Host-guest Interaction Energy Research Articles

Fragmentation Kinetics of Icosahedral Clusters: Ar12(Ar) and Ar12(Ar+)

We study the fragmentation kinetics of icosahedral Ar12(Ar) and Ar12(Ar+) clusters in the temperature range 10–300 K, using a classical dynamics method for detailed forms of host–host and host–guest interaction energies composed of short‐ and long‐range terms. The fragmentation of host atoms in charged clusters is ~20% and weakly dependent on temperature, whereas that of neutral clusters is less efficient but shows moderate temperature dependence. The dominant products from Ar12(Ar+) are 10‐Ar and 9‐Ar clusters, but a wider size distribution is found for Ar12(Ar) with the principal products 11‐ and 10‐Ar clusters. The fragmentation of Ar12(Ar+) occurs on two timescales; rapid fragmentation at short time with rate coefficients ~3 × 1011/s, and slow process at long time with ~2 × 1010/s. In neutral clusters, the extent of fragmentation is low during the early period with rate coefficients ~5 × 109/s. The fragmentation dynamics is distinctly different from Ar12(Ar+), which is attributed to an escaping host atom promoting the dissociation of neighbors, a host–host cooperative effect leading to a sigmoidal rise of fragmentation. The effect is present in the temperature range 100–300 K. Fragmentation kinetics of neutral clusters is discussed in detail.

Theoretical investigation of enantioselectivity of cage-like supramolecular assembly: the insights into the shape complementarity and host-guest interaction.

Enantioselectivity in the aza-Cope rearrangement of a guest molecule encapsulated in a cage-like supramolecular assembly [Ga4 L6 ](12-) [L = 1,5-bis(2',3'-dihydroxybenzamido)naphthalene] is investigated using density functional theory and ab initio molecular orbital calculations. Reaction pathways leading to R- and S-enantiomers encapsulated in the [Ga4 L6 ](12-) are explored. The reaction barriers and the stabilities of the prochiral structures differed in the [Ga4 L6 ](12-) , resulting that the product with an R structure is favorably produced in the Δ-structure [Ga4 L6 ](12-) . The large energy difference in the prochiral structures in the [Ga4 L6 ](12-) was attributed to the deformation of the bulky substituent. The host-guest interaction energy raises the reaction barrier for the product with an S structure. The previous study suggested that the different stability of the prochiral substrates in the assembly was the origin of the enantioselectivity, and the suggestion is supported by our computational finding. In addition, our results show that the difference in the reaction barriers also importantly contributes to the enantioselectivity.

Theoretical Study on Intermolecular Interactions in Complexes of Cyclodextrins with Bile Acids: DFT and Ab Initio Fragment Molecular Orbital Calculations

Abstract Inclusion complexes composed of cyclodextrin (CD) and bile acids have potential applications in drug delivery systems and chiral separation technology. In the present study, intermolecular interactions in 1:1 complexes of α-, β-, and γ-CDs with cholic acid (CA) or deoxycholic acid were analyzed both in the gas phase and in aqueous phase with density functional theory (B97-D and M06-2X) with the standard 6-31G(d) basis set together with the B3LYP functional for comparison. The association energies depend on the distance between CD and the guest as well as on the relative position and orientation of the guest in the cavity. The most stable binding mode for each complex is consistent with that proposed by NMR experiments. A pair interaction energy decomposition analysis based on ab initio fragment molecular orbital calculations was performed at the FMO-MP2/cc-pVDZ level of theory. It reveals that the β-CD/CA has more negative host–guest interaction energy than the γ-CD/CA and that dispersion and electrostatic interactions contribute comparably to the stabilization of the complexes. Several hydrogen bonds between CD and the guest also stabilize the complex.

Host–Guest Interactions in the Confined Geometries Formed from Molecular Aggregates of Push–Pull Molecules

We have considered push-pull molecules, aminonitroacetylene and aminonitrodiacetylene (O2N-(C≡C)n-NH2; n = 1 and 2) as the basic units to design a series of molecular aggregates containing favorable hydrogen bonding interactions. Linear, closed, and stacked geometries of dimers, trimers, tetramers, and pentamers formed from these molecules are found to have very good stabilization energies due to the strong hydrogen bonding abilities of the terminal -NO2 and -NH2 groups. The closed hydrogen-bonded assemblies can act as supramolecular hosts for accommodating some molecules and ions as guests. We have been able to find substantial host-guest interaction energies for the complexes of the hydrogen-bonded closed assemblies with some highly reactive molecules like hexahydro-1,3,5-trinitro-s-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), pentafluoroethane (R-125), and difluoromethane (R-32). Further investigations on the interaction of the ions Li(+), Na(+), K(+), Mg(2+), Ca(2+), Al(3+), F(-), Cl(-), and Br(-) with the monomers as well as the oligomers reveal the formation of strong ion-σ complexes, unlike the conventional weak ion-π complexes found in similar acetylenic systems without the end groups. This opens up the possibility of tuning the nature of ionic interactions in π-systems by varying the terminal groups.

