Template efficiency

Table III. Templating efficiency of PrxHH ( 4 x) in the absence and in the preeenca of 41 substituting for Si...

Figure 1-6 Template efficiency parameters for the tetrapyridylporphyrin templated Glaser coupling of two zinc porphyrin dimers, in dichloromethane.

Tethered reactions can be regarded as linear templated systems in which the template-substrate binding is infinitely strong. The template efficiency is therefore defined simply by the effective molarity for the intramolecular reaction the rate enhancement becomes greater than 2 when [S]q < EM, and becomes infinite at infinite dilution. 

Figure 9.4 Proposed mechanism for the formation of hemicarceplexes SOCuest (A) and 4QCuest (B) and relative templation efficiencies in the formation of SOCuest (C)...

The comparison of RNA and DNA template efficiencies is informative, but it should be recognized that the reaction condition optimal for one substrate may be suboptimal for another. In fact, the optimal conditions for a polymerization reaction with AMV RTase on RNA templates have been shown to be different from those on DNA templates (34,37). 

The template effects of potassium and lithium ions are responsible for the efficiency of the synthesis of macrocyclic ligands in 18-CROWN-6 and2,2.7,7,12,12,17,l 7-OCTAMETHYL-21,22,23,24-TETRAOXAPER-HYDROQUATERENE. 

C, 92% ee at -20 °C, 88% ee at 0°C in the reaction of acrolein and cyclopen-tadiene). This is unusual for metal-catalyzed asymmetric reactions, with only few similar examples. The titanium catalyst 10 acts as a suitable chiral template for the conformational fixing of a,/ -unsaturated aldehydes, thereby enabling efficient enantioface recognition, irrespective of temperature. 

In the elucidation of retention mechanisms, an advantage of using enantiomers as templates is that nonspecific binding, which affects both enantiomers equally, cancels out. Therefore the separation factor (a) uniquely reflects the contribution to binding from the enantioselectively imprinted sites. As an additional comparison the retention on the imprinted phase is compared with the retention on a nonimprinted reference phase. The efficiency of the separations is routinely characterized by estimating a number of theoretical plates (N), a resolution factor (R ) and a peak asymmetry factor (A ) [19]. These quantities are affected by the quality of the packing and mass transfer limitations, as well as of the amount and distribution of the binding sites. 

NaH should serve as an efficient template ion to yield cone conformers. Conformer distribution for the reaction of p-tert-h Wy calix[4]arene and ethyl bromoacetate is given in Table I. 

In conclusion, the use of glycosylamincs as chiral templates in the Ugi reaction provides an efficient and highly stereoselective access to both l- and D-amino acids. 

The optically active D- and L-em/rn.i-2-morpholmones 1 (only the d-erythro series is depicted) are efficiently brominated with (V-bromosuccinimide to afford the bromo derivatives 2 (X = Br) that serve as versatile precursors for electrophilic glycine templates which permit construction of either d- or L-a-atnino acids in high optical purity71. The corresponding chlorides 2 (X = Cl) are similarly obtained by chlorination of 1 with tert-butyl hypochlorite71. 

Induction of asymmetry into the /J-lactam-forming process was inefficient with acyclic imines having chiral groups on the nitrogen [19] but efficient with rigid, cyclic chiral imines (Table 3). One of these was used as a chiral template to produce highly functionalized quaternary systems (Eq. 5) [34]. 

In the as-synthesized MFI-crystals the tetrapropylammonium (TPA) ions are occupying the intersections between the straight (parallel) and the sinusoidal channels of the zeolite, thus providing an efficient pore filling. The detailed structure of as-synthesized MFI-TPA has been elucidated by X-ray single crystal analysis (ref. 3). Also the combination tetrabutyl-Ztetraethylammonium can be applied as template in MFI-synthesis. A 1 1 build-in is found then (Fig. 1). When only tetrabutylammonium is available as template, the MEL (ZSM-11) lattice is formed with another distance between the channel intersections. 

The cell must possess the machinery necessary to translate information accurately and efficiently from the nucleotide sequence of an mRNA into the sequence of amino acids of the corresponding specific protein. Clarification of our understanding of this process, which is termed translation, awaited deciphering of the genetic code. It was realized early that mRNA molecules themselves have no affinity for amino acids and, therefore, that the translation of the information in the mRNA nucleotide sequence into the amino acid sequence of a protein requires an intermediate adapter molecule. This adapter molecule must recognize a specific nucleotide sequence on the one hand as well as a specific amino acid on the other. With such an adapter molecule, the cell can direct a specific amino acid into the proper sequential position of a protein during its synthesis as dictated by the nucleotide sequence of the specific mRNA. In fact, the functional groups of the amino acids do not themselves actually come into contact with the mRNA template. 

Stack and coworkers immobilized phenantrohne derivative 16 on micelle-templated silica SBA-15 (Scheme 8) [55,56]. The system showed more selective and efficient catalytic activity for olefin epoxidations with peracetic acid than the analogous homogeneous catalyst. 

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