Hydrogen-bond patterns homodromic

Fig. 13.10. Hydrogen-bonding pattern in the crystal structure of methyl 1,5-dithio-a-D-ribopyra-noside quarterhydrate. Four molecules form a hydrogen-bonded cluster around the water molecule. The perimeter of the cluster is hydrophobic and the packing of the 4(C6H1203S2)-H20 clusters is van der Waals. Note the eight-membered homodromic cycle and the homodromic spiral involving the water molecule. The swivel indicates hydrogen bonding to the next asymmetric unit [MDTRPY20]...

Raffinose pentahydrate has interesting infinite chains of hydrogen bonds. The hydrogen-bonding pattern is composed of four infinite chains, three of which extend in the direction of the crystallographic axes as shown in Fig. 13.59. These chains intersect at the water molecules to form an ordered homodromic network. The five water molecules are linked together. Four are double acceptors and one (W1) is a single acceptor [507 a]. 

The hydrogen-bond pattern in a-cytidine [ACYTID] contains two cyclic trimer systems (Fig. 17.32). One is homodromic and involves n- and intramolecular bond ( ) from 0(5 ) -H to the ring oxygen 0(4 ). 

Cooperative, Homodromic, and Antidromic Hydrogen-Bonding Patterns in the a-Cyclodextrin Hydrates... 

Fig. 18.7a-e. Cyclic and chain-like hydrogen-bonding patterns O-H- -O observed in a a-cyclo-dextrin-6H20, form I b a-cyclodextrin 6 H20, form II , intramolecular c,d,e a-cyclodextrin-7.57 H20. Infinite homodromic chains are marked chain, and cycles are indicated by round arrows with one (homodromic) and two (antidromic) heads. Only atoms of water molecules and of hydroxyl groups are drawn, the former denoted by W and the latter by the nomenclature described in Fig. 18.1. Each of the pictures a to e shows only a section of the respective crystal structure [78, 109, 575]...

Hydrogen-bonding patterns in crystal structures of the cydodextrins and the simpler carbohydrates differ. The infinite, homodromic chains are common both in the low molecular-weight carbohydrates and in the cydodextrins. The principal difference lies in the frequency of occurrence of the homodromic and antidromic cycles, which are common in the cyclodextrin crystal structures and rare in the mono-, di-, and trisaccharides. The cyclic patterns are the rule in the clathrate hydrates and in the ices. From this point of view, the hydrogen-bonding patterns of the hydrated cydodextrins lie between those of the simpler hydrated carbohydrates and those of the hydrate inclusion compounds, discussed in Part IV, Chapter 21. 

Fig. 21.10. The buckled hydrate layer in pyridine 3H20, with hydrogen-bonding geometry indicated. Note that the hydrogen-bonding pattern is homodromic in the hexagon and antidromic in the pentagon and quadrilateral. Pyridine molecules are stacked above and below this layer in nearly vertical orientation to the layer and bound to it by 0(2)-H -N hydrogen bonds (not shown) [793]...

The 0-(yH) -(yH)-O interactions are not isolated but are connected to form larger systems. As displayed in Fig. 18.10b, which gives a section of the crystal structure of / -cyclodextrin 11H20, these systems can be deconvolved into two patterns with homodromic, ordered chains in which the hydrogen bonds run in either one or the other direction, with all H-atom positions A or B filled. Simultaneous occupation of A and B positions in any of the O - ( H) ( -H) - O systems is forbidden for sterical reasons. 

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