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Inorganic Reactions (inorganic + reaction)

Distribution by Scientific Domains

Chemistry	60%

Selected Abstracts

Inorganic reactions of iodine(+1) in acidic solutions

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2004
Guy Schmitz
We present a thorough analysis of the former works concerning the hydrolysis of iodine and its mechanism in acidic or neutral solutions and recommend values of equilibrium and kinetic constants. Since the literature value for the reaction H2OI+ , HOI + H+ appeared questionable, we have measured it by titration of acidic iodine solutions with AgNO3. Our new value, K(H2OI+ , HOI + H+) , 2 M at 25°C, is much larger than accepted before. It decreases slowly with the temperature. We have also measured the rate of the reaction 3HOI , IO3, + 2I, + 3H+ in perchloric acid solutions from 5 × 10,2 M to 0.5 M. It is a second order reaction with a rate constant nearly independent on the acidity. Its value is 25 M,1 s,1 at 25°C and decreases slightly when the temperature increases, indicating that the disproportionation mechanism is more complicated than believed before. An analysis of the studies of this disproportionation in acidic and slightly basic solutions strongly supports the importance of a dimeric intermediate 2HOI , I2O·H2O in the mechanism. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:480,493, 2004 [source]

The Dry Limit of Microbial Life in the Atacama Desert Revealed by Calorimetric Approaches

ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 5 2008
N. Barros
Abstract The Atacama desert in Chile is one of the driest and most lifeless environments on Earth. It rains possibly once a decade. NASA examined these soils as a model for the Martian environment by comparing their degradation activity with Martian soil and looking for "the dry limit of life". The existence of heterotrophic bacteria in Atacama soil was demonstrated by DNA extraction and by the isolation of microorganisms. So far, however, no data have been available about the metabolic activities in these soils due to the limitations of the existing methodologies when applied to desert soils. Calorimetry was used to obtain information on the metabolic and thermal properties of eleven soil samples collected at different sites in the Atacama desert. Differential scanning calorimetry and isothermal calorimetry were employed to determine the pyrolysis properties of the carbon-containing matter and to measure biomass and microbial metabolism. They were compared to other soil properties such as total carbon and nitrogen, carbon to nitrogen ratio and pH. There was measurable organic matter in nine of the eleven samples and the heat of pyrolysis of those soils was correlated to the carbon content. In five of the eleven samples no biomass could be detected and the existence of basal microbial metabolism could not be established because all samples showed endothermic activity, probably from inorganic reactions with water. Six samples showed microbial activation after the addition of glucose. Carbon content, nitrogen content and the microbial activity after glucose amendment were correlated to the altitude and to the average minimum temperature of the sampling sites calculated from meteorological data. The detectable microbial metabolism was more dissipative with increasing altitude and decreasing temperature. [source]

Conceptual models for burrow-related, selective dolomitization with textural and isotopic evidence from the Tyndall Stone, Canada

GEOBIOLOGY, Issue 1 2004
Murray K. Gingras
ABSTRACT The formation of dolomite is generally explained using models that reflect larger-scale processes that describe the relationship between the supply and transport of Mg, and geochemical conditions that are amenable to the formation of dolomite. However, heterogeneities in the substrate, such as those made by bioturbating infauna, may play a more important role in dolomitization than has been previously considered. Burrow-facilitated dolomitization is evident in the Ordovician Tyndall Stone (Red River Group, Selkirk Formation) of central Canada. The diagenetic fabrics present are attributed to dolomitizing fluids that both flowed through and evolved within burrow networks. Petrographic analysis suggests that two phases of dolomite formation took place. The first formed a fine-grained, fabric-destructive type that probably accompanied early burial; the second is a fine- to medium-grained, locally sucrosic dolomite that is interpreted to have precipitated during later burial. Isotopic analysis supports the proposed paragenetic history: (1) an apparent linking of the stable isotopes 13C and 18O strongly suggests that the micrite matrix formed during very early diagenesis and was derived from seawater; (2) the initial phase of dolomitization is potentially microbially mediated, as evidenced by the enrichment of 13C; and (3) isotopic values for the second generation of dolomite reflect the mixing of ground water and resorbed early dolomite. This paper conceptualizes the physical and chemical conditions required for the formation of dolomite in association with burrow fabrics. The proposed model reveals a composite of biological and inorganic reactions that demonstrates the interdependence of sediment fabric, organic content and microbial interactions in the development of burrow-mottled dolomitic limestone. It is suggested that where burrow-associated dolomite occurs, it is most likely to develop in two stages: first, the byproducts of the degradation of organic material in burrows locally increase the permeability and porosity around burrow fabrics in shallow diagenetic depositional environments; and, second, the passing of burrowed media into deeper dysaerobic sediment is accompanied by the establishment of fermenting micro-organisms whose byproducts mediate dolomitization. [source]

Spectrophotometric variable-concentration kinetic experiments applied to inorganic reactions

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2003
Giuseppe Alibrandi
The dependence of the observed rate constant of inorganic substitution reactions on the concentration of nucleophilic reagents was obtained by single variable-parameter kinetic runs. The experiments were carried out spectrophotometrically, varying the concentration of the nucleophile inside the reaction vessel. Software and apparatus were developed for an easy and rapid performance. The method gives accurate results and a saving in time by a factor of up to 100 compared to conventional methods. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 497,502, 2003 [source]

Can Electrophilicity Act as a Measure of the Redox Potential of First-Row Transition Metal Ions?

CHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2007
Jan Moens
Abstract Previous contributions concerning the computational approach to redox chemistry have made use of thermodynamic cycles and Car,Parrinello molecular dynamics simulations to obtain accurate redox potential values, whereas this article adopts a conceptual density functional theory (DFT) approach. Conceptual DFT descriptors have found widespread use in the study of thermodynamic and kinetic aspects of a variety of organic and inorganic reactions. However, redox reactions have not received much attention until now. In this contribution, we prove the usefulness of global and local electrophilicity descriptors for the prediction of the redox characteristics of first row transition metal ions (from Sc3+|Sc2+ to Cu3+|Cu2+) and introduce a scaled definition of the electrophilicity based on the number of electrons an electrophile ideally accepts. This scaled electrophilicity concept acts as a good quantitative estimate of the redox potential. We also identify the first solvation sphere together with the metal ion as the primary active region during the electron uptake process, whereas the second solvation sphere functions as a non-reactive continuum region. [source]