X-ray structure of beta-cyclodextrin-2,7-dihydroxy-naphthalene.4.6 H(2)O: an unusually distorted macrocycle.

The inclusion complex beta-cyclodextrin.2,7-dihydroxynaphthalene.4.6 H(2)O crystallized in the monoclinic space group P2(1), with a=14.082(3), b=19.079(4), c=12.417(3) A, beta=109.28(3) degrees, V=3149.0(11) A(3), and Z=2. An X-ray study performed at room temperature shows that the crystal packing is of the herringbone type with one 2,7-dihydroxynaphthalene included completely in the beta-CD cavity, its long axis being oriented along the beta-CD molecular axis, and 4.6 water molecules are placed in the interstitial space. The beta-CD macrocycle is elliptically distorted, and the guest molecule is held in the hydrophobic beta-CD cavity by C-H...O and C-H...pi interactions.     

Solubility of cyclomaltooligosaccharides (cyclodextrins) in H2O and D2O: a comparative study

Cyclomaltooligosaccharides (cyclodextrins, CDs) are cyclic oligomers having six, seven, or eight units of alpha-D-glucose, named as cyclomaltohexaose (alpha-CD), cyclomaltoheptaose (beta-CD) and cyclomaltooctaose (gamma-CD), respectively. The molecule of CD has a cavity in which the interior is hydrophobic relative to its outer surface. The solubility of cyclodextrins in water is unusual, as an irregular trend is observed in the series of the cyclic oligomers of glucose. beta-CD is at least nine times less soluble than the others CDs. This intriguing behavior has been investigated, and some interesting explanations in terms of the effect caused by CD on the water lattice structure have been proposed. In this work a comparative study on the solubility of alpha, beta, and gamma-cyclodextrins was carried out in H2O and D2O and reveals a much lower solubility of the three CDs in D2O. The solid-phase structure of the CDs in equilibrium with the solution is quite similar with both solvents. The results are discussed in terms of the CD molecular structure and the differences in the hydrogen bonds formed between H2O and D2O.     

Structure of the complex of beta-cyclodextrin with beta-naphthyloxyacetic acid in the solid state and in aqueous solution

The structure of the complex of beta-cyclodextrin (cyclomaltoheptaose) with beta-naphthyloxyacetic acid was studied in solid state by X-ray diffraction and in aqueous solution by 1H NMR spectroscopy. The complex crystallizes in the channel mode, space group C2, with a stoichiometry of 2:1; two beta-cyclodextrin molecules related by a twofold crystal axis form dimers, in the cavity of which one guest molecule is found on average. The above stoichiometry indicates one guest per beta-CD dimer statistically oriented over two positions or two guest molecules in pi-pi interactions in half of the beta-CD dimers and the rest of the beta-CD dimers empty. In addition, occupancy of 0.5 for the guest per every beta-CD dimer is in accord with the occupancy of the two disordered primary hydroxyls. These two hydroxyl groups, to which the carboxylic oxygen atoms of the guest are hydrogen bonded, point towards the interior of the beta-CD cavity. In aqueous solution, the 1H NMR spectroscopic study indicated that there is a mixture of complexes with host-guest stoichiometries both 1:1 and 2:1.     

H(2)O(2)-induced kinetic and chemical modifications of smooth muscle myosin: correlation to effects of H(2)O(2) on airway smooth muscle

The effect of H(2)O(2) on smooth muscle heavy meromyosin (HMM) and subfragment 1 (S1) was examined. The number of molecules that retained the ability to bind ATP and the actinactivated rate of P(i) release were measured by single-turnover kinetics. H(2)O(2) treatment caused a decrease in HMM regulation from 800- to 27-fold. For unphosphorylated and phosphorylated heavy meromyosin and for S1, approximately 50% of the molecules lost the ability to bind to ATP. H(2)O(2) treatment in the presence of EDTA protected against ATPase inactivation and against the loss of total ATP binding. Inactivation of S1 versus time correlated to a loss of reactive thiols. Treatment of H(2)O(2)-inactivated phosphorylated HMM or S1 with dithiothreitol partially reactivated the ATPase but had no effect on total ATP binding. H(2)O(2)-inactivated S1 contained a prominent cross-link between the N-terminal 65-kDa and C-terminal 26-kDa heavy chain regions. Mass spectral studies revealed that at least seven thiols in the heavy chain and the essential light chain were oxidized to cysteic acid. In thiophosphorylated porcine tracheal muscle strips at pCa 9 + 2.1 mM ATP, H(2)O(2) caused a approximately 50% decrease in the amplitude but did not alter the rate of force generation, suggesting that H(2)O(2) directly affects the force generating complex. Dithiothreitol treatment reversed the H(2)O(2) inhibition of the maximal force by approximately 50%. These data, when compared with the in vitro kinetic data, are consistent with a H(2)O(2)-induced loss of functional myosin heads in the muscle.     

