Oxidative rearrangement of 2-alkoxy-3,4-dihydro-2H-pyrans: stereocontrolled synthesis of 4,5-cis-disubstituted tetrahydrofuranones including whisky and cognac lactones and crobarbatic acid

Oxidation of 2-alkoxy-3,4-dihydro-2H-pyrans 3 with dimethyldioxirane or MTO/urea-H₂O₂ followed by Jones oxidation leads to rearrangement and stereocontrolled formation of 4,5-cis-disubstituted tetrahydrofuranones. The method is applied to the synthesis of the whisky lactone 9, cognac lactone 10 and crobarbatic acid 17.     

Towards a second generation of ionic liquid matrices (ILMs) for MALDI-MS of Peptides, proteins, and carbohydrates

Second generation ionic liquid matrices are developed, examined, and tested. They have shown a wide mass detection range (<1000 Da to >270,000 Da) for proteins and peptides with greater S/N ratios than solid matrices. These ionic liquid matrices also exhibit the ability to effectively ionize proteins of large mass without disrupting noncovalent interactions between monomers. Both the anionic and cationic moieties have been varied systematically to find an ionic liquid matrix with the best physical properties, analyte signal intensity, and widest mass detection range. It was determined that both the proton affinity and pK_a of the cation have a large effect on the ionic liquid matrices’ ability to effectively ionize the analyte. The ionic liquid matrices can be used to detect polysaccharides with fewer degradation products than solid matrices. N,N-diisopropylethylammonium α-cyano-4-hydroxycinnamate and N-isopropyl-N-methyl-t-butylammonium α-cyano-4-hydroxycinnamate were the best matrices for proteins and peptides, while N,N-diisopropylethylammonium α-cyano-4-hydroxycinnamate and N,N-diisopropylethylammonium ferulate were the best matrices for carbohydrates.     

Principal eigenvalues and an anti-maximum principle for homogeneous fully nonlinear elliptic equations

We study the fully nonlinear elliptic equation

(0.1)     

Development of dinitrophenylated cyclodextrin derivatives for enhanced enantiomeric separations by high-performance liquid chromatography

The synthesis and evaluation of new dinitrophenyl (DNP) substituted beta-cyclodextrin (beta-CD) chiral stationary phases (CSPs) for the enantioseparation of various classes of chiral analytes by HPLC are presented. The dinitrophenyl substituted beta-CD derivatives are synthesized and covalently bonded to functionalized 5 microm spherical porous silica gel. These are the first reported derivatized cyclodextrin which contains pi-electron deficient substituents (i.e., pi-acidic moieties). The column performance in terms of their ability to separate enantiomers is evaluated. A variety of different dinitro-substituted aryl groups are investigated and compared. The pH of the mobile phase buffers, the buffer composition, the number and position of the dinitro groups on the phenyl ring substituent, the degree of substitution, and the bonding strategy all greatly affect the performance of the CSPs. A large variety of racemic compounds have been separated successfully on these CSPs. The bonded dinitrophenyl-derivatized cyclodextrins are stable in all three mobile phase modes, namely, the reversed-phase, polar organic, and normal phase modes. No degradation in column performance was observed in any mode of operation even after more than 1000 injections. The analytical applicability of these types of CSPs for enantiomeric separations is discussed in detail.     

LC Enantioseparation of Aryl-Substituted β-Lactams Using Variable-Temperature Conditions

Direct reversed-phase high-performance liquid chromatographic methods were developed for the separation of enantiomers of β-lactams. The enantiomers of 7 aryl-substituted β-lactams were separated on chiral stationary phases containing the macrocyclic glycopeptide antibiotic teicoplanin (Chirobiotic T) and teicoplanin aglycone (Chirobiotic TAG) at 10-°C increments in the range 5–45 °C, using different compositions of 0.1% aqueous triethylammonium acetate (pH 4.1)/methanol (v/v) as mobile phase. The mobile phase composition and temperature were varied to achieve baseline resolutions in a single chromatographic run. The dependence of the natural logarithms of the selectivity factors ln α on the inverse of temperature, 1/T, was used to determine the thermodynamic data on the enantiomers. The thermodynamic data revealed that all the compounds in this study undergo separation via the same enthalpy-driven chiral recognition mechanism. The different methods were compared in systematic chromatographic examinations. The effects of the organic modifier, the mobile phase composition and the temperature on the separation were investigated.     

