1
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Tipping MB, Pruñonosa Lara L, Solea AB, von Krbek LKS, Ward MD. Photoswitching of Co(ii)-based coordination cages containing azobenzene backbones. Chem Sci 2024; 15:8488-8499. [PMID: 38846406 PMCID: PMC11151815 DOI: 10.1039/d4sc01575d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2024] [Accepted: 05/02/2024] [Indexed: 06/09/2024] Open
Abstract
Inclusion of photoswitchable azobenzene units as spacers into ditopic bridging ligands Lm and Lp, containing two chelating pyrazolyl-pyridine termini, allows formation of metal complex assemblies with Co(ii) that undergo a range of light-induced structural transformations. One notable result is the light-induced conversion of a Co2(Lp)3 dinuclear triple helicate (based on the E ligand isomer) to a C 3-symmetric Co4(Lp)6 assembly, assumed to be an edge-bridged tetrahedral cage, based on the Z ligand isomer. Another is the preparation of a series of Co4(Lm)6 complexes, of which Co4(E-Lm)6 was crystallographically characterised and consists of a pair of Co2(Lm)2 double helicates connected by an additional two bridging ligands which span the pair of helicate units, giving a cyclic Co4 array in which one and then two bridging ligands alternate around the periphery. A set of Co4(Lm)6 complexes could be prepared containing different ratios of Z : E ligand isomers (0 : 6, 2 : 4, 4 : 2 and 6 : 0) of which Co4(Z-Lm)2(E-Lm)4 was particularly stable and dominated the speciation behaviour, either during light-induced switching of the ligand geometry in pre-formed complexes, or when ligand isomers were combined in different proportions during the preparation. These examples of (i) interconversion between Co2L3 (helicate) and (ii) Co4L6 (cage) assemblies with Lp, and the interconversion between a series of Co4L6 assemblies Co4(Z-Lm)n(E-Lm)6-n with Lm, constitute significant advances in the field of photoswitchable supramolecular assemblies.
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Affiliation(s)
- Max B Tipping
- Department of Chemistry, University of Warwick Coventry CV4 7AL UK
| | - Lidón Pruñonosa Lara
- Kekulé-Institut für Organische Chemie und Biochemie, Rheinische Friedrich-Wilhelms-Universität Bonn Gerhard-Domagk-Str. 1 53121 Bonn Germany
| | - Atena B Solea
- Department of Chemistry, University of Warwick Coventry CV4 7AL UK
| | - Larissa K S von Krbek
- Kekulé-Institut für Organische Chemie und Biochemie, Rheinische Friedrich-Wilhelms-Universität Bonn Gerhard-Domagk-Str. 1 53121 Bonn Germany
| | - Michael D Ward
- Department of Chemistry, University of Warwick Coventry CV4 7AL UK
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2
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Dorrat JC, Taylor CGP, Young RJ, Solea AB, Turner DR, Dennison GH, Ward MD, Tuck KL. A Study on Auto-Catalysis and Product Inhibition: A Nucleophilic Aromatic Substitution Reaction Catalysed within the Cavity of an Octanuclear Coordination Cage. Chemistry 2024; 30:e202400501. [PMID: 38433109 DOI: 10.1002/chem.202400501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2024] [Revised: 02/29/2024] [Accepted: 03/01/2024] [Indexed: 03/05/2024]
Abstract
The ability of an octanuclear cubic coordination cage to catalyse a nucleophilic aromatic substitution reaction on a cavity-bound guest was studied with 2,4-dinitrofluorobenzene (DNFB) as the guest/substrate. It was found that DNFB undergoes a catalysed reaction with hydroxide ions within the cavity of the cubic cage (in aqueous buffer solution, pH 8.6). The rate enhancement of kcat/kuncat was determined to be 22, with cavity binding of the guest being required for catalysis to occur. The product, 2,4-dinitrophenolate (DNP), remained bound within the cavity due to electrostatic stabilisation and exerts two apparently contradictory effects: it initially auto-catalyses the reaction when present at low concentrations, but at higher concentrations inhibits catalysis when a pair of DNP guests block the cavity. When encapsulated, the UV/Vis absorption spectrum of DNP is red-shifted when compared to the spectrum of free DNP in aqueous solution. Further investigations using other aromatic guests determined that a similar red-shift on cavity binding also occurred for 4-nitrophenolate (4NP) at pH 8.6. The red-shift was used to determine the stoichiometry of guest binding of DNP and 4NP within the cage cavity, which was confirmed by structural analysis with X-ray crystallography; and was also used to perform catalytic kinetic studies in the solution-state.
