Spiroacetal biosynthesis in insects from Diptera to Hymenoptera: the Giant Ichneumon wasp Megarhyssa nortoni nortoni Cresson

The volatile components of the mandibular gland secretion generated by the Giant Ichneumon parasitoid wasp Megarhyssa nortoni nortoni Cresson are mainly spiroacetals and methyl ketones, and all have an odd number of carbon atoms. A biosynthetic scheme rationalizing the formation of these diverse components is presented. This scheme is based on the results of incorporation studies using (2)H-labeled precursors and [(18)O]dioxygen. The key steps are postulated to be decarboxylation of beta-ketoacid equivalents, beta-oxidation (chain shortening), and monooxygenase-mediated hydroxylation leading to a putative ketodiol that cyclizes to spiroacetals. The generality of the role of monooxygenases in spiroacetal formation in insects is considered, and overall, a cohesive, internally consistent theory of spiroacetal generation by insects is presented, against which future hypotheses will have to be compared.     

Molecular complexation and binding studied by electrophoretic NMR spectroscopy

Electrophoretic mobilities obtained on a molecularly selective manner by electrophoretic NMR can be used to provide a quantitative characterization of the composition and stoichiometry of molecular complexes. This is demonstrated in complexes formed by uncharged cyclodextrins which attain an electrophoretic mobility upon inclusion of charged surfactants.     

A Dimension Spectrum for SLE Boundary Collisions

We consider chordal SLE\({_\kappa}\) curves for \({\kappa > 4}\), where the intersection of the curve with the boundary is a random fractal of almost sure Hausdorff dimension \({{\rm min}\{2-8/\kappa,1\}}\). We study the random sets of points at which the curve collides with the real line at a specified “angle” and compute an almost sure dimension spectrum describing the metric size of these sets. We work with the forward SLE flow and a key tool in the analysis is Girsanov’s theorem, which is used to study events on which moments concentrate. The two-point correlation estimates are proved using the direct method.     

Pilicides-small molecules targeting bacterial virulence

In a time of emerging bacterial resistance there is a vital need for new targets and strategies in antibacterial therapy. Using uropathogenic Escherichia coli as a model pathogen we have developed a class of compounds, pilicides, which inhibit the formation of virulence-associated organelles termed pili. The pilicides interfere with a highly conserved bacterial assembly and secretion system called the chaperone-usher pathway, which is abundant in a vast number of Gram-negative pathogens and serves to assemble multi-protein surface fibers (pili/fimbriae). This class of compounds provides a platform to gain insight into important biological processes such as the molecular mechanisms of the chaperone-usher pathway and the sophisticated function of pili. Pili are primarily involved in bacterial adhesion, invasion and persistence to host defenses. On this basis, pilicides can aid the development of new antibacterial agents.     

Kinetic characterization of an extremely slow DNA binding equilibrium

We here exploit the recently reported thermodynamic preference for poly(dAdT)(2) over mixed-sequence calf thymus (ct) DNA of two binuclear ruthenium complexes, DeltaDelta-[mu-bidppz(bipy)4Ru2](4+) (B) and DeltaDelta-[mu-bidppz(phen)(4)Ru(2)](4+) (P), that bind to DNA by threading intercalation, to determine their intrinsic dissociation rates. After adding poly(dAdT)(2) as a sequestering agent to B or P bound to ct-DNA, the observed rate of change in luminescence upon binding to the polynucleotide reflects the rate of dissociation from the mixed sequence. The activation parameters for the threading and dissociation rate constants allow us for the first time to characterize the thermodynamics of the exceedingly slow threading intercalation equilibrium of B and P with ct-DNA. The equilibrium is found to be endothermic by 33 and 76 kJ/mol, respectively, and the largest part of the enthalpy difference between the complexes originates from the forward threading step. At physiological temperature (37 degrees C) B and P have dissociation half-lives of 18 and 38 h, respectively. This is to our knowledge the slowest dissociating noncovalently bound DNA-drug reported. SDS sequestration is the traditional method for determination of rate constants for cationic drugs dissociating from DNA. However, the rates may be severely overestimated for slowly dissociating molecules due to unwanted catalysis by the SDS monomers and micelles. Having determined the intrinsic dissociation rates with poly(dAdT)(2) as sequestering agent, we find that the catalytic effect of SDS on the dissociation rate may be up to a factor of 60, and that the catalysis is entropy driven. A simple kinetic model for the SDS concentration dependence of the apparent dissociation rate suggests an intermediate that involves both micelles and DNA-threaded complex.     

A simplified method for capillary embedment into microfluidic devices - exemplified by sol-gel-based preconcentration

We here describe an alternative method of embedding functionalized capillaries into microdevices fabricated in PDMS. The capillaries have square-shaped outer dimensions and fit into elastic PDMS channel networks of similar dimensions. By modifying the capillary off-chip, the technique makes it possible to integrate a new chip function without risking contamination of already existing chemically patterned areas because of new reagent solutions. Leak-free insertion of these capillaries has earlier been reported, where a thin layer of uncured PDMS bonded the capillary to the microchannel and the lid structure. In this new approach, oxygen plasma is used to bond the square capillary to the PDMS, eliminating the risk of clogging the microsystem with uncured prepolymer. The new embedding technique was exemplified and evaluated by inserting a square capillary piece containing monolithic sol-gel for sample preconcentration application. The assembled microdevice was run with mass spectrometric detection, showing that peptides were preconcentrated without leakage from either the sol-gel itself or around the inserted capillary. Repeated preconcentration runs showed migration times better than 3% for all peptides. We believe that the presented microchip assembling technique greatly simplifies the insertion of functionalized capillary pieces, e.g., an initial preconcentrator to a PDMS device containing other downstream modules.     

Asymmetric Reduction of Ketones with Catecholborane Using 2,6-BODOL Complexes of Titanium(IV) as Catalysts

Reductions performed with Ti^IV complexes of ligands based on bicyclo[2.2.2]octane diols 5 and 6 are effective catalysts in the reduction of prochiral ketones to optically active alcohols, with catecholborane as the reducing agent. Methyl ketones are favored and enantiomeric excesses (ee) of ≤98 % have been achieved with acetophenone as the substrate. Several other substrates were tested, among them 2-octanone, which gave 2-octanol in 87 % ee. Further details of the method were examined, for example, temperature, solvent composition, amount of molecular sieves (4 Å), and catecholborane quality, as well as the sensitivity of the ligands towards acids. NMR spectroscopic methods were used to gain some insight into the complexes formed between the ligands and [Ti(OiPr)₄]. A dimeric structure is proposed for the pre-catalyst.