Artículos de revistas: "Host and Guest Molecules"

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Malinska, Maura. "Insights into molecular recognition from the crystal structures of p-tert-butylcalix[6]arene complexed with different solvents". IUCrJ 9, n.º 1 (16 de noviembre de 2021): 55–64. http://dx.doi.org/10.1107/s2052252521010678.

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Calixarenes are host molecules that can form complexes with one or more guest molecules, and molecular recognition in calixarenes can be affected by many factors. With a view to establishing molecular recognition rules, the host p-tert-butylcalix[6]arene (TBC6) was crystallized with different guest molecules (cyclohexane, anisole, heptane, toluene, benzene, methyl acetate, ethyl acetate, dichloromethane, tetrahydrofuran and pyridine) and the obtained structures were characterized by X-ray diffraction. With most solvents, 1:1 and/or 1:3 host–guest complexes were formed, although other stoichiometries were also observed with small guest molecules, and crystallization from ethyl acetate produced the unsolvated form. The calculated fill percentage of the TBC6 cavity was ∼55% for apolar guests and significantly lower for polar solvents, indicating that polar molecules can bind to apolar cavities with significantly lower packing coefficients. The most stable crystals were formed by 1:1 host–guest inclusion complexes. The ratio between the apolar surface area and the volume was used to predict the formation of inclusion versus exclusion complexes, with inclusion complexes observed at ratios <40. These findings allow the binding of potential guest molecules to be predicted and a suitable crystal packing for the designed properties to be obtained.

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2

Meier, Herbert, Elena Karpouk, Matthias Lehmann, Dieter Schollmeyer y Volker Enkelmann. "Guest-Host Systems of 1,3,5-Tristyrylbenzenes". Zeitschrift für Naturforschung B 58, n.º 8 (1 de agosto de 2003): 775–81. http://dx.doi.org/10.1515/znb-2003-0809.

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(E,E,E)-1,3,5-Tris(3,4,5-trimethoxystyryl)benzene (1a) forms monoclinic crystals of the space group P21/c. Incorporation of three transoid diacetyl guest molecules between the three arms leads to triclinic crystals of the space group P1. The styryl groups, originally present in a nonsymmetrical conformation, are simultaneously transformed to a C3 arrangement. (E,E,E)-1,3,5-Tris- (3,4,5-tripropoxystyryl)benzene (1b) forms monoclinic crystals of the space group P21/c. The C3 arrangement of the styryl groups is present in the first, the unsymmetrical arrangement in the second modification. Incorporation of two acetone guests in the largest and the middle-sized angle space between the styryl arms in the unsymmetrical arrangement, leads to monoclinic crystals of the space group P21/n. The third (smallest) angle space is filled with a propoxy chain of the neighboring molecule. The pure host crystals show significant deviations from planarity which are strongly reduced by the incorporation of the guest molecules.

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3

Ahn, Yun-Ho, Byeonggwan Lee y Kyuchul Shin. "Structural Identification of Binary Tetrahydrofuran + O2 and 3-Hydroxytetrahydrofuran + O2 Clathrate Hydrates by Rietveld Analysis with Direct Space Method". Crystals 8, n.º 8 (18 de agosto de 2018): 328. http://dx.doi.org/10.3390/cryst8080328.

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The structural determination of clathrate hydrates, nonstoichiometric crystalline host-guest materials, is challenging because of the dynamical disorder and partial cage occupancies of the guest molecules. The application of direct space methods with Rietveld analysis can determine the powder X-ray diffraction (PXRD) patterns of clathrates. Here, we conducted Rietveld analysis with the direct space method for the structural determination of binary tetrahydrofuran (THF) + O2 and 3-hydroxytetrahydrofuran (3-OH THF) + O2 clathrate hydrates in order to identify the hydroxyl substituent effect on interactions between the host framework and the cyclic ether guest molecules. The refined PXRD results reveal that the hydroxyl groups are hydrogen-bonded to host hexagonal rings of water molecules in the 51264 cage, while any evidences of hydrogen bonding between THF guests and the host framework were not observed from PXRD at 100 K. This guest-host hydrogen bonding is thought to induce slightly larger 512 cages in the 3-OH THF hydrate than those in the THF hydrate. Consequently, the disorder dynamics of the secondary guest molecules also can be affected by the hydrogen bonding of larger guest molecules. The structural information of binary clathrate hydrates reported here can improve the understanding of the host-guest interactions occurring in clathrate hydrates and the specialized methodologies for crystal structure determination of clathrate hydrates.

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4

Lee, Rachael, Michael Probert y Jonathon Steed. "The changeable nature of urea inclusion compounds." Acta Crystallographica Section A Foundations and Advances 70, a1 (5 de agosto de 2014): C1706. http://dx.doi.org/10.1107/s205327331408293x.

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Urea inclusion compounds (UICs), the β-phase of urea, have been known only since 1949 and have revealed various structural and behavioural characteristics of interest, largely influenced by the type of guest molecule present in the crystal. These structures have a hexagonally symmetrical honeycomb structure of a hydrogen-bonded urea network encapsulating the guest molecules, a defining motif of these clathrates. The simplest of this class contains an alkane guest (C7-C20), creating an incommensurate relationship between host and guest and a significantly disordered crystal structure with respect to the guest. As a result, diffuse scattering is typical in the diffraction patterns of UICs. As the guest molecules are altered, so too is the behaviour of the host network. With certain dihaloalkanes for example, the guest may coil into an atypical conformation in order to present a commensurate relationship with the host. This increase in guest order creates a distortion of the host network away from hexagonal symmetry, creating an internal stress which causes domain switching within the system. A number of different effects such as this can be seen on changing the guest molecule, ferroelasticity being an example for certain diketone guests. In this work we are exploring examples of UICs which, due to unusual interaction between the host and guest, display atypical structural features, symmetry or behaviour. These crystal structures are under investigation at a range of temperatures and pressures, by both X-ray and neutron diffraction techniques in order to fully understand the nature and bonding of UICs.

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5

Facey, Glenn A. y Ilia Korobkov. "Investigation of the disorder of dibromo- and dichloromethane in their tri-ortho-thymotide clathrates using X-ray diffraction and solid-state 2H NMR spectroscopy". Canadian Journal of Chemistry 89, n.º 7 (julio de 2011): 854–62. http://dx.doi.org/10.1139/v10-178.

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The tri-ortho-thymotide (TOT) clathrates of dibromo- and dichloromethane were characterized by single crystal X-ray diffraction at 200 K and solid-state 2H NMR spectroscopy as a function of temperature. The host structure was found to be typical of other cage-type TOT clathrates. The X-ray results showed a substantial amount of disorder among the guest molecules. In both clathrates, multiple guest molecule positions could be modeled. The heavy atoms of all the guest molecule positions lie approximately in the same plane, with some out-of-plane distortion. The guest molecules were of two different types in positions symmetric about the crystallographic twofold rotation axis: type A guests, with carbon atoms well removed from the crystallographic twofold axis, and type B guests, with carbon atoms very close to the twofold axis. The 2H NMR spectra for the guests confirmed that the disorder was dynamic. The experimental results could be accounted for by the presence of three simultaneous types of molecular motion, all fast with respect to the 2H quadrupolar interaction: (i) twofold molecular flips about the molecular C2 symmetry axis, (ii) exchange between the type A and type B sites in a single plane, and (iii) a two-site libration of the plane containing the heavy atoms of the A and B guest sites with a temperature-dependent amplitude.

