Analyse der Alkohole

Analytical and Bioanalytical Chemistry -     

Bio-Templated Chiral Zeolitic Imidazolate Framework for Enantioselective Chemoresistive Sensing

Chiral metal–organic frameworks (MOFs) have gained rising attention as ordered nanoporous materials for enantiomer separations, chiral catalysis, and sensing. Among those, chiral MOFs are generally obtained through complex synthetic routes by using a limited choice of reactive chiral organic precursors as the primary linkers or auxiliary ligands. Here, we report a template-controlled synthesis of chiral MOFs from achiral precursors grown on chiral nematic cellulose-derived nanostructured bio-templates. We demonstrate that chiral MOFs, specifically, zeolitic imidazolate framework (ZIF), unc -[Zn(2-MeIm)₂, 2-MeIm=2-methylimidazole], can be grown from regular precursors within nanoporous organized chiral nematic nanocelluloses via directed assembly on twisted bundles of cellulose nanocrystals. The template-grown chiral ZIF possesses tetragonal crystal structure with chiral space group of P4₁, which is different from traditional cubic crystal structure of I-43 m for freely grown conventional ZIF-8. The uniaxially compressed dimensions of the unit cell of templated ZIF and crystalline dimensions are signatures of this structure. We observe that the templated chiral ZIF can facilitate the enantiotropic sensing. It shows enantioselective recognition and chiral sensing abilities with a low limit of detection of 39 μM and the corresponding limit of chiral detection of 300 μM for representative chiral amino acid, D- and L- alanine.     

Halogenation strategies in natural product biosynthesis

Halogenation is a frequent modification of secondary metabolites and can play a significant role in establishing the bioactivity of a compound. Enzymatic halogenation through oxidative mechanisms is the most common route to these metabolites, though direct halogenation via halide anion incorporation is also known to proceed through both enzymatic and nonenzymatic pathways. In this article, we review the current state of knowledge regarding the mechanisms of these transformations, highlight applications of this knowledge, and propose future opportunities and challenges for the field.     

Electric field mediated DNA motion model

Understanding the motion and the governing equations of a molecule's path in tissue is an ultimate requirement for the repeatable, site specific delivery of molecules [Joseph D. Hickey. Modelling the Motion of Ions and Molecules in Electroporation and Electrophoresis Field Conditions. University of South Florida, College of Arts and Sciences, Department of Physics, Tampa, Florida, 2003., Joseph D. Hickey and Richard Gilbert. Modeling the electromobility of ions in a target tissue. DNA and Cell Biology, 22 (12) (2003) 823-828.]. This paper describes a computationally efficient mathematical model and simulation technique for the examination of DNA fragments in a 1% agarose gel. The speed of the individual DNA fragments through the agarose gel was described through two parts. The maximum velocity was calculated using the Coulombic force divided by Stoke's law and that value was retarded by an exponential rate equation. The simulation utilizes previously published techniques modified for this specific application [Joseph D. Hickey and Richard Gilbert. Fluid flow electrophoresis model. Bioelectrochemistry, 63 (2) (2004) 365-367., Joseph D. Hickey and Richard Gilbert. Modeling the electromobility of ions in a target tissue. DNA and Cell Biology, 22 (12) (2003) 823-828.]. Five representative DNA fragment sizes that span the resolution of a 1% agarose gel were chosen for this analysis. The speeds corresponding to these five DNA fragment sizes were converted into discrete values and used in a 50 step simulation. The resultant error comparing the simulation with experimental distance was 7.76%. Through a 1-D optimization procedure, this error was reduced to 3.02% for a 52 step simulation.     

Solid phase synthesis of a prototype of a new class of biomimetic receptors for anionic carbohydrates

A solid phase synthesis for a new biomimetic receptor was developed. First binding studies show that binds anionic carbohydrates such as glucose-1-phosphate and cAMP with association constants in the lower millimolar range in 20% buffered water in DMSO using both polar and apolar interactions.     

