Quantitative Impact of a Cognitive Modeling Intelligent Tutoring System on Student Performance in Balancing Chemical Equations

The need for improved interactive tutoring capabilities in educational software for chemistry problem solving is an important one clearly articulated by teachers and students. To deliver the next generation of individualized interactive capabilities users demand, it is necessary to go beyond the conventional computer-assisted instruction methodology. The focus of this paper is the assessment with first-semester general chemistry students of a recently developed artificial intelligence (AI) tutor for balancing chemical equations. This is the first such assessment of an AI-based learning tool in chemistry. Students in CHEM 121 in the Fall 2001 semester at Duquesne University (N = 273) participated in the study. Students were divided into a test group that used the AI tutor as part of their study activities and a control group that did not use the tutor. It was found that the tutor improved the performance of the test group students to a statistically significant degree, helping the weakest students the most. This study establishes the feasibility of an AI-based approach to creating advanced new tutoring software for chemistry problem solving. Access to a Web-based demonstration of the equation-balancing tutor may be obtained by emailing the corresponding author.     

A convenient synthesis of sulfonylureas from carboxylic acids and sulfonamides via an in situ Curtius rearrangement

A one-pot reaction of carboxylic acids with sulfonamides to afford sulfonylureas is described.     

Impact of prefractionation using Gradiflow on two-dimensional gel electrophoresis and protein identification by matrix assisted laser desorption/ionization-time of flight-mass spectrometry

Prefractionation of protein samples prior to two-dimensional electrophoresis (2-DE) has the potential to increase the dynamic detection range for proteomic analysis. We evaluated a membrane-based electrophoretic separation technique (Gradiflow) for its ability to fractionate an exoproteome sample from the filamentous fungus Trichoderma reesei. The sample was separated on the basis of size and charge. Buffer optimization was found to be necessary for successful size fractionation. Fractionation by charge was used to resolve the sample into four fractions that were subjected to analysis by two-dimensional electrophoresis (2-DE). Enhanced detection of low-abundance proteins with selective removal of high-abundance species was achieved. Fractionated and unfractionated samples were examined for differences in the ability to identify proteins following 2-DE using trypsin in-gel digestion followed by peptide mass fingerprinting using matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). Fractionated samples showed marked improvement in protein identification ability and sequence coverage. This study demonstrates the utility of the Gradiflow for fractionation, resulting in an enhancement of resolution and characterization of a moderately complex proteome.     

Nonequilibrium synthesis and assembly of hybrid inorganic-protein nanostructures using an engineered DNA binding protein

We show that a protein with no intrinsic inorganic synthesis activity can be endowed with the ability to control the formation of inorganic nanostructures under thermodynamically unfavorable (nonequilibrium) conditions, reproducing a key feature of biological hard-tissue growth and assembly. The nonequilibrium synthesis of Cu(2)O nanoparticles is accomplished using an engineered derivative of the DNA-binding protein TraI in a room-temperature precursor electrolyte. The functional TraI derivative (TraIi1753::CN225) is engineered to possess a cysteine-constrained 12-residue Cu(2)O binding sequence, designated CN225, that is inserted into a permissive site in TraI. When TraIi1753::CN225 is included in the precursor electrolyte, stable Cu(2)O nanoparticles form, even though the concentrations of [Cu(+)] and [OH(-)] are at 5% of the solubility product (K(sp,Cu2O)). Negative control experiments verify that Cu(2)O formation is controlled by inclusion of the CN225 binding sequence. Transmission electron microscopy and electron diffraction reveal a core-shell structure for the nonequilibrium nanoparticles: a 2 nm Cu(2)O core is surrounded by an adsorbed protein shell. Quantitative protein adsorption studies show that the unexpected stability of Cu(2)O is imparted by the nanomolar surface binding affinity of TraIi1753::CN225 for Cu(2)O (K(d) = 1.2 x 10(-)(8) M), which provides favorable interfacial energetics (-45 kJ/mol) for the core-shell configuration. The protein shell retains the DNA-binding traits of TraI, as evidenced by the spontaneous organization of nanoparticles onto circular double-stranded DNA.     

