THE CHEMICAL REACTIVITY OF SOLIDS

1964 ◽  
Vol 56 (11) ◽  
pp. 37-38
Author(s):  
G. Parravano
Keyword(s):  
Chemical Reactivity ◽  
Reactivity Of Solids

Dislocations and the thermal reactivity of calcite

1970 ◽  
Vol 314 (1518) ◽  
pp. 429-441 ◽  
Keyword(s):  
Chemical Reactivity ◽  
Previous History ◽  
Strain Fields ◽  
Temperature Range ◽  
Reactivity Of Solids ◽  
Dislocation Movement ◽  
History Of ◽  
First Time ◽  
Kinetics Of

A study has been made of the effect of dislocation movement on the kinetics of thermal decomposition of freshly cleaved calcite crystals. It is shown for the first time that the thermal history of the crystal has a marked effect on its reactivity and two patterns of behaviour have been identified; that in the temperature range up to ca . 700 K in which the kinetics of decomposition are sensitively dependent upon the nature and extent of the crystal’s previous history, and the range above 700 K in which annealing is rapid and reproducible kinetics are obtained for all crystals studied. This effect has not been observed in previous studies of calcite. It is suggested that this is because the experiments were carried out in the temperature range where movement of dislocations is so rapid that the surface structure is virtually constant during the measurements. Tentative correlations are made between the various stages of the observed rates of decomposition and the known dislocation systems in the crystal. The influence of applied stress was studied but because of limitations in the method of stressing the crystal, the amount of plastic deformation was small and its effect on reactivity was not marked. Qualitative consideration is given to the role of dislocations in the reactivity of solids and it is concluded that the elastic energy associated with the strain fields around or at the core of the dislocation cannot be used to promote chemical reactivity but that it is the change in the stereochemical environment of molecules in the dislocated region of the crystal which is important. ‘ . . . a curious illustration of the influence of mechanical forces over chemical affinity. . . ’ M. Faraday (1834)

Novel Insights in the Magnetic Behavior of Non-Stoichiometric LaMnO3+δ Nanoparticles

2021 ◽  
Author(s):  
José M González-Calbet ◽  
Antonio Hernando ◽  
Jose Alonso ◽  
Kevin M. Sigcho ◽  
Alberto Azor-Lafarga ◽  
...  
Keyword(s):  
Chemical Reactivity ◽  
Exchange Interactions ◽  
Magnetic Behavior ◽  
Antiferromagnetic Ordering ◽  
Reactivity Of Solids ◽  
Material Sciences

LaMnO3+δ is one of the classical-formal nonstoichiometric systems in Material Sciences that, for δ=0, shows antiferromagnetic ordering by super-exchange interactions between Mn3+ ions. Nevertheless, the chemical reactivity of solids goes...

Spatially Resolved Photoelectron Spectroscopy: Recent Progress and Future Plans

1990 ◽  
Vol 48 (2) ◽  
pp. 388-389
Author(s):  
A. M. Bradshaw
Keyword(s):  
Photoelectron Spectroscopy ◽  
Chemical Reactivity ◽  
Target Material ◽  
Orbital Energy ◽  
Light Sources ◽  
Analytical Technique ◽  
Hartree Fock ◽  
Spatially Resolved ◽  
Koopmans Theorem ◽  
Surface Analytical Technique

X-ray photoelectron spectroscopy (XPS or ESCA) was not developed by Siegbahn and co-workers as a surface analytical technique, but rather as a general probe of electronic structure and chemical reactivity. The method is based on the phenomenon of photoionisation: The absorption of monochromatic radiation in the target material (free atoms, molecules, solids or liquids) causes electrons to be injected into the vacuum continuum. Pseudo-monochromatic laboratory light sources (e.g. AlKα) have mostly been used hitherto for this excitation; in recent years synchrotron radiation has become increasingly important. A kinetic energy analysis of the so-called photoelectrons gives rise to a spectrum which consists of a series of lines corresponding to each discrete core and valence level of the system. The measured binding energy, EB, given by EB = hv−EK, where EK is the kineticenergy relative to the vacuum level, may be equated with the orbital energy derived from a Hartree-Fock SCF calculation of the system under consideration (Koopmans theorem).

