Multiple hydrogen bonding based

Kubo H, Nariai H, Takeuchi T. Multiple hydrogen bonding-based fluorescent imprinted polymers for cyclobarbital prepared with 2,6-bis(acrylamido)pyridine. Chem Commun 2003 2792-2793. 

A solution leading to a successful algorithm was recently found for the folding of ribonucleic acid (RNA) [36], Natural RNA polymers (figure C2.14.1) are mainly made up from four different bases . A, C, G and U. As with DNA, multiple hydrogen bonding favours the fonnation of G-C and A-U pairs [16, 37, 38] which leads to the appearance of certain characteristic stmctures. Loop closure is considered to be the most important folding event. 

Tominaga, M Konishi, K. Aida, T. Catalysis of Nudeo-base via Multiple Hydrogen-Bonding Interactions Accderation of Aminolysis of 6-Chloropurine Derivatives by Uradls J. Am Chem Soc 1999,121,7704-7705. 

As a third example for an organocatalytic reaction, based on multiple hydrogen bonding and mechanistically investigated by DFT, we selected olefin epoxidation with hydrogen peroxide in fluorinated alcohol solvents, such as 1,1,1,3,3,3-hex-afluoro-2-propanol (HFIP) (Scheme 8). Here we encounter a new type of catalytic hydrogen bond the cooperative hydrogen bond. 

Okamura and Nakatani [65] revealed that the cycloaddition of 3-hydroxy-2-py-rone 107 with electron deficient dienophiles such as simple a,p-unsaturated aldehydes form the endo adduct under base catalysis. The reaction proceeds under NEtj, but demonstrates superior selectivity with Cinchona alkaloids. More recently, Deng et al. [66], through use of modified Cinchona alkaloids, expanded the dienophile pool in the Diels-Alder reaction of 3-hydroxy-2-pyrone 107 with a,p-unsaturated ketones. The mechanistic insight reveals that the bifunctional Cinchona alkaloid catalyst, via multiple hydrogen bonding, raises the HOMO of the 2-pyrone while lowering the LUMO of the dienophile with simultaneous stereocontrol over the substrates (Scheme 22). 

Figure 5.7 Functionalization strategies of copol3Tner 4 based on multiple hydrogen bonding interactions.

Chemical Sensing Based on Multiple Hydrogen Bonding.217... 

Chemical Sensing Based on Multiple Hydrogen Bonding Sensing Based on Interactions with Polar Moieties of Guests... 

Multiple hydrogen bonding interactions in tetrahedral building blocks have been employed by the group of Wuest to produce a remarkable tailored porous zeolite mimic, dubbed an organic zeolite because it does not contain any inorganic components at all.104 The pore-forming material is based on... 

Coordination interactions are not the only way to use self-assembly to produce closed, capsular systems capable of binding guest species in solution. Work by Julius Rebek Jr (Scripps, USA)43 has shown that multiple hydrogen-bonding interactions, because of their relatively weak, but directional, nature, are ideal for the strict self-assembly of closed spherical molecules and capsules. For example, component 10.49 consists of two intrinsically curved diphenylglycoluril units linked by a durene-based (1,2,4,5-tetramethyl benzene-based) spacer. In both solution and in the solid state, 10.49 self-assembles spontaneously to produce the tennis ball-shaped dimer (10.49)2 shown in Figure 10.43. The formation of the dimer has been observed by ... 

The use of chiral stationary phases (CSP) is a technique that relies on the formation of transient, temporary diastereoisomers between the sample enantiomers and the chiral stationary phase.1 Differences in stability between the diastereoisomers are reflected in differences in retention times the enantiomer that forms the least stable complex is eluted first. Chiral stationary phases may be classified into five different groups on the basis of mechanism of retention 77 (1) chiral phases with cavities78 80 (inclusion mechanism), shown in Figure 2.19, (2) chiral affinity phases,81,82 (3) chiral phases based on multiple hydrogen bond formation,83 (4) chiral jr-donor and... 

The mechanism of retention on chiral phases that is based on multiple hydrogen bonding formation involves the formation of base pairs and triple hydrogen bonds between the solutes and the chiral stationary phase 95 Fundamental work in this area has been done by Hara and Dobashi,96 97 using amino acid amide and tartaric acid amide phases. In addition, N,N -2,6-pyridinediyl bis(alkanamides) chemically bonded to silica gel have been described for the resolution of barbiturates 95... 

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