Guest Exchange Process Research Articles

"Turn-on" fluorescence sensing for sensitively detecting Cr(VI) via a guest exchange process in Cu NCs@MIL-101 composites.

Copper nanoclusters (Cu NCs) are a new fluorescent material that is often used for determining metal ions, but most sensing systems are based on the "turn-off" model. Here, a "turn-on" model of fluorescence sensing for the detection of Cr(VI) was developed based on Cu NCs@MIL-101 composites. The Cu NCs@MIL-101 composites were synthesized from a simple mixture of Cu NCs and MIL-101(Cr), in which the Cu NCs were uniformly distributed in MIL-101(Cr). Notably, the fluorescence intensity of Cu NCs@MIL-101 was significantly weakened due to the internal filtration effect (IFE) of MIL-101. When Cr(VI) was introduced, the fluorescence of Cu NCs@MIL-101 was recovered by the guest exchange process between Cr(VI) and the Cu NCs, which overcame the IFE of Cu NCs@MIL-101. Based on this, a "turn-on" fluorescence probe was successfully constructed for the quantitative detection of Cr(VI) with two linear ranges of 0.05-1 μM and 1-20 μM, and a low detection limit of 0.05 μM. The proposed fluorescence probe possessed excellent selectivity and anti-interference ability, and was successfully applied for the detection of Cr(VI) in real water samples with satisfactory results. This study provides a new approach for the analytical application of Cu NCs.

Comprehensive Characterization of the Self-Folding Cavitand Dynamics.

The conformational equilibria and guest exchange process of a resorcin[4]arene derived self‐folding cavitand receptor have been characterized in detail by molecular dynamics simulations (MD) and 1H EXSY NMR experiments. A multi‐timescale strategy for exploring the fluxional behaviour of this system has been constructed, exploiting conventional MD and accelerated MD (aMD) techniques. The use of aMD allows the reconstruction of the folding/unfolding process of the receptor by sampling high‐energy barrier processes unattainable by conventional MD simulations. We obtained MD trajectories sampling events occurring at different timescales from ns to s: 1) rearrangement of the directional hydrogen bond seam stabilizing the receptor, 2) folding/unfolding of the structure transiting partially open intermediates, and 3) guest departure from different folding stages. Most remarkably, reweighing of the biased aMD simulations provided kinetic barriers that are in very good agreement with those determined experimentally by 1H NMR. These results constitute the first comprehensive characterization of the complex dynamic features of cavitand receptors. Our approach emerges as a valuable rational design tool for synthetic host‐guest systems

Deciphering the Supramolecular Organization of Multiple Guests Inside a Microporous MOF to Understand their Release Profile.

Metal-organic frameworks (MOFs) give the opportunity of confining guest molecules into their pores even by a post-synthetic protocol. PUM168 is a Zn-based MOF characterized by microporous cavities that allows the encapsulation of a significant number of guest molecules. The pores engineered with different binding sites show a remarkable guest affinity towards a series of natural essential oils components, such as eugenol, thymol and carvacrol, relevant for environmental applications. Exploiting single crystal X-ray diffraction, it was possible to step-wisely monitor the rather complex three-components guest exchange process involving dimethylformamide (DMF, the pristine solvent) and binary mixtures of the flavoring agents. A picture of the structural evolution of the DMF-to-guest replacement occurring inside the MOF crystal was reached by a detailed single-crystal-to-single-crystal monitoring. The relation of the supramolecular arrangement in the pores with selective guests release was then investigated as a function of time and temperature by static headspace GC-MS analysis.

Deciphering the Supramolecular Organization of Multiple Guests Inside a Microporous MOF to Understand their Release Profile

AbstractMetal‐organic frameworks (MOFs) give the opportunity of confining guest molecules into their pores even by a post‐synthetic protocol. PUM168 is a Zn‐based MOF characterized by microporous cavities that allows the encapsulation of a significant number of guest molecules. The pores engineered with different binding sites show a remarkable guest affinity towards a series of natural essential oils components, such as eugenol, thymol and carvacrol, relevant for environmental applications. Exploiting single crystal X‐ray diffraction, it was possible to step‐wisely monitor the rather complex three‐components guest exchange process involving dimethylformamide (DMF, the pristine solvent) and binary mixtures of the flavoring agents. A picture of the structural evolution of the DMF‐to‐guest replacement occurring inside the MOF crystal was reached by a detailed single‐crystal‐to‐single‐crystal monitoring. The relation of the supramolecular arrangement in the pores with selective guests release was then investigated as a function of time and temperature by static headspace GC‐MS analysis.

