Total synthesis of echinopines A and B: exploiting a bioinspired late-stage intramolecular cyclopropanation

Total synthesis of echinopine A and B have been accomplished, based on a strategy that involved two transition-metal-mediated ene-yne cycloisomerizations. A modified Pd-catalyzed enyne cycloisomerization/intramolecular Diels-Alder cascade rendered a more streamlined synthesis of tricyclic ketone 15, and a Ru-catalyzed ene-yne cycloisomerization/cyclopropanation resembled the late-stage [5/7] → [3/5/5/7] ring-forming sequence in the proposed biosynthetic pathway.     

Chemical studies on an endemic Philippine plant: sulfated glucoside and seco-A-ring triterpenoids from Dillenia philippinensis

The leaves of the endemic Philippine plant, Dillenia philippinensis yielded 11 compounds including one new sulfated glucoside and a new seco-A-ring oleanane-type triterpenoid. The molecular structures of these compounds were elucidated by means of NMR, MS and other spectroscopic techniques, as well as by comparison with literature data. Anti-Leishmania activity and cytotoxic activity against A549 human lung adenocarcinoma cells were also examined.     

Multiple passive element enriched photoacoustic computed tomography

Recently, we presented a method using laser-induced ultrasound from an external absorber (passive element) to image the ultrasound transmission parameters of an object under photoacoustic tomographic investigation. The method suffers from long measurement times due to the requirement for a large number of views and consequently physical projections around the object. Here we propose and validate an approach that permits a multitude of views to be obtained within a limited projection scenario. The approach uses a plurality of spatially distributed external absorbers in the path of the light, that results in multiple laser-induced ultrasound sources to interrogate the object from a number of angles. This reduces the required number of rotation angles or physical projections around the object, permitting a considerable reduction in imaging time without significant degradation in image quality. The approach brings the concept of hybrid imaging of ultrasound transmission parameters together with photoacoustic imaging, into the realm of practical application.     

Moderator for neutron activation with the photoneutrons produced by a LINAC

Using Monte Carlo methods a polyethylene moderator has been designed to induce activation using the photoneutrons field of a 15 MV linear accelerator for radiotherapy. In the calculations the photoneutron spectrum at 1 m from the isocenter was used as a source term and the neutron spectra were calculated in the center of different size cylindrical moderators. The best size was selected defining the thermal-to-fast-neutron ratios as a figure of merit. The moderator was built and its performance was evaluated by inducing the activation of Mn dissolved in water, silver coins and souvenir coin. The thermal neutron fluence rate was determined with the Mn samples being 9.96 × 10⁵ cm^?2 Gy _x ^?1 .     

Use of Styrene as Sole Carbon Source by the Fungus Exophiala oligosperma: Optimization and Modeling of Biodegradation, Pathway Elucidation, and Cell Membrane Composition

Biodegradation of styrene by Exophiala sp. was tested at different initial concentrations (19.3?C170.6?mg?l^?1), pH (2.8?C8.7), and temperatures (19.8?C45.1?°C), for 120?h according to a 2³ full-factorial central composite design. The specific growth rate (SGR, per hour) and specific styrene utilization rate (SUR, milligrams of styrene per milligram of biomass per hour) values were used as the response variables for optimization purposes. The interactions between concentration and temperature (P?=?0.022), and pH and temperature (P?=?0.010) for SGR, and interactions between concentration and temperature (P?=?0.012) for SUR were found to be statistically significant. The optimal values for achieving high SGR (0.15?h^?1) and SUR (0.3622?mg styrene mg^?1 biomass h^?1) were calculated from the regression model equation. Those values are C _o ?=?89.1?mg?l^?1, pH?=?5.4, and T?=?31.5?°C for SGR and C _o ?=?69.2?mg?l^?1, pH?=?5.5, and T?=?32.4?°C for SUR. It was also observed that the Exophiala strain degrades styrene via phenylacetic acid, involving initial oxidation of the vinyl side chain. Besides, in the presence of styrene, changes in the fatty acids profile were also observed. It is hypothesized that an increasing amount of linoleic acid (18:2) may be involved in the protection of the fungus against toxic substrate.     

N-H stretching modes of adenosine monomer in solution studied by ultrafast nonlinear infrared spectroscopy and ab initio calculations

The N-H stretching vibrations of adenine, one of the building blocks of DNA, are studied by combining infrared absorption and nonlinear two-dimensional infrared spectroscopy with ab initio calculations. We determine diagonal and off-diagonal anharmonicities of N-H stretching vibrations in chemically modified adenosine monomer dissolved in chloroform. For the single-quantum excitation manifold, the normal mode picture with symmetric and asymmetric NH(2) stretching vibrations is fully appropriate. For the two-quantum excitation manifold, however, the interplay between intermode coupling and frequency shifts due to a large diagonal anharmonicity leads to a situation where strong mixing does not occur. We compare our findings with previously reported values obtained on overtone spectroscopy of coupled hydrogen stretching oscillators.     

