Rational design, synthesis, and application of a new receptor for the molecular recognition of tricarboxylate salts in aqueous media

A rational design of a tripodal receptor for the molecular recognition of tricarboxylate salts in aqueous media, based on squaramide, has been performed using high-level DFT calculations (RI-BP86/SVP level of theory) in solution using the COSMO treatment, including some preliminary ab initio calculations at the higher RI-MP2/TZVP level of theory, comparing the ability of squaramide to bind carboxylate salts with two widely used guanidinium salts. The tripodal receptor has been synthesized using a new methodology that has been recently reported by some of us, and its capability of recognizing several mono-, di-, and tricarboxylate salts has been studied experimentally by means of microcalorimetry experiments in a very high competitive media, H(2)O:EtOH 1:3. These experiments give enthalpic and entropic data, which are unfortunately scarce in the literature of molecular recognition of anions. Finally, a fluorimetric ensemble of the receptor with fluorescein has been found to be useful for the fluorimetric determination of zinc citrate in a commercial toothpaste using competition assays.     

Symmetry measures of the electron density

In this communication we define electronic symmetry operation and symmetry group measures, eSOM and eSGM, respectively, develop the basic algorithms to obtain them, and give some examples of the possible applications of these new computational tools. These new symmetry measures based on the electron density have been tested in an analysis of (a) the inversion symmetry for heteronuclear diatomic molecules, for the eclipsed and staggered conformations of ethane and tetrafluoroethane, and for a series of octahedral sulfur halides; (b) the reflection symmetry of three different conformers of tetrafluoroethene; and (c) the loss of C₆ symmetry along the B_2u distortion mode of benzene and an analysis of rotational symmetry for different six‐member ring heterocycles. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Ab initio study of [n.n]paracyclophane (n = 2, 3) complexes with cations: unprecedented through-space substituent effects

Several cation-pi complexes between substituted [n.n]paracyclophanes (n = 2, 3) and cations have been studied using high level ab initio calculations. The chemical substitution at the aromatic ring that is not interacting with the cation has a strong influence upon the binding energy. This strong through-space substituent effect has been studied using the "atoms-in-molecules" theory, which has been found useful to explain the energetic results.     

Expedient Synthesis of C‐Aryl Carbohydrates by Consecutive Biocatalytic Benzoin and Aldol Reactions

The introduction of aromatic residues connected by a C?C bond into the non‐reducing end of carbohydrates is highly significant for the development of innovative structures with improved binding affinity and selectivity (e.g., C?aril‐sLex). In this work, an expedient asymmetric “de novo” synthetic route to new aryl carbohydrate derivatives based on two sequential stereoselectively biocatalytic carboligation reactions is presented. First, the benzoin reaction of aromatic aldehydes to dimethoxyacetaldehyde is conducted, catalyzed by benzaldehyde lyase from Pseudomonas fluorescens biovar I. Then, the α‐hydroxyketones formed are reduced by using NaBH₄ yielding the anti diol. After acetal hydrolysis, the aldol addition of dihydroxyacetone, hydroxyacetone, or glycolaldehyde catalyzed by the stereocomplementary D ‐fructose‐6‐phosphate aldolase and L ‐rhamnulose‐1‐phosphate aldolase is performed. Both aldolases accept unphosphorylated donor substrates, avoiding the need of handling the phosphate group that the dihydroxyacetone phosphate‐dependent aldolases require. In this way, 6‐C‐aryl‐L ‐sorbose, 6‐C‐aryl–L ‐fructose, 6‐C‐aryl–L ‐tagatose, and 5‐C‐aryl‐L ‐xylose derivatives are prepared by using this methodology.     