A Tunable Cyclic Container: Guest-Induced Conformational Switching, Efficient Guest Exchange, and Selective Isolation of C70 from a Fullerene Mixture.

An adaptable cyclic porphyrin dimer with highly flexible linkers has been used as an artificial molecular container that can efficiently encapsulate various aromatic guests (TCNQ/C60 /C70 ) through strong π-π interactions by adjusting its cavity size and conformation. The planar aromatic guest (TCNQ) can be easily and selectively exchanged with larger aromatic guests (C60 /C70 ). During the guest-exchange process, the two porphyrin rings switch their relative orientation according to the size and shape of the guests. This behavior of the cyclic container has been thoroughly investigated by using UV/Vis spectroscopy, NMR spectroscopy, and X-ray crystal structure determination of the host-guest assemblies. The electrochemical and photophysical studies demonstrated the occurrence of photoinduced electron transfer from bisporphyrin to TCNQ/C60 /C70 in the respective host-guest assemblies. The cyclic host can form complexes with C60 and C70 with association constants of (2.8±0.2)×105 and (1.9±0.3)×108 m-1 , respectively; the latter value represents the highest binding affinity for C70 reported so far for zinc(II) bisporphyrinic receptors. This high selectivity for the binding of C70 versus C60 allows the easy extraction and efficient isolation of C70 from a C60 /C70 fullerene mixture. Experimental evidence was substantiated by DFT calculations.

Reversible C60 Ejection from a Metallocage through the Redox-Dependent Binding of a Competitive Guest.

The reversible encapsulation of a tetrapyridyl extended-tetrathiafulvalene (exTTF)-based ligand (m-Py)exTTF by a tetragonal Zn-porphyrin-based prismatic nanocage (1) is described. The reversible uptake and release of the (m-Py)exTTF guest proceeds through drastic electronic and conformational changes occurring upon oxidation of the latter. This reversible system has been explored in a guest-exchange process, by addition of (m-Py)exTTF to the host-guest complex [C60 ⊂1], leading to fullerene C60 ejection from the host cavity. Remarkably, the subsequent redox-triggered ejection of (m-Py)exTTF, leads to the recovery of the empty cage 1, which remains available for further C60 encapsulation. The C60 ejection is justified by the preferable coordination of the pyridine anchors of (m-Py)exTTF to the two Zn-porphyrin units of 1. This approach, based on the use of a switchable competitive guest, offers a promising new strategy for guest-delivery control.

Water-Stable In(III)-Based Metal–Organic Frameworks with Rod-Shaped Secondary Building Units: Single-Crystal to Single-Crystal Transformation and Selective Sorption of C2H2 over CO2 and CH4

