Living and stereoselective polymerization of [2.2]-paracyclophan-2-ENE derivatives

Paracyclophene based monomers can be polymerized in a living fashion using the alkylidene initiator Mo(NAr)(CHCMe₂Ph)(OCMe(CF₃)₂)₂. The cis-specific nature of the polymerization is critical, since small amounts of trans olefin in the backbone renders the material insoluble. These polymers have complex photophysical behavior, probably a consequence of the close proximity of chromophores along the polymer backbone. Polymerization of 9-(tert-butyldimethylsilyloxy)-[2.2]-paracyclophan-1-ene produces a new precursor material which furnishes PPV under remarkably mild conditions.     

Submicellar liquid chromatography with fluorescence detection improves the analysis of naproxen in plasma and brain tissue

Rapid, simple, and sensitive submicellar liquid chromatography with fluorescence detection was developed and validated to quantify naproxen in plasma and brain samples after oral administration of Naproxen formulations. The method used tramadol as an internal standard. Different submicellar mobile phases with organic phases ranging from 40 to 60% were studied to improve the native fluorescence of the Naproxen and decrease retention times. Separation was done in a Zorbax SB C8 column (250 × 4.6 mm, 5 μm) with a mobile phase containing acidic 0.007 M sodium dodecyl sulfate/acetonitrile (50:50, v/v) at a flow rate of 1 mL/min. Detection was performed with an excitation wavelength of 280 nm and emission of 310 nm and 360 nm for internal standard and Naproxen, respectively. The method was validated by International Conference of Harmonization standards. The method is specific, accurate, and precise (relative standard deviation <3%). Limits of detection and quantification were 0.08 and 0.25 μg/mL, respectively, for biological samples. This method was applied to analyze brain/plasma ratios in mice that had received oral administrations of Naproxen micellar formulations containing 10% w/w of sodium dodecyl sulfate, Cremophor RH 40, or Tween 80. The sodium dodecyl sulfate micelles were faster and more widely distributed in the mouse brains.     

Multi-element analysis by inductively coupled plasma optical emission spectrometry of airborne particulate matter collected with a low-pressure cascade impactor

A method was developed for the elemental analysis of size segregated particles ranging from 0.03 to 10 microns. Sampling and analysis problems are discussed in this paper. Particles were collected with a Dekati low-pressure cascade impactor. PTFE filters coated with oleic acid were used as substrate. Particles were microwave digested in closed vessels. The optimum digestion mixture was composed of HNO3 (1 mL), HF (50 microL) and H2O (1 mL). The optimal power setting and digestion time were studied in order to achieve an efficient digestion. A ca. 35 min microwave digestion cycle at a 650 W maximum power allowed complete digestion of the samples. Special emphasis was placed on the pressure in the closed vessels to avoid sample losses. Solution samples were analysed by inductively coupled plasma optical emission spectrometry using an ultrasonic nebuliser for 18 elements (Al, Ba, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, S, Sr, Ti, V, Zn). This procedure was tested with NIST Standard Reference Material 1648 Urban Particulate. Recoveries for certified elements ranged from 95 to 105% except for Al (90%). The influence of cascade impactor materials was investigated with 44 field samples. Strong artefacts due to contamination were shown for analysis at environmental concentrations of Al, Cr, Mn and Ni.     

MRI of hepatic lymphoma

Thirteen patients with biopsy proven hepatic lymphoma (2 Hodgkin, 11 Non-Hodgkin) and a control group of 15 patients with hepatic metastases were analyzed quantitatively and qualitatively by MRI. Focal hepatic lymphoma was most reliably detected (eight of eight patients) and appeared hypointense relative to liver on T₁ weighted (CNR − 7.4 ± 2.3) and hyperintense on T₂ weighted (CNR + 8.4 ± 2.9) images. The mean T₁ and T₂ relaxation times of focal hepatic lymphoma (T₁ = 832 ± 234 msec, T₂ = 84 ± 16 ms) differed significantly from adjacent non-tumorous liver (T₁ = 420 ± 121 ms, T₂ = 51 ± 9 ms; p < 0.05), however CNR values and relaxation times were similar to those of hepatic metastases. Diffuse hepatic lymphoma (microscopic periportal infiltration) was undetectable by MRI in three patients by either morphologic features or quantitative criteria. A mixed pattern of hepatic lymphoma (focal lesions and diffuse infiltration) showed focal areas of slightly decreased signal intensity on T₁ weighted images (CNR = −1.7 ± 0.4) while T₂ weighted images revealed multiple regions of focal hyperintensity (CNR = +13.3 ± 8.4) superimposed on a diffusely hyperintense liver. Our experience demonstrates that either T₁ or T₂ weighted techniques are useful in detecting focal and that T₂ weighted techniques are useful in detecting mixed hepatic lymphoma. Conventional image derived relaxation time measurements and quantitative parameters were of no additional diagnostic value.     

