Enzymatic Synthesis of a CCK-8 Tetrapeptide Fragment

The enzymatic synthesis of a tetrapeptide Phac-Met-Gly-Trp-Met-OEt is reported. It was synthesized by coupling Phac-Met-OEt with Gly-OMe. HCI, Trp-OMe and Met-OEt successively, catalyzed by α-chymotrypsin, papain and α-chymotrypsin respectively. The results of FAB-MS showed that the products had the correct molecular mass.     

Crystal Structure of Mixed Crystals of the Tetra(n-butyl)ammonium Salts of cis-Tetrafluorophthalocyaninato(2−)tantalate(V) and cis-Trifluorophthalocyaninato(2−)tantalate(IV)

cis-Trichlorophthalocyaninato(2?)tantalate(V) reacts with excess tetra(n-butyl)ammonium fluoride trihydrate yielding mixed crystals of the tetra(n-butyl)ammonium salts of cis-tetrafluorophthalocyaninato(2?)tantalate(V) and cis-trifluorophthalocyaninato(2?)tantalate(IV) in the ratio five to four. These crystallize in the monoclinic space group P2₁/ n with cell parameters: a = 13.368(2) Å, b = 13.787(2) Å, c = 23.069(3) Å, β = 93.35(1)°, Z = 4. Ta^v is octacoordinated with four F atoms and four N_iso atoms in an antiprismatic cis-arrangement. The Ta^v-F distance varies from 1.919(7) to 1.966(4) Å. Ta^IV is heptacoordinated with three F atoms in a cis-arrangement. The Ta^IV-F distance varies from 1.74(1) to 1.966(4) Å. The Ta atom is located out of the centre of the N₄ plane towards the F atoms by 1.234(3) Å. The Ta–N distances range from 2.261(6) to 2.310(6) Å.     

Trace gas analysis by a new high sensitivity thermal conductivity detector

Summary Inorganic gas analysis at the sub-ppm level requires preconcen-tration or the use of an ultrasensitive Helium detector. There are several problems with both methods if precise determinations are required. Until now, it has not been possible to use a hot-wire thermal conductivity detector for the purpose owing to its lack of sensitivity.A new TCD-system, which achieves major improvements in filament protection and in sensitivity, has been developed. The high sensitivity required for trace gas analysis has been obtained through the combination of a small-volume TC-cell, reduction of noise to a very low level and use of a built-in output-signal amplifier. Filament protection has been realized by operating the cell at constant mean temperature, and by using two electronic circuits for power cut-off when there is no carrier gas flow through the detector. With the addition of a single printed circuit card to the TCD-controller module, the detector is capable of automatic operation in conjunction with the microprocessor-controlled Varian Chromatography Data System CDS-111. Automatic operation includes auto-zeroing, auto-ranging and monitoring of the TCD. For calibration of the detector the inexpensive exponential dilution flask method was used, because commercial standards were usually either unreliable or expensive. The following concentrations were the minimum detectable with a relatively cool filament (300· C) and helium as carrier gas: argon, methane 0.1 ppm; oxygen, carbon monoxide, carbon dioxide, ethylene, acetylene 0.2 ppm; nitrogen 0.3 ppm; hydrogen 5 ppm. With nitrogen as carrier gas 0.3 ppm of hydrogen could be detected. These results can only be achieved after very careful checking and elimination of all leaks in the system. The application of such a sensitive, constant-temperature, amplified thermoconductivity detector should be of advantage for gas analysis at the sub-ppm level, which could formerly only be done with ultrasensitive but expensive helium detectors.

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Zusammenfassung Die Analyse von Spuren anorganischer Gase im unteren ppm-Konzen-trationsbereich erfordert Anreicherung oder die Benützung eines äußerst empfindlichen Heliumdetektors. Beide Methoden sind mit vielen Problemen verbunden, wenn genaue Bestimmungen erforderlich sind. Bis heute war die Anwendung eines Wärmeleitfähigkeitsdetektors (WLD) wegen dessen mangelnder Empfindlichkeit in diesem niedrigen Konzentrationsbereich nicht möglich.Die in dieser Arbeit beschriebenen Spurengasanalysen wurden mit einem neuen WLD-System erreicht, das bedeutende Verbesserungen auf dem Gebiet des Hitzdrahtschutzes sowie der Empfindlichkeit aufweist. Die für Spurengasanalysen erforderlichen hohen Empfindlichkeiten wurden erreicht durch Kombination einer rauscharmen Mikrovolumen-Detektorzelle mit einem Ausgangsverstärker. Der Schutz der Hitzdrähte wurde ermöglicht durch das Arbeiten bei konstanter Hitzdrahttemperatur; zusätzlich sind noch zwei elektronische Schutzschalter eingebaut, welche die Stromzufuhr zu den Meßdrähten unterbrechen, falls kein Trägergas durch den Detektor fließt. Mittels einer zusätzlichen Steckkarte in der Detektorelektronik kann dieser in Verbindung mit dem Varian-Chromatographie-Datensystem CDS 111 automatisiert werden. Diese Automatisierung schließt automatische Nullpunkteinstellung, automatische Empfindlichkeitsbereichswahl sowie das Ausdrucken von Detektorbedingungen mit ein.Der Detektor wurde mit der Methode der exponentiellen Verdünnung kalibriert. Diese Methode erlaubt eine billige und genaue Kalibrierung über einen genügend großen Konzentrationsbereich.Mit Helium als Trägergas und relativ niedrigen Hitzdrahttemperaturen (300° C) wurden die Nachweisgrenzen bei folgenden Konzentrationen gefunden: Argon, Methan, 0,1 ppm; Sauerstoff, Kohlenmonoxid, Kohlendioxid, Aethylen, Acetylen 0,2 ppm; Stickstoff 0,3 ppm und Wasserstoff 5 ppm. Mit Stickstoff als Trägergas konnte Wasserstoff bis zu 0,3 ppm nachgewiesen werden. Diese Werte können jedoch nur in einem leckfreien System erreicht werden.

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Presented at the International Symposium on Microchemical Techniques, May 23–27, 1977, Davos, Switzerland.     

Microarrayelectrodes for voltammetric and amperometric detection of organic pollutants

Disk and band shaped microarrayelectrodes (MAE) of gold and carbon have been developed. These electrodes can be used for electrochemical detection of different organic pollutants in organic and aqueous media. Differential pulse voltammetric, cyclic voltammetric and amperometric investigations at these MAE in stationary and flowing solutions with selected pesticides, polyaromatic hydrocarbons (PAH) and phenols have been carried out.     

Development of miniaturized potentiometric nitrate- and ammonium selective electrodes for applications in water monitoring

Mobile analysis with potentiometric sensors is well suited for field measurements. Ion-selective electrodes (ISE) based on polymeric membranes for in-situ determination of nitrate and ammonium contents in ground water, drinking water and surface water have been developed. The ISE are integrated in a multisensor module (MSM) for monitoring these ions over longer time intervals. The receptor is a PVC-membrane with tridodecylammonium nitrate (TDDA) for nitrate- and nonactine for ammonium-electrodes as ionophores. As plasticizer dibutylphthalate (DBT) was used. The main parameters for assessing the efficiency of these ISE are presented.     

General Voronovskaya and Asymptotic Theorems in Simultaneous Approximation

In the present note we prove general asymptotic and Voronovskaya theorems for simultaneous approximation. These generalize the Voronovskaya type theorems obtained recently by Floater for the Bernstein operators, and previously by Heilmann and Müller for the Durrmeyer operators.