Generalization of the lineshape useful in magnetic resonance spectroscopy

A new lineshape function is derived from the Tsallis distribution to describe electron paramagnetic resonance (EPR) spectra, and possibly nuclear magnetic resonance (NMR) spectra as well. This lineshape generalizes the Gaussian and Lorentzian lineshapes that are widely used in simulations. The main features of this lineshape function are presented: the normalization, moments, and first derivative. A number of experimental EPR spectra are compared with the results of simulations employing the new lineshape function. The results show that the new lineshape often provides a better approximation of the experimental spectrum. It is also shown that the new parameter of the lineshape function can be used to quantify the intermolecular spin-spin interactions.     

Molecular Shape Analysis of a Maillard Reaction Intermediate

Abstract

The Maillard (browning) reaction involving the polycondensation of sugars and amino acids is believed to be an important abiotic pathway for humic substance formation in nature. However, a major drawback is that the Maillard reaction is extremely slow at temperatures encountered under normal environmental conditions. In order to elucidate some details of this process molecular shape analysis was applied to investigate the initial reaction between D-glucose and glycine to form the Amadori compound fructosylglycine which is an intermediate product in the Maillard reaction. The structure of the Amadori compound was optimized at a quantum mechanical level and its ground state electron energy calculated. Molecular Iso-Density Contours (MIDCO's), electron density contour surfaces of constant electron density, were constructed for D-glucose, glycine and fructosylglycine in order to study the steric conditions for the reaction. The calculations indicate that the Amadori compound and water on one hand and the separate entities D-glucose and glycine on the other hand are very similiar to each other in terms of their ground state energy. This agrees with the experimental observation that the reaction between D-glucose and glycine to form the Amadori compound is slow.     

Molecular geometry and symmetry from a differential geometry viewpoint

Relations between an earlier generalization of molecular symmetry called symmorphy and a molecular equivalence based on diffeomorphisms of electron density functional graphs (the so-called DFG equivalence introduced in our previous work) are analyzed. Any two DFG-equivalent electron density functions can be derived from one another by a suitable transformation of the spatial coordinates and the electronic charge density scale; the classes of DFG equivalence are the orbits of a group of linear operators operating in the space of electron density functions. Within the symmorphy framework, the symmetry group is derived from the symmorphy group by taking an intersection of a subgroup of the symmorphy group and the group of isometries for a natural choice of the Riemannian metric tensor. The Riemannian metric properties provide a choice for a suitable reference electron density function for each class of equivalent densities. Such reference densities serve as tools for a systematic classification of the infinite family of electron densities of molecular conformations. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64 : 669–678, 1997     

A preliminary assessment of the provenance of ancient pottery through instrumental neutron activation analysis at the Monte Castelo site,Rondônia,Brazil

Journal of Radioanalytical and Nuclear Chemistry - This research aims to contribute to the discussion of ceramic objects found at the Monte Castelo shellmound, an archaeological site located at...     

A geometrical approach to the degree of chirality and asymmetry

A new measure of the degree of chirality and asymmetry of a finite number of particles is proposed. To this end a space of configurations of identical particles is defined as the orbit space of the group of all permutations of particles embedded in an Euclidean space. This space is shown to be a metric space and the action of the translation and orthogonal groups is also defined. The results are applied to the study of an algebra of polynomials on the configuration space and its equivalence to the algebra of symmetric Cartesian tensors is demonstrated. An illustrative example is presented. Some general features of chirality are also briefly discussed.     

Noncovalent control of absorption and fluorescence spectra

Perylene dyes with N-tert-alkyl substituents were prepared in which noncovalent interactions of the crowded substituent cause a variation of the geometry of the core and induce hypsochromic shifts in absorption and fluorescence. The interpretation of the shifts was supported by means of DFT calculations and an X-ray crystal structure analysis.     

The metric properties of the reduced nuclear configuration space: Remarks

A definition of the distance on the orbit spaces of topological groups acting continuously on metric spaces is applied to define some metric properties of the reduced nuclear configuration spaces. Straightforward proofs are given and a comparison with former results is carried out.