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Affiliation(s)
- Jack C Dorrat
- School of Chemistry, Monash University, Melbourne, VIC, 3800, Australia
| | | | - Rosemary J Young
- School of Chemistry, Monash University, Melbourne, VIC, 3800, Australia
| | - Atena B Solea
- Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK
| | - David R Turner
- School of Chemistry, Monash University, Melbourne, VIC, 3800, Australia
| | - Genevieve H Dennison
- CBRN Defence, Sensors and Effectors Division, Defence Science and Technology Group, Fishermans Bend, VIC, 3207, Australia
- Electro Optics Sensing and Electromagnetic Warfare, Sensors and Effectors Division, Defence Science and Technology Group, Edinburgh, SA, 5111, Australia
| | - Michael D Ward
- Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK
| | - Kellie L Tuck
- School of Chemistry, Monash University, Melbourne, VIC, 3800, Australia
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3
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Dorrat JC, Young RJ, Taylor CGP, Tipping MB, Blok AJ, Turner DR, McKay AI, Ovenden S, Ward MD, Dennison GH, Tuck KL. The preservation of sarin and O, O'-diisopropyl fluorophosphate inside coordination cage hosts. Dalton Trans 2023; 52:11802-11814. [PMID: 37272072 DOI: 10.1039/d3dt01378b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The host-guest chemistry of O,O'-diisopropyl fluorophosphate (DFP), a phosphonofluoridate G-series chemical warfare agent simulant, was investigated in the presence of a number of octanuclear cubic coordination cage hosts. The aim was to demonstrate cage-catalysed hydrolysis of DFP at near neutral pH: however, two octanuclear coordination cages, HPEG (containing water-solubilising PEG groups) and HW (containing water-solubilising hydroxymethyl groups), were actually found to increase the lifetime of DFP in aqueous buffer solution (pH 8.7). Crystallographic analysis of DFP with a structurally related host cage revealed that DFP binds to windows in the cage surface, not in the internal cavity. The phosphorus-fluorine bond is directed into the cavity rather than towards the external environment, with the cage/DFP association protecting DFP from hydrolysis. Initial studies with the chemical warfare agent (CWA) sarin (GB) with HPEG cage in a buffered solution also showed a drastically reduced rate of hydrolysis for sarin when bound in the host cage. The ability of these cages to inhibit hydrolysis of these P-F bond containing organophosphorus guests, by encapsulation, may have applications in forensic sample preservation and analysis.
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Affiliation(s)
- Jack C Dorrat
- School of Chemistry, Monash University, Melbourne, VIC, 3800, Australia.
| | - Rosemary J Young
- School of Chemistry, Monash University, Melbourne, VIC, 3800, Australia.
| | | | - Max B Tipping
- Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK.
| | - Andrew J Blok
- CBRN Defence Branch, Sensors and Effectors Division, Defence Science and Technology Group, Fishermans Bend, VIC, 3207, Australia
| | - David R Turner
- School of Chemistry, Monash University, Melbourne, VIC, 3800, Australia.
| | - Alasdair I McKay
- School of Chemistry, Monash University, Melbourne, VIC, 3800, Australia.
| | - Simon Ovenden
- CBRN Defence Branch, Sensors and Effectors Division, Defence Science and Technology Group, Fishermans Bend, VIC, 3207, Australia
| | - Michael D Ward
- Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK.
| | - Genevieve H Dennison
- CBRN Defence Branch, Sensors and Effectors Division, Defence Science and Technology Group, Fishermans Bend, VIC, 3207, Australia
- Weapon Seekers and Tactical Sensors Branch, Sensors and Effectors Division, Defence Science and Technology Group, Edinburgh, SA, 5111, Australia.
| | - Kellie L Tuck
- School of Chemistry, Monash University, Melbourne, VIC, 3800, Australia.
