The Effect of Copper Salts on Bioactive Compounds and Ultrastructure of Wheat Plants

Abiotic stress agents, among them metal stress, can cause oxidative damage to plant cells. In defense, plants can increase the production of secondary metabolites in order to mitigate the harmful effects caused by them. The purpose of this work was to evaluate the effect of two types of copper salts (CuSO₄ and Cu(NO₃)₂), added in two different amounts in soil (150 mg/kg, respectively 300 mg/kg), on assimilating pigments, total polyphenols, antioxidant activity and the elemental composition of wheat. The obtained results were compared with those from control plants grown in the same conditions but without copper salts. The amount of assimilating pigments, total polyphenols, and antioxidant activity respectively increases or decreases in the plants treated with copper salts compared to the control depending on the stage of development of the plant. No significant damage induced in the leaves of the wheat plants treated with the selected salts was observed following the TEM analysis. In six-week-old plants it was observed by EDX analysis that the salts are transformed into nanoparticles. The bioactive compounds, elemental composition and their interaction is influenced by concentration of metal’s salt, type of salt and exposure period.     

Complexes between H2 and neutral oxyacid beryllium derivatives. The role of angular strain

ABSTRACT

The complexes between 14 different Be-salts of oxyacids from groups 13 to 16 with one and two molecules of H₂ have been investigated by means of the MP2/aug-cc-pVTZ ab initio molecular orbital theory method, which was found to be reliable for the treatment of these weakly bound species. The main conclusion is that these Be-salts yield rather stable complexes with dihydrogen, with binding energies one order of magnitude larger than other typical H₂ complexes reported in the literature. This strong binding is shown to be due to an enhancement of the electron-deficient nature of Be when attached to an oxyacid moiety, which depends more on the type of coordination of the central atom of the oxyacid moiety. The formation of these complexes is followed by a significant lengthening of the H₂ internuclear distance and a concomitant red-shift of the H–H stretching frequency, which becomes a good indicator of the strength of the interaction. The charge shifting from the bonding region of the H₂ molecule to the interboundary Be···H₂ region is the physical phenomenon behind the stability of these complexes. Accordingly, the most important contributor to this stability is the inductive term, followed by the electrostatic interactions. The ability of Be to bind H₂ is enhanced by the angular arrangement of the O–Be–O electron-acceptor group.     

New Insights into Factors Influencing B?N Bonding in X:BH3−nFn and X:BH3−nCln for X=N2, HCN,LiCN, H2CNH,NF3, NH3 and n=0–3: The Importance of Deformation

Understanding the bonding in complexes X:BH_3?nF_n and X:BH_3?nCl_n, for X=N₂, HCN, LiCN, H₂CNH, NF₃, NH₃ with n=0–3, is a challenging task. The trends in calculated binding energies cannot be explained in terms of any of the usual indexes, including π donation from the halogen lone pairs to the p(π) empty orbital on B, deformation energies, charge capacities, or LUMO energies, which are normally invoked to explain the higher Lewis acidity of BCl₃ relative to BF₃. The results of the high‐level G3B3 ab initio calculations reported in this study suggest that the interaction energies of these complexes are determined by a combination of at least three factors. These include the decrease in the electron‐accepting ability of B as a result of π donation by the halogen atom, the increase in the electron‐acceptor capacity of B due to deformation of the acid, and the large increase in the deformation energy of the acid with increasing halogen substitution. The dominant effects are those derived from the electronic effects of acid deformation. Deformation not only has direct energetic consequences, which are reflected in the large differences between dissociation (D₀) and interaction (E_int) energies, but also leads to an enhancement of the intrinsic acidities of BH_3?nF_n and BH_3?nCl_n moieties by lowering the LUMO energies to very different extents, consistent with the frontier orbital model of chemical reactivity. Although this lowering depends on both the number and the nature of the halogen substituents, binding energies do not systematically increase or decrease as the number of halogen atoms increases.     

Playing with PtII and ZnII Coordination to Obtain Luminescent Metallomesogens

Blue–green luminescent terpyridine-containing Pt^II and Zn^II complexes are reported. Equipped with lipophilic gallate units, which act as monodentate ancillary coordinating ligands and/or as anions, they display low-temperature mesomorphic properties (lamello-columnar and hexagonal mesophases for Pt^II and Zn^II complexes, respectively). The mesomorphic properties were investigated by polarised optical microscopy, differential scanning calorimetry, thermogravimetric analysis and X-ray scattering of bulk materials and oriented thin films. The model of self-assembly into the lamello-columnar phase of the Pt^II complex has been described in detail. The optical properties of the complexes were investigated in the liquid and condensed liquid crystalline states, highlighting the delicate balance between the role of the metal in determining the type of excited state responsible for the emission, and the role of the ancillary ligand in driving intermolecular interactions for proper mesophase formation.     

