Regioselective hydroxylation of diverse flavonoids by an aromatic peroxygenase

Aromatic peroxygenases are extracellular fungal biocatalysts that selectively oxidize a variety of organic compounds. We found that the peroxygenase of the fungus Agrocybe aegerita (AaeAPO) catalyzes the H₂O₂-dependent hydroxylation of diverse flavonoids. The reactions proceeded rapidly and regioselectively yielding preferentially monohydroxylated products, e.g., from flavanone, apigenin, luteolin, flavone as well as daidzein, quercetin, kaempferol, and genistein. In addition to hydroxylation, O-demethylation of fully methoxylated tangeretin was catalyzed by AaeAPO. The enzyme was merely lacking activity on the quercetin glycoside rutin, maybe due to sterical hindrance by the bulky sugar substituents. Mechanistic studies indicated the presence of epoxide intermediates during hydroxylation and incorporation of H₂O₂-derived oxygen into the reaction products. Our results raise the possibility that fungal peroxygenases may be useful for versatile, cost-effective, and scalable syntheses of flavonoid metabolites.     

Nekhoroshev type stability results for Hamiltonian systems with an additional transversal component

We prove exponential stability theorems of Nekhoroshev type for motion in the neighbourhood of an elliptic fixed point in Hamiltonian systems having an additional transverse component of arbitrary dimension, under certain conditions on this transverse component. We consider both the cases (i) of a strongly constrained motion, and (ii) of a weak perturbation.     

Triol Crystalline Hosts Derived from Malic Acid. Synthesis,Inclusion Formation and X-ray Crystal Structures of a Free Host and its Inclusion Compound with Ethanol (1:1)

Abstract

Four new host compounds 1–3 (a, b) derived from malic acid as different optical species and having particular lateral substituents were synthesized. Their properties in crystalline inclusion formation were studied and discussed. Crystal structures of a free host compound 1 and its ethanol inclusion complex [1·EtOH (1:1)] have been determined by X-ray analysis [1: orthorhombic, P2₁2₁2₁, a = 9.304(3), b = 14.950(3), c = 15.712(3) Å, Dc = 1.248 Mg·m^?3, Z = 4, R = 0.039 for 2474 reflexions; 1·EtOH (1:1): triclinic, P 1; a = 11.945(3), b = 14.080(3), c = 16.029(4) Å, α = 106.82(2), β = 97.74(2), γ = 89.93(2)°, D_c = 1.187 Mg·m³, Z = 4, R = 0.096 for 10404 data]. Spontaneous resolution occurs during crystallization in crystals of 1. An interesting H-bonding pattern develops that probably is responsible for the inclusion formation with ethanol in the associate crystal.     

Flow control over an undulating membrane

The flow along a flexible membrane forced to undulate in the form of a streamwise travelling wave pattern is studied experimentally in detail. Flow field and force measurements confirm that the form drag of the wavy wall is significantly reduced when starting the undulatory motion. A mechanical model of an undulating membrane was built, based on previous investigations described in literature, and placed in an open water channel. The motion pattern of the membrane was prescribed in such a way to achieve a downstream travelling wave with increasing amplitude. The exploratory focus laid on the identification of hydrodynamic mechanisms of drag reduction due to undulatory motion. The wave-speed c of the travelling wave was set proportional to the incoming flow velocity U, according to an optimum ratio identified by previous numerical and experimental investigations. Poisson’s equation for the pressure was used to calculate the 2D pressure field from the experimental data of the unsteady flow field. In addition, the integral drag force of the membrane, as a function of c/U, was measured with a force balance to compare with previous published numerical findings. Furthermore, the velocities close to the surface of the membrane were measured, and the boundary layer profiles were determined. The resulting normalised velocity profiles affirm an oscillation between laminar and turbulent flow over one period of the motion. The results are in good agreement with previous experimental and numerical findings. Additionally, the characteristics of the flow along a travelling wave with increasing amplitude are discussed in more detail.     

Cationic polymerization of cyclohexyl vinyl ether within MCM‐41 channels

Cationic polymerization of cyclohexyl vinyl ether (CHVE) within mesoporous, siliceous molecular sieves (MCM‐41) yields novel MCM‐41‐polyCHVE host‐guest hybrid materials. Initiation within the channel can be achieved by triphenylmethylium or bis(4‐methoxyphenyl)methylium silanolate ion pairs, as well as by mobile acidic silanols to a certain extent. Generation of the carbenium ions on MCM‐41 is investigated by a special UV/VIS technique. The structure of poly(vinyl ether) generated within the channels of MCM‐41 depends on the mechanism of initiation as shown by means of solid state ¹³C{¹H} and ²⁹Si{¹H} CP MAS NMR spectroscopy.