Magnesium oxysulfate (MOS) cement exhibits excessive cracking when exposed to water because of the reaction of residual MgO that forms extensive Mg(OH)2, which significantly limits the application ...breadth of MOS cement. This study investigates the effects of the addition of hydromagnesite ((MgCO3)4·Mg(OH)2·4H2O) on the hydration products of MOS cement and the microstructure and physical properties of MOS paste samples. It was found that the addition of hydromagnesite increased the compressive strength and water resistance of MOS cement. This effect is mainly due to the reaction between hydromagnesite and free MgO present in the cement that forms magnesium carbonate (MgCO3·Mg(OH)2·3H2O) and acts as an additional binding phase. The use of hydromagnesite as an additive for improving the water resistance of MOS cement leads to a decrease in the residual MgO content and improves the water stability of amorphous materials.
Membrane Protein Research Group, Deparetment of Physiology, University of Alberta, Edmonton, Alberta, Canada
Submitted 24 April 2008
; accepted in final form 6 May 2008
ABSTRACT
The very last member ...of the SLC2A gene family of facilitated hexose transporters to be cloned was SLC2A7 (hGLUT7). It has been assigned to the class II of the GLUT family on the basis of sequence similarity, and its closest family member is GLUT5, an intestinal fructose transporter. GLUT7 is primarily expressed in the small intestine and colon, although mRNA has been detected in the testis and prostate as well. The protein is expressed in the apical membrane of the small intestine and colon, and it has a high affinity (<0.5 mM) for glucose and fructose. The abundance of the protein in the small intestine does change in parallel with the dietary carbohydrate. However, the distribution of GLUT7 along the small intestine does not entirely match with the availability of glucose and fructose, suggesting that the physiological substrate for this transporter has yet to be identified. Unlike GLUT13, the proton-coupled myoinositol transporter (HMIT), there is no evidence for the coupling of protons to the hexose movement via GLUT7. One area of study in which GLUT7 has provided a useful comparison with GLUT1 has been in the development of the hypothesis that the facilitated hexose transporters may have a selectivity filter at the exofacial opening of the translocation pore, which helps to determine which hexoses can be transported. If substantiated, the elucidation of this mechanism may prove useful in the design of hexose analogs for use in cancer imaging and therapeutics.
glucose transporter proteins; SLC2A7; intestinal hexose absorption; structure-function
Address for reprint requests and other correspondence: C. Cheeseman, Membrane Protein Research Group, Dept. of Physiology, Univ. of Alberta, Edmonton, Alberta, T6G 2H7, Canada (e-mail: chris.cheeseman{at}ualberta.ca )
The extent of reaction between magnesium oxide (MgO) and silica fume (SiO2) is normally limited and mixes require high water contents to give suitable rheology. The use of considerably lower water ...contents and the formation of magnesium silicate hydrate (M-S-H) gel as a binding phase is made possible by adding sodium hexametaphosphate (Na-HMP) to the mix water prior to the addition of MgO and SiO2. This results in the formation of extensive reaction products and cured samples with high compressive strength and low porosity. In this work, the effect of Na-HMP on the hydration of MgO/SiO2 mixes is investigated using high water to solids ratio samples to allow monitoring of pH and the solution chemistry during hydration. It is shown that a relatively small amount of Na-HMP inhibits the formation of Mg(OH)2 when MgO is hydrolyzed. It is proposed that this is due to adsorption of phosphate species on the MgO which inhibits the nucleation of the Mg(OH)2. This gives rise to high Mg2+ species in solution and elevated pH (>12) conditions relative to when Mg(OH)2 forms. In contrast, the phosphate does not suppress formation of M-S-H gel. In combination with the enhanced dissolution rate of SiO2 at high pH, M-S-H gel can form quickly without competition for Mg2+ ions by Mg(OH)2 precipitation. Incorporating the optimum concentration of Na-HMP into the mix water therefore transforms the properties of cement paste and mortar samples formed by reacting MgO and SiO2.
PURPOSE OF REVIEWThe goal of this article is to review the possible physiological roles of the recently identified urate transporter, solute carrier family 2 (facilitated glucose transporter), member ...9 (SLC2A9), in the renal handling of urate.
RECENT FINDINGSGlucose transporter 9 is a high affinity hexose transporter encoded by the SLC2A9 gene found on human chromosome 4. The two splice variants SLC2A9b and SLC2A9a are expressed in the apical and basolateral membranes, respectively, of the proximal convoluted tubule. Recent reports have found significant correlations between two different sets of single nucleotide polymorphisms in SLC2A9. In one case, they are associated with increases in plasma urate levels and/or the incidence of hypertension or gout. The second set of single nucleotide polymorphisms correlate with hypouricaemia in Japanese patients. Expression of SLC2A9a and b in Xenopus laevis oocytes shows that these proteins mediate rapid urate fluxes and can exchange glucose for urate. Indirect evidence also suggests that the transporter is electrogenic.
SUMMARYThis review proposes that SLC2A9 contributes significantly in two ways to the fluxes of urate across the proximal convoluted tubule. Firstly, the apical expression of SLC2A9b secretes urate back into the urine in exchange for lumenal glucose. Secondly, the basolateral membrane SLC2A9a could be the primary route for urate movement out of the epithelium into the peritubular space.
