Investigation of the steric mass action formalism in the simulation of breakthrough curves on a monolithic and a packed bed column

The simulation of the behaviour of two proteins (cytochrom c and alpha-chymotrypsinogen) on two types of stationary phases (monolithic and porous particle-based) was attempted for non-linear (simulation of breakthrough curves) and linear (simulation of elution peaks) cation exchange chromatography. It was found that the combination of a stoichiometric model (steric mass action, SMA) with the lumped pore diffusion (POR) model allows a simulation of high predictive value. Using one set of SMA and transport parameters for a given column morphology and/or protein, breakthrough curves and peaks could be simulated that agreed well with the experimental data while no dependency on either the protein load or the mobile phase composition (salt content) was observed. One of the SMA parameters, namely the characteristic charge needed some slight adjustment (within the error of the experimental determination of this parameter) in order to optimise the fit.     

ANTIBODIES TO UV IRRADIATED DNA: THE MONITORING OF DNA DAMAGE BY ELISA AND INDIRECT IMMUNOFLUORESCENCE

Abstract The enzyme-linked immunosorbant assay (ELISA) was modified to (1) characterize antibodies raised in rabbits against UV-irradiated single-stranded DNA (UVssDNA) complexed with methylated BSA and (2) directly detect pyrimidine dimers in irradiated DNA. The antisera specifically bound to UVssDNA, UVpoly(dT) and to a limited extent to UVdsDNA and UVpoly(dC) immobilized on protamine sulfate coated microliter wells. Fifty percent of the maximum antibody binding was observed at a 1-5000 dilution against UVssDNA. Binding to ssDNA and poly(dT) was observed only at much higher concentrations of antibody (1:500 dilution), whereas no binding to double stranded DNA (dsDNA) was observed. The extent of binding of the antibody was dependent on the dose of UV radiation to DNA, as well as, to the concentration of antigen immobilized on the plate. Specific binding to DNA irradiated with 5.0 J/m² was detected with as little as 10 ng of DNA. The sensitivity was further extended to less than 1 J/m² by using higher concentrations (100 ng) of UVssDNA. The ability of various irradiated molecules, DNA, homopolymers and linkers to act as inhibitors of antibody binding establish that the antigenic determinants are mainly thymine homodimers with lower affinity for cytosine dimers. Potential usefulness of the antibodies to directly quantitate pyrimidine dimers in cells exposed to UV radiation was determined by indirect immunofluorescence. Flow cytometric analysis of immunostained human lymphocytes irradiated with 254 nm radiation indicated that greater than 50% of the population had significantly higher fluorescent intensity than unirradiated control cells.     

Vibrational delocalization in ammonia aerosol particles

The present contribution investigates shape effects and surface effects in the infrared spectra of pure (NH(3)) and mixed (NH(3)-CO(2) and NH(3)-NH(2)D-NHD(2)-ND(3)) ammonia particles with sizes between about 1 and 50 nm. The particles investigated have been generated in a collisional cooling cell as aerosols at temperatures between 20 and 80 K. The contribution reveals that only the combination with a microscopic model leads to a comprehensive understanding of the various features observed in the experimental infrared spectra. As one of the major results, the corresponding exciton model explains why pronounced shape effects observed for pure particles only play a minor role in the case of mixed particles.     

Vapor–liquid equilibria and excess volumes of the binary systems ethanol + ethyl lactate, isopropanol + isopropyl lactate and n-butanol + n-butyl lactate at 101.325 kPa

Isobaric vapor–liquid equilibrium data have been experimentally determined at 101.3 kPa for the binary systems ethanol + ethyl lactate, isopropanol + isopropyl lactate and n-butanol + n-butyl lactate. No azeotrope was found in any of the systems. All the experimental data reported were thermodynamically consistent according to the point-to-point method of Fredenslund. The activity coefficients were correlated with the NRTL and UNIQUAC liquid-phase equations and the corresponding binary interaction parameters are reported. The densities and derived excess volumes for the three mixtures are also reported at 298.15 K.     

Exceptionally fast radiative decay of a dinuclear platinum complex through thermally activated delayed fluorescence

A novel dinuclear platinum(ii) complex featuring a ditopic, bis-tetradentate ligand has been prepared. The ligand offers each metal ion a planar O^N^C^N coordination environment, with the two metal ions bound to the nitrogen atoms of a bridging pyrimidine unit. The complex is brightly luminescent in the red region of the spectrum with a photoluminescence quantum yield of 83% in deoxygenated methylcyclohexane solution at ambient temperature, and shows a remarkably short excited state lifetime of 2.1 μs. These properties are the result of an unusually high radiative rate constant of around 4 × 10⁵ s⁻¹, a value which is comparable to that of the very best performing Ir(iii) complexes. This unusual behaviour is the result of efficient thermally activated reverse intersystem crossing, promoted by a small singlet–triplet energy difference of only 69 ± 3 meV. The complex was incorporated into solution-processed OLEDs achieving EQE_max = 7.4%. We believe this to be the first fully evidenced report of a Pt(ii) complex showing thermally activated delayed fluorescence (TADF) at room temperature, and indeed of a Pt(ii)-based delayed fluorescence emitter to be incorporated into an OLED.

Efficient thermally activated delayed fluorescence (TADF) in a brightly luminescent diplatinum(ii) complex results in significant enhancement of the radiative decay rate.     

