Synthesis and Structures of Dinuclear Aluminum Complexes Based on Bis(β-diketiminate) Ligands

A series of ten dinuclear aluminum alkyl complexes based on rigid, semirigid, and flexible bis(β-diketiminate) ligands (NacNac) has been obtained from the reaction of trimethylaluminum and the corresponding bis(β-diketimine)s. All compounds were fully characterized using NMR and IR spectroscopy and elemental analysis. The molecular structures of five compounds have been investigated by means of single-crystal X-ray diffraction analysis.     

A Semisynthetic Approach to New Immunoadjuvant Candidates: Site‐Selective Chemical Manipulation of Escherichia coli Monophosphoryl Lipid A

A semisynthetic approach to novel lipid A derivatives from Escherichia coli (E. coli) lipid A is reported. This methodology stands as an alternative to common approaches based exclusively on either total synthesis or extraction from bacterial sources. It relies upon the purification of the lipid A fraction from fed‐batch fermentation of E. coli, followed by its structural modification through tailored, site‐selective chemical reactions. In particular, modification of the lipid pattern and functionalization of the phosphate group as well as of the sole primary hydroxyl group were accomplished, highlighting the unusual reactivity of the molecule. Preliminary investigations of the immunostimulating activity of the new semisynthetic lipid A derivatives show that some of them stand out as promising, new immunoadjuvant candidates.     

Comparative study of the nature of chemical bonding of corrugated graphene on Ru(0001) and Rh(111) by electronic structure calculations

Recently, atomic resolved scanning tunneling microscopy investigations revealed that, depending on the substrate (Ni(111), Ru(0001), Ir(111), Pt(111), Rh(111)), graphene overlayer might present regular corrugation patterns, with periodically repeated units of a few nanometers. Variations of the interactions at the interface and the modulation of the local electronic properties are associated with the exact atomic arrangement of the carbon pairs with respect to the metal atoms of the substrate. Better understanding of the atomic structure and of the chemical bonding between graphene and the underlying transition metal is motivated by the fundamental scientific relevance of such systems, but it is also crucial in the perspective of possible applications. With the present work, we propose model systems for the two interfaces showing the most pronounced corrugation patterns, i.e. graphene/Ru(0001) and graphene/Rh(111). Our goal is to understand the nature of the interactions by means of electronic structure calculations based on Density Functional Theory. Our simulations qualitatively reproduce very well experimental results such as the STM topographies and the electrostatic potential maps, and quantitatively provide the closest agreement that has been published so far. The detailed analysis of the electronic structure at the interface highlights similarities and differences by changing the supporting transition metal. Our results point to a fundamental role of the hybridization between the π orbitals of graphene with the d band of the metal in determining the specific corrugation of the adsorbed monolayer. It is shown that differences in the response of the graphene electronic structure to the interaction with the metal can hinder the hybridization and lead to substantially different structures.     

The Renewed Interest on Brunogeierite,GeFe2O4, a Rare Mineral of Germanium: A Review

GeFe₂O₄, also known as brunogeierite, is a rare mineral of germanium. It has a normal spinel structure and, as with many other spinels, amazing functional properties thanks to its peculiar structural features. In the past, its spectroscopic, optical, magnetic and electronic properties were determined; then, for many years, this compound was left behind. Only recently, a renewed interest in this oxide has arisen, particularly for its application in the electrochemical field. In this review paper, the crystal structure of GeFe₂O₄ will be described, as well as the synthesis methods required to obtain single crystals or polycrystalline powders. Its spectroscopic, magnetic, optical and electrical properties will be reported in detail. Then, successful applications known so far will be described: its use as anode in Lithium Ion and Sodium Ion Batteries and as electrocatalyst for urea oxidation reaction.     

Treatment of High-Polyphenol-Content Waters Using Biotechnological Approaches: The Latest Update

Polyphenols and their intermediate metabolites are natural compounds that are spread worldwide. Polyphenols are antioxidant agents beneficial for human health, but exposure to some of these compounds can be harmful to humans and the environment. A number of industries produce and discharge polyphenols in water effluents. These emissions pose serious environmental issues, causing the pollution of surface or groundwater (which are used to provide drinking water) or harming wildlife in the receiving ecosystems. The treatment of high-polyphenol-content waters is mandatory for many industries. Nowadays, biotechnological approaches are gaining relevance for their low footprint, high efficiency, low cost, and versatility in pollutant removal. Biotreatments exploit the diversity of microbial metabolisms in relation to the different characteristics of the polluted water, modifying the design and the operational conditions of the technologies. Microbial metabolic features have been used for full or partial polyphenol degradation since several decades ago. Nowadays, the comprehensive use of biotreatments combined with physical-chemical treatments has enhanced the removal rates to provide safe and high-quality effluents. In this review, the evolution of the biotechnological processes for treating high-polyphenol-content water is described. A particular emphasis is given to providing a general concept, indicating which bioprocess might be adopted considering the water composition and the economic/environmental requirements. The use of effective technologies for environmental phenol removal could help in reducing/avoiding the detrimental effects of these chemicals. In addition, some of them could be employed for the recovery of beneficial ones.     

