Staircase Connected Sets

A compact set is staircase connected if every two points can be connected by a polygonal path with sides parallel to the coordinate axes, which is both x-monotone and y-monotone. denotes the smallest number of edges of such a path. is an integer-valued metric on S. We investigate this metric and introduce stars and kernels. Our main result is that the r-th kernel is nonempty, compact and staircase connected provided .     

Parallel synthesis and yeast growth inhibition screening of succinamic acid libraries

Libraries of succinamic acid derivatives resulting from the condensation of a series of succinic acid derivatives with amines are reported as putative khafrefungin analogues. A total of 480 compounds derived from the initial condensation of 8 scaffolds with 60 different amines have been synthesized using automated technology with the help of scavenger resins. A simple acetate hydrolysis of five of the above sublibraries afforded additional 300 compounds for a total of 780 compounds. Around 55% of the library members showed purities higher than 70% (HPLC-ELS-MS) thus proving the generality of this approach. Results on growth inhibition of the yeast Saccharomyces cerevisiae in the presence of selected library members are also reported as a preliminary evaluation of the antifungal activity.     

Ruthenium/TFA-catalyzed coupling of activated secondary propargylic alcohols with cyclic 1,3-diones: furan versus pyran ring formation

A catalytic system consisting of the 16-electron allyl-ruthenium(II) complex [Ru(eta(3)-2-C3H4Me)(CO)(dppf)][SbF6] (dppf = 1,1'-bis(diphenylphosphino)ferrocene) and trifluoroacetic acid (TFA) has been used to promote the coupling between secondary propargylic alcohols and cyclic 1,3-diketones. The nature of the resulting products was found to be dependent on the ring size of the dicarbonyl compound employed. Thus, whereas 6,7-dihydro-5H-benzofuran-4-ones have been selectively obtained starting from 1,3-cyclohexanediones, via furan-ring formation, the use of 1,3-cyclopentanedione leads instead to 6,7-dihydro-4H-cyclopenta[b]pyran-5-ones via a pyran-ring formation process.     

Reaction of arylhydrazines with an α-alkynyl-carbonylic compound: an unexpected hydration reaction

The acid catalyzed reactions of three arylhydrazines with 4-phenyl-3-butynone in order to obtain the corresponding arylhydrazone were realized. The arylhydrazone reaction and an unexpected alkyne hydration reaction product were obtained when diphenylhydrazine was used. This product was identified by spectroscopic methods and X-ray diffractogram. A reaction mechanism is proposed for its formation.     

Impact of Covalent Modifications on the Hydrogen Bond Strengths in Diaminotriazine Supramolecules

Melamine (M) is a popular triamine triazine compound in the field of supramolecular materials. In this work, we have computationally investigated how substituents can be exploited to improve the binding strength of M supramolecules. Two types of covalent modifications were studied: the substitution of an H atom within an amine group −NHR, and the replacement of the whole −NH₂ group (R=H, F, CH₃ and COCH₃). Through our dispersion-corrected density functional theory computations, we explain which covalent modification will show the best self-assembling capabilities, and why the binding energy is enhanced. Our charge density and molecular orbital analyses indicate that the best substituents are those that generate a charge accumulation on the endocyclic N atom, providing an improvement of the electrostatic attraction. At the same time the substituent assists the main N−H⋅⋅⋅N hydrogen bonds by interacting with the amino group of the other monomer. We also show how the selected group notably boosts the strength of hexameric rosettes. This research, therefore, provides molecular tools for the rational design of emerging materials based on uneven hydrogen-bonded arrangements.     

Determination of total polyphenol index in wines employing a voltammetric electronic tongue

This work reports the application of a voltammetric electronic tongue system (ET) made from an array of modified graphite-epoxy composites plus a gold microelectrode in the qualitative and quantitative analysis of polyphenols found in wine. Wine samples were analyzed using cyclic voltammetry without any sample pretreatment. The obtained responses were preprocessed employing discrete wavelet transform (DWT) in order to compress and extract significant features from the voltammetric signals, and the obtained approximation coefficients fed a multivariate calibration method (artificial neural network-ANN-or partial least squares-PLS-) which accomplished the quantification of total polyphenol content. External test subset samples results were compared with the ones obtained with the Folin–Ciocalteu (FC) method and UV absorbance polyphenol index (I₂₈₀) as reference values, with highly significant correlation coefficients of 0.979 and 0.963 in the range from 50 to 2400 mg L⁻¹ gallic acid equivalents, respectively. In a separate experiment, qualitative discrimination of different polyphenols found in wine was also assessed by principal component analysis (PCA).     

Preparation and characterisation of mononuclear Pd(II) complexes with 1,8-bis(3,5-dimethyl-1-pyrazolyl)-3,6-dithiaoctane (bddo) ligand: Spectroscopy studies and crystal structure of trans-[Pd(SCN)2(bddo)]

Mononuclear palladium(II) complexes containing a pyrazole-thioether ligand, with general formula trans-[Pd(X)₂(bddo)] (X = CN⁻ (1), SCN⁻ (2) or N₃⁻ (3); bddo = 1,8-bis(3,5-dimethyl-1-pyrazolyl)-3,6-dithiaoctane), have been prepared. Similar reactivity carried out with pyridine or triphenylphosphine has been assayed. When pyridine is used, a mixture of [Pd(bddo)(py)₂](BF₄)₂ ([4](BF₄)₂) and [Pd(bddo)](BF₄)₂ is obtained. When triphenylphosphine is used, only [Pd(bddo)](BF₄)₂ is obtained. The complexes have been characterised by elemental analyses, conductivity measurements, IR and NMR spectroscopies. X-ray crystal structure of trans-[Pd(SCN)₂(bddo)] (2) is presented. In this complex the metal atom is coordinated by the two azine nitrogen atoms of the pyrazole rings and two SCN⁻ anions in trans disposition.     

