referenced optical fiber refractometer using a ball lens as a sensor head has been developed and characterized. A 350-μm ball lens created at the tip of a single mode fiber has been coated with a 40-nm optically thin layer of palladium that reacts with hydrogen to form a hydride, which has a lower reflectivity than pure palladium. Optical reflectance measurements from the tip of the ball lens were performed to determine the hydrogen response. The change in reflectivity is proportional to the hydrogen concentration in the range 0% to 1% hydrogen in air with a detection limit down to 10 ppm (1σ) in air. This technique offers a simple sensor head arrangement, with a larger sampling area (∼40 times) than a typical single-mode fiber core. A statistical image analysis of a palladium film, with cracks created by accelerated failure, confirms that the anticipated sensor area for a ball lens sensor head has a more predictable reflectivity than that of a bare fiber core.

Simple bis-urea compounds based on ortho-phenylenediamine function as excellent receptors for carboxylate anions in DMSO-d6–0.5% water solution. By varying the functional groups in these compounds, the binding affinity of carboxylate anions can be modulated. Solid-state studies illustrate the cleft-like arrangement of the DDDD hydrogen bond array in the carboxylate complexes of these compounds.

The electrochemistry of a novel anion receptor is presented. The receptor 1,3-diphenylcarboxamidoanthraquinone (AAR) in the absence of an appropriate anion behaves as an anthraquinone system in the presence of a strong hydrogen bond donor. In this case, the electrochemical evidence supports the suggestion that the hydrogen bonding with the anthraquinone occurs at least partially through intra- or intermolecular interactions. It is suggested that these interactions stabilise both the semiquinone and dianion species resulting from reduction of AAR. However, in the presence of a suitable competitive anion (specifically F−), the hydrogen-bond donor groups bind to the anion rather than the quinone oxygen atoms. This removes the hydrogen bonding interaction to the redox-active quinone centre and hence alters the electrochemistry significantly. In the presence of F−, two one-electron quasireversible electrochemical processes are observed. Keywords: Anion receptor, Hydrogen bonding, Fluoride, Switchable electrochemistry

The binding constants (log Kass ) of small synthetic receptor molecules based on indolocarbazole, carbazole, indole, urea and some others, as well as their combinations were measured for small carboxylate anions of different basicity, hydrophilicity and steric demands, that is, trimethylacetate, acetate, benzoate and lactate, in 0.5 % H2 O/[D6 ]DMSO by using the relative NMR-based measurement method. As a result, four separate binding affinity scales (ladders) including thirty-eight receptors were obtained with the scales anchored to indolocarbazole. The results indicate that the binding strength is largely, but not fully, determined by the strength of the primary hydrogen-bonding interaction. The latter in turn is largely determined by the basicity of the anion. The higher is the basicity of the anion the stronger in general is the binding, leading to the approximate order of increasing binding strength, lactatebenzoateacetate≤trimethylacetate, which holds with all investigated receptors. Nevertheless, there are a number of occasions when the binding order changes with changing of the carboxylate anion, sometimes quite substantially. Principal component analysis (PCA) reveals that this is primarily connected to preferential binding of trimethylacetate, supposedly caused by an additional hydrophobic/solvophobic interaction. These findings enable making better predictions, which receptor framework or cavity is best suited for carboxylate anions in receptor design.

An optical fibre refractometer using a ball lens as a sensor head has been developed and characterised. Light from a superluminescent diode is directed to an optical fibre sensor head and the intensity of the returned beam gives a measure of the refractive index of the medium at the ball lens fibre tip. A second beam is used to reference the intensity measurements. The system is capable of detecting changes in refractive index with a resolution of 0.003 RIU. The ball lenses have been coated with an 80nm thick layer of palladium and the potential use of this system as a micromirror hydrogen sensor is demonstrated. This technique offers a simple sensor head arrangement, with a large signal sampling area compared with that of a bare fibre.

The structure of 2C16H36N+·C8H4O4 2−·C34H30N8O4, comprises tapes of encapsulated hydrogen-bonded isophthalate anions which are arranged into parallel sheets interleaved with tetrabutylammonium layers; each of the two independent neutral molecules is disposed about a centre of inversion.

Highly potent but structurally simple transmembrane anion transporters are reported that function at receptor to lipid ratios as low as 1 : 1 000 000. The compounds, based on the simple ortho-phenylenediamine-based bisurea scaffold, have been studied for their ability to facilitate chloride/nitrate and chloride/bicarbonate antiport, and HCl symport processes using a combination of ion selective electrode and fluorescence techniques. In addition, the transmembrane transport of dicarboxylate anions (maleate and fumarate) by the compounds was examined. Molecular dynamics simulations showed that these compounds permeate the membrane more easily than other promising receptors corroborating the experimental efflux data. Moreover, cell based assays revealed that the majority of the compounds showed cytotoxicity in cancer cells, which may be linked to their ability to function as ion transporters.

International audience; Two new ortho-phenylenediamine based bis-urea compounds have been synthesised with pendant amide groups. The stability constants of the new compounds with a variety of anionic guests have been measured by 1H NMR titration techniques and compared to the parent bis-urea. The X-ray crystal structure of the acetate and benzoate complexes of a bis-amide functionalised system have been solved and reveal the receptor forming a dimer with two anions bound at the termini of the hydrogen bonded assembly.

The anion-binding properties of two similar hybrid amide/urea macrocycles containing either a 2,6-dicarboxamidophenyl or a 2,6-dicarboxamidopyridine group are compared. Significant differences in anion affinity and mode of interaction with anions are attributed to the presence of intramolecular hydrogen bonds in the pyridine system. In fact, remarkably, the phenyl macrocycle undergoes amide hydrolysis under neutral conditions in DMSO/water. The anion binding abilities of the receptors are compared to those of acyclic analogues of the macrocycles that show that the phenyl receptor behaves in a similar fashion to acyclic urea-containing receptors (i.e., showing little selectivity amongst oxo anions), whilst the pyridine-containing receptor shows a high affinity and selectivity for carboxylates.

A simple bis-urea containing anion receptor, synthesised from ortho-phenylenediamine, has been shown to have excellent selectivity for carboxylates in solution, with a crystal structure elucidation of the benzoate complex showing four hydrogen bonds between the receptor and anion in the solid state.

Steric interactions in 1,3-dicarboxamidoanthraquinones have been employed to ‘twist’ isophthalamide-like anion binding sites; the crystal structure of the fluoride complex of a bis-3,5-dichlorophenylamide derivative shows the receptor acting as a ‘hydrogen-bonding corner’ in a ‘2 + 2’ fluoride containing molecular box.

Neutral 1,3-di(1H-indol-7-yl)ureas are selective dihydrogen phosphate receptors in polar solvent mixtures (DMSO-d(6)-25% water).

N1,N3-Bis(2,4-diphenyl-1H-pyrrol-3-yl)benzene-1,3-dicarbamide forms a network containing clusters of water molecules when crystallized from wet methanol.

The reliability of the mode of carboxylate binding to ortho-phenylenediamine based bis-urea clefts is demonstrated in a variety of systems including a hydrogen bonded tape suggesting that this DDDD-AA supramolecular synthon may find application in crystal engineered systems in the future.