Three new water-stable In(III)-based metal-organic frameworks, namely, [In3(TTTA)2(OH)3(H2O)]·(DMA)3 (BUT-70, DMA = N,N-dimethylacetamide), [In3(TTTA)2(CH3O)3] (BUT-70A), and [In3(TTTA)2(OH)3] (BUT-70B), with rod-shaped secondary building units (SBUs) and an new acrylate-based ligand, (2E,2'E,2″E)-3,3',3″-(2,4,6-trimethylbenzene-1,3,5-triyl)-triacrylate (TTTA3-) were obtained and structurally characterized. BUT-70A and -70B were generated in a single-crystal to single-crystal transformation fashion from BUT-70 through guest exchange followed by their removal. The solvents used for guest exchange were methanol and dichloromethane, respectively. Single-crystal structure analyses show that the guest exchange and removal process is accompanied by the substitution of coordinated water molecules of In(III) centers with uncoordinated carboxylate O atoms of TTTA3- ligands. Moreover, hydroxyl groups bridging two In(III) centers are also replaced by methoxyl groups in the transformation from BUT-70 to -70A. Overall, three metal-organic frameworks (MOFs) are constructed by infinite chains consisting of corner-sharing InO4(OR)2 (R = H or Me) octahedral entities, which are interconnected by TTTA3- ligands to form three-dimensional frameworks. Unlike most reported MOFs with infinite chains as SBUs, such as well-known MIL-53 and M-MOF-74, which have one-dimensional channels along the chain direction, the BUT-70 series contain two-dimensional intersecting channels. The Brunauer-Emmett-Teller surface area and pore volume of BUT-70A were estimated to be 460 m2 g-1 and 0.18 cm3 g-1, respectively, which are obviously lower than those of BUT-70B (695 m2 g-1 and 0.29 cm3 g-1). Gas adsorption experiments demonstrated that BUT-70A and -70B are able to selectively adsorb C2H2 over CO2 and CH4. At 1 atm and 298 K, BUT-70A uptakes 3.1 mmol g-1 C2H2, which is 3.6 times that of the CO2 uptake and 7.2 times that of the CH4 uptake. Compared with BUT-70A, BUT-70B presents an even higher C2H2 uptake of 3.9 mmol g-1 at the same conditions, but slightly lower Ideal Adsorbed Solution Theory C2H2/CO2 and C2H2/CH4 selectivities.

Simultaneous Time‐Resolved SAXS and WAXS Study on Guest Exchange Process of Syndiotactic Polystyrene with Aromatic Compounds: Size and Shape Effects of Target Molecules

SummaryOne of the important characteristics of syndiotactic polystyrene (sPS) is that it forms cocrystals with a variety of chemical compounds. The guest exchange procedure is an effective method to introduce diverse chemical compounds into the crystalline region of sPS cocrystals; it enables sPS to form cocrystals even with chemical compounds that are difficult to incorporate into the crystalline region by usual crystallization. The original guest in the sPS cocrystal is replaced by another chemical when exposed to a vapor, a liquid or a solution of the new guest. In order to study the characteristics of the guest exchange process initiated by exposure to a liquid, simultaneous time resolved SAXS and WAXS measurements were carried out to follow the structure changes during the guest exchange process. A series of aromatic compounds, benzene, toluene, xylene (o‐ and p‐isomers) and mesitylene were employed as new guests. The simultaneous measurements enabled gathering information concerning both the higher order structure and the cocrystal structure. The exchange from the old guest to the new guest was also followed by FTIR spectroscopy. It is clarified that not only the size of the new guest molecules but also the molecular shape has a significant influence on the guest exchange behavior. It is also suggested that on the liquid‐phase guest exchange an expansion of the lamellar period somewhat precedes the guest exchange in the crystalline lamellae.

Fluorophore exchange kinetics in block copolymer micelles with varying solvent-fluorophore and solvent-polymer interactions.

Fluorescence spectroscopy was employed to characterize the kinetics of guest exchange in diblock copolymer micelles composed of poly(ethylene oxide-b-ε-caprolactone) (PEO-PCL) diblock copolymers in water/tetrahydrofuran (THF) mixtures which encapsulated fluorophores. The solvent composition (THF content) of the micelle solution was varied as a means of modulating the strength of interactions between the fluorophore and solvent as well as between the micelle core and solvent. A donor-acceptor fluorophore pair was employed consisting of 3,3'-dioctadecyloxacarbocyanine perchlorate (DiO, the donor) and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI, the acceptor). Through the process of Förster resonance energy transfer (FRET), energy was transferred from the donor to acceptor when the fluorophores were in close proximity. A micelle solution containing DiO was mixed with a micelle solution containing DiI at t = 0, and the emission spectra of the mixed solution were monitored over time (at an excitation wavelength optimized for the donor). In micelle solutions containing 5 and 10 vol% THF in the bulk solvent, an increase in the acceptor peak intensity maximum occurred over time in the post-mixed solution, accompanied by a decrease in the donor peak intensity maximum, indicating the presence of energy transfer from the donor to the acceptor. At long times, the FRET ratios (acceptor peak intensity divided by the sum of the acceptor and donor peak intensities) were indistinguishable from that determined from pre-mixed micelle solutions of the same THF content (in pre-mixed solutions, DiO and DiI were encapsulated within the same micelle cores). In the micelle solution containing 20 vol% THF, the fluorophore exchange process occurred too quickly to be observed (the FRET ratios measured from the solutions mixed at t = 0 were commensurate to that measured from the pre-mixed solution). A time constant describing the guest exchange process was extracted from the time-dependence of the FRET ratio through fit of an exponential decay. An increase in the THF content in the micelle solution resulted in a decrease in the time constant, and the time constant varied over five orders of magnitude as the THF content was varied from 5-20 vol%.

