Multifaceted roles of silicon nano particles in heavy metals-stressed plants.

Heavy metal (HM) contamination has emerged as one of the most damaging abiotic stress factors due to their prominent release into the environment through industrialization and urbanization worldwide. The increase in HMs concentration in soil and the environment has invited attention of researchers/environmentalists to minimize its' impact by practicing different techniques such as application of phytohormones, gaseous molecules, metalloids, and essential nutrients etc. Silicon (Si) although not considered as the essential nutrient, has received more attention in the last few decades due to its involvement in the amelioration of wide range of abiotic stress factors. Silicon is the second most abundant element after oxygen on earth, but is relatively lesser available for plants as it is taken up in the form of mono-silicic acid, Si(OH)4. The scattered information on the influence of Si on plant development and abiotic stress adaptation has been published. Moreover, the use of nanoparticles for maintenance of plant functions under limited environmental conditions has gained momentum. The current review, therefore, summarizes the updated information on Si nanoparticles (SiNPs) synthesis, characterization, uptake and transport mechanism, and their effect on plant growth and development, physiological and biochemical processes and molecular mechanisms. The regulatory connect between SiNPs and phytohormones signaling in counteracting the negative impacts of HMs stress has also been discussed.

Exogenously-applied L-glutamic acid protects photosynthetic functions and enhances arsenic tolerance through increased nitrogen assimilation and antioxidant capacity in rice (Oryza sativa L.).

L-Glutamic acid (Glu) is used as an effective bio-stimulant to reduce arsenic (As) stress in plants. The role of Glu was studied in the protection of photosynthesis and growth of rice (Oryza sativa L. Japonica Type Taipie-309) plants grown with 50 µM As stress by studying the oxidative stress, photosynthetic and growth characteristics. Among the Glu concentrations (0, 2.5, 5 and 10 µM), 10 µM Glu maximally enhanced photosynthesis and growth parameters with the least cellular oxidative stress level. The supplementation of 10 µM Glu resulted in the reduced effects of As stress on gas exchange parameters, PSII activity and growth attributes through enhancement of antioxidant and proline metabolism. The enzymes of nitrogen (N) assimilation, such as nitrate reductase, nitrite reductase, glutamine synthetase and glutamate synthase were increased with Glu treatment under As stress. The Glu-induced metabolite synthesis showed the role of various metabolites in As stress responses. The role of Glu as a signalling molecule in reducing the adverse effects of As through accelerating the antioxidant enzymes, PSII activity, proline metabolism and nitrogen assimilation has been discussed.

Lead displacement due to tension pneumothorax following permanent pacemaker implantation.

A 62-year-old female, who had undergone dual chamber pacemaker implantation through left subclavian approach, developed tension pneumothorax of left side. This resulted in shift of entire mediastinum and lead displacement with altered lead parameters. Pacemaker implantation can be complicated by tension pneumothorax in 0.6-5% of cases. Tension pneumothorax can cause mediastinal shift and rarely cause displacement of the leads. In our patient, shift of mediastinum with change of loops and position was associated with change of parameters requiring lead revision. .

Early excited state dynamics of 6-styryl-substituted pyrylium salts exhibiting dual fluorescence.

A series of 6-styryl-2,4-diphenylpyrylium salts exhibiting dual fluorescence has been investigated by fluorescence up-conversion in conjunction with quantum chemical calculations. The short-wavelength emission is due to an excited state localized on the pyrylium fragment and the long-wavelength emission arises from a charge-transfer state delocalized over the whole molecule. The two fluorescing states do not exhibit a precursor-successor relationship. The rise time of the short-wavelength fluorescence is smaller than 200 fs, and that of the long-wavelength emission depends on the electron-donating property of the styryl group substituent. The rise is almost prompt with the weaker donors but is slower, wavelength and viscosity dependent with the strongest electron-donating group. A model involving a S(2)/S(1) conical intersection is proposed to account for these observations.

Quantifying Aromaticity at the Molecular and Supramolecular Limits: Comparing Homonuclear, Heteronuclear, and H-Bonded Systems.

The aromatic/antiaromatic characteristics of B-N and P-N analogues of benzene and cyclobutadiene have been studied using quantum chemical methods. We use established parameters such as nucleus-independent chemical shifts, charge density at the ring critical point, and stabilization energies to quantify the nature of interactions in these molecular systems. B3N3H6 and N3P3F6 resemble benzene in being aromatic, albeit to a lesser extent, while B2N2H4 and N2P2F4 are found to be aromatic, opposite to that for cyclobutadiene. A σ-π separation analysis has been performed to critically examine the contributions from the π electrons compared to that from the σ backbone. The structural aspects in the weak interaction limits such as the H-bonded cyclic trimers of HX (X = F, Cl, and Br) have also been investigated. Even in such weak interaction limits, these cyclic systems are found to be substantially stable. These H-bonded systems exhibit nonlocal polarizations across the full-perimeter of the ring that lead to aromaticity. We propose the term "H-bonded aromaticity" for such closed-loop weakly delocalized systems. This new formalism of aromaticity has the potential to explain structures and properties in supramolecular systems.