Metal-heptaiodide interactions in cyclomaltoheptaose (beta-cyclodextrin) polyiodide complexes as detected via Raman spectroscopy

The Raman spectra of the cyclomaltoheptaose (beta-cyclodextrin, beta-CD) polyiodide complexes (beta-CD)(2).NaI(7).12H(2)O, (beta-CD)(2).RbI(7).18H(2)O, (beta-CD)(2).SrI(7).17H(2)O, (beta-CD)(2).BiI(7).17H(2)O and (beta-CD)(2).VI(7).14H(2)O (named beta-M, M stands for the corresponding metal) are investigated in the temperature range of 30-140 degrees C. At room temperature all systems show an initial strong band at 178 cm(-1) that reveals similar intramolecular distances of the disordered I(2) units (approximately 2.72 A). During the heating process beta-Na and beta-Rb display a gradual shift of this band to the final single frequency of 166 cm(-1). In the case of beta-Sr and beta-Bi, the band at 178 cm(-1) is shifted to the final single frequencies of 170 and 172 cm(-1), respectively. These band shifts imply a disorder-order transition of the I(2) units whose I-I distance becomes elongated via a symmetric charge-transfer interaction I(2)<--I3(-)-->I(2). The different final frequencies correspond to different bond lengthening of the disordered I(2) units during their transformation into well-ordered ones. In the Raman spectra of beta-V, the initial band at 178 cm(-1) is not shifted to a single band but to a double one of frequencies 173 and 165 cm(-1), indicating a disorder-order transition of the I(2) molecules via a non-symmetric charge-transfer interaction I(2)<--I3(-)-->I(2). The above spectral data show that the ability of I3(-) to donate electron density to the attached I(2) units is determined by the relative position of the different metal ions and their ionic potential q/r. The combination of the present results with those obtained from our previous investigations reveals that cations with an ionic potential that is lower than approximately 1.50 (Cs(+), Rb(+), Na(+), K(+) and Ba(2+)) do not affect the Lewis base character of I3(-). However, when the ionic potential of the cation is greater than approximately 1.50 (Li(+), Sr(2+), Cd(2+), Bi(3+) and V(3+)), the M(n+)...I3(-) interactions become significant. In the case of a face-on position of the metal (Sr(2+), Bi(3+)) relative to I3(-), the charge-transfer interaction is symmetric. On the contrary, when the metal (Li(+), Cd(2+), V(3+)) presents a side-on position relative to I3(-), the charge-transfer interaction is non-symmetric.     

A new crystal form of beta-cyclodextrin-ethanol inclusion complex: channel-type structure without long guest molecules

A new crystal form of beta-cyclodextrin (beta-CD)[bond]ethanol[bond]dodecahydrate inclusion complex [(C(6)H(10)O(5))(7).0.3C(2)H(5)OH.12H(2)O] belongs to monoclinic space group C2 (form II) with unit cell constants a=19.292(1), b=24.691(1), c=15.884(1) A, beta=109.35(1) degrees. The beta-CD macrocycle is more circular than that of the complex in space group P2(1) [form I: J. Am. Chem. Soc. 113 (1991) 5676]. In form II, a disordered ethanol molecule (occupancy 0.3) is placed in the upper part of beta-CD cavity (above the O-4 plane) and is sustained by hydrogen bonding to water site W-2. In form I, an ethanol molecule located below the O-4-plane is well ordered because it hydrogen bonds to surrounding O-3[bond]H, O-6[bond]H groups of the symmetry-related beta-CD molecules. In the crystal lattice of form I, beta-CD macrocycles are stacked in a typical herringbone cage structure. By contrast, the packing structure of form II is a head-to-head channel that is stabilized at both O-2/O-3 and O-6 sides of each beta-CD by direct O(CD)...O(CD) and indirect O(CD)...O(W)...(O(W))...O(CD) hydrogen bonds. The 12 water molecules are disordered in 18 positions both inside the channel-like cavity of beta-CD dimer (W-1[bond]W-6) and in the interstices between the beta-CD macrocycles (W-7[bond]W-18). The latter forms a cluster that is hydrogen bonded together and to the neighboring beta-CD O[bond]H groups.     