Factors controlling the structure of syndiotactic polystyrene upon the guest exchange and guest extraction processes

The role of host preparation method on the structural phase transition of syndiotactic polystyrene (sPS) after the guest exchange process has been thoroughly investigated in our previous study using a series of n-alkanes [Polymer 2013; 54:6617-27]. In addition to the host preparation method, we have found that guest molecules used for the guest exchange process also have a significant role in facilitating the phase transitions of the host structure. Chloroform and toluene treated γ form samples were used as starting materials for the guest exchange process with different kind of solvents. Solvents that are capable of crystallizing sPS into the delta (δ) co-crystal are termed as clathrate guests and the solvents which are crystallizing sPS directly into the γ form are termed as γ form inducing solvents. Upon guest exchange process (performed by dipping the samples in clathrate guests and γ form inducing solvents), chloroform treated of γ form (ε clathrate) sample transformed into the mixture of ε clathrate and δ clathrate in the presence of clathrate guests, whereas the ε co-crystal is retained its structure in the presence of γ form inducing solvents. However, the toluene treated γ form (monoclinic δ) samples show different structures upon guest exchange process depending on the kind of guest molecules. In the case of clathrate guests, upon the guest exchange, the monoclinic δ retained its structure; however, the toluene treated γ form (monoclinic δ) transformed to the γ form in the presence of γ form inducing solvents. Apart from the guest exchange process, structural changes upon the guest extraction process were also investigated.

Time-resolved small-angle neutron scattering study on guest-exchange processes in co-crystals of syndiotactic polystyrene

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.

Influence of host preparation method on the structural phase transitions of syndiotactic polystyrene upon the guest exchange with n-alkanes

The starting morphology used for the preparation of the syndiotactic polystyrene (sPS)/solvent complex, has a significant role in facilitating the phase transitions of the host structure upon guest exchange process. This effect was studied on the structural changes of sPS, using guest exchange process, with a series of n-alkanes, and analyzed by X-ray diffraction and Fourier transform infrared spectroscopy. SPS–solvent complexes (monoclinic δ form) were prepared with different starting morphologies i.e. amorphous, α and γ forms using toluene and chloroform as guests. Upon guest exchange process (performed by dipping the samples in a series of n-alkanes viz. n-octane to n-decane), toluene treated amorphous and α form samples (i.e. monoclinic δ form) transformed into the triclinic δ form irrespective of the starting morphology. However, the toluene treated γ form transformed back to the γ form in presence of n-alkanes. Chloroform treated amorphous sample (i.e. monoclinic δ form), however, converted to a mixture of δ form (triclinic) and ε form, while chloroform treated α and γ forms transformed into triclinic δ form and ε form, respectively. Besides host preparation method, influence of starting δ form crystallinity on the guest exchange process was also examined.

Simultaneous SAXS and WAXS Study on the Guest Exchange Process of Syndiotactic Polystyrene: Crystalline Complex Formation with Triethylene Glycol Dimethyl Ether

AbstractSyndiotactic polystyrene (sPS) forms cocrystals with a variety of chemical compounds. The guest molecules can be easily replaced with other kinds of molecules under certain conditions. The guest‐exchange process, on exposure to liquid triethylene glycol dimethyl ether (TEGDME), is followed by time‐resolved simultaneous small‐angle and wide‐angle X‐ray scattering to clarify the structure changes in molecular‐level and higher‐order structures. It is clarified that the exchange from the original guest chloroform to the new guest TEGDME takes place mainly after a certain incubation time, in parallel with the expansion of the lamellar period. The occurrence of the ϵ cocrystal during this process and the influence of the amount of chloroform on the incubation time are also studied.magnified image

