Allelopathy, a phenomenon where compounds produced by one plant limit the growth of surrounding plants, is a controversially discussed factor in plant-plant interactions with great significance for plant community structure. Common mycorrhizal networks (CMNs) form belowground networks that interconnect multiple plant species; yet these networks are typically ignored in studies of allelopathy. We tested the hypothesis that CMNs facilitate transport of allelochemicals from supplier to target plants, thereby affecting allelopathic interactions. We analyzed accumulation of a model allelopathic substance, the herbicide imazamox, and two allelopathic thiophenes released from Tagetes tenuifolia roots, by diffusion through soil and CMNs. We also conducted bioassays to determine how the accumulated substances affected plant growth. All compounds accumulated to greater levels in target soils with CMNs as opposed to soils without CMNs. This increased accumulation was associated with reduced growth of target plants in soils with CMNs. Our results show that CMNs support transfer of allelochemicals from supplier to target plants and thus lead to allelochemical accumulation at levels that could not be reached by diffusion through soil alone. We conclude that CMNs expand the bioactive zones of allelochemicals in natural environments, with significant implications for interspecies chemical interactions in plant communities.
A new characterization of atoms in molecules is introduced as the electrotopological state index, which combines both the electronic character and the topological environment of each skeletal atom in a molecule. The electrotopological state (Estate) of a skeletal atom is formulated as an intrinsic value Ii plus a perturbation term A&, arising from the electronic interaction within the molecular topological environment of each atom in the molecule. The atom intrinsic value, for first row atoms, is expressed as I = (6' + 1)6, in which 6' and 6 are the counts of valence and sigma electrons, respectively, for the atom in the molecular skeleton. The E-state, Si, for atom i is defined as Si = Ij + "Ij, where the influence of other atoms on atom i, AIi, is given as C(Ij -Ij)/ri:; rij is the graph separation between atoms i and j, counted as number of atoms, including i and j. Information in the electrotopological state is revealed by examples of various types of organic structures, including skeletal branching and heteroatom variation. The relation of the E-state value to NMR chemical shift is demonstrated for a series of car-bony1 compounds. QSAR examples are given for hydrazide inhibition of M A 0 and for receptor binding of P-carbolines. These examples reveal the power of this approach to QSAR using atom level indexes, computed directly from molecule connection tables, in which it is possible to identify atoms and regions in the molecule which are important for activity.
QSAR models for inhibition of monoamine oxidase (MAO) by aryloxyacetohydrazide derivatives were developed for a series of MO parameters computed with the AM1 Hamiltonian. These models were compared to those based on the recently developed electrotopological state index for. skeletal atoms. The structure interpretation is the same for both types of models: the NH group adjacent to the carbonyl group together with the carbon atom, gamma to the NH group, in the hydrocarbon substituent, account for more than 90% of the computed activity. However, the model based on E‐state indexes (r2 = 0.9012) is significantly superior to the one based on MO parameters (r2 = 0.7985); the standard deviation for the MO based model (s = 0.27) is 50% larger than that from the E‐state based model (r = 0.19). Several points of comparison between the models are presented. This study supports the idea that the electrotopological state is a useful representation of molecular structure information.
The picosecond time-resolved infrared spectra of (CN)5FeCNRu(NH3)5
- were collected following optical
excitation and reverse electron transfer. The measured reverse electron transfer rates are greater than 3 ×
1012 s-1. In both formamide and deuterated water solutions, vibrational excitation in CN stretch modes is
found after reverse electron transfer. The transient spectra at both earlier (1−35 ps) and later (10 ns) times
give evidence of environment−solute coupling that can be accounted for by solvent heating and ion pair
dynamics. A simulation of the spectral dynamics in formamide solution is presented using a kinetic model
for vibrational excitation and relaxation. The simulation includes minor excitation in vibrational modes
consistent with resonance Raman derived Franck−Condon factors, but it is also found that a nontotally
symmetric mode is equally important as an acceptor.
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