Reversed-phase affinity chromatography of ecdysteroids with boronic acid-containing eluents

Selective effects of boronic acid-containing eluents on the chromatographic behaviour of ecdysteroids are described. The use of such eluents provides a simple, rapid and sensitive means to assess the presence of certain diol groups in ecdysteroids by ordinary RP-HPLC. It is demonstrated that ecdysteroids with different sets of diols in their molecules have individual shapes of chromatographic peaks. A mechanism of the boronic acid effect is discussed.     

Die Reaktion zwischen Ozon und Wasserstoffperoxyd

Zusammenfassung Es wurde die Reaktion zwischen Ozon und Wasserstoffperoxyd in Lösungen von 0.01 normaler Schwefelsäure bei 0° untersucht. Sie verläuft unter diesen Umständen so langsam, daß die Geschwindigkeit gemessen werden kann.Die nach einer gewissen Zeit verschwundene Ozonmenge ist der verschwundenen Peroxydmenge nicht äquivalent, sondern erheblich größer, und zwar um so größer, je verdünnter das Peroxyd ist.Nur bei einem großen Überschuß an letzterem verläuft die Reaktion nach der Gleichung: H₂O₂+O₃=H₂O+2 O₂.Diese Ergebnisse lassen sich durch die Annahme erklären, daß neben der genannten Reaktion eine freiwillige Zersetzung des Ozons stattfindet, deren Geschwindigkeit durch die Anwesenheit von Wasserstoffperoxyd außerordentlich stark erhöht wird. Durch diese Annahme ist auch die Möglichkeit gegeben, die früher gefundenen Unregelmäßigkeiten im zeitlichen Verlauf der Zersetzungsgeschwindigkeit des gelösten Ozons zu verstehen.Über diese Untersuchung wurde auf dem Internationalen Kongreß für angewandte Chemie in New-York (1912) in der Sektion Xb berichtet. Or. Comm. 8. intern. Congreß of applied Chemistry, Vol. XXVI, S. 611.     

Isolation of the active constituents in natural materials by 'heart-cutting' isocratic reversed-phase two-dimensional liquid chromatography

A multidimensional heart-cutting reversed-phase HPLC separation approach, where two columns were operated independently via two six-port two-position switching valves, was employed in the isolation of a major bioactive found in the ethanol-water (80:20) crude extract of Clerodendrum floribundum. In this mode of operation, the specific productivity of the multidimensional approach under overload conditions was twice that of conventional gradient methods with the same loading factor. Isolated sample purities were greater than 99% with recoveries of 95%. The independent operation of each of the two columns employed in the multidimensional approach allowed the cycle time to be less than 7 min, compared to 23 min in the gradient elution single-dimension mode of operation.     

Characterization of chemically modified carbonaceous electrode materials by x-ray fluorescence and scanning electron microscopy

An attachment scheme which utilizes cyanuric chloride as a linking agent in the preparation of chemically modified electrodes was investigated by using simultaneous scanning electron microscopy and x-ray fluorescence. Certain contaminants were discovered on the surface of the material following various steps in the reaction scheme used for attachment. The iron storage protein, ferritin, was attached to the surface of spectroscopic-grade graphite rod. Attempts were made to establish the surface distribution of the ferritin and to correlate distribution with surface morphology.     

A family of novel DNA sequencing instruments based on single-photon detection

We have developed a family of high-performance capillary DNA sequencing instruments based on a novel multicolor fluorescent detection technology. This technology is based on two technical innovations: the multilaser excitation of fluorescence of labeled DNA fragments and the "color-blind" single-photon detection of modulated fluorescence. Our machines employ modern digital and broadband techniques that are essential for achieving superior instrument performance. We discuss the design and testing results for several versions of the automated single lane DNA sequencers, as well as our approach to scaling up to multilane instruments.     

Student Questionnaries

We have developed several alternative practical laboratory examinations for the beginning organic chemistry course and have field tested these laboratory exercises as a component of the final examination in the laboratory component of that course. Data correlating practicum scores with overall scores in the laboratory course show significant scatter, suggesting to us possible shortcomings in the traditional methods of evaluation of laboratory skills.     

Rapid route to 3,4-substituted indoles via a directed ortho metalation-retro-Mannich sequence

[reaction: see text] In the presence of NXS (X = Br, I, Cl), gramine derivatives 1, derived by combined directed ortho metalation (DoM)-cross-coupling sequences, rapidly undergo retro-Mannich fragmentation (2) to afford 3-halo indoles 3 in 37-88% yields. A conceptually new methodology to diverse 3,4-substituted indoles (10, 11, 13) is thereby introduced.     

11,16 Oxetane lactones. Spectroscopic evidences and conformational analysis

Sesquiterpene lactones constitute a wide group of compounds with several biological activities, including allelopathic. The naturally occurring sesquiterpene lactones dehydrocostuslactone and cynaropicrin have been modified in three different ways: preparation of 11,13-oxetane lactones, addition of a second Michael acceptor and reduction of the α-methylene-γ-lactone in order to future structure-activity relationship (SAR) studies. We have obtained all oxetane lactones stereoisomers at C-11 and C-16 positions. This fact has allowed us to establish some correlations between experimental data, derived by NMR and X-ray analysis, and the configuration at C-11 and C-16, which could be a useful tool to establish the stereochemistry as well as to confirm the presence of an oxetane ring on similar compounds. Comparative conformational analyses as a key aspect in the biological behaviour of those compounds in future structure-activity relationship (SAR) studies are presented.     

Über die Darstellung der Methyl-3-Pentansäure und die Löslichkeitsbestimmungen ihres Calcium-, Barium- und Silbersalzes

Ohne ZusammenfassungZum Schlusse fühle ich mich verpflichtet, meinem hochverehrten Lehrer, Herrn Professor Dr. Adolf Lieben für die vielfache Unterstützung, die er meiner Arbeit angedeihen liess, meinen innigsten Dank auszusprechen.