Orientation Of Guest Research Articles

Theoretical Study of the β-Cyclodextrin Inclusion Complex Formation of Eugenol in Water

The interaction between eugenol and β-cyclodextrin in the presence of water is studied by molecular mechanics and dynamics simulations. A force field model is used in molecular mechanics to determine the interaction energy and the complex configuration at the absolute minimum. The van der Waals term is the main contribution to the total energy, and so directly determines the configuration of the inclusion complex. The formation of inclusion complexes is simulated by molecular dynamics, in which their configurations are deduced from the position probability density that represents the preferred location and orientation of the guest in the simulation. When eugenol approaches from the rims of β-cyclodextrin, it tends to enter the cavity, remain inside for a short period and then exit from it. The guest tends to include the phenyl ring inside the cavity in the most probable configurations. Two inclusion complex configurations are proposed, each with the hydroxyl and methoxyl groups pointing towards one different rim of β-cyclodextrin. The initial guest orientation is the main factor determining these configurations. The model presented in this study reproduces the experimental findings on inclusion complex formation and proposes two possible complex configurations, one previously suggested by different authors.

Guest Orientation of Front Office Employees' Service Quality and Rapport: Influences on Satisfaction in Egyptian Five and Four star Hotels

This research aims to assess the guests' perceptions of service quality of employees in front office department of five and four star hotels at Cairo and Giza in Egypt. The assessment also includes the influence of service quality on the rapport between front office employees and guests. The study also assesses the influence of service quality and rapport on guest satisfaction. The study developed a conceptual model of the constructs involved. The hypotheses were proposed regarding the relationships within the model. The conceptual model and hypotheses were then tested in a sample of hotel guests. The study found that service quality dimensions contribute to predict enjoyable interaction personal connection between front office employees and guests. Moreover, enjoyable interaction and personal connection mediates the impact of front office employees' service quality on guest satisfaction. Furthermore, service quality dimensions of front office employees contribute to predict guest satisfaction. There are significant differences between four and five star hotels in perceived service quality and guest satisfaction, but not for rapport dimension. There are no significant differences between foreigner and Arab tourists in these dimensions.

Fluorescence Polarization Measurements to Probe Alignment of a Bithiophene Dye in One-Dimensional Channels of Self-Assembled Phenylethynylene Bis-Urea Macrocycle Crystals

This paper describes the use of polarized fluorescence microscopy to directly probe guest molecule orientation in bis-urea macrocycle crystals. These macrocycles assemble to afford one-dimensional (1D) microchannels ∼9 A in diameter that have previously been shown to exhibit normal Fickian diffusion and induce selective reactivity among the confined guest molecules. In the present work, we take advantage of the quasi-1D morphology of fiber-like microcrystals with the extended dimension corresponding to the channel axis to measure excitation and emission polarization values for a bithiophene guest. Guest fluorescence is shown to be polarized along the fiber axis with emission polarization values up to 0.729, indicating a high degree of orientational order within the 1D channels. The observed behavior is consistent with calculated results for the guest orientation and electronic transition dipole moment. The results indicate the value of functional fluorescent probes as a measure of guest confinement in low...

Host–guest intermolecular hydrogen bonds and stability in aqueous media: the benzaldehyde/β-CD case study

The formation of a host–guest system is driven by several contributions. The solvent plays a fundamental role. Usually, in theoretical investigations concerning cyclodextrin inclusion compounds hydrogen bonds between host and guest are studied. Our calculations for the β-cyclodextrin/benzaldehyde semicarbazone system show that hydrogen bonds between host and guest may not determine the preferable guest orientation. In addition, gas and aqueous phase theoretical trends can be distinct in studies concerning CD-based inclusion compounds.

Predicting conformations and orientations of guests within a water soluble host: a molecular docking approach

In this study we have examined conformations and orientations of guests within a water-soluble host known by the trivial name Octa Acid (OA). Docking program Vina, which was originally developed for screening drug-like molecules, has been used to identify binding modes and affinities of select guest molecules with OA. Hydrophobic guests were encapsulated into the nonpolar cavity of OA capsule owing to solvophobic interactions. Amphiphilic guests were bound by keeping the nonpolar part within the cavity of OA, while pointing the polar anionic group out of the cavity. All these results obtained from the docking study were in accord with experimental findings. The post-complexation attributes of the guests were regulated by available free space and the specific interactions between guest–OA pair, which led to unusual conformations and orientations. This study showed that scoring function available with Vina, which was derived from protein–ligand data set, could successfully predict post-complexed structural features of guests within OA, thus opening opportunities to modulate physical and chemical behavior of guest molecules.

