High-speed counter-current chromatography for the study of defense metabolites in wheat. Characterization of 5,6-O-methyl trans-aconitic acid

High-speed counter-current chromatography (HSCCC) methods were developed for the study of induced defense metabolites in wheat (Triticum aestivum) against powdery mildew (Blumeria graminis f. sp. tritici). A single HSCCC purification step afforded extraction of mg-quantities of an induced compound with antifungal activity. Subsequent LC-MS and NMR analyses have led to the characterization of 5,6-O-methyl trans-aconitic acid, the first such report of this compound in a plant species. The inducible nature of aconitic acid was evidenced by comparing the metabolite profiles of leaf extracts from plants treated or not with soluble silicon and infected or not with powdery mildew. In a second step, dual-mode HSCCC was used to enhance the separation of other forms of aconitic acid in wheat. Based on these results, it was concluded that 5,6-O-methyl trans-aconitic acid plays an important role as a defense molecule in wheat plants and that HSCCC is a powerful separation method for purifying such compounds from complex plant-pathogen interactions.     

Synthesis by extrusion: continuous,large-scale preparation of MOFs using little or no solvent

Grinding solid reagents under solvent-free or low-solvent conditions (mechanochemistry) is emerging as a general synthetic technique which is an alternative to conventional solvent-intensive methods. However, it is essential to find ways to scale-up this type of synthesis if its promise of cleaner manufacturing is to be realised. Here, we demonstrate the use of twin screw and single screw extruders for the continuous synthesis of various metal complexes, including Ni(salen), Ni(NCS)₂(PPh₃)₂ as well as the commercially important metal organic frameworks (MOFs) Cu₃(BTC)₂ (HKUST-1), Zn(2-methylimidazolate)₂ (ZIF-8, MAF-4) and Al(fumarate)(OH). Notably, Al(fumarate)(OH) has not previously been synthesised mechanochemically. Quantitative conversions occur to give products at kg h^–1 rates which, after activation, exhibit surface areas and pore volumes equivalent to those of materials produced by conventional solvent-based methods. Some reactions can be performed either under completely solvent-free conditions whereas others require the addition of small amounts of solvent (typically 3–4 mol equivalents). Continuous neat melt phase synthesis is also successfully demonstrated by both twin screw and single screw extrusion for ZIF-8. The latter technique provided ZIF-8 at 4 kg h^–1. The space time yields (STYs) for these methods of up to 144 × 10³ kg per m³ per day are orders of magnitude greater than STYs for other methods of making MOFs. Extrusion methods clearly enable scaling of mechanochemical and melt phase synthesis under solvent-free or low-solvent conditions, and may also be applied in synthesis more generally.     

A fast algorithm for solving diagonally dominant symmetric pentadiagonal Toeplitz systems

Banded Toeplitz systems of linear equations arise in many application areas and have been well studied in the past. Recently, significant advancement has been made in algorithm development of fast parallel scalable methods to solve tridiagonal Toeplitz problems. In this paper we will derive a new algorithm for solving symmetric pentadiagonal Toeplitz systems of linear equations based upon a technique used in [J.M. McNally, L.E. Garey, R.E. Shaw, A split-correct parallel algorithm for solving tri-diagonal symmetric Toeplitz systems, Int. J. Comput. Math. 75 (2000) 303-313] for tridiagonal Toeplitz systems. A common example which arises in natural quintic spline problems will be used to demonstrate the algorithm’s effectiveness. Finally computational results and comparisons will be presented.     

Development of an optimized feeding technology for dairy cows

We have previously reported on MB-1, a designer protein with potential application in animal nutrition. Having a high content of selected essential amino acids, MB-1 should provide limiting nutrients for animals and promote growth and production. However, the protein was found to have marginal conformational and proteolytic stability, and, thus, strategies for stabilizing MB-1 were elaborated. We discuss the synthesis of MB-1-Cys dimer, a protein with an intermolecular disulfide bridge. This mutant was exposed to Pronase E protease preparation as well as to proteases extracted from ruminal microbes. It was found that in both cases, MB-1-Cys dimer had a better resistance to proteolytic degradation than MB-1. Denaturation and hydrophobic dye binding studies revealed that this enhanced stability was not owing to conformational stabilization, but rather to changes in surface exposure as a consequence of dimerization. In particular, it was found that binding of ANSA to MB-1-Cys dimer was comparable to that observed for native, compact, natural proteins. We discuss the implications of these results for the design of transgenic protein production systems.     

Temperature dependence of the penetration depth in Sr2RuO4: evidence for nodes in the gap function

We report measurements of the magnetic penetration depth in single crystals of Sr2RuO4 down to 0.04 K using a tunnel-diode based, self-inductive technique. We observe a power law temperature dependence below 0.8 K, with no sign of a second phase transition nor of a crossover predicted for a multiband superconductor. A power law dependence suggests that the gap function has nodes, inconsistent with candidate p-wave states. We argue that nonlocal effects, rather than impurity scattering, can explain the observed T2 dependence instead of the T-linear behavior expected for line nodes.     

Conformational control of HCl co-transporter: imidazole functionalised isophthalamide vs. 2,6-dicarboxamidopyridine

Replacement of the central isophthalamide core in a synthetic HCl receptor, with a 2,6-dicarboxamidopyridine, leads to a more preorganised molecular structure that exhibits higher chloride affinity and membrane transport flux.     

The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd.