Atomic force microscope studies on the interactions of Candida rugosa lipase and supported lipidic bilayers

Using the Langmuir–Blodgett technique we prepared substrate supported well-defined lipid/phospholipid (1-mono-palmitoyl-rac-glycerol (MPG)/l,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC)) bilayers in which the MPG lipid leaflet was exposed to the aqueous phase. Hydrolysis of MPG performed by Candida rugosa lipase (CRL) on the upper MPG layer of these supported bilayers on mica was imaged by real time atomic force microscope (AFM) using a liquid cell, so that the area increase of the initial structural defects could be followed over time. Our data strongly suggest that the edges of the initial structural defects are the preferred activation sites for CRL once the enzyme is adsorbed onto these interfaces. When a 2.5 nM bulk concentration of CRL was assayed on this planar lipid substrate, we found a long lag phase before a sharp increase of catalytic activity. The lag–burst kinetic behaviour was related to the interfacial activation phenomenon although we propose that it is also dependent on the gel-phase state of this interface.     

Magnetic structure of Ni(DCOO)2(D2O)2

Ni(HCOO)(2)(H(2)O)(2) is a structurally simple coordination polymer showing interesting magnetic phase transitions at low temperature (<16K). Previously published studies of these phase transitions have yielded inconsistent results, questioning the correctness of the published magnetic structure. Here heat capacity and magnetic susceptibility of a fully, a partly and a non-deuterated sample were measured, and they all exhibit magnetic phase transitions around 3 and 15 K. Neutron powder diffraction data was collected on the fully deuterated sample at various temperatures between 1.5 and 25 K. A magnetic model was refined against the neutron diffraction data using a spin system composed of two canted antiferromagnetic sublattices. The magnetic moments of the two sublattices show different magnitude, 1.7 μ(B) and 1.3 μ(B), and the temperature dependence of the magnetic sublattices is quite different. One of the sublattices shows the expected temperature behavior of an antiferromagnetic compound whereas the other sublattice follows a Brillouin like function with a slowly increasing magnetization below the Ne?el temperature.     

Sb Magnetic Resonance as a Local Probe for the Gap Formation in the Correlated Semimetal FeSb2

We report on a comparative study of the narrow-band semimetals FeSb₂ and its structural homologue RuSb₂ by means of ^121,123Sb nuclear quadrupole (NQR) and nuclear magnetic resonance (NMR) spectroscopy. From NQR for both compounds two temperature regimes could be identified by use of ¹²³(1/T ₁) measurements. Above 40 K a conventional activated behavior (with Δ/k _B ? 400 K for FeSb₂) dominates in ¹²³(1/T ₁), whereas below 40 K in both systems an unconventional ¹²³(1/T ₁) behavior with a smooth maximum at around 10 K is observed. To analyze this behavior, we propose the presence of T-dependent in-gap states forming a narrow energy level of localized spins with S = ½ near the bottom of the conduction band. These states might have originated from an inherent Sb-deficiency in both compounds. This model enables us to fit the ¹²³(1/T ₁) data in the entire investigated temperature range (2–200 K) for FeSb₂. Ab initio band structure calculations reveal more than a factor of two larger Δ value for RuSb₂ as compared with FeSb₂. This results in dissimilar behavior of ¹²³(1/T ₁) in FeSb₂ and RuSb₂ above 40 K evidencing the inefficiency of thermal activation of electrons over the large energy gap at T ≤ 300 K in RuSb₂ and dominating of quadrupole relaxation channel in RuSb₂ in this temperature range caused by phonon relaxation involving two-phonon (Raman) scattering. In addition, extra wide range field-sweep NMR measurements are performed at various temperatures on FeSb₂ and RuSb₂. The complex broad spectra could be modeled and from the shift of the ¹²¹Sb central transition the 3d component of the shift K _3d (T) could be extracted.     

Bark Suberin as a Renewable Source of Long-Chain ω-Hydroxyalkanoic Acids

Summary : Polycondensations of cis-9,10-epoxy-18-hydroxyoctadecanoic acid, isolated from birch outer bark, were performed at 75 °C in toluene as solvent and at 85 °C in bulk using immobilized Candida antarctica lipase B as catalyst. The polycondensation performed in toluene in presence of molecular sieves gave a polyester with DP 50 after 24 h. The same DP was obtained at much shorter reaction time (3 h) by bulk polymerization in an open vial without any drying agent present.     