Novel proton-conducting polymer inclusion membranes

The preparation and characterization of new polymer inclusion membranes (PIMs) for proton transport is described. PIMs were prepared with different polymeric cellulose-based compounds and PVC as supports, tris(2-butoxyethyl)phosphate (TBEP) and 2-nitrophenyl octyl ether (NPOE) as plasticizers and dinonylnaphthalenesulfonic acid (DNSA) and dinonylnaphthalenedisulfonic acid (DNDSA) as carriers. The effects of the nature and content of the supports, plasticizers and carriers on membrane proton conductivity was studied using electrochemical impedance spectroscopy (EIS). This technique was also used to evaluate the chemical stability of a CTA–NPOE–DNDSA membrane while its selectivity was monitored with respect to sodium and calcium ions through counter-transport experiments. DSC and TGA techniques were used to determine the thermal stability of these membranes. A PIM based on CTA–DNDSA–NPOE showed the highest proton conductivity (3.5 mS/cm) with no variation of its behavior during 2 months of evaluation. FTIR characterization did not show structural changes of the membrane in this period of time. Thermal analysis indicates that it is stable up to 180 °C. An empirical functional relationship between PIM resistance and composition indicates that increasing plasticizer and carrier concentrations enhances the conductivity of the membranes, while increasing CTA content tends to decrease this property. Transport experiments showed a good selectivity of the CTA–DNDSA–NPOE membrane for protons over calcium or sodium ions.     

Highly Efficient Redox Isomerisation of Allylic Alcohols Catalysed by Pyrazole‐Based Ruthenium(IV) Complexes in Water: Mechanisms of Bifunctional Catalysis in Water

The catalytic activity of ruthenium(IV) ([Ru(η³:η³‐C₁₀H₁₆)Cl₂L]; C₁₀H₁₆=2,7‐dimethylocta‐2,6‐diene‐1,8‐diyl, L=pyrazole, 3‐methylpyrazole, 3,5‐dimethylpyrazole, 3‐methyl‐5‐phenylpyrazole, 2‐(1H‐pyrazol‐3‐yl)phenol or indazole) and ruthenium(II) complexes ([Ru(η⁶‐arene)Cl₂(3,5‐dimethylpyrazole)]; arene=C₆H₆, p‐cymene or C₆Me₆) in the redox isomerisation of allylic alcohols into carbonyl compounds in water is reported. The former show much higher catalytic activity than ruthenium(II) complexes. In particular, a variety of allylic alcohols have been quantitatively isomerised by using [Ru(η³:η³‐C₁₀H₁₆)Cl₂(pyrazole)] as a catalyst; the reactions proceeded faster in water than in THF, and in the absence of base. The isomerisations of monosubstituted alcohols take place rapidly (10–60 min, turn‐over frequency=750–3000 h^?1) and, in some cases, at 35 °C in 60 min. The nature of the aqueous species formed in water by this complex has been analysed by ESI‐MS. To analyse how an aqueous medium can influence the mechanism of the bifunctional catalytic process, DFT calculations (B3LYP) including one or two explicit water molecules and using the polarisable continuum model have been carried out and provide a valuable insight into the role of water on the activity of the bifunctional catalyst. Several mechanisms have been considered and imply the formation of aqua complexes and their deprotonated species generated from [Ru(η³:η³‐C₁₀H₁₆)Cl₂(pyrazole)]. Different competitive pathways based on outer‐sphere mechanisms, which imply hydrogen‐transfer processes, have been analysed. The overall isomerisation implies two hydrogen‐transfer steps from the substrate to the catalyst and subsequent transfer back to the substrate. In addition to the conventional Noyori outer‐sphere mechanism, which involves the pyrazolide ligand, a new mechanism with a hydroxopyrazole complex as the active species can be at work in water. The possibility of formation of an enol, which isomerises easily to the keto form in water, also contributes to the efficiency in water.     

New Liquid Crystalline Materials Based on Two Generations of Dendronised Cyclophosphazenes

A divergent approach was used for the synthesis of dendritic structures based on a cyclotriphosphazene core with 12 or 24 hydroxyl groups, by starting from [N₃P₃(OC₆H₄OH‐4)₆] and using an acetal‐protected 2,2‐di(hydroxymethyl)propionic anhydride as the acylating agent. Hydroxyl groups in these first‐ and second‐generation dendrimers, G1‐(OH)₁₂ or G2‐(OH)₂₄ , were then condensed in turn with mono‐ or polycatenar pro‐mesogenic acids to study their ability to promote self‐assembly into liquid crystalline structures. Reactions were monitored by using ³¹P{¹H} and ¹H NMR spectroscopy and the chemical structure of the resulting materials was confirmed by using different spectroscopic techniques and mass spectrometry (MALDI‐TOF MS). The results were in accordance with monodisperse, fully functionalised cyclotriphosphazene dendrimers. Thermal and liquid crystalline properties were studied by using optical microscopy, differential scanning calorimetry and X‐ray diffraction. The dendrimer with 12 4‐pentylbiphenyl mesogenic units gives rise to columnar rectangular organisation, whereas the one with 24 pentylbiphenyl units does not exhibit mesomorphic behaviour. In the case of materials that contain polycatenar pro‐mesogenic units with two aromatic rings ( A4 vs. A5 ), the incorporation of a short flexible spacer connected to the periphery of the dendron (acid A5 ) was needed to achieve mesomorphic organisation. In this case, both dendrimer generations G1 A5 and G2 A5 exhibit a hexagonal columnar mesophase.