Synthesis, redox, and amphiphilic properties of responsive salycilaldimine-copper(II) soft materials

Hydrolysis of the asymmetric pyridine- and phenol-containing ligand HL (1) (2-hydroxy-4-6-di- tert-butylbenzyl-2-pyridylmethyl)imine) led to the use of bis-(3,5-di -tert-butyl-2-phenolato-benzaldehyde)copper(II), [Cu (II)(L (SAL)) 2] ( 1) as a precursor for bis-(2,4-di- tert-butyl-6-octadecyliminomethyl-phenolato)copper(II), [Cu (II)(L (2)) 2] ( 3), bis-(2,4-di- tert-butyl-6-octadecyl aminomethyl-phenolato)copper(II), [Cu (II)(L (2A)) 2] ( 3'), and bis-(2,4-di- tert-butyl-6-[(3,4,5-tris-dodecyloxy-phenylimino)-methyl]-phenolato)copper(II), [Cu (II)(L (3)) 2] ( 4). These complexes exhibit hydrophilic copper-containing head groups, hydrophobic alkyl and alkoxo tails, and present potential as precursors for redox-responsive Langmuir-Blodgett films. All systems were characterized by means of elemental, spectrometric, spectroscopic, and electrochemical techniques, and their amphiphilic properties were probed by means of compression isotherms and Brewster angle microscopy. Good redox activity was observed for 3 with two phenoxyl radical processes between 0.5 and 0.8 V vs Fc (+)/Fc, but this complex lacks amphiphilic behavior. To attain good balance between redox response and amphiphilicity, increased core flexibility in 3' and incorporation of alkoxy chains in 4 were attempted. Film formation with collapse at 14 mN.m (-1) was observed for the alkoxy-derivative but redox-response was seriously compromised. Core flexibility improved Langmuir film formation with a higher formal collapse and showed excellent cyclability of the ligand-based processes.     

Influence of the apical ligand in the thermotropic mesomorphism of cationic copper-based surfactants

A new pyridine-based bidentate ligand L (PyC18) was used to develop copper-containing surfactants that exhibit mesomorphism. Complexes [(L (PyC18)) 2Cu (II)Y]Y were synthesized, where Y is an anionic ligand bromo ( 1), nitrato ( 2), or perchlorato ( 3). The nature of these apical ligands determines the mesogenic behavior of 1- 3: The smallest bromo-substituted species 1 shows a metastable liquid crystalline phase at 110 degrees C, the nitrato-substituted 2 increases the transition temperature to 136 degrees C, and the bulky perchlorato-substituted 3 shows reversible mesophases at 153 degrees C. The behavior of these complexes shows similarities and suggests that at low temperatures the crystals of these compounds are bilayered structures with interdigitated alkyl tails. At higher temperatures the tails undergo rapid conformational changes that force these layers to swell until the opposing alkyl chains are separated from each other, and the mesophase is a monolayer smectic A. Small changes in the geometry of cationic mesogens can be imposed by the presence of apically coordinated anions, allowing for tuning in the properties of the resulting mesophases.     

Structural and electronic properties of the [FeFe] hydrogenase H-cluster in different redox and protonation states. A DFT investigation

The molecular and electronic structure of the Fe 6S 6 H-cluster of [FeFe] hydrogenase in relevant redox and protonation states have been investigated by DFT. The calculations have been carried out according to the broken symmetry approach and considering different environmental conditions. The large negative charge of the H-cluster leads, in a vacuum, to structures different from those observed experimentally in the protein. A better agreement with experimental data is observed for solvated complexes, suggesting that the protein environment could buffer the large negative charge of the H-cluster. The comparison of Fe 6S 6 and Fe 2S 2 DFT models shows that the presence of the Fe 4S 4 moiety does not affect appreciably the geometry of the [2Fe] H cluster. In particular, the Fe 4S 4 cluster alone cannot be invoked to explain the stabilization of the mu-CO forms observed in the enzyme (relative to all-terminal CO species). As for protonation of the hydrogen cluster, it turned out that mu-H species are always more stable than terminal hydride isomers, leading to the conclusion that specific interactions of the H-cluster with the environment, not considered in our calculations, would be necessary to reverse the stability order of mu-H and terminal hydrides. Otherwise, protonation of the metal center and H 2 evolution in the enzyme are predicted to be kinetically controlled processes. Finally, subtle modifications in the H-cluster environment can change the relative stability of key frontier orbitals, triggering electron transfer between the Fe 4S 4 and the Fe 2S 2 moieties forming the H-cluster.     

New chiral and restricted-access materials containing glycopeptides as selectors for the high-performance liquid chromatographic determination of chiral drugs in biological matrices

Two new chiral and restricted-access materials containing glycopeptide antibiotics as chiral selectors (chiro-Glyco-RAM) were designed, suitable for the direct HPLC injection of biological fluids containing chiral drugs without any sample pre-treatment or pre-columns coupling. The external surface of the porous silica support was covered with a bio-compatible hydrophilic polymeric network (polyvinyl alcohol, PVA) while the chiral phase based on either teicoplanin (TE) or teicoplanin aglycone (TAG) was exclusively confined to the internal region. The chiro-Glyco-RAM supports were synthesized by the following steps: (a) introduction of 3-aminopropyl groups on 100 A pore size silica gel; (b) activation of the aminopropylated silica with 1,6-diisocyanatohexane; (c) functionalization of the external region of the porous silica with PVA; (d) covalent linking of TE/TAG to the internal surface. The average pore diameter of the chiro-Glyco-RAM supports, calculated by inverse size-exclusion chromatography (ISEC), was about 80 A and able to exclude macromolecules heavier than about 20,000 Da (such as the most abundant serum proteins) from the pores. The recovery of bovine serum albumin (BSA) was almost quantitative. HPLC analyses of model chiral drugs were performed using hydro-organic mobile phases consisting of an organic solvent (acetonitrile or methanol) and aqueous solutions of ammonium acetate (0.020 M) or ammonium formate (0.0025-0.0050 M).     