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4
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Solea AB, Ward MD. A chemiluminescent lantern: a coordination cage catalysed oxidation of luminol followed by chemiluminescence resonance energy-transfer. Dalton Trans 2023; 52:4456-4461. [PMID: 36917490 PMCID: PMC10071490 DOI: 10.1039/d3dt00689a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/16/2023]
Abstract
A molecule of luminol bound as guest inside a Co8 coordination cage host undergoes oxidation by H2O2 to generate chemiluminescence by a process in which the Co(II) ions in the cage superstructure activate the H2O2: accordingly the cage not only co-locates the reactants but also acts as a redox partner in the catalysis. The luminescence from oxidation of the cavity-bound luminol can transfer its excitation energy to surface-bound fluorescein molecules in an unusual example of Chemiluminescence Resonance Energy Transfer (CRET).
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Affiliation(s)
- Atena B Solea
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.
| | - Michael D Ward
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.
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5
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Sudan S, Chen DW, Berton C, Fadaei-Tirani F, Severin K. Synthetic Receptors with Micromolar Affinity for Chloride in Water. Angew Chem Int Ed Engl 2023; 62:e202218072. [PMID: 36628647 DOI: 10.1002/anie.202218072] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Revised: 01/09/2023] [Accepted: 01/10/2023] [Indexed: 01/12/2023]
Abstract
A water-soluble coordination cage was obtained by reaction of Pd(NO3 )2 with a 1,3-di(pyridin-3-yl)benzene ligand featuring a short PEG chain. The cavity of the metal-organic cage contains one nitrate anion, which is readily replaced by chloride. The apparent association constant for chloride binding in buffered aqueous solution is Ka =1.8(±0.1)×105 M-1 . This value is significantly higher than what has been reported for other macrocyclic chloride receptors. The heavier halides Br- and I- compete with binding or self-assembly, but the receptor displays very good selectivity over common anions such as phosphate, acetate, carbonate, and sulfate. A further increase of the chloride binding affinity by a factor of 3 was achieved using a fluorinated dipyridyl ligand.
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Affiliation(s)
- Sylvain Sudan
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland
| | - Damien W Chen
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland
| | - Cesare Berton
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland
| | - Farzaneh Fadaei-Tirani
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland
| | - Kay Severin
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland
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6
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Gallen A, Jover J, Ferrer M, Martínez M. Building a molecular PrussianBlueAnalogue FeII/CoIII cube around a Cs+ ion; a preferred, tight, robust, water soluble, and kinetically inert encapsulator. Inorganica Chim Acta 2022. [DOI: 10.1016/j.ica.2022.121282] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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7
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Mozaceanu C, Solea AB, Taylor CGP, Sudittapong B, Ward MD. Disentangling contributions to guest binding inside a coordination cage host: analysis of a set of isomeric guests with differing polarities. Dalton Trans 2022; 51:15263-15272. [PMID: 36129351 PMCID: PMC9578013 DOI: 10.1039/d2dt02623f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Binding of a set of three isomeric guests (1,2-, 1,3- and 1,4-dicyanobenzene, abbreviated DCB) inside an octanuclear cubic coordination cage host H (bearing different external substitutents according to solvent used) has been studied in water/dmso (98 : 2) and CD2Cl2. These guests have essentially identical molecular surfaces, volumes and external functional groups to interact with the cage interior surface; but they differ in polarity with dipole moments of ca. 7, 4 and 0 Debye respectively. In CD2Cl2 guest binding is weak but we observe a clear