Christopher E. Marjo

Facile synthesis, stabilization, and anti-bacterial performance of discrete Ag nanoparticles using Medicago sativa seed exudates

The biogenic synthesis of metal nanomaterials offers an environmentally benign alternative to the traditional chemical synthesis routes. Colloidal silver (Ag) nanoparticles were synthesized by reacting aqueous AgNO(3) with Medicago sativa seed exudates under non-photomediated conditions. Upon contact, rapid reduction of Ag(+) ions was observed in <1 min with Ag nanoparticle formation reaching 90% completion in <50 min. Effect of Ag concentration, quantity of exudate and pH on the particle size and shape were investigated. At [Ag(+)]=0.01 M and 30°C, largely spherical nanoparticles with diameters in the range of 5-51 nm were generated, while flower-like particle clusters (mean size=104 nm) were observed on treatment at higher Ag concentrations. Pre-dilution of the exudate induced the formation of single-crystalline Ag nanoplates, forming hexagonal particles and nanotriangles with edge lengths of 86-108 nm, while pH adjustment to 11 resulted in monodisperse Ag nanoparticles with an average size of 12 nm. Repeated centrifugation and redispersion enhanced the percentage of nanoplates from 10% to 75% in solution. The kinetics of nanoparticle formation were monitored using ultraviolet-visible spectroscopy and the Ag products were characterized using transmission electron microscopy, selected-area electron diffraction, scanning electron microscopy, X-ray powder diffraction, and atomic force microscopy. X-ray photoelectron spectroscopy was used to investigate the elements and chemical environment in the top layers of the as-synthesized Ag nanoparticles, while the metabolites in the exudate were analyzed using gas chromatography-mass spectroscopy. To our knowledge, this is the first account of M. sativa seed exudate assisted synthesis and stabilization of biogenic Ag nanoparticles; the nanoplates are notably smaller and better faceted compared with those synthesized by vascular plant extracts previously reported. Stabilized films of exudate synthesized Ag nanoparticles were effective anti-bacterial agents.

Shifting paradigms: development of high-efficiency biochar fertilizers based on nano-structures and soluble components

Many biochars have a complex carbon lattice structure with aromatic and aliphatic domains, acidic and basic groups, vacancies, metallic and non-metallic elements, and free radicals. Biochars also have separate mineral oxide, silicate and salt phases, and small and large organic molecules. In the rhizosphere, such constituents can be involved in chemical and biological processes along a soil–microbe–plant continuum, including nutrient cycling, metal chelation and stabilization, redox reactions, and free radical scavenging. It is hypothesized that the greater the amount of these nanoparticles and dissolved components, the greater will be plant and microbial responses. We provide suggestions for developing low-dose, high-efficiency biochar–nanoparticle composites, as well as initial field trial results and detailed characterization of such a biochar–fertilizer composite, to highlight the potential of such biochars.

Synthesis of a new lattice inclusion host belonging to the tetrahalo aryl family

Abstract The tetrabromo diquinoline derivative 3 has been synthesised and its dichloromethane compound investigated by X-ray crystallography. This racemic host acts in an unusual manner by assembling into achiral molecular staircases and including the guests in parallel channels between these. Compound 3 belongs to a newly identified family of lattice inclusion hosts whose structural characteristics are described here for the first time.

