Liquid column-chromatographic separation and determination of long-chain primary n-alkylamines (n-C10H21NH2 to n-C22H45NH2) after their fluorescence derivatization with salicylaldehyde diphenylboron chelate

Summary Long-chain primary n-alkylamines (fatty amines) were separated by reversed-phase high-performance liquid chromatography (RP HPLC) after derivatization with salicylaldehyde diphenylboron chelate to fluorescent chelate-like azomethine compounds. Thin-layer chromatography was used as a pilot procedure. A RP-18 HPLC column and methanol/water mixtures are suitable for the separation of the derivatized fatty amines up to n-C₂₂H₄₅NH₂, they can be detected fluorimetrically. Only n-alkylamines of specific chain length ranges are separable under isocratic conditions with water concentrations of 0 to 25% by volume. On the other hand gradient elution makes it possible to separate all the n-alkylamines investigated within 45 min, thus allowing quantitative determination. The peak areas are proportional to concentrations in the range 2 × 10^–6 to 8 × 10^–5 mol/l. The determination of derivatized n-dodecylamine (concentration 5 × 10^–5 mol/l) can be performed with a relative standard deviationS _rel = 0.023 ( 2.3%). The smallest determinable concentration varies from 1.5 × 10^–6 for n-C₁₂H₂₅NH₂ to 4.5 × 10^–6 mol/l for n-C₁₈H₃₇NH₂ (sample volume 50 l).

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Flüssigkeits-chromafographische Trennung und Bestimmung von langkettigen primären n-Alkylaminen (n-C₁₀H₂₁NH₂ bis n-C₂₂H₄₅NH₂) nach ihrer Fluorescenzderivatisierung mit Salicylaldehyd-diphenylborchelat

Zusammenfassung Langkettige primäre n-Alkylamine (Fettamine) wurden nach der Derivatisierung mit Salicyl-aldehyd-diphenylborchelat zu fluorescierenden chelatartigen Azomethinverbindungen mit Hilfe der reversed-phase-Hochleistungsflüssigkeits-Chromatographie (RP-HPLC) getrennt. Als Pilot-Verfahren diente die Dünnschicht-Chromatographie. Für die Trennung der derivatisierten Fettamine bis n-C₂₂H₄₅NH₂ und deren fluorimetrischer Detektion sind eine RP-18-HPLC-Säule und Methanol/Wasser-Gemische geeignet. Unter isokratischen Bedingungen sind bei Wassergehalten zwischen 0 und 25 Vol.-% nur n-Alkylamine bestimmter Kettenlängenbereiche trennbar. Dagegen ermöglicht die Gradientelution eine für quantitative Bestimmungen geeignete Trennung aller angewendeten n-Alkylamine innerhalb von 45 min. Die Peakflächen sind den Konzentrationen im Bereich 2 · 10^–6 bis 8 · 10^–5mol/l proportional. Die Bestimmung von derivatisiertem n-Dodecylamin (Konzentration 5 · 10^–5 mol/l) ist mit einer relativen StandardabweichungS _rel = 0,023 ( 2,3%) durchführbar. Die kleinste bestimmbare Konzentration beträgt 1,5 · 10^–6 für n-C₁₂H₂₅NH₂ bis 4,5 · 10^–6 mol/l für n-C₁₈H₃₇NH₂ (Probenvolumen 50 l).

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Boron chelates and boron metal chelates, Part XVII. For Part XVI see ref. [1]

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Dedicated to Prof. Dr. H. Hartkamp on the occasion of his 60th birthday     

Formation and stability of high-spin alkali clusters

Helium nanodroplet isolation has been applied to agglomerate alkali clusters at temperatures of 380 mK. The very weak binding to the surface of the droplets allows a selection of only weakly bound, high-spin states. Here we show that larger clusters of alkali atoms in high-spin states can be formed. The lack of strong bonds from pairing electrons makes these systems nonmetallic, van der Waals-like complexes of metal atoms. We find that sodium and potassium readily form such clusters containing up to 25 atoms. In contrast, this process is suppressed for rubidium and cesium. Apparently, for these heavy alkalis, larger high-spin aggregates are not stable and depolarize spontaneously upon cluster formation.     

THE ACTION SPECTRA FOR UV-INDUCED SUPPRESSION OF MLR and MECLR SHOW THAT IMMUNOSUPPRESSION IS MEDIATED BY DNA DAMAGE

-Ultraviolet-B (UVB,280–320 nm) radiation can promote the induction of skin cancer by two mechanisms: damage of epidermal DNA and suppression of the immune system, allowing the developing tumor to escape immune surveillance. The mixed lymphocyte reaction (MLR) and the mixed epidermal cell lymphocyte reaction (MECLR) are commonly used methods to study the immunosuppressive effects of UVB radiation. To obtain a better understanding of the mechanism by which UVB radiation decreases the alloactivating capacity of in vitro-irradiated cells, action spectra for the MLR and MECLR were determined. Suspensions of peripheral blood mononuclear cells or epidermal cells were irradiated with monochromatic light of 254, 297, 302 or 312 nm and used as stimulator cells in the MLR or MECLR. Using dose-response curves for each wavelength, the action spectra were calculated. Both MLR and MECLR action spectra had a maximum at 254 nm and a relative sensitivity at 312 nm that was a thousand times lower than at 254 nm. Strikingly, the action spectra corresponded very closely to the action spectra that were found by Matsunaga et al. (Photochem. Photobiol. 54,403–410, 1991) for the induction of thymine dimers and (6-4)photoproducts in irradiated calf thymus DNA solutions, strongly suggesting that the UV-induced abrogation of the MLR and MECLR responses is mediated by UV-induced DNA damage. Furthermore, the action spectra for the MLR and MECLR were similar, suggesting that they share a common mechanism for UV-induced suppression.     

