Well-defined Hydrogen Research Articles

Poly(ethylene glycol)-based ammonium ionenes containing nucleobases

Adenine-functionalized ionenes (ionene-A) and thymine-functionalized ionenes (ionene-T) were synthesized from novel nucleobase-containing monomers from an efficient aza-Michael addition to an acrylate precursor. Complexes of ionenes with nucleobase-containing guest molecules (n-butyl thymine, nBT and n-butyl adenine, nBA) exhibited well-defined complementary hydrogen bonding interactions. Job’s analysis revealed a 1:1 stoichiometry for the hydrogen-bonded complexes of [ionene-A]:[nBT], [ionene-T]:[nBA], and [nBA]:[nBT]. A mathematical fit of the chemical shifts to the Benesi–Hildebrand method revealed the association constants of 94M−1, 130M−1, and 137M−1 for complexes of [ionene-A]:[nBT], [ionene-T]:[nBA], and [nBA]:[nBT], respectively. Furthermore, DSC thermograms of 1:1 [ionene-A/T]:[guest molecule] complexes showed the disappearance of the melting transition for the guest molecule, confirming the absence of macrophase separation of the nucleobase guest in the polymer matrix. Morphological studies including atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS) revealed a microphase-separated morphology for the nucleobase-containing ionenes and less defined microphase separation for the 1:1 complexes.

Interaction of Multiple Bonded and Unsaturated Heavier Main Group Compounds with Hydrogen, Ammonia, Olefins, and Related Molecules

We showed in 2005 that a digermyne, a main group compound with a digermanium core and aromatic substituents, reacted directly with hydrogen at 25 °C and 1 atm to give well-defined hydrogen addition products. This was the first report of a reaction of main group molecules with hydrogen under ambient conditions. Our group and a number of others have since shown that several classes of main group molecules, either alone or in combination, react directly (in some cases reversibly) with hydrogen under mild conditions. Moreover, this reactivity was not limited to hydrogen but also included direct reactions with other important small molecules, including ammonia, boranes, and unactivated olefins such as ethylene. These reactions were largely unanticipated because main group species were generally considered to be too unreactive to effect such transformations. In this Account, we summarize recent developments in the reactions of the multiple bonded and other open shell derivatives of the heavier main group elements with hydrogen, ammonia, olefins, or related molecules. We focus on results generated primarily in our laboratory, which are placed in the context of parallel findings by other researchers. The close relationship between HOMO-LUMO separations, symmetry considerations, and reactivity of the open shell in main group compounds is emphasized, as is their similarity in reactivity to transition metal organometallic compounds. The unexpectedly potent reactivity of the heavier main group species arises from the large differences in bonding between the light and heavy elements. Specifically, the energy levels within the heavier element molecules are separated by much smaller gaps as a result of generally lower bond strengths. In addition, the ordering and symmetries of the energy levels are generally different for their light counterparts. Such differences lie at the heart of the new reactions. Moreover, the reactivity of the molecules can often be interpreted qualitatively in terms of simple molecular orbital considerations. More quantitative explanations are accessible from increasingly sophisticated density functional theory (DFT) calculations. We open with a short description of the background developments that led to this work. These advances involved the synthesis and characterization of numerous new main group molecules involving multiple bonds or unsaturated configurations; they were pursued over the latter part of the last century and the beginning of the new one. The results firmly established that the structures and bonding in the new compounds differed markedly from those of their lighter element congeners. The knowledge gained from this fundamental work provided the framework for an understanding of their structures and bonding, and hence an understanding of the reactivity of the compounds discussed here.

Tautomerism in 7-Hydroxyquinoline: A Combined Experimental and Theoretical Study in Water

