Host–Guest Chemistry in the Gas Phase: Complex Formation of Cucurbit[6]uril with Proton-bound Water Dimer

The hydration of cucurbit[6]uril (CB[6]) in the gas phase is investigated using electrospray ionization traveling wave ion mobility mass spectrometry (ESI-TWIM-MS). Highly abundant dihydrated and tetrahydrated species of diprotonated CB[6] are found in the ESI-TWIM-MS spectrum. The hydration patterns of the CB[6] ion and the dissociation patterns of the hydrated CB[6] ion indicate that two water molecules are bound to each other, forming a water dimer in the CB[6] complex. Ion mobility studies combined with the structures calculated by density functional theory suggest that the proton-bound water dimer is present as a Zundel-like structure in the CB[6] portal, forming a hydrogen bond network with carbonyl groups of the CB[6]. When a large guest molecule is bound to a CB[6] portal, water molecules cannot bind to the portal. In addition, the strong binding energy of the water dimer blocks the portal, hindering the insertion of the long alkyl chain of the guest molecule into the CB[6] cavity. With small alkali metal cations, such as Li⁺ and Na⁺, a single water molecule interacts with the CB[6] portal, forming hydrogen bonds with the carbonyl groups of CB[6]. A highly stable Zundel-like structure of the proton-bound water dimer or a metal-bound water molecule at the CB[6] portal is suggested as an initial hydration process for CB[6], which is only dissolved in aqueous solution with acid or alkali metal ions.

Supramolecular Photocatalysis by Utilizing the Host–Guest Charge-Transfer Interaction: Visible-Light-Induced Generation of Triplet Anthracenes for [4+2] Cycloaddition Reactions

Supramolecular photocatalysis via charge-transfer excitation of a host–guest complex was developed by use of the macrocyclic boronic ester [2+2]_BTH-F containing highly electron-deficient difluorobenzothiadiazole moieties. In the presence of a catalytic amount of [2+2]_BTH-F, the triplet excited state of anthracene was generated from the charge-transfer excited state of anthracene@[2+2]_BTH-F by visible-light irradiation, and cycloaddition of the excited anthracene with several dienes and alkenes proceeded in a [4+2] manner in high yields.     

Study on the Inclusion Complex of C_(60) and Calix[8]arene Tetraphenyl Ether

Fullerenehasgeneratedarapidlygrowingandactiveresearchareal.InclusioncomplexesoffullerenehavebeenpreparedforCoowithavarietyofhostsystemsincludingcalixarenes,cyclotriveratrylene,andy-cyclodextrin.TheselectiveformationofaclathratefromCooandcall-c[8]areneswasexcellentlyutilizedfortheseparationofCooandC,,'.HereinwereportthatCoocanbeincludedinthecavityofanewkindoffunctionnedcalixlslarene,p-tert-butylcall-c[8]arenetetraphenylether(1).ThefixtureofCooand1(lfZmolarratio)wasrefluxedintoluenefor2--3h,d…     

Host–Guest Complexation Using Pillar[5]arene Crystals: Crystal-Structure Dependent Uptake,Release, and Molecular Dynamics of an Alkane Guest

Host–guest complexation has been mainly investigated in solution, and it is unclear how guest molecules access the assembled structures of host and dynamics of guest molecules in the crystal state. In this study, we studied the uptake, release, and molecular dynamics of n-hexane vapor in the crystal state of pillar[5]arenes bearing different substituents. Pillar[5]arene bearing 10 ethyl groups yielded a crystal structure of herringbone-type 1:1 complexes with n-hexane, whereas pillar[5]arene with 10 allyl groups formed 1:1 complexes featuring a one-dimensional (1D) channel structure. For pillar[5]arene bearing 10 benzyl groups, one molecule of n-hexane was located in the cavity of pillar[5]arene, and another n-hexane molecule was located outside of the cavity between two pillar[5]arenes. The substituent-dependent differences in molecular arrangement influenced the uptake, release, and molecular dynamics of the n-hexane guest. The substituent effects were not observed in host–guest chemistry in solution, and these features are unique for the crystal state host–guest chemistry of pillar[5]arenes.     

Interaction of the t-butylcalix[4]arene Anion with Ammonium Cations in Acetonitrile: Host–Guest Complexes or exo Counterions? A Molecular Dynamics Investigation

We report a theoretical study of the NR4+salts (R = H; Me; Et) of the t-butylcalix[4]arenemonooxyanion L- inacetonitrile solution, to compare the endocomplexes NR4+ inside the cone of thehost) with the exo ones. For a given cation, wefind that the complexes display structures of similartype in the gas phase and in acetonitrile solution.Intrinsically, the endo forms are more stablethan exo ones, but they are less well solvated.As a result, exo complexes are predicted to bemore stable than the endo ones in acetonitrile.In the gas phase and in solution, the exocomplexes of NMe4+ and NEt4+display interesting examples of fluctional intimateion pairs, where the cation oscillates between theoxygen lower rim region of L- and exo stacking with the phenolic rings ofL-. Based on free energy perturbation calculations,we compare endo NH4+/NMe4+complexes and find that the hypotheticalNH4+ complex is more stable in acetonitrile solution.     