correlation of binding free energy with guest polarity, with 1,4-DCB showing no detectable binding by NMR spectroscopy but 1,2-DCB having −ΔG = 9 kJ mol−1. In water (containing 2% dmso to solubilise the guests) we see the same trend but all binding free energies are much higher due to an additional hydrophobic contribution to binding, with −ΔG varying from 16 kJ mol−1 for 1,4-DCB to 22 kJ mol−1 for 1,4-DCB: again we see an increase associated with guest polarity but the increase in −ΔG per Debye of dipole moment is around half what we observe in CD2Cl2 which we ascribe to the fact the more polar guests will be better solvated in the aqueous solvent. A van't Hoff analysis by variable-temperature NMR showed that the improvement in guest binding in water/dmso is entropy-driven, which suggests that the key factor is not direct electrostatic interactions between a polar guest and the cage surface, but the variation in guest desolvation across the series, with the more polar (and hence more highly solvated) guests having a greater favourable entropy change on desolvation. The three dicyanobenzene isomers have obvious similarities but differ in their dipole moment: effects on binding in a coordination cage host in different solvents are discussed.![]()
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Affiliation(s)
| | - Atena B Solea
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.
| | | | - Burin Sudittapong
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.
| | - Michael D Ward
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.
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8
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Solea AB, Sudittapong B, Taylor CGP, Ward MD. Inside or outside the box? Effect of substrate location on coordination-cage based catalysis. Dalton Trans 2022; 51:11277-11285. [PMID: 35791857 PMCID: PMC9344580 DOI: 10.1039/d2dt01713j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
In this work we compare and contrast the hydrolysis of two different aromatic esters using an octanuclear cubic Co8 coordination cage host as the catalyst. Diacetyl fluorescein (DAF) is too large to bind inside the cage cavity, but in aqueous solution it interacts with the exterior surface of the cage via a hydrophobic interaction with K = 1.5(2) × 104 M−1. This is sufficient to bring it into close proximity to the layer of hydroxide ions which also surrounds the 16+ cage surface even at modest pH values, accelerating the hydrolysis of DAF to fluorescein with kcat/kuncat (the rate acceleration for that fraction of DAF in contact with the cage surface in the equilibrium) ≈50. This is far smaller than many known examples of catalysis inside a cage cavity, but at the exterior surface it is potentially general with no cavity-imposed size/shape limitations for guest binding. In contrast 4-nitrophenyl acetate (4NPA) binds inside the cage cavity with K = 3.5(3) × 103 M−1 and as such is surrounded in solution by the hydroxide ions which accumulate around the cage surface. However its hydrolysis is actually inhibited: either because of a geometrically unfavourable geometry of the bound substrate which makes it inaccessible to surface-bound hydroxide, or because the necessary volume expansion/geometry change associated with formation of a tetrahedral intermediate cannot be accommodated inside the cavity. Any 4NPA that is free in solution as part of the equilibrium undergoes catalysed hydrolysis at the cage exterior surface in the same way as DAF, but the effect is limited by the low affinity of 4NPA for the exterior surface. We conclude that exterior-surface catalysis can be effective and potentially general; and that cavity-binding of guests can result in negative, rather than positive, catalysis. The cavity is not everything! Catalysed hydrolysis of 4-nitrophenylacetate is inhibited inside a cage (left), but hydrolysis of diacetylfluorescein (right) is catalysed by the exterior surface.![]()
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Affiliation(s)
- Atena B Solea
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.
| | - Burin Sudittapong
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.
| | | | - Michael D Ward
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.