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6

Mustafa, Siti Fatimah Zaharah, Hasmerya Maarof, Mohammed Abu Naser, Hassan H. Abdallah, Ahmad Irfan y Rashid Ahmed. "Behavioral pattern exploration of single guest, hexadecane-1,16-diol and hexadecane in urea inclusion compounds via molecular dynamics simulation". Journal of Theoretical and Computational Chemistry 15, n.º 06 (septiembre de 2016): 1650047. http://dx.doi.org/10.1142/s0219633616500474.

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The urea inclusion compounds, a unique polar organic crystalline complex, are considered as a potential candidate for a molecular separator of long chain alkane molecule. A well-defined structure of the crystalline channel systems constructed from hydrogen bonding arrangement of the urea molecules, can be used to understand the fundamental aspects of the processes involving ions or molecules transportation. To do so, in our work, molecular dynamics approach is implemented to understand the behavioral pattern of the hexadecane-1,16-diol and hexadecane guests’ related to translational and rotational orientation along the urea tunnel. Our obtained results reveal that high interaction of hexadecane-1,16-diol with urea host molecules offers a restricted environment inside urea tunnel, resulting in slowing down the guest movement. Hexadecane guest system, on the contrary, exhibits lower interaction whereby the translational and rotational movement is faster. Moreover, as the distance increases (along [Formula: see text]-axis) in the urea tunnel, both guest systems favor a clockwise rotational orientation. Preference of the respected orientation indicates the influence of chiral urea tunnel on achiral guests that is clathrate inside the tunnel structure.

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7

Labuta, Jan, Shinsuke Ishihara, Daniel T. Payne, Kazuyoshi Takimoto, Hisako Sato, Lenka Hanyková, Katsuhiko Ariga y Jonathan P. Hill. "Estimation of Enantiomeric Excess Based on Rapid Host–Guest Exchange". Chemosensors 9, n.º 9 (9 de septiembre de 2021): 259. http://dx.doi.org/10.3390/chemosensors9090259.

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Chiral molecules possess enantiomers that have non-superimposable chemical structures but exhibit identical nuclear magnetic resonance (NMR) spectra. This feature prevents the use of NMR spectroscopic methods for the determination of enantiomeric excesses (ee) of chiral molecules, using simple mixtures of their enantiomers. Recently, however, it was reported that the addition of a symmetrical prochiral molecule (a reporter or host) into a solution of chiral analyte can lead to estimation of ee through interactions involving rapid exchange of the chiral analyte (guest) in the formed host–guest complex. This is due to the ee-dependent splitting of NMR resonances of the prochiral host molecule based on averaging the chemical shift non-equivalency caused by the presence of a chiral guest. The mechanism is not dependent on diastereomer formation, and 1:1 host–guest complexes can also show ee-dependent NMR peak splitting. Prochiral molecules capable of ee sensing using the NMR technique are now referred to as so-called prochiral solvating agents (pro-CSAs). pro-CSAs represent a family of reagents distinct from the commonly used NMR chiral derivatizing reagents (where chiral auxiliaries are used to derivatize enantiomers to diastereomers) or chiral solvating agents (where chiral auxiliaries interact in an asymmetric manner with analyte enantiomers). pro-CSA methods are unique since neither pro-CSA nor NMR contains chiral factors, making the technique neutral with respect to chirality. Here, we review our recent work on this matter involving several different nominally achiral receptor molecules whose unique guest binding properties and solution characteristics (especially with regard to NMR spectroscopy) allow for the estimation of ee in the corresponding chiral guests.

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8

Fu, T. Y., J. R. Scheffer y J. Trotter. "Structures and Photochemistry of Inclusion Compounds of 9,10-Dihydro-9,10-ethenoanthracene-11,12-bis(diphenylmethanol)". Acta Crystallographica Section B Structural Science 53, n.º 2 (1 de abril de 1997): 300–305. http://dx.doi.org/10.1107/s0108768196013614.

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Crystal structures have been determined for inclusion complexes of the host molecule 9,10-dihydro-9,10-ethenoanthracene-11,12-bis(diphenylmethanol), with acetone, ethanol and toluene as guest solvent molecules. The host molecule exhibits an intramolecular O--H...O hydrogen bond in each of the complexes, with intermolecular hydrogen bonds to the acetone and ethanol guests. Different photoproducts are obtained from solution and solid-state photolyses; the solid-state reaction involves a relatively small amount of molecular rearrangement, for which a mechanism is proposed.

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9

Ramaekers, Mellany, Sjors P. W. Wijnands, Joost L. J. van Dongen, Luc Brunsveld y Patricia Y. W. Dankers. "Cucurbit[8]uril templated supramolecular ring structure formation and protein assembly modulation". Chemical Communications 51, n.º 15 (2015): 3147–50. http://dx.doi.org/10.1039/c4cc08917k.

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10

Wang, Xuebin, Jiecheng Ji, Zejiang Liu, Yimin Cai, Jialiang Tang, Yunzhi Shi, Cheng Yang y Lihua Yuan. "Chiroptical Sensing of Amino Acid Derivatives by Host–Guest Complexation with Cyclo[6]aramide". Molecules 26, n.º 13 (2 de julio de 2021): 4064. http://dx.doi.org/10.3390/molecules26134064.

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A hydrogen-bonded (H-bonded) amide macrocycle was found to serve as an effective component in the host–guest assembly for a supramolecular chirality transfer process. Circular dichroism (CD) spectroscopy studies showed that the near-planar macrocycle could produce a CD response when combined with three of the twelve L-α-amino acid esters (all cryptochiral molecules) tested as possible guests. The host–guest complexation between the macrocycle and cationic guests was explored using NMR, revealing the presence of a strong affinity involving the multi-point recognition of guests. This was further corroborated by density functional theory (DFT) calculations. The present work proposes a new strategy for amplifying the CD signals of cryptochiral molecules by means of H-bonded macrocycle-based host–guest association, and is expected to be useful in designing supramolecular chiroptical sensing materials.

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11

Elemans, Johannes A. A. W., Roeland J. M. Nolte y Alan E. Rowan. "Hierarchical self-assembly of a host-guest porphyrin array". Journal of Porphyrins and Phthalocyanines 07, n.º 04 (abril de 2003): 249–54. http://dx.doi.org/10.1142/s1088424603000331.

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The construction of a porphyrin array by a stepwise, hierarchical self-assembly process is described. Four molecular clip host molecules are complexed, in a solid state self-assembly process, to one porphyrin guest molecule. When dissolved in chloroform, the 4:1 host-guest complexes spontaneously self-assemble into an array in which the porphyrins are organized in a cofacial stack. The ensemble is stabilized by a combination of π-π interactions between the porphyrins and between the aromatic surfaces of the host molecules.

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12

Barton, Benita, Ulrich Senekal y Eric C. Hosten. "Comparing the host behaviour of roof-shaped compounds trans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid and its dimethyl ester in the presence of mixtures of xylene and ethylbenzene guests". CrystEngComm 23, n.º 25 (2021): 4560–72. http://dx.doi.org/10.1039/d1ce00594d.

