Newer Analytical Chemistry Teaching Approaches at the Pharmaceutical Faculty of the Ghent University

A report is given on how teaching and training in analytical chemistry for pharmacy students has been modernized at the Ghent university in terms of (computer-assisted) lab courses, student-professor communication, and evaluation.Received January 12, 2003; accepted March 7, 2003 Published online July 16, 2003     

Synthesis of Substituted Salicylanilides under Microwave Irradiation

Summary. Salicylanilides were prepared in 70–95% yields in 4–8min from phenyl salicylate or phenyl 4-methoxysalicylate and substituted anilines under microwave irradiation under solvent free conditions.Received October 17, 2002; accepted October 22, 2002 Published online July 3, 2003     

Development and Validation of Catalytic Kinetic Spectrophotometric Method for Determination of Copper(II)

A catalytic kinetic spectrophotometric method is developed for the determination of trace amounts of Cu(II). It is based on the catalytic effect of Cu(II) on the oxidation of cysteine (RSH) by hexacyanoferrate(III) in acidic medium. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of hexacyanoferrate(III) at 420nm. The optimum operating conditions regarding concentration of reagents, pH and temperature were established. The working curve is linear in the concentration range of 0–6.35ng·mL^–1. The maximum percentage error and standard deviation for determination of Cu(II) in the range of 1.27–6.35ng·mL^–1 have been calculated to be 3.9 and 0.4 respectively. The detection limit calculated was 0.15ng·mL^–1. The interference effect of several species was also investigated, and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cu(II) in various synthetic and real samples. The typical feature of this procedure is that determination can be carried out at 25°C and/or in the absence of any precision thermostatic bath in the very short analysis time of one minute. The newly developed method was found to have fairly good selectivity, sensitivity, simplicity and rapidity compared to other kinetic methods.Received October 8, 2002; accepted April 7, 2003 Published online July 16, 2003     

A new dimension in thermal analysis

Summary An enormous development has taken place within the last five years in synchronous teaching over the Internet, i.e. both the teacher and the students are simultaneously in direct communication with each other as in a normal class-room or auditorium. With this concept it is possible to communicate orally, to exchange Power Point Presentations, documents, programmes and live web-camera pictures. It is even possible to use an electronic black board on which both the teacher and the students can work simultaneously. The great advantage with this type of teaching is that it is not restricted to a single class-room/auditorium with limited access, but in a virtual room accessible to everybody in principle all over the world, and which certainly open up new possibilities in teaching. The purpose of this paper is to present and to discuss the concept of virtual class-room teaching, how the system operates in practice, its advantages and, finally, how its inherent limitations can be overcome.     

Gel Chromatographic Fractionation and Partial Physicochemical Characterization of Gelatins

Summary Gel chromatography on Sephacryl S-400 HR was used to fractionate a type A and a type B gelatin on a semi-preparative scale. Fractionation was performed at 40 °C in 50 mM ammonium acetate, 0.02% (w/v) sodium azide. Five fractions, enriched in microgels, -chains, -chains, -chains and subfragments, were isolated. Their molar mass distribution was controlled by FPLC on Superose 6 and SDS-PAGE. No significant differences in amino-acid composition and hexose content were observed between the original gelatins and their fractions. The specific absorption coefficient at 230 nm was found to be the same for both type A and type B gelatin and the chromatographic fractions (2.0 L·g^–1·cm^–1).Presented at: International Symposium on Separation and Characterization of Natural and Synthetic Macromolecules, Amsterdam, The Netherlands, February 5–7, 2003     

Metal Sorption,Solid Phase Extraction and Preconcentration Properties of Two Silica Gel Phases Chemically Modified with 2-Hydroxy-1-Naphthaldehyde