Theoretical analyses of the host–guest interaction within chlorine hydrate

The host–guest interaction is necessary for the stabilization of hydrates. Using Density Function Theory methods, the host–guest interaction within an unconventional chlorine hydrate was investigated, in combination with typical noncovalent analyses. The host–guest interaction energy was predicted to be as high as 17.51 kcal/mol, which was stronger than the typical van der Waals (vdW) interaction, due to an involvement of up to 20 Cl…O interactions. Polarization and dispersion energies made up the main contribution to the total interaction energy. Further visualization of the host–guest interaction validated, together with the general Cl…O interaction, another vdW interaction between the guest‐Cl atom and the five‐membered H2O cluster. Isosurfaces associated with two patterns of vdW interactions yielded a better “fit” in shape, suggesting their cooperativity in stabilizing the steric configuration. The σ‐region on the guest‐Cl atom was verified to regulate the electron redistribution over the molecular space. These results are useful for understanding specific halogen behavior, and the origin and nature of host–guest interaction in hydrates. © 2013 Wiley Periodicals, Inc.

A model for the shuttle motions of puerarin and daidzin inside the cavity of β-cyclodextrin in aqueous acetic acid: insights from molecular dynamics simulations

Acetic acid acts as one component of the mobile phase to influence separation of puerarin from daidzin when using β-cyclodextrin-substituted media. In this work considering an explicit acetic acid solution, host-guest complexes of β-cyclodextrin (β-CD) with puerarin and daidzin were investigated by molecular dynamics simulations. Computational results indicate different shuttle motions of puerarin and daidzin inside the cavity of β-CD. A model detailing the shuttle motion was constructed, and the relationships between shuttle depth and guest rotation angles, hydrogen bonds, and host-guest interaction energies were analyzed. The results can be used to explain the chromatographic retention mechanisms of puerarin and daidzin with β-CD, and to explore the complexity of host-guest interactions involving β-CD.

SsDNA templated assembly of oligonucleotides and bivalent naphthalene guests

The hybridization of oligothymine templates with oligomeric adenine and naphthalene diaminotriazine guests has been studied by UV-vis and circular dichroism (CD) spectroscopy. First, the length of the oligothymine template and the oligoadenine guest has been systematically varied. The studies reveal that increasing the length of multivalent guests results in a stabilization of the templated assemblies. Hybridization studies also show that guest–guest interactions between the multivalent guests additionally enhance the stability. Based on these results, a bivalent naphthalene diaminotriazine guest has been synthesized, showing a higher stability than the monovalent naphthalene diaminotriazine guest; the host–guest interaction energy is higher while the guest–guest interaction remains the same.

Molecular Insights into the Self-Aggregation of Aromatic Molecules in the Synthesis of Nanoporous Aluminophosphates: A Multilevel Approach

Fluorescence spectroscopy and a range of computer simulation techniques are used to study the structure directing effect of benzylpyrrolidine (BP) and (S)-(-)-N-benzylpyrrolidine-2-methanol (BPM) in the synthesis of nanoporous aluminophosphate frameworks with AFI (one-dimensional channels) and SAO (three-dimensional interconnected channels) topologies. We study the supramolecular chemistry of BP and BPM molecules in aqueous solution and compare it with the aggregation state of the molecules found when they are inside the AlPO nanopores after crystallization. The aggregation of the molecules within the structures can be explained by a combination of thermodynamic and kinetic effects. The former are given by the stability of the molecular species interacting with the oxide networks relative to their stability in solution; the latter depend on the aggregation behavior of the molecules in the synthesis gels prior to crystallization. Whereas BPM only forms one type of aggregate in solution, which has the appropriate conformation to match the empty channels of the forming nanoporous frameworks, BP forms aggregates with different molecular orientations, of which only one matches the framework interstices. This different supramolecular chemistry, together with the higher interaction of BPM with the oxide networks, makes BPM a better structure directing agent (SDA); it is also responsible for the higher incorporation of BPM as dimers in the frameworks, especially in the AFI structure, observed experimentally. The concentration of the SDA molecules in the gels, and so the density per volume of the SDAs, determines the exclusion zone from which the pores and/or cavities of the framework will arise, and so the porous network of the formed material. A clear relationship between the SDA density in solution and in the framework is observed, thus enabling an eventual control of the material density by adjusting the SDA concentration in the gels. The topological instability intrinsic to these open framework structures is compensated by a high host-guest interaction energy; the SAO topology is further stabilized by doping with Zn. Our computational results account for and rationalize all the effects observed experimentally, providing a complete picture of the mode of structure direction of these aromatic molecules in the synthesis of nanoporous aluminophosphates.