A vibrating flexible chain in a molecular cage: crystal structure of the complex cyclomaltoheptaose (beta-cyclodextrin)-1,4-butanediol.6.25H2O.

A single crystal X-ray diffraction study of the title complex carried out at room temperature revealed space group P2(1), a = 21.199(12), b = 9.973(3), c = 15.271(8) A, beta = 110.87(3) degrees, V = 3017(3) A3, 4681 unique reflections with Fo greater than 1 sigma (Fo). The structure was refined to R = 0.069, resolution lambda/2sin theta max = 0.89 A. The crystal packing is of the cage type and is isomorphous to that of beta-cyclodextrin (beta CD) dodecahydrate. One 1,4-butanediol and approximately 1.25 water molecules are enclosed in each beta CD cavity. The hydroxyl groups of the 1,4-butanediol molecule are located at each end of the cavity and form hydrogen bonds with neighboring water and beta CD molecules. The flexible (CH2)4 moiety vibrates extensively in the central part of the cavity. Water molecules and hydroxyl groups are chelated between O-6 and O-5 of at least five glucose residues.     

Inclusion complexes of bisphenol A with cyclomaltoheptaose (beta-cyclodextrin): solubilization and structure

The inclusion complexation behavior and the solubilization effects of Bisphenol A (BPA, an endocrine-disrupting chemical) by cyclomaltohexaose, -heptaose, and -octaose (alpha-, beta-, and gamma-cyclodextrins) were investigated by (1)H NMR spectroscopy and by elemental analysis. The results showed that beta- and gamma-cyclodextrins gave the satisfactory solubilization ability to BPA up to 7.2x10(3)mgL(-1) and 9.0x10(3)mgL(-1), respectively. X-ray crystallographic diffraction and ROESY spectroscopy were also employed to investigate the structure of the beta-CD/BPA inclusion complex in both aqueous solution and the solid state. The result showed that this complex adopted a 2:2 stoichiometry in the solid state, that is, a head-to-head beta-CD dimer accommodated two BPA molecules. The inclusion of BPA led to the desolvation of the beta-CD cavity and the destruction of the circularly closed hydrogen-bond network in the secondary side of beta-CD, which made the complex more soluble.     

Crystal form III of beta-cyclodextrin-ethanol inclusion complex: layer-type structure with dimeric motif

The crystal form III of the beta-cyclodextrin (beta-CD)-ethanol inclusion complex [2(C(6)H(10)O(5))(7).1.5C(2)H(5)OH.19H(2)O] belongs to the triclinic space group P1 with unit cell constants: a=15.430(1), b=15.455(1), c=17.996(1)A, alpha=99.30(1) degrees , beta=113.18(1) degrees , gamma=103.04(1) degrees . beta-CD forms dimers comprising two identical monomers that adopt a 'round' conformation stabilized by intramolecular, interglucose O-3(n)cdots, three dots, centeredO-2(n+1) hydrogen bonds. The two beta-CD monomers of form III are isostructural to that of form I in the monoclinic space group P2(1) [Steiner, T.; Mason, S. A.; Saenger, W. J. Am. Chem. Soc.1991, 113, 5676-5687], but exhibit a striking difference from that of form II in the monoclinic space group C2 [Aree, T.; Chaichit, N. Carbohydr. Res.2003, 338, 1581-1589]. The small guest EtOH molecule orients differently in the large beta-CD cavity. In form III, two disordered EtOH molecules are embedded in the beta-CD-dimer cavity. A half occupied EtOH molecule (#1) is located above the O-4 plane of beta-CD #1, whereas another doubly disordered EtOH molecule (#2, #3) is situated at about the middle of the beta-CD-dimer cavity. The three EtOH sites are maintained in positions by making van der Waals contacts to each other and to the surrounding water sites and beta-CD O-3-H group. The EtOH molecules disordered (occupancy 0.3) above the beta-CD O-4 plane in form I and fully occupied beneath the O-4 plane in form II are strongly held in positions by hydrogen bonding with the surrounding water site and beta-CD O-6-H, O-3-H groups. Occurrence of the beta-CD dimer as a structural motif of channel-type packing (form II) and layer-type packing (form III) is attributed to the higher tendency for self aggregation under the moderate acidic conditions. At weak acidic conditions, beta-CD prefers a herringbone mode (form I).     