The effect of a semi‐industrial masterbatch process on the carbon nanotube agglomerates and its influence in the properties of thermoplastic carbon nanotube composites

This study details an industrial process to prepare polypropylene (PP) composites reinforced with different loadings (0.5–10wt.%) of carbon nanotubes (CNTs) from a direct dilution of a masterbatch produced by an optimized extrusion compounding process. The work demonstrates how the anisotropy in the distribution of CNTs can have a positive effect on the electrical conductivity and fracture toughness of the resulting composites. The composite with the highest loading of CNTs had an electrical conductivity of 10^?2 S/m comparable with those reported in the available literature. The composites showed anisotropy in their properties that seems to be caused by the non‐homogeneous distribution of the agglomerates produced by the orientation of the flow direction during the injection process. The composites produced in this work exhibited a fracture toughness up to 55% higher than neat PP and failed by polymer ductile tearing. It was found that the CNT agglomerates distributed throughout the matrix increased the toughness of PP by promoting plastic deformation of the matrix during the fracture process and by a slight load transfer between the polymer matrix and the CNTs of the agglomerates. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 189–197     

Molecular features of thymidine analogues governing the activity of human thymidine kinase

Modified uridines seem to be able to work as hypoxic tumour cell radiosensitisers. Before they sensitise cells to ionising radiation, they have to be incorporated into the genomic DNA and the latter process has to be preceded by the phosphorylation of the modified uridine, which in human cells is executed by human thymidine kinase 1 (hTK1). In the current study, we present the quantitative structure-activity relationship (QSAR) model allowing to identify and understand the molecular features of nucleoside derivatives governing the hTK1 kinase activity. The developed model meets all requirements of a reliable QSAR model and is based on only two molecular properties: the shape of the nucleoside determined by atom substitutions and the ability of the molecule to intermolecular interactions with the enzyme. These results have important implications for the rational designing of new hTK1 substrates and should significantly reduce the time and cost of studies on new radiosensitisers.     

An extension of flanders theorem to several matrices

The Flanders Theorem relates the matrices AB and BA and provides a necessary and sufficient condition for the consistency of the matrix system P = AB Q = BA In this paper, we generalize the Flanders condition for several matrices.     

Key role of the hemicellulose content and the cell morphology on the nanofibrillation effectiveness of cellulose pulps

The effect of the hemicellulose content and that of the fibre morphology on the nanofibrillation behaviour of delignified cellulose pulps were studied. For this purpose, pulps from two non-woody plants, alfa (Stipa tenacissima) and sunflower (Helianthus annuus), were delignified using NaClO₂/acetic acid and the NaOH pulping processes to obtain fibres with different hemicellulose contents. The ensuing fibres were characterized by chemical analysis, SEM, FTIRS and X-ray diffraction. The fibres were then disintegrated into nanofibrillated cellulose (NFC) using either a high pressure homogenizer or a domestic blender. The degree of fibrillation and the morphology of the nanofibrillated fractions were evaluated by centrifugation and Field-emission scanning electron microscopy. Pulps containing the highest hemicellulose content showed higher yields of the nanofibrillated fraction and a better aptitude for the individualization of the microfibrils. Furthermore, it was shown that fibres from sunflowers exhibiting a thinner cell wall were easier to fibrillate and could be disintegrated into NFC by just using a simple domestic-blender once deliginification process was carried out using the NaClO₂/acetic acid method. Eucalyptus fibres were also used to further confirm the key role of hemicelluloses in the nanofibrillation process of woody plants.     

Pseudosymmetry analysis of molecular orbitals

We introduce a pseudosymmetry analysis of molecular orbitals by means of the newly proposed irreducible representation measures. To do that we define first what we consider as molecular pseudosymmetry and the relationships of this concept with those of approximate symmetry and quasisymmetry. We develop a general algorithm to quantify the pseudosymmetry content of a given object within the framework of the finite group algebra. The obtained mathematical expressions are able to decompose molecular orbitals by means of the irreducible representations of any reference symmetry point group. The implementation and usefulness of the pseudosymmetry analysis of molecular orbitals is demonstrated in the study of σ and π orbitals in planar and nonplanar polycyclic aromatic hydrocarbons and the t_2g and e_g character of the d‐orbitals in the [FeH₆]^3? anion in its high spin state along the Bailar twist pathway. © 2013 Wiley Periodicals, Inc.