Hybridization competition reactions

Appropriately substituted triplet 1,4-biradicals can undergo direct 1,5-and 1,6-cyclization to triplet cyclopentenylcarbenes or triplet 1,2-cyclohexa-dienes, respectively (Sch. 7) [44 16]. The typical substitution pattern for such competitive reactions is the presence of a sp-hybridized C-atom linked to one... 

Competition reactions are carried out as outlined above except that the reaction mixture contains an excess of unlabeled, sheared, single-stranded DNA that competes with the labeled probe for hybridization sites on the filter-bound DNA. If the supplemental heterologous DNA shows the same interference to probe binding as is found in vials containing excess homologous DNA, the two DNAs are considered homologous. If more probe... 

Since the periodic DFT calculations, especially the NEB calculations, are extremely time consuming, we use a hybrid approach for rational catalyst design. The OME was taken as the reactant, whereas adsorbed EO and acetaldehyde were considered as the products of different competitive reactions. ADE was used to provide initial guesses for species geometries to enhance efficiency. As a first step, structures of the reactants and products were optimized on the periodic Ag slab. Two NEB calculations were performed for the formation of adsorbed EO and acetaldehyde starting from the common OME intermediate. The difference between these two activation energies is the main factor responsible for the selectivity to the... 

The adduct formation from the reaction of the 3,5-dinitropyridine with MeONa was first reported by Fyfe.13 In DMSO solution the reaction is accompanied by the disappearance of the NMR spectrum of the substrate and the appearance of three new signals of equal intensity. Furthermore, one of the three ring proton signals is much more shielded than in the substrate, due to the hybridization change from sp2 to sp3. The observed pattern is in agreement with structure 1. Subsequent NMR and spectrophotometric studies have shown that the isomeric adduct 2 competitively forms together with 1 and eventually turns into the latter, due to a substantial difference in stability.35,36,45 The conversion 2 — 1 is accelerated by methanol. The more... 

With adequately tailored short Z-form DNA duplexes, H-transfer occurs by intrastrand P-H2 -abstraction [reaction (44) Kawai and Saito 1999 Kawai et al. 2000a], while competitive HI - and a-H2 -abstractions occurs in B-form DNA (Sugiyama et al. 1990,1993, 1996). Predominant Hl -abstraction is observed in a DNA-RNA hybrid (Sugiyama et al. 1997). 

Experimental and computational studies of the pericyclic Meisenheimer rearrangement and a competitive rearrangement of A-propargyl morphol i nc N-oxide revealed a novel inverse secondary kinetic isotope effect (kn/kD 0.8) for the rate-determining cyclization step, probably occurring because of a C(sp) to C(sp2) change in hybridization at the reaction center (Scheme 3).5... 

Chemical modification specifically tailored for macromolecular structures of lignocellulosic materials is a fascinating scientific endeavor in its own right as well as a useful art for the creation of specialty polymeric materials for technological applications. By utilizing suitable chemical reactions, new products with hybrid properties of nature and synthesis will take an important position with regard to utilization in the competitive world. 

A number of analogues has been prepared for photochemical studies. The photochemical reaction of 5-halouracil derivatives in DNA has been investigated for some time. Hydrogen abstraction of the sugar moiety from the 5 side by dU is largely conformation-dependent. Competitive CT and C2 p H abstractions are observed in B-DNA, predominant CT H abstraction occurs in DNA-RNA hybrids, and stereospecific C2 a-hydroxylation occurs efficiently in Z-DNA. In a more recent study, the photoreaction of 5-iodouracil con-... 

By using a multistep procedure, DNA molecules have been covalently attached to SWNTs. First, the purified SWNTs were oxidized to form carboxylic acid groups at the ends and sidewalls, followed by reaction with thionyl chloride and ethylenediamine to produce amine-terminated sites. The amines were then reacted with the heterobifunctional cross-linker succinimi-dyl 4-(iV-maleimidomethyl)cyclohexane-l-carboxylate (SMCC), leaving the surface terminated with maleimide groups. Finally, thiol-terminated DNA reacted with these groups to produce DNA-modified SWNTs [161]. AAHien DNA is covalently attached to SWNTs, a better stability, accessibility and selectivity are expected during competitive hybridization. 

As mentioned earlier, research on creating hybrid catalytic materials has been an area of interest for some time, and thus, there are a variety of methods that are used to immobilize catalytic species onto support materials. Some common examples are physisorption of the catalyst to the surface, electrostatic catalyst/surface interactions, and encapsulation of the catalyst into the pores of microporous materials [2], These methods can suffer from leaching in many solvents, competitive binding with charged or polar substrates, and limited usable substrate size and diffusion due to the support s small pore size, respectively. The method that offers the most promise of stability of attachment as well as flexibility in synthesis is covalent reaction between the catalyst and the support. This is the method employed in our research. By approaching the tethering process in a controlled and defined way, the surface catalytic species can be more uniform and behave more similarly to very well-defined homogeneous catalysts. 

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