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Each p-Xy guest molecule is surrounded by six dicarboxylic acid host molecules, forming a continuous intermolecular hydrogen-bonded motif through their carboxylic acid functionalities to form a cage-like structure in which the guests are trapped.

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13

Lebedinskiy, Konstantin, Ivan Barvík, Zdeněk Tošner, Ivana Císařová, Jindřich Jindřich y Radim Hrdina. "Spatial arrangements of cyclodextrin host–guest complexes in solution studied by ¹³C NMR and molecular modelling". Beilstein Journal of Organic Chemistry 20 (20 de febrero de 2024): 331–35. http://dx.doi.org/10.3762/bjoc.20.33.

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13C NMR spectroscopic analyses of Cs symmetric guest molecules in the cyclodextrin host cavity, combined with molecular modelling and solid-state X-ray analysis, provides a detailed description of the spatial arrangement of cyclodextrin host–guest complexes in solution. The chiral cavity of the cyclodextrin molecule creates an anisotropic environment for the guest molecule resulting in a splitting of its prochiral carbon signals in 13C NMR spectra. This signal split can be correlated to the distance of the guest atoms from the wall of the host cavity and to the spatial separation of binding sites preferred by pairs of prochiral carbon atoms. These measurements complement traditional solid-state analyses, which rely on the crystallization of host–guest complexes and their crystallographic analysis.

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14

LEE, WONBAE, JUN CHUN, YOON KYUNG CHANG, YOUNG KWAN LIM, CHEON-GYU CHO y HAIWON LEE. "IMMOBILIZATION AND CHARACTERIZATION OF AN ARTIFICIALLY ASSEMBLED TRI-STRAND β-SHEET STRUCTURE ON A RIGID Au(111) SURFACE". International Journal of Nanoscience 05, n.º 06 (diciembre de 2006): 803–8. http://dx.doi.org/10.1142/s0219581x06005182.

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We designed and synthesized diurea type host molecules for the recognition of the tri-peptide guest molecule through the artificial formation of three-strand β-sheet structures on a rigid surface. The immobilizations of those host molecules on Au (111) surface, and the insertion of the guest molecules into the corresponding sites of immobilized host molecules were successfully carried out. Their binding characteristics were monitored by analyzing STM images before and after the insertion of guest peptides, and the characterization of the insertion in bulk phase was accomplished by NMR study.

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15

Suzuki, Akira, Yuya Miyake, Ryoga Shibata y Kazuyuki Takai. "Spin and charge interactions between nanographene host and ferrocene". Beilstein Journal of Organic Chemistry 20 (2 de mayo de 2024): 1011–19. http://dx.doi.org/10.3762/bjoc.20.89.

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Ferrocene (FeCp2) was introduced as a non-magnetic guest molecule to activated carbon fibers (ACFs) as a nanographene-based host having localized spins originating from zigzag edges of graphene. The introduction of the guest molecule was confirmed by FTIR for ACFs-FeCp2 introduced at 55 (150) °C (FeCp2-ACFs-55(150)). The appearance of satellite Fe2p peaks and the increase in shake-up peak intensity of the C1s in the XPS spectrum proved the emergence of charge-transfer host–guest interaction in FeCp2-ACFs-150, supported by the red-shift of the G-band in the Raman spectrum. The six-times enhancement in the spin concentration in FeCp2-ACFs-150 compared with ACFs indicates the spin magnetism of the non-magnetic guest FeCp2+ molecule induced by a charge-transfer host–guest interaction in the nanographene host. The larger ESR linewidth than that expected from the dipolar interaction estimated by the localized spin concentration suggests the exchange interaction between the nanographene and FeCp2 spins. The narrowing of the ESR linewidth of FeCp2-ACFs-55 upon higher excitation microwave power suggests the inhomogeneity of the environment for FeCp2+ molecules in the nanographene host. The observed induction of spin magnetism by the interfacial interactions between the nanographene host and the guest molecules will be a promising strategy for developing a new class of molecular magnets.

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16

Nishikiori, Shinichi, Christopher I. Ratcliffe y John A. Ripmeester. "Molecular motion of guests trapped in N-methyl-1,3-diaminopropanecadmium(II) tetracyanonickelate(II) host lattices". Canadian Journal of Chemistry 71, n.º 11 (1 de noviembre de 1993): 1810–15. http://dx.doi.org/10.1139/v93-225.

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The molecular motion of guest molecules in Cd(mtn)Ni(CN)4•0.5G clathrates (mtn = N-methyl-1,3-diaminopropane, G = toluene, nitrobenzene, dichloromethane, and chloroform) were studied by using CP/MAS 13C and 2H NMR techniques. At room temperature, application of 13C CP/MAS NMR with dipolar dephasing showed the presence of large amplitude molecular motion in all cases. Temperature dependent 2H NMR spectra for the toluene-d8 clathrate shows that the methyl group rotated at all temperatures down to 77 K. Also, a 2-site in-plane reorientation process of the entire molecule is activated above 180 K, which goes over into axially symmetric in-plane rotation around 450 K. Severely restricted motions were also observed for the nitrobenzene and haloalkane guests. The rather complicated dynamic behaviour of the guest molecules at low and room temperatures can be attributed to the presence of static disorders which disappear at higher temperatures due to time averaging.

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17

Rissanen, Kari. "Crystallography of encapsulated molecules". Chemical Society Reviews 46, n.º 9 (2017): 2638–48. http://dx.doi.org/10.1039/c7cs00090a.

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18

Toda, Fumio. "Crystalline inclusion complexes as media of molecular recognitions and selective reactions". Pure and Applied Chemistry 73, n.º 7 (1 de julio de 2001): 1137–45. http://dx.doi.org/10.1351/pac200173071137.

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Hexaol host compounds which include guest molecules maximum in 1:6 ratio were prepared. Aromatic hexaol host, hexahydroxytriphenylene, was found to form chiral inclusion crystal by complexation with achiral guest molecules. Some interesting and important optical resolutions of rac-guests by inclusion complexation with a chiral host were described. When chemical reaction and the inclusion complexation procedures in a water suspension medium are combined, new economical and ecological method of the preparation of optically active compound can be established. When photochemical reactions are carried out in an inclusion crystal with a chiral host, enantioselective reactions occur, and optically active product can be obtained. Several successful reactions are described.

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19

Sheng, Xinru, Errui Li y Feihe Huang. "Construction of pillar[4]arene[1]quinone–1,10-dibromodecane pseudorotaxanes in solution and in the solid state". Beilstein Journal of Organic Chemistry 16 (2 de diciembre de 2020): 2954–59. http://dx.doi.org/10.3762/bjoc.16.245.

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We report novel pseudorotaxanes based on the complexation between pillar[4]arene[1]quinone and 1,10-dibromodecane. The complexation is found to have a 1:1 host–guest complexation stoichiometry in chloroform but a 2:1 host–guest complexation stoichiometry in the solid state. From single crystal X-ray diffraction, the linear guest molecules thread into cyclic pillar[4]arene[1]quinone host molecules in the solid state, stabilized by CH∙∙∙π interactions and hydrogen bonds. The bromine atoms at the periphery of the guest molecule provide convenience for the further capping of the pseudorotaxanes to construct rotaxanes.

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20

Kaneko, Fumitoshi, Aurel Radulescu y Koichi Ute. "Time-resolved small-angle neutron scattering study on guest-exchange processes in co-crystals of syndiotactic polystyrene". Journal of Applied Crystallography 47, n.º 1 (8 de enero de 2014): 6–13. http://dx.doi.org/10.1107/s1600576713030343.