Time-resolved SANS studies on guest exchange processes in co-crystals of syndiotactic polystyrene

In-situ time-resolved small angle neutron scattering is applied to the guest exchange phenomenon in the co-crystals of syndiotactic polystyrene for the first time, exploiting the significant difference in coherent scattering length between two isotopologues, fully protonated and deuterated compounds, employed as originally-occupying and subsequently-occupying guests. The vapor-induced guest exchange process between protonated toluene and deuterated one is followed by monitoring the reflection due to crystalline lamellae, which confirms that the exchange of small guest molecules like toluene proceeds smoothly in the crystalline region. In such a case, the rate of exchange is much higher than the rate of crystalline complex formation from the amorphous state induced by exposure to a vapor of guest.

ATR FTIR spectroscopic study on acceleration effect of additives on guest exchange process of Syndiotactic polystyrene complexes

Syndiotactic polystyrene (sPS) forms co-crystal structures with a variety of chemical compounds. The guest exchange procedure is an effective way to prepare sPS co-crystals. The substitution is caused by exposing an sPS co-crystal film to a vapor, a liquid or a solution of the new guest molecule. In particular, the addition of an additive, such as chloroform, to the liquid of new guest molecule promotes the guest exchange process and makes bulky molecules easily incorporated into the crystalline region of sPS co-crystals. In order to obtain further information about the influence of additive as accelerant, the sorption and desorption processes of new and old guests during the guest exchange of sPS/chloroform (CHCl3) co-crystal film were followed with ATR FTIR spectroscopy. A series of n-alkanes from n-hexane to n-decane and deuterated chloroform (CDCl3) were employed as new guests and an accelerant additive. The apparent diffusion coefficients of the new and old guests were evaluated from the intensity changes of their IR bands. It has been shown that the addition of CDCl3 promotes the guest exchange between the original guest (CHCl3) and n-alkanes significantly and this effect becomes more pronounced as n-alkane chain-length increases. The diffusion of n-alkanes in atactic polystyrene was also studied for comparison, which suggested that the additive plays an important role at the stage of n-alkane uptake from the amorphous region to the crystallites.

Does Size Really Matter? The Steric Isotope Effect in a Supramolecular Host–Guest Exchange Reaction

Does size really matter? Inverse kinetic isotope effects of up to 11 % are observed in the guest-exchange process from a highly charged supramolecular host (see picture). While the observed isotope effects can be understood in terms of the smaller steric requirements of deuterium, they are more fully explained in terms of coupling of the host aperture dilation with the guest CH/D vibrational modes.

Guest‐Driven Luminescence: Lanthanide‐Based Host–Guest Systems with Bimodal Emissive Properties Based on a Guest‐Driven Approach

A series of discrete closed, semi-closed, and polymeric lanthanide-based [{Ln(H(2)O)(8)}(3+)subsetLn(III)(2)L(4)] host-guest systems with tetragonal prism-like structure have been designed and synthesized through the ligand-dominated approach. These nanoscopic cages are robust and can be maintained upon guest exchange. Within the restricting space, the luminescence intensity of the encapsulated [Ln(H(2)O)(8)](3+) species is dramatically enhanced due to the vibrational movements originating from the O-H oscillators in the coordinated water molecules being effectively reduced by the host-guest H-bonding interactions. Based on the guest-driven approach, tunable emission and bimodal emission (UV/Vis/NIR) of these [{Ln(H(2)O)(8)}(3+)subsetLn(III)(2)L(4)] supramolecular systems are successfully realized. Moreover, the strong luminescence originating from [{Ln(H(2)O)(8)}(3+)subsetLn(III)(2)L(4)] host-guest system can be quenched by encapsulation of d-block metal quenchers, such as Fe(3+) and Cu(2+), through solid-state f-d metal exchange. Additionally, this study demonstrates that the photoinduced solid-state guest-independent emission spectrum could be one of the most diagnostic techniques for monitoring the solid-state guest-exchange process.

