Hydrogen bond array

Kim, Chin, and co-workers have described a highly interesting oxyanion hole mimic that transforms L-amino acids to D-amino acids [97]. The mechanism involves stabilization of the enolate intermediate by an internal hydrogen bond array generated by urea group (Scheme 4.14). In the presence of an external base, such as triethylamine, the receptors readily promote the epimerization of a-amino acids, favoring the D-amino acids due to unfavorable steric interactions in the receptor-L-amino acid complex. These receptors can also be viewed as chiral mimics of pyridoxal phosphate [98]. 

Block Copolymers Containing Other Hydrogen Bonding Arrays... 

Fig. 15 Crystal structure of TTCA showing a single sheet viewed perpendicular to the plane of the sheet. Dashed lines indicate N-H---S hydrogen bonds, and different types of hydrogen bonded array are indicated by the green and red lines...

The folded form of proteins, reported by Astbury, was identified with the a-helix, the extended one described in terms of intermolecularly hydrogen-bonded array of chains was known in the earlier literature as the... 

Multiple cyclic proton transfers occur in hydrogen bonded arrays of heterocyclic units [8.220, 8.221] or inside rings such as porphyrins [8.222]. Macrocyclic polyamines present various protonation patterns [3.13a] that could be of interest as information units. Data storage in a molecular memory by hole burning makes... 

Addition of a second proton donor, as in p-nitroaniline (PNA), serves to link acentric chains together (8-10). These chains form an acentric hydrogen-bonded array, as shown. PNA is a centric crystal because the hydrogen-bonded sheets pack with an inversion center between them. There are no inversion centers within the layer. 

A diacetylene moiety served as the polymerizable unit and was incorporated into the hydrogen-bonding array via short flexible linkers such that minor changes of the geometry during the polymerization might be compensated. 

Fig. 16 a The quasi-hexagonal guanidinium sulfonate (GS) hydrogen-bonded array, b The shifted ribbon GS array [208]... 

Fig. 21 The hexagonal melamine-cyanuric acid hydrogen-bonded array [ 166]...

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