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Syndiotactic polystyrene (sPS) occupies a peculiar position among crystalline polymers: it forms co-crystals with many different kinds of chemical compounds, where the molecules are confined as guests in the regularly arranged cavities surrounded by the side phenyl groups. The guest molecules can be replaced smoothly by exposure to a vapour or a liquid of another compound, keeping the framework of the host polymer crystallites. It has been confirmed that the guest-exchange procedure is an effective way to incorporate a variety of chemical species into the crystalline region of syndiotactic polystyrene. In order to elucidate its characteristics, the guest-exchange process in co-crystals of syndiotactic polystyrene has been studied byin situtime-resolved small-angle neutron scattering measurements, exploiting the scattering length difference between fully protonated and deuterated isotopologues of guest compounds and employing fully deuterated syndiotactic polystyrene as the host matrix to avoid strong incoherent scattering. In this study, the guest-exchange process induced by exposure to the gas of small guest molecules was followed by monitoring of the reflections from crystalline lamellae. The lamellar reflections showed significant variations in intensity during the guest exchange, from which the diffusion coefficients of the guest molecules in the crystalline region could be evaluated.

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21

Tanaka, Koichi, Naoki Daikawa y Shigeru Ohba. "Novel Bisurea Host Compounds". Journal of Chemical Research 2002, n.º 11 (noviembre de 2002): 579–81. http://dx.doi.org/10.3184/030823402103170853.

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New host molecules, 4,4′-bis(dimethylamino-urea)diphenylmethane (1) and its derivatives (2 and 3), are reported. These hosts are shown to give inclusion complex crystals with a wide variety of organic guest molecules with high selectivity. The crystal structure of 1:2 inclusion complex of 1 with THF has been determined from X-ray crystal structure analysis. The cyclic N–H...O intermolecular hydrogen bonds between host molecules were found to form columns for accommodation of the guest molecules.

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22

Zhou, Mingming, Caichao Ye y Dong Xiang. "Theoretical Studies on the Role of Guest in α-CL-20/Guest Crystals". Molecules 27, n.º 10 (19 de mayo de 2022): 3266. http://dx.doi.org/10.3390/molecules27103266.

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The contradiction between energy and safety of explosives is better balanced by the host–guest inclusion strategy. To deeply analyze the role of small guest molecules in the host–guest system, we first investigated the intermolecular contacts of host and guest molecules through Hirshfeld surfaces, 2-D fingerprint plots and electrostatic interaction energy. We then examined the strength and nature of the intermolecular interactions between CL-20 and various small molecules in detail, using state-of-the-art quantum chemistry calculations and elaborate wavefunction analyses. Finally, we studied the effect of the small molecules on the properties of CL-20, using density functional theory (DFT). The results showed that the spatial arrangement of host and guest molecules and the interaction between host and guest molecules, such as repulsion or attraction, may depend on the properties of the guest molecules, such as polarity, oxidation, hydrogen content, etc. The insertion of H2O2, H2O, N2O, and CO2 had significant influence on the electrostatic potential (ESP), van der Waals (vdW) potential and chemical bonding of CL-20. The intermolecular interactions, electric density and crystal orbital Hamilton population (COHP) clarified and quantified the stabilization effect of different small molecules on CL-20. The insertion of the guest molecules improved the stability of CL-20 to different extents, of which H2O2 worked best.

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23

Wen, Huimin, Wengang Li, Jiewei Chen, Gen He, Longhua Li, Mark A. Olson, Andrew C. H. Sue, J. Fraser Stoddart y Xuefeng Guo. "Complex formation dynamics in a single-molecule electronic device". Science Advances 2, n.º 11 (noviembre de 2016): e1601113. http://dx.doi.org/10.1126/sciadv.1601113.

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Single-molecule electronic devices offer unique opportunities to investigate the properties of individual molecules that are not accessible in conventional ensemble experiments. However, these investigations remain challenging because they require (i) highly precise device fabrication to incorporate single molecules and (ii) sufficient time resolution to be able to make fast molecular dynamic measurements. We demonstrate a graphene-molecule single-molecule junction that is capable of probing the thermodynamic and kinetic parameters of a host-guest complex. By covalently integrating a conjugated molecular wire with a pendent crown ether into graphene point contacts, we can transduce the physical [2]pseudorotaxane (de)formation processes between the electron-rich crown ether and a dicationic guest into real-time electrical signals. The conductance of the single-molecule junction reveals two-level fluctuations that are highly dependent on temperature and solvent environments, affording a nondestructive means of quantitatively determining the binding and rate constants, as well as the activation energies, for host-guest complexes. The thermodynamic processes reveal the host-guest binding to be enthalpy-driven and are consistent with conventional 1H nuclear magnetic resonance titration experiments. This electronic device opens up a new route to developing single-molecule dynamics investigations with microsecond resolution for a broad range of chemical and biochemical applications.

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24

Bruns. "Exploring and Exploiting the Symmetry-Breaking Effect of Cyclodextrins in Mechanomolecules". Symmetry 11, n.º 10 (5 de octubre de 2019): 1249. http://dx.doi.org/10.3390/sym11101249.

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Cyclodextrins (CDs) are cone-shaped molecular rings that have been widely employed in supramolecular/host–guest chemistry because of their low cost, high biocompatibility, stability, wide availability in multiple sizes, and their promiscuity for binding a range of molecular guests in water. Consequently, CD-based host–guest complexes are often employed as templates for the synthesis of mechanically bonded molecules (mechanomolecules) such as catenanes, rotaxanes, and polyrotaxanes in particular. The conical shape and cyclodirectionality of the CD “bead” gives rise to a symmetry-breaking effect when it is threaded onto a molecular “string”; even symmetrical guests are rendered asymmetric by the presence of an encircling CD host. This review focuses on the stereochemical implications of this symmetry-breaking effect in mechanomolecules, including orientational isomerism, mechanically planar chirality, and topological chirality, as well as how they support applications in regioselective and stereoselective chemical synthesis, the design of molecular machine prototypes, and the development of advanced materials.

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25

Marjo, CE, R. Bishop, DC Craig y ML Scudder. "A Tetrachloro Guest in a Molecular Box". Australian Journal of Chemistry 49, n.º 3 (1996): 337. http://dx.doi.org/10.1071/ch9960337.

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The new lattice inclusion host exo-7,exo-15-dibromo-6,7,14,15-tetrahydro-6,14-methanocycloocta[1,2-b:5,6-b'] diquinoxaline (6) has been synthesized in three steps from bicyclo [3.3.1]nonane-2,6-dione and benzofurazan oxide. It preferentially forms crystalline inclusion compounds with small polyhaloalkane guest molecules, and the crystal structure of the 1,1,2,2-tetrachloroethane compound [(C21H14N4Br2)2.C2H2Cl4, Pbcn , a 11.663(2), b 13.195(3), c 27.444(5) Ǻ, Z 4, R 0.041] is described. The key characteristic of this compound is a series of molecular boxes in which the guest molecules reside. Construction of the six surrounding walls is achieved with the aromatic rings of just four host molecules, and the guest molecule occupies a fixed position within the box. The intermolecular forces resulting in formation of this novel inclusion structure are analysed in detail.

