Iron(I)-carbonyl clusters tethered to (trifluoromethyl)thiophenolates

Two diironhexacarbonyl clusters containing (trifluoromethyl)thiophenolates, as models for the active site of [Fe?CFe] hydrogenase enzyme, have been prepared and characterized. The crystal and electronic structures of the complexes have been probed by X-ray crystallography and spectroscopic methods. Cyclic voltammetric studies in the presence of acetic acid show that both compounds catalyze the electrochemical reduction of acetic acid to produce hydrogen with favorable overpotentials.     

Diironcarbonyl-coumarin complex: preparation, intramolecular electron transfer, and electro-generation of hydrogen

A new organometallic complex coupling photoactive coumarin to a diironhexacarbonyl unit has been successfully prepared and its composition and electronic structure confirmed by elemental and spectroscopic analyses. Emission spectral analysis of the complex reveals photoinduced intramolecular electron transfer from coumarin to the iron-carbonyl moiety. The compound is electrochemically reduced at −1.24 V vs. Fc/Fc⁺. This reduction is irreversible, attesting to the instability of the complex. Electrochemical evolution of hydrogen in the presence of the complex has been studied and results are discussed.      

Competition and interplay between σ-hole and π-hole interactions: a computational study of 1:1 and 1:2 complexes of nitryl halides (O2NX) with ammonia

Quantum calculations at the MP2/cc-pVTZ, MP2/aug-cc-pVTZ, and CCSD(T)/cc-pVTZ levels have been used to examine 1:1 and 1:2 complexes between O(2)NX (X = Cl, Br, and I) with NH(3). The interaction of the lone pair of the ammonia with the σ-hole and π-hole of O(2)NX molecules have been considered. The 1:1 complexes can easily be differentiated using the stretching frequency of the N-X bond. Thus, those complexes with σ-hole interaction show a blue shift of the N-X bond stretching whereas a red shift is observed in the complexes along the π-hole. The SAPT-DFT methodology has been used to gain insight on the source of the interaction energy. In the 1:2 complexes, the cooperative and diminutive energetic effects have been analyzed using the many-body interaction energies. The nature of the interactions has been characterized with the atoms in molecules (AIM) and natural bond orbital (NBO) methodologies. Stabilization energies of 1:1 and 1:2 complexes including the variation of the zero point vibrational energy (ΔZPVE) are in the ranges 7-26 and 14-46 kJ mol(-1), respectively.     

DNA and RNA aptamers: from tools for basic research towards therapeutic applications

The systematic evolution of ligands by exponential enrichment (SELEX) is a combinatorial oligonucleotide library-based in vitro selection approach in which DNA or RNA molecules are selected by their ability to bind their targets with high affinity and specificity, comparable to those of antibodies. Nucleic acids with high affinity for their targets have been selected against a wide variety of compounds, from small molecules, such as ATP, to membrane proteins and even whole organisms. Recently, the use of the SELEX technique was extended to isolate oligonucleotide ligands, also known as aptamers, for a wide range of proteins of importance for therapy and diagnostics, such as growth factors and cell surface antigens. The number of aptamers generated as inhibitors of various target proteins has increased following automatization of the SELEX process. Their diagnostic and therapeutic efficacy can be enhanced by introducing chemical modifications into the oligonucleotides to provide resistance against enzymatic degradation in body fluids. Several aptamers are currently being tested in preclinical and clinical trials, and aptamers are in the process of becoming a new class of therapeutic agents. Recently, the anti-VEGF aptamer pegaptanib received FDA approval for treatment of human ocular vascular disease.     

Synthesis,characterization, and crystal structure of 2′,2″-dihydroxy-3,3‴-bichalcone and its related chalcone–flavanone and biflavanone analogs

The synthesis of 3,3′-diformyl-1,1′-biphenyl 1 and its reaction in basic media with 2′-hydroxyacetophenone and paeonol, respectively, are described. The products, a bichalcone 2, it’s partially cyclized analog, a flavanone–chalcone 3 and the fully cyclized biflavanone 4, are reported as products for the first reaction, while only the chalcone 5 for the second. The crystalline and molecular structure, solved by X-ray diffraction analysis, for compounds 2 and 5 are also presented in this work.     