Synthesis and Characterization of Layered Double Hydroxides Containing Optically Active Transition Metal Ion

The acetate intercalated layered double hydroxides of Zn and Mn, have been synthesized by chimie douce method. The materials were characterized by XRD, TGA, CHN, IR, XPS, SEM-EDX and UV-visible spectroscopy. The photoluminescence properties was also studied. The optical properties of layered hydroxides are active transition metal ion dependent, particularly d1−10 system plays an important role. Simultaneously the role of host – guest orientation has been considered the basis of photoluminescence. Acetate ion can be exchanged with iodide and sulphate ions. The decomposed product resulted the pure phase Mn doped zinc oxide are also reported.

Enantiopure Alleno-Acetylenic Helicages Containing Multiple Binding Sites.

Enantiopure alleno-acetylenic ligands, containing two chiral allene moieties, assemble diastereoselectively with zinc(II) ions to form trinuclear triple-stranded helicates, featuring two internal cavity binding sites ("helicages"). The addition of cycloalkanes or heteroalicycles results in inclusion complex formation with two guest molecules bound in one helicate. While no positive allosteric effects were observed, the chiroptical responses increased strongly upon complexation, with guest-induced circular dichroism (ICD) signals reaching up to ΔΔϵ=205 m-1 cm-1 . The highest binding affinity was observed for six-membered 1,4-dichalcogens, with binding constants (K1 ) of up to 2400 m-1 for 1,4-oxathiane in CD3 OD. The X-ray co-crystal structure of 1,4-dioxane bound to a dinuclear triple-stranded helicate confirmed the previously predicted guest orientation inside the helicage, with the two oxygen atoms facing towards the electropositive zinc(II) metal centers.

Inclusion Complexation of Acetanilide into the β-Cyclodextrin Nanocavity: A Computational Approach

Host–guest inclusion complexation of acetanilide (AA) into the β-cyclodextrin (β-CD) nano-hydrophobic cavity has been investigated using computational technique. Two different orientation of guest (AA) into host (β-CD) are considered for the inclusion of AA in to the nanocavity through the 2o rim of β-CD. The energy differences in the inclusion process are calculated using PM3 semi-empirical method. By the investigation of stabilization energies, it is found that the “orientation 1” in which the benzene ring of AA oriented towards 2o rim of β-CD nanocavity is the stable complex. The conclusions obtained from the computational analysis are in good correlation with the docking analysis.

DFT study the interaction of β‐cyclodextrin with benzyl azide and phenyl acetylene in synthesis of 1,2,3‐triazoles

The phenyl acetylene and benzyl azide cycloaddition reaction in water in the presence of β‐cyclodextrin (β‐CD) as a phase transfer catalyst (PTC) can get a better yield in a shorter time. The interaction between β‐CD and phenyl acetylene or benzyl azide plays an important role in this reaction. This paper studies the complexes of β‐CD with phenyl acetylene and benzyl azide using density functional theory (DFT) method. In order to find out the orientations of guests in the cavity of β‐CD, binding energy and deformation energy are investigated, and the calculated results are confirmed by 1H nuclear magnetic resonance (1HNMR). The data from single point energy indicate that the inclusion complexes can improve the solubilities of phenyl acetylene and benzyl azide in water. The 13C and 15N spectra show that the most obvious variation concentrates on C6 and C8 of phenyl acetylene and N15 of benzyl azide in complexes. Mulliken charge and frontier orbital are employed for revealing the charge distribution. The effect of β‐CD is discussed in terms of the calculated parameters. Copyright © 2014 John Wiley & Sons, Ltd.

Steric effect is a decisive factor on the orientation preference of guest into host: evidence from 5-indanol/β-CD model

The present study evidences the role of steric effect in the orientation preference of guest into host using the 1:1 inclusion complex of 5-indanol/β-CD model. Two different orientations of guest (5-indanol) into host (β-CD) are considered for the inclusion of 5-indanol into the cavity through the 2° rim of β-CD. The energy differences in the inclusion process are calculated using PM3 semi-empirical method and HF/6-31G** basis set. By the investigation of stabilisation energies, it is found that the energy of both orientations increases to maximum value due to the increase of steric repulsive effect when the crowding of bulky group of 5-indanol occurs at 1° or 2° rim of β-CD. On comparing the fluorescence spectral data of 5-indanol:β-CD complex and 2-napthol:β-CD complex, it is observed that the steric effect is intensified due to the presence of bulky group.

