CYCLOBUTANE DIMERS AND (6-4)PHOTOPRODUCTS IN HUMAN CELLS ARE MENDED WITH THE SAME PATCH SIZES

The size of excision repair patches corresponding to excision of (6-4) pyrimidine-pyrimidone photoproducts and (5-5, 6-6) cyclobutane dimers have been independently determined by using bromodeoxyuridine substitution and density increases in isopycnic gradients of small DNA fragments. The two classes of photoproducts were distinguished by using (a) a xeroderma pigmentosum (XP) revertant cell line that excises (6-4) photoproducts normally, but does not excise cyclobutane dimers from bulk DNA or from an actively transcribed sequence; (b) an XP cell line containing the denV gene of bacteriophage T4, which repairs only cyclobutane dimers by a unique glycosylase mechanism, and (c) normal cells analyzed during time intervals in which cyclobutane dimer repair is the main repair process in action. The patch sizes for the two lesions were similar under all conditions and were estimated to be approximately 30-40 bases. These values are slightly large than corresponding estimates for Escherichia coli and Saccharomyces cerevisiae but close to estimates from in vitro experiments with human cell extracts. The size of 30 bases may consequently be very close to the actual distance between cleavage sites made on either side of a photoproduct during repair.     

A Mild Transamination Route to [EtGaNEt]6: A Twelve-Vertex Gallium-Nitrogen Cluster

The reaction of [EtGa(NMe₂)₂]₂ with neat, excess EtNH₂ afforded a glassy solid whose IR spectrum did not exhibit any N–H absorptions and ¹H NMR spectrum indicated the presence of more than one compound. Refluxing a toluene solution of this solid afforded the imido gallium compound, (EtGaNEt)₆ (1), in 56% yield. Compound 1 crystallized in space group R¯3 with a hexagonal prismatic structure constructed with two planar Ga₃N₃ rings.     

Reaction dynamics on bifurcating potential energy surfaces

Classical trajectories were run on a local fit to the bifurcating transition region of the Valtazanos and Ruedenberg ab initio potential energy surface for the cyclopropylidene to allene reaction, and also on several variations of this local surface. The trajectory results were analyzed to determine the outcome as a function of initial conditions, and several plots of these are presented.Camille and Henry Dreyfus Teacher-Scholar; Alfred P. Sloan Foundation fellow     

A convenient method for the synthesis of α-Ketoesters from aldehydes

An efficient two step, two carbon homologation of aldehydes to α-ketoesters is described.     

Preparation of derivatives of 5-,6-, and 8-hydroxy-2-aminoanthracene

Three phenolic derivatives of 2-aminoanthracene have been prepared as their diacetyl derivatives by Bucherer-type amination of appropriately substituted anthracenes.     

Electronic structure of tungsten carbide and its catalytic behavior

The different observations concerning the platinum-like electronic structure found in X-ray photoelectron spectra as contrasted by the platinum-unlike density of states detected by soft X-ray appearance potential spectroscopy is reconciled. The platinum-like catalytic activity of WC results from changes in the electron distribution when C is added to W; core level chemical shifts indicate electron transfer from W valence orbitals to C_2p orbitals.     

Summary of reference materials for the determination of the nutrient composition of foods

Certified reference materials (CRMs) play a critical role in validating the accuracy of nutrient data for food samples. A number of available food CRMs of differing matrix composition have assigned concentrations for various nutrients, along with associated uncertainty intervals (UIs) for those values. These CRMs have been used extensively in the United States Department of Agriculture’s (USDA) ongoing National Food and Nutrient Analysis Program (NFNAP) to monitor the accuracy of assays of key foods and nutrients consumed in the United States. A total of 690 assigned values for individual nutrients, including proximates, vitamins, macroelements, microelements, fatty acids, amino acids, and selected phytochemicals (e.g., carotenoids), were compiled from the certificates of analysis for 63 CRMs, and the specified UI in each case was expressed as a percentage of the assigned certified or reference concentration. Across all nutrients, 63.5% of the UIs were less than 10% of the assigned value, 25.5% were 10–20%, and 11% were greater than 20% of the assigned value. The UIs for proximates, minerals, and trace elements were most consistently less than 10% of the assigned value. The relative uncertainties were significantly higher for vitamins, suggesting greater challenges in measuring and certifying these components. These high UIs (greater than 10% assigned value) in the best available reference materials are likely to be indicative of the precision and accuracy that can be obtained by current measurement systems for these components. These data suggest that care must be taken in choosing CRMs to monitor food composition analysis, including evaluating what levels of uncertainty are required in assigned values and which analytical measurement systems for food components need closer examination and improvement. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Presented at ‘BERM-10’, April 2006, Charleston, SC, USA.     

An intermediate neglect of differential overlap model for second-row transition metal species

An intermediate neglect of differential overlap (INDO ) model for elements of the second transition series is described. Values of exponents for the radial portion of the Slater basis atomic orbitals, the orbital ionization energies, and the beta (or bonding) parameters for these elements are reported. Use of the model to investigate equilibrium geometries, relative energy ordering of geometric isomers, spectroscopic transition energies, energy ordering of state wave functions of different symmetry, trends in dipole moments, and equilibrium stretching frequencies is reported. The results indicate that the INDO method is capable of yielding quality results for species containing atoms of the second transition series.