Triple Hydrogen Bonding

The prototypical DDA-AAD dimer (HB-181) has been studied extensively in chloroform [9]. Many DDA and AAD monomers have been designed. Generally, the A a values of this kind of heterodimers, such as HB-182 and HB-183, are remarkably higher than those of the DAD-ADA motifs, which reflect the important elfect of the secondary interactions. 

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Complementary triple hydrogen-bond formation involving transition metal complexes has been little studied. Mingos et al. [68] have investigated the cocrystallisation of platinum(II) complexes of the uracil derivative orotic acid (2,6-dioxo-l,2,3,6-tetrahydropyrimidine-4-carboxylic acid), which generally coordinates as the dianion, and 2,6-diaminopyridine (2,6-dap), in which complementary A-D-A---D-A-D triple hydrogen bonds are formed between the orotate... 

Figure 5.22 Cu UPD on a Au/mica substrate modified by a hybrid nanostructure consisting of a hydrogen-bonded network and a thiol SAM. (a) Cartoon ofthe hybrid structure and molecular structures of the components. The hydrogen-bonded network is composed of 1,3,5-triazine-2,4,6-triamine (melamine, triangles) and perylene-3,4,9,10-tetracarboxylic di-imide (PTCDI, rectangles) that interact via a triple hydrogen bond (dotted lines). Pores ofthe...

Later, oxyanion holes were also discovered in other proteases, such as the cysteine protease papain, and in esterases and lipases, enzymes capable of esterification or ester hydrolysis. Interestingly, in these esterases, sometimes up to three hydrogen bond donors can be located within 3 A of the carbonyl oxygen atom, whereas such triple hydrogen bonding motifs have not yet been found in the proteases. 

Lehn and Rotello s groups extensively studied diacyldiaminopyridines that form triple hydrogen bonded associated structures with uracil and thymine groups (Gulik-Krzywicki et al. 1993 Carroll et al. 2003 Stubbs and Week 2003 Sanyal et al. 2004). lUian et al. (2000) studied the formation of vesicles from mixtures of randomly functionalized complementary copolymers containing thymine groups and... 

Hemideprotonation of a metalated nucleobase and the resulting selfcomplementarity is also the key in rationalizing the triple hydrogen-bonding pattern seen in an associate of a neutral and an anionic purine-6-thione Ru(III) complex (130), which is analogous to that seen with 2-thiouracil [(84), see Section II. D]. 

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... 

D. M. P. (1995). Multidimensional crystal engineering of bifunctional metal complexes containing complementary triple hydrogen bonds. Chem. Soc. Rev. 24, 329. 

The preparation of 2-hydroxy-3 -pyridinecarboxaldehyde and its 6-acetamido derivative, and their condensation with Fischer s base to give the corresponding spiropyridopyrans have been described. The acetamido spiro compound selectively recognizes guanine, which traps the open colored form by triple hydrogen bond complementarity, thus signaling the presence of guanosine derivatives.79... 

Although the triple hydrogen bond systems that have been addressed so far in this review contain a linear arrangement of the hydrogen bonding groups, this is not necessarily the case. The functionalised ds,ds-cyclohexane-l,3,5-tricarbox-... 

Since riboflavin (RF) is surface-active and possesses a high fluorescence quantum yield, the dye is very suitable for TIR fluorescence measurements at a water/oil interface. For TIR experiments, an aqueous RF solution was poured onto a CCI4 solution containing a diamino-j-triazine derivative (DTT), which acted as a flavin receptor via triple hydrogen bonds. On the basis of fluorescence dynamic measurements of RF adsorbed on a water/oil... 

Trivalent hydrogen-bonding systems have been used very extensively for guiding and influencing the structuring of polymers. As mentioned in Sect. 1, Fig. 5, the most important triple-hydrogen bonds derive from 2,6-diamino-pyridines, 2,6-diamino-1,3,5-triazines and their complexes with flavine- and... 

An important contribution towards the effect of triple hydrogen bonds on polymer behavior was demonstrated by Meijer et al. [83] in early 1995. 

Fig. 18 Formation of pseudo-block copolymers consisting of poly(isobutylene)-poly(ether-ketone) telechelics held together by triple hydrogen bonds...

Fig. 19 Reversible attachment of a Cu(I)-catalyst to a solid support via triple hydrogen bonds, acting as a reversible catalyst for atom transfer radical polymerization (ATRP)...

Fig. 21 Assembly of polymers via triple-hydrogen bonds, a Formula of the flavine/2,6-diamino-triazine and thymine/2,6-diaminotriazine interactions, b Formation of nanopar-ticles/polymer aggregates, c Polymersome formation by aggregation of poly(norbornenes) and poly(styrenes) bearing N-bisacyl-2,6-diamino-pyridine and thymine side-chains, respectively. Reprinted with permission from [104,105]...

Fig. 72 (left) Binding of polymers via selective triple-hydrogen-bonding interactions. (right) Selective binding of POSS functionalized with DAP units to SAM surfaces via triple-hydrogen-bonding interactions. Redrawn with permission from [244]... 

Such a chiral host is able to bind ammonium ions by inclusion and triple hydrogen bonds between the ammonium ion and three oxygens of the crown enantiodiscrimina-tion is due to steric reasons so that the host-guest complexation of one enantiomer is favoured over the other. Accordingly, the spectrum of application is quite narrow as it is restricted only to chiral primary amines including primary a- and f)-amino acids. 

The rigid binaphthyl units occupy planes that are perpendicular to the plane of the cyclic ether. One of the naphthalene rings forms a wall that extends along the sides and outward from the other face of the cyclic ether. The substituents attached at the 3-position of the naphthalene rings extend along the side or over the face of the cyclic ether. In the presence of a chiral primary amine, it forms a triple hydrogen bond with the primary ammonium cation. The same complex is formed whether the guest approaches from the top or from the bottom of the crown ether, as the crown ether... 

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