The
recognition of the solvent effect on the enol–enol tautomerism
in curcumin can guide the rationalization of systems of chemical and
biological interest. Although the phenomenon is widely studied, the
nature of the proton rearrangement involving the explicit solvation
remains an important issue. In this study, we describe the phenomenon
by an ab initio approach in gas-phase and methanol
solution. The mechanism involved in the proton rearrangement has been
investigated by Car–Parrinello molecular dynamics and the static
M062X/DFT method. The free-energy landscape and potential energy surface
in the methanol environment were explored and compared with the gas-phase
one. The energy profile in methanol medium shows asymmetrical proton
distribution in the curcumin enol forms and, inversely, a symmetrical
behavior in the gas phase. The Gilli π-delocalization index
and the HOMO orbital shape show a slight decrease in the resonance-assisted
hydrogen bond (RAHB) in the solvated enol forms, different from the
gas-phase system. The thermal rate constant of the intramolecular
proton transfer indicated that the tunneling effect plays an important
role when the curcumin molecule is under the influence of methanol.
These results suggest a criterion to characterize the symmetry of
the potential energy profile for the intramolecular proton transfer.
As part of the search for sustainability in production systems, systems of annual crops intercropped with tropical forage plants have recently been used for silage production. Therefore, in the present study we aimed to evaluate the dry matter yield, fermentative parameters and nutritional value of the silage of sorghum intercropped with Paiaguas palisadegrass in different forage systems and maturity stages in a crop-livestock integration system. The experiment was conducted at the Goiano Federal Institute (Instituto Federal Goiano), Rio Verde Campus, Goiás, Brazil, in a completely randomised design with four replications in a 5 × 3 factorial arrangement with five forage systems (monocropped sorghum, monocropped Paiaguas palisadegrass, sorghum row intercropped with Paiaguas palisadegrass, sorghum inter-row intercropped with Paiaguas palisadegrass and sorghum oversown and intercropped with Paiaguas palisadegrass) and three maturity stages of the sorghum (milky, soft dough and hard dough). The results show that for all sowing methods, the silages of the intercropping systems harvested in the hard-dough stage provide a higher yield per area than did the monocropped sorghum and Paiaguas palisadegrass. The intercropping of sorghum with Paiaguas palisadegrass in crop-livestock integration systems could become an important option for the production of silage because intercropping minimises the inconveniences resulting from the fermentation process of the silage of monocropped grasses and improves the quality of the silage. These findings show this intercropping method to be advantageous strategy for the production of supplemental roughage in addition to contributing to the formation of pasture after the crops have been harvested for ensiling.
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