Study of DNA-ellipticine interaction by capillary electrophoresis with laser-induced fluorescence detection

Ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole), an alkaloid isolated from Apocynaceae plants, exhibits an antitumor activity, which is exceptionally high against several specific types of tumors. Ellipticine is also interesting as an anticancer drug as it has limited side effects and lacks of hematological toxicity. Various methods to study intercalating activity of this drug have been developed. However, to our best knowledge, capillary electrophoresis (CE) as a technique combining high separation resolution with various detection options has never been used for these purposes. In this study, a novel separation method based on CE with laser-induced fluorescence (CE-LIF) detection has been developed for the determination of ellipticine and for the monitoring of ellipticine-DNA interaction. Sodium acetate (50 mM, pH 4.5) was used as a background electrolyte and LIF detection at λ(ex) = 488 nm. The limit of detection for ellipticine was determined to be 5 × 10?? M. A total of 20% dimethyl sulfoxide was found optimal as sample solvent. Additionally, intercalation of ellipticine into the double-stranded DNA was investigated. Signal corresponding to ellipticine was decreasing and a new peak appeared and was growing. It can be concluded that CE-LIF is a method applicable to in vitro studies of ellipticine-DNA complexes.     

Structural changes in metallothionein isoforms revealed by capillary electrophoresis and Brdicka reaction

Metallothionein (MT) as a potential cancer marker is at the center of interest and its properties, functions and behavior under various conditions is intensively studied. In the present study, two major mammalian MT isoforms (MT‐1 and MT‐2) were separated using capillary electrophoresis (CE) coupled with UV detector in order to describe their basic behavior. Under the optimized conditions, the separation of both isoforms was enabled as well as estimation of detection limits as subunits and units of ng per μL for MT‐2 and MT‐1, respectively. Further, the effects of thermal treatment and the presence of denaturing agent such as urea on MT‐1 and MT‐2 isoforms were studied by CE‐UV. Thermal treatment caused an increase in the signals of both isoforms. A new parameter called precipitation rate has been defined based on this finding. This parameter can be expressed as a slope of the linear regression of the time dependency curve recalculated on the MT concentration. The thermal precipitation rate for MT‐1 and MT‐2 was determined as 1.1 and 0.9 ng of MT/min, respectively. The chemical precipitation rate calculated from the linear regression for both isoforms provided the same value of 0.25 ng of MT/min. The results were confirmed by manual spectrometric measurements and by differential pulse voltammetry Brdicka reaction. Based on these results, a model of MT behavior under the conditions studied was suggested.     

Microphase separation and rheology of a semicrystalline poly(ether-ester) multiblock copolymer

A microphase separation transition (MST) of a thermoplastic elastomer based on soft segments of poly(tetra methylene oxide) and hard crystalline segments of poly(tetra methylene terephthalate) has been studied by means of rheological measurements, differential scanning calorimetry (DSC), and wide-angle X-ray scattering (WAXS), showing that the MST is entirely caused by melting/crystallization, and that no separate segmental mixing/demixing transition is involved. DSC and WAXS measurements show that melting starts at 190°C, leading to crystal reorganization effects up to above 200°C, and that a gradual decrease in crystallinity occurs from below 210°C up to 224°C, above which temperature no crystals are left. Rheological measurements reveal a wide MST (207–224°C) upon heating, which coincides perfectly with the melting range. From this coincidence together with the Maxwell fluid behavior directly following the MST, it is concluded that melting leads to a one-phase liquid, and that no separate segmental mixing transition occurs. Similar results are obtained upon cooling, indicating that crystallization is the driving force for phase separation and that no separate segmental demixing step precedes crystallization. The wide MST implies a large processing window over which the rheological properties change from highly elastic, with a distinct yield stress, to normal pseudoplastic, enabling application in preparation of structured blends. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1795–1804, 1998     

Multiple emissions and brilliant white luminescence from gold(I) O,O'-di(alkyl)dithiophosphate dimers

The Au(I) dimers Au(2)[S(2)P(OR)(2)](2) for R = Me, Et are found to exhibit a structure in which aurophilic interactions yield one-dimensional Au...Au chains with intermolecular contacts (3.09-3.16 A) similar to the Au...Au distances within the dimers (3.10-3.18 A). The dimers are luminescent in the solid state and become brilliantly emissive at low temperatures. At 77 K, Au(2)[S(2)P(OMe)(2)](2) shows multiple emission bands. The two higher energy bands at 415 and 456 nm are assigned to (1)MC and (3)MC on the basis of lifetime measurements (20 ns and 2.16 micros, respectively) and concentration-related effects, while the lower energy band at 560 nm is attributed to a LMCT excited state. In frozen glasses of different solvents, Au(2)[S(2)P(OMe)(2)](2) as well as the Et and n-Pr derivatives exhibit a bright luminescence of different colors and striking thermochromism of the emission.