Optimization of the selectivity of a cyanopropyl stationary phase for the gas chromatographic analysis of trans fatty acids

The quantification of monounsaturated and polyunsaturated trans fatty acids in partially hydrogenated fats by gas-liquid chromatography on a CP-Select CB-FAME capillary column was optimized using equivalent chain length values of fatty acids methyl esters that could coelute in the temperature range from 155 to 200 degrees C. The most appropriate temperature for the simultaneous determination of these trans isomers is around 197 degrees C. It is proposed a system to discriminate trans from cis octadecenoic fatty acid methyl esters based on the angular coefficient values of the equivalent chain length curves. The limits of detection and quantification were 0.28 and 0.93 mg g(-1). Quantification was performed in the range from 0.93 to 280 mg g(-1). Quantification accuracy was estimated by spike recovery of elaidic and trans-13-octadecenoic acids in hydrogenated fat samples. The obtained levels were from 97.60 to 103.28% for elaidic acid and from 98.12 to 99.27% for trans-13-octadecenoic acid. These results indicate that the accuracy of the methodology proposed for the quantification of monounsaturated and polyunsaturated trans fatty acids in hydrogenated fats is adequate.     

The ergodic problem for some subelliptic operators with unbounded coefficients

We study existence and uniqueness of the invariant measure for stochastic processes with degenerate diffusion, whose infinitesimal generators are linear subelliptic operators in the whole space \({{\mathbb{R}}^N}\) with possibly unbounded coefficients. Such a measure together with a Liouville-type theorem will play a crucial role in two applications: the ergodic problem studied through stationary problems with vanishing discount and the long time behavior of the solution to a parabolic Cauchy problem. In both cases, the constants will be characterized in terms of the invariant measure.     

Isometric actions on spheres with an orbifold quotient

Mathematische Annalen - We classify representations of compact connected Lie groups whose induced action on the unit sphere has the orbit space isometric to a Riemannian orbifold.     

Synthesis and electrochemical investigation of <Emphasis Type="Italic">beta</Emphasis>-substituted thiophene-based donor–acceptor copolymers with 3,4-ethylenedioxythiophene (EDOT)

The present work reports the synthesis of four electron-acceptor beta-substituted thiophenes that were studied as monomers for electrochemical polymerization with 3,4-ethylenedioxythiophene (EDOT), an electron-donating monomer, aiming the combination of electron-acceptor and donor monomer thiophene to a simpler and convenient build up of novel donor–acceptor copolymeric materials via electrochemical polymerization. Four novel copolymers poly(EDOT-co-3-thiophene phenylacetate), (PEDOT-co-PPhTAc-2a), poly(EDOT-co-3-thiophene(4-nitrophenyl)acetate) (PEDOT-co-PPhTAc-2b), poly(EDOT-co-3-thiophenephenylcarboxylate) (PEDOT-co-PPhTCb), and poly(EDOT-co-3-(phenoxymethyl)thiophene) (PEDOT-co-PPhOMT) were electrochemically polymerized. The monomers were characterized by spectrometric techniques (FTIR, ¹H NMR, and ¹³C NMR), and the copolymers were identified by electrochemical analyses and FT-IR. Although the corresponding homopolymers could not be obtained, in the presence of EDOT, the copolymers were formed in a quasi-reversible electrochemical kinetics. The infrared spectra of the copolymers as well the electrochemical profile corroborates their obtaining. The mass variation during the electrosynthesis was analyzed using a quartz crystal microbalance. The film’s morphologies were investigated by SEM. Interestingly, the combination of electron-rich monomer thiophene (EDOT) and these electron-deficient carboxy-substituted thiophenes might be a convenient building block couple to increase the performance control of physic-chemical properties of mixed polythiophenes with innovative applications and they also showed a possible applicability as charge storage device.     

UVA self-photosensitized oxygenation of beta-ionone

The steady-state UVA (350 nm) photolysis of ( E )-β-ionone ( 1 ) in aerated toluene solutions was studied by ¹H NMR spectroscopy. The formation of the 1,2,4-trioxane ( 2 ) and 5,8-endoperoxide ( 5 ) derivatives in the ratio of 4:1 was observed. Time-resolved laser induced experiments at 355 nm, such as laser-flash photolysis, photoacoustic and singlet oxygen ¹O₂ phosphorescence detection, confirmed the formation of the excited triplet state of 1 with a quantum yield Φ _T = 0.50 as the precursor for the generation of singlet oxygen ¹O₂ ( Φ _Δ = 0.16) and the isomeric α-pyran derivative ( 3 ), which was a reaction intermediate detected by NMR. In turn, the reaction of ¹O₂ with 1 and 3 occurred with rate constants of 1.0 × 10⁶ and 2.5 × 10⁸  m ⁻¹s⁻¹ to yield the oxygenated products 5 and 2 , respectively, indicating the relevance of the fixed s-cis configuration in the α-pyran ring in the concerted [2+4] cycloaddition of ¹O₂.