Peptide synthesis using unprotected peptides through orthogonal coupling methods.

We describe an approach to the synthesis of peptides from segments bearing no protecting groups through an orthogonal coupling method to capture the acyl segment as a thioester that then undergoes an intramolecular acyl transfer to the amine component with formation of a peptide bond. Two orthogonal coupling methods to give the covalent ester intermediate were achieved by either a thiol-thioester exchange mediated by a trialkylphosphine and an alkylthiol or a thioesterification by C alpha-thiocarboxylic acid reacting with a beta-bromo amino acid. With this approach, unprotected segments ranging from 4 to 37 residues were coupled to aqueous solution to give free peptides up to 54 residues long with high efficiency.

Quaternary ammonium-functionalized silica sorbents for the solid-phase extraction of aromatic amines under normal phase conditions

Quaternary ammonium-functionalized silica materials were synthesized and applied for solid-phase extraction (SPE) of aromatic amines, which are classified as priority pollutants by US Environmental Protection Agency. Hexamethylenetetramine used for silica surface modification for the first time was employed as SPE sorbent under normal phase conditions. Hexaminium-functionalized silica demonstrated excellent extraction efficiencies for o-toluidine, 4-ethylaniline and quinoline (recoveries 101–107%), while for N,N-dimethylaniline and N-isopropylaniline recoveries were from low to moderate (14–46%). In addition, the suitability of 1-alkyl-3-(propyl-3-sulfonate) imidazolium-functionalized silica as SPE sorbent was tested under normal phase conditions. The recoveries achieved for the five aromatic amines ranged from 89 to 99%. The stability of the sorbent was evaluated during and after 150 extractions. Coefficients of variation between 4.5 and 10.2% proved a high stability of the synthesized sorbent. Elution was carried out using acetonitrile in the case of hexaminium-functionalized silica and water for 1-alkyl-3-(propyl-3-sulfonate) imidazolium-functionalized silica sorbent. After the extraction the analytes were separated and detected by liquid chromatography ultraviolet detection (LC-UV). The retention mechanism of the materials was primarily based on polar hydrogen bonding and π–π interactions. Comparison made with activated silica proved the quaternary ammonium-functionalized materials to offer different selectivity and better extraction efficiencies for aromatic amines. Finally, 1-alkyl-3-(propyl-3-sulfonate) imidazolium-functionalized silica sorbent was successfully tested for the extraction of wastewater and soil samples.

Cost-Effective Force Field Tailored for Solid-Phase Simulations of OLED Materials

A united atom force field is empirically derived by minimizing the difference between experimental and simulated crystal cells and melting temperatures for eight compounds representative of organic electronic materials used in OLEDs and other devices: biphenyl, carbazole, fluorene, 9,9′-(1,3-phenylene)bis(9H-carbazole)-1,3-bis(N-carbazolyl)benzene (mCP), 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (pCBP), phenazine, phenylcarbazole, and triphenylamine. The force field is verified against dispersion-corrected DFT calculations and shown to also successfully reproduce the crystal structure for two larger compounds employed as hosts in phosphorescent and thermally activated delayed fluorescence OLEDs: N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPD), and 1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (TPBI). The good performances of the force field coupled to the large computational savings granted by the united atom approximation make it an ideal choice for the simulation of the morphology of emissive layers for OLED materials in crystalline or glassy phases.

Dissolved organic carbon concentrations, amino sugar concentrations and highly significantly correlating FT-ICR mass peak magnitudes obtained from solid phase extracted marine dissolved organic matter during POLARSTERN cruise ANT-XXV/1

Dissolved organic matter (DOM) was extracted with solid phase extraction (SPE) from 137 water samples from different climate zones and different depths along an Eastern Atlantic Ocean transect. The extracts were analyzed with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with electrospray ionization (ESI). D14C analyses were performed on subsamples of the SPE-DOM. In addition, the amount of dissolved organic carbon was determined for all water and SPE-DOM samples as well as the yield of amino sugars for selected samples. Linear correlations were observed between the magnitudes of 43% of the FT-ICR mass peaks and the extract D14C values. Decreasing SPE-DOM D14C values went along with a shift in the molecular composition to higher average masses (m/z) and lower hydrogen/carbon (H/C) ratios. The correlation was used to model the SPE-DOM D14C distribution for all 137 samples. Based on single mass peaks a degradation index was developed to compare the degradation state of marine SPE-DOM samples analyzed with FT-ICR MS. A correlation between D14C, degradation index, DOC values and amino sugar yield supports that SPE-DOM analyzed with FT-ICR MS reflects trends of bulk DOM. A relative mass peak magnitude ratio was used to compare aged SPE-DOM and fresh SPE-DOM regarding single mass peaks. The magnitude ratios show a continuum of different reactivities for the single compounds. Only few of the compounds present in the FT-ICR mass spectra are expected to be highly degraded in the oldest water masses of the Pacific Ocean. All other compounds should persist partly thermohaline circulation. Prokaryotic (bacterial) production, transformation and accumulation of this very stable DOM occurs probably primarily in the upper ocean. This DOM is an important contribution to very old DOM, showing that production and degradation are dynamic processes.

Method of analysis and quality-assurance practices for determination of pesticides in water by solid-phase extraction and capillary-column gas chromatography/mass spectrometry at the U.S. Geological Survey California District Organic Chemistry Laboratory, 1996-99 /

Mode of access: Internet.

Controlling Long-Range Ordered Self-assembly of Solid-Binding Peptide Monolayers on Atomically Flat Layered Materials

Thesis (Master's)--University of Washington, 2016-06

Solid phase microextraction of stale flavour volatiles from the headspace of UHT milk

Solid phase microextraction (SPME) offers a solvent-free and less labour-intensive alternative to traditional flavour isolation techniques. In this instance, SPME was optimised for the extraction of 17 stale flavour volatiles (C3-11,13 methyl ketones and C4-10 saturated aldehydes) from the headspace of full-cream ultrahigh-temperature (UHT)-processed milk. A comparison of relative extraction efficiencies was made using three fibre coatings, three extraction times and three extraction temperatures. Linearity of calibration curves, limits of detection and repeatability (coefficients of variation) were also used in determining the optimum extraction conditions. A 2 cm fibre coating of 50130 gm divinylbenzene/Carboxen/polydimethylsiloxane in conjunction with a 15 min extraction at 40 degrees C were chosen as the final optimum conditions. This method can be used as an objective tool for monitoring the flavour quality of UHT milk during storage. (c) 2005 Society of Chemical Industry.