Synthesis of the branched-chain sugar aceric acid: a unique component of the pectic polysaccharide rhamnogalacturonan-II

Described herein is the synthesis of 3-C-carboxy-5-deoxy-L-xylose (aceric acid), a rare branched-chain sugar found in the complex pectic polysaccharide rhamnogalacturonan-II. The key synthetic step in the construction of aceric acid was the stereoselective addition of 2-trimethylsilyl thiazole to 5-deoxy-1,2-O-isopropylidene-alpha-L-erythro-pentofuran-3-ulose (2), which was prepared from L-xylose. The thiazole group was efficiently converted into the required carboxyl group via conventional transformations. Aceric acid was also synthesized by dihydroxylation of a 3-C-methylene derivative of 2 followed by oxidation of the resulting hydroxylmethyl group. The C-2 epimer of aceric acid was also synthesized using thiazole addition chemistry, starting from L-arabinose.     

Studies on polymers and composites from lignin and fiber derived from sugar cane

Sugarcane fiber (i.e. bagasse) lignin has a larger fraction of aromatics unsubstitution in the ortho position than hardwood or softwood lignin and hence has the greater ability to be derivatized. Furthermore, organosolv lignin has a higher purity than sulfonated and kraft lignins. This work examines the purification of organosolv lignin derived from bagasse and the physico‐chemical properties of the lignin and lignin‐phenol formaldehyde (PF) resin coatings, and composites. The wetability tests have shown that lignin and lignin‐PF resin films are effective water barrier coatings, though the contact angles of lignin‐PF resin films were considerably less than the wax films. The overall mechanical properties (i.e. peak stress, peak strain and modulus) of the bagasse fiber composites were lower than the values obtained with the composites without the inclusion of bagasse fiber. Copyright © 2007 John Wiley & Sons, Ltd.     

Electronic structure of unstable intermediates

The geometry of the linear molecule HBO, has been investigated within the restricted Hartree-Fock LCAO-MO-SCF approximation. The calculated bond lengths for the near Hartree-Fock calculation were R(H-B)=2.1913 bohr, R(B-O)=2.2284 bohr. Several one electron properties have been calculated for the minimum energy configuration.     

SEARCH THEORY IN NATURAL RESOURCE MODELING

The role of search theory in the exploitation of natural resources is discussed in this paper. After a brief history and taxonomy of search problems, the mathematics of search is discussed. This includes underlying probability distributions, the differential equations of search, Bayesian use of search information and optimization problems in search theory. The theory is illustrated by applications in fisheries, pest control, animal foraging, and oil and mineral exploration.     

General continuum boundary conditions for miscible binary fluids from molecular dynamics simulations

Molecular dynamics simulations are used to explore the flow behavior and diffusion of miscible fluids near solid surfaces. The solid produces deviations from bulk fluid behavior that decay over a distance of the order of the fluid correlation length. Atomistic results are mapped onto two types of continuum model: Mesoscopic models that follow this decay and conventional sharp interface boundary conditions for the stress and velocity. The atomistic results, and mesoscopic models derived from them, are consistent with the conventional Marangoni stress boundary condition. However, there are deviations from the conventional Navier boundary condition that states that the slip velocity between wall and fluid is proportional to the strain rate. A general slip boundary condition is derived from the mesoscopic model that contains additional terms associated with the Marangoni stress and diffusion, and is shown to describe the atomistic simulations. The additional terms lead to strong flows when there is a concentration gradient. The potential for using this effect to make a nanomotor or pump is evaluated.     

A chemo-enzymatic route to enantiomerically pure cyclic tertiary amines

Deracemization of racemic chiral tertiary amines has been achieved by combination of an enantioselective amine oxidase, obtained through directed evolution, and ammonia borane in a one-pot process.     

Investigations on organo-sulfur-nitrogen rings and the thiocyanogen Polymer, (SCN)x

The synthesis and full characterisation of a series of 1,2,4-thiadiazoles is reported. (SCN)(x) has been studied by a variety of techniques and the data compared with 1,2,4-thiadiazole and 1,2,4-dithiazoles. The observed data suggest that the polymer consists of 1,2,4-dithiazole rings linked by nitrogen atoms. For (SCN)(x), the MALDI-TOF mass spectroscopy showed a parent ion at 1149 and a series of peaks with (SCN)(2) repeat units (116 m/z); this result implies that (SCN)(2) may be the monomer unit of the polymer. Its IR spectrum shows a very broad peak with maximum at 1134 cm(-1) consisting of several overlapping peaks in the same region as ring vibrations for 1,2,4-thiadiazole and 1,2,4-dithiazole compounds. Peaks in the Raman spectrum in the range 400-480 cm(-1) support the presence of disulfide units within the polymer. The solid-state (13)C NMR (99 % (13)C-labelled) spectrum is dominated by two singlets of equal intensity at approximately 187 and 184 ppm with low intensity peaks in the range 152-172 ppm, in approximately the same range as both 1,2,4-thiadiazoles and 1,2,4-dithiazoles. The solid-state (15)N NMR (99 % (15)N labelled) spectrum displays two major peaks of similar intensity at 236.9 and 197.2 ppm, which are clearly very different environments to those observed in bis(3-bromo-1,2,4-thiadiazol-5-yl) disulfide, but similar to 1,2,4-dithiazoles. The X-ray structures of seven C-S-N systems are reported. Preliminary studies on (SeCN)(x) suggest that literature references to this polymer may be in error with the red solid actually being red selenium.     

Selectivity differences between sol-gel coated and immobilized liquid film open-tubular columns for gas chromatography

The solvation parameter model is used to determine the system constants for two sol-gel coated open-tubular columns at five equally spaced temperatures in the range 60-140 degrees C. Differences in the system constants as a function of temperature are used to determine the affect of sol-gel structure on the selectivity of SolGel-l and SolGel-Wax columns compared with conventionally coated and immobilized poly(dimethylsiloxane) and poly(ethylene glycol) stationary phases. The sol-gel columns should be suitable for similar separations to those presently performed on conventional immobilized liquid film columns of the same type but selectivity differences for polar compounds, which depend on temperature, should be anticipated.     

A novel piezo-optical styrene sensor incorporating polymer-supported tribromide ion

Encapsulation of Amberlyst A-26 supported tribromide in a 10,000 MW polyethylene glycol matrix gives a robust colour-sensitive reagent matrix which can be deposited on indium-tin oxide coated polyvinylidene fluoride (PVDF) piezoelectric film for the detection of styrene (and other alkene) vapours.     

Synthesis of gold nanoparticles within a supramolecular gel-phase network

Gold nanoparticles with diameters of ca. 13 nm were synthesised by UV irradiation of a supramolecular organogel into which HAuCl4 and tetraoctylammonium bromide had been diffused-the gel network plays an essential role in nanoparticle stabilisation.