Active silica gel phase (I) was chemically modified to the corresponding amino- (SiNH₂) and chloro- (SiCl) derivatives via silylation reactions. These were used to synthesize two newly modified silica gel phases (II, III) by direct chemical reaction with 2-hydroxynaphthaldehyde (2-HNA). The surface coverage values are 370, 432µmolg^–1 and 320, 355µmolg^–1 for (II) and (III), on the basis of thermal desorption and metal probe testing method, respectively. The metal sorption properties of silica gel phases (II, III) were studied and compared with active silica gel phase (I). The maximum determined metal capacity values were found to be 10–110, 20–290 and 20–370µmolg^–1 for phases I, II and III, respectively. The distribution coefficient values (K_d) were also determined for a series of metal ions, and the results showed that the two new chemically modified phases (II and III) were highly selective for Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺ and Pb²⁺. The potential applications of silica gel phases (II, III) as solid phase extractors for the same five metal ions spiked in drinking tap water (1.000µgmL^–1) were found to give percentage recovery values in the range of 90.2–96.3±4.1–6.3%, while pre-concentration of the same five metal ions spiked in drinking tap water (50.0ngmL^–1) was successfully accomplished with a percentage recovery range of 92.6–95.8±4.8–5.7%.Received December 16, 2002; accepted May 14, 2003 published online September 1, 2003     

Systematic Errors in the Determination of Trace Metals by GFAAS Technique,Part I

The behaviour of solutions containing 7 metals in trace range (pH=2) prepared in borosilicate glass and polyethylene containers and transferred into commercial polyethylene–polypropylene and home-made quartz autosampler cups for measurements were studied using graphite furnace atomic absorption spectrometry. The different interactions between metal solution and vessel material were observed for the metals studied. The most significant losses of chromium and nickel occurred on a polyethylene surface, while the highest absorbance signals were registered from quartz containers. Higher absorbance signals from quartz containers were also obtained for cadmium and copper solutions. Contrary to these results, the absorbance signals for lead solutions were lowest when measured from quartz vessels. The container material had no influence on the analytical signals of cobalt and manganese.Received January 15, 2003; accepted April 15, 2003 published online August 22, 2003     

Reduction of CuO-containing catalysts: CuO/ZnO

CO reduction of CuO in CuO/ZnO samples at 423 K isnot retarded by the support and occurs with no evidence of Cu₂O formation as reported (Porta et al. 1989). The positive order with regard to CO concentration varies with the precise range of CO partial pressure.

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CuO CO CuO/ZnO 423 Cu₂O , (Porta etal Solid State Ionics 32–33, 1019, (1989)). CO CO.

     

Kinetics of reduction of magnesium sulfate by carbon oxide

The thermodynamic analysis and the results of thermogravimetric investigation of the reduction of magnesium sulfate by carbon oxide are reported.The isothermal experiments were carried out in the temperature range 640 to 675°. A shrinking-core model was found to fit the reaction rate. An activation energy of 209.7±8.6 kJ/mol was obtained.

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Zusammenfassung Es wird über thermodynamische Analyse und Resultate einer thermogravimetrischen Untersuchung der Reduktion von Magnesiumsulfat mit Kohlendioxid berichtet. Die isothermen Experimente wurden im Temperaturbereich 640 bis 675° durchgeführt. Zur Erklärung der Reaktionsgeschwindigkeit wurde eine Shrinking-Modell gefunden. Es wurde eine Aktivierungsenergie von 209.7±8.6 kJ/mol erhlten.

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. 640–675°. , . 209,7±8,6 /.

     

Studies of vanadium catalysts for sulfur dioxide oxidation by51V-NMR

Studies of the⁵¹V-NMR spectra of a series of industrial catalysts and systems modelling the active catalyst component indicate that the catalyst composition depends on the preparation method and during thermal treatment the support interacts with the active component. The local environment of vanadium is being formed in the process of catalytic reactions.

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⁵¹V , -I-4, , : KVO₃, KVO₃–SiO₂, KVO₃–K₂SO₄ , , . .

     

Oxidation of CO on Ag-based composite oxides

Thermal stability of the oxidized state of silver was increased in the Cr, Mn, Fe and Co oxides. However, Ni and Cu oxides did not stabilize Ag, leading to its aggregation to form metallic Ag at 400°C. The Ag in the former group exhibited high catalytic activity in the oxidation of CO due to the formation of composite oxides with these transition metals.

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Cr, Mn, Fe Co. , Ni Cu Ag, 400°C. Ag CO, .