Tautomerism in the ground and excited states of 7-hydroxyquinoline (7HQ) was studied in different solvents using steady-state and lifetime spectroscopic measurements, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations. Equilibrium between the enol and the keto/zwitterion tautomers exists in 7HQ, which is solvent-dependent. Of the solvents used in this study, only in water does the absorbance spectrum of 7HQ show absorption from both the enol and zwitterion tautomers. In addition, in aqueous media, fluorescence is observed from the zwitterion tautomer only, which is attributed to self-quenching of the enol fluorescence by energy transfer to the ground-state zwitterion tautomer and energetically favorable excited-state proton transfer. Solvation of the hydrogen bonding sites of 7HQ was studied in binary mixtures of 1,4-dioxane and water, and three water molecules were estimated to connect the polar sites and induce intermolecular proton transfer. The results are confirmed by DFT calculations showing that three water molecules are the minimum number required to form a stable solvent wire. Mapping the water density around the polar sites using MD simulations shows well-defined hydrogen bonds around the amino and hydroxyl groups of the enol tautomer and slightly less well-defined hydrogen bonds for the zwitterion tautomer. The presence of three-member water wires connecting the polar centers in 7HQ is evident in the MD simulations. The results point to the unique spectral signatures of 7HQ in water, which make this molecule a potential probe to detect the presence of water in nanocavities of macromolecules.

Cathodic Stripping Voltammetric Determination of Tellurium(IV) with in situ Plated Bismuth-Film Electrode

A very sensitive and reliable method is proposed for the determination of tellurium(IV) [Te(IV)] by Osteryoung square-wave cathodic stripping voltammetry. This method is based on the reduction of Te(IV) with bismuth(III) onto an edge-plane pyrolytic graphite electrode, followed by a cathodic potential scan. The reduced Te gave a well-defined catalytic hydrogen wave at −1200 mV vs. Ag/AgCl. The peak height of the catalytic wave was directly proportional to the initial Te(IV) concentration in the concentration ranges of 0.01–0.10 and 0.1–1.0 µg L−1 with 30 s deposition time. A 3σ detection limit of 1.0 ng L−1 Te(IV) was obtained with the same deposition time. The relative standard deviation was 3% on replicate runs (n = 5) for the determination of 0.1 µg L−1 Te(IV). Analytical results of natural water samples demonstrate that the proposed method is applicable to the determination of traces of Te(IV).

Dimerization of Fibril-forming Segments of α-Synuclein

We have performed replica-exchange molecular dynamics (REMD) simulations on the dimer formation of fibril- forming segments of α-Synuclein (residues 71 - 82) using implicit solvation models with two kinds of force fields- AMBER parm99SB and parm96. We observed spontaneous formation of dimers from the extensive simulations, demonstrating the self-aggregating and fibril forming properties of the peptides. Secondary structure profile and clustering analysis showed that dimers with antiparallel β-sheet conformations, stabilized by well-defined hydrogen boding, are major species corresponding to global free energy minimum. Parallel dimers with partial β-sheets are found to be off-pathway intermediates. The relative instability of the parallel arrangements is due to the repulsive interactions between bulky and polar side chains as well as weaker backbone hydrogen bonds.

Self-Assembled Monolayers As Nucleating Centers for the Preparation of Multilayers of Catalytically Active Pt Films

A soft route for the preparation of catalytically active multilayers of Pt films free from poisoning effects is reported. The SAMs (self-assembled monolayers) were initially formed on the gold substrates and they act as nucleating centers initiating the formation of multilayers of Pt on gold substrates. The nanoscale to mesoscale structures of Pt thus prepared were characterized by SEM and XPS. The SAM-based Pt structures exhibited well-defined hydrogen adsorption, desorption regions associated with very high charge indicating high surface area Pt. The electrocatalytic activity of the multilayers of Pt was characterized by methanol oxidation and a comparison was made with two commercial Pt catalyst preparations.

A study of the second coordination sphere in 8-azaxanthinato salts of divalent metal aquacomplexes

The interaction of the 4,6-dimethyl and 4-monomethyl derivatives of 1,2,3-triazolo[4,5- d]pyrimidin-5,7-dione (which may be named also as purine derivatives, 1,3-dimethyl-8-azaxanthine, Hdmax and 3-methyl-8-azaxanthine, H3max) with the divalent cations of Mn, Co, Ni, Zn and Cd in aqueous media generate solids with formulation ML 2 · 6H 2O. The crystal structure of the Mn and Cd compounds with dmax and the Cd compound with 3max have been determined by single-crystal X-ray diffraction revealing that the compounds are salts with [M(H 2O) 6] 2+ as cations and dmax − or 3dmax − as anions. The second-sphere interactions in these compounds have been analysed, consisting in a network of very well-defined hydrogen bonds, with all available potential donor and acceptor positions involved. The topology of the motifs generated by these hydrogen bonds has been characterised, adapting to the second coordination sphere concepts usually applied to the first (chelate, bridge, monodentate, …). Monodimensional (tapes) superstructures with the building blocks rather tightly bounded appear in the compounds with dmax − as anion, whereas the corresponding superstructure in the Cd compound with 3max − is bidimensional. These superstructures further interact among them in a less tight fashion to generate the three dimensional crystal structures. Powder X-ray diffraction strongly suggests that Mn, Co, Zn and Cd compounds of each ligand are isostructural, so the results of the samples determined by single-crystal X-ray diffraction may be extended to all these compounds. On the other hand, powder X-ray diffraction indicates that the nickel compounds have a different structure and the spectroscopic data for these compounds suggest that the ligand is directly attached to the metal for them.

