Hydrogen flip-flop

Hydrogen Bond Flip-Flop Disorder Conformational and Configurational... 

When this type of disorder occurs in long cooperative chains or in cyclic systems of hydrogen bonds, it has been described as a. flip-flop mechanism [118], because it must proceed from bond to bond like a domino effect and involves only two well-defined states. 

Table 9.5a. Intramolecular interglucose hydrogen bonds of the flip-flop type 0-( )D D( )-0 observed in, 8-eyclodextrin at room temperature (neutron diffraction). The occupational parameters of the oxygen atoms are 1.0, those of the deuterium atoms vary between 0.344 and 0.654. (For atom numbering scheme see Chapter 18 [454].)... 

Table 9.5 b. The intramolecular hydrogen bonds in y5-cyclodextrin undecahydrate at 120 K are all of the three-center type, one is a flip-flop. Data taken from a neutron diffraction study [455]. (For atom numbering see Part IIB, Chap. 18)... 

Flip-Flop Hydrogen Bonds in yS-Cyclodextrin 11H20... 

The net result is the same two different states with nearly identical geometry and, presumably, nearly identical energy. This is favorable for entropical reasons and we expect considerable entropic stabilization of the disordered flip-flop hydrogen bonds. 

As shown in Fig. 18.12, which displays a view of the / -cyclodextrin molecule occurring in the )ff-cyclodextrin 11H20 crystal structure, all the seven glucoses are linked by flip-flop type hydrogen bonds (see also Thble 9.5 a). This might be a... 

Fig. 18.11. The infinite flip-flop chain in /1-cyclodextrin-11H20 is composed of water molecule Wl and hydroxyl groups 0(3)7 and 0(2)6 which belong to the same yff-cyclodextrin molecule (see also Fig. 18.12). The operation of a 2, screw axis produces the infinite chain which is also anchored in the crystal lattice by many hydrogen bonds to and from adjacent hydroxyl groups (not shown) [454]...

The intramolecular flip-flop hydrogen bonds are of the three-center type. All... 

Do the flip-flop hydrogen bonds represent dynamical or statical disorder ... 

Fig. 18.13 a, b. Shown are hydrogen-bond patterns occurring in the crystal structure of / -cyclodextrin 11H20 at 120 K. Because the total scheme is too complicated to be shown in one picture, it is broken up into two different schemes. In these, water molecules are denoted by W, and hydroxyl groups by two numbers, e.g., 64 means 0(6)4, hydroxyl 0(6) of glucose number 4 in the yff-cyclodextrin macrocycle, a, Hydrogen-bonding details for flip-flop... 

Fig. 18.16. The quadrilateral flip-flop cycle and its deconvolution into two cycles with homodromic O-H- -O hydrogens bond in clockwise and anticlockwise orientation hydrogen atom positions a, b are only half occupied...

In this chapter, we discuss the hydrogen bonding in structures where water is the sole or majority molecular species present. These are structures which are determined wholly or primarily by the hydrogen-bonding characteristics of the water molecules. They demonstrate the consequences of the dual hydrogen-bond donor-acceptor functionality, which, when combined with the cooperative and flip-flop dynamic properties of the hydroxyl groups, are essential for the formation of the hydration shells around the proteins and nucleic acids, and help to maintain their three-dimensional structures. 

Saenger W, Betzel Ch, Hingerty BE, Brown GM (1982) Flip-flop hydrogen bonding in a partially disordered system. Nature (Lond) 296 581-583... 

Betzel CH, Saenger W, Hingerty BE, Brown GM (1984) Circular and flip-flop hydrogen bonding in / -cyclodextrin undecahydrate a neutron diffraction study. J Am Chem Soc 106 7545-7557... 

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