Enhancement of the hydrolysis of geranyl pyrophosphate by bivalent metal ions. A model for enzymic biosynthesis of cyclic monoterpenes

Hydrolysis of geranyl pyrophosphate is catalyzed by salts of Mn²⁺ and involves C-O bond cleavage. The first order rate constants reach limiting values with [Mn²⁺] > 10^?2 M, and the most reactive species is GPP(Mn²⁺)₂ at the optimum pH of 6.5–7. The products are similar to those from acid hydrolysis except that more cyclic hydrocarbons are formed in the presence of metal ions. Hydrolysis of geranyl phosphate is inhibited, and that of citronnellyl pyrophosphate is weakly catalyzed by Mn²⁺. Other divalent metal cations catalyze the hydrolysis of geranyl pyrophosphate and the sequence of effectiveness is Cu²⁺ > Mn²⁺ > Zn²⁺ > Co²⁺ < Mg²⁺ ~ Ca²⁺.     

Hydrogenation of citral over pt and pt-fe/sio2 catalysts

Summary Pt/SiO₂ and Pt-Fe/SiO₂ catalysts having a Pt loading ranging from 0.5 to 3.0 wt.% and a fixed amount of Fe in the bimetallic series, 1.0 wt.% have been prepared by the impregnation procedure, followed by calcinations and reduction in H₂ flow at 773 K. The samples were characterized by N₂ adsorption at 77 K, H₂ chemisorption at 298 K, TEM, TPR and XPS. The hydrogenation of citral at 363 K and 8.3 bar over a series of Pt/SiO₂ and Pt-Fe/SiO₂ catalysts was studied. Thus, the selectivity towards the unsaturated alcohol (geraniol + nerol) decreases at high loads of monometallic Pt. An effect of polarization of the C=O bond due to the presence of Fe³⁺ species leads to catalysts active and highly selective to the hydrogenation of the carbonyl bond. Characterization results showed that Pt is present as Pt^o and Fe mainly asFe³⁺.     

Magneto-responsive hybrid materials based on cellulose nanocrystals

We fabricated self-standing films of cellulose nanocrystals (CNC) and electrospun composite fibers with CNC and polyvinyl alcohol both with magnetic properties arising from cobalt iron oxide nanoparticles in the CNC matrix. Aqueous dispersions of cobalt-iron oxide nanoparticles (10–80 nm diameter) and CNCs (ca. 150 nm length) were used as precursor systems for the films and composite fibers. The properties of the hybrid material were determined by electron and atomic force microscopy, X-ray diffraction, thermogravimetry and magnetometry. The CNC-inorganic system was ferromagnetic, with a saturation magnetization of ca. 20 emu g^?1 of the magnetic phase. We demonstrate potential applications of the precursor dispersions, including magnetic fluid hyperthermia and highlight possible uses of the CNC-based magneto-responsive systems in biomedical and magneto-optical components.     

Interactions between nonpolar surfaces coated with the nonionic surfactant hexaoxyethylene dodecyl ether C12E6 and the origin of surface charges at the air/water interface

The interactions between nonpolar surfaces coated with the nonionic surfactant hexaoxyethylene dodecyl ether C12E6 were investigated using two techniques and three different types of surfaces. As nonpolar surfaces, the air/water interface, silanated negatively charged glass, and thiolated uncharged gold surfaces were chosen. The interactions between the air/water interfaces were measured with a thin film pressure balance in terms of disjoining pressure as a function of film thickness. The interactions between the solid/liquid interfaces were determined using a bimorph surface force apparatus. The influence of the nature of the surface on the interaction forces was investigated at surfactant concentrations below and above the cmc. The adsorption of the nonionic surfactant on the uncharged thiolated surface does not, as expected, lead to any buildup of a surface charge. On the other hand, adsorption of C12E6 on the charged silanated glass and the charged air/water interface results in a lowering of the surface charge density. The reduction of the surface charge density on the silanated glass surfaces is rationalized by changes in the dielectric permittivity around the charged silanol groups. The reason for the surface charge observed at the air/water interface as well as its decrease with increasing surfactant concentration is discussed and a new mechanism for generation of OH- ions at this particular interface is proposed.     

A nuclear magnetic resonance (1H and 13C) and isotope ratio mass spectrometry (δ13C, δ2H and δ18O) study of Andalusian olive oils

We have determined δ¹³C, δ²H and δ¹⁸O isotopic abundances in Andalusian olive oils. In addition, the fatty acid composition and the distribution of isomers at positions 1,3 and 2 of glycerol were determined by ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, respectively. Isotopic results obtained for four series of oil samples extracted from olives harvested in the 2004/05 and 2005/06 seasons are discussed in terms of olive variety, ripeness, geographical origin, fatty acid composition and growing altitude. A distinction was also established between olives grown in irrigated and in dry land by studying selected samples of the previous series and others from the 2005/06, 2006/07, 2007/08 and 2008/09 seasons. The results showed that olive ripeness does not influence the abundance of any of the three isotopes studied. On the other hand, the olive variety influences the abundance of the oxygen and hydrogen isotopes, and also, less markedly, that of carbon. No clear‐cut effect of height or latitude on isotope values is observed, probably because the olive variety also changes with height and latitude, thus masking such influences. The oil samples from dryland‐grown olives had increased δ¹³C values relative to irrigation‐grown olives. In addition, no definite relationship appears to exist between isotope distribution and fatty acid composition. Finally, oil samples from olives harvested in the 2005/06 season in Italy could be distinguished from those from Spain in terms of their isotopic values (δ²H mainly). Copyright © 2010 John Wiley & Sons, Ltd.     

