Modelling conformations and IR spectra of p-tert-butylthiacalix[4]arene tetraester using DFT method

The infrared spectra of the cone, partial cone and 1,3-alternate conformers of p-tert-butyltetrakis(ethoxycarbonyl)methoxytetrathiacalix[4]arene (TEMT) have been recorded. The structural optimization and normal mode analysis were performed for this molecule on the basis of the density functional theory. These calculations gave the frequencies of vibrations and infrared intensities for the cone, partial cone (paco) and 1,3-alternate (1,3-alt) conformers. The energy difference between the paco and 1,3-alt conformers is 3.1 kcal/mol. The cone conformer is likely to be less stable compared to the paco and 1,3-alt conformers. The calculated in gas phase dipole moments 5.65, 3.33, and 0.02 D for the cone, paco and 1,3-alt conformers of the TEMT are in good accordance with theoretical values for the thiacalix[4]arene. Complete assignments were made for the experimental IR spectra of all conformers. The softness of sulphur atoms to nucleophilic and electrophilic attack is higher than softness of oxygen atoms of ester groups in the lower rim. The bands characteristic for each conformation were defined. IR spectroscopy combined with DFT computation provides unique detailed information about the structure of the technologically relevant materials, which could not be obtained before with any other technique.     

Calix[4]arene‐Based Bis(Nitric Oxide) Complexes: Synthesis,Physical Properties,and Structural Characterization

Calix[4]arene‐based molecules hold great promise as candidate sensors and storage materials for nitric oxide (NO), owing to their unprecedented binding affinity for NO. However, the structure of calix[4]arene is complicated by the availability of four possible conformers: 1,3‐alternate, 1,2‐alternate, cone, and partial cone (paco). Whilst complexes of NO with several of these conformers have previously been established, the 1,2‐alternate conformer complex, that is, [1,2‐alter ? NO]⁺, has not been previously reported. Herein, we determine the crystal structure of the NO complex with the 1,2‐alternate conformer for the first time. In addition, we have also found that the 1,2‐alternate and 1,3‐alternate conformers can combine with two NO molecules to form stable bis(nitric oxide) complexes. These new complexes, which exhibit remarkable binding capacity for the construction of NO‐storage molecules, were characterized by using X‐ray crystallography and NMR, IR, and UV/Vis spectroscopy. These findings will extend our understanding of the interactions between nitric oxide and cofacially and non‐cofacially arrayed aromatic rings, and we expect them to aid in the design and development of new supramolecular sensors and storage materials for NO with high capacity and efficacy.     

Unexpected effect of charge density of the aromatic guests on the stability of calix[6]arene-phenol host-guest complexes

The pi-pi interaction-based inclusion complexation of calix[6]arene hexasulfonate as host with neutral aromatic guest molecules was studied in aqueous media. To vary the electron density on the guest's aromatic rings, the phenol parent compound was functionalized in the para-position with different electron-withdrawing groups, such as NO2 and Cl, as well as H and CH3 groups. To study the interaction between calixarene and the guests, PL, DSC, and quantum-chemical methods were used. The results indicate 1:1 stoichiometry for all examined host-guest complexes. Although the enthalpy change predicts strong interaction between the host and the guest, the Gibbs free energy change of the complex formation is small, resulting in a relatively low complex stability. This property is due to the high and negative entropy change during the complex formation. Comparing the thermodynamic parameters observed on the series of the guests, we observed a decrease of the enthalpy change when the electron density on the guest's aromatic ring increased. However, the Gibbs free energy and therefore, the stability of the complexes increased when the enthalpy change lowered. These unexpected results are based on the enthalpy-entropy compensation effect and probably due to the quite different entropy change related to the high and low electron density on the aromatic rings of different guest molecules. Using molecular dynamic calculations, a redistribution of the electron density of calixarene rings, followed by the reordering of the solvent molecules, was identified as a background of this unexpected entropy change at molecular level.     

