Regioselective hydration of alpha-alkynyl esters and ketones by using a cationic NHC-AuI catalyst results in beta-keto esters and beta-diketones, respectively. Controlled release of water in acetone ...by aldol self-condensation under the reaction conditions makes acetone as better solvent than 1,4-dioxane/water for the hydration of alpha-alkynyl esters having sensitive ester moieties.
Various 1,4-diols are easily accessible from alkenes through iron-catalyzed aerobic hydration. The reaction system consists of a user-friendly iron phthalocyanine complex, sodium borohydride, and ...molecular oxygen. Furthermore, the effect of additional ligands on the iron complex was examined for a model reaction. The second hydroxy group is installed by direct C(sp3)H oxygenation, which is based on a 1,5hydrogen shift process of a transient alkoxy radical that is formed by formal hydration of the olefin. PUBLICATION ABSTRACT
The facile construction of biologically active beta-adrenergic receptor agonists/blockers and analogues is a great fundamental and practical challenge in medical chemistry. Herein, we report a ...hydration-asymmetric transfer hydrogenation cascade to realize the one-pot enantioselective transformation of aromatic haloalkynes into chiral aromatic halohydrins, which can be converted readily into chiral beta-adrenergicreceptor blockers. Such a one-pot cascade process involves the Au-catalyzed hydration of aryl-substituted haloalkynes to aryl-substituted alpha-halomethyl ketones and the Ru-catalyzed asymmetric transfer hydrogenation of aryl-substituted alpha-halomethyl ketones to aryl-substituted 2-haloethanols. The significant benefits of this procedure are that it provides chiral aromatic halohydrins in high yields, with excellent enantioselectivities, and a wide variety of functional groups are tolerated under mild conditions. The study described herein offers a useful approach to construct chiral beta-adrenergic blockers, which is an attractive practical organic transformation that is performed in a one-pot manner.
Supplementary cementitious materials (SCMs) are key components of sustainable, low carbon cements. To maximize their use in blended cements, the impact of SCMs on cement hydration needs to be ...understood and accurately captured by models. A central element in such models is the reactivity of the SCM, which is tedious to measure. Establishing relationships between SCM properties and their intrinsic reactivity is therefore highly important. Moreover, mechanisms enhancing or limiting SCM reactivity in blended cements need to be well-understood. This work reviews recent progress in the description and understanding of the reactivity of SCMs and their impact on Portland clinker hydration. Insights derived from fundamental work using synthetic SCMs, dissolution experiments and model systems are discussed as well as recent work studying the impact of common SCMs on hydration and microstructure of blended cements. Particular attention is paid to recent work on calcined clays, which are currently receiving substantial interest.
Progress in understanding hydration mechanisms of alite and Portland cement is reviewed. Up to the end of the induction period, dissolution rates determined by the undersaturation of the solution ...dominate the reaction, but, better understanding is needed about the alite solution interface. The main heat evolution peak hydration is dominated by the growth of outer C-S-H with a spiky or “needle” like morphology. Growth is rapid over several hours (acceleration period) and then slows (deceleration period). At later ages the consumption of water and lack of water filled pores above about 10 nm, along with the consumption of anhydrous material are major factors leading to the continual reduction in the rate of reaction. There is no evidence that diffusion becomes the rate controlling mechanism even at this stage. The microstructure of cement differs significantly from that of alite, largely due to the influence of alumina on C-S-H growth and distribution.
Introducción/Objetivos: Las proyecciones de población de Naciones Unidas para 2050 (United Nations: World Population Prospects: The 2004 Revisión) calculan que España será el tercer país más viejo ...del mundo, con un 34,1% de población mayor en 2050. En las personas mayores, es difícil establecer unos requerimientos generales de agua, que serían la cantidad necesaria para equilibrar las pérdidas (muy variables) y mantener una carga tolerable de solutos por los riñones (que depende de los componentes de la dieta, entre otros factores).Para muchas personas ese objetivo es a veces difícil de conseguir por su avanzada edad, por su incapacidad física que dificulta el acceso al agua, por enfermedades crónicas, demencia o por la menor sensación de sed. Referencias: EFSA (2010) Panel on Dietetic Products, Nutrition, and Allergies (NDA); Scientific Opinion on Dietary reference values for water.