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9
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Danjo H, Asai K, Tanaka T, Ono D, Kawahata M, Iwatsuki S. Preparation of tricationic tris(pyridylpalladium(II)) metallacyclophane as an anion receptor. Chem Commun (Camb) 2022; 58:2196-2199. [PMID: 35072179 DOI: 10.1039/d1cc05563a] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
A tricationic tris(pyridylpalladium(II)) metallacyclophane was prepared from 3,5-dibromopyridine by a successive treatment with tetrakis(triphenylphosphine)palladium(0), diphosphine, and silver salt. Single-crystal X-ray diffraction analysis revealed that the metallacyclophane incorporated one of three counter anions into its hole-shaped cavity to form multidentate C-H⋯anion interactions. Solution-phase 1H NMR experiments in DMSO-d6 indicated that the metallacyclophane exhibited selective binding behavior toward nitrate, tetrafluoroborate, p-toluenesulfonate, perchlorate, and hydrogen sulfate ions, whereas the hexafluoroantimonate ion exhibited only weak interaction toward the metallacyclophane. This anion recognition behavior was further demonstrated by an extraction experiment of water-soluble sulfonate dyes.
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Affiliation(s)
- Hiroshi Danjo
- Department of Chemistry, Konan University, 8-9-1 Okamoto, Higashinada, Kobe 658-8501, Japan.
| | - Kohei Asai
- Graduate School of Natural Science, Konan University, 8-9-1 Okamoto, Higashinada, Kobe 658-8501, Japan
| | - Tomoya Tanaka
- Department of Chemistry, Konan University, 8-9-1 Okamoto, Higashinada, Kobe 658-8501, Japan.
| | - Daiki Ono
- Department of Chemistry, Konan University, 8-9-1 Okamoto, Higashinada, Kobe 658-8501, Japan.
| | - Masatoshi Kawahata
- Showa Pharmaceutical University, 3-3165 Higashi-Tamagawagakuen, Machida, Tokyo 194-8543, Japan
| | - Satoshi Iwatsuki
- Department of Chemistry, Konan University, 8-9-1 Okamoto, Higashinada, Kobe 658-8501, Japan.
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10
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Lewis JEM. Molecular engineering of confined space in metal–organic cages. Chem Commun (Camb) 2022; 58:13873-13886. [DOI: 10.1039/d2cc05560k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
The host–guest chemistry of metal–organic cages can be modified through tailoring of structural aspects such as size, shape and functionality. In this review, strategies, opportunities and challenges of such molecular engineering are discussed.
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Affiliation(s)
- James E. M. Lewis
- School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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11
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Gonzálvez MA, Bernhardt PV, Font-Bardia M, Gallen A, Jover J, Ferrer M, Martínez M. Molecular Approach to Alkali-Metal Encapsulation by a Prussian Blue Analogue Fe II/Co III Cube in Aqueous Solution: A Kineticomechanistic Exchange Study. Inorg Chem 2021; 60:18407-18422. [PMID: 34766767 PMCID: PMC8715505 DOI: 10.1021/acs.inorgchem.1c03001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The preparation of a series of alkali-metal inclusion complexes of the molecular cube [{CoIII(Me3-tacn)}4{FeII(CN)6}4]4- (Me3-tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), a mixed-valent Prussian Blue analogue bearing bridging cyanido ligands, has been achieved by following a redox-triggered self-assembly process. The molecular cubes are extremely robust and soluble in aqueous media ranging from 5 M [H+] to 2 M [OH-]. All the complexes have been characterized by the standard mass spectometry, UV-vis, inductively coupled plasma, multinuclear NMR spectroscopy, and electrochemistry. Furthermore, X-ray diffraction analysis of the sodium and lithium salts has also been achieved, and the inclusion of moieties of the form {M-OH2}+ (M = Li, Na) is confirmed. These inclusion complexes in aqueous solution are rather inert to cation exchange and are characterized by a significant decrease in acidity of the confined water molecule due to hydrogen bonding inside the cubic cage. Exchange of the encapsulated cationic {M-OH2}+ or M+ units by other alkali metals has also been studied from a kineticomechanistic perspective at different concentrations, temperatures, ionic strengths, and pressures. In all cases, the thermal and pressure activation parameters obtained agree with a process that is dominated by differences in hydration of the cations entering and exiting the cage, although the size of the portal enabling the exchange also plays a determinant role, thus not allowing the large Cs+ cation to enter. All the exchange substitutions studied follow a thermodynamic sequence that relates with the size and polarizing capability of the different alkali cations; even so, the process can be reversed, allowing the entry of {Li-OH2}+ units upon adsorption of the cube on an anion exchange resin and subsequent washing with a Li+ solution.