Linker Effects on Amino Acid and Peptide Recognition by Molecular Tweezers

AbstractTransition from monotopic symmetrical to ditopic unsymmetrical molecular recognition frequently occurs when a general, powerful, but unspecific receptor molecule is transformed into a specific ditopic host. Especially in water, this endeavor is accompanied by great challenges, comprising, among other things, host–guest orientation, orthogonal recognition modes, and the nature of the linker unit. This work presents a case study on a powerful general host for basic amino acids and peptides. The symmetrical molecular tweezer skeleton was systematically desymmetrized and modified with various common linker units, and the profound influence of these changes on the molecular recognition profile was studied in detail by NMR spectroscopy, fluorescence titrations, X‐ray crystallography, and molecular simulations. A number of diverse effects were revealed that could be attributed to the chemical nature of the different linkers. In general, long alkyl tethers block the cavity of the tweezers by van der Waals contacts to CH groups around its entrance; alkoxyalkyl tethers likewise lower tweezer affinities for basic amino acids by competing self‐inclusion. As a general trend, affinities for linkers with ester and carboxylate moieties were substantially higher than those for tethers with ethers and alcohols, likely because the electron‐rich carbonyl group keeps the cavity open. Additional hydrogen bonds between the linker unit and suitable amino acid or peptide guests greatly support the complexation process; finally, high solvent polarity and salt load shift the binding equilibrium from external ion pairing to guest inclusion.

Quantum Chemical Challenges for the Binding of Simple Alkanes to Supramolecular Hosts

Binding of hydrocarbon guests to supramolecular hosts can lead to unusual geometric changes such as bending or coiling of guests upon encapsulation. Cucurbiturils (CBs) are classic cation binders that were recently used for the selective binding of small-membered hydrocarbons with a very high association constant (Ka ≈ 10(6) M(-1)). In this study, we have systematically investigated the binding of some alkanes to CB-[6] using a series of quantum chemical methods. The calculated binding free energies are very strong and are largely influenced by guest orientations inside the host and reorganization of host and guests. The computed (1)H NMR chemical shifts of the encapsulated alkanes agree with the experimental estimates thus confirming guest encapsulation. Further, we have shown that although binding of both cyclopentane and neopentane have very strong binding affinities (>20 kcal mol(-1)), the selectivity of cyclopentane to neopentane at CB-[6] is a kinetically driven process through the computation of approximate transition state structures of both alkanes to CB-[6]. The calculated binding affinities with dispersion corrected density functionals (DFs) are very close to the experimental estimates, whereas DFs that lack dispersion correction predict that alkane binding to CB-[6] is largely unfavorable. Finally, we have investigated the binding of some long chain alkanes to several supramolecular hosts using dispersion corrected semiempirical methods which cannot be routinely studied through density functional theory methods due to the larger size of the system.

Host–Guest Interactions and Orientation of Dyes in the One-Dimensional Channels of Zeolite L

A combined experimental and modeling study of methylacridine (MeAcr(+)) dye-zeolite L composites unravels the microscopic origin of their functional properties. The anisotropic orientation of the cationic dye inside the ZL channel is unambiguously determined and understood. The most stable orientation of MeAcr(+), which features both its long and short molecular axes nearly perpendicular to the channel axis, is mainly determined by dye-ZL electrostatic interactions but also depends on the cosolvent water. In ZL, MeAcr(+) is not hydrogen bonded to water or ZL framework oxygens and is hydrophobically solvated by water molecules. These findings further support the hypothesis that the cosolvent can importantly influence properties of dye-zeolite composites. Of relevance for a deeper comprehension of the physical chemistry of these hybrids is the observation that trivial energy transfer processes (self-absorption) are often playing a significant role in the optical properties of the composites.

ChemInform Abstract: Carcerands and Hemicarcerands

AbstractReview: 189 refs.

Theoretical study of inclusion of a dinuclear platinum(II) complex in α, β, and γ‐cyclodextrins

AbstractThis study has focus on inclusion compounds formed by native cyclodextrins (CD) and dinuclear platinum(II) complex (bisPt), investigated by density functional theory and hybrid our own N‐layered integrated molecular orbital and molecular mechanics (ONIOM) approaches. The main goal here is to get insights on the molecular features governing the stability of bisPt@CD inclusion complexes, accounting for cavity size, host–guest orientation, and stoichiometry. The results indicate that the β‐CD is the most attractive host to form inclusion complex with bisPt, with ΔG found negative for the six orientations tested (A–F), ranging from −3.69 to −20.08 kcal mol−1 (ONIOM values). Besides the favorable size/shape relationship for bisPt@β‐CD complex, the higher stability is also due the hydrogen bonds between the bisPt amine groups and the β‐CD oxygen atoms. © 2012 Wiley Periodicals, Inc.