Rapid determination of complex mixtures by dual-column gas chromatography with a novel stationary phase combination and spectrometric detection

Fast GC separations of a broad range of analytes are demonstrated using a capillary column coated with a novel immobilized ionic liquid (IIL) stationary phase. Both completely cross-linked and partially cross-linked columns were evaluated, yielding approximately 1600 and approximately 2000 theoretical plates per meter, respectively. Enhanced separation is demonstrated using a dual-column ensemble comprised of an IIL column, a commercially coated Rtx-1 column, and a pneumatic valve connecting the inlet to the junction point between the two columns. Enhanced separation of 20 components, with two sets of co-eluting peaks is shown in approximately 150 s, while sacrificing only a length of time equivalent to the sum of the stop flow pulses, or about 15.5 s. A novel application of a band trajectory model that shows band position as a function of analysis time as analytes move through the column ensemble is employed to determine pulse application times. The model predicts component retention times within a few seconds. Another method of selectivity enhancement of the IIL stationary phase-coated columns is demonstrated using a differential mobility spectrometer (DMS) that provides a second dimension separation based on ion mobility in a high-frequency electrical field. The DMS is able to separate all but one set of co-eluting components from the IIL column. The separation of 13 components found in the headspace above U.S. currency is demonstrated using the IIL column in a dual-column ensemble as well as with the DMS.     

Systems analysis of hybrid, multi-scale complex flow simulations using Newton-GMRES

We present a methodology to analyze the stationary states and stability of complex fluid flows by using hybrid, discrete, and/or continuum multi-scale simulations. Building on existing theories, our scheme extracts dynamical and equilibrium characteristics from carefully chosen time integrations of these multi-scale evolution equations. Two canonical problems are presented to demonstrate the ability and accuracy of the formalism. The first is an investigation of flow-induced transitions seen in homogeneous, hard- rod liquid crystal suspensions subjected to a linear shear flow. In the second problem, we study the phenomenon of draw resonance, a dynamical instability in an isothermal fiber-spinning process, by using a multi-scale hybrid simulation that incorporates both stochastic and continuum models.     

Experimental validation of a dynamic resonant wall shear stress sensor

Experimental measurements are used to validate a numerical model of a dynamic resonant wall shear stress sensor. The numerical model consists of an unsteady two-dimensional boundary-layer model for the flow and a simple mechanical model for the sensor itself. The sensor’s sensitivity to wall shear stress is experimentally determined in a flat-plate boundary layer, and the results agree closely with those from the numerical simulations. Using the validated model, it is determined that the energy lost in each sensor oscillation due to the interaction between the sensor and fluid increases with increasing mean wall shear stress.     

能源采集,终于等到了

背景＂能量采集＂的概念自2000年初就出现了,但凭借着近期的技术发展,相关的概念才推展至商业化阶段。目前,全球的工程师们都积极地开发着利用非传统型能源的新颖方法。     

Studies of iron(II) and iron(III) complexes with fac-N2O, cis-N2O2 and N2O3 donor ligands: models for the 2-His 1-carboxylate motif of non-heme iron monooxygenases

Enzymes in the oxygen-activating class of mononuclear non-heme iron oxygenases (MNOs) contain a highly conserved iron center facially ligated by two histidine nitrogen atoms and one carboxylate oxygen atom that leave one face of the metal center (three binding sites) open for coordination to cofactor, substrate, and/or dioxygen. A comparative family of [Fe(II/III)(N(2)O(n))(L)(4-n))](±x), n = 1-3, L = solvent or Cl(-), model complexes, based on a ligand series that supports a facially ligated N,N,O core that is then modified to contain either one or two additional carboxylate chelate arms, has been structurally and spectroscopically characterized. EPR studies demonstrate that the high-spin d(5) Fe(III)g = 4.3 signal becomes more symmetrical as the number of carboxylate ligands decreases across the series Fe(N(2)O(3)), Fe(N(2)O(2)), and Fe(N(2)O(1)), reflecting an increase in the E/D strain of these complexes as the number of exchangeable/solvent coordination sites increases, paralleling the enhanced distribution of electronic structures that contribute to the spectral line shape. The observed systematic variations in the Fe(II)-Fe(III) oxidation-reduction potentials illustrate the fundamental influence of differential carboxylate ligation. The trend towards lower reduction potential for the iron center across the [Fe(III)(N(2)O(1))Cl(3)](-), [Fe(III)(N(2)O(2))Cl(2)](-) and [Fe(III)(N(2)O(3))Cl](-) series is consistent with replacement of the chloride anions with the more strongly donating anionic O-donor carboxylate ligands that are expected to stabilize the oxidized ferric state. This electrochemical trend parallels the observed dioxygen sensitivity of the three ferrous complexes (Fe(II)(N(2)O(1)) < Fe(II)(N(2)O(2)) < Fe(II)(N(2)O(3))), which form μ-oxo bridged ferric species upon exposure to air or oxygen atom donor (OAD) molecules. The observed oxygen sensitivity is particularly interesting and discussed in the context of α-ketoglutarate-dependent MNO enzyme mechanisms.