Synthesis of (thia)calix[4]arene oligomers: towards calixarene-based dendrimers

Thiacalix[4]arenes bearing two or four carboxylic functions on the lower rim served as starting compounds for the synthesis of novel calixarene oligomers connected by amidic functions. The cone conformers react smoothly with four molecules of 5-amino-calix[4]arene to yield the corresponding pentakis-calixarenes. On the other hand, because steric hindrance, the 1,3-alternate condenses only with two molecules leading thus to tris-calixarene, possessing a novel type of inherent chirality based on the 25,26-substitution pattern. The title compounds, which connect together ‘classical’ calixarene and thiacalixarene building blocks, represent a first step towards calixarene-based dendritic structures.     

The hydrogen bonding and conformations of p-tert-butylcalix[4]arene as studied by IR spectroscopy and by DFT calculations

IR and far IR spectra of p-tert-butylcalix[4]arene were recorded at various temperatures between 16 and 180 degrees C and spectra of solutions and crystalline solids were obtained. Ab initio density functional calculations gave vibrational frequencies and infrared intensities for four conformers: cone, partial cone, 1,2- and 1,3-alternate. Complete assignments were made for experimental IR spectra of the cone conformer. The bands characteristic for each conformation were defined. It was revealed that O--H stretching low-frequency shift Deltanu in the cone conformation exceeds Deltanu shifts for other conformers. The effect was stipulated by a cooperative interaction of cyclic hydrogen bonds. The obtained spectra-structure correlation can be used for characteristic of calixarenes conformation.     

Complexation of phenols by calix[4]arene Diethers in a low-permittivity solvent. Self-switched complexation by 25,27-Dibenzyloxycalix[4]arene

To improve the selectivity of sensing, the thermodynamics of the complex formation of some calix[4]arene hosts with neutral phenol guests was studied in carbon tetrachloride as nonpolar solvent. The molecular shape of calixarenes was varied by the selective functionalization with tBu and O-CH2-Ph (O-benzyl) or OPr groups at the upper and lower rim, respectively. To vary the electron density on the guest's aromatic rings, the parent phenol was functionalized in the para position with electron-withdrawing Cl, as well as H, and electron-releasing CH3 and tBu groups. To study the interaction between calixarene and the guests, PL and quantum-chemical methods were applied. The results revealed an overall 1:1 complex stoichiometry except for the parent dibenzyloxycalix[4]arene, where 1:2 host-guest stoichiometries were observed irrespective of the quality of phenol. In the latter case, the complex formation shows a self-switched character: the first phenol molecule is included in the calixarene cavity, and only afterward, a second guest molecule is bound by the two benzyloxy aromatics. Although the enthalpy change predicts strong interaction between the host and the guest, the Gibbs free energy change of the complex formation is small, resulting in a relatively low complex stability. The solvent-relaxation measurements support that the unexpected entropy change could be the consequence of the reorientation of solvent molecules around the calixarene building block. The reorientation is assisted by dispersive forces between solute and solvent molecules. IR and RAMAN analysis of the complexes exclude a considerable participation of the phenolic OH group in the stabilization of the complex. This result is in agreement with earlier findings where deterministic role of pi-pi interaction in the complex stability was assumed.     

Binding mechanisms of nano-baskets toward alkali metals

Thirty-four nano-basket derivatives of di-ionizable calix[4]arene conformers in nine scaffolds bearing two pendant groups of N-(R)-sulfonyl carboxamides were synthesized and examined using isothermal titration calorimetry. The binding mechanisms of synthesized conformers toward alkali metal cations were evaluated and two main interactions were assessed including cation?C?? interaction between alkali metal and the aromatic unit of conformer as well as the strong binding ion?Cdipole interaction between nitrogen atoms in the pendant groups and alkali cation. The ITC data revealed that the bindings of cone and partial-cone conformers toward alkali metal cations exhibited one-step mechanism, while both 1,2 alternate conformer bounds the alkali metal cations in a two-step mechanism.     

