Synthetic surfaces for ribonuclease adsorption

Intact RNA and DNA are of central importance to biochemical research and biotechnology. The preservation of these nucleic acids requires the absence of nuclease activity. Here, radical-mediated polymerization of vinylsulfonate on resin and glass surfaces is shown to produce a high-density poly(vinylsulfonate) coating that sequesters ribonucleases from aqueous solutions quickly and completely. The adsorptive efficacy of this coating exceeds that of other known coatings by > or =10(7)-fold. Surfaces coated with poly(vinylsulfonate) could be used to maintain the integrity of ribonucleic acids in a variety of contexts.     

Endo entry to the nortricyclyl-norbornenyl cation system: stereochemistry in the fragmentation of endo-5-norbornenyl-2-oxychlorocarbene

Fragmentation of (S)-endo-5-norbornenyl-2-oxychlorocarbene [(S)-8] in cyclohexane-d12 gives approximately 20% (S)-endo-2-chloro-5-norbornene [(S)-7] with approximately 50% ee, 65-70% (R)-exo-2-chloro-5-norbornene [(R)-4] with >95% ee, and approximately 12% (R)-3-nortricyclyl chloride [(R)-5] with approximately 22% ee. (Analogous stereochemical results were also obtained starting with the enantiomeric carbene (R)-8.) The (S)-8 to (S)-7 and (S)-8 to (R)-4 conversions are ascribed mainly to retention and inversion S(N)i transition states, respectively. These have been located by computational methods and are nearly isoenergetic. In more polar solvents (CDCl3 and CD3CN), the fragmentation of (S)-8 increasingly occurs via competitive ion pair pathways in which steroselectivity is diminished, and escape to the norbornenyl-nortricyclyl cation directs the products away from endo-2-chloro-5-norbornene toward exo-chloride 4 and nortricyclyl chloride 5.     

Diastereoselective cascade synthesis of azabicyclo[3.1.0]hexanes from acyclic precursors

The diastereoselective synthesis of azabicyclo[3.1.0]hexanes bearing different substituents on all positions of the cyclopropane ring has been achieved in moderate to good yields.     

The application of C-N.M.R. spectroscopy to the determination of the stereochemistry of Diels-Alder adducts

Long-range (³J) ¹³C-H coupling is a reliable probe to evaluate the stereochemistry of cycloaddition products. The method is best applied to carbonyl containing adducts but not restricted to them. Several structures have been revised and new ones evaluated.     

Fabrication of nanoscale metallic spirals using phospholipid microtubule organizational templates

We describe the fabrication of metallic Cu spiral/helical nanostructures prepared via selective electroless metallization of a phospholipid microtubule template. The metallization template is created through selective, sequential adsorption of the oppositely charged polyelectrolytes, sodium poly(styrenesulfonate) (PSS) and poly(ethyleneimine) (PEI), onto nanoscale seams naturally occurring on the microtubule surface. A negatively charged Pd(II) nanoparticle catalyst is bound to the terminal cationic PEI layer of the multilayer film and initiates selective template metallization to form the helical Cu nanostructures. Details of the process are presented, and a mechanism and factors affecting the control of the feature critical dimensions are discussed.     

Application of high-field NMR and cryogenic probe technologies in the structural elucidation of poecillastrin a,a new antitumor macrolide lactam from the sponge poecillastra species

Poecillastrin A (1), a new polyketide-derived macrolide lactam, was isolated from a deep-water collection of the marine sponge Poecillastra species. The structure of poecillastrin A (1) was assigned using NMR data acquired at 500 MHz with an inverse-detection cryogenic probe and at 800 MHz with a room-temperature probe.     

Mechanism for semiquinone formation in the oxygen negative chemical ionization mass spectrometry of 2,3,7,8-tetrachlorodibenzo-p-dioxin

The high toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) has led to the development of selective and highly sensitive quantitative methods for mass spectral analysis. Analytical selectivity has been demonstrated for the oxygen negative chemical ionization (ONCI) reaction of TCDD in an oxygen-rich plasma. While the reaction product (4,5-dichloro-1,2-benzoquinone anion) of 2,3,7,8-TCDD and oxygen is well known, the mechanism of its formation has not been studied thoroughly. In this report the results of a study involving the reaction of ¹⁸O₂ with 2,3,7,8-TCDD under high pressure and low pressure ONCI conditions are reported. A mechanism is proposed which is compatible with the observation that one ¹⁸O atom is incorporated into the product anion.