A calorimetric, volumetric and combined SANS and SAXS study of hybrid siloxane phosphocholine bilayers

Siloxanes are molecules used extensively in commercial, industrial, and biomedical applications. The inclusion of short siloxane chains into phospholipids results in interesting physical properties, including the ability to form low polydispersity unilamellar vesicles. As such, hybrid siloxane phosphocholines (SiPCs) have been examined as a potential platform for the delivery of therapeutic agents. Using small angle X-ray and neutron scattering, vibrating tube densitometry, and differential scanning calorimetry, we studied four hybrid SiPCs bilayers. Lipid volume measurements for the different SiPCs compared well with those previously determined for polyunsaturated PCs. Furthermore, the different SiPC\u27s membrane thicknesses increased monotonically with temperature and, for the most part, consistent with the behavior observed in unsaturated lipids such as, 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine and 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine, and the branched lipid 1,2-diphytanoyl-sn-glyerco-3-phosphocholine (DPhyPC)

A chemoenzymatic route to chiral siloxanes

An approach employing two enzymes—toluene dioxygenase and immobilized lipase B from Candida antarctica (N435)—was explored as a potential biocatalytic method for the coupling of chiral diols with siloxane species. Analysis of reaction mixtures using1H NMR spectroscopy suggested that up to 66% consumption of the siloxane starting materials had occurred. Oligomeric species were observed and chiral products from the coupling of a cyclic diol with a siloxane molecule were isolated and characterized by MALDI-ToF MS and GPC. Immobilized lipases from Rhizomucor miehei and Thermomyces lanuginosus were also explored as potential catalysts for the coupling reactions, however, their use only returned starting material

Data from: Endophytic-insect parasitic fungi translocate nitrogen directly from insects to plants

Most plants obtain nitrogen through nitrogen-fixing bacteria and microbial decomposition of plant and animal material. Most vascular plants are able to form close symbiotic associations with endophytic fungi. Metarhizium is a common plant endophyte found in a large number of ecosystems. This abundant soil fungus is also a pathogen to a large number of insects, a source of nitrogen. It is possible that endophytic capability and insect pathogenicity of Metarhizium are coupled to provide an active method of nitrogen transfer to plant hosts via fungal mycelia. In this study we used soil microcosms to test the ability of M. robertsii to translocate insect-derived nitrogen to plants. Insects were injected with 15N-labelled nitrogen, and we tracked the incorporation of 15N into amino acids in two plant species, haricot bean (Phaseolus vulgaris) and switchgrass (Panicum virgatum), in the presence of M. robertsii. These findings are evidence that active nitrogen acquisition by plants in this tripartite interaction may play a larger role in soil nitrogen cycling than previously thought

Cyclotetrasiloxane Frameworks for the Chemoenzymatic Synthesis of Oligoesters

Immobilized lipase B from Candida antarctica (Novozym® 435, N435) was utilized as part of a chemoenzymatic strategy for the synthesis of branched polyesters based on a cyclotetrasiloxane core in the absence of solvent. Nuclear magnetic resonance spectroscopy and matrix-assisted laser desorption ionization time-of-flight mass spectrometry were utilized to monitor the reactions between tetraester cyclotetrasiloxanes and aliphatic diols. The enzyme-mediated esterification reactions can achieve 65– 80% consumption of starting materials in 24–48 h. Longer reaction times, 72–96 h, resulted in the formation of cross-linked gel-like networks. Gel permeation chromatography of the polymers indicated that the masses were Mw ¼ 11 400, 13 100, and 19 400 g mol 1 for the substrate pairs of C7D4 ester/ octane-1,8-diol, C10D4 ester/pentane-1,5-diol and C10D4 ester/octane-1,8-diol respectively, after 48 h. Extending the polymerization for an additional 24 h with the C10D4 ester/octane-1,8-diol pair gave Mw ¼ 86 800 g mol 1. To the best of our knowledge this represents the first report using lipase catalysis to produce branched polymers that are built from a cyclotetrasiloxane core.Natural Sciences and Engineering Research Council (NSERC) of Canada Brock University Advanced Biomanufacturing Centr

raw data plant insect met exp.

Atom% 15N present in plant samples analyzed by NOI-5 emissions spectrophotometer. Each day represents the treatment run in triplicate with a minimum of 2 data points obtained per replicate. Mass spec provided are the molecular ion/molecular ion + 1 ratios obtained through liquid chromatography/mass spec analysis

Analysis of Trisiloxane Phosphocholine Bilayers

We have synthesized unique siloxane phosphocholines and characterized their aggregates in aqueous solution. The siloxane phosphocholines form nearly monodisperse vesicles in aqueous solution without the need for secondary extrusion processes. The area/lipid, lipid volume, and bilayer thickness were determined from small-angle X-ray scattering experiments. The impetus for the spontaneous formation of unilamellar vesicles by these compounds is discussed

Synthesis of polyesters containing disiloxane subunits: Structural characterization, kinetics, and an examination of the thermal tolerance of Novozym-435

This paper reports the Novozym-435 mediated polymerization of disiloxane-containing polyester monomers under solvent-free conditions. The thermal tolerance of the immobilized enzyme was examined by conducting polymerization cycles over a temperature range of 35-150 °C. Increasing the temperature up to 100 °C afforded an increase in the apparent second order rate constant. Residual activity was measured using the production of octyl palmitate. The enzyme was shown to retain on average greater than 90% of its residual activity regardless of the polymerization temperature. This prompted a study of the long term thermal tolerance of the biocatalyst in which it was determined that over ten reaction cycles there was a significant decrease in the initial polymerization rate, but no change in the degree of monomer conversion after 24 h. The disiloxane containing polyesters were characterized using nuclear magnetic resonance spectroscopy and Fourier-transform infrared spectroscopy. Differential scanning calorimetry was used to determine the thermal properties of the disiloxane-containing polyesters. © 2012 Elsevier B.V. All rights reserved

Characterization of self-assembled hybrid siloxane-phosphocholine bilayers

© 2018 Elsevier B.V. We have synthesized six new hybrid siloxane phosphocholines (SiPCs) and examined their self-assembly behaviour in aqueous dispersions. Employing small angle X-ray scattering we have characterized SiPC bilayers. SiPCs exhibit differential self-assembly behaviour that results from the interplay between the siloxane fatty acid in the sn-2 position and the differing chain length fatty acids in the sn-1 position. SiPCs that possess a fatty acid chain of a C8–C14 chain length in the sn-1 position form unilamellar vesicles. Extending the fatty acid chain length to C16 and C18 allows for the formation of both unilamellar and multilamellar vesicles. We propose that the preferential formation of unilamellar vesicles is the result of an enhanced hydrophobic effect imparted by siloxane chains at the termini of lipid tails