Development of reactive thiol-modified monolithic capillaries and in-column surface functionalization by radical addition of a chromatographic ligand for capillary electrochromatography

Reactive thiol-modified capillary columns for capillary electrochromatography (CEC) were developed by transforming the pendent 2,3-epoxypropyl groups of poly(glycidyl methacrylate-co-ethylene dimethacrylate) (poly(GMA-co-EDMA)) monoliths into 3-mercapto-2-hydroxy-propyl residues by a nucleophilic substitution reaction, employing sodium-hydrogen sulfide as nucleophilic reagent. Conditions for this modification reaction were systematically optimized with respect to different parameters, such as reaction temperature, pH-value, reaction time, type and concentration of organic modifier, and concentration of the sodium-hydrogen sulfide solution. The amount of thiol groups that was generated on the monolith surface was determined directly in the capillaries by a disulfide-exchange reaction employing 2,2'-dipyridyl disulfide (DPDS). This reaction in the capillary liberates pyridine-2-thione in equimolar amount to the surface sulfhydryls, which was collected into a vial and determined photometrically at 343 nm by RP-HPLC. About 17% of the total lateral epoxide moieties of the monolithic substrate could be transformed to reactive sulfhydryl groups, which corresponds to about 0.7 mmol g(-1) monolithic polymer, with a column-to-column repeatability of 3.2% R.S.D. The reactive thiol groups can be utilized to attach any chromatographic ligand with appropriate anchor in a second step, e.g. by radical addition, graft polymerization, nucleophilic substitution, disulfide formation or Michael addition reaction. To demonstrate the feasibility of the concept, we chose an anion exchange type chromatographic ligand based on a quinine derivative, O-9-tert-butylcarbamoylquinine (t-BuCQN) which was attached to the monolith in a radical addition reaction, for a further in-column surface functionalisation. About 78% of the sulfhydryl groups were derivatized with t-BuCQN as determined from differential DPDS assays before and after the selector immobilization reaction. The applicability of these surface-functionalised monolithic capillary columns could be shown by an electrochromatographic separation of the enantiomers of N-3,5-dinitrobenzoyl-leucine, which performed fairly well compared to an analogous capillary that was fabricated by an in situ copolymerization approach.     

Are Collapse Models Testable via Flavor Oscillations?

Collapse models predict the spontaneous collapse of the wave function, in order to avoid the emergence of macroscopic superpositions. In their mass-dependent formulation, they claim that the collapse of any system’s wave function depends on its mass. Neutral K, D, B mesons are oscillating systems that are given by Nature as superposition of two distinct mass eigenstates. Thus they are unique laboratory for testing collapse models that are sensitive to the mass. In this paper we derive—for the single mesons and bipartite entangled mesons—the effect of the mass-proportional CSL (Continuous Spontaneous Localization) collapse model on the dynamics on neutral mesons. We compare the theoretical prediction with experimental data from different accelerator facilities.     

The spectrum of permutation orbifolds

We study the spectrum of permutation orbifolds of 2d CFTs. We find examples where the light spectrum grows faster than Hagedorn, which is different from known cases such as symmetric orbifolds. We also describe how to compute their partition functions using a generalization of Hecke operators.

     

MgBr2 · OEt2: A Lewis Acid Catalyst for the O- and N-Boc Protection of Phenols and Amines

MgBr₂ · OEt₂ efficiently catalyzes the O- and N-tert-butoxycarbonylation of functionalized phenols and amines. The presented procedure is operationally simple and done under solvent-free conditions.     

Ylide Chemistry: An Account of Structural,Conformational and Redox Investigations

Abstract

Structural data of phosphorus ylides are summarized and discussed. Conformational preferences in solution and in the solid state, as followed by NMR spectroscopy and X-ray diffraction, indicate a strong gauche effect for the lone pairs of electrons at the ylidic carbon atom. One- and two-electron oxydation of ylide carbanions is accomplished with copper(II) as the oxidant, leading to oxidative coupling or to halogenation, respectively.     

Ecotoxicological characterisation of exhaust particulates from diesel-powered light-duty vehicles

Diesel exhaust is one of the major sources of fine and ultrafine particulate matter in urban air. Toxicity of diesel-powered engine emissions has been quite widely assessed, however, much less information is available on their ecotoxicity. In our study the kinetic version of the Vibrio fischeri bioluminescence inhibition bioassay, based on the ISO 21338:2010 standard, was used to characterise the ecotoxicity of diesel-powered cars. The method is sensitive enough to test the ecotoxic effect of the emission of individual vehicles. In general, significant positive correlation was found between ecotoxicity (expressed as Toxic Unit /TU/values) and total carbon (TC) as well as between TU and polycyclic aromatic hydrocarbon (PAH) concentrations.      

Comparison of two force fields in MD-simulations of α-helical structures in keratins

Molecular dynamic (MD) simulations based on two different force fields, CVFF and CFF91, were carried out in order to check their feasibility for the structural investigation of the wool intermediate filament (IF) monomeric unit. Selecting an ideal α-helix as start conformation, all MD-simulations with CVFF in vaccum show the α-helix to be unstable. Independently of the amino acid sequence of the α-helix, a new helical structure with a larger diameter arises during the MD-simulation, due to a shift of the intrahelical hydrogen bonds. However in simulations with surrounding water the α-helix remains stable throughout the simulations with the CVFF force field. In contrast to this, MD-simulations in vaccume based on the CFF91 force field are able to determine different stabilities for the α-helical start conformation of various IF-segments, that agree well with secondary structure predictions. The simulation results obtained with CFF91 in vacuum can like wise be verified using an explicit water environment. We found that higher partial charges attributed to the atoms of the amide groups that form the intrahelical hydrogen bonds are the reason for the superiority of the CFF91 force field.     

Preparation of dimethoxyborane and analysis by Fourier transform infrared spectroscopy

Dimethoxyborane was prepared by the reaction of trimethoxyboroxine, sodium borohydride and trimethyl borate in diethylene glycol dimethyl ether solvent at 70°C under atmospheric pressure followed by distillation to increase the purity and analyzed in liquid phase by FT-IR. The concentration of dimethoxyborane was identified by hydrolysis with water, which yields boric acid, methanol and hydrogen, whereas the generated hydrogen was analyzed by the mass detector of a volumetric flow apparatus. The FT-IR absorbance peak area showed a linear dependence on dimethoxyborane concentration in the wavenumber range 873 to 950 cm⁻¹ for samples with dimethoxyborane concentrations 0 to 6.2 wt% in trimethyl borate. Data fitting using the least square method gave an R ² value of 97%.     

Nanoscale molecular superfluidity of hydrogen

We present a microscopic quantum theoretical analysis of the nanoscale superfluid properties of solvating clusters of para-H2 around the linear OCS molecule. Path-integral calculations with N=17 para-H2 molecules, constituting a full solvation shell, show the appearance of a significant superfluid response to rotation around the molecular axis at T=0.15 K. This low-temperature superfluid response is highly anisotropic and drops sharply as the temperature increases to T approximately 0.3 K. These calculations provide definitive theoretical evidence that an anisotropic superfluid state exists for molecular hydrogen in this microscopic solvation layer.