Comparison of the chromatographic behavior of monolithic capillary columns in capillary electrochromatography and nano-high-performance liquid chromatography

Porous monoliths based on N,N-dimethylacrylamide (DMAA) or methacrylamide (MAA) were prepared inside fused silica capillaries as stationary phases for nano-chromatography. The columns were characterized in terms of flow rate and backpressure and showed, e.g. differences as a function of the salt concentration added to the polymerization mixture. When the columns were investigated for the separation of uncharged (polar hydroxylated aromatic compounds) and charged (amino acids) analytes under pressure driven conditions (pLC), differences to the previously observed behavior under voltage driven conditions (CEC) were observed. Whereas the non-charged analytes showed similar behavior in both cases--thus, corroborating the previous assumption of a mainly chromatographic separation mode driven by hydrophilic interactions in CEC--the charged amino acids did not. Assuming that the separation was governed by chromatographic phenomena in the pLC mode and by both chromatographic and electrophoretic effects in the CEC mode, the experiments allowed deconvoluting the two contributions. In particular, the charged amino acids appeared to interact with the stationary phases mainly by electrostatic interactions modified by some hydrophilic effects.     

Heterocyclic studies—XXIV: Mass spectra of some pteridin-4(3H)-ones and 3-methoxypteridin-4(3H)-ones

Mass spectra of pteridin-4(3H)-one and all its mono-, di- and tri-C-methyl derivatives are recorded. Spectra of 3-methoxypteridin-4(3H)-one and four of its mono- and dimethyl derivatives are also recorded. Pteridin-4(3H)-one fragments mainly by loss of CO and HCN in either order. Methyl substitution in the pyrazine ring leads to that ring fragmenting in preference to the oxygen bearing pyrimidine ring. Elucidation of fragmentation pathways was facilitated by changes in peak positions with changing methyl substitution patterns. 3-Methoxypteridin-4(3H)-ones fragment mainly through initial loss of CH₂O, but the ions so produced break down differently from isomeric molecular ions of pteridin-4(3H)-ones. Several fragmentation pathways are discussed.     

Low-resolution accurate mass measurement in self-chemical ionization mass spectrometry

Low-resolution (2000, 10% valley definition) accurate mass measurements using self-chemical ionization (self-CI) have been evaluated as an alternative to the conventional chemical ionization (CI) method. In conventional CI experiments a high pressure of reagent gas is required to induce ionization while in self-CI no reagent gas is used and the self-CI is produced presumably by molecular/fragment ion–molecule reactions. Nine compounds ranging in mass from 50–500 daltons were examined. Results obtained by the self-CI method indicate that the elemental composition assignment can be obtained simultaneously for the protonated molecule and/or molecular ion. It is also shown that perfluorokerosene can be used routinely in self-CI as an internal reference standard over a broad mass range (50–500 daltons). It is sometimes difficult to use a single reference standard in conventional low-resolution CI accurate mass spectrometry over a similar mass range.     

L-Phenylalanine Cyclohexylamide: A simple and convenient auxiliary for the synthesis of optically pure α,α-disubstituted (R)- and (S)-amino acids

This work describes L -phenylalanine cyclohexylamide ( 5c ) as a simple, cheap, and powerful chiral auxiliary for the synthesis of a series of optically pure α,α-disubstituted (R)- and (S)-amino acids of type 1 , such as (R)- and (S)-2-methyl-phenylalanine ( 1a ), (R)- and (S)-2-methyl-2-phenylglycine ( 1b ), and (R)- and (S)-2-methylvaline ( 1c ; Scheme 3). These amino acids were efficiently transformed into the suitably protected and activated amino acid building blocks (R)- and (S)- 12b and (R)- and (S)- 12c (Scheme 4) which are ready for incorporation into peptides by solution or solid-phase techniques. Based on the crystal structures of 6b, 6c , and 7a belonging to the diastereoisomeric peptides series 6 and 7 , the absolute configurations of each member of the series were determined. β-Turn geometries of type II′ and I were observed for 6b and 7a , respectively, whereas 6c crystallized in an extended conformation. The impacts of side-chain variation on conformation and crystal packing of these triamides are discussed.     

Observations relevant to the mechanism of the reductive aminations of ketones with sodium cyanoborohydride and ammonium acetate

Fortimicin B (2) has been converted to 6'-epi-fortimicin B 5 and 6'-epi-fortimicin A 4 both of which have the same diaminosugar moiety as that present in gentamicin C₂3. The syntheses of the 6'-epi-fortimicins and their antibacterial activities are reported.Although reductive amination of 1,2'-di-N-benzyloxycarbonyl-6'-oxo-fortimicin B-4,5-carbamate 17 with sodium cyanoborohydride and ammonium acetate in methanol gave a mixture of 1,2'-di-N-benzyloxycarbonyl-6'-epi-fortimicin B-4,5-carbamate 18 and 1,2'-di-N-benzyloxycarbonylfortimicin B-4,5-carbamate 14, attempted reduction of 1,2'-di-N-benzyloxycarbonyl-6'-iminofortimicin B-4,5-carbamate 16, under identical conditions gave only recovered imine. The significance of these results relative to the mechanism of the reductive amination of carbonyl compounds with sodium cyanoborohydride and amine salts is discussed.