Thermoplastic Elastomers Based on Strong and Well-Defined Hydrogen-Bonding Interactions

In order to investigate the effects of strong and well-defined hydrogen bonding on the properties of thermoplastic elastomers (TPEs), we have applied two distinct and strongly dimerizing 2-ureido-4-[1H]-pyrimidinone (UPy) quadruple hydrogen-bonding units as physical cross-linker. While the UPy groups consequently serve as the “hard phase” or “hard block” in these TPEs, an amorphous polyester has been used as the “soft phase” or “soft block”. The UPy unit has been flanked with either a sterically demanding isophorone spacer or a linear hexamethylene, where these spacers have been derived from isophorone diisocyanate (IPDI) or hexamethylene diisocyanate (HDI), respectively. This difference on a molecular level leads to a homogeneous amorphous material in the IPDI case (polymer 1) and to a nanophase-separated material in the HDI case (polymer 2) as revealed by AFM and DSC experiments. Apart from this distinctive difference in morphology and nanoscopic organization, the macroscopic properties of both material...

Syntheses, characterization, and luminescence of two lanthanide complexes [Ln 2(acetate) 6(H 2O) 4]·4H 2O (Ln=Tb(1), Sm(2))

Two dinuclear compounds [Ln 2(acetate) 6(H 2O) 4]·4H 2O (Ln=Tb(1), Sm(2)) were obtained by the hydrothermal reaction of Ln 2O 3 with malonic acid at 150 °C. Both compounds were characterized by elemental analyses, infrared spectra, and single crystal X-ray diffraction. The results showed that complexes 1 and 2 were isomorphous and crystallize in triclinic space group P'1. The coordination geometry around Ln(III) ions in the complexes 1 and 2 was a distorted tricapped trigonal prism with a nine coordination. In the crystal, the molecular organization was further stabilized by well-defined weak hydrogen bonding interactions between the neutral dinuclear molecular units that led to the formation of a three-dimensional network. The fluorescence properties of the two complexes 1 and 2 in organic solvents were also studied. The results show that the ligand acetate favored energy transfer to the emitting energy level of Tb(III) in complex 1. Some factors that influence the fluorescent intensity were also discussed in the article.

The common role of water molecule and lone electron pair as a bond-valence mediator in oxalate complexes: the crystal structures of Rb2(C2O4) · H2O and Tl2(C2O4)

The crystal structure of rubidium oxalate monohydrate, Rb2(C2O4) · H2O, has been refined using an imaging-plate diffractometer system and graphite-monochromatized MoK α radiation. The complex crystallizes in the monoclinic system, space group C2/c, with unit cell dimensions of a = 9.617(6), b = 6.353(5), c = 11.010(8) Å, β = 109.46(3)°, V = 634.2(8) Å3, and Z = 4. The structure was solved and refined to R = 0.026 for 2646 independent reflections [I o > 2σ(I o)]. In Rb2(C2O4) · H2O, oxalate anions [(C2O4)2–] and cations (Rb+) constitute a two-dimensional layered structure parallel to (001); interlayered water molecules (H2O)0 occupy a well-defined position and form hydrogen bonds to the layers to prop up the structure, where (H2O)0 is structurally an essential component. The relationship among the crystal structures of M2(C2O4) · nH2O (M = Li+, Na+, K+, Rb+, Cs+, Tl+, NH4 +, Ag+; n = 0, 1, 2) showed that ionic radii of the cations decide whether the corresponding oxalate complexes have water molecules or not. On the other hand, anhydrous thallium oxalate, Tl2(C2O4), has a similar structure to Rb2(C2O4) · H2O except for the water molecules. Tl+ cation exhibits stereochemical activity of its 6s2 lone electron pairs (LEP), which is absent from Rb+ in the latter oxalate. Comparison between interlayer spaces occupied by LEP and (H2O)0 in these two structures reveals the existence of the first uncharged substitution: 2 × LEP → (H2O)0, where the directions of the former occupants are opposite to each other, and nearly perpendicular to a dipole direction of the latter. In the layer sites of these two structures, two LEP of Tl+ seem to work like a dipole moment of the water molecule in Rb-oxalate monohydrate by shifting away from the nucleus to stabilize the structure of Tl2C2O4. The crucial role common to water molecules and LEP which acts as a bond-valence mediator in oxalate complexes is discussed quantitatively in terms of a valence-matching principle.