Insights into Structure Direction of Microporous Aluminophosphates: Competition between Organic Molecules and Water

A combination of experimental characterisation techniques and computational modelling has allowed us to gain insight into the molecular features governing structure direction in the synthesis of microporous aluminophosphates. The occlusion of three different structure-directing agents (SDAs), triethylamine (TEA), benzylpyrrolidine (BP) and (S)-(-)-N-benzylpyrrolidine-2-methanol (BPM), within the AFI structure during its crystallisation, together with the simultaneous incorporation of water, has been experimentally measured. We found a higher incorporation of organic molecules in the structure obtained with BPM, while a higher water (and lower organic) content is found for the ones obtained with TEA and BP as SDAs. The computational study provides a thermodynamic explanation for the observed behaviour in terms of the relative stabilisation energy of the SDAs and water molecules within the AFI framework compared with when they are in aqueous solution, and demonstrates that a competition for preferential occupation exists between water and organic SDAs, which is a function of the interaction with the inorganic framework. The lower interaction of TEA and BP molecules with the AFI structure promotes the simultaneous incorporation of water molecules in the 12-membered-ring (MR) channel, to increase the host-guest interaction energy and thus the thermodynamic stability. The presence of strongly interacting methanol groups in the BPM molecules leads to the incorporation of only organic molecules within the 12-MR channels. Our results demonstrate the essential role that water molecules play in the stabilisation of hydrophilic microporous aluminophosphates; a minimum amount of organic SDA is, however, essential for a templating role of the microporous architecture.

Origin and Model for Cooperative Host–Guest Interaction Affecting the Orientation of Guests in Oriented Nematic Hosts

It has been observed for the binary systems of oriented nematic hosts and nonmesomorphic guests (substituted anthraquinones) that the orientational orders of amino-substituted anthraquinones ascend with increasing guest concentrations. A new quantitative and experimental procedure has been proposed for obtaining the host–guest isotropic dispersion, isotropic electrostatic, anisotropic dispersion, and anisotropic electrostatic interaction energies. Among these four host–guest interaction energies, the host–guest isotropic dispersion interaction energy alone is demonstrated to be well correlated with the concentration dependence of the orientational order of the guest. A model is also proposed for the cooperative and isotropic host–guest interaction.

Theoretical Investigations and Mechanisms of the Inclusion Processes of bi(3-sulfonatophenyl) (4-tert-butylphenyl) phosphine in the β-cyclodextrin

Quantum mechanical calculations on the bi(3-sulfonatophenyl) (4-tert-butylphenyl) phosphine/β-cyclodextrin inclusion complex (TPP/CD) are carried out using semiempirical quantum calculations. Inclusion process pathways described in the present work lead straight to the most probable structures of the 1:1 association. These investigations suggest that the most stable structure obtained is that where the aromatic ring bearing the tert-butyl (tBu) group is included into the hydrophobic cavity of the β-cyclodextrin from the side of the primary hydroxyl groups. Theoretical investigations of the Hartree-Fock level of the inter-proton proximity between the host and guest molecules in the inclusion complex and their corresponding electronic properties suggest a deep insertion of the tBu group into the cavity. The host-guest interaction energy of the complex at different levels of the insertion pathway is reported with the corresponding basis set superposition error (base). The host–guest association is thermodynamically stable when compared to the separated states and the calculated binding energy is 40.6 kcal mol−1.

Energetically preferred locations of hydrocarbons in the structure of a Pt-Sn/γ-Al2O3 catalyst: docking method

Abstract The use of methods dealt with in computational chemistry for the design of efficient catalysts has become increasingly frequent. In our study, molecular modeling methods were used to find the catalytic sites of a Pt-Sn/γ-Al2O3 catalyst. Five different catalyst models including one support model were constructed. With the docking method, the most probable locations of hydrocarbon molecules on the micropore surface were determined. The host–guest interaction energy was calculated for all locations, using the CVFF approach. The results revealed a very strong influence of the platinum centers and a considerably weaker one of the tin centers, comparable to those of the support atoms. Calculations were also carried out to establish the distance of the adsorbed hydrocarbon molecules from the catalyst model—the distance of the shortest contact. Aliphatic hydrocarbons adsorb much closer to the micropore surface than do cyclic hydrocarbons.