An electrophilic cleavage procedure for the asymmetric dihydroxylation: direct enantioselective synthesis of cyclic boronic esters from olefins

A variation within the osmium-catalysed asymmetric dihydroxylation (AD) of olefins is described that yields cyclic boronic esters from olefins in a straight-forward manner. This process represents the first real product alteration in asymmetric dihydroxylation, since all previous protocols lead to free diols exclusively. A protocol based on the Sharpless AD conditions (for enantioselective oxidation of prochiral olefins) was developed that gives cyclic boronic esters with excellent enantiomeric excesses (ee's). Some of the ee's are higher than those reported for conventional AD. The unprecedented role of phenyl boronic acid on the course of the AD reaction was investigated in detail. PhB(OH)2 does not interfere with the chiral ligand, leaving the enantioselective step of olefin oxidation intact. The main role of the boronic acids-apart from protecting the diol products against potential overoxidation-relies on removing the diol entity in an electrophilic cleavage, which is in contrast to the conventional hydrolytic cleavage of the AD protocols. Thus, a mechanistically new cleavage for enantioselective dihydroxylation reactions is introduced within the present work.     

Copper-Catalyzed Carbonylative Hydroamidation of Styrenes to Branched Amides

Amides are one of the most ubiquitous functional groups in synthetic and medicinal chemistry. Novel and rapid synthesis of amides remains in high demand. In this communication, a general and efficient procedure for branch-selective hydroamidation of vinylarenes with hydroxyamine derivatives enabled by copper catalysis has been developed for the first time. The reaction proceeds under mild conditions and tolerates a broad range of functional groups. Applying a chiral phosphine ligand, an enantioselective variant of this transformation was achieved, affording a variety of chiral α-amides with excellent enantioselectivities (up to 99 % ee) and high yields.     

Quantum interference spectroscopy of rubidium-helium exciplexes formed on helium nanodroplets

Femtosecond multiphoton pump-probe photoionization is applied to helium nanodroplets doped with rubidium (Rb). The yield of Rb+ ions features pronounced quantum interference (QI) fringes demonstrating the coherence of a superposition of electronic states on a time scale of tens of picoseconds. Furthermore, we observe QI in the yield of formed RbHe exciplex molecules. The quantum interferogram allows us to determine the vibrational structure of these unstable molecules. From a sliced Fourier analysis one cannot only extract the population dynamics of vibrational states but also follow their energetic evolution during the RbHe formation.     

Dynamic forces on agglomerated particles caused by high-intensity ultrasound

In this paper the acoustic forces on particles and agglomerates caused by high-intensity ultrasound in gaseous atmosphere are derived by means of computational fluid dynamics (CFD). Sound induced forces cause an oscillating stress scenario where the primary particles of an agglomerate are alternatingly pressed together and torn apart with the frequency of the applied wave. A comparison of the calculated acoustic forces with respect to the inter particle adhesion forces from Van-der-Waals and liquid bridge interactions reveals that the separation forces may reach the same order of magnitude for 80 μm sized SiO₂-particles. Hence, with finite probability acoustically agitated gases may de-agglomerate/disperse solid agglomerate structures. This effect is confirmed by dispersion experiments in an acoustic particle levitation setup.     

Oxidative diamination of alkenes with ureas as nitrogen sources: mechanistic pathways in the presence of a high oxidation state palladium catalyst

A first palladium-catalyzed intramolecular diamination of unfunctionalized terminal alkenes has recently been reported. This study investigates the details of its mechanistic course based on NMR titration, kinetic measurements competition experiments, and deuterium labeling. It concludes a two-step procedure consisting of syn-aminopalladation with an unligated palladium(II) catalyst state followed by oxidation to palladium(IV) and subsequent C-N bond formation to give the final products as cyclic diamines. Related reactions employing sulfamides give rise to aminoalkoxy-functionalization of alkenes. This process was investigated employing deuterated alkenes and found to follow an identical mechanism where stereochemistry is concerned. It exemplifies the importance of cationic palladium(IV) intermediates prior to the final reductive elimination from palladium and proves that the nucelophile for this step stems from the immediate coordination sphere of the palladium(IV) precursor. These results have important implications for the general development of alkene 1,2-difunctionalization and for the individual processes of aminopalladation and palladium-catalyzed C(alkyl)-N bond formation.     

Enhanced deterministic phase retrieval using a partially developed speckle field

A technique for enhanced deterministic phase retrieval using a partially developed speckle field (PDSF) and a spatial light modulator (SLM) is demonstrated experimentally. A smooth test wavefront impinges on a phase diffuser, forming a PDSF that is directed to a 4f setup. Two defocused speckle intensity measurements are recorded at the output plane corresponding to axially-propagated representations of the PDSF in the input plane. The speckle intensity measurements are then used in a conventional transport of intensity equation (TIE) to reconstruct directly the test wavefront. The PDSF in our technique increases the dynamic range of the axial intensity derivative for smooth phase objects, resulting in a more robust solution to the TIE. The SLM setup enables a fast and accurate recording of speckle intensity. Experimental results are in good agreement with those obtained using the iterative phase retrieval and digital holographic methods of wavefront reconstruction.