Enantiodifferentiation through Frequency‐Selective Pure‐Shift 1H Nuclear Magnetic Resonance Spectroscopy

A frequency‐selective 1D ¹H nuclear magnetic resonance (NMR) experiment for the fast and sensitive determination of chemical‐shift differences between overlapped resonances is proposed. The resulting fully homodecoupled ¹H NMR resonances appear as resolved 1D singlets without their typical J(HH) coupling constant multiplet structures. The high signal dispersion that is achieved is then exploited in enantiodiscrimination studies by using chiral solvating agents.     

A Computational Study on 3‐Azonia‐, 3‐Phosphonia‐, and 3‐Arsoniaspiro[2.2]pentanes and Related Three‐Membered Heterocycles

A theoretical study at the ab initio MP2/6‐311++G(d,p) level of theory is carried out to characterize several heterocyclic spiro[2.2]pentane cations with N, P, and As as spiro atoms. The strain and relative stability of the spiropentanes are obtained through isodesmic reactions. Nucleus‐independent chemical shifts (NICS) and 3D NICS isosurfaces show σ‐aromatic characteristics, similar to those found in cyclopropane. The interaction with the Cl^? anion, which results in four different stationary structures, is studied and characterized by means of the atoms in molecules methodology, and Cl ??? pnicogen, Cl ??? H, and Cl ??? C interactions are found. The most stable structure in all cases corresponds to opening of one of the three‐membered rings, due to the attack of the Cl atom, and C?Cl bond formation. Furthermore, the reaction with the 3‐boranuidaspiro[2.2]pentane anion results in the formation of a new compound through cleavage of one ring of both reactants.     

Stabilized finite element method for Navier-Stokes equations with physical boundary conditions

This paper deals with the numerical approximation of the 2D and 3D Navier-Stokes equations, satisfying nonstandard boundary conditions. This lays on the finite element discretisation of the corresponding Stokes problem, which is achieved through a three-fields stabilized mixed formulation. A priori and a posteriori error bounds are established for the nonlinear problem, ascertaining the convergence of the method. Finally, numerical tests are presented, including mesh refinement via error indicators.

     

A new method for the determination of short-chain fatty acids from the aliphatic series in wines by headspace solid-phase microextraction-gas chromatography-ion trap mass spectrometry

A new analytical method for the determination of nine short-chain fatty acids (acetic, propionic, isobutyric, butyric, isovaleric, 2-methylbutyric, hexanoic, octanoic and decanoic acids) in wines using the automated HS/SPME-GC-ITMS technique was developed and optimised. Five different SPME fibers were tested and the influence of different factors such as temperature and time of extraction, temperature and time of desorption, pH, strength ionic, tannins, anthocyans, SO(2), sugar and ethanol content were studied and optimised using model solutions. Some analytes showed matrix effect so a study of recoveries was performed. The proposed HS/SPME-GC-ITMS method, that covers the concentration range of the different analytes in wines, showed wide linear ranges, values of repeatability and reproducibility lower than 4.0% of RSD and detection limits between 3 and 257 μgL(-1), lower than the olfactory thresholds. The optimised method is a suitable technique for the quantitative analysis of short-chain fatty acids from the aliphatic series in real samples of white, rose and red wines.     

Analysis of the prediction capacity of a categorization method for urban noise assessment

A street categorization method to study urban noise was tested by comparing its results and predictive capacity with those of a reference method – the standard grid method (mentioned in the ISO 1996 standard). To this end, two independent noise surveys were carried out simultaneously in the city of Cáceres (Spain), each using one of these two methods. In a first step, the overall values of each procedure were obtained and the differences analyzed. Then, to analyze the predictive capacity of the categorization method, the two noise maps were constructed, and their predicted values (the noise levels of the squares of the grid for the grid method, and of the categories for the categorization method) were compared with the data of the other procedure used as control.It was found that the categorization method yielded similar results for the overall analysis of the city to those obtained with the value of the points of the grid method with considerably fewer sampling points.The categorization method also seems to be a more suitable predictor for new measurements, particularly for levels in the noisiest streets of the town.