Collapse of telechelic star polymers to watermelon structures

Conformational properties of star-shaped polymer aggregates that carry attractive end groups, called telechelic star polymers, are investigated by simulation and analytical variational theory. We focus on the case of low telechelic star polymer functionalities, f < or = 5, a condition which allows aggregation of all attractive monomers on one site. We establish the functionality- and polymerization-number dependence of the transition temperature from the "star burst" to the "watermelon" macroparticle structure. Extensions to telechelic stars featuring partially collapsed configurations are also discussed.     

Synthesis of large-pore micelle-templated silico-aluminas at different alumina contents

The EPR spectra of radical surfactant probes embedded in cetyltrimethylammonium bromide (CTAB) and trimethylbenzene (TMB) stable water emulsions (TMB/CTAB = 13) were analyzed to provide information on the kinetics of formation of micelle-templated silicoaluminas (MTSA) at 343 K, obtained by means of silica and alumina, solved in alkaline solutions, at different Si/Al ratios. Textural (surface area, pore volume, pore size, surfactant content) and structural characterization of both as-synthesized and calcined MTSA were performed by means of nitrogen sorption isotherms, TEM, and chemical analysis. This analysis showed that TMB worked as a swelling agent of the CTAB micelles, providing large-pore homogeneous and stable MTSA at TMB/CTAB = 13 for Si/Al from infinity to 10. A demixing of the emulsion occurs at Si/Al < 10: at Si/Al = 7, a double wide-and-narrow pore structure was formed; then, at Si/Al = 5, an amorphous material was obtained. At Si/Al > or = 10, the computer-aided analysis of the EPR spectra as a function of the synthesis time indicated the distribution of the probes in two different environments: "micellar" probes inserted in the surfactant aggregates, whose mobility decreases over the synthesis time, thus reporting on the progressive modification of the surfactant aggregates structure and the solid condensation, and "interacting" probes due to probe-surfactant heads electrostatically interacting with the charged surface sites induced by alumina incorporation in the silica network. This last fraction increases its relative amount over the synthesis time, informing about the condensation and structuration of the MTSA. Without alumina, the "interacting" component is absent in the EPR spectra because TMB preferentially interacts with the surfactant headgroups by cation-pi interactions, thus preventing the interactions of these headgroups with silanols. When alumina is added, the negatively charged silicoaluminate at the surface promotes the interaction of the ammonium headgroups with the surface, and some Na+ cations also interact with TMB by cation-pi interaction and contribute to decreasing the interaction of the headgroups with TMB. Therefore, increasing alumina contents promote electrostatic interactions between the positively charged surfactant heads and the negatively charged silicoaluminate groups. The strong interaction of the surfactants with the silicoaluminate surface allows the formation of a monolayerlike structure of surfactant, which is not observed in the absence of alumina. The synthesis is slowed by increasing alumina contents due to a destructuration effect of alumina in the MTSA formation.     

Synthetic scope of alcohol transfer dehydrogenation catalyzed by Cu/Al2O3: a new metallic catalyst with unusual selectivity

A method for the anaerobic oxidation of a wide series of alcohols including cyclohexanols and steroidal alcohols, has been set up. It relies on a transfer dehydrogenation reaction from the substrate alcohol to styrene catalyzed by a heterogeneous, reusable copper catalyst under very mild liquid-phase experimental conditions (90 degrees C, N(2)) and shows unusual selectivity. Thus, the method is selective for the oxidation of secondary and allylic alcohols even in the presence of unprotected primary and benzylic alcohols. Electronic effects and the choice of the hydrogen acceptor account for the selectivity observed.     