Identification of the decomposition products of nitrobenzanthracenes in solution

Air oxidation products of nitrobenzanthracenes and nitrodibenzanthracenes were separated with high-performance liquid chromatography. The major products were identified as quinones, and the bulk fo the minor products were identified as nitroquinones. Tentative structures are assigned on the basis of mass spectrometry.     

CP/MAS 13C-NMR spectroscopy applied to structure and interaction studies on cellulose I

Solid-state Cross-Polarization Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance (CP/MAS 13C-NMR) has been used to investigate the structure and interactions of cellulose I. The use of spectral fitting for the extraction of information from CP/MAS 13C-NMR spectra is reviewed and results obtained are discussed. Examples are shown where the method has been used to monitor the structural changes occurring in wood cellulose during kraft pulping. The effects observed on the cellulose and hemicelluloses are further investigated using a model system. Assignments of signal intensities originating from xylan-cellulose interactions are made.     

Photoactivation of vascular iNOS and elevation of cGMP in vivo: possible mechanism for photovasorelaxation and inhibition of restenosis in an atherosclerotic rabbit models

Recently, intravascular low-power red laser light (LPRLL) therapy has been proposed for the prevention of postangioplasty restenosis due to the observed inhibition of experimental neointimal formation. The objective of this study was to determine the impact of endoluminal LPRLL on vascular levels of inducible nitric oxide synthase (iNOS) and cyclic guanosine monophosphate (cGMP) to help define the mechanism of this effect. Eight atherosclerotic male adult New Zealand White rabbits weighing 4-6 kg were used in these studies. The iliac arteries were treated in separate zones with: (1) balloon inflation only; (2) laser illumination only; and (3) balloon inflation + laser illumination. An uninjured zone of the iliac artery served as a control. Laser irradiation (630 nm) was delivered to the vessel wall via a Cold laser Illuminator (Cook, Inc., Bloomington, IN), with a 3 mm-diameter balloon. Experiments demonstrated that vascular cGMP levels obtained immediately following treatment in the balloon only group was the lowest (0.29 +/- 0.05 pmol/mg protein) and significantly lower compared with the uninjured controls (1.01 +/- 0.07 pmol/ mg protein) (P < 0.001). In the laser only treated group cGMP levels were significantly increased (2.87 +/- 0.12 pmol/mg protein) compared with the uninjured control (P < 0.001) and the balloon only group (P < 0.001). Vascular cGMP levels in the balloon + laser group (2.09 +/0.07 pmol/mg protein) was also increased compared to the balloon only (P < 0.001) and control (P < 0.001) groups. Qualitative analysis of Western blot demonstrated that laser illumination induces iNOS. In contrast balloon dilatation did not induce iNOS. Balloon + laser treatment, however, tended to restore the expression of iNOS. Our study demonstrated that intravascular low dose laser irradiation induces iNOS and elevates vascular cGMP in an in vivo atherosclerotic rabbit model.     

The stereochemical course of formic acid reduction of enamines

Formic acid reduction of enamines derived from 2-methyl- and 2-(β-cyanoethyl)-cyclohexanone has been shown to proceed with high stereoselectivity, the cis to trans ratio of the resulting cyclohexylamines being about 9. The stereochemistry of the isomers has been established by Cope-eliminations of the corresponding N-oxides and by applying the boiling point and refractive index relations of the Auwers-Skita rules.     

Strong N−H⋅⋅⋅O Hydrogen Bonding in a Model Compound of the Catalytic Triad in Serine Proteases

Low-barrier hydrogen bond (LBHB) involvement in enzyme catalysis is examined by analysis of experimental nuclear and electron densities of a model compound for the catalytic triad in serine proteases (shown schematically), which is based on a cocrystal of betaine, imidazole, and picric acid. The three short, strong N−H⋅⋅⋅O hydrogen bonds in the structure have varying degrees of covalent bonding contributions suggesting a gradual transition to the LBHB situation.