Variability of soil chemistry following irrigation with recycled municipal effluent: a Great Western vineyard case study

In areas of Australia where viticultural operations have been limited by lack of an acceptable irrigation water source, considerable expansion has occurred through the use of recycled wastewater. Despite this rapid expansion, little is known of the potential impacts of the water’s chemical constituents on soil properties, or the long-term sustainability of the vineyards using the water. In order to establish the impacts of drip irrigated recycled wastewater on a vineyard in Great Western, Australia, a study comparing the soils from the vineyard inter-row and row area was undertaken. Chemical and physical properties of the soil with varying distances from the drip emitter were also investigated. During the irrigation season, significant differences between the inter-row and row area were found for several chemical parameters including pH(1:5soil/water) (P<0.001), electrical conductivity (EC1:5) (P<0.001), water-soluble sodium (WS Na+) (P<0.001), and water-soluble chloride (WS Cl-) (P<0.001). This paper will discuss differences observed between soil properties of the inter-row and vine row area, as well as the spatial distribution of solutes under the drip emitter.

The quest for single-enantiomer outcomes in free-radical chemistry

A significant challenge facing free-radical chemists is in the area of stereocontrol, specifically the ability to control the direction of reagent attack at a prochiral radical. While significant inroads have been made in the area of diastereoselective radical chemistry, less successful have been attempts to provide truly enantioselective processes. This article highlights recent efforts in the area of enantioselective free-radical reduction chemistry and describes how single-enantiomer outcomes are possible when simple enantiopure stannanes are used in conjunction with large, sterically-demanding Lewis acids. Selectivities in excess of 90% are now possible, with one example in excess of 99.5% ee provided.

Calcium chemistry of Blue Lake, Mt Gambier, Australia, and relevance to remarkable seasonal colour changes

Calcium speciation and other water quality variables in the Blue Lake, Mt Gambier, Australia, were monitored between August 1999 and August 2000 in order to test previously proposed mechanisms for the seasonal colour changes of this lake. The concentration of calcite was found to be highest in winter when the lake appears grey, and lowest in summer when the lake appears blue. A potential component of the colour change mechanism is therefore identified in which the lake is grey in winter because of non-selective scattering of light by calcite particles, and blue in summer because of the absence of absorbing or scattering impurities.

Single enatiomer free-radical chemistry - Lewis acid-mediated reductions of racemic halides using chiral non-racemic stannanes

Additions of one to two equivalents of Lewis acids that include magnesium salts to free-radical reduction reactions involving ester functionalized radicals and (1R,2S,5R)-menthyldiphenyltin hydride 4, bis((1R,2S,5R)-menthyl)phenyltin hydride 5, tris((1R,2S,5R)-menthyl)tin hydride 6, bis((1R,2S,5R)-menthyl)-[8-(N,N-dimethylamino)naphthyl]tin hydride 12, bis((1R,2S,5R)-menthyl)-[1-((S)-N,N-dimethylaminoethyl)phenyl]tin hydride 13 or 3α-dimethylstannyl-5α-cholestane 14 result in remarkable enantioselectivities. Examples include (S)-naproxen ethyl ester 16, produced in 74% yield and greater than 99% ee at −78°C from the bromide and 5 in the presence of MgBr₂, and ethyl (R)-N-trifluoroacetyl-_D-phenylglycinate 18, obtained in 78% yield and 99% ee under identical conditions. Kinetic and computational studies provide insight into the origins of these observations.

Synthesis and structure of an ether-bridged double ladder compound: potential in host - guest chemistry

The synthesis of the first example of an organotin double ladder (6) containing a functional group within the spacer is reported. In the solid state, compound 6 shows an interlaminar cavity whose size and shape suggest the possibility of host–guest chemistry. ¹¹⁹Sn-NMR and ESMS show that compound 6 undergoes extensive dissociation in solution. ESMS of compound 6 to which have been added Li⁺, Na⁺, Mg²⁺ or Cu²⁺ show only minimal interaction.

Synthesis and structure of 1,3,5-tris(diorganohydroxysilyl)benzenes. Novel building blocks in supramolecular silanol chemistry

The 1,3,5-tris(diorganohydroxysilyl)benzenes 1,3,5-(HOR₂Si)₃C₆H₃ (TMSB, R = Me; TPSB, R = Ph) have been prepared and fully characterized by X-ray crystallography. The crystal structure of TMSB features pairwise connected layers, in which the molecules are involved in interlayer hydrogen bonding. The supramolecular hydrogen bond motif may be described as a 12-membered ring that adopts a chair conformation. TPSB forms an equimolar inclusion complex with water, which is associated via hydrogen bonding and apparently fills a void in the crystal packing. In this case, the supramolecular hydrogen bond motif may be described as an eight-membered ring. Two of the water molecules are also associated, giving rise to a water dimer entrapped in the silanol matrix. Besides the hydrogen bonds, the crystal structure of the TPSB·H₂O complex reveals intra- and intermolecular C-H··· π stacking of most of the phenyl groups. Electrospray mass spectrometry shows that TPSB undergoes supramolecular complex formation with a variety of N-donors such as 4-(dimethylamino)pyridine, N,N,N',N'-tetramethylethylenediamine, imidazole, 2-(dimethylamino)pyridine, and 2,2'-dipyridylamine.