This review examines the development of structure and function of the human GLUT proteins, gene family hSLC2A. These proteins are essential for moving the key metabolites, glucose, galactose, and ...fructose in and out of cells, as well as a number of other important substrates. Despite over five decades of research, it is still not fully understood how they work at the molecular level, although the recent publication of a crystal structure of GLUT1 suggests this may be resolved soon. The GLUT family is divided into three classes based on their sequence homology. The physiological roles of Class I GLUTs, ie, 1, 2, 3 (14), and 4 have been extensively studied for their contributions to metabolism and development. However, the other two classes have received far less attention. Genetic diseases associated with GLUTs are very rare, emphasizing their critical roles, but it is likely that as our understanding of these transporters increases, there may be more clinical conditions found to be associated with subtle changes in their activity. Another promising area of investigation is the changes in expression levels of GLUTs associated with, and likely in consequence of, disease processes. It has long been known that GLUT1 expression increases significantly in cancer cells, but it is now becoming appreciated that other GLUTs may also be involved. Determination of alterations in expression patterns may prove to be a useful diagnostic tool, and in some cases these are already being taken advantage of for the imaging of cancers. Finally, as we better understand how GLUTs bind and transport their substrates, it may be possible to design drugs that can be delivered into target cells for the treatment of a number of diseases.
Xenopus laevis oocytes are a useful heterologous expression system for expressing glucose transporters (GLUTs) and examining their functions. In this chapter, we provide a detailed protocol on oocyte ...extraction and preparation for GLUT9 protein expression. Furthermore, we describe the determination of GLUT9 overexpression level by biotinylation and Western blotting analysis. Finally, we also describe how GLUT9-expressing oocytes can be used to measure urate kinetics by radioisotopes as well as two-microelectrode voltage clamping techniques.
Many thousands of people in developing country cities depend on recycling materials from waste for their livelihoods. With the focus of the Millennium Development Goals on poverty reduction, and of ...waste strategies on improving recycling rates, one of the major challenges in solid waste management in developing countries is how best to work with this informal sector to improve their livelihoods, working conditions and efficiency in recycling.
The general characteristics of informal recycling are reviewed, highlighting both positive and negative aspects. Despite the health and social problems associated with informal recycling, it provides significant economic benefits that need to be retained. Experience shows that it can be highly counterproductive to establish new formal waste recycling systems without taking into account informal systems that already exist. The preferred option is to integrate the informal sector into waste management planning, building on their practices and experience, while working to improve efficiency and the living and working conditions of those involved. Issues associated with integrating informal recycling into the formal waste management sector are discussed.
In low- and middle-income developing countries, the informal (collection and) recycling sector (here abbreviated IRS) is an important, but often unrecognised, part of a city’s solid waste and ...resources management system. Recent evidence shows recycling rates of 20–30% achieved by IRS systems, reducing collection and disposal costs. They play a vital role in the value chain by reprocessing waste into secondary raw materials, providing a livelihood to around 0.5% of urban populations. However, persisting factual and perceived problems are associated with IRS (waste-picking): occupational and public health and safety (H&S), child labour, uncontrolled pollution, untaxed activities, crime and political collusion. Increasingly, incorporating IRS as a legitimate stakeholder and functional part of solid waste management (SWM) is attempted, further building recycling rates in an affordable way while also addressing the negatives. Based on a literature review and a practitioner’s workshop, here we develop a systematic framework—or typology—for classifying and analysing possible interventions to promote the integration of IRS in a city’s SWM system. Three primary interfaces are identified: between the IRS and the SWM system, the materials and value chain, and society as a whole; underlain by a fourth, which is focused on organisation and empowerment. To maximise the potential for success, IRS integration/inclusion/formalisation initiatives should consider all four categories in a balanced way and pay increased attention to their interdependencies, which are central to success, including specific actions, such as the IRS having access to source separated waste. A novel rapid evaluation and visualisation tool is presented—integration radar (diagram) or InterRa—aimed at illustrating the degree to which a planned or existing intervention considers each of the four categories. The tool is further demonstrated by application to 10 cases around the world, including a step-by-step guide.
Novel lightweight bricks have been produced by sintering mixes of dried water treatment sludge and rice husk. Samples containing up to 20
wt.% rice husk have been fired using a heating schedule that ...allowed effective organic burn-out. Rice husk addition increased the porosity of sintered samples and higher sintering temperatures increased compressive strengths. Materials containing 15
wt.% rice husk that were sintered at 1100
°C produced low bulk density and relatively high strength materials that were compliant with relevant Taiwan standards for use as lightweight bricks.
► Reusing both Waelz slag and foundry sand in red clay bricks has been studied. ► Reductions of porosity and CO2 and NOx emissions during production were found. ► Other physico-chemical and ...mechanical properties were not significantly affected. ► Environmental behaviour of the new bricks during service and end life was assessed. ► Decreasing mobility of pollutants in relation to samples with only slag or sand.
Foundry sand and Waelz slag have been used to replace clay in the production of red clay bricks. These are both problematic wastes in Northern Spain that are currently landfilled. A semi-scale industrial trial incorporating 20–40 weight percent additions to bricks has been completed. Trial samples have been compared with control bricks containing no waste additions. The physico-chemical, mechanical and environmental properties have been evaluated. Incorporating Waelz slag and foundry sand in the mix allows the production of more resource efficient, lower cost bricks. Performance benefits included improved extrusion properties during forming, lower water absorption of the sintered brick due to reduced connected porosity, significant reductions in CO2 and NOx emissions during firing and improvements in potential leachability of some pollutants in relation to samples containing only Waelz slag or foundry sand. However, it is necessary to limit the addition of Waelz slag to less than 30wt.% in order to meet regulatory leaching limits for Mo. Other physico-chemical and mechanical parameters were not significantly affected by the addition of these industrial by-products.
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