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26

Sinawang, Garry, Motofumi Osaki, Yoshinori Takashima, Hiroyasu Yamaguchi y Akira Harada. "Supramolecular self-healing materials from non-covalent cross-linking host–guest interactions". Chemical Communications 56, n.º 32 (2020): 4381–95. http://dx.doi.org/10.1039/d0cc00672f.

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27

Goubitz, Kees, Pavla Čapková, Klára Melánová, Wim Molleman y Henk Schenk. "Structure determination of two intercalated compounds VOPO4·(CH2)4O and VOPO4·OH—(CH2)2—O—(CH2)2—OH; synchrotron powder diffraction and molecular modelling". Acta Crystallographica Section B Structural Science 57, n.º 2 (1 de abril de 2001): 178–83. http://dx.doi.org/10.1107/s0108768100015603.

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The crystal structures of two intercalated compounds have been determined using a combination of synchrotron powder diffraction and molecular mechanics simulations: (1) vanadyl phosphate intercalated with tetrahydrofuran, VOPO4·(CH2)4O, and (2) vanadyl phosphate intercalated with diethylene glycol, VOPO4·HO(CH2)2O(CH2)2OH. Both intercalates preserve the tetragonal space group P4/n, as found in the host structure VOPO4·2H2O. (1): a = 6.208, c = 8.930 Å, Z = 2, Dx = 2.51 g cm−3; (2): a = 6.223, c = 11.417 Å, Z = 2, Dx = 2.66 g cm−3. Both intercalates exhibit the same type of orientational disorder in the arrangement of guest molecules, as observed in the same host compound intercalated with water. These two intercalates also exhibit, rather surprisingly, perfect ordering in layer stacking without the displacement disorder, characteristic of many intercalated layered structures. Thanks to this regularity in the arrangement of guests and layers, synchrotron powder diffraction could be used in the present structure determination. The present results also enabled the analysis of the effect of geometrical parameters characterizing the mutual host–guest complementarity and the effect of host–guest and guest–guest interaction on the crystal packing of intercalates.

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28

Journal, Baghdad Science. "The formation, structure, and electronic properties of Lansoprazol drug and cucurbit [7]urils complex (Theoretical Study)". Baghdad Science Journal 13, n.º 2 (5 de junio de 2016): 34–39. http://dx.doi.org/10.21123/bsj.13.2.34-39.

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The current study deals with host-guest complex formation between cucurbit [7] urils as host and lansoprazole as guesti using PM3 (semi empirical molecules orbital calculations) also DFT calculations. In this complex, the formation of hydrogen bonding may be occurred through portal oxygen atoms(O2) of cucurbit [7] urils and amine groups (NH 2 )of the drug. The energies of HOMO and LUMO orbital’s have been computed for the host guest complex and its components. The result of the stabilization energy explained a complex formation.

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29

Boland, Patricia G., Sara J. Accardi, Carrie A. Snow y Brian D. Wagner. "Investigations of the supramolecular host properties of a fluorescent bistren cage compound". Canadian Journal of Chemistry 87, n.º 2 (febrero de 2009): 448–52. http://dx.doi.org/10.1139/v08-179.

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The host properties of a bistren cage compound, previously reported to be an efficient anion sensor, are shown to include encapsulation of small aromatic guest molecules. It is also shown that the intrinsic fluorescence of this cage compound, arising from the anthracenyl moiety in its structure, is sensitive to the encapsulation of aromatic guests in aqueous solution and can be used to measure the binding constants for any such guest. This makes this bistren cage a rare example of a fluorescent host for aromatic guests, and suggests potential applications of this compound as a versatile fluorescent sensor for a variety of guests of interest. The binding of a number of benzene derivatives was studied; these were all found to form 1:2 host–guest inclusion complexes with a wide range in total binding constants (K1K2), from 6.4 × 103 to 3.5 × 107 (mol/L)–2, indicating a significant degree of selectivity for different benzene derivatives. The binding strength was found to depend on both the guest polarity and aqueous solubility.

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30

Kalchenko, Olga, Sergiy Cherenok, Sergiy Suikov y Vitaly Kalchenko Vitaly Kalchenko. "Study of Calixarene Complexation with Biologically Active". French-Ukrainian Journal of Chemistry 5, n.º 2 (2017): 49–55. http://dx.doi.org/10.17721/fujcv5i2p49-55.

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Host-Guest complexation of octakis(diphenoxyphosphoryloxy)tetramethylcalix[4]resorcinarene CRA and 5,17-bis-(N-tolyliminomethyl)-25,27-dipropoxycalix[4]arene CA with bio relevant aromatic, pyridine and diterpenoid carboxylic acids in water-organic solution had been studied by the RP HPLC and molecular modelling methods. The stability constants KA (387-1914 М-1) of the supramolecular complexes had been determined. It was shown the Host-Guest interactions are depended on structure of the Host molecules and log P values of the Guests. The complexation is determined by the hydrogen bonds of the COOH group of the carboxylic acids with P=O oxygen atom of diphenoxyphosphoryl group of the calixresorcinarene CRA, and oxygen or nitrogen atoms located on the lower or the upper rim of the calixarene CA.

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31

Tanaka, Koichi, Takaichi Hiratsuka, Yuko Kojima y Yasuko T. Osano. "Synthesis, Structure and Chiral Inclusion Crystallisation of Tetrakis(4-Ethynylphenyl)Ethylene Derivatives". Journal of Chemical Research 2002, n.º 5 (mayo de 2002): 209–12. http://dx.doi.org/10.3184/030823402103171889.

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Achiral host molecules, tetrakis(4-ethynylphenyl)ethylene 3 and tetrakis(4-bromoethynylphenyl)ethylene 4, formed chiral host–guest inclusion crystals with achiral guest molecules via weak intermolecular interactions.

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32

Eikeland, Espen, Solveig Madsen, Jacob Overgaard, Mark Spackman y Bo Iversen. "Exploring Host-Guest Interactions: a Single Crystal High-Pressure study". Acta Crystallographica Section A Foundations and Advances 70, a1 (5 de agosto de 2014): C756. http://dx.doi.org/10.1107/s2053273314092432.

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Single crystal X-ray diffraction data from several Hydroquinone clathrate systems, with various small guest molecules (e.g. HCOOH, MeOH), have been obtained up to a pressure of 10 GPa, using a diamond anvil cell (DAC). Hydroquinone clathrates are key examples of supramolecular aggregates, having a diverse structural chemistry controlled, to a large extent, by the detailed intermolecular interactions between the host and the guest molecules. Although supramolecular chemistry is the foundation for the design and development of advanced materials (e.g. for catalysis, targeted drug delivery, chemical separation and nonlinear optics) the basic understanding leading to such complex systems are often lacking. High pressure (HP) crystallography is an excellent method of systematically increasing host-guest interactions by forcing the molecules closer together, often leading to interesting and unexpected results. At ambient pressure smaller guest molecules are often disordered inside the clathrate cavities. As the external pressure increases the cavities shrink, and it seems likely that guest molecules will order inside the cavity breaking the host symmetry. Guest ordering transitions are also found upon cooling. In this work, results from HP studies of the hydroquinone – formic acid system reveal that the structure is stable up to 10 GPa, at which pressure the guest cavity volume is reduced by more than 50 % without ordering of the guest atoms. Earlier studies have shown that the empty Hydroquinone clathrate undergoes a phase transition into a nonporous structure already at 0.4 GPa. [1] This indicates that formic acid stabilizes the host framework through strong intermolecular host-guest interactions, but without lowering the host symmetry.

