Dipyrrylmetheneboron Difluorides as Labels in Two-Photon Excited Fluorometry. Part II–Nucleic Acid Hybridization Assays

Five two-photon excitable dipyrrylmetheneboron difluoride labels (dipyrrylmethene-BF₂ labels) with fluorescence emission maximum between 530 and 590 nm, and a frequently used rhodamine label, TAMRA, were conjugated to aminomodified oligonucleotides. The performance of the labeled oligonucleotides was studied in a separation-free nucleic acid hybridization assay using ArcDia^™ TPX bioaffinity assay technology. The results show that oligonucleotide conjugates of dipyrrylmethene-BF₂ labels provide higher two-photon excited fluorescence yield and better assay sensitivity than corresponding TAMRA conjugate. The effect of conjugation on photophysical properties of the labels and performance of the labeled oligonucleotides in separation-free hybridization assay is discussed.     

Hydrophilic Labeling Reagents of Dipyrrylmethene-BF2 Dyes for Two-Photon Excited Fluorometry: Syntheses and Photophysical Characterization

Recently introduced bioaffinity assay technology, ArcDia TPX, is based on two-photon excited fluorescence (TPE) and it enables separation-free ultra-sensitive immunoassays from microvolumes. Here we present syntheses of novel two-photon excitable fluorescent labeling reagents which have been specially designed to be used as label molecules in the ArcDia TPX assay technique. The labeling reagents are based on dipyrrylmetheneboron difluoride (dipyrrylmethene-BF2) chromophore, which have been substituted with aryl, heteroaryl or arylalkenyl chemical groups to extend the pi-electron conjugation. These substitutions results in a series of dipyrrylmethene-BF2 fluorophores with different photophysical properties. Dipyrrylmethene-BF2 fluorophores have been further substituted with a dipeptide linker unit and finally activated as succinimidyl esters to enable specific coupling with primary amino groups. The dipeptide linker serves as a spacer arm between the label and a target, and enhances the solubility of the label in aqueous solutions. Study of the chemical and photophysical performance of the new labeling reagents is described. The new labeling reagents exhibit high fluorescence quantum yields, and molar absorption coefficients. The results show that the new labels with the hydrophilic dipeptide linker unit provide large two-photon excitation cross-sections, high fluorescence quantum efficiency and good solubility in aqueous solutions. The results suggest that the novel dipyrrylmethene-BF2 labels are highly applicable to bioaffinity assays based on two-photon excitation of fluorescence.     

LC–MS Analysis of the Essential Oils of Achillea millefolium and Achillea crithmifolia

The chemical composition of the hydro-distilled essential oils of Achillea millefolium and Achillea crithmifolia was analyzed by GC, GC–MS, ¹³C NMR and high resolution LC–MS. For the first time, the use of the combination of different chromatographic and spectral methods, primarily the advantage of LC-Orbitrap over standard methods, enabled the detection of azulenes and their progenitors, in minute quantities, in previously believed proazulene free Achillea taxon (A. crithmifolia). Furthermore, the LC-Orbitrap hyphenated method provided the means for detection of these and related non-volatile (GC-injector compared to water steam distillation) metabolites up to know unreported as essential oil constituents.     

Hot-electron-driven enhancement of spin-lattice coupling in Gd and Tb 4f ferromagnets observed by femtosecond x-ray magnetic circular dichroism

Femtosecond x-ray magnetic circular dichroism was used to study the time-dependent magnetic moment of 4f electrons in the ferromagnets Gd and Tb, which are known for their different spin-lattice coupling. We observe a two-step demagnetization with an ultrafast demagnetization time of 750 fs identical for both systems and slower times which differ sizeably with 40 ps for Gd and 8 ps for Tb. We conclude that spin-lattice coupling in the electronically excited state is enhanced up to 50 times compared to equilibrium.     