Diffusion of hydrocarbons in the reforming catalyst: molecular modelling

This is an analysis of the diffusion and adsorption of the model reagents involved in the reforming process (heptane, methylcyclohexane and toluene) in the support (γ-Al 2O 3) and catalyst (Pt/γ-Al 2O 3) made use of in this process. Since the properties of these catalytic systems are influenced by the interactions between the atoms of the catalyst structure (host) and the atoms of the reagents (guest), analysis was carried out at the molecular level, using advanced computer simulations (molecular dynamics and forced diffusion) implemented in the MSI Software. The virtual host–guest model constructed with this software enabled a simulation of the real reforming system (reforming catalyst–reagents) and analysis of the diffusion phenomenon in this system. The results show that the propensity of the reagents to adsorption and the host–guest interaction energy are correlated with the coefficients of diffusion. The diffusion coefficient values are lower in the catalyst than in the support, probably because of the increased adsorption at the active Pt centres. The decrease in pore diameter from 17 to 10 Å brings about a decrease in the diffusion coefficients not only due to steric hindrance, but also as a result of capillary condensation. The favourable influence of temperature is more distinct in models characterised by a larger pore size. This is so because molecular diffusion dominates over the mechanism of Knudsen diffusion, which increases the temperature-dependence of diffusion.

Structure Analysis of Montmorillonite Intercalated with Cetylpyridinium and Cetyltrimethylammonium: Molecular Simulations and XRD Analysis

Molecular mechanics and molecular dynamics simulations combined with X-ray powder diffraction were used in structure investigation of montmorillonite intercalated with cetylpyridinium (CP) and cethyltrimethylammonium (CTA) cations. Molecular modeling revealed the interlayer structure and differences in intercalation behavior of CP and CTA cations in montmorillonite. The experimental and calculated values of basal spacing were in good agreement for both intercalates: in the case of CP–montmorillonite dexp=20.59 Å, dcalc=20.60 Å; for CTA–montmorillonite dexp=18.00 Å and dcalc=18.10 Å. CTA–montmorillonite exhibits significantly higher total sublimation energy and higher host–guest interaction energy than the CP–montmorillonite. The main difference between both intercalates is in charge distribution on the host layers and guest species. The charge transfer from the guest species to the host layer is higher in CTA–montmorillonite than in CP–montmorillonite, and consequently the charge polarization between the host and guest layers is much higher in CTA–montmorillonite. This leads to much stronger host–guest electrostatic interaction in the case of CTA–montmorillonite.

Probing Host-Guest Interaction Energies in Solid Inclusion Compounds from Experimental Studies of Competitive Inclusion

An approach to assess host-guest interaction energies in solid inclusion compounds with tunnel host structures is described, based on experimental studies of competitive inclusion of two different types of potential guest molecules X(S) q X and X(S) r X (q ≠ r) within the host tunnel. The proportions (m and 1-m) of the two types of guest molecule included within the host tunnel depend on the proportions (γ and 1-γ) of the two types of guest in the external “pool” of potential guest molecules and the relative “affinities” (χ and 1/χ) of the host tunnel for including the two types of guest. Expressions linking χ, m and γ can be applied to determine χ directly from experimental measurements of m for inclusion compounds prepared with different values of γ. The value of χ depends on the intermolecular interaction energies per unit length of tunnel for the two types of guest molecule, and χ may be expressed in terms of the host-guest interaction energies for the spacer units S and the end-groups X, and the guest-guest (X…X) interaction energy. Preliminary experimental results for urea inclusion compounds containing binary mixtures of α,Ω-dibromoalkane guest molecules are presented.

Micellar electrokinetic chromatography of monohydroxybenzo[a]pyrene positional isomers using γ-cyclodextrin

Cyclodextrin-modified micellar electrokinetic chromatography was applied to the separation of benzo[a]pyrene and 12 positional isomers of monohydroxybenzo[a]pyrenes using γ-cyclodextrin together with sodium dodecyl sulfate. The optimum running conditions were found to be 20 mM phosphate–5 mM borate buffer (pH 8.5) containing 20 mM γ-cyclodextrin and 50 mM sodium dodecyl sulfate with an effective voltage of 12 kV at 20 °C. Octanol–water distribution coefficients of the compounds in the presence of γ-cyclodextrin were measured as an index of the association constants for complexes of γ-cyclodextrin with these compounds. The migration time of the analytes correlated well with their distribution coefficients, suggesting that their migration order could be correctly predicted on the basis of calculations of host–guest interaction energies. The relationship between the migration order and the structures of monohydroxybenzo[a]pyrene isomers is discussed.