Effect of water molecules on the fluorescence enhancement of Aflatoxin B1 mediated by Aflatoxin B1:beta-cyclodextrin complexes. A theoretical study.

In order to explain the observed fluorescence enhancement of Aflatoxin B1 (AFB1) when forming AFB1:beta-cyclodextrin (AFB1:beta-CD) inclusion complexes, we have performed a theoretical (quantum chemistry calculations) study of AFB1 and AFB1:beta-CD in vacuum and in the presence of aqueous solvent. The AM1 method was used to calculate the absorption and emission wavelengths of these molecules. With the help of density functional theory (DFT) and time-dependent DFT (TDDFT) vibrational frequencies and related excitation energies of AFB1 and AFB1.(H2O)m = 4,5,6,11 were calculated. On the basis of these calculations we propose a plausible mechanism for the fluorescence enhancement of AFB1 in the presence of beta-CD: (1) before photoexcitation of AFB1 to its S1 excited state, there is a vibrational coupling between the vibrational modes involving the AFB1 carbonyl groups and the bending modes of the nearby water molecules (CG + WM); (2) these interactions allow a thermal relaxation of the excited AFB1 molecules that results in fluorescence quenching; (3) when the AFB1 molecules form inclusion complexes with beta-CD the CG + WM interaction decreases; and (4) this gives rise to a fluorescence enhancement.     

Crystal structure of beta-cyclodextrin-dimethylsulfoxide inclusion complex

beta-Cyclodextrin (beta-CD) crystallizes from 27% DMSO-water as beta-CD.0.5DMSO.7.35H(2)O in the monoclinic space group P2(1) with unit cell constants: a=15.155(1), b=10.285(1), c=20.906(1) A, beta=109.86(1) degrees. Anisotropic refinement of 888 atomic parameters against 9,127 X-ray diffraction data converged at an R-factor of 0.055. The beta-CD macrocycle adopts a 'round' conformation stabilized by intramolecular, interglucose O-3(n) triplebond O-2(n+1) hydrogen bonds. In the beta-CD cavity, DMSO, water sites W-1, W-3 (occupancies 0.5, 0.25, 0.75) are not located concurrently with the water site W-2 because the interatomic distances to W-2 are too short (1.56-1.75 A). DMSO is placed in the beta-CD cavity such that its S-atom is shifted from the O-4 plane center to the beta-CD O-6-side ca. 0.9 A and the C-S bond which is inclined 13.6 degrees to the beta-CD molecular axis. It is maintained in position by hydrogen bonding to water site W-3 and the O-31-H group. 7.35 water molecules are extensively disordered in 13 positions both inside (W-1-W-4) and outside (W-5-W-13) the beta-CD cavity. They act as hydrogen bonding mediators contributing significantly to the stability of the crystal structure.     

Water structure in [Phe4 Val6] antamanide X 12H2O crystallized from dioxane

Crystals of [Phe4 Val6] antamanide (cyclic [ValProProPhePhe]2) grown from dioxane/H2O, with space group P21212 and cell parameters a = 15.099(4), b = 22.008(5) and c = 11.024(3) A, are almost identical to crystals grown from H2O/acetone, the structure of which was determined a number of years ago. Per peptide molecule there are the equivalent of 12 water molecules occupying 16 sites in both crystals; however, in the new investigation a number of water molecules present at one-half occupancy have been found in different positions than in the earlier analysis. The interpretation of the hydrogen bonding between peptide/water and between water/water is much more satisfactory. Pentagonal water assemblies are present in the solvent channel. There is a distinct indication of the occurrence of a bifurcated bond between two water molecules, as well as the presence of three-center hydrogen bonds joining three water molecules. This may be the first experimental example of a bifurcated bond between two water molecules.     

Kinetic studies of iron deposition in horse spleen ferritin using H2O2 and O2 as oxidants

The reaction of horse spleen ferritin (HoSF) with Fe2+ at pH 6.5 and 7.5 using O2, H2O2 and 1:1 a mixture of both showed that the iron deposition reaction using H2O2 is approximately 20- to 50-fold faster than the reaction with O2 alone. When H2O2 was added during the iron deposition reaction initiated with O2 as oxidant, Fe2+ was preferentially oxidized by H2O2, consistent with the above kinetic measurements. Both the O2 and H2O2 reactions were well defined from 15 to 40 degrees C from which activation parameters were determined. The iron deposition reaction was also studied using O2 as oxidant in the presence and absence of catalase using both stopped-flow and pumped-flow measurements. The presence of catalase decreased the rate of iron deposition by approximately 1.5-fold, and gave slightly smaller absorbance changes than in its absence. From the rate constants for the O2 (0.044 s(-1)) and H2O2 (0.67 s(-1)) iron-deposition reactions at pH 7.5, simulations of steady-state H2O2 concentrations were computed to be 0.45 microM. This low value and reported Fe2+/O2 values of 2.0-2.5 are consistent with H2O2 rapidly reacting by an alternate but unidentified pathway involving a system component such as the protein shell or the mineral core as previously postulated [Biochemistry 22 (1983) 876; Biochemistry 40 (2001) 10832].     