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33

Mohd Sarjidan, Mohd Arif, Siti Hajar Basri y W. H. Abd Majid. "Fabrication and Characterization of Organic Light-Emitting Diodes Containing Small Molecules Blends as Emissive Layer". Advanced Materials Research 795 (septiembre de 2013): 106–9. http://dx.doi.org/10.4028/www.scientific.net/amr.795.106.

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Organic light-emitting diodes (OLEDs) were fabricated containing guest molecule of Tris (8-hydroxyquinoline) aluminum (Alq3) blend with host molecules of N,N-diphenyl-N,N-bis (3-methylphenyl)-1,1-biphenyl-4,4-diamine (TPD) and 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) small molecules. Optical, photoluminescence (PL) and electroluminescence (EL) properties were investigated with respect to blend systems. The obtained optical energy gap and PL intensity in the blend systems increased due to the transfer of high energy from the host to guest molecules. Luminance and current efficiency were enhanced for blended OLEDs as compared to that of pure Alq3, related to high exiton recombination in guest caused by high injection and accumulation of charge carrier.

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34

Knoblauch, Stephan, H. Fred Koch, Catherine Polydore y D. Max Roundhill. "A computational approach to seeking methylmercury(II) thiolate calix[4]arene hosts for both octasulfur and organosulfur compounds as guests". Canadian Journal of Chemistry 79, n.º 5-6 (1 de mayo de 2001): 977–82. http://dx.doi.org/10.1139/v00-197.

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Calculations have been carried out on the conformational preferences of calix[4]arene thiols and their methylmercury(II) derivatives. Calculations have also been carried out on hostguest combinations of methylmercury(II) ethanethiolate calix[4]arenes and 1,4-dithiacyclohexane, octasulfur, thiacyclopropane, and thiophene. For the 1,4-dithiacyclohexane, thiacyclopropane, and thiophene guests, calculations have been carried out for both 1:1 and 1:4 ratios of the methylmercury(II) ethanethiolate calix[4]arene to the sulfur containing guests. For octasulfur only the 1:1 hostguest ratio has been considered because it has four sulfurs that are conformationally arranged to bind to the four mercury(II) centers. The computational results generally show that hostguest formation is enthalpically favored over the separated molecules in cases where adducts with mercury-sulfur donor atom interactions are allowed to reach energy minima.Key words: calixarene, methylmercury, octasulfur, organosulfur compounds.

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35

Nagatomo, Nao, Hisashi Oishi, Yutaka Kuwahara, Makoto Takafuji, Reiko Oda, Taisuke Hamada y Hirotaka Ihara. "Enantioselective Self-Assembled Nanofibrillar Network with Glutamide-Based Organogelator". Nanomaterials 11, n.º 6 (23 de mayo de 2021): 1376. http://dx.doi.org/10.3390/nano11061376.

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A chiral molecular gelation system, as a chiral host, was used to effectively realize enantioselectivity using the simple carboxylic acid functional group. For this purpose, an L-glutamic-acid-based lipidic amphiphile (G-CA) with a carboxylic head group was selected and its responsiveness to cationic guest molecules was investigated. The dispersion morphology of G-CA in its solution state was examined by confocal and transmission electron microscopies, while interactions between the G-CA, as the host system, and guest molecules were evaluated by UV-visible, circular dichroism, and fluorescence spectroscopies. As a result, enantioselectivity was effectively induced when G-CA formed highly ordered aggregates that provide negatively charged surfaces in which carboxyl groups are assembled in highly ordered states, and when the two cationic groups of the guest molecule are attached to this surface through multiple interactions.

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36

Archana Sumohan Pillai, Sivaraj Ramasamy, Varnitha Manikandan, Aleyamma Alexander y Israel V.M.V. Enoch. "Anticancer Activity of the Host-Guest Complex of Camptothecin with β-Cyclodextrin-Folate Conjugate. Encapsulation and Efficacy". International Journal of Research in Pharmaceutical Sciences 11, SPL4 (21 de diciembre de 2020): 1286–91. http://dx.doi.org/10.26452/ijrps.v11ispl4.4294.

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Cyclodextrins are cyclic oligosachcharides that act as molecular hosts and accommodate drug molecules forming host: guest complexes. They aid in the sustained release of the encapsulated drugs through diffusion in solution and protect their unstable forms. In this paper, we report the synthesis of a β-cyclodextrin-folate by a simple coupling reaction. The compound is characterized using IR, NMR, and mass spectroscopic techniques. The amide carbonyl band is observed at 1680 cm-1. The mass spectrum shows the molecular ion peak of the β-cycloxetrin-folate conjugate at an m/z value of 1615.35. An inclusion complex of the anticancer drug, camptothecin, with the β-cycloxetrin-folate is formed on the stepwise addition of the β-cycloxetrin-folate to the guest molecule. The complex formation is studied using UV-visible and fluorescence spectroscopy. The formation of host: guest complexes is known to enable the sustained release of the encapsulated drug molecule. Herein, we examined the in vitro anticancer activity of the host: guest complex against cervical cancer (HeLa) cells. The host: guest complex formation results in enhanced efficacy of the drug. Dose-dependent cytotoxicity is observed for the β-cyclodextrin-folate: camptothecin complex. The cytotoxicity is more for the complex than for the free drug in solution.

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37

He, Ying-Chun, Ji-Gang Pan y Dian-Sheng Liu. "Structural study of the novel deuterated calix[4]pyrrole complex d 12-meso-tetrakis(4-methoxyphenyl)-meso-tetramethylcalix[4]pyrrole–pyridine N-oxide–acetonitrile (1/1/1)". Acta Crystallographica Section C Structural Chemistry 73, n.º 3 (7 de febrero de 2017): 254–58. http://dx.doi.org/10.1107/s2053229617001309.

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Calix[4]pyrroles act as powerful receptors for electron-rich neutral guests and anionic guests in organic solvents. For the electron-rich neutral guest pyridine N-oxide, calix[4]pyrrole, with a deep cavity, provides an appropriate environment. The ability of calix[4]pyrrole to host binding guest molecules is the result of hydrogen bonding, π–π, C—H...π and hydrophobic interactions of the cavity. The novel title complex, C52H40D12N4O4·C5H5NO·C2H3N, based on d 12-meso-tetrakis(4-methoxyphenyl)-meso-tetramethylcalix[4]pyrrole, has been assembled using an excess of pyridine N-oxide and is the first deuterated complex of calix[4]pyrrole. A single-crystal X-ray study shows that the receptor adopts a cone conformation with the N-oxide fragment encapsulated deep within the cavity. 1H NMR spectroscopy was used to probe the molecular binding formation in CD3CN. The results are consistent with the single-crystal X-ray study in identifying that the pyridine N-oxide molecule occupies the cavity of the calix[4]pyrrole molecule. UV–vis spectroscopy revealed that the calix[4]pyrrole receptor molecules are able to form 1:1 inclusion complexes in CH3CN.