A theoretical framework for the experimental determination of host–guest interaction energies in solid inclusion compounds

A mathematical model is developed to provide the framework of an experimental approach for determining host–guest interaction energies in solid inclusion compounds with one-dimensional tunnel host structures. The approach considers the competitive inclusion of two different types of potential guest molecules X(S)qX and X(S)rX (q≠r) within the tunnel host structure, where X represents a given type of end group (e.g., CH3, halogen, etc.) and S represents an appropriate spacer unit (e.g., CH2, CH, etc.). Sequential and simultaneous models for the growth of the guest substructure within the host tunnel are considered. The relative proportions (m and 1−m) of the two types of guest molecule included within the host tunnel depend on the relative proportions (γ and 1−γ) of the two types of guest molecule in the external “pool” of potential guest molecules and the relative “affinities” (χ and 1/χ) of the host tunnel structure for including the two different types of guest molecule. Expressions linking χ, m, and γ are developed, and can be applied to determine χ directly from experimental measurements of m for a series of inclusion compounds prepared for different (known) values of γ. Fundamentally, the value of χ depends on the intermolecular interaction energies per unit length of tunnel for the two different types of guest molecule, and χ may be expressed in terms of the host–guest interaction energies for the spacer units S and the end groups X, and the guest–guest (X⋯X) interaction energy. The mathematical model provides a framework for assessing these different energy contributions from experimental measurements of m for sets of inclusion compounds prepared for different values of the parameters q, r, and γ, and with the same host tunnel structure.

Host-guest Interactions in Intercalates Zr(HPO 4 ) 2 ·2C 2 H 5 OH and VOPO 4 ·2C 2 H 5 OH

Molecular mechanics simulations using Cerius2 modelling environment combined with vibrational spectroscopy (IR and Raman) have been used to study the host-guest interactions in zirconium and vanadyl phosphate intercalated with ethanole. The strategy of investigation is based on the comparison of vibrational spectra for the host compound, intercalate and guest species. This comparison confirmed the rigidity of VOPO4- and Zr(HPO4)2-layers during the intercalation and provided us with the basis for the strategy of modelling. Molecular mechanics simulations revealed the structure of intercalates and enabled to analyse the host-guest interaction energy and bonding geometry. The bilayer arrangement of ethanole molecules in the interlayer space with two differently bonded ethanole molecules has been found in both intercalates. The average interaction energy ethanole-layer for two differently bonded ethanole molecules is : 127.5 and 135.7 kcal·mol-1 in Zr(HPO4)2·2C2H5OH, respectively 94.0 and 104.4 kcal·mol-1 in VOPO4·2C2H5OH. The Coulombic contribution to the ethanole-layer interaction energy is predominant in all cases, but the hydrogen bonding contribution is much higher in Zr(HPO4)2·2C2H5OH than in VOPO4·2C2H5OH. Present results of modelling enabled the interpretation of vibrational spectra and explanation of small changes in positions and shapes of spectral bands, in infrared and Raman spectra, proceeding from the host structure to intercalates.

Stochastic models for guest–guest interactions in one–dimensional inclusion compounds

The intrinsic relative preferences of XX, XY and YY interactions between functional groups X and Y can be obtained by considering a set of onedimensional inclusion compounds containing guest molecu...

Study of the palmitic-choleic acid by vapour pressure measurements and Van Der Waals' energy calculations

Vaporization studies in pure palmitic acid (CH 3(CH 2) 14COOH; hereafter referred to as PAL) and the PAL-choleic acid (DCAPAL) were accomplished by resorting to the torsion effusion method. The vapour pressure in equilibrium with the condensed phase was determined for PAL as log P (kPa) = (9.77 ± 0.16) - (4677 ± 62)/ T and for DCAPAL as log P (kPa) = (25.28 ± 0.56) - (12355 ± 224)/ T By the second-law treatment of the vapour pressure data, Δ H 0 379 = 89 ± 2 and Δ H 0 445 = 237 ± 5 kJ mol −1 were derived for PAL vaporization from the pure compound and from DCAPAL, respectively. Moreover, van der Waals' energy calculations were performed on DCAPAL to obtain an empirical correlation between the host-guest interaction energy and the enthalpy change associated with the release of PAL from the crystal of DCAPAL.