Cycloalkane-1,2-diamine derivatives as chiral solvating agents. Study of the structural variables controlling the NMR enantiodiscrimination of chiral carboxylic acids

A family of pincer-like receptors (2-5) has been synthesized and tested for the NMR enantiodiscrimination (CSA) of chiral carboxylic acids. Starting from a previous design (1), different structural variables have been mapped on the receptor frame. The splitting of the signals of the acids upon the addition of the CSAs largely depends on these structural variables. Thus, we concluded that the C₂ symmetrical pyridine-2,6-biscarboxamide moiety is a key structural feature for the efficiency of the CSA. Structural studies by NMR and molecular modeling showed that this moiety promotes the U-shape-folded pincer-like conformation by intramolecular H-bonds. On the other hand, we also observed that the cyclohexane-1,2-diamine derivative 5 is a more versatile CSA than its cyclopentane analogue 1, as 5 shows a better performance for more structurally different acids. However, the original cyclopentane derivative (1) remained the best for the arylpropionic acids. Finally, combination of NMR and modeling studies allowed us to propose a reasonable model for the interaction and, accordingly, for the observed NMR enantiodiscrimination.     

Synthesis of a π-extended TTF-perylenediimide donor-acceptor dyad

A donor-acceptor dyad containing perylenediimide as the electron acceptor and π-extended tetrathiafulvalene as electron donor has been successfully synthesized by means of a Wittig reaction. Cyclic voltammetry and absorption spectroscopy show that both electroactive units preserve their nature, whereas preliminar photophysical investigations show a strong fluorescence quenching.     

Conformational changes and gating at the selectivity filter of potassium channels

The translocation of ions and water across cell membranes is a prerequisite for many of life's processes. K(+) channels are a diverse family of integral membrane proteins through which K(+) can pass selectively. There is an ongoing debate about the nature of conformational changes associated with the opening and closing and conductive and nonconductive states of potassium (K(+)) channels. These changes depend on the membrane potential, the K(+) concentration gradient, and large scale motions of transmembrane helices and associated residues. Experiments also suggest that local structural changes in the selectivity filter may act as the dominant gate referred to as C-type inactivation. Herein we present an extensive computational study on KirBac, which supports the existence of a physical gate or constriction in the selectivity filter (SF) of K(+) channels. Our computations identify a new selectivity filter structure, which is likely associated with C-type inactivation. Specifically, the four peptide chains that comprise the filter adopt an unusual structure in which their dihedrals alternate between left- and right-handed Ramachandran angles, which also justifies the need for conservation of glycine in the K(+) selectivity filter, since it is the only residue able to play this bifunctional role.     

Pressure-induced magnetic switching and linkage isomerism in K0.4Fe4[Cr(CN)6]2.8 x 16 H2O: X-ray absorption and magnetic circular dichroism studies

The effect of applied pressure on the magnetic properties of the Prussian blue analogue K0.4Fe4[Cr(CN)6]2.8 x 16 H2O (1) has been analyzed by dc and ac magnetic susceptibility measurements. Under ambient conditions, 1 orders ferromagnetically at a critical temperature (T(C)) of 18.5 K. Under application of pressure in the 0-1200 MPa range, the magnetization of the material decreases and its critical temperature shifts to lower temperatures, reaching T(C) = 7.5 K at 1200 MPa. Pressure-dependent Raman and Mossbauer spectroscopy measurements show that this striking behavior is due to the isomerization of some Cr(III)-C[triple bond]N-Fe(II) linkages to the Cr(III)-N[triple bond]C-Fe(II) form. As a result, the ligand field around the iron(II) centers increases, and the diamagnetic low-spin state is populated. As the number of diamagnetic centers in the cubic lattice increases, the net magnetization and critical temperature of the material decrease considerably. The phenomenon is reversible: releasing the pressure restores the magnetic properties of the original material. However, we have found that under more severe pressure conditions, a metastable sample containing 22% Cr(III)-N[triple bond]C-Fe(II) linkages can be obtained. X-ray absorption spectroscopy and magnetic circular dichroism of this metastable sample confirm the linkage isomerization process.     

A mesoporous 3D hybrid material with dual functionality for Hg2+ detection and adsorption