Circular Hydrogen Bond Networks on the Surface of β-Ribofuranose in Aqueous Solution

This paper examines the hydration structure on the surface of beta-ribofuranose in aqueous solution, using the ab initio molecular dynamics method. In particular, we focus on circular hydrogen bond networks involving two ribofuranose oxygens and three water molecules. In our simulations, the circular hydrogen bond networks near the ring oxygen of beta-ribofuranose are found to be significantly influenced by the orientation of the hydroxymethyl group. The arrangements of hydrogen bonds observed in the circular hydrogen bond networks are both homodromic and antidromic. To explain these observations, we analyze the electronic properties of the first-hydration-shell water molecules and the OH groups of beta-ribofuranose, using the centers of their maximally localized Wannier functions. The dipole moments of the proton-accepting first-hydration-shell water molecules in our well-defined circular hydrogen bond networks are found to increase by about 0.3 D compared with that of liquid water, indicating the relatively strong polarization effects created by the interactions between the OH groups of the solute and the surrounding water molecules. Our analysis also implies that circular H-bond networks cannot be fully explained from a simple geometrical point of view.

GSH 23.0−0.7+117: A Neutral Hydrogen Shell in the Inner Galaxy

GSH 23.0-0.7+117 is a well-defined neutral hydrogen shell discovered in the Very Large Array (VLA) Galactic Plane Survey (VGPS). Only the blueshifted side of the shell was detected. The expansion velocity and systemic velocity were determined through the systematic behavior of the H I emission with velocity. The center of the shell is at (l, b, v) = (2305, - 077, + 117 km s-1). The angular radius of the shell is 68, or 15 pc at a distance of 7.8 kpc. The H I mass divided by the volume of the half-shell implies an average density nH = 11 ± 4 cm-3 for the medium in which the shell expanded. The estimated age of GSH 23.0-0.7+117 is 1 Myr, with an upper limit of 2 Myr. The modest expansion energy of 2 × 1048 ergs could have been provided by the stellar wind of a single O4-O8 star over the age of the shell. The 3 σ upper limit to the 1.4 GHz continuum flux density (S1.4 < 248 mJy) is used to derive an upper limit to the Lyman continuum luminosity generated inside the shell. This upper limit implies a maximum of one O9 star (i.e., O8-O9.5, taking into account the error in the distance) inside the H I shell, unless most of the incident ionizing flux leaks through the H I shell. To allow this, the shell should be fragmented on scales smaller than the beam (2.3 pc). If the stellar wind bubble is not adiabatic or the bubble has burst (as suggested by the H I channel maps), agreement between the energy and ionization requirements is even less likely. The limit set by the nondetection in the continuum provides a significant challenge for the interpretation of GSH 23.0-0.7+117 as a stellar wind bubble. A similar analysis may be applicable to other Galactic H I shells that have not been detected in the continuum.

Effects of Base Substitutions in an RNA Hairpin from Molecular Dynamics and Free Energy Simulations