Synthesis and Crystal Structure of Complex of Sodium Perrhenate with Tetraethyl p-tert-Butylcalix[4]arene Tetraacetate

Recently,theconformationofthecalixarenehasbeenshowntobeimportantincontrollingtheseIectivityofthereceptor.Forexample,sodiumioncouldbeboundverystronglybyesterderivativesofcalix[4]areneintheconeconformationl.Wehavefoundthatinthepresenceofcertainamountofsodiumion,microamountofReO4-canbequantitativelyextractedintol,2-dichloroethanebytheligandtetraethylp-tert-butylcalix[4]arenetetraacetate(L).ItshowsthatthepresenceofNa inaqueoussolutioncanpromotetheformationofhydrophobiccomplex[NaL] .ReO'-whichc…     

Host–guest association of Morin with β-CD and C-hexylpyrogallol[4]arene: Structure of the complexes and the effect of pH

The study of the host–guest association of Morin hydrate (MO) with β-cyclodextrin (β-CD) and C-hexylpyrogllol[4]arene (C-HPA) is reported in this paper. The iInclusion complexation of MO is studied by ultraviolet-visible, steady-state fluorescence, time-resolved fluorescence, ¹H nuclear magnetic resonance (NMR), and two dimentional rotating-frame nuclear overhauser effect correlation (2D ROESY) spectroscopic techniques. The stoichiometry and the binding constant for the MO–β-CD complex are derived from the linearity of the Benesi–Hildebrand equation. The binding constant for the MO–C-HPA complex is calculated from the nonlinear curve fitting of fluorescence intensities. The effects of the acid strength on the absorption and fluorescence spectra of MO are studied in the absence and the presence of β-CD/C-HPA host molecules. The pK _a values of the ground and the excited states are reported.     

Effect of the Composition of the Water–Dimethyl Sulfoxide Solvent on the Thermodynamics of the Formation of the [Ag(18-Crown-6)]+Complex

The effect of a water–dimethyl sulfoxide solvent (X _DMSO= 0–0.97, where X _DMSOis the mole fraction of DMSO) on the thermodynamics of complexation between Ag⁺and 18-crown-6 and the solvation of all reagents involved in this equilibrium were studied. In aqueous solutions, the complex is stable mainly because of the enthalpy contribution to _r G°. For X _DMSO> 0.3, the contributions from entropy and enthalpy become comparable in magnitude, but they are opposite in sign. In the binary solvent, the complex is most stable at X _DMSO= 0.2 to 0.3. Analysis of the enthalpy characteristics of reagent solvation showed that this solvent effect was due to the superposition of two opposite solvation contributions occurring with an increase in the DMSO concentration in the binary solvent, namely, the destabilization of the ligand solvate sphere and the formation of stable Ag⁺complexes with DMSO.     

Smart Materials Based on Synthetic Host Molecules: The Role of Host–Guest Chemistry in the Fabrication and Application

Stimuli-responsive or smart materials have recently shown a significant impact on the frontier of material science and engineering. The exponential development of synthetic host molecules (SHMs) over the last decades and their corresponding host–guest chemistry, have empowered researchers with new opportunities to design and construct tailored or guest-specific smart materials. In this Minireview, we present the recent advancements in synthetic host based smart materials, ranging from the fabrication strategies to the state-of-art applications including adsorption, separation, luminescence, self-healing and actuation. The role that the host–guest chemistry plays in these systems is highlighted throughout to give a better prospective of the available possibilities for emerging materials of future economies.     

Effect of the Loading of Metal Salts on the Formation of Fe–Co Solid Solution Nanoparticles in the IR-Pyrolyzed Chitosan Matrix

Russian Journal of General Chemistry - In this study, metal-carbon nanocomposites have been synthesized via the method of simultaneous formation of bimetallic Fe–Co nanoparticles and carbon...     

Formation of Diazepam–Lanthanides(III) Complexes in the 50–50 Volume % Ethanol–Water Solvent System and Study of the Effect of Temperature on the Complex Formation Constants

Diazepam (7-chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one) is an important derivative of the 1,4-benzodiazepine compound commercially distributed as Valium. The complex formation constants of diazepam with some light lanthanide(III) metal ions have been studied by potentiometric measurements. All titrations were performed in 50–50% (volume/volume) ethanol–water solvent mixtures at constant ionic strength (0.10 mol⋅dm⁻³). The ionic strength was maintained by using sodium perchlorate. The complex formation constants were determined at 25.00, 35.00 and 45.00 °C. With increasing temperature, a decrease was observed in the protonation constant (pK) of diazepam.     

