JOURNRL OF
Chemical € ducation: Software Abstracts for Volume IVC, Number 1 Demo-Deck: A Hypercard Stack of Chemistry Demonstrations Fred Juergens University of Wisconsin-Madison Madison, WI 53706
Demo-Deck is a HyperCard 2.0 database that catalogs nearly 1400 chemical demonstrations published during the past 20 years in references 1 4 . Each demonstration is summarized on a separate card that gives a complete reference to the original article describing the demonstration. Each card also contains a brief description and up to ten keywords that categorize the demonstration in terms of substances used or concepts (kinetics, catalysis, activation energy, ...). The search capabilities built into HyperCard allow you to find all cards that contain one or a pair of terms-not necessarily keywords. All words on each card are searched. Demo-Deck does not contain procedures for the cited demonstrations, since this would violate copyright restrictions; its purpose is to allow you to find original articles that contain procedures and, in many instances, information about safety and waste disposal. Demo-Deck allows you to enter your own procedure, safety information, etc. for any demonstration listed. This information is linked to Demo-Deck so that when a successful search has been done you can display your own description and procedure for the demonstration you found.
Frost Diagrams: A Tool for Predicting Redox Reactions James P. Birk Heidi Hocker Ar zona State Lnlverslty Tempe,AZ 85287-1604
Frost Diagrams is a Hypercard stack that provides an easily used format for making redox reaction predictions for one or two elements by comparing slopes of the lines connecting two oxidation states. Comparisons are simplified by copying the Frost diagram for one element to a new
card, then overlaying the diagram for the second element, so that the second diagram remains transparent and movable. The two diagrams can be aligned in any way desired, and any two half reactions can be compared. In addition, some common reduction half-reactions are collected on a single card with their lower energies aligned, thus making oossible oredictions of which common reduction half-reac;ions can'cause a desired oxidation half reaction. Frost Diagrams contains diagrams for 98 elements, each of which can be selected by clicking on that element's symbol in a periodic table. ~
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About This Issue John W. Moore and Jon L. Holmes, Editors University of WisconsiwMadison
With all the journals, books, and other publications about chemical demonstrations, how do you actually fmd a description and a procedure for a demonstration that will effectively get across exactly the point you want to teach? Use Demo-Deck. Fred Juergens has collected in one rapidly accessible form descriptions of about 1400 chemical demonstrations to help you illustrate chemistry better. The database and search capabilities of Hypercard make this an easy-to-use and veiy valuable resource. Frost diagrams, plots of free energy versus oxidation state, are useful tools for predicting whether oxidation-reduction reactions will occur. James Birk and Heidi Hocker have made it much easier to explore Frost diagrams by using the graphics capabilities of HyperCard. Each element can be selected from a periodic table by clickingwith a mouse, its Frost diagram is quickly displayed, and diagrams for two elements can easily be overlaid and compared. In addition to Demo-Deck and Frost Diagrams, there is a note with part of the index to the Journal of Chemical Education as a text file, continuing the practice of publishing such files that was begun in our first Macintosh issue. Hardware Requirements Demo-Deck requires a Macintosh t h a t can r u n Hypercard 2.0 with at least 2MB RAM, a hard disk is strongly recommended. Frost Diagrams requires a Macintosh that can run Hypercard 1.2.2or greater. For those who wish to use Frost Diagrams for class presentations a large monitor or overhead projection panel for the Macintosh will be needed. Several such panels and monitors are available (7). Literature Cited 1. sha~hashlri, B. Z. Chemieul &monsfmtionsA Handbook for D m k m ofchsmistry, Volumes 1 4 , Universih.ofWkconsin Madison, 1983,1985, 1989, and 1992. 2. Smmerlin, L.R.; Ealy, J. L.Jr. Chemical Dpmonsfrafions:ASourcebook for lbacham, Volvme 1,2nd ed.; Ameviran Chemical Society Washington, DC, 1988. 3. Summerlin, L. R.; Borgford, C. L.: Ealy, J. B., JL Chemical Demons1mtions:A Soumeboakfol Teachers. Volume2.2nd ed.: AmericsnChemicsl Society: WashingDn, DC,1988. 4. Journal of Chemical Educofion 1969 D present. All &ides having demonstration pmeedurea, hom the "nsted Demonstration# m1and others. Demonstrations prior to 1969 can be found by wingthe deanid indexes t o J Chem. Educ. 5. Chem ~ ~ N P w1978 s , to present. All articles havingdemonatration pmeedurea. 6. Saquis. M.; Sarquis, J. Fun uith Chamisfry:A Guiddwk o f K ~ 1 Aetiuitlps, 2 Vol. I, Institute for Chemieal Education: OepartmentafChemistry, Uuiversity ofwiaeonsin-Madison, 1101 University Avenue, Madinon, WI 53706. 7. Susskind, T.Y.J C h . Educ:Soft 1988 IA(1). 16-24.