Obtaining new flavanones exhibiting antifungal activities by methyltrioxorhenium-catalyzed epoxidation-methanolysis of flavones

New 3-hydroxy-2-methoxyflavanones have been obtained through epoxidation-methanolysis of the corresponding flavone with urea-hydrogen peroxide (UHP)/methyltrioxorhenium (CH₃ReO₃, MTO) catalytic system in methanol as nucleophilic solvent. After acetylation of the reaction mixtures, the corresponding cis- and trans-3-acetoxy-2-methoxyflavanones have been isolated and characterized by spectroscopic analyses. Their antifungal activity has been tested in vitro against three fungal strains of common saprotrophic soil and seed fungi, such as Trichoderma koningii, Fusarium solani and Cladosporium herbarum, potentially pathogenic for humans. Some aspects of the structure-activity relationship of the most active compounds have been evaluated. The mycelial growth of T. koningii and C. herbarum has been totally inhibited from cis-3-acetoxy-2,6-dimethoxyflavanone 7c and cis-3-acetoxy-2,7-dimethoxyflavanone 13c at the lowest concentration (0.5×10⁻⁴ M).     

Mechanism of indium(III) exchange between NTA and transferrin: a kinetic approach

The equilibria and kinetics for the process of In(3+) exchange between nitrilotriacetic acid (NTA) and bovine serum transferrin (T) have been investigated in aqueous solution containing sodium bicarbonate. The metal exchange equilibria have been measured by difference ultraviolet spectroscopy at 25 degrees C, pH=7.4, and I=0.2 M (NaClO4). The acid dissociation constants of NTA and the binding constants of In(III) to NTA have also been measured. Kinetic experiments revealed that the process of In(3+) uptake by transferrin from [In(NTA)2](3-) is biphasic, the fast phase being completed in a few seconds, the slow phase lasting for hours. The fast phase has been investigated by the stopped-flow method and results in monoexponential kinetics. It involves rapid interaction of the 1:1 complex ML (M=In, L=NTA) with TB (T=transferrin, B=CO3(2-)) to give a quaternary intermediate MLTB which then evolves to an "open" MTB* ternary complex complex with expulsion of L. In turn, this complex interconverts to a "closed", more stable, form MTB. Neither the prevailing complex M2L nor the TB2 form of transferrin are directly involved in the exchange process but act as metal and protein reservoirs. The pH dependence of the reaction has been also investigated. The slow phase has not been investigated in detail; it takes several hours to go to the completeness, its slowness being ascribed to metal redistribution between the C-site and N-site of the protein, and/or metal release from polynuclear In(III) species.     

Thermodynamics and kinetics of the nickel(II)-salicylhydroxamic acid system. Phenol rotation induced by metal ion binding

The kinetics and the equilibria of Ni(II) binding to p-hydroxybenzohydroxamic acid (PHBHA) and salicylhydroxamic acid (SHA) have been investigated in an aqueous solution at 25 degrees C and I=0.2 M by the stopped-flow method. Two reaction paths involving metal binding to the neutral acid and to its anion have been observed. Concerning PHBHA, the rate constants of the forward and reverse steps are k1=(1.9+/-0.1)x10(3) M-1 s-1 and k-1=(1.1+/-0.1)x10(2) s-1 for the step involving the undissociated PHBHA and k2=(3.2+/-0.2)x10(4) M-1 s-1 and k-2=1.2+/-0.2 s-1 for the step involving the anion. Concerning SHA, the analogous rate constants are k1=(2.6+/-0.1)x10(3) M-1 s-1, k-1=(1.3+/-0.1)x10(3) s-1, k2=(5.4+/-0.2)x10(3) M-1 s-1, and k-2=6.3+/-0.5 s-1. These values indicate that metal binding to the anions of the two acids concurs with the Eigen-Wilkins mechanism and that the phenol oxygen is not involved in the chelation. Moreover, a slow effect was observed in the SHA-Ni(II) system, which has been put down to rotation of the benzene ring around the C-C bond. Quantum mechanical calculations at the B3LYP/lanL2DZ level reveal that the phenol group in the most stable form of the Ni(II) chelate is in trans position relative to the carbonyl oxygen, contrary to the free SHA structure, where the phenol and carbonyl oxygen atoms both have cis configuration. These results bear out the idea that the complex formation is coupled with phenol rotation around the C-C bond.