Introdução: O estresse térmico resulta em queda no desempenho das operações militares e aumento de distúrbios relacionados ao calor. Para minimizar estes efeitos recomenda-se a reposição adequada de ...fluidos. Objetivos: Avaliar o conhecimento de hidratação e comparar o estado de hidratação após diferentes protocolos de hidratação seguidos de uma corrida. Métodos: 46 militares foram alocados em três grupos: privação da ingestão de líquidos (GA), ingestão recomendada pelo Colégio Americano de Medicina do Esporte (ACSM) (GB) e ingestão ad libitum (GC). Resultados: A taxa de sudorese de GA e GC foi superior à GB (26,81 ± 5,5 ml.min-1, 15,92 ± 10,69 ml.min-1 vs 4,47 ± 6,5 ml. min-1). Em relação à ingestão, GB apresentou valor superior a GA e GC (453,0 ± 91,0 vs 0,0 ml ± 0,0 ml, 165,0 ± 136,0 ml). Conclusão: As recomendações do ACSM foram adequadas para manterem os militares hidratados, no entanto, os militares apresentaram um baixo nível de conhecimento e hábitos de hidratação inadequados.
•The action mechanism of limestone powder includes four effects.•The physical effect of limestone powder depends on its particle size and amount.•The chemical effect of limestone powder relies on the ...alumina content.
Limestone powder (LS) has been widely used in cement-based materials; and reportedly, can influence their properties by filler, nucleation, dilution and chemical effects. The action mechanism of LS mainly depends on its particle size and amount. The filler effect of LS refines the microstructure and reduces the porosity of cement-based materials. Its nucleation effect accelerates the hydration of C3S, increases the amount of hydration products and reduces the porosity of cement-based materials at early ages. Its dilution effect reduces the hydration peak of C3S, decreases the amount of hydration products and increases the porosity of cement-based materials. Its chemical effect promotes the appearance of third hydration peak, forms carboaluminate and reduces the porosity of cement-based materials.
Magnesium potassium phosphate cements (MKPCs) are prepared using calcined magnesia (MgO) and an acidic solution of potassium dihydrogen phosphate (KH2PO4). Their fast setting and high heat of ...hydration can be problematic when large volumes of materials are produced. Boric acid (B(OH)3) is thus commonly added as a set retarder. This work investigates MKPC hydration in paste (water-to-cement ratio w/c = 1) and its retardation by B(OH)3. The precipitation of K-struvite (MgKPO4·6H2O) is preceded by that of phosphorösslerite (MgHPO4·7H2O) and Mg2KH(PO4)2·15H2O. Cattiite (Mg3(PO4)2·22H2O), an end-product in diluted suspension (w/c = 100), is not observed. B(OH)3 slows down the formation of hydrates in two ways: (i) by stabilizing in solution the cations that outbalance the negative charges of the polyborates formed at pH above 6, and (ii) through the precipitation of an amorphous mineral containing borate and orthophosphate. The first process occurs both in diluted suspensions and pastes, the second is specific to pastes.
Progress in understanding hydration is summarized. Evidence supports the geochemistry dissolution theory as an explanation for the induction period, in preference to the inhibiting layer theory. The ...growth of C–S–H is the principal factor controlling the main heat evolution peak. Electron microscopy indicates that C–S–H “needles” grow from the surface of grains. At the peak, the surface is covered, but deceleration cannot be attributed to diffusion control. The shoulder peak comes from renewed reaction of C3A after depletion of sulfate in solution, but release of sulfate absorbed on C–S–H means that ettringite continues to form. After several days space becomes the major factor controlling hydration.
The use of new analytical technique is improving our knowledge of the action of superplasticizers and leading to the design of molecules for different applications. Atomistic modeling is becoming a topic of increasing interest. Recent publications in this area are reviewed.
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