Determination of the β-Glucosidase Activity in Different Soils by Pre Capillary Enzyme Assay Using Capillary Electrophoresis with Laser-Induced Fluorescence Detection

Enzyme activities can provide indication for quantitative changes in soil organic matter (SOM). It is known that the activities of most enzymes increase as native SOM content reflecting larger microbial communities and stabilization of enzymes on humic materials. β-Gucosidase (β-Glu) activities have been frequently used as indicators of changes in quantity and quality of SOM. In this study we propose a simple and very sensitive method, which has lower limit of detection compared with classic spectrophotometric method with the aim of determinate the β-Glu activity in soil samples using Fluorescein mono-β-D-glucopyranoside (FMGlc) as a substrate. The fluorescein released by the enzymatic reaction was quantified by capillary electrophoresis-laser induced fluorescence (CE-LIF) method. The background electrolyte (BGE) consisted in 40 mM phosphate buffer, pH 6. The LOD and LOQ for fluorescein were 1.3 10⁻⁷ mg mL⁻¹ and 6.4 10⁻⁶ mg mL⁻¹, respectively. This work deals with the minimization of the mixture for the enzymatic reaction and with the optimization conditions of CE separation. To the best of our knowledge, this is the first time that an enzymatic activity was detected in soil using CE-LIF system.     

Sulfenylation of nitroalkanes and hydroxyaryls

The sulfenylation of nitroalkanes and hydroxyaryls in DMSO using aryl disulfides as sulfenylating reagents was studied. The corresponding arylthionitroalkanes and arylthiohydroxyaryls were obtained in moderate to good yields in very mild conditions, thus improving the reported procedures for the synthesis of these compounds.     

Dissolving Hydroxyolite: A DNA Molecule into Its Hydroxyapatite Mold

In spite of the clinical importance of hydroxyapatite (HAp), the mechanism that controls its dissolution in acidic environments remains unclear. Knowledge of such a process is highly desirable to provide better understanding of different pathologies, as for example osteoporosis, and of the HAp potential as vehicle for gene delivery to replace damaged DNA. In this work, the mechanism of dissolution in acid conditions of HAp nanoparticles encapsulating double‐stranded DNA has been investigated at the atomistic level using computer simulations. For this purpose, four consecutive (multi‐step) molecular dynamics simulations, involving different temperatures and proton transfer processes, have been carried out. Results are consistent with a polynuclear decalcification mechanism in which proton transfer processes, from the surface to the internal regions of the particle, play a crucial role. In addition, the DNA remains protected by the mineral mold and transferred proton from both temperature and chemicals. These results, which indicate that biomineralization imparts very effective protection to DNA, also have important implications in other biomedical fields, as for example in the design of artificial bones or in the fight against osteoporosis by promoting the fixation of Ca²⁺ ions.     

On Clique-Transversals and Clique-Independent Sets

A clique-transversal of a graph G is a subset of vertices intersecting all the cliques of G. A clique-independent set is a subset of pairwise disjoint cliques of G. Denote by _C (G) and _C (G) the cardinalities of the minimum clique-transversal and maximum clique-independent set of G, respectively. Say that G is clique-perfect when _C (H)= _C (H), for every induced subgraph H of G. In this paper, we prove that every graph not containing a 4-wheel nor a 3-fan as induced subgraphs and such that every odd cycle of length greater than 3 has a short chord is clique-perfect. The proof leads to polynomial time algorithms for finding the parameters _C (G) and _C (G), for graphs belonging to this class. In addition, we prove that to decide whether or not a given subset of vertices of a graph is a clique-transversal is Co-NP-Complete. The complexity of this problem has been mentioned as unknown in the literature. Finally, we describe a family of highly clique-imperfect graphs, that is, a family of graphs G whose difference _C (G)– _C (G) is arbitrarily large.     

General approach for the stereocontrolled construction of the beta-lactam ring in amino acid-derived 4-alkyl-4-carboxy-2-azetidinones

The first general approach toward the asymmetric synthesis of 4-alkyl-4-carboxy-2-azetidinones derived from amino acids is described. The stereoselective construction of the beta-lactam ring was achieved through base-mediated intramolecular cyclization of the corresponding N(alpha)-chloroacetyl derivatives bearing (+)- or (-)-10-(N,N-dicyclohexylsulfamoyl)isoborneol as chiral auxiliary (ee up to 82%).