Simultaneous electrophoretic analysis of proteins of very high and low molecular mass using Tris‐acetate polyacrylamide gels

To separate and analyze giant and small proteins in the same electrophoresis gel, we have used a 3–15% polyacrylamide gradient gel containing 2.6% of the crosslinker bisacrylamide and 0.2 M of Tris‐acetate buffer (pH 7.0). Samples were prepared in a sample buffer containing lithium dodecyl sulphate and were run in the gel described above using Tris‐Tricine‐SDS‐sodium bisulfite buffer, pH 8.2, as electrophoresis buffer. Here, we show that this system can be successfully used for general applications of SDS‐PAGE such as CBB staining and immunoblot. Thus, by using Tris‐acetate 3–15% polyacrylamide gels, it is possible to simultaneously analyze proteins, in the mass range of 10–500 kDa, such as HERC1 (532 kDa), HERC2 (528 kDa), mTOR (289 kDa), Clathrin heavy chain (192 kDa), RSK (90 kDa), S6K (70 kDa), β‐actin (42 kDa), Ran (24 kDa) and LC3 (18 kDa). This system is highly sensitive since it allows detection from as low as 10 μg of total protein per lane. Moreover, it has a good resolution, low cost, high reproducibility and allows for analysis of proteins in a wide range of weights within a short period of time. All these features together with the use of a standard electrophoresis apparatus make the Tris‐acetate‐PAGE system a very helpful tool for protein analysis.     

Fragmentation trees for the structural characterisation of metabolites

Metabolite identification plays a crucial role in the interpretation of metabolomics research results. Due to its sensitivity and widespread implementation, a favourite analytical method used in metabolomics is electrospray mass spectrometry. In this paper, we demonstrate our results in attempting to incorporate the potentials of multistage mass spectrometry into the metabolite identification routine. New software tools were developed and implemented which facilitate the analysis of multistage mass spectra and allow for efficient removal of spectral artefacts. The pre‐processed fragmentation patterns are saved as fragmentation trees. Fragmentation trees are characteristic of molecular structure. We demonstrate the reproducibility and robustness of the acquisition of such trees on a model compound. The specificity of fragmentation trees allows for distinguishing structural isomers, as shown on a pair of isomeric prostaglandins. This approach to the analysis of the multistage mass spectral characterisation of compounds is an important step towards formulating a generic metabolite identification method. Copyright © 2012 John Wiley & Sons, Ltd.     

A Comparative Study of 8‐Hydroxyquinoline and 8‐Hydroxyquinoline‐5‐sulfonic Acid for Antimony(III) Determination by AdSV. Substituent Effect on Sensitivity II

A sensitive and selective method for the determination of Sb³⁺ based on the formation of its complexes with 8‐hydroxyquinoline (HQ) and 8‐hydroxyquinoline‐5‐sulfonic acid (HQS) is proposed. The best analytical conditions are: pH 5.4 and 2.2 for HQ and HQS, respectively; C_HQ from 15.0 to 25.0 µmol L^?1 and C_HQS from 70.0 to 200.0 µmol L^?1. The detection limits are 100.0 and 14.0 ng L^?1 (t_acc=30 s) for Sb³⁺ with HQ and HQS, respectively. The method using HQS as ligand has a 2.2‐fold higher sensitivity than that with HQ and the former was chosen for Sb³⁺ determination.     

Evidence of C non-covalent isotope effects obtained by quantitative C nuclear magnetic resonance spectroscopy at natural abundance during normal phase liquid chromatography

Quantitative isotopic ¹³C NMR at natural abundance has been used to determine the site-by-site ¹³C/¹²C ratios in vanillin and a number of related compounds eluted from silica gel chromatography columns under similar conditions. Head-to-tail isotope fractionation is observed in all compounds at the majority of carbon positions. Furthermore, the site-specific isotope deviations show signatures characteristic of the position and functionality of the substituents present. The observed effects are more complex than would be obtained by simply summing the individual effects. Such detail is hidden when only the global ¹³C content is measured by mass spectrometry. In particular, carbon positions within the aromatic ring are found to show site-specific isotope fractionation between the solute and the stationary phase. These interactions, defined as non-covalent isotope effects, can be normal or inverse and vary with the substitution pattern present.     

Synthesis and Structures of some Lithium and Sodium (Aminoalcoholato)hydrido Aluminates

LiAlH₄ and NaAlH₄ were allowed to react in a 1 : 1, 1 : 2 and 1 : 3 ratio with 2-dimethylaminoethanol, 1-dimethylamino-2-propanol, and (–)-N-methylephedrine. Reactions in the 1 : 1 ratio leads to mixtures of M(AlH_4–n(OR′NMe₂)_n) in thf solution showing a temperature dependent composition. From the solutions obtained in a 1 : 2 or 1 : 3 ratio the following compounds were isolated as single crystals: (thf)NaAlH₂ · (OCH₂–CH₂NMe₂)₂ ( 2 ), LiAlH₂(OCHMe–CH₂NMe₂)₂ ( 3 ), LiAlH₂(OCHPh–CHMe–NMe₂)₂ ( 4 ), LiAlH(OCH₂CH₂NMe₂)₃ ( 5 ), NaAlH(OCH₂CH₂NMe₂)₃ ( 6 ). All compounds are dimers in the solid state and their Al atoms are pentacoordinated. M–H–Al bridges were found only in the dihydridoaluminate  2 .