Hydrogen Atoms Location in Os<Subscript>3</Subscript>(μ-H)(CO)<Subscript>9</Subscript>(μ<Subscript>3</Subscript>, η<Superscript>2</Superscript>-C<Subscript>2</Subscript>H) from Accurate X-Ray Data at 100 K

Abstract  

The structure of the complex Os₃(μ-H)(CO)₉(μ₃, η²-C₂H) has been determined using X-ray data collected at low temperature (100 K); all hydrogen atoms have been located. The asymmetric unit is formed by two molecules joined through hydrogen bonds involving the hydrogen atoms of C₂H moiety and the oxygen atoms of carbonyl groups. The complex crystallizes in the monoclinic space group P2₁/c with a = 12.94040(2), b = 15.4705(2), c = 16.0164(2) ?, β = 106.0860(10)°, and V = 3,080.85(7) ?³, Z = 8. A molecule is formed by a triangular Os₃ cluster, with metal atoms bearing terminal CO groups. The acetylenic residual is formally π-bonded to two Os atoms in a perpendicular mode and σ-linked to the third Os atom. A bridging hydride atom completes the coordination.     

An original approach to determining traces of tetracycline antibiotics in milk and eggs by solid-phase extraction and liquid chromatography/mass spectrometry

An original and highly specific method able to identify and quantify traces of five tetracycline antibiotics (TCAs) in milk and eggs is presented. This method uses a single solid-phase extraction (SPE) cartridge for simultaneous extraction and purification of TCAs in the above matrices. After diluting 5 mL of intact whole milk or 2 g egg samples with Na(2)EDTA-containing water, samples are passed through a 0.5-g Carbograph 4 extraction cartridge. After analyte elution from the SPE cartridge, an aliquot of the final extract is injected into a liquid chromatography/mass spectrometry (LC/MS) instrument equipped with an electrospray ion source and a single quadrupole. MS data acquisition is performed in the positive-ion mode and by a time-scheduled multiple-ion selected ion-monitoring program. With methanol as organic modifier, the in-source collision-induced dissociation (CID) process generated fragment ions able to pick up one methanol molecule. In several cases, these methanol-adduct fragment ions have m/z values higher than those of the protonated molecules. This event is rarely encountered in MS, thus making the analysis of TCAs by this method extremely specific. Compared with a conventional published method, the present protocol extracted larger amounts of TCAs from both milk and egg and decreased the analysis time by a factor of 3. Recovery of TCAs in milk at the 25-ppb level ranged between 81 and 96% with relative standard deviation (RSD) no larger than 9%. Recovery of TCAs in egg at the 50-ppb level ranged between 72 and 92% with RSD no larger than 7%. Estimated limits of quantification(S/N = 10) of the method were 2-9 ppb TCAs in whole milk and 2-19 ppb TCAs in eggs.     

Modulation of αVβ6 integrin in osteoarthritis-related synovitis and the interaction with VTN(381–397 a.a.) competing for TGF-β1 activation

Osteoarthritis is characterized by structural alteration of joints. Fibrosis of the synovial tissue is often detected and considered one of the main causes of joint stiffness and pain. In our earlier proteomic study, increased levels of vitronectin (VTN) fragment (amino acids 381–397) were observed in the serum of osteoarthritis patients. In this work, the affinity of this fragment for integrins and its putative role in TGF-β1 activation were investigated. A competition study determined the interaction of VTN_{(381–397 a.a.)} with α_Vβ₆ integrin. Subsequently, the presence of α_Vβ₆ integrin was substantiated on primary human fibroblast-like synoviocytes (FLSs) by western blot and flow cytometry. By immunohistochemistry, β₆ was detected in synovial membranes, and its expression showed a correlation with tissue fibrosis. Moreover, β₆ expression was increased under TGF-β1 stimulation; hence, a TGF-β bioassay was applied. We observed that α_Vβ₆ could mediate TGF-β1 bioavailability and that VTN_{(381–397 a.a.)} could prevent TGF-β1 activation by interacting with α_Vβ₆ in human FLSs and increased α-SMA. Finally, we analyzed serum samples from healthy controls and patients with osteoarthritis and other rheumatic diseases by nano-LC/Chip MS–MS, confirming the increased expression of VTN_{(381–397 a.a.)} in osteoarthritis as well as in lupus erythematosus and systemic sclerosis. These findings corroborate our previous observations concerning the overexpression of VTN_{(381–397 a.a.)} in osteoarthritis but also in other rheumatic diseases. This fragment interacts with α_Vβ₆ integrin, a receptor whose expression is increased in FLSs from the osteoarthritic synovial membrane and that can mediate the activation of the TGF-β1 precursor in human FLSs.Subject terms: Osteoarthritis, Cell culture     