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Affiliation(s)
- Miguel A Gonzálvez
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Queensland 4072, Australia.,Secció de Química Inorgànica, Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain
| | - Paul V Bernhardt
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Queensland 4072, Australia
| | - Mercè Font-Bardia
- Unitat de Difracció de Raigs, X. Centre Científic i Tecnològic,Departament de Cristal·lografia, and Mineralogia i Dipòsits Minerals, Facultat de Geologia, Universitat de Barcelona, 08028 Barcelona, Spain
| | - Albert Gallen
- Secció de Química Inorgànica, Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain
| | - Jesús Jover
- Secció de Química Inorgànica, Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain.,Institut de Química Teòrica i Computacional, Universitat de Barcelona, 08028 Barcelona, Spain
| | - Montserrat Ferrer
- Secció de Química Inorgànica, Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain.,Institute of Nanoscience and Nanotechnology, Universitat de Barcelona, 08028 Barcelona, Spain
| | - Manuel Martínez
- Secció de Química Inorgànica, Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain.,Institute of Nanoscience and Nanotechnology, Universitat de Barcelona, 08028 Barcelona, Spain
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12
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Ludden MD, Taylor CGP, Tipping MB, Train JS, Williams NH, Dorrat JC, Tuck KL, Ward MD. Interaction of anions with the surface of a coordination cage in aqueous solution probed by their effect on a cage-catalysed Kemp elimination. Chem Sci 2021; 12:14781-14791. [PMID: 34820094 PMCID: PMC8597839 DOI: 10.1039/d1sc04887b] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Accepted: 10/25/2021] [Indexed: 11/21/2022] Open
Abstract
An octanuclear M8L12 coordination cage catalyses the Kemp elimination reaction of 5-nitro-1,2-benzisoxazole (NBI) with hydroxide to give 2-cyano-4-nitrophenolate (CNP) as the product. In contrast to the previously-reported very efficient catalysis of the Kemp elimination reaction of unsubstituted benzisoxazole, which involves the substrate binding inside the cage cavity, the catalysed reaction of NBI with hydroxide is slower and occurs at the external surface of the cage, even though NBI can bind inside the cage cavity. The rate of the catalysed reaction is sensitive to the presence of added anions, which bind to the 16+ cage surface, displacing the hydroxide ions from around the cage which are essential reaction partners in the Kemp elimination. Thus we can observe different binding affinities of anions to the surface of the cationic cage in aqueous solution by the extent to which they displace hydroxide and thereby inhibit the catalysed Kemp elimination and slow down the appearance of CNP. For anions with a -1 charge the observed affinity order for binding to the cage surface is consistent with their ease of desolvation and their ordering in the Hofmeister series. With anions that are significantly basic (fluoride, hydrogen carbonate, carboxylates) the accumulation of the anion around the cage surface accelerates the Kemp elimination compared to the background reaction with hydroxide, which we ascribe to the ability of these anions to participate directly in the Kemp elimination. This work provides valuable mechanistic insights into the role of the cage in co-locating the substrate and the anionic reaction partners in a cage-catalysed reaction.
