Thermal rearrangement of spiro[naphthalene(naphthopyranofurazan)]oxides to spiro[naphthalene(phenalenofurazan)oxides. A probable furazan oxide triggered tandem isomerisation process

Thermal rearrangement of (±)-spiro{naphthalene-1(2H),4′-(naphtho-[2′,1′:2,3]pyrano[4,5-c]furazan)}-2-one-11′-oxides in DMF or acetic anhydride at 140 °C gave an isomeric mixture of (±)-spiro{naphthalene-1(2H),1′-(5′-hydroxyphenalene[1,2-c]furazan)}-2-one-2′-oxides and 4′-oxides. The rearranged structure was confirmed from X-ray analysis and was consistent with the through space NOE data. The rearrangement is suggested to be an overall tandem isomerization process. Using variable temperature ¹H NMR spectroscopy the lower limit for the isomerisation barrier for a pair of tautomers was calculated to be 22 kcal mol⁻¹ at 423 K. The isomerisation equilibrium for a pair of isomers was studied by variable temperature ¹H NMR. The lower limit for the isomerisation barrier was calculated to be 22 kcal mol⁻¹ at 423 K. This low value may be indicative of the difficulty encountered in separating the isomers by chromatography. Semi-empirical AM1 and molecular mechanics calculations suggest that the (±)-spiro{naphthalene-1(2H),1′-(5′-hydroxyphenalene[1,2-c]furazan)}-2-one-2′-oxides are more stable than their 4′-oxide counterparts, in accordance to the X-ray structure. The lower population of the 4′-oxide isomers relative to that of the 2′-oxide isomers was explained in terms of an unfavourable intramolecular steric interaction found in the low energy structure of the former.     

Comparison of cysteine and penicillamine ligands in a Co(II) maquette

l-Penicillamine (Pen) has been investigated as a ligand for metalloprotein design by examining the binding of Co(II) to the sequence NH(2)-KL(Pen)EGG.(Pen)IG(Pen)GA(Pen).GGW-CONH(2). For comparison, we have studied Co(II) binding to the analogous sequence with Cys ligands, the ferredoxin maquette ligand IGA that was originally designed to bind a [4Fe-4S] cluster. The Co(II) affinity and UV-vis spectroscopic properties of IGA indicate formation of a pseudotetrahedral tetrathiolate ligated Co(II). In contrast, IGA-Pen showed formation of a pseudotetrahedral complex with Co(II) bound by three Pen ligands and an exogenous H(2)O. EXAFS data on both Co(II) complexes confirms not only the proposed primary coordination spheres but also shows six Co(II)-C(beta) methyl group distances in Co(II)-IGA-Pen. These results demonstrate that ligand sterics in simple peptides can be designed to provide asymmetric coordination spheres such as those commonly observed in natural metalloproteins.     

Multiresolution stochastic simulations of reaction-diffusion processes

Stochastic simulations of reaction-diffusion processes are used extensively for the modeling of complex systems in areas ranging from biology and social sciences to ecosystems and materials processing. These processes often exhibit disparate scales that render their simulation prohibitive even for massive computational resources. The problem is resolved by introducing a novel stochastic multiresolution method that enables the efficient simulation of reaction-diffusion processes as modeled by many-particle systems. The proposed method quantifies and efficiently handles the associated stiffness in simulating the system dynamics and its computational efficiency and accuracy are demonstrated in simulations of a model problem described by the Fisher-Kolmogorov equation. The method is general and can be applied to other many-particle models of physical processes.     

A convenient synthesis of new enantiomerically pure trihydroxypyrrolizidines using l-erythrose glycosylhydroxylamine as a masked acyclic chiral nitrone

A route has been developed for the synthesis of enantiomerically pure trihydroxylated pyrrolizidines starting from l-erythrose glycosylhydroxylamine. The latter acts as a masked acyclic nitrone and reacts diastereoselectively from its Re-face with methyl acrylate to give the corresponding isoxazolidines, which after reductive N-O cleavage are recyclized to trihydroxypyrrolizidines via a Mitsunobu condensation.     

