Molecular conformational rigidity: An approach to quantification

A method is proposed for ordering molecules on a scale of conformational rigidity on the basis of a parameter (the F number), which to a first approximation is evaluated with the three-states rotational isomeric-state scheme. Some particularly rigid paraffins are discussed.

     

Inputs of heavy metals due to agrochemical use in tobacco fields in Brazil’s Southern Region

Only a few studies have assessed the joint incorporation of heavy metals into agricultural systems based on the range of agrochemicals used on a specific agricultural crop. This study was conducted to assess the heavy metals input through application of the main agrochemicals used in Brazilian tobacco fields. A total of 56 samples of different batches of 5 fertilizers, 3 substrates, 8 insecticides, 3 fungicides, 2 herbicides, and 1 growth regulator commonly used in the cultivation of tobacco in Brazil’s Southern Region were collected from 3 warehouses located in the States of Rio Grande do Sul, Santa Catarina, and Paraná. The total As, Cd, Co, Cr, Cu, Hg, Fe, Mn, Ni, Pb, and Zn content of the samples was then determined and compared with the regulations of different countries and information found in the available literature. The fertilizers were identified as the primary source of heavy metals among the agrochemicals used. Application of pesticides directly to the shoots of tobacco plants contributed very little to the supply of heavy metals. The agrochemicals used in Brazilian tobacco fields provide lower inputs of the main heavy metals that are nonessential for plants than those registered in the international literature for the majority of crop fields in different regions of the world.     

Why are enzymes macromolecules?

The possible reasons for the macromolecular nature of enzymes are discussed. They are recognized in the necessity of creating a highly specific stereochemistry and microenvironment in the active site, in the necessity of maintaining the protein conformational rigidity, its fit with the physiological environment and overall stability, in allostery, and in the possible existence of fossil sequences, molecular tinkering, and specific hydrodynamic properties.     

The pictographic molecular paradigm

Chemistry, molecular biology and biology have turned into visive sciences in which ideas and information are communicated by artistic impressions and cartoons. These sciences have, in fact, become dominated by what we term the Pictographic molecular paradigm under which reality is acritically approximated by drawings of some kind. But it goes further than this and has both social and philosophical implications of which, we feel, there is insufficient general awareness. Important questions should be asked in connection with this way of doing science, including, for example, as to whether drawings of chemical formulae and graphical representation in biology meet the criterion of objectivity. This paper discusses some of the implications of the pictographic molecular paradigm and its limits and dangers.