Simulations of p-tert-butylcalix[4]arene with multiple occupancies of small guest molecules

Classical molecular dynamics simulations were used to study low-density beta(0)-phase p-tert-butylcalix[4]arene inclusion compounds with multiple calix occupancies of xenon, carbon dioxide, methane, and hydrogen guest molecules with guest-host ratios ranging from 1:4 to 4:1. Custom parameterized force fields were used for the guests and the AMBER force field for the calixarene units was validated in our previous work (Chem. Eur. J. 2006, 12, 5231). The inclusion energy and unit cell volume of the calixarene inclusion compound were determined for various guest occupancies and for occupancies greater than 1:1, strong guest-guest interaction effects are observed. The structure and energetics of the 2:1 CO(2)/beta(0)-phase inclusion compound were compared to those of the low-temperature 2:1 CO(2)/calixarene in which the guest molecules occupy both cage and interstitial sites.     

Chiral conformations induced by cyclodextrin

Studies of chiroptical properties need separation or at least enrichment of enantiomers. The separation is difficult with chiral conformers of molecules with very low barriers of internal rotation. However, in association with cyclodextrin, these labile molecules can exhibit a strong Cotton effect in solution: one chiral conformer is favoured by complexation. The cyclodextrins have the advantage to yield inclusion complex in solution as well as crystalline clathrates. Therefore, the absolute configuration of the guest can be obtained by determining the structure of the cyclodextrin. In this work, the first CD spectrum of 4-helicene is recorded and crystal structures of several clathrates of labile molecules are studied.     

Cationic recognition by tert-butylcalix[4]arene-functionalized nanoprobes

A nanoparticle-based strategy has been demonstrated using structurally-tailored tert-butylcalixarenes immobilized on gold nanoparticles to tune the guest access to the calixarene cone cavity for cationic recognition. This strategy exploits the interparticle charge-induced aggregation upon selective capture of metal cations into the nanoparticle-immobilized tert-butylcalixarenes, which produces calorimetric changes for the detection. A possible pathway for the binding of M(n+) into the t-BCA structure and the interparticle interaction is proposed for the formation of an electric double layer inducing the interparticle association responsible for the red-shifted surface plasmon resonance band of the nanoparticles. The value of this class of calorimetric nanoprobes will be in the area of designing advanced host-guest probes using a variety of calixarene ligands for ionic recognition in a simplistic detection format.     

Selective binding behaviors of p-sulfonatocalixarenes in aqueous solution

The complex structures, binding abilities, molecular selectivities, and thermodynamic origin of p-sulfonatocalixarenes upon complexation with kinds of guests are outlined in this review article, including inorganic cations, organic ammonium cations, pyridiniums and viologens, neutral organic molecules, dye molecules, and others. Calorimetric and spectroscopic investigations afford the complex stability constants, thermodynamic parameters and binding manners of the inclusion complexation of p-sulfonatocalixarenes with guest molecules. The π-stacking, hydrophobic and charge interactions are the main driving-forces during the course of the host–guest inclusion complexation. The molecular binding abilities and selectivities are influenced by not only the frameworks of calixarene cavities, structures of guest molecules, and their binding manners but also the conditions of solutions (mainly pH), which are discussed from the correlation between the structural features and molecular-recognition abilities. Moreover, the further applications and potentials of p-sulfonatocalixarenes are briefly described.     

Many-body interaction in glycine-(water)3 complex using density functional theory method

Various configurations were investigated to find the most stable structures of glycine-(water)3 complex. Five different optimized conformers of glycine-(water)3 complex are obtained from density functional theory calculations using 6-311++G* basis set. Relaxation energy and many body interaction energies (two, three, and four body) are also calculated for these conformers. Out of the five conformers, the most stable conformer has the BSSE corrected total energy -513.917 967 7 Hartree and binding energy -27.28 Kcal/mol. It has been found that the relaxation energies, two body energies and three body energies have significant contribution to the total binding energy whereas four body energies are very small. The chemical hardness and chemical potential also confirmed the stability of the conformer having lowest total energy.     