Bidirectional Transport of Guest Molecules through the Nanoporous Tunnel Structure of a Solid Inclusion Compound

Confocal Raman microspectrometry is used to probe, for the first time, the transport of guest molecules along the one-dimensional tunnels in a crystalline urea inclusion compound under conditions of guest exchange in which new guest molecules are introduced simultaneously at both ends of the urea tunnel structure. We focus on the system comprising 1,8-dibromooctane as the original type of guest and pentadecane as the new type of guest, and results are presented for experiments in which the guest exchange process is probed both ex situ and in situ. The Raman data, recorded as a function of position along the tunnel direction and, in the case of the in situ experiments, as a function of time, demonstrate that pentadecane guest molecules enter the tunnels at both ends of the crystal and that transport of guest molecules occurs in both directions along the crystal. Mechanistic aspects of this bidirectional transport process are discussed, particularly in relation to the corresponding process for unidirectional transport of guest molecules in urea inclusion compounds reported previously.

Kinetic Investigations of the Process of Encapsulation of Small Hydrocarbons into a Cavitand−Porphyrin

Exchange of guest molecules into capsule shaped host molecules is the most fundamental process in host-guest chemistry. Several examples of quantitative measurements of guest exchange rates have been reported. However, there have been no reports on the activation energies of these processes. A molecule known as cavitand-porphyrin (H2CP) has been reported to have a flexible host structure capable of facilitating moderate guest exchange rates suitable for kinetic measurements of the guest exchange process with 1H NMR. In this article, various kinetic and thermodynamic parameters related to the process of encapsulation of small hydrocarbons into H2CP in CDCl3 solution were determined by 2D exchange spectroscopy (EXSY): association and dissociation rate constants (k(ass) = 320 M-1 s-1, k(diss) = 1.4 s-1 for methane at 25 degrees C), the corresponding activation energies (E(a,ass) = 27 kJ.mol-1, E(a,diss) = 58 kJ.mol-1), and thermodynamic parameters for each process (DeltaG++(ass) = 59 kJ.mol-1, DeltaG++(diss) = 72 kJ.mol-1, DeltaH++(ass) = 25 kJ.mol-1, DeltaH++(diss) = 55 kJ.mol-1, DeltaS++(ass) = -113 J.K-1.mol-1, and DeltaH++(diss) = 58 J.K-1.mol-1 for methane). The thermodynamic parameters (DeltaG degrees = -13 kJ.mol-1, DeltaH degrees = -31 kJ.mol-1, DeltaS degrees = -60 J.K-1.mol-1 for methane) for this encapsulation equilibrium determined by EXSY were comparable to those for methane determined by 1D 1H NMR titration (DeltaG degrees = -11 kJ.mol-1, DeltaH degrees = -33 kJ.mol-1, DeltaS degrees = -75 J.K-1.mol-1 for methane). In addition, the structure of the methane encapsulation process was revealed by ab initio MO calculations. The activation energies for methane association/dissociation were estimated from MP2 calculations (E(a,ass) = 58.3 kJ.mol-1, E(a,diss) = 89.1 kJ.mol-1, and DeltaH degrees = -30.8 kJ.mol-1). These values are in accord with the experimentally determined values. The observed guest exchange rates and energies are compared with the corresponding values of various reported capsule-shaped hosts.

Guest-Induced Helical Metallacyclic Chains in a Porous Coordination Solid Constructed from a Flexible Ester-Containing Ligand

A porous metal−organic framework [Co(SCN)2(EDPC)2(H2O)3]n (1; EDPC = 1,2-ethanediyl di-3-pyridinecarboxylate) has been synthesized and structurally characterized. Immersing the crystals of 1 in THF solution led to the dynamic framework of 1 undergoing a crystal-to-crystal guest-exchange process to afford the helical metallacyclic polymer [Co(SCN)2(EDPC)2(THF)]n [1⊃THF]. The guest THF molecules were accommodated in the cavities of the metallacyclic chains and showed the handness of the helical chains by their oxygen atoms as probes.