     

Kinetic analysis of thermogravimetric data. XII

Shape and position parameters and are proposed for the characterization of TG curves and are defined by Eqs (6), (7) and (8), respectively. These parameters being reduced to the standard conditionsn=0 andq=1/6 K sec^–1, the nomogram given in Fig. 1 can be constructed by means fo Eqs (9), (11) and (12). An iteration method is proposed, allowing derivation of the kinetic parametersn, E andZ of simple thermal decomposition reactions, from the parameters n,E andZ, by using the empirica formulae (9), (10), (11) and (12) and the nomogram. Table 3 contains data necessary to construct this nomogram.

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Zusammenfassung Die Gestalts- und Positionsparameter , und werden zur Charakterisierung von TG-Kurven vorgeschlagen, bzw. durch die Gleichungen (6), (7) und (8) definiert. Durch Reduktion dieser Parameter auf die Standardbedingungenn=0 undq=1/6 K sec^–1 mit Hilfe der Gleichungen (9), (11) und (12) kann das Nomogramm in Abb. 1 konstruiert werden. Eine Iterationsmethode wird vorgeschlagen, welche die Ableitung der kinetischen Parameter,n, E undZ einfacher thermischer Zersetzungsreaktionen aus den Parametern and unter Anwendung der empirischen Formeln (9), (10), (11) und (12) sowie des Nomogramms ermöglicht. Tabelle 3 enthält die zur Konstruktion des Nomogramms nötigen Angaben.

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Résumé Pour caractériser les courbes TG, on propose les paramètres de forme et de position , et définis par les équations (6), (7) et (8). En réduisant ces paramètres aux conditions standardsn=0 etq=1/6 K sec^–1, à l'aide des équations (9), (11) et (12), le nomogramme donné dans la figure 1 peut être construit. On propose une méthode d'itération pour déduire les paramètres cinétiquesn, E etZ à partir des paramètres , et dans le cas des réactions simples de décomposition thermique, en utilisant les formules empiriques (9), (10), (11) et (12) ainsi que le nomogramme. Le tableau 3 contient les données nécessaires pour construire ce nomogramme.

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G , , (6), (7) (8). « » =0 q=1/6 ^–1 , . 1, (9), (11) (12). , , E Z , (9), (10), (11) (12) . 3 , .

     

Capacité calorifique molaire du composé Bi.4 Te.6 dans les états solide et liquide

The heat capacities of Bi.4Te. 6 in the solid and liquid states are calculated from the results of the experimental drop calorimetric method, and the heat of fusion of the compound is deduced.

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Zusammenfassung Die Wärmekapazitäten von Bi.4Te. 6 in fester und flüssiger Phase werden aus experimentellen Daten berechnet, die mit der tropfenkalorimetrischen Methode erhalten wurden. Die Schmelzwärme der Verbindung wird abgeleitet.

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« » Bi₄Te₆ , .

     

Performance of a new differential scanning calorimeter cell

A calorimeter cell has been developed utilizing a geometry which optimizes dynamicgas flow and quantitative heat transfer to each sensing thermocouple. The basis of the cell is a sensitive thin form differential thermocouple which is symmetrically and rigidly positioned, containing a center port. The thin form differential thermocouple serves as a sample and sample container support as well as a differential detector. The dynamic gas enters through the center port permitting good contact with the sample and sample pan adjacent to it. The theoretical aspects are discussed and the necessity of having a high thermal resistance between the heat source and sample and a low thermal resistance between the sample and detecting thermocouple is demonstrated. Applications which show both qualitative and quantitative capabilities are presented.

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Zusammenfassung Es wird über eine kalorimetrische Zelle mit einer Geometrie, die einen optimalen Gasstrom und quantitative Wärmeübermittlung zu jedem Thermoelement ermöglicht, berichtet. Die Zelle besteht aus einem empfindlichen dünnen Thermoelement, das symmetrisch und fest angelagert ist und eine Öffnung in der Mitte besitzt. Das dünne Thermoelement dient zum Halten der Probe, des Probebehälters und als Differentialdetektor. Das dynamische Gas tritt durch die Öffnung ein, wodurch eine gute Berührung mit Probe und umgebendem Probebehälter ermöglicht wurde. Die theoretischen Aspekte werden erörtert und es wird bewiesen, daß zwischen der Wärmequelle und der Probe ein hoher, zwischen dem messenden Thermoelement und der Probe ein niedriger thermischer Widerstand nötig ist. Anwendungen informieren über die qualitativen und quantitativen Fähigkeiten der Zelle.