Spacetime Coarse Grainings and the Problem of Time in the Decoherent Histories Approach to Quantum Theory

We investigate the possibility of assigning consistent probabilities to sets of histories characterized by whether they enter a particular subspace of the Hilbert space of a closed system during a given time interval. In particular we investigate the case that this subspace is a region of the configuration space. This corresponds to a particular class of coarse grainings of spacetime regions. We consider the arrival time problem, as a warm up, to deal with the problem of time in reparametrization invariant theories (as for example in canonical quantum gravity) which subsequently we examine. Decoherence conditions and probabilities for those application are derived. The resulting decoherence condition does not depend on the explicit form of the restricted propagator that was problematic for generalizations such as application in quantum cosmology. Closely related to our results, is the problem of tunnelling time as well as the quantum Zeno effect. Some interpretational comments conclude, and we discuss the applicability of this formalism to deal with the arrival time problem and the problem of time in general.     

Microwave-Assisted Extraction Coupled to HPLC-UV Combined with Chemometrics for the Determination of Bioactive Compounds in Pistachio Nuts and the Guarantee of Quality and Authenticity

Two novel microwave-assisted extraction (MAE) methods were developed for the isolation of phenols and tocopherols from pistachio nuts. The extracts were analyzed by reversed-phase high-pressure liquid chromatography coupled with a UV detector (RP-HPLC-UV). In total, eighteen pistachio samples, originating from Greece and Turkey, were analyzed and thirteen phenolic compounds, as well as α-tocopherol, (β + γ)-tocopherol, and δ-tocopherol, were identified. The analytical methods were validated and presented good linearity (r² > 0.990) and a high recovery rate over the range of 82.4 to 95.3% for phenols, and 93.1 to 96.4% for tocopherols. Repeatablility was calculated over the range 1.8–5.8%RSD for intra-day experiments, and reproducibility over the range 3.2–9.4%RSD for inter-day experiments, respectively. Principal component analysis (PCA) was employed to analyze the differences between the concentrations of the bioactive compounds with respect to geographical origin, while agglomerative hierarchical clustering (AHC) was used to cluster the samples based on their similarity and according to the geographical origin.     

Oxidative cyclization in the synthesis of 5‐ and 6‐membered N,O‐heterocycles

The versatility and potential of oxidative cyclization in the synthesis of 5‐ and 6‐membered N‐ and/or O‐heterocycles is presented through judiciously selected examples.© 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:642–670, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10200     

Comparison of distillation and ultrasound-assisted extraction methods for the isolation of sensitive aroma compounds from garlic (Allium sativum)

A comparative study of traditional simultaneous distillation extraction (SDE), microwave assisted hydrodistillation extraction (MWHD) and ultrasound-assisted extraction (USE) is presented, for the extraction of essential oils from fresh garlic (Allium sativum) cloves. Each method is evaluated in terms of qualitative and quantitative composition of the isolated essential oil. The highly reactive sulfur molecules of the garlic volatile fraction show variable response to the different isolation methods. The application of ultrasound for the extraction of the essential oil is considered to cause a lesser damage of thermal-sensitive molecules, thus, providing a better approach of the compounds primarily responsible for the characteristic odor and taste of freshly chopped garlic. All heat-involving isolation procedures have been shown to differentiate the volatile-fraction profile as analyzed by GC-MS. Especially when grouping the compounds into cyclic and acyclic, the percentage concentrations drop from 77.4% to 8.7% for the acyclic while that of the cyclic compounds increase from 4.7% to 70.8%. The observed fact may be attributed to the effect of the heat applied, which changes from harsh thermal treatment (SDE) to short time thermal (MWHD) and room-temperature isolation (USE). The use of USE proves to be crucial in order to provide reliable insight into garlic's chemistry.     

DAPNe with micro-capillary separatory chemistry-coupled to MALDI-MS for the analysis of polar and non-polar lipid metabolism in one cell

The cellular metabolome is considered to be a representation of cellular phenotype and cellular response to changes to internal or external events. Methods to expand the coverage of the expansive physiochemical properties that makeup the metabolome currently utilize multi-step extractions and chromatographic separations prior to chemical detection, leading to lengthy analysis times. In this study, a single-step procedure for the extraction and separation of a sample using a micro-capillary as a separatory funnel to achieve analyte partitioning within an organic/aqueous immiscible solvent system is described. The separated analytes are then spotted for MALDI-MS imaging and distribution ratios are calculated. Initially, the method is applied to standard mixtures for proof of partitioning. The extraction of an individual cell is non-reproducible; therefore, a broad chemical analysis of metabolites is necessary and will be illustrated with the one-cell analysis of a single Snu-5 gastric cancer cell taken from a cellular suspension. The method presented here shows a broad partitioning dynamic range as a single-step method for lipid analysis demonstrating a decrease in ion suppression often present in MALDI analysis of lipids.

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