Structure–Properties Relations in Werner β-[Ni(NCS)2(4-MePy)4] Clathrates. Part 2. Host–Host Interactions as a Function of the Guest Molecular Size and Shape and the Amount of Absorbed Guest Compound

Careful analysis of changes in the geometry of the host lattice structure on inclusion of different guest molecules was performed for 11 -[Ni(NCS)₂(4-methylpyridine)₄] clathrates reported in the literature, and specific features were established for the geometry of the host crystal lattice structure, which are characteristic for different modes of location of the guest molecules. A new method is suggested for the analysis of the volume and shape of the empty space in clathrates. Experimental data are reported on the dependence of the a and c parameters of the unit cell of clathrate phases (with furan and dichloromethane as guest components) from the guest uptake. Consideration of these data permit us to construct a model of the changes of host–host interactions in the -[Ni(NCS)₂(4-methylpyridine)₄] clathrates with change of guest uptakes. Modeling of the process of diffusion of the guest molecule through the channel of the -[Ni(NCS)₂(4-methylpyridine)₄] clathrate allowed the nature of the rate-determining step of diffusion to be established. Part 1 of this series has been published as [3].     

Effect of Water–Ethanol Solvents on the Protonation Constants of Cryptand[2.2.2]

The protonation constants of cryptand[2.2.2] are determined potentiometrically at 298 K in water–ethanol solvents of variable composition. An increase in the concentration of a solution’s nonaqueous component reduces the equilibrium constants of the reactions of mono- and biprotonated cryptand[2.2.2] formation. The contribution from the resolvation of reagents to the change in the Gibbs energy of the studied reactions is estimated. The reduction in the protonation constants of cryptand[2.2.2] in water–ethanol solvents is mainly due to enhancement of the solvation of protons in water–ethanol mixtures.     

A,C-Bridged Calix[6]arene： Relationship between the Length of Bridge and Conformation

Three new A,C-diamide bridged p-tert-butylcalix[6]arenes were synthesized from p-tert-butylcalix[6]arenes by bridging ClCH2CONH(CH2)nNHCOCH2Cl(n=3,4,6) in acetonitrile using K2CO3 as a base in 17%-25% yields.It was found that the bridged calix[6]arenes with shorter bridges (n=2,3,4 in N′,N′-bischloroacetodiamines) adopt cone conformation, but the last one (n=6) adopts alternate conformation, i.e., accompanying the lengthening of bridge, the conformation of A,C-bridged calix[6]arenes changes from cone to alternate.     

Synthesis and Complexation Abilities of Novel Multiple-Sites Calix[4]arene Receptors: Calix[4]arene Derivatives with Anthraquinone Groups on Lower Rims and Hydrazone Groups on Upper Rims

By formylation of 1,3-bisubstituted calix[4]arene anthraquinone derivative 1 in hexamethylenetetramine/trifluoroacetic acid system, the corresponding formylated gecalix[4]arene anthraquinone derivative 2 was synthesized in yield of 63%. By further reacting compound 2 with salicylic hydrazide, 2,4-dinitrophenyl hydrazine, nicotinyl hydrazine or phenyl thiosemicarhazide, novel calix[4]arene derivatives with anthraquinone and hydrazone groups 3a–3d were obtained in yields of 74–83%. The extracting experiments for series of metallic cations showed that compounds 3a–3d possessed high extracting abilities and extracting selectivity for tested cations. The complexation UV-Vis spectra for a series of anions indicated compounds 3a–3d exhibited the strong complexation abilities for tested anions. The ¹H-NMR titration study showed that compound 3d possessed excellent complexation abilities for ion-pair of NaH₂PO₄ in 1:1 host-guest complex with the association constant of 4.6 × 10⁴ M^?1.     

Effect of a Nitrogen-Containing Base on the Kinetics of Formation of the Zinc–Octa(m-trifluoromethylphenyl)porphyrazine Complex in Benzene

Russian Journal of Physical Chemistry A - The effect additions of n-butylamine, tert-butylamine, piperidine, and morpholine have on the kinetics of the complexation of zinc acetate with...     

Effect of cationic and anionic surfactants on the addition–elimination-type interaction between o-toluidine and d-glucose

The kinetics of the o-toluidine–d-glucose reaction has been studied as a function of [o-toluidine], [d-glucose], [acetic acid], and temperature by UV–visible spectrophotometry at 630 nm in the absence and presence of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). The reaction follows second-order kinetics, being unity in each of the reactants in both media. The effect of added surfactants has also been investigated. The model of micellar catalysis, such as the Menger–Portony model modified by Bunton, is applied to explain the catalytic role of CTAB and SDS micelles. The association/incorporation constants (K _s and K _n), the rate constant in micellar media (k _m), and the activation parameters of this system have been calculated and discussed. The value of the rate constant is found to be higher in SDS than in CTAB. Hydrophobic and electrostatic interactions are responsible for higher reaction rates in SDS. From all observed facts, a reaction mechanism involving a nucleophilic addition–elimination path has been suggested.     

Separation of Phenolic Compounds and Organic Anions Using ODS Column Coated with Meso-octamethylcalix[4]pyrrole and Water as Eluent

Octadecylsilanized silica (ODS) was coated with meso-octarnethylcalix[4]pyrrole to obtain a novel calix[4]pyrrole containing stationary phase for HPLC. Compared to ODS, the new stationary phase showed a relatively large retention and an improved separation for phenolic compounds and organic anions, using pure water as mobile phase. The results can be ascribed to the interaction between analytes and calix[4]pyrrole.