Isolation and Characterisation of a Ferrirhodin Synthetase Gene from the Sugarcane Pathogen Fusarium sacchari

FSN1, a gene isolated from the sugar‐cane pathogen Fusarium sacchari, encodes a 4707‐residue nonribosomal peptide synthetase consisting of three complete adenylation, thiolation and condensation modules followed by two additional thiolation and condensation domain repeats. This structure is similar to that of ferricrocin synthetase, which makes a siderophore that is involved in intracellular iron storage in other filamentous fungi. Heterologous expression of FSN1 in Aspergillus oryzae resulted in the accumulation of a secreted metabolite that was identified as ferrirhodin. This siderophore was found to be present in both mycelium and culture filtrates of F. sacchari, whereas ferricrocin is found only in the mycelium, thus suggesting that ferricrocin is an intracellular storage siderophore in F. sacchari, whereas ferrirhodin is used for iron acquisition. To our knowledge, this is the first report to characterise a ferrirhodin synthetase gene functionally.     

Multi‐phosphorylation of the Intrinsically Disordered Unique Domain of c‐Src Studied by In‐Cell and Real‐Time NMR Spectroscopy

Intrinsically disordered regions (IDRs) are preferred sites for post‐translational modifications essential for regulating protein function. The enhanced local mobility of IDRs facilitates their observation by NMR spectroscopy in vivo. Phosphorylation events can occur at multiple sites and respond dynamically to changes in kinase–phosphatase networks. Here we used real‐time NMR spectroscopy to study the effect of kinases and phosphatases present in Xenopus oocytes and egg extracts on the phosphorylation state of the “unique domain” of c‐Src. We followed the phosphorylation of S17 in oocytes, and of S17, S69, and S75 in egg extracts by NMR spectroscopy, MS, and western blotting. Addition of specific kinase inhibitors showed that S75 and S69 are phosphorylated by CDKs (cyclin‐dependent kinases) differently from Cdk1. Moreover, although PKA (cAMP‐dependent protein kinase) can phosphorylate S17 in vitro, this was not the major S17 kinase in egg extracts. Changes in PKA activity affected the phosphorylation levels of CDK‐dependent sites, thus suggesting indirect effects of kinase–phosphatase networks. This study provides a proof‐of‐concept of the use of real‐time in vivo NMR spectroscopy to characterize kinase/phosphatase effects on intrinsically disordered regulatory domains.     

Identification of New N‐Acylhomoserine Lactone Signalling Compounds of Dinoroseobacter shibae DFL‐12T by Overexpression of luxI Genes

Bacteria of the Roseobacter clade are widespread in the ocean and occur in many different habitats. In the genome of Dinoroseobacter shibae DFL‐12, luxI homologous genes that encode synthases responsible for the formation of N‐acylhomoserine lactones (AHLs) have been described. These compounds are known autoinducers that regulate several biological traits—namely, flagella formation and cell differentiation—in D. shibae through quorum sensing. The AHLs produced by D. shibae mainly consisted of N‐octadecadienoylhomoserine lactone (C18:2‐AHL) and N‐octadecenoylhomoserine lactone (C18:1‐HSL). In the wild type these AHLs are synthesized only in low abundance. The luxI genes were therefore expressed in Escherichia coli; this resulted in the formation of AHLs mostly different from those found in the D. shibae wild type. A luxI₁‐deficient mutant of D. shibae was then reprovided with an overexpressed luxI₁ gene. This strain produced large amounts of C18:2‐AHL and C18:1‐AHL, allowing full characterization of these compounds by mass spectrometric techniques and derivatization. Synthesis of the proposed structures confirmed that the major compound is (2E,11Z)‐N‐octadeca‐2,11‐dienoylhomoserine lactone ( 6 , C18:2‐HSL), accompanied by (Z)‐N‐octadec‐11‐enoylhomoserine lactone ( 5 , C18:1‐HSL). AHL 6 has not been reported before from other organisms and contains an unusual 2E double bond.     

Characterizing Weave Geometry in Textile Ceramic Composites Using Digital Image Correlation

Techniques for characterizing tow architectures and defects in woven ceramic composites are required for generating high‐fidelity geometric models and subsequently probing effects of defects on composite performance. Although X‐ray computed tomography (CT) has been shown to provide the requisite information with potentially sub‐μm resolution, the technique is inherently limited to probing only small volumes: on the order of a few unit cells of typical weaves. Here, we present an assessment of the efficacy of a complementary 2D technique, based on surface topography mapping via 3‐D (three‐dimensional) digital image correlation (DIC), with potential for ascertaining long‐range features in weaves and defects that cannot be gleaned from CT imaging alone. Upon comparing surfaces reconstructed from CT and DIC data, we find that DIC is capable of resolving surface heights with a root mean square(RMS) error of ~10 μm (about twice the CT voxel size, 4.4 μm) and a spatial resolution of ~20 μm over areas of several cm². Achieving this level of resolution requires use of sufficiently small speckles (~50 μm) and small subset size (~300 μm) relative to the characteristic tow dimensions (~1 mm). The error is somewhat higher (about 20 μm) in areas where surface discontinuities or rapid changes in topography exist (e.g., at tow boundaries).     