DME构象的ADF研究

用ＡＤＦ方法对游离状态下的１,２－二甲氧基乙烷（ＤＭＥ）的构象进行了研究。结果表明,能量最低的３种构象ｔｇｇ,’ｔｇｔ,ｔｔｔ的能量相近,其中ｔｔｔ不是能量最低的构象,而且说明ＤＭＥ在气态、液态、固态和游离状态下分别采用哪种构象为最优构象,除了与构象的能量有关外,还受分子间相互作用及分子的对称性是否适合于紧密堆积的影响。     

Molecular conformational structures of 2-fluorobenzoyl chloride, 2-chlorobenzoyl chloride, and 2-bromobenzoyl chloride by gas electron diffraction and normal coordinate analysis aided by quantum chemical calculations

The gas phase molecular structures and conformational compositions of 2-fluorobenzoyl chloride, 2-chlorobenzoyl chloride, and 2-bromobenzoyl chloride have been investigated using gas electron diffraction data obtained from experiments performed in the laboratories of the University of Oslo and Oregon State University. The refinements on the experimental data have been aided by normal coordinate calculations as well as extensive ab initio molecular orbital and density functional theory calculations up to the levels of MP4(SDQ) and B3LYP with larger basis sets up to the level of 6-311 + G(2d,p) for the computed molecular geometries, electronic energies, vibrational zero-point energies and entropy corrections, gas mixture conformational compositions, and MP2(fc) quantum mechanical force fields. The three title molecules each exist in the gas phase as two stable non-planar conformers anti and gauche with respect to the halogen atom positions with anti the lower energy conformer in each case. Among the three title molecules there have been found considerable experimental and theoretical support for several trends in molecular or conformational behavior with increasing ortho halogen atomic size: An increasing although disputable trend in the C=O bond distance values; an increasing trend in the average phenyl ring C–C bond distance values; an increasing trend in the contribution of the gauche conformer to the gaseous mixture lowering the standard free energy difference values (ΔG ^o) correspondingly; and an increasing deviation from full planarity (C _s symmetry) in both the anti and the gauche conformers of the title molecules with increasing ortho halogen atomic size. Only in the anti conformer of 2-fluorobenzoyl chloride does the experimental data refinements suggest close to full planarity for these 2-halobenzoyl chloride molecules.     

Potential energy distributions and potential scans for the internal rotation of two rotors in 3,3-dichloro and 3,3,3-trichloropropanals.

The conformational behavior and structural stability of 3,3-dichloropropanal and 3,3,3-trichloropropanal were investigated by ab initio calculations. The 6-311 + + G** basis set was employed to include polarization and diffuse functions in the calculations at B3LYP level. From the calculation, the trans conformer of 3,3,3-trichloropropanal was predicted to be the predominant conformer with about 2 kcal mol(-1) of energy lower than the cis form. Additionally, 3,3 dichloro-propanal was predicted to exist as a mixture of three stable conformers. The potential function scans were calculated for the two molecules from which the rotational barriers could be estimated. The vibrational frequencies were computed at B3LYP level and complete vibrational assignments were made based on normal coordinate calculations for the conformers of the two molecules. Vibrational Raman and infrared spectra of the mixture of the stable conformers were computed at 300 K.     

含杯芳烃聚合物的合成与应用

杯芳烃在主客体化学中是继冠醚和环糊精之后被广泛关注的第三代主体分子,能够选择性地与客体分子或离子形成络合物。近年来,含杯芳烃聚合物逐渐受到人们的重视。结合聚合物稳定性好,易于加工的特性,含杯芳烃聚合物将有望被开发成为新型功能高分子材料。本文详细介绍了含杯芳烃聚合物的合成及其应用。     

Calorimetric, NMR, and UV Investigations of Aliphatic l-Amino Acids Complexation by Calix[4]arene Bis-hydroxymethylphosphous Acid

The stability constants, enthalpy ΔH ⁰, entropy ΔS ⁰, and Gibbs energy ΔG ⁰ were determined for the host–guest complexes (1:1) of calix[4]arene bis-hydroxymethylphosphous acid with glycine, l-alanine, l-valine, l-leucine, l-isoleucine residues in methanol solution with the aid of the titration experiments followed by calorimetric and spectroscopic (¹H NMR, UV) methods. The experimental data indicated that the host–guest complexation was under control of the direct electrostatic interaction between negatively charged calixarene phosphoryl group and amino acid residue NH ₃ ⁺ group, modulated by the hydrophobic interaction, which drive the inclusion of the residue alkyl side-chain into the calixarene cavity. The stability of the inclusion complexes was found correlated with the size of the aliphatic amino acid’s side-chain. The experimental data were additionally analyzed in the terms of the three state model corresponding to coexistence of 2:1 and 1:1 complexation equilibria.     