Dual-function hybrid material U1 was designed for simultaneous chromofluorogenic detection and removal of Hg(2+) in an aqueous environment. Mesoporous material UVM-7 (MCM41 type) with homogeneously distributed pores of about 2-3 nm in size, a large specific surface area exceeding 1000 m(2) g(-1), and nanoscale particles was used as an inorganic support. The mesoporous solid is decorated with thiol groups that were treated with squaraine dye III to give a 2,4-bis(4-dialkylaminophenyl)-3-hydroxy-4-alkylsulfanylcyclobut-2-enone (APC) derivative that is covalently anchored to the inorganic silica matrix. The solid was characterised by various techniques including X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and nitrogen adsorption. This hybrid solid is the chemodosimeter for Hg(2+) detection. Hg(2+) reacts with the APC fragment in U1 with release of the squaraine dye into the solution, which turns deep blue and fluoresces strongly. Naked-eye Hg(2+) detection is thus accomplished in an easy-to-use procedure. In contrast, U1 remains silent in the presence of other thiophilic transition metal ions, alkali and alkaline earth metal ions, or anions ubiquitously present in water such as chloride, carbonate, sulfate, and phosphate. Material U1 acts not only as chemodosimeter that signals the presence of Hg(2+) down to parts-per-billion concentrations, but at the same time is also an excellent adsorbent for the removal of mercury cations from aqueous solutions. The amount of adsorbed mercury ranges from 0.7 to 1.7 mmol g(-1), depending on the degree of functionalisation. In addition, hybrid material U1 can be regenerated for both sensing and removal purposes. As far as we know, U1 is the first example of a promising new class of polyfunctional hybrid supports that can be used as both remediation and alarm systems by selective signalling and removal of target species of environmental importance. Model compounds based on silica gel (G1), fumed silica (F1), and micrometre-sized MCM-41 scaffolds (M1) were also prepared and studied for comparative purposes.     

Using hyperbranched macromers as crosslinkers of methacrylic networks prepared by photopolymerization

Hyperbranched polymers were modified with terminal methacryloyl groups to be used as crosslinkers. The photoinitiated polymerization of several methacrylic monomers was examined in the presence of the hyperbranched macromers and bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819^®) as a photoinitiator, upon UV irradiation. The photopolymerization kinetics was systematically studied by fluorescence and photoDSC in real time and in situ. Six types of monofunctional methacrylic monomers, two types of difunctional methacrylic monomers and four types of (meth)acrylate-modified hyperbranched macromers with different structures were employed for series of photopolymerization reactions. The incorporation of the hyperbranched macromers allows to increase the conversion at gelation and thus, final conversion. This behaviour is dependent on monomer and macromer nature and has been explained as due to an increase of the free volume fraction and confirmed by fluorescence. The results indicate that H-bonding and π-stacking induce self-assembly of hyperbranched macromers leading to reaction induced phase separation at the highest concentration of hyperbranched macromer used.     

Sun beds and cod liver oil as vitamin D sources

The objective of this study was to (1) to determine the contribution of moderate sun bed exposure to serum 25(OH)D(3) levels; (2) to estimate the decay time of a high 25(OH)D(3) level obtained by sun bed exposure; and (3) to evaluate if the recommended ingestion of vitamin D is sufficient to maintain the 25(OH)D(3) concentration obtained by sun bed exposure. Ten volunteers (20-35 y.o.), skin type I and II, living in Olso, Norway were whole body exposed twice per week to the radiation of a commercial and approved sun bed (Life Sun S 100 W, Wolff System), starting with 0.5 MED (minimal erythema dose) and escalating to up to 1 MED per exposure for 4 weeks. After that, half of the volunteers were given a daily supplement of 200 IU vitamin D in the form of cod liver oil capsules, while the other half of the persons received no supplements. Erythema did not occur at any time and a slight pigmentation was seen in most of the volunteers after the sun bed exposures. Serum level of 25(OH)D(3) increased by about 40% on the average. The initial serum 25(OH)D(3) level was different among the volunteers (40-100 nmol/L). Within eight weeks after the last exposure the 25(OH)D(3) level decreased to the initial value in all volunteers irrespective of vitamin D supplementation or not.     

Rational design of cationic cyclooligosaccharides as efficient gene delivery systems

Self-assembled cyclodextrin (CD)-DNA nanoparticles (CDplexes) exhibiting transfection efficiencies significantly higher than PEI-based polyplexes have been prepared from homogeneous seven-fold symmetric polyaminothiourea amphiphiles constructed on a beta-cyclodextrin scaffold.     

Component exchange as a synthetically advantageous strategy for the preparation of bicyclic cage compounds

Macrobicyclic triphosphazides are able to reversibly exchange one of their tripodal components by means of a dynamic disassembly-reassembly process; surprisingly this strategy provides better yields of cage compounds than a direct tripod-tripod coupling.     

Copper(II) complexes with N,N-dimethylbiguanide

The N,N-dimethylbiguanide (HDMBG) complexes [Cu₂(HDMBG)₂Cl₄] (1) and respectively [Cu(HDMBG)₂]Cl₂·2H₂O (2) exhibit in vitro antimicrobial activity. The complexes were characterised by IR, electronic as well as EPR spectra. The IR spectra of complexes show the pattern of N,N-dimethylbiguanide coordinated as chelate. The electronic and EPR data are in agreement with a square pyramidal stereochemistry for (1) and a square planar one for (2). The in vitro qualitative and quantitative antimicrobial activity assays showed that the complexes exhibited variable antimicrobial activity against Gram-negative strains (Escherichia coli, Klebsiella spp. and Enterobacter sp.) isolated from the hospital environment. The thermal analysis has evidenced the thermal intervals of stability and also the thermodynamic effects that accompany them. The thermal behaviour in nitrogen is complex according to TG and DTA curves including melting, dehydration as well as compounds decomposition.