986 resultados para GENERAL CHEMISTRY


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A new methodology for the construction of combinatorial libraries is described. The approach, termed dendrimer-supported combinatorial chemistry (DCC), centers on the use of dendrimers as soluble supports. Salient features of DCC include solution phase chemistry, homogeneous purification, routine characterization of intermediates, and high support loadings. To demonstrate the feasibility of DCC, single compounds and a small combinatorial library were prepared via the Fischer indole synthesis. Excellent product yields and purities were obtained, and dendrimer-protected intermediates could be routinely analyzed by 1H and 13C NMR and by mass spectrometry. The results indicate that DCC is a general and efficient strategy for the generation of combinatorial libraries.

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One option to optimize carbon materials for supercapacitor applications is the generation of surface functional groups that contribute to the pseudocapacitance without losing the designed physical properties. This requires suitable functionalization techniques able to selectively introduce a given amount of electroactive oxygen groups. In this work, the influence of the chemical and electrochemical oxidation methods, on the chemical and physical properties of a zeolite templated carbon (ZTC), as a model carbon material, have been studied and compared. Although both oxidation methods generally produce a loss of the original ZTC physical properties with increasing amount of oxidation, the electrochemical method shows much better controllability and, unlike chemical treatments, enables the generation of a large number of oxygen groups (O = 11000- 3300 μmol/g), with a higher proportion of active functionalities, while retaining a high surface area (ranging between 1900-3500 m2/g), a high microporosity and an ordered 3-D structure.

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The methodological approach a teacher uses in the competence teaching-learning process determines the way students learn. Knowledge can be acquired from a series of perspectives, mainly: “know-what” (concept), where facts and descriptions of (natural or social) phenomena are pursued; “know-how” (procedure), where methods and procedures for their application are described; and “know-why” (competence), where general principles and laws that explain both the facts and their applications are sought. As all the three cases are interconnected, the boundaries between them are not fully clear and their application uses shared elements. In any case, the depth of student’s acquired competences will be directly affected by the teaching-learning perspective, traditionally aiming to a “know-why” approach for full competence acquisition. In this work, we discuss a suitable teaching-learning methodology for evaluating whether a “know-how”, “know-what” or combined approach seems better for enhancing competence learning in students. We exemplify the method using a selection of formative activities from the Physical Chemistry area in the Grades of Chemistry and Chemical Engineering.

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Ocean acidification is considered a major threat to marine ecosystems and may particularly affect calcifying organisms such as corals, foraminifera and coccolithophores. Here we investigate the impact of elevated pCO2 and lowered pH on growth and calcification in the common calcareous dinoflagellate Thoracosphaera heimii. We observe a substantial reduction in growth rate, calcification and cyst stability of T. heimii under elevated pCO2. Furthermore, transcriptomic analyses reveal CO2 sensitive regulation of many genes, particularly those being associated to inorganic carbon acquisition and calcification. Stable carbon isotope fractionation for organic carbon production increased with increasing pCO2 whereas it decreased for calcification, which suggests interdependence between both processes. We also found a strong effect of pCO2 on the stable oxygen isotopic composition of calcite, in line with earlier observations concerning another T. heimii strain. The observed changes in stable oxygen and carbon isotope composition of T. heimii cysts may provide an ideal tool for reconstructing past seawater carbonate chemistry, and ultimately past pCO2. Although the function of calcification in T. heimii remains unresolved, this trait likely plays an important role in the ecological and evolutionary success of this species. Acting on calcification as well as growth, ocean acidification may therefore impose a great threat for T. heimii.

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Here, the pelagic carbonate system and the ?13C signature of dissolved inorganic carbonate (DIC) were investigated in a tidal basin of the southern North Sea, the Jade Bay, with respect to tidal cycles and a transect towards the North Sea in winter time (January and November, 2010). Physical parameters, major and trace elements, and nutrient concentrations were considered, too. Primary production and pelagic organic matter respiration were negligible during winter time. Both, the compositional variations on the transects as well as during the tidal cycles indicate the mixing of North Sea with fresh water. The combined spatial co-variations of different parameters indicate an introduction of fresh water that was enriched in DI12C, metabolites (e.g., ammonia), protons, and dissolved redox-sensitive elements (e.g., Mn2+). During the January campaign, the discharge via the flood gates was limited due to ice cover of the hinterland drainage ditches, allowing for an observation of tidal variations without significant mixing contributions from surface water discharges. Considering a binary mixing model with North Sea and fresh water as end-members, the extrapolated fresh water end-member composition for this campaign is estimated to contain about 3.8 mmol/kg DIC , and enhanced concentrations of NH4+, Mn2+, and protons compared to North Sea water. The fast temporal response of dissolved geochemical tracers on tidal variations in the Jade Bay indicates a continuous supply of a fresh water component. The measured composition of fresh waters entering the Jade Bay via flood gates (end of October, 2010) did not match the values estimated by the binary mixing model. Therefore, the overall fresh water component likely is a mixture between sources originating from flood gates and (in January) dominating submarine groundwater discharge entering the Jade Bay. This model is consistent with the results obtained during the November campaign, when a more important contribution from flood gates is expected and a more variable fresh water end-member is estimated. The co-variations of the concentrations and the stable carbon isotope composition of DIC are applied to evaluate possible superimposed sink-source-transformation processes in the coastal waters and a general co-variation scheme is suggested.

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"Feed Materials Production Center, National Lead Company of Ohio"--Cover.

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The literature relative to the chemistry and technology of magnesium sulfate is presented. The literature titles and chemical abstracts numbers are given, together with a subject index.

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Mode of access: Internet.

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Edited by Sir William Ramsay, William Macnab, and others.

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"International atomic weights, 1937" on end lining-paper.

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A monograph, "Old and remarkable trees," issued as an appendix to [3rd] ser., v. 11, 1863/65 (112 p.) was originally intended to introduce a series of installments with subsequent volumes of the Transactions. No more were published in this form, but similar material compiled by Robert Hutchison was issued in the Transactions as follows: 4th ser., v. 11, p. 43-71; v. 12, p. 129-171; v. 13, p. 174-225; v. 15, p. 70-101; v. 16, p. 184-207; 5th ser., v. 4, p. 80-94.

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Mode of access: Internet.

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Editors: 1896-1932, W. D. Bancroft (with J. E. Trevor, 1896-1909);--1933-51, S. C. Lind;--1952-<53> W. A. Noyes.

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Supplements to v. 14 issued 1951-69 (8 v.)