A Rapid Gas-Chromatography/Mass-Spectrometry Technique for Determining Odour Activity Values of Volatile Compounds in Plant Proteins: Soy,and Allergen-Free Pea and Brown Rice Protein

Plant-based protein sources have a characteristic aroma that limits their usage in various meat-alternative formulations. Despite being the most popular plant-based protein, the allergenicity of soy protein severely restricts the potential adoption of soy protein as an animal substitute. Thereby, allergen-free plant-protein sources need to be characterized. Herein, we demonstrate a rapid solid-phase-microextraction gas-chromatography/mass-spectrometry (SPME-GC/MS) technique for comparing the volatile aroma profile concentration of two different allergen-free plant-protein sources (brown rice and pea) and comparing them with soy protein. The extraction procedure consisted of making a 1:7 w/v aqueous plant protein slurry, and then absorbing the volatile compounds on an SPME fibre under agitation for 10 min at 40 °C, which was subsequently injected onto a GC column coupled to an MS system. Observed volatile concentrations were used in conjunction with odour threshold values to generate a Total Volatile Aroma Score for each protein sample. A total of 76 volatile compounds were identified. Aldehydes and furans were determined to be the most dominant volatiles present in the plant proteins. Both brown rice protein and pea protein contained 64% aldehydes and 18% furans, with minor contents of alcohols, ketones and other compounds. On the other hand, soy protein consisted of fewer aldehydes (46%), but a more significant proportion of furans (42%). However, in terms of total concentration, brown rice protein contained the highest intensity and number of volatile compounds. Based on the calculated odour activity values of the detected compounds, our study concludes that pea proteins could be used as a suitable alternative to soy proteins in applications for allergen-free vegan protein products without interfering with the taste or flavour of the product.     

Carbohydration of 1,4,8,11-tetraazacyclotetradecane (cyclam): synthesis and binding properties toward concanavalin A

Two novel glycocluster ligands with cyclam core bearing thiourea-linked d-glucose and 2-acetamido-2-deoxy-d-glucose at the periphery have been synthesized. The interaction with concanavalin A has been studied by isothermal titration microcalorimetry for characterizing protein-ligand interactions. The sugar-containing multivalent ligands showed higher association affinity compared to the sugar monomers, which is attributed to an entropy driven glycoside clustering effect.     

Triostin A Derived Cyclopeptide as Architectural Template for the Alignment of Four Recognition Units

The DNA bisintercalator triostin A is structurally based on a disulfide-bridged depsipeptide scaffold that provides preorganization of two quinoxaline units in 10.5 Å distance. Triostin A analogues are synthesized with nucleobase recognition units replacing the quinoxalines and containing two additional recognition units in between. Thus, four nucleobase recognition units are organized on a rigid template, well suited for DNA double strand interactions. The new tetra-nucleobase binders are synthesized as aza-TANDEM derivatives lacking the N-methylation of triostin A and based on a cyclopeptide backbone. Synthesis of two tetra-nucleobase aza-TANDEM derivatives is established, DNA interaction analyzed by microscale thermophoresis, cytotoxic activity studied and a nucleobase sequence dependent self-aggregation investigated by mass spectrometry.     

Surface Roughness and Charge Influence the Uptake of Nanoparticles: Fluorescently Labeled Pickering‐Type Versus Surfactant‐Stabilized Nanoparticles

The influence of surface roughness and charge on the cellular uptake of nanoparticles in HeLa cells is investigated with fluorescent, oppositely charged, rough, and smooth nanoparticles. Flow cytometry, cLSM, and TEM reveal that rough nanoparticles are internalized by the cells more slowly and by an unidentified uptake route as no predominant endocytosis route is blocked by a variety of inhibitory drugs, while the uptake of smooth nanoparticles is strongly dependent on dynamin, F‐actin, and lipid‐raft. Negatively charged nanoparticles are taken up to a higher extent than positively charged ones, independent of the surface roughness.

     

A Set of Homo‐Oligomeric Standards Allows Accurate Protein Counting

Techniques based on fluorescence microscopy are increasingly used to count proteins in cells, but few stoichiometrically well‐defined standards are available to test their accuracy. A selection of bacterial homo‐oligomers were developed that contain 10–24 subunits and fully assemble when expressed in mammalian cells, and they can be used to easily validate/calibrate molecular counting methods. The utility of these standards was demonstrated by showing that nuclear pores contain 32 copies of the Nup107 complex.     

Studies on the metabolism of mitragynine,the main alkaloid of the herbal drug Kratom,in rat and human urine using liquid chromatography‐linear ion trap mass spectrometry

Mitragynine (MG) is an indole alkaloid of the Thai medicinal plant Mitragyna speciosa (Kratom in Thai) and reported to have opioid agonistic properties. Because of its stimulant and euphoric effects, Kratom is used as a herbal drug of abuse. The aim of the presented study is to identify the phase I and II metabolites of MG in rat and human urine after solid‐phase extraction (SPE) using liquid chromatography‐linear ion trap mass spectrometry providing detailed structure information in the MSⁿ mode particularly with high resolution. The seven identified phase I metabolites indicated that MG was metabolized by hydrolysis of the methylester in position 16, O‐demethylation of the 9‐methoxy group and of the 17‐methoxy group, followed, via the intermediate aldehydes, by oxidation to carboxylic acids or reduction to alcohols and combinations of some steps. In rats, four metabolites were additionally conjugated to glucuronides and one to sulfate, but in humans, three metabolites to glucuronides and three to sulfates. Copyright © 2009 John Wiley & Sons, Ltd.     

Microwave-assisted synthesis of 3,1,2- and 2,1,8-Re(I) and 99mTc(I)-metallocarborane complexes

Microwave heating was used to prepare eta5-rhenium carborane complexes in aqueous reaction media. For carboranes bearing sterically demanding substituents, isomerization of the cage from 3,1,2 to 2,1,8 derivatives occurred concomitantly with complexation. Microwave heating was equally effective at the tracer level using technetium-99m, affording access to a new class of synthons for designing novel molecular imaging agents.     

Exploring the chemical enhancement for surface-enhanced Raman scattering with Au bowtie nanoantennas

Single metallic bowtie nanoantennas provide a controllable environment for surface-enhanced Raman scattering (SERS) of adsorbed molecules. Bowties have experimentally measured electromagnetic enhancements, enabling estimation of chemical enhancement for both the bulk and the few-molecule regime. Strong fluctuations of selected Raman lines imply that a small number of p-mercaptoaniline molecules on a single bowtie show chemical enhancement >10(7), much larger than previously believed, likely due to charge transfer between the Au surface and the molecule. This chemical sensitivity of SERS has significant implications for ultra-sensitive detection of single molecules.     

Synthesis and properties of imidazo[1,2-a]pyridinium-3-olate. Some revised structures

Reaction of 2-anilinopyridine with chloroacetyl chloride in the presence of N,N-dimethylacetamide resulted in the formation of the mesoion imidazo[1,2-a]pyridinium-3-olate instead of the reported 4-oxopyrimidinium-5-olate. We performed some functionalizations and present two single crystal X-ray analyses.