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Affiliation(s)
- Michael D Ludden
- Department of Chemistry, University of Warwick Coventry CV4 7AL UK
| | | | - Max B Tipping
- Department of Chemistry, University of Warwick Coventry CV4 7AL UK
| | - Jennifer S Train
- Department of Chemistry, University of Sheffield Sheffield S3 7HF UK
| | | | - Jack C Dorrat
- School of Chemistry, Monash University Melbourne VIC3800 Australia
| | - Kellie L Tuck
- School of Chemistry, Monash University Melbourne VIC3800 Australia
| | - Michael D Ward
- Department of Chemistry, University of Warwick Coventry CV4 7AL UK
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13
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Abstract
New synthetic routes are presented to derivatives of a (known) M8L12 cubic coordination cage in which a range of different substituents are attached at the C4 position of the pyridyl rings at either end of the bis(pyrazolyl-pyridine) bridging ligands. The substituents are (i) –CN groups (new ligand LCN), (ii) –CH2OCH2–CCH (containing a terminal alkyne) groups (new ligand LCC); and (iii) –(CH2OCH2)3CH2OMe (tri-ethyleneglycol monomethyl ether) groups (new ligand LPEG). The resulting functionalised ligands combine with M2+ ions (particularly Co2+, Ni2+, Cd2+) to give isostructural [M8L12]16+ cage cores bearing 24 external functional groups; the cages based on LCN (with M2+ = Cd2+) and LCC (with M2+ = Ni2+) have been crystallographically characterised. The value of these is twofold: (i) exterior nitrile or alkene substituents can provide a basis for further synthetic opportunities via ‘Click’ reactions allowing in principle a diverse range of functionalisation of the cage exterior surface; (ii) the exterior –(CH2OCH2)3CH2OMe groups substantially increase cage solubility in both water and in organic solvents, allowing binding constants of cavity-binding guests to be measured under an increased range of conditions.
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Ludden MD, Taylor CGP, Ward MD. Orthogonal binding and displacement of different guest types using a coordination cage host with cavity-based and surface-based binding sites. Chem Sci 2021; 12:12640-12650. [PMID: 34703549 PMCID: PMC8494021 DOI: 10.1039/d1sc04272f] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Accepted: 08/24/2021] [Indexed: 12/13/2022] Open
Abstract
The octanuclear Co(ii) cubic coordination cage system H (or HW if it bears external water-solubilising substituents) has two types of binding site for guests. These are (i) the partially-enclosed central cavity where neutral hydrophobic organic species can bind, and (ii) the six 'portals' in the centres of each of the faces of the cubic cage where anions bind via formation of a network of CH⋯X hydrogen bonds between the anion and CH units on the positively-charged cage surface, as demonstrated by a set of crystal structures. The near-orthogonality of these guest binding modes provides the basis for an unusual dual-probe fluorescence displacement assay in which either a cavity-bound fluorophore (4-methyl-7-amino-coumarin, MAC; λem = 440 nm), or a surface-bound anionic fluorophore (fluorescein, FLU; λem = 515 nm), is displaced and has its emission ‘switched on’ according to whether the analyte under investigation is cavity-binding, surface binding, or a combination of both. A completely orthogonal system is demonstrated based using a Hw/MAC/FLU combination: addition of the anionic analyte ascorbate displaced solely FLU from the cage surface, increasing the 515 nm (green) emission component, whereas addition of a neutral hydrophobic guest such as cyclooctanone displaced solely MAC from the cage central cavity, increasing the 440 nm (blue) emission component. Addition of chloride results in some release of both components, and an intermediate colour change, as chloride is a rare example of a guest that shows both surface-binding and cavity-binding behaviour. Thus we have a colourimetric response based on differing contributions from blue and green emission components in which the specific colour change signals the binding mode of the analyte. Addition of a fixed red emission component from the complex [Ru(bipy)3]2+ (Ru) provides a baseline colour shift of the overall colour of the luminescence closer to neutral, meaning that different types of guest binding result in different colour changes which are easily distinguishable by eye. Orthogonal binding of neutral or anionic fluorophores to the cavity or surface, respectively, of a coordination cage host allows a dual-probe displacement assay which gives a different fluorescence colorimetric response according to where analyte species bind.![]()
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Affiliation(s)
- Michael D Ludden
- Department of Chemistry, University of Warwick Coventry CV4 7AL UK
| | | | - Michael D Ward
- Department of Chemistry, University of Warwick Coventry CV4 7AL UK
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