The Role of Resveratrol in Human Male Fertility

Resveratrol (RSV) (3,4′,5 trihydroxystilbene) is a natural non-flavonoid polyphenol widely present in the Mediterranean diet. In particular, RSV is found in grapes, peanuts, berries, and red wine. Many beneficial effects of this molecule on human health have been reported. In fact, it improves some clinical aspects of various diseases, such as obesity, tumors, hypertension, Alzheimer’s disease, stroke, cardiovascular diseases, and diabetes mellitus. However, little is known about the relationship between this compound and male fertility and the few available results are often controversial. Therefore, this review evaluated the effects of RSV on human male fertility and the mechanisms through which this polyphenol could act on human spermatozoa.     

Rapid determination of lithium in serum samples by capillary electrophoresis

Lithium salts are still one of the most popular therapeutic approaches to the treatment of bipolar disorders, notwithstanding the introduction of more modern, less toxic drugs. Because of a narrow therapeutic range, lithium serum concentrations must be strictly monitored during the treatment to avoid life-threatening neurotoxicity. For this purpose, methods based on flame photometry or ion-selective electrodes are usually applied. The aim of the present work was to develop and validate a simple method for the determination of lithium in serum based on capillary zone electrophoresis with indirect detection. A validation of the method was carried out, including a comparison with an automated routine method based on ion-selective electrodes.     

High-spin molecules: synthesis,X-ray characterization,and magnetic behavior of two new cyano-bridged Ni(II)(9)Mo(V)(6) and Ni(II)(9)W(V)(6) clusters with a S = 12 ground state

The preparations, X-ray structures, and magnetic characterizations are presented for two new pentadecanuclear cluster compounds: [Ni(II)(Ni(II)(MeOH)(3))(8)(mu-CN)(30)(M(V)(CN)(3))(6)].xMeOH.yH(2)O (M(V) = Mo(V) (1) with x = 17, y = 1; M(V) = W(V) (2) with x = 15, y = 0). Both compounds crystallize in the monoclinic space group C2/c, with cell dimensions of a = 28.4957(18) A, b = 19.2583(10) A, c = 32.4279(17) A, beta = 113.155(6) degrees, and Z = 4 for 1 and a = 28.5278(16) A, b = 19.2008(18) A, c = 32.4072(17) A, beta = 113.727(6) degrees, and Z = 4 for 2. The structures of 1 and 2 consist of neutral cluster complexes comprising 15 metal ions, 9 Ni(II) and 6 M(V), all linked by mu-cyano ligands. Magnetic susceptibilities and magnetization measurements of compounds 1 and 2 in the crystalline and dissolved state indicate that these clusters have a S = 12 ground state, originating from intracluster ferromagnetic exchange interactions between the mu-cyano-bridged metal ions of the type Ni(II)-NC-M(V). Indeed, these data show clearly that the cluster molecules stay intact in solution. Ac magnetic susceptibility measurements reveal that the cluster compounds exhibit magnetic susceptibility relaxation phenomena at low temperatures since, with nonzero dc fields, chi"(M) has a nonzero value that is frequency dependent. However, there appears no out-of-phase (chi"(M)) signal in zero dc field down to 1.8 K, which excludes the expected signature for a single molecule magnet. This finding is confirmed with the small uniaxial magnetic anisotropy value for D of 0.015 cm(-1), deduced from the high-field, high-frequency EPR measurement, which distinctly reveals a positive sign in D. Obviously, the overall magnetic anisotropy of the compounds is too low, and this may be a consequence of a small single ion magnetic anisotropy combined with the highly symmetric arrangement of the metal ions in the cluster molecule.     

Chemoselective esterification of phenolic acids and alcohols

[formula: see text] The Mitsunobu reaction can distinguish between alcohol and phenol hydroxyls in esterification reactions, providing an expeditious and broadly applicable entry into various phenolics and polyphenolics of biomedical and nutritional relevance.