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Résumé On a mis au point une cellule calorimétrique dont la conception est favorable à la circulation d'un courant gazeux et au transfert quantitatif de la chaleur vers chaque thermocouple détecteur. Le fond de la cellule est constitué par un thermocouple différentiel fin et sensible, disposé symétriquement et d'une manière rigide, et dont le centre est muni d'un orifice. Ce fin thermocouple différentiel sert de support d'échantillon et de détecteur différentiel. La circulation du gaz s'effectue par l'orifice central qui permet un bon contact avec l'échantillon et le support d'échantillon qui lui est adjacent. Les aspects théoriques sont discutés et l'on montre la nécessité d'une résistance thermique élevée entre la source de chaleur et l'échantillon et faible entre l'échantillon et le thermocouple détecteur. Des applications illustrent les possibilités qualitatives et quantitatives de ce dispositif.

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, . , , , , . , . , , . . .

     

On the Laplacian spectral radii of trees with perfect matchings

Denote by the set of trees of order 2k with perfect matchings. GUO [Guo, Linear Algebra Appl. 368:379–385, 2003.] determined the largest value of Laplacian spectral radii μ(T) of the trees T in and gave the corresponding tree T in whose μ(T) reaches this largest value. In this paper, we determine the second to the sixth largest values of μ(T) of the trees T in and also give the corresponding trees T in whose μ(T) reach these values.     

Partial oxidation of methane on Cr2O3/Al2O3

The oxidation of methane on supported chromia was studied at temperatures varying between 423 and 743 K and CH₄/O₂ ratios between 1 and 9 in a differential reactor. The main reaction products observed were carbon monoxide and formaldehyde. The rates of reaction obey a power law expression.

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, 423 743 CH₄/O₂ 1 9, . . .

     

Determination of total,and bound Se in sera by INAA

In this study we report on the comparison between the total selenium in serum (total Se) with that which is apparently bound to high molecular weight (>12,000 D) species, presumably proteins (bound Se). Nine hundred seventy seven (977) serum samples arising out of a population-based epidemiological study were prepared in duplicate for the determination of total Se by pipeting directly into irradiation vials; and separate duplicate aliquots were dialyzed against DI water for the determination of bound Se. All samples were analyzed by neutron activation analysis via^77mSe (17.4 s). A small dialyzable Se component (6%) (free Se), defined as the difference between the total Se minus the bound Se, was identified.     

Kinetic studies on MeWO4-tungstates grown under mild hydrothermal conditions (Me=Mn2+, Fe2+, Zn2+)

The reaction mechanims and the kinetics of formation of MeWO₄-tungstates (Me=Mn²⁺, Fe²⁺, Zn²⁺) have been studied by reacting metal (II) chlorides and sodium tungstate at 493 K in a special autoclave, allowing continuous removal of the reactants.

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MeWO₄ ( Me=Mn²⁺, Fe²⁺, Zn²⁺) - (II) 493 , .

     

Distribution of components in the rare earth ammonia synthesis catalysts and effect of additives

The distribution of components in the HG-1 ammonia catalyst promoted by rare earth oxide (successfully developed by the authors) was analyzed by electron microprobe photography. The results enable us to explain the effect of additives upon the activity as well as the remarkably high lifetime of catalyst.

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HG-1, ( ) , . , .

     

Molecular mechanics and dynamics study of DNA-furocoumarins complexes: Effect of methylation of the angular derivatives on the intercalation geometry

Summary Results of molecular mechanics calculations on intercalation complexes between DNA and angelicin derivatives: angelicin, 4-methylangelicin, 5-methylangllicin, 4,4-dimethylangelicin, 4,5-dimethylangelicin, 4,6,4-trimethylangelicin and 4,6,5-trimethylangelicin, are presented. The correlation between the presence of methyl groups and an increase in DNA photobinding affinity is discussed on the basis of the molecular structures. The influence of the orientation of the angelicins within the intercalation cavity is also discussed. Finally, the consequences of the dynamical behaviour of angelicin in the intercalation cite are studied.Abbreviations CNDO complete neglect of differential overlap - NMR nuclear magnetic resonance - rms root mean square - UV-A ultraviolet light of class A (320<<400 nm)