Calix[6]arene-based cuprous "funnel complexes": a mimic for the substrate access channel to metalloenzyme active sites

Two calixarene-based model systems (a and b) for monocopper enzymes are compared. Both present a tris(pyridine) coordination site for Cu that mimics the imidazole-rich neutral binding site in enzymes. Upon reaction with 1 equiv of copper(I), the tridentate ligands gave rise to ill-defined unsymmetrical complexes. However, in the presence of an organonitrile RCN (R = Me, Et, Ph), tetrahedral species were obtained, with the nitrilo ligand included in the calixarene hydrophobic cone. System b presents a larger cavity than system a, with a wider opening thanks to the removal of three tBu groups from the calixarene structure. As a result, the recognition pattern for MeCN vs PhCN is inverted, and the relative affinity constants differ by 3 orders of magnitude. The mechanism of the acetonitrile exchange at the cuprous centers was studied by (1)H NMR spectroscopy. Thermodynamic and kinetic data show that it follows a dissociative pathway in both cases. The main differences between systems a and b stem from the presence of a door that entraps the guest in case a. In system b indeed, the removal of three calixarene tBu groups led to a 100-fold acceleration of the MeCN exchange rate. Hence, these supramolecular systems provide a rare and interesting model for the hydrophobic substrate channel giving access to a metalloenzyme active site.     

Vibrational analysis of n-butyl, isobutyl, sec-butyl and tert-butyl nitrite

Raman and infrared spectra of n-butyl, isobutyl, sec-butyl and tert-butyl nitrite are reported. Density functional theory and M?eller-Plesset calculations with 6-31G* and 6-311G* basis sets were used to determine ground state molecular geometries and vibrational frequencies of these compounds. Calculations and spectral data of these molecules were used to perform partial vibrational mode assignments for the observed transitions. In agreement with previous investigations of alkyl nitrites, cis and trans rotational conformers of n-butyl, isobutyl and sec-butyl nitrite were observed in the gas phase infrared spectra and the condensed phase Raman and infrared spectra. Among the several predicted geometries of these compounds, the cis-trans geometry (cis with respect to the C-O-N=O dihedral angle and trans with respect to the C-C-O-N dihedral) was calculated to be the most stable conformer of n-butyl and isobutyl nitrite, while the cis-gauche conformer was found to be the most stable geometry of sec-butyl nitrite. The cis-type structures of these three molecules are favored due to formation of a pseudo hydrogen bond between the nitrite group and the alpha-carbon hydrogen atoms. Hindrance with the alkyl moiety, however, causes the trans conformer (trans with respect to the C-O-N=O dihedral) of tert-butyl nitrite to lie lower than its cis conformer, a result that was supported by our spectroscopic measurements. The characteristic N=O stretch frequency for the trans conformers of all the compounds examined was observed to decrease with increasing branching at the alpha-carbon, while the same mode for the cis conformers shows no change among the primary and secondary nitrites. Evidence is also provided that suggests that the relative number of cis conformers to trans conformers decreases as the alpha-carbon branching increases.     

First enantiopure calix[6]aza-cryptand: synthesis and chiral recognition properties towards neutral molecules

The synthesis of the first enantiopure calix[6]aza-cryptand was achieved in five steps from the known 1,3,5-tris-O-methylated calix[6]arene. A ¹H NMR spectroscopic study has shown that the chiral tren cap constrains the calixarene core in a straight cone conformation ideal for host–guest chemistry applications. As a result, the tetra-protonated derivative displays remarkable host properties towards polar neutral molecules and enantioselective recognition processes have been evidenced with chiral guests.