Contributions of individual interactions in the GGC GCAAGCC hairpin containing a GCAA tetraloop were studied by computer simulations using base substitutions. The G in the first tetraloop position was replaced by inosine (I) or adenosine (A), and the G in the C-G basepair closing the tetraloop was replaced by I. These substitutions eliminate particular hydrogen bonds proposed in the nuclear magnetic resonance model of the GCAA tetraloop. Molecular dynamics simulations of the GCAA tetraloop in aqueous solvent displayed a well-defined hydrogen pattern between the first and last loop nucleotides (G and A) stabilized by a bridging water molecule. Substitution of G→I in the basepair closing the tetraloop did not significantly influence the loop structure and dynamics. The ICAA loop maintained the overall structure, but displayed variation in the hydrogen-bond network within the tetraloop itself. Molecular dynamics simulations of the ACAA loop led to conformational heterogeneity of the resulting structures. Changes of hairpin formation free energy associated with substitutions of individual bases were calculated by the free energy perturbation method. The calculated decrease of the hairpin stability upon G→I substitution in the C-G basepair closing the tetraloop was in good agreement with experimental thermodynamic data. Our theoretical estimates for G→I and G→A mutations located in the tetraloop suggest larger loop destabilization than corresponding experimental results. The extent of conformational sampling of the structures resulting from base substitutions and its impact on the calculated free energy was discussed.

Crystal structures of two potent nonamidine inhibitors bound to factor Xa.

There has been intense interest in the development of factor Xa inhibitors for the treatment of thrombotic diseases. Our laboratory has developed a series of novel non-amidine inhibitors of factor Xa. This paper presents two crystal structures of compounds from this series bound to factor Xa. The first structure is derived from the complex formed between factor Xa and compound 1. Compound 1 was the first non-amidine factor Xa inhibitor from our lab that had measurable potency in an in vitro assay of anticoagulant activity. The second compound, 2, has a molar affinity for factor Xa (K(iapp)) of 7 pM and good bioavailability. The two inhibitors bind in an L-shaped conformation with a chloroaromatic ring buried deeply in the S1 pocket. The opposite end of these compounds contains a basic substituent that extends into the S4 binding site. A chlorinated phenyl ring bridges the substituents in the S1 and S4 pockets via amide linkers. The overall conformation is similar to the previously published structures for amidine-based inhibitors complexed with factor Xa. However, there are significant differences in the interactions between the inhibitor and the protein at the atomic level. Most notably, there is no group that forms a salt bridge with the carboxylic acid at the base of the S1 pocket (Asp189). Each inhibitor forms only one well-defined hydrogen bond to the protein. There are no direct charge-charge interactions. The results indicate that electrostatic interactions play a secondary role in the binding of these potent inhibitors.

Organization of microcrystals on glass by adenine-thymine hydrogen bonding.

Shaking of adenine-tethering glass plates in an aqueous suspension of micrometer-sized, thymine-tethering zeolite crystals such as ZSM-5 (0.6 mum x 1.7 mum x 2.5 mum) or zeolite-A (1.7 mum x 1.7 mum x 1.7 mum) for 3 h at room temperature leads to facile assembly of monolayers of the zeolite microcrystals on the glass plates through the hydrogen-bonding interaction between the tethered adenine and thymine. Control experiments show that the presence of adenine and thymine on the respective solid surface is essential for the monolayer assembly. This establishes that even the micrometer-sized building blocks can be organized by a large number of well-defined weak hydrogen bonding. Increase in the assembly temperature to annealing temperatures leads to a marked increase in the rate of monolayer assembly and in the size of the domain in which zeolite crystals are closely packed in the same three-dimensional orientation.

Femtosecond mid-infrared photon echo study of an intramolecular hydrogen bond

The vibrational dephasing dynamics of O–H stretching excitations in a sterically well-defined intramolecular hydrogen bond (H bond) is studied by femtosecond photon echo spectroscopy in the mid-infrared. The O–H stretching vibration of phthalic acid monomethyl ester in inert solution displays a fast decay of phase coherence on a sub-100 fs time scale. Anharmonic coupling of the stretching motion to an underdamped low-frequency mode of the H bond gives rise to oscillations in the transient grating decay and the 3-pulse photon echo peak shift. Spectral diffusion dynamics on longer time scales is absent in such intramolecular H bonds, as opposed to the weaker intermolecular H bonds in water.

A refined substrate model for human cytochrome P450 2D6.