CD and MCD of CytC3 and taurine dioxygenase: role of the facial triad in alpha-KG-dependent oxygenases

The alpha-ketoglutarate (alpha-KG)-dependent oxygenases are a large and diverse class of mononuclear non-heme iron enzymes that require FeII, alpha-KG, and dioxygen for catalysis with the alpha-KG cosubstrate supplying the additional reducing equivalents for oxygen activation. While these systems exhibit a diverse array of reactivities (i.e., hydroxylation, desaturation, ring closure, etc.), they all share a common structural motif at the FeII active site, termed the 2-His-1-carboxylate facial triad. Recently, a new subclass of alpha-KG-dependent oxygenases has been identified that exhibits novel reactivity, the oxidative halogenation of unactivated carbon centers. These enzymes are also structurally unique in that they do not contain the standard facial triad, as a Cl- ligand is coordinated in place of the carboxylate. An FeII methodology involving CD, MCD, and VTVH MCD spectroscopies was applied to CytC3 to elucidate the active-site structural effects of this perturbation of the coordination sphere. A significant decrease in the affinity of FeII for apo-CytC3 was observed, supporting the necessity of the facial triad for iron coordination to form the resting site. In addition, interesting differences observed in the FeII/alpha-KG complex relative to the cognate complex in other alpha-KG-dependent oxygenases indicate the presence of a distorted 6C site with a weak water ligand. Combined with parallel studies of taurine dioxygenase and past studies of clavaminate synthase, these results define a role of the carboxylate ligand of the facial triad in stabilizing water coordination via a H-bonding interaction between the noncoordinating oxygen of the carboxylate and the coordinated water. These studies provide initial insight into the active-site features that favor chlorination by CytC3 over the hydroxylation reactions occurring in related enzymes.     

Conversion of perhydropolysilazane into a SiOx network triggered by vacuum ultraviolet irradiation: access to flexible, transparent barrier coatings

The photochemical conversion of 200-500 nm layers of perhydropolysilazane --(SiH2-NH)n-- (PHPS) in the presence of oxygen into an SiOx network was studied. Different UV sources in the wavelength range of 160-240 nm, that is, 172 nm Xe2* and 222 nm KrCl* excimer, and 185 nm Hg low-pressure (HgLP) lamps were used for these purposes. The role of both ozone and O(1D) as well as of catalytic amounts of tertiary amines in the degradation process of PHPS and the formation of SiOx were studied. In this context, the kinetics of the entire reaction were elucidated and allowed both a continuous and discontinuous process to be established for the production of fully transparent, flexible barrier coatings. Barrier improvement factors (BIFs) of 400 were achieved with one single layer on 23 microm poly(ethyleneterephthalate) (PET), which translated into oxygen transmission rates (OTRs) of 0.20 cm3 m(-2) day(-1) bar(-1). Double layers prepared by this technique allowed the realization of OTRs of or=800.     

A chirp-compensated, injection-seeded alexandrite laser

A Q-switched alexandrite laser suitable for high-resolution spectroscopy is described which produces pulses of 35 mJ energy in a 10 MHz bandwidth, with a high-purity TEM₀₀ mode. The laser can be synchronised to external event to within 100 ns. The output pulse length is 120 ns and the repetition rate 25 Hz. The laser is injection-seeded by a Ti:sapphire laser operating around 730 nm. To preserve single-mode seeding under external triggering conditions, and to obtain small time-jitter, active cavity length control was used. In order to achieve the 10 MHz output bandwidth, intra-cavity electro-optic modulators were used to compensate for the frequency chirp. The refractive index of alexandrite was found to vary linearly with inversion density with a constant of proportionality equal to 1.6᎒^-24 cm³. In pulsed operation at 730 nm, the index change due to this effect is only partially compensated by changes due to ground state phonon relaxation.     

Polystyrene with Pendant Mixed Functional Ruthenium(II)‐Terpyridine Complexes

A vinyl substituted 2,2′:6′,2″‐terpyridine and a mixed, bifunctional ruthenium(II)‐terpyridine complex bearing a vinyl and a hydroxymethyl group are utilized as comonomers for radical copolymerization with styrene. The resulting polymers are characterized by means of UV‐vis spectroscopy and gel permeation chromatography, coupled with an in‐line diode array spectrophotometer.