Metal and complementary molecular bioimaging in Alzheimer's disease

Alzheimers disease (AD) is the leading cause of dementia in the elderly, affecting over 27 million people worldwide. AD represents a complex neurological disorder which is best understood as the consequence of a number of interconnected genetic and lifestyle variables, which culminate in multiple changes to brain structure and function. These can be observed on a gross anatomical level in brain atrophy, microscopically in extracellular amyloid plaque and neurofibrillary tangle formation, and at a functional level as alterations of metabolic activity. At a molecular level, metal dyshomeostasis is frequently observed in AD due to anomalous binding of metals such as Iron (Fe), Copper (Cu), and Zinc (Zn), or impaired regulation of redox-active metals which can induce the formation of cytotoxic reactive oxygen species and neuronal damage. Metal chelators have been administered therapeutically in transgenic mice models for AD and in clinical human AD studies, with positive outcomes. As a result, neuroimaging of metals in a variety of intact brain cells and tissues is emerging as an important tool for increasing our understanding of the role of metal dysregulation in AD. Several imaging techniques have been used to study the cerebral metallo-architecture in biological specimens to obtain spatially resolved data on chemical elements present in a sample. Hyperspectral techniques, such as particle-induced X-ray emission (PIXE), energy dispersive X-ray spectroscopy (EDS), X-ray fluorescence microscopy (XFM), synchrotron X-ray fluorescence (SXRF), secondary ion mass spectrometry (SIMS), and laser ablation inductively coupled mass spectrometry (LA-ICPMS) can reveal relative intensities and even semi-quantitative concentrations of a large set of elements with differing spatial resolution and detection sensitivities. Other mass spectrometric and spectroscopy imaging techniques such as laser ablation electrospray ionization mass spectrometry (LA ESI-MS), MALDI imaging mass spectrometry (MALDI-IMS), and Fourier transform infrared spectroscopy (FTIR) can be used to correlate changes in elemental distribution with the underlying pathology in AD brain specimens. Taken together, these techniques provide new techniques to probe the pathobiology of AD and pave the way for identifying new therapeutic targets. The current review aims to discuss the advantages and challenges of using these emerging elemental and molecular imaging techniques, and highlight clinical achievements in AD research using bioimaging techniques.

Crystal Engineering Involving C−H···N Weak Hydrogen Bonds: A Diquinoxaline Lattice Inclusion Host with a Preference for Polychlorocarbon Guests

The di(1,8-naphthryridine) 7 and diquinoxaline 12 derivatives were synthesised as potential new lattice inclusion hosts where strong hydrogen bonding interactions would be absent. A number of potential supramolecular synthons (such as aryl face-face, aryl edge-face, halogen-halogen, C−H···N, nitrogen-halogen) were expected to be accessible, with competing combinations of these weak attractions providing the best (but probably different) type of host-guest structure in each case. While the former compound turned out to be unstable, the latter proved to be a versatile host which preferred to trap small polychloroalkane guests. The X-ray structures of 12·(chloroform)2, (12)2·(tetrahydrofuran), and (12)2·(1,1,2,2-tetrachloroethane) are reported and shown to have different lattice packing where the guests occupy layers, parallel tubes, and molecular boxes, respectively. The detailed interplay of the above synthons in forming these structures is described in crystal engineering terms. Most significantly, the C−H···N weak hydrogen bond plays a major role in all three inclusion structures. Both single linear and double cyclic interactions are involved in molecular edge-edge assembly of the host 12. Several new types of double cyclic interactions were discovered revealing that the C−H···N interaction is a key synthon for crystal engineering involving nitrogen heteroaromatic compounds.

Novel phenazine crystals enable direct electron transfer to methanogens in anaerobic digestion by redox potential modulation

With one billion tons of methane produced annually by microorganisms, biogas production can be appreciated both for its role in global organic matter turnover and as an energy source for humankind. The importance of electron transfer from electrically conductive surfaces or from bacteria to methanogenic Archaea has been implicated in widespread commercial anaerobic digestion processes, though a mechanism for reception of electrons from conductive surfaces or pili by methanogens has never been demonstrated. Here we describe a novel crystalline form of the synthetic phenazine neutral red that harvests electrons from reduced inorganic and organic microbial sources in anaerobic environments and makes them available to methanogenic Archaea. The novel crystalline form is so effective at harvesting reducing equivalents because it displays a potential for reduction 444 mV higher than the soluble form (E′ = 70 mV). Neutral red molecules solubilised in the reduced state by protonation at the point of methanogen cell contact with the crystal surface deliver electrons to methanogens at a negative midpoint potential (E′ = −375 mV). We demonstrate that soluble neutral red delivers reducing equivalents directly to the membrane bound HdrED heterodisulfide reductase of Methanosarcina, replenishing the CoM-SH and CoB-SH pool for methanogenesis and generating proton motive force. An order of magnitude increase in methane production is recorded in pure acetate fed Methanosarcina and coal and food waste fed mixed cultures in the laboratory. The phenomenon is also demonstrated at field scale in a sub-bituminous coal seam 80 m below ground level.