Cytochromes P450 (P450s) constitute a large superfamily of heme-containing enzymes, capable of oxidizing and reducing a variety of substrates. Cytochrome P450 2D6 is a polymorphic member of the P450 superfamily and is absent in 5-9% of the Caucasian population as a result of a recessive inheritance of gene mutations. Recently, the importance of aspartic acid 301 (Asp301) for the catalytic activity of P450 2D6, as indicated by a preliminary homology model, was confirmed by site-directed mutagenesis experiments. In this study, the heme moiety and the I-helix containing Asp301 were incorporated into the previously derived substrate model for P450 2D6, in the spatial orientations as derived from a recently improved protein model for P450 2D6, thereby incorporating steric restrictions and orientational preferences into the substrate model. The direction of well-defined hydrogen bonds formed between Asp301 and basic nitrogen atoms of P450 2D6 substrates was incorporated into the substrate model as well. Also, the position(s) of the basic nitrogen atom(s) of the substrates was/were allowed more flexibility. This was established through the attachment of an aspartic acid residue (representing Asp301) to the (protonated) basic nitrogen atom(s) of the substrates and superimposing the C alpha- and C beta-atoms of this aspartic acid residue in the fitting procedure instead of the basic nitrogen atoms. A variety of 8 substrates of P450 2D6 (comprising 17 known P450 2D6 dependent metabolic pathways) has been incorporated successfully into this refined and more restrictive substrate model.

Solution conformation by NMR and molecular modeling of three sulfide-free somatostatin octapeptide analogs compared to angiopeptin

The conformation in dimethylsulfoxide of the somatostatin derivative angiopeptin and of three disulfide-free analogs was estimated by two-dimensional nuclear magnetic resonance spectroscopy at room temperature. The resulting 3D molecular graphics were compared and shown to reflect the observed differences in the inhibition of restenosis after rat aorta balloon injury by these octapeptide inhibitors. Angiopeptin and its active analog 2 displayed a relatively rigid conformation of the cyclic hexapeptide backbone due to the presence of two well-defined hydrogen bonds, further stabilized by a third hydrogen bond outside the ring. No such constraints were detected for the two biologically inactive analogs, which, compared to 2, had a two-atom longer or shorter hexapeptide ring. The well-defined structure of compound 2 may serve as an improved pharmacophore for this new class of drugs.

The stability of the lattice structure in low salt T-state haemoglobin crystals

The reconstruction of the electron density of molecules in crystals from X-ray diffraction measurements depends on the exactness of the packing of the molecules in the unit cell and the crystal lattice. Crystals of T-state haemoglobin, the low affinity form of the molecule, grow from high salt solutions or from low salt solutions in the presence of polyethylene glycol. The low salt lattice has the special property that it allows the haemoglobin molecule to bind oxygen and other ligands without the crystal breaking up. The stability of the low salt T-state crystals appears to arise from a small number of well-defined salt bridges and hydrogen bonds that are concentrated in specific lattice directions. These together form a framework within which the molecule can make adjustments which are sufficient to accommodate ligand binding but in which the larger quaternary movements normally associated with oxygenation are prevented. In these crystals therefore interactions with ligands can be studied directly by X-ray diffraction and the structural basis of the T-state’s low affinity for oxygen can be analysed.

Neutron diffraction of alpha, beta and gamma cyclodextrins: hydrogen bonding patterns.

Cyclodextrins (CD's) have proved useful as model systems for the study of hydrogen bonding. They are torus-shaped molecules composed of six(alpha), seven(beta) or eight(gamma) (1----4) linked glucoses. Because of their particular geometry, they are able to act as a "host" to form inclusion complexes with "guest" molecules very much like enzymes. Cyclodextrins have been shown to exert catalytic activity on suitable included-substrate molecules; they catalyze the hydrolysis of phenylacetates, of organic pyrophosphates and of penicillin derivatives. They also accelerate aromatic chlorinations and diazo coupling by means of their primary and/or secondary hydroxyl groups, so that the rates of hydrolysis are enhanced by up to a factor of 400. In order to understand the hydrogen bonding in these enzyme models, neutron diffraction data were collected to unambiguously determine the hydrogen atom positions, which could not be done from the x-ray diffraction data. alpha-CD has been shown to have two different structures with well-defined hydrogen bonds, one "tense" and the other "relaxed". An "induced-fit"-like mechanism for alpha-CD complex formation has been proposed. Circular hydrogen bond networks have also been found for alpha-CD due to the energetically favored cooperative effect. beta-CD with a disordered water structure possesses an unusual flip-flop hydrogen bonding system of the type O-H...H-O representing an equilibrium between two states: O-H...O in equilibrium O...H-O. gamma-CD with a disordered water structure similar to beta-CD also possesses the flip-flop hydrogen bond. This study demonstrates that hydrogen bonds are operative in disordered systems and display dynamics even in the solid state.