Crystal structure of beta-cyclodextrin-benzoic acid inclusion complex

The inclusion complex of beta-cyclodextrin (beta-CD) with benzoic acid (BA) has been characterized crystallographically. Two beta-CDs cocrystallize with two BAs, 0.7 ethanol and 20.65 water molecules [2(C(6)H(10)O(5))(7).2(C(7)H(6)O(2)).0.7(C(2)H(6)O).20.65H(2)O] in the triclinic space group P1 with unit cell constants: a=15.210(1), b=15.678(1), c=15.687(1) A, alpha=89.13(1), beta=74.64(1), gamma=76.40(1) degrees. The anisotropic refinement of 1840 atomic parameters against 16,201 X-ray diffraction data converged at R=0.078. In the crystal lattice, beta-CD forms dimers stabilized by direct O-2(m)_1/O-3(m)_1...O-2(n)_2/O-3(n)_2 hydrogen bonds (intradimer) and by indirect O-6(m)_1...,O-6(n)_2 hydrogen bonds with one or two bridging water molecules joined in between (interdimer). These dimers are stacked like coins in a roll constructing endless channels where the guest molecules are included. The BA molecules protrude with their COOH groups at the beta-CD O-6-sides and are maintained in positions by hydrogen bonding to the surrounding O-6-H groups and water molecules. Water molecules (20.65) are distributed over 30 positions in the interstices between beta-CD molecules, except the water sites W-1, W-2 that are located in the channel of the beta-CD dimer. Water site W-2 is hydrogen bonded to the disordered ethanol molecule (occupancy 0.7).     

Reduction of the suppressive effects of gurmarin on sweet taste responses by addition of beta-cyclodextrin

Cyclodextrins (CDs) have the remarkable ability to form inclusion complexes with a wide variety of guest molecules. In the present study, possible influences of CDs on gurmarin inhibition of the chorda tympani responses to sucrose were examined in C57BL mice. Responses to sucrose were suppressed to approximately 50% of control by treatment of the tongue with 30 micrograms/ml (approximately 7.1 microM) gurmarin. Rinsing the tongue with 15 mM beta-CD after gurmarin gave rapid recovery of the suppressed sucrose responses to approximately 85% of control, whereas 15 mM alpha- or gamma-CD did not. When gurmarin was mixed with beta-CD, the suppressive effects of gurmarin on sucrose responses were largely reduced. No such reduction was observed for mixtures with alpha- and gamma-CD. Gurmarin includes tyrosine and tryptophan residues whose aromatic rings are directed outward and can probably form inclusion complexes with beta-CD. Therefore, the observed reduction of the effects of gurmarin may be due to steric hindrances in inclusion complexes of gurmarin with beta-CD that may interfere with gurmarin binding to sweet taste receptors.      

An orthorhombic crystal form of cyclohexaicosaose, CA26.32.59 H(2)O: comparison with the triclinic form.

Cycloamylose containing 26 glucose residues (cyclohexaicosaose, CA26) crystallized from water and 30% (v/v) polyethyleneglycol 400 in the orthorhombic space group P2(1)2(1)2(1) in the highly hydrated form CA26.32.59 H(2)O. X-ray analysis of the crystals at 0.85 A resolution shows that the macrocycle of CA26 is folded into two short left-handed V-amylose helices in antiparallel arrangement and related by a twofold rotational pseudosymmetry as reported recently for the (CA26)(2).76.75 H(2)O triclinic crystal form [Gessler, K. et al. Proc. Natl. Acad. Sci. USA 1999, 96, 4246-4251]. In the orthorhombic crystal form, CA26 molecules are packed in motifs reminiscent of V-amylose in hydrated and anhydrous forms. The intramolecular interface between the V-helices in CA26 is dictated by formation of an extended network of interhelical C-H...O hydrogen bonds; a comparable molecular arrangement is also evident for the intermolecular packing, suggesting that it is a characteristic feature of V-amylose interaction. The hydrophobic channels of CA26 are filled with disordered water molecules arranged in chains and held in position by multiple C-H...O hydrogen bonds. In the orthorhombic and triclinic crystal forms, the structures of CA26 molecules are equivalent but the positions of the individual water molecules are different, suggesting that the patterns of water chains are perturbed even by small structural changes associated with differences in packing arrangements in the two crystal lattices rather than with differences in the CA26 geometry.     