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The determination of urea with hypobromite: a theme for the discussion of numerous fundamental concepts in chemistry

Over the past century, numerous aspects of the reaction between urea and hypobromite have been exploited to quantify urea in clinical and industrial process samples. A review of these analytical approaches provides an interesting illustration of changes in a chemical system that indicate a reaction has occurred-the production of a gas, a color change, the release of heat, and the emission of light-and a variety of instruments that were developed to measure these changes and quantify a reacting species. In this paper we describe how we have used this material in a tutorial class for first-year undergraduate (freshman) students and a follow-up assignment, which we have included in the supporting material. In addition to the concepts exemplified by the above phenomena, we discuss the reaction pathway, which includes examples of ion and atom transfer. These are
often overlooked in favor of electron transfer in the teaching of redox chemistry.

Use of spreadsheet simulations in university chemistry education

Students who are strong in logical-mathematical intelligence have a natural advantage in learning and understanding chemistry, which is full of abstractions that are remote from the material world. Simulations provide more-inclusive learning activities for students who are weak in logical-mathematical intelligence.

A second advantage of using simulations is that they are not limited by (for example) the quantised energies, integral masses and discrete expectation values of real atoms and molecules. Numerical experiments can be used to investigate the effect of continuously varying atomic mass, bond distance or any other property, from one value to another.

Finally, students are more familiar with spreadsheets than more advanced mathematical packages such as MathCAD, MAPLE, Mathematica and other symbolic algebra software. Use of these advanced packages presents additional learning hurdles for students and should be used only for advanced classes. Furthermore, spreadsheets are capable of a level of sophistication that is greater than commonly expected. This can be achieved without the use of MACROs.

Examples from the author's teaching are used to discuss the advantages of spreadsheet simulations for learning chemistry.

Chemistry of carbon nanotubes

Judicious application of site-selective reactions to non-aligned and aligned carbon nanotubes has opened a rich field of carbon nanotube chemistry. In order to meet specific requirements demanded by particular applications (e.g. biocompatibility for nanotube biosensors and interfacial strength for blending with polymers), chemical modification of carbon nanotubes is essential. The tips of carbon nanotubes are more reactive than their sidewalls, allowing a variety of chemical reagents to be attached at the nanotube tips. Recently, some interesting reactions have also been devised for chemical modification of both the inner and outer nanotube walls, though the seamless arrangement of hexagon rings renders the sidewalls relatively unreactive. This review provides a brief summary of very recent progress in the research on chemistry of carbon nanotubes.

The modelling ability of non-major chemistry students and their understanding of the sub-microscopic level

This case study examined the ability of three first year non-major chemistry students to understand chemical concepts according to Johnstone’s three levels of chemical representations of matter. Students’ background knowledge in chemistry proved to be a powerful factor in their understanding of the submicroscopic level. The results show that modelling ability is not necessarily innate, but it is a skill to be learnt. Each of the students’ modelling abilities with chemical representations improved with instruction and practice. Generally, as modelling skills improved so did students’ understanding of the relevant chemical concept. Modelling ability is described according to Grosslight et al.’s three–tiered level and the ability to traverse the three levels of chemical representation of matter.

Achieving greater feedback and flexibility using online pre-laboratory exercises with non-major chemistry students

Compulsory online pre-laboratory exercises were required of non-major, first-year university chemistry students in response to poor student preparation for laboratory sessions. The online pre-laboratory exercises were designed to be straightforward, endeavoring to help students maximize the benefits of the introductory laboratory class. Diagrams and pictures were included in the exercises to improve descriptions. Students were allowed multiple attempts with immediate feedback provided to help them learn from their mistakes. The study is a descriptive account of students' perceptions of the impact of online pre-laboratory exercises on their learning. Students recognized the value of the exercises in improving their organization, their preparedness for the laboratory class, and their understanding of the chemistry concepts of the weekly experiments. The increased flexibility of doing pre-laboratory exercises online and the increased feedback to students were two important aspects of this project that nearly all students recognized as being beneficial to their learning.

Oxygen and hydrogen isotopic ratios and chemistry in semiarid land river water, Southwest Victoria, Australia

Salt in a salt lake accumulated as a result of perfect evaporation of inflow water during the dry season. Water in a salt lake had a high salinity and its isotope indicated a little evaporation in the wet season because precipitation replenished the salt lake and there was no residual water during evaporation process in salt lake. In a marsh, both perfect and partial disappearance of water by repeated evaporation and water supply from upstream contributed to high salinity and high isotopic ratios because residual water had high isotopic ratios and dried areas accumulated salt. On the other hand, salinity and isotopic ratios depended on ratio of evaporation and water supply during evaporation excluding perfect disappearance of water.