Complete assignment of the 1H and 13C NMR spectra of antimicrobial 4‐arylamino‐ 3‐nitrocoumarin derivatives

Herein, we describe the synthesis and complete assignment of the ¹H and ¹³C NMR chemical shifts of a series of antimicrobial 4‐arylamino‐3‐nitrocoumarin derivatives based on a combination of ¹H and ¹³C NMR, ¹H‐¹H‐COSY, NOESY, HSQC and HMBC experiments. Conformational effects upon the chemical shifts of the coumarin moiety arising from the anisotropy of the aryl side group are briefly discussed. This study provides the first complete and fully assigned NMR data for this important group of antimicrobial compounds and bridges the gap existing in the literature with regard to NMR structural data for 4‐arylamino‐3‐nitrocoumarins. Copyright © 2010 John Wiley & Sons, Ltd.     

Insights into the Pamamycin Biosynthesis

Pamamycins are macrodiolides of polyketide origin with antibacterial activities. Their biosynthesis has been proposed to utilize succinate as a building block. However, the mechanism of succinate incorporation into a polyketide was unclear. Here, we report identification of a pamamycin biosynthesis gene cluster by aligning genomes of two pamamycin‐producing strains. This unique cluster contains polyketide synthase (PKS) genes encoding seven discrete ketosynthase (KS) enzymes and one acyl‐carrier protein (ACP)‐encoding gene. A cosmid containing the entire set of genes required for pamamycin biosynthesis was successfully expressed in a heterologous host. Genetic and biochemical studies allowed complete delineation of pamamycin biosynthesis. The pathway proceeds through 3‐oxoadipyl‐CoA, a key intermediate in the primary metabolism of the degradation of aromatic compounds. 3‐Oxoadipyl‐CoA could be used as an extender unit in polyketide assembly to facilitate the incorporation of succinate.     

Determination of neomycin and oxytetracycline in the presence of their impurities in veterinary dosage forms by high-performance liquid chromatography/tandem mass spectrometry

Two HPLC/MS/MS methods, one for determination of neomycin sulfate and the other for determination of oxytetracycline hydrochloride in the presence of their impurities, were developed and validated. Separations were achieved with gradient elution on a C18 column. All components were ionized by positive-ion electrospray and detected by multiple reaction monitoring. Calibration curves were linear, with correlation coefficients >0.99. Precision of the methods was confirmed by RSD values of 0.34 and 0.71% for neomycin and oxytetracycline, respectively. Recovery values of 101.5 and 101.0%, respectively, indicated adequate accuracy. Analysis time for neomycin was 24 min, with the retention time of the main compound at 10.1 min; for oxytetracycline, the analysis time was 18 min, with the main peak at 9.95 min. Longer retention times than expected were a consequence of the necessity of chromatographic separation of isomers with the same ion transition. All impurities defined in the pharmacopoeias were determined and their identities confirmed. The methods were tested for QC of veterinary dosage forms (commercial powders and injections containing these antibiotics).     

A novel monochromator for experiments with ultrashort X‐ray pulses

Aiming at advancing storage‐ring‐based ultrafast X‐ray science, over the past few years many upgrades have been undertaken to continue improving beamline performance and photon flux at the Femtoslicing facility at BESSY II. In this article the particular design upgrade of one of the key optical components, the zone‐plate monochromator (ZPM) beamline, is reported. The beamline is devoted to optical pump/soft X‐ray probe applications with 100 fs (FWHM) X‐ray pulses in the soft X‐ray range at variable polarization. A novel approach consisting of an array of nine off‐axis reflection zone plates is used for a gapless coverage of the spectral range between 410 and 1333 eV at a designed resolution of E/ΔE = 500 and a pulse elongation of only 30 fs. With the upgrade of the ZPM the following was achieved: a smaller focus, an improved spectral resolution and bandwidth as well as excellent long‐term stability. The beamline will enable a new class of ultrafast applications with variable optical excitation wavelength and variable polarization.