~749 ~54 Fig. 10a-e. <strong>The</strong> enlarged section <strong>of</strong> a void in an organo-mineral com- plex (V; geometry <strong>and</strong> energy optimization: bonds <strong>and</strong> angles, torsions, van de Waals forces, hydrogen bridges) is shown in which atrazine is trapped <strong>and</strong> fixed via a distinct hydrogen bond <strong>and</strong> SOM is bound to the mineral matrix via hydrogen bonding in addition to <strong>three</strong> covalent bonds, a Section (Sticks, Atoms, Number) is shown with the displayed selected distances between atrazine I <strong>and</strong> II <strong>and</strong> III are as follows: Starting from C1 (i, I) (atom 1, molecule I) the dis- tances to H (256, III) are 0.7947 nm (HyperChem ® out- put 7.947477 Angstrom), to H (255, III) 1.0466 nm, to O (225, III) 0.3737 nm, O (187, III) 0.3431 nm, O (100, III) 0.8717 nm <strong>and</strong> to the hydrogens <strong>of</strong> the long aliphatic chain (see lower part <strong>of</strong> V in Fig. 9) H (1004, II) 0.6051 nm <strong>and</strong> H (1011, II) 0.8632 nm. From H (3, I) to H (950, II) a distance <strong>of</strong> 0.3074 nm, to H (996, II) <strong>of</strong> 0.2160 nm <strong>and</strong> to H (1004, II) <strong>of</strong> 0.4177 nm was measured for the lower part <strong>of</strong> the void. In the upper part, for in- stance between H (17, I) <strong>and</strong> H (902, II) 0.3074 nm, H (749, II) 0.4468 nm, H (745, II) 0.6537 nm, C (400, II) 0.7601 rim, O (577, II) 0.4885 nm were obtained. Despite the apparent proximity between H (19, I) <strong>and</strong> H (251, III) a distance <strong>of</strong> 1.1614 nm was found <strong>and</strong> clearly demon- strated the necessity <strong>of</strong> exactly calculated coordinate systems. Moreover, the distance between H (21, I) <strong>and</strong> O (606, II) was <strong>of</strong> interest, because it narrowed with progressing geometry optimization from >1rim to 0.2221 nm generating a hydrogen bond which immobi- lized the atrazine molecule in the HA void. <strong>The</strong> more the total energy content <strong>of</strong> the organo-mineral complex V is / 1 6 4 6~4 "~ 71 atoms labelled by numbers; b Section (Sticks, Atoms, Symbols) is shown with atoms labelled by element symbols; c Section (Rendering; Disks, Perspective) is shown as colour plot illustrating the space re- quirements <strong>of</strong> the pesticide <strong>and</strong> the available <strong>three</strong>-<strong>dimensional</strong> trap- ping space lowered, the more shrinking <strong>of</strong> the hollow space <strong>and</strong> con- sequently stronger bonding <strong>of</strong> the atrazine is observed. In summary, one can assume that without operator interfer- ence energy minimization simulates aging processes. <strong>The</strong> results <strong>of</strong> the <strong>three</strong>-<strong>dimensional</strong> <strong>structure</strong> <strong>and</strong> dis- tance measurements furthermore allow to evaluate the space between the trapped molecule <strong>and</strong> its host, the organo-mineral complex. In particular the space filling <strong>of</strong> trapped biological or anthropogenic <strong>substances</strong> is sup- posed to have an essential influence on their presumable fate in SOM. Clearly air (N2, O2) <strong>and</strong> water (HzO) <strong>and</strong> small organic acids (CH3COOH) can invade the gaps be- tween the pesticide <strong>and</strong> organic or inorganic <strong>soil</strong> surfaces. Thus, non-metabolic decomposition processes are easily possible at this stage. Metabolic processes, however, can be excluded as microorganisms such as bacteria (> 200 to 1000 nm) <strong>and</strong> fungi (> 10000 nm) have no access into the described voids <strong>and</strong> even enzymes are too large to react with the trapped materials when the front <strong>and</strong> back side <strong>of</strong> the void is closed by recalcitrant SOM or inorganic <strong>substances</strong>. <strong>The</strong> latter is much more likely, as the organic matter in agricultural <strong>soil</strong>s is only around 3°70. Thus, in nature the inorganic matrix represented here by the hypothetic model III should be larger by at least a factor <strong>of</strong> 30.
72 Fig. 10b \ Fig. 10c
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