Comparison of reversed-phase liquid chromatography and hydrophilic interaction/cation-exchange chromatography for the separation of amphipathic alpha-helical peptides with L- and D-amino acid substitutions in the hydrophilic face

Mixed-mode hydrophilic interaction/cation-exchange chromatography (HILIC/CEX) is a novel high-performance technique which has excellent potential for peptide separations. Separations by HILIX/CEX are carried out by subjecting peptides to linear increasing salt gradients in the presence of high levels of acetonitrile, which promotes hydrophilic interactions overlaid on ionic interactions with the cation-exchange matrix. In the present study, HILIC/CEX has been compared to reversed-phase liquid chromatography (RP-HPLC) for separation of mixtures of diastereomeric amphipathic alpha-helical peptide analogues, where L- and D-amino acid substitutions were made in the centre of the hydrophilic face of the amphipathic alpha-helix. Unlike RP-HPLC, temperature had a substantial effect on HILIC/CEX of the peptides, with a rise in temperature from 25 to 65 degrees C increasing the retention times of the peptides as well as improving resolution. Our results again highlight the potential of HILIC/CEX as a peptide separation mode in its own right as well as an excellent complement to RP-HPLC.     

A quantitative determination of the polymerization of benzoxazine thin coatings by time-of-flight secondary ion mass spectrometry

Phenol-paraphenylenediamine (P-pPDA) benzoxazines exhibit excellent barrier properties, adequate to protect aluminum alloys from corrosion, and constitute interesting candidates to replace chromate-containing coatings in the aeronautical industry. For the successful application of P-pPDA coatings, it is necessary to decrease the curing temperature to avoid the delamination of the coating while preserving the mechanical properties of the alloy, as well as the barrier properties of the coating. However, decreasing the curing temperature leads to less polymerized films, the extent of which requires a quantitative assessment. While the conversion rate of the polymerization reaction is commonly evaluated for bulk samples using differential scanning calorimetry (DSC), a tool for its evaluation in thin films is missing. Therefore, a new approach was developed for that matter using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The relation between the SIMS data integrated from inside thin films and the DSC results obtained on bulk samples with the same curing cycle allowed to calibrate the SIMS data. With this preliminary calibration of the technique, the polymerization of P-pPDA coatings can be locally determined, at the surface and along the depth of the coating, using dual-beam depth profiling with large argon cluster beam sputtering.     

Determination of 8-hydroxy-2'-deoxyguanosine in untreated urine by capillary electrophoresis with UV detection

A capillary electrophoresis method with UV detection was developed for the determination of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in untreated urine samples. The calibration graph for 8-OHdG in urine is linear in the concentration range 10-500 mg/l. and the detection limit is 5 mg/l (17 microM). 8-OHdG was determined in urine from oncological patients treated by radiation therapy. Its concentrations relative to creatinine were found to be in the range 10-47 microg 8-OHdG/l mg creatinine (4-19 micromol 8-OHdG/mmol creatinine). The overall time of the analysis of a urine sample was less than 15 min.     

Synthesis of beta-lactams from a N-rhenaimine: effect of the transition metal on the energetic profile of the Staudinger reaction

As depicted in the scheme, the alkylidenamido complex 1, a N-rhenaimine, reacts with ketenes to afford the beta-lactams 2-4, which possess a {Re(CO)3(bpy)} fragment as substituent at nitrogen. Clean demetalations using HOTf or MeOTf yield the free beta-lactams or N-methyl-beta-lactams along with [Re(OTf)(CO)3(bpy)]. DFT calculations help to rationalize why the reaction is faster than those of non transition metal N-substituted imines.     

High-throughput capillary electrophoretic method for determination of total aminothiols in plasma and urine.

Increased interest in the analysis of aminothiols in body fluids during the last years results in a request for high-throughput analytical methods for their determination. We report here a novel, high-throughput method for the determination of total concentrations of biogenous aminothiols - homocysteine, cysteine, glutathione, cysteinylglycine, gamma-glutamylcysteine, and of penicilamine, mercaptopropionylglycine, and cysteamine, three compounds used to treat disorders of aminothiol metabolism in plasma and urine. Samples were reduced with tris(carboxyethyl)phosphine and labeled with 5-(bromomethyl)fluorescein. Capillary electrophoretic separations were performed in 60 mmol/L borate - 15 mmol/L sodium dodecyl sulfate - 2-amino-2-methyl-1-propanol, pH 10.0, with laser-induced fluorescence detection. Analysis time was less than 2 min. The assay is linear (r > 0.999) up to 500 micromol/L. Reproducibilities of migration times (coefficient of variation, CV) were < 0.5%. Interassay repeatabilities (CV, n = 10) were 5.08% and 6.09% for 5 micromol/L addition of homocysteine and 0.60% and 3.78% for 100 micromol/L addition of cysteine in plasma and urine, respectively. Recovery values were within 94-106% and sensitivity was better than 0.19 micromol/L for all analyzed compounds. Results agreed well with a standard high-performance liquid chromatography (HPLC) method. The diagnostic usefulness of the method has been proven on 79 samples of cystinuric patients and 12 samples of homocystinuric patients. We report here a novel method for the determination of aminothiols in body fluids by capillary electrophoresis (CE). Determination is fast and sensitive enough for diagnostic purposes.     

Copper‐Catalyzed Enantioselective Allylboration of Alkynes: Synthesis of Highly Versatile Multifunctional Building Blocks

The first copper‐catalyzed enantioselective allylboration of alkynes is reported. The method employs a multitasking chiral NHC‐Cu catalyst and provides access to densely functionalized molecules from simple starting materials with excellent levels of chemo‐, regio‐, and enantioselectivity. These multifunctional products display highly versatile reactivity as shown by the synthesis of a variety of non‐racemic molecular scaffolds. DFT calculations were conducted to gain insight into the high selectivity levels of this catalytic process.     

Calorimetric study of melts in the System KF - K<Subscript>2</Subscript>NbF<Subscript>7</Subscript>

The relative enthalpies of melts in the system KF - K₂NbF₇ were measured by drop-calorimetry at the temperatures 1058, 1140 and 1208 K as a function of composition. Heat capacities of melted mixtures and enthalpies of mixing were determined using the experimental data. The molar heat capacity of melts diverges slightly from additivity. The molar enthalpy of mixing of melts shows small negative deviation from ideality which decreases with decreasing temperature. The thermal effect at mixing was assigned predominantly to association reactions producing more complex fluoroniobate anions.      

The effect of macromolecular architecture in nanomaterials: a comparison of site isolation in porphyrin core dendrimers and their isomeric linear analogues

The influence of macromolecular architecture on the physical properties of polymeric materials has been studied by comparing poly(benzyl ether) dendrons with their exact linear analogues. The results clearly confirm the anticipation that dendrimers are unique when compared to other architectures. Physical properties, from hydrodynamic volume to crystallinity, were shown to be different, and in a comparative study of core encapsulation in macromolecules of different architecture, energy transduction from the polymer backbone to a porphyrin core was shown to be different for dendrimers as compared to that of isomeric four- or eight-arm star polymers. Fluorescence excitation revealed strong, morphology dependent intramolecular energy transfer in the three macromolecular isomers investigated. Even at high generations, the dendrimers exhibited the most efficient energy transfer, thereby indicating that the dendritic architecture affords superior site isolation to the central porphyrin it surrounds.