Revealing Unexpected Mechanisms for Nucleophilic Attack on S?S and Se?Se Bridges

The reactivity of disulfide and diselenide derivatives towards F^? and CN^? nucleophiles has been investigated by means of B3PW91/6‐311+G(2df,p) calculations. This theoretical survey shows that these processes, in contrast with the generally accepted view of disulfide and diselenide linkages, do not always lead to S? S or Se? Se bond cleavage. In fact, S? S or Se? Se bond fission is the most favorable process only when the substituents attached to the S or the Se atoms are not very electronegative. Highly electronegative substituents (X) strongly favor S? X bond fission. This significant difference in the observed reactivity patterns is directly related to the change in the nature of the LUMO orbital of the disulfide or diselenide derivative as the electronegativity of the substituents increases. For weakly electronegative substituents, the LUMO is a σ‐type S? S (or Se? Se) antibonding orbital, but as the electronegativity of the substituents increases the π‐type S? X antibonding orbital stabilizes and becomes the LUMO. The observed reactivity also changes with the nature of the nucleophile and with the S or Se atom that undergoes the nucleophilic attack in asymmetric disulfides and diselenides. The activation strain model provides interesting insights into these processes. There are significant similarities between the reactivity of disulfides and diselenides, although some dissimilarities are also observed, usually related to the different interaction energies between the fragments produced in the fragmentation process.     

Are Boryl Radicals from Amine–Boranes and Phosphine–Boranes the Most Stable Radicals?

The relative stability of the radicals that can be produced from amine–boranes and phosphine–boranes is investigated at the G3‐RAD level of theory. Aminyl ([RNH]^.:BH₃) and phosphinyl ([RPH]^.:BH₃) radicals are systematically more stable than the boryl analogues, [RNH₂]:BH₂^. and [RPH₂]:BH₂^.. Despite similar stability trends for [RNH]^.:BH₃ and [RPH]^.:BH₃ radicals with respect to boryl radicals, there are significant dissimilarities between amine– and phosphine–boranes. The homolytic bond dissociation energy of the N?H bond decreases upon association of the amines with BH₃, whereas that of the P?H bond for phosphines increases. The stabilization of the free amine is much smaller than that of the corresponding aminyl radical, whereas for phosphines this is the other way around. The homolytic bond dissociation energy of the B?H bond of borane decreases upon complexation with both amines and phosphines.     

Spontaneous H2 Loss through the Interaction of Squaric Acid Derivatives and BeH2

The most stable complexes between squaric acid and its sulfur‐ and selenium‐containing analogues (C₄X₄H₂; X=O, S, Se) with BeY₂ (Y=H, F) were studied by means of the Gaussian 04 (G4) composite ab initio theory. Squaric acid derivatives are predicted to be very strong acids in the gas phase; their acidity increases with the size of the chalcogen, with C₄Se₄H₂ being the strongest acid of the series and stronger than sulfuric acid. The relative stability of the C₄X₄H₂ ? BeY₂ (X=O, S, Se; Y=H, F) complexes changes with the nature of the chalcogen atom; but more importantly, the formation of the C₄X₄H₂ ? BeF₂ complexes results in a substantial acidity enhancement of the squaric moiety owing to the dramatic electron‐density redistribution undergone by the system when the beryllium bond is formed. The most significant consequence of this acidity enhancement is that when BeF₂ is replaced by BeH₂, a spontaneous exergonic loss of H₂ is observed regardless of the nature of the chalcogen atom. This is another clear piece of evidence of the important role that closed‐shell interactions play in the modulation of physicochemical properties of the Lewis acid and/or the Lewis base.     

Ni(+) reactions with aminoacetonitrile, a potential prebiological precursor of glycine

The gas-phase reactions between Ni(+) ((2)D(5/2)) and aminoacetonitrile, a molecule of prebiological interest as possible precursor of glycine, have been investigated by means of mass spectrometry techniques. The mass-analyzed ion kinetic energy (MIKE) spectrum reveals that the adduct ions [NC--CH(2)--NH(2), Ni(+)] spontaneously decompose by loosing HCN, H(2), and H(2)CNH, the loss of hydrogen cyanide being clearly dominant. The structures and bonding characteristics of the aminoacetonitrile-Ni(+) complexes as well as the different stationary points of the corresponding potential energy surface (PES) have been theoretically studied by density functional theory (DFT) calculations carried out at B3LYP/6-311G(d,p) level. A cyclic intermediate, in which Ni(+) is bisligated to the cyano and the amino group, plays an important role in the unimolecular reactivity of these ions, because it is the precursor for the observed losses of HCN and H(2)CNH. In all mechanisms associated with the loss of H(2), the metal acts as hydrogen carrier favoring the formation of the H(2) molecule. The estimated bond dissociation energy of aminoacetonitrile-Ni(+) complexes (291 kJ mol(-1)) is larger than those measured for other nitrogen bases such as pyridine or pyrimidine and only slightly smaller than that of adenine.