Seedlings of zea mays l. (poaceae) and pterogyne nitens tul. (fabaceae): Morphoanatomic and terminological considerations / Plântulas de zea mays l. (poaceae) e pterogyne nitens tul. (fabaceae): Considerações morfoanatômicas e terminológicas

Seedlings of Zea mays L. (maize), Poaceae, and Pterogyne nitens Tul. (wild peanut), Leguminosae, are described morphologically and anatomically in order to characterize the species, but particularly to disseminate the terminology about the seedling, which is little known by non-specialist researchers and undergraduate students. Seedlings were obtained in the laboratory, using Petri dishes. Seedling was considered as the initial plant development phase, which comprises the period from germination to formation of the eophyll. Zea mays seedling is hypogeal and cryptocotyledonous, and it consists of coleorhiza, considered the primary root, endogenous embryonic root, commonly considered in the literature as radicle, reduced hypocotyl, and coleoptile, considered here as eophyll. The second seedling leaf of Z. mays is made up of uniseriate epidermis and homogeneous mesophyll. Pterogyne nitens exhibits epigeal and phanerocotyledonous seedling, and consists of primary root, long hypocotyl, two cotyledons, epicotyl, and opposite eophylls difoliolated or trifoliolated. The hypocotyl has root/shoot transition structure and the eophylls are dorsiventral consisting of one cell layer palisade parenchyma and pluriseriate spongy parenchyma. Seedlings of both species show significant morphological and anatomical differences and specific terminology, especially that of Z. mays.

The Grotthuss mechanism for bifunctional proton transfer in poly(benzimidazole)

Poly(benzimidazole) (PBI) has received considerable attention as an effective high-temperature polymer electrolyte membrane for fuel cells. In this work, the Grotthuss mechanism for bifunctional proton transfer in PBI membranes was studied using density functional theory and transition state theory. This study focused on the reaction paths and kinetics for bifunctional proton transfer scenarios in neutral ([PBI] 2 ), single (H + [PBI] 2 ) and double-protonated (H 2+ [PBI] 2 ) dimers. The theoretical results showed that the energy barriers and strength for H-bonds are sensitive to the local dielectric environment. For [PBI] 2 with ε = 1, the uphill potential energy curve is attributed to extraordinarily strong ion-pair H-bonds in the transition structure, regarded as a ‘dipolar energy trap’. For ε = 23, the ion-pair charges are partially neutralized, leading to a reduction in the electrostatic attraction in the transition structure. The dipolar energy trap appears to prohibit interconversion between the precursor, transition and proton-transferred structures, which rules out the possibility for [PBI] 2 to be involved in the Grotthuss mechanism. For H + [PBI] 2 and H 2+ [PBI] 2 with ε = 1, the interconversion involves a low energy barrier, and the increase in the energy barrier for ε = 23 can be attributed to an increase in the strength of the protonated H-bonds in the transition structure: the local dielectric environment enhances the donor–acceptor interaction of the protonated H-bonds. Analysis of the rate constants confirmed that the quantum effect is not negligible for the N–H + … N H-bond especially at low temperatures. Agreement between the theoretical and experimental data leads to the conclusion that the concerted bifunctional proton transfer in H 2+ [PBI] 2 in a high local dielectric environment is ‘the rate-determining scenario’. Therefore, a low local dielectric environment can be one of the required conditions for effective proton conduction in acid-doped PBI membranes. These theoretical results provide insights into the Grotthuss mechanism, which can be used as guidelines for understanding the fundamentals of proton transfers in other bifunctional H-bond systems.

Can Aromaticity of Fused Aromatic Ring in 1,3-Pentadiene Modulate its Reactivity towards [1,5]-Halo Shift? - A DFT Study

In (Z)-1,3-pentadienes, [1,5]-H migration is suprafacially allowed while fluorine shift in this system takes place by a Contra Hoffmann antarafacial pathway for which aromaticity is the driving force. If aromaticity of the transition structure (TS) can drive a reaction towards a disallowed pathway as found in the case of fluorine, the role of aromatic ring annealed to (Z)-1,3-pentadienes in determining the reaction pathway and barrier is worth noting. Hence, the combined role of aromaticity of transition state and the loss in aromaticity of the annealed ring has been explored during the [1,5]-X (X = H, F, Cl, Br) shifts in aromatic (benzene/naphthalene) annealed 1,3-pentadiene system. Notable correlations between various aromaticity index NICS(0,1) with activation barriers show that aromaticity of transition structure in pericyclic reaction can drive the stereochemical course of a reaction. The distinct effect of fluorine to other halogens is the antara migration while the other halogens (Cl & Br) prefer supramode.