Evaporative cooling of speleothem drip water

This study describes the first use of concurrent high-precision temperature and drip rate monitoring to explore what controls the temperature of speleothem forming drip water. Two contrasting sites, one with fast transient and one with slow constant dripping, in a temperate semi-arid location (Wellington, NSW, Australia), exhibit drip water temperatures which deviate significantly from the cave air temperature. We confirm the hypothesis that evaporative cooling is the dominant, but so far unattributed, control causing significant disequilibrium between drip water and host rock/air temperatures. The amount of cooling is dependent on the drip rate, relative humidity and ventilation. Our results have implications for the interpretation of temperature-sensitive, speleothem climate proxies such as δ18O, cave microecology and the use of heat as a tracer in karst. Understanding the processes controlling the temperature of speleothem-forming cave drip waters is vital for assessing the reliability of such deposits as archives of climate change.

Microstructural and associated chemical changes during the composting of a high temperature biochar: Mechanisms for nitrate, phosphate and other nutrient retention and release

Recent studies have demonstrated the importance of the nutrient status of biochar and soils prior to its inclusion in particular agricultural systems. Pre-treatment of nutrient-reactive biochar, where nutrients are loaded into pores and onto surfaces, gives improved yield outcomes compared to untreated biochar. In this study we have used a wide selection of spectroscopic and microscopic techniques to investigate the mechanisms of nutrient retention in a high temperature wood biochar, which had negative effects on Chenopodium quinoa above ground biomass yield when applied to the system without prior nutrient loading, but positive effects when applied after composting. We have compared non-composted biochar (BC) with composted biochar (BCC) to elucidate the differences which may have led to these results. The results of our investigation provide evidence for a complex series of reactions during composting, where dissolved nutrients are first taken up into biochar pores along a concentration gradient and through capillary action, followed by surface sorption and retention processes which block biochar pores and result in deposition of a nutrient-rich organomineral (plaque) layer. The lack of such pretreatment in the BC samples would render it reactive towards nutrients in a soil-fertilizer system, making it a competitor for, rather than provider of, nutrients for plant growth.

Subcellular tracking reveals the location of dimethylsulfoniopropionate in microalgae and visualises its uptake by marine bacteria

Phytoplankton-bacteria interactions drive the surface ocean sulfur cycle and local climatic processes through the production and exchange of a key compound: dimethylsulfoniopropionate (DMSP). Despite their large-scale implications, these interactions remain unquantified at the cellular-scale. Here we use secondary-ion mass spectrometry to provide the first visualization of DMSP at sub-cellular levels, tracking the fate of a stable sulfur isotope (34S) from its incorporation by microalgae as inorganic sulfate to its biosynthesis and exudation as DMSP, and finally its uptake and degradation by bacteria. Our results identify for the first time the storage locations of DMSP in microalgae, with high enrichments present in vacuoles, cytoplasm and chloroplasts. In addition, we quantify DMSP incorporation at the single-cell level, with DMSP-degrading bacteria containing seven times more 34S than the control strain. This study provides an unprecedented methodology to label, retain, and image small diffusible molecules, which can be transposable to other symbiotic systems. DOI: http://dx.doi.org/10.7554/eLife.23008.001

Polymorphism and a metastable solvate of duloxetine hydrochloride.

Duloxetine hydrochloride (1) is an important antidepressant that acts as a serotonin and noradrenaline reuptake inhibitor that has only recently been characterized by single-crystal X-ray diffraction. This study describes an investigation into polymorphism of duloxetine hydrochloride, discusses the challenges of characterizing new structures, and reports a new metastable solvate (1(acetone)) where acetone is trapped in a duloxetine hydrochloride host lattice. In view of the importance of formulation processing and bioavailability characteristics of the crystalline forms of 1, a comprehensive structural study of 1(acetone) was carried out using single-crystal and powder X-ray diffraction, infrared and Raman spectroscopies, and solid-state NMR spectroscopy. The rapid desolvation from 1(acetone) to the stable unsolvated form was investigated, and the structures of free and solvated forms are discussed in terms of the noncovalent intermolecular interactions.