Mechanism of azole antifungal activity as determined by liquid chromatographic/mass spectrometric monitoring of ergosterol biosynthesis

A liquid chromatography/mass spectrometry (LC/MS) method for separation and characterization of ergosterol biosynthetic precursors was developed to study the effect of Posaconazole on sterol biosynthesis in fungi. Ergosterol biosynthetic precursors were characterized from their electron ionization mass spectra acquired by a normal-phase chromatography, particle beam LC/MS method. Fragment ions resulting from cleavage across the D-ring and an abundant M - 15 fragment ion were diagnostic for methyl substitution at C-4 and C-14. Comparison of the sterol profile in control and treated Candida albicans incubations showed depletion of ergosterol and accumulation of C-4 and C-14 methyl-substituted sterols following treatment with Posaconazole. These C-4 and C-14 methyl sterols are known to be incapable of sustaining cell growth. The results demonstrate that Posaconazole exerts its antifungal activity by inhibition of ergosterol biosynthesis. Furthermore, Posaconazole appears to disrupt ergosterol biosynthesis by inhibition of lanosterol 14alpha-demethylase.     

High-energy (neodymium) laser pyrolysis of U.S. coals

As part of a study exploring conditions that influence coal pyrolysis, the effects of neodymium laser heating upon five different rank coals have been studied. Gaseous products from neodymium-laser pyrolysis of all coal types can be explained by condensation reactions during the cooling of high-temperature systems. The use of neutral or reducing atmospheres (helium, hydrogen or deuterium at two atmospheres) does not significantly alter the product distributions, although some deuteration of products was observed. High-speed photography was used to determine the dynamics of the laser interactions.     

Mutagenesis approaches to deduce structure-function relationships in terpene synthases

This review highlights mutagenesis studies of terpene synthases, specifically sesquiterpene synthases and oxidosqualene cyclases. Mutagenesis studies of these enzymes have provided mechanistic insights, structure-function relationships for specific enzymatic residues, novel terpene structures and enzymes with novel activities. The literature through 2002 is reviewed and 113 references cited.     

Untersuchungen an diazoverbindungen und aziden-LIII : Abfangreaktionen instabiler azomethinimin-dipole mit ethanol

The reaction of the diazo compounds 1a-o with 4-phenyl-1,2,4-triazolin-3,5-dione (2) in dichloromethane-ethanol leads to the urazoles 5a-o; they arise from the primarily formed unstable azomethinhnine dipoles 4a-o by ethanol addition. Acidic hydrolysis of 5k and 5o yields the α-diketones 8 and 10 besides 4-phenyl urazole (9). Bistriazolindiones (13a,b) react analogously with diazo compounds (1l, m) in the presence of ethanol to give the bisurazoles 14a-c.     

Microporous hypercrosslinked polystyrene Styrosorb as a restricted access packing in sample clean-up for high performance liquid chromatography. Part I: Evaluation of restricted access properties

Summary Styrosorb is a beaded microporous polystyrene with particle sizes between 2 and 4 m. In spite of hypercrosslinkage the material was seen to swell in organic solvents. The native material is functionalized with Tris-groups at the outer surface of the particles. The average pore diameter was determined as 1.45±0.3 nm from size exclusion data using polystyrene and polyethylene standards in THF. The reversed phase behavior of the restricted access phase Styrosorb was investigated by injection of two test mixtures. Mixture I contained five aromatic amines, mixture II consisted of Amperozide^R and four related compounds. The optimum range of mobile phase composition was assessed so that analytes were separated whilst any proteins present were eluted unretained. Due to the small particle size short columns of 29×4 mm can be used for both sample clean-up and analytical separation of Amperozide^R and its metabolite.