Mathematical Modeling of Drying of Liquid/Solid Slurries in Steady State One-Dimensional Flow

ABSTRACT

A mathematical model of simultaneous mass, heat and momentum transfer for two-phase flow of a gas and a solid/liquid slurry was developed. The model was applied to calculation of the drying process of coal-water slurry droplets in a gas medium in a steady one-dimensional flow. The model was based on the well-known two-stage drying process for slurry droplets. After the first period of drying, in which the evaporation rate is controlled by the gas phase resistance, the evaporating liquid diffuses through the porous shell (crust) and then, by convection, into the gas medium. Inside the dry external crust of the drop, a wet central core forms, which shrinks as evaporation proceeds. The temperature of the slurry droplet rises. The process ends when the temperature of the dry outer crust reaches the coal ignition temperature in the case of combustion or when the moisture of the particle reaches the final required moisture. The developed model was based on one-dimensional balance equations of mass, energy and momentum for the liquid/solid and gas phases. The system of governing equations was represented by first-order differential equations and solved simultaneously. The numerical solution of the governing equations was obtained using Gear's method. The model permitted calculation     

Failure of silver nanowire transparent electrodes under current flow

Silver nanowire transparent electrodes have received much attention as a replacement for indium tin oxide, particularly in organic solar cells. In this paper, we show that when silver nanowire electrodes conduct current at levels encountered in organic solar cells, the electrodes can fail in as little as 2 days. Electrode failure is caused by Joule heating which causes the nanowires to breakup and thus create an electrical discontinuity in the nanowire film. More heat is created, and thus failure occurs sooner, in more resistive electrodes and at higher current densities. Suggestions to improve the stability of silver nanowire electrodes are given.     

Fe(PyTACN)‐Catalyzed cis‐Dihydroxylation of Olefins with Hydrogen Peroxide

A family of iron complexes with general formula [Fe(II)(^R,Y,XPyTACN)(CF₃SO₃)₂], where ^R,Y,XPyTACN=1‐[2′‐(4‐Y‐6‐X‐pyridyl)methyl]‐4,7‐dialkyl‐1,4,7‐triazacyclononane, X and Y refer to the groups at positions 4 and 6 of the pyridine, respectively, and R refers to the alkyl substitution at N‐4 and N‐7 of the triazacyclononane ring, are shown to be catalysts for efficient and selective alkene oxidation (epoxidation and cis‐dihydroxylation) employing hydrogen peroxide as oxidant. Complex [Fe(II)(^Me,Me,HPyTACN)(CF₃SO₃)₂] ( 7 ), was identified as the most efficient and selective cis‐dihydroxylation catalyst among the family. The high activity of 7 allows the oxidation of alkenes to proceed rapidly (30 min) at room temperature and under conditions where the olefin is not used in large amounts but instead is the limiting reagent. In the presence of 3 mol% of 7 , 2 equiv. of H₂O₂ as oxidant and 15 equiv. of water, in acetonitrile solution, alkenes are cis‐dihydroxylated reaching yields that might be interesting for synthetic purposes. Competition experiments show that 7 exhibits preferential selectivity towards the oxidation of cis olefins over the trans analogues, and also affords better yields and high [syn‐diol]/[epoxide] ratios when cis olefins are oxidized. For aliphatic substrates, reaction yields attained with the present system compare favourably with state of the art Fe‐catalyzed cis‐dihydroxylation systems, and it can be regarded as an attractive complement to the iron and manganese systems described recently and which show optimum activity against electron‐deficient and aromatic olefins.     

Synthesis and properties of aminopropyl nucleic acids

Oligonucleotides that contain up to three aminopropyl nucleoside analogues have been synthesized. Dimers of aminopropyl adenine and thymidine were prepared and used as building blocks by applying phosphoramidite chemistry. Both R and S isomers of the aminopropyl nucleosides were used. This incorporation led to a reduction of thermal stability of double-stranded DNA. Furthermore, the (R)-adenine analogue, which yielded (S)-APNA, can be considered as a candidate for universal base pairing.