The Effect of Inclusion of Dichloromethane in the δ-Clathrate Phase of Syndiotactic Polystyrene

Inclusion of molecules in the crystalline phases of s-PS induces on the guest long range order and strongly reduces the guest diffusivity and mobility with respect to a random dispersion at the molecular level in polymeric amorphous phases. Moreover, when included in highly oriented s-PS films, the degree of guest orientation is comparable to the host orientation and detailed information on directional properties within molecules can be unambiguously achieved. In this paper, the behavior of dichloromethane in the δ-clathrate phase of syndiotactic polystyrene is studied by combined FTIR and solid state 2H NMR techniques, defining the molecular orientation in the crystalline phase and the constrained reorientational dynamics of the guest molecules in the cavities.

PH Influenced molecular switching with micelle bound cavitands

A series of resorcinarene host-amphiphilic guest complexes have been developed where guest orientation in the host is drastically influenced by pH. Guests appended with a trimethylammonium and a tert-butyl group switch orientation by 180° in response to a buildup of negative charge in the cavitand host.

Molecular dynamics simulation of NMR powder lineshapes of linear guests in structure I clathrate hydrates

We perform molecular dynamics simulations (up to 6 ns) for the structure I clathrate hydrates of linear molecules CS, CS(2), OCS, and C(2)H(2) in large cages at different temperatures in the stability range to determine the angular distribution and dynamics of the guests in the large cages. The long axes of linear guest molecules in the oblate large structure I clathrate hydrate cages are primarily confined near the equatorial plane of the cage rather than axial regions. This non-uniform spatial distribution leads to well-known anisotropic lineshapes in the solid-state NMR spectra of the guest species. We use the dynamic distribution of guest orientations in the cages during the MD simulations at different temperatures to predict the (13)C NMR powder lineshapes of the guests in the large cages. The length of the guests and intermolecular interactions of the guests in the water cages determine the angular distribution and the mobility of the guests in the sI large cages at different temperatures. At low temperatures the range of motion of the guests in the cages are limited and this is reflected in the skew of the predicted (13)C lineshapes. As the guest molecules reach the fast motion limit at higher temperatures, the lineshapes for CS, OCS, and C(2)H(2) are predicted to have the "standard" powder lineshapes of guest molecules.

Controlled Orientation of Polyconjugated Guest Molecules in Tunable Host Cavities

Linear conjugated guest molecules with high aspect ratios form inclusion compounds with guanidinium organodisulfonate (GDS) host frameworks in which organodisulfonate "pillars" connect opposing GS sheets to generate lamellar architectures that reflect templating by the guest. Through judicious selection of pillars having adjustable lengths (l(S-S), as measured by the separation between distal sulfur atoms) and guests of various lengths (l(g)), the framework architecture can be controlled systematically in a manner that enables regulation of the guest orientation and aggregation in the host framework. Inclusion compounds for which l(g)/l(S-S) ≤ 0.9 exhibit a bilayer architecture with 1-D channels containing guests oriented parallel to the long axis of the pillar. Guests with values of l(g) comparable to l(S-S), however, promote the formation of a brick architecture in which the guests and the pillar are arranged in a herringbone motif. Surprisingly, longer guests (l(g) = 1.25l(S-S)) favor the formation of the bilayer architecture despite their larger volume because the guests are forced to align end-to-end as single-file arrays due to the vertical constraints of the 1-D channels. Bithiophene and biphenyl guests (l(g) < l(S-S)) are exceptional, promoting bilayer structures in which turnstile rotations of the pillars afford an unusual motif in which the guests are isolated from one another. The ability to synthesize a large family of compounds based on a common supramolecular building block (the GS sheet) permits construction of a structural "phase diagram" based on two simple molecular parameters, l(g) and l(S-S), that can be used to sort the inclusion compounds according to their framework architectures and enable prediction of crystal structures for new host-guest combinations. The effects of these different framework architectures and packing motifs is manifested as bathochromic shifts in the absorption and emission spectra of the guests compared with their spectra in methanol solutions. This behavior is supported by ab initio TDDFT calculations that reproduce the bathochromic shifts associated with the effects of guest-guest and guest-host interactions, combined with conformational constraints imposed on the guest molecules by the rigid host framework.

Discrete stack of an odd number of polarized aromatic compounds revealing the importance of net vs. local dipoles

Three polarized aromatic guest molecules (pyrene-4,5-dione, 1) form a triple-layered stack in the box-shaped cavity of an organic pillared coordination cage in water. The cavity size strictly limits the number of stacked planar guests but does not restrict guest orientation, and thus enables the study of discrete stacks of polarized guests and their preferred conformations. Crystallographic study shows that the guest molecules in the cavity are rotated 120 degrees with respect to each other, cancelling the net dipole moment rather than the local dipole moment. The unique conformation of a discrete, triple stack of 1 sharply contrasts to the standard head-to-tail conformation in infinite stacks of 1.