Volume 69 Number 6 June 1992
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Urinary Excretion of Paracetamol A Thin-Layer Chromatography Exercise for Nursing Students Raymond J. S. Hickman School of Nursing, Flinders University of South Australia, GPO Box 21 00, Adelaide 5001, Australla Thin-layer chromatography (TLC) is a remarkable technique. It combines economy, versatility, and technical and conceptual simplicity. I t can be used to good effect in settings as different as a research laboratory and a junior teachine .. laboraton. This DaDer . . describes its use by nursing students in a faboratory exercise designed to &firm some im~ortantfeatures of the usual textbook description of drug metabolism and excretion. Most drugs are excreted in urine either unchanged or as metabolites. These metabolites are usually formed in the of the drug liver and oRen by" coniupation " - molecule with an endogenous substance such as g l u c u r o ~ cacid. Conjugation has a ~rotectiveeffect, because it produces substances that are less toxic, and &ore soluble in water, than the original drug. The lower toxicity reduces the adverse effects that the drug has while it remains in the body and the higher solubility in water increases the rate a t which it is cleared from the body as a component of urine. The conjugated form of a drug often can be hydrolyzed to re-form the original drug. Hydrolysis may be achieved by simple chemical means, such as heating with a strong acid, or by use of a suitable enzyme. Where an enzyme is used for hydrolysis the identity of the enzyme that regenerates the original drug will reveal the type of metabolite present. In this exercise the enzyme P-glucuronidase is used to investigate the metabolism of paracetarnol (also known as acetaminophen or p-hydroxyaceta~lide). Methods Thin-layer chromatography was carried out on commercially prepared (Merck)plastic sheets coated with silica gel HF25a. Each chromatography plate was a 80 x 50 mm section cut from one of these sheets. Samples were applied to the plate using calibrated micropipets. The developing solvent was a mixture of butyl acetate, chloroform, and 90% formic acid (9:4:1). Because 90% formic acid is capable of causing contact bums to tissue and produces fumes that are imtating to the skin, eyes and respiratory system ( I ) , the developing solvent should be prepared in a fume cupboard.
'CAUTION: Safety glasses and protective gloves should be worn during this operation. Plates were developed in glass jars fitted with tight-fitting, screw-down lids, and the developed plates were dried in a fume cupboard using a hair drier. In this way the concentration of organic solvent in the atmosphere of the laboratory was kept to a minimum throughout the practical sessions. Spots were detected by viewing the plates under ultraviolet light of wavelength 254 nm. The p-glucuronidase was from mollusks and was supdied bv BDH. The ethvl acetate used for liauid-liauid extraction was of analytical grade. The buffer solution used was NaH9P0,. 0.2 mu1 L-'Ma9HPO3.0.2 mol L-' 193:7. DH = 5.5). he piacetamol inges&d wasin the form of 500 k g tablets (Panamax by Winthrop). Urine samples were processed in 100 x 16mm sample tubes fitted with screw caps and manufactured by Wheaton.
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Journal of Chemical Education
Experiment Urine was collected on two successive mornings from a human volunteer. On the first occasion no paracetamol had been ingested the previous evening and the urine obtained was used in the preparation of "normal" samples. On the second occasion, the volunteer had ingested 1g of paracetamol prior to retiring, and the urine obtained was used in the preparation of "test" samples. A set of normal urine samples was prepared by mixing 3-mL aliquots of the normal urine with 2-mL aliquots of buffer solution in separate sample tubes. Two sets of test samples were prepared. The first set was obtained by mixing 3 mL of test urine with 2 mL of buffer solution and then adding 1mg of p-glucuronidase to each sample tube. The second s e t was identical to t h i s except t h a t Pglucuronidase was not added. All three sets of sample tubes were then placed in a thermostat bath, a t 37 'C, and agitated gently overnight. They were then ready to be used by students in the laboratory session. Students worked in groups of three and subjected each urine sample to extraction with ethyl acetate (1x 2 mL) by vortex mixing for 1min. This led to the formation of emulsions that were broken by centrifugation. Thin-layer chromatographicexammation ofthe ethyl acetate laver in each test tube was carried out in the usual manner (2.a n d a m parison made with a solution of authentic paracetamol. Results and Discussion Although very few of the students attempting this exercise had had any previous experience with TLC, most of them were able to obtain a convincing result a t this first attempt to use the technique. Under the chromatographic conditions used, the &value observed for paracetamol was 0.38. In an account of student laboratory work published previously in this Journal (31, it was reported that paracetamol was not detectable by TLC in the urine of people who had ineested the comoound. In the Dresent case. however. the test sample containing no P-glu&ronidase displayed a small. faint. but unmistakable ~aracetamol. . spot . showing that some of the compound reaches the urine unchanged a s is reported in the original literature dealing with paracetamol metabolism. Thus, Prescott reports (4)that 5% of a nontoxic dose of paracetamol is excreted unchanged in the urine of humans. It is likely that the ethyl acetate extraction used in the present procedure is the reason this small level of paracetamol can be detected so readily by the TLC technique. The extraction produces a "cry riean sample in the sense that only a smnllam(~untof the normal urine components that ahsorb ultraviolet radiation of wavelength 254 nm is extracted along with the paracetamol. None of this material appears to shift from the original spot during development of the TLC plate and so the region of the plate in which paracetamol spots are detected,-after de\dnpment, is completely free of ultra\iolet-abwrbing substances other than parncetamol itself.
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