Cluster analysis for large data sets: applications to individual aerosol particles from the mid-pacific

1992 ◽  
Vol 50 (2) ◽  
pp. 1488-1489
Author(s):  
Thomas W. Shattuck ◽  
James R. Anderson ◽  
Neil W. Tindale ◽  
Peter R. Buseck
Keyword(s):  
Cluster Analysis ◽  
Chemical Reactivity ◽  
Large Data ◽  
Large Data Sets ◽  
Particle Analysis ◽  
Data Sets ◽  
Halogen Chemistry ◽  
Complete Study ◽  
Components Analysis ◽  
Automated Scanning

Individual particle analysis involves the study of tens of thousands of particles using automated scanning electron microscopy and elemental analysis by energy-dispersive, x-ray emission spectroscopy (EDS). EDS produces large data sets that must be analyzed using multi-variate statistical techniques. A complete study uses cluster analysis, discriminant analysis, and factor or principal components analysis (PCA). The three techniques are used in the study of particles sampled during the FeLine cruise to the mid-Pacific ocean in the summer of 1990. The mid-Pacific aerosol provides information on long range particle transport, iron deposition, sea salt ageing, and halogen chemistry.Aerosol particle data sets suffer from a number of difficulties for pattern recognition using cluster analysis. There is a great disparity in the number of observations per cluster and the range of the variables in each cluster. The variables are not normally distributed, they are subject to considerable experimental error, and many values are zero, because of finite detection limits. Many of the clusters show considerable overlap, because of natural variability, agglomeration, and chemical reactivity.

Structure Revision of Protoaculeine B, a Posttranslationally Modified N-Terminal Residue in the Peptide Toxin Aculeine B

2020 ◽  
Author(s):  
Raku Irie ◽  
Kei Miyako ◽  
Satoko Matsunaga ◽  
Ryuichi Sakai ◽  
Masato Oikawa
Keyword(s):  
Mass Spectra ◽  
Chemical Reactivity ◽  
Model Compounds ◽  
Structural Revision ◽  
Structure Revision ◽  
Peptide Toxin ◽  
One Step ◽  
Marine Peptide ◽  
Synthetic Models ◽  
Long Chain

<div>Here, we newly propose the structure of protoaculeine B, an N-terminal moiety of the marine peptide toxin aculeine B, as possessing the cis-disubstituted tetrahydro-beta-carboline framework. We prepared two truncated model compounds that lack long-chain polyamine by one-step Pictet-Spengler reaction of tryptophan, and compared the NMR and mass spectra and chemical reactivity with those of natural protoaculeine B. The synthetic models reproduced the profiles of the natural product well, which was conclusive for the structural revision.</div>

Atom Condensed Fukui Function for Condensed Phases and Biological Systems and Its Application to Enzymatic Fixation of Carbon Dioxide

2019 ◽  
Author(s):  
Javier Oller ◽  
David A. Sáez ◽  
Esteban Vöhringer-Martinez
Keyword(s):  
Carbon Dioxide ◽  
Aqueous Solution ◽  
Molecular System ◽  
Chemical Reactivity ◽  
Nucleophilic Attack ◽  
Stable Conformation ◽  
Fukui Functions ◽  
Reactivity Descriptors ◽  
Dynamics Simulations ◽  
Fixation Of Carbon Dioxide

<div><div><div><p>Local reactivity descriptors such as atom condensed Fukui functions are promising computational tools to study chemical reactivity at specific sites within a molecule. Their applications have been mainly focused on isolated molecules in their most stable conformation without considering the effects of the surroundings. Here, we propose to combine QM/MM Born-Oppenheimer molecular dynamics simulations to obtain the microstates (configurations) of a molecular system using different representations of the molecular environment and calculate Boltzmann weighted atom condensed local reac- tivity descriptors based on conceptual DFT. Our approach takes the conformational fluctuations of the molecular system and the polarization of its electron density by the environment into account allowing us to analyze the effect of changes in the molecular environment on reactivity. In this contribution, we apply the method mentioned above to the catalytic fixation of carbon dioxide by crotonyl-CoA carboxylase/reductase and study if the enzyme alters the reactivity of its substrate compared to an aqueous solution. Our main result is that the protein en- vironment activates the substrate by the elimination of solute-solvent hydrogen bonds from aqueous solution in the two elementary steps of the reaction mechanism: the nucleophilic attack of a hydride anion from NADPH on the α, β unsaturated thioester and the electrophilic attack of carbon dioxide on the formed enolate species.</p></div></div></div>

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