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38

Enright, Gary D., Eric B. Brouwer, Konstantin A. Udachin, Christopher I. Ratcliffe y John A. Ripmeester. "A reexamination of the low-temperature crystal structure of the p-tert-butylcalix[4]arene–toluene inclusion compound. Differences in spatial averaging with Cu and Mo Kα radiation". Acta Crystallographica Section B Structural Science 58, n.º 6 (28 de noviembre de 2002): 1032–35. http://dx.doi.org/10.1107/s0108768102018803.

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The low-temperature crystal structure of the p-tert-butylcalix[4]arene–toluene inclusion compound, C44H56O4·C7H8, exhibits significant guest-induced distortion of the host calixarene molecule. This distortion persists long enough to establish a correlation in the orientation of guests in adjacent host molecules. Remarkably, the space group and unit cell that best describe the structure appear to depend on the wavelength of the incident radiation. This behaviour appears to arise from spatial averaging over the different scattering volumes required to establish the diffraction peaks.

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39

Prochnow, Peter, Michael Wark, Günter Schulz-Ekloff, Dieter Wöhrle, Arnost Zukal y Jiri Rathousky. "Cobalt(II)-phthalocyanine encapsulated in NaY faujasite: aggregation of Co(II)-phthalocyanine encapsulated in NaY zeolite due to the acidity of Ti(IV) oxide species mediated by pyridine". Journal of Porphyrins and Phthalocyanines 06, n.º 08 (agosto de 2002): 494–501. http://dx.doi.org/10.1142/s1088424602000622.

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Co (II)-phthalocyanine ( CoPc ) was synthesized in the cages of a NaY faujasite matrix and in NaY with co-encapsulated highly dispersed Ti (IV) oxide species. As expected the encaged complexes were immobilized and could not be removed by extraction procedures. Unexpected were reversible aggregations of the CoPc molecules, revealed from DR-UV-vis spectra. The phenomena were attributed to frequently observed (i) local enrichments of the CoPc molecules, i.e., their non-uniform distribution throughout the zeolite crystals, and (ii) local damages, facilitating the contact between CoPc molecules. The aggregations are mediated by co-guests, like Ti (IV) oxide species or pyridine, i.e. by guest-guest interactions, whereas the segregation is induced by host-guest interactions between CoPc and the zeolite framework.

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40

Minceva-Sukarova, Biljana, Liljana Andreeva, Ljupco Pejov y Vladimir Petrusevski. "Vibrational spectroscopic and quantum theoretical study of host-guest interactions in clathrates: I. Hofmann type clathrates". Journal of the Serbian Chemical Society 65, n.º 5-6 (2000): 417–30. http://dx.doi.org/10.2298/jsc0006417m.

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Hofmann type clatharates are host-guest compounds with the general formula M(NH3)2M'(CN)4.2G, in which M(NH3)2M'(CN)4 is the host lattice and G is benzene, the guest molecule. In previous studies, host-guest interactions have been investigated by analyzing the RT and LNT vibrational (infrared, far infrared and Raman) spectra of these clathrates. All the observed changes in the vibrational spectra of these clathrates are referred to a host-guest interaction originating from weak hydrogen bonding between the ammonia hydrogen atoms from the host lattice and the p electron cloud of the guest (benzene) molecules. In order to obtain an insight into the relative importance of the local crystalline field vs. the anharmonicity effects on the spectroscopic properties of the guest species upon enclathration, as well as to explain the observed band shifts and splittings, several quantum theoretical approaches are proposed.

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41

Bock, Hans, Norbert Nagel y Christian Näther. "Wechselwirkungen in Molekülkristallen, 147 [1, 2]. Isostrukturelle Wirt/Gast-Einschluß-Verbindungen von N,N'-Ditosyl- p-phenylendiamin mit Aceton, Cyclopentanon, Cyclopent-2-en-l-on, 1,3-Dioxolan, Tetrahydrofuran und 2,5-Dihydrofuran / Interactions in Molecular Crystals, 147 [1, 2], Isostructural Host/Guest-Inclusion Compounds of N,N'-Ditosyl-p-phenylenediamine with Acetone, Cyclopentanone, Cyclopent-2-ene-l-one, 1,3-Dioxolane, Tetrahydrofurane, and 2,5-D ihydrofurane". Zeitschrift für Naturforschung B 53, n.º 12 (1 de diciembre de 1998): 1401–12. http://dx.doi.org/10.1515/znb-1998-1202.

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Abstract Six isostructural inclusion compounds of various ketone and ether guest molecules into the hydrogen-bonded host-matrix of N,N’-ditosyl-p-phenylenediamine are presented. Crystal growth, structure determinations as well as the arrangement within the clathrates formed is reported and discussed in detail. Packing coefficients and especially the volume ratios between the guest-containig channels and the unit cells allow to estimate the size-limit of guest molecules, which can cocrystallize. Additional crystal growth experiments yield information concerning other types of guest molecules, inclusion from solvent mixtures and guest removal as well as guest exchange processes observed for the N,N′-ditosyl-p-phenylenediamine host matrix.

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42

Ye, Yanan, Peihua Ma, Yue Ma, Naqin Yang, Xiaoqian Chen, Xinan Yang, Lingyi Shen y Xin Xiao. "Study on the host–guest interactions between tetramethyl cucurbit[6]uril and 2-heterocyclic-substituted benzimidazoles". RSC Advances 14, n.º 4 (2024): 2652–58. http://dx.doi.org/10.1039/d3ra07810h.

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The different interaction modes between TMeQ[6] and the guests indicate that the benzimidazole ring and heterocyclic substituted groups of the guest molecules are in competition with the cavity of TMeQ[6].

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43

Chandra, Falguni, Kaushik Pal, Sushil Lathwal y Apurba L. Koner. "Supramolecular guest relay using host-protein nanocavities: an application of host-induced guest protonation". Molecular BioSystems 12, n.º 9 (2016): 2859–66. http://dx.doi.org/10.1039/c6mb00423g.

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44

Chen, Kaifei, Seyed Hesam Mousavi, Ranjeet Singh, Randall Q. Snurr, Gang Li y Paul A. Webley. "Gating effect for gas adsorption in microporous materials—mechanisms and applications". Chemical Society Reviews 51, n.º 3 (2022): 1139–66. http://dx.doi.org/10.1039/d1cs00822f.

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External stimuli or host–guest interactions induce structural changes, producing a gating effect in which an adsorbent suddenly becomes accessible to guest molecules. This effect greatly facilitates gas separation, storage, and molecular detection.

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45

Hayashida, Osamu, Yudai Tanaka y Takaaki Miyazaki. "Synthesis and Guest-Binding Properties of pH/Reduction Dual-Responsive Cyclophane Dimer". Molecules 26, n.º 11 (22 de mayo de 2021): 3097. http://dx.doi.org/10.3390/molecules26113097.