Sugar interaction with metal ion: crystal structure and spectroscopic study of SrCl2.galactitol.4H2O

The crystal structure of SrCl(2).galactitol.4H(2)O has been determined. It belongs to monoclinic system, C2/c space group with unit cell dimensions: a=13.9849(3), b=14.1601(5), c=8.3026(3) A, beta=104.621(2) degrees, V=1590.9(9) A(3) and Z=4. Each Sr(2+) ion in the unit cell binds to two molecules of galactitol through O2 and O3 in one alditol and O2' and O3' in the other, as well as to four water molecules. Sr-O distances in SrCl(2).galactitol.4H(2)O complex range from 2.5420 to 2.6359 A. FT-IR, Raman and far-IR spectra of SrCl(2).galactitol.4H(2)O all show that SrCl(2) coordinates with galactitol through OH groups of the sugar molecule to form the new complex.     

Analysis of solvent structure in proteins using neutron D2O-H2O solvent maps: pattern of primary and secondary hydration of trypsin.

A method of determining the water structure in protein crystals is described using neutron solvent difference maps. These maps are obtained by comparing the changes in diffracted intensities between two data sets, one in which H2O is the major solvent constituent, and a second in which D2O is the solvent medium. To a good first approximation, the protein atom contributions to the scattering intensities in both data sets are equal and cancel, but since H2O and D2O have very different neutron-scattering properties, their differences are accentuated to reveal an accurate representation of the solvent structure. The method also employs a series of density modification steps that impose known physical constraints on the density distribution function in the unit cell by making real space modifications directly to the density maps. Important attributes of the method are that (1) it is less subjective in the assignment of water positions than X-ray analysis; (2) there is threefold improvement in the signal-to-noise ratio for the solvent density; and (3) the iterative density modification produces a low-biased representation of the solvent density. Tests showed that water molecules with as low as 10% occupancy could be confidently assigned. About 300 water sites were assigned for trypsin from the refined solvent density; 140 of these sites were defined in the maps as discrete peaks, while the remaining were found within less-ordered channels of density. There is a very good correspondence between the sites in the primary hydration layer and waters found in the X-ray structure. Most water sites are clustered into H-bonding networks, many of which are found along intermolecular contact zones. The bound water is equally distributed between contacting apolar and polar atoms at the protein interface. A common occurrence at hydrophobic surfaces is that apolar atoms are circumvented by one or more waters that are part of a larger water network. When the effects on surface accessibility by neighboring molecules in the crystal lattice are taken into consideration, only about 29% of the surface does not interface ordered water. About 25% of the ordered water is found in the second hydration sphere. In many instances these waters bridge larger clusters of primary layer waters. It is apparent that, in certain regions of the crystal, the organization of ordered water reflects the characteristics of the crystal environment more than those of trypsin's surface alone.     

Crystal structure of the dimeric beta-cyclodextrin complex with 1,12-dodecanediol

The structure of the complex of beta-cyclodextrin (beta-CD) with 1,12-dodecanediol has been determined at 173 K and refined to a final R=0.0615 based on 22,386 independent reflections. The complex crystallizes in the triclinic space group P1; with a=17.926(4), b=15.399(3), c=15.416(3) A, alpha=103.425(4), beta=113.404(4), gamma=98.858(4) degrees, D(c)=1.362 Mg cm(-3) and V=3651.4(13) A(3) for Z=1. One molecule of the diol is located as a guest in the hydrophobic cavity of a beta-CD-dimer, forming a [3]pseudorotaxane. The guest molecule shows a disorder over two positions. The hydroxyl groups of the diol emerge from the primary faces of the beta-CD dimer and form several hydrogen bonds with water molecules lying in the interstitial space, similarly to dimeric complexes of beta-CD with other alpha,omega-bifunctional guests.     

H2O2 activates ryanodine receptor but has little effect on recovery of releasable Ca2+ content after fatigue.

We studied whether hydrogen peroxide (H(2)O(2)) at 相似文献