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A water-soluble cyclophane dimer having two disulfide groups as a reduction-responsive cleavable bond as well as several acidic and basic functional groups as a pH-responsive ionizable group 1 was successfully synthesized. It was found that 1 showed pH-dependent guest-binding behavior. That is, 1 strongly bound an anionic guest, 6-p-toluidinonaphthalene-2-sulfonate (TNS) with binding constant (K/M−1) for 1:1 host-guest complexes of 9.6 × 104 M−1 at pH 3.8, which was larger than those at pH 7.4 and 10.7 (6.0 × 104 and 2.4 × 104 M−1, respectively), indicating a favorable electrostatic interaction between anionic guest and net cationic 1. What is more, release of the entrapped guest molecules by 1 was easily controlled by pH stimulus. Large favorable enthalpies (ΔH) for formation of host-guest complexes were obtained under the pH conditions employed, suggesting that electrostatic interaction between anionic TNS and 1 was the most important driving force for host-guest complexation. Such contributions of ΔH for formation of host-guest complexes decreased along with increased pH values from acidic to basic solutions. Upon addition of dithiothreitol (DTT) as a reducing reagent to an aqueous PBS buffer (pH 7.4) containing 1 and TNS, the fluorescence intensity originating from the bound guest molecules decreased gradually. A treatment of 1 with DTT gave 2, having less guest-binding affinity by the cleavage of disulfide bonds of 1. Consequently, almost all entrapped guest molecules by 1 were released from the host. Moreover, such reduction-responsive cleavage of 1 and release of bound guest molecules was performed more rapidly in aqueous buffer at pH 10.7.

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46

Lee, Yen, Boyeong Kang y Jiwon Seo. "Metalloporphyrin Dimers Bridged by a Peptoid Helix: Host-Guest Interaction and Chiral Recognition". Molecules 23, n.º 11 (24 de octubre de 2018): 2741. http://dx.doi.org/10.3390/molecules23112741.

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Co-facial porphyrins have been designed to construct porphyrin tweezers with versatile molecular recognition capabilities. In this study, we synthesized metalloporphyrin–peptoid conjugates (MPPCs) displaying two metalloporphyrins on a peptoid scaffold with either achiral unfolded (1) or helical (2 and 3) secondary structures. Host–guest complexation of MPPCs was realized with various guests of different lengths and basicities, and the extent of complexation was measured by UV-vis and circular dichroism (CD) spectroscopic titration. Intermolecular and intramolecular chirality induction were observed on achiral and chiral peptoid backbones, respectively. Spectroscopic data indicated that a broad scope of achiral guests can be recognized by chiral 2; in particular, longer and more flexible guests were seen to bind more tightly on 2. In addition, chiral 2 provided a distinct CD couplet with dl-, d-, or l-Lys-OMe, which was a result of the diastereomeric host–guest complex formation. Our results indicated that MPPCs can recognize, contrast, and analyze various achiral, chiral, or racemic molecules. Based on co-facial metalloporphyrins present on peptoid scaffolds, we developed a novel class of porphyrin tweezers, which can be further utilized in asymmetric catalysis, molecular sensing, and drug delivery.

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47

Kobayashi, Mutsumi, Mei Takatsuka, Ryo Sekiya y Takeharu Haino. "Molecular recognition of upper rim functionalized cavitand and its unique dimeric capsule in the solid state". Organic & Biomolecular Chemistry 13, n.º 6 (2015): 1647–53. http://dx.doi.org/10.1039/c4ob02251c.

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Calix[4]resorcinarene-based cavitand recognized the methyl group of the guests to form 1 : 1 host–guest complexes. In the solid state, the cavitand formed a dimeric capsule in which two molecules of nitromethane were entrapped by weak noncovalent interactions.

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48

Bhaskar Reddy, Manda, Myadaraboina Shailaja, Alla Manjula, Joseph Richard Premkumar, Garikapati Narahari Sastry, Katukuri Sirisha y Akella Venkata Subrahmanya Sarma. "Design and synthesis of Tröger's base ditopic receptors: host–guest interactions, a combined theoretical and experimental study". Organic & Biomolecular Chemistry 13, n.º 4 (2015): 1141–49. http://dx.doi.org/10.1039/c4ob02266a.

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The host–guest interaction between flexible ditopic receptors and bisammonium ion has been investigated experimentally and computationally. The conformation folding of guest bisammonium ion molecules leads to the oscillation of the host–guest interaction.

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49

Danylyuk, Oksana, Karolina Kedra-Krolik, Marta Worzakowska, Joanna Osypiuk-Tomasik y Vladimir Fedin. "Phase transformations in cucurbituril host-guest complexes". Acta Crystallographica Section A Foundations and Advances 70, a1 (5 de agosto de 2014): C646. http://dx.doi.org/10.1107/s205327331409353x.

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The retention of crystallinity upon desolvation of molecular crystals is not common, as the molecules are rigidly and densely packed in the crystals and the original framework usually collapses once solvent is removed from the structure. However, in rare cases the host framework remains substantially unaffected by solvent (guest) removal yielding structure with open channels or discrete lattice voids that can show permanent porosity. [1] Furthermore, sometimes happens, the desolvation process proceeds as single-crystal to single-crystal transformation resulting in distortion and sliding of the structure, changes in conformation, coordination modes and/or space group. Here we would like to present crystallographic study and thermal analysis on the dehydration process of the crystalline supramolecular complex between macrocyclic host cucurbit[6]uril and dopamine. In the solid state the 1:1 host-guest complex assembles into hexameric tubes with water-filled interior channels. Another set of water channels is created between three neighboring tubes in the crystal lattice. The crystals of such supramolecular assembly are not stable when out from mother solution and immediately start to loose water upon exposure to air. However, despite severe cracking the crystals dried in air maintained their integrity and still gave satisfactory diffraction pattern. The X-ray analysis showed significant decrease in the unit cell volume of the partially dehydrated crystals that corresponds to the liberation of some of the water molecules from the channels. Moreover, the reorganization of dopamine guest molecules has occurred in the crystal lattice as a response to the escape of water molecules from the structure. The partial dehydration and reorganization of the supramolecular framework proceeds via a single-crystal to single-crystal mechanism.

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Kon, Noriyoshi, Nobuhiko Iki, Yuichiro Sano, Satoshi Ogawa, Chizuko Kabuto y Sotaro Miyano. "Tuning of the Cavity of Water-Soluble Thiacalix[4]arene for the Control of Inclusion Ability Toward Water-Miscible Organic Molecules". Collection of Czechoslovak Chemical Communications 69, n.º 5 (2004): 1080–96. http://dx.doi.org/10.1135/cccc20041080.

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Inclusion abilities of water-soluble thiacalix[4]arenetetrasulfonate (3) and mono-O-carboxymethylated derivatives 5 and 6 toward water-miscible organic molecules such as alcohols, ketones, and nitriles in water were investigated by 1H NMR. The limit chemical shift change of the guest upon inclusion in the host suggested that the hosts regioselectively encapsulate the guests from the side of aliphatic moiety. Large guests such as pentan-1-ol showed folding of the alkyl chain to be included inside the cavity. On the other hand, mono-O-substituted 6 included a guest molecule less deep in the cavity than 3 did. Binding constants (K) of 3 toward guest molecules increased with hydrophobicity of the guest, suggesting that hydrophobic effect plays a main role for the complexation. On the contrary, mono-O-carboxymethyl derivatives 5 and 6 showed the opposite dependency of stability on hydrophobicity; higher affinities toward less hydrophobic guests. Among the guests examined, the smallest entities such as CH3OH and CH3CN were best included in 5 with the highest binding constant ever reported (K > 102 M-1). It was concluded that introduction of the carboxymethyl group into one of the phenolic OH of thiacalix[4]arene led to tuning of the cavity shape for stereospecific inclusion of small guests. The tuning of cavity by the O-alkylation was actually confirmed by X-ray crystal analysis of a complex of 5 with diethyl ketone.

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